Synthesis and characterization of PWA based inorganic ion-exchange membrane

Abstract

Phosphotungstic acid (PWA) based inorganic ion-exchange membrane (IEM) was prepared on graphite support using a simple synthesis protocol. Top layer of the membrane was obtained by immobilizing PWA in silica derived from TetraEthylOrthoSilicate (TEOS) precursor. After casting, the top layer was heat-treated at 150 °C. Membrane surface morphology was observed by using Scanning Electron Microscope (SEM) and the top layer was found to be about 30 μm thick. Fourier transform infrared spectroscopy (FTIR) was used to determine the functional groups and X-ray Diffraction (XRD) was used to study the crystallinity of the top layer. The membrane was found to be thermally stable up to 250 °C obtained from Thermo Gravimetric Analysis (TGA). Static transport number for cation (t+) was determined in the pH range of 2–11 using membrane potential measurements. It was found to be above 0.95 in the pH range of 4–9. Ohmic resistance of the membrane was determined from impedance measurement and it was found to be 12 Ω cm2 which is lower than the reported value for inorganic IEMs and comparable to some of the organic IEMs. Membrane surface was hydrophilic with water contact angle of 9° and this hydrophilic nature might be useful for its use as electrolyte filled separators for batteries and super-capacitors.