Selectivity Map for the Late Stages of CO and CO₂ Reduction to C₂ Species on Copper Electrodes

The electrochemical CO and CO₂ reduction reactions (CORR and CO₂ RR) using copper catalysts and renewable electricity hold promise as a carbon-neutral route to produce commodity chemicals and fuels. However, the exact mechanisms and structure sensitivity of Cu electrodes toward C₂ products are still under debate. Herein, we investigate ethylene oxide reduction (EOR) as a proxy to the late stages of CORR to ethylene, and the results are compared to those of acetaldehyde reduction to ethanol. Density functional theory (DFT) calculations show that ethylene oxide undergoes ring opening before exclusively reducing to ethylene via *OH formation. Based on generalized coordination numbers (CN), a selectivity map for the late stages of CORR and CO₂ RR shows that sites with moderate coordination (5.9 < CN < 7.5) are efficient for ethylene production, with pristine Cu(100) being more active than defective surfaces such as Cu(311). In contrast, kinks and edges are more active for ethanol production, while (111) terraces are relatively inert.