Product selectivity in the electrochemical reduction of CO on copper electrodes depends significantly on the surface structure of the Cu catalyst. Experiments have shown that Cu(111) surfaces favor methane formation, which is a dominant C 1 product of CORR, whereas Cu(100) surfaces preferentially produce ethylene . Despite many DFT studies on reaction pathways involving COH* and CHO* intermediates, the exact mechanisms remain unclear due to the absence of direct experimental identification of these transient species. To address these uncertainties, more advanced methods such as the RPA for Cu(100) and the embedding approach for Cu(111) have been employed to Datasets for energies and structures are available at catalysishub.org .