Strontium cross-linked sPEEK proton exchange membranes for fuel cell

In order to alleviate the high water uptake and dissolution properties at elevated temperatures, the major drawbacks of the highly sulfonated polyetheretherketone (sPEEK) electrolyte membranes (above 60%), crosslinks are created by accommodation of the strontium (Sr) earth metal via ionic bonding with sulfonic groups of the sPEEK. The effect of crosslinking on water uptake, thermal and mechanical stability, methanol permeability, and proton conductivity, etc. of membranes is investigated. Addition of a small amount of Sr up to 10 wt.% considerably decreases water uptake and thus increases the mechanical strength in water at 80 °C. Although the crosslinking decreases not only the methanol permeability but proton conductivity, incorporation of 2-6% Sr results in higher selectivity than Nafion® with much less water uptake. Those crosslinking effects on membrane properties are closely related with the ionic cluster dimension of membrane revealed by small angle X-ray (SAXs) pattern.