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

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 (VOs), which are randomly distributed in the nanocatalyst. Notably, the impact of VO 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-RuOx) with the presence of urea, showing the VOs distributed away from Se dopants, which is significantly different from the Se-doped Ru oxide synthesized without urea (Se-RuOx), showing VOs distributed relatively close to the Se dopants. The Ur-Se-RuOx demonstrates superior oxygen evolution reaction performance over Se-RuOx. Particularly, Ur-Se-RuOx 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 VOs engage in long-range cooperation with spatially decoupled Se dopants in Ur-Se-RuOx, 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.