Decoding Hydrogen Spillover: Unraveling the Dual-Site Relay-Guided C-C Coupling Mechanism in CO₂ Electroreduction

The electrochemical reduction of CO₂ into valuable C₂₊ products presents a sustainable and efficient strategy for the utilization of CO₂ and long-term renewable energy storage. Yet, enhancing the efficiency of the electrocatalytic CO₂ reduction reaction (eCO₂RR) in aqueous systems remains challenging due to the difficulty in activating both CO₂ and H₂O molecules. In this study, we focus on water activation generating reactive hydrogen species (*H) to boost C₂₊ product selectivity. Toward this target, we develop a series of bimetallic Cu-based catalysts with modulated Co loadings to form dual active sites. The optimized 0.24% Co-Cu₂O catalyst demonstrated exceptional performance, achieving a faradaic efficiency (FE) of 76.1% for C₂₊ products at a high-current density of 400 mA cm^-2. Remarkably, it maintained stable FE_C2+ values of >70% for over 24 h under continuous operation, indicating robust operational stability. Experimental studies and DFT calculations revealed that Co sites promote water activation to generate *H. The generated *H subsequently spills over to Cu sites, modulating the *H coverage on Cu surfaces, which enhances the conversion of *CO to *CHO intermediates. Subsequently, the asymmetric coupling between *CHO and *CO at the Cu sites generates C₂₊ products. This site-segregation strategy optimizes the selectivity and FE for the CO₂-to-C₂₊ conversion.