Diazenyl derivative as high-performance anolyte for aqueous organic redox flow batteries

High-efficiency and economical energy storage technologies are crucial to providing a consistent power supply from renewable sources. The aqueous organic redox flow battery (AORFB) is a potential energy storage device that stores energy in redox-active organic molecules submerged in aqueous electrolytes. This technology has been extensively highlighted as a cost-effective and safe alternative for commercial high-cost redox flow battery systems. Herein, we presented a low molecular mass diazenyl anolyte having high solubility in an alkaline aqueous medium (>1.5 M) and has shown suitable charge-discharge capacity when coupled with the potassium ferrocyanide K₄[Fe(CN)₆] catholyte in ambient environment realizing a cell potential of 1.1 V. This study can shift the focus towards designing simple azo-based organic molecules with water-soluble functionalities for AORFBs that can offer a suitable cell voltage. The designed anolyte (E)-2-((4- (dimethylamino)phenyl)diazenyl)benzoic acid has sustained a discharge capacity of 18 mAh g⁻¹ after 100 charge-discharge cycles (with 10 min of charging and discharging) achieved at a current density of 10 mA cm⁻². The achieved Coulombic efficiency of about 72 % with an average decay rate of 0.037 per cycle, capacity retention (99.96 %) for 100 cycles, and a volumetric capacity of 720 mAh L⁻¹. These results demonstrate the promising electrochemical stability and practical viability of the designed anolyte for future redox flow battery applications.