Fig. 3. Redox-solubility maps of quinones of different sizes. E ⁰ and ΔG0solv distributions of (a) BQs, (b) NQs, and (c) AQs. The functional groups that effectively tune the E ⁰ and ΔG0solv are highlighted in color. AQDS molecule, which was successfully used for the negative side of an aqueous flow battery due to its low value of E ⁰ (0.222 V: calculated and 0.213 V: measured) as well as a high aqueous solubility (greater than 1 M at pH 0),¹ is marked as reference point.