Proton conducting membranes for the high temperature-polymer electrolyte membrane-fuel cell (HT-PEMFC) based on functionalized polysiloxanes

A new membrane material has been developed, based on a polysiloxane framework with functional proton conducting groups such as sulfonic acid and heterocyclic groups, e.g., imidazole and benzimidazole, covalently bonded at the siloxane backbone. Sulfonated siloxane based block-copolymers are used to improve the flexibility of the membranes at high temperatures, up to 180 degrees C. The new membranes are investigated by measuring their proton conductivity under real conditions, in the temperature range from room temperature to 180 degrees C in the dry state and at full humidification, using impedance spectroscopy in the frequency range from 1 Hz to 100 kHz. The proton conductivities under full humidification are approximately 3 x 10(-2) S cm(-1). In the dry state the conductivity increases at elevated temperatures and reaches values of 2 x 10(-3) S cm(-1) at 180 degrees C. The methanol diffusion coefficients are measured and compared for different membrane materials. They are in the range from 5 to 9 X 10(-2) cm(2) s(-1) for the new type of bifunctional proton conducting polysiloxane membranes.