Metallic interconnects for solid oxide fuel cell: Performance of reactive element oxide coating during long time exposure

Abstract

AbstractOne of challenges in improving the performance and cost‐effectiveness of SOFCs (solid oxide fuel cells) is the development of suitable interconnects 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 are unacceptable regarding the long‐term operation (>40 000 h). A previous study 1 demonstrated that in air, the addition of a nanometric reactive element oxide (La2O3) layer applied by metal organic chemical vapor deposition (MOCVD) drastically improved both corrosion rate and electrical properties of Crofer22APU and Haynes230 alloys for 100 h at 800 °C. In this present study coating performances were checked after 10 months (7500 h) and 20 months (15 000 h) at 800 °C in air. The corrosion products were carefully analyzed by SEM, EDX, and XRD. ASR measurements are realized after long time exposure. This study demonstrates that the Crofer22APU alloy has a good oxidation resistance after 15 000 h in air but this alloy has an ASR value equal to 0.370 Ω cm2. The coatings composed of a thin reactive element oxide such as La2O3 resulted in an important improvement in the high temperature oxidation resistance; the ASR values are equal to 0.154 Ω cm2. Haynes230 alloy has a better oxidation resistance but the formation of an insulating Al2O3/SiO2 layer could be detrimental.