Evaluation of Perovskite Overlay Coatings on Ferritic Stainless Steels for SOFC Interconnect Applications

Conductive oxide coatings are used to improve electrical performance and surface stability of metallic interconnects, as well as to mitigate or prevent chromium poisoning in solid oxide fuel cells (SOFCs). To further understand materials suitability and shed light on mass transport, two conductive perovskites, (LSF) and (LSC), were taken as examples and applied as dense coatings via radio frequency (rf)-sputtering on three stainless steels: E-brite, Crofer22 APU, and AL453. Oxidation, electrical, and microstructural investigations indicated the perovskite coatings improved both surface stability and electrical performance of the stainless steel substrates. In comparison, LSC was more effective than LSF due to its lower ionic conductivity that led to slower subscale growth and formation of internal oxides. Among the three selected stainless steels, E-brite possessed the highest oxidation resistance, so, for a given perovskite composition, the coated E-brite exhibited a slower subscale growth rate than coated Crofer22 APU or AL453. To avoid chromium poisoning of cathodes, nonchromium containing LSF would appear to be preferable to LSC. Due to chromium outward diffusion from the steel into the perovskite coatings, however, it is doubtful that an LSF coating can be an effective barrier to chromium release from the steel.