First-Principles Study of Oxygen Evolution Reaction Mechanisms in RuO2 and IrO2

Electrocatalytic water splitting has received a great deal of attention as an attractive way of storing energy in the form of pure hydrogen. RuO2 and IrO2 catalysts are archetypical materials used for the anodic oxygen evolution reaction (OER) in acidic media, but even for these oxides atomistic understanding of activity-stability relationships remains incomplete. For example, unlike other metal-oxide catalysts, it is still disputed whether lattice oxygen can be involved in OER in RuO2 and IrO2. In this work employing the density functional theory calculations we demonstrate that the lattice oxygen mechanism (LOM) can indeed outperform the conventional adsorbate evolving mechanism (AEM) at the active sites involving structural defects. These defects include metal vacancies that are known to be formed during electrocatalytic dissolution and metal dopants in the parent structure such as nickel and cobalt. According to calculations IrO2 should be less prone to LOM than RuO2 that is consistent with its greater stability under OER conditions. The obtained theoretical results will be discussed in the context of interplay between different OER mechanisms across OER electrocatalysts, as well as available experimental data.