Polybenzimidazole/zwitterion-coated silica nanoparticle hybrid proton conducting membranes for anhydrous proton exchange membrane application

Polybenzimidazole (PBI)/H3PO4/zwitterion-coated silica nanoparticle hybrid proton conducting membranes for anhydrous proton-exchange membrane application were synthesized and characterized. Fluorine-containing PBI was synthesized via the condensation polymerization of 3,3-diaminobenzidine and 2-bis(4-carboxyphenyl) hexafluoropropane in poly(phosphoric acid) at 170 °C. Zwitterion-coated silica nanoparticles were synthesized via the hydrolysis and polycondensation of zwitterionic organosiloxane, and applied as the additive for the PBI-based hybrid proton conducting membranes. The synthesized phosphoric acid doped polymeric composite membranes were transparent, flexible and showed high proton conductivities of up to 1 × 10−2 S cm−1 at 160 °C under anhydrous conditions. Addition of zwitterion-coated silica nanoparticles to the PBI membrane dramatically increased the phosphoric acid doping capacity, and slightly improved the chemical stability of the composite membranes. Compared with pure PBI membranes, zwitterion-coated SiO2 nanoparticles are effective in preventing the release of the phosphoric acid component from the composite membranes. These properties enable this type of hybrid membrane to be suitable for high-temperature polymer electrolyte membrane fuel cells.