Structure and Reactivity of IrO<i>_x</i> Nanoparticles for the Oxygen Evolution Reaction in Electrocatalysis: An Electronic Structure Theory Study

Abstract

In this work, we employ electronic structure methods to investigate the structure and reactivity of IrOx nanoparticle models as catalysts for the oxygen evolution reaction (OER). Based on the explicit inclusion of the potential and pH in a constant potential framework, a computational approach is applied to investigate the thermodynamics of the proton and electron transfer process of IrOx cluster models. We address structural changes of the clusters under electrochemical conditions by constructing potential–pH diagrams from our computational results. Comparison of two IrOx cluster structures suggests that the charge transport to the clusters strongly depends on the pH. As a result, structures with a maximum number of on-top hydroxyl (OHμ1) species are stable at low potentials and deprotonation becomes favorable with increasing potential. An assessment of the Ir oxidation states in our models shows that mixed oxidation states, i.e., IrIV and IrV, occur around the OER onset potential and increase to higher oxidation states (IrVI) in the high potential regime. Furthermore, an investigation of the water adsorption mechanism is carried out at different potentials.The results suggest that the potential controls the energetics of intermediates as well as transition states during the OER.