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

• Polyphosphazene graft copolystyrenes with alkylsulfonate chains were designed and synthesized.
• Composite membrane containing sulfonated single-walled carbon nanotubes were prepared.
• Composite membrane exhibited excellent proton conductivity, methanol resistance, and subsequently selectivity.
• Composite membrane presented lowered activation energy compared with native membrane.
• Composite membrane attained well-separated nanophase and interconnected ionic channel.

As polymer electrolyte candidates, a series of composite membranes CF3-PSx-PSBOSy-SCNT of copolymer poly[(4-trifluoromethylphenoxy)(4-methylphenoxy)phosphazene]-g-poly{(styrene)x-r-[4-(4-sulfobutyloxy)styrene]y} (CF3-PSx-PSBOSy) 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.

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