ArticlePDF AvailableLiterature Review

Recent Advances and Future Perspectives of Metal‐Based Electrocatalysts for Overall Electrochemical Water Splitting

November 2022
The Chemical Record 23(2)

November 2022
23(2)

DOI:10.1002/tcr.202200149

Authors:

Asif Hayat

Fuzhou University

Muhammad Sohail

Beijing Institute of Technology

Hamid Ali

Taha Abdel Mohaymen Taha Hemaida

Minoufia University

Show all 15 authorsHide

Recently, the growing demand for a renewable and sustainable fuel alternative is contingent on fuel cell technologies. Even though it is regarded as an environmentally sustainable method of generating fuel for immediate concerns, it must be enhanced to make it extraordinarily affordable, and environmentally sustainable. Hydrogen (H2) synthesis by electrochemical water splitting (ECWS) is considered one of the foremost potential prospective methods for renewable energy output and H2 society implementation. Existing massive H2 output is mostly reliant on the steaming reformation of carbon fuels that yield CO2 together with H2 and is a finite resource. ECWS is a viable, efficient, and contamination‐free method for H2 evolution. Consequently, developing reliable and cost‐effective technology for ECWS was a top priority for scientists around the globe. Utilizing renewable technologies to decrease total fuel utilization is crucial for H2 evolution. Capturing and transforming the fuel from the ambient through various renewable solutions for water splitting (WS) could effectively reduce the need for additional electricity. ECWS is among the foremost potential prospective methods for renewable energy output and the achievement of a H2‐based economy. For the overall water splitting (OWS), several transition‐metal‐based polyfunctional metal catalysts for both cathode and anode have been synthesized. Furthermore, the essential to the widespread adoption of such technology is the development of reduced‐price, super functional electrocatalysts to substitute those, depending on metals. Many metal‐premised electrocatalysts for both the anode and cathode have been designed for the WS process. The attributes of H2 and oxygen (O2) dynamics interactions on the electrodes of water electrolysis cells and the fundamental techniques for evaluating the achievement of electrocatalysts are outlined in this paper. Special emphasis is paid to their fabrication, electrocatalytic performance, durability, and measures for enhancing their efficiency. In addition, prospective ideas on metal‐based WS electrocatalysts based on existing problems are presented. It is anticipated that this review will offer a straight direction toward the engineering and construction of novel polyfunctional electrocatalysts encompassing superior efficiency in a suitable WS technique. Electrochemical water splitting is one of the most promising approaches for sustainable energy generation. This article thoroughly reviews the characteristics of H2 and O2 kinetics interactions on water electrolysis cell electrodes by focusing on fundamental techniques and recent progress to evaluate the achievements of electrocatalysts. Moreover, a realistic application scenario is presented for future research opportunities in renewable system‐driven water splitting.

Content uploaded by Hamid Ali

Content may be subject to copyright.

Recent Advances and Future Perspectives

of Metal-Based Electrocatalysts for

Overall Electrochemical Water Splitting

Asif Hayat+,*[a, b] Muhammad Sohail+,[c] Hamid Ali,[d] T. A. Taha,[e, f] H. I. A. Qazi,[g]

Naveed Ur Rahman,[h] Zeeshan Ajmal,[i] Abul Kalam,[j, k] Abdullah G. Al-Sehemi,[j, k]

S. Wageh,[l, m] Mohammed A. Amin,[n] Arkom Palamanit,[o] W. I. Nawawi,[p]

Emad F. Newair,[q] and Yasin Orooji*[b]

Abstract: Recently, the growing demand for a renewable and sustainable fuel alternative is

contingent on fuel cell technologies. Even though it is regarded as an environmentally sustainable

method of generating fuel for immediate concerns, it must be enhanced to make it

extraordinarily affordable, and environmentally sustainable. Hydrogen (H2) synthesis by

electrochemical water splitting (ECWS) is considered one of the foremost potential prospective

methods for renewable energy output and H2society implementation. Existing massive H2

output is mostly reliant on the steaming reformation of carbon fuels that yield CO2together

with H2and is a finite resource. ECWS is a viable, efficient, and contamination-free method for

H2evolution. Consequently, developing reliable and cost-effective technology for ECWS was a

top priority for scientists around the globe. Utilizing renewable technologies to decrease total fuel

[a] A. Hayat+

College of Chemistry and Life Sciences, Zhejiang Normal Univer-

sity, 321004 Jinhua, Zhejiang, P. R. China

E-mail: asifncp11@yahoo.com

[b] A. Hayat,+Y. Orooji

College of Geography and Environmental Sciences, Zhejiang

Normal University, 321004 Jinhua, China

E-mail: orooji@zjnu.edu.cn

[c] M. Sohail+

Yangtze Delta Region Institute (Huzhou), University of Electronic

Science and Technology of China, 313001 Huzhou, P. R. China

[d] H. Ali

Multiscale Computational Materials Facility, Key Laboratory of

Eco-Materials Advanced Technology, College of Materials Science

and Engineering, Fuzhou University, 350100 Fuzhou, China

[e] T. A. Taha

Physics Department, College of Science, Jouf University, PO Box

2014, Sakaka, Saudi Arabia

[f] T. A. Taha

Physics and Engineering Mathematics Department, Faculty of

Electronic Engineering, Menoufia University, Menouf, 32952,

Egypt

[g] H. I. A. Qazi

College of Optoelectronic Engineering, Chongqing University of

Posts and Telecommunications, 400065 Chongqing, China

[h] N. Ur Rahman

Department of Physics, Bacha Khan University Charsadda, KP,

Pakistan

[i] Z. Ajmal

School of Chemistry and Chemical Engineering, Northwestern

Polytechnical University 710072 Xian, P. R. China

[j] A. Kalam, A. G. Al-Sehemi

Research Center for Advanced Materials Science (RCAMS), King

Khalid University, P.O. Box 9004, 61413 Abha, Saudi Arabia

[k] A. Kalam, A. G. Al-Sehemi

Department of Chemistry, College of Science, King Khalid

University, P.O. Box 9004, 61413 Abha, Saudi Arabia

[l] S. Wageh

Department of Physics, Faculty of Science, King Abdulaziz

University, 21589 Jeddah, Saudi Arabia

[m] S. Wageh

Physics and Engineering Mathematics Department, Faculty of

Electronic Engineering, Menoufia University, 32952 Menouf, Egypt

[n] M. A. Amin

Department of Chemistry, College of Science, Taif University, P.O.

Box 11099, 21944 Taif, Saudi Arabia

[o] A. Palamanit

Energy Technology Program, Department of Specialized Engineer-

ing, Faculty of Engineering, Prince of Songkla University, 15

Karnjanavanich Rd., 90110 Hat Yai, Songkhla, Thailand

[p] W. I. Nawawi

Faculty of Applied Sciences, Universiti Teknologi MARA, 02600

Cawangan Perlis, Arau Perlis, Malaysia

[q] E. F. Newair

Chemistry Department, Faculty of Science, Sohag University, 82524

Sohag, Egypt

[+]These authors are contributed equally to the formation of this article.

Review

THE

CHEMICAL

RECORD

doi.org/10.1002/tcr.202200149

tcr.wiley-vch.de

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 1/65] 1

15280691, 0, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/tcr.202200149 by University Of Electronic, Wiley Online Library on [21/11/2022]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License

utilization is crucial for H2evolution. Capturing and transforming the fuel from the ambient

through various renewable solutions for water splitting (WS) could effectively reduce the need

for additional electricity. ECWS is among the foremost potential prospective methods for

renewable energy output and the achievement of a H2-based economy. For the overall water

splitting (OWS), several transition-metal-based polyfunctional metal catalysts for both cathode

and anode have been synthesized. Furthermore, the essential to the widespread adoption of such

technology is the development of reduced-price, super functional electrocatalysts to substitute

those, depending on metals. Many metal-premised electrocatalysts for both the anode and

cathode have been designed for the WS process. The attributes of H2and oxygen (O2) dynamics

interactions on the electrodes of water electrolysis cells and the fundamental techniques for

evaluating the achievement of electrocatalysts are outlined in this paper. Special emphasis is paid

to their fabrication, electrocatalytic performance, durability, and measures for enhancing their

efficiency. In addition, prospective ideas on metal-based WS electrocatalysts based on existing

problems are presented. It is anticipated that this review will offer a straight direction toward the

engineering and construction of novel polyfunctional electrocatalysts encompassing superior

efficiency in a suitable WS technique.

Keywords: Electrolysis, Evaluation Parameters, Metal-based Electrocatalysts, Overall Water

Splitting, Solar Cell, etc.

1. Introduction

With the on-growing energy demand, swift exhaustion of fossil

fuels, and worsening environmental pollution, acquiring addi-

tional renewable fuel alternatives, such as energy production,

hydroelectricity, geothermal power, and biofuels is

essential.[1–20] Owing to outstanding energy conversion profi-

ciency, larger gravimetric energy output than petroleum (120

vs. 44 MJ/kg1), absence of carbon dioxide (CO2) emitters, and

environmental adaptability hydrogen (H2) is often regarded as

the cleanest and most ideal energy source in order to replace

fossil fuels.[21–33] Moreover, H2is also used in industries like

ammonia synthesis, cracking of crude oil, and methanol

synthesis. But, the H2does not exist in nature, instead it needs

to be produced from other sources. Numerous techniques,

including the oxidation reaction of hydrocarbons and gas-

ification, are commonly employed in order to generate H2

sources nowadays. Still, these methods often consume fossil

fuels and thus produce CO2, which adversely affects the

environment.[34–42] Recently, renewable energy sources such as

photovoltaic fuel and turbine technology have been utilized

widely daily. However, these are afflicted by regular and yearly

intermittency and geographical variation. The best manner to

alleviate such a problem might be to turn this unsteady power

into stabilized chemical vitality, such as H2.[43,44] Therefore,

electrochemical water splitting (ECWS) for H2production has

drawn huge attention. For this, water has been utilized as a

crude content to produce H2without producting of green-

house gases or any polluting gases.[11,45–55] The ECWS

demonstrates two kinds of half-reactions: namely, hydrogen

evolution reaction (HER) at the cathode, while that oxygen

evolution reaction (OER) at the anode. Such kinds of half-

reactions need efficient electrocatalysts to improve reaction

kinetics. The most common electrocatalysts, which are being

used as an effective material for efficient HER and OER

activity are included Pt and Ru/Ir oxides-based materials.[56,57]

But their usage is still very limited owing to elemental scarcity

and high cost.[52,58–63] Tremendous efforts have been made to

design effective electrocatalysts for both HER and OER.

Preferably, combining the benefits of both HER and OER

catalysts to fabricate effective materials for overall water

splitting (OWS) may be an emerging route, enhancing the

materials’functionality and reducing their cost.[64–70] Lately,

many materials and their composites are being widely

investigated, and used as metal electrocatalysts for the ECWS.

They include sulfides, carbides, nitrides, oxides or hydroxides,

and phosphides. In the evaluation, capabilities of HER and

OER reactions at various electrodes and basic techniques to

assess the performance of electrocatalysts are presented. In

addition, the potential of various metal-based electrocatalysts

was analyzed and evaluated. Additionally, the constraints in

designing bifunctional electrocatalysts are also discussed. This

may offer guidance in developing electrocatalysts with better

functionality and cheap in a real OWS process. The overview

of this manuscript has been manifested in Figure 1 respec-

tively.

2. Electrochemical Processes of Water Splitting

(WS)

The conventional electrochemical cells for WS utilizing

bifunctional electrocatalysts consist of three components: the

anode, cathode, and the aqueous electrolyte, are presented in

Figure 2.[71] It consists of two half-cell processes, water

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 2/65] 1

reductions and water oxidations at the cathodic and anodic

portions. These are also known as HER and OER at the

cathode and anode, respectively. Based on electrolyte, different

electrochemical reactions (ECR) at electrodes occur, but the

overall reaction remains the same.[71,72]

Overall reaction :2H2O=2H2!O2(1)

In the acidic electrolyte

Cathodic :2Hþþ2e!H2Ec¼0:0V(2)

Anodic :2H2O!O2þ4Hþþ4eEa¼1:23 V(3)

In aqueous electrolytes,

Cathodic :2H2Oþ2e!H2þ2OH

Ec¼0:83 V(4)

Anodic :4OH!O2þ2H2Oþ4e

Ea¼  0:40 V(5)

The theoretical thermodynamics value is 1.23 V at 25 °C

and 1 atm irrespective of the reaction media of WS reactions.

The Ecand Eavalues were calculated from a standard hydrogen

electrode (SHE). But a higher potential is often required

compared to the thermodynamic potential during the real WS

reaction. Such surplus capability is termed as overpotential (ŋ)

of the WS cell, which is mostly to get around the inherent

activation hindrances at both the cathode (ŋc) and the anode

(ŋa), as well as other hindrances like interaction susceptibility

and solution permeability. Thus, the practical operational

potential (EOP) of the OWS reaction may represent as follows:

EOP ¼1:23 Vþaþcþother (6)

The equation (6) suggests that the reduction of over-

potential is the main aim to facilitate the OWS reaction for

prominent performance. The ŋcand ŋavalues can be efficiently

decreased by employing effective HER and OER electro-

Figure 1. Graphical illustration of the overview of this manuscript.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 3/65] 1

catalysts, while ŋother would reduce by improving the electro-

lyzed synthesis. To develop low-cost OWS, the key task is to

design an effective electrocatalyst.

2.1. Hydrogen Evolution Reaction (HER)

The HER is known by a two-electron exchange scheme,

followed by a multi-step process at the cathode. Typically, it

involves two distinct pathways involving three processes

(Figure 3a).[74] In acidic electrolytes, HER includes the

following steps.[74]

(1) A proton from hydronium cation (H3O+) captures an

electron from the electrocatalyst interface, producing an

immobilized hydrogen intermediate (H*) on the interface of

the catalyst.

H3Oþþeþ*!H*þH2O Volmer reaction (7)

(2) Hydrogen intermediates deposited on the surface are

linked with protons and an electron immediately to form a

hydrogen moiety.

H*þH3Oþþe!H2þH2Heyrosky reaction (8)

(3) Interaction of adjacently immobilized hydrogen to

generate hydrogen ligands.

H*þH*!H2Tafel reaction (9)

However, in an electrolytic cell, HER follows the Volmer

and Heyrosky processes:

(1) The protonated hydrogen radical (H*) is formed by

the combination of a proton from the water molecules (H2O)

and electrons.

H2Oþeþ*!H*þOHVolmer reaction (10)

(2) The immobilized hydrogen radical immediately inter-

acts with water molecules and electrons to form hydrogen

units.

H*þH2Oþe!H2þOHHeyrosky reaction (11)

(3) Like acidic electrolytes, two immobilized hydrogen

intermediates are combined collectively to produce hydrogen

molecules.

H*þH*!H2Tafel reaction (12)

2020, Elsevier.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 4/65] 1

Herein, (*) denotes the electrocatalyst interface, and H* is

the adsorbed hydrogen intermediates. The HER multiphase

process is instigated with proton discharge, known as the

Volmer process. Later, the immobilized H2formation includes

two different reaction routes, the initial phase is electro-

chemical adsorption, known as the Heyrovsky process, and the

next is chemical deactivation, also known as the Tafel

response. The HER in the basic solution is comparably slow to

the acid solution, due to the water dispersion preceding the

creation of H*. In both routes of HER, H* is often involved.

Consequently, the free energy of hydrogen adsorption (ΔGH*)

is extensively considered an indicator in hydrogen-evolution

materials. A good catalyst for HER, like Pt, should have a ΔGH*

that is near zero, as the feeble adsorption usually leads to

limited connections between protons and the electrode surface.

On the other hand, comparatively larger ΔGH* to breakdown

the bonds between catalyst surface sites and the hydrogen

hinders the hydrogen desorption process. A volcano relation-

ship of the experimental plot for ΔGH* of numerous electro-

catalysts measured through DFT vs the coefficient of their

respective exchange current concentrations (log j0) demon-

strates the HER functions of different materials (Figure 3b).[75]

This diagram of a volcano helps us to recognize and evaluate

the distinct materials, which enables the way to enhance the

synthesis of materials. The HER pathway could be derived

from the electrocatalyst Tafel gradient, which is an integral

feature.[76] Under standard conditions, the estimated Tafel

slopes should be 118, 39, and 29 mV/dec1for the Volmer,

Heyrovsky, and Tafel processes. This was reported that the

Tafel curve obtained from the Pt electrode with Pt (110)

lattice for the HER is ~ 30 mV/dec1, which implies the Tafel

response is the process that sets the probability. While the rate-

determining process for the Pt (100) plane could also be the

Heyrovsky response.[77] Therefore, the calculated Tafel curve of

~ 30 mV/dec1is not only related to the Tafel reaction. So,

either the Tafel rate-finding process or the Heyrovsky rate-

Figure 3. (a) HER mechanisms where yellow ball represents e, the light blue ball represents Hþ; big light green balls represent H2; small light green balls

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 5/65] 1

finding phase could be associated with the amount of hydro-

gen ions that have been trapped in the electrode interface.

Moreover, the Tafel slope may also vary based on applied

potentials and calcination. So, it’s also important to know how

to estimate and evaluate the curve of the Tafel to elucidate the

basic phases. In addition, overgeneralized assessment of the

Tafel curve might cause an incorrect description of the

reaction.[77,78]

2.2. Oxygen Evolution Reaction (OER)

The OER at the anode occurs via a multiphase process

requiring the transport of four electrons, which is more

significant than the HER at the cathode. Despite the sluggish

dynamics, the OER process and reaction routes are more

complicated than the HER process. Water is activated to

oxygen and hydrogen atoms in acidic electrolytes, but hydroxyl

ions are converted to water and oxygen in medium or basic

electrolytes. These OER reactions typically include three

adsorption substituents such as OH*, O*, and OOH* on the

catalyst interface (Figure 3c).[79] In alkaline electrolytes, all

mechanisms contain OH* formation via hydroxide coordina-

tion to the active sites followed by other intermediate

formations. In every reaction setting, similar mediators,

including OH* and O* are produced in all suggested OER

mechanisms, with the only significant difference being the

synthesis of oxygen. Depending on theoretically proposed

models, the common mechanisms of OER in different

conditions can be shown below:

OER in acidic electrolyte

H2Oþ*!HO*þHþþe(13)

HO*!O*þHþþe(14)

O*þH2O!HOO*þHþþe(15)

HOO*!*þO2þHþþe(16)

OER in alkaline electrolyte

OHþ*!HO*þe(17)

HO*þOH!O*þH2Oþe(18)

O*þOH <C!! HOO*þe(19)

HOO*!*þO2þH2Oþe(20)

Figure 3d represents the volcano graph of O2generation

efficiency on first-row transition metal oxide interfaces versus

oxide transition enthalpy in both acid and base

circumstances.[80] RuO2and IrO2are at the pinnacle of the

graph due to their reduced oxidation prospective and high

conductance. However, the increased price and insufficient

HER behavior render such valuable metal-based oxides

unsuitable as electrocatalysts for significant WS. On the other

hand, inexpensive and more reliable polyfunctional transition

metal electrocatalysts such as cobalt phosphates/phosphides

and nickel sulfide nanomaterials have exhibited exemplary

behavior for both HER and OER, while maintaining electro-

catalytic stimulation.

2.3. Assessment Methods for ECWS

The pivotal factors for evaluating catalytic performance in the

ECWS are the overpotential, Tafel slope, exchange current

density, turnover frequency, stability, Faradaic efficiency, mass,

and specific functions.

2.3.1. Overpotential

The thermodynamical probabilities for activating HER and

OER in WS under any electrolyte are 0 and 1.23 V (vs. RHE).

However, due to the inherent thermochemical impediment, an

extra possibility, symbolized by the symbol h, is mandated to

squeeze ECWS (Figure 4).[81] The WS technique has three

types of overpotentials: stimulation overpotentials, intensity

overpotentials, and impedance overpotentials. The stimulation

overpotential is an inherent attribute of the electrocatalyst that

could be significantly reduced by choosing an adequate

electrocatalyst. The intensity overpotential is proportional to

the electrolytic intensity variation among the bulk solution,

and the electrode layer. When electrode response begins, an

intensity overpotential occurs due to a spontaneous reduction

in intensity interfacial. As a result of the existence of an

interfacial film, it can be reduced in portion by mixing the

solution. The impedance overpotential, also known as the

intersection overpotential, is imposed by the electrolytic

surfaces and occurs at the assessment state substrates and

functionalities. The additional potential difference caused by

the impedance of all over the structured interfaces causes the

evaluated potential of the electrode to be greater than the

actual value. An efficient manner to eliminate the impedance

overpotential is to perform Ohmic drop reparation, also

known as IR reparation. The stimulation overpotential, also

known as the acute overpotential, is the most significant

feature of overpotential for the HER because its reactions are

significantly quicker than that of the OER. Furthermore, the

vapors influence cannot be overlooked. During the ECWS,

many vapors are formed on the electrode interface, and some

of these bubbles become firmly attached to the electrode,

resulting in a leakage of efficient active region and, as a result,

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 6/65] 1

a boost in kinetics overpotential. The overpotential at a

specified current intensity is typically approximated using the

modulation slope determined by the current density vs.

overpotential. The lower the overpotential at the identical

current density, the improved the electrocatalyst behavior.

2.3.2. Tafel Slope and Exchange Current Density

Tafel slope and exchange current density are two significant

thermodynamic variables that the Tafel formula can

produce.[82,83]

N¼aþb log j (1)

In eq. (1), h designates the overpotential, b the Tafel curve,

and j the applied voltage. The Tafel curve can be used to

calculate the potential thermodynamics probability of the

catalysts as well as to illustrate the chemical reactivity. A lesser

Tafel curve demonstrates that enhancing the identical applied

voltage necessitates a relatively small overpotential, implying

an accelerated charge carrier speed. If the h amount is zero, the

associated j value determined from the Tafel formula is the

transfer electric potential (j0), which demonstrates the integral

electron transport among an analyte and an electrode under

optimum situations and is only related to the catalyst

components, electrolyte, and temperature. As a result, the

larger the amplitude of the exchange applied voltage, the better

the catalyst efficiency in WS will be. In summary, an efficient

electrocatalytic activity during water electrolysis has a reduced

overpotential, a modest Tafel curve, and a high exchange

applied voltage (Figure 5).[84]

2.3.3. Turnover Frequency (TOF)

Turnover frequency (TOF) is the number of particles

interacting at each accessible active site per time. It could

represent the inherent assets of each catalytic active site under

specific response circumstances.[85] The TOF can be calculated

using the eq. (2).[83,86]

TOF ¼ ðJAÞ=ðaFnÞ(2)

Figure 4. The overpotential of overall water splitting. Reprinted with permission from Ref. [81]

Figure 5. (A) The impedance analogous circuit. Rc is an electrode-film interaction resistor. Rm is MoSx electrical resistivity. (B) Plots of MoS3Rct, Rm, and Cct

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 7/65] 1

In this equation, j represents the associated conductance

achieved from the linear sweep voltammogram (LSV) at a

specified overpotential; A is the surface area of the working

electrode; αdesignates the photons amount of the catalyst

(electrons/mol1); F is the Faraday value of 96485.3 C/mol1

under appropriate conditions, and n signifies the number of

moles (mol) of coated metal atoms over the electrode acquired

by separating mass (g/mol1). However, determining the

detailed valuation of the TOF intensity for a heterogeneous

electrocatalytic reaction occurring at the electrode interface is

frequently difficult. As a result, a reasonable technique for

calculating the TOF is entirely based on the materials’ surface

atoms or widely obtainable catalyzed spots. Occasionally, the

TOF valuation is estimated because of the total number of

catalyzed species occurring in the material, regardless of

whether they are all attainable, uniformly available, or none at

all. Although this doesn’t offer the accurate validity or provide

a miscalculated valuation in practice, it’s often accomplished

since there is no accessible method for determining all

attainable reactive groups in the electrocatalyst. However, such

findings can still be significant and beneficial, when comparing

specific compounds. For example, in the OWS, two-electrode

electrolyze arrangements were built; one employed Iridium on

vertical graphene (Ir_VG) materials for both cathodic and

anodic, while another featured Pt/C (cathode) and IrO2

electrodes (anode). The electrolyzed properties in acid and

alkaline media are shown in Figure 6a–b.[87] In acids, Ir_VG

(10 =1.58 V) outperformed the Pt/C–IrO2pair (1.61 V) and

other conventional electrocatalysts, including Pt/CCIr/CC,

Ni5P4, and FeP NTs, and was equivalent to the Ir-GF.[88] The

TOF of every activated Ir unit on the interface was computed

for HER presuming a faradaic performance of 100 %, as

shown in Figure 6c. The masses concentration, the proportion

of charge density to loaded capacity at a particular specific

capacity, is also a useful indicator of the catalytic performance.

As demonstrated in Figure 6d, we detected exceptionally high

mass activation in the HER due to the minimal catalyzed

input quantity utilized in our tests.

Figure 6. Bi-functional activities, TOF, and Mass behavior: In acidic (a) and alkaline conditions, (b) WS occurs at 1.58 V and 1.57 V. (c) Approximated TOF

per metals Ir unit of Ir VG composite at various overpotentials for HER; (d) Exceptionally significant mass behavior in HER, exhibiting outstanding quality over

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 8/65] 1

2.3.4. Stability

Stability is a pivotal factor that can be used to appraise a

catalyst’s capabilities to sustain its efficiency over a long period

of time.[19,89–97] Two simple electrochemical techniques are

used to characterize and evaluate catalytic consistency: CV or

LSV and galvanostatic or potentiostatic electrolysis

assessment.[85] Cycling analyses using a CV or LSV strategies

are conducted by replicating the substantial phase. Cycle levels

greater than 5000 are used to demonstrate the high durability

of materials. The galvanostatic or potentiostatic electrolysis

assessment seeks to determine the variance in potential or

applied voltage with time at a relatively constant level. In this

case, the applied voltage of 10 Ma/cm2is frequently used as

the model to evaluate catalytic consistency. The measurements

typically continue for several hours, and a stable catalyst

provides an applied voltage more than 10 mA/cm2for over

10 h or more than 5000 cycles. Figure 7a demonstrates the

current voltage, that goes down with the passage of time. The

supplied current arcs were acquired between PCFC activity

employing similar testing settings as the reliability analysis to

determine cell deterioration at recurring times. I–V–P param-

eters showed steady efficiency deterioration throughout

sustainability tests (Figure 7b). EIS data under OCV at 650 °C

demonstrate the principal deterioration pathways (Figure 7c–

d). Rtot rose from 0.300 to 0.407 cm2, while Rohmic rose from

0.115 to 0.135 cm2.[98]

2.3.5. Faradaic Efficiency

Faradaic efficiency can be described as the effectiveness of the

exterior circuit electron transport in promoting the electro-

chemical redox reactions.[99] It is also the proportion among

the theoretical and experimentally H2generation, which could

be evaluated from the voltage source based on a Faradaic

output of 100 percent. Consequently, the experimental H2

production could be evaluated using gas chromatography

(GC) or the standard water gas dispersion technique. The

conceptual H2developments could be determined using

galvanostatic or potentiostatic electrolysis assimilation. The

technique of twisting ring disc electrode voltammetry could be

used to evaluate the quantity of O2, which can be implemented

Figure 7. Durability evaluation at 0.5 A/cm2galvanostatic and electrochemical assessment: (a) Variation in voltage level under continuous current performance of

PCFC with a period, (b) Potential polarized patterns, (c) EIS observations under OCV condition, and (d) overall, impedance, and electrode ASR levels. Reprinted

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 9/65] 1

to OER. The following expression can be used to determine

the Faradaic efficiency (FE) of the OER electrocatalyst.[86,100]

FE¼IRnD=IDnRNCL

where IRand nRare the current and the number of

electrons transferred at the circle, respectively, ID and nD are

the current and the number of electrons transferred at the disc,

respectively. It is a useful approach for determining the

accurate behavior of an OER material, which may retain

Faradaic effectiveness due to the appearance of one or more

redox peaks within the potential range, undesirable side

interactions, and thermal loss during the electrocatalytic

technique. Typically, the majority of faradaic reduction is

caused by the configuration of byproducts or energy loss.

Nanosized Ag motivators can supply moderate interfacial Ag

atoms, that stabilize the COOHC intermediary by lowering

the primary electron transport resistance. The Faradaic yield

for CO and H2on crystalline Ag, and oxide-based Ag, at

multiple capabilities in CO2dissolved in 0.1 m K2HPO4and

KHCO3, is depicted in Figure 8.[101]

2.3.6. Mass and Specific Activities

Mass and specific activity are two additional statistical

energetic factors, which are being used to evaluate the

efficiency of materials in WS. The mass activity, measured in

amperes per gram (A/g1), is the voltages standardized by the

reaction conditions. At the same time, the specialized behavior

is the voltages adjusted by the electroactive surface area, which

reveals the inherent catalyzed function of materials.[76] The

mass and specific activities must be accomplished at an

overpotential identical to TOF. It is important to note that the

six variables listed above frequently exhibit inherent relation-

ships. The Tafel calculation, for example, could establish the

association among the Tafel curve and transfer applied voltage.

The transfer applied voltage and overpotential could be

achieved from the polarization graph, and the exchange current

density is typically characterized as the current density value

Figure 8. Faradaic yield for CO and H2on crystalline Ag, (a, c) and oxide-based Ag, (b, d) at multiple capabilities in CO2dissolved in 0.1 m K2HPO4and

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 10/65] 1

correlating to zero overpotential. In addition, the current

density and overpotential have a robust relationship with the

turnover intensity, which can describe the inherent catalytic

efficiency of each active center and influence its reliability. In

addition, Faradaic reliability is predicated on the applied

voltage, and mass and specialized functions are frequently

accomplished at a unique overpotential. In assessing an

electrocatalyst, the three primary variables, overpotential, Tafel

slope, and stability, are required. Electrocatalysts with a

reduced overpotential, a limited Tafel curve, and a high

transfer applied voltage are regarded as effective for water

electrolysis. Moreover, the electrochemical active surface area

(ECSA) is applied to determine the aggregate binding sites on

a particular surface for a specific electrode material.[102]

Typically, a massive ECSA facilitates the accumulation of

water molecules and derivatives, enhancing interaction with

the electrolyte and providing abundant reactive groups for

catalytic performance interactions.[103,104] ECSA is ascertained

for common constituents and composites using three empirical

methods: CO voltammetric,[105] hydrogen underpotential

diffusion adsorbent voltammetry[106] and Cu underpotential

diffusion preventing voltammograms.[107] Moreover, the pH

range is also important. A variety of materials can show better

activity at different pH ranges. However, electrocatalysts that

can function over a broad pH spectrum have also been

intensively investigated. Consequently, the vast majority of

published research has focused on electrocatalysts, that operate

at a specific pH level, such as 1.0 M KOH, 0.5 M H2SO4, and

neutral solution. Jia et. al.[108] demonstrates the advancement

of proton exchange membrane fuel cells (PEMFCs) is

contingent upon the utilization of limited platinum in the

cathode for the oxygen reduction reaction (ORR) as man-

ifested in Figure 9. Similarly, Figure 9a demonstrates that the

mass function of P1NA at the EOL phase is under the DOE

2017 goals due to the significant interaction deficit (66%)

upon durability process, while the mass functions of all P2-

based PtNi3/C electrocatalysts at both the BOL and EOL

phases significantly increase the DOE aims.[109] Additionally,

the excellent effectiveness of P2-based electrocatalyst highlights

in PEMFCs by comparing the behavior of earlier published

dealloyed PtMx/C,[110] conventional Pt/C,[111] and Pt3Co/C[109]

electrocatalysts (Figure 9b). The poor endurance of the

Figure 9. (a) Mass performance, (c) specific performance, and (d) electrochemical surface area (ECSA) of the four PtNi3/C catalysts. Reprinted with permission

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 11/65] 1

permeable P1NA is due to the dramatic decrease in

specialized performance and ECSA throughout MEA activa-

tion (Figure 9c, d), which could be ascribed to the retardation

of strains and/or ligands influences resulting from the

reduction of M and also particulate development.

2.4. Two-Electrode Electrolysis of Water

The ECWS is a potential technique for generating environ-

mental-friendly hydrogen fuel.[112] Theoretically, ECWS ensues

at +1.23 V, and basically, about 1.8 V is mandated to

ameliorate the stimulation obstacle of the response.[113] The

above significant overpotential accounts for the slow four-

electron (e) transition dynamics of the oxidation process at

the anode along with the simpler process of two (e) transfer

kinetics at the cathodic reduction process.[114] The complete set

up of WS technique in an efficient manner with the distinct

cathodic and anodic processes is considered as a difficult task,

because distinctive catalysts behave diversely and are reliable at

varying pH levels. In regard, employing distinctive electro-

catalysts in an identical framework frequently necessitates

using distinct equipment and procedures, which makes the

mechanism comprehensive and costly. Furthermore, in the

WS procedure, the hydrophilicity of the electrocatalyst in the

electrolyte and the as-arise gas bubbles rapid deposition from

electrode surface sites are of paramount importance.[115] A slow

exclusion of gas bubbles from the electrode surface obstructs

the electrocatalyst’s active site and reduces the electrolyte’s

dispersion over the catalyst/electrolyte surface.[116] Thus,

aerophobic and hydrophilicity of electrodes are crucial for

enhancing the effectiveness and consistency of the WS

procedure.[117] Therefore, designing an energetic, reliable, and

inexpensive polyfunctional electrocatalyst for WS is

essential.[118]

2.4.1. Electrocatalysts for OWS

For OWS, a perfect bifunctional electrocatalyst must be a

cheap, efficient, and cost-effective synthesis route, that can

offer long operational stability for both HER and OER.[119]

The utilization of a perfect electrocatalyst is difficult to

electrolyze water. Therefore, it becomes crucial to design

various types of bifunctional electrocatalysts with improved

activity to encourage the H2fuel sector.[120] Transition metal

oxides,[121] sulfides,[122] and selenides,[123] phosphides,[124]

nitrides[125] had already erupted as promising applicants for

non-noble metal electrocatalysts. The Ni3S2/MnSO nano-

composites on the surface of Ni foam (NF/T(Ni3S2/MnSO))

have been used as anodic and cathodic for OWS (Figure 10a),

and showed a current density of (1.54 V) and applied voltage

of (10 Ma/cm2) were obligated.[126] The use of NiCo2O4/GF/

NiCo-nitrides as both cathodic and anodic sides were

suggested by Dai and Liu et. al. in a two-electrode system. The

total current for ECWS was found to be 1.68 V in 1.0 M

KOH to obtain 20 Ma/cm2(Figure 10b).[127] Similarly, the

polyfunctional catalyst was implemented by He and Sun et. al.

to catalyze the water electrolysis out of Fe-boosted Ni2P

nanomaterials on NF that are self-supported in three

dimensions (3D). The Ni0.33Fe0.672P is part of a two-electrode

electrolyzer Ni0.33Fe0.67. To get 10 mA/cm2from 2P electrodes

in a solution of 1.0 M KOH, a reduced cell output of 1.49 V

was needed. Wang and his colleagues recommended a nano-

material, highly permeable Ni3FeN nanocomposites by ther-

mal treatment of the Ni3FeLDHs intermediates in an NH3

environment. The highly permeable Ni3FeN was used as both

the anodic and the cathodic in a two-electrode system for

OWS in 1.0 M KOH. This process needed a current of

1.495 V at 10 mA/cm2, which could require a 1.5 V

voltage.[125] Metal-free electrocatalysts were also demonstrated

to work well, with more stability, and less cost than metal-

based electrocatalysts to make WS last longer.[128] Likewise, Yu,

Chen, Dai, et. al. created a metal-free polyfunctional catalyst

Figure 10. (a) An illustration of a two-electrode system for OWS using NF/T(Ni3S2/MnSO) as anodic and cathodic counterparts. Reprinted with permission

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 12/65] 1

with ultraportable agglomerated black phosphorus (EBP)

nanocomposites on coupled-coupled graphene (EBP/NG).

