Proton Conductivity and Methanol Permeability of Sulfonated Syndiotactic Polystyrene Membranes

Abstract

Proton conductivity of innovative ionomeric membranes based on partially sulfonated syndiotactic polystyrene (SsPS) was investigated. The membranes were prepared with various levels of sulfonation by chlorosulfonic reaction on sPS films, in its clathrate form, obtained by solution-casting. The actual sulfonation degree of sPS membranes was evaluated by elemental analysis and their proton conductivity was measured using a galvanostatic four-points-probe electrochemical impedance spectroscopy technique. The dependence of conductivity on the level of sulfonation, hydration condition, and temperature was studied. At higher sulfonation degrees, SsPS membranes showed the best performance in vapor phase at 100% RH. In particular, the best SsPS membrane with sulfonation degree about 26 mol% exhibited conductivity equal to 8.8 × 10⁻² Ω⁻¹ cm⁻¹ at 31.5 °C. This property is stable during time and increases with temperature. For the membranes with the highest degree of sulfonation, we measured a methanol permeability very close to that of Nafion.

Keywords:

• Clathrate form
• Conductivity
• Polyelectrolyte membranes
• Sulfonation
• Syndiotactic polystyrene

ACKNOWLEDGMENTS

The authors thank Prof. Giuseppe Mensitieri of University of Naples and Dr. Pellegrino Musto of National Research Council of Italy for useful discussions.