Preparation, Proton Conductivity and Mechanical Properties of Nafion 117–Zirconium Phosphate Sulphophenylphosphonate Composite Membranes

Nafion–zirconium phosphate (ZrP) composite membranes, containing 20 to 40 wt.-% ZrP were treated with aqueous solutions of meta-sulphophenylphosphonic acid (H2SPP) in order to functionalise the filler particles with strongly acidic sulphonic groups. The functionalised samples (Nafion/ZrSPP) were characterised by 31P MAS NMR, water uptake determinations, stress–strain mechanical tests and conductivity measurements. The Nafion/ZrSPP membranes are more hydrophilic than Nafion 117 and stiffer than the parent Nafion/ZrP membranes: at room temperature, the elastic modulus of the membranes with 20 and 40 wt.-% ZrP increases from 191 and 329 N mm–2 to 342 and 470 N mm–2, respectively, after functionalisation. At 100 °C and in the RH range of 30–90% the conductivity of the Nafion/ZrSPP membranes decreases with the increase in the filler loading, being however always higher than that of the parent Nafion/ZrP membranes and nearly coincident with that of Nafion 117. Conductivity measurements as a function of temperature in the range of 80–150 °C showed that, at 90% RH, the conductivity of the Nafion/ZrSPP membranes is stable up to 140 °C thus indicating a better dimensional stability of the composite membrane in comparison with neat Nafion 117.