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Ruthenium Dioxide (RuO2), as one of the most promising alternatives to IrO2, suffers from the severe dissolution and overoxidation of Ru active sites during the acidic oxygen evolution reaction (OER), which hinders its practical application. Herein, the study constructs a short‐range ordered tantalum single atoms‐doped RuO2 catalyst (Ta‐RuO2) with asymmetric Ru‐O‐Ta(‐O‐Ta) active units for the enhanced acidic OER. The Ta‐RuO2 catalyst exhibits superior catalytic activity with an overpotential of 201 mV at 10 mA cm−2 and a long‐lasting stability of 280 h. Physical characterizations combined with electrochemical tests reveal that the incorporation of atomically arranged Ta atoms induces significant tensile strain, effectively optimizing the adsorption strength of oxygen‐containing intermediates by regulating the Ru d‐band center and weakening the Ru‐O covalency, thus boosting the catalytic activity. Furthermore, the formed Ru‐O‐Ta(‐O‐Ta) active local structure is well maintained during the OER process owing to the synergy of strong corrosion resistance of Ta‐O bonds and the electron transfers from Ta to Ru via oxygen bridge stabilizing the Ru sites, contributing to the enhanced stability. This study provides a novel method via incorporation of corrosion‐resistant and short‐range ordered single atoms to significantly enhance the acidic OER stability and activity of cost‐effective catalysts. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis (PEMWE) is considered a promising technology for coupling with renewable energy sources to achieve clean hydrogen production. However, constrained by the sluggish kinetics of the anodic oxygen evolution reaction (OER) and the acidic abominable environment render the grand challenges in developing the active and stable OER electrocatalyst, leading to low efficiency of PEMWE. Herein, we develop the rutile‐type IrO2 nanoparticles with abundant grain boundaries and the continuous nanostructure through the joule heating and sacrificial template method. The optimal candidate (350‐IrO2) demonstrates remarkable electrocatalytic activity and stability during the OER, presenting a promising advancement for efficient PEMWE. DFT calculations verified that grain boundaries can modulate the electronic structure of Ir sites and optimize the adsorption of oxygen intermediates, resulting in the accelerated kinetics. 350‐IrO2 affords a rapid OER process with 20 times higher mass activity (0.61 A mgIr−1) than the commercial IrO2 at 1.50 V vs. RHE. Benefiting from the reduced overpotential and the preservation of the stable rutile structure, 350‐IrO2 exhibits the stability of 200 h test at 10 mA cm−2 with only trace decay of 11.8 mV. Moreover, the assembled PEMWE with anode 350‐IrO2 catalyst outputs the current density up to 2 A cm−2 with only 1.84 V applied voltage, long‐term operation for 100 h without obvious performance degradation at 1 A cm−2. [ABSTRACT FROM AUTHOR]

Developing ruthenium‐based heterogeneous catalysts with an efficient and stable interface is essential for enhanced acidic oxygen evolution reaction (OER). Herein, we report a defect‐rich ultrathin boron nitride nanosheet support with relatively independent electron donor and acceptor sites, which serves as an electron reservoir and receiving station for RuO2, realizing the rapid supply and reception of electrons. Through precisely controlling the reaction interface, a low OER overpotential of only 180 mV (at 10 mA cm−2) and long‐term operational stability (350 h) are achieved, suggesting potential practical applications. In situ characterization and theoretical calculations have validated the existence of a localized electronic recycling between RuO2 and ultrathin BN nanosheets (BNNS). The electron‐rich Ru sites accelerate the adsorption of water molecules and the dissociation of intermediates, while the interconnection between the O‐terminal and B‐terminal edge establishes electronic back‐donation, effectively suppressing the over‐oxidation of lattice oxygen. This study provides a new perspective for constructing a stable and highly active catalytic interface. [ABSTRACT FROM AUTHOR]

RuO2 is widely used as an acidic electrocatalyst to achieve high catalytic activity, but the severe leaching and scarcity of the Ru element restrict application on a large scale. Strategies such as designing nanostructures and adjusting metals' electronic properties to regulate the adsorption of reaction intermediates can be used for the design and preparation of catalysts. Herein, we designed an acid-treated RuO2/Co3O4 nanostructure electrocatalyst with low Ru content and an intimate heterogeneous interface to disrupt the trade-off relationship between stability and activity. The resulting acid-treated RuO2/Co3O4 displayed an overpotential of 152 mV in a 0.5 M H2SO4 electrolyte, greatly exceeding that of commercial RuO2 (221 mV). Despite continuous operation for 150 h, it still exhibited good stability with a degradation rate of 0.67 mV·h–1. Multiple characterization analyses revealed that an electron transfer occurs from Ruoct to Cooct(III) sites through the mutual O atoms in acid-treated RuO2/Co3O4, which is further strengthened by the presence of oxygen vacancies. The oxygen vacancy and heterogeneous interface synergistically regulate electronic dispersion, optimize the adsorption of the oxygen intermediates (*OOH), and improve the reaction kinetics of the oxygen evolution reaction (OER). This work brings to light the significance of oxygen vacancies for modulating the electronic structure of RuO2 nanoparticles and enhancing stability on Co3O4 support, thus highlighting the use of nanostructure and interfacial engineering to achieve better acidic OER catalyst design. [ABSTRACT FROM AUTHOR]

The scale-up deployment of ruthenium (Ru)-based oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane water electrolysis (PEMWE) is greatly restricted by the poor stability. As the lattice-oxygen-mediated mechanism (LOM) has been identified as the major contributor to the fast performance degradation, impeding lattice oxygen diffusion to inhibit lattice oxygen participation is imperative, yet remains challenging due to the lack of efficient approaches. Herein, we strategically regulate the bonding nature of Ru-O towards suppressed LOM via Ru-based high-entropy oxide (HEO) construction. The lattice disorder in HEOs is believed to increase migration energy barrier of lattice oxygen. As a result, the screened Ti23Nb9Hf13W12Ru43Ox exhibits 11.7 times slower lattice oxygen diffusion rate, 84% reduction in LOM ratio, and 29 times lifespan extension compared with the state-of-the-art RuO2 catalyst. Our work opens up a feasible avenue to constructing stabilized Ru-based OER catalysts towards scalable application. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction. RuO2 is regarded as a promising alternative to IrO2 for the anode catalyst of proton exchange membrane water electrolyzers due to its superior activity and relatively lower cost compared to IrO2. However, the dissolution of Ru induced by its overoxidation under acidic oxygen evolution reaction (OER) conditions greatly hinders its durability. Herein, we developed a strategy for stabilizing RuO2 in acidic OER by the incorporation of high-valence metals with suitable ionic electronegativity. A molten salt method was employed to synthesize a series of high-valence metal-substituted RuO2 with large specific surface areas. The experimental results revealed that a high content of surface Ru4+ species promoted the OER intrinsic activity of high-valence doped RuO2. It was found that there was a linear relationship between the ratio of surface Ru4+/Ru3+ species and the ionic electronegativity of the dopant metals. By regulating the ratio of surface Ru4+/Ru3+ species, incorporating Re, with the highest ionic electronegativity, endowed Re0.1Ru0.9O2 with exceptional OER activity, exhibiting a low overpotential of 199 mV to reach 10 mA cm−2. More importantly, Re0.1Ru0.9O2 demonstrated outstanding stability at both 10 mA cm−2 (over 300 h) and 100 mA cm−2 (over 25 h). The characterization of post-stability Re0.1Ru0.9O2 revealed that Re promoted electron transfer to Ru, serving as an electron reservoir to mitigate excessive oxidation of Ru sites during the OER process and thus enhancing OER stability. We conclude that Re, with the highest ionic electronegativity, attracted a mass of electrons from Ru in the pre-catalyst and replenished electrons to Ru under the operating potential. This work spotlights an effective strategy for stabilizing cost-effective Ru-based catalysts for acidic OER. [ABSTRACT FROM AUTHOR]

