CeO2-x(111) defect structure and the role of excess electron hopping in the oxygen migration: A view from computational modeling

M. V. GANDUGLIA PIROVANO; G. E. MURGIDA; V. FERRARI; A. M. LLOIS; D. ZHANG; Z.-K. HAN; Y. GAO

Barcelona

Congreso; 3rd Fundamentals and applications of cerium dioxide in catalysis; 2018

Deep understanding of the structure of reduced ceria (CeO2) surfaces, and the the diffusion of oxygen vacancies, are essential to tailor their functionality in applications. For the CeO2-x(111) surface, whether oxygen vacancies prefer the surface or the subsurface, whether surface oxygen vacancies attract or repel, and which is the most stable vacancy structure for varying vacancy concentration and temperature, are being heatedly debated.In this work, recent results on the CeO2-x(111) surface will be discussed, putting the emphasis on theoretical studies. Isolated vacancies prefer the subsurface with multiple local minima with respect to the cationic sites on which the excess electrons driving the Ce4+ to Ce3+ reduction localize, 1,2 and a (2x2) ordered subsurface vacancy structure is predicted,3 in line with the results of AFM experiments. Also, by direct imaging, five periodic structures representing reduction stages from CeO2 to Ce2O3 have been observed upon annealing and are explained.4 In addition, a novel explanation for the observed surface oxygen vacancy clustering in STM experiments5 is provided.6 Finally, we elucidate the oxygen diffusion process at different temperatures, showing that is entangled with the hopping of the Ce3+, and that distinct dynamical regimes exist within the 300-900 K temperature range.7