Sulfonated titania submicrospheres-doped sulfonated poly(ether ether ketone) hybrid membranes with enhanced proton conductivity and reduced methanol permeability

Sulfonated titania submicrospheres (TiO2–SO3H) prepared through a facile chelation method are incorporated into sulfonated poly(ether ether ketone) (SPEEK) to fabricate organic–inorganic hybrid membranes with enhanced proton conductivity and reduced methanol permeability for potential use in direct methanol fuel cells (DMFCs). The pristine titania submicrospheres (TiO2) with a uniform particle size are synthesized through a modified sol–gel method and sulfonated using 4,5-dihydroxy-1,3-benzenedisulfonic acid disodium salt as the sulfonation reagent. The sulfonation process is confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectra (XPS). The hybrid membranes are systematically characterized in terms of thermal property, mechanical property, ionic exchange capacity (IEC), swelling behavior, and microstructural features. The methanol barrier property and the proton conductivity of the SPEEK/TiO2–SO3H hybrid membranes are evaluated. The presence of the fillers reduces methanol crossover through the membrane. Compared with the unsulfonated TiO2-doped membranes, the TiO2–SO3H-doped ones exhibit higher proton conductivity due to the additional sulfonic acid groups on the surface of TiO2. The hybrid membrane doped with 15 wt.% TiO2–SO3H submicrospheres exhibits an acceptable proton conductivity of 0.053 S cm−1 and a reduced methanol permeability of 4.19 × 10−7 cm2 s−1.

Research highlights
► A kind of novel hybrid membrane with improved proton-conducting ability and alcohol-rejecting property was fabricated by incorporating TiO2–SO3H submicrospheres into SPEEK.
► The doping of inorganic TiO2–SO3H submicrospheres provided additional proton transfer sites and impeded methanol diffusion, thus crossing the hurdle of “trade-off” phenomenon occurred in most polymer membranes.
► The as-prepared hybrid membrane exhibited an acceptable proton conductivity of 0.053 S cm−1 and a low methanol permeability of 4.19 × 10−7 cm2 s−1.