Engineering Surface Structure of Spinel Oxides via High-Valent Vanadium Doping for Remarkably Enhanced Electrocatalytic Oxygen Evolution Reaction

CoFe2O4/Ag Heterocatalysts Grown on Carbonized Wood for Light-Promoted Oxygen Evolution Reaction

The sluggish reaction kinetics of oxygen evolution reaction (OER) significantly limit the efficiency of electrochemical water splitting (EWS) process, making the development of efficient and stable OER electrocatalysts for sustainable EWS important but still challenging to achieve. Herein, a light-assisted improved design of low-budget carbonized wood (CW) with outstanding OER performance is developed by firmly growing CoFe2O4 nanorods and Ag nanoparticles on the CW channels to form self-supporting electrode (CoFe2O4/Ag-CW). The coordination of active CoFe2O4/Ag and porous CW framework results in substantial effective interfaces and abundant electrochemical active sites, and accelerated electrolyte diffusion, electron transfer, and oxygen escaping. Electrochemical measurements and density functional theory calculations suggest the presence of dual microparticle synergies, conducive to optimizing the electronic structure of CoFe2O4/Ag-CW and lowering the energy barrier of O-H bond breaking in H2O for remarkably enhanced OER activity. Under light field assistance, CoFe2O4/Ag-CW exhibits excellent photothermal effect and carrier separation efficiency with ultralow overpotential of 258 mV and long-term stability at 100 mA cm-2. The photothermal effect and the generation of photogenerated carriers enhance OER dynamics and charge transfer efficiency, leading to improved OER performance under light exposure. Overall, the proposed strategy looks promising for efficient and low-cost oxygen generation.

Exploring P-(Fe,V)-Codoped Metastable-Phase β-NiMoO4 for Improving the Performance of Overall Water Splitting

It is especially essential to develop high-performance and low-cost nonprecious metal catalysts for large-scale hydrogen production. A large number of electrochemical catalysts composited by transition metal centers has been reported; however, it is still a great challenge to design and manipulate target electrocatalysts to realize high overall water-splitting activity at the atomic level. Herein, we develop totally new P-(Fe,V)-codoped metastable-phase β-NiMoO4. As an electrocatalyst, it can realize oxygen evolution at only 163 mV and hydrogen evolution at only 44 mV at 10 mA cm-2. It, as both an anode and a cathode, is fabricated into a cell for overall water splitting, which has an ultralow voltage value of 1.48 V to drive a current density of 10 mA cm-2 and can remain stable for at least 100 h. In the target electrode, the P element plays three important roles: (1) it can stabilize the metastable-phase structure of β-NiMoO4; (2) it can further optimize the electronic structure; and (3) it can provide more active sites. The synergistic effect for multimetal centers with different redox couples is key for the great improvement of catalytic activity. The related mechanism is discussed in detail.

Boosting the Performance of Alkaline Anion Exchange Membrane Water Electrolyzer with Vanadium-Doped NiFe2O4

Developing efficient, economical, and stable catalysts for the oxygen evolution reaction is pivotal for producing large-scale green hydrogen in the future. Herein, a vanadium-doped nickel-iron oxide supported on nickel foam (V-NiFe2O4/NF) is introduced, and synthesized via a facile hydrothermal method as a highly efficient electrocatalyst for water electrolysis. X-ray photoelectron and absorption spectroscopies reveal a synergistic interaction between the vanadium dopant and nickel/iron in the host material, which tunes the electronic structure of NiFe2O4 to increase the number of electrochemically active sites. The V-NiFe2O4/NF electrode exhibited superior electrochemical performance, with a low overpotential of 186 mV at a current density of 10 mA cm-2, a Tafel slope value of 54.45 mV dec-1, and minimal charge transfer resistance. Employing the V-NiFe2O4/NF electrode as an anode in an alkaline anion exchange membrane water electrolyzer single-cell, a cell voltage of 1.711 V is required to achieve a high current density of 1.0 A cm-2. Remarkably, the cell delivered an energy conversion efficiency of 73.30% with enduring stability, making it a promising candidate for industrial applications.

