| Summary: | Doping CeO<sub>2</sub> with Y cations was achieved in this study using three strategies: doping only during the hydrothermal process (H-Y-doped CeO<sub>2</sub>), doping only during the impregnation process (I-Y-doped CeO<sub>2</sub>), and doping during both the hydrothermal and impregnation processes (H/I-Y-doped CeO<sub>2</sub>). During the three synthesis strategies of Y-doped CeO<sub>2</sub>, these Y ions could be incorporated into the CeO<sub>2</sub> lattice in the +3 state while holding the cubic fluorite structure, and no impurity phases were detected. Pure CeO<sub>2</sub> crystal itself contained a certain number of intrinsic <i>V</i><sub>O</sub> defects, and Y-doping was beneficial for the creation of extrinsic <i>V</i><sub>O</sub> defects. The relative concentrations of <i>V</i><sub>O</sub> defects were quantified by the values of <i>A</i><sub>592</sub>/<i>A</i><sub>464</sub> obtained from Raman spectra, which were 1.47, 0.93, and 1.16 for the H-Y-, I-Y-, and H/I-Y-doped CeO<sub>2</sub>, respectively, and were higher than that of the undoped one (0.67). Moreover, the OSCs of the three Y-doped CeO<sub>2</sub> were enhanced, and the sequence of OSCs was: H-Y-doped CeO<sub>2</sub> (0.372 mmol/g) > H/I-Y-doped CeO<sub>2</sub> (0.353 mmol/g) > I-Y-doped CeO<sub>2</sub> (0.248 mmol/g) > Undoped CeO<sub>2</sub> (0.153 mmol/g); this result was in good agreement with the Raman spectroscopy results.
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