The as-prepared (EBP/NG) has enhanced behavior in HER

and OER in the presence of 1.0 M KOH. To accomplish

10 mA/cm2, the enhanced two-electrode cell with (EBP/NG)

as anodic and cathodic required a propensity of 1.54 V.[129]

Most documented polyfunctional metal catalysts have reduced

prospective in commercial technologies than the evaluating

IrO2/Pt electrode (1.57 V at 10 Ma/cm2) and basic paired

nickel and stainless steel (1.73 V at 10 mA/cm2).[130]

2.5. Strategies to Enhance the Electrocatalytic Activity

2.5.1. Morphological Modification

Morphology modification is a useful method for improving

the overall performance of materials to be used in a wide

variety of research fields.[27,131–140] The morphological manipu-

lation of the electrode material has begun to counteract the

prospective decrease caused by the production of gas bubbles

on the electrodes. This problem diminishes when the interface

of electrocatalysts becomes hard and increases

lipophilicity.[141,142] By modifying the shape of electrode

material, the number of electrocatalytically activated holes and

the effectiveness of charge transport may be altered.[143] Various

crystalline planes of a material exhibit distinct electrocatalytic

activities and morphological manipulation might facilitate the

exposure of a specific crystal plane.[144] Morphologies with

dimensions in the nanoscale region improve the proportion of

a material density to its surface area, enhancing its electro-

chemical performance.[145] The formation of gases bubbling at

the electrodes in water electrolysis is a major problem that

produces a large current loss, particularly at greater over-

potentials. The approach of morphological manipulation may

be used to increase the hydrophilicity of the Ni catalysts. The

shape of Ni catalysts is governed by changes in electro-

deposition conditions (Figure 11a–d), and lipophilicity rises

with rising interface imperfection (Figure 11e).[146] The OER

electrochemical performance is discovered to improve as

surface texture increases. Compared to other topologies, the

oxygen bubble separation mechanism is shown to be quickest

in Ni catalysts with a hierarchy needle-like shape. The Ni

Figure 11. SEM pictures of (a–b) MMNSNFs1, (c–d) MMNSNFs2, (e–f) MMNSNRs1and (g) MMNSNRs2; (h) TEM imaging of MMNSNRs2; I HER

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 13/65] 1

catalysts with a hierarchy architecture show the minimum

OER catalytic performance degeneration rate.[141] The OER-

catalyzed capability of NiO also exhibits a beneficial influence

of interface imperfection. Contrasted to 3D nanomaterials

(NiONPTs), 1D NiO hollow nanofibers (NiO/NFBs) have a

rougher texture and outstanding function.[147] The electro-

chemical properties of electrode material may be improved by

enhancing its interface irregularity within a limited range. The

surface area and hydrophilicity increase by increasing the

interface imperfection. Therefore, beyond a certain threshold,

this will disclose crystal faces that might or might not be

kinetically activated. Moreover, increasing the interface irregu-

larity to a higher degree promotes the hydrophilic nature,

which has a negative effect on the catalytic performance.[148]

Consequently, the electrochemical performance of the material

will gradually decline. As most electrocatalysts are hydrophilic,

the prospect of enhanced electrocatalytic activity with in-

creased surface imperfection is relevant to the vast majority of

electrocatalysts.[149] Consequently, the stated modulating range

may differ amongst electrocatalysts. In principle, electro-

chemical performance rises as crystallinity decreases. Con-

versely, NiONPTs exhibits lower performance while meeting

desirable conditions.[32] During the electrochemical process,

the nanomaterials aggregate due to the elevated interfacial

charge, reducing the catalytic performance of NiONPTs. On

the other hand, NiONFBs with a spherical configuration,

have a greater electrochemical surface area (ECSA) and

facilitate mass and vertically charged transmission.[147] The

shape of the Co film placed on electrocatalytic activated carbon

cloth (EACC) influences the HER catalytic performance,

whereas the OER catalytic performance. After adjusting the

material’s temperatures, many Co films are formed on EACC

using ultrasonic lasers accumulation (PLD).[150] Once the

surface temperatures are below 300 °C, tightly compacted

nanocrystallites are generated, whereas pyramid-capped nano-

wires are created above 300 °C (Co/EACC-300). Once the

temperatures decrease below 400 °C, the nanocrystals grow

finer, and the nanowires lose their homogeneity. As a result of

its pyramidal form, Co/EACC-300 has the greatest ECSA and

has higher HER catalytic performance. Despite their initial

shape, all Co films undergo a comparable transformation

during OER, resulting in comparable OER catalytic

properties.[150] The shape of the MnOx film may be altered by

varying the Mn intermediates.[151] Nanowires and nanospheres

with a membranous pattern are created, whenever the

constituent is Mn(NO3)2, while interconnecting nanowires are

generated whenever the constituent is Mn(CH3COOH). Once

MnCl2is employed as the starting material for the electro-

chemical deposition, a leaf-like pattern is developed. The

MnOx film made from Mn(NO3)2has better OER catalytic

effects, which are similar to that synthesized from MnCl2

[151]

owing to microstructure differences. The shape of hydrous

nickel pyrophosphate thinner films produced on stainless steel

(SS) material by chemical deposition is altered by altering the

proportion of nickel to phosphate intermediates.[152] Whenever

the quantity of phosphate in the starting material is lowered,

the willow-like shape transforms into a microflower having

hexagonal petals. The nickel pyrophosphate with a shape like a

woody branch had the highest quantity of activated areas and

the superior OER catalytic performance of all materials.[152]

Variable morphologies Mo/MnNixSy/NF may be manufac-

tured by adjusting the ratios of C2H5NS/CO(NH2)2and

H2O/ethanol in the chemical phase. Synthesis of Mo/

MnNixSy/NF with floral, grapes, and nanorod-like structures

is seen in their respective FE-SEM pictures (Figure 11a–g).[153]

The TEM picture (Figure 11h) displays the core configuration

of MMNSNRs2, in which the shells and base are composed

of MnNi0.96@NiS nanostructure and MoNi3S2nanowires.

The core configuration and large surface area of MMNS-

unique NRs2enable it to exhibit better electrochemical

performance toward both HER and OER (Figure 11i, j).[153]

2.5.2. Doping

Doping may efficiently modify the inherent molecular

configuration of a material, influencing its substrate’s adsorb-

ent capacity and electrochemical stability.[154–156] Doping a

material with external materials generates crystalline imperfec-

tions that may also drastically modify its electrochemical

performance. Moreover, including defectives, increases the

number of electrocatalytically adsorption sites inside

catalysts.[157] The following portion covers the relationship

between elements loading and an increase in the electro-

chemical properties of noble-metal-free catalysts. Various types

of metallic ions may be used as dopants to improve the

performance of metal-free catalysts. Doping with such materi-

als may drastically modify the electrical and systemic properties

of materials, hence changing their inherent properties.[158]

Prolonged X-ray absorbance finer structural (EXAFS) spectrum

reveals that the Mo loading in the hybrid state Co9Se8/CoSe

leads to structural shrinkage.[159] Reduction in binding energy

promotes metallic character in CoSe and increases its intrinsic

conductance. The projection densities state (PDOS) of CoSe

moves toward the Fermi level (EF) following Mo loading,

which is consistent with the quantitative findings. Co9Se8

displays remarkable HER catalytic performance, while CoSe

demonstrates low stimulation. Mo loading increases the H-

adsorption productivity of CoSe, and Mo at the interface

functions as an extra energetic site. After Mo treatment, the

electrocatalytic HER performance of CoSe increases, with

Co0.8Mo0.2Se exhibiting the maximum performance.[159] In a

hydrothermal process, nanostructure Fe-doped and undoped

CoSe2nanobelts are synthesized, and Co holes are formed

during the exfoliating process. With argon plasma etching, Se

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 14/65] 1

holes are produced in the agglomerated Fe-doped CoSe2

nanobelts (Figure 12a).[160] The electrocatalytic tests demon-

strate that including Fe and Co vacancies into CoSe2nanobelts

boosts the OER catalytic performance (Figure 12b). In

contrast, forming a Se hole has no appreciable effect on the

catalytic performance of Fe-loaded CoSe2. Computational and

observational studies imply that the electroactive location is

the Co-site next to the Co hole closest to the interface Fe-site.

As illustrated in Figure 12c, d, the Fe loading, and Co hole

effectively modify the molecular states of the energetic center,

resulting in optimum -OH adsorbents potential.

2.5.3. Imperfection Engineering

Dopants of any material containing heterogeneous elements

may result in imperfections. Such imperfection domains

increase the number of highly reactive activated locations and

promote the mechanism of the rate of diffusion.[161] It is also

possible to produce imperfections in the crystalline phase of

materials without heteroatom loading. Several physicochemical

techniques, such as ion illumination, UV-ozone therapy,

alkaline peeling, etc., are used to generate and design flaws in

non-metallic catalysts.[162] Consequently, imperfection manipu-

lation may be considered one of the most important

techniques for enhancing the electrochemical performance of

non-metallic catalysts. δ-MnO2nanostructures (NS-MnO2)

comprising of two monolayers are synthesized in situ hydro-

thermally on NF metal surface. Physiochemical properties

investigations show the existence of O holes in NS-MnO2,

which leads to the formation of coordination-unsaturated

Mn3+groups.[163] NS-MnO2has a high concentration of

electrocatalytically activated spots and a high electrically

conductance. According to a DFT simulation, the O gaps

promote the H2O absorption phase, while the coordination of

unbalanced Mn3+atoms gives δ-MnO2its semi-metallic

character. Consequently, NS-MnO2has enhanced polyfunc-

tional catalytic performance against both HER and OER.[163]

On carbon black that has been processed with acid, a

hydrothermal process produces a nanomaterial of Co3O4rich

in imperfection. The imperfection frequency in Co3O4nano-

particles may be altered by changing the hydrothermal

response time.[164] The maximum O-defect concentration and

Co2+/Co3+ratio were observed in the hexagonal Co3O4

produced after a 3-hour process (Co3O4-3 h). The comparative

oxygen vacancies rate in Co3O4-3 h is determined to be 8.5

atomic percent. The Co3O4-3 h nanomaterials have the highest

Figure 12. (a) Diagrammatic representation of the process for incorporating Fe loaded (DFe) CoSe2with Se vacant position (VSe) or Co vacancy (VCo); (b) Cell

voltage needed for particular electrocatalyst to accomplish 2.5 A F1power density in 1.0 M NaOH; (c) Energy band transitions of CoSe, CoO, FeSe, and

FeO peaks as a result of dopants and distinct vacant positions; (d) Gradient graph of estimated hypothesized cell voltage. Reprinted with permission from

Ref. [160].

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 15/65] 1

OER catalytic performance among all produced nanomaterials.

The hydrothermal process may generate an imperfection in an

electrode material, that can be amplified by extending the

process duration, although, the imperfection proportion could

be managed.[164] Removing electron-deficient components,

such as O, from a metal oxide raises the percentage of metal

with a reduced oxidized form. Such alteration in the valence

state of the metal pushes the electronic structure toward the

EF of the metal oxide, hence increasing its electronic

conductance.[164] The removal of anions from metal chalcoge-

nides by pyrolysis in a decreasing atmosphere may lead to

crystalline structure.[165] Two defect-engineered β-MoO2 nano-

particles are produced on silicon surfaces by heating modified

MoO3frameworks.[166] The XPS examination verifies the

presence of OHon the surfaces of the 7 h treated MoO2+OH

material (Figure 13a). As indicated by the XPS of the 9 h

heated material (MoO2x+OH), more O holes are absorbed

into the material as the heating duration increases (Fig-

ure 13b). The improved OER catalytic performance of

MoO2x+OHover MoO2+OHand MoO2(Figure 13c) implies

that O holes and OHsaturation boost the effectiveness in a

synergic manner. According to DFT simulations, the O holes

in the MoO2framework greatly decrease the OER redox

potential relative to those located on the interface. The

existence of OHon the surface significantly lowers the power

density. The OHfunctions as a coating material and speeds

the O2dissociation from the MoO2interface by decreasing the

binding ability of chemical mediators. In contrast, the O holes

improve MoO2conductance and lower its charging transport

impedance. After OER activation, the number of holes

decreases, suggesting that OHradicals from the electrolytes

penetrate the structure of MoO2x+OHthroughout the

procedure.[165] Rather than varying the pyrolysis duration, the

pyrolysis degree has indeed been altered in an identical manner

for Co3O4. Hydrothermally produced Co3O4intermediate is

heated at 300, 500, and 700 °C in air to produce defect-rich

Co3O4.[167] After pyrolysis, the Co imperfection and interfacial

oxygen are observed in the oxides developed. The Co3O4

produced at 300°C (Co-300) had the greatest imperfection

content compared to the other samples. The imperfection

proportion drops steadily as the heating degree rises. Simu-

lations imply that the Co imperfections modify the superficial

electrical properties of Co3O4by delocalizing electrons. Such

modification improves the material‘s conductance, the quan-

tity of catalytic active locations, and basic water absorption

capability. Owing to the largest imperfection density of all the

generated oxides, Co-300 has the maximum OER catalytic

performance.[167] The O holes are synthesized in a lattice,

NiFe2O4(NFO), by processing it with a mixture of H2and N2

vapor, and the imperfection intensity may be altered by

varying the reducing rate.[168] Computational simulations

reveal that O holes raise the d-band-center (Figure 13d, e),

Figure 13. O 1s spectrum for MoO2materials treated in 1.0 M KOH for (a) 7 h (MoO2+OH) and (b) 9 h (MoO2x+OH); (c) OER polarized graphs for MoO2x

Society, Estimated PDOS of (d) defect-free and (e) one O-vacancy integrated NiFe2O4. Reprinted with permission from Ref. [168] (f) HER polarized curves for

Chemistry.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 16/65] 1

increase the H2O absorption capacity, and thus increase the

catalytic active locations in NFO. The O gaps improve the

charge transport performance of NFO by adjusting its

electronics phase and introducing a large variety of imperfect

donor modes within the band structure. The defect-rich

microporous NFO with the greatest proportion of imperfec-

tion locations demonstrates higher OER catalytic performance

than to pure NFO.[169] Imperfection concentration increases

with the increasing heating degree, but the rise is capped at a

specific temperature. Although additional tuning is required,

thus, at 320 °C could be the upper heat range for NFO.[169] By

heating the mixture of cerium oxide (CeOx) material in the

air, the defect-rich NiCeOx material is immediately formed on

the NF.[170] Ni ions permeate from the NF throughout the

annealing operation and combine with the CeOx surface to

generate an O-vacancy-rich NiCeOx level. The O-hole

imperfections boost the OER catalytic performance of

NiCeOx by enhancing the number of activated locations and

decreasing mass transport resistance.[170] Heat treatment metal

oxides in an H2and/or N2environment generate the same

types of imperfections as in air, indicating that the N2in air

functions as a reduction gas.[170] To control the electrochemical

performance of transition-metal dichalcogenides (TMDs),

including MoS2and WS2,[171] imperfection manipulation is

widely applied. Temperature and time variations are discovered

to influence the imperfection density in an electrocatalyst.

Consequently, the impact of concurrent alteration in these

factors must also be comprehended.[172] Vertically aligned

2HWS2is processed in a hydrogen environment to integrate

S defects and embellish the framework with W metallic

nanoparticles. The annealed range, duration, and H2content

influence the S/W proportion in defect-rich materials, and,

therefore, the HER catalytic performance of the material. In

such a technique, the reduction environment not only

destabilizes the crystalline framework of WS2but also produces

a substantial quantity of metallic W. Computational simu-

lations indicate that the S-holes and W nanostructures in

defect-rich tungsten sulfide with a lower S/W ratio have extra

inherent catalytic performance than the WS2base plane. This

finding is supported by the HER catalytic performance of the

severely deficient tungsten sulfide (WS0.44) (Figure 13f). The

W metallic aggregates on faulty or immaculate basal planes

serve as catalytic active locations and improve the electrical

conductance of imperfect WS2.[171]

2.5.4. Strain Engineering

Computational and quantitative studies reveal that strain

propagation in a material may significantly affect its electrical

composition.[173] Because the catalytic performance of materials

is closely tied to their electronic configuration, and strain

designing may effectively adjust it. There are various

techniques to induce lattice strain in catalysts, with structural

mechanisms having the most promise. When structural input

is delivered to catalyst surface, a crystalline strain is

produced.[174,175] Whenever strong structural energy is given by

striking, and a strain is formed, the bond length in a catalyst

fluctuates.[176] Another successful approach for regulating

crystalline strain is to create a layering crack among the

catalysts and medium.[177] Temperature-induced aerial oxida-

tion is used to form a thin layer of n-loaded TiO2immediately

over NiTi foil. Its catalytic performance is studied after the

regulated tensile stresses are imposed.[178] Tensile tension

increases the interface reactive groups while decreasing the

activating obstacles in the catalyzed reaction. Furthermore, the

strain decreases the kinematic threshold for O-hole production

and increases the H-absorbance effectiveness of TiO2. As a

consequence, as the strain increases, the electrocatalytic

functionality of the films towards HER steadily increases.

Because the substrate is hard in composition, fractures form

when more strain is applied, which is a significant disadvantage

of such a method. Surprisingly, the catalytic HER performance

of TiO2increases even after fracture generation when strain

exceeds 5 %. On contrast, the catalytic OER performance of

TiO2increases up to 2 % implemented strain and thereafter

decreases.[178] Comparative research was carried out for MoS2

using a stretchable substrate.[174] The influence of dynamic

strain on the HER catalytic performance of dispersion of

MoS2nanostructures (NSs) is examined using interaction

printing on an Ag/polyethylene terephthalate working elec-

trode. Tensile-strain-induced MoS2has higher stimulation

than strain-free MoS2, and the production increases with

increased strain. When tensile strain is applied to MoS2, the

spacing among Mo particles increases, causing a change in the

d-band core. Such change boosts the quantity of electronic

configuration at the EF, which facilitates HER dynamics. On

the other hand, the substantial mass of MoS2nanostructure in

the working electrode, limits the electronic conductivity,

negating the impact of compressive strain on its catalytic

performance.[174] A compressive strain is formed in NiFe LDH

by ball milling, and Williamson-Hall evaluation of the X-ray

diffraction (XRD) variations indicates that the strain rises with

improving milling duration (Figure 14a, b).[179] Because of the

tensile strain production, the strength of the metal-oxygen

interactions in NiFe LDH increases, and as a result, its d-band

axis moves towards EF. Such transition occupies the anti-

bonding positions in the LDH, thereby, facilitating the

absorption of O-containing intermediates. Ball milling gen-

erates coordinatively unstable metal centers in the LDH, that

aids in the adsorbed process. Such two circumstances work

together to boost the catalytic OER performance of NiFe

LDH. The electrochemical investigation backs up this con-

clusion, and the NiFe LDH ball-milled for 15 hours is shown

to be more reactive than the pure one (Figure 14c).[179] The

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 17/65] 1

heterojunction of Ni2P/Co2P on NF is accomplished from

ZIF-67 by hydrothermal and phosphorylation methods.[180]

Throughout the phosphorylation procedure, the dissolving

and re-deposition of Ni2+generate many imperfections in the

Co(OH)F starting material, which produces stacked imperfec-

tions in the heterojunction. The stacked heterojunction

imperfection induces the tensile strain in Co2P along its (01–

1) plane. The lattice expansions downshift in the d-band

center of Co2P, and as a consequence, the heterojunction

exhibits optimal H-adsorption performance,[180] as indicated by

its improved HER catalytic performance. The impact of

stacked-induced imperfection stacking-defect-induce strain

production on the catalytic performance of various perovskite

materials has been widely studied.[180] PLD generates epitaxial

LaCoO3(LCO) films with a mismatched lattice to the

adsorbent.[181] Over insulating (001)-oriented SrTiO3(STO),

(LaAlO3)0.3(Sr2AlTaO6)0.7 (LSAT), and LaAlO3(LAO) sub-

strates, the films are generated on a surface of conducting

La0.67Sr0.33MnO3. Evaluation of the XRD spectrum reveals that

all three layers are ultrathin stretched. The progression in

catalytic performance toward OER is as follows: LAO <STO

<LSAT. The modest tensile stress generates a modification in

the electronic configuration of LCO, that is conducive to

achieving a higher level of activity. The insertion of tensile

strain modifies the localized symmetric of the LCO, which

increases the substrate’s adsorbent performance by modifying

the availability. The electrical transport performance of the

substrate and the strain-induced formation of defects in LCO

might also affect its electrochemical performance.[181] A

comparable experiment reveals that the perovskite-type

SrCoOx (P-SCO) film exhibits hole formation. The films’O-

holes and Co4 +/Co3+proportion are governed by the

interfacial strain (Figure 14d).[182] PSCO films with various

strains are developed using the same method as LCO films in

the preceding study. The increased tensile strain increases the

comparative quantity of Co3+in the film, which works as an

1perovskite catalyst in its intermediary electronic states. The

P-SCO film with a 4.2 % strain equals the performance of the

most advanced IrO2catalyst (Figure 14e, f). Similarly, the O

hole output is increased by the catalytic performance of films

despite the consequent decrease in its conductance. Such

findings imply that the catalytic performance of P-SCO film is

exclusively dependent on the adsorption-desorption perform-

ance of the substrate.[182] The number of holes may be

controlled by altering the strain type.[183] PLD is used to

develop La0.7Sr0.3CoO3(LSC) films on singular crystalline

LAO (100) and STO (100) substrates. LSC films generated on

STO (LSC/STO) and LAO (LSC/LAO) exhibit compressive

Figure 14. (a) XRD images and (b) matching Williamson-Hall analyses for NiFe LDH before to and after varied ball-milling durations, (c) OER polarized

patterns for pure and 15 h ball-milled NiFe LDH. Reprinted with permission from Ref. [179] (d) Plot illustrating the transition in Co4+vs. Co3+ratio and O

holes in SrCoOx(P-SCO) film with adjusting strain; (e) OER polarization graphs for the P-SCO film under various stains and IrO2in 0.1 M KOH; and (f

American Chemical Society.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 18/65] 1

and tensile strains in the planes. The catalytic OER efficiency

of the film under compressive strain (i. e., LSC/LAO) is greater

than that of the film under tensile strain (i. e., LSC/STO).

Theoretically, models suggest that the O holes generation

efficiency for LSC/STO is less than that of LSC/LAO, which

the XPS study verifies. The tensile strain generates more holes

in LSC than the compressive stress. Increased O holes in LSC/

STO increase accommodation in the egphases and lower the

bandgap energy among the O 2p and Co 3d band center

energies. As a result, the catalytic performance of LSC/STO is

lower than that of LSC/LAO. The OER-catalyzed efficiency of

both LSC/STO and LSC/LAO declines when excess holes are

introduced.[183] The OER catalytic performance of perovskite

may be simultaneously influenced by strain rate and O hole.

PLD is used to develop epidermal ultraportable NdNiO3

(NNO) films on single crystalline (001)t-oriented SrLaAlO4

(SLAO), (001)pc-oriented LAO, (110)o-oriented NdGaO3

(NGO), and (001)c-oriented STO substrates (subscripts “t”,

“pc”, “o”, and “c” stand for tetragonal, pseudocubic, and

orthorhom. For the NNO films formed on SLAO, LAO,

NGO, and STO, the computed strain ratios are 1.39,

0.47, +1.26, and +2.49 % (“” and “ +” represent tensile

and compression strain, correspondingly). The compression

strain is preferable to the tensile strain for OER catalysis,

whenever the O holes in the NNO film are minimal.

Compression strain produces the splitting of d-orbitals which

increases availability in d3z

2-r2and reduces NiO interactions

in coordination sites. The catalytic OER efficiency of NNO

rises, as the quantity of O hole rises owing to a relatively

enough tensile strain. The greater O hole in NNO enhances

the partial reduction of Ni3+to Ni2+. As a result, the occupant

in the egphase grows significantly more than 1, and the OER

catalytic performance of perovskite increases.[184] Recent

research reveals that the egoccupant determines the OER

catalytic performance of perovskite and that the one with an eg

occupant of one has the highest performance.[185] Whenever

the proportion of the O hole is minimal, the OER catalytic

performance of a squeezed perovskite is comparable to that of

a torsion strain perovskite.[183,184] Tensile strain promotes hole

development in perovskite, and its functionality increases as

the hole zone increases.[182]

2.5.5. Phase Engineering

Phase manipulation has demonstrated promising strategy for

modulating the electrochemical performance of metal materi-

als, particularly TMDs (like CoSe2, NiSe2, MoS2, MoS2

etc.).[186,187] The metal state of catalysts has the best ionic

conductance and substrate sorption desorption performance

relative to its semi-metallic or semiconductor materials

state.[186,187] The primary objective of phase manipulation is to

increase the proportion of catalysts in their metal state. The

mechanical annealed process in Ar environment was used to

generate cubic CoSe2(c-CoSe2) from its orthorhombic

structure (o-CoSe2).[188] According to DFT simulations, the

CoSe bond strength in cCoSe2is larger than in o-CoSe2.

Stronger CoSe bonds in c-CoSe2increase H2O absorption

(Figure 15a) and improve ΔGH* (Figure 15b) by targeting

additional electrons on the Se particle. Compared to oCoSe2,

metal c-CoS2has better electrical properties (Figure 15c). As a

result, c-CoSe2has better HER catalytic performance than o-

CoSe2(Figure 15d).[188] Furthermore, c-CoSe2exhibits higher

OER catalytic performance than its orthorhombic

structure.[187] The interstitial c-CoSe2/diethylenetriamine com-

posites were exfoliated using an Ar/O2plasma technique.[189]

Throughout the exfoliation, c-CoSe2is transformed into an

ultraportable o-CoSe2nanostructure with O vacancy-rich

oxide films on the interface (o-CoSe2

O UNs). Presumably,

estimated DOS indicates that the electronic structure is located

far enough from the EF of o-CoSe2

O (Figure 15e), facilitat-

ing the adsorption of O-containing substrates in OER.

Observational and computational findings indicate that phases

change and vacant position oxide interface output work

together to assist o-CoSe2

O attain higher OER catalytic

performance (Figure 15f). The findings of this study do not

support the effectiveness of oCoSe2as an OER catalyst. On its

interface, an O-vacancy-rich oxide layer emerges, which might

accelerate the process.[190] The selenization of the ZIF-67

catalyst with Se particles results for the synthesis of CoSe2

nanomaterials enclosed in carbon frameworks.[150] When the

selenization degree changes, an orthorhombic to cubic crystal

changeover happens in the encased CoSe2. The selenization

degrees of 350 and 600 °C, lead to the formation of the

completely crystallized o-CoSe2and c-CoSe2. Compared to the

oCoSe2, the c-CoSe2is reported to be more effective against

both HER and OER.[187] To manipulate the phasing of NiSe2,

an identical approach has been used. Comparable to CoSe2,

NiSe2is more efficient toward HER and OER in its cubic state

than in its orthorhombic structure.[191] NiSe2 NSs are

synthesized in a hierarchy structure using a two-step hydro-

thermal procedure on CC. At varying temperatures for the

selenization process, distinct stages of NiSe2NSs are produced.

When the heating rate falls below 120 °C, orthorhombic NiSe2

is produced, and the stage change begins. The cubic phases are

produced when the NiSe2mixing state forms at a temperature

of up to 180 °C. Comparing materials of NiSe2with a cubic

structure to those with orthorhombic and mixing phases, the

cubic phase NiSe2exhibits greater polyfunctional electro-

chemical performance.[191] A material first forms its extremely

robust modes at a moderate temperature, which are sub-

sequently transformed into its metastable stages as the temper-

ature rises.[187,191]

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 19/65] 1

2.5.6. Heterostructure Formation

Heterojunction generation is a frequently used technique for

enhancing the effectiveness and sustainability of

catalysts.[192–206] The integration of two or more transitional

metal compounds simultaneously increases their unique

catalytic performance.[207–215] Employing one substance effec-

tively towards OWS yields the polyfunctional performance of

HER and others concerning OER.[207,208] Whenever a material

creates a heterojunction with carbon-containing components,

its number of activated sites and functional reliability

improve.[216] The FeV nanomaterials adorned over the NiO

nanostructure exhibit simultaneous improvement of electro-

chemical properties towards OER. The heterojunction is

formed immediately on NF base using a two-step hydro-

thermal procedure, demonstrating better performance after in-

situ oxidation.[207] During the oxidization, the Fe and V ions

are absorbed into the NiO structure, forming polymorphic

(oxy)-hydroxides. The electrochemical performance of the

heterojunction developed after 10 hours of oxidation is better.

The higher functionality of heterojunction is due to its

hierarchy design and synergistic connection among the

constituent pieces.[207] The microscopic “Kirkendall Effect”

during the synthesis of Co2+of ZIF-67, OH, and MoO4

2is

used to generate CoMoO4-Co(OH)2hollowed intermediates.

By interacting with NH3, the material is transformed into a

CoO-Mo2N hollowed heterojunction.[217] The hollowed heter-

ojunction aids mass transport during the operation, while the

CoO accelerates the water hydrolysis stage. All constituents of

the heterojunction promote the HER-catalyzed mechanism,

resulting in higher performance.[217] The electrocatalytic OER

performance of MnO2is restricted by its low electromagnetic

conductance.[218] The CoP3has a good internal affinity towards

OER and outstanding electrical conductance. The integration

of CoP3with MnO2improves the latter‘s electrical properties

and OER catalytic performance.[218] A two-step hydrothermal

approach is used to immediately construct a NiCo2O4/Ni3S2

heterojunction on the NF.[219] The NiCo2O4in the hetero-

junction enables water absorption and shields the Ni3S2from

electrochemical deposition and catalytic toxicity. Because of

the improved electron transport mechanism and synergy

interactions among the analogs, the heterojunction exhibits

better OER catalytic performance.[219] Edge-terminated MoS2

is developed using two microwave hydrothermal fabrication

methods, accompanied by a layer of NiCo-LDH.[220] The

interaction of the MoS2/NiCo-LDH heterojunction is impor-

tant in HER processing because it accelerates the rate-

determining water separation phase (Figure 16a, b). The DFT

simulations indicate that the interaction facilitated the H

adsorption activity on MoS2and the OHadsorption processes

on the LDH in a symbiotic way. As a result, the fabricated

heterojunction outperforms MoS2and NiCo-LDH in HER

catalytic activity.[221] By effectively linking 2H phase MoS2

with its 1T phase and MoO3, the HER catalytic performance

Figure 15. (a) Predicted H2O absorption potential and (b) HER energy storage graph for cubed (cCoSe2) and orthorhombic CoSe2(o-CoSe2) materials;

(c) thermally activated impedance of c-CoSe2and o-CoSe2; and (d) HER polarized graphs in 1.0 M KOH for bare carbon cloth (CC), Co(OH)F/CC, oCoSe2/

CoOx; (f) Polarization curves for c-CoSe2/diethylenetriamine (DETA), Ar plasma initiated electrospun CoSe2ultraportable nanostructure (c-Ar-CoSe2UNs), Ar/

O2plasma driven exfoliated CoSe2ultraportable nanostructure. Reprinted with permission from Ref. [190].

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 20/65] 1

of 2D MoS2film is increased. During the hydrothermal

process, glycine is agglomerated into the MoS2layers, assisting

in the formation of this heterojunction.[172] A one-pot hydro-

thermal approach is used to create CoSe2/CNT composites

with an intertwined configuration of CNTs incorporating

ultra-small NPs (Figure 16c).[222]The quantity of CNT is

tuned in the perspective of HER catalytic properties, and the

hybrid comprises 14.7 wt.% CNT outperforms the others

(Figure 16d). The higher functionality of the mixture is

attributable to (i) the abundance of catalytic activated sites

caused by the creation of tiny CoSe2NPs and (ii) increased

electron transport kinetics caused by the existence of an

optimal quantity of CNT.[223] According to previous debates,

heterojunction development between two materials may be

advantageous in various ways. When the components of a

heterojunction can each accelerate a similar electrochemical

process, the catalytic performance of the heterojunction is

effectively boosted.[224] A conducting substance may be used to

increase the electrical properties of a catalyst. When an

electrocatalyst is combined with a carbon-containing substance

with a large specific surface area, the catalytic activated

locations increases.[224] An outer-layer material contained in a

heterojunction may shield the internal catalyst from electro-

chemical deterioration.[224] A heterostructure surface has a

considerable impact on its electrochemical properties.[225] On

the CC, a hierarchy-stemmed heterojunction of CoP-FeP is

immediately produced, which has better reactivity against both

HER and OER.[226] The n-type semiconductors CoP has a

band structure of 1.7 eV and a CB of 0.21 eV. On the other

hand, FeP, has a band structure of 0.8 V and a CB location of

0.059 V (Figure 16e). The binding energy of CoP is lesser

than that of FeP. As a result, electrons are emitted from CoP

to FeP till their surface energy achieves equivalence (Fig-

ure 16f). The improved electron configuration and dissipation

factor throughout electrochemical processes enhance electron

transport and substrate absorption.[227] For CoSx/Ni3S2hetero-

structures formed directly on NF using a one-step hydro-

thermal procedure, a synergistic impact toward polyfunctional

WS performance is shown.[228] The increase in catalytic activity

is ascribed to I the production of CoSNi in the interfacial

area, (ii) an increase in the number of catalytically active sites,

and (iii) an improvement in substrate adsorption-desorption

kinetics.[228] Similarly, better polyfunctional performance is

seen for the CoSx/MoS2hierarchy heterojunction.[229] The

XPS study demonstrates that the VB of the CoSx changes

following heterostructure generation with the MoS2. In

addition to the other impacts, this alters the electrochemical

performance of materials.[229]

Figure 16. (a) ECSA standardized polarization curves for MoS2and MoS2/NiCo-LDH in 1.0 M KOH; (b) energy storage schematic of the dominant Volmer-

Elsevier, (e) Graphical of CoP and FeP band structures before heterostructure development, and (f) electron transport among CoP and FeP at the CoP-FeP

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 21/65] 1

2.6. Electrolytic Cell

In the traditional water electrolysis process, scientists used

noble metal or transition electrocatalysts and flanges in an

aqueous medium (alkaline water electrolysis, AWE) catalysts

along with proton-conducting substrate in an acid medium

(PEM water electrolysis).[230]

2.6.1. Alkaline Water Electrolysis (AWE)

Since, the first discovery of the process of water electrolysis via

Troostwijk and Diemann in 1789, the alkaline water

electrolysis process is a recognized method of H2generation.

