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a) SEM image of Ar‐plasma graved Co3O4 nanosheets. b) The LSV curves of OER for pristine Co3O4 (0 s) and the plasma engraved Co3O4 (120 s). a,b) Reproduced with permission.78 Copyright 2016, Wiley‐VCH. c) Calculated DOS and corresponding schematic bond formation of atomic oxygen through coupling of O 2p to the highest occupied d‐state on CoOOH with/without O vacancy (cyan spheres‐cobalt and redoxygen). The d) LSV curves and e) corresponding Tafel plots for pristine CoOOH (0 s), plasma engraved CoOOH (60 s), and RuO2. c–e) Reproduced with permission.95 Copyright 2017, Elsevier.
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Co, Ni‐based (hydr)oxides with stoichiometric or nonstoichiometric composites are playing significant roles in renewable energy technologies, such as electrocatalytic reactions for transforming earth abundant resources into value‐added chemicals. In the past several years, attributed to the development of novel synthesis strategies, characterizatio...
Citations
... Metal-doping engineering has proven to be an effective strategy to promote the electrocatalytic activity and/or stability of catalysts for several electrochemical reactions by modifying their electronic structure to modulate the adsorption free energy of the intermediates and improve the electron transfer property. [22,23] As a typical example, nanosheets made of Fe-doped Ni 5 P 4 and Fedoped Ni(OH) 2 have been fabricated, they deliver excellent oxygen evolution reaction (OER) and HER catalytic properties in alkaline media. [24] Notably, recent studies have shown that the introduction of some transition metals (Mn, Ni, Nb, Rh) into RuO 2 can significantly improve the electrocatalytic activity and stability toward OER in acidic conditions by reducing the adsorption of oxygen intermediates on active Ru sites. ...
The realization of large‐scale industrial application of alkaline water electrolysis for hydrogen generation is severely hampered by the cost of electricity. Therefore, it is currently necessary to synthesize highly efficient electrocatalysts with excellent stability and low overpotential under an industrial‐level current density. Herein, Ir‐incorporated in partially oxidized Ru aerogel has been designed and synthesized via a simple in situ reduction strategy and subsequent oxidation process. The electrochemical measurements demonstrate that the optimized Ru 98 Ir 2 ‐350 electrocatalyst exhibits outstanding hydrogen evolution reaction (HER) performance in an alkaline environment (1 M KOH). Especially, at the large current density of 1000 mA cm ⁻² , the overpotential is as low as 121 mV, far exceeding the benchmark Pt/C catalyst. Moreover, the Ru 98 Ir 2 ‐350 catalyst also displays excellent stability over 1500 h at 1000 mA cm ⁻² , denoting its industrial applicability. This work provides an efficient route for developing highly active and ultra‐stable electrocatalysts for hydrogen generation under industrial‐level current density.
... Furthermore, active-site engineering in newly designed materials may enhance electrocatalytic activity, contributing to the optimization of adsorption energies and reaction barrier for intermediates and electrocatalytic reactions, respectively. 48 ...
Electrochemical water splitting represents a promising technology for green hydrogen production. To design advanced electrocatalysts, it is crucial to identify their active sites and interpret the relationship between their structures and performance. Materials extensively studied as electrocatalysts include noble‐metal‐based (e.g., Ru, Ir, and Pt) and non‐noble‐metal‐based (e.g., 3d transition metals) compounds. Recently, advancements in characterization techniques and theoretical calculations have revealed novel and unusual active sites. The present review highlights the latest achievements in the discovery and identification of various unconventional active sites for electrochemical water splitting, with a focus on state‐of‐the‐art strategies for determining true active sites and establishing structure–activity relationships. Furthermore, we discuss the remaining challenges and future perspectives for the development of next‐generation electrocatalysts with unusual active sites. By presenting a fresh perspective on the unconventional reaction sites involved in electrochemical water splitting, this review aims to provide valuable guidance for the future study of electrocatalysts in industrial applications.
