Synthesis And Characterization Of Sulphonated Poly(Ether Ether Ketone-benzimidazole)s As Proton Exchange Membrane For Direct Methanol Fuel Cells

Proton-exchange membrane, which plays the roles as separator and proton conducting media, is one of the key parts in Direct Methanol Fuel Cell (DMFC). In this paper, a novel alternating copolymer of sulfonated poly(ether ether ketone-alt-benzimidazole)s (SPEEK-BI) was synthesized by polycondensation of aromatic bisphenol containing benzimidazole and a mixture of sulfonated and non-sulfonated difluorobenzophenones.By varying the amount of two difluorobenzophenones, the ratio of sulfonic acid unit to imidazole base was controlled straightforwardly. The polymer structure was confirmed by ~1H-NMR and IR spectroscopies. Two different methods of ion exchange capacity measurement supported a strong inter- and intra-molecular interaction between acid and base units, which resulted in an improved mechanical strength as well as avoiding phase separation. Tough membranes with good mechanical stability in hot water (80°C) and alcohol were obtained by solution casting.The proton conductivity, methanol permeability and mechanical properties of resulted membranes were determined for estimating their potential application in DMFC. The relatively high proton conductivity, extremely low methanol permeability and excellent mechanical properties make the SPEEK-BI membranes a promising candidate for DMFC.