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Nafion Polymer

• Sulfonated tetrafluoroethylene based fluoropolymer-copolymer which is part of a family of polymers with ionic properties
• Often used as a proton conductor for PEM membranes
• Disadvantages : high electro-osmotic drag, high methanol cross-over, and high ionic cross-over, enhancing the self-discharge rate and leading to a decrease in battery performance.
• Nafion is a perfluorosulfonic acid (PFSA)

Due to their preferential cation transport, dense cation exchange membranes like Nafion membranes may be unsuitable for Zn/Br redox flow batteries which require bi-ionic transport of Zn2+ and Br- ions.

In zinc-bromine redox flow batteries (ZBRBs) the cycle time with a 16 μm-thick Nafion-filled porous membrane was 1 hour for 10 to 40 ${\text{mAcm}}^{-2}$

Some Nafion membranes require surface activation:

• immersed in 0.5 L stirred deionised water
• purification step with hydrogen peroxide
• three washing steps in deionized water
• acid treatment
• three additional washing steps in deionized water were applied.

The temperature during all steps was set to 80 °C while the duration of each step was one hour.

However given the acidic nature of the

Nafion monomer

C(=C(F)F)(OC(C(C(F)(F)F)(OC(C(F)(F)S(=O)(=O)O)(F)F)F)(F)F)F.C(=C(F)F)(F)F

Nafion polymer