Preparation and characterization of hybrid membranes for fuel cell applications: hydrogenated styrene-butadiene rubber filled with alkyl, phenyl or tolyl sulfonated silica

摘要

Polymers with ionic groups attached (ionomers) are indispensable electrolyte materials for proton exchange membrane fuel cells. Nafion~R, a widely used membrane, has many disadvantages: price, high methanol crossover and conductivity loss at temperatures above 80 °C. This work reports the preparation and characterization of hybrid membranes, alternatives to commercial Nafion, based on blends of hydrogenated polybutadiene-block-polystyrene copolymer and organophilized silicas. The films obtained were crosslinked to improve mechanical stability, and heterogeneously sulfonated to convert them to proton-conducting systems. Structural characterization involved differential scanning calorimetry and dynamic mechanical analysis to determine their thermal and mechanodynamical transitions, attenuated total reflectance Fourier transform infrared spectroscopy for verifying the introduction of sulfonic groups and scanning electron microscopy linked with energy-dispersive X-ray analysis for obtaining more information on the location and distribution of silica within the polymer matrix. Electrical characterization was made using electrochemical impedance spectroscopy, giving high conductivity values of ca 2.6-5.8 x 10~(-2) S cm~(-1). Also, methanol crossover was determined: low permeabilities were found. The results showed that sulfonation of the styrene rings had occurred effectively. Conductivities were higher and methanol crossover lower than for Nafion for all samples.