A High Energy Density Bromine-Based Flow Battery with Two-Electron Transfer

Bromine-based flow batteries have been widely used for large-scale energy storage because of their attractive features of low cost and high redox potential. At present, bromine redox chemistry mainly based on a single-electron electrochemical reaction of Br 2 /Br – and a higher valence to Br + suffers from serious side reactions. Herein, a two-electron-transfer electrochemical reaction was realized by employing BrCl 2 – /Br – as a positive redox couple. In this design, the side reaction of Br + could be inhibited by the introduction of Cl – via the complexing effect in an acid environment. As a proof of concept, by using TiO 2+ /Ti 3+ as a negative redox couple, a Ti–Br–Cl flow battery (TBCFB) demonstrated a discharge capacity up to 96 Ah L –1 and continuously ran for more than 300 cycles without obvious performance decay. With the high redox potential, high energy density, and high stability, the BrCl 2 – /Br – -based flow batteries demonstrate very promising perspectives for large-scale energy storage applications.