Preparation And Characterization Of Proton Exchange Membranes For Direct Methanol Fuel Cells

Direct methanol fuel cell(DMFC) have many advantages, such as safe and reliable, easy to carry, rich source of methanol,et al. It is considered as a promising alternative energy source. Proton exchange membrane is one of the key materials in direct methanol fuel cell. Currently the membrane which is the most widely used is Nafion membrane. However, because of poor water retention, high methanol crossover, high costs and other factors, It has limited the large-scale commercialization of DMFC.In order to improve capacity of water retention and methanol resistant and reduce the cost, three novel proton exchange membranes are fabricated. The innovative achievements obtained are mainly as follows:Novel inorganic-organic composite membranes based on Nafion modified by doping hydrophilic inorganic. The SiO2 molecular sieve was sulfonated firstly. Then Nafion/sulfonated SiO2 molecular sieve was fabricated. It was shown by SEM and XRD that molecular sieve was distributed uniformly in the membrane. It was observed that the composite membrane had higher liquid content and better Anti-swelling capacity than Nafion membrane. The membrane with the best overall performance is Nafion/S-SiO2(5wt%) membrane. Compared with Nafion membrane, its methanol permeability had decreased by about one order of magnitude.At the same time, its proton conductivities are all above 0.01S/cm.This membrane can meet the requirements of fuel cell applications.A novel sulfonated polyimide was modified by one-step method. Then the SPI membranes were fabricated. It was observed that the liquid content and swelling degree of SPI membrane were higher than Nafion membrane. But they were not sensitive to temperature and methanol concentration. Proton conductivity of SPI membranes increased as the sulfonation degree increased, and is a little lower than Nafion's. Methanol permeability of SPI membranes also increased as the temperature increased,but it was still lower than Nafion's.SPI/PVDF blend membranes were fabricated by the methodology of polymer blend. It was shown by SEM and XRD that PVDF was distributed uniformly in the membrane. However, the phase separation existed in blend membranes when the content of PVDF is high. Compared with pristine SPI membrane, liquid content of blend membranes reduced and swelling degree also decreased. Proton conductivity of SPI/PVDF blend membranes reduced as the content of PVDF increased, but they were all above 10-3S/cm. Methanol permeability of SPI membranes also reduced as the content of PVDF increased, and were much lower than Nafion's. Blend membranes had good methanol resistant performance.There are 64 figures,3 tables and 76 references in this thesis.