Investigation Of The Cathode With Cr-poison Resistance And High Performance For Solid Oxide Fuel Cell

Intermediate temperature (700⁸00°C) solid oxide fuel cells (IT-SOFCs) have significant advantages in stability, reducing thermal stress, enhancing cell's life. It can use alloy interconnect that is of cost effectiveness, high conductivity, and facility to be machining, among which Cr-alloy is assumed as the most promising interconnect material. While, when Cr-alloy is used in SOFC stack, the performance of traditional cathodes, such as (La,Sr)MnO3 (LSM) and (La,Sr)(Co,Fe)O3 (LSCF), could decline rapidly because of Cr-poison. So research of novel cathodes with Cr-poison resistance and high performace is important. LaNi_0.6Fe_0.4O_3-δ (LNF) material is assumed as the most promising cathode with Cr-poison resistance and high performace.In this article, the preparation, characterization and optimization of the LaNi_0.6Fe_0.4O_3-δ cathode was investigated. LaNi_0.6Fe_0.4O_3-δ was prepared using a combustion synthesis technique. X-ray diffraction (XRD) pattern showed single-phase LaNi_0.6Fe_0.4O_3-δ perovskite could be obtained after heat treatment at 600°C. The TEM images of the synthesized powder showed the grains were 50-100nm. La2Zr2O7 was detected by XRD when LaNi_0.6Fe_0.4O_3-δ and Sc_0.1Zr_0.9O_1.95 (ScSZ) was co-calcined in 1100°C.The symmetric cell LaNi_0.6Fe_0.4O_3-δ/Sc_0.1Zr_0.9O_1.95/LaNi_0.6Fe_0.4O_3-δ was fabricated with screen print method. According to the electrochemical impedance spectra (EIS), the polarization resistance of the symmetric cell sintered in 1050oC was the least (0.12Ω·cm², 0.28Ω·cm², 0.70Ω·cm², 1.91Ω·cm² and 5.62Ω·cm² at 850°C, 800°C, 750°C, 700°C and 650°C, respectively). In the presence of the Fe-Cr alloy interconnect at 750°C, the cathode performance showed that, with the time increasing, a few Cr2O3(s) deposited at the LaNi0.6Fe0.4O3?δ/ScSZ interface repressing the diffusion of active particle and increasing the polarization resistance.Nevol LaNi_0.6Fe_0.4O_3-δ-Gd_0.2Ce_0.8O_2-α composite cathode was prepared by infiltration means. The least polarization resistance of the optimized composite cathode (Gd_0.2Ce_0.8O_2-α content is 21%, LNF-GDC21 composite cathode) is 0.03Ω·cm², 0.06Ω·cm², 0.12Ω·cm², 0.29Ω·cm² and 0.71Ω·cm² at 850°C, 800°C, 750°C, 700°C and 650°C, respectively. At 750°C the polarization resistance of novel composite cathode was only 1/7 of the pure LaNi_0.6Fe_0.4O_3-δ cathode. The Activation Energy of the optimized composite (136.80kJ/mol) is the smallest among others. In the present of Fe-Cr alloy at 750°C, EIS showed that the ohm resistance and polarization resitance of the optimized cathode was increased as the time increasing from 0 to 610h, and gradually had a stabilization in 0.92Ω·cm² and 2.94Ω·cm², respectively, from 634 to 1042h. As a small quantity of the deposition of Cr species in cathode/electrolyte interface, LNF-GDC21 composite cathode can stay low polariszation resistance and high stability from 634 to 1042h. LNF-GDC21 composite cathode is a promising cathode with Cr-poison resistance and high performance for SOFC.