Broadband dielectric spectroscopy of Nafion-117, sulfonated polysulfone (sPSF) and sulfonated polyether ketone (sPEK) membranes

Nafion®-117, sulfonated polysulfone (sPSF) and sulfonated polyetherketone (sPEK) are characterized using broadband dielectric spectroscopy in the frequency range of 10 MHz–100 mHz. Overall, there are 4-5 relaxation processes in these sulfonated membranes and a comparison of their spectral features allows assigning the relaxation processes. At an optimum amplitude of ~100 mVrms, all the relaxations are clearly defined as the electrode polarization is minimized. At low temperatures (-130°C), these membranes show a broad relaxation peak in the mid-frequency region, which quickly shifts towards the high-frequency region as the temperature is increased to -90°C. This peak is observed in proton exchange membranes for the first time due to the use of low ac amplitude, and it is assigned to the relaxation of the confined water in the micro-pores. With all the membranes, the peak associated with -SO3H group relaxation is observed in the same frequency range at a temperature of ~-80°C