Sub-Freezing Conductivity of PFSA Membranes

Some properties of perfluorosulphonic acid (PFSA) membranes at sub-freezing temperatures are presented in this work. Both commercial PFSAs and PFSA-based membranes, developed within the Autobrane project, have been investigated. The proton conductivity at temperatures between -25 and 0 degrees C, has been determined by AC Impedance Spectroscopy. At each given condition, the different PFSA membranes exhibit similar values of proton conductivity. At -25 degrees C, the proton conductivities under ice-saturated conditions were three to ten times higher than under reduced pH(2)O conditions. As expected, proton conductivities decreased with decreasing temperature. The phase behaviour of water in the PFSA membranes has been investigated by differential scanning calorimetry (DSC) at temperatures between 20 and -60 degrees C. Water contents of membrane samples were estimated by thermo-gravinnetrical analysis (TGA) before the measurement (in fully hydrated state) and after measurement at -25 degrees C. For all the membranes, there was a remarkable decrease in the hydration number after the experiment at -25 degrees C. This fact may also contribute to the decrease in conductivity observed. No evidence of damage as a consequence of the measuring conditions could be detected for any of the membranes.