Thus, alkaline electrocatalysis has become the most extensively

used electrolysis technique around the world.[231] This AWE

usually employs 20–30 % KOH solution as the electrolyte.[232]

The alkaline electrolyzer configurations consist of a conformist

alkaline electrolyzer, a “zero-gap” and a membraned or

disentangled alkaline electrolyzer. Typically, anodes and

cathodes are positioned on either edge of the plain power

source in an alkaline electrolyzer to facilitate a sequential

interaction among cells.[233] The generation of H2and O2

usually occurs in distinctive electrolyte vessels, and a mem-

brane prevents their mixture (Figure 17a). This technique

seems to be handy for mass-volume H2production. However,

the adsorbed gas bubbles reduce the effective surface area of

the electrodes and increase the electrolyte barrier, resulting in

reduced applied voltage. The other problem with AWE

electrodes made from Ni-premised materials is that their

performance for HER and OER keeps worsening over time.

Electrolyte impurities cause metal ions deposition on the

electrode surface, which results a reduced activity for HER.

Schuhmann and Ventosa et. al. came up with a solution

mainly depending upon the self-synthesis of electrocatalyst in

the electrochemical cell technique to make immensely stabi-

lized catalyzed films that have the capability to recover

themselves (Figure 17b, c). They have shown that zinc

particulates in the electrolyte can cause the cathode to become

inactive. This can be fixed by inactivating the catalyst through

self-assembling and self-healing films. In this electrochemical

reaction, zinc particulates accumulated at the cathode, which

increased the HER overpotential. However, the coated zinc

was covered by a catalyst film, which kept coming together

and fixing itself. This brought the HER overpotential back to

where it was supposed to be.[234]

In “zero-gap” conformation, the thin cellulose stack

constituted in space among electrodes absorbs electrolyte that

is constrained among two hydrophilic splitters firmly attached

to the cathode and anode. The cathode and anode should be

porous in nature to allow the electrolyte. Hence, vapors

formed at the internal side of the electrode would be

proficiently removed.[233] For example, Dunnill et. al. demon-

Figure 17. (a) Diagram depicting a typical alkaline electrolyzer. Reprinted with permission from Ref. [233] (b) diagram depicting the configuration of the catalyst

film, (c) Scheme depicting cathode depletion due to the accumulation of detectable metal particulates and the transform significant potential in an electrolytic

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 22/65] 1

strated that using a zero-gap cell framework could decrease

30% of ohmic resistance compared to a common 2-mm gap

aqueous electrolyte (Figure 18a, b). In all current densities,

especially over 500 Ma/cm2, the zero-gap setup battery

performed more effectively than the traditional cell. Moreover,

foam electrodes have higher surface area and hence possess a

low ohmic resistance than a coarse mesh electrodes. Hence, the

zero-gap setup is considered cheap and effective in aqueous

electrolysis.[235] The anode and cathode can also be modified

upon separator to further reduce the gaps.[236] For example,

Tour et. al. utilized laser-induced graphene (LIG) as OER and

HER electrocatalysts on both sides of a polyimide (PI) film to

fabricate effective electrodes for the water electrolysis. LIG was

designed on both edges of a (PI film, and LIGCoP and

LIGNiFe) were compiled over different sides via the electro-

deposition process (Figure 18c, d). OHions could penetrate

through a tiny pinhole at the film’s end, which in massive

technologies may be surrounded by ion transfer membranes.

This LIGCoP and LIGNiFe instruments for WS obligated

1.66 V to achieve 10 mA cm2current density in 1.0 M

KOH.[237]

During the aqueous electrolysis of water, the electrolyte

solution’s permeability is far significantly higher than that of

the electrolyte membrane, deriving remarkable resistive

liabilities.[238] As a result, Gillespie and Kriek created a non-

membrane DEFT alkaline electrolytic cell to produce H2. This

electrolyzer can resolve emerging innovations’power density

threshold constraints, making it a superlative alternative

towards H2evolution (Figure 19a). The scale-up technology

took a distinct path from the initially evaluated stacking,

which included multiple thin electrodes in a vacuum filtration

device (Figure 19b, c). The pilot plant could have a low flow

rate, and the space between the electrodes could only be

2.5 mm. The pilot plants’ efficiency was comparable with

previously acquired outcomes. The mesh electrode used in

plant productivity testing had a surface area of 344.32 cm2. At

parameters of 0.04 m/s1, 30 % KOH, 2 V direct current

(VDC), and 80 °C, the NiO anode and Ni cathode mixture

Figure 18. (a) Mechanism depicts reducing the gap among electrodes by employing a cell with zero gap, (b) Zero-gap cell framework, such as machined stream

field panels, silicone gaskets, grid electrode materials, and Zirconia air splitter. Reprinted with permission from Ref. [235] (c) illustration and (d) image of an

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 23/65] 1

achieved a maximum of 508 mA/cm2. Owing to the sensitivity

of gas-liquid isolation process, gas volume was inadequate

compared to earlier studies.[239] Gillespie and Kriek created a

comprehensive and simple mono-circuit filtration press

(MCFP) reactor for DEFT alkali electrolysis to produce highly

purified gas in the DEFT electrolyzer (Figure 19d). At a

flowing velocity of 0.07 m/s1and electrode spacing of 2.5 mm,

the applied gas/liquid separating technique rallies the gas

purity of H2to 99.81 vol % and O2to 99.50 vol %. Every

30 mm circular mesh electrode pairing has an individual

pressurized container with oblique electrolytes infusion. By

including gas purging, longer-lasting gas purification could be

achieved. The power density for the Ni/Ni catalyst was

1.14 A/cm2(2.5 VDC) at 0.075 m/s1, 60°C, and 2.5-mm

electrode spacing. Power density achieved of 1.91 A/cm2at 2.5

VDC, indicating the availability of multilayered highly porous

electrodes for the DEFT concept (Figure 19e).[240,241]

Using redox intermediates to separate the two half-

reactions of WS inhibits the mingling of as-generated H2and

O2, and these are particularly advantageous for large-scale

practical uses[242] Grader et. al. designed an electrochemical

thermally induced chemical (E-TAC) cycle with two steps for

OWS. The H2was produced at the cathode by the HER. The

conventional OER was swapped with two stages. The

oxidation of Ni(OH)2anode led to the formation of NiOOH

in the first stage via four one-electron oxidation processes.

Followed by the second step, the NiOOH is dynamically

decreased to Ni(OH)2and simultaneously, O2and anode

regeneration are produced. Researchers also postulated a

multicell setup with constant cathode and anode in every cell

to generate pure H2and O2gas, as shown in Figure 19e. The

low-temperature based electrolyte was passed across cell A,

propelling the as-generated H2towards H2separator. During

this time, electrolytes with high temperature tend to be flowed

via cell B in order to recharge the anode counterpart, thereby,

propelling the as-produced O2towards O2separation site. In

the functioning of such kind of multicell setup, solitary

migration of cold and hot electrolytes is initiated.[241]

2.6.2. PEM Water Electrolysis

In the 1960s, General Motors came up with the idea of solid

polymer electrolyte (SPE) for water electrolyzers to make up

for alkaline electrolyzers. Grubb perfected such an assumption

Figure 19. (a) Schematic depicting the integrated filtering mesh electrode in a single insertion configuration, (b) an image of the DEFT electrolyzer stacking for

and (e) a diagram depicting the multicell setup using the E-TAC method. Reprinted with permission from Ref. [241]

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 24/65] 1

using solid sulfonated polystyrene membranes as the electro-

lyte. One such process is called PEM water electrolysis, which

is rarely called SPE water electrolysis.[243] This PEM could

provide high conductivities, reduced air transfer, a compressed

procedure layout, and work at high heat.[244] The advantages of

polymer electrolytes include thin membranes (20–300 m). The

covering of the catalyst and Nafion ionomer on the edge of a

Nafion 117 membrane was uniform after the PTFE sheets

were detached from the membrane and compressed against all.

On the surface of the membrane, the margin across the

catalysts coatings and membrane was visible. By adjusting the

quantity of catalyst ink, the coating thicknesses could be

modified.[245] In the commercialized PEM aqueous electrolyzer,

the other sides of a Nafion 117 membranes were treated with a

Pt/C and Nafion ionomer membrane, as well as a covering of

IrO2or RuO2catalysts and Nafion ionomer (Figure 20a). The

PEM water electrolyzer anode was loaded with water. Water

ran across the separating layers and voltage detectors in

succession. Once water contacts the interface of a catalyst

material, it decomposes into protons, electrons, and polyatom-

ic oxygen. After leaving the anode, such protons passed via the

cathodic edge through the ionomer and membrane, interacting

with electrons to form H2with the aid of catalysts.

Subsequently, H2escaped the cells via the cathode collectors

and the barriers. The electrons immediately left the cathode-

catalyzed phase through the power detector, the separating

planes, and the cathode edge. The O2would return to the

separating planes through the catalyst surface and voltage

detector before leaving the cell (Figure 20b).[246] The PEM

electrolyzers can run at power concentrations of more than

2 A/cm2, which reduces operating expenses. The ohmic

degradation limited the maximum density of currents. The

membrane’s exceptional proton conductance and increased

current intensities result from its thinness. Due to the reduced

gas crossing ratio of the polymer electrolytes membranes, the

PEM electrolyzer could function with a broad variety of energy

demands. In PEM electrolysis, the phenomena of cross-

permeation grew with increasing operating force.[247] Compres-

sive stress (more than 100 bar) necessitated the use of broader

membranes to reduce the merging of H2and O2to sustain

peripheral quantities under the safety threshold (4 vol % H2in

O2). The corrosive acidic location in PEM electrolysis

necessitated the use of specific materials that require resistance

to intense low pH erosion (pH ~ 2) and significant overload

(2 V).

2.6.3. Seawater Electrolysis

Electrolysis of the water scheme generally comprised of two

half-reactions: HER at the cathode and OER at the anode. In

comparison to purified water, salt water is the highest

prevalent aquatic electrolyte. Bennett investigated saltwater

electrolysis,[248], whereas HER occurred at the cathode and the

chlorine evolving process (ClER) occurred at the anode.[249]

ClER is a two-electron technique that produces chlorine or

hypochlorite as a value-added output.[250] Trasatti subsequently

studied the sensitivity of anodic processes using multiple

anodes in freshwater electrolysis.[251] Dionigi et. al. investigated

the constraints of freshwater electrolysis in 2016 and devised a

technique for fabricating specialized freshwater splitting

Figure 20. (a) Schematic illustrating the operational mechanism and (b) component of a PEM water electrolysis. Reprinted with permission from Ref. [246]

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 25/65] 1

electrocatalysts.[252] The membranes, including Zirfon in the

freshwater electrolysis technique, are relatively strong and

impervious to obstructions since most of the obstructing ions,

like H+, Na +, OH, and Cl, may move across it.[249] The

ClER at the anode and HER at the cathode were obtained

using a RuO2/Ti working electrode and a Pt counter electrode

(Figure 21a). The FE of hypochlorite drove up progressively as

the electric voltage at the anode moved up to 99 % of the

electric voltage of 1.5 V vs. RHE on the RuO2/Ti electrode

(Figure 21b).[253]

2.7. WS Driven by a Photoelectrode Device

A two-electrode setup may efficiently create H2from electro-

lyzed water. However, tremendous electrical energy is required

to surmount the kinetics obstacle in water electrolysis. In the

photo-electrochemical (PEC) electrolysis cell,[254] the photo-

anode collects solar energy to generate photovoltaic energy,

which conveniently drives WS, while substantially reducing

the additional energy required.[255] To reduce additional energy

utilization and realize unaided overall light-induced WS, a

tandem arrangement with complementing optical emission

among distinct semiconductor electrodes may generate a

comprehensive photovoltage.[256,257] To reduce further energy

consumption and accomplish unassisted global light-induced

WS, a tandem setup with complementary optical emissions

between different semiconductor electrodes may be used to

yield total photocurrent. Such a tandem setup produced a

complete voltage of 1.87 volts, sufficient to meet the essential

thermodynamics and kinematic prospective of 1.6 volts, and

no additional input is needed for water electrolysis.[258] The

Jun and Lee et. al. (Figure 22b) proposed the cobalt carbonate

catalyzed, H2and 3 % of Mo/BiVO4(CoCi/H, 3 % Mo:

BiVO4) device in series with CH3NH3PbI3single-junction

PSC would realize wireless solar WS under AM 1.5G without

external energy production. The STH performance of such a

system was increased to at least 3.0 % through the

enhancement of photoanode activity (Figure 22a).[259] Luo et.

al. demonstrated that a semi-translucent CH3NH3PbBr3PSC

paired with a CuInxGa1xSe2(CIGS) multilayered photo-

cathode would panchromatically capture the sun radiation for

optimal OWS (Figure 22c). Over 6% STH performance was

achieved for this PV-PEC system employing a single-junction

PSC as a bias generator under AM 1.5G illumination. In

contrast, its performance could be increased by more than

20% by putting an optimized perovskite absorption at the

top.[260] Qiu et. al. fabricated a single PSC in conjunction with

a nanostructured Mo/BiVO4photo-anode PEC cell by using a

beam splitting to divide a normal sunlight beam into two light

photons (Figure 22d). The PSC-PEC sequential device accom-

plished unaided WS with a STH performance of 6.2% and

protracted durability over 10 h (only 5.8 % degradation).[261]

Dye-sensitized solar cells (DSSC) in conjunction with photo-

electrodes are a viable solution for unmanned WS due to their

efficient energy supply, low cost, and eco-friendly character.[262]

The Sivula et al. constructed a mechanism for unimpeded WS

employing WO3or Fe2O3photo-anode in conjunction with a

DSSC. In such a system, the photoanode received light well

before the underlying DSSC. The STH activation performance

of the WO3/DSSC serial device was 3.10 %, whereas the

Fe2O3/DSSC tandem system was 1.17 %. The optic trans-

mittances and spectrum sensitivities of such two tandem

devices were following the oxide band gaps, defining the

potentiostatic and device functionality. The functionality of

Fe2O3/DSSC PEC tandem cells was maintained at 80 % for

more than 8 h, which could be attributed to DSSC disintegra-

Figure 21. (a) Schematic of the electrocatalytic cell that makes HER at the cathode and hypochlorite at the anode, (b) The FE of hypochlorite depends on the

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 26/65] 1

tion. As a result, the arrangement is determined by the redox

agents and catalysts used in the DSSC and photo-anodes,

correspondingly.[263] Wang and Park et al. demonstrated a

5.7 % STH with no outside bias in an unaided monolithic

twin device combining the high stability of BiVO4-sensitized

macroporous WO3films/Pt with a singular DSSC (Fig-

ure 22e). The BiVO4treatment on the porous WO3film, on

the other hand, retained the high transmittance, permitting

sufficient light to penetrate the dye-sensitized photo-anode.

The porphyrin-dye activated photo-anode with a cobalt

electrolyte can accomplish wirelessly photovoltaic WS in the

dual setup.[264] Mora-Sero and Gimenez et al. created a dual

system for WS without outside biases by connecting a CdS qds

customized TiO2photo-anode to a DSSC (Figure 22f). This

gadget has a 0.78 % STH yield and greater durability. This

was critical to construct composite photo-anodes with diverse

photon absorbance in order to create successful WS

systems.[265]

2.8. WS Driven by Solar Cells

Solar cells, such as Si solar cells, CIGS solar cells, PSCs,

organic solar cells (OSCs), and DSSCs[257,267] etc. may convert

excess solar energy into storable and composable fuel sources.

The photovoltage of solar cells placed in sequence may also be

utilized to electrolyze water.[268]

2.8.1. By Conventional Solar Cells

Various associated prismatic standard solar cells, including Si

and CIGS solar cells, are potential in WS employing the

photovoltaic (PV) cell due to significant STH performance

and sun-driven stability for H2production.[269] The Gan and

Zhang et al. created a bimetal complex NiFeSP on conven-

tional NF (NiFeSP/NF) for OWS in conjunction with a Si

solar cell (Figure 23a). The potential of the dual device

integration of the Si solar cell and the polyfunctional NiFeSP/

NF electrodes for WS was 1.58 V to achieve a current density

of 10 Ma/cm2, equating to a STH converting performance of

9.2 %.[270] Whereas Shen et al. explored the combination of

three Si solar cells in sequence (total area of 3 cm2) with a

double-layer NiCoS/NiCoP catalyst on NF (NCS/NCP/

NF) electrodes for unimpeded WS (Figure 23b). At 1.49 V, a

current density of 10 mA/cm2was reached using the NCS/

NCP/NF as polyfunctional catalysts for WS. Ultimately, the

whole solar WS was completed with a STH performance of

10.8 %.[271] Ryu and Kim et. al. investigated WS by connecting

four Si-doped solar cells in series with polyfunctional NiFe

nanomaterials catalysts (Figure 23c). The overpotential of the

NiFe inverted opal electrolyzer for WS was 160 mV, resulting

in a STH transformation performance of 9.54 % after 24 h of

operation under impartial circumstances.[272] In contrast to Si

solar cells, the advantage of CIGS is that the band-gap energy

American Chemical Society, (b) Structure of CoCi/H, 3 % Mo: BiVO4and TiO2/CH3NH3PbI3dual cell. Reprinted with permission from Ref. [266] Copyright

Association for the Advancement of Science, (e) illustration of the WO3/BiVO4photo-anode dual framework, Ref. [264] (f) graphical illustration of the PEC-

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 27/65] 1

could be regulated to effectively capture the sun spectra,

allowing it to be widely used for WS.[273] To circumvent the

shortage of modest potential to operate OWS, integrated serial

into a monolith circuit may be used to generate adequate fuel

for the complete response. For example, Jacobsson et al.

claimed that three series-connected composite semiconductor

CIGS PV electrolysis may successfully generate solar WS at

AM 1.5G illumination (Figure 23d). The current density was

8.5 Ma/cm2, and the STH converting performance was

10.5 %.[274] Jacobsson et. al. demonstrated that such a CIGS

solar cell could convert WS into H2. Researchers used a p–n

circuit to segregate the charges and fabricated a catalyst on the

interface to significantly improve the functionality of a PEC

cell arrangement (Figure 23e). In this case, the efficient

charging segregation of the catalyst enhances the endurance of

CIGS in photoexcitation. Furthermore, the photocurrents in

such a system might exceed 20 Ma/cm2. The full capability of

CIGS as an absorbing medium for WS was shown. Researchers

have shown the maximum capabilities of CIGS as an effective

absorption agent for WS[275].

2.8.2. By Perovskite Solar Cells

As we talked about in the last category, modular mechanisms

of WS should utilize three or four linked cells in sequence to

get reasonable productivity. This is because Si solar cells have a

low open-circuit prospective. In contrast, Perovskite Solar

Cells (PSCs) have reached open-circuit potency between 0.9

and 1.5 V,[276] which is sufficient for functional WS with just

two parallel connectors.[277] The Gratzel created the dual PSC

in electrolytic WS with effectiveness. In this study, a WS setup

was integrated with a solution-processed dual PSC and NiFe

LDH used as anode and cathode in an alkaline medium

(Figure 24a, b). The dual two-electrode setup yielded a photo-

current intensity of 10 Ma/cm2with a STH performance of

12.3 percent.[278] The Bhattacharyya et al. suggested that NiFe-

alloy nanomaterials endorsed by N, S-doped nanoporous

structure from seaweeds would be promising electrocatalysts

(Figure 24c). Just 1.61 V was required to keep 10 mA/cm2of

current flowing through OWS for an additional than 200 h.

When used with PSCs, the OWS electrolyzer gave a STH

performance of 9.7 %, which is fueled completely by renewable

radiation.[279] Jin et. al. suggested using a polyfunctional

bimetal phosphide (Ni0.5Co0.5P/CP) with all-inorganic PSCs

(predicated on a CsPb0.9Sn0.1IBr2photo adsorbent and a

carbon-based electrode) to make an efficient OWS. The WS

electrolyzer could get a current density of 10 Ma/cm2at

1.61 V with a STH converting effectiveness of 3.12 % and

excellent stability.[277]

American Chemical Society (b) using NCS/NCP/NF electrodes and Si photovoltaic panels as the photoanode for unaided WS. Reprinted with permission from

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 28/65] 1

2.9. WS Through Thermoelectric Device

WS, with the use of solar cells, is a prevalent energy-driven

method. However, the sunlight transformation performance of

photovoltaic systems is relatively modest since they are most

effective for UV and visible light. Traditional semiconductors’

solar energy generation equipment could not utilize infrared

light adequately. Integrating TE technology with infrared-

active materials provides a specialized approach for converting

infrared sunshine to energy, hence improving solar energy

usage performance.[280,281] Consequently, the exploration of

WS mediated by TE technology is prevalent.

2.9.1. By Surface-Modified Thermoelectric Device

Infrared light generally provides energy as heat via photo-

thermal effect.[282] Converting this released heat to electricity is

a distinctive technique for using infrared light. Such trans-

formation would likely be accomplished by TE technology.[283]

However, the surface of conventional TE technology is

incapable of absorbing infrared light. To improve the perform-

ance of TE devices, it is necessary to increase their ability to

absorb infrared light.[284] Thus, it encourages integrating

photo-thermal materials onto the TE device to improve the

activity of photo-thermoelectric transformation.[285] Materials

with a significant photodynamic transformation performance

often include Group VIII materials, graphene oxide (GO),[286]

carbon nanostructures, transitional metals oxide (e. g. MoO2,

WO3, FeO3), and chalcogenides (e. g., Cu2S).[287] The photo-

thermal impact of GO was first suggested for a TE device in

2014.[285]. The GO drop-coated on the surface of the TE

device can turn infrared light into energy which could be

utilized immediately in a photo-electrocatalytic system with no

electric voltage. The thermal infrared portrait demonstrates

Figure 24. (a) Graphical illustration and (b) a broad description of the energy of the dual PSC for WS. Reprinted with permission from Ref. [278] (c) strategy

2018, Royal Society of Chemistry.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 29/65] 1

that impregnation of the GO layer might also improve the TE

device’s reactionand make the TE device’s reaction. Research-

ers also put a sheet of light-absorbing carbon nanoparticles

(CNP) on the edge of the STEGs to make them better at

absorbing illumination. Here, the black CNP sheet on the

heated portion of a conventional TE device was made using a

simple candle fire method (CNP generator). Such a CNP sheet

must have a 3D permeable configuration which helps it absorb

light, and the energy from this STEG device can run an

electrolyzer to separate water (Figure 25a, b). In such a WS

scheme powered by a TE device, 6 pairs of CNP-coated

thermoelectric generator devices were associated in sequence to

create enough capacity for water electrolysis. After integrating

the TE machine into the electrolytic system, the solar spectrum

caused a huge number of balloons to form at the cathode and

anode. The average rate of making H2and O2was 20 and

10 mol/h1, highest between 11: 40 am and 12 : 40 pm (Fig-

ure 25c). Such research proved that the yield power supply of

the TE device could move the H2production from WS by

encasing the warm edge of the TE device with nanoparticles

which dissipate light and turn it into heat.[288] Researchers then

made an array of Ni nanostructures that grew on the outer

edge of a TE device to electrolyze water. They were motivated

by a double design impact of surface plasmon resonance (SPR)

photo-thermal transformation and effective catalytic perform-

ance for group VIII metals. Ni nanostructures cluster was used

as an electrocatalyst and a light-absorbing sheet in this

interaction. The output power of such an incorporated scheme

was used immediately to electrolyze water. It can replace

traditional energy consumption. It was found that the Ni

nanostructured array worked well as the photodynamic trans-

formation layer for TE and as an electrode material for HER

(Figure 25d, e). This electrolyzer-TE device was made to

divide water into H2and O2in a two systems at a rate of

1.818 and 0.912 mmol/h, (Figure 25f). The incorporated TE

device was very helpful in modeling WS systems, making it

easy to utilize solar thermal energy and waste heat in the

future.[289]

2.9.2. By Integrated Photo-Electrochemical Thermoelectric

Device

Factors that affect TE conversion efficiency are the Setback

coefficient (or thermopower), and electrical and thermal

conductivity.[290] Based on these factors, the energy conversion

efficiency of the TE device (5–10 %) is low, in comparison to

PVs (up to 46 %).[291] Therefore, researchers have hypothesized

that coupling of TE and PEC interaction may significantly

enhance solar energy harvesting and WS performance.[292] In

1984, Nikola Getoff was the pioneer to use this conjunction of

PEC and photothermal-electrochemical cycles for H2synthesis

with solar energy,[293] conducted in an acidic aqueous solution

with I2and I3as the activator in the existence of ferrous ions.

With the inclusion of the TE device, the unconsumed

radiation creates heat that the TE device converts partly into

energy. Consequently, the performance of H2production was

Figure 25. (a) Temperature dispersion of (i) hot and (ii) cold part of bare generator; (iii) hot edge and (iv) cold edge of CNP engine under 1 solar radiation,

(b) configuration that shows how 6 STEG devices wrapped in sequence motivate the OWS process, (c) The WS scheme makes both H2and O2at distinct times.

film (II), and Ni nanostructure/Ni film (III), (e) depiction of electrolyzer-TE hybrid device, (f) H2/O2generation versus time. Reprinted with permission from

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 30/65] 1

increased by 30 % relative to a simple PEC round. Since,

however, no more research on photothermal-electrochemical

WS has been conducted till 2015. Sun-Mi Shin team[294–296]

suggested two studies about the incorporated PEC-TE device

in WS that uses photovoltaic fuel and waste heat energy to

make H2energy that can be stored and moved. When a

composite of WS devices was used in a WS process, 55 mW/

cm2of electricity was generated for H2generation, which is

about 4-fold more than a single PEC cell. In aspects of overall

charge transported, the amount of H2assessed was the same as

the conceptual valuation of 100 % Faraday effectiveness (FE),

which means that all of the charges that has been made to

make H2. Also, this composite procedure didn’t need to utilize

noble metals like Pt or Ir even though the thermovoltage sole

can counteract the thermodynamics overpotential.[16] The

researcher explained that WS could be improved by changing

the Fermi threshold of the counter electrode with ΔT

(Figure 26a–c). Even though, the energy band probabilities of

semiconductors must be between the reactive sites of H2and

O2for the full PEC process with no exterior bias. As the

minimal VB of silicon proved insufficient for oxidizing the

water source, and therefore silicon cannot be regarded a

possible semiconductor in spontaneously WS (Figure 26b).[294]

A TE device is coupled to a PEC cell, and the supplied VTE

may modify the Fermi state of the counter electrode. Although

the working (p-Si) and counter (Pt) electrodes were connected

to the positive and negative terminals of the TE device,

therefore the electrons infused from the Pt counter electrode

traveled via the wires to the TE device anode. Consequently,

the Fermi energy barrier decreased towards greater bright

prospects, whereby the Fermi energy value of Pt matched that

of the TE device (Figure 26c). As the Fermi barrier of metal is

often smaller than the oxidation state of water, and the

application of VTE causes water molecules to be spontaneously

oxidized.[294] Wang et. al. constructed a unique PV-TE

composite system consisting of a sequential DSSC, a solar

selected absorber (SSA), and a TE generation, providing some

impetus for developing a highly optimal PV-TE composite

system. The researcher has demonstrated that solar radiation

may be split into two streams, with UV–visible light absorbed

by a solar cell and infrared light absorbed by a TE generating

for transformation into energy in this composite system, which

enhanced the efficiencies by 13 %. Subsequently, researchers

conducted substantial research on WS using a TE device

paired with a PV cell or other electric production system.[297]

The Wang team created a composite fuel cell consisting of a

TENG, a solar cell, and a TE device, that may collect

mechanically, renewable, and/or thermal fuels simultaneously

or independently. Such composite fuel cell-generated output

may be employed immediately to spilled water without an

additional power source (Figure 26d–f). At a producing rate of

4 × 10 4mL/s1, the amount of H2produced changed linearly

with the split duration (Figure 26f). Figure 26e depicts the two

routes for WS. After combining points “1” and “3”, this

composite fuel cell may be employed immediately in WS,

whereby a solar cell is in conjunction with the rectifying

Figure 26. (a) Schematic representation of a PEC-TE composite system, (b) solo PEC and (c) a PEC-TE composite circuit illustrate the impact of qVTE.

Society of Chemistry.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 31/65] 1

TENG. Secondly, once point “1” is connected to point “2,”

the created energy may be deposited in a Li-ion battery and

subsequently utilized for water electrolysis.[298] The combina-

tion of PEC cells with TE devices has been the subject of

much research in an effort to boost solar H2production.

However, such studies use the method of series-connecting PV

cells, TE devices, and WS electrodes. Therefore, the resultant

frameworks were very complex and not cohesive. Exploring

how to actualize the combination of photo driving features

and WS components is, therefore, a significant step, whether

for the efficient use of solar energy or WS. The research of

embedded systems will provide substantial advantages for

developing OWS systems with combined structures suitable

for practical applications. In addition, the construction of an

exceptional composite system with long-term endurance of

solar WS might be an intriguing issue for future research.

2.10. WS Through a Triboelectric Nanogenerator

As described above, WS utilizing hybrid energy cells includes a

PV cell or a TE cell (Figure 27) facilitates the WS driven by

other energy devices. Since 2012 after its discovery by the

Wang team, TENG has been utilized as an external energy

source in WS.[299,300] Addressing the power transformation of

TENG, the transport of interaction particles among two

triboelectric materials of opposed polarities produced a voltage

differential upon their detachment 301. Eventually, this

potential difference may deliver electrons/ions to the external

circuits, thereby serving as the energy supplier.[302] In 2014,

Tang et al.[303] presented an autonomous composite device

consisting of a water-driven TENG and a WS cell (Fig-

ure 27a). Figure 27b depicts the schematic diagram of this WS

and the configuration of disc TENG. With a constructed

TENG rotating at 600 rpm, the generation rate of H2was

determined to be 6.25 × 103mL/min1in a 30-wt % KOH

mixture. This study proposed a TENG-driven WS for H2

synthesis without using an external energy supply. In 2017,

Figure 27. (a) The model for the TENG-driven WS scheme, (b) the circuits schematic of the splitting mechanism and the disk physical composition TENG.

fuel graph for solar WS premised on n-type semiconductors, (e) photocurrent of as-synthesized Au-coated TiO2with various biases. Reprinted with permission

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 32/65] 1

the same team suggested a combined TENG-PEC composite

cell with a TiO2photo-anode, in which a movable TENG was

utilized to gather ambient kinetic energies before powering the

Li-ion batteries for WS (Figure 27c, d).[304] This study

indicates that the electrostatic force supplied by a TENG-

charged battery performed a crucial function in electrolysis and

improved the solar energy usage performance by increasing the

photo-current (Figure 27e). Consequently, the TENG-PEC

composite cell provided a simple and effective method for

transforming mechanical and photovoltaic energy into chem-

ical energy. Additionally, the Zhong et. al. suggested a self-

powered PEC WS system, which included a rotatory disk-

shaped TENG (RD-TENG) and a titanium-fabricated hema-

tite (TiFe2O4) photo-anode.[302] Notable is the effect of

TENG rotational speed modification on the variance of the

current yield peak during the dark and light conditions. With

a modest rotational speed, the voltage peak under augmented

light condition dramatically relative to the dark; however, no

difference was recorded at a high rotation speed, representing

an efficient water electrolysis process at an elevated rotation

speed.

In addition to water-driven TENG, research on wind-

driven TENG was also carried out for depth

understanding.[305,306] For that aim, a helical rotatory standing

TENG (CRF-TENG) was used by Fan et. al. in order to

capture the renewable power via electro-spinning polyvinyli-

dene fluoride (PVDF) nanofiber membranes as triboelectric

materials (Figure 28a–c).[307] On this basis, a CRF-TENG-

based self-powered device for WS to create H2was built. With

average wind speed (10 m/s1), H2production efficiency in a

(1.0 M KOH) solution was determined to be 6.9685 L/min1

(Figure 28d, e).

2.11. WS Through Other Devices

Lately, WS utilizing pyro-electric element has drawn huge

attention since it offers a different route to produce H2energy

from instant low-grade waste heat or natural temperature

variations.[308] The Xie and Brown et al. showed the use of

pyro-electric impact to generate a sufficient electromotive force

among two electrodes for separating water into H2and O2

gases. Such pyro-electric WS systems employed lead zirconate

titanate (PZT-5H) and PVDF thin film as their

electrocatalyst.[308] The Zhang et al. has established a pyro-

electric WS device employing pure lead PZT as an external

charging source subjected to cold-hot thermoelectric cycling.

Such device design was used to implement the WS using

outside deployed pyroelectric components (Figure 29a). As

well documented, the time-dependent variation in ferroelectric

polarization throughout heat treatments was the motivating

force behind the formation of pyro-electric charges in hot and

cold oscillations. Consequently, the effects of ionic strength

and heating–cooling regularity were investigated (Figure 29b–

d). As proven, the thicknesses and size of the PZT layer are

figured prominently in powering WS, where the width may be

used to provide a sufficient potential to commence WS, and

the size must be optimized to gather the maximum level of

accessible surface charge.[309] Consequently, future research can

concentrate on the configuration of pyro-electric nanoparticles

to boost the surface area of the pyro-electric element or on the

investigation of the elevated thermal transition rates of other

pyro-electric materials in order to enhance the amplitude along

with the velocity of temperature changes.[310]

WGS reaction was the key route in industrial H2

generation.[311] In conventional WGS reactions, high pressure

and temperatures are required, and the resulting H2is often

polluted with CO2, CH4, and remaining CO.[312,313] Bao et. al.

suggested a unique electrical and chemical water–gas shift

(EWGS) approach for primary H2production with 99.99 %

efficiency and 100 % FE under moderate circumstances.

Despite electrocatalytic WS, the WGS process offers a

promising innovative method for H2synthesis with an

extremely modest voltage level, achieved via the logical

engineering of an electrolytic cell and electrocatalysts. CO is

destroyed at the anode during the WGS reaction mechanism

of an electrochemical cell, whereas H2is produced by the H2O

reductions at the cathode (Figure 30a). Whereas anion ex-

changer membranes were employed to segregate the cathode

and anode, preserve the electrolyte ionic strength equilibrium,

and avoid cross-contamination of the anodic (CO2) and

cathodic (H2) products in the process. By manufacturing a

hydrophilic PTFE layer on the catalysts and designing the

anode Pt3Cu catalyst, water-free chambers were created at the

junction among PTFE and the catalysts to enable CO

transport and diminish Cu association with CO on the anode

catalytic interface (Figure 30b–d). Such an innovative electro-

lytic cell produced H2with a purity of 99.99 % and a FE of

about 100 % directly under moderate circumstances.[314]

3. Synthesis of Transition Metals for WS

Owing to their superior electrocatalytic activity, natural

availability, and low cost, first-row transition metal complexes,

such as Co, Ni, and Fe-based hybrid materials, were

extensively explored as efficient polyfunctional electrocatalysts

for OWS.[315,316] The majority of current efforts fall into this

category of catalysts. The HER–OER rate of these polyfunc-

tional catalysts is greater than that of noble metal catalysts.

