Dynamic Evolution of Cu ^δ+ Quantification in Mutually Reinforced Copper–Ceria Catalysts for Electrochemical CO ₂ Reduction

Low-valence copper species (Cu δ+, 0 < δ < 1) on Cu-based electrocatalysts are crucial for C–C coupling to form C 2+ products, yet the stability of Cu δ+ especially at industrial-scale current, remains a significant challenge. Herein, we designed a strongly correlated metal–metal oxide nanosphere catalyst (Cu@CeO 2 – x ) that stabilizes Cu δ+ species and establishes a Cu 0 –Cu + interface to better regulate hydrogen adsorption, achieving a maximum faradaic efficiency for C 2+ products of 82.5% at 300 mA cm –2 and −0.62 V RHE, while maintaining stable CO 2 reduction reaction performance for over 72 h. Operando X-ray absorption fine structure and in-situ Raman spectroscopy indicated that Cu@CeO 2 – x underwent in-situ surface reconstruction, enabling a CeO 2 -mediated Cu δ+ redox cycle. This dynamic charge equilibrium forms a Cu 0 –Cu + interface through the self-sacrifice of Ce sites to avoid an immoderate reduction of Cu. Furthermore, density functional calculations together with in-situ attenuated total reflection–surface-enhanced infrared absorption spectroscopy indicated that Cu 0 –Cu + interface enhances *CO adsorption, and facilitates C–C coupling for C 2+ products formation. The findings provide a blueprint for designing Cu-based electrocatalysts to combat rapid deactivation, enhancing performance toward higher-value products.