Novel Phenazine-Based Compounds

Abstract

The present invention relates to novel phenazine-based compounds and compositions comprising the same and their use as redox flow battery electrolytes.

Claims

1. A substituted phenazine compound characterized by Formula (I) ##STR00028## wherein: R.sub.1 is selected from the group consisting of R.sub.d, R.sub.b—R.sub.c, R.sub.d(R.sub.c).sub.y, R.sub.a—R.sub.d—R.sub.c, R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.b—R.sub.c, R.sub.e(R.sub.d—R.sub.c).sub.2, N(R.sub.b—R.sub.c).sub.3X, —N(R.sub.d—R.sub.c).sub.3X, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), and R.sub.e(R.sub.b—R.sub.c).sub.2; R.sub.2 and R.sub.3 are selected independently from each other from the group consisting of R.sub.a—R.sub.b—R.sub.c, R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.c, R.sub.d—R.sub.c, R.sub.b—R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), R.sub.b—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.d—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.b—R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.d—R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.c, R.sub.d, R.sub.a—R.sub.d, —N(R.sub.b—R.sub.c).sub.3X, —N(R.sub.d—R.sub.c).sub.3X, R.sub.b—N(R.sub.b—R.sub.c).sub.3X, R.sub.d—N(R.sub.b—R.sub.c).sub.3X, R.sub.b—N(R.sub.d—R.sub.c).sub.3X, and R.sub.d—N(R.sub.d—R.sub.c).sub.3X; wherein: R.sub.a is selected from the group consisting of —SO.sub.3—, —SO.sub.2(NH)—, —(NH)SO.sub.2—, —SO.sub.2(NR.sub.d)—, —(NR.sub.d)SO.sub.2—, —OSO.sub.3—, —OSO.sub.2(NH)—, —(NH)SO.sub.2O—, —OSO.sub.2NR.sub.d—, —(NR.sub.d)SO.sub.2O—, —PO.sub.3H—, —PO.sub.2H(NH)—, —PO.sub.2HNR.sub.d—, —OPO.sub.3H—, —OPO.sub.2H(NH)—, —OPO.sub.2HNR.sub.d—, —CO.sub.2—, —CO(NH)—, —(NH)CO—, —CONR.sub.d—, —(NR.sub.d)CO—, —O—, —NH—, —NR.sub.d—, -heteroaryl-, and -heterocyclyl-; R.sub.b is selected from the group consisting of —CH.sub.2C(OH)HR.sub.d—, —R.sub.d—O—R.sub.d—, —R.sub.d—(OC.sub.2H.sub.4).sub.n—, and —R.sub.d—(OCH.sub.2C(CH.sub.3)H).sub.n—; R.sub.b is selected from the group consisting of —H, —OH, —OR.sub.d, —OC(═O)R.sub.d, —NH.sub.2, —NH(R.sub.d), —N(R.sub.d).sub.2, —N(R.sub.d).sub.3X, —C(═O)NH.sub.2, —C(═O)(NH)R.sub.d, —C(═O)OH, —C(═O)R.sub.b—H, —SO.sub.3H, —SO.sub.3R.sub.d, —SO.sub.2NH.sub.2, —SO.sub.2(NH)R.sub.d, —OSO.sub.3H, —OSO.sub.3R.sub.d, —OSO.sub.2NH.sub.2, —OSO.sub.2(NH)R.sub.d, —PO.sub.3H.sub.2, —PO.sub.3HR.sub.d, —PO.sub.3(R.sub.d).sub.2, —OPO.sub.3H.sub.2, —OPO.sub.3HR.sub.d, —OPO.sub.3(R.sub.d).sub.2, -halogen, -aryl, —CHO, —CN, -heteroaryl, and -heterocyclyl; R.sub.d is selected from the group consisting of a linear or branched, saturated or unsaturated C.sub.1-C.sub.9 hydrocarbon group; R.sub.e is selected from the group consisting of PO.sub.3, OPO.sub.2, and N; or two of R.sub.1, R.sub.2 and/or R.sub.3 being adjacent substituents on the phenazine ring system together form a cyclic system; and wherein: X is selected from the group consisting of Cl.sup.−, Br.sup.−, I.sup.−, and % SO.sub.4.sup.2−; m is selected from any number of 0, 1, 2, and 3; p is selected from any number of 0, 1, 2, 3, and 4; y is selected from any number of 2, 3, 4, 5, and 6; and n is selected from any number of 1 to 50; or a salt thereof.

2. The substituted phenazine compound of claim 1, wherein: R.sub.a of R.sub.a—R.sub.d—R.sub.c is selected from —NH—, —SO.sub.3—, —SO.sub.2(NH)—, —(NH)SO.sub.2—, —SO.sub.2(NR.sub.d)—, —(NR.sub.d)SO.sub.2—, —OSO.sub.3—, —OSO.sub.2(NH)—, —(NH)SO.sub.2O—, —OSO.sub.2NR.sub.d—, —(NR.sub.d)SO.sub.2O—, —PO.sub.3H—, —PO.sub.2H(NH)—, —PO.sub.2HNR.sub.d—, —OPO.sub.3H—, —OPO.sub.2H(NH)—, —OPO.sub.2HNR.sub.d—, —(NH)CO— or —(NR.sub.d)CO—, and R.sub.c of R.sub.a—R.sub.d—R.sub.c is any substituent as defined other than —H, and R.sub.1 is any substituent as defined other than R.sub.d; or R.sub.c of R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c) and R.sub.d(R.sub.c).sub.y is any substituent as defined other than —H, and R.sub.1 is any substituent as defined other than R.sub.d.

