UBC Theses and Dissertations
Air plasma spraying of copper-based SOFC anodes for direct oxidation of hydrocarbon fuels Light, Nir
This thesis investigates the utilization of atmospheric plasma spraying (APS) utilizing a DC axial injection torch to produce porous composite SOFC anodes for direct oxidation of hydrocarbon fuels based on samaria doped ceria (SDC) or gadolinia doped ceria (GDC) and Cu or Cu-Co. Currently, these anodes are manufactured by multi-step wet ceramic processes, which makes them difficult to produce economically at moderate volumes. In contrast to wet ceramic processing, APS allows rapid, easy-to-automate processing and easy scale-up to mass production of SOFCs. The main challenge in producing these anodes by APS is to co-deposit materials with a large difference between their melting temperatures in a coating having a porous structure, which is required in SOFC anodes for good mass transport and high performance. In addition, in the case of Cu-Co based anodes, surface alloying of the Cu and Co phases enriches the surface of this mixture with Cu. This mechanism was suggested to explain the excellent tolerance of Cu-Co anodes manufactured by wet ceramics process for carbon deposition. However, it is not clear whether surface alloying occurs during APS due to the larger mixing scale and rapid solidification of the deposited materials. A range of plasma process parameters has been examined in this work for the production of homogeneously mixed anode coatings from pre-mixed spray dried micron-sized agglomerated feedstock powders. Fine and coarse powders have been used to produce anode coatings, which were characterized for crystallography, composition, microstructure, porosity, and gas permeation. Anode electrochemical performances were also characterized by impedance spectroscopy, and the extent of carbon deposition was determined by weight gain of the anode during exposure to methane. By adequate control and refinement of processing parameters and starting powders, it is possible to achieve coatings with properties not typical to the plasma spray process. This work overcame processing challenges stemming from a material set having a large difference between the melting temperatures of each material, demonstrating the feasibility of obtaining fairly homogenous Cu-SDC and Cu-Co-SDC/GDC anodes with performances comparable to those of Cu-based anodes fabricated by wet ceramic processing.
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