Preparation And Characterization Of Cathode Materials La_0.8Sr_0.2FeO₃/Sm_0.2Ce_0.8O_1.9 For Intermediate Temperature Solid Oxide Fuel Cells

Lowing the operating temperature to intermediate temperature (600-800℃) for solid oxide fuel cell is attracting more attention, for which can not only reduce the material cost by using common metal material, but also improve the stability of operating system. However, area specific resistance for traditional cathode material, such as La1-xSrxMnO3, increases rapidly with the operating temperature decreasing, so it is not fit for the intermediate temperature solid oxide fuel cell (IT-SOFC). It is necessary to select the cathodes which present perfect conductivity and compatibility with electrolytes at intermediate temperature.It is well known that higher electronic conductivity is determined to lower ohm loss; higher ionic conductivity gets more oxygen transportation. In recent years, perovskite structure oxide, which is mixed oxygen ionic and electronic conductor (MIEC), is regarded as the promising candidate for IT-SOFC. Lanthanum ferrite becomes alternative material for cathodes because of its favourable chemical stability and catalytic activity. Electrolytes are mixed with cathode materials to form composite cathodes in order to modify the chemical compatibility with electrolytes and increase the ionic conductivity. The performance of cathode is also influenced by the content of SDC greatly. As the mass ratio of SDC reaches 50%, the conductivity appears best, for the most continuous ionic and electronic phase.The preparation method is fateful to powder and electrode micro-structure, which affect the performance of electrode greatly. So, it is critical to choose a suitable preparation method.Lao.8Sro.2Fe03 (LSF) powders were prepared by sol-gel method. The powders were investigated by X-ray diffraction (XRD), thermogravimetry-differential thermal analysis (TG-DTA), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Electrochemical performances were analyzed by AC electrochemical impedance spectroscopy (ACEIS). The results showed that impurity perovskite phase was detected from 600℃, the electrodes exhibited smaller grain sizes and better-proportioned porosity, the area specific resistance (ASR) value of LSF was 0.12Ω·cm2,7-9 times lower than that of sample prepared by solid state reaction (SSR). In conclusion, the performances of cathodes by sol-gel route were better. It was also revealed that preparation way had a major influence on electrochemical performance.Composite cathode La0.8Sr0.2FeO3-Sm0.2Ce0.8O1.9 (LSF-SDC) was synthesized by SSR, Ag added to modify the electrode performance. The result showed that ASR value of LSF-SDC-Ag10wt% is 1.73Ω·cm2 at 600℃, and the performance has been improved compared to LSF-SDC.We explored a sol-gel route for preparing LSF-SDC by one step. The crystal-structure, microstructure and ASR were detected. We also discussed the doping principle. The result indicated that ASR value was a little decrease than that of traditional SSR.