Effect of tri- and tetravalent metal doping on the electrochemical properties of lanthanum tungstate proton conductors

Metal doping on lanthanum tungstates at W2 site was confirmed by TOF-NPD. TGA and EIS demonstrated proton conductivity.</p

Local Structure of Proton-Conducting Lanthanum Tungstate La28–xW4+xO54+δ: a Combined Density Functional Theory and Pair Distribution Function Study

Lanthanum tungstate (La28–xW4+xO54+δ) is a good proton conductor and exhibits a complex fluorite-type structure. To gain further understanding of the short-range order in the structure we correlate the optimized configurations obtained by density functional theory (DFT) with the experimental atomic pair distribution function analysis (PDF) of time-of-flight neutron and synchrotron X-ray data, collected at room temperature. The local atomic arrangements cannot be described by means of any average symmetric structure. Tungsten forms WO6 octahedra in alternating directions, La1 is mainly 8-fold coordinated in relatively symmetric cubes, and La2 is coordinated with 6 or 7 oxygens in heavily distorted cubes. Both DFT and PDF confirm that the excess tungsten (x) is incorporated in La2 (1/4, 1/4, 1/4) sites in the La27W5O55.5 composition. This additional tungsten can be considered as a donor self-dopant in the material and has implications to the conducting properties and the defect structure

Preparation of stabilized Gd-doped BaPrO₃ materials by Zr substitution

The synthesis of a Gd-doped BaPrO3–BaZrO3 solid solution has been investigated in an effort to stabilize the BaPrO3 perovskite, a system with poor chemical stability and endurance for humid, CO2 and reducing conditions. The phases BaZrxPr1−xGd0.3O3−δ (x = 0–0.7, Δx = 0.1) have been prepared by acrylamide combustion synthesis. The solid solution is characterized by X-ray powder diffraction, scanning electron microscope (SEM) and durability against CO2, moisture and reducing conditions investigated. Crystal structure parameters were obtained from X-ray powder diffraction data and results show its symmetry increases by increasing Zr content. BaZr0.1Pr0.6Gd0.3O3−δ has a maximum weight increase due to reaction with CO2 of nearly 13%, while this is reduced below 2% for BaZr0.5Pr0.2Gd0.3O3−δ. The material appears to be unaltered by 5%H2/Ar for x ≥ 0.5, and under wet Ar for x ≥ 0.4, and thus render a higher chemical stability and confirms the stabilizing role of BaZrO3. However, microstructure investigations reveal gadolinium segregation due to the high doping level of the perovskite

Chemical and electrical properties of BaPr_0.7Gd_0.3O_{3<em>−</em>}_δ

Doped perovskites have a growing interest as electrolytes for IT-SOFCs. In the search for proton conducting electrolytes, Gd-doped BaPrO3 was studied. The present work reports the chemical stability and electrical conductivity of BaPr0.7Gd0.3O3-delta powders. This system is found to be highly reactive under water, CO2 and hydrogen containing atmospheres. Comparison of the conduction behaviour measured at different atmospheres indicates that the system behaves as a p-type electronic conductor. The total conductivity is about 1 x 10(-3) S cm(-1) at 300 degrees C, in dry O-2. The resistance of the system seems to be dominated by the grain boundary contribution. However, structure investigation reveals there is a gadolinia segregation, which may act as a resistive barrier. The material is not suitable for SOFC applications due to its low stability. (c) 2007 Elsevier B.V. All rights reserved.</p

Proton hydration and transport properties in proton-conducting ceramics: Fundamentals and highlights

International audienc

Nano coated interconnects for SOFC (NaCoSOFC)

The NaCoSOFC project is focused on the development of nano coatings for SOFC interconnects. The project is sponsored by the Nordic Top Level Research Initiative and has four project partners: Sandvik Materials Technology which is producing coated interconnects, Chalmers University of Technology and the University of Oslo that characterize samples with respect to e.g. corrosion, Cr evaporation and ASR as well as Topsoe Fuel Cell that is testing the developed interconnects in its stacks. The developed coatings are based on a combination of Co with RE elements and exhibit high corrosion resistance, 10 fold decrease in Cr evaporation and ASR values that are approximately 50% of the uncoated material