Manufacturing Solid Oxide Fuel Cells

Manufacturing Solid Oxide Fuel Cells

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Author: Z. Tang and A. Burgess (Fellow) | Visits: 2234 | Page Views: 2241
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Manufacturing Solid Oxide Fuel Cells with an Axial-injection Plasma Spray System
Z. Tang and A. Burgess Northwest Mettech Corp., North Vancouver, BC, Canada

O. Kesler1, 2, B. White1 and N. Ben-Oved1 Dept of Mechanical Engineering, University of British Columbia, Vancouver, BC, Canada 2 National Research Council - Institute for Fuel Cell Innovation, Vancouver, BC, Canada

Abstract Atmospheric plasma spraying has emerged as a cost-effective alternative to traditional sintering processes for solid oxide fuel cell (SOFC) manufacturing. However, the use of plasma spraying for SOFCs presents unique challenges, mainly due to the high porosity required for the electrodes and fully dense coatings required for the electrolytes. By using optimized spray conditions combined with appropriate feedstocks, SOFC electrolytes and electrodes with required composition and microstructure could be deposited with an axial plasma spray system. In this paper, the challenges for manufacturing SOFC anodes, electrolytes, and cathodes are addressed. The effects of plasma parameters and different feedstocks on coating microstructure are discussed, and examples of optimized coating microstructures are given. Introduction Plasma spraying is a widely used process to deposit metallic and ceramic coatings for thermal barrier and wear- and corrosion- resistant coatings. In recent years, an increasing number of research and development efforts have been devoted to manufacturing solid oxide fuel cells (SOFCs) by plasma spraying [1]. SOFCs are very highly efficient energy conversion devices that convert fuel electrochemically to electricity with negligible pollution emissions. Typically, SOFCs are produced using wet ceramic techniques based on tape casting, screen printing, and subsequent sintering processes [2]. The use of plasma spraying for SOFC manufacturing presents many advantages over wet ceramic processing with regards to both performance and cost. One obvious advantage is the speed of processing that results from elimination of the sintering steps, so that the cell layers can be processed in rapid succession, with the possibility of introducing functional gradients in both composition and microstructure to improve thermo-mechanical and electrochemical performance. The elimination of sintering also facilitates the use of robust, inexpensive metallic substrates as the mechanical support and electrical

interconnects of the cells, with the more expensive active cell layers produced in thin layers. The plasma spraying process is also rapid and easy to automate, making the process potentially very well suited for mass production [3]. However, the use of plasma spraying for SOFCs presents significant challenges, mainly due to the fully dense coatings required for electrolytes and the high porosity required for the electrode layers. Plasma sprayed coatings currently manufactured for common applications such as thermal barrier coatings typically exhibit porosities in the range of 5-15% [4]. However, for the successful production of SOFCs, this range must be extended down to 0% open porosity for electrolytes, and up to 40% open porosity for optimal electrode coatings. This significantly wider range of coating porosities requires substantial modification to the spraying process from procedures that have been established previously for other applications. Significant work has been aimed at overcoming these challenges and extending the range of porosities with considerable success [5-9]. In this paper, efforts are focused on SOFC deposition using a plasma torch with axial powder feeding, which is capable of dense electrolyte deposition with fine powders (