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 Go-based alloys and ceramic materials (e.g. (La,Sr)CrO3). The oxida tion kinetics of Fe-16Cr alloy (SUS 430) has been studied in H-2-H2O gas mi xtures (p(H2)/p(H2O) = 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 anod e 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, k(p), on temperature can be described as k(p) = 6.8 x 10(-4) exp(-202.3 kJ mol(-1)/RT) for the H-2-H2O gas mixture with p(H2)/p(H2O) = 94/6. The determined parabolic rate consta nt is independent of the oxygen partial pressure in the experimental range of 5.2 x 10(-22) to 0.21 atm at 1073 K, which means that the growth rates o f scale on Fe-16Cr alloy in the above-mentioned atmospheres are comparable. The increase in electrical resistance of the chromia scale growing on Fe-1 6Cr alloy vs, time, calculated from k(p) and the specific resistance of Cr2 O3 scale, in comparison with the constant electrical resistance of a cerami c interconnector, made of (La,Sr)CrO3, indicates the necessity to modify th e studied alloy surface. At 1073 K, the resistance of the Fe-16Cr alloy coa ted with La0.6Sr0.4CoO3, by a spray-pyrolysis method is low, the average of 45 m Omega cm(2) in the H-2-H2O gas mixture (PH2/PH2O = 94/6) and the aver age of 20 m Omega cm(2) in air, in comparison with the ceramic interconnect or, La0.85Sr0.15CrO3, 0.5 cm thick. This indicates the applicability of SUS 430 alloy as interconnector for SOFC. (C) 2001 Elsevier Science B.V. All r ights reserved.