Oxygen-vacancy ordering and dynamics at the reduced CeO2(111) surface and the entanglement with polaron hopping

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

Lauzanne

Conferencia; CECAM Molecular and materials simulation at the turn of a decade: 50 years of CECAM.; 2019

CECAM

The ability of ceria (CeO 2 ) to store, release, and transport oxygen is crucial to its functionality in applicationsin catalysis, fuel cells, sensors, and recently in biology. Deep understanding of the structure and dynamics ofoxygen vacancies at ceria surfaces is essential for the rational design of improved systems in suchapplications. For the ceria (111) surface, whether oxygen vacancies prefer the subsurface or the surface andif surface oxygen vacancies attract or repel as well as whether oxygen migration and polaron (Ce 3+ ) hoppingare entangled, are still heavily debated. Also, a number of ordered phases have been observed uponreduction, but their structures have remained elusive. Here, supported by experimental and theoreticalresults, obtained employing density functional theory in combination with statistical thermodynamics, MonteCarlo simulations, and ab-initio molecular dynamics, the current understanding of the structure of thereduced ceria (111) surface will be discussed [1-6]. We predict the preference of polarons for next-nearestcationic sites to the vacancies [1-3], and that at low temperature and low vacancy concentrations, vacanciesprefer subsurface sites with a local (2 × 2) ordering, whereas mostly linear surface vacancy clusters do formwith increased temperature and degree of reduction [3,7]. Moreover, we explain the nature of the observedreduced ceria (111) surface reconstructions [4-6]. Finally, in the 300-900 K range, we identify differentdynamic regimes in the migration of oxygen vacancies and in the hopping of polarons and show that theirdynamic behaviors are entangled [7].