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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.

The counter-ions of montmorillonite have been exchanged for ammonium cations containing either a sulfonic acid or a carboxylic acid in order to improve the performances of sulfonated membranes in direct methanol fuel cell. These layered silicates have been dispersed within Nafion ® by solution mixing. Comparison with conventional organo-modified montmorillonite (Cloisite 30B) shows that the incorporation of carboxylic acid in the clay galleries improves the filler dispersion and, consequently, the methanol barrier properties. Moreover, the negative impact of Cloisite 30B on the ionic conductivity is restricted.

Direct methanol fuel cells (DMFCs) that use a proton exchange membrane (PEM) as electrolyte, is a promising alternative source of energy for the future. However, methanol crossover from the anodic side to the cathodic one is a major problem in DMFC. Proper dispersion of layered silicates within the fuel cell membrane has been proposed as a strategy for improving the barrier properties of the membrane. The validity of this approach has been tested in case of a model membrane consisting of phosphotungstic acid doped poly(vinyl alcohol). A solvent casting technique has been used, which allows the nanofiller to be delaminated by an ultrasonic pretreatment, as confirmed by TEM and XRD analysis. The layered silicates have a favourable impact on the methanol permeability, whose the decrease overcompensates some loss in ionic conductivity.

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