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... Such modified structures with high electronic-tuning feasibility facilitate the introduction of nanostructure defects and oxygen-vacancy generation due to lattice distortion, enabling a fine-tuning of the electrocatalysis reaction pathways. [35,36] Here, a bifunctional ternary P−NiCuFe−LDH hierarchical catalyst has been developed to overcome the limitations of LDHcatalyst systems. Experimental and theoretical analyses indicate that the Fe doping and phosphidation of NiCu LDH causes a structural transformation and surface reconstruction of the LDH. ...
The design and synthesis of low‐cost electrocatalysts with high catalytic activity and long‐term stability is a challenging task. This study utilizes a combination of electronic tuning and surface reconstruction to synthesize a ternary layered double hydroxide (LDH)/phosphide (P−NiCuFe−LDH) hierarchical‐structure catalyst that improves the kinetics of the hydrogen/oxygen evolution reactions in water electrolysis by facilitating the thermodynamically limited reaction pathways. Spectroscopic analyses indicate synergistic electronic interactions among the metal atoms in the LDH and phosphide layers via the P‐bridge effect. This cross‐layer interaction optimizes the electron transport pathways and reaction kinetics, enabling the proposed hierarchical electrocatalyst to exhibit high intrinsic activity. Theoretical calculations confirm the configuration of the cross‐phase bridges and elucidate the origin of the enhanced electrocatalytic effect of P−NiCuFe−LDH. For overall water splitting, the P−NiCuFe0.06−LDH || P−NiCuFe0.06−LDH system requires only 1.517 V to attain a current density of 10 mA cm⁻². The P−O‐containing surface (generated in situ during water electrolysis) prevents metal‐ion leaching and endows P−NiCuFe−LDH with excellent operational stability; as demonstrated by the continuous long‐term stability test over 1000 h with negligible performance degradation. This study provides important insights into the design of rational hierarchical structures for a wide range of applications beyond water splitting.
... The catalytic processes are closely correlated to the physicochemical properties of catalyst surfaces, which directly affect the adsorption and desorption of reaction species [43]. Through years of efforts, various strategies, including facet engineering, defect engineering, chemical doping, and surface functionalization, have been developed to enhance the electrocatalytic performance of catalysts (Fig. 3a) [44]. These promoting strategies have a considerable effect on modulating the electronic structure of catalytic material for favorable reaction kinetics [43]. ...
An environmentally benign, sustainable, and cost-effective supply of H2O2 as a rapidly expanding consumption raw material is highly desired for chemical industries, medical treatment, and household disinfection. The electrocatalytic production route via electrochemical oxygen reduction reaction (ORR) offers a sustainable avenue for the on-site production of H2O2 from O2 and H2O. The most crucial and innovative part of such technology lies in the availability of suitable electrocatalysts that promote two-electron (2e-) ORR. In recent years, tremendous progress has been achieved in designing efficient, robust, and cost-effective catalyst materials, including noble metals and their alloys, metal-free carbon-based materials, single-atom catalysts, and molecular catalysts. Meanwhile, innovative cell designs have significantly advanced electrochemical applications at the industrial level. This review summarizes fundamental basics and recent advances in H2O2 production via 2e--ORR, including catalyst design, mechanistic explorations, theoretical computations, experimental evaluations, and electrochemical cell designs. Perspectives on addressing remaining challenges are also presented with an emphasis on the large-scale synthesis of H2O2 via the electrochemical route.
... Hydrogen is a clean and renewable energy source with high energy density and has attracted great attention from scientific researchers [4,5]. Hydrogen production via water electrolysis has been considered as one of the most attractive pathways for storing renewable energy sources such as solar, wind and tidal energy [6,7]. However, electrolysis of water is an energyintensive process with high cost, mainly due to the high overpotential and the slow kinetic reaction process of the anodic OER [8]. ...
