FexCo0.5−xNi0.5-SDC anodes for low-temperature solid oxide fuel cells

Trimetal alloys, Fe_xCo_0.5−xNi_0.5 (x = 0.1, 0.2, 0.25, 0.3, 0.4), were studied as anodes for low-temperature solid oxide fuel cells (LT-SOFCs) based on GDC (Ce_0.9Gd_0.1O_1.95) electrolytes. The alloys were formed by in situ reduction of Fe_xCo_0.5−xNi_0.5O_y composites, which were synthesized using a glycine-nitrate technique. Symmetrical cells consisted of Fe_xCo_0.5−xNi_0.5-SDC electrodes and GDC electrolytes, and single cells consisted of Fe_xCo_0.5−xNi_0.5-SDC (Ce_0.8Sm_0.2O_1.9) anodes, GDC electrolytes, and SSC (Sm_0.5Sr_0.5CoO₃)-SDC cathodes were prepared using a co-pressing and co-firing process. Interfacial polarization resistances and I-V curves of these cells were measured at temperature from 450 to 600 °C. With Fe_0.25Co_0.25Ni_0.5-SDC as anodes, the cells showed the lowest interfacial resistance and highest power density. For example, at 600 °C, the resistance was about 0.11 Ω cm² and power density was about 750 mW cm⁻² when humidified (3% H₂O) hydrogen was used as fuel and stationary air as oxidant. Further, the cell performance was improved when the molar ratio of Fe:Co:Ni approached 1:1:2, i.e. Fe_0.25Co_0.25Ni_0.5. In addition, higher power density and lower interfacial resistance were obtained for cells with the Fe_0.25Co_0.25Ni_0.5-SDC anodes comparing to that with Ni-SDC anodes, which have been usually used for LT-SOFCs. The promising performance of Fe_xCo_0.5−xNi_0.5 as anodes suggests that trimetallic anodes are worth considering for SOFCs that operate at low-temperature.