Preparation And Properties Of Novel Polymer Electrolyte Membranes From Poly (Arylene Ether Sulfone)s For Fuel Cell Applications

Fuel cells, as a novel type of energy system with high efficiency, have shown great potentials for transportation, stationary and potable power applications. In a polymer electrolyte membrane (PEMFC) system, polymer electrolyte membrane (PEM) is one of the key components. This thesis focused on the development of novel PEMs based on poly(arylene ether sulfone)s (SPAES) and their properties for fuel cell applications were investigated in detail.A series of novel SPAES copolymers were successfully synthesized from 6F-bisphenol A (HFBPA),9,9'-bis(4-hydroxyphenyl) fluorine (BHPF),4,4'-difluorodiphenyl sulfone (DFDPS) and 3,3'-disulfonate-4,4'-difluorodiphenyl sulfone (SDFDPS) via high temperature nucleophilic copolymerization. The rigidity of the polymer backbone was adjusted by the feed ratio of BHPF to HFBPA. The results indicated that the SPAES membranes displayed lowered water uptakes and proton conductivities but increased stability towards water with the increase of the rigid moiety of BHPF. The membrane of SPAES50-50, with 50/50 molar of BHPF/HFBPA and 50%, of sulfonation degree, exhibited dimensional change of 0.12 and 0.13 in the plane and thickness direction, respectively, and proton conductivity of 0.137 S/cm in water and at 60℃. The membrane also showed weight loss of 7% after aging treatment for 200 h in water at 130℃, suggesting their potential application for high temperature fuel cells.With the equivalent molar content of BHPF and HFBPA, a series of novel SPAES were synthesized successfully from HFBPA, BHPF, DFDPS and SDFDPS by varying the amount of DFDPS and SDFDPS. The result indicated that the SPAES membranes showed increased ion exchange capacities and water uptakes, but decreased dimensional stability and water stability with the increase of SDFDPS, which is unfavorable for the long-term stability of the PEMs. The membrane of SPAES50-50 with the molar ratio of HFBPA:HPF:DFDPS:SDFDPS of 1:1:1:1 showed fairly good comprehensive properties.Organic-inorganic composite membranes were prepared by SPAES derived from DFDPS, SDFDPS,4,4'-biphenol (BP) and nano-Ti02. And the water uptake, dimensional change, water stability, proton conductivity and mechanical properties were characterized. The result showed that the appropriate addition of nano-TiO2 had advantages to enhance the proton conductivity at low relative humidity, for example, the membrane containing 2.5 wt% nano-TiO2 exhibited proton conductivity of 33 mS/cm with 50% relative humidity at 60℃.A serious of novel cross-linking anion exchange membranes were successfully prepared using DFDPS and BPA as the monomers while aliphatic diamines with different length as the cross-linking reagents, via procedures including high temperature copolymerization, chloromethylation, quaternization and alkalization. The effects upon the membrane properties of the length of aliphatic amines were investigated. The results indicated that the obtained cross-linked membranes from aliphatic diamine with longer length showed better stability under alkaline condition, while the lowered dimensional changes were achieved when the same amount of cross-linking reagent was utilized, however, the water uptakes and proton conductivities decreased accordingly.