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ZnO is one of the most promising candidate for photoelectrochemical splitting of water for hydrogen production. To increase the efficiency of ZnO based photoelectrochemical cell, its band-gap and band edges should be tailored to match visible light spectra and water redox potential respectively. In this paper, First-principles density functional th...
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It is known that the optical absorption property of a material is linked to its crystal structure. Therefore, it can be modified or displaced when the material is subjected to thermal treatments, generating displacements of the unit cell, atomic positions and bond angles of its atoms. In this work, the analysis of three samples of BiFeO 3 powders s...
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... However, ZnO has poor absorption in the visible region, its prominent drawback [28,29]. To increase absorption in the visible region in ZnO for PEC splitting, doping is an effective strategy, but it has its limitations [30][31][32][33]. ...
Herein, Au plasmons and their synergistic effects with ZnO nanorods (ZNs) have been investigated for photoelectrochemical (PEC) water splitting application. Au plasmons and ZNs are deposited electrochemically. Au-modified nanostructures have absorption in the visible region as plasmons enhance charge transfer and inhibit charge recombination. ZNs modified with Au (deposition duration ~ 60 s) have a photo-current density of ~ 660 μA cm⁻², at a bias of 1.0 V/SCE. X-ray diffraction (XRD) and scanning electron microscopy were used to study the structure and surface morphology of fabricated photoanodes. In addition, UV–Visible absorption and Photoluminescence spectroscopy were used for optical characterization. We have recorded current–voltage measurements and photo-conversion efficiency measurements to substantiate our observations of the synthesized photoanodes for future application in PEC splitting of water. We have also carried out Mott-Schottky and electrochemical impedance spectroscopy analysis. The analysis reveals that Au-modified ZNs-based photoanodes are a better proposition than their bare counterparts for PEC water splitting application.
... ZnO has poor absorption in the visible region, its prominent drawback [28,29]. To increase absorption in the visible region in ZnO for PEC splitting, doping is an effective strategy, but it has its limitations [30][31][32][33]. ...
In this paper, Au plasmons and their synergistic effects with ZnO nanorods (ZNs) have been investigated for photoelectrochemical (PEC) water splitting application. Au plasmons and ZNs are deposited electrochemically. Au modified nanostructures have absorption in the visible region as plasmons enhance charge transfer and inhibit charge recombination. ZNs modified with Au (deposition duration ∼ 60 s) has a photo-current density of ∼ 660 µA cm ⁻² , at a bias of 1.0V/SCE. X-ray diffraction and scanning electron microscopy were used to study the structure and surface morphology of fabricated photoanodes. UV-Visible absorption and Photoluminescence spectroscopy were used for optical characterization. We have recorded current-voltage measurements and photo-conversion efficiency measurements to substantiate our observations of the synthesized photoanodes for prospective application in PEC splitting of water. We have also carried out Mott-Schottky, and electrochemical impedance spectroscopy analysis. The analysis reveals that Au modified ZNs based photoanodes are a better proposition than their bare counterparts for PEC water splitting application.
... In our previous reports, we had investigated the effect of impurity doping (i.e., transition metals) in ZnO to increase absorption in visible region for PEC splitting of water [40][41][42]. Recently, we have shown the influence of carbon and phosphorus, i.e., anionic dopants on the electronic properties of ZnO [43]. ...
The influence of Ag plasmons and reduced graphene oxide (RGO) on ZnO nanorods (Z-NRs)-based photoanodes for photoelectrochemical splitting of water is the main focus of the present experimental study. Plasmonic layer of Ag is incorporated either as a base (Ag-Z-NRs) layer or as a top layer (Z-NRs-Ag) in an electrochemically deposited Z-NRs-based photoanodes. Z-NRs-Ag photoanodes exhibited better optical absorption as plasmonic layer stimulates charge transfer and restrain charge recombination. It had shown the photocurrent density of ~0.79 mA cm⁻², at a bias of 1.4 V/RHE. A mediator layer of RGO when introduced in Z-NRs-Ag photoanodes synergistically with Ag plasmons enhances the photocurrent density to ~1.3 mA cm⁻² at a bias of 1.4 V/RHE. Structure and surface morphology of the synthesized photoanodes was studied using x-ray diffraction and field emission scanning electron microscopy. Elemental analysis and optical characterization was done using energy-dispersive x-ray analysis, UV–Visible absorption spectroscopy and Raman spectroscopy. The current–voltage characteristics, electrochemical impedance spectroscopy, Mott–Schottky analysis, photoconversion efficiency and incident photon to current conversion efficiency measurements have been used to substantiate our observations of synthesized photoanodes.
