Tailoring the Oxygen Vacancy Distribution in Se‐Doped RuO_x to Enhance Its Stability in Acidic Water Electrolysis

Abstract Developing durable ruthenium (Ru)‐based catalysts for proton exchange membrane water electrolyzer (PEMWE) remains challenging due to irreversible Ru dissolution and lattice oxygen instability. Although elemental doping is a general method to improve stability, it inadvertently induces oxygen vacancies (V O s), which are randomly distributed in the nanocatalyst. Notably, the impact of V O distribution on the stability of Ru‐based catalysts remains unresolved. Herein, we synthesized the Se‐doped Ru oxide via annealing the mixture of ruthenium (III) chloride and selenium (Se) in the air (Ur‐Se‐RuO x ) with the presence of urea, showing the V O s distributed away from Se dopants, which is significantly different from the Se‐doped Ru oxide synthesized without urea (Se‐RuO x ), showing V O s distributed relatively close to the Se dopants. The Ur‐Se‐RuO x demonstrates superior oxygen evolution reaction performance over Se‐RuO x . Particularly, Ur‐Se‐RuO x delivers a low working voltage (1.62 V@1 A cm −2 ) and excellent durability (>1000 h@200 mA cm −2 ) in PEMWE tests. Experimental and theoretical results reveal that V O s engage in long‐range cooperation with spatially decoupled Se dopants in Ur‐Se‐RuO x , synergistically enhancing reaction kinetics via an intramolecular oxygen coupling mechanism, while inhibiting the lattice oxygen mechanism and suppressing Ru dissolution, which demonstrates a new strategy to break the activity–stability trade‐off in promising Ru‐based catalysts.