3. The substituted phenazine compound of claim 1, wherein: R.sub.1 is selected from the group consisting of R.sub.b—R.sub.c, R.sub.d(R.sub.c).sub.y, R.sub.a—R.sub.d—R.sub.c, R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.e(R.sub.d—R.sub.c).sub.2, N(R.sub.b—R.sub.c).sub.3X, —N(R.sub.d—R.sub.c).sub.3X, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), R.sub.e(R.sub.b—R.sub.c).sub.2 and R.sub.b—R.sub.a—R.sub.b—R.sub.c; R.sub.2 and R.sub.3 are selected independently from each other from the group consisting of R.sub.a—R.sub.b—R.sub.c, R.sub.a—R.sub.d—R.sub.c, R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), R.sub.b—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.d—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.b—R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.c, R.sub.d, —N(R.sub.b—R.sub.c).sub.3X, —N(R.sub.d—R.sub.c).sub.3X, R.sub.b—N(R.sub.b—R.sub.c).sub.3X, and R.sub.b—N(R.sub.d—R.sub.c).sub.3X; wherein: R.sub.a is selected from the group consisting of SO.sub.3—, —SO.sub.2(NH)—, —(NH)SO.sub.2—, —SO.sub.2(NR.sub.d)—, —(NR.sub.d)SO.sub.2—, —OSO.sub.3—, —OSO.sub.2(NH)—, —(NH)SO.sub.2O—, —OSO.sub.2NR.sub.d—, —(NR.sub.d)SO.sub.2O—, —CO(NH)—, —(NH)CO—, —CONR.sub.d—, —(NR.sub.d)CO—, —O—, —NH—, -heteroaryl-, and -heterocyclyl-; R.sub.b is selected from the group consisting of —CH.sub.2C(OH)HR.sub.d- and —R.sub.d—(OCH.sub.2C(CH.sub.3)H).sub.n—; R.sub.c is selected from the group consisting of —H, —OH, —OR.sub.d, —NH.sub.2, —NH(R.sub.d), —N(R.sub.d).sub.2, —N(R.sub.d).sub.3X, —C(═O)NH.sub.2, —C(═O)(NH)R.sub.d, —C(═O)OH, —SO.sub.3H, —SO.sub.3R.sub.d, —SO.sub.2NH.sub.2, —SO.sub.2(NH)R.sub.d, —OSO.sub.3H, —OSO.sub.3R.sub.d, —OSO.sub.2NH.sub.2, —OSO.sub.2(NH)R.sub.d, and -halogen; R.sub.d is selected from the group consisting of a linear or branched, saturated or unsaturated C.sub.1-C.sub.9 hydrocarbon group; R.sub.e is selected from the group consisting of PO.sub.3, OPO.sub.2, and N; and wherein: X is selected from the group consisting of Cl.sup.−, Br.sup.−, I.sup.−, and ½SO.sub.4.sup.2−; m is selected from any number of 0, 1, 2, and 3; p is selected from any number of 0, 1, 2, 3, and 4; y is selected from any number of 2, 3, 4, 5, and 6; and n is selected from any number of 1 to 50.

4. The substituted phenazine compound of claim 1, wherein: R.sub.1 is selected from the group consisting of R.sub.b—R.sub.c, R.sub.d(R.sub.c).sub.y, R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.b—R.sub.c, R.sub.a—R.sub.d—R.sub.c, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), and R.sub.e(R.sub.b—R.sub.c).sub.2, wherein R.sub.c in R.sub.d(R.sub.c).sub.y and R.sub.e(R.sub.d—R.sub.c).sub.2 is any substituent as defined other than H.

5. The substituted phenazine compound of claim 1, wherein: R.sub.1 is selected from the group consisting of R.sub.b—R.sub.c, R.sub.d(R.sub.c).sub.y, R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, and R.sub.b—R.sub.a—R.sub.b—R.sub.c.

6. The substituted phenazine compound of claim 1, wherein: R.sub.2 and R.sub.3 are selected independently from each other from the group consisting of R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.b—R.sub.c, R.sub.d—R.sub.a—R.sub.b—R.sub.c, R.sub.b—R.sub.a—R.sub.d—R.sub.c, R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.e(R.sub.d—R.sub.c)(R.sub.b—R.sub.c), R.sub.b—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.d—R.sub.e(R.sub.b—R.sub.c).sub.2, R.sub.b—R.sub.e(R.sub.d—R.sub.c).sub.2, R.sub.c, R.sub.d, —N(R.sub.b—R.sub.c).sub.3X, and —N(R.sub.d—R.sub.c).sub.3X, with R.sub.2 preferably being selected from R.sub.c and R.sub.d.

7. The substituted phenazine compound of claim 1, wherein: R.sub.a is selected from the group consisting of —SO.sub.3—, —SO.sub.2(NH)—, —(NH)SO.sub.2—, —OSO.sub.3—, —OSO.sub.2(NH)—, —(NH)SO.sub.2O—, —CO(NH)—, —(NH)CO—, and —O—, —NH—.

8. The substituted phenazine compound of claim 1, wherein R.sub.b is selected from the group consisting of —CH.sub.2C(OH)HR.sub.d- and —R.sub.d—(OCH.sub.2C(CH.sub.3)H).sub.n—.

9. The substituted phenazine compound of claim 1, wherein R.sub.c is selected from the group consisting of —H, —OH, —OR.sub.d, —NH.sub.2, —N(R.sub.d).sub.2, —N(R.sub.d).sub.3X, —C(═O)NH.sub.2, —C(═O)(NH)R.sub.d, —C(═O)OH, —SO.sub.3H, —OSO.sub.3H, and —OSO.sub.2(NH)R.sub.d, with R.sub.c preferably being selected from —H, —OH, —SO.sub.3H and —C(═O)OH.

10. The substituted phenazine compound of claim 1, wherein R.sub.d is selected from the group consisting of a linear or branched, saturated or unsaturated C.sub.1-C.sub.5 hydrocarbon group, preferably a linear, saturated C.sub.1 to C.sub.5 hydrocarbon group.

11. The substituted phenazine compound of claim 1, wherein R.sub.e is selected from N.

12. The substituted phenazine compound of claim 1, wherein X is selected from the group consisting of Cl.sup.−, and ½SO.sub.4.sup.2−.

