| Sulfonated polymers have attracted much attention in the past decade because of their important applications in polymer electrolyte membrane fuel cells (PEMFCs) which provide clean, quiet and portable power sources for vehicular transportation and for other applications. At present, sulfonated perfluoropolymers such as DuPont's Nafion are typical membranes that are used in practical systems due to their high thermal, electrochemical and chemical stability. However, the high cost, low conductivity at low humidity and/or high temperature, and high methanol crossover are the major drawbacks associated with these perfluoropolymers seriously limit their industrial applications. The development of low cost and high performance polymers as alternative materials is strongly desired.Up to now, a large number of sulfonated hydrocarbon polymers such as sulfonated polysulfone, sulfonated poly(ether ether ketone), sulfonated polysulfide, sulfonated polyphenylene and sulfonated polyimides have been developed. However, the poor water stability is a serious problem associated with most of the sulfonated hydrocarbon polymers of high ion exchange capacities (IECs) which is essential to provide high proton conductivity. Cross-linking is a common and effective method to suppress membrane swelling and to improve the mechanical properties of the membranes. In this thesis, a novel cross-linking approach was successfully developed for the preparation of a series of cross-linked sulfonated poly(sulfide sulfone) (SPSSF) membranes., i.e., the SPSSF membranes were treated with polyphosphoric acid at 180 oC for 1.5 h. The occurrence of cross-linking was confirmed by solubility test, FT-IR spectra and titration measurements. Cross-linking caused significant improvement in membrane performance, i.e., the cross-linked membranes showed better mechanical properties, higher water stability and lower methanol permeability than the corresponding uncross-linked ones, while high...
|
PDF Full Text Request