O vacancies on steps on the CeO2(111) surface

Abstract

Cerium dioxide is a compound important for heterogeneous catalysis, energy technologies, biomedical applications, etc. One of its most remarkable properties is low O vacancy (O_vac) formation energy E_f. Nanostructuring of ceria was shown to decrease E_f and to make the oxide material more active in oxidative reactions. Here we investigate computationally formation of O_vac on CeO₂(111) surfaces nanostructured by steps with experimentally observed structures. To facilitate the search for O_vac + 2Ce³⁺ configurations that yield the lowest E_f values we proposed and employed an efficient computational scheme where DFT + U calculations were preceded by a pre-screening procedure based on the results of plain DFT calculations. E_f values on the steps were calculated to be up to 0.7 eV lower than on a regular CeO₂(111) surface. Some energetically stable O_vac + 2Ce³⁺ configurations were found to include subsurface Ce³⁺ ions. The present results quantify to what extent the roughness of the CeO₂(111) surface affects its reducibility.