Preparation And Properties Of Novel Sulfonated Poly (Ether Ether Ketone) /HPA Composite Membranes

The proton exchange membrane is a key component in proton exchange membrane fuel cell (PEMFC), which acts as a separator to prevent mixing of reactant gas and provides ionic pathways for protons transport. The most commonly used proton exchange membranes are perfluorinated copolymers with pendant sulfonic acid group, such as Nafion (Dupont), Dow membrane (DOW), which combine high conductivity and excellent chemical stability. However, the high price and limited operating temperature have prevented the perfluorinated sulfonated membranes applications in large scale. In addition, the high methanol permeation restrains their use in DMFC. Many efforts have been spent on searching for new alternative materials during past years. Among these materials, sulfonation of aromatic polymers is one of the main approaches due to their excellent thermal and mechanical properties as well as their resistance to oxidation and stability under acidic conditions. In addition, the organic-inorganic composite membranes represent one way to improve the PEM properties. Heteropolyacids are one of the most attractive inorganic modifiers because of their high proton conductivity and thermal stability. In our work, we prepared some novel sulfonated poly(arylene ether ketone) copolymer materials by molecular design. Here, we present the synthesis and characterization of three series of high molecular weight, sulfonated poly(ether ether ketone)s with different sulfonation degree by direct copolymerization and prepared the HPA (phosphotungstic acid) composite membranes. All the coplolymers exhibited high intrinsic viscosities and well membrane formation, which indicated obtained copolymers with high molecular weight. The copolymer structure and sulfonate degree were determined by 1HNMR and FTIR. IR spectrum also indicated that the HPA particles interacted primarily with the sulfonic acid groups. The composite membranes were tough and transparent, and the SEM image indicated that the HPA particles homogenously distributed within the polymer matrix. However, the introduction of fluorine atom restrained HPA particles dispersed in sulfonated copolymer, especially for the copolymer with lower DS, SFFPEEK20, due to the high hydrophobic property of fluorine. Though the introduction of HPA to sulfonate polymer reduced the stabilities of sulfonate groups, which may be due to the high acidity of HPA, the composite membranes were stable below 200℃satisfying the requirement of Fuel Cell working conditions. The water uptake and proton conductivity of the composite membranes increased with the rise of DS, temperature and relative humidity. The membranes of highly sulfonated polymer showed good proton conductivity, but their excessive swellings at high temperature limited their practical use. For the composite membranes, their conductivities were lower than their mother polymers at lower temperature, but with the temperature up, the conductivities of composite membranes showed much higher increase than pure copolymers and comparable with them at above...