Proton exchange membrane

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A proton exchange membrane (PEM) is a semipermeable membrane generally made from ionomers and designed to conduct protons while being impermeable to gases such as oxygen or hydrogen. This is their essential function when incorporated into a proton exchange membrane fuel cell: separation of reactants and transport of protons. PEMs can be made from either pure polymer membranes or from composite membranes where other materials are embedded in a polymer matrix. One of the most common and commercially available PEM materials is Nafion which is made by DuPont. While nafion is an ionomer with a perfluorinated backbone like Teflon, there are many other structural motifs used to make ionomers for proton exchange membranes. Many use polyaromatic polymers while others use partially fluorinated polymers.