Only a few such electrocatalysts demonstrated efficiency

superior to that of noble metal catalysts. Conventional

polyfunctional catalysts include transition metal phosphides,

oxides, nitrides, and sulfides, and they are largely categorized

by their metal configurations, such as Co-based, Ni-based, and

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 33/65] 1

Fe-based materials. The subsequent sections will include in-

depth analyses of their integration and OWS function.

3.1. Co-Based Compounds

Recently, Cobalt has become an interesting metal due to its

low cost and promising catalytic performance in WS.

Numerous attempts have been made to synthesize inorganic

heterogeneous polyfunctional catalysts based on Co.[317,318]

Cobalt phosphates were the most extensively researched

polyfunctional catalysts in WS.[319] Numerous research teams

have used diverse strategies to develop cobalt phosphates-based

chemicals for OWS. Cobo et. al. created a Janus nano-

particulate H2

CoCat using reduced electro-deposition of

Figure 28. (a) Schematic of a CRF-TENG renewable power generator motivated self-powered WS mechanism, (b) the yield current and (c) the yield voltages of

the CRF-TENG renewable power generator with a transmitter at various wind velocities, (d) the resulted H2amount as a function of the work periods, and

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 34/65] 1

cobalt salts in a phosphate buffer in 2012 (Figure 31a).[320] In

2012, Cobo et. al. developed a Janus nanoparticulate

CoCat by reducing the electro-deposition of cobalt salts in

a phosphate medium. The H2

CoCat may also be transformed

into amorphous type cobalt oxide film (O2

CoCat or CoPi) in

order to accelerate the generation of O2at the anode

(Figure 31b). Surprisingly, the transition between these two

catalytic types was fully reversible (Figure 31c). Researchers

said the as-created CoCat was a durable, polyfunctional, and

swappable catalyst (Figure 31d). Jiang et. al. proposed a cobalt

phosphorous-based (CoP) film using the potentiodynamic

electro-deposition strategy for catalysis of OWS. Employing

1.0 M KOH, the synthesized CoP film demonstrated out-

standing catalytic activity for both HER and OER. To

generate a current density of 10 Ma/cm2, HER and OER

required overpotentials was (94 mV and 345 mV vs. RHE),

correspondingly. In addition, their respective Tafel gradients

were as low as (42 and 47 mV/dec1). Cobalt metallic and

CoP were the primary constituents of this as-grown and post-

HER film, which was largely changed into cobalt oxide

throughout the OER. The functionality of the developed

electrolyzer using CoP films as both cathode and anode

catalysts is greater than the incorporated Pt and IrO2catalyst

pair. Subsequently, the production of porous Co phosphide/

phosphate by nano-structuring might give the materials

extraordinary performance, such as a larger surface area and

more efficient masses transportation route. The Tours team

formed a porous Co phosphide/phosphate-based thin film

(PCPTF) for such an objective by treating an anodized Co

oxide porosity film with phosphorus vapors (Figure 31e).[321]

The developed porous film may immediately serve as an

electrode for accelerating the production of H2and O2with

outstanding efficiency at 35 and 220 mV vs. RHE and Tafel

slopes of 53 and 65 mV/dec1. Alternating phases allowed the

mixture phase film to simultaneously create H2and O2in a

single electrolyzer (Figure 31f).

Phosphide-based materials are considered as the key types

of compounds having excellent electro-catalytic performance

toward HER.[322] CoP have been explored specifically as

potential HER catalysts.[323] Researchers have just begun to

examine its polyfunctional effectiveness in accelerating HER

and OER sources.[324,325] You and his team created CoP/NC

nano-polyhedrons for OWS using a metal-organic frame

(MOF)-derived method. CoP and Co2P nanomaterials were

Figure 29. (a) Schematic illustration of pyro-electric as an outer supplier for WS, (b) polarization–electric field cycle of PZT layer and illustration of pyroelectric

charges surface, (c) H2advancement from outer pyro-electric WS with working time from (1 to 6) hours, and (d) the quantity and transformation level of H2and

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 35/65] 1

injected into the N-doped carbon matrix to form the nano-

polyhedrons (Figure 32a).[324] CoP/NC materials exhibit

greater specific surface areas (183 m2/g1) and larger mesoporos-

ity. Notable, the CoP/NC has demonstrated unique activity

towards OER and HER. The CoP/NC generated a current

density of 10 mA/cm2in 1.0 M KOH at significant over-

potentials of (154 mV vs. RHE) for HER and (319 mV) at

RHE for the OER. In contrast, the CoP/NC-based overall

water electrolyzer has achieved a substantial current density of

(165 mA/cm2) at 2.0 V (Figure 32b), while exhibiting en-

hanced stability (Figure 32c). Using a sandwich-type MOF/

GO as a model and precursor, the Niu team presented a

multilayer CoP/rGO hybrid as an electrocatalyst for both

HER and OER 326. The hybrid (CoP/rGO-400) successfully

generated H2and O2in a single alkaline electrolyzer upon heat

treatment at 400 °C. Such exceptional electrocatalytic capa-

bility and endurance may be due to the synergism impact of

the CoP and rGO highly porous nanomaterials, increased

electrical conductance, and excellent stability during the HER

and OER. Song et. al. constructed networks of CoP highly

porous nanorods endorsed by Ni foam to further enhance the

conductance of Co phosphide and enable charge transfer at the

electrode.[325] Due to the good fabrication of mesoporous and

increased electrochemical surface area of materials, it may be

used as extensible polyfunctional electrodes for both HER and

OER. The efficiency of the extensible CoP nanowires array

electrodes in an alkaline electrolyzer was exceptional (h10 mA/

cm21

4390 mV) and superior durability compared to Pt and

IrO2electrodes. This catalyst’s outstanding electrode design

and an array of illuminated nanorods were the primary

contributors to its increased electric connectivity and mass

transfer. CoP-based polyfunctional catalysts, as well as the

energetic materials for HER and OER, are routinely charac-

terized after the process. For a deeper knowledge of electro-

catalysts’mechanical and chemical development during elec-

trolysis, however, in situ spectroscopic study is very desired.

This method is currently being investigated. Earlier CoSe2

catalysts have displayed more efficiency in producing either H2

or O2in WS.[327,328] Combining CoSe2with other materials

may provide it with polyfunctional OWS capability. For

Figure 30. (a) Schematic of the EWGS system comparison to the conventional WGS system, (b) schematic of the solids/liquids and gases interfaces on the PTFE-

coated Pt exterior, (c) adsorbents of H2O at 25 °C on Pt/C and Pt/CNTs with and without PTFE procedure observed by an intellectual gravimetric detector, and

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 36/65] 1

example, the Feng team created 3D linked tertiary complexes

(EG/Co0.85Se/NiFe-LDH) by attaching NiFe stacked double-

hydroxide (NiFe-LDH) to (Co0.85Se) nano-sheets laterally

cultivated on exfoliated graphene (EG) foil.[329] As-synthesized

hierarchical hybrid showed exceptional OER efficiency, requir-

ing just (1.50 V vs. RHE) in order to produce a 150 Ma/cm2

current density. In alkaline circumstances, EG/Co0.85Se/NiFe-

LDH was superior to previously known non-noble metal OER

electrocatalysts and Ir/C catalysts. In addition to the out-

standing HER performance of (EG/Co0.85Se/NiFe-LDH)

nanostructure, a water electrolyzer was constructed using the

tertiary complexes as both cathode and anode. A potential of

1.71 V was sufficient to generate a current density of 20 mA/

cm2in 1.0 M KOH. However, Wu et. al. coupled CoO

domain with CoSe2nanotubes on Ti (designated as CoO/

CoSe2)[330]. In neutral electrolytes, this catalyst was exploited as

an effective self-supported polyfunctional electrocatalyst for

both OER and HER.

Masa et al. presented amorphous Co2B as an outstanding

electrocatalyst for OER in alkaline media. In contrast, Co2B

may be employed for HER.[331] The catalyst (Co2B-500) can

produce O2more efficiently than IrO2and RuO2after heating

at 500°C, and has demonstrated remarkable durability in

electrolysis experiments (at 10 mA/cm2) for over 60 hours. The

B element induced lattice distortion into the crystalline lattice

of the metal, therefore lowering the thermal decomposition

barriers of the hydroxylation response and accelerating the

creation of the OOH* intermediate to promote the OER

reaction. At medium voltage level, overall water electrolysis

experiments employing Co2B-500 as the anode and Co2B-500/

NG as the cathode are shown in a two-electrode cell, and

robust and steady gas generation is seen. In context of the

chemical closeness of Co2B, CoP, and CoSe2, the unique

Figure 31. (a) SEM photos of altered electrodes via electrolysis, (b) A SEM photograph of an H2

CoCat film on FTO electrodes, (c) Voltage penetrated on FTO

electrodes, (d) Specialized generation rates of H2(red) and O2(blue). Reprinted with permission from Ref. [320] (e) The production technique is shown

schematically, beginning with glasses, silica, ceramics, or stainless-steel substrates, (f) CV testing of polyfunctional water electrolysis in 1 M KOH aqueous

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 37/65] 1

electrolytic behavior of such materials shows that charge

transport capabilities, architectural flaws, and surface area may

significantly impact their electrocatalytic behavior. In terms of

the electrocatalytic activity of a catalyst, greater electronic

conductance is of immense benefit. Graphitic carbon is often

used as the supportive element to increase the conductance of

hybrid electrocatalysts, and the capacity of carbon to be doped

with adjustable hetero-atoms grants it enhanced catalytic

performance. The association between carbon and metal oxide

nanomaterials may boost the overall physicochemical and

optoelectronic properties to enable the flow of electrons at the

contact.[133,332–337] Using a one-pot thermal treatment techni-

que, Jin et al. developed cobalt–cobalt oxide/N-doped carbon

hybrids (CoOx@CN) towards the efficient HER and OER

(Figure 33a). As-grown CoOx@CN comprising Co, CoO, and

Co3O4exhibited a modest onset voltage (85 mV), a modest

charge-transfer resistance (41 U), and a high level of HER

durability in 1.0 M KOH.[338] The exceptional efficiency of

CoOx/CN for HER may be attributed to the high electronic

conductance of N-coupled carbon, the reciprocal impact

among metallic Co and Co oxides, and the improved

durability of Co nanostructures trapped in carbon. In addition,

the CoOx/CN composite has demonstrated superior efficiency

for OER, providing 10 mA/cm2of current density at an

overpotential of just 0.26 V. In addition, after 30 minutes of

HER, the electrocatalytic commotion of CoOx/CN for OER

Figure 32. (a) Schematic depicting the two-step fabrication of CoP/NC nanopolyhedrons. (b) Polarization rates for OWS catalytic pairs of CoP/NC and Pt/

American Chemical Society.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 38/65] 1

was greatly heightened. The researchers attributed this to the

increase in Co2+concentration. Lastly, the construction of an

alkaline electrolyzer was accomplished via CoOx/CN as both

the cathode and anode counterparts along with a potential of

just (1.55 V) to generate 20 mA/cm2of current density

(Figure 33b). The intrinsic HER–OER performance of bimet-

allic oxides is anticipated to be greater than that of single metal

oxides. Moreover, the productivity of bimetal oxides may be

readily enhanced by the modulation strategy of valence and

electronic levels of any metal.[339,340] For example, Gao et al.

suggested the dynamically induced fabrication of Ni-incorpo-

rated hierarchy NiCo2O4hollowed microcuboids. The hol-

lowed microcuboids have demonstrated superior performance

and stability for the OER and HER.[341] The NiCo2O4

electrodes have confirmed good OWS activity. By putting

1.65 V between two electrodes, the current density was

Figure 33. (a) Demonstration of the CoOx/CN constituent, in which cobalt oxide was most essential for the OER and carboned-capsulated Co nanostructures

were primarily essential for the HER, (b) A photograph of the water electrolyzer producing H2and O2bubble. Reprinted with permission from Ref. [338]

two-electrode version of the CoMnO/CN superlattice catalysts, (e) Graphical representation of the solar WS cell with no extra applied current using a standard Si

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 39/65] 1

increased to 10 Ma/cm2, and the voltage remained very robust

for a minimum 36 hours. In addition, the Zheng team devised

a carbon-coated CoMn oxide nanomaterial super-lattice

(CoMnO/CN) as a polyfunctional electrocatalyst for WS.[342]

This allows the synthesized catalyst to exploit the synergic

effect of bimetals, N-dopants, and carbon atoms. CoMnO

nanomaterials functioned as an efficient OER reagent because

to their narrower bandgap, better OH adsorption, and poorer

O2adsorbents than CoO and MnO. The scientists underlined

that the adjacent N-doped carbon frameworks acted as active

HER catalytic sites and facilitated efficient electron and ion

transport toward the CoMnO nanostructures. In particular,

the organized super-lattice configuration with a carbon layer

among neighboring CoMnO nanoparticles was beneficial in

enhancing catalytic sites and inhibiting nanomaterials agglom-

eration or disintegration (Figure 33c). Consequently, this

CoMnO/CN super-lattice configuration may drive OER and

HER catalysis in a similar alkaline medium (Figure 33d). This

CoMnO/CN super-lattice polyfunctional material, once com-

bined with a silicon photovoltaic cell, permitted sustained solar

WS for about 5 days, equal to a solar-to-hydrogen trans-

formation rate of almost 8 % (Figure 33e). Hierarchical 3D

nanomaterials with hollowed and micropores architectures

have been exploited intensively for electrochemical processes.

It is intriguing to generate active electro-catalysts comprising

1D nanomaterials with hierarchy 3D porous material and

hollow interiors, even though the 1D nanowire/nanotube

appearance, particularly when firmly connected to conducting

substrates, ensures an elevated surface area revealed, desirable

permeability, and rapid charge transfer during electrolysis,

thereby enabling outstanding catalytic effectiveness. Sivanan-

tham et al. constructed 1D arrays of NiCo2S4nanowires (NW)

developed immediately on Nickel foam (NF).[343] Substantial

polyfunctional WS performance was seen in 3D NiCo2S4

NW/NF arrays. The 3DNi foam accelerated the horizontal

development of the NiCo2S4NW at the electrode-electrolyte

interaction, exposing additional reactive groups to participate

in HER and OER. NiCo2O4and Ni0.33Co0.67S2are the OER

and HER electro-catalysts, correspondingly.[344] Once con-

structed, the NiCo2O4j jNi0.33Co0.67S2nanorods constituted a

novel, homologous, and highly efficient OWS system. Using

the cation and anion transfer method, the Zheng team has also

suggested a similar CoNi-based nanotube configuration.[345]

CoNi(OH)x and NiNx nanomaterials demonstrated increased

current densities at low overpotentials and excellent OER and

HER stability. Moreover, the efficiency and stability of the

combination CoNi(OH)xj jNiNx nanotube electrolyzer for

WS seem promising.

3.2. Ni-Based Compounds

Ni, particularly Ni foam, is often used as the cathode material

in conventional electro-catalytic electrolysis devices employing

alkaline electrolytes. As a motivator, however, Ni metal is

inefficient and more stable in WS. Doping Ni metal or nickel

oxide with other substances may thus be an alternative to this

issue.[346,347] In 2014, by loading Fe into Ni(OH)2, the Gratzel

team suggested a polyfunctional earth-abundant catalyst, NiFe

LDHs, with dramatically increased efficiency for both HER

and OER in an alkaline medium (Figure 34a–b).[348] In a

perovskite solar cell, the mixture generated 10 mA/cm2with a

solar-to-hydrogen conversion yield of 12.3 % (Figure 34c–d).

In addition, the mixing of Ni with non-metals has garnered

considerable interest. Electrocatalysts comprised of Ni-based

phosphide and chalcogenide (containing Ni sulfides and Ni

selenides) are very promising in total WS.

Hitherto, Ni phosphide catalysts were primarily utilized as

efficient cathodic electro-catalysts in H2evolution. But, revolu-

tionary works were performed by the Hu team, that displayed

that nickel phosphide (Ni2P) also showed higher performance

in O2production[349] Ni2P nanoparticles showed better OER

performance (h10 Ma/cm21

4290 mV vs. RHE) with good

persistence in 1.0 M KOH. The energetic composites for OER

were a hybrid core-shell Ni2P/NiOx that was generated in situ

during catalytic cycling (Figure 35a–e). Subsequently, an

alkaline water electrolyzer using Ni2P as a mediator for both

HER and OER was created (Figure 35f). Lou and colleagues

created Ni–P permeable nanoplates from NiNi Prussian blue

analog intermediates as efficient polyfunctional electrode

materials for OER and HER.[350] During the O2generation

process, the researchers underlined that surface nickel

phosphide was partly oxidized to nickel oxide or hydroxide.

Subsequently, the oxidized nickel sheet formed in situ served

as an effective location for OER. This selective oxidation event

is consistent with Hu team research. Large active sites and

improved electrical connections among the 3D electrode and

catalysts often result in greater catalytic performance in 3D

catalyst-containing electrodes. The Ni foam is widely used as a

conducting medium in developing 3D catalysts. The Ni foam

provides a long-range structured porous structure that accel-

erates charge mobility functionality and enhances mass transfer

efficiency.[351] For example, Qiao and his colleagues made 3D

porous Ni/Ni8P3and Ni/Ni9S8electrodes by phosphorizing or

sulfurizing Ni-foam that had been treated with acid.[352] The

obtained materials are immediately applicable as probable

polyfunctional electrodes for complete electrochemical WS in

an alkaline medium. The researchers also examined the

catalytic function of Ni/Ni8P3and Ni/Ni9S8in aspects of

intermediary adsorbent over the catalysts and the NiP/S

bond angle in order to explain the superior behavior of Ni/

Ni8P3. Finally, a better water electrolyzer was created by using

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 40/65] 1

Ni/Ni8P3as both the anode and cathode in a 1.0 M KOH

mixture at a cell potential of 1.61 V, it generated 10 mA/cm2

WS conductance. Such high overall WS performance may be

attributed to the 3D self-sustained nature, robust physical

interaction, quicker charge transfer, and structure-induced

electronics impact. Shalom team created a self-supported,

organized Ni5P4sheets 3D electrode using conventional Ni

foils as the Ni catalyst.[353] The catalyst efficiency and

durability towards the HER were tested in both 0.5 M H2SO4

and 1.0 M KOH. The electrochemical performance of Ni5P4

for OER in 1.0 M KOH was superior to that of the pure Ni

or Pt. Noticeably, when used as a polyfunctional catalyst for

complete WS in an alkaline media, the Ni5P4may generate a

current intensity of 10 mA/cm2at a voltage of less than 1.7 V.

This high performance of Ni5P4was attributed to its 3D

hierarchy configuration, which facilitated the synthesis of

catalyst efficiency of NiOOH on Ni5P4. In this instance, the

creation of the Ni5P4/NiOOH heterostructure has altered the

electrical characteristics, leading in reducing in OER over-

potentials. In addition, the Shalom team presented an

alternative method for embedding Mn-coupled Ni materials

into N-doped carbon as the catalysts with a greater surface area

for HER and OER.[354] This extremely permeable material

could easily change from an effective HER catalyst to an OER

catalyst through heat processing in air. Such a convenient

procedure also formed metal oxides on the surface, so increased

the surface area. Finally, an OWS performance of 70% was

achieved.

Nickel chalcogenides have become prominent as interesting

HER catalysts.[355] Nickel sulfide has recently shown promising

function in the OER mechanism, and NiSOH serves as the

energetic reagent.[356] Feng et al. subsequently showed the

production of robust, elevated, prismatic Ni3S2nanostructured

arrays implanted on nickel foam (NF) as an effective polyfunc-

tional HER–OER catalyst.[357] Due to its nano catalytic

properties and elevated indexing aspects, the Ni3S2/NF

Figure 34. (a) OER properties of various catalyst electrodes in a three-electrode setup; (b) HER parameters of various catalytic electrodes in a three-electrode

design, monitored from negative to positive voltage. (c) OWS properties of various catalyst electrodes in a two-electrode arrangement; (d) Graphical representation

2014, The American Association for the Advancement of Science.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 41/65] 1

material exhibited efficient and ultra-stable electrocatalytic

activity towards HER and OER (Figure 36a, b). Simulations

revealed that the additive impact of the nanocomposite array

design and the 210 elevated indexing aspects was responsible

for the material’s excellent catalytic activity for OWS (Fig-

ure 36c–d). Also, Tang et al. created NiSe nanowire film

(NiSe/NF) endorsed by nickel foam for OWS.[358] Such a

complex was produced by the hydrothermal process of NF

with NaHSe. NiSe/NF, while used as a 3D electrode for the

OER, exhibited an anodic current density of 20 Ma/cm2at an

overpotential of 270 mV vs. RHE also demonstrated excellent

durability in 1.0 M KOH. The NiOOH particles produced on

the NiSe interface were discovered to be effective agents. The

3D electrode was also more effective in stimulating the

production of H2under alkali circumstances. Using a voltage

of 10 mA/cm2and a cell voltage of 1.63 V, an alkaline water

electrolyzer including this polyfunctional electrode achieved a

higher level of functionality. Increasing the surface area and

the number of energetic locations might be effective strategies

for reducing the overpotential. In alkaline media, the Feng

team has proven the interfacial synthesis of MoS2/Ni3S2

heterojunctions on nickel foam as an improved electrocatalyst

Figure 35. (a) HRTEM of the Ni2P catalyst, (b) Nickel elemental mapping. (c) Oxygen elemental mapping. (d) Phosphorus elemental depiction. (e) Elemental

illustration of Ni, O, and P. (f) Current–potential behavior of an alkaline electrolyzer containing Ni2P as an OER and HER catalyst. Reprinted with permission

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 42/65] 1

for OER and HER.[359] The voltage level of an alkali electro-

lytic cell employing MoS2/Ni3S2heterojunction polyfunctional

catalyst was only 1.56 V. At such intensity, the heterojunction

may provide a current intensity of 10 mA/cm2, which is much

less than the existing catalysts for OWS. Utilizing DFT

analyses, the researchers asserted that the developed integra-

tions among Ni3S2and MoS2and the in situ constituted

functionalities among NiO and MoS2mediated the instanta-

neous aggregation of H2and O2based composites, which

finally improved the OWS-performance. Aside from nickel

phosphides and chalcogenides, nickel nitrides-based materials

have also been focused on their OWS behavior. The Jia et al.

constructed Ni3FeN nanoparticles (Ni3FeNNPs) with

100 nm-sized particles by using heating ammonolysis on

ultraportable NiFe-LDH nanostructure. Ni3FeNNPs was an

OWS electrocatalyst that performed very well.[360] The

enhanced functionality of Ni3FeNNPs is attributable to the

composite‘s metallic nature and unique electronic properties,

enabling charge transport and H2O absorption. In addition, it

was believed that the nanoparticle impact increased the

availability of energetic locations for the catalytic performance.

In particular, Zhang et al. suggested using clusters of hierarchy

TiN/Ni3N nanowires to create an efficient electrochemical WS

system 361. Throughout this system, the TiN/Ni3N nanowire

clusters performed as polyfunctional electrocatalysts for both

HER and OER in an alkali solution.

3.3. Fe-Based Compounds

Fe has a greater natural abundance than Co and Ni.

Consequently, Fe has gained increased interest in the develop-

ment of low-cost catalysts. Electrocatalysts based on Fe have

been extensively researched in the HER and the OER.[362]

However, polyfunctional effective Fe-based materials for WS

have been seldom studied. Recently research by Martindale

and Reisner revealed the efficiency of an iron-only catalyst for

both WS half-reactions in alkaline media. The efficiency of the

presented catalyst was superior to that of polyfunctional Co

and Ni catalysts.[363] The dynamic functionality arose from the

interaction between the Fe(0) state under a cathodic gradient

Figure 36. The steady-state conductivity in alkali medium (pH 14) over Ni3S2/NF in (a) HER and (b) OER as a consequence of input voltages. The highest

robust sackings of the (c) 210 and (d) (001) Ni3S2interfaces, (e) Estimated free-energy graph of HER at optimum voltage across 210 and (001) materials.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 43/65] 1

and the iron oxide–hydroxide (FeOx) state within an anodic

gradient. In addition, the scientists said that this interaction of

catalytically energetic ions at the interface of the catalyst was

reversed and swappable, ensuring the scheme endurance and

balance. Motivated by the polyfunctional performance of Co

and Ni phosphides for both HER and OER, as well as the

benefits of 3D structural catalyst, Wang’s team created a

versatile 3D electrode based on iron phosphide nanotubes

(IPNT) for OWS (Figure 37a).[362] The composite comprises

FeP coated with iron oxide/phosphate particles to catalyze the

H2generation from both acidic and alkaline electrolytes with

low startup overpotentials (35 and 31 mV vs. RHE). Surpris-

ingly, the in situ generated surface iron oxide/phosphate may

be employed immediately to drive O2production at an initial

overpotential of just 250 mV relative to RHE. Furthermore,

the extensible iron phosphide nanotube electrode for the

planned alkaline electrolyzer with a flow of 10 mA/cm2at a

potential of 1.69 V has demonstrated exceptional functionality

and endurance (Figure 37b). Numerous approaches have been

applied to generate transition metal-based electrocatalysts for

OWS, as shown in the preceding section. However, it is now

vital to build more generic and affordable approaches for

Figure 37. (a) Synthesis procedure of IPNT catalyst. (b) CV plot, Inset: graphical scheme for polyfunctional OWS. Reprinted with permission from Ref. [362]

(c–g) Depiction of TMO morphology evolution under galvanostatic phases, (h) The HER performance of 2-phases NiFeOx/CFP, (i) Two phases of NiFeOx/

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 44/65] 1

designing polyfunctional HER–OER catalysts regarding the

nonmetals. Read et al., who generated transition metal

phosphide electrodes by treating conventional metal foils (Fe,

Co, Ni, Cu, and NiFe) with different organophosphine

donors, have offered a good illustration of a universal and

accessible technique.[364] Such new prototype phosphide

electrodes exhibited outstanding electrocatalytic activity against

HER and OER. The Cui team proposed a lithium-induced

transformation process (Figure 37c–g) to increase the catalyzed

performance of different transition metal oxide nanomaterials

(Fe, Co, and Ni oxides, as well as their paired oxides).[365] Due

to the metal centers’enhanced valence state, lithium’s electro-

chemical extraction significantly improved the OER perform-

ance of these transition metal oxides. In addition, the higher

density of electroactive locations and the covalently mixing of

the M-3d and O-2p phases are also accountable for such

enhanced OER efficiency. In a two-electrode arrangement, the

lithium-extracted ultra-small NiFeOx nanomaterials exhibited

exceptional performance, requiring merely 1.51 V to achieve a

current intensity of 10 Ma/cm2. Moreover, no noticeable

reduction of functionality was seen even after 200 hours of

electrolysis (Figure 37h–i). Such well-potential electrode mate-

rials augment the class of very effective polyfunctional OWS

catalysts. Co, Ni, and Fe-based polyfunctional WS catalysts’

catalytic efficiency does not vary much; their polyfunctional

function on OWS depends more on the design and particular

specific surface area than on the metal used. This indicates that

designing the form and stoichiometry to increase the concen-

tration of catalytically active spots is essential.

3.4. Other Emerging Compounds

Several transition metal complexes, such as Mo and Cu-based

oxides, were shown to be polyfunctional and energetic toward

HER and OER. Jin et al. reported the easy wet-chemical

production of porous MoO2nanostructure pursued by

heating. Perforated MoO2nanostructure demonstrated superi-

or simultaneous efficiency for HER and OER against pure

MoO2

[366] Researchers had attributed the such exceptional

performance to the nanostructure‘s large surface area and

many activated spots. In addition, permeable MoO2required

just 1.53 V of voltage level to achieve a power density of

10 Ma/cm2and sustained its functionality for nearly 24 hours

in an alkali electrolyzer. The WS arrangement may also be

Prior studies demonstrated that Cu nanoparticles displayed

bioinspired reactivity with O2similar to the reduced stimula-

tion of O2in enzymes and laccase proteins[367] Lately, Jahan

et al. made a Cu–MOF matrix by combining GO with a

copper-centered MOF to make a functionalized catalyst for

the HER, OER, and ORR (Figure 38)[368] It is known that this

Cu-based functionalized catalyst works better in an acidic

electrolytic cell than other OWS catalysts that have been

reported. Many WS compounds can only work in an alkaline

environment. The GO–MOF mixture has good electrochem-

ical behavior due to its highly permeable framework, its

optimized capacity to transport charges, and the synergic

impact of the MOF and GO. Metal-free components,

particularly specialized carbon materials like graphene nano-

structure and carbon nanotubes coated with heteroatoms, were

used a lot as energetic O2or H2catalysts.[369] Dopants of

carbon-based metals with nonmetal substituents may signifi-

cantly boost the electrochemical activity of the specified

multifunctional carbon electrocatalyst. To do this, faults in the

electronic configuration of carbon structures might promote

the amplification of catalytic activity.[370] However, studies of

polyfunctional efficiency on similar carbon interfaces for both

HER and OER are presently uncommon; hence, analyses of

the uses of functional carbon-based composites for overall WS

need extensive research endeavors. Lai et al. suggested the

construction of an O, N, and P co-doped amorphous graphite

nanocarbon as a polyfunctional free-standing 3D electrode

(ONPPGC/OCC) for OWS at all pH levels.[371] The

fabricated alkaline water electrolyzer has shown excellent

capability by adopting ONPPGC/OCC for both HER and

OER catalysts, which could yield a power density Ma/cm2at a

voltage level of only 1.66 V while maintaining excellent

durability. Such outstanding electrochemical performance of

ONPPGC/OCC is attributable to its distinctive 3D permeable

design, greater accessibility of activated spots, increased transfer

characteristics, and excellent electric conductance. Without a

surprise, our study has demonstrated an intriguing new avenue

for investigating the use of multifunctional carbon materials

for OWS.

3.5. Transition Metal Borides (TMBs)

Additionally, TMBs have unique qualities for WS that have

gotten a lot of interest.[372] Electrons will concentrate at

metallic locations in specific polymorphic TMB complexes as a

result of reversed transport of electrons from boron to metals,

boosting the electrochemical processes. The energetic compo-

nents such as borates, boron oxides, TM oxides, and so forth

are produced as a consequence of the external oxidation of

TMBs, which is unavoidable.[373] The catalyzing processes will

be significantly impacted by this, and their HER and OER

potential were studied as earlier as the 800s of the previous

decade. TMBs have shown excellent promise for use as

electrocatalysts throughout a broad pH region. For instance,

Liang et al. produced the agglomerated NiB composite nano-

materials on Ni foam (NiB/NF) showed great efficiency and

endurance of OER and HER in basic conditions.[374]

Amorphous Co2B was shown to be a polyfunctional electro-

catalyst by Schuhmann et al.[375] The ternary transition metal

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 45/65] 1

boride (CoNiB/NF) was created by Xu et al. on Ni foam

and exhibits pretty good efficiency for OER with moderate

redox potential and strong durability.[376] Co nanostructures

and CoFe-boron nanosheets which offer robust functioning

under extended heavy-loading circumstances, were deposited

on NF by Liu et al. using a practical and appropriate

electrochemical method.[377] For the catalytic characteristics,

the boride concentration is essential. In order to accomplish

the current density of 10 mA cm2with an approximately

100 % faradaic effectiveness, Li et al. placed FeB2nanoparticles

(NPs) over conducting Ni foam (FeB2/NF) as both self-

supported cathodes and anodes for OWS (Figure 39A–C).[378]

Theoretically, boron-rich active regions encourage electron

density distribution and make it easier to regulate the

adsorption process and dissociation of reactive species, low-

ering the ΔGH* and favoring the HER phase. Bimetal NixFe1-xB

catalysts were also developed and displayed outstanding HER

and OER catalytic activity.[379] According to DFT calculations,

the synergic impact of Ni and Fe in the NixFe1-xB catalyst was

directly connected to the increased OER efficiency, and the

reduced ΔGH* quantity for NixFe1-xB than for FeB and NiB was

advantageous to the elevated HER. A strong catalytic perform-

ance and excellent durability may also be obtained by

embedding TMBs on conducting carbon nanostructures. A

very effective polyfunctional catalyst was developed by Chen

et al. by attaching ultraportable nickel boride (NixB) nano-

materials to MWCNTs with interface functionalization. The

NixB/f-MWCNT mixture outperformed conventional IrO2

and Pt/C electrocatalysts and had much higher electrochemical

performance than NixB nanomaterials separately, requiring

only 1.60 V to get the current densities of 10 mAcm2.[380]

3.6. Transition Metal Nitrides (TMNs)

Lately, metal nitrides have attracted more and more concern.

These are intermediate compounds with N particles intro-

Figure 38. (a, b, c) Cyclic voltammetry, (d, e) HER, (f, g) OER, and (h, i) ORR reactions of GO/Cu–MOF composites. Reprinted with permission from

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 46/65] 1

duced into the bridging locations and parental elements.[381]

Wu et al. were established a 3D N linked activated carbons

(Co5.47 N NP/N-PC) polyhedral with superior catalytic

efficiency and high durability.[382] In terms of electrocatalytic

activity, bimetal nitrides outperform monometallic nitrides

due to their large range of exciting ligands.[383] Jia et al.

produced Ni3FeN nanoparticles (NPs) from ultraportable

NiFe-LDH nanostructure using thermally ammonolysis, with

a particle diameter of around 100 nm and a width of about

9 nm (Figure 39D–I). Smaller Tafel slopes, high stability, and

reduced power density pointed to unusual Ni3FeN capabilities

for both HER and OER.[384] If conductivity materials are

employed, the electrocatalytic efficiency of Ni3FeN might be

improved even more. For instance, the WS efficiency of a 3D

Ni3FeN NPs/reduced graphene oxide (rGO) hydrogel was

good.[385] The nanohybrids made of TMNs and other materials

demonstrated very active electrochemical performance. Dutta

et al. constructed an integrative Co4NVN1xOxframework

over the polyaniline (PANI) encased CC (CVN/CC), that

demonstrated improved HER and OER efficiency.[386] Addi-

tionally, molybdenum-based carbide/nitride heterojunction

nanostructure (h-TMCN) with controlled hole diameters were

effective OWS electrocatalysts.[387] Mo2C and Mo2N chemical

bonding produced many NMoC surfaces, which were

crucial to the good electrochemical properties.

3.7. Transition Metal Carbides (TMCs)

Metal carbides have great sensitivity, excellent catalyzed

performance, robust durability, and exceptional corrosive

endurance. Metal carbides have drawn a lot of fascination and

concern since tungsten carbide Pt-like catalytic characteristics

were discovered in 1973. Numerous of the aforementioned

tactics were also employed jointly to enhance the WS

capabilities of TMCs.[388] Yu et al. created a permeable carbon-

supported Ni/Mo2C (Ni/ Mo2C-PC) hybrid catalyst (Fig-

ure 40) with excellent polyfunctional capability and effective

catalyst activities for HER and OER in an alkaline medium.

