Polymer electrolytes containing ionic liquids with acidic counteranion (DMRImH2PO4, R = ethyl, butyl and octyl)

Ionic liquids with acidic counteranion and having composition: 2,3-dimethyl-1-alkylimidazolium dihydrogenphosphate (DMRImH2PO4, R = ethyl, butyl, octyl) have been prepared and the effect of alkyl (R) sidechain length on the conductivity and viscosity behavior has been studied. DMEtImH2PO4 with highest conductivity (0.07 S/cm at 120 °C) has been incorporated in polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) to obtain polymer electrolytes in the membrane form. The conductivity of membranes has been found to depend upon the concentration of ionic liquid, phosphoric acid and temperature. Polymer electrolytes containing different ionic liquids are thermally stable up to 225 °C and can be used as high temperature membranes for fuel cells.