Interdiffusion and Charge Transport Across Surface-Modified Current Collectors in Planar SOFCs

摘要

Current collectors are a key component of planar SOFCs, separating air and fuel supplied onto the electrodes and connecting the cells in series. One of main challenges in the SOFC technology development is to suppress degradation processes, often associated with the interconnect materials, and to provide low contact resistivity in oxidizing atmospheres. The present work is focused on the studies of near-surface interdiffusion phenomena in Crofer 22 APU ferritic steel interconnects with Ni-based protective layers. Particular emphasis was centered on the area-specific resistance (ASR) between the current collectors and La_(0.8)Sr_(0.2)MnO_3 (LSM) cathodes, which exhibit time dependencies governed by the protective interlayer composition and interface microstructure alterations. The ASR changes, tested during over 30,000 hours at atmospheric oxygen pressure, can be described in terms of a model assuming that the current across the interconnector | LSM interface is essentially controlled by electron transfer via the interfacial Schottky barrier. The experimental observations validate this approach, explaining the junction resistivity and Schottky barrier height variations as a result of metal interdiffusion between the current collector and Ni-based protective coating.