Redox flow battery electrolytes

A combination comprising:

• (a) a first redox active composition comprising a first redox active compound, the first redox active compound corresponding in structure to any one of general formulas (1′)-(3′), or mixtures thereof;
• and
• (b) a second redox active composition comprising:
• (i) a second redox active compound, the second redox active compound corresponding in structure to any one of general formulas (1′)-(3′), or mixtures thereof;
• and/or
• (ii) an another second redox active compound;
• wherein General Formula (1′) is:
• General Formula (2′) is:
• General Formula (3′) is:
• wherein
• each of R1-R18 is independently selected from hydrogen;
• hydroxyl;
• carboxy;
• linear or branched, optionally substituted C1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S;
• a carboxylic acid;
• an ester;
• a halogen;
• optionally substituted C1-6 alkoxy;
• optionally substituted amino;
• amide;
• nitro;
• carbonyl;
• phosphoryl;
• phosphonyl;
• cyanide;
• and sulfonyl;
• wherein at least one of R1-R4 in General Formula (1′), at least one of R5-R10 in General Formula (2′) and/or at least one of R11-R18 in General Formula (3′) of the first redox active compound is a substituted amine selected from —NHR/N2R+, —NR2/NHR2+ and —NR3+, where R is selected from the group consisting of —CnH2nOH, —CnH2nNH2, —CnH2nNR2, —CnH2nCO2H and —CnH2nSO3H, wherein n is an integer selected from 1, 2, 3, 4, 5, or 6, where R is H, C1-6 alkyl, or substituted C1-6 alkyl comprising at least one heteroatom selected from N, O and S.