Communication—Aliphatic Chain Substitution for Enhancing Energy Density of p-Benzoquinone Redox Couple for Non-Aqueous Flow Batteries

Although p-benzoquinone (BQ) is electrochemically reversible in non-aqueous media, the physicochemical properties of BQ are insufficient for its practical use as a negative redox couple for flow batteries. The voltage and solubility drawbacks of BQ can be resolved by using an aliphatic chain, which introduces electron-donating and melting-point-decreasing functional groups. The former negatively shifted the redox potential of BQ and the latter increased the solubility of BQ 1.5-fold. Furthermore, the reversibility of the redox couple is retained even after tert-butyl substitution with increased energy density. Finally, the designed tert-butyl-p-benzoquinone molecule exhibits a stable voltage profile during the flow battery cycling.