DFT Study on the Mechanism of the Electrochemical Reduction of CO2 Catalyzed by Cobalt Porphyrins

The electrochemical reduction of CO2 is a promising way to store renewable energy in fuels or other chemicals. However, the high overpotential and low efficiency of the reaction hinder the development of the area. More work is needed on the investigation of the mechanism in order to obtain new insights into developing efficient catalysts. We report here a density functional theory (DFT) study of the electrochemical reduction of CO2 on cobalt porphyrin. The CO2- anion adduct is demonstrated to be the key intermediate formed only when the cobalt center of the complex is in the Co-I oxidation state. We find that formic acid can be produced as minor product through a [Co(P)-(OCHO)] intermediate, while CO is the main product through a decoupled proton electron transfer. CH4 is produced as minor product from subsequent CO reduction by concerted proton-coupled electron transfers assumed for each electrochemical step. Our theoretical interpretations are consistent with the experimental results presented in our recent experiments and give deeper insights into the mechanism of the CO2 electrochemical reduction on cobalt porphyrin complexes.