| Progress in fabrication CEThnology of solid oxide fuel cells(SOFCs) has enabled cell operating temperature decreased from high temperature(about 1000oC) to the lower temperatures(600oC-800oC), which made metallic alloys can be practically utilized as interconnects. Among the high temperature oxidation resistance alloy, Cr2O3-forming ferritic stainless steels have become the candidate materials for SOFCs interconnect applications due to their excellent comprehensive properties. Nevertheless, there remain several issues during long-term operation for Fe-Cr ferritic stainless steel, including chromia-scale evaporation, unacceptable cathode Cr poisoning, and the resistance increase due to the scale growth of the metallic interconnects surface and potential spallation. Thus surface modification of the metallic interconnects with numerous conductive coatings is a practical approach to overcome the issues. Among all of the possible coatings,(Mn,Co)3O4 spinel is regarded as one of the most promising candidates due to its relatively high conductivity, compatible CTE with metallic interconnects and good chromium retention capability.A low-cost and Cr-free spinel oxide was used as barrier materials on the metallic interconnect SUS 430 alloy to reduce the rate of cathode degradation by Cr poisoning and the interfacial resistance to improve the surface stability. In particular, MnCu0.5Co1.5O4 spinel shows electrical conductivity of 105.46 S?cm-1 at 750oC in air and an average CET value of 12.27x10-6 K-1 at temperature range of 20~950oC, which was selected as a coating on SUS 430 alloy. Then, MnCu0.5Co1.5O4 coated SUS 430 alloy is evaluate in the simulated cathode and anode SOFCs working environments at 750oC for long-term oxidation behaviors test about the microstructure, oxidation resistance and electrical conductivity.The result confirms that the coating layer is stable enough after 2000 h cyclic oxidation in cathode atmosphere, which is identified as MnCu0.5Co1.5O4. While the MnCu0.5Co1.5O4 coating is reduced into MnO, Co and Cu after 1000 h cyclic oxidation in anode atmosphere, which had a very fast phase evolution in the first 15 h. The dense coating layer is effective in blocking the Cr migration/transport and depressing the growth of Cr2O3 and formation of MnCr2O4 in both situations. In cathode atmosphere, the oxidation kinetics obeys the parabolic law with a rate constant as low as 2.76x10-15g2·cm-4·s-1 and the ASR contributed by the oxide scale is 8.04 m?·cm2 at 750oC. In anode atmosphere, the kinetics of cyclic oxidation does not obey the parabolic rate law due to the reduction process, and the ?m/A of MnCu0.5Co1.5O4 coated SUS 430 alloy is 0.238 mg?cm-2 after 1000 h oxidation. Moreover, the ASR contributed by the oxide scale is172.40 m?·cm2 at 750oC, MnO will be the main reason of the measured high ASR in anode atmosphere.Generally, the overall performance of the MnCu0.5Co1.5O4 coated SUS 430 alloy is superior to those of bare SUS 430 and other ferritic candidate alloys. MnCu0.5Co1.5O4 spinel coating effectively improved the oxidation resistance of the matrix alloy, and Cr poisoning performance, especially in the cathode atmosphere. |
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