13. The substituted phenazine compound of claim 1, wherein m is selected from 0 or 1.

14. The substituted phenazine compound of claim 1, wherein p is selected from any number of 0, 1, 2, and 3, in particular 1, 2, and 3.

15. The substituted phenazine compound of claim 1, wherein y is selected from 2 or 3.

16. The substituted phenazine compound of claim 1, wherein n is selected from any number of 1 to 10 or 1 to 5.

17-19. (canceled)

20. The substituted phenazine compound of claim 1, wherein R.sub.1 is positioned at ring positions 7 or 8.

21. The substituted phenazine compound of claim 1, wherein p is 1 or 2, and, preferably, R.sub.2 is positioned at ring positions 2 and/or 3.

22. The substituted phenazine compound of claim 1, wherein m is 0 or 1 and, preferably, if m is 1, R.sub.3 is positioned at ring positions 7 or 8.

23. The substituted phenazine compound of claim 1, wherein m is 1 and R.sub.3 is positioned at ring positions 7 or 8, R.sub.1 is positioned at the other of ring positions 7 or 8; and p is 2 and R.sub.2 is positioned at ring positions 2 and 3.

24. The substituted phenazine compound of claim 1, wherein m is 0; R.sub.1 is positioned at ring positions 7 or 8; and p is 2 and R.sub.2 is positioned at ring positions 2 and 3.

25. The substituted phenazine compound of claim 1, wherein R.sub.1 is selected from the group consisting of —OH, —OR.sub.x, —NH.sub.2, —NHR.sub.x, —NR.sub.xR.sub.y, and —N(H)C(═O)R.sub.x, preferably —OR.sub.x, —NHR.sub.x, and —NR.sub.xR.sub.y, wherein R.sub.x and R.sub.y are selected from an unsubstituted or a substituted C.sub.1-4 alkyl, preferably an unsubstituted or a substituted C.sub.1-3 alkyl, more preferably an unsubstituted or a substituted methyl or unsubstituted or a substituted ethyl, wherein the substituent is preferably selected from the group consisting of —C(═O)OH, ═O, —SO.sub.3H, —OH, substituted or unsubstituted phenyl, and —NH.sub.2, and wherein R.sub.1 is positioned at ring position 7 or 8.

26. The substituted phenazine compound of claim 25, wherein R.sub.1 is selected from the group consisting of —OR.sub.x, —NHR.sub.x, —NR.sub.xR.sub.y and —N(H)C(═O)R.sub.x, preferably —OR.sub.x, —N(H)C(═O)R.sub.x, and —NR.sub.xR.sub.y, more preferably —OR.sub.x and —NR.sub.xR.sub.y wherein R.sub.x and R.sub.y are selected from an unsubstituted or a substituted C.sub.1-4 alkyl, preferably an unsubstituted or a substituted C.sub.1-3 alkyl, more preferably an unsubstituted or a substituted methyl or unsubstituted or a substituted ethyl, wherein the substituent is selected from the group consisting of —C(═O)OH, ═O, —SO.sub.3H, —OH, substituted or unsubstituted phenyl, and —NH.sub.2, and wherein R.sub.1 is positioned at ring position 7 or 8.

27. The substituted phenazine compound of claim 1, wherein R.sub.2 is selected from the group consisting of —H, —OH, —SO.sub.3H, alkyl, in particular methyl, and —C(═O)OH, in particular —OH, —SO.sub.3H, and —C(═O)OH or alkyl.

28. The substituted phenazine compound of claim 1, wherein R.sub.2 is selected from —SO.sub.3H, preferably positioned at ring position 2 and/or 3.

29. The substituted phenazine compound of claim 1, wherein R.sub.3 is selected from the group consisting of —H, —OH and a member of the group as defined for R.sub.1 by claim 24, in particular —OH and a member of the group as defined for R.sub.1 by claim 24.

30. The substituted phenazine compound of claim 29, wherein R.sub.3 is selected from —OH and positioned at ring position 7 or 8, wherein R.sub.1 is preferably —OH at the other of ring positions 7 or 8.

31. The substituted phenazine compound of claim 25, wherein R.sub.1 is selected from —OR.sub.X, —NH.sub.2, —NHR.sub.x, and —NR.sub.xR.sub.y, wherein R.sub.x and R.sub.y are selected from an unsubstituted or a substituted C.sub.1-4 alkyl, preferably an unsubstituted or a substituted C.sub.1-3 alkyl, more preferably an unsubstituted or a substituted methyl or an unsubstituted or substituted ethyl, wherein the substituent is selected from the group consisting of —C(═O)OH, —SO.sub.3H, —OH, ═O, substituted or unsubstituted phenyl, and —NH.sub.2, and wherein R.sub.1 is positioned at ring position 7 or 8, wherein p is 1 or 2 and R.sub.2 is selected from methyl, —SO.sub.3H or —C(═O)OH, preferably —SO.sub.3H, and preferably positioned at ring position 1, 2 and/or 3, and R.sub.3 is selected from —OH or identical with R.sub.1 and positioned at the other of ring positions 7 or 8.

32. The substituted phenazine compound of claim 25, wherein R.sub.1 is —NR.sub.xR.sub.y, wherein R.sub.x is a substituted C.sub.1-4 alkyl, preferably a substituted methyl or ethyl, and R.sub.y is an unsubstituted C.sub.1-4 alkyl, preferably methyl, or R.sub.1 is selected from —OR.sub.x, wherein R.sub.x is a substituted C.sub.1-4 alkyl, preferably a substituted ethyl or C.sub.3 alkyl.

33. The substituted phenazine compound of claim 25, wherein R.sub.x or R.sub.y, in particular R.sub.x, is/are a substituted C.sub.1-4 alkyl, wherein the substituent is a terminal substituent.

34. The substituted phenazine compound of claim 25, wherein R.sub.x or R.sub.y, in particular R.sub.x, is/are a substituted C.sub.1-4 alkyl, wherein the substituent is selected from —C(═O)OH and —SO.sub.3H.

