Effect of Dopants on the Energy of Oxygen-Vacancy Formation at the Surface of Ceria: Local or Global?

Abstract

Doping of oxides is used to modify their catalytic properties. The question we address here is whether a dopant affects only the oxygen atom next to it or also the ones further away. We find that low-valence dopants (Na and Li dopants in MgO and La and Y dopants in CeO2) have both a long-range and a short-range effect. In contrast, Pt, Ru, Zr, Ta, Mo, and W dopants in CeO2(111) affect only the oxygen atoms next to them. Furthermore, these dopants lower the energy of making an oxygen vacancy next to them by roughly the same amount. This is puzzling because these dopants have vastly different dopant–oxygen bond strength in their own oxide. By analyzing the electronic structure of the doped oxide and the changes caused by vacancy formation, we suggest that they have similar effects on vacancy formation energy because when they dope ceria, they become tetravalent, just like the Ce atom they replace.