Diethlyamine bisulphate/sulphate, an ionic liquid, was synthesised and characterised for high temperature fuel cell applications. Composite hybrid membranes of PBI and the ionic liquid diethlyamine bisulphate/sulfate were fabricated at different composition ratios PBI/xDESH. FTIR spectra showed that the IL did not change the PBI structure. The ionic liquid only weakly interacts with PBI and remains free inside the structure allowing for the observed ionic conduction. PBI/xDESH membranes could operate under a higher temperature values/low humidity conditions with conductivity >0.01 S cm(-1). The measured proton conductivity, from symmetrical H-2 cell, however, is ca. 4 times lower than that of the measured ionic conductivity. This could be estimated roughly by considering proton conduction where the proton is associated with two anions A(-) resulting in ionic agglomerate HA(2-) with more than double the ionic radius of A(-) and consequently less than half of its diffusivity. Additionally, considering the solvation number of that agglomerate to be 1.0 will result not only in a slower proton diffusion and lower conductivity but will also cause serious flooding and mass transport limitation at the cathode. This cumulative effect will limit the life of the cell due to the IL migration from anode and membrane to the cathode. (C) 2013 Elsevier B.V. All rights reserved.