Optimization Research Of MnCo Protective Coatings For Sofc Metallic Interconnects

With recent progress in lowering the operating temperature， chromiaforming ferritic stainless steels are considered as promising interconnectmaterials for solid oxide fuel cells (SOFCs).To block the chromium evaporationand chromium poisoning,(Mn,Co)3O4spinel is one of the most promisingcoatings for solid oxide fuel cell (SOFC) stainless steel interconnects. It hasgood electrical conductivity, thermal conductivity and chemical stability, thermalexpansion coeffcient (TEC) matching those of electrodes and electrolyte. Currentcoating methods mainly include screen printing, sol-gel, electrophoreticdeposition, chemical vapor deposition, physical vapor deposition, spin coatingmethod, pulse plating and so on. Coatings with Mn/Co (40:60) was tested as theoptimized recipe to maintain Mn1.5Co1.5O4composition after long term operationdue to Mn diffusion from substrate and the coating can effectively inhibit thediffusion of Cr. Therefore, in this work, the thickness of the Mn40Co60coatingwere optimized and performance of coating are tested in the air and both gasmixture under (Air+3%H2O//H2+3%H2O).Mn/Co (40:60) coatings were fabricated in thickness of approximately800nm,1500nm,3000nm on ferritic stainless steels SUS430using magnetronsputtering. Oxidation behavior of sputtered samples was investigated afteroxidized at800℃in air for2h,250h,500h,1000h, respectively.SEM is usedto observe the surface morphology, grain growth and grain size; EDS for analysisthe coating surface elements and element distribution; XRD for analyzingchemical phase formation and structures of the coatings. Area Surface resistance(ASR) test is used to analyze the conductivity of coating.According to the ASR performance tests and performance analysis ofcoating, ASR of Mn40Co60-1500nm and Mn40Co60-3000nm coatings are smallerthan that of Mn40Co60-800nm coating. With the increasing of oxidation time, theASR of Mn40Co60-1500nm and Mn40Co60-3000nm coatings tend to stabilize,while ASR value of Mn40Co60-1500nm and Mn40Co60-3000nm coatingsbasically are very close. Then based on by Wagner oxidation theory, it isextrapolated that the ASR values of1500nm and3000nm after40,000h are94mΩcm2and89mΩcm2, respectively, which can definitely meet the requirementof100mΩcm2presented by U.S. Department of Energy. Considering the costissue,1500nm coating is the optimized Mn40Co60protection coating thickness forSOFC interconnects. In addition, to verify performance of interconnect coating in real fuel cellapplication, the coated steel samples were experienced dual atmosphere exposurewith anodic side and cathodic of air of SOFC. The results show that the coatingcan effectively suppress Cr diffusion in reduction and oxidation atmosphere,With extending the test time, the coatings showed serious Fe2O3insulating layerin the cathode atmosphere and spallation issue. Fe2O3insulating layer greatlyincrease ASR of the coating. With need further study to meet the ASRrequirement, in the future work diffusion mechanisms and long term stabilitywill be studied in dual atmosphere.