Enhanced Oxygen Buffering by Substitutional and Interstitial Ni Point Defects in Ceria: A First-Principles DFT+U Study

Abstract

The defect chemistry and electronic structure of NiO/CeO2 solid solutions are studied by means of DFT+U calculations in the limit of low Ni doping. We consider four representative solid solutions in which the Ni atoms are present as substitutional and interstitial point defects in bulk crystalline CeO2, both in its stoichiometric form and in the presence of O vacancies. In all cases, Ni-doping significantly enhances the O buffering effect of ceria, controlled by O vacancy formation, but the actual microscopic mechanisms are different depending on the specific type and charge state of the point defects. The oxidation state of the Ni dopant is shown to univocally characterize the type of defect, whether interstitial (Ni+) or substitutional (Ni2+). Interstitial Ni+ defects result from a charge redistribution between the Ni and Ce cations that leads to the formation of characteristic Ni+−Ce3+ defect complexes. O release via vacancy formation in these interstitial solid solutions proceeds similarly as in pure ...