Rational design of composite supporting electrolyte required for achieving high performance aqueous organic redox flow battery

Although aqueous organic redox flow batteries (AORFBs) have many benefits, their organic active materials have the limitations in solubility and chemical instability. To overcome the problems, efforts to develop new organic active materials is usually made. However, these efforts have still limitations in some prospects. Thus, in this study, instead of developing new organic active materials, a rationally designed composite supporting electrolyte is suggested to improve energy density, power density, life-cycle, and efficiency of AORFB using 2-hydroxy-1,4-naphthoquinone (Lawsone) and potassium ferrocyanide as redox couple. The composite supporting electrolyte consists of potassium hydroxide (KOH) and potassium sulfite and is optimized by density functional theory (DFT). DFT predicts that sulfite anions help the solubility and stability of Lawson to improve, while hydroxide anions promote reactivity. The predictions are proved by electrochemical evaluations. With that, when the optimal composite supporting electrolyte is used, high capacity and excellent retention of AORFB (90 % at 100th cycle (from 20.27 to 18.42 Ah·L−1)) are achieved, while high power of 12.4 W is produced by AORFB short stack.