Active Site Cycling in Alkaline Hydrogen Evolution via Dual Hydrogen/Hydroxyl Spillover for...

While most studies on the alkaline hydrogen evolution reaction (HER) focus on constructing abundant active sites to achieve high-current-density performance, the critical role of rapid active site cycling is often overlooked. This neglect ultimately limits both the catalytic activity and long-term stability under industrial operating conditions. We report a dual spillover strategy through Ru-doped cobalt phosphide nanoneedle arrays with P vacancies (Ru-CoP_v) to address this limitation. Experimental and theoretical analyses reveal that Ru species and P vacancies modulate Co sites' electronic states, accelerating water adsorption/dissociation. The generated *H rapidly migrates to Ru sites, while *OH undergoes rapid spillover to P sites via a Ru-P_v-Co bridge, forming a dynamic dual spillover mechanism that enables efficient active site utilization and regeneration. Ru_0.06-CoP_v-2 achieves a 150 mV overpotential at 500 mA cm^-2 in 1.0 M KOH, with a turnover frequency of 16.9 s^-1 at 150 mV (256-fold enhancement over CoP_v-2 and comparable to that of Pt catalysts). Stable operation over 2000 h at 500 mA cm^-2 demonstrates outstanding durability, highlighting the strategy's effectiveness in overcoming traditional limitations of transition metal-based HER catalysts.