Papers by Author: Hans Peter Buchkremer

Abstract: 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.

Abstract: Due to their direct conversion of electrochemical into electrical energy solid oxide fuel cells (SOFCs) have great potential for a future additional energy supply. Even in the last two years numerous developers of SOFCs, both industry and research institutions, have demonstrated long-term stable operation of stacks of various dimensions (ranging from 1 to 125 kWel, with durations of up to 25000 hours of operation). Besides technical proof, single component availability (cells, bipolar plates, sealing…), stable and low-aging operation, as well as cost efficient manufacturing of the components is becoming more and more evident in preparation for a market launch. Close cooperation between SOFC stack developers, SOFC users and manufacturers of powders, semifinished parts or stack components is a prerequisite for success. Within a collaboration project funded by the German Federal Ministry of Economics and Labor (BMWA) the development of an SOFC as an auxiliary power unit (APU) is being promoted. The industrial users are BMW for automotive applications and Liebherr for use in construction vehicles or aircraft. The content of this presentation will be the transfer of the manufacturing knowledge developed at Research Center Jülich to CeramTec; including on the one hand the problems and limitations and, on the other hand the successes and positive perceptions. In detail, the transfer of, for example tape casting and screen printing will be addressed, powder characteristics concerning paste or slip formulation and special tests with reference to SOFCs are presented, and single cell tests of various cells manufactured with different powders or fabrication processes are described. Additionally, some remarks will concern different priorities in either R&D or industry (e.g. R&D: high power density; industry: reproducibility), process windows for manufacturing and the search for alternative fabrication methods.