A new hydroxyanthraquinone derivative with a low and reversible capacity fading process as negolyte in alkaline aqueous redox flow batteries

2,3-dihydroxylated anthraquinone (2,3-DHAQ) is evaluated for the first time in a redox flow battery. This compound exhibits a good solubility in alkaline media (0.7 M in KOH at pH > 13.5) and a suitable potential (−0.85 V vs Ag/AgCl) leading to a 1.11 V theoretical open circuit voltage at 50% state of charge with potassium ferrocyanide as posolyte. It is implemented in a 25 cm2 cell during 180 cycles with a capacity fading of 0.022% per cycle and a current efficiency higher than 99.7%. Owing to its high solubility, an initial energy density up to 17 Wh L−1 (7.7 Wh L−1 when both posolyte and negolyte are considered) is obtained. 2,3-DHAQ exhibits a good chemical stability compared with other dihydroxyanthraquinone (around 0.1% per cycle). After more than 3000 cycles, 2,3-DHAQ is observed as the main product, showing its high chemical stability. Moreover, the capacity fading process is reversible since changing the discharge conditions allows a full recovery of the initial capacity. This opens up new perspectives as the capacity loss is often used to evaluate the relevance of new molecules. A wider range of active materials in AORFB can be considered if the capacity fading they exhibit can be reversible. [Display omitted] •2,3-DHAQ is a new and promising negolyte for AORFB.•This aqueous RFB exhibits high energy efficiency and good cycling stability.•A 3000 cycles experiment was reported.•The observed capacity fading was reversible by modifying discharge parameters.