Electroreduction of Carbon Dioxide to Acetate using Heterogenized Hydrophilic Manganese Porphyrins

Abstract

The electrochemical reduction of carbon dioxide (CO ₂) to value‐added chemicals is a promising strategy to mitigate climate change. Metalloporphyrins have been used as a promising class of stable and tunable catalysts for the electrochemical reduction reaction of CO ₂ (CO ₂RR) but have been primarily restricted to single‐carbon reduction products. Here, we utilize functionalized earth‐abundant manganese tetraphenylporphyrin‐based (Mn‐TPP) molecular electrocatalysts that have been immobilized via electrografting onto a glassy carbon electrode (GCE) to convert CO ₂ with overall 94 % Faradaic efficiencies, with 62 % being converted to acetate. Tuning of Mn‐TPP with electron‐withdrawing sulfonate groups (Mn‐TPPS) introduced mechanistic changes arising from the electrostatic interaction between the sulfonate groups and water molecules, resulting in better surface coverage, which facilitated higher conversion rates than the non‐functionalized Mn‐TPP. For Mn‐TPP only carbon monoxide and formate were detected as CO ₂ reduction products. Density‐functional theory (DFT) calculations confirm that the additional sulfonate groups could alter the C−C coupling pathway from *CO→*COH→*COH‐CO to *CO→*CO‐CO→*COH‐CO, reducing the free energy barrier of C−C coupling in the case of Mn‐TPPS. This opens a new approach to designing metalloporphyrin catalysts for two carbon products in CO ₂RR.