Shifting the Oxygen-Evolution Reaction Pathway via Cation Engineering to Activate Lattice Oxygen in Metal-Organic Frameworks

Metal-organic frameworks (MOFs) as promising electrocatalysts have been widely studied, but their performance is limited by conductivity and coordinating saturation. This study proposes a cationic (V) modification strategy and evaluates its effect on the electrocatalytic performance of CoFe-MOF nanosheet arrays. The optimal V-CoFe-MOF/NF electrocatalyst exhibits excellent oxygen-evolution reaction (OER)/hydrogen-evolution reaction (HER) performance (231 mV at 100 mA cm-2/86 mV at 10 mA cm-2) in alkaline conditions, with its OER durability exceeding 400 h without evident degradation. Furthermore, as a bifunctional electrocatalyst for water splitting, a small cell voltage is achieved (1.60 V at 10 mA cm-2). The practicability of the catalyst is further evaluated by membrane electrode assembly (MEA), showing outstanding activity (1.53 V at 10 mA cm-2) and long-term stability (at 300 mA cm-2). Moreover, our results reveal the apparent reconstruction properties of V-CoFe-MOF/NF in alkaline electrolytes, where the partially dissolved V promotes the formation of more active β-MOOH. The mechanism study shows the OER mechanism shifts to a lattice oxygen oxidation mechanism (LOM) after V doping, which directly avoids complex multistep adsorption mechanism and reduces reaction energy. This study provides a cation mediated strategy for designing efficient electrocatalysts.

A Doping-Induced SrCo0.4Fe0.6O3/CoFe2O4 Nanocomposite for Efficient Oxygen Evolution in Alkaline Media

Perovskite and spinel oxides are promising alternatives to noble metal-based electrocatalysts for oxygen evolution reaction (OER). Herein, a novel perovskite/spinel nanocomposite comprised of SrCo0.4Fe0.6O3 and CoFe2O4 (SCF/CF) is prepared through a simple one-step method that incorporates iron doping into a SrCoO3- δ matrix, circumventing complex fabrication processes typical of these materials. At a Fe dopant content of 60%, the CoFe2O4 spinel phase is directly precipitated from the parent SrCo0.4Fe0.6O3 perovskite phase and the number of active B-site metals (Co/Fe) in the parent SCF can be maximized. This nanocomposite exhibits a remarkable OER activity in alkaline media with a small overpotentional of 294 mV at 10 mA cm-2. According to surface states analysis, the parent SCF perovskite remains in its pristine form under alkaline OER conditions, serving as a stable substrate, while the second spinel CF is covered by 5/8 monolayer (ML) O*, exhibiting considerable affinity toward the oxygen species involved in the OER. Analysis based on advanced OER microkinetic volcano model indicates that a 5/8 ML O* covered-CF is the origin for the remarkable activity of this nanocomposite. The results reported here significantly advance knowledge in OER and can boost application, scale-up and commercialisation of electrocatalytic technologies toward clean energy devices.

Dopant Site Engineering on 2D Co3O4 Enables Enhanced Toluene Oxidation in a Wide Temperature Range

Development of cost-effective oxide catalysts holds the key to the removal of toluene, one of the most important volatile organic compounds. However, the catalysts follow varied working mechanisms at different reaction temperatures, posing a challenge to achieving efficient toluene removal over a wide temperature range. Here we report an agitation-assisted molten salt method, which achieves the rational doping on a two-dimensional Co3O4 catalyst and forms two different structures of active sites to enhance catalytic oxidation of toluene in specific temperature intervals, enabling a facile tandem design for working in a wide temperature range. Specifically, Co3O4 is doped with Cu at the octahedral site (Cu-Co3O4) and Zn at the tetrahedral site (Zn-Co3O4) to form CuOh-O-CoTe and ZnTe-O-CoOh structures on the surface, respectively. Mechanistic studies reveal the different working mechanisms of these two active sites toward remarkable performance enhancement at specific temperature intervals, and the improved performance derived from accelerated consumption of intermediates adsorbed on the catalyst surface. Taken together, Cu-Co3O4 and Zn-Co3O4 achieve excellent toluene purification performance over a wide temperature range. This work provides insights into the mechanism-oriented design of active sites at the atomic level.