Developing for highly active and stable electrocatalysts for oxygen evolution reaction (OER) is of significant importance for some renewable energy conversion and storage systems. While, the prerequisite for further optimizing the activity of electrocatalysts is whether their original composition has potential for development. Herein, we firstly managed to combine theoretical and experimental efforts to establish Ru 0.4 Sn 0.3 Ce 0.3 O 2 (RSCO) as a promising electrocatalyst for acidic OER. The X-ray absorption and density functional theory studies reveal that the local coordination environment and electronic structure of Ru sites in RSCO is optimized by the oxygen atom bridged Sn and Ce at heterogeneous interfaces, thereby resulting in a low energy barrier. In addition, the electrochemical results indicate that the activity and stability of RSCO obviously surpasses that of the RuO 2 prepared by same method as RSCO. Most encouragingly, the OER activity of RSCO can be substantially enhanced only by optimizing the calcination temperature, meaning the possibility of further improvement the intrinsic activity of such oxygen atom bridged Ru based complex by proper surface or interfacial engineering. • RSCO electrocatalyst is synthesized with low content of Ru and abundant interface sites. • Oxygen atom assist the redistribution of electron around Ru sites at heterogeneous interfaces. • Tuning the species of metal precursor and calcination temperature allows the optimization of the synergistic effect between different atoms. • The low Gibbs free energy endows RSCO electrocatalyst with great potential in acidic OER. [ABSTRACT FROM AUTHOR]

The development of efficient and stable catalysts with high mass activity is crucial for acidic oxygen evolution reaction (OER). In this study, CeO2-Ir heterojunctions supported on carbon nanotubes (CeO2-Ir/CNTs) are synthesized using a solvothermal method based on the heterostructure strategy. CeO2-Ir/CNTs demonstrate remarkable effectiveness as catalysts for acidic OER, achieving 10.0 mA cm−2 at a low overpotential of only 262.9 mV and maintaining stability over 60.0 h. Notably, despite using an Ir dosage 15.3 times lower than that of c-IrO2, CeO2-Ir/CNTs exhibit a very high mass activity (2542.3 A gIr−1@1.53 V), which is 58.8 times higher than that of c-IrO2. When applied to acidic water electrolyzes, CeO2-Ir/CNTs display a prosperous potential for application as anodic catalysts. X-ray photoelectron spectrometer (XPS) analysis reveals that the chemical environment of Ir nanoparticles (NP) can be effectively modulated through coupling with CeO2. This modulation is believed to be the key factor contributing to the excellent OER catalytic activity and stability observed in CeO2-Ir/CNTs. [ABSTRACT FROM AUTHOR]

Designing nanocomposites with heterointerface as bifunctional electrocatalysts is a potential strategy to overcome the intrinsic activity limitation of electrocatalytic water splitting in acidic media, but it remains challenging. Herein, the highly efficient RuO2/Co3O4 electrocatalyst with a uniform nanoflower structure is prepared by hydrothermal growth combined with interface engineering. Benefiting from the unique nanostructure, the migration of electrons and intermediates is optimized by the sufficient exposure of abundant micropores and defects. Moreover, the formation of strong electronic interaction at the RuO2/Co3O4 heterointerfaces boosts the electrochemical active surface area and accelerates the reaction kinetics, which effectively improve the catalytic activity and stability of the catalyst. Based on enhanced intrinsic activity and electron transfer, the as‐synthesized RuO2/Co3O4 displays impressive hydrogen evolution reaction and oxygen evolution reaction activity, which respectively require low overpotentials of 240 and 100 mV to achieve a current density of 10 mA cm−2 in 0.5 m H2SO4. As a bifunctional electrode, RuO2/Co3O4 exhibits a low operating voltage of 1.58 V at 10 mA cm−2 for overall electrochemical water splitting. This study demonstrates the importance of heterostructure engineering in providing an avenue to achieve acid‐stable bifunctional electrocatalysts for energy conversion applications. [ABSTRACT FROM AUTHOR]

Designing nanocomposites with heterointerface as bifunctional electrocatalysts is a potential strategy to overcome the intrinsic activity limitation of electrocatalytic water splitting in acidic media, but it remains challenging. Herein, the highly efficient RuO2/Co3O4 electrocatalyst with a uniform nanoflower structure is prepared by hydrothermal growth combined with interface engineering. Benefiting from the unique nanostructure, the migration of electrons and intermediates is optimized by the sufficient exposure of abundant micropores and defects. Moreover, the formation of strong electronic interaction at the RuO2/Co3O4 heterointerfaces boosts the electrochemical active surface area and accelerates the reaction kinetics, which effectively improve the catalytic activity and stability of the catalyst. Based on enhanced intrinsic activity and electron transfer, the as‐synthesized RuO2/Co3O4 displays impressive hydrogen evolution reaction and oxygen evolution reaction activity, which respectively require low overpotentials of 240 and 100 mV to achieve a current density of 10 mA cm−2 in 0.5 m H2SO4. As a bifunctional electrode, RuO2/Co3O4 exhibits a low operating voltage of 1.58 V at 10 mA cm−2 for overall electrochemical water splitting. This study demonstrates the importance of heterostructure engineering in providing an avenue to achieve acid‐stable bifunctional electrocatalysts for energy conversion applications.

Electrocatalytic water splitting is an efficient way to produce high-purity hydrogen. However, the oxygen evolution reaction (OER) exhibits sluggish kinetics, severely hindering large-scale hydrogen production. The development of OER electrocatalysts with high activity, excellent durability, and cost-effectiveness, especially under high working potential and corrosive acidic conditions, plays a crucial role in the electrochemical process. Co 3 O 4 -based materials have emerged as promising candidates for replacing noble iridium (Ir)- and ruthenium (Ru)-based materials due to their flexible electronic structure, high activity, and long-term stability toward OER in acid. In this review, the recent progress of Co 3 O 4 -based electrocatalytic materials for the acidic OER is first presented, with particular reference to the catalytic mechanism and guidelines for the design principles from both experimental and theoretical perspectives. Afterward, emerging strategies are outlined to improve the catalytic performance of Co 3 O 4 -based acidic OER catalysts, including phase engineering, component regulation with doping, composite with carbon-based materials, and multi-phase hybridization. Then, some challenges and future directions in developing high-performance Co 3 O 4 -based electrocatalysts for OER in acid are proposed. The recent progress of Co 3 O 4 -based acidic OER materials is first presented, with particular reference to the catalytic intrinsic activity and guideline for the design principles of highly efficient catalysts from both theoretical and experimental perspectives. The prospects of developing advanced Co 3 O 4 -based catalysts for OER in acid toward industrial applications are discussed. [Display omitted] • Recent trends of advanced Co 3 O 4 -based catalysts for OER in acid are reviewed. • Strategies to improve the catalytic performance of Co 3 O 4 -based acidic OER catalysts are summarized. • The design principles of advanced Co 3 O 4 -based acidic OER catalysts are proposed. • Developing high-performance Co 3 O 4 -based acidic OER catalysts towards industrial application is discussed. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) suffers from sluggish kinetics even on the benchmark RuO2 catalyst, due to the complex four sequential proton‐coupled electron transfer steps. Severe electrochemical oxidation and dissolution issues also make RuO2 fail as an alternative to highly expensive iridium‐based OER catalysts applied in proton exchange membrane water electrolysis. Herein, an acid‐stable W18O49‐δ matrix‐confined Ru solid solution oxide is developed with considerably reduced Ru loadings beyond commercial RuO2, to enhance the acidic OER kinetics and extend the long‐term durability simultaneously by incorporating Brønsted acid sites. The representative Ru0.6W17.4O49‐δ with 3D urchin‐like morphology achieves an excellent catalytic stability with ultra‐slow degradation rate and a high mass activity of 27 110 A g−1Ru @ 1.53 V versus RHE in 0.1 m HClO4 electrolyte, which is ≈10.8 times higher than that of commercial RuO2. The enhanced electron transfer from W to Ru during the OER process prevents the over‐oxidation of surface Ru sites extending the long‐term stability, while the incorporated Ru‐Obri‐W Brønsted acid sites accelerate the deprotonation step by promoting the mobility of proton from the oxo‐intermediate to the neighboring Obri sites, thus boosting the acidic OER kinetics. [ABSTRACT FROM AUTHOR]