The development of high-efficiency oxygen evolution reaction (OER) electrocatalysts is of great importance for electrolytic H2 generation. In this work, we report in-situ growth of MnCo2O4 nanoneedles and NiFeRu layered double hydroxide (LDH) nanosheets on nickel foam (NF) (MnCo2O4@NiFeRu-LDH/NF) that can function a highly efficient electrode toward electrocatalysis of OER. Such electrode demands an overpotential of as low as 205 mV to reach 10 mA cm⁻² in alkaline electrolyte and can run stably over 120-hours continuous operation. A hybrid flow acid/alkali electrolyzer is set up by using the Pt/C as the acidic cathode coupling with the MnCo2O4@NiFeRu-LDH/NF as the alkaline anode, which only requires an applied voltage of 0.59 V and 0.94 V to attain an electrolytic current density of 10 mA cm⁻² and 100 mA cm⁻², respectively. The present work could push forward the further development of the electricity-saving electrolytic technique for H2 generation.
... The TM-O orbital hybridization, valence state, and charge-transfer capability have been recently summarized. [23][24][25][26] In this minireview, we mainly focus on regulating the spin state of active centers. ...
Developing efficient and stable transition metal oxides catalysts for energy conversion processes such as oxygen evolution reaction and oxygen reduction reaction is one of the key measures to solve the problem of energy shortage. The spin state of transition metal oxides is strongly correlated with their catalytic activities. In an octahedral structure of transition metal oxides, the spin state of active centers could be regulated by adjusting the splitting energy and the electron pairing energy. Regulating spin state of active centers could directly modulate the d orbitals occupancy, which influence the strength of metal‐ligand bonds and the adsorption behavior of the intermediates. In this review, we clarified the significance of regulating spin state of the active centers. Subsequently, we discussed several characterization technologies for spin state and some recent strategies to regulate the spin state of the active centers. Finally, we put forward some views on the future research direction of this vital field.
... A variety of cathode materials have been investigated, such as manganese-based oxides, Prussian blue analogs, conducting polymers, and vanadium-based oxides, over the past few years [13][14][15][16][17]. Among these cathode materials, the vanadium-based oxides have been widely studied for ZIBs because of their multivalence, open skeleton structure, and high theoretical capacities [13,14,[18][19][20][21]. Vanadium pentoxide (V2O5) is one of the promising materials due to its high theoretical capacity and layered structure with it having a large interspace [1,3,22,23]. ...
Water molecules and cations with mono, binary, and triple valences have been intercalated into V2O5 to significantly improve its electrochemical properties as a cathode material of zinc-ion batteries. Sn as a tetravalent element is supposed to interact aggressively with the V2O5 layer and have a significant impact on the electrochemical performance of V2O5. However, it has been rarely investigated as a pre-intercalated ion in previous works. Hence, it is intriguing and beneficial to develop water molecules and Sn co-doped V2O5 for zinc-ion batteries. Herein, Sn-doped hydrated V2O5 nanosheets were prepared by a one-step hydrothermal synthesis, and they demonstrated that they had a high specific capacity of 374 mAh/g at 100 mA/g. Meanwhile, they also showed an exceptional rate capability with 301 mAh/g even at a large current density of 10 A/g, while it was only 40 mAh/g for the pristine hydrated V2O5, and an excellent cycling life (87.2% after 2500 cycles at 5 A/g), which was far more than the 25% of the pure hydrated V2O5. The dramatic improvement of the rate and cycling performance is mainly attributed to the faster charge transfer kinetics and the enhanced crystalline framework. The remarkable electrochemical performance makes the Sn-doped hydrate V2O5 a potential cathode material for zinc-ion batteries.
... Currently, activity, stability, and cost are three key aspects that need to be considered in the design of OER electrocatalyst for industrial applications. Iridium (Ir) and ruthenium (Ru)-based materials are placed at the level of state-of-the-art OER electrocatalysts with high intrinsic activity and low activation energy barrier [16]. ...
