Nafion/Protic Ionic Liquid Blends: Nanoscale Organization and Transport Properties

In this work, the possibility of using the protic ionic liquids N-ethylimidazolium trifluoromethylsulfonate, [EIm][TfO], and N-ethylimidazolium bis(trifluoromethylsulfonyl)imide, [EIm][TFSI], as charge carriers in appropriately modified Nafion membranes has been investigated. The superior thermal stability of ionic liquids, as compared to that of water-based electrolytes, hypothetically offers a wider temperature range of fuel cell operation as well as an increased electrochemical performance even at low-humidity conditions. The nano- and microstructure of Nafion membranes swollen with these protic ionic liquids has been studied in detail, with focus on the correlation with the observed ionic conductivity. Although the presence of the ionic liquid within the hydrophilic domains of Nafion suppresses the thermomechanical properties of the polymer, satisfactory conductivities are achieved between 90 and 150 degrees C, namely, in the range 0.2-1.2 X 10(-3) S/cm.