Preparation and properties of nanocomposite membranes of polybenzimidazole/sulfonated silica nanoparticles for proton exchange membranes

Sulfonated silica nanoparticles (SA-SNP) are utilized as a functional additive to prepare polybenzimidazole (PBI)/SA-SNP nanocomposite membranes. The sulfonic acid groups of SA-SNP form ionic linkages with PBI chains, improve the compatibility between SA-SNP and PBI, and enhance the mechanical strength of the PBI/SA-SNP nanocomposite membranes. After acid doping with phosphoric acid, PBI/SA-SNP nanocomposite membranes exhibit depressions on methanol permeability and enhancements on proton conductivity comparing to the pristine PBI membrane. The proton conductivity of PBI/SA-SNP-10 (possessing 10 wt% SA-SNP) membrane is of about 3-folds of that observed with pristine PBI membrane. The selectivity (the ratio of proton conductivity to the methanol permeability) of PBI/SA-SNP-15 is of about 1.3-folds of that of the Nafion® 117 membrane. The above results indicate the PBI/SA-SNP nanocomposite membranes could be utilized as the proton exchange membranes for direct methanol fuel cells.