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CFY-stack: From electrolyte supported cells to high efficiency SOFC stacks

: Megel, S.; Kusznezoff, M.; Trofimenko, N.; Sauchuk, V.; Schilm, J.; Schöne, J.; Beckert, W.; Michaelis, A.; Bienert, C.; Brandner, M.; Venskutonis, A.; Skrabs, S.; Sigl, L.S.

European Fuel Cell Forum -EFCF-:
10th European Solid Oxide Fuel Cell Forum, SOFC 2012. Proceedings : Fundamentals, Materials, Systems, Applications; 26 - 29 June 2012, Lucerne/Switzerland
Oberrohrdorf/Switzerland: European Fuel Cell Forum, 2012
European Solid Oxide Fuel Cell Forum (SOFC) <10, 2012, Luzern>
Fraunhofer IKTS ()
redox cycles; power degradation

The stack concept with electrolyte supported cells (ESC) has the highest potential for realization of robust SOFC stacks. However, to achieve high power density and efficiency comparable to anode supported cell (ASC) stacks, a high ionic conducting electrolyte on basis of fully scandia stabilized zirconia should be used. The utilization of this electrolyte is only possible with TEC (thermal expansion coefficient) adjusted metallic CFY interconnects. To achieve robust SOFC stacks, all components have to be optimized to withstand high temperature corrosion, temperature cycling and repetitive reduction / oxidation (RedOx cycles) on the fuel side of the stack. Tests on material and interface level have been developed and applied on different scales to prove the long-term stability and cyclab ility of the stack components. Optimizing materials and material combinations, the long-term power degradation has been reduced from 3 % / 1.000h to <1,5 % / 1.000h. Power losses of <0,5% per 20 cycles during thermal cycling have been achieved as well. The most challenging issue is RedOx cycling of the stack; a special RedOx procedure was set to compare different material combinations in the stack. The current stack can withstand up to 25 full RedOx cycles with a power degradation of 3-8%. A system relevant RedOx procedure for stacks shows lower degradation in comparison to full RedOx cycles. This showes that in the stack the cyclability of electrolyte supported cells can be efficiently supported by system related issues.