Pendant-sulfonated poly(arylene ether ketone) (PAEK) membranes cross-linked with a proton conducting reagent for fuel cells

Poly(arylene ether ketone) (PAEK) bearing a pendent sulfonic acid group was synthesized to prepare polymer electrolyte membranes for fuel cells. For preparation of this membrane, the precursor possessing the reactive carboxylic acid functional group was first synthesized to control the degree of sulfonation and cross-linking. A variety of essential properties for fuel cell membranes such as proton conductivity, water uptake, methanol permeability, and chemical, thermal, and mechanical stability were investigated. The proton conductivity was comparable to Nafion ^® 117 and it did not significantly decrease by addition of the cross-linker because of the sulfonic acid proton conducting group attached to it. Methanol permeability was very low and it decreases with cross-linking density - it decreased down to a fourth of that of Nafion ^® at 30% cross-linking density. Cross-linking reduced water uptake and thus enhanced dimensional stability of the membrane. The resistance to oxidation and hydration was also improved by cross-linking. Among a series of cross-linked membranes, the 20% cross-linked system exhibited the best cell performance associated with excellent membrane properties.