Rob Hui

Mesoporous Nanostructured Nb-Doped Titanium Dioxide Microsphere Catalyst Supports for PEM Fuel Cell Electrodes

Crystalline microspheres of Nb-doped TiO(2) with a high specific surface area were synthesized using a templating method exploiting ionic interactions between nascent inorganic components and an ionomer template. The microspheres exhibit a porosity gradient, with a meso-macroporous kernel, and a mesoporous shell. The material has been investigated as cathode electrocatalyst support for polymer electrolyte membrane (PEM) fuel cells. A uniform dispersion of Pt particles on the Nb-doped TiO(2) support was obtained using a microwave method, and the electrochemical properties assessed by cyclic voltammetry. Nb-TiO(2) supported Pt demonstrated very high stability, as after 1000 voltammetric cycles, 85% of the electroactive Pt area remained compared to 47% in the case of commercial Pt on carbon. For the oxygen reduction reaction (ORR), which takes place at the cathode, the highest stability was again obtained with the Nb-doped titania-based material even though the mass activity calculated at 0.9 V vs RHE was slightly lower. The microspherical structured and mesoporous Nb-doped TiO(2) is an alternative support to carbon for PEM fuel cells.

Proton Exchange Membrane Fuel Cells: Materials Properties and Performance

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Thin Film Solid Oxide Fuel Cells Deposited by Spray Pyrolysis

Two techniques of spray pyrolysis, namely, electrostatic and pneumatic spray deposition, were used to deposit samaria-doped ceria (SDC) electrolyte and lanthanum strontium cobalt ferrite (LSCF) cathode on cermet or metal supported anodes for solid oxide fuel cells (SOFCs) operated at reduced temperature. The deposition processes, the properties of the deposited films, and the electrochemical performances of the fabricated cells are reported in this paper. The deposited SDC electrolytes were dense and gas-tight, and had good adhesion to the underlying anodes. The deposited LSCF cathode had a preferred morphology to facilitate the transport of oxygen gas and effective contact with the electrolyte. Button cell testing indicated that the SOFCs with electrolyte or cathode deposited by spray pyrolysis had good electrochemical performance. This study demonstrated that spray pyrolysis is a cost-effective process for fabricating thin film SOFCs, especially metal supported SOFCs.

Proton Conductivity and Stability of Ba2In2O5 in Hydrogen Containing Atmospheres

Ba 2 In 2 O 5 is one of the oxygen deficient ceramic materials widely investigated for both oxygen ion conduction and proton conduction in oxidizing atmospheres. However, its electrochemical properties have not been studied in hydrogen containing atmospheres. In this work, the electrical conductivity of Ba 2 In 2 O 5 in hydrogen containing atmospheres was investigated by ac impedance spectroscopy in the temperature range between 100 and 500°C and compared to its conductivity in air and nitrogen in order to estimate the contribution of proton conductivity to the total conductivity. A stable electrical conductivity of over 0.3 S/cm was achieved in the temperature range of 300-480°C in a 50% vol H 2 /50% vol N 2 atmosphere. Electromotive force measurements (and complimentary open circuit cell voltage measurements) revealed high proton transport numbers over the temperature range. Ba 2 In 2 O 5 shows chemical stability in hydrogen containing atmospheres at temperatures up to 480°C, while decomposing at higher temperatures. Mechanical instability was noticed in humid atmospheres at 400°C and above. This previously unreported high conductivity in H 2 atmosphere creates an opportunity for use of Ba 2 In 2 O 5 as a proton conductive material for a range of intermediate temperature electrochemical devices.

Suspension Plasma Spraying of Intermediate Temperature SOFC Components Using an Axial Injection DC Torch

Intermediate temperature SOFC components, such as dense, nanostructured SDC electrolytes (samarium doped ceria) and porous anode sublayers were fabricated by suspension plasma spraying using an axial feed dc plasma torch. The liquid carrier employed in this approach allowed for controlled injection of much finer particles than in conventional thermal spraying, leading to thin coatings with a refined microstructure. Dense, thin (<10(m) and non-fractured electrolytes were created. Various processing routes for SOFC half-cells, using tape-cased, plasmasprayed and suspension-sprayed anodes, were explored. Loss of integrity and non-continuous coverage of the anode constituted the principal difficulties in the subsequent electrolyte deposition. The role of suspension feedstock particle size is discussed. Amongst various schemes investigated, a processing route that employs sequential suspension plasma spraying steps for both the electrolyte and the anode, using relatively large primary particles in the feedstock, constituted the most promising approach.

