CFY-stack development for long-term operation with high efficiency

Planar Solid Oxide Fuel Cells (SOFC) are considered to be power generators with high efficiency and low emissions level even as small power units (1-200 kWel). Current work of most planar stack developers is concentrated on light-weight ferritic interconnector and anode supported cell as a core stack components. The recently developed and up-scaled net-shape technology for powder metallurgical production of bipolar plates allows new options for application of electrolyte supported cells with ASR < 0,3 Ωcm² on basis of scandia stabilized zirconia. Based on the cross flow design of bipolar plate with lateral dimensions of 140x140 mm² and MEA active area of 90x90 mm² as a starting point the optimization of flow-field and overall stack design has been made to achieve homogeneous temper ature distribution over the active stack area, to increase the effective utilization of interconnect area in every repeating unit and to simplify the stack manufacturing process. As a result the new stack design with an active area of 128 cm² has been developed and verified by simulation as well as in operation under laboratory conditions (air / H2:N2:H2O). The influence of contacting materials, protective coatings and temperature distribution as well as the art of operating conditions (self-sustaining operation in hotbox vs. operation in the furnace) on stack power density has been investigated. It has been shown that the protective coating as well as the cathode and anode contacting are important for starting performance and the degradation rate observed during experiments. Using differe nt contacting materials different degradation behavior is observed. During the durability tests (3.000 h) with preferred contacting concept only the short-term degradation (first 800 h) has been observed. The possible reasons for observed ASR degradation are discussed.