Tetra-alkylsulfonate functionalized poly(aryl ether) membranes with nanosized hydrophilic channels for efficient proton conduction

The microstructure of polymer electrolyte membranes plays a key role in ion conductivity and water transport.Herein,fluorinated poly(aryl ether)s with tetra-alkylsulfonate side chains(SFPAEs)have been successfully synthesized from the copolymerization of a newly developed tetra-allyl-containing bisphenol(TABP)monomer,followed by the thiol-ene addition with sodium 3-mercapto-1-propanesulfonate to attach the ionic groups at the end of the flexible chains.Being the first of its kind,the densely distributed and lengthy alkylsulfonate group possesses the benefit of ease to self-assemble into hydrophilic domains during membrane preparation via solution casting.Indeed,the TEM characterizations revealed that distinct hydrophilic channels of 1-2 nm width had been formed,much larger than those of a home-made control sample where only di-alkylsulfonate side chains were attached.The SFPAE-4-45 with an IECw of 2.0 mmol g^-1 exhibited an enhanced proton conductivity of 143.7 m S cm^-1 at room temperature,which was superior to that of Nafion 212(91.0 m S cm^-1).Furthermore,the oxidative stabilities of SFPAEs were significantly higher than those of non-fluorinated analogs in literature.This study offered a new route to engineering the pendent structure of ionomers for well-defined microscopic morphologies.

Side Chain Engineering of Sulfonated Poly(arylene ether)s for Proton Exchange Membranes

Proton conductivity of proton exchange membranes(PEMs)strongly relies on microscopic morphology,which can be modulated by engineering the distribution of ionic groups.Herein,poly(arylene ether)s with densely distributed allyl functionalities are polymerized from a tetra-allyl bisphenol A monomer.The subsequent thiol-ene addition with sodium 3-mercapto-1-propanesulfonate yields comb-shaped sulfonated fluorinated poly(arylene ether)s(SFPAEs)with ion exchange capacities(lECs)ranging from 1.29 mmol·g^-1 to 1.78 mmol g^-1.These SFPAEs exhibit superior proton conductivity over the whole temperature range,which is attributed to the enhanced hydrophilic/hydrophobic phase separation as evidenced by small angle X-ray scattering characterizations.The SFPAE-4-40 with an IEC of 1.78 mmol·g^-1 shows the largest proton conductivity of 93 mS-crrr1 at room temperature under fully hydrated condition,higher than that of Nafion 212.Furthermore,the vanadium redox flow battery(VRFB)assembled with SFPAE-4-40 separator exhibits higher energy efficiency than the VRFB assembled with Nafion 212.