| Summary: | 碩士 === 大同大學 === 材料工程研究所 === 88 === A fuel cell is a new power generation device that directly converts the chemical energy of fuels into electricity and heat through electrochemical reaction. Since electricity is generated without combustion process. The energy conversion efficiency of fuel cell is high. It can solve both the problems of energy shortage and environmental pollution associated with power generation at the same time. Its grave drawback so far is limited commercial viability. This is more an economic than a technological concern.
The solid oxide fuel cell (SOFC) is an all-solid-state power system, which operates at high temperatures to ensure adequate ionic and electronic conductivity of its component. This is the only fuel cell system, which operates under two phases (gas and solid) condition. Two-phase contact reduces corrosion and eliminates any problems of electrolyte. Yttria-stabilized zirconia was the electrolyte used in the first SOFC to be demonstrated. The oxide ion transport number for 12% yttria-stabilized zirconia is close to unity, and it is highly stable in reducing and oxidizing environments. However, to increase the ionic conductivity of YSZ to the appli-cable level, a high operating temperature (1000℃) to the cell is necessary. In order to reduce inner cell resistance, one approach is to reduce the thickness of the YSZ layer (~150mm) . Along this approach, manufactured problems will be raised. Another possibility is to use a new ionic conductor with higher ionic conductivity than YSZ. Cation-doped ceria with a fluorite structure is a potential solid electrolyte because of its high oxygen ionic conductivity. Moreover, this electrolyte can be used at low temperature. The potentially lower operating temperature open up the possibilities of reduction construction cost and operating efficiency. Lots of studies of rare-earth doped ceria have been reported.
CeO2-Gd2O3 material system has been proved to be a good candidate as an electrolyte of SOFC. In order to improve the high temperature conductivity, substitution of CaO-LiO1.5 in electrolyte Ce0.8Gd0.2Oy and Ce0.9Gd0.1Oywere studied. The results show that the high temperature conductivity is enhanced. At 800℃, conductivity of Ce0.8Gd0.19(CaLiO1.5)0.01Oy and Ce0.9Gd0.085(CaLiO1.5)0.015Oy are 0.2 Ω-1-cm-1 and 0.16Ω-1-cm-1 respectively. The increase of conductivity is attributed to appropiate lattice cell size which results from interaction between defects and ions. Both substituted and unsubstituted electrolytes have the dominant ionic conduction ion conductivity for oxygen pressure greater than 3×10 -7 atm. For SOFC interconnect material, La0.7Ca0.3Cr0.98O3, high electronic conductivity is achieved under sintering at 1300℃ for 10 hours. Acording to the EDX and x-ray diffraction results,there is no much interaction between interconnecter and electrolyte.
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