Understanding Hydroxyl-Mediated Hydrogen Spillover Mechanisms in Cu ⁺ Stabilization of Core–Shell Cu ₂ O@SiO ₂ Catalysts toward CO ₂ Reduction

The instability of Cu+ species under reductive conditions severely limits the efficiency and durability of electrochemical CO2 reduction to ethylene (C2H4). Here we report a hydroxyl-mediated hydrogen spillover strategy utilizing a core–shell Cu2O@SiO2 catalyst to achieve robust Cu+ stabilization and enhanced C2H4 selectivity. The amorphous SiO2 shell contains abundant surface hydroxyl (Si–OH) groups generated in situ upon hydration, which serve as active channels for hydrogen spillover to deplete adsorbed hydrogen (*H) from the Cu2O core. This process lowers local *H coverage on Cu sites, suppressing both the hydrogen evolution reaction (HER) and the reduction of Cu+ to Cu0. Meanwhile, strong interfacial interaction between Cu2O and SiO2 further stabilizes Cu–O bonds, promoting the persistence of catalytically active Cu+ species. As a result, the Cu2O@SiO2 catalyst achieves a C2H4 Faradaic efficiency (FE) of 46.2% at −1.2 V vs RHE, 2.2 times higher than that of pristine Cu2O, and maintains stable ethylene production for over 50 h. This work demonstrates a generalizable approach for manipulating the catalyst microenvironment via hydroxyl-mediated hydrogen spillover and provides pathways for designing high-performance CO2 electroreduction catalysts with durable Cu+ stabilization.