Electron Localization Determines Defect Formation on Ceria Substrates

TLDR

The high performance of ceria as an oxygen buffer and active support for noble metals in catalysis relies on efficient lattice oxygen supply governed by oxygen vacancy formation. High‑resolution scanning tunneling microscopy and density functional calculations were used to elucidate the local structure of surface and subsurface oxygen vacancies on the (111) surface. Released oxygen leaves electrons that localize on cerium ions, and clusters of more than two vacancies—especially those involving subsurface sites—expose these reduced cerium ions, underscoring the importance of subsurface vacancies in vacancy cluster formation and informing oxidation mechanisms on reducible rare‑earth oxides.

Abstract

The high performance of ceria (CeO2) as an oxygen buffer and active support for noble metals in catalysis relies on an efficient supply of lattice oxygen at reaction sites governed by oxygen vacancy formation. We used high-resolution scanning tunneling microscopy and density functional calculations to unravel the local structure of surface and subsurface oxygen vacancies on the (111) surface. Electrons left behind by released oxygen localize on cerium ions. Clusters of more than two vacancies exclusively expose these reduced cerium ions, primarily by including subsurface vacancies, which therefore play a crucial role in the process of vacancy cluster formation. These results have implications for our understanding of oxidation processes on reducible rare-earth oxides.