Atomically Incorporated Iridium in Cobalt Manganese Oxide for Highly Stable Acidic Oxygen Evolution Reaction

Abstract Developing cost-effective and durable oxygen evolution reaction (OER) catalysts is pivotal for advancing proton exchange membrane water electrolyzers toward large-scale hydrogen production. Cobalt manganese spinel oxides (i.e., Co2MnO4) have emerged as promising nonprecious alternatives owing to their tunable composition and intrinsic OER activity. However, their deployment in acidic media is severely constrained by Mn dissolution and sluggish reaction kinetics governed by adsorbate evolution mechanism (AEM). Herein, we demonstrate that introducing Ir into Co2MnO4 spinels serves a dual function of stabilizing the lattice and enabling a controlled shift toward oxide pathway mechanism (OPM) alongside AEM without lattice oxygen involvement. Density functional theory and spectroscopic analyses reveal that Ir preferentially substitutes Co at octahedral sites, increasing the Mn4+ population and enhancing Mn–O covalency, while facilitating *O–O formation via the OPM pathway. The optimized Ir-Co2MnO4 achieves an overpotential of 222 mV at 10 mA cm–2 and delivers high durability over 416 h at 100 mA cm–2 in 0.5 M H2SO4, including 1000 h of sustained industrial-level operation, surpassing both pristine Co2MnO4 and commercial IrO2. This work provides fundamental insights into Ir-mediated modulation of active sites and establishes a design strategy for high-performance, low-Ir OER catalysts in acidic water electrolysis.