| Summary: | 碩士 === 逢甲大學 === 材料科學所 === 96 === The performanceS of direct methanol fuel cells are affected by the methanol cross-over, due to the concentration gradient and electrosmosis between the anode and cathode.Methanol cross-over results in decrease of
open circuit voltage, andreduces the power out of cells. In order to improve the efficiency of the cells, it is necessary to diminish the menthol permeability. In this study, we developed the techniques of plasma surface modification and sputtering of Polyterafluorethylene (PTFE) to solve the problem of the methanol cross-over. The surface modified films were measured by atomic force microscopy (AFM), Flourier transformed infrared spectrocopy (FTIR), gas chromatography and AC impedance
spectroscopy. The results show that sputter deposition of a PTFE layer on Nafion solid polymer electrolyte can effectively reduce the methanol cross-over. However, the plasma modification resulted in severe methanol cross-over. The difference between their methods is that sputtered PTFE layer can form a barrier layer on the Nafion. It can avoid direct contact between methanol solution and polymer electrolyte . Therefore, the
barrier layer effectively retard methanol molecules. On the other hand,the plasma surface modification cause damages to the surface of Nafion,which increase the permeability of methanol molecules. The results demonstrate that PTFE coating reduce the methanol cross-over of Nafion membrane,without significant influences on the ion conductivity.The technique developed here therefore show great potential for the application in Direct Methanol Fuel Cell.
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