Recent progress on the development of non-fluorinated proton exchange membrane-A review

Proton exchange membranes (PEMs) are widely employed in energy conversion and storage devices including fuel cells (FCs), redox flow batteries (RFBs) and PEM water electrolysis (PEMWE). As one of the main components of these devices, a high-performance PEM is always desirable considering the cost challenges from both energy utilization efficiency and production cost. From this century, governments of countries worldwide have introduced PFAS (per-and polyfluoroalkyl substances) restriction related policies, which facilitate the extensive research on non-fluorinated PEMs. Besides, non-fluorinated PEMs become hot topics of all kinds of PEMs due to the advantages including excellent conductivity, high mechanical property, reduced swelling, low cost and reduced ion permeation of electrochemical active species. In this review, various types of non-fluorinated PEMs including main-chain-type hydrocarbon membranes, microphase separation membranes and membranes with rigid-twisted structure are comprehensively summarized. The basic properties of different types of non-fluorinated PEMs including water uptake, swelling ratio, oxidative stability, tensile strength and conductivity are compared and the corresponding application performance in FCs, RFBs and PEMWE are discussed. The state-of-the-art of the structural design in both monomers and polymers are reviewed for the construction of fast ion transport channels and high resistance of free radical attacks. Also, future challenges and possibilities for the development of non-fluorinated PEMs are comprehensively foretasted.