The Ni/Mo2C-PC material developed energetic species of

HER (a greater Ni valence) and OER (a lesser Mo valence) as

Figure 39. (a) Polarization patterns for FeB2

NF, Fe2BNF, FeB2

Cu, and FeB2

CC generated in a two-electrode arrangement (5 mV s1). (b) Four common H*

adsorbent locations on FeB2 (001) and (110) interfaces with comparatively lower ΔGH*. (c) Estimated free-energy distribution of HER across FeB2and Fe2B

(d) Ni3FeN nanomaterials generation is shown schematically. (e) HER linear sweep voltammetry (LSV) patterns recorded at a 5 mV s1scanning speed. (f) OER

LSV curves at 5 mV s1. (g) Design of the Ni3FeN atomic configuration. (h) Adsorbent coefficients of H2O on the interfaces of Ni3FeN, Ni3N, NiO, and Fe2O3as

determined by DFT calculations. (i) Ni3FeN, Ni3N, NiO, and Fe2O3total and partial electronics density of states (TDOS and PDOS) calculations. 0 eV is

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 47/65] 1

a consequence of the electron carriers from Ni to Mo2C

throughout the good electrochemical activity.[389] A composite

electrode material comprising Co and b-Mo2C nanomaterials

encased in N-doped carbon nanotubes (Co/bMo2C@N-

CNTs) displayed outstanding polyfunctional capabilities.[390]

Nickel carbides (NiCx) are also suitable for developing highly

active electrocatalysts due to their inexpensive price and strong

electrical conductance.[391] Several other techniques, such as

heteroatom dopants or mixtures with carbon sources, have also

been used to increase the electrochemical performance of metal

carbide catalysts.[392] Fan et al. discovered, for instance, that Fe

treatment may improve both the electrical characteristics and

the interfacial properties of Ni3C via electron transport among

various valance metals, absorption and emission of radicals

might be efficiently regulated.[393] Wang et al.[394] constructed a

Ni3ZnC0.7 catalyst with a proportion of Ni (0) and Ni (II) to

increase the electrochemical performance of HER and OER in

an alkaline solution. This was made possible by cationic

manipulation.

3.8. Heteroatom-Doped Nanocarbons

In current decades, non-metallic nanocatalysts, notably heter-

oatom-embedded carbon nanostructures, have emerged as a

significant frontier in the study of catalytic reactions.[395] Its

distinctive characteristics include ecological compatibility,

cheap price, significant electrochemical performance, robust

structural composition, and great acidified environmental

resistance.[396] In addition, its OER and HER may be

significantly adjusted by altering the localized electronic

properties and irregularly twisting the carbon crystalline

intensity. Pavodi et al.[397] conducted N loading in multiwalled

CNTs and revealed that pyridinic N units are prominent

locations for HER and OER owing to their distinctive

electron-withdrawing activity. Furthermore, based on the

Figure 40. (A) Schematic of the Ni/Mo2C-PC fabrication from NiMoO4 nanowire. (B) NiMoO4, (C) NiMoO4/PDA, and (D) Ni/Mo2C-PC TEM photos. The

electronic pictures that relate to the insets. (E) The HER polarizing graphs for several catalysts at 5 mVs1scan rate. (F) OER polarizing graphs with 0.50 mg cm2

of stacking on a GC electrode. (G) LSV patterns of OWS in a setup with two electrodes. The inset shows an electronic photograph of H2and O2bubbling.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 48/65] 1

interaction impact from co- or tri-heteroatoms loading in

carbon materials, N and F multiple-loaded porous graphene

nanosheets (NFPGNS) were developed as excellent metal-free

polyfunctional electrode material.[398] Co-doping may signifi-

cantly change the electron acceptor–donor characteristics and

electron density close to C, resulting in high adsorbent and a

decreased ΔGH* ratio.[399] Qu et al. demonstrated that the S

adsorbent can improve the spinning intensity at the C location

in N, S sandwich carbon composite (Figure 41) and the

electrochemical performance activated spots. One more study

found N-, O-, and P-doped hollow carbons (NOPHCs)

effective and reliable non-metallic polyfunctional electrode

materials.[400] Gao et al. deposited C60 onto single-walled

carbon nanotubes (SWCNTs) to induce interatomic electron

transport, resulting in improved HER and OER activity over

conventional Pt and RuO2.[401]

3.9. Metals and Their Alloys

3.9.1. Single Metals

Miles and Thomason determined the catalytic performance of

cheap metals in the sequence Ni >Mo >Co>W>Fe >Cu >

Mn employing the cyclic voltammetry (CV) technique.[402]

Weak consistency in strong alkaline or acidic electrolyte levels

is perceived as a significant concern with simple metal

electrocatalysts.[403] Furthermore, transition elements in their

traditional states of pure or organized particulates offer fewer

benefits. The addition of supporting or interfaces not only

disperses and protects the metal center from erosion in the

combative atmosphere, but also accelerates the electrochemical

process. A prominent strategy for improving WS efficiency is

to combine transitional elements with different nitrogen-

treated carbonaceous elements.[404] Ren et al., placed Ni nano-

materials mediator on nitrogen-enriched carbon to perform

OWS. Carbon participation is thought to assist Ni nano-

particles in distributing and minimizing interaction impedance

among them and surfaces nitrogen spots, as well as modify the

electronic properties of the catalyzed sites to improve catalytic

performance.[405] Graphene is another common and great

Figure 41. (A) N, S-CNT synthesis by a two-step “graft-and-pyrolyze” method. (B) TEM imaging and (C) enlarged TEM photos (D) The HER polarized

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 49/65] 1

choice among several carbon-containing compounds. Xu and

colleagues synthesized Ni nanomaterials encased in multilayer

nitrogen-treated graphene (Ni/NC) (Figure 42).[406] The syner-

gic impacts of the Ni NPs and the N-based thin graphene

layer led to extremely effective and ultra-stable OWS efficiency

in alkaline conditions with an activation potential of 1.60 V to

attain 10 mA cm 2conductance. In an attempt to improve

functionality, numerous shapes and sizes of carbon materials

were compiled into one platform. In the meantime, associating

of such activated carbons with deficient alloys can thus

enhance the inherent reactivity of activated centers and kinetic

overpotential of adsorbent. Chen et al. described Ni quantum

dots (QD) enclosed in N-treated carbon (NC) over graphene

(Ni-QD/NC/rGO) as nanocomposites. The polyfunctional

Ni-QD/NC/rGO catalysts achieved a minimum potential of

1.563 V at 10 mA cm2for alkali electrolysis of water.[407]

3.9.2. Alloys

Developing multi-metal systems is a viable technique to go

over individual materials because alloying may modify the d-

band electrons saturation and influence the affinities of the

alloy electrode material toward the adsorbent surface of

significance. Nickel and cobalt-based alloys were actively

explored for years owing to their inexpensive and aggressive

performance. The catalytic capabilities of nickel-containing

ternary alloys for HER were determined in the order listed as

NiMo >NiCo >NiW>NiFe>NiCr.[408] To enhance

the reactive groups and improve OWS efficiency, several

morphologies, including nanoparticles,[409] spheres,[410] hol-

lowed nanorods,[411] nanowires,[412] and others, have been

developed. Furthermore, the geometry of supporting or

sorbents is a significant component in developing alloy

catalysts. Zhang and colleagues synthesized bimetal nickel-iron

alloy nanomaterials that were entrapped and disseminated in

nitrogen-treated carbon nanoparticles. The NiFe/NC/NiFe/

NC two-electrode device required 1.58 V to operate the OWS

at 10 mA cm2without apparent deterioration in 24 hours. In

addition to the regularly employed conducting metals, other

metals with distinctive morphologies might be appropriate

alternatives for support.[413] Feng group developed a MoNi4

catalyst anchoring on MoO2cuboid arrays with a tiny

overpotential of 15 mV at 10 mAcm2and a lower Tafel slope

of 30 mV dec1for HER in 1 M KOH. The insertion of the

MoNi4electrode material significantly accelerated the Volmer

process, according to DFT simulations (Figure 43).[414]

Metallic catalysts, particularly those used in OER, are

thought to have a serious issue with poor durability in acidic

Figure 42. (A) Graphical depiction of the fabrication of Ni/NC intermediates from Ni over MOF constituents. (B) HRTEM picture of Ni/NC composites

derived from Ni-based MOF intermediates, with a graphical representation of the Ni/NC framework inset. (C) Linear sweep voltammetric graphs of OWS

utilizing Ni/NC-800/Ni foam as both cathode and anode at a scan speed of 5 mVs1 in a 1.0 M KOH condition. (D) Chronoamperometric slope at 1.62 V input

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 50/65] 1

electrolytes. Corresponding to this, several metals improve

their resistance to oxidation erosion and OER via shielding

against and assistance from carbon. An optimal and robust

catalyst for OER in an acid medium is a valuable metal like

iridium. Feng team scattered Ir nanomaterials on 3D graphite

foam (Ir/GF) through calcination to produce an Ir3+/polyani-

line mixture (Figure 44a, b). Correspondingly, the HER and

OER overpotentials at 10 mA cm2were only 7 mV and

290 mV in a mixture of 0.5 M H2SO4.[415] A further method

of lowering consumption and improving catalytic efficiency

involves integrating non-noble metals like Ni, Co, and Fe into

Ir. On a carbon surface, microparticles IrM nanoclusters (1.5–

2 nm; M=Ni, Co, Fe) have demonstrated a 1.58 V at

10 mA cm2in acid, which is a poor cell potential 403. Such

studies pave the way for developing acidic stable polyfunctional

electrocatalysts for OWS (Figure 44c–h).[416] The increased

composition of accessible, energetic locations, improved

electron transport from conductive structures to catalyst

interfaces, and built-in catalyst sustain interference to modify

the electronic properties of the energetic locations or partic-

ipate directly in the reaction are all potential benefits of

bifunctional support systems and sorbents. Non-metal material

boosting is a noteworthy alternative method for enhancing the

internal performance of electrocatalysts. A texture nitride

Ni2Co, for instance, was presented by Gao et al. to isolate

NiCo metallic locations by the Co/NiN groups. This

material demonstrated an almost 100% Faraday performance

and a minimal and steady power density of 1.59 V

(10 mA cm2).[417] If the amount of dopants might be properly

controlled, adding a third or more metal to a binary alloy

might improve OER capabilities and be beneficial for

HER.[418] Yang and colleagues created graphene-wrapped

FeCoNi tertiary alloys that had been nitrogen treated. DFT

analysis demonstrated that the electrical frameworks of

FeCoNi alloys might be aligned by varying the metal

Figure 43. (A) A simulated diagram of a nickel-foam-supported MoO2cuboid-supported MoNi4catalyst. (B) Plasmonic graph of permeable MoNi4systems,

conventional Pt/C, and Ni foam for OWS in a two electrodes arrangement after being heated at 300, 450, and 600°C. (C) Image of a WS instrument powered

by one AA battery (1.5 V). (D) Estimated kinetic parameters for the adsorbed water energized water, OH, and hydrogen. Reprinted with permission from

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 51/65] 1

compositions, which would then affect the HER and OER

functions.[418]

4. Conclusion

Diverse electrocatalysts based on transition metals were already

developed for the overall water-splitting process (OWS). All of

the recent analysis efforts intended to obtain extremely

energetic, plentiful, and inexpensive catalysts to substitute the

expensive and unusual noble metal-based ones for industrial

use. To develop a polyfunctional electrocatalytic activity that

can be used for pragmatic activities. Enormous attempts have

already been managed to make: (1) nanomaterials configura-

tion and improvement of the transition metal-based polyfunc-

tional catalysts such that they can be used as anode and

cathode material with very effective reliability; (2) immediate

production of electrocatalyst upon conductive components to

prevent carbon preservatives or polymer adhesives because

more energetic spots can be supplied, outstanding electrical

cohesion could be accomplished, and much more effective.

Although there are prospects of advancement in the develop-

ment of catalysts predicated on transition metals, there are still

obstacles to address. (1) Computational modeling and predic-

tions of the efficiency and catalyzed processes of the catalysts

used in water electrolysis are absent. DFT simulations provide

an understanding of chemical transitions and forecast the

energetic component at the microscopic level. Further work is

required to comprehend the catalysis and reactivity mecha-

nisms in greater depth. DFT analyses are used to determine

the Gibbs activation energies of transitional adsorbent,

comprehend the preferential reactive groups for transitional

adsorbate on the surface of the electrode during the HER/

OER procedure,[419], and deduce the modifications of the

electrical and sensitivity fuel constraints to comprehend the

electrocatalytic activity.[420] In addition, in-situ characterization

methods[421], such as spectroscopic strategies, must be designed

to observe the alteration of phase throughout the OER and

HER electrocatalysis activities. Understanding the kinetic

model by a mix of DFT simulations and in-situ depictions

may aid in creating innovative polyfunctional electrode

Figure 44. Diagrammatic representation of the Ir/GF fabrication process in, (A) conventional graphite foil and artificial 3D graphite foam. (B) Ir/GF, Pt/CC, Ir/

(D) IrNi NC size variation. (E) 95% iR-compensated polarized patterns in 0.1 M HClO4. The related Tafel graphs are inset, and the scan speed is 1.0 mV/s1.

Standard Pt/C, Ir NCs, and IrNi NC polarized graphs for (F) OER and (G) HER in 0.5 M H2SO4. (H) IrNi NCs in a two-electrode polarization curve and the

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 52/65] 1

materials. For instance, optic microscopy may be used to

evaluate the electrochemical reaction, which could be paired

with DFT computations to examine the performance of

polyfunctional catalysts in OWS.[422] Although scanning

electrochemical cell microscopy (SECCM) with analytical

characterization capability may be used with DFT simulations

to reveal the molecular process.[423] Moreover, Raman spectro-

scopy and XPS observations may be paired with DFT

simulations to identify catalysis energetic regions.[424,425]

(2) The behaviors of polyfunctional catalysts depend on several

variables, including the nanomaterials of the electrocatalyst

and the association among the catalyst and supporting

material, as well as the kind of electrolytes and operational

circumstances. It is difficult to immediately comprehend the

consequences of all such variables. The required properties,

however, such as overpotential, Tafel slopes, and durability,

may be measured accurately using benchmark techniques.

(3) For instance, the overpotential may be determined by

analyzing the polarization gradient. In principle, the reduced

overpotential at a similar current density indicates the superior

electrocatalytic activity of catalysts. Whereas the Tafel gradient

may be derived using linear sweep voltammetric (LSV)

readings, the Tafel angle cannot be derived. The shallower the

Tafel gradient, the greater the WS efficiency of the catalysts.

In addition, the durability of an electrocatalyst is often

determined by cyclic voltammetry and the galvanostatic/

potentiostatic electrolytic procedure. Typically, a robust

catalyst could generate a power density greater than 10 mA/

cm2for greater than 10 h (galvanostatic/potentiostatic electrol-

ysis) or greater than 5000 cycles (cyclic voltammetry). (4) In

particular, additional scientific methodologies for efficiently

identifying catalysts must be developed. For instance, an

electrolytic cell coupled with Ambient pressure X-ray photo-

electron spectroscopy (APXPS) may be developed to examine

the alterations happening at the catalyzed interface of the

heterogeneous catalyst under working circumstances.[425] (5) A

consistent current can be used with the electrolytic system and

optical microscopy to observe the complexation and improve-

ment mechanisms in real-time. (6) As of now, almost all of the

polyfunctional electrocatalysts that have been written about

have been employed in alkaline electrolytic cells. A few have

been used in acidic and/or neutral electrolytes, although most

nonprecious metal catalysts are not stable enough to be used in

acidic situations or at elevated current densities. So, it’s

important to make a reliable, extremely engaged polyfunctional

electrocatalyst that can perform at a wide scope of pH values

in the electrolyte. (7) Assembling electrodes with greater

surfaces employing polyfunctional catalysts are comparably

challenging.

5. Future Contests

Hydrogen is considered one of the foremost environmentally

benign and renewable fuels as an efficient fossil fuels substitute,

thereby alleviating the rising critical energy problem. Numer-

ous alternative energy technologies developed for effective H2

production are summarized in this study. Owing to significant

endeavors in inventing and engineering polyfunctional electro-

catalysts with remarkable catalytic performance, the developed

two-electrode electrolysis of water system can produce OWS

with superior efficiency at a reduced cell voltage and long

photostability. Various sustainable technologies using photo-

electrodes, pyroelectric devices, TENG devices, TE devices,

solar cells, as well as EWGS systems may successfully utilize

alternative sources for WS with little or no additional power

supply. As a result, developing a green energy infrastructure is

critical for harnessing alternative sources for WS. Despite

major advancements in green energy systems driven by water

splitting, this industry still confronts several hurdles. To begin,

conventional non-noble metal polyfunctional WS catalysts

perform well in alkali solutions, but uncommonly reduced-cost

WS catalysts operate well in acidic electrolytes. With the

inclusion of PEM in acidic electrolytes, the use of reduced-

price WS catalysts appears appealing. As a result, the primary

emphasis should be on developing an extremely effective non-

noble electrocatalyst for HER and OER in PEM water

electrolyzers. Furthermore, several conventional reduced alkali

WS catalysts cannot achieve sufficient current density and

long-term durability for commercial purposes. As a result,

good durability, plentiful catalytic activity, and wide electrode

sizes for HER and OER are critical for commercial purposes.

Additionally, converting solar energy/thermal energy/wind

energy/water energy to electrical energy for supplying WS via

photovoltaic devices/TE devices/pyroelectric devices/TENG

equipment is a potential technique to accomplish renewable

energy-driven H2production. However, using photovoltaic/

TE/pyroelectric/TENG devices in conjunction with an electro-

lyzer will certainly raise the cost of H2production. Thus,

merging PV devices/TE devices/pyroelectric devices/TENG

devices with an electrolyzer into a unified platform may

minimize the total price of H2production in prospective

commercial deployments by enhancing device flexibility and

systemic reliability. Currently, the various driving devices for

WS have developed significant growth and achieved numerous

remarkable results. With ongoing endeavors, WS powered by

renewable technologies could provide a substantial addition to

large-scale commercial implementations of green power tech-

nologies in the coming period. We expect that this study will

inspire greater attempts to build unique green power methods

for H2fuel generation to accomplish the entire procedure with

a reduced price, pollution-free, and fuel conservation process-

ing in real-world applications.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 53/65] 1

Acknowledgements

Authors acknowledge support and funding of King Khalid

University through Research Center for Advanced Materials

Science (RCAMS) under grant no: RCAMS/KKU/0010/21.

References

[1] X. Li, X. Duan, C. Han, X. Fan, Y. Li, F. Zhang, G. Zhang,

W. Peng, S. Wang, Carbon 2019,148, 540–549, https://doi.

org/10.1016/j.carbon.2019.04.021.

[2] J. Joo, T. Kim, J. Lee, S.-I. Choi, K. Lee, Adv. Mater. 2019,

31, 1806682, https://doi.org/10.1002/adma.201806682.

[3] M. Sohail, H. Xue, Q. Jiao, H. Li, K. Khan, S. Wang, Y.

Zhao, Mater. Res. Bull. 2017,90, 125–130.

[4] J. Hu, H. Li, S. Muhammad, Q. Wu, Y. Zhao, Q. Jiao, J.

Solid State Chem. 2017,253, 113–120.

[5] M. Sohail, H. Xue, Q. Jiao, H. Li, K. Khan, S. Wang, C.

Feng, Y. Zhao, Mater. Res. Bull. 2018,101, 83–89.

[6] M. Sohail, J. Huang, Z. Lai, Y. Cao, S. Ruan, M. N. Shah,

F. U. Khan, H. I. A. Qazi, B. Ullah, J. Inorg. Organomet.

Polym. Mater. 2020,30, 5168–5179.

[7] A. M. Alenad, T. Taha, M. A. Amin, A. Irfan, J. Oliva, Y. Al-

Hadeethi, A. Palamanit, A. Hayat, S. K. B. Mane, M. Sohail,

J. Photochem. Photobiol. A 2022,423, 113591.

[8] A. Hayat, M. Sohail, T. A. Taha, S. Kumar Baburao Mane,

A. G. Al-Sehemi, A. A. Al-Ghamdi, W. I. Nawawi, A.

Palamanit, M. A. Amin, A. M. Fallatah, Z. Ajmal, H. Ali, W.

Ullah Khan, M. Wajid Shah, J. Khan, S. Wageh, J. Colloid

Interface Sci. 2022,627, 621–629, https://doi.org/10.1016/j.

jcis.2022.07.012.

[9] R. Mendoza, J. Oliva, K. P. Padmasree, A. I. Mtz-Enriquez, A.

Hayat, V. Rodriguez-Gonzalez, Ceram. Int. 2022,48, 30967–

30977, https://doi.org/10.1016/j.ceramint.2022.07.055.

[10] I. Uddin, H. Ali, A. G. Al-Sehemi, S. Muhammad, N. Hamad,

T. A. Taha, H. S. AlSalem, A. M. Alenad, A. Palamanit, A.

Hayat, M. Sohail, S. Afr. J. Bot. 2022,149, 109–116, https://

doi.org/10.1016/j.sajb.2022.05.061.

[11] P. Kongto, A. Palamanit, P. Ninduangdee, Y. Singh, I.

Chanakaewsomboon, A. Hayat, M. Wae-hayee, Energy Rep.

2022,8, 5640–5652, https://doi.org/10.1016/j.egyr.2022.04.

033.

[12] A. Hayat, Z. A. Alrowaili, T. A. Taha, J. Khan, I. Uddin, T.

Ali, F. Raziq, I. Ullah, A. Hayat, A. Palamanit, A. Irfan, W. U.

Khan, Synth. Met. 2021,278, 116813, https://doi.org/10.

1016/j.synthmet.2021.116813.

[13] A. U. Rehman, M. Z. Shah, A. Ali, T. Zhao, R. Shah, I. Ullah,

H. Bilal, A. R. Khan, M. Iqbal, A. Hayat, M. Zheng, Int. J.

Energy Res. 2021,45, 4746–4754, https://doi.org/10.1002/er.

6077.

[14] N. Shaishta, W. U. Khan, S. K. B. Mane, A. Hayat, D.-D.

Zhou, J. Khan, N. Mehmood, H. K. Inamdar, G. Manjuna-

tha, Int. J. Energy Res. 2020,44, 8328–8339, https://doi.org/

10.1002/er.5376.

[15] A. U. Rehman, A. Hayat, A. Munis, T. Zhao, M. Israr, M.

Zheng, Proc. Inst. Civ. Eng. 2019,173, 60–67, http://doi.org/

10.1680/jener.19.00018.

[16] M. Khan, A. Hamid, L. Tiehu, A. Zada, F. Attique, N.

Ahmad, A. Ullah, A. Hayat, I. Mahmood, A. Hussain, Y.

Khan, I. Ahmad, A. Ali, T. K. Zhao, Diamond Relat. Mater.

2020,107, 107897, https://doi.org/10.1016/j.diamond.2020.

107897.

[17] M. u. Rahman, A. Hayat, Int. J. Energy Res. 2019,43, 4820–

4827.

[18] A. Hayat, F. Raziq, M. Khan, I. Ullah, M. Ur Rahman, W. U.

Khan, J. Khan, A. Ahmad, J. Photochem. Photobiol. A 2019,

379, 88–98, https://doi.org/10.1016/j.jphotochem.2019.05.

011.

[19] A. Hayat, M. U. Rahman, I. Khan, J. Khan, M. Sohail, H.

Yasmeen, S.-y. Liu, K. Qi, W. Lv, Molecules 2019,24, 1779.

[20] A. Hayat, S. K. B. Mane, N. Shaishta, J. Khan, A. Hayat, G.

Keyum, I. Uddin, F. Raziq, M. Khan, G. Manjunatha, J.

Electrochem. Soc. 2019,166, B1602–B1611, http://doi.org/10.

1149/2.0491915jes.

[21] W. Wang, M. Xu, X. Xu, W. Zhou, Z. Shao, Angew. Chem.,

Int. Ed. Engl. 2020,59, 136–152, http://doi.org/10.1002/anie.

201900292.

[22] X. Li, X. Hao, A. Abudula, G. Guan, J. Mater. Chem. A 2016,

4, 11973–12000, http://doi.org/10.1039/C6TA02334G.

[23] F. Pan, M. Sohail, T. A. Taha, A. G. Al-Sehemi, S. Ullah,

H. S. AlSalem, G. A. M. Mersal, M. M. Ibrahim, A. M.

Alenad, O. A. Al-Hartomy, M. A. Amin, Z. Ajmal, A.

Palamanit, A. Hayat, A. Zada, W. I. Nawawi, Mater. Res. Bull.

2022,152, 111865, https://doi.org/10.1016/j.materresbull.

2022.111865.

[24] M. Sohail, U. Anwar, T. Taha, H. Qazi, A. G. Al-Sehemi, S.

Ullah, H. Gharni, I. Ahmed, M. A. Amin, A. Palamanit, Arab.

J. Chem. 2022,15, 104070.

[25] A. Hayat, M. Sohail, T. Taha, S. K. B. Mane, A. G. Al-

Sehemi, A. A. Al-Ghamdi, W. Nawawi, A. Palamanit, M. A.

Amin, A. M. Fallatah, J. Colloid Interface Sci. 2022,627, 621–

629.

[26] A. Hayat, M. Sohail, U. Anwar, T. Taha, K. S. El-Nasser,

A. M. Alenad, A. G. Al-Sehemi, N. A. Alghamdi, O. A. Al-

Hartomy, M. A. Amin, J. Colloid Interface Sci. 2022,624,

411–422.

[27] A. Hayat, M. Sohail, M. S. Hamdy, M. A. Amin, S. Alharthi,

T. Taha, M. M. Rahman, A. Palamanit, J. Khan, S. K. B.

Mane, J. Mol. Catal. 2022,518, 112064.

[28] E. Gul, P. E. Campana, A. Chandrasekaran, S. Subbiah, H.

Yang, Q. Yang, J. Yan, H. Li, U. Desideri, L. Barelli, G.

Bidini, F. Fantozzi, I. Uddin, A. Hayat, K. A. b. Alrawashdeh,

P. Bartocci, in Advanced Technology for the Conversion of Waste

Into Fuels and Chemicals, ed. by A. Khan, A. Pizzi, M. Jawaid,

N. Azum, A. Asiri, I. Isa, Woodhead Publishing, 2021,

pp. 181–219.

[29] A. Hayat, M. Sohail, T. A. Taha, A. M. Alenad, A. Irfan, N.

Shaishta, A. Hayat, S. K. B. Mane, W. U. Khan, CrystEng-

Comm 2021,23, 4963–4974, http://doi.org/10.1039/

D1CE00405 K.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 54/65] 1

[30] A. Hayat, N. Shaishta, S. K. B. Mane, J. Khan, A. Hayat, ACS

Appl. Mater. Interfaces 2019,11, 46756–46766.

[31] A. Hayat, N. Shaishta, S. K. B. Mane, A. Hayat, J. Khan,

A. U. Rehman, T. Li, J. Colloid Interface Sci. 2020,560, 743–

754, https://doi.org/10.1016/j.jcis.2019.10.088.

[32] A. Hayat, F. Raziq, M. Khan, J. Khan, S. K. B. Mane, A.

Ahmad, M. U. Rahman, W. U. Khan, J. Colloid Interface Sci.

2019,554, 627–639.

[33] A. Hayat, T. Li, Int. J. Energy Res. 2019,43, 5479–5492,

https://doi.org/10.1002/er.4667.

[34] Y.-J. Tang, H.-J. Zhu, L.-Z. Dong, A. M. Zhang, S.-L. Li, J.

Liu, Y.-Q. Lan, Appl. Catal. B. 2019,245, 528–535, https://

doi.org/10.1016/j.apcatb.2019.01.007.

[35] H. Cao, X. Gong, T. Liu, F. Xiao, X. Lv, J. Zhou, L. Gai, J.

Alloys Compd. 2019,797, 341–347, https://doi.org/10.1016/j.

jallcom.2019.05.103.

[36] A. Hayat, J. A. Shah Syed, A. G. Al-Sehemi, K. S. El-Nasser,

T. A. Taha, A. A. Al-Ghamdi, M. A. Amin, Z. Ajmal, W.

Iqbal, A. Palamanit, D. I. Medina, W. I. Nawawi, M. Sohail,

Inter. J. Hydro. Energy 2022,47, 10837–10867, https://doi.

org/10.1016/j.ijhydene.2021.11.252.

[37] A. Qadeer, M. Anis, Z. Ajmal, K. L. Kirsten, M. Usman, R. R.

Khosa, M. Liu, X. Jiang, X. Zhao, Sustain Cities Soc. 2022,83,

103962, https://doi.org/10.1016/j.scs.2022.103962.

[38] A. Hayat, J. A. S. Syed, A. G. Al-Sehemi, K. S. El-Nasser, T.

Taha, A. A. Al-Ghamdi, M. A. Amin, Z. Ajmal, W. Iqbal, A.

Palamanit, Int. J. Hydrogen Energy 2022,47, 10837–10867.

[39] A. Ullah, J. Khan, M. Sohail, A. Hayat, T. K. Zhao, B. Ullah,

M. Khan, I. Uddin, S. Ullah, R. Ullah, J. Photochem. Photobiol.

A2020,401, 112764.

[40] A. Hayat, Z. Chen, Z. Luo, Y. Fang, X. Wang, Res. Chem.

Intermed. 2021,47, 15–27, http://doi.org/10.1007/s11164-

020-04345-y.

[41] M. Khan, A. Hayat, S. K. Baburao Mane, T. Li, N. Shaishta,

D. Alei, T. K. Zhao, A. Ullah, A. Zada, A. Rehman, W. U.

Khan, Int. J. Hydrogen Energy 2020,45, 29070–29081,

https://doi.org/10.1016/j.ijhydene.2020.07.274.

[42] A. Hayat, J. Khan, M. U. Rahman, S. B. Mane, W. U. Khan,

M. Sohail, N. U. Rahman, N. Shaishta, Z. Chi, M. Wu, J.

Colloid Interface Sci. 2019,548, 197–205, https://doi.org/10.

1016/j.jcis.2019.04.037.

[43] F. Raziq, J. He, J. Gan, M. Humayun, M. B. Faheem, A.

Iqbal, A. Hayat, S. Fazal, J. Yi, Y. Zhao, K. Dhanabalan, X.

Wu, A. Mavlonov, T. Ali, F. Hassan, X. Xiang, X. Zu, H.

Shen, S. Li, L. Qiao, Appl. Catal. B 2020,270, 118870,

https://doi.org/10.1016/j.apcatb.2020.118870.

[44] A. Ullah, J. Khan, M. Sohail, A. Hayat, T. K. Zhao, B. Ullah,

M. Khan, I. Uddin, S. Ullah, R. Ullah, A. U. Rehman, W. U.

Khan, J. Photochem. Photobiol. A 2020,401, 112764, https://

doi.org/10.1016/j.jphotochem.2020.112764.

[45] Y. Shi, B. Zhang, Chem. Soc. Rev. 2016,45, 1529–1541,

http://doi.org/10.1039/C5CS00434A.

[46] A. Qadeer, Z. A. Saqib, Z. Ajmal, C. Xing, S. Khan Khalil, M.

Usman, Y. Huang, S. Bashir, Z. Ahmad, S. Ahmed, K. H.

Thebo, M. Liu, Sustain. Cities Soc. 2020,53, 101959, https://

doi.org/10.1016/j.scs.2019.101959.

[47] A. Qadeer, Z. Ajmal, M. Usman, X. Zhao, S. Chang, Resour.

Conserv. Recycl. 2021,175, 105855, https://doi.org/10.1016/j.

resconrec.2021.105855.

[48] A. Qadeer, S. Liu, M. Liu, X. Liu, Z. Ajmal, Y. Huang, Y.

Jing, S. K. Khalil, D. Zhao, D. Weining, X.-Y. Wei, Y. Liu, J.

Cleaner Prod. 2019,231, 1070–1078, https://doi.org/10.

1016/j.jclepro.2019.05.203.

[49] W. Li, M. Sohail, U. Anwar, T. Taha, A. G. Al-Sehemi, S.

Muhammad, A. A. Al-Ghamdi, M. A. Amin, A. Palamanit, S.

Ullah, A. Hayat, Z. Ajmal, Int. J. Hydrogen Energy 2022 47,

21067–21118.

[50] A. Hayat, M. Sohail, W. Iqbal, T. Taha, A. M. Alenad, A. G.

Al-Sehemi, S. Ullah, N. A. Alghamdi, A. Alhadhrami, Z.

Ajmal, Journal of Science: Adv. Mater. Devices 2022, 100483,

https://doi.org/10.1016/j.jsamd.2022.100483.

[51] M. Sohail, T. Altalhi, A. G. Al-Sehemi, T. A. M. Taha, K. S.

El-Nasser, A. A. Al-Ghamdi, M. Boukhari, A. Palamanit, A.

Hayat, M. A. Amin, Nanomaterials 2021,11, 3245.

[52] Z. Ajmal, M. u. Haq, Y. Naciri, R. Djellabi, N. Hassan, S.

Zaman, A. Murtaza, A. Kumar, A. G. Al-Sehemi, H. Algarni,

O. A. Al-Hartomy, R. Dong, A. Hayat, A. Qadeer, Chemo-

sphere 2022,308, 136358, https://doi.org/10.1016/j.chemo-

sphere.2022.136358.

[53] A. Hayat, M. Sohail, A. Qadeer, T. A. Taha, M. Hussain, S.

Ullah, A. G. Al-Sehemi, H. Algarni, M. A. Amin, M.

Aqeel Sarwar, W. I. Nawawi, A. Palamanit, Y. Orooji, Z.

Ajmal, Chem. Rec. 2022, e202200097, https://doi.org/10.

1002/tcr.202200097.

[54] Z. Ajmal, M. Kashif Irshad, A. Qadeer, M. Zia Ul Haq, R.

Ullah, M. Aqeel Sarwar, T. Saeed, M. Abid, A. Hayat, A. Ali,

A. Noman, R. Dong, Int. J. Environ. Sci. Technol. 2022, 1–16,

http://doi.org/10.1007/s13762-022-04452-w.

[55] M. Sohail, U. Anwar, T. A. Taha, H. I. A. Qazi, A. G. Al-

Sehemi, S. Ullah, H. Algarni, I. M. Ahmed, M. A. Amin, A.

Palamanit, W. Iqbal, S. Alharthi, W. I. Nawawi, Z. Ajmal, H.

Ali, A. Hayat, Arab. J. Chem. 2022,15, 104070, https://doi.

org/10.1016/j.arabjc.2022.104070.

[56] M. S. Faber, S. Jin, Energy Environ. Sci. 2014,7, 3519–3542

10.1039/C4EE01760A.

[57] A. Hayat, M. Sohail, M. S. Hamdy, T. Taha, H. S. AlSalem,

A. M. Alenad, M. A. Amin, R. Shah, A. Palamanit, J. Khan,

Surf. Interfaces 2022,29 101725.