Green synthesis of zinc oxide nanoparticles (ZnO NPs) by natural sources has
become a novel area of science in the upcoming field of nanotechnology. Nanotechnology is a young and modern discipline of science which is nothing but
constructing innovative biological active nanostructures i.e., nanoparticles of various
shapes and sizes. It is one of the fastest emerging research fields and has become a
promising tool and revolutionized all industries like medicine, drug delivery, cosmetics, agriculture and food. Synthesis of ZnO NPs from plant extracts is gaining much popularity because it is ecofriendly, easy, simple, cost effective and non-toxic. ZnO NPs can be synthesized from any part of the plant like seed, stem, flower, fruit, peel, aerial part but most popular is leaf. ZnO NPs have various, vast and wide applications in medicine, cosmetics, catalysis, biosensors, UV-shielding materials, pharmaceutical,photo-electrochemical, drug delivery and textiles industry and have properties like antibacterial, antifungal, cytotoxic, photo catalytic, wound healing, plant growth promoter. This review summarizes natural sources especially plants for the synthesis of ZnO NPs and enlist some plant mediated synthesized ZnO NPs showing promising antimicrobial, antioxidant, cytotoxic and photocatalytic properties. Their mechanism of action is also discussed. Green synthesized ZnO NPs can be used as novel natural source of drug molecules which can be therapeutically used to treat different diseases after further investigations especially by in vivo models.
Keywords: Zinc oxide nanoparticles, green synthesis, plant extracts, antimicrobial,
antioxidant, cytotoxic, photocatalytic
This work attempts to optimize the catalytic activity of the carbon-based materials by engineering their morphological structure. Several flake-like quantum dots with different shapes such as triangulene, elliptical, rhomboid, and square, as well as hydrocarbons having sunflower, kekulene, and snow-like structures, are considered and their electrocatalytic activities toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are theoretically evaluated. The activity analysis indicates that the OER overpotentials for the examined carbon materials vary in the range between 0.56 and 1.22 V. Benefiting from the improved electronic properties due to the proper morphology, remarkable catalytic activity was achieved for the snow-like morphology affording overpotentials of 0.56 V for OER and −0.05 V for HER. In addition to snow-like, other morphologies such as triangulene and square can effectively promote acidic hydrogen evolution via Volmer-Heyrovsky mechanism. On contrary, the high values of free energies for H2O dissociation step reveal that, under the alkaline condition, the examined carbon materials cannot be considered as efficient HER catalysts.
The development of renewable and sustainable energy sources along with efficient storing strategies has been the focus of utmost importance within the community to address the current energy crisis and rising energy demands. In this respect, solar hydrogen production through the route of photoelectrochemical (PEC) water-splitting is considered as a highly promising option. This review begins with a focus on understanding the PEC fundamentals in terms of the charge-transfer processes and energy requirements followed by the prerequisite properties of photoelectrode materials. We then highlighted the recent progress in different semiconductor materials and PEC device configurations. Various photoelectrode materials and device designs were classified based on their performances, with the realization of their advantages and limitations. Recent investigations in theoretical studies carried out in this field were summarised to understand the knowledge-gap and futuristic requirements. Challenges responsible for the limited efficiencies of the existing PEC water-splitting technology, considering both the material development and PEC device designs, have been discussed. Accordingly, certain possible strategies and solutions were recommended with an aim to make the PEC water-splitting a practically feasible technology.
