For long-term operation of solid oxide fuel cells, ferritic stainless steel-based metallic interconnects with high durability are considered to be one of the most viable materials. However, the formation of a thick chromia layer during the long-term operation results into an increase in the area specific resistance (ASR), ultimately shortening the lifetime of the SOFC [1, 2]. In this study, we developed novel nano-oxide dispersed ferritic steel SUS430 based alloys and tested their long-term performance as interconnect materials for SOFC application. Nano-oxides of CeO₂, LaCrO₃, and Y₂O₃ (particle size <50 nm) were dispersed into the commercial SUS430 powder by using high-energy ball milling in specific binder and solvent conditions to get a uniform distribution. The highly dense rectangular pellets specimens were prepared by uniaxial and then cold isostatic pressing (CIP) methods, followed by sintering in H₂ at 1400 ^oC for 10 h. Physical properties, microstructural and phase analysis of the sintered nano-oxide dispersed stainless steel alloys were examined before the long-term testing. The developed alloy samples were tested for oxidation characteristics and long-term ASR behavior in air at 800 ^oC for 1000 h. Post-test analysis of the samples were conducted by SEM, EDS, and XRD techniques. The long-term ASR results show that the dispersion of nano-oxide particles significantly improved the ASR properties of the ferritic stainless steel based alloys. Especially, the total increase in the ASR of nano-CeO₂ dispersed ferritic steel during the 1000h long-term test was much less than that of the SUS430, comparable to one of Crofer APU22. LaCrO₃ addition also improved the ASR property but Y₂O₃ dispersion did not so. The dispersed nano-oxides decreased the grain size of the ferritic steel and the oxide particles were distributed at the grain boundaries of the steel. In this work, these electric and oxidation behaviors for long-term test were discussed as related to the microstructure, oxide scale formation mechanism and nano-oxide distribution of the samples.

References:

[1] L. Niewolak, F. Tietz, W.J. Quadakkers, Interconnects, in: K. Kendall, M. Kendall (Eds.), High-Temperature Solid Oxide Fuel Cells 21st Century, 2nd ed., Academic Press, Boston, 2016: pp. 195–254.

[2] N. Shaigan, W. Qu, D.G. Ivey, W. Chen, A review of recent progress in coatings, surface modifications and alloy developments for solid oxide fuel cell ferritic stainless steel interconnects, J. Power Sources. 195 (2010) 1529–1542.