Metallic Interconnects for Solid Oxide Fuel Cell: Performance of Reactive Element Oxide Coating During 10, 20 and 30 Months Exposure

Abstract

One of challenges in improving the performance and cost-effectiveness of SOFCs (Solid Oxide Fuel Cells) is the development of suitable interconnect materials. Chromia-forming alloys and especially ferritic stainless steels, like Crofer22APU, are considered to be among the most promising candidate materials as interconnects in SOFC stacks. However, the performance of chromia-forming materials can be limited by the low electronic conductivity of the oxide scale (high ASR—area specific resistance—value). Such degradation is unacceptable regarding the long-term operation (>40,000 h). A previous study demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) layer applied by Metal Organic Chemical Vapour Deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU for 100 h at 800 °C. In the present study, coating performances were checked after 10 months (7,700 h), 20 months (15,400 h) and 30 months (23,100 h) exposure in air at 800 °C. The corrosion products were characterized by SEM, EDX and XRD. ASR measurements are realized after long time exposure. The study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 23,100 h in air but this alloy has a high ASR value equal to 0.410 Ω cm2. The coatings composed of thin reactive element oxides made of La2O3 or Y2O3 resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.180 and 0.160 Ω cm2 respectively.