Correlations between Oxygen Uptake and Vacancy Concentration in Pr-Doped CeO₂

The oxygen uptake of a series of Pr–CeO₂ materials was measured using thermogravimetric analysis at 420 and 600 °C, and at both temperatures, 20% Pr–CeO₂ was found to have the highest uptake. The materials were characterized using X-ray diffraction and scanning transmission electron microscopy. Defects in the materials were identified using Raman spectroscopy, and ultraviolet–visible spectroscopy was used to show the presence of Pr cations in the +3 oxidation state. The existence of these species was attributed to be responsible for the ability of the materials to uptake oxygen. Electron energy loss spectroscopy was used to investigate the effect of Pr addition to CeO₂; the Ce M₅/M₄ and O I_B/I_C ratios were calculated to indicate the relative changes in the Ce³⁺ and oxygen vacancy concentration, respectively. There was no observable increase in the Ce³⁺ concentration; however, the oxygen vacancy concentration increased with an increase in the Pr content. Thus, Pr increases the defect concentration and the ability of the materials to uptake oxygen.