Investigations on effects of the incorporation of various ionic liquids on PVA based hybrid membranes for proton exchange membrane fuel cells

PVA (Polyvinylalcohol) based hybrid membranes were prepared by incorporating inorganic fillers and ionic liquids (ILs) like 1-butyl-3-methylimidazolium Bis (trifluoromethanesulfonyl)imide (BMITFSI) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4) using sol-gel method. Hybrid composite membranes were investigated with respect to its structural and thermal properties, water uptake capability and proton conductivity. TG-DTA studies confirmed the thermal stability of membranes and both ILs based membranes are stable up to 370 °C. As compared between two ILs, EMI-BF4 contained membranes showed better thermal stability and a complete degradation of main chain polymer backbone is occurred at about 640 °C. Thus, the thermal stability of the membranes was importantly enhanced by the presence of both EMI-BF4 and SiO2. From the experimental data, the conductivity of PVA based hybrid membranes depends on the ILs and its concentration. Significantly, the maximum conductivity of PVA/PMA/SiO2/BMITFSI and PVA/PMA/SiO2/EMI-BF4 hybrid membranes at 60 °C were 0.83 × 10−3 S/cm and 0.58 × 10−3 S/cm with constant relative humidity of 50%, respectively. It was found that, the proton conductivity essentially reduced with an increasing ILs fraction accompanied with the increase in cross-linking density, which impedes the proton conductivity due to the enhanced compact nature of membranes.