A review of proton exchange membranes based on protic ionic liquid/polymer blends for polymer electrolyte membrane fuel cells

Recently, increasing research attention has been devoted to protic ionic liquids (ILs) because of their versatile properties. Protic ILs are ideal electrolytes for proton exchange membrane fuel cells (PEMFCs) owing to their high proton conductivity, that does not rely on water, and their excellent electrochemical and thermal stabilities. Therefore, they can extend the operating temperature of PEMFCs above 100 °C, which is important to raise their effectiveness and efficiency. However, to be employed as polymer electrolyte membranes (PEMs) in PEMFCs, protic ILs are preferred to be in solid films; therefore, several polymers have been blended with different protic ILs to form various PEMs. This review article provides a comprehensive literature survey for protic IL/polymer blends applied as PEMs in PEMFCs. In particular, five conventional polymers combined with protic ILs as PEMs are discussed in detail; Nafion, polybenzimidazole (PBI), poly(vinylidene fluoride-co-hexafluoropropene) (PVdF-HFP), sulfonated polyimide (SPI), and sulfonated poly(ether ether ketone) (SPEEK). Also, some other polymers used in PEMs based on protic ILs are studied to provide comprehensive coverage for all research ideas developed in this topic. Finally, this review addresses the current challenges facing the development of this promising category of PEMs and the recommended research directions that need more investigation.