Tailoring the Oxygen Vacancy Distribution in Se-Doped RuO_x 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 (V_Os), 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_Os distributed away from Se dopants, which is significantly different from the Se-doped Ru oxide synthesized without urea (Se-RuO_x), showing V_Os 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_Os 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.