Surface-Driven Electron Localization and Defect Heterogeneity in Ceria

The exceptional performance of ceria (CeO₂) in catalysis and energy conversion is fundamentally governed by the presence of defects in the material, particularly oxygen vacancies. The formation of each oxygen vacancy (V_O), which carries an effective +2 charge, is assumed to be compensated by two localised electrons on cations (Ce³⁺) close to the V_O. We show that, while this 1V_O : 2Ce³⁺ ratio accounts for the global charge compensation, it does not apply at the local scale. Combined state-of-the-art calculations and synchrotron spectroscopy measurements show that electrons have a strong preference to localise and segregate on the surface, which can overcome the trapping force from the V_O sites in the bulk. This preference leads to a non-uniform defect distribution, with a higher 2Ce³⁺/ V_O ratio at the surface than in the bulk, an effect particularly pronounced in small nanoparticles. Such surface-driven localisation is expected to alter both the surface chemical reactivity and the bulk ionic conductivity of ceria, providing a new framework for understanding the defect chemistry in easily reducible oxides.

Authors: Xingfan Zhang, Akira Yoko, Yi Zhou, Woongkyu Jee, Alvaro Mayoral, Taifeng Liu, Jingcheng Guan, You Lu, Thomas W. Keal, John Buckeridge, Kakeru Ninomiya, Maiko Nishibori, Susumu Yamamoto, Iwao Matsuda, Tadafumi Adschiri, Osamu Terasaki, Scott M. Woodley, C. Richard A. Catlow, Alexey A. Sokol

DOI: https://doi.org/10.1021/jacs.5c10679