Here,nonprecious high‐entropy chalcogenide glasses (N‐HECGs) consisting of Co, Fe, Ni, Mo, W, and Te are demonstrated in a first demonstration of acidic oxygen evolution reaction (OER). N‐HECGs electrocatalysts with high activity and stability are synthesized using a hierarchical hybrid approach based on a combination of electrochemical deposition and tellurization process. The as‐prepared CoFeNiMoWTe N‐HECGs electrocatalysts exhibit an amorphous, porous structure of arrayed nanosheets with abundant active sites and the increased valence states of metal cations due to the incorporated non‐metallic Te, enabling the enhancement of glass forming ability and the valence states of metal elements. Thanks to the combination of their unique geometrical and chemical structure, as well as high configuration entropy nature and high corrosion‐resistance ability, the resultant CoFeNiMoWTe N‐HECGs exhibit excellent acidic OER catalytic performance with a superior overpotential of 373 mV and outstanding stability of 100 h at the current density of 10 mA cm−2 in 0.5 m H2SO4. Moreover, the CoFeNiMoWTe‐based proton exchange membrane water electrolyzer is demonstrated to require a cell voltage of 1.81 V at 70 °C to obtain the practically high current density of 1 A cm−2, and exhibits remarkably long‐term stability for 100 h with small potential degradation of only 30 mV. [ABSTRACT FROM AUTHOR]

Water electrolysis is one of the most efficient and environmentally benign methods for the hydrogen production using renewable but intermittent power sources. Proton exchange membrane （PEM） water electrolyzers hold great significance for renewable energy storage and conversion. The acidic oxygen evolution reaction （OER） is one of the main roadblocks that hinder the practical application of PEM water electrolyzers. Highly active, cost-effective, and durable electrocatalysts are indispensable for lowering the high kinetic barrier of OER to achieve boosted reaction kinetics. To date, a wide spectrum of advanced electrocatalysts has been designed and synthesized for enhanced acidic OER performance, though Ir and Ru based nanostructures still represent the state-of-the-art catalysts. In this Progress Report, recent research progress on novel electrocatalysts with acidic OER performance is reviewed. First, the basic understanding of acidic OER, including the reaction mechanism, is discussed. On this basis, the design and synthesis progress of noble metal acidic OER electrocatalysts are reviewed for noble metal Ir, Ru single atoms, alloys, oxides, etc. Finally, the future development of acidic OER is prospected from the aspects of reaction mechanism research and more efficient electrocatalyst design. [ABSTRACT FROM AUTHOR]

Developing acid‐stable electrocatalysts with high activity for the oxygen evolution reaction (OER) is of paramount importance for many energy‐related technologies. This work reports that ultrathin nitrogen‐doped carbon coated oxygen‐vacancy (Vo·) rich RuO2 nanoparticles on carbon nanotubes (CNTs) (NC@Vo·‐RuO2/CNTs‐350), synthesized through the controlled calcination in air, is an efficient acid‐stable electrocatalyst for the OER. It only needs an overpotential of 170.0 mV to drive 10.0 mA cm−2 and shows excellent stability with no distinguishable activity loss observed for >900 h. Its mass activity is >110 times higher than the commercial RuO2. In particular, an electrolyzer assembled with this catalyst shows a record‐low cell voltage of 1.45 V to deliver 10.0 mA cm−2 and exhibits a low performance drop for >1000 h. The NC@Vo·‐RuO2/CNTs‐350 also shows super‐high catalytic activities and excellent stabilities for OER in neutral and alkaline media. DFT calculations indicate that its high catalytic activity mainly arises from the strong electronic coupling between RuO2 and NC/CNTs, which increases the oxidation state and catalytic activity of Ru at the active site and improves the stabilities of lattice oxygen and surface Ru during the OER processes. The presence of Vo· can strengthen the electronic coupling between RuO2 and NC/CNTs. [ABSTRACT FROM AUTHOR]

Proton exchange membrane water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction. RuO2 is regarded as a promising alternative to IrO2 for the anode catalyst of proton exchange membrane water electrolyzers due to its superior activity and relatively lower cost compared to IrO2. However, the dissolution of Ru induced by its overoxidation under acidic oxygen evolution reaction (OER) conditions greatly hinders its durability. Herein, we developed a strategy for stabilizing RuO2 in acidic OER by the incorporation of high-valence metals with suitable ionic electronegativity. A molten salt method was employed to synthesize a series of high-valence metal-substituted RuO2 with large specific surface areas. The experimental results revealed that a high content of surface Ru4+ species promoted the OER intrinsic activity of high-valence doped RuO2. It was found that there was a linear relationship between the ratio of surface Ru4+/Ru3+ species and the ionic electronegativity of the dopant metals. By regulating the ratio of surface Ru4+/Ru3+ species, incorporating Re, with the highest ionic electronegativity, endowed Re0.1Ru0.9O2 with exceptional OER activity, exhibiting a low overpotential of 199 mV to reach 10 mA cm−2. More importantly, Re0.1Ru0.9O2 demonstrated outstanding stability at both 10 mA cm−2 (over 300 h) and 100 mA cm−2 (over 25 h). The characterization of post-stability Re0.1Ru0.9O2 revealed that Re promoted electron transfer to Ru, serving as an electron reservoir to mitigate excessive oxidation of Ru sites during the OER process and thus enhancing OER stability. We conclude that Re, with the highest ionic electronegativity, attracted a mass of electrons from Ru in the pre-catalyst and replenished electrons to Ru under the operating potential. This work spotlights an effective strategy for stabilizing cost-effective Ru-based catalysts for acidic OER.

Designing an efficient and durable electrocatalyst for the sluggish anodic oxygen evolution reaction (OER) has been the primary goal of using proton exchange membrane electrolyzer owing to the highly acidic and oxidative environment at the anode. In this work, it is reported that high-valence manganese drives the strong anchoring of the Ir species on the manganese dioxide (MnO2) matrix via the formation of an Mn-O-Ir coordination structure through a hydrothermal-redox reaction. The iridium (Ir)-atom-array array is firmly anchored on the Mn-O-Ir coordination structure, endowing the catalyst with excellent OER activity and stability in an acidic environment. Ir-MnO2(160)-CC shows an ultralow overpotential of 181 mV atj =10 mA cm-2 and maintains long-term stability of 180 h in acidic media with negligible decay, superior to most reported electrocatalysts. In contrast, when reacting with low-valence MnO2, Ir species tend to aggregate into IrOx nanoparticles, leading to poor OER stability. Density functional theory (DFT) calculations further reveal that the formation of the Mn-O-Ir coordination structure can optimize the adsorption strength of *OOH intermediates, thus boosting the acidic OER activity and stability. [ABSTRACT FROM AUTHOR]

Construction of strong interactions between oxides is compelling for modulating the active sites towards acidic oxygen evolution reaction (OER) electrocatalysts. Here, a solid solution oxide electrocatalyst constructed by alloying of IrO 2 and CrO 2 (labeled as Ir 0.3 Cr 0.7 O 2) is reported with an overpotential of 255 mV at a current density of 10 mA cm−2 for OER in 0.5 M H 2 SO 4 solution, which is much lower than that of the state-of-the-art IrO 2 (357 mV). The mass activity at 1.50 V vs. RHE is 47 folds than that of IrO 2 , and it can maintain such OER stability for more than 200 h. Detailed analysis concludes that the organic ligands-assisted synthesis of Ir 0.3 Cr 0.7 O 2 can enlarge the surface-active area and provide more active sites for water oxidation, while the leaching of Cr and its strong interaction with Ir sites resulting in the formation of high chemical state oxides of Ir with superior activity for acidic OER. It is found that the significantly increasement of oxygen vacancies content during electrochemical test together with the two points mentioned above jointly promote the water oxidation activities of Ir 0.3 Cr 0.7 O 2 electrocatalyst in acidic media. Ir 0.3 Cr 0.7 O 2 solid solution oxides with nanosphere packing morphology exhibit outstanding electrocatalytic activity and ultralong stability (over 200 h) for efficient oxygen evolution in acidic media. [Display omitted] • Ir 0.3 Cr 0.7 O 2 solid solution oxide catalyst is rationally designed and synthesized. • Ir 0.3 Cr 0.7 O 2 exhibits stable and remarkable behaviors for acidic water oxidation. • Ir 0.3 Cr 0.7 O 2 realizes η 10 at 255 mV and OER stability within 200 h in 0.5 M H 2 SO 4. [ABSTRACT FROM AUTHOR]

