Low-Iridium Catalysts with High Atom Utilization for Acidic Oxygen Evolution Reaction: Design Strategies, Controllable Synthesis, and Mechanisms

Mn incorporated RuO2 nanocrystals as an efficient and stable bifunctional electrocatalyst for oxygen evolution reaction and hydrogen evolution reaction in acid and alkaline

Three-dimensional hierarchically porous iridium oxide-nitrogen doped carbon hybrid: An efficient bifunctional catalyst for oxygen evolution and hydrogen evolution reaction in acid

To develop stable electrocatalysts for the oxygen evolution reaction (OER) in acid, it is essential to understand the degradation mechanisms on the catalyst surface. In this work, we compare the OER performance of two Ni–Ir bimetallic oxides (Li2Ir1–xNixO3−δ with x = 0.25 and 0.75) in sulfuric acid. A dynamic structure transformation is observed on LINO-0.25 due to fast delithiation from the layered structure. The resulting catalyst demonstrates ∼10 times enhanced electrochemical activity but 70% less Ir dissolution compared to that of LINO-0.75 oxide. We propose that creating dynamic Li+/H+ exchange channels in structure may be beneficial for achieving a stable OER performance in acid.

Design strategies of electrocatalysts for acidic oxygen evolution reaction

ABSTRACTProton exchange membrane water electrolyzers (PEMWEs) are positioned as a transformative technology for renewable energy conversion and storage systems. The acidic oxygen evolution reaction (AOER), serving as the pivotal half-reaction governing overall efficiency, operational stability and system cost in water electrolysis, has become a focal point of contemporary electrochemical research. In this Review, we comprehensively summarize the recent advancements in both noble metal-based (Ir and Ru) and non-noble-metal-based (Mn and Co) heterogeneous electrocatalysts (HEs) for the AOER. The analysis commences with fundamental AOER mechanisms and the key factors that influence them, elucidating critical structure–activity relationships essential for rational catalyst engineering. Subsequently, we systematically evaluate state-of-the-art design strategies and corresponding breakthroughs in catalyst development, followed by a forward-looking perspective on the emergence and application of AI for science in the AOER. This review provides valuable guidance for the design of next-generation HEs for the AOER, ultimately aiming to bridge the gap between laboratory-scale achievements and industrial implementation of PEMWE technologies.

Ruthenium dioxide has attracted extensive attention as a promising catalyst for oxygen evolution reaction in acid. However, the over-oxidation of RuO2 into soluble H2RuO5 species results in a poor durability, which hinders the practical application of RuO2 in proton exchange membrane water electrolysis. Here, we report a confinement strategy by enriching a high local concentration of in-situ formed H2RuO5 species, which can effectively suppress the RuO2 degradation by shifting the redox equilibrium away from the RuO2 over-oxidation, greatly boosting its durability during acidic oxygen evolution. Therefore, the confined RuO2 catalyst can continuously operate at 10 mA cm–2 for over 400 h with negligible attenuation, and has a 14.8 times higher stability number than the unconfined RuO2 catalyst. An electrolyzer cell using the confined RuO2 catalyst as anode displays a notable durability of 300 h at 500 mA cm–2 and at 60 °C. This work demonstrates a promising design strategy for durable oxygen evolution reaction catalysts in acid via confinement engineering.

Hydrogen generated by proton exchange membrane (PEM) electrolyzer holds a promising potential to complement the traditional energy structure and achieve the global target of carbon neutrality for its efficient, clean, and sustainable nature. The acidic oxygen evolution reaction (OER), owing to its sluggish kinetic process, remains a bottleneck that dominates the efficiency of overall water splitting. Over the past few decades, tremendous efforts have been devoted to exploring OER activity, whereas most show unsatisfying stability to meet the demand for industrial application of PEM electrolyzer. In this review, systematic considerations of the origin and strategies based on OER stability challenges are focused on. Intrinsic deactivation of the material and the extrinsic balance of plant-induced destabilization are summarized. Accordingly, rational strategies for catalyst design including doping and leaching, support effect, coordination effect, strain engineering, phase and facet engineering are discussed for their contribution to the promoted OER stability. Moreover, advanced in situ/operando characterization techniques are put forward to shed light on the OER pathways as well as the structural evolution of the OER catalyst, giving insight into the deactivation mechanisms. Finally, outlooks toward future efforts on the development of long-term and practical electrocatalysts for the PEM electrolyzer are provided.

