Promoted Electrochemical CO ₂ Methanation over Ultrastable Cu(II)-V _O Pair Sites in Cu-CeO ₂ Catalyst: Water Activation and Intermediate Adsorption Tuning

Electrochemical CO₂ methanation powered by renewable electricity provides a sustainable strategy for producing value-added products, solving global energy problems, and realizing carbon recycling. However, it is hindered by unexpected intermediate desorption and slow water dissociation kinetics, greatly restricting the activity and selectivity of electrochemical CO₂ methanation. Here, we designed a Cu-CeO₂ catalyst with Cu(II)-oxygen vacancy (V_O) pair sites, which shows high activity and selectivity in electrochemical CO₂ reduction to methane (CH₄). The catalytic system achieves a remarkable CH₄ Faradaic efficiency (FE) of 70% with a current density as high as 485 mA cm^-2 at -1.1 V vs RHE in the flow cell. A combination of <i>in situ</i> characterizations and theoretical calculation unveiled that the isolated Cu(II) site strongly adsorbs the *CO intermediate, while V_O effectively accelerates water dissociation to provide abundant *H. The synergistic effect of isolated Cu(II) sites and V_O promotes *CO hydrogenation, resulting in high activity and selectivity of CH₄. This work provides valuable insights for the rational design of efficient multisite synergistic catalytic systems.