Crystal Facet‐Dependent Metal‐Support Interaction for Stabilizing Cu δ+ Species Toward Efficient CO 2 Electroreduction

ABSTRACT Cu δ+ species are recognized as optimal active sites for the electrocatalytic CO 2 reduction reaction. While metal‐support interactions (MSIs) modulate the local microenvironment of Cu δ+ , the intrinsic contribution of support crystallographic facets to these interactions remains obscured by interfering oxygen vacancies. In this work, we present a definitive study decoupling the facet effect from vacancy‐related variables by utilizing CeO 2 supports with comparable oxygen vacancy concentrations. Our findings reveal that Cu single atoms supported on various CeO 2 facets follow a pronounced facet‐dependent stability order of Cu/CeO 2 ‐(110) > Cu/CeO 2 ‐(100) > Cu/CeO 2 ‐(111), yet exhibit facet‐independent methane Faraday efficiency (∼80% at −200 mA/cm 2 ). Mechanistic studies unravel this dichotomy, revealing that identical Cu coordination environments drive the uniform initial activity, whereas distinct surface electronic structures dictate long‐term stability by modulating facet‐dependent MSIs. Specifically, the (110) facet exhibits the strongest MSI, acting as a robust “electron buffer” that securely anchors high‐valent Cu δ+ species and effectively retards their irreversible reductive agglomeration into clusters. By establishing an unambiguous structure–performance relationship under single‐variable conditions, this study provides a rational geometric descriptor for designing long‐lasting CO 2 conversion catalysts.