Metal corroles as electrocatalysts for oxygen reduction

Abstract

The rotating ring disk electrode method has been used to study O₂ electroreduction with metal corroles. Catalysis begins at potentials that are 0.5–0.7 V more positive than the expected potential of the M^III/II couple based on studies in non-aqueous solutions. The path of O₂ reduction depends on the nature of the metal ion. Cobalt corroles promote O₂ reduction to H₂O₂. Iron corroles catalyse O₂ reduction via parallel two- and four-electron pathways, with a predominate four-electron reaction. The rate constants for the individual O₂ reduction paths are given at pH 7. Mechanisms are proposed on the basis of pH dependence, inhibition studies, and Tafel slopes. An imidazole-tailed iron corrole catalyses H₂O₂ disproportionation analogous to catalase.