Deciphering the Selectivity of the Electrochemical CO Reduction to CO by a Cobalt Porphyrin Catalyst in Neutral Aqueous Solution: Insights from DFT Calculations.

Density functional theory (DFT) calculations were conducted to investigate the cobalt porphyrin-catalyzed electro-reduction of CO to CO in an aqueous solution. The results suggest that Co -porphyrin (Co -L) undertakes a ligand-based reduction to generate the active species Co -L⋅ , where the Co center antiferromagnetically interacts with the ligand radical anion. Co -L⋅ then performs a nucleophilic attack on CO , followed by protonation and a reduction to give Co -L-COOH. An intermolecular proton transfer leads to the heterolytic cleavage of the C-O bond, producing intermediate Co -L-CO. Subsequently, CO is released from Co -L-CO, and Co -L is regenerated to catalyze the next cycle. The rate-determining step of this CO RR is the nucleophilic attack on CO by Co -L⋅ , with a total barrier of 20.7 kcal mol . The competing hydrogen evolution reaction is associated with a higher total barrier. A computational investigation regarding the substituent effects of the catalyst indicates that the CoPor-R3 complex is likely to display the highest activity and selectivity as a molecular catalyst.