Sulfonated PEEK-WC membranes for Proton Exchange Membrane Fuel Cell: Effect of the increasing level of sulfunation on electrochemical performances

Sulfonation of PEEK-WC powder (a glassy poly-ether ether ketone) has been performed at 80 oC for 3 h using H2SO4 conc. (96%). The degree of sulfonation varied from 15 to 40%, depending on the reaction time. The sulfonated polymers (S-PEEK-WC) were used to prepare dense membranes for possible fuel cell application. In particular, two membranes were prepared by solvent evaporation technique, usingDMAas the solvent for the 2- and 3-h sulfonated polymers. The dense character of both membranes has been confirmed by SEM analysis. The chemical-physical characterization has showed an increasing water solubility of the sulfonated polymers with the increasing level of sulfonation: from 7 to 11% of weight loss at 80 oC in pure water. Despite this, a water uptake increase up to 15% has been found for the dense membranes at 80 oC. Furthermore, if compared with a commercial Nafion membrane, S-PEEK-WC membranes exhibit comparable electrochemical performances even if at higher temperature, especially the membrane prepared with the 3-h sulfonated polymer. A power density of 284 mW/cm2 was obtained for S-PEEK-WC membrane at 120 oC in H2/air fuel cell, slightly above the corresponding value found for Nafion. At the same temperature, a Tafel slope of 70mV was reached for the S-PEEK-WC membrane versus 100mV for the Nafion. Finally, the specific conductivity is about 1.7×10-2 S/cm versus 1.4×10-1 S/cm of the commercial Nafion membrane.