35. The substituted phenazine compound of claim 1, wherein m is 1 and R.sub.3 is identical with R.sub.1, wherein R.sub.1 and R.sub.3 are preferably positioned at positions 7 and 8.

36. The substituted phenazine compound of claim 32, wherein R.sub.1 is —N(H)C(═O)R.sub.x, wherein R.sub.x is preferably selected from a substituted ethyl, wherein the substituent is more preferably selected from —C(═O)OH and —SO.sub.3H and/or wherein the substituent is more preferably a terminal substituent, wherein R.sub.1 and R.sub.3 are most preferably identical.

37. The substituted phenazine compound of claim 1, wherein R.sub.1 is selected from the group consisting of —N(CH.sub.3)—CH.sub.2—C(═O)OH, —N(H)—(CH.sub.3)—(CH.sub.2).sub.2—C(═O)OH, —N(CH.sub.3)—CH.sub.2—SO.sub.3H, —N(CH.sub.3)—(CH.sub.2).sub.2—SO.sub.3H, —N(H)—CH.sub.2-Aryl, in particular —N(H)—CH.sub.2-Phenyl, —N(H)—(CH.sub.2).sub.2-Aryl, in particular —N(H)—(CH.sub.2).sub.2-Phenyl, —N(H)—CH.sub.2—OH, —N(H)—(CH.sub.2).sub.2—OH; —N(H)—CH.sub.3, —N(H)—C.sub.2H.sub.5, —O—CH.sub.3, —O—C.sub.2H.sub.5, —O—CH.sub.2—SO.sub.3H, —O—(CH.sub.2).sub.2—SO.sub.3H, —O—(CH.sub.2).sub.3—SO.sub.3H, —O—CH.sub.2—CH(OH)—CH.sub.2—SO.sub.3H, —O—CH.sub.2—CH(OH)—CH.sub.2—OH, —O—CH.sub.2—CH(OH)—CH.sub.2—C(═O)OH, —N(H)C(═O)—(CH.sub.2).sub.2—C(═O)OH, —N(H)C(═O)—(CH.sub.2).sub.2—SO.sub.3H, and —O—CH.sub.2—CH(OH)—CH.sub.2—NH.sub.3.sup.+.

38. The substituted phenazine compound of claim 1, wherein p is 2, and R.sub.2 is preferably selected from —SO.sub.3H and methyl.

39. The substituted phenazine compound of claim 1, wherein p is 0, m is preferably 1, and R.sub.1 and R.sub.3 are more preferably identical.

40. A composition, comprising at least one or at least two substituted phenazine compounds of claim 1 and a solvent.

41-45. (canceled)

46. A redox flow battery, comprising a first half cell comprising an electrolyte solution comprising a composition of claim 40, which, optionally, contains at least one further substituted low molecular weight aromatic redox active compound other than the compound of claim 1; and a second half-cell comprising an electrolyte solution comprising a redox active species.

47-48. (canceled)

49. The redox flow battery of claim 46, wherein said redox flow battery comprises at least one carbon-based electrode.

50. The redox flow battery of claim 49, wherein the redox flow battery comprises a carbon-based electrode other than carbon felt, carbon cloth and carbon paper.

51. (canceled)

52. The redox flow battery of claim 46, wherein the second (optionally aqueous) electrolyte solution comprises a salt of Fe(CN).sub.6.sup.3−, Fe(CN).sub.6.sup.4− and/or combinations thereof, preferably an alkali salt or combinations of alkali salts, more preferably a Na+ and/or K+ salt.

53. (canceled)

Description

FIGURES

[0537] FIG. 1: Galvanostatic charge and discharge cycle (voltage as a function of time) with phenazine compound (III) (see Table 1) in a FT Cell.

[0538] FIG. 2: Galvanostatic charge and discharge cycle (voltage as a function of time) of phenazine compound (II) (see Table I) in a FT-Cell.

[0539] FIG. 3: Galvanostatic charge and discharge cycle (voltage as a function of time) of phenazine compound (II) (see Table I) in a FB-Cell.

EXAMPLES

[0540] The examples shown in the following are merely illustrative and shall describe the present invention in a further way. These examples shall not be construed to limit the present invention thereto. The following preparations and examples are given to enable those skilled in the art to more clearly understand and to practice the present invention. The present invention, however, is not limited in scope by the exemplified embodiments, which are intended as illustrations of single aspects of the invention only, and methods, which are functionally equivalent are within the scope of the invention. Indeed, various modifications of the invention in addition to those described herein will become readily apparent to those skilled in the art from the foregoing description, accompanying figures and the examples below. All such modifications fall within the scope of the appended claims.

[0541] In the following example section, the alternative nomenclature of the synthesized compounds, in particular, considering the denotation of the ring positions according to Formula (I)(a) and (I)(b) is provided below by the terms set in brackets (“ . . . ”).

I. Synthesis of Phenazine Compounds According to the Present Invention

Example 1: [(3-hydroxyphenazin-2-yl)(methyl)amino]acetic acid (“[(7-hydroxyphenazin-8-yl)(methyl)amino]acetic acid”)]

[0542] ##STR00011##

[0543] Methoxybenzoquinone (MBQ) (2-Methoxy-1,4-benzoquinone) was first converted to 2-[2-(methylamino)acetic acid]-1,4-benzoquinone by reacting MBQ (2.44 g, 20 mmol, 1 eq) with 2-(methylamino)acetic acid (3.56 g, 40 mmol, 2 eq) in methanol (30 ml) in a 100 ml round bottom flask. After stirring at 60° C. for 40 hours the reaction mixture was filtered, and the mother liquor was concentrated on the rotary evaporator to dryness. The resulting dark-red product 2-[2-(methylamino)acetic acid]-1,4-benzoquinone was used after analysing by HPLC without further purification. 2-[2-(methylamino)acetic acid]-1,4-benzoquinone (0.49 g, 2.5 mmol, 1 eq) was dissolved in methanol (15 ml) and o-phenylenediamine (0.27 g, 2.5 mmol, 1 eq) was added to the reaction mixture. Stirring for 50 hours at room temperature gave a dark-red suspension which was filtered off and concentrated under vacuum. The crude product was diluted in DI water (10 ml) and filtered again. The obtained solid was dried at 60 C to give the final product [(3-hydroxyphenazin-2-yl)(methyl)amino]acetic acid (“[(7-hydroxyphenazin-8-yl)(methyl)amino]acetic acid”) (0.25 g, 0.9 mmol) in 36% yield which was analysed by HPLC.

