Interfacial Ce/Cu engineering enables selectivity switching between methane and C2 products during CO2 electroreduction

Electrocatalytic CO 2 reduction reaction (CO 2 RR) provides a sustainable route for transforming CO 2 into value-added chemicals, yet achieving controllable selectivity remains a major challenge. Here, we constructed Ce-rich and Cu-rich Ce-Cu interfaces (CeCu 0.55 O x and CeCu 2.67 O x ) to elucidate the interfacial regulation of CO 2 RR pathways. CeCu 0.55 O x delivers a CH 4 Faradaic efficiency (FE) of 45% at –400 mA/cm 2 , whereas CeCu 2.67 O x achieves over 50% FE toward C 2 products. Operando Raman measurements reveal comparable Cu oxidation states during CO 2 RR, indicating that interfacial composition rather than Cu valence dominates selectivity. The Ce-rich interface accelerates H 2 O dissociation, increasing *H coverage and promoting sequential hydrogenation of *CO to CH 4 . In contrast, the Cu-rich interface strengthens *CO adsorption and increases its surface coverage, steering C−C coupling toward *OC-CO and enabling C 2 product formation. This work clarifies how tuning the Ce/Cu ratio modulates *H and *CO intermediate coverages, providing a mechanistic basis for designing oxide-metal interfaces with programmable CO 2 RR selectivity.