Redox flow battery electrolytes

1. A redox flow battery comprising:

a positive electrode;

a first redox active composition comprising a first redox active compound corresponding in structure to any one of General Formulas (1)-(3), or a mixture thereof as a positive electrode electrolyte, the positive electrode electrolyte contacting the positive electrode;

a negative electrode;

a second redox active composition comprising

(i) a second redox active compound corresponding in structure to any one of General Formulas (1)-(3), or a mixture thereof; and/or

(ii) another second redox active compound selected from the group consisting of a metal, a metal oxide, a metal-ligand coordination compound, bromine, chlorine, iodine, oxygen, an organic dye, a salt thereof, and a mixture thereof as a negative electrode electrolyte, the negative electrode electrolyte contacting the negative electrode; and

a separator interposed between the positive electrode and the negative electrode;

wherein

wherein

R 1 -R 18 is each independently selected from hydrogen; hydroxyl; carboxy; linear or branched, optionally substituted C 1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S; a carboxylic acid; an ester; a halogen; optionally substituted C 1-6 alkoxy; optionally substituted amino; nitro; carbonyl; phosphoryl; phosphonyl; cyanide; and sulfonyl; and

wherein at least one of R 1 -R 4 in General Formula (1), at least one of R 5 -R 10 in General Formula (2) and/or at least one of R 11 -R 18 in General Formula (3) of the first redox active compound is a substituted amine selected from —NHR/NH 2 R+, —NR 2 /NHR 2 + and —NR 3 + , where R is selected from the group consisting of —C n H 2n OH, —C n H 2n NH 2 , —C n H 2n NR 2 , —C n H 2n CO 2 H and —C n H 2n SO 3 H, wherein n is an integer selected from 1, 2, 3, 4, 5 or 6, where R is H or C 1 -C 6 alkyl or substituted C 1 -C 6 alkyl comprising at least one heteroatom selected from N, O and S.

2. The redox flow battery according to claim 1 , further comprising:

a positive electrode reservoir comprising the positive electrode immersed within the positive electrode electrolyte, said positive electrode reservoir forming the first redox flow battery half-cell; and

a negative electrode reservoir comprising the negative electrode immersed within the negative electrode electrolyte, said negative electrode reservoir forming the second redox flow battery half-cell.

3. The redox flow battery according to claim 1 , further comprising:

a first circulation loop comprising a storage tank containing the positive electrode electrolyte, piping for transporting the positive electrode electrolyte, a chamber in which the first electrode is in contact with the positive electrode electrolyte, and a pump to circulate the positive electrode electrolyte through the circulation loop;

optionally a second circulation loop comprising a storage tank containing the negative electrode electrolyte, piping for transporting the negative electrode electrolyte, a chamber in which the second electrode is in contact with the negative electrode electrolyte, and a pump to circulate the negative electrode electrolyte through the circulation loop; and

optionally control hardware and software.

4. A redox flow battery cell stack comprising at least two redox flow batteries according to claim 1 .

5. An energy storage system comprising a redox flow battery according to claim 1 or a redox flow battery cell stack comprising the redox flow battery; connected to an electrical grid.

6. A method of storing electrical energy, the method comprising applying a potential difference across the first and second electrode of a redox flow battery according to claim 1 , wherein the first redox active compound is oxidized or wherein the second redox active compound comprised by the second redox active composition is reduced.

7. A method of providing electrical energy, the method comprising applying a potential difference across the first and second electrode of a redox flow battery according to claim 1 , wherein the first redox active compound is reduced or wherein the second redox active compound is oxidized.

8. The redox flow battery according to claim 1 , wherein the first and second redox active compound correspond in structure to different General Formulas (1)-(3).

9. The redox flow battery according to claim 1 , wherein said first and second redox active compound are water-soluble.

10. The redox flow battery according to claim 1 , wherein said first and second redox active composition are liquid.

11. The redox flow battery according to claim 1 , wherein the first and second redox active composition are provided in separate compartments.

12. The redox flow battery according to claim 11 , wherein the first and second redox active composition are each provided in a half-cell of a redox flow battery.

13. The redox flow battery according to claim 1 , wherein the first redox active composition comprises at least one first redox active compound corresponding in structure to any one of General Formulas (1), (2) or (3), or a mixture thereof;

optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1)(a) or (b), (2)(a) or (b), or (3)(a) or (b); or a mixture thereof.

14. The redox flow battery according to claim 1 , wherein the second redox active composition comprises at least one second redox active compound corresponding in structure to any one of General Formulas (1), (2) or (3), or a mixture thereof;

optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1)(a) or (b), (2)(a) or (b), or (3)(a) or (b); or a mixture thereof.

15. The redox flow battery according to claim 1 , wherein the first redox active composition comprises

as a first redox active compound at least one benzohydroquinone corresponding in structure to General Formula (1), optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1)(a) or (b); or a mixture thereof.

16. The redox flow battery according to claim 1 , wherein the second redox active composition comprises

as the second redox active compound at least one anthraquinone corresponding in structure to General formula (3), optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General formula (3) (a) or (b); or a mixture thereof; or

as the second redox active compound at least one benzohydroquinone corresponding in structure to General Formula (1), optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General Formula (1)(a) or (b); or a mixture thereof; or

as the second redox active compound at least one naphthoquinone corresponding in structure to General formula (2), optionally including at least one reduction and/or oxidation product thereof corresponding in structure to General formula (2)(a) or (b); or a mixture thereof.