Alkaline water electrolysis provides a promising route for “green hydrogen” generation, where anodic oxygen evolution reaction (OER) plays a crucial role in coupling with cathodic hydrogen evolution reaction (HER). To date, the development of highly active and durable OER catalysts based on earth‐abundant elements has drawn wide attention, nevertheless, their performance under high current densities (HCDs ≥1000 mA cm−2) has been less emphasized. This situation has seriously impeded large‐scale electrolysis industrialization. In this review, in order to provide a guideline for designing high‐performance OER electrocatalysts, the effects of HCD on catalytic performance involving electron transfer, mass transfer, and physical/chemical stability are summarized. Furthermore, the design principles were pointed out for obtaining efficient and robust OER electrocatalysts in the light of recent progress of OER electrocatalysts working above 1000 mA cm−2. These include the aspects of developing self‐supported catalytic electrodes, enhancing intrinsic activity, enhancing the catalyst‐support interaction, engineering surface wettability, and introducing protective layer. Finally, summaries and outlooks in achieving OER at industrially‐relevant HCDs are proposed.
... 198,199 Structural defects have been confirmed to tune the Fermi level, narrow the bandgap, and change the absorption energy of various reactive species. 200,201 Consequently, the ratecontrolling step may be changed and the reaction rate of the overall reaction is increased. In this mechanism, the electrocatalytic reaction rate can be promoted by a very small defect concentration. ...
Carbon dioxide generated by the combustion of fossil fuels exacerbates global environmental problems and hydrogen produced by renewable energy is a viable alternative in the continuous transition to sustainable and eco‐conscience development. Electrocatalysts are vital to electrocatalytic reactions and plasma surface modification is one of the promising techniques to modify nanoscale electrocatalysts for water splitting. Up to now, a comprehensive review on the latest developments, challenges, and opportunities of plasma‐tailored defective electrocatalysts for water electrolysis and hydrogen fuel cells is lacking. This paper systematically summarizes the current status of hydrogen production and fuel cell technologies, plasma principles and advantages, plasma‐tailored defective electrocatalysts from the perspective of water splitting and fuel cell applications, advanced characterization of defects, relationship between materials structure and catalytic activity of electrocatalysts, and finally challenges, opportunities, and future roadmap of plasma technologies. This review serves as a reference for future development of hydrogen technologies and offers insights into the structural tailoring of catalytic materials.
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... As the main half-reaction of water-splitting and metal-air batteries, oxygen evolution reaction (OER) usually suffers from slow kinetics of the four-electron transfer process and is the main impediment to catalytic efficiency [1][2][3][4]. Although RuO 2 and IrO 2 have displayed high electrocatalytic activities, shortcomings such as low earthabundance, high price, and poor stability severely restrain their industrial applicability [5][6][7][8][9]. ...
Cost-efficient electrocatalysts composed of earth-abundant elements are highly desired for enhanced oxygen evolution reaction (OER). As a promising candidate, metallic Co4N already demonstrated electrocatalytic performance relying on specific nanostructures and electronic configurations. Herein, nickel was introduced as the dopant into one-dimensional (1D) hierarchical Co4N structures, achieving effective electronic regulation of Co4N toward high OER performance. The amount of Co3+ increased after Ni-doping, and the in-situ formed surface oxyhydroxide during OER enhanced the electrocatalytic kinetics. Meanwhile, the 1D hierarchical structure further promoted the performances of Co4N owing to the high electrical conductivity and abundant active-sites on the rough surface. As expected, the optimal Ni-doped Co4N with a Ni/Co molar ratio of 0.25 provides a small overpotential of 233 mV at a current density of 10 mAcm−2, with a low Tafel slope of 61 mV dec−1, and high long-term stability in 1.0 mol L−1 KOH. Following these results, the enhancement by doping the Co4N nanowire bundles with Fe and Cu was further evidenced for the OER.