Electrochemical water splitting (oxidation) leading to the oxygen evolution at anode and hydrogen generation at cathode is a topic of growing scientific and technological interest. The reaction provides not only means for producing oxygen but, more importantly, for generation of highly pure hydrogen, a carrier for storing renewable energy and further utilization in low-temperature fuel cells. Among important issues are choice of the catalytic material, its morphology and operating conditions including temperature, electrolyte, pH etc. In some cases of electrolysis cells, at cathode, the hydrogen evolution could be accompanied by CO2-reduction (to simple organic molecules), regardless of water oxidation, at anode.The suitability of polynuclear mixed-valence inorganic materials (e.g. polyoxometallates, infinite metal oxides, cyanometallates) for the preparation of thin electrocatalytic films on electrode surfaces has been recognized in recent years. Among such systems, Prussian Blue (iron hexacyanoferrate) and the metal-substituted (e.g. with Co, Ni or Ru) analogues known as transition metal cyanometallates have received considerable attention owing to their physicochemical stability, well-defined redox transitions, counter-ion-sorption selectivity and catalytic electroactivity. In the present work, we explore Prussian-Blue-like cobalt(II,III) hexacyanoferrate(II,III) together with ruthenium oxide/cyanoruthenate, a mixed-valence polynuclear ruthenium oxide structure cross-lined with cyanides. While cobalt hexacyanoferrate has already been demonstrated to exhibit activity toward electrooxidation of water, the oxocyanoruthenium system is known as highly specific electrocatalyst during oxidations.The mixed, or multi-layered, cyanometallates of cobalt, ruthenium and iron (with and without nickel square-planar cross-linking ions) were fabricated through electrodeposition in the appropriate mixtures for modification. Special attention was paid to their morphological and structural properties. Electrochemical measurements were performed using cyclic voltammetry, chronoamperometry and chronocoulometry. The systems’ structural modifications as well as their effect on the electroactivity of the catalyst towards the oxygen evolution reaction in acid and neutral media were addressed. It is noteworthy that some of the hybrid cobalt-ruthenium hexacyanoferrate compositions showed remarkable catalytic ability towards the oxygen evolution reaction in acid electrolyte. In other words, co-electrodeposition of the cyanide-linked ruthenium-oxo species was used to promote the oxygen evolution on the cobalt hexacyanoferrates. The enhanced catalytic activities of the as-synthesized electrodes should also be attributed to such features as high population of hydroxyl groups and high Broensted acidity (due to presence of Ru-oxo sites) and related fast electron transfers coupled to unimpeded proton displacements. The possibility of metal-metal interactions between nanosized metals (Co and Ru) cannot be excluded.Acknowledgements: This work was supported by the National Science Center (Poland) under Opus Project (2018/29/B/ST5/02627).

