Materials for high-performance aqueous organic redox flow batteries

A flow battery comprising:

• a positive electrode;
• a positive electrode electrolyte including water and a first redox couple, the positive electrode electrolyte flowing over and contacting the positive electrode, the first redox couple including an organic compound having formula I and a reduction product of the organic compound, the organic compound having formula I being reduced during discharge:
• a negative electrode;
• and
• a negative electrode electrolyte including water and a second redox couple, the negative electrode electrolyte flowing over and contacting the positive electrode, the second redox couple also includes the organic compound having formula I, the reduction product of the organic compound having formula I being oxidized during discharge:
• wherein:
• p is 0, 1, 2, 3, or 4;
• o is 0, 1, 2, or 3;
• r is 0, 1, 2, or 3;
• R1 and R2 are each independently —SO3H, —SO3Na, —SO3K, —CO2H, —OH, —OCH3, C1-10 alkyl, —(CH2CH2O)nOCH3, —NH2, N(CH3)2, —I, —Cl, —Br, —F, —CF3, —CF2H, —NO2, —CCl3, —CN, —PO3H2, —PO32−M+2, —COO−M+, —COOR, —CHO, —O−M+, —NHR, —N(R)2, —NHCOR, —OR, phenyl, —COR, C6-10 aryl, pyridinyl, imidazoyl, or pyrroyl,
• R3 is —SO3H, —SO3Na, —SO3K, —CO2H, —OH, —OCH3, C1-10 alkyl, —(CH2CH2O)nOCH3, —NH2, —N(CH3)2, —I, —Cl, —Br, —F, —CF3, —CF2H, —NO2, —CCl3, —CN, —PO3H2, —PO32−M+2, —COO−M+, —COOR, —CHO, —O−M+, —COR, C6-10 aryl, pyridinyl, imidazoyl, or pyrroyl;
• R is H or C1-10 alkyl;
• M+ is Na+ or K+;
• X is —(CH2)n, —(CH2OCH2)n, C4-15 branched alkyl chains or other substituted alkyl chains;
• and
• n is 1 to 10;
• and
• wherein the first redox couple and the second redox couple include the same organic compound having formula I.