What kind of polymers are used for the membrane?
The proton conducting polymer is a polymeric organic acid, generally a sulfonic acid. (A sulfonic acid can be thought of as a sulfuric acid (H2SO4) with one oxygen replaced by an organic group.) While there are a variety of polymers that can be used, most membranes are made from a saturated polymer (no double bonds) that has all of its hydrogen atoms replaced by fluorine atoms. These are referred to as perfluorosulfonic acid (PFSA) polymers. The most common variety is Nafion (a trademark of DuPont). An alternate way to think of these perfluorinated polymers is to consider them to be molecules of polytetrafluoroethylene (PTFE, also known as Teflon) with side chains attached to them that are terminated by sulfonate (-SO3) groups.