Green hydrogen production from renewable energy can help overcome difficult energy challenges worldwide. It can help decarbonize hard-to-abate sectors such as steel, chemicals, and ammonia fertilizer. Polymer Electrolyte Membrane (PEM) water electrolyzer serves as a promising technology when coupled with the fluctuating renewable energies for hydrogen production, with the advantages of fast response, dynamic operation, and excellent overload capacity. However, the only technically feasible anode catalysts for PEM are built on scarce iridium and require more than 40 years of annual production for 1 TW-scale. The scarce metal iridium has become a bottleneck limiting the scale development of PEM water electrolysis technology. Therefore, identifying earth-abundant catalysts with high activity and acid tolerance is essential to realizing large-scale hydrogen production via water electrolysis. Various 3d transition metals have been investigated as potential OER catalysts. In 2019, we reported how manganese oxide shows exceptional stability among earth-abundant materials for oxygen evolution reaction (OER) in acid. At the time, non-precious metal catalysts had difficulty maintaining activity for more than a week at 10 mA cm-2. In comparison, manganese oxide (γ-MnO2) was able to electrolyze water for over 11 months at 10 mA cm-2. This was made possible by identifying a stable potential window for γ-MnO2 in which the OER can be catalyzed efficiently while simultaneously suppressing deactivation pathways. After that, a binary spinel oxide catalyst (Co2MnO4) was synthesized by mixing stable manganese with active cobalt using a thermal decomposition method. Cobalt oxides were shown to be active for the OER but unstable in acid. By incorporating Mn into the Co3O4 spinel lattice, the lifetime was extended by two orders of magnitude while maintaining the activity. The water electrolysis with Co2MnO4 in acid can be sustained over 1500 hours at 200 mA cm-2. The activation barrier of the obtained spinel Co2MnO4 is comparable to state-of-the-art iridium oxides, which are reported to have activation energies of 25-30 kJ mol-1 in acidic conditions. The catalyst dissolution was experimentally analyzed by spectroscopy methods. It is clarified that the tetrahedral Co is the preferable dissolution site and the dissolution rate is suppressed in Co2MnO4 compared to Co3O4, resulting in outstanding stability. The active working time of Co2MnO4 as a function of current density for the OER reaction and other earth-abundant electrocatalysts reported in the literature were summarized. The marked improvement of the activity and stability in acid makes cobalt manganese spinel materials an intriguing candidate for non-noble metal water electrolysis. Acknowledgments: This work was supported by the New Energy and Industrial Technology Development Organization (NEDO). Figure caption: Long-term stability of Co2MnO4 during the OER in acid. a, Time dependence of the electrochemical potential necessary to perform OER at 100, 200, 500 and 1,000 mA cm-2 geo in H2SO4 (pH 1) and H3PO4 (pH 1), respectively. The stabilities of Co3O4 and γ-MnO2 in H2SO4 (pH 1) are shown for comparison. All the experiments were performed at 25 °C using an FTO substrate except for curve IX, for which a Pt/Ti mesh was used. b, A comparison of the stability of Co2MnO4 with Co3O4 and other Earth-abundant OER catalysts reported in the literature12-28 (Please refer Nat Catal 5, 109–118 (2022)) (upwards and downwards triangles represent lifetime and operation time, respectively). The measurements were performed under acidic conditions. Data points with roman numerals (I to XI) correspond to curves I to XI in a. Diagonal lines indicate the total amount of charge transferred before deactivation. Only studies that report stability at pH < 3 were included in the literature survey. Figure 1

Proton-exchange membrane (PEM) water electrolyzers generate “green hydrogen” from water and electricity; however, acidic oxygen evolution reaction (OER) electrocatalysts with high activity, extended durability, and lower costs are needed. Degradation of the OER electrocatalyst occurs particularly at low catalyst loadings which are needed to reduce costs, and understanding factors affecting degradation in OER electrocatalysts can enable the development of improved catalysts. We have explored how metal substituents influence OER activity and degradation in acidic Ir and Ru-containing OER catalysts.1-3 We have recently explored how titanium substitution into rutile RuO2 affects OER activity and metal dissolution using accelerated durability tests.1,2Exposure to highly oxidative potentials where oxygen evolution and metal dissolution occur results in surface reconstruction and changes to the active catalytic sites and OER activity. We determined that OER-specific activity changes with cycling, and there are significant differences between RuO2 and Ru0.8Ti0.2O2. While the OER-specific activity of RuO2 initially increased and then decreased, the OER-specific activity of Ru0.8Ti0.2O2 increases and then remains stable with further cycling. Ru0.8Ti0.2O2 showed a 19 times lower Ru dissolution rate than RuO2. Scanning transmission electron microscopy analysis supports that repeated cycling under OER conditions results in surface reconstruction for RuO2 and Ru0.8Ti0.2O2. RuO2 particles form a disordered surface (~1-2 nm thick) after cycling. Electron energy loss spectroscopy analysis supports that after cycling, Ru-O bonding within the surface is altered compared to the pristine material. Our work furthers understanding of metal substituents and surface reconstruction affects OER catalytic activity and degradation, which can lead to the development of improved OER electrocatalysts. References Ospina-Acevedo, F.; Godínez-Salomón, J.F.; Naymik, Z.G.; Matthews, K.C.; Warner, J.H.; Rhodes, C.P.; Balbuena, P.B. Impacts of Surface Reconstruction and Metal Dissolution on Ru1-xTixO2 Acidic Oxygen Evolution Electrocatalysts, Journal of Physical Chemistry C 2025,129, 3595–3613. DOI: 10.1021/acs.jpcc.4c08119.Godinez-Salomon, J. F.; Ospina-Acevedo, F.; Albiter, L. A.; Bailey, K. O.; Naymik, Z. G.; Mendoza-Cruz, R.; Balbuena, P. B.; Rhodes, C. P. Titanium Substitution Effects on the Structure, Activity, and Stability of Nanoscale Ruthenium Oxide Oxygen Evolution Electrocatalysts: Experimental and Computational Study. ACS Appl. Nano Mater. 2022, 5 (8), 11752–11775. DOI: 10.1021/acsanm.2c02760.Godínez-Salomón, F.; Albiter, L.; Alia, S.; Pivovar, B.; Forero, L. C.; Balbuena, P.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Rhodes, C. P. Self-Supported Hydrous Iridium-Nickel Oxide Two-dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catal. 2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171

