Mild generation of surface oxygen vacancies on CeO₂ for improved CO₂ photoreduction activity

The vacancy defects of semiconductor photocatalysts play key roles in enhancing their photocatalytic CO₂ reduction activity. In this work, CeO₂ was chosen as a model catalyst and oxygen vacancies were introduced on its surface by a facile and mild oxalic acid treatment followed by moderate heating in N₂. Such a treatment resulted in a much increased ratio of Ce³⁺/Ce⁴⁺ in CeO₂, and the oxygen vacancy-enriched CeO₂ showed remarkably enhanced photocatalytic activity in CO₂ reduction, with CO being the dominant reduction product, whose yield was about 8 times that on the pristine CeO₂. In situ FT-IR spectra showed that the abundant oxygen vacancies substantially improved the CO₂ adsorption/activation on the surface of CeO₂, which facilitated the subsequent reduction of CO₂. However, the carbonates strongly adsorbed on the photocatalyst surface might be the main obstacle to maintaining the high CO₂ reduction activity and stability of CeO₂ with O vacancies.