The development of inexpensive, active, and robust nonprecious metal electrocatalysts toward the oxygen evolution reaction (OER) in acid media is highly imperative for renewable energy conversion techniques, yet greatly challenging. Inspired by the vanadium‐containing oxygen‐fixing enzymes in haloperoxidase in nature, herein, the atomically dispersed V sites anchored on N‐doped multichannel carbon nanofibers (designated as V@NMCNFs hereafter) are rationally designed as high‐efficiency electrocatalyst for the acidic OER. Substantial characterizations validate that the local coordination microenvironment of the V site is identified as an asymmetrical penta‐coordinated V‐O2N3 moiety with axial VO coordination, which is further theoretically substantiated as an energetically favorable configuration with a reduced OER energy barrier by the density functional theory calculations. Consequently, the well‐dispersed isolated V‐O2N3 sites with exceptional intrinsic activity and unique nano‐architecture furnish the well‐designed V@NMCNFs with distinguished OER performance in a 0.5 m H2SO4 electrolyte, as reflected by the ultralow overpotential of 196 mV at 10 mA cm−2 and remarkable long‐term electrochemical durability, representing one of the most impressive nonprecious OER electrocatalysts to date. The synthetic methodology for SAC preparation and concept of electronic regulation proposed in this work offer perspectives to aid the design of other functional SAC systems with regulated coordination environments for efficient electrocatalysis. [ABSTRACT FROM AUTHOR]

Abstract Designing an efficient and durable electrocatalyst for the sluggish anodic oxygen evolution reaction (OER) has been the primary goal of using proton exchange membrane electrolyzer owing to the highly acidic and oxidative environment at the anode. In this work, it is reported that high‐valence manganese drives the strong anchoring of the Ir species on the manganese dioxide (MnO2) matrix via the formation of an Mn–O–Ir coordination structure through a hydrothermal‐redox reaction. The iridium (Ir)‐atom‐array array is firmly anchored on the Mn–O–Ir coordination structure, endowing the catalyst with excellent OER activity and stability in an acidic environment. Ir‐MnO2(160)‐CC shows an ultralow overpotential of 181 mV at j = 10 mA cm−2 and maintains long‐term stability of 180 h in acidic media with negligible decay, superior to most reported electrocatalysts. In contrast, when reacting with low‐valence MnO2, Ir species tend to aggregate into IrOx nanoparticles, leading to poor OER stability. Density functional theory (DFT) calculations further reveal that the formation of the Mn–O–Ir coordination structure can optimize the adsorption strength of *OOH intermediates, thus boosting the acidic OER activity and stability.

Electricity-driven proton exchange membrane water electrolyzers are a promising technology to produce dihydrogen gas (H2). However, this technology is limited by the anodic oxygen evolution reaction that controls the overall operation efficiency, since only few electrocatalysts are efficient under the strongly acidic and oxidative conditions. Accordingly, there is a need for electrocatalysts with high activity, high stability, and low cost for the reaction of acidic oxygen evolution. Here, we review electrocatalysis using the acidic oxygen evolution reaction. We discuss two mechanisms of the oxygen evolution reaction: the adsorbate evolution mechanism and the lattice oxygen mechanism. We then summarize strategies to improve the performance of electrocatalysts by active site engineering, electron distribution optimization, interaction modulation, vacancy engineering, and lattice strain regulation. Challenges include the understanding of mechanisms of the oxygen evolution reaction, the operation durability at industrial currents, the flow reactor design of proton exchange membrane water electrolyzers, the alternative reactions, the development of nonprecious metal-based electrocatalysts, and large-scale synthetic approaches of electrocatalysts. Finally, precautions for electrochemical tests are proposed. [ABSTRACT FROM AUTHOR]

Although iridium-based electrocatalysts are commonly regarded as the sole stable operating acidic oxygen evolution reaction (OER) catalysts in proton-exchange membrane water electrolysis (PEMWE) devices, their exorbitant cost and scarcity severely restrict their widespread application. Herein, we introduce a promising alternative to iridium: zinc-doped ruthenium dioxide (TE-Zn/RuO 2 ), which exhibits remarkable and enduring activity for acidic OER. In situ characterizations elucidate that the dynamic cycling of zinc dopants serves as both electron acceptors and donors, facilitating the activation of Ru sites at low overpotentials while thwarting peroxidation at high overpotentials, thus concurrently achieving heightened activity and robust stability. Additionally, the incorporation of zinc induces weakened Ru-O covalency, thereby stabling *OOH intermediates and instigating a sustained adsorbate evolution mechanism, dramatically stabilizing the RuO 2 lattice. Importantly, the TE-Zn/RuO 2 catalyst as an anode exhibits good stability over 300 h at a water-splitting current of 500 mA cm -2 in the PEMWE device, underscoring its considerable promise for practical applications.

The high overpotential and unsatisfactory stability of RuO 2 -based catalysts seriously hinder their application in acidic oxygen evolution reaction (OER). Herein, a Ru@RuO 2 core/shell catalyst doped with atomically dispersed Mn species, denoted as Ru@Mn-RuO 2 , is reported, which is prepared by a facile one-pot method. Detailed structural characterizations confirm that Mn is homogeneously and atomically distributed in RuO 2 shell, which causes lattice contraction of RuO 2 . The as-prepared Ru@Mn-RuO 2 exhibits a very low overpotential of 190 mV at the current density of 10 mA cm -2 and an excellent stability of 360 h, far surpassing the control samples Ru@RuO 2 without atomically dispersed Mn dopants and home-made RuO 2 nanoparticles without metallic Ru core. With the further assistance of density functional theory calculations, the enhanced OER activity of Ru@Mn-RuO 2 is attributed to multiple synergistic effects, including the MnO x -Ru (oxide shell) synergy, MnO x -Ru (metal core) synergy, and the Ru (core)-RuO 2 (shell) synergy. Besides, the atomically dispersed Mn doping can increase the formation energy of soluble Ru cations, thus leading to the excellent stability of the Ru@Mn-RuO 2 catalyst. This work shines light on the design of electrocatalysts with multiple synergistic effects towards efficient acid water splitting., (© 2024 Wiley‐VCH GmbH.)

The development of efficient and durable electrocatalysts for the acidic oxygen evolution reaction (OER) is essential for advancing renewable hydrogen energy technology. However, the slow deprotonation kinetics of oxo-intermediates, involving the four proton-coupled electron steps, hinder the acidic OER progress. Herein, a RuTiO x solid solution electrocatalyst is investigated, which features bridged oxygen (O bri ) sites that act as proton acceptors, accelerating the deprotonation of oxo-intermediates. Electrochemical tests, infrared spectroscopy, and density functional theory results reveal that the moderate proton adsorption energy on O bri sites facilitates fast deprotonation kinetics through the adsorbate evolution mechanism. This process effectively prevents the over-oxidation and deactivation of Ru sites caused by the lattice oxygen mechanism. Consequently, RuTiO x shows a low overpotential of 198 mV at 10 mA cm -2 geo and performance exceeding 1400 h at 50 mA cm -2 geo with negligible deactivation. These insights into the OER mechanism and the structure-function relationship are crucial for the advancement of catalytic systems., (© 2024 Wiley‐VCH GmbH.)

