Performance and Microstructure of a Novel Cr-Getter Material with LSCF-Based Cells in a Generic Stack Test Fixture

Abstract

Cr poisoning has been identified as a leading cause for degradation of solid oxide fuel cells. Mitigation can be achieved by protective coatings such as Mn-Co spinel or aluminization on ferritic stainless steel, a leading candidate for metallic interconnect. This has been successfully demonstrated in short and medium term operation, although the long-term integrity of these coatings remains to be validated. In addition to the passive means for Cr mitigation via protective coatings, Pacific Northwest National Laboratory has teamed with University of Connecticut to adopt an active means to tackle the issue by including a novel Cr-getter material in the system. A novel Sr-Ni-oxide developed at University of Connecticut as Cr-getter has proven promising in small button cell testing. In this work, commercial YSZ/NiO anode-supported YSZ cells (50 mm x 50 mm) with either LSCF or LSM cathode were tested in a generic stack test fixture using humidified (~4.75%) air and diluted hydrogen. Two Cr-getter locations were investigated: one upstream of the cell and one “on cell.” Pre-oxidized AISI 441 metal stripes were used as the Cr source. In this study, we validated the candidate Cr-getter materials made either by a nitrate solution method or the solid-state reaction method. Candidate getter materials from nitrate solution approach were impregnated into a porous alumina form, while getter materials obtained by solid state reaction were sintered into small cylinders. For comparison, plain cells with and without a Cr source were also tested to provide baseline data. All cells were tested at constant current for ~1000h at 800oC. Cell performance and impedance were recorded, followed by post-mortem optical/electron microscopy and cathode microstructure/composition analysis. The results showed promising gettering performance with no Cr detected within cathode areas.