Preparation And Electrochemical Performances Of The Sm_0.5-xBa_xSr_0.5Co_0.8Fe_0.2O_3-δ/SDC Gradient Composite Cathode

With the emergence of environmental problems, the main direction future ofenergy development and utilization will point to the efficient and clean energy, so thesolid oxide fuel cells become a hot point of researchers,attention. To maintain goodoutput performance of the battery, changing the microstructure of the batterycomponents and lowering the temperature are necessary. It is important for the SOFCto improve the performance of the cathode materials, many researchers pay moreattention on the study of the cathode of the SOFC.Perovskite-type oxide Sm_0.5-xBa_xSr_0.5Co_0.8Fe_0.2O_3-δ（SBSCF, x=0.00,0.05,0.10,0.15,0.20） powders are prepared using a sol-gel synthesis method.Sol-gel-Low-temperature combustion prepares the solid electrolyte Sm_0.2Ce_0.8O_2-δ（SDC）. Then discuss the structure and the performance of the material. The crystalstructure is characterized by XRD. The thermal expansion coefficient （TEC） ismeasured using the thermal expansion coefficient dilatometer. The electricalconductivity is measured using the method of DC four-probe. The results show thatthe powder has being well perovskite structure after being sintered for5h at950oC.The thermal expansion coefficient （TEC） is16.79-18.80×10^-6K^-1from25oC to900oCand it is not obviously of the change for the TEC of SBSCF sample. But when dopedthe SDC, the TEC decreases obviously. It decreases to13.38×10^-6K^-1and11.10×10^-6K^-1. Under the350oC the electrical conductivity of the SBSCF changesgently, and follows the small polaron conduction mechanism. But with the increasingof the temperature the electrical conductivity decreased obviously after350oC. Itshows the metal conduction behavior.The gradient composite cathodes are prepared by screen printing. The cathodepolarization behavior was measured through AC impedance. Observing thecross-section structure and surface morphology of electrode by the SEM.The resultsshow that the content of Ba²⁺ doped has an important effect on the polarizationresistance of gradient composite cathodes SBSCF-50%SDC-30%SDC. With theincreasing of the Ba²⁺, the polarization resistance of the cathode material decreases,while it increases when x=0.15, the smallest polarization resistance is0.0297·cm²at750oC when Ba²⁺ content was0.20.