(Mn,Co)3O4 spinel coatings on ferritic stainless steels for SOFC interconnect applications

(Mn,Co)₃O₄ spinel with a nominal composition of Mn_1.5Co_1.5O₄ demonstrates excellent electrical conductivity, satisfactory thermal and structural stability, as well as good thermal expansion match to ferritic stainless steel interconnects. A slurry-coating technique was developed for fabricating the spinel coatings onto the steel interconnects. Thermally grown layers of Mn_1.5Co_1.5O₄ not only significantly decreased the contact resistance between a LSF cathode and stainless steel interconnect, but also acted as a mass barrier to inhibit scale growth on the stainless steel and to prevent Cr outward migration through the coating. The level of improvement in electrical performance and oxidation resistance (i.e. the scale growth rate) was dependent on the ferritic substrate composition. For E-brite and Crofer22 APU, with a relatively high Cr concentration (27 wt% and 23%, respectively) and negligible Si, the reduction of contact ASR and scale growth on the ferritic substrates was significant. In comparison, limited improvement was achieved by application of the Mn_1.5Co_1.5O₄ spinel coating on AISI430, which contains only 17%Cr and a higher amount of residual Si.