Conductivity and Methanol Permeability of Nafion–Zirconium Phosphate Composite Membranes Containing High Aspect Ratio Filler Particles

Gels of exfoliated α‐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 (σthp) and in‐plane (σinp) 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 out 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 (σthp/P = 1.4 × 105 S cm–3 s) was found for the membrane filled with 1 wt.‐% ZrPexf: this value is seven times higher than that of Nafion. For the Nafion/ZrPexf membranes, the ratio σinp/σthp increases with the filler loading, thus indicating that the preferred orientation of the ZrP sheets is parallel to the membrane surface.