Thermodynamic and Kinetic Competition between C–H and O–H Bond Formation Pathways during Electrochemical Reduction of CO on Copper Electrodes

Carbon monoxide is the key intermediate in the electrochemical CO2 reduction reaction and determines the overpotentials and selectivities for C1 and C2 products on copper electrodes. The kinetic model based on Marcus charge transfer theory was applied to understand the competing C–H and O–H bond formation pathways involved in the CO reduction reaction on different facets of copper. The electrochemical reduction of CO adopts a thermodynamics-controlled CHO* pathway on Cu(110) and Cu(211) surfaces, and it follows a kinetics-controlled COH* pathway on Cu(111) and Cu(100) surfaces. It was found that the initial competing hydrogenation of CO to produce the CHO* or COH* intermediate plays an important role in determining the catalytic activity and selectivity. The simulated potential-dependent rate constant profiles show that the catalytic activity increases as Cu(111) < Cu(110) < Cu(211) < Cu(100). We suggest that catalyst structure engineering, aiming to decrease the onset potential of the COH* pathway with a lower reaction activation barrier, could be an effective way to promote the electrocatalytic activity of the CO reduction reaction.