Behaviour of 3,4‐Dihydroxy‐9,10‐Anthraquinone‐2‐Sulfonic Acid in Alkaline Medium: Towards a Long‐Cycling Aqueous Organic Redox Flow Battery

The performance of a redox compound in flow batteries (RFB) highly depends on the electrolytic medium and operating conditions. It is exemplified this work with commercially available relatively low-cost dye 3,4-dihydroxy-9,10-anthraquinone-2-sulfonic acid (ARS), which was used as negolyte basic medium. At high pH, ARS behavior revealed interesting features for RFB applications, such low half-wave potential −0.99 V (vs Ag/AgCl), negatively shifted by phenolate groups, an improved solubility compared acidic depending nature cations. For soluble potassium salt (ARSK), maximum power density 117 mW cm−2 demonstrated energy 20 Wh L−1 were obtained K4[Fe(CN)6] posolyte. capacity slightly decreased during cycling, reaching 90 % after 325 cycles. A long cycling sodium (ARSNa) over 11 months work. slow chemical degradation highlighted giving rise to formation 3-hydroxy-9,10-anthraquinone-2-sulfonic (HAQS) main product due hydrodeoxygenation reaction. Interestingly, exhibited good stability loss 0.29 per day.