Electrocatalytic Oxygen Evolution Over Co3 − xMnxO4: Correlating Structure with Reactivity

Abstract

Water electrolysis, driven by renewable energy, offers a sustainable route for alternate energy. The oxygen evolution reaction, the key anodic reaction of water electrolysis is a complex reaction due to its four-electron process involving multiple oxygen intermediates. Mixed-valence spinel oxides, such as Co₃O₄ and Mn₃O₄ have attracted significant attention as anodic catalyst owing to the low cost, earth abundance, low toxicity, and multiple oxidation states. Despite extensive studies on activity descriptors and the mechanistic aspects of the oxygen evolution reaction over these spinel oxides, a comprehensive understanding of the structure–reactivity correlation remains underexplored. While Co₃O₄ adopts a cubic structure, Mn₃O₄ crystallizes in a tetragonal form due to Jahn–Teller distortion, making intermediate Co_3 − xMn_xO₄ solid solutions ideal for studying structure–reactivity correlations. Phase-pure Co₂MnO₄ (cubic) and CoMn₂O₄ (tetragonal) were synthesized via combustion synthesis. Despite similar porosity and surface area, CoMn₂O₄ showed higher electrochemical surface area, better charge transfer, and more oxygen vacancies. Mn-rich CoMn₂O₄ exhibited superior OER activity, requiring just 260 mV overpotential at 10 mA cm^− 2, alongside a low Tafel slope of 55 mV dec^− 1 and activation energy of 10 kJ mol^− 1. Surface analysis confirmed the formation of \(\:{\text{C}\text{o}}_{\text{o}\text{h}}^{3+}\)_–OOH intermediates, highlighting the role of optimal doping and structural tuning in enhancing oxygen evolution reaction performance and stability.