Preparation And Characterization Of The Key Materials For Solid Oxide Fuel Cells Based On Doped Ceria Electrolytes

Solid oxide fuel cells (SOFC) are a promising technology with less emission of pollution for electric power generation in the 21st century. Because a SOFC based on YSZ electrolyte has to work at higher temperature(> 800℃), its application is limited. To realize the commercialization of a practical SOFC, it is desirable to lower the operation temperature of a SOFC to intermediate range(500-750℃). Two methods can be employed to carry out it. The first one is to develop some new electrolyte materials with high oxygen ionic conductivity at intermediate (or reduced) temperatures. The potential candidates are doped ceria (DCO) and some perovskite type compounds such as doped-LaGaO3. The second one is to reduce the thickness of YSZ electrolyte layer. This thesis deals with the preparation and characterization of the key materials for SOFC based on DCO electrolytes.At present, most doped-ceria electrolytes are prepared by coprecipitation, sol-gel. and some other methods. These methods need either high pure predecessors or complex processing, and their application is limited. In the second chapter of this thesis, Ce0.8Sm0.2O1.9 (SDC) powder was prepared by a modified gel-casting process with organic aided. The properties of the powder, including its phase composition, particle size, as well as its sinterability, electrical conductivity were all characterized. It was shown that the gel-casting method can produce SDC powder with nanometer size, and the resulting SDC powder had a relatively high sinterability and electrical conductivity.To match the thermal expansion coefficients between the electrolyte and theanode materials, Ni/DCO materials are usually employed when DCO is used as the electrolyte of a SOFC. In the third chapter of this thesis, NiO/SDC predecessor and Ni/SDC anode were prepared by the mechanical mixing method. And the effects of the properties of NiO raw materials, and the processing parameters on the properties of the anode were studied. It was found that both the sintering temperature and the characteristics of the raw material play a key role in determining the properties of the Ni/DCO anode material. Therefore, it is desirable to optimize the composition of the anode, the characteristics of the raw materials and the processing parameters.In the last chapter of the thesis, a novel buffer-solution method was employed to prepare NiO/SDC powders, which were subsequently used to fabricate the Ni/SDC anode materials. And the properties of resulting Ni/SDC anodes were compared with those of Ni/SDC anodes prepared by the mechanical mixing method. The test results had shown that the buffer-solution method can prepare NiO/SDC powder with nanometer size, which had more homogeneous distribution of NiO and SDC particles. This made that Ni particles can easily form a constituent network configuration in the Ni/SDC anode. Because of it, the properties of the Ni/SDC anode prepared from the buffer-solution powders were better than those of Ni/SDC anodes prepared from the mechanical mixing powders.