Sulfonated poly(arylene ether sulfone)/Laponite-SO3H composite membrane for direct methanol fuel cell

Polymer nanocomposite membranes based on sulfonated poly(arylene ether sulfonate) (SPAES) containing a flake filler (Laponite) with varying degrees of sulfonation, were prepared and characterized for application in direct methanol fuel cells (DMFCs). Unlike most other clays, Laponite crystals are very small in size with a very low aspect ratio (diameter to thickness ratio) of 25–30. They improve the mechanical, thermal properties and decreased the fuel permeability. However, polymer composite membranes containing non-proton conducting inorganic particles tend to show low proton conductivity, as compared with pristine polymer membranes. To resolve this problem, prior to the preparation of the composite membranes, Laponite-Na+(NLa) was sulfonated with various amounts of organo silanes (3-Mercaptopropyl trimethoxysilane (SH-silane)) via an ion exchange method. Functionalized Laponite with the organic silane compound showed higher ion exchange capacity and ion conductivity, respectively. In order to minimize the loss of proton conductivity while reducing the methanol permeability, various amounts (0.5–2.0 wt%) of the organically sulfonated Laponite (SLa) were introduced into the SPAES matrices. The performances of hybrid membranes for DMFCs in terms of mechanical properties, behavior of water in membranes, proton conductivity and methanol permeability were investigated.