Example 2: [(3-hydroxy-7-sulfophenazin-2-yl)(methyl)amino]acetic acid (“[(7-hydroxy-3-sulfophenazin-8-yl)(methyl)amino]acetic acid”)

[0544] ##STR00012##

[0545] 2-[2-(Methylamino)acetic acid]-1,4-benzoquinone (0.49 g, 2.5 mmol, 1 eq) was dissolved in methanol (15 ml) and 3,4-diaminobenzene-sulfonic acid (65 wt %; 0.72 g, 3.8 mmol, 1.5 eq) was added to the reaction mixture. The purple coloured reaction mixture was stirred for 3 hours at 60° C. before it was concentrated on the rotary evaporator. To the obtained crude product isopropanol (40 ml) was added, suspended and filtered off. The alcohol was evaporated under vacuum to give [(3-hydroxy-7-sulfophenazin-2-yl)(methyl)amino]acetic acid (“[(7-hydroxy-3-sulfophenazin-8-yl)(methyl)amino]acetic acid”) which was analysed by HPLC.

Example 3: 2-[(3-hydroxy-1-methoxyphenazin-2-yl)(methyl)amino]ethane-1-sulfonic acid (“2-[(7-hydroxy-9-methoxyphenazin-8-yl)(methyl)amino]ethane-1-sulfonic acid”)

[0546] ##STR00013##

[0547] Dimethoxybenzoquinone (DMBQ) (2,6- Dimethoxybenzoquinone) was first converted to 2-[(2,4-dimethoxy-3,6-dioxocyclohexa-1,4-dien-1-yl)(methyl)amino]ethane-1-sulfonic acid by reacting DMBQ (1.85 g, 10 mmol, 1 eq), in methanol (20 ml), with N-methyltaurine sodium salt (62-66% in water) (3.2 g, 4.1 ml, 13 mmol, 1.3 eq). The amine was dissolved in methanol (15 ml) too and added slowly to the DMBQ slurry. After heating for 23 hours at 60° C. the reaction mixture was concentrated on the rotary evaporator to dryness and washed with acetone (2×20 ml). The resulting purple-red product 2-[(2,4-dimethoxy-3,6-dioxocyclohexa-1,4-dien-1-yl)(methyl)amino]ethane-1-sulfonic acid (3.6 g, 9.4 mmol, 94%) was used after analysing by HPLC without further purification. O-Phenylenediamine (0.31 g, 2.86 mmol, 1 eq) was weighed into a 100 ml round bottom flask, dissolved in methanol (15 ml) and 2-[(2,4-dimethoxy-3,6-dioxocyclohexa-1,4-dien-1-yl)(methyl)amino]ethane-1-sulfonic acid (0.83 g, 2.86 mmol, 1 eq) was added. After stirring for 16 hours at room temperature gave a brown suspension which was filtered off. The solid was washed with methanol (2×5 ml) and analysed by HPLC. Upon drying the brown solid the final product 2-[(3-hydroxy-1-methoxyphenazin-2-yl)(methyl)amino]ethane-1-sulfonic acid (“2-[(7-hydroxy-9-methoxyphenazin-8-yl)(methyl)amino]ethane-1-sulfonic acid”) (0.10 g, 0.28 mmol) was obtained. Yield: 10%.

Example 4: 3-(benzylamino)phenazin-2-ol (“8-(benzylamino)phenazin-7-ol”)

[0548] ##STR00014##

[0549] O-Phenylenediamine (0.20 g, 2.0 mmol, 1 eq) was weighed into a 100 ml round bottom flask, dissolved in DI water (15 ml) and 2-benzylamino-1,4-benzoquinone (0.43 g, 2.0 mmol, 1 eq) was added. After stirring for 26 hours at 60° C. the reaction mixture was concentrated on rotary evaporator. Suspended in methanol (15 ml) filtered and the filtrate was dried under vacuum to obtain 3-(benzylamino)phenazin-2-ol (“8-(benzylamino)phenazin-7-ol”) as product (0.42 g, 1.4 mmol) as a brown solid in 70% yield. Analytic followed by HPLC.

Example 5: 7-(benzylamino)-8-hydroxyphenazine-2-sulfonic acid (“8-(benzylamino)-7-hydroxyphenazine-3-sulfonic acid”)

[0550] ##STR00015##

[0551] 7-(benzylamino)-8-hydroxyphenazine-2-sulfonic acid (“8-(benzylamino)-7-hydroxyphenazine-3-sulfonic acid”) was prepared from 2-benzylamino-1,4-benzoquinone (0.43 g, 2 mmol, 1 eq) and 3,4-diaminobenzenesulfonic acid (65 wt %; 0.78 g, 4.2 mmol, 1 eq) in methanol (15 ml) at 60° C. After 16 hours stirring the reaction mixture was filtered and the filtrate was dried under vacuum to obtain 7-(benzylamino)-8-hydroxyphenazine-2-sulfonic acid (“8-(benzylamino)-7-hydroxyphenazine-3-sulfonic acid”) as brown-red product (0.66 g, 1.7 mmol) in 85% yield. Product identity was verified by HPLC.

