A Critical Review of Electrolytes for Advanced Low- and High-Temperature Polymer Electrolyte Membrane Fuel Cells

In the 21st century, proton exchangemembrane fuel cells (PEMFCs)represent a promising source of power generation due to their highefficiency compared with coal combustion engines and eco-friendlydesign. Proton exchange membranes (PEMs), being the critical componentof PEMFCs, determine their overall performance. Perfluorosulfonicacid (PFSA) based Nafion and nonfluorinated-based polybenzimidazole(PBI) membranes are commonly used for low- and high-temperature PEMFCs,respectively. However, these membranes have some drawbacks such ashigh cost, fuel crossover, and reduction in proton conductivity athigh temperatures for commercialization. Here, we report the requirementsof functional properties of PEMs for PEMFCs, the proton conductionmechanism, and the challenges which hinder their commercial adaptation.Recent research efforts have been focused on the modifications ofPEMs by composite materials to overcome their drawbacks such as stabilityand proton conductivity. We discuss some current developments in membranesfor PEMFCs with special emphasis on hybrid membranes based on Nafion,PBI, and other nonfluorinated proton conducting membranes preparedthrough the incorporation of different inorganic, organic, and hybridfillers.