Comparative Study of Computational Hydrogen Electrodes and Constant Electrode Potential Models Applied to Electrochemical Reduction of CO2 and Oxygen Evolution Reaction on Metal Oxides/Copper Catalysts

The electrochemical reduction of CO2 (ERCO2) and the oxygen evolution reaction (OER) are important electrochemical reactions for practical applications and theoretical studies. In theoretical studies of electrochemical reactions, the applied potential (U) has been incorporated either by adding |e|U to the reaction free energy based on the computational hydrogen electrode (CHE) model or by following a self-consistent procedure using the constant electrode potential (CEP) model. Herein, we investigated ERCO2 to CH4(g)/CH3OH(l) and OER on metal-oxide/copper (MO)4/Cu­(100), M = Fe, Co, and Ni) catalysts using both CHE and CEP models and compared the resulting potential-limiting steps and product selectivity. Our results show that the CEP model predicts a product selectivity and limiting potential different from those of the CHE model for ERCO2. On the other hand, limiting potentials predicted based on both models are consistent for the OER. These results suggest that care must be taken when using the CHE to predict the potential limiting step and limiting potential for a reaction involving multiple proton–electron transfer steps. The CEP model, which accounts for the effect of applied potential on the stability of the reaction intermediates and nonredox steps, is essential to develop a complete understanding of the reaction mechanism and quantify the limiting potential.