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 CO 2 reduction to ethylene (C 2 H 4 ). Here we report a hydroxyl-mediated hydrogen spillover strategy utilizing a core–shell Cu 2 O@SiO 2 catalyst to achieve robust Cu + stabilization and enhanced C 2 H 4 selectivity. The amorphous SiO 2 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 Cu 2 O core. This process lowers local *H coverage on Cu sites, suppressing both the hydrogen evolution reaction (HER) and the reduction of Cu + to Cu 0 . Meanwhile, strong interfacial interaction between Cu 2 O and SiO 2 further stabilizes Cu–O bonds, promoting the persistence of catalytically active Cu + species. As a result, the Cu 2 O@SiO 2 catalyst achieves a C 2 H 4 Faradaic efficiency (FE) of 46.2% at −1.2 V vs RHE, 2.2 times higher than that of pristine Cu 2 O, 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 CO 2 electroreduction catalysts with durable Cu + stabilization.