A new anhydrous proton conducting material based on phosphoric acid doped polyimide

A new anhydrous proton conducting material based on polyimide and phosphoric acid composite was prepared. The interaction between polyimide (PI) and phosphoric acid was investigated by FTIR. The results show that phosphoric acid interacts with polyimides mainly by hydrogen bonds rather than by protonation of PI at room temperature. Environmental scanning electron microscopy (ESEM) was employed to study the surface morphology of the membranes. The results show that the surface of PI–xH3PO4 membranes is very compact and homogeneous. Proton conductivity and methanol permeability of PI doped with phosphoric acid (PI–xH3PO4) were also studied. Proton conductivity of PI–xH3PO4 membranes increases with increasing concentration of phosphoric acid. Hydrogen bond seems to play an important role in the proton conductivity of this system. Effects of osmotic on the direct diffusion process of methanol in the membranes can be negligible due to the absence of micro-pore structure as already shown in ESEM results. Effects of methanol concentration and temperature on the methanol permeability of PI–xH3PO4 membranes were also discussed. Methanol permeability in PI–xH3PO4 membranes decreases with increasing methanol concentration, and increases with increasing temperature.