Electrocatalytic Mechanism of Defect in Spinels for Water and Organics Oxidation

Spinels display promising electrocatalytic ability for oxygen evolution reaction (OER) and organics oxidation reaction because of flexible structure, tunable component, and multifold valence. Unfortunately, limited exposure of active sites, poor electronic conductivity, and low intrinsic ability make the electrocatalytic performance of spinels unsatisfactory. Defect engineering is an effective method to enhance the intrinsic ability of electrocatalysts. Herein, the recent advances in defect spinels for OER and organics electrooxidation are reviewed. The defect types that exist in spinels are first introduced. Then the catalytic mechanism and dynamic evolution of defect spinels during the electrochemical process are summarized in detail. Finally, the challenges of defect spinel electrocatalysts are brought up. This review aims to deepen the understanding about the role and evolution of defects in spinel for electrochemical water/organics oxidation and provide a significant reference for the design of efficient defect spinel electrocatalysts.

Microwave solvothermal synthesis of Component-Tunable High-Entropy oxides as High-Efficient and stable electrocatalysts for oxygen evolution reaction

Transition-metal-based high-entropy oxides (HEOs) are appealing electrocatalysts for oxygen evolution reaction (OER) due to their unique structure, variable composition and electronic structure, outstanding electrocatalytic activity and stability. Herein, we propose a scalable high-efficiency microwave solvothermal strategy to fabricate HEO nano-catalysts with five earth-abundant metal elements (Fe, Co, Ni, Cr, and Mn) and tailor the component ratio to enhance the catalytic performance. (FeCoNi₂CrMn)₃O₄ with a double Ni content exhibits the best electrocatalytic performance for OER, namely low overpotential (260 mV@10 mA cm^-2), small Tafel slope and superb long-term durability without obvious potential change after 95 h in 1 M KOH. The extraordinary performance of (FeCoNi₂CrMn)₃O₄ can be attributed to the large active surface area profiting from the nano structure, the optimized surface electronic state with high conductivity and suitable adsorption to intermediate benefitting from ingenious multiple-element synergistic effects, and the inherent structural stability of the high-entropy system. In addition, the obvious pH value dependable character and TMA⁺ inhibition phenomenon reveal that the lattice oxygen mediated mechanism (LOM) work together with adsorbate evolution mechanism (AEM) in the catalytic process of OER with the HEO catalyst. This strategy provides a new approach for the rapid synthesis of high-entropy oxide and inspires more rational designs of high-efficient electrocatalysts.

Mechanochemical Synthesized CaO/ZnCo2O4 Nanocomposites for Biodiesel Production

Biodiesel has been recognized as an environmentally friendly, renewable alternative to fossil fuels. In this work, CaO/ZnCo2O4 nanocomposites were successfully synthesized via simple mechanochemical reaction between ZnCo2O4 and CaO powders by varying the CaO loading from 5 to 20 wt.%. The synthesized materials were found to be highly efficient heterogeneous catalysts for transesterification of tributyrin with methanol to produce biodiesel. The nanocomposite, which contained 20 wt.% CaO and 80 wt.% ZnCo2O4 (CaO/ZnCo2O4-20), exhibited superior and stable transesterification activity (98% conversion) under optimized reaction conditions (1:12 TBT to methanol molar ratio, 5 wt.% catalyst and 180 min. reaction time). The experimental results revealed that the reaction mechanism on the CaO/ZnCo2O4 composite followed pseudo first-order kinetics. The physicochemical characteristics of the synthesized nanocomposites were measured using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Fourier-transformed infrared spectroscopy (FTIR), X-ray photoelectron spectrometer (XPS), N2-physisorption, and CO2- temperature-programmed desorption (CO2-TPD) techniques. The results indicated the existence of coalescence between the CaO and ZnCo2O4 particles, Additionally, the CaO/ZnCo2O4-20 catalyst was found to possess the greater number of highly basic sites and high porosity, which are the key factors affecting catalytic performance in transesterification reactions.

