Synthesis, Sintering, and Electrical Properties of BaCe0.9−xZrxY0.1O3−δ

BaCe0.9−xZrxY0.1O3−δ powders were synthesized by a solid-state reaction. Different contents of cerium and zirconium were studied. Pellets were sintered using either conventional sintering in air at 1700◦C or the Spark Plasma Sintering (SPS) technique. The density of the samples sintered by SPS is much higher than by conventional sintering. Higher values of ionic conductivity were obtained for the SPS sample

The formation of oriented barium carbonate from the decomposition of yttria-doped barium zirconate films

Yttria doped barium zirconate (BZY) thin films show promise thanks to their high proton conductivities and their possibility for use in studying fundamental processes such as exsolution. This work demonstrates that highly oriented BZY thin (45 nm) films on (100) single crystal strontium titanate decompose into oriented barium carbonate rods and yttria stabilized zirconia when exposed to industrial grade Ar or pure CO at 800 °C. It is shown with transmission electron microscopy that the rods nucleate on the BZY surface. The causes and modes of decomposition in these thin films are discussed in detail

Fabrication of Yttrium-Doped Barium Zirconate for High Performance Protonic Ceramic Membranes

Barium zirconate has emerged as the leading candidate material for fabricating dense ceramic membranes for hydrogen separation. B-sites in the ABO3 perovskite are acceptor-doped with a +3 cation – most commonly yttrium – charge-compensated by the formation of oxygen ion vacancies in the lattice. A minor fraction of B-sites can be filled with cerium to give BaZr0.9-xCexY0.1O3-d, x ≤ 0.2. Upon hydration at elevated temperatures, weakly-bound protons are formed in the lattice. This produces a cubic perovskite ceramic proton conductor useful in diverse applications, such as protonic ceramic fuel cells, electrolysers, and catalytic membrane reactors operating at temperatures between 600 and 800 °C. A necessary requirement for fabricating thin ceramic membranes for proton diffusion is to maximize grain size while eliminating percolating porosity. However, high-density, large-grained barium zirconate is a very difficult material to prepare by traditional powder sintering methods. This chapter describes a new methodology for making protonic ceramic membranes with large grains and virtually no residual porosity. This discovery has the potential to have a profound impact on energy conversion efficiency of the various membrane devices envisioned for the coming hydrogen energy economy

Elaboration et caractérisation du matériau d électrolyte pour pile à combustible à conduction protonique (BaCe(0,9-x)ZrxY0,1 O3-delta)

Le composé BaCe(0,9-x)ZrxY0,1 O3-delta (x=0 ; 0,3 ; 0,7 et 0,9) est étudié en tant que matériau d électrolyte de pile à combustible à conduction protonique (PCFC). Des pastilles denses ont été fabriquées à partir de poudres synthétisées par chamottage, puis frittées à 1700C. Elles ont été caractérisées chimiquement par ICP AES, morphologiquement par MEB, structuralement par DRX et Raman et mécaniquement par dilatométrie. L insertion de protons après traitement sous atmosphère humide a été mise en évidence par profilométrie SIMS, XPS et DRX. La quantification des défauts protoniques entre 400C et 600C par mesure de la prise en eau a montré l augmentation de la concentration protonique avec le taux de cérium et lorsque la température diminue. Grâce à des mesures en courant continu sous atmosphère humide, la conductivité totale a été décomposée en deux termes : une contribution de type p aux fortes pressions partielles en oxygène et une contribution ionique. L étude de l effet isotopique a révélé une contribution protonique significative à 500C et 600C. Lorsque le taux de cérium augmente, l énergie d activation, déterminée d après les courbes d Arrhenius obtenues par spectroscopie d impédance, augmente et la résistivité des joints de grains par rapport au volume diminue. Une optimisation du procédé de mise en forme et de contrôle de la microstructure permettrait l amélioration de ces résultats déjà prometteurs. Des tests de frittage par Spark Plasma Sintering (SPS) ont été réalisés sur des échantillons sans cérium, lesquels présentent des valeurs de conductivité plus importantes que les échantillons frittés conventionnellement.BaCe(0.9-x)ZrxY0.1 O3-delta (x=0, 0.3, 0.7 et 0.9) compounds have been studied as electrolyte material for protonic ceramic fuel cell (PCFC). The powders were synthesized by a solid state reaction, and sintered to form dense pellets at 1700C. Chemical, morphological, structural and mechanical characterizations were performed on the samples, using respectively ICP AES, SEM, XRD, Raman and dilatometry. SIMS, XPS and XRD studies showed the insertion of protonic species in the samples, when treated in a moisturized atmosphere. Water uptake experiments provided quantification of the proton content between 400C and 600C: the protonic concentration increases with increasing cerium content and with decreasing temperature. The DC conductivity measured in wet atmosphere can be expressed as the sum of a p-type component, prominent at high oxygen partial pressure, and an ionic contribution. A study of the conductivity isotope effect revealed a significant protonic conductivity at 500C and 600C. When the cerium content increases, the activation energy, determined with the Arrhenius plots of the conductivity, increases and the resistivity of grain boundaries decreases compared to that of the bulk. An optimisation of the fabrication process and the control of the microstructure would improve these promising results. Spark Plasma Sintering (SPS) experiments have been performed on BaZr0.9Y0.1O3-delta samples, which exhibit higher conductivity values than the conventional sintered samples.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Ni-Infiltrated Spherical Porcelain Support as Potential Steam Reforming Microchannel Reactor

