Coated Ferritic Stainless Steels as Interconnects in Solid Oxide Fuel Cells

Licentiate thesis, 2013

Solid oxide fuel cells (SOFCs) have gained increased research interest as they are promising devices for a decentralized and clean electricity and heat production. Several material challenges have to be solved to reach sufficient efficiencies and life times. One important aspect are ferritic stainless steels as interconnect materials which are corrosion resistant, mechanically stable and cost optimized. This work is aimed to investigate economic solutions for interconnect materials and understand the underlying degradation mechansims. Two substrates, the commercial available steel AISI 441 and the ferritic stainless steel optimized for an SOFC application Sandvik Sanergy HT, were combined with different barrier coatings and exposed in cathode atmosphere. The ferritic stainless steel AISI 441 coated with different reactive element and reactive element/cobalt coatings was investigated concerning corrosion resistance and chromium volatilization. Uncoated 441 suffered from severe corrosion, which was successfully improved by coatings of cerium and lanthanum. Cerium/cobalt-coated AISI 441 was showing excellent and promising properties for a interconnect application. Sandvik Sanergy HT coated with novel conversion coatings of copper with manganese or iron was examined in a similar way. Coatings of copper and iron improved the corrosion and chromium evaporation properties significantly and were promising for further developments. In contrast did copper combined with manganese as coating on Sandvik Sanergy HT not result in an improvement in corrosion properties and chromium evaporation.