Synthesis and substituent effect of polyether electrolyte membranes containing sulfofluorenyl groups

A new series of poly(arylene ether) ionomers containing sulfofluorenyl groups (SPE1-4) has been synthesized for the applications to polymer electrolyte fuel cells (PEFCs). The SPE-1 membrane shows high stability to heat, oxidation and hydrolysis, high mechanical stability, high proton conductivity and low gas permeation. In order to improve the proton conductivity at low relative humidity (RH), methyl groups substituted polyether ionomers SPE2-4 with higher IEC have been developed. The parent polyethers were synthesized by polycondensation and regioselectively substituted with sulfonic acid groups to give the title ionomers with the ion exchange capacity up to 3.26 meq/g. The SPE-4 (IEC = 3.26 meq/g) showed higher proton conductivity than that of Nafion at 80°C and 20 - 100% RH. The proton conductivity was durable over 10000 h at 100°C and 80% RH. These properties of the new ionomers seem promising as an electrolyte membrane for high temperature PEFCs.