Dynamic Roles of Oxygen Vacancies for Surface Hydroxylation in Enhanced Alkaline Hydrogen Evolution

Oxygen vacancies (VO) in metal oxide electrocatalysts are widely recognized as key contributors to enhanced hydrogen evolution reaction (HER) activity, yet their precise function during catalysis remains elusive. Here, we investigate VO-rich Co₃O₄ (a transition-metal oxide with moderate activity) and VO-rich RuO₂ (a high-performance oxide catalyst) as model catalysts to elucidate the dynamic evolution of VO during alkaline HER. Electrochemical analysis demonstrates that VO-rich oxides exhibit significantly enhanced intrinsic HER activity compared to their VO-poor counterparts. Comprehensive operando spectroscopies, ex situ characterizations, and ab initio molecular dynamics (AIMD) simulations reveal that VO is not inert but is dynamically consumed during HER, facilitating extensive surface hydroxylation. Such surface hydroxylation and reconstruction optimize water molecule adsorption and dissociation, regulate interfacial water distribution, and enhance the connectivity of the hydrogen-bond network at the interface, collectively shifting the reaction pathway from Volmer-Heyrovsky to Volmer-Tafel. These synergistic effects lead to accelerated reaction kinetics and superior HER performance. This work supports the generality of the proposed mechanism across oxide electrocatalysts with vastly different intrinsic activities, provides new insights into the structural dynamics of VO, and highlights the critical role of its induced surface hydroxylation in regulating the interfacial water and hydrogen-bond network, thereby boosting electrocatalytic hydrogen evolution.