| Direct methanol fuel cells (DMFC) have numerous benefits such as fuel cheapand available, easy fuel carriage, high efficiency, high power density and environmentfriendly. DMFC are expected to find wide application in communication, military andtransportation as a mobile power. However, there are two major technology problemsin DMFC. One is that the methanol diffusion resistance of proton exchangemembrane is poor. The other is slow methanol oxidation kinetics on the anodecatalyst.Alkaline anion exchange membranes for direct methanol fuel cells (AMDMFC)use an anion exchange membrane as polyelectrolyte and the whole system is basic.The methanol oxidative rate is faster in alkaline media than in acid. And there is noreaction intermediate which can make electrode catalyst poisoned. In AMDMFC, thedirection of OH- anion motion opposes that of the methanol flux through themembrane leading to an intrinsic reduction in methanol permeability. AMDMFC canovercome the drawback of DMFC.Anion exchange membrane is one of the key parts of AMDMFC. In this study,novel anion exchange membranes were synthesized and their application inAMDMFC evaluated.Poly (vinyl alcohol) (PVA) is a water-permselective polymer, which hasexcellent methanol resistant ability and film forming property. We used(2,3-epoxypropyl) trimethylammonium chloride (EPTMAC) as etherifying agent tointroduce quaternary ammonium groups into the structure of PVA throughelectrophilic reaction and produced quaternized PVA (QAPVA). GA was added as across-linking agent and produced cross-linked QAPVA membranes with differentcross-linking degree. The methanol permeability of the cross-linked QAPVAmembranes decreased with increasing cross-linking degree, which is better thanNafion117 membrane. Because of dimensional effect caused by hydroxyl groups shrinking and water-permselective performance, the methanol permeability of thecross-linked QAPVA membranes decreased with increasing the methanolconcentration.Quaternized chitosan (HACC) which contains quaternary ammonium groups wassynthesized. Cross-linked composite membranes were synthesized with differentcontent HACC and QAPVA, and GA as a cross-linking agent. The methanolpermeability of composite membranes was 5.68×10-7-4.42×10-6 cm2·s-1. whichwas lower than that of Nafionl17 membrane. The conductivity of the compositemembranes is 10-3-10-2 S·cm-1.The QAPVA/SiO2 hybrid membranes with different SiO2 content weresynthesized with QAPVA and TEOS as precursor through a sol-gel reaction. Theintroducing of inorganic particles increased the thermal stability and conductivity, anddecreased the methanol permeability of the hybrid membranes. The methanolpermeability of the hybrid membranes was one order of magnitude lower than that ofNafionl 17 membrane. The best conductivity of the hybrid membranes is 1.4×10-2S·cm-1.OH-form quaternized PEK-C (QPEK-C) membranes were synthesized throughchloromethylation, quaternization and alkalization reaction. QPEK-C membraneshave good thermal stability, excellent anti-oxidative performance. After staying in 3%H2O2 solution for one week, the mass and conductivity of the QPEK-C membraneschanged little. Methanol permeability of the QPEK-C membranes is lower than 10-9mol·cm-2·min-1. The quantity of introduced quaternary ammonium groups is small,which caused little IEC (0.11 mmol·g-1). The conductivity of the QPEK-C membraneswas from 1.6×10-3 to 1.4×10-2 S·cm-1.
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