Acidic oxygen evolution reaction (OER) electrocatalysts that have high activity, extended durability, and lower costs are needed to further the development of proton-exchange membrane (PEM) electrolyzers. Within acidic OER catalysts, stability remains a critically important but significantly less studied factor relative to activity. Our work involves investigating relationships between structure, activity, and stability within bimetallic acidic OER electrocatalysts. Bimetallic catalysts that interact iridium or ruthenium with non-noble metals provide an approach to lower the amount of noble metal and increase the OER activity and stability. Non-noble metals have different electronegativities and atomic radii compared to iridium and ruthenium which alters the surface atomic and electronic structure and influences both OER activity and metal dissolution. Our prior work showed that the inclusion of nickel or cobalt within iridium-metal two-dimensional nanoframes resulted in differences in the surface structure that significantly changed the OER activity and electrochemical degradation.1,2 Bimetallic structures can undergo very different degradation processes compared to monometallic structures, as shown by our prior study.1 Our recent work has explored the effects of interacting non-noble metals within ruthenium oxide on the structure, OER activity and stability. Nanostructured bimetallic oxides were synthesized using solution-phase chemistry and through utilizing various temperature/atmosphere treatments. The synthesis and processing conditions significantly affected the resulting material’s structure and properties. The materials’ composition, morphology and structure are probed using energy dispersive X-ray spectroscopy, scanning electron microscopy, nitrogen physisorption, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Rotating disk electrode measurements are used to evaluate the electrochemical oxygen evolution activity and stability of the bimetallic oxides which were compared to baseline OER catalysts. Metal dissolution that occurs during accelerated durability testing is evaluated using inductively coupled mass spectroscopy measurements. Our recent efforts towards understanding the relationships between structure, activity, and stability within nanostructured bimetallic oxides/hydroxides will be presented. References Ying, Y.; Godínez-Salomón, J.F.; Moreno, A.; Lartundo-Rojas, L.; Meyer, B.; Damin, C.A.; Rhodes, C.P. Hydrous Cobalt-Iridium Oxide Two-Dimensional Nanoframes: Insights into Activity and Stability of Bimetallic Acidic Oxygen Evolution Electrocatalysts. Nanoscale Advances 2021, 3, 1976-1996. DOI: 10.1039/D0NA00912A Godínez-Salomón, F.; Albiter, L.; Alia, S.M.; Pivovar, B.S.; Camacho-Forero, L.E.; Balbuena, P.B.; Mendoza-Cruz, R.; Arellano-Jimenez, M.J.; Rhodes, C.P. Self-Supported Hydrous Iridium-Nickel Oxide Two-dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catalysis 2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171

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.

