Origin of the low formation energy of oxygen vacancies in CeO2

Abstract

Oxygen vacancies play a crucial role in determining the catalytic properties of Ce-based catalysts, especially in oxidation reactions. The design of catalytic activity requires keen insight into oxygen vacancy formation mechanisms. In this work, we investigate the origin of oxygen vacancies in CeO2 from the perspective of electron density via high-energy synchrotron powder x-ray diffraction. Multipole refinement results indicate that there is no obvious hybridization between bonded Ce and O atoms in CeO2. Subsequent quantitative topological analysis of the experimental total electron density reveals the closed-shell interaction behavior of the Ce–O bond. The results of first-principles calculation indicate that the oxygen vacancy formation energy of CeO2 is the lowest among three commonly used redox catalysts. These findings indicate the relatively weak bond strength of the Ce–O bond, which induces a low oxygen vacancy formation energy for CeO2 and thus promotes CeO2 as a superior catalyst for oxidation reactions. This work provides a new direction for design of functional metal oxides with high oxygen vacancy concentrations.