PNNL

Abstract

The oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR) are quintessential chemical-to-electrical energy conversion reactions. Molecular iron porphyrins have been long known to catalyze both reactions, though often only at high overpotentials. Recently, an iron porphyrin bearing four cationic ortho-trimethylanilinium groups has been reported to perform both the ORR and CO2RR with fast rates and at much lower overpotentials. This work seeks to understand how the charged functional groups affect the various pre-equilibria of both reactions, specifically acetate, dioxygen, and carbon dioxide binding. Both experimental studies and density functional theory calculations were used to understand how intramolecular electrostatic interactions affect i) the thermodynamics of these pre-equilibria and ii) the stabilization of generated O2•- and CO2•- adducts. The results of this study highlight how electrostatic secondary sphere motifs affect specific small molecule binding in nonaqueous media and underscore their utility catalyst design.