Bifunctional oxygen electrocatalysts that facilitate the acidic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the same electrode are critical components of unitized regenerative fuel cells (URFCs) and metal-air batteries. Obtaining bifunctional oxygen catalysts that simultaneously provide high ORR and OER activity, high stability, and lower precious metal content remains a significant challenge. Our recent work has explored bimetallic two-dimensional (2D) nanoframes as an approach to obtain carbon-free, unsupported nanostructures and demonstrated nickel-platinum and nickel-iridium 2D nanoframes function as high activity, separate ORR and OER catalysts respectively.1,2 To obtain high activity bifunctional oxygen catalysts, we investigated the combination of NiPt and CoIr 2D nanoframes. Bimetallic 2D nanoframes were prepared by microwave-assisted synthesis of noble metal-decorated transition metal hydroxide nanosheets followed by thermal reduction and chemical leaching steps. The 2D nanoframes utilize noble metal (Pt,Ir)-transition metal (Ni, Co) interactions to alter surface electronic structure, and the unsupported nanostructure provides a carbon-free matrix with three-dimensional accessibility to the catalytically active sites. Electrochemical testing using a rotating disk electrode configuration showed the two-component 2D nanoframe bifunctional oxygen electrocatalysts have higher ORR mass activity, OER mass activity, and round-trip efficiency compared with baseline Pt-IrO2 catalysts. Accelerated durability testing consisting of repeated voltage cycles over ORR/OER potential ranges showed that the 2D nanoframe catalysts exhibit similar ORR stability and improved OER stability compared with Pt-IrO2. The ability to combine highly catalytically active surfaces within a carbon-free 3D nanoarchitecture provides the opportunity to design bifunctional catalysts with improved activity and stability. References Godinez-Salomon, F.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Jose-Yacaman, M.; Rhodes, C. P., Metallic Two-Dimensional Nanoframes: Unsupported Hierarchical Nickel-Platinum Alloy Nanoarchitectures with Enhanced Electrochemical Oxygen Reduction Activity and Stability. ACS Appl. Mater. Interfaces 2017, 9, 18660-18674. DOI: 10.1021/acsami.7b00043Godínez-Salomón, F.; Albiter, L.; Alia, S. M.; Pivovar, B. S.; Camacho-Forero, L. E.; Balbuena, P. B.; Mendoza-Cruz, R.; Arellano-Jimenez, M. J.; Rhodes, C. P., Self-Supported Hydrous Iridium–Nickel Oxide Two-Dimensional Nanoframes for High Activity Oxygen Evolution Electrocatalysts. ACS Catal. 2018, 8, 10498-10520. DOI: 10.1021/acscatal.8b02171

ConspectusThe acidic oxygen evolution reaction (OER) is a critical component in industrial hydrogen production via proton exchange membrane water electrolysis (PEMWE). However, under the harsh operating conditions of strong acid and high potential, catalysts often reach high oxidation states to achieve high catalytic activity, which concomitantly accelerates the dissolution of active components and leads to structural degradation, making it challenging to simultaneously attain both high activity and long-term stability. Therefore, developing more precise strategies to regulate acidic OER catalysts to balance activity and stability is essential for advancing PEMWE technology.Notably, charge effects play a crucial role in regulating catalytic performance. This dependence arises not only from the intrinsic electronic structure of the catalysts but also from the dynamic generation, redistribution, and migration of charge during the reaction. This is particularly evident in the acidic OER, where under sustained high-potential conditions, active sites undergo continuous valence-state evolution, dynamic adsorption and desorption of intermediates, and both the interfacial double layer and the local coordination environment are subject to real-time change. In such a dynamic regime, design strategies based solely on static electronic structures or equilibrium properties often fail to predict or control catalytic behavior under practical operating conditions. Consequently, the systematic understanding and regulation of dynamic charge-state evolution is an essential step for balancing activity and stability in acidic OER.In this account, we focus on the dynamic regulation of charge states during operation and illustrate its central role in governing both the activity and stability of the acidic OER. First, we provide an overview and analysis of the fundamental characteristics of charge effects during the reaction, including: (i) the tunability of operational charge states, which enables adaptive response to electronic demands; (ii) the directionality of reaction-induced charge distribution, which governs the evolution of reaction pathways and local environments; (iii) the sustainability of charge-transferring and buffering capacity, which underpins long-term structural and performance stability. Then, based on our recent research advances in this field, we systematically outline the strategies for modulating these dynamic charge behaviors across multiple scales through active-site engineering, support engineering, and surface engineering. Furthermore, we summarize how in situ characterization, electrochemical analysis, and theoretical calculations are jointly employed to probe charge state evolution, and to correlate it with reaction pathway selection and stability. Finally, we discuss the limitations and emerging opportunities in dynamic charge regulation concerning in situ mechanism elucidation, cross-scale integration, and material system expansion. This account provides insights for designing acidic OER catalysts with charge evolution tailored to PEMWE operating conditions.

