CO Spillover Is Not a Promoter for C─C Bond Formation in CO₂ Electroreduction on Cu-Ag Bimetallic Catalysts.

Cu-based bimetallic catalysts have been shown to improve the multi-carbon (C₂₊) selectivity in CO₂ electroreduction, with the assumption that CO spillover from the CO-selective catalysts to adjacent Cu domains via their bimetallic interface promotes C-C coupling. Here, through systematically controlling the Cu-Ag interface densities of bimetallic catalysts, we report that CO spillover via the bimetallic interface is unlikely to enhance the formation of C₂₊ products. Conversely, the abundant Cu-Ag interface preferentially promotes CH₄ formation while suppressing C─C bond formation. CO stripping studies also reveal that the Cu-Ag interface does not favor C─C coupling. Further computational modelling suggests that Cu-Ag bimetallic interface significantly enhances the energy barrier of CO dimerization while lowering the energy barrier for *CO hydrogenation toward CH₄, thus inhibiting C─C coupling toward C₂₊ products while facilitating CH₄ formation.