Deciphering the Selectivity of the Electrochemical CO(2) 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(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.