Stable positive side material for all-organic flow battery

A flow battery comprising:

• a positive electrode;
• a positive electrode electrolyte including water and a first redox couple that includes a first organic compound, the first organic compound being a fully substituted sulfonated quinone, the positive electrode electrolyte flowing over and contacting the positive electrode;
• a negative electrode;
• a negative electrode electrolyte including water and a second redox couple, the negative electrode electrolyte flowing over and contacting the negative electrode;
• and
• a polymer electrolyte membrane interposed between the positive electrode and the negative electrode, wherein the first organic compound is selected from the group consisting of compounds having formulae 1 and 2 with a reduction product H2Q1 selected from compounds having formulae 1′ and 2′, respectively:
• wherein R1, R2 can be electron withdrawing groups or electron donating groups depending on a predetermined electrode potential.