Effect of filler surface functionalization on the performance of Nafion/Titanium oxide composite membranes

The phenylsulfonic functionalized nanometric titania (TiO2-PhSO3H) was synthesized to be used as filler in Nafion-based composite membranes for direct methanol fuel cell (DMFC) applications. The organic moieties were covalently bound on the surface of TiO2 nanoparticles and the hybrid product was characterized by Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric and differential thermal analysis (TG/DTA), field emission scanning electron microscopy (FE-SEM), and X-ray diffraction (XRD) analysis. TiO2-PhSO3H showed higher ion exchange capacity (IEC) and proton conductivity values with respect to those of TiO2. The incorporation of TiO2-PhSO3H in Nafion led to a mechanical reinforcement of the membranes and higher conductivity than that obtained with unfilled Nafion. The composite membrane containing 10 wt.% of TiO2-PhSO3H showed an increased crystallinity and the highest conductivity, reaching 0.11 S cm-1 at 140°C. DMFC tests were carried out showing that the use of the organic-inorganic hybrid filler leads to a general improvement in the cell performance, in terms of higher current and power density and reduced methanol crossover. © 2014 Elsevier Ltd. All rights reserved.