Proton-conducting membranes based on side-chain-type sulfonated poly(ether ketone/ether benzimidazole)s via one-pot condensation

A series of side-chain-type sulfonated poly(ether ketone/ether benzimidazole)s containing side-chain sulfonate groups and main-chain benzimidazole rings were successfully synthesized via benzimidazolization and acylation in a one-pot method. By varying the amount of sulfonate monomers, the ratio of sulfonate acid unit to benzimidazole base unit was easily controlled. 1H NMR and IR spectra were used to characterize the polymer structure. The resulting membranes exhibited excellent mechanical properties (11-45 MPa tensile stress and 9-23% elongation at break) and good thermal stability. The proton conductivity of SPEKEBI-4 was136 mS cm−1 at 30 °C, much higher than Nafion® 115 membrane; while the methanol permeabilities of all the membranes were lower than Nafion® 115 membrane. Moreover, the passive direct methanol fuel cells (DMFCs) with SPEKEBI-2 membrane exhibited a maximum power density of 39.3 mW cm−2 at 25 °C, which show great potential for application in polymer electrolyte membrane fuel cells.