Nanocomposite Membranes Based on Imidazole-Functionalized Chitin Nanowhiskers for Direct Methanol Fuel Cell Applications

Abstract

Chitin nanowhiskers (Chws) were prepared from shrimp shells and modified by imidazole groups, using 3-Glycidoxypropyltrimethoxysilane (GPTMS), as a coupling agent, for application in direct methanol fuel cell (DMFC) membranes. New nanocomposite membranes were fabricated by incorporating the ChWs or imidazole modified chitin nanowhiskers (Chw-Im) into chitosan (CS) and Nafion (a perfluorinated ionomer) matrices as representative polycationic and polyanionic polymers, respectively. The electrostatic and hydrogen bond interactions between the positively charged imidazole groups on the surface of the Chw-Im and the proton conducting sites on Nafion or CS chains can form new proton conducting pathways at the interface of the Chw-Im and the polymer matrix, which results in an improvement in the membrane performance. The characteristics of these nanocomposite membranes, as well as the Chws and Chw-Im, were investigated by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), ion exchange capacity (IEC) and water uptake, as well as the proton conductivity method. The results showed that the incorporation of the modified nanowhiskers could conduct at a lower methanol permeability, in parallel to an enhancement in the selectivity parameter (the ratio of proton conductivity to the methanol permeability) in the nanocomposite membranes, compared to neat Nafion or pristine CS membranes, which shows that the nanocomposites based on Chw-Im can be utilized as an efficient polyelectrolyte membrane for application in DMFCs.

Keywords:

• chitin nanowhiskers
• direct methanol fuel cells
• methanol permeability
• polyelectrolyte membranes
• proton conductivity

Acknowledgment

The authors thank Mr. J.Jafari from the Sahand University of Technology for helpful fundamental discussions. This research was partially supported by Amirkabir University of Technology, Tehran, Iran.