Sol-gel derived sulfonated diphenyldimethoxysilane with hydrophilic -SO_3H functional groups were used as the additive to reduce the methanol permeability of Nafion. The sulphonated composite membrane(N-sDDS) performs better than the unsulfonated monomer with the same amount of silica. N-sDDS composite membranes were prepared by mixing Nafion-DMSO solutions with sulfonated diphenyldimethoxysilane sol and casting to membranes. SW, EW tests and SEM characterization show the physical propertities of the composite membranes and FT-IR analysis reveals the incorporation of the sDDS monomer within the composite membranes. The methanol permeability and cell performances of the N-sDDS membranes are evaluated and compared with the bare recast Nafion membrane and unsulphonated DDS composite membrane. It was found that, compared with the bare recast Nafion membrane, the composite membranes have a lower methanol permeability, which is meaningful in the direct methanol fuel cell (DMFCs) than bare recast membrane, and a better single cell performance than the unsulphonated DDS composite membrane.
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