Controlled Electrophoretic Deposition Strategy of Binder-Free CoFe2O4 Nanoparticles as an Enhanced Electrocatalyst for the Oxygen Evolution Reaction

The kinetic-sluggish oxygen evolution reaction (OER) is the main obstacle in electrocatalytic water splitting for sustainable production of hydrogen energy. Efficient water electrolysis can be ensured by lowering the overpotential of the OER by developing highly active catalysts. In this study, a controlled electrophoretic deposition strategy was used to develop a binder-free spinel oxide nanoparticle-coated Ni foam as an efficient electrocatalyst for water oxidation. Oxygen evolution was successfully promoted using the CoFe₂O₄ catalyst, and it was optimized by modulating the electrophoretic parameters. When optimized, CoFe₂O₄ nanoparticles presented more active catalytic sites, superior charge transfer, increased ion diffusion, and favorable reaction kinetics, which led to a small overpotential of 287 mV for a current density of 10 mA cm^-2, with a small Tafel slope of 43 mV dec^-1. Moreover, the CoFe₂O₄ nanoparticle electrode exhibited considerable long-term stability over 100 h without detectable activity loss. The results demonstrate promising potential for large-scale water splitting using Earth-abundant oxide materials via a simple and cheap fabrication process.

Recent Progress on Bimetallic-Based Spinels as Electrocatalysts for the Oxygen Evolution Reaction

Electrocatalytic water splitting is a promising and viable technology to produce clean, sustainable, and storable hydrogen as an energy carrier. However, to meet the ever-increasing global energy demand, it is imperative to develop high-performance non-precious metal-based electrocatalysts for the oxygen evolution reaction (OER), as the OER is considered the bottleneck for electrocatalytic water splitting. Spinels, in particular, are considered promising OER electrocatalysts due to their unique properties, precise structures, and compositions. Herein, the recent progress on the application of bimetallic-based spinels (AFe₂ O₄ , ACo₂ O₄ , and AMn₂ O₄ ; where A = Ni, Co, Cu, Mn, and Zn) as electrocatalysts for the OER is presented. The fundamental concepts of the OER are highlighted after which the family of spinels, their general formula, and classifications are introduced. This is followed by an overview of the various classifications of bimetallic-based spinels and their recent developments and applications as OER electrocatalysts, with special emphasis on enhancing strategies that have been formulated to improve the OER performance of these spinels. In conclusion, this review summarizes all studies mentioned therein and provides the challenges and future perspectives for bimetallic-based spinel OER electrocatalysts.

Isovalent anion-induced electrochemical activity of doped Co3V2O8 for oxygen evolution reaction application

The activity of an OER electrocatalyst is a strong function of the reaction kinetics at the active sites, which can be influenced by catalytic engineering (e.g., heterostructure, doping, and the addition of cocatalysts). Herein, we report the improved reaction kinetics of cobalt oxide for the OER via the addition of high valence vanadium and thereafter doping with sulphur (S-Co₃V₂O₈). The addition of vanadium increases the oxygen vacancy while the doping of sulphur increases the electronic conductivity of the electrocatalyst. The synergic effect of the oxygen vacancy and electronic conductivity increases the activity of S-Co₃V₂O₈. Furthermore, S-Co₃V₂O₈ showed the least Tafel slope, which showed the activity enhancement towards the oxygen evolution reaction. Moreover, the underlying reaction mechanism is explored by electrochemical impedance spectroscopy, which reveals that the ratio of polarisation resistance to double-layer capacitance is minimum for S-Co₃V₂O₈, indicating the highest activity.

