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.

Automated summary

This study evaluates the application of 2,3-dihydroxylated anthraquinone in a redox flow battery for the first time. The compound demonstrates good solubility in alkaline media and suitable potential, leading to high battery performance and chemical stability. This research provides new perspectives for the development of new active materials.