Current Status of Rapid Evaluation of Durability of Six SOFC Stacks within Nedo Project

Abstract

Six solid oxide fuel cell stacks manufactured by Kyocera, Mitsubishi Hitachi Power Systems (MHPS), TOTO, NGK SPARK PLUG, NGK INSULATORS, and Murata Manufacturing have been investigated to identify their performance degradation behavior, extract major sources of degradations, clarify the degradation mechanism, and predict the time dependent contributions of such degradations to life time. Stack performance was analyzed into several contributions, and in addition to identification of respective degradation rates, an interesting correlation between the overpotential values and the ohmic losses has been extracted. Respective degradation issues have been examined experimentally with SIMS, FIB-SEM, STEM and described as key simulation matters to predict the long life up to 90,000 h. Emphases have been placed on degradation of cathodes with Cr or S; to ensure the appropriateness for overcoming such poisoning effects, care was exercised to measure the impurity level after long term operations in various environments. For simulation, focus was made to overcome some gaps between knowledge on stacks and on single (or buttons) cells appearing in several degradations.