Thin Film Synthesis of Novel Electrode Materials for Solid-Oxide Fuel Cells
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ABSTRACT Electrode materials for solid-oxide fuel cells are developed using sputter deposition. A thin film anode is formed by co-deposition of nickel and yttria-stabilized zirconia. This approach is suitable for composition grading and the provision of a mixed-conducting interfacial layer to the electrolyte layer. Similarly, synthesis of a thin film cathode proceeds by co-deposition of silver and yttria-stabilized zirconia. The sputter deposition of a thin film solid-oxide fuel cell is next demonstrated. The thin film fuel cell microstructure is examined using scanning electron microscopy whereas the cell perfomance is characterized through current-voltage measurement and corresponding impedance spectroscopy.
INTRODUCTION A solid-oxide fuel cell (SOFC) device consists of manifolded stacks of cells which combine a fuel and oxidant at elevated temperatures to generate electric current. The basis of each fuel cell is an anode and cathode separated by an electrolyte layer. SOFCs provide an efficient and enviromentally clean method of energy conversion. SOFCs are routinely made using bulk ceramic powder processing.' A traditional synthesis approach uses a cermet electrode on which an electrolyte is layered, for example, by tape casting. The unit cell is completed by lamination to the counterpart electrode. SOFCs are traditionally operated at temperatures exceeding 900'C. The common approach to incorporate thin film technologies in SOFCs is based on coating the cermet electrodes with an electrolyte layer. To decrease the thickness below that obtainable using tape calendaring, thin ceramic films can be deposited by a variety of techniques including variations of sol-gel and colloidal deposition. 2 In addition, thin electrolyte layers can be dc magnetron sputtered from metal alloy targets to optimize ion conductivity and rf magnetron sputtered from oxide targets to form continuous coatings on porous substrates. 3 -5 A thin electrolyte reduces the path for oxygen ion diffusion. A decrease in the electrolyte thickness from -100 gm to
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