The influence of various ionic liquids on the properties of SPEEK membrane doped with mesoporous silica

Abstract

Anhydrous proton conducting membranes made of different ionic liquids (ILs), sulfonated poly (ether ether ketone) (SPEEK), and mesoporous silica (SiO2) are successfully prepared. Influences of different ionic liquids on the properties of composite membranes doped with 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm][Tfo]), 1-butyl-3-methylimidazolium chloride ([BMIm]Cl), diethylmethylammonium trifluoromethanesulfonate ([dema][Tfo]), and 1-ethylimidazolium trifluoromethanesulfonate ([EIm][Tfo]) ionic liquids are described. Fourier transform infrared spectroscopy (FT-IR) analysis showed that there were interactions between ionic liquids, SPEEK and mesoporous silica. IL leaching studies demonstrated that IL loss decreased significantly after doping with SiO2. The proton conductivity study showed that both anions and cations of IL influenced the proton conductivity of the composite membranes. Proton conductivity of composite membranes displayed a positive correlation with the number of hopping sites within IL cation structures. Of all the conducting membranes studied, SP/SiO2-7.5/[BMIm][BF4]-50 showed the highest anhydrous proton conducting ability (15mScm−1 at 200°C). Therefore, it is expected to find applications in proton exchange membrane fuel cells under medium temperature, anhydrous conditions.