Enhanced photon-to-electron conversion and improved water resistance of hydrogenated ceria in photocatalytic oxidation at gas–solid interface

Hydrogenation has been widely employed in solar-driven photocatalysis, to enhance the light absorption and photon-to-electron (PE) conversion of semiconductors. However, there still remain controversies in this field, such as the precise roles of bulk and surface oxygen vacancies (V O ). Furthermore, the influence of hydrogenation on surface reactions in photocatalysis at gas-solid interface has been rarely discussed. Herein, gray CeO 2 was prepared by treating pristine CeO 2 in H 2 /Ar, presenting surface plasma resonance (SPR) like visible light absorption. No modifications on microstructural surface disordering or valence band edge were detected in gray CeO 2 . Hydrogenation induced abundant V O inside both the bulk lattice and the surface layer. Gray CeO 2 presented much enhanced performance as well as improved water resistance in photocatalytic oxidation of gaseous hydrocarbons. Additional post-annealing in air was applied to remove surface V O and discolored the material. With series of characterization including XPS, Raman, EPR and in-situ FTIR, it was found bulk V O mostly contributes to the enhanced PE conversion, while surface V O is mainly responsible for the improved water resistance. Our results unambiguously confirmed hydrogenation as an efficient approach to simultaneously optimize oxide semicomductors in various elementary steps of photocatalysis.