Climate change has become an urgent issue due to the high carbon emission from various industrial sectors. As a result, achieving carbon neutrality has become a priority for society. Hydrogen is widely used in various industries and stands out as a promising zero-carbon energy carrier. However, most hydrogen is currently produced from steam reforming of natural gas, which is unsustainable due to its consumption of fossil fuel and the enormous amount of COx and NOx by products released. Water electrolysis presents an attractive alternative for clean hydrogen production when coupled with renewable electricity. In recent years, the proton exchange membrane water electrolyzer (PEMWE) has received significant attention due to its ability to produce hydrogen at high rate, high efficiency, and high purity. The current bottleneck of PEMWE technology comes from its reliance on pricey Ru or Ir-based catalysts with limited durability. Thus, finding a low-cost catalyst with high activity and stability for the acidic oxygen evolution reaction (OER) on the anode is crucial for the next generation PEMWE products.Co3O4, as an alternative to Ru and Ir-based catalysts, has attracted much attention due to its low cost, good activity, and acid tolerance. A significant amount of effort has been devoted to further improving the performance of Co3O4 and related spinel oxides, in order to reach the superior performance of noble-metal-based catalysts1. However, the maintenance of both high activity and acid corrosion resistivity has remained challenging. These two factors are closely related to the OER reaction mechanism, and direct oxo coupling (DOC) has been proposed as an ideal mechanism that optimizes both activity and stability2. Nevertheless, the DOC mechanism requires tight control of lattice parameters and metal site distances3,4, consequently non-noble-metal-based spinel oxide structures that enable acidic OER via the DOC mechanism have not been reported.In this work, we present a facile method of hydrothermal synthesis that produces aggregated needle-like spinel NiCo2O4 nanostructures. In 0.5M H2SO4, the NiCo2O4 nanostructure exhibits remarkable activity and record-high durability for acidic OER. In-situ x-ray absorption spectroscopy revealed a higher stability during acidic OER catalysis of the Co and Ni coordination environment in NiCo2O4 compared to its less stable Co3O4 counterpart. This observation indicates the formation of fewer oxygen vacancies on NiCo2O4 under reactive potential, avoiding the critical structural deformation that would impair catalyst durability. Furthermore, we conducted density functional theory calculations to confirm the decreased OER overpotential arising from replacement of Co with Ni in octahedral lattice sites and to learn the preferred reaction pathway for DOC.In conclusion, this research presents NiCo2O4 as an acidic OER catalyst with superior activity and stability. This investigation into NiCo2O4 provides insights into the design of anode catalysts for PEMWE, advancing toward sustainable hydrogen production with high yield and low cost.References Yang, X.; Li, H.; Lu, A.-Y.; Min, S.; Idriss, Z.; Hedhili, M. N.; Huang, K.-W.; Idriss, H.; Li, L.-J., Highly acid-durable carbon coated Co3O4 nanoarrays as efficient oxygen evolution electrocatalysts. Nano Energy 2016, 25, 42-50.Wang, L.-P.; Van Voorhis, T., Direct-Coupling O2 Bond Forming a Pathway in Cobalt Oxide Water Oxidation Catalysts. The Journal of Physical Chemistry Letters 2011, 2 (17), 2200-2204.Fang, Y.-H.; Liu, Z.-P., Mechanism and Tafel Lines of Electro-Oxidation of Water to Oxygen on RuO2(110). Journal of the American Chemical Society 2010, 132 (51), 18214-18222.Lin, C.; Li, J.-L.; Li, X.; Yang, S.; Luo, W.; Zhang, Y.; Kim, S.-H.; Kim, D.-H.; Shinde, S. S.; Li, Y.-F.; Liu, Z.-P.; Jiang, Z.; Lee, J.-H., In-situ reconstructed Ru atom array on α-MnO2 with enhanced performance for acidic water oxidation. Nature Catalysis 2021, 4 (12), 1012-1023.