Aprotic ionic liquids as electrolyte components in protonic membranes

In this paper we describe the preparation and the properties of a series of aprotic ionic liquid-based, proton-conducting membranes. The ionic liquids (ILs) 1,2-dimethyl-3-n-propylimidazolium bis(trifluoromethanesulfonyl)imide and the 3-methyl-1-n-propylpyridinium bis(trifluoromethanesulfonyl)imide are used as the casting solvents of PVdF gel-type membranes; the proton conductivity is achieved by the addition of a superacid component, namely, trifluoromethanesulfonic acid (HTf) or N,N-bis(trifluoromethanesulfonyl)imide (HTFSI). The polymer electrolytes showed good thermal and electrochemical properties in the temperature range of interest for PEMFC applications. The strong coordination between the ILs and the HTFSI, which have the same anion, improves the thermal stability of this kind of membrane, but lowers the chemical properties and the conductivity, due to an increase in viscosity. HTf-added samples have an ionic conductivity of 2 x 10(-2) S cm(-1) at 100 degrees C, showing the best overall properties and making these membranes of interest applications in fuel cells.