Performance Investigation On Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ-Based Composite Cathode For Intermediate Temperature Fuel Cells

A fuel cell is electrochemical device of generate electricity, which differs from common battery because it directly converts chemical energy to electric energy with high-efficiency and low pollution, the fuel cells are believed to be a promising power source compared with coal burning power plants. Therefore, the fuel cells have received considerable attention in recent years.Among the various kinds of fuel cells, solid oxide fuel cells (SOFCs) have many benefits, such as high-energy efficiency, completely solid component, no leak, no causticity, and simple equipment. So they are attracted much attention in world. SOFC is made up of electrolyte, anode, cathode and copulative material. As a key part of SOFC, cathodes deeply affect on performance of SOFC. In this work, we mainly investigate composite cathode of SOFC in order to enhance performance of SOFC.A novel cathode material, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF), is suitable as cathode for reduced-temperature SOFC operation, due to its high rate of oxygen diffusivity at low temperature. But the disadvantage of BSCF cathode material was its lower electrical conductivity compared with the commonly cathode. The lack of electrical conductivity would limit performance of BSCF as a cathode material in SOFC. For this reason, we added Sm_0.5Sr_0.5CoO_3-δ (SSC) and Ag with high electrical conductivity into BSCF in order to enhance conductivity and performance of cathodes.BSCF-SSC composite cathodes have been investigated. The BSCF-SSC cathodes with pores have been prepared by doping different amount of SSC powders into BSCF. The composite materials BSCF-SSC were investigated thoroughly by X-ray diffraction (XRD), thermal expansion coefficient measurements, electrical conductivity and electrochemical impedance spectra. The results showed that addition of SSC enhanced not only conductivities of cathodes but also performance of cathodes. For example, around 176S·cm^-1 at 500℃for the x=30wt.% composite, which was nearly 7 times higher than that of BSCF, the total polarization resistance value of BSCF-30wt.%SSC was only 0.71Ω·cm² at 550℃, about one seventh of that BSCF at 550℃. These indicated that BSCF-xSSC composites were suitable as cathodes for IT-SOFCs.BSCF-Ag composite cathodes have been investigated. The BSCF-Ag cathodes with pores have been prepared by impregnating method and Solid-State reaction method, respectively. The composite materials BSCF-Ag were investigated thoroughly by X-ray diffraction (XRD), thermal expansion coefficient measurements, electrical conductivity and electrochemical impedance spectra. The results showed that addition of Ag enhanced not only conductivity of cathode materials but also performance of cathodes. The material added with 20wt.% Ag has the best electrochemical properties, for example, the total polarization resistance value of BSCF-20wt.%Ag was only 0.099Ω·cm² at 550℃, about one fifth of that BSCF at 550℃. These indicated that BSCF-Ag composites were suitable as cathodes for IT-SOFCs.