Investigation Of Some Key Materials Of Solid Oxide Fuel Cells

The solid oxide fuel cell (SOFC) is a novel energy conversion device that convertschemical energy to electricity with high efficiency, it has been recognized as the optimalsolution about energy crisis. It has attracted more attention from researchers for its applicationand development. However, the performance of cells is closely related to the materials,including the electrodes and electrolyte. So it is quite necessary to choose the proper materialsto guarantee the high performance of the cells.This thesis aims to achieve the goal above. At first, we have researched the performanceof the cathode materials prepared by different ways. Then the LSGM powder with higherionic conductivity was synthetized using solid state reaction and applied in the DC-SOFC.The performance of cathode material is closely related to the microstructure，sizedistribution and sinterability. La0.8Sr0.2MnO3(LSM) cathode powders were prepared by usingsolid-state reaction，glycine-nitrate process and sol-gel process, respectively. Then thepowders were sintered at different temperatures and the lowest temperature of forming theperovskite phase was900C confirmed by XRD measurement. The microstructures of thepowders were investigated by SEM, showing that the powders prepared by GNP and sol-gelmethode can satisfy the demand of cathode material. The electrical conductivity wascalculated by measuring the resistance with Van-der Pauw method, showing that theconductivities of cathode pellets prepared by three methods can exceed100S/cm. Theactivation behavior of LSM was investigated by three-electrode method, showing that theinterfacial resistance of LSM cathode prepared by sol-gel process on YSZ electrolyte was thelowest. The anode-supported SOFCs with LSM cathode were assembled and tested byfour-probe setup, and the single cell with LSM cathode prepared by sol-gel process showedthe highest power density of317mW/cm2at800C. The results show that LSM powder madeby sol-gel process is availably content with the requirement for the cathode of SOFC.Now, most attention has been focused on the conventional electrolyte YSZ. However, theionic conductivity of YSZ below1000C is not satisfying，resulting in higher ohmicresistance and lower output performance. However, LSGM show higher oxygen ionconductivity at relatively low temperatures and has been regarded as a promising electrolyte material for intermediate temperature SOFC. In this paper, we prepared the LSGM powder bysolid state reaction, and characterized by XRD and SEM. Then the LSGM-supported tubeswere successfully fabricated by dip-coating technique. The performance of LSGM-supportedSOFC with activated carbon as fuel was tested. The cell of LSGM-supported DC-SOFC givesthe maximum power density of383mW·cm-2, which is nearly1.2times higher than that ofYSZ-supported DC-SOFC (297mW·cm-2). Also, the RΩfor LSGM were smaller than thosefor YSZ in the testing temperature range. For example, the RΩat850C was reduced from0.80Ω·cm2for YSZ to0.52Ω·cm2for LSGM, representing a35%improvement. The resultsshow that LSGM-supported DC-SOFC exhibits higher electrochemical performance than thatof YSZ-supported DC-SOFC because of the application of electrolyte with higher ionicconductivitity. The life-time test on LSGM-supported DC-SOFC shows that the outputperformance degraded with the time, and smaller amount of carbon fuel resulted in shorteroperation life and lower carbon utilization.