October 2019 - Organic redox flow batteries have the potential to surpass the challenges posed by inorganic electrolytes commonly used in flow batteries, thus achieving high performance and a sophisticated storage solution for the grid. Herein, we demonstrated a high performance aqueous organic redox flow battery (AORFB) utilizing a redox-active resource from nature, indigo carmine (5,5′-indigodisulfonic acid sodium salt) (IC-Na), as the anolyte. The 5,5′-indigodisulfonic acid (IC-H) is obtained through the substitution of sodium ions in IC-Na with protons (H+). The aqueous solubility of IC-H was increased dramatically from 0.035 to 0.760 M (1.52 M electron concentration) in protic solvents. The diffusion coefficients (IC-Na, 1.06 × 10–5 cm2 s –1; IC-H, 2.19 × 10–5 cm2 s –1) and reaction rate constants (IC-Na, 1.93 × 10–4 cm s –1; IC-H, 1.86 × 10–4 cm s–1) of IC-Na and IC-H indicate rapid reaction kinetics. The highly soluble and affordable IC-H with fast redox kinetics was used as a sustainable anolyte by pairing with different catholytes. Moreover, a computational study was conducted which signifies the prospect of further improvements in solubility and voltage window by tuning the structure. Therefore, the environmentally benign and earth-abundant IC-H represents a promising choice for green and sustainable redox active anolyte of AORFB.