Example 6: 7-[(2-hydroxyethyl)(methyl)amino]-8-hydroxyphenazine-2-sulfonic acid (“8-[(2-hydroxyethyl)(methyl)amino]-7-hydroxyphenazine-3-sulfonic acid”) (IV)

[0552] ##STR00016##

[0553] Synthesis of the precursor 2-[(2-hydroxyethyl)(methyl)amino]cyclohexa-2,5-diene-1,4-dione occurred by treating Methoxybenzoquinone (MBQ) (2-methoxy-1,4-benzoquinone) (2.01 g, 14.6 mmol, 1 eq) with the amine 2-Methylaminoethanol (3.27 g, 43.5 mmol, 3 eq), dissolved in ethyl acetate (15 ml), at room temperature. After stirring for 18 h the reaction mixture was filtered off and the obtained solid was characterised by HPLC as 2-[(2-hydroxyethyl)(methyl)amino]cyclohexa-2,5-diene-1,4-dione (2.56 g, 14.6 mmol, 100%). For the preparation of 7-[(2-hydroxyethyl)(methyl)amino]-8-hydroxyphenazine-2-sulfonic acid (“8-[(2-hydroxyethyl)(methyl)amino]-7-hydroxyphenazine-3-sulfonic acid”), the starting materials 2-[(2-hydroxyethyl)(methyl)amino]cyclohexa-2,5-diene-1,4-dione (2.65 g, 14.6 mmol, 1 eq) and 3,4-diaminobenzenesulfonic acid (65 wt %; 3.71 g, 19.7 mmol, 1 eq) were both weighed into a round bottom flask and suspended in DI water (15 ml). Stirring for 3 hours at room temperature gave a purple red suspension which was filtered off. Filtrate was disposed and the solid dried at 60° C. to give 7-[(2-hydroxyethyl)(methyl)amino]phenazine-2-sulfonic acid (“8-[(2-hydroxyethyl)(methyl)amino]-7-hydroxyphenazine-3-sulfonic acid”) as product (5.37 g, 16 mmol, >100%) that was analysed by HPLC.

Example 7: 8-hydroxy-7-(methylamino)phenazine-2-sulfonic acid (“7-hydroxy-8-(methylamino)phenazine-3-sulfonic acid”)

[0554] ##STR00017##

[0555] The precursor 2-methoxy-5-(methylamino)cyclohexa-2,5-diene-1,4-dione (5a) was synthesised by adding Methylamine (33 wt % in ethanol; 1.03 g, 33.0 mmol, 3 eq) to a stirred solution of Methoxybenzoquinone (MBQ) (2-methoxy-1,4-benzoquinone) (0.50 g, 3.6 mmol, 1 eq) in ethyl acetate (10 ml) at 60° C. After 15 min stirring the reaction mixture was filtered off and the solid was washed with ethyl acetate (2×10 ml) to give 2-methoxy-5-(methylamino)cyclohexa-2,5-diene-1,4-dione (0.25 g, 1.5 mmol) as a red solid in 42% yield. For the preparation of 8-hydroxy-7-(methylamino)phenazine-2-sulfonic acid (“7-hydroxy-8-(methylamino)phenazine-3-sulfonic acid”), the starting material 2-methoxy-5-(methylamino)cyclohexa-2,5-diene-1,4-dione (0.25 g, 1.5 mmol, 1 eq) was diluted in methanol (15 ml) and under stirring at room temperature 3,4-diaminobenzenesulfonic acid (65 wt %; 0.38 g, 1.8 mmol, 1 eq) was added. The reaction mixture was heated up to 60° C. and after 48 hours filtered off. The obtained red solid was washed with methanol (2×10 ml) and characterised by HPLC as 8-hydroxy-7-(methylamino)phenazine-2-sulfonic acid (“7-hydroxy-8-(methylamino)phenazine-3-sulfonic acid”) (0.14 g, 0.46 mmol, 34%).

Example 8: 7-(dimethylamino)-8-hydroxyphenazine-2-sulfonic acid (“8-(dimethylamino)-7-hydroxyphenazine-3-sulfonic acid”) (I)

[0556] ##STR00018##

[0557] The starting material 2-(dimethylamino)-5-methoxycyclohexa-2,5-diene-1,4-dione was prepared by adding dimethylamine (7.74 ml, 43.4 mmol, 1 eq) to a stirred solution of Methoxybenzoquinone (MBQ) (2-methoxy-1,4-benzoquinone) (6.0 g, 43.4 mmol, 1 eq) in ethyl acetate (100 ml) at room temperature. After 45 min stirring the reaction mixture was filtered off. The filtrate was concentrated on a rotary evaporator till dryness to obtain the product 2-(dimethylamino)-5-methoxycyclohexa-2,5-diene-1,4-dione (6.0 g, 33.1 mmol) as a purple red solid in 76% yield and analysed by HPLC. For the preparation of 7-(dimethylamino)-8-hydroxyphenazine-2-sulfonic acid (“8-(dimethylamino)-7-hydroxyphenazine-3-sulfonic acid”), both starting materials 2-(dimethylamino)-5-methoxycyclohexa-2,5-diene-1,4-dione (2.0 g, 11.1 mmol, 1 eq) and 3,4-diaminobenzene-sulfonic acid (97 wt %; 2.08 g, 11.05 mmol, 1 eq) were weighed into a 100 ml round bottom flask and suspended in methanol (40 ml). The reaction mixture was heated up to 60° C. for 3 days. Filtration of the suspension and washing the solid with methanol (2×10 ml) the product was air dried. Isolation of the red solid led to 7-(dimethylamino)-8-hydroxyphenazine-2-sulfonic acid (“8-(dimethylamino)-7-hydroxyphenazine-3-sulfonic acid”) (2.47 g, 7.72 mmol, 70%).

