Novel proton exchange membranes with dimensional stability and permeability resistance based on sulfonate polynorbornenes

The novel proton exchange membranes of a direct methanol fuel cell (DMFC), the sulfonated functional polynorbornenes P(BN/NOH/NS), are successfully prepared via the sulfobutylation of poly(butoxymethylenenorbornene-co-norbornenemethanol) [P(BN/NOH)] with 1,4-butane sultone, and a crosslinked composite membrane consisting of P(BN/NOH/NS), P(BN/NOH), 4,5-imidazole dicarboxylic acid (IDA), and H3PO4 has also been developed. Adding the IDA/H3PO4 to the membrane promotes the proton conductivity of the cross-linked composite membrane to 2.79 x 10(-3) S/cm at 80 degrees C, which is six times higher than the P(BN/NOH/NS) membrane. At the same time, the rigid polynorbornene backbones remarkably improved the methanol permeability resistance and dimensional stability of P(BN/NOH/NS) and its cross-linked membrane, compared with the Nafion 115 membrane. A single cell based on the cross-linked composite membrane showed an open-circuit voltage of 0.483 V and power density of 1.35 mW/cm(2).