Evaluation of Protective Coatings for SOFC Interconnects

Michele Bianco, Jan Van Herle
2015
Journal paper

Abstract

Chromium poisoning is a widely recognized degradation process in solid oxide fuel cells (SOFC). Stainless steel interconnect plates, in direct contact with the cathode, have been identified as the major chromium source, raising a need for electrically conducting protective coatings for the interconnects. This work evaluates four different manganese-cobalt protective coatings manufactured on thin steel foils, made by three commercial companies and a research centre. Area specific resistance, coating microstructure, and chromium retention are compared. Measurements were done in a humid atmosphere over 1000 hours at 700 °C. An innovative measurement setup was used, in which the coated steel samples are stacked adjacent to thin palladium foils with a screen-printed lanthanum strontium cobalt layer, replicating an SOFC cathode. As a conclusion, TeerCoating Ltd’s and Turbocoating S.p.A’s coatings performed similar to the Sandvik Material Technology’s ceriumcobalt reference coating, and could be employed as such in SOFC applications.

Official source

https://infoscience.epfl.ch/record/253214?ln=en

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Chromium evaporation is identified as a major degradation mechanism in solid oxide fuel cell (SOFC) stacks. The major chromium source is the commonly used stainless steel interconnects, thus raising a need for protective coatings on the interconnect steel. Ex situ characterization methods of protective coatings involve chromium evaporation measurements, area specific resistance (ASR) measurements and long-term exposure tests. To replicate stack conditions, commonly used ASR measurement setups should be further developed. This work presents an improved characterization method for steels and coatings and aims to be an extension to state-of-the-art characterization methods. The studied steel samples, bare or coated, are placed adjacent to palladium foils with a screenprinted lanthanum-strontium-cobalt (LSC) layer and the resistivity over the pair is measured. The method offers similar contact materials, chromium migration mechanisms, electrical contacts and chemical interactions, as seen in stacks. Further, it enables post-test chromium migration analysis with electron microscopy. Demonstration of the method validated that protective coatings hindered both oxidation and chromium migration from the substrate steels. The presented method could aid in accelerating protective coating development.

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