This paper describes the fabrication of kaolinite (Al2O3-2SiO2-2H2O) spherical bulbs by slip casting. The bisque-fired parts present a porosity of about 30% with submicron porosity confirmed by scanning electron microscopy. In addition, plate-like grains with channels were observed. After nickel infiltration of the specimens, nanosized Ni particles covered the surfaces of the channels of these grains. Permeation tests in 5% H2 at 400 and 600 °C resulted in fluxes between 0.05 and 0.06 mol·m−2·s−1 at a pressure gradient of 200 MPa·m−1. Potential applications of these specimens include supports for hydrocarbon (namely ethanol) steam reforming

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

This review paper focuses on the phenomenon of thermochemical expansion of two specific categories of conducting ceramics: Proton Conducting Ceramics (PCC) and Mixed Ionic-Electronic Conductors (MIEC). The theory of thermal expansion of ceramics is underlined from microscopic to macroscopic points of view while the chemical expansion is explained based on crystallography and defect chemistry. Modelling methods are used to predict the thermochemical expansion of PCCs and MIECs with two examples: hydration of barium zirconate (BaZr1−xYxO3−δ) and oxidation/reduction of La1−xSrxCo0.2Fe0.8O3−δ. While it is unusual for a review paper, we conducted experiments to evaluate the influence of the heating rate in determining expansion coefficients experimentally. This was motivated by the discrepancy of some values in literature. The conclusions are that the heating rate has little to no effect on the obtained values. Models for the expansion coefficients of a composite material are presented and include the effect of porosity. A set of data comprising thermal and chemical expansion coefficients has been gathered from the literature and presented here divided into two groups: protonic electrolytes and mixed ionic-electronic conductors. Finally, the methods of mitigation of the thermal mismatch problem are discussed

Oxygen electrodes for protonic ceramic cells

Protonic ceramic cells (PCCs), including protonic ceramic fuel cells (PCFCs) and electrolysis cells (PCECs), are attracting increasing attention owing to several advantages such as their low activation energy for proton diffusion, fuel flexibility, absence of fuel dilution, and potentially lower housing/stacking costs at intermediate operating temperatures (400–600 °C). However, one of the major challenges for PCCs is the design and realization of oxygen electrodes for efficient oxygen reduction and water splitting reactions. Many research groups have devoted efforts to this research topic and have obtained encouraging results showing improved power output and current density in PCCs owing to the improvement of the oxygen electrode. This trend needs to be continued to enable the commercialization of the PCC technology. This review article describes the research progress in oxygen electrodes for PCCs, comprehensively summarizing literature work and offering prospective pathways for further development of high-performance oxygen electrodes