| Summary: | 博士 === 國立臺灣科技大學 === 化學工程系 === 99 === Polymer-silica membranes are interesting hybrid architectures with excellent physicochemical properties. More specifically, the swelling-resistance and water-retentive properties of hydrophilic silica and siloxane segments is of particular interest when such hybrid membranes are used as polymer electrolytes in fuel cells. This thesis focuses on the choice of materials, the development of synthetic methods and the analysis of the fuel cell-relevant properties of the new hybrid materials in order to improve the performance of both polymer electrolyte membrane fuel cells and direct methanol fuel cells. Highly conductive and hydration retentive hybrid membranes were prepared by incorporating mesoporous silica and organically modified mesoporous silica in to Nafion, using a surfactant assisted sol-gel process. These hybrid membranes exhibit an increased water uptake and an associated conductivity enhancement at 100% relative humidity (RH) compared to unmodified Nafion. More significantly, the functionalized silica/Nafion membranes show high proton conductivities at 80˚C and 50% relative humidity, which is more than six times higher than that of Nafion. These modified Nafion composites have promising potential for applications in polymer electrolyte membrane fuel cells (PEMFCs). In another approach, a new and facile synthetic method to form polyimide (PI)-silica hybrid membranes was developed. The new surfactant assisted sol-gel process improves the particle dispersion and the compatibility between the organic and inorganic phases. Moreover, this synthetic strategy allows the sol-gel process to proceed in the presence of a fully imidized, high molecular weight polyimide to generate a chemically well-defined silica phase. It was found that the macroscopic homogeneity and the connectivity of the silica network achieved by the functionalization of silica segments facilitated the percolation of the conducting phase in the hydrated membranes. Thus, sulfonic acid functionalized silica/PI membranes showed reasonably good conductivities. Such membranes with swelling-resistant conducting-inorganic networks were found to be beneficial in preventing methanol permeation. The superior electrochemical selectivity of these composite membranes for protons over methanol, compared to commercial Nafion 117, makes these systems interesting candidates for applications in direct methanol fuel cells (DMFCs).
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