Polymer-SnO₂ composite membranes

When designing sulfonic acid based ionomers, high ion exchange capacity (IEC) comes at the expense of the mechanical properties. With too high IEC, the membrane will excessively swell or even dissolve in water. Therefore a suitable compromise must be found between high charge carrier concentration and adequate mechanical properties. It has been demonstrated that this compromise can be found at higher IEC when the mechanical properties are improved by increasing crystallinity, increasing molecular weight, crosslinking or reinforcement of the membrane by dispersion of interacting particles therein. This work utilizes the latter approach and makes use of particles of tin dioxide (SnO₂).

Polymer-SnO₂ composite membranes were successfully prepared using an ion-exchange method. SnO₂ was incorporated into membranes by ion-exchange in solutions of SnCl₂ ∙ 2 H₂O in methanol, followed by oxidation to SnO₂ in air. The content of SnO₂ proved controllable by adjusting the concentration of the ion-exchange solution.

The prepared nanocomposite membranes were characterized by powder XRD, ¹¹⁹Sn MAS NMR, electrochemical impedance spectroscopy, water uptake and tensile stress-strain measurements. For Nafion 117™, addition of about 4 wt% of SnO₂ particles provided a substantial increase in elastic modulus with conductivity similar to the parent membrane.