Vanadium-Based Trimetallic Metal-Organic-Framework Family as Extremely High-Performing and Ultrastable Electrocatalysts for Water Splitting

This is the first time that the pore-space-partition (PSP) strategy is being successfully applied in the electrochemical field for water splitting, realizing the highly efficient construction of a series of ultrastable pristine MOF electrocatalysts. On integrating the vanadium-based trimetallic building cluster (M₂V), the target M₂V-MOFs exhibit excellent electrocatalytic activity for HER, OER, and water splitting. In particular, ultralow overpotentials of 314 and 198 mV for Fe₂V-MOF as OER and HER electrocatalysts, respectively, can drive a current density of 10 mA cm^-2. The fabricated Fe₂V-MOF||Pt/C two-electrode configuration for the overall water splitting yields a current density of 10 mA cm^-2 at only 1.6 V vs RHE, which is superior to that of the commercial IrO₂||Pt/C couple. Notably, high structural and chemical stabilities still can be observed in alkaline condition. This work opens up an exciting pathway to design efficient and stable electrocatalysts based on pristine MOF by integrating the PSP strategy and multimetallic centers.

Electronic metal-support interaction constructed for preparing sinter-resistant nano-platinum catalyst with redox property

Generally, support materials with particular structural properties could effectively anchor metal nanoparticles and provide lower activation barriers in heterogeneous catalysis. To tailor the structure of stable iron oxide, NiFe₂O₄ of inverse spinel structure was obtained by combining nickel with iron element under an alkaline environment and high-temperature calcination. The p-type conductivity of NiFe₂O₄ provides the possibility of constructing electronic interfacial interaction with Pt nanoparticles by electron transfer. The constructed metal-support interaction could effectively stabilize Pt nanoparticles and be further enhanced during long-term harsh calcination (700 °C for 48 h) even under an O₂ atmosphere. Meanwhile, the abundant structural defects of NiFe₂O₄ are beneficial for constructing low-temperature redox centers with the aid of Pt nanoparticles. Pt/NiFe₂O₄ exhibited not only excellent activity in room-temperature oxidation (CO and HCHO) and reduction reactions (chemo-selective hydrogenation of nitroarenes), but also high stability even after storage for more than 6 months. A self-adjusting mechanism triggered by structural defects is disclosed by in situ characterization and systematic reaction results. This work demonstrates an alternative concept to construct sinter-resistant and highly-effective nano-platinum catalysts robust for oxidation and reduction reactions.

Advanced Transition Metal-Based OER Electrocatalysts: Current Status, Opportunities, and Challenges

Oxygen evolution reaction (OER) is an important half-reaction involved in many electrochemical applications, such as water splitting and rechargeable metal-air batteries. However, the sluggish kinetics of its four-electron transfer process becomes a bottleneck to the performance enhancement. Thus, rational design of electrocatalysts for OER based on thorough understanding of mechanisms and structure-activity relationship is of vital significance. This review begins with the introduction of OER mechanisms which include conventional adsorbate evolution mechanism and lattice-oxygen-mediated mechanism. The reaction pathways and related intermediates are discussed in detail, and several descriptors which greatly assist in catalyst screen and optimization are summarized. Some important parameters suggested as measurement criteria for OER are also mentioned and discussed. Then, recent developments and breakthroughs in experimental achievements on transition metal-based OER electrocatalysts are reviewed to reveal the novel design principles. Finally, some perspectives and future directions are proposed for further catalytic performance enhancement and deeper understanding of catalyst design. It is believed that iterative improvements based on the understanding of mechanisms and fundamental design principles are essential to realize the applications of efficient transition metal-based OER electrocatalysts for electrochemical energy storage and conversion technologies.

