Oxygen Vacancy‐Mediated Oxide Pathway Mechanism in Proton‐Exchange Membrane Water Electrolysis

Abstract The development of highly active and acid‐stable iridium‐based (Ir‐based) oxygen evolution reaction (OER) electrocatalysts is crucial for efficient hydrogen production via proton‐exchange membrane water electrolysis (PEMWE). Conventional mechanisms face fundamental limitations: the adsorbate evolution mechanism faces activity suppression due to linear scaling relationships, while the lattice oxygen mechanism encounters stability issues because irreversible oxidative release of lattice oxygen can over‐oxidize Ir species. Here, we found that introducing an optimal concentration of oxygen vacancy (O _V ) in IrO ₂ (O _V −IrO ₂ ) triggers the oxide pathway mechanism (OPM) that simultaneously circumvents these constraints. In situ experiments and theoretical calculations reveal that O _V serves dual functions: i) as electronic regulator — O _V causes upshifted Ir 5 d −band center and charge redistribution, which facilitates ^* OH adsorption and deprotonation, accelerating ^* O radical formation; ii) as structural modifier — O _V reduces Ir−Ir interatomic distances, which lowers the energy barrier of direct ^* O− ^* O coupling, triggering the OPM pathway. Consequently, the O _V −IrO ₂ demonstrates a lower overpotential ( η ₁₀ = 263 ± 4 mV), and maintains an industrial‐grade current density of 2 A cm ⁻² at 1.81 V for ≈500 h with low degradation of 4.12 µV h ⁻¹ in PEMWE. This work highlights the importance of O _V engineering in optimizing catalytic pathways to enhance the OER performance.