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Vacancy Generation and Oxygen Uptake in Cu-Doped Pr-CeO2 Materials using Neutron and in Situ X‑ray Diffraction
journal contribution
posted on 2016-12-02, 18:48 authored by Anita M. D’Angelo, Nathan A. S. Webster, Alan L. ChaffeeThe oxygen uptake ability of Pr-CeO2-based oxygen carriers, catalysts, and solid oxide fuel cells
can be attributed to 3+ cation generation and the presence of vacant
oxygen sites. Oxygen occupancies of CeO2, Pr-CeO2, and 5% Cu-doped Pr-CeO2 were investigated using neutron
diffraction and related to the oxygen uptake as determined using thermogravimetric
analysis (TGA). The presence of vacant tetrahedral oxygen sites at
room temperature did not correspond to low-temperature oxygen uptake.
The materials did not uptake oxygen at 420 °C, but oxygen uptake
was observed at 600 °C, which indicated that a minimum temperature
needs to be met to generate sufficient vacancies/3+ cations. Variations
in the lattice parameter as a function of temperature were revealed
using in situ X-ray diffraction (XRD). With increasing temperature
the lattice parameter increased linearly due to thermal expansion
and was followed by an exponential increase at ∼300–400
°C as cations were reduced. Despite segregation of Cu into CuO
at high dopant concentration, at 600 °C a higher O2 uptake was obtained for Ce0.65Pr0.20Cu0.15O2−δ (120 μmol g–1), in comparison to Ce0.75Pr0.2Cu0.05O2−δ (92 μmol g–1), and was higher than that for Ce0.8Pr0.2O2−δ (55 μmol g–1). Both
Pr and Cu introduce vacancies and promote the O2 uptake
of CeO2.
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