Block Copolymer-Based Membranes for Vanadium Redox Flow Batteries: Synthesis, Characterization, and Performance

Nonfluorinated polymers have been widely proposed to replace Nafion as raw materials for redox flow battery ion-exchange membranes. Hereby, block copolymers based on polysulfone (PSU) and polyphenylsulfone (PPSU) are synthesized and employed as precursors of membranes for vanadium redox flow batteries. A series of copolymers with varying molar proportions of PSU (75/25, 60/40, 50/50 mol %) were prepared. The 60/40 and 75/25 copolymers exhibit concentrated sulfonic groups predominantly in the PSU unit, favoring the formation of hydrophobic and hydrophilic domains. The 50/50 copolymer presents a balanced degree of sulfonation between the two units, leading to a homogeneous distribution of sulfonic groups. An ex situ study of these materials comprising vanadium ion permeability and chemical and mechanical stability was performed. The best performance is achieved with 50/50 membranes, which exhibited performance comparable to commercial Nafion membranes. These results signify a promising breakthrough in the pursuit of high-performance, sustainable membranes for next-generation VRFBs.