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

Abstract

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.