UBC Theses and Dissertations
Aqueous suspension plasma spraying of yttria stabilized zirconia solid oxide fuel cell electrolytes Waldbillig, David
In order to meet increasing world energy demand in a sustainable manner, clean and efficient new energy technologies need to be developed. Fuel cells have been proposed as a potential energy conversion technology to help facilitate this transition to cleaner energy. Solid oxide fuel cells (SOFC) in particular are thought to be a practical, near term clean energy technology; however, current state-of-the-art wet ceramic fabrication techniques make SOFC manufacturing labour-intensive, fairly expensive and difficult to automate, and the high firing temperatures required limit the usable materials sets and increase production times. Plasma spraying (PS) is a potential next generation SOFC fabrication process that can rapidly produce fully sintered ceramic layers without the need for post deposition heat treatments; however, it is difficult to produce the thin, fully dense layers required for SOFC electrolytes using conventional plasma spray techniques, as the carrier gas based feeding configurations typically require large feedstock powders. Suspension plasma spraying (SPS) is a modification of conventional PS processes that uses micron or sub-micron sized feedstock powders suspended in a carrier liquid. SPS has the potential to significantly improve coating quality and microstructural control. Thus plasma spray manufacturing methods may have the ability to both reduce cell fabrication and material costs and improve cell performance, making them an important step toward successful SOFC commercialization. This project investigated the properties of metal supported aqueous SPS yttria stabilized zirconia (YSZ) layers that could be used as SOFC electrolytes and developed a thorough understanding of the relationships between the base layers (substrate and cathode), suspension and plasma spraying parameters and the resulting coating properties. Using this understanding, plasma sprayed full cells (cathode, electrolyte and anode) with optimized electrolyte microstructures with 96% density were produced and electrochemically tested. The measured open circuit voltage values were approximately 90% of the Nernst voltages, and electrolyte area specific resistances below 0.1 Ω cm² were obtained at 750⁰C for electrolyte thicknesses below 20 μm. Least-squares fitting was used to estimate the contributions of the YSZ bulk material, its microstructure, and the contact resistance to the measured series resistance values.
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