Promoted Electrochemical CO₂ Methanation over Ultrastable Cu(II)-V_O Pair Sites in Cu-CeO₂ 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 (VO) 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 in situ characterizations and theoretical calculation unveiled that the isolated Cu(II) site strongly adsorbs the *CO intermediate, while VO effectively accelerates water dissociation to provide abundant *H. The synergistic effect of isolated Cu(II) sites and VO 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.