New Proton-Conducting Membranes Based on Phosphorylated Polybenzimidazole and Silica

We have synthesized hybrid membranes based on N-phosphorylated polybenzimidazole, containing different percentages of silica (2–20 wt %). The materials have been characterized by scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, IR spectroscopy, and impedance spectroscopy. The membranes have been shown to contain silica nanoparticles with a bimodal size distribution: 3–5 and 20–60 nm. The hybrid membranes have high proton conductivity (9.7 mS/cm at 130°C), which has a maximum when the dopant content is 2–10 wt %. The phosphonic groups grafted onto the polymer ensure additional hydration of the membranes at increased humidity. The addition of silica helps to reduce the gas permeability of the membranes by a factor of ~1.5.