Reversible lattice oxygen participation in Ru_1−xO_2−x for superior acidic oxygen evolution reaction

A stable and efficient RuO₂-based electrocatalyst for the acidic oxygen evolution reaction (OER) is essential to replace the current IrO₂ anode in proton-exchange membrane water electrolysis (PEMWE). Herein, we introduce RuO₂ catalysts designed with coexisting oxygen and ruthenium vacancies using a metal-organic pyrolysis method. In 0.5 M H₂SO₄ using a three-electrode configuration, the catalyst delivers a low overpotential of 193 mV at 10 mA cm⁻². Experimental and theoretical analyses reveal facet-dependent mechanisms: oxygen vacancies stabilize (110) and (101) facets by suppressing excessive Ru vacancy formation during reconstruction, while Ru vacancies on (101) uniquely activate lattice oxygen to enable a reversible lattice oxygen-mediated (LOM) cycle. DFT calculations rationalize this behavior: Ru vacancies lower the deprotonation of adsorbed hydroxyl (RDS) to 1.51 eV on (101) facets, while lattice oxygen coupling via the LOM proceeds at a remarkably low barrier of 1.02 eV, synergistically promoting rapid oxygen replenishment and durable cycling. In contrast, the (110) facet suffers from prohibitive barriers (>2.0 eV) in both adsorbate-driven and lattice oxygen pathways. Consequently, the (101)-dominant catalyst operates stably at 100 mA cm⁻² in PEMWE for 200 h, outperforming the conventional IrO₂ benchmark.