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 Bronsted acid. Online electrocatalytic CO₂ results show that the local proton donor-'propanoic acid' indeed enhanced the conversion of CO₂ to CO