[58] R. Li, X. Li, D. Yu, L. Li, G. Yang, K. Zhang, S. Ramakrishna,

L. Xie, S. Peng, Carbon 2019,148, 496–503, https://doi.org/

10.1016/j.carbon.2019.04.002.

[59] A. Qadeer, K. L. Kirsten, Z. Ajmal, X. Jiang, X. Zhao,

Environ. Sci. Technol. 2022,56, 1482–1488, http://doi.org/

10.1021/acs.est.1c08365.

[60] A. Qadeer, K. L. Kirsten, Z. Ajmal, Z. Xingru, Environ. Sci.

Technol. 2022,56, 5294–5297 10.1021/acs.est.2c01849.

[61] Z. Ajmal, M. Kashif Irshad, A. Qadeer, M. Zia Ul Haq, R.

Ullah, M. Aqeel Sarwar, T. Saeed, M. Abid, A. Hayat, A. Ali,

A. Noman, R. Dong, Int. J. Environ. Sci. Technol. 2022,

http://doi.org/10.1007/s13762-022-04452-w.

[62] A. Essekri, N. Aarab, A. Hsini, Z. Ajmal, M. Laabd, M.

El Ouardi, A. Ait Addi, R. Lakhmiri, A. Albourine, J.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 55/65] 1

Dispersion Sci. Technol. 2022,43, 1359–1372, http://doi.org/

10.1080/01932691.2020.1857263.

[63] I. Ullah, T. Taha, A. M. Alenad, I. Uddin, A. Hayat, A.

Hayat, M. Sohail, A. Irfan, J. Khan, A. Palamanit, Surf.

Interfaces 2021,25, 101227.

[64] M. I. Jamesh, J. Power Sources 2016,333, 213–236, https://

doi.org/10.1016/j.jpowsour.2016.09.1.

[65] A. Hayat, M. sohail, U. Anwar, T. A. Taha, K. S. El-Nasser,

A. M. Alenad, A. G. Al-Sehemi, N. Ahmad Alghamdi, O. A.

Al-Hartomy, M. A. Amin, A. Alhadhrami, A. Palamanit, S.

Kumar Baburao Mane, W. I. Nawawi, Z. Ajmal, J. Colloid

Interface Sci. 2022,624, 411–422, https://doi.org/10.1016/j.

jcis.2022.05.139.

[66] Z. Ajmal, Y. Naciri, A. Hsini, B. M. Bresolin, A. Qadeer, M.

Nauman, M. Arif, M. K. Irshad, K. A. Khan, R. Djellabi,

C. L. Bianchi, M. Laabd, A. Albourine, R. Dong, in Progress

and Prospects in the Management of Oxyanion Polluted Aqua

Systems, ed. by N. A. Oladoja, E. I. Unuabonah, Springer

International Publishing, Cham, 2021, pp. 185–217.

[67] Z. Ajmal, A. Muhmood, M. Usman, S. Kizito, J. Lu, R. Dong,

S. Wu, J. Colloid Interface Sci. 2018,528, 145–155, https://

doi.org/10.1016/j.jcis.2018.05.084.

[68] Z. Ajmal, M. Usman, I. Anastopoulos, A. Qadeer, R. Zhu, A.

Wakeel, R. Dong, J. Environ. Manage. 2020,264, 110477,

https://doi.org/10.1016/j.jenvman.2020.110477.

[69] A. Malik, M. Hussain, F. Uddin, W. Raza, S. Hussain, U.-e.

Habiba, T. Malik, Z. Ajmal, Water Environ. Res. 2021,93,

2931–2940, https://doi.org/10.1002/wer.1639.

[70] A. Hayat, M. Sohail, J. Ali Shah Syed, A. G. Al-Sehemi, M. H.

Mohammed, A. A. Al-Ghamdi, T. Taha, H. Salem AlSalem,

A. M. Alenad, M. A. Amin, Chem. Rec. 2022,22,

e202100310.

[71] Y. Yan, B. Y. Xia, B. Zhao, X. Wang, J. Mater. Chem. A 2016,

4, 17587–17603, http://doi.org/10.1039/C6TA08075H.

[72] Z. Tao, T. Wang, X. Wang, J. Zheng, X. Li, ACS Appl. Mater.

Interfaces 2016,8, 35390–35397, https://doi.org/10.1021/

acsami.6b13411.

[73] J. Wang, X. Yue, Y. Yang, S. Sirisomboonchai, P. Wang, X.

Ma, A. Abudula, G. Guan, J. Alloys Compd. 2020,819,

153346, https://doi.org/10.1016/j.jallcom.2019.153346.

[74] C. G. Morales-Guio, L.-A. Stern, X. Hu, Chem. Soc. Rev.

2014,43, 6555–6569, https://doi.org/10.1039/

C3CS60468 C.

[75] T. R. Cook, D. K. Dogutan, S. Y. Reece, Y. Surendranath,

T. S. Teets, D. G. Nocera, Chem. Rev. 2010,110, 6474–502,

https://doi.org/10.1021/cr100246c.

[76] S. Anantharaj, S. R. Ede, K. Sakthikumar, K. Karthick, S.

Mishra, S. Kundu, ACS Catal. 2016,6, 8069–8097, https://

doi.org/10.1021/acscatal.6b02479.

[77] G. Zhao, K. Rui, S. X. Dou, W. Sun, Adv. Funct. Mater.

2018,28, 1803291, https://doi.org/10.1002/adfm.

201803291.

[78] W. Sheng, H. A. Gasteiger, Y. Shao-Horn, J. Electrochem. Soc.

2010,157, B1529.

[79] N.-T. Suen, S.-F. Hung, Q. Quan, N. Zhang, Y.-J. Xu, H. M.

Chen, Chem. Soc. Rev. 2017,46, 337–365, https://doi.org/10.

1039/C6CS00328A.

[80] I. C. Man, H. Y. Su, F. Calle-Vallejo, H. A. Hansen, J.

Martínez, N. G. Inoglu, J. Kitchin, T. F. Jaramillo, J. Nørskov,

J. Rossmeisl, ChemCatChem 2011,3, 1159–1165.

[81] H. Seo, K. H. Cho, H. Ha, S. Park, J. S. Hong, K. Jin, K. T.

Nam, J. Korean Ceram. Soc. 2017,54, 1–8.

[82] Y. Shi, B. Zhang, Chem. Soc. Rev. 2016,45, 1529–1541.

[83] E. V. Gomez, Adv. Mater. 2019 32, 1907348, https://doi.org/

10.1002/adma.201907348.

[84] H. Vrubel, T. Moehl, M. Grätzel, X. Hu, Chem. Commun.

2013,49, 8985–8987, https://doi.org/10.1039/

C3CC45416A.

[85] X. Zou, Y. Zhang, Chem. Soc. Rev. 2015,44, 5148–5180.

[86] S. Anantharaj, S. R. Ede, K. Sakthikumar, K. Karthick, S.

Mishra, S. Kundu, ACS Catal. 2016,6, 8069–8097.

[87] S. B. Roy, K. Akbar, J. H. Jeon, S. K. Jerng, L. Truong, K.

Kim, Y. Yi, S. H. Chun, J. Mater. Chem. A 2019,7, 20590–

20596.

[88] J. Zhang, G. Wang, Z. Liao, P. Zhang, F. Wang, X. Zhuang,

E. Zschech, X. Feng, Nano Energy 2017,40, 27–33.

[89] W. Li, M. Sohail, U. Anwar, T. A. Taha, A. G. Al-Sehemi, S.

Muhammad, A. A. Al-Ghamdi, M. A. Amin, A. Palamanit, S.

Ullah, A. Hayat, Z. Ajmal, Int. J. Hydrogen Energy 2022,47,

21067–21118, https://doi.org/10.1016/j.ijhydene.2022.04.

247.

[90] F. Pan, M. Sohail, T. A. Taha, A. G. Al-Sehemi, S. Ullah,

H. S. AlSalem, G. A. M. Mersal, M. M. Ibrahim, A. M.

Alenad, O. A. Al-Hartomy, M. A. Amin, Z. Ajmal, A.

Palamanit, A. Hayat, A. Zada, W. I. Nawawi, Mater. Res. Bull.

2022,152, 111865, https://doi.org/10.1016/j.materresbull.

2022.111865.

[91] S. Kizito, T. Lv, S. Wu, Z. Ajmal, H. Luo, R. Dong, Sci. Total

Environ. 2017,592, 197–205, https://doi.org/10.1016/j.scito-

tenv.2017.03.125.

[92] S. Ahmed, H. U. Rehman, Z. Ali, A. Qadeer, A. Haseeb, Z.

Ajmal, Surf. Interf. 2021,23, 100953, https://doi.org/10.

1016/j.surfin.2021.100953.

[93] M. Sohail, U. Anwar, T. A. Taha, H. I. A. Qazi, A. G. Al-

Sehemi, S. Ullah, H. Algarni, I. M. Ahmed, M. A. Amin, A.

Palamanit, W. Iqbal, S. Alharthi, W. I. Nawawi, Z. Ajmal, H.

Ali, A. Hayat, Arab. J. Chem. 2022,15, 104070, https://doi.

org/10.1016/j.arabjc.2022.104070.

[94] A. Hayat, M. Sohail, W. Iqbal, T. A. Taha, A. M. Alenad,

A. G. Al-Sehemi, S. Ullah, N. A. Alghamdi, A. Alhadhrami, Z.

Ajmal, A. Palamanit, W. I. Nawawi, H. S. AlSalem, H. Ali, A.

Zada, M. A. Amin, J. Sci. Adv. Mater. Devices 2022, 100483,

https://doi.org/10.1016/j.jsamd.2022.100483.

[95] A. Hayat, M. Sohail, T. A. Taha, S. Kumar Baburao Mane,

A. G. Al-Sehemi, A. A. Al-Ghamdi, W. I. Nawawi, A.

Palamanit, M. A. Amin, A. M. Fallatah, Z. Ajmal, H. Ali, W.

Ullah Khan, M. Wajid Shah, J. Khan, S. Wageh, J. Colloid

Interface Sci. 2022,627, 621–629, https://doi.org/10.1016/j.

jcis.2022.07.012.

[96] W. Li, M. Sohail, U. Anwar, T. A. Taha, A. G. Al-Sehemi, S.

Muhammad, A. A. Al-Ghamdi, M. A. Amin, A. Palamanit, S.

Ullah, A. Hayat, Z. Ajmal, Int. J. Hydrogen Energy 2022,47,

21067–21118, https://doi.org/10.1016/j.ijhydene.2022.04.

247.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 56/65] 1

[97] A. Hayat, M. Sohail, W. Iqbal, T. A. Taha, A. M. Alenad,

A. G. Al-Sehemi, S. Ullah, N. A. Alghamdi, A. Alhadhrami, Z.

Ajmal, A. Palamanit, W. I. Nawawi, H. S. AlSalem, H. Ali, A.

Zada, M. A. Amin, Journal of Science: Adv. Mater. Devices

2022, 100483, https://doi.org/10.1016/j.jsamd.2022.100483.

[98] K.-Y. Park, Y.-D. Kim, J.-I. Lee, M. Saqib, J.-S. Shin, Y. Seo,

J. H. Kim, H.-T. Lim, J.-Y. Park, ACS Appl. Mater. Interfaces

2018,11, 457–468.

[99] I. Roger, M. A. Shipman, M. D. Symes, Nat. Chem. Rev. 2016

1, 0003.

[100] A. Hayat, M. Sohail, T. Taha, A. M. Alenad, I. Uddin, A.

Hayat, T. Ali, R. Shah, A. Irfan, W. U. Khan, Catalysts 2021,

11, 935.

[101] M. Ma, Angew. Chem. Int. Ed. 2016,55, 9748–9752; Angew.

Chem. 2016,128, 9900–9904.

[102] Y. Jiao, Y. Zheng, M. Jaroniec, S. Z. Qiao, Chem. Soc. Rev.

2015,44, 2060–2086, https://doi.org/10.1039/C4CS00470A.

[103] J. Yu, Q. Li, N. Chen, C. Y. Xu, L. Zhen, J. Wu, V. P.

Dravid, ACS Appl. Mater. Interfaces 2016,8, 27850–27858,

https://doi.org/10.1021/acsami.6b10552.

[104] Y. Xu, L. Wang, X. Liu, S. Zhang, C. Liu, D. Yan, Y. Zeng, Y.

Pei, Y. Liu, S. Luo, J. Mater. Chem. A 2016,4, 16524–16530,

https://doi.org/10.1039/C6TA06534A.

[105] H. A. Gasteiger, N. Markovic, P. N. Ross, E. J. Cairns, J. Phys.

Chem. 1994,98, 617–625.

[106] A. Pozio, M. Francesco, A. Cemmi, F. Cardellini, L. Giorgi, J.

Power Sources 2002,105, 13–19.

[107] C. L. G. and, A. R. J. Kucernak, J. Phys. Chem. B 2002,106,

1036–1047.

[108] Q. Jia, J. Li, K. Caldwell, D. E. Ramaker, J. M. Ziegelbauer,

R. S. Kukreja, A. Kongkanand, S. Mukerjee, ACS Catal. 2016,

6, 928–938.

[109] Q. Jia, J. Li, K. Caldwell, D. E. Ramaker, J. M. Ziegelbauer,

R. S. Kukreja, A. Kongkanand, S. Mukerjee, ACS Catal. 2016,

6, 928–938.

[110] Q. Jia, W. Liang, M. K. Bates, P. Mani, W. Lee, S. Mukerjee,

ACS Nano 2015,9, 387–400, https://doi.org/10.1021/

nn506721f.

[111] F. Hasché, M. Oezaslan, P. Strasser, T.-P. Fellinger, J. Energy

Chem. 2016,25, 251–257.

[112] E. Hu, Y. Feng, J. Nai, D. Zhao, Y. Hu, X. W. Lou, Energy

Environ. Sci. 2018,11, 872–880.

[113] L. A. Xiao, B. Jya, J. A. Jin, A. Aw, A. Lz, B. Tx, L. Hong, A.

Wz, Nano Energy 2019,62, 127–135.

[114] J. Jia, T. Xiong, L. Zhao, F. Wang, H. Liu, R. Hu, J. Zhou,

W. Zhou, S. Chen, ACS Nano 2017,11, 12509–12518.

[115] L. Wen, X. Shan, J. Liu, H. Mu, Y. Xiao, B. Mei, W. Liu, G.

Lin, Z. Jiang, L. Jiang, Angew. Chem. Int. Ed. 2020,59,

1659–1665; Angew. Chem. 2020,132, 1676–1682.

[116] G. dos Santos, C. T. Eckert, E. De Rossi, R. A. Bariccatti,

E. P. Frigo, C. A. Lindino, H. J. Alves, Renewable Sustainable

Energy Rev. 2017,68, 563–571.

[117] D. Jeon, J. Park, C. Shin, H. Kim, J.-W. Jang, D. W. Lee, J.

Ryu, Sci. Adv. 2020,6, eaaz3944.

[118] L. Zeng, L. Yang, J. Lu, J. Jia, J. Yu, Y. Deng, M. Shao, W.

Zhou, Chin. Chem. Lett. 2018,29, 1875–1878.

[119] Z. Cai, A. Wu, H. Yan, C. Tian, D. Guo, H. Fu, Energy

Technol. 2020,8, 1901079.

[120] Y. Yan, B. Y. Xia, B. Zhao, X. Wang, J. Mater. Chem. A.

2016,4, 17587–17603.

[121] K. Chi, X. Tian, Q. Wang, Z. Zhang, S. Wang, J. Catal.

2020,381, 44–52.

[122] Y. Deng, Z. Liu, A. Wang, D. Sun, Y. Chen, L. Yang, J. Pang,

H. Li, H. Li, H. Liu, Nano Energy 2019,62, 338–347.

[123] N. Li, Y. Zhang, M. Jia, X. Lv, X. Tao, Electrochim. Acta

2019,326, 134976.

[124] Z. Gao, F.-q. Liu, L. Wang, F. Luo, Inorg. Chem. 2019,58,

3247–3255.

[125] Y. Wang, X. Chao, D. Liu, X. Huang, S. Wang, ACS Appl.

Mater. Interfaces 2016,8, 18652–18657.

[126] Y. Zhang, J. Fu, H. Zhao, R. Jiang, R. Zhang, Appl. Catal. B.

2019,257, 117899.

[127] Z. Liu, H. Tan, D. Liu, X. Liu, J. Xin, J. Xie, M. Zhao, L.

Song, L. Dai, H. Liu, Advan. Sci. 2019,6, 1801829.

[128] L. Hui, Y. Xue, H. Yu, Y. Liu, Y. Fang, C. Xing, B. Huang, Y.

Li, J. Am. Chem. Soc. 2019,141, 10677–10683.

[129] Z. Yuan, J. Li, M. Yang, Z. Fang, J. Jian, D. Yu, X. Chen, L.

Dai, J. Am. Chem. Soc. 2019,141, 4972–4979.

[130] Y. Zhou, Z. Wang, Z. Pan, L. Liu, J. Xi, X. Luo, Y. Shen,

Adv. Mater. 2019,31, 1806769.

[131] A. Hsini, Y. Naciri, M. Benafqir, Z. Ajmal, N. Aarab, M.

Laabd, J. A. Navío, F. Puga, R. Boukherroub, B. Bakiz, A.

Albourine, J. Colloid Interface Sci. 2021,585, 560–573,

https://doi.org/10.1016/j.jcis.2020.10.036.

[132] A. Hsini, Y. Naciri, M. Laabd, M. El Ouardi, Z. Ajmal, R.

Lakhmiri, R. Boukherroub, A. Albourine, J. Mol. Liq. 2020,

316, 113832, https://doi.org/10.1016/j.molliq.2020.113832.

[133] S. Kizito, H. Luo, S. Wu, Z. Ajmal, T. Lv, R. Dong, J.

Environ. Manage. 2017,201, 260–267, https://doi.org/10.

1016/j.jenvman.2017.06.057.

[134] A. Essekri, A. Hsini, Y. Naciri, M. Laabd, Z. Ajmal, M.

El Ouardi, A. Ait Addi, A. Albourine, Int. J. Phytorem. 2021,

23, 336–346, https://doi.org/10.1080/15226514.2020.

1813686.

[135] L. Brini, K. H’Maida, A. Imgharn, A. Hsini, Y. Naciri, Z.

Ajmal, A. Bouziani, A. Boulahya, M. Arahou, B. Bakiz, A.

Albourine, M. Fekhaoui, Int. J. Environ. Anal. Chem. 2021,

1–17, https://doi.org/10.1080/03067319.2021.1994557.

[136] L. Brini, A. Hsini, Y. Naciri, A. Bouziani, Z. Ajmal, K.

H’Maida, A. Boulahya, M. Arahou, B. Bakiz, A. Albourine, M.

Fekhaoui, Water Sci. Technol. 2021,84, 2265–2277, https://

doi.org/10.2166/wst.2021.446.

[137] A. Hayat, Z. A. Alrowaili, T. A. Taha, J. Khan, I. Uddin, T.

Ali, F. Raziq, I. Ullah, A. Hayat, A. Palamanit, A. Irfan, W. U.

Khan, Synth. Met. 2021,278, 116813, https://doi.org/10.

1016/j.synthmet.2021.116813.

[138] A. Hayat, A. G. Al-Sehemi, K. S. El-Nasser, T. A. Taha, A. A.

Al-Ghamdi, S. Jawad Ali Shah, M. A. Amin, T. Ali, T. Bashir,

A. Palamanit, J. Khan, W. I. Nawawi, Int. J. Hydrogen Energy

2022,47, 5142–5191, https://doi.org/10.1016/j.ijhydene.

2021.11.133.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 57/65] 1

[139] A. Hayat, M. Sohail, T. A. M. Taha, A. M. Alenad, M. A.

Amin, A. Hayat, A. Irfan, A. Palamanit, Y. Al-Hadeethi,

S. K. B. Mane, Int. J. Energy Res. 2022,46, 1882–1893.

[140] W. Li, M. Sohail, U. Anwar, T. A. Taha, A. G. Al-Sehemi, S.

Muhammad, A. A. Al-Ghamdi, M. A. Amin, A. Palamanit, S.

Ullah, A. Hayat, Z. Ajmal, Int. J. Hydrogen Energy 2022,47,

21067–21118, https://doi.org/10.1016/j.ijhydene.2022.04.

247.

[141] S. H. Ahn, I. Choi, H.-Y. Park, S. J. Hwang, S. J. Yoo, E.

Cho, H.-J. Kim, D. Henkensmeier, S. W. Nam, S.-K. Kim,

J. H. Jang, Chem. Commun. 2013,49, 9323–9325 10.1039/

C3CC44891F.

[142] S. Wang, Y. Zhao, H. Xue, J. Xie, C. Feng, H. Li, D. Shi, S.

Muhammad, Q. Jiao, Mater. Lett. 2018,223, 186–189.

[143] B. Zhao, R. Wang, Y. Li, Y. Ren, X. Li, X. Guo, R. Zhang,

C. B. Park, J. Mater. Chem. C 2020,8, 7401–7410, https://

doi.org/10.1039/D0TC00987C.

[144] Y. Sugawara, H. Kobayashi, I. Honma, T. Yamaguchi, ACS

Omega 2020,5, 29388–29397 10.1021/acsomega.0c04254.

[145] X. Zhang, G. Jin, D. Wang, Z. Chen, M. Zhao, G. Xi, J.

Alloys Compd. 2021,875, 160054, https://doi.org/10.1016/j.

jallcom.2021.160054.

[146] Z. Yang, Y. Lin, F. Jiao, J. Li, W. Wang, Y. Gong, X. Jing,

Appl. Surf. Sci. 2020,502, 144147.

[147] V. D. Silva, E. P. Nascimento, J. P. F. Grilo, T. A. Simões,

R. R. Menezes, D. A. Macedo, E. S. Medeiros, Open Ceramics

2021,5, 100087, https://doi.org/10.1016/j.oceram.2021.

100087.

[148] C. D. Daub, J. Wang, S. Kudesia, D. Bratko, A. Luzar,

Faraday Discuss. 2010,146, 67–77.

[149] M. Zhu, Z. Zhang, H. Zhang, H. Zhang, X. Zhang, L. Zhang,

S. Wang, J. Colloid Interface Sci. 2018,509, 522–528, https://

doi.org/10.1016/j.jcis.2017.09.076.

[150] K. Kordek-Khalil, A. de Rosset, P. Rutkowski, Appl. Surf. Sci.

2020,509, 145263.

[151] M. Nasiruzzaman Shaikh, M. A. Aziz, A. N. Kalanthoden, A.

Helal, A. S. Hakeem, M. Bououdina, Catal. Sci. Technol.

2018,8, 4709–4717, https://doi.org/10.1039/C8CY00936H.

[152] S. J. Marje, P. K. Katkar, S. B. Kale, A. C. Lokhande, C. D.

Lokhande, U. M. Patil, J. Alloys Compd. 2019,779, 49–58,

https://doi.org/10.1016/j.jallcom.2018.11.213.

[153] Y. Gong, Z. Yang, Y. Zhi, Y. Lin, T. Zhou, J. Li, F. Jiao, W.

Wang, Dalton Trans. 2019,48, 6718–6729, https://doi.org/

10.1039/c9dt00957d.

[154] F. Yu, Y. Gao, Z. Lang, Y. Ma, L. Yin, J. Du, H. Tan, Y.

Wang, Y. J. N. Li, Nanoscale 2018,10, 6080–6087.

[155] A. Hayat, M. Sohail, U. Anwar, T. A. Taha, K. S. El-Nasser,

A. M. Alenad, A. G. Al-Sehemi, N. Ahmad Alghamdi, O. A.

Al-Hartomy, M. A. Amin, A. Alhadhrami, A. Palamanit,

S. K. B. Mane, W. I. Nawawi, Z. Ajmal, J. Colloid Interface

Sci. 2022,624, 411–422, https://doi.org/10.1016/j.jcis.2022.

05.139.

[156] F. Pan, M. Sohail, T. A. Taha, A. G. Al-Sehemi, S. Ullah,

H. S. AlSalem, G. A. M. Mersal, M. M. Ibrahim, A. M.

Alenad, O. A. Al-Hartomy, M. A. Amin, Z. Ajmal, A.

Palamanit, A. Hayat, A. Zada, W. I. Nawawi, Mater. Res. Bull.

2022,152, 111865, https://doi.org/10.1016/j.materresbull.

2022.111865.

[157] Y. Tong, H. Liu, M. Dai, L. Xiao, X. Wu, Chin. Chem. Lett.

2020,31, 2295–2299.

[158] J.-F. Qin, J.-H. Lin, T.-S. Chen, D.-P. Liu, J.-Y. Xie, B.-Y.

Guo, L. Wang, Y.-M. Chai, B. Dong, J. Energy Chem. 2019,

39, 182–187.

[159] Y. Zhou, J. Zhang, H. Ren, Y. Pan, Y. Yan, F. Sun, X. Wang,

S. Wang, J. Zhang, Appl. Catal. B 2020,268, 118467.

[160] Y. Dou, C.-T. He, L. Zhang, H. Yin, M. Al-Mamun, J. Ma,

H. Zhao, Nat. Commun. 2020,11, 1–9.

[161] S. Wang, R. Zhao, S. Yao, B. Li, R. Liu, L. Hu, A. Zhang, R.

Yang, X. Liu, Z. Fu, J. Mater. Chem. A. 2021,9, 23506–

23514.

[162] X. L. Wang, L. Z. Dong, M. Qiao, Y. J. Tang, J. Liu, Y. Li,

S. L. Li, J. X. Su, Y. Q. Lan, Angew. Chem. Int. Ed. 2018,57,

9660–9664; Angew. Chem. 2018,130, 9808–9812.

[163] M. Jiang, C. Fu, J. Yang, Q. Liu, J. Zhang, B. Sun, Energy

Storage Mater. 2019,18, 34–42, https://doi.org/10.1016/j.

ensm.2018.09.026.

[164] X. Yang, X. Qin, D. Li, J. Zhang, C. Song, Y. Liu, L. Wang,

H. Xin, J. Phys. Chem. Solids 2015,86, 74–81.

[165] P. Guha, B. Mohanty, R. Thapa, R. Kadam, P. V. Satyam,

B. K. Jena, ACS Appl. Energ. Mater. 2020,3, 5208–5218.

[166] P. Guha, B. Mohanty, R. Thapa, R. Kadam, P. V. Satyam,

B. K. Jena, ACS Appl. Energ. Mater. 2020,3, 5208–5218.

[167] R. Zhang, Y.-C. Zhang, L. Pan, G.-Q. Shen, N. Mahmood,

Y.-H. Ma, Y. Shi, W. Jia, L. Wang, X. Zhang, W. Xu, J.-J.

Zou, ACS Catal. 2018,8, 3803–3811, https://doi.org/10.

1021/acscatal.8b01046.

[168] Q. Yue, C. Liu, Y. Wan, X. Wu, X. Zhang, P. Du, J. Catal.

2018,358, 1–7.

[169] R. Shen, J. Xie, Q. Xiang, X. Chen, J. Jiang, X. Li, Chin. J.

Catal. 2019,40, 240–288, https://doi.org/10.1016/S1872-

2067(19)63294-8.

[170] J. Yu, Q. Cao, Y. Li, X. Long, S. Yang, J. K. Clark, M.

Nakabayashi, N. Shibata, J. J. Delaunay, ACS Catal. 2019,9,

1605–1611.

[171] L.-m. Fang, Y. Zeng, M. Ekholm, C.-f. Hu, Q.-g. Feng, J.

Cent. South Univ. Technol. (Engl. Ed.) 2021,28, 3728–3736.

[172] L. Wu, A. J. Van Hoof, N. Y. Dzade, L. Gao, M.-I. Richard,

H. Friedrich, N. H. De Leeuw, E. J. Hensen, J. P. Hofmann,

Phys. Chem. Chem. Phys. 2019,21, 6071–6079.

[173] S. K. Yadav, R. Ramprasad, Appl. Phys. Lett. 2012,100, 1232-

[174] H. L. Ji, W. S. Jang, W. H. Sun, K. B. Hong, Langmuir 2014,

30, 9866–9873.

[175] A. Hayat, M. Sohail, A. Qadeer, T. Taha, M. Hussain, S.

Ullah, A. G. Al-Sehemi, H. Algarni, M. A. Amin, M.

Aqeel Sarwar, Chem. Rec. 2022, e202200097.

[176] Y. Huang, L. W. Jiang, B. Y. Shi, K. M. Ryan, J. J. Wang,

Adv. Sci. 2021,8, 2101775.

[177] H. Zhang, H. Li, S. Niu, Y. Zhou, Z. Ni, Q. Wei, A. Chen, S.

Zhang, T. Sun, R. Dai, Y. Yang, G. Hu, Cell Rep. 2021,2,

100586, https://doi.org/10.1016/j.xcrp.2021.100586.

[178] I. P. Handayani, A. M. Utama, M. Rosi, A. M. Rafli, A.

Setiawan, Mater. Res. Express. 2021,8, 026405.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 58/65] 1

[179] D. Zhou, S. Wang, Y. Jia, X. Xiong, H. Yang, S. Liu, J. Tang,

J. Zhang, D. Liu, L. J. A. C. I. E. Zheng, Angew. Chem. 2019,

58, 736–740.

[180] Y. Qiu, H. Yang, B. Wen, L. Ma, Y. Lin, J. Colloid Interface

Sci. 2021,590, 561–570, https://doi.org/10.1016/j.jcis.2021.

02.003.

[181] K. A. Stoerzinger, W. S. Choi, H. Jeen, H. N. Lee, Y. Shao-

Horn, J. Phys. Chem. Lett. 2015,6, 487–492, https://doi.org/

10.1021/jz502692a.

[182] J. R. Petrie, H. Jeen, S. C. Barron, T. L. Meyer, H. N. Lee, J.

Am. Chem. Soc. 2016,138, 7252–7255.

[183] K. Artyushkova, S. Pylypenko, M. Dowlapalli, P. Atanassov, in

Book Evaluation of Structure-to-Property Relationships in Fuel

Cell Durability Performance by Multivariate Analysis, ed., ed. by

Editor, Electrochem. Soc., Inc., City, 2010, Chap., pp. 575–

575.

[184] X. Liu, L. Zhang, Y. Zheng, Z. Guo, Y. Zhu, H. Chen, F. Li,

P. Liu, B. Yu, X. Wang, Adv. Sci. 2019,6, 1801898.

[185] J. R. Petrie, H. Jeen, S. C. Barron, T. L. Meyer, H. N. Lee, J.

Am. Chem. Soc. 2016,138, 7252–7255.

[186] P. Chen, K. Xu, S. Tao, T. Zhou, Y. Tong, H. Ding, L.

Zhang, W. Chu, C. Wu, Y. Xie, Adv. Mater. 2016,28, 7527–

32, https://doi.org/10.1002/adma.201601663.

[187] Jiaojiao, Gao, Liu, Hua-Jun, Qiu, Wang, Nanotechnology

2017,28, 315401–315401.

[188] P. Chen, K. Xu, S. Tao, T. Zhou, Y. Tong, H. Ding, L.

Zhang, W. Chu, C. Wu, Y. Xie, Adv. Mater. 2016,28, 7527–

7532.

[189] C. Wang, J. Zhang, Z. Zhang, G. Ren, D. Cai, RSC Adv.

2020,10, 38906–38911.

[190] X. Wang, L. Zhuang, Y. Jia, H. Liu, X. Yan, L. Zhang, D.

Yang, Z. Zhu, X. Yao, Angew. Chem. Int. Ed. 2018,57,

16421–16425; Angew. Chem. 2018,130, 16659–16663.

[191] M. Chen, Y. Zhang, P. Duan, Y. Wang, Z. Chen, Y. Zhong,

Z. Wu, Z. Zhang, Appl. Phys. Lett. 2022,121, 023901.

[192] A. Hayat, M. Sohail, A. G. Al-Sehemi, N. A. Alghamdi, T. A.

Taha, H. S. AlSalem, A. M. Alenad, M. A. Amin, A.

Palamanit, C. Liu, S. K. Baburao Mane, W. I. Nawawi, O. A.

Al-Hartomy, Int. J. Hydrogen Energy 2022,47, 14280–14293,

https://doi.org/10.1016/j.ijhydene.2022.01.219.

[193] A. Hayat, J. A. Shah Syed, A. G. Al-Sehemi, K. S. El-Nasser,

T. A. Taha, A. A. Al-Ghamdi, M. A. Amin, Z. Ajmal, W.

Iqbal, A. Palamanit, D. I. Medina, W. I. Nawawi, M. Sohail,

Int. J. Hydrogen Energy 2022,47, 10837–10867, https://doi.

org/10.1016/j.ijhydene.2021.11.252.

[194] A. Hayat, M. Sohail, J. Ali Shah Syed, A. G. Al-Sehemi, M. H.

Mohammed, A. A. Al-Ghamdi, T. A. Taha, H. Salem AlSalem,

A. M. Alenad, M. A. Amin, A. Palamanit, C. Liu, W. I.

Nawawi, M. Tariq Saeed Chani, M. Muzibur Rahman, Chem.

Rec. 2022,22, e202100310, https://doi.org/10.1002/tcr.

202100310.

[195] A. Hayat, M. Sohail, M. S. Hamdy, T. A. Taha, H. S.

AlSalem, A. M. Alenad, M. A. Amin, R. Shah, A. Palamanit, J.

Khan, W. I. Nawawi, S. K. B. Mane, Surf. Interfaces 2022,29,

101725, https://doi.org/10.1016/j.surfin.2022.101725.

[196] A. Hayat, M. Sohail, M. S. Hamdy, S. K. B. Mane, M. A.

Amin, A. Zada, T. A. Taha, M. M. Rahman, A. Palamanit,

D. I. Medina, J. Khan, W. I. Nawawi, J. Mol. Catal. 2022,

518, 112064, https://doi.org/10.1016/j.mcat.2021.112064.

[197] T. A. Taha, M. H. Mahmoud, A. Hayat, Journal of Materials

Science: Mater. Electron. 2021,32, 27666–27675, 10.1007/

s10854-021-07147-z.

[198] M. Sohail, T. Altalhi, A. G. Al-Sehemi, T. A. M. Taha, K. S.

El-Nasser, A. A. Al-Ghamdi, M. Boukhari, A. Palamanit, A.

Hayat, M. A. Amin, Nanomaterials 2021,11, 3245.

[199] A. Hayat, T. A. M. Taha, A. M. Alenad, L. Yingjin, S. K. B.

Mane, A. Hayat, M. Khan, A. U. Rehman, W. U. Khan, N.

Shaishta, Energy Technol. 2021,9, 2100091. https://doi.org/

10.1002/ente.202100091.

[200] A. Hayat, T. A. Taha, A. M. Alenad, T. Ali, T. Bashir, A.

Ur Rehman, I. Ullah, A. Hayat, A. Irfan, W. U. Khan, Int. J.

Energy Res. 2021,45, 19921–19928, https://doi.org/10.1002/

er.7063.

