Integrated Copper/Alumina Heterojunction with Oxygen Vacancy Promotes the Activity and Selectivity of Electrochemical Methanation

Abstract Copper (Cu) can efficiently catalyze the CO ₂ electrochemical reduction reaction (CO ₂ RR) to produce high‐value‐added fuels and chemicals, of which methane (CH ₄ ) is of interest due to its high mass‐energy density. However, the poor activity of Cu toward a specific product, as well as the relatively weak adsorption of ^* CO intermediates on the Cu surface, favors competitive ^* CO dimerization, thus limiting the selectivity for CH ₄ . Here, a heterojunction strategy is proposed by importing catalytically inert oxide containing oxygen vacancies to Cu (namely Cu _y /Al ₂ O _{3‐ x} @C), which accelerates CO ₂ electromethanation by altering the local geometries and electronic structures of catalysts, resulting in strong adsorption of ^* CO on the catalyst. By adjusting the composition of the catalyst, the Faraday efficiency (FE) toward CH ₄ can be effectively nearly doubled from 39.2% to 74.6%. In situ Raman spectroscopy and Density functional theory (DFT) calculations reveal that oxygen vacancies in the catalyst can enrich proton donors and enhance the adsorption energy of ^* CO on the catalyst, thereby reducing the reaction energy barrier for the hydrogenation of ^* CO to CH ₄ . This work provided a new pathway for the Cu‐based electrocatalyst design to achieve high selectivity by modulating the adsorption behavior of key intermediates.