Processing and Properties of Advanced Solid Oxide Fuel Cells

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Up to now, Solid Oxide Fuel Cell (SOFC) materials and processing does not meet the cost goals for commercialization. This resulted in a worldwide increase in R&D activities dealing with advanced materials and effective manufacturing methods. The present paper describes efforts to process novel SOFC materials as well as optimization of well known ones. The R&D trends are explained for key components such as anode, electrolyte, cathode, contact- and protective layers. Typical SOFC manufacturing methods include tape casting, extrusion, calendaring and axial pressing. Each of these techniques has advantages and limitations. Examples for the highly efficient use of these methods are given for electrolyte supported cells as well as anode and cathode supported designs. An evaluation in reference to automation, process complexity and costs is given under the present limiting factors. Exemplary the processing by tape casting and the micro structural fine tuning of an advanced anode-supported system is discussed in detail. To produce the layered components of an SOFC, techniques like screen printing, wet powder spraying, PVD and CVD are under development. While the layer properties are excellent, PVD and CVD are nowadays too expensive in some cases, due to the low deposition rates. If thin layers are required, these techniques become interesting under cost considerations. The effectiveness of a PVD interlayer between electrolyte and high power density cathodes is shown in comparison to a sintered layer. In thin electrolyte concepts, the cathode becomes the power limiting component at operating temperatures below around 750°C. Thus new cathode materials and adjusted processing parameters are under development. The possibilities to manufacture advanced cathode layers by screen printing, wet powder spraying and other wet chemical methods are discussed. As an example screen printing of LSCF is described which results in a high power density cathode layer for low temperature SOFC operation. Finally, future needs to achieve the technical and economic goals are summarized.