Engineering the Metal/Oxide Interfacial O‐Filling Effect to Tailor Oxygen Spillover for Efficient Acidic Water Oxidation

Abstract The oxygen spillover on the metal/oxide electrocatalysts interface acts as an essential role in promoting the oxygen evolution reaction (OER) for proton exchange membrane water electrolyzers (PEMWEs). However, oxygen spillover mechanisms and corresponding regulatory strategies are still unclear for addressing slow OH‐migration kinetics. Herein, an interface is constructed between Iridium (Ir) and Niobium (Nb)‐doped Titanium oxide (TiO₂) with abundant oxygen vacancies area by plasma processing, enabling oxygen spillover from the metal Ir to supports. The optimized Ir/Nb‐doped TiO₂ with a significant OER activity (η = 253 mV) and durability in acids compared to commercial IrO₂. In situ experiments combined with theoretical computations reveal the presence of interfacial oxygen vacancies not only regulates the Ir structure toward boosted activity but also constructs a directional spillover pathway from Ir to interfacial oxygen vacancies area and then TiO₂ via the OH^*‐filling route, which strikingly mitigates the OH^* migration barriers. In addition, the optimized Ir/Nb‐doped TiO₂ exhibits excellent performance (1.69 V/1.0 A cm⁻²@80 °C) and long‐term stability (≈500 h@1.0 A cm⁻²) with practical potential in PEMWEs. This work provides a unique insight into the role of oxygen spillover, paving the way for designing Ir‐based catalysts for PEMWEs.