A Proton Exchange Membrane (PEM) is a thin, nonporous, semipermeable membrane that allows protons to pass through it while blocking other ions. It is used in a variety of applications, such as fuel cells, water electrolysis, and wastewater treatment. The PEM separates two electrolyte solutions and allows the transfer of protons between them while blocking the transfer of other ions. This allows the separation of charged particles, such as in a fuel cell, and the generation and management of electrical current.