Oxygen Vacancy Generation and Stabilization in CeO_{2- x} by Cu Introduction with Improved CO₂ Photocatalytic Reduction Activity

Introducing O vacancies into the lattice of a semiconductor photocatalyst can alter its intrinsic electronic properties and band gap, thus enhancing the visible light absorption, promoting the separation/transfer of photogenerated charge carriers, and resultantly elevating the photocatalytic activity of oxide semiconductors. Moreover, O vacancies can help adsorb and activate CO₂ on photocatalyst surfaces, which, however, are prone to being filled by O atoms during the photoreduction reaction. In this work, Cu was introduced to increase the O vacancy concentration in CeO_2-x and promote the photocatalytic activity of CeO_2-x. The sample Cu/CeO_2-x-0.1 showed the highest photocatalytic activity with a CO yield of 8.25 μmol g^-1 under 5 h irradiation, which is ∼26 times that on CeO_2-x. According to the analysis of Raman and X-ray photoelectron spectroscopy (XPS) spectra, it has been evidenced that Cu introduction benefits the chemical stabilization of O vacancies in CeO_2-x during photocatalytic CO₂ reduction, which is responsible for the improved and sustained photocatalytic activity.