Study On Preparation Of Component Materials And Cell Operating Performance For Intermediate Temperarue Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) has many advantages of high efficiency, low emissions of sulfur, nitrogen oxides and hydrocarbon pollutants, which is considered to be one of the key techniques resolving the energy problems in the 21ths. High operating temperature and carbon deposition in anode are the two main problems hampering the development of SOFC. The high operating temperature results in numerous disadvantages such as the difficulties of sealing SOFC, the deterioration of thermodynamic compatibility between electrodes and electrolyte components, the emerging of chemical reactions at the boundary of electrodes and electrolyte, the increase of SOFC fabrication cost, and the deduction of long-term. The carbon deposition can result in the deterioration of cell capability in a short time. So, it is necessary to develop novel electrolyte and anode materials to resolve the above problems. The electrolyte material should have highly pure ionic conductivity at the low and intermediate temperatures (below 850℃), the anode material should have high ion-electronic conductivity at the low and intermediate temperatures and which can reduce or avoid the carbon deposition in anode.La_1-xSr_xGa_1-yMg_yO_3-δ(LSGM) material has high ionic conductivity over the large range of oxygen partial pressure at the low and intermediate temperatures, which is excellent electrolyte candidate for intermediate temperature solid oxide fuel cell(ITSOFC).But it is difficult to synthesize LSGM electrolyte material with a single phase, with low-conductivity phase such as SrLaGa₃O₇ and SrLa(GaO₄ forming for inappropriate operations when using solid-state reaction method especially. These impurities have very bad impacts on the structure, chemical stability and conductivity of LSGM. One of our tasks is to modify experimental condition and prepare single-phase LSGM.LaCrO₃-based material is considered to be one of anode materials which can resolve carbon deposition. The elements in A-site and B-site have different impacts on the performance of the material. For example, the La element can heighten the stability of material, the conductivity will increase when partial La is substituted by Sr. The material has excellent catalytic property for the Mn element in B-site and goodtolerance to sulfur properties for the Cr element in B site. So, another task is synthesizing and Characterization Lai.xSrxCri.yMny03.5(LSCM) as anode material.According to the LSGM preparation experimental, the following conclusions are obtained. Perovskite phase began to form after the precursors material was sintered at 1000"C. A small amount of SrLaGa3C>7 was formed when sintering at 1300°C. A single-phase perovskite was both identified after sintering at 1450°C and 1480 °C for 24h, respectively. The ionic conductivity of LSGM was stable and increased with the temperature increasing. The 1.2xlO"2S/cm conductivity in 800"C was similar to that of samples measured by other researchers. The sintering temperature, density of sample and grain boundary resistance has big impacts on the ionic conductivity of LSGM.According to the LSGM synthesis experimental, one can draw the following conclusions. Perovskite phase began to form after the precursors material was sintered at 1000°C. Many impurities such as LaiCh and Sri.sLao.sMnC^ were formed at the low temperatures. A single-phase perovskite was both identified after sintering at 1250'C and 1350 °C for 15h, respectively. The grain and grain boundary resistances decreased and the ionic conductivity increased with the temperature increasing over the temperature range of 300⁸00°C. But the grain boundary resistances were big even at high temperature. The electronic conductivity increased linely with temperature increasing over the range of 300⁶50°C, which increased more quickly when the temperature is over 650°C and was about 1.5S/cm at 850"C.Moreover, the compatibilities between LSGM and LSCM and novel LSFC cathode materials were studied in order to promote the application of the above three materials. They have good chemical capability between LSGM and LSMC and LSFC, but a little impurity such as La2C?3, La4Ga2C>9 emerged resulted from the evaporation of the element Ga in LSGM material in the heating process of the mixed powder with LSGM and LSMC at 1200°C for 15h. Porous LSCM anode film with a 10um thickness was obtained in LSGM pellet, and anode film was well cohered on the LSGM electrolyte substrate. It shows a good thermodynamic capability between LSGM and LSCM. The desired LSFC cathode film wasn't obtained in LSGM pellet. It shows that they haven't good thermodynamic capability between LSGM and LSFC.The single cell was fabricated using LSCM, LSFM and LSGM as anode, cathode and electrolyte materials, respectively. The open circuit voltage is about 1.06V at850°C when the flux of hydrogen is 0.5L/min and that of air is 0.2L/min, which is similar to the theoretical electromotive force. It shows that the sealing of cell is very good. The max powder density is about 25mW/cm2 at 850"C, which is relatively small for the big boundary resistances between electrodes and electrolyte and current collectors. The fabrication technique must be modified in the future in order to get better powder density.