Proton exchange membrane water electrolysers promise to usher in a new era of clean energy, but they remain a formidable obstacle in designing active and durable electrocatalysts for the acidic oxygen evolution reaction (OER). In this study, a protonated iridium oxide embedded with single-atom dispersed ruthenium atoms (H 3.8 Ir 1- x Ru x O 4 ) that demonstrates exceptional activity and stability in acidic water oxidation is introduced. The single Ru dopants favorably induce localized oxygen vacancies in the Ir─O lattice, synergistically strengthening the adsorption of OOH* intermediates and enhancing the intrinsic OER activity. In addition, the preferential oxidation of Ru and the electronegativity of the oxygen vacancies significantly stabilize the Ir─O active sites, improving the OER stability. Consequently, the H 3.8 Ir 1─ x Ru x O 4 catalyst shows an overpotential of 255 mV at 10 mA cm -2 and displays exceptional catalytic endurance in acidic electrolytes, surpassing 1100 h, representing a remarkable one-order-of-magnitude increase in stability compared to that of pristine H 3.8 IrO 4 . A proton exchange membrane electrolyser utilizing the H 3.8 Ir 1- x Ru x O 4 catalyst as an anode exhibits stable performance for more than 1280 h under a high current density of 2 A cm -2 ., (© 2024 Wiley‐VCH GmbH.)

[Display omitted] • A heterogeneous interface between RuO 2 and MnO 2 was constructed in situ. • The OER performance of RuO 2 /MnO 2 catalysts is crystal form dependent. • RuO 2 and MnO 2 -γ form a Ru-O-Mn structure at the interface. • RuO 2 /MnO 2 -γ promotes *OOH formation while following the AEM pathway. • The prepared RuO 2 /MnO 2 -γ exhibits high OER performance under acidic conditions. Oxygen evolution reaction (OER) of ruthenium dioxide (RuO 2) in acidic media usually faces the problem of poor stability caused by excessive oxidation and dissolution. To address this issue, the present work prepares heterojunction catalysts by introducing RuO 2 into manganese dioxide (MnO 2) with different crystal types. The obtained RuO 2 /MnO 2 -γ exhibited excellent acid OER activity (η = 220 mV at 10 mA·cm−2) and could operate stably for 80 h. Mainly because the Ru-O-Mn bonds generated at the RuO 2 /MnO 2 -γ heterointerface fine-tune the charge environment of RuO 2. The formation of this particular interface can enable MnO 2 -γ to produce more reactive oxygen defects, which promotes the transfer of electrons. At the same time, it can also minimize the peroxidation reaction and structural collapse of RuO 2 under acidic conditions, thereby suppressing the Lattice Oxygen Mechanism (LOM) to improve stability. Density functional theory (DFT) results show that RuO 2 /MnO 2 -γ lowers the energy barrier for the *O to *OOH conversion. This research findings provides a new perspective for elucidating the role of the regulated electronic environment arising from heterogeneous interfaces. [ABSTRACT FROM AUTHOR]

• Acid-resistant transition metals (Mn, Sn, and Sb) modify Co 3 O 4 's electrocatalytic properties. • Mn integrates smoothly into Co 3 O 4 ; Sn and Sb modify surface chemistry, altering the Co2+/Co3+ ratio. • The Sn-Co 3 O 4 variant shows compelling OER activity and durability. • Proven durability in PEMWE cells, maintaining performance at 100 mA/cm2 and 80 °C for over 120 h. Spinel cobalt oxide (Co3O4) is a promising, cost-effective, and precious group metal (PGM)-free alternative to iridium-based catalysts for the oxygen evolution reaction (OER) in polymer electrolyte membrane water electrolyzers (PEMWE). However, its application is limited by poor stability under acidic conditions. This study tackles this issue by modifying Co 3 O 4 with acid-resistant elements including tin (Sn), antimony (Sb), and manganese (Mn). Advanced characterization methods were employed to decipher the structure-property relationships of the hydrothermally synthesized catalyst materials. The modified Co 3 O 4 catalysts were thoroughly tested for their OER performance, where the tin-modified Sn-Co 3 O 4 exhibited the highest activity and stability in aqueous acidic electrolytes. Successful integration in a practical PEM water electrolysis cell is demonstrated, delivering a current density over 100 mA/cm2. Our results show notable improvements in both the performance and durability of the Co 3 O 4 spinel catalysts, which is attributed to the promoting effect of the stable Sn-oxide promoters. This study outlines the groundbreaking exploration into enhancing spinel cobalt oxide's electrocatalytic properties through the strategic addition of stable transition metals. Utilizing hydrothermal synthesis, the nuanced effects of metal incorporation on structural and catalytic behaviors are unveiled. Our study particularly focuses on the elemental integration's impact on grain size, surface chemistry, and the oxygen evolution reaction, leading to improved performance in proton exchange membrane water electrolysis cells. [Display omitted] [ABSTRACT FROM AUTHOR]

With the increasing production of renewable energy and concomitant depletion of fossil resources, the demand for efficient water splitting electrocatalysts continues to grow. Iridium (Ir) and iridium oxides (IrOx) are currently the most promising candidates for an efficient oxygen evolution reaction (OER) in acidic medium, which remains the bottleneck in water electrolysis. Yet, the extremely high costs for Ir hamper a widespread production of hydrogen (H2) on an industrial scale. Herein, the authors report a concept for the synthesis of electrode coatings with template‐controlled mesoporosity surface‐modified with highly active Ir species. The improved utilization of noble metal species relies on the synthesis of soft‐templated metal oxide supports and a subsequent shape‐conformal deposition of Ir species via atomic layer deposition (ALD) at two different reaction temperatures. The study reveals that a minimum Ir content in the mesoporous titania‐based support is mandatory to provide a sufficient electrical bulk conductivity. After ALD, a significantly enhanced OER activity results in dependency of the ALD cycle number and temperature. The most active developed electrocatalyst film achieves an outstanding mass‐specific activity of 2622 mA mgIr–1 at 1.60 VRHE in a rotating‐disc electrode (RDE) setup at 25 °C using 0.5 m H2SO4 as a supporting electrolyte. [ABSTRACT FROM AUTHOR]

Constructing the pore structures in amorphous metal oxide nanosheets can enhance their electrocatalytic performance by efficiently increasing specific surface areas and facilitating mass transport in electrocatalysis. However, the accurate synthesis for porous amorphous metal oxide nanosheets remains a challenge. Herein, a facile nitrate-assisted oxidation strategy is reported for synthesizing amorphous mesoporous iridium oxide nanomeshes (a-m IrO x NMs) with a pore size of ∼4 nm. X-ray absorption characterizations indicate that a-m IrO x NMs possess stretched Ir─O bonds and weaker Ir-O interaction compared with commercial IrO 2 . Combining thermogravimetric-fourier transform infrared spectroscopy with differential scanning calorimetry measurements, it is demonstrated that sodium nitrate, acting as an oxidizing agent, is conducive to the formation of amorphous nanosheets, while the NO 2 produced by the in situ decomposition of nitrates facilitates the generation of pores within the nanomeshes. As an anode electrocatalyst in proton exchange membrane water electrolyzer, a-m IrO x NMs exhibit superior performance, maintaining a cell voltage of 1.67 V at 1 A cm -2 for 120 h without obvious decay with a low loading (0.4 mg catalyst cm -2 ). Furthermore, the nitrate-assisted method is demonstrated to be a general approach to prepare various amorphous metal oxide nanomeshes, including amorphous RhO x , TiO x , ZrO x , AlO x , and HfO x nanomeshes., (© 2024 Wiley‐VCH GmbH.)

