Ceo < Sub > 2 < / Sub > Oxygen Ion Conductive Composite Materials Research

Solid Oxide Fuel Cell (SOFC) is a device to transform directly a chemical energy to electrical energy. Electrolyte material is a key component in a SOFC for that the performance of the electrolyte determines the operating temperature and the work efficiency of SOFC. The electrolyte with high performance is important to reduce the operation temperature and to improve the performance of SOFC. In this thesis, samarium doped ceria (Ce0.8Sm0.2O1.9, SDC) with cubic fluorite structure and strontium and magnesium doped gallium lanthanum (La0.9Sr0.1Ga0.8Mg0.2O2.85, LSGM) with perovskite structure were prepared by co-precipitation method. The influnce of doping and composite technology on the oxygen ionic conductivity and the relevant conductive mechanism have been investigated. The work includes the following aspects:(1) SDC and LSGM powders have been synthesized by co-precipitation method, and the related ceramics were obtained by conventional sintering process. X-ray diffraction and AC impedance test were employed to analyze the phase component and the conductivities of the ceramics, respectively. The results show that high-purity and single-phase SDC and LSGM powders were obtained. The conductivities of SDC and LSGM ceramics are1.01×10-2S/cm and1.76×10-2S/cm at700℃, respectively.(2) SDC-LSGM composite materials were prepared by a two-step co-precipitation method. The composite electrolyte have a main phase of fluorite type of CeO2, the second phase of perovskite type of LaGaO3, and a small amount of impurity phase of LaSrGa3O7. At the test temperature range, the impedance of the grain boundary effect of the composite ceramics is obviously smaller than that of the single phase SDC. The conductivity of the composite ceramics with10wt%of LSGM has the highest ionic conductivity, which is3.4×10-2S/cm at700℃, is about2times larger than those of single phase SDC and LSGM. AC impedance data analysis shows that the conductivity improvement of composite ceramics, comparing to the single phase ceramics, is mainly attributed to the increase in the grain boundary conductivity. These indicate that the composite process is an available way to improve the conductivity of an electrolyte.(3) SDC-LSGM nano-composite powders with the average grain size of15nm were prepared by a two-step co-precipitation method. The effect of the La2O3excess in the conductivity of the composite materials has studied. The results reveal that the oxide-ionic conductivities of the composite sample with3wt%excess of La2O3show the highest ones. The highest conductivity of the composite sample is9.6×10-2S/cm at700℃and is nearly one order of magnitude highter than that of single phase SDC. The change of the interface structure of the composite materials is the most import reason for the increase of conductivity.(4) SDC-LSGM composite powders were prepared by a two-step co-precipitation method, and the ceramics were obtained by the hot-pressure sintering process. The main phase of the composite electrolyte materials is the fluorite structure of CeO2, and the second phase is the perovskite structure of LaGaO3. There also has a small amount of impurity phase LaSrGa3O7. The conductivity of the hot-pressure sintered SDC is higher, about one order of magnitude at200℃, than that of the conventionally sintered SDC. The conductivity of hot pressure sintered composite ceramics with15wt%of LSGM has the highest ionic conductivity, which is5.86×10-2S/cm at700℃and is about2times larger than that of the conventionally sintered oness.