Ion track grafting: A way of producing low-cost and highly proton conductive membranes for fuel cell applications

Proton conductive individual channels through a PVDF matrix have been designed using the ion track grafting technique. The chosen polyelectrolyte, a sulfonated polystyrene (PSSA), has been radiografted all along the linear and cylindrical ion tracks of irradiated PVDF leading to the creation of privileged paths for proton conduction from the anode to the cathode without inducing any further porosity. Consequently, such ion track grafted PVDF-g-PSSA membranes have good gas permeation properties against H2 and O2 and keep this gas barrier property up to 10 bars. A degree of grafting of 140wt% was chosen to ensure a perfect coverage of PSSA onto PVDF-g-PSSA surface and allows a sufficient exchange with the active layers of the Membrane Electrolyte Assembly (MEA). Fuel cell test has been performed during three days feeding the cell with pure H2 and O2, at the anode and cathode side respectively. Temperature has been progressively increased from 50 to 80°C and performance has been evaluated by recording polarisation curves and electrochemical Impedance Spectroscopy at different current densities. From these last measurements, it has been possible to determine the resistance of the MEA during the fuel cell tests and, then to evaluate the conductivity of the membrane. The proton conductivities of such membranes have been estimated to be ranged between 36 mS.cm -1 and 61 mS.cm -1 depending on the conditions. These values are similar to that of perfluorosulfonated membrane such as Nafion in the same conditions.