A proton exchange membrane (PEM) is a semipermeable polymer electrolyte that facilitates the transport of protons while acting as an electronic insulator and gas separator in electrochemical devices ^[1]. Typically constructed from perfluorosulfonic acid polymers, the membrane contains sulfonic acid groups that enable proton conduction through water-mediated mechanisms, requiring controlled hydration to maintain ionic conductivity ^[2]. In fuel cell and electrolyzer assemblies, the PEM is positioned between the anode and cathode, allowing protons to migrate between the electrodes while preventing the direct mixing of fuel and oxidant or of product gases ^[3]. The membrane must simultaneously satisfy requirements for high proton conductivity, low electronic conductivity, chemical stability under oxidizing and reducing conditions, and mechanical integrity across hydration and temperature cycles ^[4]. PEMs are distinguished from other electrolyte types—such as alkaline membranes or solid oxides—by their polymer-based architecture and by the proton, rather than hydroxyl or oxide ion, as the charge carrier ^[5].