Conductivity and methanol permeability of Nafion – zirconium phosphate composite membranes containing high aspect ratio filler particles

Gels of exfoliated alpha-zirconium phosphate (ZrPexf) in dimethylformamide (DMF) were used to prepare Nafion/ZrPexf composite membranes with filler loadings up to 7 wt% by casting mixtures of Nafion 1100 solutions in DMF and suitable amounts of 2 wt% ZrP gels in DMF. TEM pictures showed that the ZrPexf particles had aspect ratio of at least 20. All samples were characterised by methanol permeability (P) and through-plane (sigmathp) and in-plane (sigmainp) conductivity measurements at 40°C and 100% RH. The methanol permeability of Nafion membranes containing in situ grown ZrP particles with low aspect ratio (Nafion/ZrPisg) was also determined. The methanol permeability and the swelling behaviour of the composite membranes turned to be strongly dependent on the filler morphology. As a general trend both permeability and swelling decreased according to the sequence: Nafion/ZrPisg > Nafion > Nafion/ZrPexf. The maximum selectivity (P/sigmathp = 140000 S cm-3 s) was found for the membrane filled with 1 wt% ZrPexf: this value is 7 times higher than that of Nafion. For the Nafion/ZrPexf membranes the ratio sigmainp /sigmathp increases with the filler loading thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface