| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 91 === Yttria-stabilized Zirconia (YSZ) is the most commonly used electrolyte material for Solid Oxide Fuel Cells (SOFCs) because of its unique combination of properties such as high chemical and thermal stability and pure ionic conductivity over a wide range of conditions. The oxide-ion conductivity of YSZ is poor; Therefore, the high operation temperature (900-1000℃)is required for an SOFC. Due to the high operation temperature (900-1000℃) the material demand upon SOFC components are quite stringent. Currently, the goal of SOFC development is to decrease the operating temperature, so that the material selection for cell construction will be easier. The operating temperature can be decreased by lowering the electrolyte resistance either by decreasing the electrolyte thickness or with alternative materials of higher ionic conductivity at lower temperatures.
The electrophoretic deposition (EPD) is a colloidal fabrication process and has advantage of short formation times, little restriction in the shape of substrates, simple deposition apparatus, and for mass production. Therefore, the EPD method is seen as a low-cost method for preparing electrolyte thin films for SOFC. In the past , the preparation of YSZ film on a porous LaMnO3-based oxide and nickel-Y2O3-stabilized ZrO2 substrates were investigated using EPD to produce SOFCs. However YSZ reacts easily with the LaMnO3-based cathode oxide to form an La2Zr2O7 phase when sintering of the green film , and the resulting poorly conducting La2Zr2O7 compound at the electrolyte/cathode interface is undesirable for SOFCs. Therefore, sintering YSZ film on a porous LaMnO3-based oxide substrate is more difficult than sintering on an anode substrate.
In this study, LixNi2-xO2-YSZ was used to replace LaMnO3-based oxide substrate to avoid the reaction between electrode and electrolyte when sintering the YSZ film. YSZ films with thickness of about 20μm have been successfully prepared on LixNi2-xO2-YSZ substrate via EPD process. Dense and crack-free YSZ film can be obtained when the green film was sintered at 1400℃ for 2h.
LixNi2-xO2 was reduced to metallic Nickel by a heat treatment in 20% H2, 80% Ar2 atmosphere at 800℃ for 24h. Subsequently, LixNi2-xO2-YSZ substrate became a porous material after reducing. From the thermal expansion analysis it was observed, the sintering temperature of LixNi2-xO2-YSZ substrate was decreased and dimensional change increased when the amount of Li was increased. The thermal expansion behavior of Li0.2Ni1.8O2-YSZ is close to that of YSZ electrolyte.
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