[Display omitted] • Main electrocatalysts for acidic oxygen evolution reaction (OER) are discussed. • Design strategies of electrocatalysts for enhancing OER performance in acidic conditions are summarized. • Current important issues and other viable strategies in facilitating the development of acidic OER catalysts are proposed. Water electrolysis is presently recognized as one of the most effective and ecological technologies for producing sustainable hydrogen energy. Compared with alkaline electrolyzers, the acidic electrolyzers with proton exchange membranes (PEMs) hold much greater advantages, including high efficiency, few side reactions, and effective suppression of gas crossover. However, the development and application of PEMs water electrolysis is limited by the high theoretical voltage and slow reaction kinetics. Additionally, the fact that many OER catalysts dissolve and corrode rapidly in harsh acidic environments, resulting in reduced catalytic activity. There is an urgent need to find acid-resistant and high activity catalysts to meet the demands of industrial applications of PEMs water electrolysis. In this review, the general mechanism of OER, different kinds of acidic OER catalysts, the design and synthesis strategies are firstly summarized and discussed. The pertinent foundational researches on OER catalyst synthesis and the correlation between catalytic activity and coordination environment are particularly emphasized to provide a detailed comprehension for catalysis at the atomic level. Then, current important issues and viable strategies are proposed to promote the development of acidic OER catalysts. [ABSTRACT FROM AUTHOR]

The oxygen evolution reaction (OER) is the efficiency-determining half-reaction process of high-demand, electricity-driven water splitting due to its sluggish four-electron transfer reaction. Tremendous effects on developing OER catalysts with high activity and strong acid-tolerance at high oxidation potentials have been made for proton-conducting polymer electrolyte membrane water electrolysis (PEMWE), which is one of the most promising future hydrogen-fuel-generating technologies. This review presents recent progress in understanding OER mechanisms in PEMWE, including the adsorbate evolution mechanism (AEM) and the lattice-oxygen-mediated mechanism (LOM). We further summarize the latest strategies to improve catalytic performance, such as surface/interface modification, catalytic site coordination construction, and electronic structure regulation of catalytic centers. Finally, challenges and prospective solutions for improving OER performance are proposed. [ABSTRACT FROM AUTHOR]

The unsatisfactory oxygen evolution reaction (OER) activity of IrO 2 has intensively raised the cost and energy consumption of hydrogen generation from proton exchange membrane water electrolyzers. Here, the acidic OER activity of the rutile IrO 2 is significantly enhanced by the incorporation of trivalent metals (e.g., Gd, Nd, and Pr) to increase the Ir-O covalency, while the high-valence (pentavalent or higher) metal incorporation decreases the Ir-O covalency resulting in worse OER activity. Experimental and theoretical analyses indicate that enhanced Ir-O covalency activates lattice oxygen and triggers lattice oxygen-mediated mechanism to enhance OER kinetics, which is verified by the finding of a linear relationship between the natural logarithm of intrinsic activity and Ir-O covalency described by charge transfer energy. By regulating the Ir-O covalency, the obtained Gd-IrO 2-δ merely needs 260 mV of overpotential to reach 10 mA cm -2 and shows impressive stability during a 200-h test in 0.5 м H 2 SO 4 . This work provides an effective strategy for significantly enhancing the OER activity of the widely used IrO 2 electrocatalysts through the rational regulation of Ir-O covalency., (© 2023 Wiley‐VCH GmbH.)

• Oxygen evolution (OER) in acid is important for electrochemical energy conversion. • Current advances in OER catalysis by mixed metal oxides are summarized. • Ionic-electronic conducting mixed metal oxides are promising electrocatalysts. • Instability induced by metal leaching is a challenge for oxide catalyzed acid OER. • Future directions in developing robust mixed metal oxides for acid OER are devised. Shaping the energy landscape through development of more efficient electrochemical energy conversion and storage devices requires significant advancements in the catalysis of key electrochemical processes involving oxygen. This is especially the case for the oxygen evolution reaction (OER), which is largely challenged by the cost-ineffectiveness of the best performing electrocatalysts (i.e., Ru, Ir), along with their limited stability under acidic conditions. This presents a roadblock in the development of robust acid-based polymer exchange membrane electrochemical systems, currently the most advanced technologies for electrochemical energy conversion. Approaches such as dilution of Ru/Ir into flexible mixed metal oxide frameworks have been used as alternative strategies in designing robust OER electrocatalysts. Herein, we discuss the state of research in this area and detail the effect of the composition and structure of mixed metal oxides on their acidic OER activity and stability. Future directions for developing mixed metal oxide electrocatalysts suitable for acidic electrochemical environments are devised. [ABSTRACT FROM AUTHOR]

The development of cost-effective catalysts for oxygen evolution reaction (OER) in acidic media is of paramount importance. This work reports that Sr-doped solid solution structural ultrafine IrMnO 2 nanoparticles (NPs) (≈1.56 nm) on the carbon nanotubes (Sr-IrMnO 2 /CNTs) are efficient catalysts for the acidic OER. Even with the Ir use dosage 3.5 times lower than that of the commercial IrO 2 , the Sr-IrMnO 2 /CNTs only need an overpotential of 236.0 mV to drive 10.0 mA cm -2 and show outstanding stability for >400.0 h. Its Ir mass activity is 39.6 times higher than that of the IrO 2 at 1.53 V. The solid solution and Sr-doping structure of Sr-IrMnO 2 are the main origin of the high catalytic activity and excellent stability of the Sr-IrMnO 2 /CNTs. The density function theory calculations indicate that the solid solution structure can promote strong electronic coupling between Ir and Mn, lowering the energy barrier of the OER rate-determining step. The Sr-doping can enhance the stability of Ir against the chemical corrosion and demetallation. Water electrolyzers and proton exchange membrane water electrolyzers assembled with the Sr-IrMnO 2 /CNTs show superb performance and excellent durability in the acid media., (© 2023 Wiley‐VCH GmbH.)

The development of highly active and acid-stable electrocatalysts for oxygen evolution reaction (OER) is of great significance for water electrolysis technology. Herein, a highly efficient molybdenum-doped mesoporous ruthenium dioxide sphere (Mo-RuO 2 ) catalyst is fabricated by a facile impregnation and post-calcination method using mesoporous carbon spheres to template the mesostructure. The optimal Mo 0.15 -RuO 2 catalyst with Mo doping amount of 15 mol.% exhibits a significantly low overpotential of 147 mV at 10 mA cm -2 , a small Tafel slope of 38 mV decade -1 , and enhanced electrochemical stability in acidic electrolyte, far superior to the commercial RuO 2 catalyst. The experimental results and theoretical analysis reveal that the remarkable electrocatalytic performance can be attributed to the large surface area of the mesoporous spherical structure, the structural robustness of the interconnected mesoporous framework, and the change in the electronic structure of Ru active sites induced by Mo doping. These excellent advantages make Mo-doped mesoporous RuO 2 spheres a promising catalyst for highly efficient electrocatalytic OER in acidic media., (© 2023 Wiley-VCH GmbH.)

Designing robust bifunctional catalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction in all-pH conditions for overall water splitting (OWS) is an effective way to achieve sustainable development. Herein, a composite Ru-VO 2 containing Ru-doped VO 2 and Ru nanoparticles (NPs) is synthesized, and it shows a high OWS performance in full-pH range due to their synergist effect. In particular, the OER mass activities of Ru-VO 2 at 1.53 V (vs RHE) in acidic, alkaline, and PBS solutions are ≈65, 36, and 235 times of commercial RuO 2 in the same conditions. The "Ru-VO 2 || Ru-VO 2 " two-electrode electrolyzer only needs a voltage of 1.515 V (at 10 mA cm -2 ) in acidic water splitting, which can operate stably for 125 h at 10 mA cm -2 without significant voltage decay. In situ Raman spectra and in situ differential electrochemical mass spectrometry prove that the OER of Ru-VO 2 in acid follows the adsorption evolution mechanism. Density functional theory calculations further reveal the synergistic effect between Ru NP and Ru-doped VO 2 , which breaks the hydrogen bond network formed by *OH adsorbed on the Ru single-atom site, and thereby significantly enhances the OER activity. This work provides new insights into the design of novel bifunctional pH-universal catalysts for OWS., (© 2023 Wiley-VCH GmbH.)

