Four-Electron Electrocatalytic O₂ Reduction by a Ferrocene-Modified Glutathione Complex of Cu

In this manuscript, we design non-precious-metal electrocatalysts for the O2 reduction reaction (ORR) based on Cu complexes of the tripeptide glutathione modified with ferrocene (Cu-GSH-NHFc). Homogenous catalysis experiments demonstrate that the covalently bound Cu-GSH-NHFc catalyst exhibits enhanced activity compared to mixtures of the individual catalyst components. Heterogeneous catalysis results on rotating disk electrodes (RDE) and rotating ring-disk electrodes (RRDE) show that Cu-GSH-NHFc catalyzes the ORR via a four-electron pathway at pH 4–7, while the same catalyst without ferrocene produces significant quantities of H2O2. Cyclic voltammetry reveals electronic coupling between the appended ferrocene moieties and the Cu active site. From these studies, we propose an ORR reaction pathway, in which fast electron transfer facilitated by ferrocene explains the high selectivity of the Cu-GSH-NHFc catalyst. We envision that this understanding will lead to future developments in the design of non-precious-metal ORR catalysts, which are instrumental to fuel cell technologies.