Insights into the Surface-Defect Dependence of Photoreactivity over CeO₂ Nanocrystals with Well-Defined Crystal Facets

Crystal facet engineering (CFE) has been widely employed to regulate the photoreactivity of crystalline materials, mostly concerning the surface atomic and electronic structures. However, surface defects ubiquitous in real catalysts have long been less recognized. An integrated examination of various influence factors is necessary for the elucidation of an accurate structure–function relationship. Herein, we carefully studied the heterogeneous photoreactivity of CeO₂ nanocrystals (NCs) with well-defined crystal facets in multiple processes, including photocatalytic oxidation of volatile organic compounds (VOCs), O₂ evolution, and ·OH generation. Variable reactivity priorities were found between different nanoshapes as well as samples of identical nanoshapes. With integrated examinations of the coexisting surface factors (i.e., atomic, electronic, and defect structures), surface defects were evidently proved to compete with other surface factors in deciding the final photoreactivity orders. Surface-defect structure (e.g., Ce³⁺ ions and O vacancies) was suggested to greatly influence the surface properties of ceria NCs, including the activation of reactants as well as the mobility of surface lattice oxygen. The results clearly confirm the surface-defect dependence of photoreactivity and provide further insights into the complex surface effects in semiconductor photocatalysis. It also underscores the significance of surface-defect structure as an essential supplement to the traditional CFE strategy for achieving desired solar energy utilization