“…Recently, CPEMs based on inorganic additives such as graphene oxide (GO), sulfonated graphene oxide, MoS 2 , graphene nanofibers, sulfonated MoS 2, sulfonated carbon nanotubes (CNTs), amine-functionalized CNT, metal–organic frameworks (MOFs), montmorillonite (MTM), and polymers like poly(vinyl alcohol) (PVA), polybenzimidazole (PBI), sulfonated polyether ether ketone (SPEEK), sulfonated poly(arylene ether nitrile) (SPEN), sulfonated polyethersulfone (SPES), poly(perfluorosulfonic acid), poly(vinylidene fluoride) (PVDF), and sulfonated poly(arylene ether sulfone) (SPAES) have been extensively investigated as an alternative for Nafion. Polymer backbone or the inorganic fillers have also been modified to introduce functional groups such as sulfonate, phosphate, chloride, nitride, quaternary ammonium salt, a quaternary phosphonium salt, etc., to further enhance the ionic conductivities in the CPEMs .…”