Mechanistic Explanation of the pH Dependence and Onset Potentials for Hydrocarbon Products from Electrochemical Reduction of CO on Cu (111)

Energy and environmental concerns demand development of more efficient and selective electrodes for electrochemical reduction of CO_2 to form fuels and chemicals. Since Cu is the only pure metal exhibiting reduction to form hydrocarbon chemicals, we focus here on the Cu (111) electrode. We present a methodology for density functional theory calculations to obtain accurate onset electrochemical potentials with explicit constant electrochemical potential and pH effects using implicit solvation. We predict the atomistic mechanisms underlying electrochemical reduction of CO, finding that (1) at acidic pH, the C_1 pathway proceeds through COH to CHOH to form CH_4 while C_2 (C_3) pathways are kinetically blocked; (2) at neutral pH, the C_1 and C_2 (C_3) pathways share the COH common intermediate, where the branch to C–C coupling is realized by a novel CO–COH pathway; and (3) at high pH, early C–C coupling through adsorbed CO dimerization dominates, suppressing the C1 pathways by kinetics, thereby boosting selectivity for multi-carbon products.