[201] A. Hayat, T. A. Taha, A. M. Alenad, I. Ullah, S. J. Ali Shah, I.

Uddin, I. Ullah, A. Hayat, W. U. Khan, Surf. Interfaces 2021,

25, 101166, https://doi.org/10.1016/j.surfin.2021.101166.

[202] F. Raziq, A. Hayat, M. Humayun, S. K. Baburao Mane, M. B.

Faheem, A. Ali, Y. Zhao, S. Han, C. Cai, W. Li, D.-C. Qi, J.

Yi, X. Yu, M. B. H. Breese, F. Hassan, F. Ali, A. Mavlonov, K.

Dhanabalan, X. Xiang, X. Zu, S. Li, L. Qiao, Appl. Catal. B.

2020,270, 118867, https://doi.org/10.1016/j.apcatb.2020.

118867.

[203] M. Khan, L. Tiehu, S. B. A. Zaidi, E. Javed, A. Hussain, A.

Hayat, A. Zada, D. Alei, A. Ullah, Polym. Int. 2021,70,

1733–1740, https://doi.org/doi.org/10.1002/pi.6274.

[204] S. Ghufran, Z. Arif, Q. U. Hassan, M. Mohsin, I. Uddin, A.

Hayat, in Book Biochemical analysis of root exudates of canola

plant in response to chemical and physical abiotic stress, 2nd

iiScience International Conference 2021: Recent Advances in

Photonics and Physical Sciences, SPIE, 2021, 1187706,

pp. 34–39.

[205] I. Ullah, T. A. Taha, A. M. Alenad, I. Uddin, A. Hayat, A.

Hayat, M. Sohail, A. Irfan, J. Khan, A. Palamanit, Surf.

Interfaces 2021,25, 101227, https://doi.org/10.1016/j.surfin.

2021.101227.

[206] N. Arif, I. Uddin, A. Hayat, W. U. Khan, S. Ullah, M.

Hussain, Polym. Int. 2021,70, 1273–1281, https://doi.org/10.

1002/pi.6195.

[207] Z. Xiao, W. Zhou, B. Yang, C. Liao, Q. Kang, G. Chen, M.

Liu, X. Liu, R. Ma, N. Zhang, NMS 2022, https://doi.org/10.

1016/j.nanoms.2022.07.002.

[208] G. Tontini, M. Greaves, S. Ghosh, V. Bayram, S. Barg, J.

Phys. Materials 2020,3, 022001.

[209] A. Hayat, A. G. Al-Sehemi, K. S. El-Nasser, T. A. Taha, A. A.

Al-Ghamdi, S. Jawad Ali Shah, M. A. Amin, T. Ali, T. Bashir,

A. Palamanit, J. Khan, W. I. Nawawi, Int. J. Hydrogen Energy

2022,47, 5142–5191, https://doi.org/10.1016/j.ijhydene.

2021.11.133.

[210] A. Hayat, M. Sohail, T. A. M. Taha, A. M. Alenad, M. A.

Amin, A. Hayat, A. Irfan, A. Palamanit, Y. Al-Hadeethi,

S. K. B. Mane, J. Khan, Int. J. Energy Res. 2022,46, 1882–

1893, https://doi.org/10.1002/er.7304.

[211] A. Hayat, M. Sohail, T. A. Taha, A. M. Alenad, I. Uddin, A.

Hayat, T. Ali, R. Shah, A. Irfan, W. U. Khan, A. Palamanit, Y.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 59/65] 1

Al-Hadeethi, J. A. S. Syed, M. A. Amin, J. Khan, S. K.

Baburao Mane, Catalysts 2021,11, 935.

[212] A. Hamid, M. Khan, A. Hayat, J. Raza, A. Zada, A. Ullah, F.

Raziq, T. Li, F. Hussain, Spectrochim. Acta Part A 2020,235,

118303.

[213] A. U. Rehman, M. Khan, Z. Maosheng, A. R. Khan, A. Hayat,

Heat Mass Transfer 2021,57, 765–775, https://doi.org/10.

1007/s00231-020-02990-y.

[214] I. Uddin, G. Wang, D. Gao, Z. Hussain, M. Naz, B. Hou, A.

Hayat, Biomass Convers. Biorefin. 2021, 1–10, https://doi.org/

10.1007/s13399-021-01470-5.

[215] A. Hayat, N. Shaishta, I. Uddin, M. Khan, S. K. B. Mane, A.

Hayat, I. Ullah, A. Ur Rehman, T. Ali, G. Manjunatha, J.

Colloid Interface Sci. 2021,597, 39–47, https://doi.org/10.

1016/j.jcis.2021.03.159.

[216] M. S. Ahmed, B. Choi, Y.-B. Kim, Sci. Rep. 2018,8, 2543,

https://doi.org/10.1038/s41598-018-20974-1.

[217] V. Marangon, D. Di Lecce, F. Orsatti, D. J. Brett, P. R.

Shearing, J. Hassoun, Sustain. Energy Fuels 2020,4, 2907–

2923.

[218] S. Ye, G. Li, Frontiers of Chem. Sci. and Engineering 2018,12,

473–480, https://doi.org/10.1007/s11705-018-1724-9.

[219] Z. Sun, J. Zhang, J. Xie, M. Wang, X. Zheng, Z. Zhang, X.

Li, B. Tang, Dalton Trans. 2018,47, 12667–12670, https://

doi.org/10.1039/C8DT02097C.

[220] H. Wang, X. Xiao, S. Liu, C.-L. Chiang, X. Kuai, C.-K. Peng,

Y.-C. Lin, X. Meng, J. Zhao, J. Choi, J. Am. Chem. Soc. 2019,

141, 18578–18584.

[221] J. Hu, C. Zhang, L. Jiang, H. Lin, Y. An, D. Zhou, M. K.

Leung, S. Yang, Joule 2017,1, 383–393.

[222] J. Lu, Y. Zeng, X. Ma, H. Wang, L. Gao, H. Zhong, Q.

Meng, Polymer 2019,11, 828.

[223] H. Yue, B. Yu, F. Qi, J. Zhou, X. Wang, B. Zheng, W. Zhang,

Y. Li, Y. Chen, Electrochim. Acta 2017,253, 200–207.

[224] A. Naujokaitis, P. Gaigalas, C. Bittencourt, S. Mickevicius, A.

Jagminas, Int. J. Hydrogen Energy 2019,44, 24237–24245.

[225] Z. Niu, C. Qiu, J. Jiang, L. Ai, ACS Sustain. Chem. Eng.

2018,7, 2335–2342.

[226] Z. Niu, C. Qiu, J. Jiang, L. Ai, ACS Sustainable Chem. Eng.

2019,7, 2335–2342, https://doi.org/10.1021/acssuschemeng.

8b05089.

[227] Z. Niu, C. Qiu, J. Jiang, L. Ai, ACS Sustainable Chem. Eng.

2018,7, 2335–2342.

[228] S. Shit, S. Chhetri, W. Jang, N. C. Murmu, H. Koo, P.

Samanta, T. Kuila, ACS Appl. Mater. Interfaces 2018,10,

27712–27722, https://doi.org/10.1021/acsami.8b04223.

[229] S. Shit, S. Chhetri, S. Bolar, N. C. Murmu, W. Jang, H. Koo,

T. Kuila, ChemElectroChem 2019,6, 430–438, https://doi.org/

10.1002/celc.201801343.

[230] I. Vincent, D. Bessarabov, Renewable Sustainable Energy Rev.

2018,81, 1690–1704.

[231] C. Panda, P. W. Menezes, M. Zheng, S. Orthmann, M.

Driess, ACS Energy Lett. 2019,4, 747–754.

[232] M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen

Energy 2013,38, 4901–4934.

[233] S. Marini, P. Salvi, P. Nelli, R. Pesenti, M. Villa, M.

Berrettoni, G. Zangari, Y. Kiros, Electrochim. Acta 2012,82,

384–391.

[234] S. Barwe, B. Mei, J. Masa, W. Schuhmann, E. Ventosa, Nano

Energy 2018,53, 763–768.

[235] R. Phillips, A. Edwards, B. Rome, D. R. Jones, C. W. Dunnill,

Int. J. Hydrogen Energy 2017,42, 23986–23994.

[236] A. Gabler, C. I. Müller, T. Rauscher, T. Gimpel, R. Hahn, M.

Köhring, B. Kieback, L. Röntzsch, W. Schade, Int. J. Hydrogen

Energy 2018,43, 7216–72, https://doi.org/10.1016/j.ijhydene.

2018.02.130.

[237] J. Zhang, C. Zhang, J. Sha, H. Fei, Y. Li, J. M. Tour, ACS

Appl. Mater. Interfaces 2017,9, 26840–26847.

[238] S. M. H. Hashemi, P. Karnakov, P. Hadikhani, E. Chinello, S.

Litvinov, C. Moser, P. Koumoutsakos, D. Psaltis, Energy

Environ. Sci. 2019,12, 1592–1604.

[239] M. I. Gillespie, R. J. Kriek, J. Power Sources 2017,372, 252–

259.

[240] A. Mig, B. Rjk, J. Power Sources 2018,397, 204–213.

[241] H. Dotan, A. Landman, S. W. Sheehan, K. D. Malviya, G. S.

Grader, Nat. Energy 2019,4, 786–795.

[242] Y. Niu, X. Liu, Y. Wang, S. Zhou, Z. Lv, L. Zhang, W. Shi,

Y. Li, W. Zhang, B. Zhang, Angew. Chem. Int. Ed. 2019,58,

4232.

[243] T. W. Grubb, J. Phys. Chem. 1959,63, 55–67.

[244] M. Zhu, Q. Shao, Y. Qian, X. Huang, Nano Energy 2019,56,

330–337.

[245] W. Xu, K. Scott, Int. J. Hydrogen Energy 2010,35, 12029–

12037.

[246] M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen

Energy 2013,38, 4901–4934.

[247] P. Millet, R. Ngameni, S. A. Grigoriev, V. N. Fateev, Int. J.

Hydrogen Energy 2011,36, 4156–41633.

[248] J. E. Bennett, Int. J. Hydrogen Energy 1980,5, 401–408.

[249] R. K. Karlsson, A. Cornell, Chem. Rev. 2016,116, 2982–

3028.

[250] Y. Kuang, M. J. Kenney, Y. Meng, W. H. Hung, Y. Liu, J. E.

Huang, R. Prasanna, P. Li, Y. Li, L. Wang, Proc. Nat. Acad.

Sci. 2019,116, 201900556.

[251] S. Trasatti, Electrochim. Acta 1984,29, 1503–1512.

[252] F. Dionigi, T. Reier, Z. Pawolek, M. Gliech, P. Strasser,

ChemSusChem 2016,9, 962–972.

[253] X. Li, L. Zhao, J. Yu, X. Liu, X. Zhang, H. Liu, W. Zhou,

Micro Nano Lett. 2020,12, 1–29.

[254] J. Li, J. Xu, R. Li, Z. Yue, X. Wang, X. Liu, H. Jiao, Appl.

Catal. B. 2018,240, S0926337318308099-.

[255] J. K. Stolarczyk, S. Bhattacharyya, L. Polavarapu, J. Feldmann,

ACS Catal. 2018,8, 3602–3635.

[256] N. S. Lewis, D. G. Nocera, Proc. Nat. Acad. Sci. 2006,103,

15729–15735.

[257] M. Chen, Y. Liu, C. Li, A. Li, X. Chang, W. Liu, Y. Sun, T.

Wang, J. Gong, Energy Environ. Sci. 2018,11, 2025–2034.

[258] Gurudayal, D. Sabba, M. H. Kumar, L. H. Wong, J. Barber,

M. Gr?Tzel, N. Mathews, Nano Lett. 2015,15, 3833–3839.

[259] D. Sabba, M. H. Kumar, L. H. Wong, J. Barber, M. Grätzel,

N. Mathews, Nano Lett. 2015,15, 3833–3839.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 60/65] 1

[260] J. Luo, Z. Li, S. Nishiwaki, M. Schreier, M. T. Mayer, P.

Cendula, Y. H. Lee, K. Fu, A. Cao, M. K. Nazeeruddin, Adv.

Energy Mater. 2015,5, 1501520.

[261] Y. Qiu, W. Liu, W. Chen, W. Chen, G. Zhou, P.-C. Hsu, R.

Zhang, Z. Liang, S. Fan, Y. Zhang, Sci. Adv. 2016,2,

e1501764.

[262] K. P. Sokol, W. E. Robinson, J. Warnan, N. Kornienko,

M. M. Nowaczyk, A. Ruff, J. Z. Zhang, E. Reisner, Nat.

Energy 2018,3, 944–951.

[263] J. Brillet, J. H. Yum, M. Cornuz, T. Hisatomi, R. Solarska, J.

Augustynski, M. Graetzel, K. Sivula, Nat. Photonics 2012,6,

824.

[264] X. Shi, K. Zhang, K. Shin, M. Ma, J. Kwon, I. T. Choi, J. K.

Kim, H. K. Kim, D. H. Wang, J. H. Park, Nano Energy 2015,

13, 182–191.

[265] V. González-Pedro, I. Zarazua, E. M. Barea, F. Fabregat-

Santiago, E. de la Rosa, I. n. Mora-Seró, S. Giménez, J. Phys.

Chem. C 2014,118, 891–895.

[266] J. H. Kim, Y. Jo, J. H. Kim, J. W. Jang, H. J. Kang, Y. H. Lee,

D. S. Kim, Y. Jun, J. S. Lee, ACS Nano 2015,9, 11820–

11829.

[267] V. González-Pedro, I. Zarazua, E. M. Barea, F. Fabregat-

Santiago, E. de la Rosa, I. n. Mora-Seró, S. Giménez, J. Phys.

Chem. C 2014,118, 891–895.

[268] J. Yuan, Y. Zhang, L. Zhou, G. Zhang, H.-L. Yip, T.-K. Lau,

X. Lu, C. Zhu, H. Peng, P. A. Johnson, Joule 2019,3, 1140–

1151.

[269] J. Wei, M. Zhou, A. Long, Y. Xue, H. Liao, C. Wei, Z. J. Xu,

Nano-Micro Lett. 2018,10, 1–15.

[270] Y. Xin, X. Kan, L.-Y. Gan, Z. Zhang, ACS Nano 2017,11,

10303–10312.

[271] X. Zhou, J. Zhou, G. Huang, R. Fan, S. Ju, Z. Mi, M. Shen,

J. Mater. Chem. A 2018,6, 20297–20303.

[272] H. Song, S. Oh, H. Yoon, K.-H. Kim, S. Ryu, J. Oh, Nano

Energy 2017,42, 1–7.

[273] Y. Jang, J. Park, J. Kang, S.-Y. Lee, ACS Appl. Electron. Mater.

2022,4, 1427–1448.

[274] T. J. Jacobsson, V. Fjällström, M. Sahlberg, M. Edoff, T.

Edvinsson, Energy Environ. Sci. 2013,6, 3676–3683.

[275] T. J. Jacobsson, C. Platzer-Björkman, M. Edoff, T. Edvinsson,

Int. J. Hydrogen Energy 2013,38, 15027–15035.

[276] C. Wang, Z. Song, C. Li, D. Zhao, Y. Yan, Adv. Funct. Mater.

2019,29, 1808801.

[277] L. Ma, W. Zhang, P. Zhao, J. Liang, Y. Hu, G. Zhu, R. Chen,

Z. Tie, J. Liu, Z. Jin, J. Mater. Chem. A 2018,6, 20076–

20082.

[278] J. Luo, J. H. Im, M. T. Mayer, M. Schreier, M. K. Nazeer-

uddin, N. G. Park, S. D. Tilley, H. J. Fan, M. Graetzel, Science

2014,345, 1593–1596.

[279] A. Kumar, D. K. Chaudhary, S. Parvin, S. Bhattacharyya, J.

Mater. Chem. A 2018,6, 18948–18959.

[280] Y. Liu, N. Sun, J. Liu, Z. Wen, X. Sun, S.-T. Lee, B. Sun,

ACS Nano 2018,12, 2893–2899.

[281] L. Xu, Y. Xiong, A. Mei, Y. Hu, Y. Rong, Y. Zhou, B. Hu, H.

Han, Adv. Energy Mater. 2018,8, 1702937.

[282] D. Zhang, Y. Wang, Y. Yang, Small 2019,15, 1805241.

[283] A. Majumdar, Science 2004,303, 777–778.

[284] L. Yang, Z. G. Chen, M. S. Dargusch, J. Zou, Adv. Energy

Mater. 2018,8, 1701797.

[285] S. Sun, W. Wang, D. Jiang, L. Zhang, J. Zhou, Appl. Catal. B

.2014,s158–159, 136–139.

[286] V. Georgakilas, J. N. Tiwari, K. C. Kemp, J. A. Perman, A. B.

Bourlinos, K. S. Kim, R. Zboril, Chem. Rev. 2016,116, 5464–

5519.

[287] X. Huang, W. Zhang, G. Guan, G. Song, R. Zou, J. Hu, Acc.

Chem. Res. 2017,50, 2529–2538.

[288] X. Zhang, W. Gao, X. Su, F. Wang, B. Liu, J.-J. Wang, H.

Liu, Y. Sang, Nano Energy 2018,48, 481–488.

[289] L. Zhao, Z. Yang, Q. Cao, L. Yang, X. Zhang, J. Jia, Y. Sang,

H.-J. Wu, W. Zhou, H. Liu, Nano Energy 2019,56, 563–570.

[290] L. Huang, G. Cai, R. Zeng, Z. Yu, D. Tang, Anal. Chem.

2022,94, 9487–9495.

[291] V. Andrei, K. Bethke, K. Rademann, Energy Environ. Sci.

2016,9, 1528–1532.

[292] J.-Y. Jung, D. W. Kim, T. J. Park, J.-H. Lee, ACS Appl. Energ.

Mater. 2019,3, 1046–1053.

[293] N. Getoff, Int. J. Hydrogen Energy 1984,9, 997–1004.

[294] S. M. Shin, J. Y. Jung, M. J. Park, J. W. Song, J. H. Lee, J.

Power Sources 2015,279, 151–156.

[295] M.-J. Park, J.-Y. Jung, S.-M. Shin, J.-W. Song, Y.-H. Nam,

D.-H. Kim, J.-H. Lee, Thin Solid Films 2016,599, 54–58.

[296] S.-M. Shin, J.-Y. Jung, M.-J. Park, J.-W. Song, J.-H. Lee, J.

Power Sources 2015,279, 151–156.

[297] Y. Zhou, X. Yin, Q. Zhang, N. Wang, A. Yamamoto, K.

Koumoto, H. Shen, H. Lin, Mater. Today Energy 2019,12,

363–370.

[298] Y. Yang, H. Zhang, Z.-H. Lin, Y. Liu, J. Chen, Z. Lin, Y. S.

Zhou, C. P. Wong, Z. L. Wang, Energy Environ. Sci. 2013,6,

2429–2434.

[299] Z.-S. Wu, G. Zhou, L.-C. Yin, W. Ren, F. Li, H.-M. Cheng,

Nano Energy 2012,1, 107–131.

[300] H. Xue, J. Wang, S. Wang, S. Muhammad, C. Feng, Q. Wu,

H. Li, D. Shi, Q. Jiao, Y. Zhao, New J. Chem. 2018,42,

15340–15345.

[301] A. N. Simões, D. J. Carvalho, E. d. S. Morita, H. L. Moretti,

H. V. Vendrameto, L. Fu, F. Torres, A. N. d. Souza, W. A.

Bizzo, T. Mazon, Machines 2022,10, 215.

[302] A. Wei, X. Xie, W. Zhen, H. Zheng, H. Lan, H. Shao, X.

Sun, J. Zhong, L. Shuit-Tong, ACS Nano 2018,12, 8625–

8632.

[303] W. Tang, Y. Han, C. B. Han, C. Z. Gao, X. Cao, Z. L. Wang,

Adv. Mater. 2015,27, 272–276.

[304] T. Li, Y. Xu, F. Xing, X. Cao, J. Bian, N. Wang, Z. L. Wang,

Adv. Energy Mater. 2017,7, 1700124.

[305] T. Y. Feng, L. Zhang, Y. Zheng, D. Wang, F. Zhou, W. Liu,

Nano Energy 2019,55, 260–26.

[306] B. Hla, B. Mha, C. Qj, W. Y. D, B. Swa, L. B. Ying, A. Yz,

L. E. Jing, L. A. Ning, B. Ym, Nano Energy 2019,56, 269–

276.

[307] X. Ren, H. Fan, C. Wang, J. Ma, H. Li, M. Zhang, S. Lei, W.

Wang, Nano Energy 2018,50, 562–570.

[308] Mengying, Xie, Steve, Dunn, Emmanuel, Le, Boulbar,

Chris, R. Bowen, Int. J. Hydrogen Energy 2017,42, 23437–

23445.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 61/65] 1

[309] Y. Zhang, S. Kumar, F. Marken, M. Krasny, E. Roake, S.

Eslava, S. Dunn, E. Da Como, C. R. Bowen, Nano Energy

2019,58, 183–191.

[310] T. Ding, L. Zhu, X. Q. Wang, K. H. Chan, X. Lu, Y. Cheng,

G. W. Ho, Adv. Energy Mater. 2018,8, 1802397.1-

1802397.8.

[311] L. Kuai, S. Liu, S. Cao, Y. Ren, E. Kan, Y. Zhao, N. Yu, F. Li,

X. Li, Z. Wu, Chem. Mater. 2018,30, 5534–5538.

[312] D. B. Pal, R. Chand, S. N. Upadhyay, P. Mishra, Renewable

Sustainable Energy Rev. 2018,93, 549–565.

[313] A. Hayat, M. Sohail, T. Taha, A. M. Alenad, A. Irfan, N.

Shaishta, A. Hayat, S. K. B. Mane, W. U. Khan, CrystEng-

Comm 2021,23, 4963–4974.

[314] X. Cui, H.-Y. Su, R. Chen, L. Yu, J. Dong, C. Ma, S. Wang,

J. Li, F. Yang, J. Xiao, Nat. Commun. 2019,10, 1–8.

[315] Y. Naciri, A. Hsini, Z. Ajmal, J. A. Navío, B. Bakiz, A.

Albourine, M. Ezahri, A. Benlhachemi, Adv. Colloid Interface

Sci. 2020,280, 102160, doi.org/10.1016/j.cis.2020.102160.

[316] Y. Naciri, A. Hsini, A. Bouziani, R. Djellabi, Z. Ajmal, M.

Laabd, J. Navío, A. Mills, C. Bianchi, H. Li, Crit. Rev.

Environ. Sci. Technol. 2022,52, 2339–2382.

[317] J. Wang, W. Cui, Q. Liu, Z. Xing, A. M. Asiri, X. Sun, Adv.

Mater. 2016,28, 215–230.

[318] S. Cobo, J. Heidkamp, P.-A. Jacques, J. Fize, V. Fourmond, L.

Guetaz, B. Jousselme, V. Ivanova, H. Dau, S. Palacin, Nat.

Mater. 2012,11, 802–807.

[319] P. Tran, A. Morozan, S. Archambault, J. Heidkamp, P.

Chenevier, H. Dau, M. Fontecave, A. Martinent, B. Jousselme,

V. Artero, Chem. Sci. 2015,6, 2050–2053.

[320] S. Cobo, J. Heidkamp, P.-A. Jacques, J. Fize, V. Fourmond, L.

Guetaz, B. Jousselme, V. Ivanova, H. Dau, S. Palacin, Nat.

Mater. 2012,11, 802–807.

[321] Y. Yang, H. Fei, G. Ruan, J. M. Tour, Adv. Mater. 2015,27,

3175–3180.

[322] R. Bernasconi, M. I. Khalil, D. S. Cakmakci, Y. Bektas, L.

Nobili, L. Magagnin, C. Lenardi, J. Mater. Sci. 2022,57, 1–

19.

[323] Y. Wang, N. Ma, M. Fan, W. Tang, J. Electrochem. Soc. 2021,

168, 114504.

[324] B. You, N. Jiang, M. Sheng, S. Gul, J. Yano, Y. Sun, Chem.

Mater. 2015,27, 7636–7642.

[325] J. Song, C. Zhu, B. Z. Xu, S. Fu, M. H. Engelhard, R. Ye, D.

Du, S. P. Beckman, Y. Lin, Adv. Energy Mater. 2017,7,

1601555.

[326] Q. Niu, J. Guo, Y. Tang, X. Guo, J. Nie, G. Ma, Electrochim.

Acta 2017,255, 72–82, https://doi.org/10.1016/j.electacta.

2017.09.125.

[327] K. Lan, J. Li, Y. Zhu, L. Gong, F. Li, P. Jiang, F. Niu, R. Li,

J. Colloid Interface Sci. 2019,539, 646–653, https://doi.org/

10.1016/j.jcis.2018.12.044.

[328] I. H. Kwak, H. S. Im, D. M. Jang, Y. W. Kim, K. Park, Y. R.

Lim, E. H. Cha, J. Park, ACS Appl. Mater. Interfaces 2016,8,

5327–34, https://doi.org/10.1021/acsami.5b12093.

[329] H. Yang, M. R. Lohe, Z. Jian, S. Liu, X. Feng, Energy Environ.

Sci. 2015,9, 478–483.

[330] Z. Wu, Z. Zou, J. Huang, F. Gao, ACS Appl. Mater. Interfaces

2018,10, 26283–26292.

[331] J. Masa, P. Weide, D. Peeters, I. Sinev, W. Xia, Z. Sun, Adv.

Energy Mater. 2016,6, 1502313.

[332] X. Li, Z. Niu, J. Jiang, L. Ai, J. Mater. Chem. 2016,4, 3204–

3209.

[333] Z. Ajmal, A. Muhmood, R. Dong, S. Wu, J. Environ. Manage.

2020,253, 109730, https://doi.org/10.1016/j.jenvman.2019.

109730.

[334] Y. Naciri, A. Hsini, A. Ahdour, B. Akhsassi, k. Fritah, Z.

Ajmal, R. Djellabi, A. Bouziani, A. Taoufyq, B. Bakiz, A.

Benlhachemi, M. Sillanpää, H. Li, Chemosphere 2022,300,

134622, https://doi.org/10.1016/j.chemosphere.2022.134622.

[335] Y. Naciri, A. Hsini, Z. Ajmal, A. Bouddouch, B. Bakiz, J. A.

Navío, A. Albourine, J. C. Valmalette, M. Ezahri, A.

Benlhachemi, J. Colloid Interface Sci. 2020,572, 269–280,

https://doi.org/10.1016/j.jcis.2020.03.105.

[336] H. Ullah, M. Sohail, U. Malik, N. Ali, M. A. Bangash, M.

Nawaz, Mater. Res. Express. 2016,3, 075016.

[337] S. Rauf, H. I. A. Qazi, J. Luo, C. Fu, R. Tao, M. Sohail, L.

Yang, H. Li, IEEE Sens. J. 2021,22, 3122–3128.

[338] H. Jin, J. Wang, D. Su, Z. Wei, Z. Pang, Y. Wang, J. Am.

Chem. Soc. 2015,137, 2688–2694.

[339] J. Yin, P. Zhou, L. An, L. Huang, C. Shao, J. Wang, H. Liu,

P. Xi, Nanoscale 2016,8, 1390–1400.

[340] Y. Li, P. Hasin, Y. Wu, Adv. Mater. 2010,22, 1926–1929.

[341] X. Gao, H. Zhang, Q. Li, X. Yu, Z. Hong, X. Zhang, C.

Liang, Z. Lin, Angew. Chem. Int. Ed. 2016,55, 6290–6294;

Angew. Chem. 2016,128, 6398–6402.

[342] J. Li, Y. Wang, T. Zhou, H. Zhang, X. Sun, J. Tang, L.

Zhang, A. M. Al-Enizi, Z. Yang, G. Zheng, J. Am. Chem. Soc.

2015,137, 14305–12, https://doi.org/10.1021/jacs.5b07756.

[343] A. Sivanantham, P. Ganesan, S. Shanmugam, Adv. Funct.

Mater. 2016,26, 4660–4660.

[344] Z. Peng, D. Jia, A. M. Al-Enizi, A. A. Elzatahry, G. Zheng,

Adv. Energy Mater. 2015,5, 1402031.

[345] S. Li, Y. Wang, S. Peng, L. Zhang, A. M. Al-Enizi, H. Zhang,

X. Sun, G. Zheng, Adv. Energy Mater. 2016,6, 1501661.

[346] Liu, Lifeng, Xiong, Dehua, Wang, Xiaoguang, Wei, J.

Mater. Chem. 2016,4, 5639–5646.

[347] C. Dong, X. Liu, X. Wang, X. Yuan, Z. Xu, W. Dong, M. S.

Riaz, G. Li, F. Huang, J. Mater. Chem. A 2017,5, 24767–

24774.

[348] J. Luo, J.-H. Im, M. T. Mayer, M. Schreier, M. K. Nazeer-

uddin, N.-G. Park, S. D. Tilley, H. J. Fan, M. Grätzel, Science

2014,345, 1593–1596.

[349] L. A. Stern, L. Feng, S. Fang, X. Hu, Energy Environ. Sci.

2015,8, 2347–2351.

[350] X.-Y. Yu, Y. Feng, B. Guan, X. W. D. Lou, U. Paik, Energy

Environ. Sci. 2016,9, 1246–1250.

[351] X. Lu, C. Zhao, Nat. Commun. 2015,6, 1–7.

[352] G.-F. Chen, T. Y. Ma, Z.-Q. Liu, N. Li, Y.-Z. Su, K. Davey,

S.-Z. Qiao, Adv. Funct. Mater. 2016,26, 3314–3323, https://

doi.org/10.1002/adfm.201505626.

[353] M. Ledendecker, S. Krick Calderón, C. Papp, H. P. Steinrück,

M. Antonietti, M. Shalom, Angew. Chem. Int. Ed. Engl. 2015,

54, 12361–12365, https://doi.org/10.1002/anie.201502438.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 62/65] 1

[354] M. Ledendecker, G. Clavel, M. Antonietti, M. Shalom, Adv.

Funct. Mater. 2015,25, 393–399, https://doi.org/10.1002/

adfm.201402078.

[355] H. Vandenborre, P. Vermeiren, R. Leysen, Electrochim. Acta

1984,29, 297–301.

[356] X. Xu, F. Song, X. Hu, Nat. Commun. 2016,7, 1–7.

[357] L.-L. Feng, G. Yu, Y. Wu, G.-D. Li, H. Li, Y. Sun, T. Asefa,

W. Chen, X. Zou, J. Am. Chem. Soc. 2015,137, 14023–

14026.

[358] C. Tang, N. Cheng, Z. Pu, W. Xing, X. Sun, Angew. Chem.

2015,127, 9483–9487; Angew. Chem. Int. Ed. 2015,54,

9351–9355.

[359] J. Zhang, T. Wang, D. Pohl, B. Rellinghaus, R. Dong, S. Liu,

X. Zhuang, X. Feng, Angew. Chem. 2016,128, 6814–6819;

Angew. Chem. Int. Ed. 2016,55, 6702–6707.

[360] Xiaodan, Jia, Yufei, Zhao, Guangbo, Chen, Lu, Shang,

Run, Shi, Adv. Energy Mater. 2016,6, https://doi.org/doi.org/

10.1002/aenm.201670063.

[361] Q. Zhang, Y. Wang, Y. Wang, A. M. Al-Enizi, A. A. Elzatahry,

G. Zheng, J. Mater. Chem. 2016,4, 5713–5718.

[362] R. Xiang, Y. Duan, C. Tong, L. Peng, J. Wang, S. S. A. Shah,

T. Najam, X. Huang, Z. Wei, Electrochim. Acta 2019,302,

45–55.

[363] B. C. Martindale, E. Reisner, Adv. Energy Mater. 2016,6,

1502095.

[364] C. G. Read, J. F. Callejas, C. F. Holder Raymond, ACS Appl.

Mater. Interfaces 2016,8, 12798–12803.

[365] H. Wang, H. W. Lee, Y. Deng, Z. Lu, P. C. Hsu, Y. Liu, D.

Lin, Y. Cui, Nat. Commun. 2015,6, 7261.

[366] Y. Jin, H. Wang, J. Li, X. Yue, Y. Han, P. K. Shen, Y. Cui,

Adv. Mater. 2016,28, 3785–3790, https://doi.org/10.1002/

adma.201506314.

[367] S.-K. Lee, S. D. George, W. E. Antholine, B. Hedman, K. O.

Hodgson, E. I. Solomon, J. Am. Chem. Soc. 2002,124, 6180–

6193, https://doi.org/10.1021/ja0114052.

[368] M. Jahan, Z. Liu, K. P. Loh, Adv. Funct. Mater. 2013,23,

5363–5372, doi.org/10.1002/adfm.201300510.

[369] J. Zhang, L. Qu, G. Shi, J. Liu, J. Chen, L. Dai, Angew. Chem.

2016,128, 2270–2274; Angew. Chem. Int. Ed. 2016,55,

2230–2234.

[370] Y. Pan, Y. Liu, Y. Lin, C. Liu, ACS Appl. Mater. Interfaces

2016,8, 13890–13901.

[371] J. Lai, S. Li, F. Wu, M. Saqib, R. Luque, G. Xu, Energy

Environ. Sci. 2016,9, 1210–1214.

[372] J. Lao, D. Li, C. Jiang, C. Luo, R. Qi, H. Lin, R. Huang,

G. I. N. Waterhouse, H. Peng, Nanoscale 2020,12, 10158–

10165, https://doi.org/10.1039/C9NR10230B.

[373] Z. Chen, X. Duan, W. Wei, S. Wang, Z. Zhang, B.-J. Ni,

Nano Res. 2020,13, 293–314, https://doi.org/10.1007/

s12274-020-2618-y.

[374] Y. Liang, X. Sun, A. M. Asiri, Y. He, Nanotechnology 2016,

27, 12lt01, https://doi.org/10.1088/0957-4484/27/12/12lt01.

[375] V. Eßmann, S. Barwe, J. Masa, W. Schuhmann, Anal. Chem.

2016,88, 8835–40, 10.1021/acs.analchem.6b02393.

[376] N. Xu, G. Cao, Z. Chen, Q. Kang, H. Dai, P. Wang, J. Mater.

Chem. A 2017,5, 12379–12384, https://doi.org/10.1039/

C7TA02644G.

[377] Y. Zhang, Q. Shao, S. Long, X. Huang, Nano Energy 2018,

45, 448–455, https://doi.org/10.1016/j.nanoen.2018.01.022.

[378] H. Li, P. Wen, Q. Li, C. Dun, J. Xing, C. Lu, S. Adhikari, L.

Jiang, D. L. Carroll, S. M. Geyer, Adv. Energy Mater. 2017,7,

1700513, https://doi.org/10.1002/aenm.201700513.

[379] W. Hong, S. Sun, Y. Kong, Y. Hu, G. Chen, J. Mater. Chem.

A2020,8, 7360–7367, https://doi.org/10.1039/

C9TA14058A.

