Trends in Oxygen Evolution Reaction Activity and Limiting Steps for Different Active Sites on Co3O4(001)

Cobalt spinel (Co₃O₄) is a dynamically restructuring catalyst under oxygen evolution reaction (OER) conditions. So far, little is known about the mechanistic complexity of the OER at different active sites of Co₃O₄ at the atomic level. Using the A- and B-terminations of a single-crystal Co₃O₄(001) model electrode, we apply a combination of density functional theory calculations and ab initio molecular dynamics simulations to identify three main types of active sites of Co₃O₄ under OER conditions. In addition to tetrahedral and octahedral surface sites, we report the formation of pseudo-octahedral sites due to a change in the local environment upon adsorption of intermediate species. For all these active sites, we analyze the elementary steps of the OER by descriptor-based analysis and the concept of degree of span control. While octahedral and pseudo-octahedral sites are catalytically more active than tetrahedral sites, we show structural sensitivity with respect to the key limiting reaction step, which ranges from O─O bond formation to O₂ desorption and *OH oxidation. Our modeling strategy, which captures changes in the local environment, elementary steps of the OER, and the contribution of different reaction steps to the current density, provides an integrated and comprehensive framework for describing complex oxide materials under applied bias.