Distribution of Oxygen Vacancies in RuO2 Catalysts and Their Roles in Activity and Stability in Acidic Oxygen Evolution Reaction

By combining density functional theory (DFT) calculations and the cluster expansion (CE) model in an active-learning framework, we comprehensively studied the distribution features of oxygen vacancies (O_V’s) as well as their contributions to the stability and activity of the RuO₂ catalyst in acidic oxygen evolution reaction (OER). The results show that O_V’s prefer to be located at bridge oxygen sites on the RuO₂(110) surface and the next-nearest-neighbor trans positions of surface RuO₆ octahedra in pairs due to interactions between two O_V’s, and high concentrations of O_V’s exhibit a continuous zigzag distribution in the (110) plane of RuO₂. The oxygen vacancy distribution can be explained by the charge repulsion between the low-valent Ru and O, which is referred to as the “heterovalent ion-oxygen exclusion principle”. In addition, the DFT results show that the presence of O_V’s cannot improve the inherent OER activity of specific Ru sites since low-valent Ru sites hinder deprotonation of the second water molecule. Nevertheless, O_V’s can improve the stability of RuO₂ by suppressing the lattice oxygen mechanism (LOM) path. In summary, this work provides deeper insights into the mechanism of the OER of RuO₂ with O_V’s in acidic media and a possible way to improve catalyst performance by using oxygen vacancy engineering.