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 Br2/Br– and a higher valence to Br+ suffers from serious side reactions. Herein, a two-electron-transfer electrochemical reaction was realized by employing BrCl2–/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 TiO2+/Ti3+ 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 BrCl2–/Br–-based flow batteries demonstrate very promising perspectives for large-scale energy storage applications.