Triggering Reverse Hydrogen Spillover at a RuO _x ‐Mo ₂ C Cluster‐Cluster Heterostructure for Superior Alkaline Hydrogen Evolution

ABSTRACT The rational construction of a reverse hydrogen spillover channel within the catalyst effectively accelerates hydrogen evolution reaction (HER) kinetics, whereas the driving forces and mechanisms that control hydrogen surface migration remain insufficiently investigated. Therefore, we constructed a strongly coupled RuO _x ‐Mo ₂ C cluster‐cluster heterostructure catalyst to effectively induce the reverse hydrogen spillover effect. Owing to the high‐density accessible active sites and efficient mass transport pathways provided by the strongly coupled cluster structure, hydrogen can migrate directionally and rapidly from Mo ₂ C sites to RuO _x sites via the reverse hydrogen spillover effect. This well‐defined interfacial coupling and functional partitioning substantially reduce the integrated energy barrier for water dissociation, H ^* transport, and H‐H coupling, leading to drastically accelerated HER kinetics and excellent electrocatalytic activity toward hydrogen evolution. It exhibits an overpotential of only 15 mV at 10 mA cm ⁻² . Moreover, the catalyst maintains stable performance for up to 1000 h under continuous electrolysis without significant degradation, demonstrating outstanding structural and catalytic stability. Furthermore, an anion exchange membrane water electrolyzer with RuO _x ‐Mo ₂ C as the cathode delivers superior catalytic activity, exhibiting a cell voltage of 1.76 V at 1.0 A cm ⁻² and long‐term stability over 1500 h, holding great promise for industrial high‐current applications.