Co9S8as a Catalyst for Electroreduction of O2: Quantum Chemistry Predictions

Abstract

The slab band quantum computational approach in the Vienna ab initio simulation package (VASP) is used to calculate the adsorption energies of reactants, reaction intermediates, and products in O₂ reduction and in water oxidation in acid on three crystallographic surfaces of pentlandite structure Co₉S₈. Reversible potentials for the reaction steps involving electron and proton transfer are determined by using the energies in a linear Gibbs free energy relationship. On the basis of these results, we find that the partially OH-covered (202) surface is active toward O₂ reduction and should have overpotential behavior similar to that observed for platinum electrodes. One structure in the predicted four-electron reduction mechanism is novel: S^2- provides an adsorption site for O following O−O bond scission, which, unlike the case of platinum electrodes, takes place prior to the first reduction step.