Combined Experimental and Theoretical Study of Cobalt Corroles as Catalysts for Oxygen Reduction Reaction

Bioinspired transition-metal complexes may serve as efficient and low-cost potential catalysts for oxygen reduction reaction (ORR) in fuel cells, instead of precious group metal-free (PGM-free) materials. Herein, we present a study of the ORR electrocatalytic activity of different mesosubstituted Co-corroles with varying electronegativity using both experimental and theoretical methods. Specifically, we studied the influence of different mesosubstituted Co-corroles on catalytic activity. Using density functional theory (DFT), we computed lowest unoccupied molecular orbital (LUMO) energies, vertical excitation energies, electrostatic potentials, and O₂ adsorption energies and compared them with the ORR catalytic activity obtained from cyclic voltammetry and rotating ring-disk electrode measurements. We found that the first one-electron reduction for all the corroles occurs at the Co-center based on computed LUMOs, and that this is a necessary step for the ORR mechanism to take place. The ORR reduction potential trends observed from theory and experiments are in good agreement. Based on this work, we conclude that the role of the substituents is significant and an important factor that affects the overpotential required for the ORR.