Ex-situ experimental benchmarking of solid oxide fuel cell metal interconnects

Solid oxide fuel cells (SOFCs) can convert hydrocarbon fuels, such as methane, into heat and electricity with a high conversion efficiency. The fuel flexibility of the SOFC derives from the high operating temperature (600-900 °C). Such a high temperature stresses the materials used in the SOFC stacks, notably the metals constituting the interconnect (IC). Research centers developed in the last twenty years specific alloys and coatings compositions. This led to a vast literature production of solutions to mitigate the degradation of the metals used in SOFC stacks. Unfortunately, the testing method and conditions change from one laboratory to another making the comparison of the results often impossible. This article compares systematically more than sixty different solutions to limit the degradation in the IC. The samples differed for the steel composition, the coating deposition technique, and the coating composition. A modified 4-probe technique and SEM/EDS post-test characterization measure the area-specific resistance and chromium retention of the samples. Testing results indicate that i) deposition technique is the most relevant parameter, ii) in presence of coatings, the performances are independent of the type of ferritic stainless steel substrate iii) nitriding helps to limit the outward chromium diffusion in case of porous coatings.