Example 9: 2-hydroxy-3-[(3-hydroxyphenazin-2-yl)oxy]-N,N,N-trimethylpropane-1-aminium (“2-hydroxy-3-[(7-hydroxyphenazin-8-yl)oxy]-N,N,N-trimethylpropane-1-aminium”)

[0558] ##STR00019##

[0559] 2,3-Dihydroxyphenazine (“7,8-Dihydroxyphenazine”) (51 wt %; 6.24 g, 29.4 mmol, 1 eq) was placed in a 250 ml round bottom flask and suspended in acetone (70 ml). Under vigorously stirring potassium carbonate (4.77 g, 34.5 mmol, 2 eq) was added and stirred for 5 min at 50° C. Afterwards glycidyltrimethylammonium chloride (76 wt % in water; 5.64 g, 37.2 mmol, 2 eq) was added and the vigorously stirring at 50° C. continued for 24 hours. The solvent was decanted, and the residue dissolved in DI water (15 ml) which was acidified with concentrated hydrochloric acid (37 wt %, 3 ml). Cooling the acidic solution in ice bath lead to a brown precipitation that was vacuum filtrated and washed the brown solid once with diluted hydrochloric acid (20 ml) and DI water (20 ml). Drying the solid at 60 C gave 2-hydroxy-3-[(3-hydroxyphenazin-2-yl)oxy]-N,N,N-trimethylpropan-1-aminium (“2-hydroxy-3-[(7-hydroxyphenazin-8-yl)oxy]-N,N,N-trimethylpropan-1-aminium”) (4.61 g, 12.8 mmol, 85%) as green-brown powder.

Example 10: Mixture of 3-[(3-hydroxyphenazin-2-yl)oxy]propane-1-sulfonic acid (“3-[(7-hydroxyphenazin-8-yl)oxy]propane-1-sulfonic acid”) and 3,3′-[phenazine-2,3-diylbis(oxy)]di(propane-1-sulfonic acid) (“3,3′-[phenazine-7,8-diylbis(oxy)]di(propane-1-sulfonic acid)”) (III)

[0560] ##STR00020##

[0561] 2,3-Dihydroxyphenazine (“7,8-Dihydroxyphenazine”) (51 wt %; 5.12 g, 35.9 mmol, 1 eq) was placed in a 250 ml round bottom flask and suspended in acetone (70 ml). Under vigorously stirring potassium hydroxide (85 wt %; 3.58 g, 55.4 mmol, 2 eq) was added and stirred for 5 min at 50° C. before propane-1,3-sulton (4.3 mL, 48.2 mmol, 2 eq) was added. The vigorously stirring at 50° C. continued for 24 hours and was filtered off. The residue was washed with acetone (2×20 ml) and dried on air. Afterwards the crude product was placed in a 250 ml beaker and dissolved in DI water (70 ml) and acidified with concentrated hydrochloric acid (37 wt %, 3 ml). The green suspension was left for 12 hours at room temperature then vacuum filtrated. The acidic filtrate contained 3-[(3-hydroxyphenazin-2-yl)oxy]propane-1-sulfonic acid (“3-[(7-hydroxyphenazine-8-yl)oxy]propane-1-sulfonic acid”) and 3,3′-[phenazine-2,3-diylbis(oxy)]di(propane-1-sulfonic acid) (“3,3′-[phenazine-7,8-diylbis(oxy)]di(propane-1-sulfonic acid”) as products which were isolated as a green solid after washing the solid with diluted hydrochloric acid (20 ml) and DI water (20 ml). After drying at 60 C the desired molecule mixture (2.9 g, 8.67 mmol) was obtained in 36% yield.

Example 11: 7,8-Dihydroxy-3-methylphenazine-2-sulfonic acid (“7,8-Dihydroxy-2-methylphenazine-3-sulfonic acid”)

[0562] ##STR00021##

[0563] Structural formulae presented below according to the alternative nomenclature as defined by (“ . . . ”):

##STR00022##

[0564] 2,5-Dihydroxy-1,4-benzoquinone (3.12 g, 22 mmol, 1 eq) and 4,5-diamino-2-methylbenzene-1-sulfonic acid (4.5 g, 22 mmol, 1 eq) were suspended in 110 mL water in a 250 mL round-bottom flask at room temperature. The mixture was heated under stirring to 70° C. and a complete conversion of the starting material was observed after 19 hours. After three days the brown precipitate was vacuum filtered at room temperature, washed with 20 mL water and dried under reduced pressure. The product was analyzed by HPLC. Final yield: 5.43 g, 79.5%.

Example 12: 7,8-Dihydroxy-4-methylphenazine-2-sulfonic acid (“7,8-Dihydroxy-1-methylphenazine-3-sulfonic acid”)

[0565] ##STR00023##

[0566] Structural formulae presented below according to the alternative nomenclature as defined by (“ . . . ”):

##STR00024##

[0567] 3,4-Diamino-5-methylbenzene-1-sulfonic acid (3.5 g, 17 mmol, 1 eq) was dissolved in 150 mL hot water and filtered prior to its use. The hot filtrate of the sulfonic acid was added to 2,5-dihydroxy-1,4-benzoquinone (2.0 g, 14 mmol, 0.8 eq) and in a 250 mL round-bottom flask and stirred for one hour. The mixture was heated to 60° C. for 26 hours and the brown precipitate vacuum filtrated. The solid was washed with 30 mL acetone and dried under ambient atmosphere. The product was analyzed by HPLC. Final yield: 3.7 g, 86%.

Example 13: Mixture of 7,8-Dihydroxy-3-methylphenazine-2-sulfonic acid (“7,8-Dihydroxy-2-methylphenazine-3-sulfonic acid”) and 7,8-Dihydroxy-4-methylphenazine-2-sulfonic acid (“7,8-Dihydroxy-1-methylphenazine-3-sulfonic acid”) (II)

[0568] ##STR00025##

[0569] Structural formulae presented below according to the alternative nomenclature as defined by (“ . . . ”):

##STR00026##

[0570] A mixture of and 4,5-diamino-2-methylbenzene-1-sulfonic acid and 3,4-diamino-5-methylbenzene-1-sulfonic acid (18.8 g, 93 mmol, 1 eq) was suspended in 400 mL water and heated to 70° C. Under vigorous stirring 2,5-dihydroxy-1,4-benzoquinone (13.0 g, 93 mmol, 1 eq) was added portionwise. After one hour the reaction mixture was vacuum filtrated and the obtained solid dried under ambient atmosphere. The product was analyzed by HPLC. Final yield: 14.1 g, 49%.

