Highly conductive proton exchange membranes from sulfonated polyphosphazene-graft-copolystyrenes doped with sulfonated single-walled carbon nanotubes

As polymer electrolyte candidates, a series of composite membranes CF₃-PS_x-PSBOS_y-SCNT of copolymer poly[(4-trifluoromethylphenoxy)(4-methylphenoxy)phosphazene]-g-poly{(styrene)_x-r-[4-(4-sulfobutyloxy)styrene]_y} (CF₃-PS_x-PSBOS_y) doped with sulfonated single-walled carbon nanotubes (S-SWCNTs) were prepared. Most of them showed higher proton conductivity than that of Nafion 117. Compared with native membranes, the composite membranes exhibited higher proton conductivity but also a significantly reduced methanol permeability, suggesting a great enhancement effect of S-SWCNTs on the proton conduction and methanol resistance. Specifically, membranes CF₃-PS₁₁-PSBOS₃₃-SCNT and CF₃-PSBOS₄₅-SCNT showed proton conductivity at 0.46 S/cm and 0.55 S/cm under fully hydrated conditions at 100 °C, respectively, which were 2.2-2.6 times as much as that of Nafion 117. Excellent selectivity much more than that of Nafion 117 were also obtained for the composite membranes.