Lasted edited by Andrew Munsey, updated on June 15, 2016 at 2:14 am.
A proton exchange membrane (PEM) is a semipermeable membrane generally made from ionomers and designed to conduct protons while being impermeable to gasses 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 imbedded 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.