Superoxo and Peroxo Complexes on Single-Atom Catalysts: Impact on the Oxygen Evolution Reaction

In this work, we demonstrate the essential role of the formation of superoxo and peroxo complexes on single-atom catalysts (SACs), an aspect that is often neglected in the study of these systems. By means of density functional theory calculations, we consider a representative set of 11 transition metal atoms (Sc, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, Pd, Pt) anchored on nitrogen-doped graphene, and we show that most of them form stable superoxo and peroxo intermediates when they react with molecular oxygen. Their formation has a direct impact on the oxygen evolution reaction (OER), and we develop the corresponding microkinetic models showing that this step of the reaction cannot be neglected. Depending on the transition metal atom, the inclusion of the superoxo/peroxo complexes in the analysis of the reaction profile can change the kinetics by several orders of magnitude. This work reveals the important role of dioxygen complexes species in the OER and reinforces the notion of SACs as analogs of coordination compounds.