Degradation Analysis of SOFC Stack Performance-Durability Test and Verification of Improved SOFCs-

Central Research Institute of Electric power Industry (CRIEPI) has operated six types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG, NGK INSULATORS, and MURATA, to reveal their durability and find dominant degradation factor for each SOFC stack under NEDO’s project. The target of this NEDO durability project is set at 0.11%/1,000hr. In order to evaluate a performance degradation of the SOFC quantitatively and in order to quantify a performance change with time, the performance factor analysis method is required. We have been developed the electrode polarization models which is able to express SOFC performance factors such as Nernst loss (ηne), anode polarization (ηa), cathode polarization (ηc), and internal resistance IR drop (ηiR) with high prediction accuracy for six types of SOFCs. This gives us enable to make detail comparison among different type of SOFCs with the same performance analysis method inside the NEDO project. The MHPS’s stack which was operated until 16,000 hours, showed better stability and no further degradation factor has been identified. On the other hand, peculiar degradation behaviors arising from some impurities in air have been observed in our test for the stacks of Kyocera’s, TOTO’s, NTK’s, NGK’s, and Murata’s. For example, performance test exibited a rapid voltage drop within initial operation period for flattened tubular segment-in-series stack. The factor of this rapid voltage drop was increment of cathode overvoltage from a performance factor analysis result. One of possible reason for the negative effect to cathode overvoltage is sulfur contamination in the supply air from air compressor or thermal insulating foam on furnace. In this study, we report our recent activities on the durability and the dominant performance factors, and the peculiar degradation behaviors.