| A Solid Oxide Fuel Cell (SOFC) is an all solid-state energy conversion device that produces electricity by electrochemically combining fuel and oxidant gases across an oxyanion conducting oxide. Developers of SOFC technology are following two divergent routes to commercialization. One strategy envisages the construction of multi-Megawatt pressurized SOFC/gas turbine units capable of operating at projected electrical efficiencies around 70%. The other is development of intermediate temperature Solid Oxide Fuel Cell (ITSOFC) without compromising the cell resistance and electrode kinetics such as standalone SOFC systems for micro combined heat and power (CHP), remote generators, and electric vehicles. From the point of efficiency, state-of-the-art SOFC systems are normally operated in the temperature regime of 850 000 C. Primary drivers for lowering the operating temperature of SOFC towards or below 850 without losing the direct internal reforming (DIR) characteristics are not only to get an optimum trade-off between performance and life time of the stack , to reduce the overall system cost, and to broaden the market potential, but also to increase the conversion efficiency of electric energy and the open-circuit voltage according to the analysis of thermodynamics for SOFC system. However, to reduce the operating temperature of SOFC, two major problems must be solved:(i)reduction of the high ohmic resistance without decreasing electrolyte thickness below 5 p.m and (ii) development of high-performance cathodes compatible with the electrolyte material. Thereby, it is important that study and exploitation of novel cathode material for realizing commercialization of the ITSOFC. On the basis of the cathodic characteristics of SOFC and main requirements for its components materials, ~ (LSCMC) and ~ (LSCCF) materials belonging to pervoskite-type oxides, which are entitled compositely doped materials by authors, have been presented as novel cathode materials for ITSOFC.In this dissertation, the solid reaction synthesis and structure, behaviors of electrical conduction and thermal expansion for these pervoskite-type oxides have been discussed besides their chemical stability, thermal and chemical compatibility with YSZ electrolyte at high temperature with oxidation atmosphere, catalysis, mechanism of doped-defect formation and oxygen surface exchange behavior. The major research results are as follows:1. Solid reaction synthesis was used for preparation the novel materials designed on the basis of comparison and analysis. By use of DSC/TG and X-ray diffraction at different temperatures, the synthesized process for compositely doped-materials could be divided into three steps: (i) decomposition of reactants, (ii) creation of LaMn(Co)03-based oxide, and (iii)formation of solid solution. The microphotOgraPh of selected samPles, content anddistribution of all elements were observed via EPMA. The prtcle size for unreacted mixtUreand synthesized poWder were measured, which indicates poWder particles assembled inprePared process that definite sintering is produced resulting in increase of particle size anddecrease of specific surface area. Then the calciIlation curve was protracted for preparationthese oxides according to the frontal discussion.2. The electrical conductivity increases with temPeratUre for Lal#CaxMn,.Co,O3-8 oxides(LCMC, x==0.l-0.4; po0.l-0.3) in ait, and La0.,Ca0.,Mn0.,Co,.,O,. has the maximum. Theconductivity for La0. 8 S r0.,-CaxCo,.,F eo. l O,. (L S C CF) system increas es with temPeratUrethrough a maximtun, then decreases and the maximum exceeds l00 S cm-l. The plot withbetter linear relationship betwCen lnaT and l/T suggeSts that the adiabatic mechanismprevail over a wide temPeratUre range. The mechanism of electrical conductivity for doped-defect solid so1ution was discussed using double-exchange and small polaron effects. At thesame time, the factors including doped componellts, sifitering temPeratWe, reactamcomPosition, and modes of temPeratUr ch...
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