Hydrogen-Spillover Catalysis Enabled by Ni Cluster Water-Activation Centers through Interfacial Electronic Modulation

Abstract Hydrogen spillover has emerged as an effective strategy for accelerating alkaline hydrogen evolution by spatially decoupling water activation and hydrogen evolution. However, most reported hydrogen-spillover catalysts rely on noble metals as water-activation centers and suffer from pronounced interfacial work-function mismatches, giving rise to Schottky barriers that hinder interfacial hydrogen intermediate (H*) transfer. Herein, a non-noble-metal hydrogen-spillover electrocatalyst comprising ultrasmall Ni clusters anchored on defective N-doped Ni3S2 hierarchical microspheres is developed for alkaline urea-water splitting. The synergistic N-doping and sulfur vacancy engineering tailor the electronic structure of Ni3S2, thereby lowering its work function. The reduced work-function difference (ΔΦ) between Ni3S2 and the Ni clusters weakens the built-in electric field and facilitates H* transfer across the heterointerface. Operando ATR-IR and Raman spectroscopies, together with isotope experiments, electrochemical mechanistic analysis, and density functional theory calculations, collectively reveal the spatially decoupled H-spillover pathway, in which H2O dissociation preferentially occurs on the Ni clusters followed by the interfacial migration of H* to neighboring N-doped Ni3S2 domains for H2 evolution. As a result, the optimized Ni/N10-Ni3S2 catalyst exhibits bifunctional electrocatalytic activity toward both hydrogen and oxygen evolution reactions, enabling an anion-exchange-membrane electrolyzer to deliver 1 A cm−2 at 2.61 V. Moreover, the hydrogen-spillover pathway is maintained during urea-assisted water electrolysis, demonstrating the robustness of interfacial H* transfer. This work provides a general strategy for engineering transition-metal-based hydrogen-spillover electrocatalysts through interfacial electronic structure modulation.