The content below lists materials advances for these organic based systems. Quinones and their derivatives are the basis of many organic redox systems including NARFBs and AORFBs. In one study, 1,2-dihydrobenzoquinone-3,5-disulfonic acid (BQDS) and 1,4-dihydrobenzoquinone-2-sulfonic acid (BQS) were employed as cathodes, and conventional Pb/PbSO4 was the anolyte in an acid AORFB. These first AORFBs are hybrid systems as they use organic redox active materials only for the cathode side. The quinones accepts two units of electrical charge, compared with one in conventional catholyte, implying that such a battery could store twice as much energy in a given volume.  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. 0.55 V) and a low energy density (< 4 Wh/L). Hydrobromic acid used as an electrolyte has been replaced with a far less toxic alkaline solution (1M KOH) and ferrocyanide. The higher pH is less corrosive, allowing the use of inexpensive polymer tanks. The increased electrical resistance in the membrane was compensated by increasing the voltage. The cell voltage was 1.2 V.