Valence-State Effect of Iridium Dopant in NiFe(OH)2 Catalyst for Hydrogen Evolution Reaction

Engineering high-performance electrocatalysts is of great importance for energy conversion and storage. As an efficient strategy, element doping has long been adopted to improve catalytic activity, however, it has not been clarified how the valence state of dopant affects the catalytic mechanism and properties. Herein, it is reported that the valence state of a doping element plays a crucial role in improving catalytic performance. Specifically, in the case of iridium doped nickel-iron layer double hydroxide (NiFe-LDH), trivalent iridium ions (Ir³⁺ ) can boost hydrogen evolution reaction (HER) more efficiently than tetravalent iridium (Ir⁴⁺ ) ions. Ir³⁺ -doped NiFe-LDH delivers an ultralow overpotential (19 mV @ 10 mA cm^-2 ) for HER, which is superior to Ir⁴⁺ doped NiFe-LDH (44 mV@10 mA cm^-2 ) and even commercial Pt/C catalyst (40 mV@ 10 mA cm^-2 ), and reaches the highest level ever reported for NiFe-LDH-based catalysts. Theoretical and experimental analyses reveal that Ir³⁺ ions donate more electrons to their neighboring O atoms than Ir⁴⁺ ions, which facilitates the water dissociation and hydrogen desorption, eventually boosting HER. The same valence-state effect is found for Ru and Pt dopants in NiFe-LDH, implying that chemical valence state should be considered as a common factor in modulating catalytic performance.

Work Function Tuning in Hydrothermally Synthesized Vanadium-Doped MoO3 and Co3O4 Mesostructures for Energy Conversion Devices

The wide interest in developing green energy technologies stimulates the scientific community to seek, for devices, new substitute material platforms with a low environmental impact, ease of production and processing and long-term stability. The synthesis of metal oxide (MO) semiconductors fulfils these requirements and efforts are addressed towards optimizing their functional properties through the improvement of charge mobility or energy level alignment. Two MOs have rising perspectives for application in light harvesting devices, mainly for the role of charge selective layers but also as light absorbers, namely MoO3 (an electron blocking layer) and Co3O4 (a small band gap semiconductor). The need to achieve better charge transport has prompted us to explore strategies for the doping of MoO3 and Co3O4 with vanadium (V) ions that, when combined with oxygen in V2O5, produce a high work function MO. We report on subcritical hydrothermal synthesis of V-doped mesostructures of MoO3 and of Co3O4, in which a tight control of the doping is exerted by tuning the relative amounts of reactants. We accomplished a full analytical characterization of these V-doped MOs that unambiguously demonstrates the incorporation of the vanadium ions in the host material, as well as the effects on the optical properties and work function. We foresee a promising future use of these materials as charge selective materials in energy devices based on multilayer structures.

A CoV2O4 precatalyst for the oxygen evolution reaction: highlighting the importance of postmortem electrocatalyst characterization

Vanadium-doped cobalt oxide materials have emerged as a promising class of catalysts for the oxygen evolution reaction. Previous studies suggest vanadium doping in crystalline Co spinel materials tunes the electronic structure and stabilizes surface intermediates. We report a CoV2O4 material that shows good activity for the oxygen evolution reaction. However, postmortem characterization of the catalyst material shows dissolution of vanadium resulting in an amorphous CoOx material, suggesting that this vanadium-free material, and not CoV2O4, is the active catalyst. This study highlights the importance of postmortem characterization prior to mechanistic and computational analysis for this class of materials.

Growth kinetic control over MgFe2O4 to tune Fe occupancy and metal–support interactions for optimum catalytic performance

For the first time, the growth behavior with size-dependent Fe occupancies at different sites of MgFe₂O₄ was examined. Hybrid catalysts of Pt/MgFe₂O₄ with a support size of 20.6 nm exhibited an optimal performance of CO oxidation.