STEM HAADF Tomography of Molybdenum Disulfide with Mesoporous Structure

A highly ordered mesoporous molybdenum disulfide has been developed for catalysis in heavy oil refining. The morphology, structure, and composition of the material have been systematically characterized with advanced electron microscopy techniques. Scanning transmission electron microscopy with high‐angle annular dark field tomography has been used to investigate the porous structure to give spatial information on the nanometre scale, and offer a direct view of individual porous particles in three‐dimensions. The pore‐size distribution, connectivity of the pores, and the mesoporous surface area have also been analyzed and offer useful information towards catalyst design.

Electrochemical Properties of Low-Temperature Solid Oxide Fuel Cells Under Chromium Poisoning Conditions

Rapid performance degradations of solid oxide fuel cells were observed when the chromium-forming metallic alloys were used as interconnects. The formation of strontium chromium oxide (SrCrO4) on the surface of Sr-doped perovskite cathode was believed to be one of the main causes for the cell degradation. This chromium-poisoning effect was not mitigated when the operating temperature was lowered to 600°C. The SrCrO4 that formed mainly on the cathode surface was found in both La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) and Sm0.5Sr0.5CoO3 (SSCo) cathode, suggesting that all strontium-containing cathodes may develop low conductive chromite oxide compounds. However, this chromium-poisoning effect can be effectively mitigated by coating a protective layer on the surface of the interconnect.

Preparation and Characterization of Nanocrystalline Ba2In2 − x M x O5 − δ ( M = Ce , Zr )

Nanocrystalline, oxygen-deficient perovskite materials-Ce-doped Ba 2 In 2 O 5-δ (BIC) and Zr-doped Ba 2 In 2 O 5-δ (BIZ) powders-have been successfully synthesized via reactive spray deposition technique processing. The mean particle size, surface areas, and phases of BIC and BIZ powders were analyzed. The transmission electron microscopy images showed a particle size of ∼ 10 nm and the existence of nanopowder agglomeration. The sintering studies of the nanopowders of BIC and BIZ indicated that the grain size increases significantly with calcining temperatures beyond 1250°C. The BIC sintered at 1250°C showed much higher electrical conductivities than that sintered at 1500°C.

A Study on Co and Cu Oxides as Sintering Aids for Sm0.2Ce0.8O1.9 Electrolyte

In this study, an addition of Co and Cu oxides to Sm0.2Ce0.8O1.9 (SDC) was studied to improve the SDC sinterability. It has been found that both Co and Cu oxide are very effective as sintering aids, and the SDC sintering temperature can be reduced from 1400°C without aids to below 1000°C with only 1at.% of either Cu or Co. As compared to the pure SDC, a slight decrease of ionic conductivity was observed in SDC with Cu sintering aid. There is no obvious effect on electrochemical property of SDC with Co sintering aid under 2.5at.%.

Development Status of SOFC Cell and Stack Technology at NRC-IFCI

Solid Oxide Fuel Cell (SOFC) development was started at the National Research Council of Canada’s Institute for Fuel Cell Innovation (NRCIFCI) in 2003 with the goal to develop the next generation of SOFC’s for Canadian Industry. To accomplish this task, work focused on the development of low temperature cermet and metal supported cells, direct deposition methods, low temperature sintering, seal and stack technology. As of November 2006, 5 cm x 5 cm cermet supported cell performance has been improved to 900 mW/cm at 600°C. These components have been incorporated into short stacks developed at IFCI to continue the push to commercialize this technology. At the same time, direct deposition technology has progressed rapidly to the point where metal supported 5 x 5 cells can be fabricated using sintering temperatures below 850°C. Results of this work will be presented, along with the development path at IFCI.