(16d) Covalently Crosslinked Hybrid Membranes with Improved Dimensional Stability

Direct methanol fuel cells (DMFC) are attractive as promising power source for portable applications due to their obvious advantages. Proton exchange membranes are the key components of DMFC systems, which serves as barrier for fuels and electrolyte for transporting protons from anode to cathode. While the commercially available membranes such as Nafion applied for hydrogen fuel cells are not suitable for direct methanol fuel cells (DMFC) due to their high cost and methanol crossover. Much effort has been made to develop alternative non-fluorinated membranes such as polyaromatic membranes. Although most of them could show relatively good properties, the practical usages of these materials are greatly limited due to their extreme swelling behavior in methanol aqueous solution at elevated temperatures and relatively increased methanol crossover at high sulfonation degree. In this study, crosskinked sulfonated poly ether ether ketone membranes were prepared by a novel modification method. Firstly, sulfonated poly ether ether ketone was reduced to get partial hydroxylized polymer which was then reacted with isocyanatopropyltriethoxysilane to get a side chained polymer bearing triethoxysilyl groups. Theses groups were subsequently reacted with tetraethoxysilane (TEOS) to form a crosslinked network in the membranes. The obtained hybrid membranes with covalent bonds between organic and inorganic phases exhibited much lower methanol swelling ratio and water uptake. With the increase of silica content, the methanol permeability coefficient of the hybrid membranes decreased at first and then increased. At silica content of about 6 wt.%, the methanol permeability coefficient reached a minimum of 7.15×10-7 cm2/s, a five fold decrease compared with that of the pristine poly ether ether ketone membrane.