Improving the Performance of Nafion®-Based Fuel Cell Membranes by Introducing Histidine Functionalized Carbon Nanotubes

A new polymer nanocomposite membrane based on Nafion and functionalized carbon nanotubes (CNTs) was developed for proton exchange membrane fuel cell (PEMFC) applications. Histidine, an imidazole-based amino acid, was used for modifying the surface of CNTs. The modification of CNTs was characterized by means of Fourier transform infrared spectroscopy (FTIR) and their Zeta potential. The imidazole groups, due to forming and breaking of hydrogen bonding, can facilitate proton transport across the polymer matrix by the Grotthuss mechanism. The final structure of the Nafion/CNT nanocomposites was investigated by small angle X-ray scattering (SAXS). The results confirm that the transport properties of the fabricated new membranes were significantly improved in comparison with unmodified and conventional Nafion (R) membranes. The power density of the imidazole-CNT (Im-CNT) Nafion (R) composite membranes was about three times more than Nafion (R) membranes. Also, the experimental results showed that the proton conductivity for the conventional Nafion (R) membranes decreased over 100 degrees C but the conductivity for the Nafion (R)/Im-CNT remained at a nearly constant value above 100 degrees C up to 120 degrees C. Thus, the nanocomposite based on Nafion/imidazole functionalized CNT can be considered as an anhydrous PEMFC membrane for high-temperature applications.