Preparation, characterization and evaluation of proton-conducting hybrid membranes based on sulfonated hydrogenated styrene–butadiene and polysiloxanes for fuel cell applications

This paper describes the preparation of proton-conducting hybrid membranes (HMs) obtained by a solvent casting procedure using a solution containing sulfonated hydrogenated styrene–butadiene (HSBS-S) and an inorganic–organic mixture (polysiloxanes) previously prepared by a sol–gel route. HSBS-S copolymers with different sulfonation degrees were obtained and characterized by means of elemental analysis (EA), chemical titration and electrochemical impedance spectroscopy (EIS). HSBS-S with the best properties in terms of proton conductivity and solubility for the casting procedure was selected to prepare the HMs. The solvent casting procedure permitted the two phases to be homogeneously distributed while maintaining a relatively high proton conductivity in the membrane. HMs with different blend ratios were characterized using structural (Fourier transform infrared–attenuated total reflectance (FTIR–ATR), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC)), electrical (EIS), physicochemical (water uptake, ion-exchange capacity) and thermal (TGA–MS) methods. Finally, the optimized HSBS-S membrane and HMs were tested in hydrogen single fuel cells to obtain the polarization and power curves at different cell temperatures and gas pressures. Results indicate that HMs show a considerable improvement in performance compared to the optimized HSBS-S membrane denoting the benefit of incorporating the inorganic–organic network in the hydrogenated styrene–butadiene matrix. A Nafion membrane was used as reference material throughout this work.