|英文要約||Title: Technology development for SOFC commercialization promotion. Basic study on rapid evaluation method of SOFC durability (FY2013-FY2019) FY2017 Annual Report
Durability tests were finalized on seven different stacks. MPHS stacks exhibited excellent cell performance for long period of time such as 30,000 h with/without Cr containing vapors. Effects of Cr containing vapors are found to be very small; cathode degradation can be evaluated to be small enough even after 160,000 h, and the corresponding microstructural changes in cathode and SDC interlayer caused by Cr are also found to be small. After the improvement in filtering air in CRIEPI, other intermediate-temperature stacks exhibited reasonable cathode performance as follows: Those Kyocera cells tested by Osaka Gas for 30,000-40,000 h are found to have only a small amount of impurities(Cr,S) deposited in cathodes in good agreement with performance data. TOTO 2016 FY cells exhibit a small degradation for cathode, ohmic loss and anode after the improvement of cathode performance. NGK SPARK PLUG cells exhibit some effects on impurities such as K in cathode and P in anode, leading to different degradation mechanisms from other stacks. NGK INSULAORS cells improved cathode performance without any peculiar behavior but anomalous ohmic loss increase remains unresolved. Murata cells show a large ohmic loss increase after some improvement of cathode degradation. Denso cells exhibit a rather large cathode degradation which can be ascribed to cross leak across the cell. Contamination of air with sulfur in CRIEPI site makes is possible to consider the mechanism of affecting cathode performance by changes in thickness of YSZ electrolyte, microstructural feature (porous or dense) of ceria interlayer or humidity in anode. This leads to establishment of more general cathode degradation model based on those surface composition changes of Sr or Co on LSCF which can be controlled by (1)reactions with impurities (Cr/S), (2)interactions with protons in cathode to enhance the Sr volatilization, and (3)diffusion of Sr/Co from inside to surface of LSCF. Many issues extracted from the stack degradations has been analyzed by simulation technology: Electrode performance loss was evaluated/predicted from the observed changes in microstructure of electrodes. Since the electrical conductivity degradation of YSZ was found to be complicated and affected by many factors such as temperature, cathode/anode overpotential, current density etc, simulation technology was established to predict electrical conductivity as functions of location in YSZ electrolyte and operation time. Detailed comparison with experimental results enables to find out additional kinetic effect appearing at lower temperatures. Correlation between cathode and ohmic loss degradation leads to considerations on current constriction inside cells from micro to macro scales.