Preparation and properties of molecular sieve supported heteropoly acid-polyimide composite proton exchange membranes

Series of molecular sieve (13X, MCM-41,Y) supported Phosphotungstic acid (PWA)-polyimide (PI) composite proton exchange membranes were prepared. The water uptake and degree of swelling of PI-PWA-13X and PI-PWA-MCM-41 composite membranes all increased as PWA content increased. The conductivity of the composite membranes increased with temperature. The reason might be that Grotthuss mechanism was the dominant proton conducting mechanism. So that the proton hopping among active sites was improved at high temperature. The proton conducting activation energy of PWA supported membrane (For PI-M1, Ea = 27.7×10³J·mol^-1) was lower than the blank membrane (for PI0, Ea´=51.3×10³J·mol^-1). With the addition of good proton conductor of PWA, the proton conductivity of PWA composite membrane was much higher than blank membrane. Supporting PWA on molecular sieve can prevent the loss of PWA, which is helpful to get higher proton conductivities. Zeolite MCM-41 supported PWA composite membranes (PI-PWA-MCM41) had much higher proton conductivities than PI-PWA-Y membranes with the same PWA content because MCM-41 has higher specific area to support PWA. The methanol permeability of PI-PWA-13X membrane (3.4×10^-7cm²·s^-1) was lower than that of Nafion 117 membrane (16.5×10^-7cm²·s^-1).