A dopamine-based high redox potential catholyte for aqueous organic redox flow battery

Abstract

Organic redox flow batteries with many technological advantages over conventional metal-based flow batteries represent a new generation flow battery technology for electric grid storage applications. Herein, we report a dopamine-based catholyte with a high redox potential of 0.77 V for aqueous organic redox flow batteries. In sulfuric acid, the dopamine exhibits an excellent combination of good electrochemical reversibility and high solubility up to 0.7 M, and undergoes a fast two-electron transfer redox reaction with a rate constant of 1.82 × 10−3 cm s−1. Paired with V3+/V2+, the dopamine-vanadium full cell delivers an average round-trip efficiency of 65% at 20 mA cm−2 and achieves a capacity retention of 50% for 100 consecutive charge-discharge cycles. Moreover, an energy efficiency of 51.3% can be steadily realized at an increased current density of 60 mA cm−2, while an enhanced capacity retention over extended 200 charge-discharge cycles is also observed by introducing saturated ammonium chloride into sulfuric acid. The proposed dopamine-based catholyte not only successfully offers a new alternative for aqueous organic redox flow batteries, but its performance can be also further promoted by rational molecule design and optimizations in mass transfer and electrode kinetics.