Computational-experimental study of the onset potentials for CO2 reduction on polycrystalline and oxide-derived copper electrodes

The electrocatalytic reduction of CO2 (CO2RR) is a promising yet intricate process to alleviate the alarming imbalance in the carbon cycle. One of the intricacies of CO2RR is its structural sensitivity, which is illustrated by the varying onset potentials and selectivities of the reaction products depending on the electrode morphology. Here, using electrochemical real-time mass spectrometry (EC-RTMS), we accurately determine the onset potentials for seven CO2RR products including C-1, C-2, and C-3 species on polycrystalline and oxide-derived Cu electrodes. Density functional theory calculations affordably including solvent and cation effects produce onset potentials of C-2 species matching those obtained with EC-RTMS. Our analysis leads us to conclude that the elusive active sites at oxide-derived Cu, known to enhance ethanol production, are undercoordinated square ensembles of Cu atoms.