Preparation and characterisation of non-aqueous proton-conducting membraneswith the low content of ionic liquids

In this study, we prepared ionic liquid based composite membranes applicable for anhydrous and high temperature polymer electrolyte membrane fuel cells (PEMFCs). It is intended to minimise an increase in ionic conductivity of composite membranes by reducing the content of ionic liquids up to 30 wt% along with the addition of acids having the same anions as the ionic liquids. For this purpose, we prepared the composite membrane by solution recasting with 5 wt% Nafion solution, ionic liquids such as 1-ethyl-3- methylimidazolium trifluoro-methanesulphonate (EMITf) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), and acids such as trifluoromethanesulphonic acid (HTf) and tetra-fluoroboric acid (HBF4). The composite membranes were characterised by using small-angle X-ray scattering (SAXS), thermogravimetric analyser (TGA) and impedance spectroscopy. It was observed that the addition of the acids results in an increase in the proton conductivity of the composite membranes by reducing the viscosity of ionic liquids inside the composite membranes and also by providing additional proton ions due to the dissociation of the acids. In addition, the composite membranes exhibited better thermal stability over 300°C.