Biphenol based membranes with ionic channels for fuel cell application

Copolymers with cross-linkable pendant carboxylic acid moieties were successfully synthesized via direct copolymerization. Two types of copolymers were prepared. In the first type of copolymers, sulfonic groups were introduced on the biphenol monomers. The second type consisted of a series of copolymers having sulfonic groups on the sulfone monomers. Cross-linking of these copolymers was carried out with the prepared hexafluoro-bisphenol-A epoxy resin (HFB) and membranes were cast on glass plates. Cross-linking caused reduction in excessive fuel cross over, water and methanol uptake without compromising much on the basic membrane properties such as proton conductivity, ion exchange capacity, and selectivity ratio. The proton conductivity increased with the rise in temperature but decreased with further rise in epoxy content. The stability of the cross-linked membranes toward radical oxidation in fuel cell ambiance was revealed from Fenton’s test as cr-6FB-SP-HFB membranes exhibited highest oxidative stability. The improvement in the performance of the cross-linked membranes was found by comparing them with pristine membranes. Atomic force microscopy (AFM) and X-ray diffraction (XRD) analyses confirmed phase separation and amorphous behavior of these membranes. Mechanical properties were determined with the help of a Universal testing machine (UTM). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analyses revealed excellent thermal stability of these membranes.