Oxygen vacancies in self-assemblies of ceria nanoparticles

Abstract

Cerium dioxide (CeO2, ceria) nanoparticles possess size-dependent chemical properties, which may be very different from those of the bulk material. Agglomeration of such particles in nanoarchitectures may further significantly affect their properties. We computationally model the self-assembly of CenO2n particles (n = 38, 40, 80)-zero-dimensional (0D) structures-in one- and two-dimensional (1D and 2D) nanoarchitectures by employing density-functional methods. The electronic properties of 1D Ce80O160 and 2D Ce40O80 resemble those of larger 0D crystallites, Ce140O280, rather than those of their building blocks. These 0D, 1D and 2D nanostructures are employed to study the size dependence of the formation energy of an oxygen vacancy, Ef(Ovac), a central property in ceria chemistry. We rationalize within a common electronic structure framework the variations of the Ef(Ovac) values, which are computed for the CenO2n nanostructures with different sizes and dimensionalities. We identify: (i) the bandwidth of the unoccupied density of states projected onto the Ce 4f levels as an important factor, which controls Ef(Ovac); and (ii) the corner Ce atoms as the structural motif essential for a noticeable reduction of Ef(Ovac). These results help to understand the size dependent behaviour of Ef(Ovac) in nanostructured ceria.