All-carbon backbone aromatic polymers for proton exchange membranes

Proton exchange membranes (PEMs) play a crucial role in energy storage and conversion technologies such as fuel cells, redox flow batteries, and water electrolysis. Currently, perfluorosulfonic acid polymer (PFSA) membranes are the most commonly used PEM materials. However, PFSA membranes possess certain drawbacks, including the high dependence of proton conductivity on humidity, low glass transition temperatures, and complex synthesis processes. In recent decades, significant efforts have been dedicated to developing various alternative PEM materials, such as the sulfonated products of polyether ether ketone, poly(phenylene oxide), polysulfone, and polyimide. However, the backbones of these polymers often contain heteroatoms that are prone to breaking under practical working conditions, leading to reduced chemical stability. In contrast, all-carbon backbone aromatic polymers exhibit excellent chemical stability, thermal stability, and mechanical properties, as well as high proton conductivity upon incorporating suitable acidic groups, which makes them promising alternatives for PEM materials. This review aims to summarize the recent research progress about all-carbon backbone aromatic polymers, with a specific focus on synthesis strategies, structure-performance relationships, and applications in PEMs.