Synthesis and properties of fluorine-containing polybenzimidazole/silica nanocomposite membranes for proton exchange membrane fuel cells

Novel polybenzimidazole (PBI)/silica nanocomposite membranes were prepared via sol–gel process from an organosoluble, fluorine-containing PBI copolymer with a silica precursor, tetraethoxysilane (TEOS), and a bonding agent. The introduction of the bonding agent results in the reinforced interfacial interaction between PBI chains and silica nanoparticles. Transmission electron microscopy (TEM) analyses showed that the silica particles were well dispersed in the PBI matrix on a nanometer scale. The thermooxidative stability of the PBI membranes increased slightly with the increase of silica content. The coefficients of the thermal expansion (CTEs) of the nanocomposite membranes decreased slightly with increasing amounts of silica. The mechanical properties and the methanol barrier ability of the PBI films were improved by the addition of silica. The modulus of the PBI/10 wt.% silica nanocomposite membranes had a 37% increase compared to the pure PBI films, and the methanol permeability decreased by 58% with respect to the pure PBI membranes. The conductivities of the acid-doped PBI/silica nanocomposites were slightly lower than the acid-doped pure PBI.