Proton exchange membranes with microphase separated structure from dual electrospun poly(ether ketone) mats: Producing ionic paths in a hydrophobic matrix

• Novel fully sulfonated and non-sulfonated poly(ether ketone)s were synthesized.
• Sulfonated and non-sulfonated poly(ether ketone)s were simultaneously electrospun.
• Non-sulfonated fibers were melted and fully sulfonated fibers were surrounded by them as a matrix.
• Proton exchange membranes with microphase separated structures were prepared.
• Membranes with excellent dimensional stability, reasonable proton conductivity were obtained.

With the purpose of preparing membranes containing separated hydrophobic/hydrophilic regions, fully sulfonated and non-sulfonated poly(ether ketone)s (PEK)s were synthesized and then electrospun simultaneously. After that, non-sulfonated fibers were melted and the fully sulfonated fibers were surrounded by them as a matrix. Four membranes with different contents of fully sulfonated fibers were prepared in this way. For comparison, two membranes from random sulfonated PEKs with the same structures were prepared by usual solution casting method. Investigation of properties revealed that membranes obtained from electrospinning process showed much better proton conductivities in comparison with membranes casted from random sulfonated copolymers with equivalent ion exchange capacities. Moreover, proton conductivity – particularly at higher temperatures – was comparable with Nafion whereas, maximum water absorption of prepared membranes was 13.2% and their swelling ratios were below 1.5%. Additionally, because PEKs are thermally stable polymers, prepared membranes can tolerate much higher temperatures compared to Nafion.

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