Proton exchange membrane

A proton exchange membrane, often proton exchange membrane (PEM) or polymer electrolyte membrane ( PEM) referred to, is a semipermeable membrane generally made of ionomer. PEMs are permeable to protons, while the transport of gases such as oxygen or hydrogen is prevented. For this purpose, the PEMs are primarily for use in polymer electrolyte fuel cells. They are made either from pure polymer or composite membranes, in which other materials are embedded in a polymer matrix. The commercially most widely used PEM is Nafion by chemical giant DuPont.