Tuning the C₁/C₂ Selectivity of Electrochemical CO₂ Reduction on Cu–CeO₂ Nanorods by Oxidation State Control

Ceria (CeO 2 ) is one of the most extensively used rare earth oxides. Recently, it has been used as a support material for metal catalysts for electrochemical energy conversion. However, to date, the nature of metal/CeO 2 interfaces and their impact on electrochemical processes remains unclear. Here, a Cu–CeO 2 nanorod electrochemical CO 2 reduction catalyst is presented. Using operando analysis and computational techniques, it is found that, on the application of a reductive electrochemical potential, Cu undergoes an abrupt change in solubility in the ceria matrix converting from less stable randomly dissolved single atomic Cu 2+ ions to (Cu 0 ,Cu 1+ ) nanoclusters. Unlike single atomic Cu, which produces C 1 products as the main product during electrochemical CO 2 reduction, the coexistence of (Cu 0 ,Cu 1+ ) clusters lowers the energy barrier for C–C coupling and enables the selective production of C 2+ hydrocarbons. As a result, the coexistence of (Cu 0 ,Cu 1+ ) in the clusters at the Cu–ceria interface results in a C 2+ partial current density/unit Cu weight 27 times that of a corresponding Cu‐carbon catalyst under the same conditions.