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 (OV'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 OV'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 OV's, and high concentrations of OV'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 OV's cannot improve the inherent OER activity of specific Ru sites since low-valent Ru sites hinder deprotonation of the second water molecule. Nevertheless, OV'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 OV's in acidic media and a possible way to improve catalyst performance by using oxygen vacancy engineering.