Tracking the Facet Transformation of CeO₂ by ¹⁷O Solid-State Nuclear Magnetic Resonance

CeO₂ nanomaterials expose various crystal facets with distinct surface geometry, resulting in different surface reactivities and material behaviors that ultimately determine their performances and suitability for a wide range of applications. Here, we apply ¹⁷O solid-state nuclear magnetic resonance (NMR) to follow the facet transformation of CeO₂ at increased temperatures, observing a transition from (100) to (110) and finally to the more stable (111), based on the characteristic NMR shifts associated with the unique surface structure of each facet. In addition, we explore the effects of Pt ions on the conversion of different facets, which are found to promote the formation of the thermally stable (111) facet. Furthermore, ¹⁷O solid-state NMR provides a semiquantitative method for measuring the fractions of exposed facets. This work offers new insights and a more comprehensive understanding of crystal facet structures, and the new approach can be readily extended to study the facets of other oxide-based materials.