The oxygen evolution reaction (OER) is the efficiency-determining half-reaction process of high-demand, electricity-driven water splitting due to its sluggish four-electron transfer reaction. Tremendous effects on developing OER catalysts with high activity and strong acid-tolerance at high oxidation potentials have been made for proton-conducting polymer electrolyte membrane water electrolysis (PEMWE), which is one of the most promising future hydrogen-fuel-generating technologies. This review presents recent progress in understanding OER mechanisms in PEMWE, including the adsorbate evolution mechanism (AEM) and the lattice-oxygen-mediated mechanism (LOM). We further summarize the latest strategies to improve catalytic performance, such as surface/interface modification, catalytic site coordination construction, and electronic structure regulation of catalytic centers. Finally, challenges and prospective solutions for improving OER performance are proposed.

The p-n heterojunction Co 3 O 4 /RuO 2 anchored on carbon matrix (Co 3 O 4 /RuO 2 -C) is constructed for acidic water oxidation, wherein the electron could diffuse from RuO 2 to Co 3 O 4 to pre-modify electronic structure of RuO 2 , facilitating redox of Ru sites and dominating adsorbate evolution mechanism of oxygen evolution to endow Co 3 O 4 /RuO 2 -C with excellent activity in water oxidation without trade-off stability. [Display omitted] • A p-n heterojunction of Co 3 O 4 /RuO 2 anchored on carbon matrix is facilely developed for improved acidic oxygen evolution reaction. • The experimental and theoretical results indicate electron flow could occur from RuO 2 to Co 3 O 4 , achieving pre-modifying electronic structure of RuO 2. • In situ total reflection infrared (ATR-IR) can validate adsorbate evolution mechanism of oxygen generation for heterojunction of Co 3 O 4 /RuO 2. • In situ Raman test suggest facile evolution of Ru active sites after formation of p-n heterojunction of Co 3 O 4 /RuO 2. Development of Ru-based electrocatalysts for acidic oxygen evolution reaction without a trade-off between activity and durability remains challenging. Herein, we constructed Co 3 O 4 /RuO 2 heterojunctions anchored on carbon (Co 3 O 4 /RuO 2 -C) with a low Ru loading (2.74 wt%), in which strong coupled p-n junctions facilitated electron transfer from RuO 2 to Co 3 O 4. The Co 3 O 4 /RuO 2 -C demonstrated a low overpotential of 170 mV at 10 mA cm−2 and long-term stability in 0.1 M HClO 4 due to its unique structure. The origin of its high performance in acidic OER was revealed by the combination of in-situ attenuated total reflection infrared and Raman tests. Concretely, oxygen generation for Co 3 O 4 /RuO 2 -C was dominated by the adsorbate evolution mechanism, and the introduction of Co 3 O 4 facilitated the redox of RuO 2 , generating active sites for OER. Theoretical calculations further substantiated that the Co 3 O 4 /RuO 2 heterojunctions possessed lower energy barriers for OER. This work provides a compelling synthesis route for effective and stable electrocatalysts for acidic OER. [ABSTRACT FROM AUTHOR]

Achieving the oxide path mechanism (OPM) through bimetallic catalysis is a promising approach for developing highly active and stable electrocatalysts for the acidic oxygen evolution reaction (OER). However, optimizing atomic-level and local ligand structures to enhance the synergistic interaction of bimetallic active sites still remains a challenge. Here, through the introduction of tetrahedral Co (Co tet) cationic defects and selectively substituting atomic Ru on the octahedral Co (Co cot) sites in Co 3 O 4 , we present an effective strategy to significantly enhance the orbital hybridization and the synergistic interaction of bimetallic active sites. Experimental and theoretical calculations show that this approach facilitates thermodynamic mechanism for diatomic oxygen formation. Cationic defects are utilized as electron acceptors, facilitating the transfer of electrons from Ru to Co, enhancing the overlap in the density of states, and optimizing the d -band center of Ru and Co. Therefore, the orbital hybridization and synergistic effect of bimetallic active sites are improved. Remarkably, the catalyst with a minimal Ru mass loading of around 45.5 μg∙cm−2, featuring a low overpotential of 150 mV and a minimal potential decay rate of just 0.35 mV∙h−1 at 10 mA∙cm−2. Our work offers an effective strategy to enhance the synergistic interaction of bimetallic sites, and the mechanism of cationic defects improve the acidic OER performance of bimetallic sites has been thoroughly investigated, which is expected to contribute to clean energy production. [Display omitted] • Cation defects enhance the orbital hybridization between Ru and Co, increasing the density of states near the Fermi level and boosting synergy. • Cationic defects accelerate oxygen release and slow surface reconstruction in the OPM pathways, enhancing OER performance in acidic conditions. • The Ru-CovO4 catalyst shows a low overpotential of 150 mV at 10 mA∙cm-2 and a minimal decay rate of 0.35 mV∙h-1, highlighting its superior stability. [ABSTRACT FROM AUTHOR]

Heterogeneous oxides with multiple interfaces provide significant advantages in electrocatalytic activity and stability. However, controlling the local structure of these oxides is challenging. In this work, unique heterojunctions are demonstrated based on two oxide types, which are formed via pyrolysis of a ruthenocene metal-organic framework (Ru-MOF) at specific temperatures. The resulted Ru-MOF-400 exhibits excellent electrocatalytic activity, with an overpotential of 190 mV at a current density of 10 mA cm -2 in 0.1 m HClO 4 , and a mass activity of 2557 A g Ru -1 , three orders of magnitude higher than commercial RuO 2 inhibits the disolution of Ru. Operando electrochemical investigations and density functional theory results reveal that the Ru-MOF-400 undergo asymmetric dual-active site oxide path mechanism during the acidic oxygen evolution reaction process, which is predominantly mediated by the asymmetric Ru─Co dual active site present at the interfaces between Co 2 inhibits the disolution of Ru. Operando electrochemical investigations and density functional theory results reveal that the Ru-MOF-400 undergo asymmetric dual-active site oxide path mechanism during the acidic oxygen evolution reaction process, which is predominantly mediated by the asymmetric Ru─Co dual active site present at the interfaces between Co 3 O 4 and CoRuO x ., (© 2023 Wiley-VCH GmbH.)

Noble metal-based electrocatalysts are crucial for efficient acidic water oxidation to develop green hydrogen energy. However, traditional noble metal catalysts loaded on inactive substrates show limited intrinsic catalytic activity, and their large sizes have compromised the atom efficiency of these noble metals. Herein, IrO x nanoclusters with sizes below 2 nm, displaying high atom-utilization efficiency of Ir species, were supported on a redox-active MnO 2 nanosubstrate (IrO x /MnO 2 ) with different phases (α-MnO 2 , δ-MnO 2 , and ε-MnO 2 ) to explore the optimal combination. Electrochemical measurements showed that IrO x /ε-MnO 2 had excellent OER performance with a low overpotential of 225 mV at 10 mA cm -2 in 0.5 M H 2 SO 4 , superior to its counterpart, IrO x /α-MnO 2 (242 mV) and IrO x /δ-MnO 2 (286 mV). Moreover, it also delivered robust stability with no obvious change in operating potential at 10 mA cm -2 during 50 h of continuous operation. Combining the XPS results and Bader charge analysis, we demonstrated that the strong metal-support interactions of IrO x /ε-MnO 2 could effectively regulate the electronic structures of the active Ir atoms and stabilize IrO x nanoclusters on supports to suppress their detachment, resulting in significantly enhanced catalytic activity and stability for acidic OER. DFT calculations further supported that the enhanced catalytic OER performance of IrO x /ε-MnO 2 could be ascribed to the appropriate strength of interactions between the active Ir sites and the reaction intermediates of the potential-determining step (*O and *OOH) regulated by the redox-active substrates.

