Abstract
Density functional theory (DFT) calculations were conducted to investigate the cobalt porphyrin-catalyzed electro-reduction of CO(2) to CO in an aqueous solution. The results suggest that Co(II) -porphyrin (Co(II) -L) undertakes a ligand-based reduction to generate the active species Co(II) -L⋅(-) , where the Co(II) center antiferromagnetically interacts with the ligand radical anion. Co(II) -L⋅(-) then performs a nucleophilic attack on CO(2) , followed by protonation and a reduction to give Co(II) -L-COOH. An intermolecular proton transfer leads to the heterolytic cleavage of the C-O bond, producing intermediate Co(II) -L-CO. Subsequently, CO is released from Co(II) -L-CO, and Co(II) -L is regenerated to catalyze the next cycle. The rate-determining step of this CO(2) RR is the nucleophilic attack on CO(2) by Co(II) -L⋅(-) , with a total barrier of 20.7 kcal mol(-1) . 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.