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.