Metal-Organic Framework-Derived Fe-Doped Co1.11 Te2 Embedded in Nitrogen-Doped Carbon Nanotube for Water Splitting

A rational design is reported of Fe-doped cobalt telluride nanoparticles encapsulated in nitrogen-doped carbon nanotube frameworks (Fe-Co_1.11 Te₂ @NCNTF) by tellurization of Fe-etched ZIF-67 under a mixed H₂ /Ar atmosphere. Fe-doping was able to effectively modulate the electronic structure of Co_1.11 Te₂ , increase the reaction activity, and further improve the electrochemical performance. The optimized electrocatalyst exhibited superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances in an alkaline electrolyte with low overpotentials of 107 and 297 mV with a current density of 10 mA cm^-2 , in contrast to the undoped Co_1.11 Te₂ @NCNTF (165 and 360 mV, respectively). The overall water splitting performance only required a voltage of 1.61 V to drive a current density of 10 mA cm^-2 . Density function theory (DFT) calculations indicated that the Fe-doping not only afforded abundant exposed active sites but also decreased the hydrogen binding free energy. This work provided a feasible way to study non-precious-metal catalysts for an efficient overall water splitting.

Efficient Oxygen Evolution and Gas Bubble Release Achieved by a Low Gas Bubble Adhesive Iron-Nickel Vanadate Electrocatalyst

Surface chemistry is a pivotal prerequisite besides catalyst composition toward advanced water electrolysis. Here, an evident enhancement of the oxygen evolution reaction (OER) is demonstrated on a vanadate-modified iron-nickel catalyst synthesized by a successive ionic layer adsorption and reaction method, which demonstrates ultralow overpotentials of 274 and 310 mV for delivering large current densities of 100 and 400 mA cm^-2 , respectively, in 1 m KOH, where vigorous gas bubble evolution occurs. Vanadate modification augments the OER activity by i) increasing the electrochemical surface area and intrinsic activity of the active sites, ii) having an electronic interplay with Fe and Ni catalytic centers, and iii) inducing a high surface wettability and a low-gas bubble-adhesion for accelerated mass transport and gas bubble dissipation at large current densities. Ex situ and operando Raman study reveals the structural evolution of β-NiOOH and γ-FeOOH phases during the OER through vanadate-active site synergistic interactions. Operando dynamic specific resistance measurement evidences an accelerated gas bubble dissipation by a significant decrease in the variation of the interfacial resistance during the OER for the vanadate-modified surface. Achievement of a high catalytic turnover of 0.12 s^-1 suggests metallic oxo-anion modification as a versatile catalyst design strategy for advanced water oxidation.

Three-Dimensional and In Situ-Activated Spinel Oxide Nanoporous Clusters Derived from Stainless Steel for Efficient and Durable Water Oxidation

Developing cost-effective and highly efficient oxygen evolution reaction (OER) electrocatalysts based on earth-abundant elements is vital to hydrogen production from electrocatalytic water splitting. Herein, a three-dimensional and in situ-activated electrocatalyst derived from stainless steel is successfully fabricated via a two-step laser direct writing strategy. The electrocatalyst appears in the form of nanoparticle-stacked porous clusters on the multiscale stainless steel with irregular microcone arrays and microspheres, which exposes more active sites and facilitates the mass transport. Especially, the clusters undergoe a self-optimizing morphological and compositional reconfiguration induced by the leaching of Cr species under OER conditions for favorable charge transfer and enhanced intrinsic catalytic activity. As a result, the in situ-activated, Ni/Cr-doped Fe₃O₄ electrocatalyst exhibits an outstanding OER performance with a small overpotential of 262 mV to reach 10 mA cm^-2, a low Tafel slope of 35.0 mV dec^-1, and excellent long-term stability of 120 h, among the best spinel Fe-rich OER electrocatalysts. Finally, we also verify the feasibility of the affordable and efficient electrocatalyst coupled with the commercial Ni cathode in the practical water electrolysis. This work may open up a new avenue to design nanostructured metal oxides for various energy applications and beyond.