Proton conducting organic–inorganic composite membranes under anhydrous conditions synthesized from tetraethoxysilane/methyltriethoxysilane/trimethyl phosphate and 1-butyl-3 methylimidazolium tetrafluoroborate

Abstract

Anhydrous proton conducting organic–inorganic hybrid membranes were fabricated by sol–gel process with tetraethoxysilane/methyltriethoxysilane/trimethyl phosphate and 1-butyl-3 methylimidazolium tetrafluoroborate (BMIMBF 4) ionic liquid as precursors. Chemical stability of these hybrid membranes was investigated by Fourier transform infrared spectroscopy and 31P, 1H, and 13C magic angle spinning nuclear magnetic resonance measurements. Thermogravimetric analysis and differential thermal analysis measurements confirmed that the hybrid membranes were thermally stable up to 280 °C. The effect of ionic liquid addition on the microstructure of the hybrid membranes was examined by Scanning electron microscopy and Energy dispersive X-ray analysis micrographs and no phase separation was observed at the surfaces of the composite membranes and also homogeneous distribution of all the elements was confirmed. For all the prepared composite membranes the conductivities were measured within the temperature range (− 30)–150 °C, and a maximum conductivity of 6.74 × 10 − 3 S/cm at 150 °C was achieved for 40 wt.% ionic liquid based hybrid membrane, under non-humidified conditions. The hydrogen permeability values were decreased with the temperature increment from 20 °C to 150 °C and the measured H 2 permeability value for 40 wt.% ionic liquid based hybrid membrane was 0.5 × 10 − 12 mol/cm s Pa at 150 °C. For 40 wt.% [BMIMBF 4] doped hybrid membrane, membrane electrode assemblies were prepared and a maximum power density value of 2 mW/cm 2 at 4.73 mA/cm 2 as well as a current density of 7.4 mA/cm 2 was obtained at 150 °C under non-humidified conditions when utilized in a H 2/O 2 fuel cell.