Effect of precursor materials on the performance of the NiFe2O4-based spinel layer for SOFC cathode-side contact application

Simulated cathode/contact/interconnect cells are used to investigate the effects of different precursors on the microstructure and performance of the thermally-converted NiFe2O4-based spinel contact layer. The precursor materials include a mixture of NiO and Fe2O3 powders (NiO + Fe2O3), a mixture of pure Ni and Fe powders (Ni + Fe), an Fe-Ni alloy (Invar 36) powder, and an Fe-Ni-Co alloy (Kovar) powder. The isothermal area specific resistance (ASR) of the test cells is evaluated at 800 °C in air for 1000 h, which shows significant variation depending on the contact precursors. The cells with the metallic precursors exhibit much reduced ASRs compared to the one with the mixed oxides, due to the unique reactive sintering of the spinel layer with the metallic precursors. Furthermore, the cell ASR values with the alloy precursors are lower than that with the Ni + Fe mixture. While the cell ASR with the Invar 36 precursor decreases gradually with time, the Kovar precursor leads to the lowest ASR. Thermal cycling does not negatively affect the cell ASR performance with the Kovar-derived contact layer. Cross-sectional observation of the tested cells is conducted to assess the compatibility of the contact layer with adjacent components as well as its effectiveness in blocking Cr migration from the interconnect to the cathode.