Defects and transport in Pr_xCe_1−xO_2−δ: Composition trends

Abstract

Nonstoichiometric mixed ionic and electronic conductors (MIECs) find use as oxygen permeation membranes, cathodes in solid oxide fuel cells, oxygen storage materials in three-way catalysts, and chemoresistive gas sensors. Praseodymium-cerium oxide (Pr x Ce 1Àx O 2Àd ) solid solutions exhibit MIEC behavior in a relatively high and readily accessible oxygen partial pressure (P O 2 ) regime and as such serve as model systems for investigating the correlation between thermodynamic and kinetic properties as well as exhibiting high performance figures of merit in the above applications. In this paper, we extend recently published results for Pr 0.1 Ce 0.9 O 2Àd to include values of x 5 0, 0.002, 0.008, 0.1, and 0.20 (in Pr x Ce 1Àx O 2Àd ) to test how both defect and transport parameters depend on Pr fraction. Important observed trends with increasing x include increases in oxygen ion migration energy and MIEC and reductions in vacancy formation and Pr ionization energies. The implications these changes have for potential applications of Pr x Ce 1Àx O 2Àd are discussed.

Ionic/Electronic Conductivity, Thermal/Chemical Expansion and Oxygen Permeation in Pr and Gd Co-Doped Ceria PrxGd0.1Ce0.9-xO1.95-δ

“…This indicates that Ce will be more readily reduced upon a higher Pr concentration. A similar trend was also observed in purely Prdoped ceria 35 and purely Gd-doped ceria. 53 It is also found that the reducibility of Ce 4+ and Pr 4+ in ceria tends to be facilitated by the increasing oxygen nonstoichiometry, leading to a non-ideal reduction behavior.…”

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

“…This conclusion was also partially confi rmed with the results of ionic conductivities of Ce 1-x Pr x O 2-δ ( x = 0-0.2) shown in Figure 14 b. [ 373 ] The oxygen ionic conductivity fi rst increased by doping Pr into CeO 2 and reach the highest value for Pr 0.1 Ce 0.9 O 2-δ , then a decreased ionic conductivity was observed when 20% Ce was replaced by Pr. For instance, the electrical conductivity reached as high as 0.1 S cm −1 at 800 °C.…”

“…[ 374,375 ] The ionic conductivity reached ≈0.05 S cm −1 at 800 °C when the dopant concentration of Pr was 10%. [ 373 ] So, through appropriate ion REVIEW wileyonlinelibrary.com doping, the Pr doped cceria was possible to be used as oxygen reduction electrode for SOFCs. For example, an improved total conductivity (most likely the enhanced electronic conductivity) was obtained by adding 2 mol% CoO x into a Ce 0.9 Pr 0.1 O 2-δ phase.…”

High temperature X-ray diffraction and thermo-gravimetrical analysis of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ under different atmospheres

“…The low creep resistance questioning the actual use of BSCF in high temperature gas separation membranes and several attempts to stabilize BSCF by chemical substitution have appeared, both to avoid the formation of the hexagonal polymorph and to increase the creep resistance [22][23] . Chemical expansion [24][25] , particularly for ceria and perovskite materials with transition metals (Co, Fe) on the Bsite is another concern with respect to the mechanical stability of oxygen permeation membranes [26][27][28][29][30][31][32] . The chemical and thermal expansion of BSCF has also been reported by several groups [33][34][35][36][37][38] , showing lower chemical expansion than other similar candidate membrane materials due to smaller changes in oxygen stoichiometry and a generally larger unit cell, which is less sensitive to temperature and stoichiometry changes 38 .…”