The acidic oxygen evolution reaction (OER) strongly depends on the spin-related electronic configuration of metal sites at catalyst surfaces, which can directly affect the structural stability and catalytic activity. Recently, layered two-dimensional IrO 2 nanostructures with typical metallic characteristic have been successfully realized. However, the electronic state coupling between magnetic dopants and structural strain still need be understood as they can effectively enhance the catalytic activity. Herein, a series of magnetic dopants are intentionally implanted into the IrO 2 monolayers with different structural deformations in order to trigger the spin-related electronic reconfigurations for regulating the orbital interactions and charge transfer with reactants. Accordingly, the acidic OER performance is obviously enhanced because doped magnetic dopants with half-filled 3d orbitals can donate some valence electrons to the intermediates more easily, leading to a lower activation energy. This work provides a new insight into designing catalysts for acidic OER by particular electronic state coupling. • Magnetic dopants are implanted into IrO2 monolayers with different structural deformations for enhancing OER performance. • Spin-related electronic reconfigurations are triggered to regulate orbital interaction and charge transfer with reactants. • The doped magnetic dopants with half-filled 3d orbitals can lead to lower activation energy. [ABSTRACT FROM AUTHOR]

We report Ca 2- x IrO 4 nanocrystals exhibit record stability of 300 h continuous operation and high iridium mass activity (248 A g Ir -1 at 1.5 V RHE ) that is about 62 times that of benchmark IrO 2 . Lattice-resolution images and surface-sensitive spectroscopies demonstrate the Ir-rich surface layer (evolved from one-dimensional connected edge-sharing [IrO 6 ] octahedrons) with high relative content of Ir 5+ sites, which is responsible for the high activity and long-term stability. Combining operando infrared spectroscopy with X-ray absorption spectroscopy, we report the first direct observation of key intermediates absorbing at 946 cm -1 (Ir 6+ ═O site) and absorbing at 870 cm -1 (Ir 6+ OO- site) on iridium-based oxides electrocatalysts, and further discover the Ir 6+ ═O and Ir 6+ OO- intermediates are stable even just from 1.3 V RHE . Density functional theory calculations indicate the catalytic activity of Ca 2 IrO 4 is enhanced remarkably after surface Ca leaching, and suggest IrOO- and Ir═O intermediates can be stabilized on positive charged active sites of Ir-rich surface layer.

• Morphology engineering of iridium electrodes with pillar-structured ti substrates is developed. • Surface treatments of Ti substrates with different acids and etching times are optimized. • The electrode morphology, interfacial resistance and catalytic activity are investigated. • The pillar-structured electrodes exhibit enhanced oxygen evolution reaction performances. Nowadays, Ti is the well-chosen anode substrate material for proton exchange membrane electrolyzer cells (PEMECs) and modifications of the substrate surfaces are essential for the fabrication of highly efficient electrodes. Herein, we introduce the morphology engineering of Ir/Ti electrodes with different acid treatments of hydrochloric acid (HCl) and oxalic acid (OA), and the comparative benefits of these two acid treatment methods are studied from the aspects of their impacts on the morphology, interfacial contact resistance (ICR), and oxygen evolution reaction (OER) performances of resultant electrodes. Notably, compared to the flat surface from OA treatment, Ti substrates with the pillar structure could be successfully achieved via HCl etching. The HCl and the oxalic acid (OA) treatments would reduce the interfacial contact resistance (ICR) to 15.2% and 5.5% of the pristine Ti substrate at 1.38 MPa, respectively. By iridium electrodeposition on Ti substrates, Ir/Ti electrodes with different catalyst loadings are fabricated. With similar low-loadings of about 0.05 mg Ir cm−2, an Ir/Ti electrode with HCl treated substrate exhibits a lower overpotential of ∼283 mV at 10 mA cm−2 current density than 305 mV from OA treatment, due to the boosted reaction areas from HCl treatment. [Display omitted] [ABSTRACT FROM AUTHOR]

• RuCo@NG/N-GNs catalyst were fabricated via one-step annealing strategy. • RuCo@NG/N-GNs holds unique structure and plenty of active sites. • RuCo@NG/N-GNs exhibits a top-level acidic OER and alkaline HER performance. • DFT calculations reveals the critical role of Co in enhancing HER and OER. There remain certain critical issues for hydrogen production in both proton exchange membrane (PEM) and alkaline water electrolysis, the former of which faces daunting challenges in the development of high-activity and high-stability catalysts for acidic oxygen evolution reaction (OER), while the latter one strongly demands enhancing the sluggish kinetic of alkaline cathodic hydrogen evolution reaction (HER). Herein, we reported a facile one-step annealing strategy for fabricating hybrid electrocatalyst with RuCo alloy nanoparticles encapsulated by N-doped graphite loading on N-doped graphite nanosheets (RuCo@NG/N-GNs), which manifests highly desirable electrocatalytic features toward both acidic OER and alkaline HER with impressively high activity, fast kinetic and excellent stability. The optimized RuCo@NG/N-GNs requires a quite low overpotential of 209 mV at 10 mA cm−2 for acidic OER with a quite low Tafel slope of 56 mV dec−1, and demands a striking low overpotentials of 9 mV at 10 mA cm−2 toward alkaline HER with a Tafel slope of as low as 30 mV dec−1. Experiments combined with density functional theory (DFT) calculations reveal that the critical role of Co element in enhancing the HER and OER performance. For HER, the surface Co improves the oxophilicity of catalyst that indirectly aids the proton donation in alkaline; and for OER, surface Co itself acts as active sites to directly aid the reaction. The relatively low-cost electrocatalyst in this work is expected to inspire more innovative researches to step forward the large-scale commercial practice feasibility of PEM and alkaline water splitting. [ABSTRACT FROM AUTHOR]

The theoretical simulation indicates that the strong coupling between the Ru atoms and neighboring C atoms in GDY makes the Ru to be a unique electron-mediating-vehicle (EMV) for fast reversible redox-switching endowing the catalyst with excellent catalytic performances. Our experimental study is fully in accordance with the theoretical simulation, which shows that the high-activity and ultra-high selectivity of the Ru atomic catalyst. For example, Ru/GDY can deliver 10 mA cm−2 at a low overpotential of 44 mV and exhibits a very small Tafel slope of 30 mV dec−1, comparable to commercial Pt/C, in hydrogen evolution reaction (HER) in acidic conditions. We also found that Ru/GDY has higher catalytic activity and stability for oxygen evolution reaction (OER) than RuO 2 in 0.5 M H 2 SO 4 solutions. Image 1 • Atomic catalysts consisting of GDY and isolated Ru atoms were synthesized for efficient water splitting in acidic media. • The determined electron and chemical structure of the catalyst brings a unique electron-mediating-vehicle (EMV) mechanism. • Ru/GDY exhibits higher mass activity and turnover frequency than commercial Pt/C and RuO 2 in HER and OER, respectively. [ABSTRACT FROM AUTHOR]

Acidic proton exchange membrane water electrolysis is a prospective energy conversion technology for future hydrogen production. However, its wide application is limited by the excessive dependence of oxygen evolution reaction on precious metals at anode. To address this issue, herein, we report a class of IrM (M = Ni, Co, Fe) catalysts with diluted Ir content fabricated via a eutectic-directed self-templating strategy. Manipulated by the eutectic reaction and dealloying inheritance effect, the IrM catalysts show a unique network structure composed of intertwining nanoporous nanowires. The catalytic activities of IrM nanowires show a transition-metal-dependent feature, among which IrNi delivers the best activity with an exceptionally low overpotential to drive 10 mA cm -2 (283 mV) and a high mass activity at 1.53 V vs reversible hydrogen electrode (0.732 A mg -1 ). Such performance represents a major leap forward compared to that of commercial IrO 2 and most of state-of-the-art Ir-based acidic catalysts toward oxygen evolution reaction. First-principles calculations indicate that the 3d transition-metal-dependent catalytic activity of IrM electrocatalysts is related to ligand effect, wherein the negative shift of Ir d-band center after alloying can effectively weaken the adsorption of reaction intermediates.