Sulfonated aromatic polymer as a future proton exchange membrane: A review of sulfonation and crosslinking methods

Sulfonated aromatic polymers (SAP) have been shown to be promising materials for proton exchange membranes (PEM) due to their high thermal and chemical stability as well as lower-cost production compared to commercial available perfluoro sulfonated polymers. Two key main steps to achieve high-performance PEM of SAP are sulfonation of the aromatic polymer and subsequent membrane crosslinking techniques. In this review, the common post-sulfonation methods for development of SAP and the state of the art crosslinking procedures are mostly covered. This review is targeting to bring the reader up to date of all available techniques. To obtain an overview is especially important, because no single sulfonation and/or crosslinking procedure can be considered ideal in all cases, and for each SAP the best method is dependent on the type of polymer and its applications.