A comparative study on sPEEK-based composite membranes with various inorganic fillers using different preparation routes for DMFCs

In this study, proton-conducting sulfonated polyether ether ketone (sPEEK) membranes including tungstic acid, organically modified montmorillonite, and silicon dioxide were prepared using solution casting method for direct methanol fuel cells. All obtained composite membranes had adequate thermal stability for fuel cells, and their surfaces became more hydrophilic due to the incorporation of additives. The ion exchange capacities of the composite membranes were found to be very close to the sPEEK membrane. While the proton conductivity of the sPEEK membrane was 8.6 mS cm(-1), the addition of additives led to an enhancement in the proton conductivity values. Among the prepared composite membranes, sPEEK-H2WO4-5 had the highest proton conductivity (36.5 mS cm(-1)) which was comparable to Nafion117 in water at room temperature. On the other hand, the methanol permeabilities of the composite membranes were in the same order compared to sPEEK but showed minor changes depending on the added materials and their compositions. Among the membranes obtained by solution casting, sPEEK-H2WO4-5 was found to be the best composite membrane due to its high proton conductivity and acceptable methanol permeability. Layer-by-layer modified sPEEK membranes were also obtained in the study for comparison and it was found that sPEEK-PAH/H2WO4-2 displayed the best selectivity value.