Atmosphere Induces Tunable Oxygen Vacancies to Stabilize Single‐Atom Copper in Ceria for Robust Electrocatalytic CO₂ Reduction to CH₄

Electrochemical carbon dioxide reduction (ECO₂RR) shows great potential to create high-value carbon-based chemicals, while designing advanced catalysts at the atomic level remains challenging. The ECO₂RR performance is largely dependent on the catalyst microelectronic structure that can be effectively modulated through surface defect engineering. Here, we provide an atmosphere-assisted low-temperature calcination strategy to prepare a series of single-atomic Cu/ceria catalysts with varied oxygen vacancy concentrations for robust electrolytic reduction of CO₂ to methane. The obtained Cu/ceria catalyst under H₂ environment (Cu/ceria-H₂) exhibits a methane Faraday efficiency (FE_CH4) of 70.03 % with a turnover frequency (TOF_CH4) of 9946.7 h^-1 at an industrial-scale current density of 150 mA cm^-2 in a flow cell. Detailed studies indicate the copious oxygen vacancies in the Cu/ceria-H₂ are conducive to regulating the surface microelectronic structure with stabilized Cu⁺ active center. Furthermore, density functional theory calculations and operando ATR-SEIRAS demonstrate that the Cu/ceria-H₂ can markedly enhance the activation of CO₂, facilitate the adsorption of pivotal intermediates *COOH and *CO, thus ultimately enabling the high selectivity for CH₄ production. This study presents deep insights into designing effective electrocatalysts for CO₂ to CH₄ conversion by controlling the surface microstructure via the reaction atmosphere.