9,10-Anthraquinone-2,7-disulfonic acid (AQDS), also a quinone, has been evaluated as well. AQDS undergoes rapid, reversible two-electron/two-proton reduction on a glassy carbon electrode in sulfuric acid. An aqueous flow battery with inexpensive carbon electrodes, combining the quinone/hydroquinone couple with the / redox couple, yields a peak galvanic power density exceeding 6,000 W/m2 at 13,000 A/m2. Cycling showed >99 % storage capacity retention per cycle. Volumetric energy density was over 20 Wh/L. Anthraquinone-2-sulfonic acid and anthraquinone-2,6-disulfonic acid on the negative side and 1,2-dihydrobenzoquinone- 3,5-disulfonic acid on the positive side avoids the use of hazardous Br2. The battery was claimed to last for 1,000 cycles without degradation although no official data were published. While this total organic system appears robust, it has a low cell voltage (ca. 0.55V) and a low energy density (< 4Wh/L).