Oxygen Vacancy Generation and Stabilization in CeO_2–<i>x</i> 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 CeO2–x and promote the photocatalytic activity of CeO2–x. The sample Cu/CeO2–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 CeO2–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 CeO2–x during photocatalytic CO2 reduction, which is responsible for the improved and sustained photocatalytic activity.