Beneficial effect of carbon nanotubes on the performances of Nafion membranes in fuel cell applications

Multi-walled carbon nanotubes (MWCNTs) were dispersed by melt-extrusion within Nafion® membranes in order to decrease the methanol permeability without deleterious effect on the ionic conductivity. The risk of short-circuits was minimized by keeping the carbon nanotubes content lower than the percolation threshold. Two series of carbon nanotubes grafted by carboxylic acid groups were used, i.e., commercially available carbon nanotubes and MWCNTs home-grafted by carboxylic acid containing alkyl radicals. The second series of nanotubes were more resistant to break-up during melt-processing. Methanol permeability was decreased by approximately 60% without any decrease in the ionic conductivity. In parallel, the Young's modulus was increased by 140% and 160% as compared to pure Nafion® at MWCNT contents of 1 and 2 wt%, respectively.