Development and Evaluation of Butyl Norbornene Based Cross-Linked Anion Exchange Membranes for Enhanced Nonaqueous Redox Flow Battery Efficiency

Nonaqueous redox flow batteries (NARFBs) have been plagued by the lack of appropriate separators to prevent crossover. In this article, the synthesis and characterization of poly(norbornene) (PNB) anion-exchange membranes (AEMs) were studied. PNB is a copolymer of butyl norbornene (BuNB) and bromobutyl norbornene (BrBuNB) with varying amounts of tetramethyl hexadiamine cross-linker. The performance of the AEMs was investigated in nonaqueous redox flow batteries under ideal conditions. Performance evaluation encompassed several key factors, including durability in a nonaqueous solvent, charge-carrying ions permeability, electric cell resistance, crossover of redox-active molecules, and mechanical properties. The BuNB-based AEMs outperformed the commercial Fumasep membrane in battery cycling tests, showcasing their superior performance characteristics. Long-term performance tests showed that the top performing PNB membrane exhibited an impressive 83% total capacity retention over 1000 charge/discharge cycles. The low loss was primarily due to minimal crossover. In contrast, the FAPQ-375 commercial membrane experienced significantly lower capacity retention, measuring only 28%, due to high crossover.