Preparation And Electrochemical Performances Of The Sm_0.5-xBa_xSr _0.5Co_0.8 Fe_0.2 O_3-δ/SDC Gradient Composite Cathode

With the emergence of environmental problems, the main direction future of energy development and utilization will point to the efficient and clean energy, so the solid oxide fuel cells become a hot point of researchers, attention. To maintain good output performance of the battery, changing the microstructure of the battery components and lowering the temperature are necessary. It is important for the SOFC to improve the performance of the cathode materials, many researchers pay more attention 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 crystal structure is characterized by XRD. The thermal expansion coefficient (TEC) is measured using the thermal expansion coefficient dilatometer. The electrical conductivity is measured using the method of DC four-probe. The results show that the powder has being well perovskite structure after being sintered for 5h at 950oC. The thermal expansion coefficient (TEC) is 16.79-18.80×10-6K-1 from 25oC to 900oC and it is not obviously of the change for the TEC of SBSCF sample. But when doped the SDC, the TEC decreases obviously. It decreases to 13.38×10-6K-1 and 11.10×10-6K-1. Under the 350oC the electrical conductivity of the SBSCF changes gently, and follows the small polaron conduction mechanism. But with the increasing of the temperature the electrical conductivity decreased obviously after 350oC. It shows the metal conduction behavior.The gradient composite cathodes are prepared by screen printing. The cathode polarization behavior was measured through AC impedance. Observing the cross-section structure and surface morphology of electrode by the SEM .The results show that the content of Ba²⁺doped has an important effect on the polarization resistance of gradient composite cathodes SBSCF-50%SDC-30%SDC. With the increasing of the Ba²⁺, the polarization resistance of the cathode material decreases, while it increases when x=0.15, the smallest polarization resistance is 0.0297Ω·cm2 at 750 oC when Ba²⁺content was 0.20.