Metallic interconnects for SOFC: effect of water vapour on oxidation resistance of differently coated alloys.
Résumé
The need of interconnect to separate fuel and oxidant gasses and connect individual cells into electrical series in a SOFC stack appears as one of the most important point in fuel cell technology. Due to their high electrical and thermal conductivities, thermal expansion compatibility with the other cell components and low cost, Ferritic Stainless Steels (FSS) are now considered to be among the most promising candidate materials as interconnects in SOFC stacks. Despite the formation at 800°C of a protective chromia Cr2O3 scale, it can transform in presence of water vapour in volatile chromium species leading to the lost of its protectiveness and then the degradation of the fuel cell. A previous study [1] demonstrated that in air the application by Metal Organic Chemical vapour deposition (MOCVD) of a nanometric layer of reactive element oxides (La2O3, Y2O3) on FSS improved both the electrical conductivity and the oxidation resistance. The beneficial effect of this type of coating on FSS on oxidation resistance in H2/H2O (anode side) is not yet completely understood. So, the goal of this study is to realise reactive element oxide coating (La2O3, Y2O3) on differently FSS and performed oxidation tests in H2/10%H2O. The corrosion products were analysed after 100 hours ageing at 800°C by SEM, EDX, TEM, SIMS and XRD. The corrosion kinetic of the uncoated alloys in H2/10%H2O is slightly faster than in air. The application of a reactive element oxide coating improves the oxidation resistance but the parabolic rate law constant is slightly superior to those obtained in air. In H2/10%H2O, the morphologies of the oxide layers are very different from those observed in air but the oxide phases are almost unchanged.