Hydroxyl spillover-driven dynamic refilling of oxygen vacancy in RuO₂ via MoO_x cluster for stable acid oxygen evolution reaction

Ruthenium dioxide (RuO₂) is renowned for its exceptional catalytic activity toward the oxygen evolution reaction (OER), primarily attributed to the fast lattice oxygen mechanism (LOM). However, the LOM pathway included in OER often leads to excessive oxidation of Ru and its subsequent dissolution, ultimately compromising the catalyst’s long-term stability. In this work, to address the catalyst instability arising from the continuous accumulation of oxygen vacancies, which leads to structural breakdown, we propose a strategy that utilizes hydroxyl spillover to dynamically refill oxygen vacancies, effectively addressing the instability of catalysts caused by the continuous accumulation of oxygen vacancies during the OER. Engineered spatial coupling is achieved by anchoring MoO_x clusters onto RuO₂, resulting in a RuO₂/MoO_x composite catalyst capable of dynamically refilling oxygen vacancies under operating conditions. The RuO₂/MoO_x exhibits outstanding OER performance, delivering an ultra-low overpotential of 195 mV at 10 mA cm⁻² and maintaining excellent stability for over 1350 h under constant current operation. Moreover, a proton exchange membrane (PEM) electrolyzer employing RuO₂/MoO_x as the anode achieved stable operation for 200 h at 200 mA cm⁻². Mechanistic studies show that the MoO_x clusters act as a localized “hydroxyl pump” that preferentially adsorbs and activates hydroxyl intermediates. These intermediates then migrate to the RuO₂ surface, helping to refill the oxygen vacancy created during the OER process while maintaining the catalyst’s structural stability. This study introduces a novel strategy for designing durable OER catalysts that function in acidic conditions and offers a new pathway to enhance the stability of Ru-based OER catalysts.