Hydrobromide Salt of Tribromodopamine as a Positive Electroactive Species with a Three-Electron Redox Process for Redox Flow Battery Applications

The hydrobromide salt of tribromodopamine (DABr 3 ·HBr) was synthesized for redox flow battery applications. It exhibited two redox processes at ∼0.74 V (due to the DABr 3 /DQBr 3 redox couple) and 1.0 V (due to the Br – /Br 2 redox couple) vs Ag/AgCl in H 2 SO 4, thereby leading to a 3e – reaction per molecule. An aqueous organic redox battery was constructed using DABr 3 ·HBr catholyte and anthraquinone-1,5-disulfonic acid disodium salt (1,5-AQDS) anolyte. A capacity decay of only ∼0.028%/cycle was observed over 2500 galvanostatic charge–discharge (GCD) cycles. The high cycle life (2500 GCD cycles) with ∼99% Coulombic efficiency (CE) is due to the effective Br 2 -capturing ability of DABr 3 ·HBr through ammonium polybromide formation. The energy efficiency (EE) of the DABr 3 ·HBr-1,5-AQDS static battery was found to be 66% at a current density of 20 mA cm –2 .