Xingfan Zhang, University College London

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) is assumed to be compensated by two localised electrons on cations (Ce³⁺) close to the vacancy. We show that while this 1V_O : 2Ce³⁺ ratio accounts for the global charge compensation, it does not apply at the local scale. Hybrid QM/MM defect calculations with ChemShell, together with synchrotron X-ray photoelectron spectroscopy (XPS) measurements and unbiased Monte Carlo simulations, 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.

Citation:

X. Zhang, A. Yoko, Y. Zhou, W. Jee, A. Mayoral, T. Liu, J. Guan, Y. Lu, T. W. Keal, J. Buckeridge, K. Ninomiya, M. Nishibori, S. Yamamoto, I. Matsuda, T. Adschiri, O. Terasaki, S. M. Woodley, C. R. A. Catlow and A. A. Sokol (2025) “Surface-Driven Electron Localization and Defect Heterogeneity in Ceria”, J. Am. Chem. Soc., 147, 33888–33902. DOI: 10.1021/jacs.5c10679