Hybrid Nafion–inorganic oxides membrane doped with heteropolyacids for high temperature operation of proton exchange membrane fuel cell

Performance of the proton exchange membrane fuel cell (PEMFC) with composite Nafion–inorganic additives such as silicon oxide (SiO₂), titanium dioxide (TiO₂), tungsten oxide (WO₃), and SiO₂/phosphotungstic acid (PWA) has been studied for the operation of temperature of above 100 °C. These composite membranes are prepared by the way of blending of the inorganic oxides with Nafion solution by the recasting procedure. The physico-chemical properties studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques have proved the uniform and homogeneous distribution of these oxides and the consequent enhancement of crystalline character of these membranes. The thermogravimetry analysis (TGA) results have indicated that the additives TiO₂ and WO₃ have accelerated decomposition of the membrane at an earlier temperature than that of the Nafion membrane. The modified membranes have shown higher uptake of water relative to that of the unmodified membranes. The proton conductivity of the modified membranes, except that of the Nafion/TiO₂, is found to be close to that of the native Nafion membrane at high temperature and at 100% relative humidity (RH), however, it was much higher at low RH. The performance of these modified membranes in the PEMFC operated at 110 °C and 70% RH is better than that of Nafion membrane and is found in the order of Nafion/SiO₂/PWA > Nafion/SiO₂ > Nafion/WO₃ > Nafion/TiO₂.