Improving proton conductivity of poly(oxyphenylene benzimidazole) membranes with sulfonation and magnetite addition

Flexible membranes of poly(oxyphenylene benzimidazole) (PBIO) polymer with oxygen in the main chain were prepared. Proton conductivity was improved by sulfonation and adding magnetite to the PBIO membrane. A hydrophilic PBIO polymer/polyvinylidene difluoride (PVDF) mixture was used to prepare the membrane. DMF/acetone solvent pair was used to obtain homogeneous solutions of these two polymers. By modifying the PBIO with sulfuric acid, the PBIO membrane and PBIOsm composite membrane were obtained through sulfuric acid modification as well as the addition of magnetite. The structures of the obtained cast PBIO membranes were illuminated by FTIR, TGA, SEM, and EDX analyses. According to XRD analysis, the crystallization percentages of PBIO, PBIOs, and PBIOsm were compared and a synergistic effect of the degree of crystallization on the ability of the ion exchange was observed. The highest degree of crystallinity was determined at 79% for PBIOsm. Upon the addition of magnetite, the water-holding capacity and proton conductivity of the PBIO membranes increased. The proton conductivity values were measured at 90, 120, and 140 °C. The proton conductivity was found to be higher in the sulfonated PBIOs and sulfonated-magnetite doped membranes. The highest proton conductivity of 36.78 mS/cm was obtained from the combination of sulfuric acid and PBIOsm composite membrane. The proton conductivity of the PBIO membrane was measured to be 36.61 mS/cm.