Role of Defects in the Interplay between Adsorbate Evolving and Lattice Oxygen Mechanisms of the Oxygen Evolution Reaction in RuO2 and IrO2

The mechanistic interplay between the oxygen evolution reaction (OER) and material degradation during water electrolysis is not yet well understood even for the most studied OER electrocatalysts such as RuO2 and IrO2. It is still disputed whether the lattice oxygen mechanism (LOM) may be competitive with the conventional adsorbate evolving mechanism (AEM) of the OER in these materials and, if so, under what conditions. Herein, we employ density functional theory calculations to demonstrate that the LOM can give rise to higher OER activity than the AEM at the active sites involving structural defects, both intrinsic and extrinsic. Specifically, we show that, although the AEM is preferred for the perfect (110) and (211) surfaces, the formation of metal vacancies due to catalyst dissolution may lead to much lower OER overpotentials for the LOM. Also, by screening several metal impurities in RuO2, we reveal that dopants such as Ni and Co can promote the LOM over the AEM even for the perfectly structured surfaces. Overall, we demonstrate that defective IrO2 is less LOM active than RuO2 that should contribute to its superior stability under OER conditions.