Different isomers of (CrO3)n (n = 1–10) cluster units have been investigated using Density functional approach. Their stability and reactivity has been analyzed by plotting chemical potential and HOMO-LUMO gap as a function of cluster size. The CrO3, (CrO3)6 and (CrO3)9 are identified as the most reactive species. Reactivity of each atomic site in the cluster has been interpreted using local reactivity descriptors called Fukui Function plots. The clusters have been doped with sulfur by adding it as substitutional impurity, effect of sulfur doping has been understood by analyzing excitation energies and absorption wavelengths using time dependent-DFT(TDDFT) at CAM-B3LYP level of theory.
One step electrodeposition method has been used to realize highly porous ZnO pin hole (ZP) and ZnO rosette sheets (ZS) nanostructure based photo-anodes for efficient photoelectrochemical (PEC) splitting of water. Electrodeposited ZP and ZS based photo-anodes exhibit enhanced photocurrent density of 0.62 mA/cm ² and 0.76 mA/cm ² respectively (at a bias of 0.75 V). Further on hydrothermal amination (A), these electrodeposited ZP and ZS (A-ZP and A-ZS) nanostructure based photo-anodes had shown enhanced photocurrent density of 1.02 mA/cm ² and 1.27 mA/cm ² , respectively. Surface morphology, evolution and elemental study were done using FESEM and EDX. Raman spectra of aminated photo-anodes have peaks at ∼270 cm ⁻¹ and ∼511 cm ⁻¹ related to stretching vibration mode between Zn[sbnd]N and Zn[sbnd]O. The peaks at wave number ∼558 cm ⁻¹ and ∼571 cm ⁻¹ is due to formation of Zn[sbnd]C bonds and because of complex defects respectively. ZnO exhibits low PEC activity, but on nano-structuring in the form of ZP and ZS improves its light absorption capacity. Hydrothermal amination red shifts (∼25 nm) the absorption band at ∼ 425 nm. The N and C act as electron reservoirs in A-ZP and A-ZS photo-anodes and efficiently separate the photo-generated electron/hole pairs and restrain charge recombination to generate photo-reactive sites. Electrochemical impedance spectroscopy (EIS) revealed that A-ZP and A-ZS had low charge transfer resistance compared to their bare counterparts. This lead to considerably improved PEC performance. An unprecedented increase in IPCE values in A-ZP and A-ZS can be assigned to the decrease in band gap and thereby significant enhancement in photocurrent density. These result in to proper charge segregation and improved charge transportation. The maximum value of IPCE is 9.6% for A-ZS sample and it is also clear that ZP and ZS nanostructured film have higher IPCE values at ∼400 nm than traditional ZnO thin film. A-ZP and A-ZS based photo-anodes have exhibited enhanced PEC performance as evident from IPCE measurements and thus can be a prospective candidate for PEC and optoelectronic applications.
Today the utilization of solar energy to split water and its conversion to hydrogen and oxygen has been considered as a powerful way to solve the environmental crisis. Hierarchical porous nanostructured ZnO and ZnO/reduced graphene oxide (rGO) composite photoanodes are synthesized by innovated sol-gel method using triethylenetetramine (TETA) as a stabilizer. The hierarchical porous ZnO structure containing large agglomerates each consisting of tiny nanoparticles are formed. The X-ray diffraction analysis and Raman spectroscopy confirm the in-situ reduction of graphene oxide sheets during synthesis and formation of ZnO/rGO nanocomposite. Although the band gap and transmittance of the porous nanocomposites do not dramatically change by rGO addition, the main photoluminescence peak quenches entirely showing prolonging exciton lifetime. The ZnO/rGO porous structure achieved remarkably improved current density (1.02 mA cm⁻² at 1.5 V vs. Ag/AgCl) in 1 wt% rGO, up to 12 times higher compared to the bare ZnO (0.09 mA cm⁻² at 1.5 V vs. Ag/AgCl), which attributes to positive role of ZnO hierarchical porous structure and rGO electron separation/transportation. These findings provide new insights into the broad applicability of this methodology for promising future semiconductor/graphene composite in the field of photoelectrochemical water splitting.
