Deciphering the Selectivity of the Electrochemical CO2 Reduction to CO by a Cobalt Porphyrin Catalyst in Neutral Aqueous Solution: Insights from DFT Calculations

Abstract

Abstract Density functional theory (DFT) calculations were conducted to investigate the cobalt porphyrin‐catalyzed electro‐reduction of CO2 to CO in an aqueous solution. The results suggest that CoII−porphyrin (CoII−L) undertakes a ligand‐based reduction to generate the active species CoII−L⋅−, where the CoII center antiferromagnetically interacts with the ligand radical anion. CoII−L⋅− then performs a nucleophilic attack on CO2, followed by protonation and a reduction to give CoII−L−COOH. An intermolecular proton transfer leads to the heterolytic cleavage of the C−O bond, producing intermediate CoII−L−CO. Subsequently, CO is released from CoII−L−CO, and CoII−L is regenerated to catalyze the next cycle. The rate‐determining step of this CO2RR is the nucleophilic attack on CO2 by CoII−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.

Keywords

• CO2 reduction
• cobalt-porphyrin
• density functional calculations
• reaction mechanisms
• selectivity