Compositional effect on the properties of sulfonated and nonsulfonated polymer blend membranes for direct methanol fuel cell

Abstract

In order to retain the proton conductivity and reduce the methanol permeability of the polymer membranes in the direct methanol fuel cell (DMFC), blend membranes were prepared. Highly sulfonated poly(arylene ether sulfone) copolymer with 55mol% sulfonation (sPAES55) were synthesized via nucleophilic aromatic substitution polycondensation of 4-4’-biphenol (BP), 3,3’-disulfonated -4’4-dichlorodiphenyl sulfone (SDCDPS), 4-4’-dichlorodiphenyl sulfone (DCDPS). As methanol crossover barrier, poly ether sulfone copolymer (RH-2000, Solvay) was blended with sPAES55. By varying the drying condition (HT, FD1, FD2) and composition (5 to 5, 6 to 4, 7 to 3, 8 to 2) of the blend solution, various blend membranes and morphologies were obtained. As a result, important properties such as proton conductivity, methanol permeability and water uptake in DMFC were also changed. Morphology of the blend membranes was measured by SEM and AFM. The AC impedance spectroscopy was used to measure the proton conductivity and Abbe refractometer was utilized to investigate the methanol permeability of the blend membranes. The blend membranes on different drying condition and different compositions were investigated and then the transport properties of the blend membranes were discussed. The cross-sections of blend membranes showed phase separated morphologies. The effect of phase-separated morphology on the properties of blend membranes was investigated. The blend membranes at HT and FD1 drying condition showed sea island morphology of either RH2000 matrix or sPAES55 matrix depending on blend ratios. Otherwise, in case of FD2 blend membranes co-continuous morphology was observed on most intended blend ratios and the morphology was influenced on the transport properties of the blend membrane. In this thesis, the effect of the composition and the drying condition on the phase separation and morphology was investigated and then the swelling, mechanical and the transport properties of t...