Application of Fe–16Cr ferritic alloy to interconnector for a solid oxide fuel cell
Iron-base scaling-resistant alloys (Fe–Cr) as materials for interconnectors of planar-type solid oxide fuel cells (SOFC) are proposed for application in automobile industry because of their advantages in comparison with other Ni- or Co-based alloys and ceramic materials (e.g. (La,Sr)CrO3). The oxidation kinetics of Fe–16Cr alloy (SUS 430) has been studied in H2–H2O gas mixtures (pH2/pH2O=94/6 and 97/3), and in air in the temperature range of 1023–1173 K for 3.6 up to 1080 ks, in the conditions simulating the anode and cathode environments in SOFC. It has been found that the oxide scale, composed mainly of Cr2O3, grows in accordance with the parabolic rate law. The dependence of the parabolic rate constant, kp, on temperature can be described as kp=6.8×10−4 exp(−202.3 kJ mol−1/RT) for the H2–H2O gas mixture with pH2/pH2O=94/6. The determined parabolic rate constant is independent of the oxygen partial pressure in the experimental range of 5.2×10−22 to 0.21 atm at 1073 K, which means that the growth rates of scale on Fe–16Cr alloy in the above-mentioned atmospheres are comparable. The increase in electrical resistance of the chromia scale growing on Fe–16Cr alloy vs. time, calculated from kp and the specific resistance of Cr2O3 scale, in comparison with the constant electrical resistance of a ceramic interconnector, made of (La,Sr)CrO3, indicates the necessity to modify the studied alloy surface. At 1073 K, the resistance of the Fe–16Cr alloy coated with La0.6Sr0.4CoO3 by a spray-pyrolysis method is low, the average of 45 mΩ cm2 in the H2–H2O gas mixture (pH2/pH2O=94/6) and the average of 20 mΩ cm2 in air, in comparison with the ceramic interconnector, La0.85Sr0.15CrO3, 0.5 cm thick. This indicates the applicability of SUS 430 alloy as interconnector for SOFC.