[380] X. Chen, Z. Yu, L. Wei, Z. Zhou, S. Zhai, J. Chen, Y. Wang,

Q. Huang, H. E. Karahan, X. Liao, Y. Chen, J. Mater. Chem.

2019,7, 764–774, https://doi.org/10.1039/C8TA09130G.

[381] P. Chen, K. Xu, Y. Tong, X. Li, S. Tao, Z. Fang, W. Chu, X.

Wu, C. Wu, Inorg. Chem. Front. 2016,3, 236–242, https://

doi.org/10.1039/C5QI00197H.

[382] Z. Chen, Y. Ha, Y. Liu, H. Wang, H. Yang, H. Xu, Y. Li, R.

Wu, ACS Appl. Mater. Interfaces 2018,10, 7134–7144,

https://doi.org/10.1021/acsami.7b18858.

[383] L. Yu, S. Song, B. McElhenny, F. Ding, D. Luo, Y. Yu, S.

Chen, Z. Ren, J. Mater. Chem. A 2019,7, 19728–19732,

https://doi.org/10.1039/C9TA05455 C.

[384] X. Jia, Y. Zhao, G. Chen, L. Shang, R. Shi, X. Kang, G. I. N.

Waterhouse, L.-Z. Wu, C.-H. Tung, T. Zhang, Adv. Energy

Mater. 2016,6, 1502585, doi.org/10.1002/aenm.201502585.

[385] Y. Gu, S. Chen, J. Ren, Y. A. Jia, C. Chen, S. Komarneni, D.

Yang, X. Yao, ACS Nano 2018,12, 245–253, https://doi.org/

10.1021/acsnano.7b05971.

[386] S. Dutta, A. Indra, Y. Feng, H. Han, T. Song, Appl. Catal. B.

2019,241, 521–527, https://doi.org/doi.org/10.1016/j.apcatb.

2018.09.061.

[387] Z. Kou, T. Wang, Q. Gu, M. Xiong, L. Zheng, X. Li, Z. Pan,

H. Chen, F. Verpoort, A. K. Cheetham, S. Mu, J. Wang, Adv.

Energy Mater. 2019,9, 1803768, https://doi.org/10.1002/

aenm.201803768.

[388] Y. Hui, C. Yingxi, W. Chunbao, W. Guangjin, J. Alloys

Compd. 2020,842, 155939, https://doi.org/10.1016/j.jallcom.

2020.155939.

[389] Z.-Y. Yu, Y. Duan, M.-R. Gao, C.-C. Lang, Y.-R. Zheng, S.-

H. Yu, Chem. Sci. 2017,8, 968–973, https://doi.org/10.1039/

C6SC03356 C.

[390] T. Ouyang, Y.-Q. Ye, C.-Y. Wu, K. Xiao, Z.-Q. Liu, Angew.

Chem. Int. Ed. 2019,58, 4923–4928, doi.org/10.1002/

anie.201814262.

[391] L. Qiao, A. Zhu, W. Zeng, R. Dong, P. Tan, Z. Ding, P.

Gao, S. Wang, J. Pan, J. Mater. Chem. A 2020,8, 2453–2462,

https://doi.org/10.1039/C9TA10682K.

[392] S. Zhang, G. Gao, J. Hao, M. Wang, H. Zhu, ACS Appl.

Mater. Interfaces 2019,11, 43261–43269, https://doi.org/10.

1021/acsami.9b16390.

[393] H. Fan, H. Yu, Y. Zhang, Y. Zheng, Y. Luo, Z. Dai, B. Li, Y.

Zong, Q. Yan, Angew. Chem. Int. Ed. 2017,56, 12566–

12570, https://doi.org/10.1002/anie.201706610.

[394] Y. Wang, W. Wu, Y. Rao, Z. Li, N. Tsubaki, M. Wu, J.

Mater. Chem. 2017,5, 6170–6177, https://doi.org/10.1039/

C7TA00692F.

[395] C. N. R. Rao, M. Chhetri, Adv. Mater. 2019,31, 1803668,

https://doi.org/10.1002/adma.201803668.

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 63/65] 1

[396] H. Wang, S. Min, C. Ma, Z. Liu, W. Zhang, Q. Wang, D. Li,

Y. Li, S. Turner, Y. Han, Nat. Commun. 2017,8, 1–9.

[397] F. Davodi, M. Tavakkoli, J. Lahtinen, T. Kallio, J. Catal.

2017,353, 19–27, https://doi.org/10.1016/j.jcat.2017.07.001.

[398] X. Yue, S. Huang, J. Cai, Y. Jin, P. K. Shen, J. Mater. Chem. A

2017,5, 7784–7790, https://doi.org/10.1039/C7TA01957B.

[399] K. Qu, Y. Zheng, Y. Jiao, X. Zhang, S. Dai, S.-Z. Qiao, Adv.

Energy Mater. 2017,7, 1602068, https://doi.org/10.1002/

aenm.201602068.

[400] S. Huang, Y. Meng, Y. Cao, S. He, X. Li, S. Tong, M. Wu,

Appl. Catal. B. 2019,248, 239–248, https://doi.org/10.1016/

j.apcatb.2019.01.080.

[401] R. Gao, Q. Dai, F. Du, D. Yan, L. Dai, J. Am. Chem. Soc.

2019,141, 11658–11666.

[402] L. Jiao, Y.-X. Zhou, H.-L. Jiang, Chem. Sci. 2016,7, 1690–

1695, https://doi.org/10.1039/C5SC04425A.

[403] L. Li, P. Wang, Q. Shao, X. Huang, Chem. Soc. Rev. 2020,49,

3072–3106, https://doi.org/10.1039/D0CS00013B.

[404] Y. Huang, Q. Liu, J. Lv, D. D. Babu, W. Wang, M. Wu, D.

Yuan, Y. Wang, J. Mater. Chem. A 2017,5, 20882–20891,

https://doi.org/10.1039/C7TA06677E.

[405] J. Ren, M. Antonietti, T.-P. Fellinger, Adv. Energy Mater.

2015,5, 1401660, https://doi.org/10.1002/aenm.201401660.

[406] Y. Xu, W. Tu, B. Zhang, S. Yin, Y. Huang, M. Kraft, R. Xu,

Adv. Mater. 2017,29, 1605957, https://doi.org/10.1002/

adma.201605957.

[407] Z. Chen, H. Xu, Y. Ha, X. Li, M. Liu, R. Wu, Appl. Catal. B.

2019,250, 213–223, doi.org/10.1016/j.apcatb.2019.03.032.

[408] I. A. Raj, K. I. Vasu, J. Appl. Electrochem. 1990,20, 32–38,

https://doi.org/10.1007/BF01012468.

[409] T. Zhang, X. Liu, X. Cui, M. Chen, S. Liu, B. Geng, Adv.

Mater. Interfaces 2018,5, 1800359, https://doi.org/10.1002/

admi.201800359.

[410] M. Y. Gao, C. Yang, Q. B. Zhang, J. R. Zeng, X. T. Li, Y. X.

Hua, C. Y. Xu, P. Dong, J. Mater. Chem. A 2017,5, 5797–

5805, https://doi.org/10.1039/C6TA10812 A.

[411] J. Tian, N. Cheng, Q. Liu, X. Sun, Y. He, A. M. Asiri, J.

Mater. Chem. A 2015,3, 20056–20059, https://doi.org/10.

1039/C5TA04723D.

[412] M. Fang, W. Gao, G. Dong, Z. Xia, S. Yip, Y. Qin, Y. Qu,

J. C. Ho, Nano Energy 2016,27, 247–254, https://doi.org/10.

1016/j.nanoen.2016.07.005.

[413] X. Zhang, H. Xu, X. Li, Y. Li, T. Yang, Y. Liang, ACS Catal.

2016,6, 580–588, https://doi.org/10.1021/acscatal.5b02291.

[414] J. Zhang, T. Wang, P. Liu, Z. Liao, S. Liu, X. Zhuang, M.

Chen, E. Zschech, X. Feng, Nat. Commun. 2017,8, 15437,

https://doi.org/10.1038/ncomms15437.

[415] J. Zhang, G. Wang, Z. Liao, P. Zhang, F. Wang, X. Zhuang,

E. Zschech, X. Feng, Nano Energy 2017,40, 27–33, https://

doi.org/10.1016/j.nanoen.2017.07.054.

[416] Y. Pi, Q. Shao, P. Wang, J. Guo, X. Huang, Adv. Funct.

Mater. 2017,27, 1700886, https://doi.org/10.1002/adfm.

201700886.

[417] X. Gao, Y. Yu, Q. Liang, Y. Pang, L. Miao, X. Liu, Z. Kou, J.

He, S. J. Pennycook, S. Mu, J. Wang, Appl. Catal. B. 2020,

270, 118889, https://doi.org/10.1016/j.apcatb.2020.118889.

[418] Y. Yang, Z. Lin, S. Gao, J. Su, Z. Lun, G. Xia, J. Chen, R.

Zhang, Q. Chen, ACS Catal. 2017,7, 469–479, https://doi.

org/10.1021/acscatal.6b02573.

[419] Kailong, Mingxing, Hinokuma, Satoshi, Ohto, Tatsuhiko,

Wakisaka, Mitsuru, Fujita, Jun-ichi.

[420] R. Zhang, J. Huang, G. Chen, W. Chen, C. Song, C. Li, K.

Ostrikov, Appl. Catal. B. 2019.

[421] ACS Nano 2015,9, 12496.

[422] X. Li, Y. Fang, J. Wang, B. Wei, C. Su, Small 2019,15,

e1902427.

[423] A. Kumatani, C. Miura, H. Kuramochi, T. Ohto, M.

Wakisaka, Y. Nagata, H. Ida, Y. Takahashi, K. Hu, S. Jeong,

Adv. Sci. 2019,6, 1900119.

[424] Y. Deng, L. Ting, P. Neo, Y. J. Zhang, A. A. Peterson, B. S.

Yeo, ACS Catal. 2016,6, 7790–7798.

[425] Z. W. Seh, J. Kibsgaard, C. F. Dickens, I. Chorkendorff, J. K.

Nørskov, T. F. Jaramillo, Science 2017,355, eaad4998.

Manuscript received: May 29, 2022

Revised manuscript received: October 15, 2022

Version of record online: ■■

■■

,■■■■

Review THE CHEMICAL RECORD

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 64/65] 1

REVIEW

Electrochemical water splitting is one of the most promising approaches for sustain-

able energy generation. This article thoroughly reviews the characteristics of H2and O2

kinetics interactions on water electrolysis cell electrodes by focusing on fundamental

techniques and recent progress to evaluate the achievements of electrocatalysts.

Moreover, a realistic application scenario is presented for future research opportunities

in renewable system-driven water splitting.

A. Hayat*+, M. Sohail+, H. Ali, T. A.

Taha, H. I. A. Qazi, N. Ur Rahman, Z.

Ajmal, A. Kalam, A. G. Al-Sehemi, S.

Wageh, M. A. Amin, A. Palamanit,

W. I. Nawawi, E. F. Newair, Y. Orooji*

1 – 65

Recent Advances and Future Per-

spectives of Metal-Based Electrocata-

lysts for Overall Electrochemical

Water Splitting

Wiley VCH Montag, 21.11.2022

2299 / 273382 [S. 65/65] 1

Covalent Molecular Anchoring of Metal-Free Porphyrin on Graphitic Surfaces toward Improved Electrocatalytic Activities in Acidic Medium

Article

Full-text available

Jun 2024

Robust engineering of two-dimensional (2D) materials via covalent grafting of organic molecules has been a great strategy for permanently tuningtheir physicochemical behaviors toward electrochemical energy applications. Herein, we demonstrated that a covalent functionalization approach of graphitic surfaces including graphene by a graftable porphyrin (g-Por) derivative, abbreviated as g-Por/HOPG or g-Por/G, is realizable. The efficiency of this approach is determined at both the molecular and global scales by using a state-of-the-art toolbox including cyclic voltammetry (CV), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), and scanning tunneling microscopy (STM). Consequently, g-Por molecules were proven to covalently graft on graphitic surfaces via C-C bonds, resulting in the formation of a robust novel hybrid 2D material visualized by AFM and STM imaging. Interestingly, the resulting robust molecular material was elucidated as a novel bifunctional catalyst for both the oxygen evolution (OER) and the hydrogen evolution reactions (HER) in acidic medium with highly catalytic stability and examined at the molecular level. These findings contribute to an in-depth understanding at the molecular level ofthe contribution of the synergetic effects of molecular structures toward the water-splitting process.

Advancements in water splitting for sustainable energy generation: A review

Article

Full-text available

May 2024

Water splitting, the process of converting water into hydrogen and oxygen gases, has garnered significant attention as a promising avenue for sustainable energy production. One area of focus has been the development of efficient and cost-effective catalysts for water splitting. Researchers have explored catalysts based on abundant and inexpensive materials such as nickel, iron, and cobalt, which have demonstrated improved performance and stability. These catalysts show promise for large-scale implementation and offer potential for reducing the reliance on expensive and scarce materials. Another avenue of research involves photoelectrochemical (PEC) cells, which utilize solar energy to drive the water-splitting reaction. Scientists have been working on designing novel materials, including metal oxides and semiconductors, to enhance light absorption and charge separation properties. These advancements in PEC technology aim to maximize the conversion of sunlight into chemical energy. Inspired by natural photosynthesis, artificial photosynthesis approaches have also gained traction. By integrating light-absorbing materials, catalysts, and membranes, these systems aim to mimic the complex processes of natural photosynthesis and produce hydrogen fuel from water. The development of efficient and stable artificial photosynthesis systems holds promise for sustainable and clean energy production. Tandem cells, which combine multiple light-absorbing materials with different bandgaps, have emerged as a strategy to enhance the efficiency of water-splitting systems. By capturing a broader range of the solar spectrum, tandem cells optimize light absorption and improve overall system performance. Lastly, advancements in electrocatalysis have played a critical role in water splitting. Researchers have focused on developing advanced electrocatalysts with high activity, selectivity, and stability for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). These electrocatalysts contribute to overall water-splitting efficiency and pave the way for practical implementation.

Facile fabrication of SnO2/MnTe nanocomposite as an efficient electrocatalyst for OER in basic media

Article

May 2024
J ALLOY COMPD

The rational design of bifunctional MOF-ZnFe2O4 hollow sphere-based nanocomposites for ultra-efficient electrochemical oxygen evolution reaction and high-performance symmetric supercapacitor electrodes

Article

May 2024
J ALLOY COMPD

Enhanced Electrocatalysis of Bismuth Doped Zinc Stannate Towards OER and HER Through Oxygen Vacancies: p-block Metal Ion Doping Empowering d-block

Article

May 2024

In order to meet the energy requirements of the future society, hydrogen production by electrocatalytic water splitting is considered as one of the efficient methods to produce pure hydrogen on...

Catalysts for Electrocatalytic Water Splitting

Chapter

Full-text available

May 2024

Water electrolysis or electrochemical water splitting is considered a promising technology for delivering a portable and sustainable energy source through hydrogen fuel. The crucial aspect for advancing toward industrial implementation rests in the utilization of cost-effective electrocatalysts with high efficiency. This book chapter provides a comprehensive overview of catalysts for electrochemical water splitting, emphasizing their importance, state-of-the-art advancements, challenges, and opportunities. Since catalysts play a critical role in facilitating efficient hydrogen production by improving reaction kinetics and selectivity, various catalyst types and their performance and stability evaluation are also explored. It highlights recent advancements in catalyst design, including nanostructuring and surface engineering. Challenges such as degradation, cost, and material availability are discussed, along with opportunities for innovation in earth-abundant catalysts and improved durability. This chapter aims to foster progress in catalyst design and development and inspire future research in electrolysis and electrochemical water splitting for sustainable hydrogen production.

Al-Ce co-doped BaTiO3 nanofibers as a high-performance bifunctional electrochemical supercapacitor and water-splitting electrocatalyst

Article

Full-text available

Apr 2024

Supercapacitors and water splitting cells have recently played a key role in offering green energy through converting renewable sources into electricity. Perovskite-type electrocatalysts such as BaTiO3, have been well-known for their ability to efficiently split water and serve as supercapacitors due to their high electrocatalytic activity. In this study, BaTiO3, Al-doped BaTiO3, Ce-doped BaTiO3, and Al-Ce co-doped BaTiO3 nanofibers were fabricated via a two-step hydrothermal method, which were then characterized and compared for their electrocatalytic performance. Based on the obtained results, Al-Ce co-doped BaTiO3 electrode exhibited a high capacitance of 224.18 Fg⁻¹ at a scan rate of 10 mVs⁻¹, high durability during over the 1000 CV cycles and 2000 charge–discharge cycles, proving effective energy storage properties. Additionally, the onset potentials for OER and HER processes were 11 and − 174 mV vs. RHE, respectively, demonstrating the high activity of the Al-Ce co-doped BaTiO3 electrode. Moreover, in overall water splitting, the amount of the overpotential was 0.820 mV at 10 mAcm⁻², which confirmed the excellent efficiency of the electrode. Hence, the remarkable electrocatalytic performance of the Al-Ce co-doped BaTiO3 electrode make it a promising candidate for renewable energy technologies owing to its high conductivity and fast charge transfer.

In-situ hierarchical self-assembly of NiFeHCF nanoparticles on nickel foam: Highly active and ultra-stable bifunctional electrocatalysts for water splitting and its environmental assessments towards green energy

Article

Jan 2024

3D hierarchical nickel-iron hexacyanoferrate electrocatalyst was successfully grown on nickel foam with energy efficient in-situ self-assembly method. The as-prepared NiFeHCF@NF electrode has good morphology and intimate contact with NF than...

Recent Advance in MOFs and MOF-based Composites: Synthesis, Properties, and Applications

Article

Full-text available

Feb 2024

Polyoxometalate-mediated growth of O-SnS@Cu2S heteronanosheets for high-performance oxygen and hydrogen evolution reactions

Article

Feb 2024

To properly exploit undepleted sources of energy through energy conversion devices using water splitting reactions, there is a need for cost-effective, easily accessible, and long-lasting materials that are capable of performing bifunctional activity like hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this study, oxygen incorporation into SnS@Cu2S (O-SnS@Cu2S) heteronanosheets was architecture on Nickel foam utilizing polyoxometalate as bimetal precursors, and then this material exhibited superior activity, requiring only a small overpotential to generate high current densities compared to individual O-SnS and O-Cu2S arrays for the electrocatalytic HER activity. The Tafel slopes (26 mV dec−1) and electrochemical impedance spectroscopy (EIS) (Rct = 1.2 Ω), further confirmed the favorable kinetics and conductivity of the O-SnS@Cu2S array. When compared to the O-Cu2S and O-SnS nanosheet arrays, the bimetal sulphides O-SnS@Cu2S array had much lower overpotentials, requiring only 170 mV and 232 mV, respectively, to achieve a current density of 10 mA cm−2 in an alkaline solution for HER and OER. The O-SnS@Cu2S nanosheet array outperformed SnS and Cu2S, requiring lower overpotentials to achieve high current densities. The smaller value of Tafel slopes (23 mV dec−1 for O-SnS@Cu2S) indicated improved kinetics, and EIS demonstrated a lower polarization resistance (Rct = 0.2 Ω) for the O-SnS@Cu2S array. Importantly, the O-SnS@Cu2S array exhibited remarkable stability in alkaline electrolyte cycling experiments, making it an outstanding material for practical applications in energy conversion devices. This research proposes a feasible technique for the development of efficient and stable bifunctional bimetal-sulfide electrocatalysts with enormous potential for use in renewable energy.

A sustainable avocado-peel based electrode for efficient graphene supercapacitors: Enhancement of capacitance by using Sr doped LaMnO3 perovskites

Article

Full-text available

Jul 2022
CERAM INT

Electronic waste has become a serious worldwide problem due to the high consumption of electronic devices. To palliate this problem, we fabricated flexible and biodegradable supercapacitors (SCs) using electrodes made of avocado-peel + graphene (AVG electrode). The electrochemical efficiency of these SCs was enhanced by depositing LaMnO3 (LM) and LaSrMnO3 (LSM) perovskites on their electrodes. Those perovskites are formed by microparticles with irregular shape/morphology and have sizes of 0.8–4 μm. The electrochemical evaluation of the avocado based SCs revealed a maximum capacitance/energy-density of 1100.9 F g⁻¹/97.8 Wh kg⁻¹ and 703.7 F g⁻¹/62.6 Wh kg⁻¹ for the SCs containing the LaSrMnO3 and LaMnO3 perovskites (AVG/LM-SC and AVG/LSM-SC devices), respectively. If no perovskite is added on the SC electrodes, a lower capacitance/energy-density of 230.3 F g⁻¹/18.1 Wh kg⁻¹ is obtained (AVG-SC device). Thus, adding the Sr dopant in the LM perovskite deposited on the SCs electrodes improved the energy density and capacitance of the SCs by ˜ 56% (with respect to the AVG/LM-SC device). The avocado based SCs were subjected to mechanical deformations (500 bending cycles) and the maximum loss of capacitance was 22.4, 14.3 and 11.5% for the AVG-SC, AVG/LM-SC and AVG/LSM-SC devices, respectively. In addition, the analysis by XPS, UV-VIS absorbance and Raman indicated the presence of the Mn²⁺/Mn³⁺/Mn⁴⁺ species and oxygen vacancies in the SCs and worked as redox sites for the storage of charge. In general, this investigation showed that efficient and biodegradable SCs can be fabricated using the avocado-peel, which is an abundant waste produced in the Mexican food industry.

Nanostructured Materials Based on g-C3N4 for Enhanced Photocatalytic Activity and Potentials Application: A Review

Article

Full-text available

Jul 2022

Semiconductor-based photocatalytic technology is regarded as an efficient pathway for resolving the energy scarcity across the globe. In this regard, graphitic carbon nitride (g- C3N4)-based materials could be alternatively employed in photochemical applications such as photovoltaic energy generation via CO2 photoreduction and water splitting, along with natural resource purification via organic/inorganic pollutant degradation. Indeed, this kind of assertion has been made by considering the intrinsic physicochemical properties of g- C3N4 nanomaterials, owing to their increased surface area, quantum yield, surface charge isolation, distribution, and ease of modification through material configuration or incorporation of preferred interfacial capabilities. This review article has been designed to provide the most up-to-date information regarding the further assessment of the important advancements in fabrication along with photochemical applications of various g-C3N4 nanomaterials, while specifically focusing on the scientific reason behind its success in each assessment. The discovery of interventions to alleviate such restrictions and boost photocatalytic performance has gained substantial interest. Following photo-excitation fundamentals, this work explains two distinct photoexcitation mechanisms, the carrier and charge transfer techniques, wherein the significant exciting state impact of g-C3N4 has still not been widely focused on in past studies. In this regards, we cautiously introduce the updated advances and associated functions of the alteration techniques, including morphological features, elemental dopants, deficiency engineering, and heterojunction implemented in photocatalytic performance, which are equated from the carrier and charge transport perceptions. The future perspectives in designing and properly tuning the highly active hierarchical or copolymer g-C3N4 nanoparticles in a photocatalytic system, which may improve the renewable energy cultivation and reduction efficiency are critically deciphered in detail and outlined thoroughly.

Recent Advancement in Rational Design Modulation of MXene: A Voyage from Environmental Remediation to Energy Conversion and Storage

Article

Sep 2022

Use of MXenes (Ti3C2Tx), which belongs to the family of two‐dimensional transition metal nitrides and carbides by encompassing unique combination of metallic conductivity and hydrophilicity, is receiving tremendous attention, since its discovery as energy material in 2011. Owing to its precursor selective chemical etching, and unique intrinsic characteristics, the MXene surface properties are further classified into highly chemically active compound, which further produced different surface functional groups i. e., oxygen, fluorine or hydroxyl groups. However, the role of surface functional groups doesn't not only have a significant impact onto its electrochemical and hydrophilic characteristics (i. e., ion adsorption/diffusion), but also imparting a noteworthy effect onto its conductivity, work function, electronic structure and properties. Henceforth, such kind of inherent chemical nature, robust electrochemistry and high hydrophilicity ultimately increasing the MXene application as a most propitious material for overall environment‐remediation, electrocatalytic sensors, energy conversion and storage application. Moreover, it is well documented that the role of MXenes in all kinds of research fields is still on a progress stage for their further improvement, which is not sufficiently summarized in literature till now. The present review article is intended to critically discuss the different chemical aptitudes and the diversity of MXenes and its derivates (i. e., hybrid composites) in all aforesaid application with special emphasis onto the improvement of its surface characteristics for the multidimensional application. However, this review article is anticipated to endorse MXenes and its derivates hybrid configuration, which is discussed in detail for emerging environmental decontamination, electrochemical use, and pollutant detection via electrocatalytic sensors, photocatalysis, along with membrane distillation and the adsorption application. Finally, it is expected, that this review article will open up new window for the effective use of MXene in a broad range of environmental remediation, energy conversion and storage application as a novel, robust, multidimensional and more proficient materials. The two‐dimensional MXenes were described and classified according to the synthesis techniques used, mechanical mixing, self‐assembly, in situ decorating, oxidation, properties and application. Herein, the MXenes and its derivates are emphasized onto the improvement of its surface characteristics for multidimensional application. This review article anticipating MXenes for emerging into environmental decontamination, photocatalysis, electrochemical use, and pollutant detection via electrocatalytic sensors, photocatalysis, along with membrane distillation and the adsorption application.

Recent advancement in conjugated polymers based photocatalytic technology for air pollutants abatement: Cases of CO2, NOx, and VOCs

Article

Sep 2022
CHEMOSPHERE

According to World Health Organization (WHO) survey, air pollution has become the major reason of several fatal diseases, which had led to the death of 7 million people around the globe. The 9 people out of 10 breathe air, which exceeds WHO recommendations. Several strategies are in practice to reduce the emission of pollutants into the air, and also strict industrial, scientific, and health recommendations to use sustainable green technologies to reduce the emission of contaminants into the air. Photocatalysis technology recently has been raised as a green technology to be in practice towards the removal of air pollutants. The scientific community has passed a long pathway to develop such technology from the material, and reactor points of view. Many classes of photoactive materials have been suggested to achieve such a target. In this context, the contribution of conjugated polymers (CPs), and their modification with some common inorganic semiconductors as novel photocatalysts, has never been addressed in literature till now for said application, and is critically evaluated in this review. As we know that CPs have unique characteristics compared to inorganic semiconductors, because of their conductivity, excellent light response, good sorption ability, better redox charge generation, and separation along with a delocalized π-electrons system. The advances in photocatalytic removal/reduction of three primary air-polluting compounds such as CO2, NOX, and VOCs using CPs based photocatalysts are discussed in detail. Furthermore, the synergetic effects, obtained in CPs after combining with inorganic semiconductors are also comprehensively summarized in this review. However, such a combined system, on to better charges generation and separation, may make the Adsorb & Shuttle process into action, wherein, CPs may play the sorbing area. And, we hope that, the critical discussion on the further enhancement of photoactivity and future recommendations will open the doors for up-to-date technology transfer in modern research.

Novel magnetite nano-rods-modified biochar: a promising strategy to control lead mobility and transfer in soil-rice system

Article

Aug 2022

Environment-friendly and cost-effective remediation strategies are highly needed to reclaim the lead (Pb) contaminated soils. The present study evaluated the efficacy of novel magnetic wood-modified biochar (MWB) and pristine wood biochar (WB) at different application rates (0.5–1.75%) for remediation of Pb-contaminated soil. Both MWB and WB amendments effectively reduced the transfer and bioavailability of Pb in the soil. MWB (1.75%) amendment remarkably influenced rice plant growth in terms of improved biochemical and physiological attributes. The amendment of Pb-contaminated soil with MWB also proved beneficial in reducing oxidative stress in rice plants. A significant increase in root iron plaque (Fe-plaque) formation was also observed with 1.75% MWB treatment. The sequential extraction results demonstrated the increased transformation of exchangeable Pb fractions to non-exchangeable Pb fractions. Application of 1.75% MWB reduced the Pb content in roots and shoots by 48.6% and 60.2%, respectively. Present findings clearly validated the usefulness of MWB as a cost-effective remediation strategy for Pb-contaminated soil.

Tuned d-band states over lanthanum doped nickel oxide for efficient oxygen evolution reaction

Article

Jul 2022

The d-band state of materials is an important descriptor for activity of oxygen evolution reaction (OER). For NiO materials, there is rarely concern about tuning their d-band states to tailor the OER behaviors. Herein, NiO nanocrystals with doping small amount of La³⁺ were used to regulate d-band states for promoting OER activity. Density of states calculations based on density functional theory revealed that La³⁺ doping produced upper shift of d-band center, which would induce stronger electronic interaction between surface Ni atoms and species of oxygen evolution reaction intermediates. Further density functional theory calculation illustrated that La³⁺ doped NiO possessed reduced Gibbs free energy in adsorbing species of OER intermediate. Predicted by theoretical calculations, trace La³⁺ was introduced into crystal lattice of NiO nanoparticles. The La³⁺ doped NiO nanocrystal showed much promoted OER activity than corresponding pristine NiO product. Further electrochemical analysis revealed that La³⁺ doping into NiO increased the intrinsic activity such as improved active sites and reduced charge transfer resistance. The in-situ Raman spectra suggested that NiO phase in La³⁺ doped NiO could be better maintained than pristine NiO during the OER. This work provides an effective strategy to tune the d-band center of NiO for efficient electrocatalytic OER.

Synergetic effect of Bismuth vanadate over copolymerized carbon nitride composites for highly efficient photocatalytic H2 and O2 generation

Article

Jul 2022
J COLLOID INTERF SCI

The development of copolymerized carbon nitride (CN)-based photocatalysts may support advances in photocatalytic overall water splitting. However, the recombination of charge carriers is the main bottleneck that reduces its overall photocatalytic activity. To overcome this problem, the construction of heterojunction technology has emerged as an effective approach to reduce the charge carrier recombination, thereby improving charge separation and transport efficiency. In this work, an innovative heterojunction was prepared between Quinolinic acid (QA) modified CN (CN-QAx) and novel nanorod-shaped bismuth vanadate (BiVO4) (BiVO4/CN-QAx) for overall water splitting through a simple in-situ solvent evaporation technique. The obtained results show that the synthesized samples have efficient and improved activities for releasing H2 (862.1 μmol/h) and O2 (25.52 μmol/h) under visible light irradiation. Furthermore, an exceptional apparent quantum yield (AQY) of 64.52 % has been recorded for BiVO4/CN-QA7.0 at 420 nm, which might be due to the substantial isolation of photoinduced charge carriers. Therefore, this work opens up a new channel toward efficient CN-based photocatalysts in the sustainable energy production processes.

Si/TiSi 2 /G@void@C composite with good electrochemical performance as anode of lithium ion batteries

Article

Jul 2022
APPL PHYS LETT

Silicon anode has been vigorously developed as an up-and-coming candidate for anode materials of lithium ion batteries, as it is featured by the sizeable theoretical capacity and resource superiority. However, it cannot be unrestrictedly adopted in practice because of the enormous volumetric change during the process of lithiation–delithiation again and again, as well as the low electrical conductivity. Herein, we expect to solve its intrinsic weakness through a synergy strategy that combines metal alloying, cavity structure, and carbon compositing. Si/TiSi 2 /G@void@C (STGvC) composites were designed and synthesized by induction melting and mechanical ball milling methods, adopting silicon waste produced in the photovoltaic industry and titanium-bearing blast furnace slag produced in the steel industry as raw materials. Meanwhile, the synthesis employs NaCl as a pore-forming agent, and polyvinyl pyrrolidon and waste graphite as carbon sources. As a result, the optimized STGvC sample with adding appropriate amount of NaCl harvests favorable cycling performance. It still records a discharge capacity of 886.6 mAh g ⁻¹ after 300 cycles during the circulating process at 1600 mA g ⁻¹ . This investigation presents a unique strategy to prepare Si-based anodes with bright future and makes the effective utilization of industrial solid waste in the battery industry possible.

Molecular Engineering Optimized Carbon Nitride Photocatalyst for CO2 Reduction to Solar Fuels

Article

Jun 2022

The structural alteration of carbon nitride (CN) for photocatalytic CO2 reduction is a promising research topic in environmental and energy sectors. This work discusses the fabrication of photocatalyst through a heterojunction architecture, obtained from the molecular engineering of electron-rich organic monomer 2,6-pyridinedicarboxylic acid (PDA) with CN precursor (CN/PDAx). The successful integration of PDA in the structure of CN served as a charge inducting entity to enhance charge separation and photocatalytic CO2 reduction under visible light (λ = 420 nm). The DFT results indicated that the upshift in HOMO level of CN after integration of PDA in its framework was the most lawful for the charge separation and for obtaining a high reduction potential. As-synthesized photocatalysts were demonstrated for various integral analysis and after evaluated the process of photocatalytic CO2 reduction under visible light region (λ = 420 nm). The optimized sample CN/PDA10 has the most excellent photocatalytic activity producing 85.4 μmole/h of CO and 21.3 μmole/h of H2 achieving a 7.5-fold enhanced catalytic efficiency as compared of pure CN. We hope that this work will attract more attention to synthesize efficient photocatalysts for energy production and environmental remediation.

Contactless Photoelectrochemical Biosensor Based on the Ultraviolet–Assisted Gas Sensing Interface of Three-Dimensional SnS 2 Nanosheets: From Mechanism Reveal to Practical Application

Article

Jun 2022

This work reports a contactless photoelectrochemical biosensor based on an ultraviolet-assisted gas sensor (UV-AGS) with a homemade three-dimensional (3D)-SnS2 nanosheet-functionalized interdigitated electrode. After rigorous examination, it was found that the gas responsiveness accelerated and the sensitivity increased using the UV irradiation strategy. The effects of the interlayer structure and the Schottky heterojunction on the gas-sensitive response of O2 and NH3 under UV irradiation were further investigated theoretically by 3D electrostatic field simulations and first-principles density functional theory to reveal the mechanism. Finally, a UV-AGS device was developed to quantify the blood ammonia bioassay in a small-volume whole blood sample by alkalizing blood to release gas-phase ammonia with a linear range of 25-5000 μM with a limit of detection (LOD) of 29.5 μM. The device also enables a rapid immunoassay of human cardiac troponin I (cTnI) with a linear range of 0.4-25.6 ng/mL and an LOD of 0.37 ng/mL using a urease-labeled antibody as the immune recognition molecule. Both analyses showed satisfying specificity and stability, suggesting that the device can be applied to practical assays and is of great potential to increase the value of gas-sensitive sensors in chemical biosensing.

Recent Advances and Future Perspectives of Metal‐Based Electrocatalysts for Overall Electrochemical Water Splitting

Abstract

Recommended publications

A Targeted Review of Current Progress, Challenges and Future Perspective of g‐C3N4 based Hybrid Phot...

Recent Advancement in Rational Design Modulation of MXene: A Voyage from Environmental Remediation t...

Nanostructured Materials Based on g-C3N4 for Enhanced Photocatalytic Activity and Potentials Applica...

Current progresses in two-dimensional MXene-based framework: prospects from superficial synthesis to...