A local proton source from carboxylic acid functionalized metal porphyrins for enhanced electrocatalytic CO 2 reduction

The effect of intramolecular carboxylic groups on the activity of metal porphyrins for CO 2 reduction has been investigated. Metal porphyrins functionalized with aromatic carboxylic acid (benzoic acid) at the para -position exhibited CO 2 catalytic current only in the presence of external proton sources and an Fe metal center obtained the highest CO 2 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 CO 2 catalytic activity with its “benzoic acid” counterpart in the presence of H 2 O and Brønsted acid. Online electrocatalytic CO 2 results show that the local proton donor-“propanoic acid” indeed enhanced the conversion of CO 2 to CO.