A local proton source from carboxylic acid functionalized metal porphyrins for enhanced electrocatalytic CO2 reduction

The effect of intramolecular carboxylic groups on the activity of metal porphyrins for CO2 reduction has been investigated. Metal porphyrins functionalized with aromatic carboxylic acid (benzoic acid) at the para-position exhibited CO2 catalytic current only in the presence of external proton sources and an Fe metal center obtained the highest CO2 catalytic current value among Cu, Co, Ni metal centers. In the absence of external proton donors, Fe porphyrins grafted with aliphatic carboxylic acid (propanoic acid) as a local proton source could achieve comparable CO2 catalytic activity with its “benzoic acid” counterpart in the presence of H2O and Brønsted acid. Online electrocatalytic CO2 results show that the local proton donor-“propanoic acid” indeed enhanced the conversion of CO2 to CO.