Influence of structure construction on water uptake, swelling, and oxidation stability of proton exchange membranes

Proton exchange membrane fuel cells (PEMFCs) have become the most rapidly developing fuel cells in recent years. Proton exchange membranes (PEMs) are one of the most essential components of PEMFCs; however, their performance cannot adapt to the rapid development of today's society. In addition, to replace traditional low-performance membranes and meet technical development and commercial needs, most studies are focusing on the design and preparation of ideal PEMs with low electron permeability, low fuel and oxidizer permeability, high proton conductivity, excellent mechanical and chemical properties, and low cost. Herein, we review PEMs based on polymers in the aromatic hydrocarbon family. Owing to their rigid backbone structure, most aryl polymers are lowly soluble in most solvents. The solubility of a polymer can be improved by introducing different monomers that modify the aromatic hydrocarbon compounds in the main or side chain. The PEM can then be prepared using the solution casting method. To improve the proton conductivity, water uptake, mechanical properties, and oxidation stability of PEMs, many researchers have reported the use of various approaches: sulfonation, immersion in hydrochloric acid or phosphoric acid (PA), blending, crosslinking, and addition of inorganic fillers or metal–organic frameworks. The insights provided by this review will assist the development of higher-performance, safer, and cheaper PEMs.