Research On Performance Of GdBaCo₂O_5+δ As Cathode Material For Intermediate Temperature Solid Oxide Fuel Cell

Intermediate temperature solid oxide fuel cell (IT-SOFC) is the tendency of the solid oxide fuel cell commercializing development. Because reducing the operating temperature makes the performance of conventional cathode La_1-xSr_xMnO₃ (LSM) decrease rapidly, so it is important to develop new cathode materials with high performance at intermediate temperature in order for the development of IT-SOFC.Due to high electronic and ionic conductivity, cobaltite oxides with perovskite structure are of great interest as potential cathode material for IT-SOFC. The sample of GdBaCo₂O_5+δ(GBCO) was prepared by the conventional solid state reaction method. By way of the basic physical performance measurement, it is found that GBCO had very high conductivity, its conductivity was about 512-290S/cm in the operational temperature range 500-800℃of IT-SOFC, met the requirement for use as IT-SOFC cathode. But its thermal expansion coefficient (TEC) was about 20.1×10^-6K^-1 between room temperature and 900℃, which was much larger than that of electrolyte material, such as doped ceria (DCO), hence the poor thermal expansion match with electrolyte was one main problem for GBCO cathode.According to the XRD pattern of the GBCO and Sm_0.2Ce_0.8O_1.9 (SDC) mixture sintered, GBCO showed a good chemical compatibility with SDC electrolyte material, there were not probed reactions between GBCO and SDC after the mixture sintered at 1100℃. Using polarization curve and impedance spectra, the electrochemical performance of GBCO in the temperature range of 500-800℃on SDC electrolyte, and the effect of sintering temperature on performance of cathode were investigated. The SEM images of GBCO cathodes sintered at different temperatures showed sintering temperature had an effect on microstructure and adhesion of the cathode to electrolyte, thereby affected the electrochemical performance of cathode. The optimum sintering temperature was 1050℃for GBCO cathode on the SDC electrolyte, which sintered at this temperature exhibited good electrochemical performance, its polarization resistance was 0.15Ω·cm² at 750℃, and 1.11Ω·cm² at 600℃.In order to reduce the thermal expansion coefficient of GBCO cathode, SDC electrolyte which has lower TEC was added to GBCO cathode. Through the examination of basic physical performance and electrochemical performance of GBCO-SDC composite cathodes, it is found that the addition of SDC not only decreased the thermal expansion coefficient of GBCO, adjusted the thermal compatibility towards the electrolyte, but also improved the electrochemical performance of GBCO cathode. Although the addition of SDC resulted in the decrease of conductivity, when the addition of SDC was below 40wt.%, the conductivity values of GBCO-SDC composite cathodes were still above 100S/cm in the temperature range of 500-800℃, met the requirement for use as IT-SOFC cathode material. In addition, when the SDC content was 40wt.%, the GBCO-SDC composite cathode had the best electrochemical performance, its polarization resistance was 1.39Ω·cm² at 500℃, the value was about 19% of pure GBCO.These results above mentioned indicate that GBCO compound is a promising cathode material for IT-SOFC.