Layered tetratitanate intercalating sulfanilic acid for organic/inorganic proton conductors

A hydrous layered tetratitanate derivative intercalating sulfanilic acid (SA-H ₂Ti ₄O ₉) to be used as filler in proton conducting nanocomposite membranes for fuel cell applications was synthesized and characterized. The morphology, composition and structural features of the organic/inorganic compound were investigated by field emission scanning electron microscopy (FE-SEM), elemental analysis, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and its thermal stability was tested by thermogravimetric and differential thermal analysis (TG/DTA). The effects caused by the presence of the organic guest molecules bearing sulfonic acid groups on the proton conductivity of the material were investigated. Conductivity was measured by electrochemical impedance spectroscopy (EIS) while water mobility was tested by dynamic vapour sorption (DVS) measurements. The higher conductivity shown by SA-H ₂Ti ₄O ₉ with respect to that of H ₂Ti ₄O ₉ is correlated to an increase of both the amount of proton-donor groups and water mobility due to the intercalation of sulfanilic acid. Sulfonated polyetheretherketone (SPEEK)-based composite membranes containing different amount of SA-H ₂Ti ₄O ₉ were prepared and characterized in terms of microstructural (FE-SEM) features and proton conductivity (EIS). The composite membranes showed higher conductivity values than those of pure SPEEK due to the presence of the organically-modified two-dimensional filler.