Sulfonated polyimide and PVDF based blend proton exchange membranes for fuel cell applications

Sulfonated polyimide (SPI) is synthesized by a polycondensation reaction and proton exchange membranes (PEMs) are prepared from the SPI/poly(vinylidene fluoride) (PVDF) blends. Compared to commercial Nafion, the SPI/PVDF blend PEMs have significantly improved swelling ratio of <3% (vs. similar to 18% for Nafion), as well as high proton conductivity of 75 mS cm(-1) for 50 wt% of SPI content (vs. similar to 62 mS cm(-1) for Nafion). The proton conducting mechanism in blend membrane was studied and dramatic increases in proton conductivity and water uptake at similar to 30 wt% SPI were observed, which are proved by TEM to be due to the transition from isolated SPI ionic domains in PVDF matrix to a bi-continuous morphology - a percolation phenomenon.