17. The redox flow battery according to claim 1 , wherein in General Formula (1):

R 1 is selected from —H, —SO 3 H, optionally substituted C 1-6 alkyl, and optionally substituted amine;

R 2 is selected from —H, —OH, —SO 3 H, C 1-6 alkoxy, and optionally substituted amine;

R 3 is selected from —H, —OH and C 1-6 alkoxy; and

R 4 is selected from —H, —SO 3 H, optionally substituted C 1-6 alkyl, optionally substituted amine, and halogen.

18. The redox flow battery according to claim 17 , wherein R 1 and/or R 4 are independently selected from substituted C 1-6 alkyl selected from R 5 —SO 3 H and R 5 —CO 2 H, wherein R 5 is a C 1-6 alkyl optionally comprising at least one heteroatom selected from N, O and S.

19. The redox flow battery according to claim 18 , comprising

(1) a first redox active compound selected from at least one of the following benzohydroquinones:

a mixture thereof, and optionally an oxidation product thereof; and

(2) a second redox active compound selected from the following at least one anthraquinone:

and optionally a reduction product thereof; or

at least one of the following benzohydroquinones:

a mixture thereof, and optionally an oxidation product thereof.

20. The redox flow battery according to claim 17 , wherein R 1 , R 2 and/or R 4 are independently selected from —NH 2 /NH 3 + , —NHR/NH 2 R + , —NR 2 /NHR 2 + and —NR 3 + , where R is H or optionally substituted C 1-6 alkyl, optionally comprising at least one heteroatom selected from N, O and S.

21. The redox flow battery according to claim 20 , wherein the compound of General Formula (1) is one of the following compounds:

or a quinone form thereof.

22. The redox flow battery according to claim 1 , wherein in General Formula (2):

R 5 and R 6 are independently selected from —H, —OH and C 1-6 alkoxy; and

R 7 -R 10 are independently selected from —H and —SO 3 H.

23. The redox flow battery according to claim 1 , wherein in General Formula (3):

R 11 , R 12 and R 14 are independently selected from —H, —OH and C 1-6 alkoxy; and

R 13 and R 15 -R 18 are independently selected from —H and —SO 3 H.

24. The redox flow battery according to claim 1 , wherein in General Formula (3):

R 11 is —SO 3 H;

R 12 is —SO 3 H, R 11 , R 13 and R 14 are —OH;

R 16 is —SO 3 H, R 11 and R 14 or R 11 , R 12 and R 14 are —OH;

R 12 and R 16 are —SO 3 H, R 11 and R 14 or R 11 , R 13 and R 14 are —OH;

R 13 and R 16 are —SO 3 H, R 11 , R 12 and R 14 are —OH;

R 12 and R 17 are —SO 3 H; or

R 11 and R 14 are —SO 3 H;

wherein each of the others of R 11 -R 18 is/are C 1-6 alkoxy or —H.

25. The redox flow battery according to claim 24 , wherein the compound of General Formula (3) is the compound below or a hydroquinone form thereof:

26. The redox flow battery according to claim 1 , wherein the first redox active composition and/or the second redox active composition is a liquid.

27. The redox flow battery according to claim 1 , wherein the first and/or the second redox active composition further comprises a solvent, optionally selected from water, an ionic liquid, methanol, ethanol, propanol, isopropanol, acetonitrile, acetone, dimethylsulfoxide, glycol, a carbonate, a polyether, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, diethylformamide, CO 2 , supercritical CO 2 , and a mixture thereof.

28. The redox flow battery according to claim 27 , wherein the solvent comprises at least about 40 wt %, at least about 50 wt %, at least about 60 wt %, at least about 70 wt %, at least about 75 wt %, at least about 80%, at least about 85 wt %, at least about 90 wt %, at least about 95 wt %, or at least about 98 wt % water, relative to the total solvent.

29. The redox flow battery according to claim 1 , wherein the first and/or the second redox active composition has a pH between <zero and about 14, between about zero and about 14, between about 7 and about 14, between about 9 to about 14, between about 10 and about 12, or between about 12 and about 14.

30. The redox flow battery according to claim 1 , wherein the first and/or the second redox active compound are present in a concentration of between about 0.3 M and about 12 M, between about 0.5 M and about 2 M, between about 2 M and about 4 M, between about 4 M and about 6 M, or between about 6 M and about 10 M.

31. The redox flow battery according to claim 1 , wherein the first redox active compound has a standard reduction potential that is at least 0.3 volts higher than the standard reduction potential of the second redox active compound.

32. The redox flow battery according to claim 1 , wherein the first redox active compound has a standard reduction potential of at least about 0.0 volts, at least about +0.5 V, at least about +0.6 V, at least about +0.7 V or more against a standard hydrogen electrode; and/or wherein the second redox active compound has a standard electrode potential of about +0.3 V or less, about +0.1 V or less, about 0.0 V or less, about −0.5 V or less, about −0.6V or less, about −1.0V or less or about −1.2 V or less against a standard hydrogen electrode.