Progress and Perspective of the Cathode Materials towards Bromine-Based Flow Batteries

Bromine-based flow batteries (Br-FBs) have been one of the most promising energy storage technologies with attracting advantages of low price, wide potential window, and long cycle life, such as zinc-bromine flow battery, hydrogen-bromine flow battery, and sodium polysulfide-bromine flow battery. The research and development of aqueous Br-FBs are very fast and many achievements have been realized. However, Br-FBs suffer from the sluggish kinetics of Br 2 /Br - redox couple and serious self-discharge caused by the diffusion of bromine, which hinder the further commercialization and industrialization of the aqueous Br-FBs. A series of mitigation strategies have been developed to figure out these challenges, especially the modifications on electrode materials. Electrode, one of the critical components in a Br-FB, provides the reactions sites for redox couples, upon which its properties exert a significant effect on the performance of Br-FBs. Up to now, extensive research has been carried out on electrode modifications to solve the aforementioned notorious issues of Br-FBs, including surface treatment and surface modification. In this review, various electrode materials and relevant modification approaches used for Br-FBs are overviewed and summarized. Moreover, the relevant mechanisms are illustrated deeply, providing comprehensive and available instruction to pursue and develop high-performance cathodes for Br-FBs with high power density and long lifespan.