Structural and Spectroscopic Characterization of A Nanosized Sulfated TiO2 Filler and of Nanocomposite Nafion Membranes

Abstract

A large number of nano-sized oxides have been studied in the literature as fillers for polymeric membranes, such as Nafion ® . Superacidic sulfated oxides have been proposed and characterized. Once incorporated into polymer matrices, their beneficial effect on peculiar membrane properties has been demonstrated. The alteration of physical-chemical properties of composite membranes has roots in the intermolecular interaction between the inorganic filler surface groups and the polymer chains. In the attempt to tackle this fundamental issue, here we discuss, by a multi-technique approach, the properties of a nanosized sulfated titania material as a candidate filler for Nafion membranes. The results of a systematic study carried out by synchrotron X-ray diffraction, transmission electron microscopy, thermogravimetry, Raman and infrared spectroscopies are presented and discussed to get novel insights about the structural features, molecular properties, and morphological characteristics of sulphated TiO 2 nanopowders and composite Nafion membranes containing different amount of sulfated TiO 2 nanoparticles (2%, 5%, 7% w/w).

Critical Filler Concentration in Sulfated Titania-Added Nafion™ Membranes for Fuel Cell Applications

“…The inorganic S-TiO 2 additive was obtained as previously reported [31] by a very convenient 1-step synthesis procedure. A careful characterization of the filler nanoparticles has been already reported by us in [31] and is here omitted.…”

“…The inorganic S-TiO 2 additive was obtained as previously reported [31] by a very convenient 1-step synthesis procedure. A careful characterization of the filler nanoparticles has been already reported by us in [31] and is here omitted. Briefly X-ray diffraction (XRD) and Raman spectroscopy of S-TiO 2 highlighted the crystallization of the anatase lattice with minor contaminations from the TiO 2 -B phase, typical of nanometric samples.…”

“…In fact the sulfated titania nanoparticles show a mean diameter of about 7.6˘2.5 nm [31]. Therefore the size of the sulfated titania nanoparticles are small enough to be fully immersed into the hydrophilic and the hydrophobic domains of the Nafion™ membranes as only minor local deformations may allow the accommodation of these particles within the polymeric structure.…”

“…Raman spectra were collected from the four samples at different RH and at two different temperatures: room temperature (approximately 25˝C) and 60˝C. A detailed analysis of the Raman spectra at ambient humidity and temperature of the fillers and composite membranes have been published elsewhere [31] and is omitted to avoid redundancies. Here our goal is to show and discuss the shift of the energy position of the peak attributed to the SO 3v ibration mode approximately at 1060 cm´1 in respect to RH at two different temperatures for all the composite membranes.…”

Sulfated titania as additive in Nafion membranes for water electrolysis applications

“…Due to their intrinsic super-acidity and tunable properties, sulfated metal oxides (S-MO 2 ) are very attractive candidates as additives to form hybrid, nano-composite membranes having adequate performances at high temperature. Recently, in our laboratories sulfated zirconium [22][23][24][25][26], titanium [27][28][29][30], aluminum [31] and tin [32,33] oxides have been investigated as proton conductors or fillers in polymer systems. The potentiality of this family of compounds in PEMs for water electrolysis was proved by combining a S-ZrO 2 /Nafion membrane with IrO 2 anode and Pt cathode [34].…”