Mark Robertson

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.

Tribological properties of boride based thermal diffusion coatings

Abstract Engineering components, e.g. tubing systems for the down-hole applications in the oil and gas industry (in particular, sucker rod pumps, progressing cavity pumps and some other components of the artificial lifting systems), as well as numerous valves and seats, bearings, gears and plungers, require protection against friction and sliding abrasion service conditions. The hard boride based coatings on steels and alloys obtained through the thermal diffusion process have a high potential for these severe application conditions over many other types of coatings as they can be obtained on the entire working surfaces of large size and complex shape products. Intensive tribological studies of the iron boride based coatings on carbon steel obtained at Endurance Technologies Inc. have been conducted using the Cameron–Plint testing unit (reciprocating sliding of the metallic rod under the load over a flat surface of the coated samples). The friction wear loss, friction coefficient and structural changes of the coatings have been studied in dry and lubricating (water–oil) friction conditions, which simulate actual application conditions. It was demonstrated that the obtained boride coatings have the friction loss significantly smaller than untreated steel (e.g. ∼10–30 times in the dry conditions and at least 5 times in the lubricating conditions) with no peeling and flaking-off. The friction coefficients of the boride coatings are steady over the test duration. The influence of the thickness on the boride coatings performance is demonstrated. The encouraging results are explained by the specific coating structure of the hard coating obtained through the thermal diffusion process and the thin ‘tribofilm’ formed during a friction mode.

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.

Boride-based coatings for protection of cast iron against wear

The components made of cast irons require protection against wear in severe service conditions. Surface engineering can be used to prevent mechanical failures of cast iron components due to excessive friction-related wear. The iron boride-based coatings can be applied on the entire working surfaces of large-size complex shape cast iron components through the thermal diffusion process. Tribological properties of these coatings obtained have been studied using the pin-on-disc test configuration in simulating application conditions. The obtained iron boride coatings demonstrated significantly lower wear losses compared to bare cast iron, stable behaviour of coefficient of friction during time and no structural degradation and spalling. The superior wear resistance of boride-based coatings on cast iron is dealt with the combination of their high hardness, specific ‘sawtooth’ double-layer morphology obtained through the thermal diffusion process, diffusion-related bonding to the substrate, self-lubricating thin ‘tribo-film’ formed during friction and high thermal and chemical stability.

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.%.

Mechanical Strength and Interface Adhesion of a Solid Oxide Fuel Cell with Doped Ceria Electrolyte

An SOFC must have sufficient mechanical strength and interface adhesion to ensure it can be handled without breakage during fabrication and assembly, and has desired performance and reliability. Methods for measuring mechanical properties and interface adhesion of an SOFC have been developed and measurements made on a cermet-supported SOFC with a SDC electrolyte. The SOFC evaluated had a porous NiO-YSZ substrate, a porous NiO-SDC anode and a dense SDC electrolyte fabricated using tape-casting, screen-printing and co-firing techniques. The flexural strength and interface adhesion of the substrate, the anode and the electrolyte, along with their Young’s modulus, hardness and residual stress, were quantitatively measured. The results of the measurements indicate that the NiO-YSZ supported, SDC electrolyte SOFC has adequate mechanical strength and sufficient interface adhesion.

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.