Fabrication and characterization of fullerene–Nafion composite membranes

Fullerene–Nafion composite membranes have been fabricated through a new solution casting for the first time. The fullerenes used for the composites included C60 and polyhydroxy fullerene (PHF), C60(OH)n (n ∼ 12). The dispersion of the fullerene in the composite membrane was much more refined with smaller agglomeration particles, relative to the previously prepared fullerene–Nafion composites in which the fullerene was introduced through doping. The miscibility of the hydrophobic fullerene, C60, in the Nafion matrix was further improved by a new fullerene dispersant, poly[tri(ethylene oxide)benzyl]fullerene, C60[CH2C6H4(OCH2CH2O)3OCH3]n (n ∼ 5), synthesized in this work. The solution-cast fullerene composites also demonstrated a significant improvement in the physical stability relative to the fullerene-doped Nafion composites through a better integration of the fullerene into the Nafion matrix. Furthermore, increased loadings of the fullerene in Nafion were made possible through the new solution-casting method, compared to the previous doping method. The water characteristics in the fullerene composites have been examined by TGA and 1H pulse NMR measurements. The interactions between the fullerene and the Nafion have been studied through ATR FT-IR and molecular dynamics simulations which suggested PHF resides primarily in the hydrophobic domain of Nafion when the loading was low. The voltammetric measurements also have shown that the fullerene composites have the reduced limiting current density, compared to Nafion membranes without fullerenes.