Sulfonated PEEK-WC membranes for possible fuel cell applications

Sulfonated polyetheretherketones are polymers of some interest for preparing membranes as alternative to the expensive perfluorinated membranes (e.g. Nafion) presently used for fuel cell applications. Sulfonated poly(oxa-p-phenylene-3,3-phtalido-p-phenylene-oxa-p-phenilene-oxy-phenylene) (PEEK-WC) with various degrees of substitution (DS) was prepared and then characterized by FT-IR analyses. Sulfonated PEEK-WC dense membranes were tested for their permeability to various gases and vapors. At 60 °C, the permeability coefficient of methanol in a sulfonated PEEK-WC membrane with 70% DS was about two orders of magnitude lower in comparison with that in a Nafion 117 membrane. Conductivity measurements were carried out by the impedance technique as a function of relative humidity (RH), at 100 °C, and as a function of temperature, in the range 50–115 °C, at 100% RH. The proton conductivity strongly increases with temperature and DS and reaches 2.5×10−2 S cm−1 at 115 °C and 100% RH for DS=0.82. The hydration of the sulfonated polymer was also determined under the same conditions used for conductivity measurements.