Metal Interconnects for Solid Oxide Fuel Cell Power Systems. SECA Core Technology Program. Phase I Topical Report. (Report of October 1, 2002 - September 30, 2003).
Interconnect development is identified by the U.S. Department of Energy as a key technical area requiring focused research to meet the performance and cost goals under the Solid State Energy Conversion Alliance initiative. In the Phase I SECA Core Technology Program, Ceramatec investigated a commercial ferritic stainless steel composition for oxidation resistance properties by measuring the weight gain when exposed to air at the fuel cell operating temperature. A pre-treatment process that results in a dense, adherent scale was found to reduce the oxide scale growth rate significantly. A process for coating the surface of the alloy in order to reduce the in-plane resistance and potentially inhibit chromium oxide evaporation was also identified. The combination of treatments provided a very low resistance through the scale. The resistance measured was as low as 10 milliohm-cm(sup 2) at 750 C in air. The oxide scale was found to be stable in humidified air at 750 C. The resistance value was stable over several thermal cycles. A similar treatment and coating for the fuel side of the interconnect also showed an exceptionally low resistance of one milliohm-cm(sup 2) in humidified hydrogen at 750 C, and was stable through multiple thermal cycles. Analysis of the scale after exposure to various atmospheres showed the presence of a stable composition. When exposed to a dual (air and hydrogen) atmosphere however, the scale composition contains a mixture of phases. Based on results to-date, the alloy selection and the treatment processes appear to be well suited for SOFC interconnect application.
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