Example 14: 4,4′-(phenazine-2,3-diyldiazanediyl)bis(4-oxobutanoic acid) (“4,4′-(phenazine-7,8-diyldiazanediyl)bis(4-oxobutanoic acid)”)

[0571] ##STR00027##

[0572] 2,3-Diaminophenazine (“7,8-Diaminophenazine”) (5.00 g, 23.3 mmol) was dissolved in pyridine (30 mL) and succinic anhydride (5.95 g, 58.3 mmol, 2.5 eq) was added in portions. After complete addition, the reaction mixture was stirred for 4 h at 50° C. Then, the solvent was removed under reduced pressure and the residue was extracted using an aqueous solution of KOH (1 M, 300 mL) and EtOAc (3×100 mL). The aqueous layer was acidified with aqueous citric acid solution (10% w/w). The acidic aqueous layer was extracted with EtOAc (3×100 mL). The combined organic layers were dried over Na.sub.2SO.sub.4, filtered, and concentrated under reduced pressure. The product was obtained as a red solid (2.90 g, 7.07 mmol, 30%).

II. Synthesis of Compounds of General Formulae (1) to (6)

Example 1: Synthesis of 7,8-Dihydroxyphenazine-2-sulfonic acid (“7,8-Dihydroxyphenazine-3-sulfonic acid”) (DHPS)

[0573] 2,5-Dihydroxy-1,4-benzoquinone (8.1 g, 57.4 mmol) was added to 150 mL boiling water, then 3,4-diaminobenezenesulfonic acid (10.8 g, 57.4 mmol) was added within a few minutes. The brown suspension was stirred at 95° C. for 18 h, cooled to room temperature and 150 mL acetone were added to the reaction mixture. After filtration the product was obtained as a brown solid (14.1 g, 84%).

Example 2: Synthesis of 7,8-Dihydroxyphenazine-2-carboxylic acid (“7,8-Dihydroxyphenazine-3-carboxylic acid”)

[0574] 2,5-Dihydroxy-1,4-benzoquinone (2.8 g, 20 mmol) was added to 100 mL boiling water, then 3,4-diaminobenzoic acid (3.1 g, 20 mmol) acid was added within a few minutes. The brown suspension was stirred at 95° C. for 18 h, cooled to room temperature and 150 mL acetone was added to the reaction mixture. After filtration the product was obtained in a quantitative yield.

Example 3: Synthesis of 2,3-Dihydroxyphenazine (“7,8-Dihydroxyphenazine”)

[0575] 2,5-Dihydroxy-1,4-benzoquinone (4.0 g, 28.5 mmol) was added to 100 mL boiling water, then 1,2-phenylenediamine (3.1 g, 28.5 mmol) was added within a few minutes. The brown suspension was stirred at 80° C. for 18 h, cooled to room temperature and 130 mL acetone were added to the reaction mixture. After filtration the product was obtained in a quantitative yield.

Example 4: Synthesis of Phenazine and 2,3-Dihydroxyphenazine (“7,8-Dihydroxyphenazine”)

[0576] 1,2-Dihydroxybenzene (0.3 g, 2.8 mmol) and 1,2-phenylenediamine (0.3 g, 2.8 mmol) were heated in a microwave vial to 210° C. for 15 minutes. The melt solidified, was cooled to room temperature and washed several times with water. The insoluble product (0.2 g) contained phenazine and 2,3-dihydroxyphenazine (“7,8-Dihydroxyphenazine”) according to HPLC and absorption spectroscopy. Washing the product mixture with 2 M aqueous sodium hydroxide (with an aqueous solution of sodium hydroxide (2 M)) yielded the desired phenazine.

[0577] By a specific embodiment, the “substituted phenazine compound” is not one of the compounds presented above resulting from the synthesis according to nay of Examples 1 to 4.

III. Flow Cell Experiments

FT-Cells (“Flow Through”):

[0578] For electrochemical characterization, a small laboratory cell was used. A graphite felt (with an area of 6 cm.sup.2, 6 mm in thickness, supplier: SGL Sigracell GFA 6EA) in combination with a bipolar plate (4.1 cm×4.1 cm, SGL Sigracell TF6) was employed as both the positive and negative electrode. A cation exchange membrane (630K or 620PE, supplier: fumatech) was used to separate the positive and negative electrolytes. The membrane was conditioned in 0.5 M Base (KOH/NaOH=50 mol %/50 mol %) for at least 150 h prior to each test. An anolyte volume of 12 mL was used for every experiment while the pH of the anolyte solution is adjusted using a 1:1 mixture of KOH/NaOH or solely KOH. The catholyte compositions are listed in table 1 and the catholyte was always employed in at least 1.05 fold stoichiometric excess in order to obtain charge limitation solely due to the phenazine electrolyte (see table 1). The catholyte volume for (IV) is 60 mL (0.4 M KOH; 0.4 M NaOH), for (III) 30 mL (0.2 M KOH and 0.2 M NaOH), and for (I) 20 mL (0.3 M KOH and 0.3 M NaOH). Both electrolytes were pumped by peristaltic pumps (Drifton BT100-1L, Cole Parmer Ismatec MCP and BVP Process IP 65) at a rate of 24 mL/min to the corresponding electrodes, respectively. The electrolyte reservoirs were purged with N.sub.2 gas for 1 h before start of charging and the inert atmosphere was maintained during the course of the experiments.

FB-Cells (“Flow By”):

[0579] For electrochemical characterization, a small laboratory cell was used. A cell assembly with pressed carbon electrodes (80% graphite-20% PP electrodes with carbon black surface, 41 mm×41 mm×0.72 mm, regularly rhombus shaped surface pattern with maximal height of structures of 1.4 mm) as both the positive and negative electrode was employed. The gap between the base electrode surface and membrane was 1.5 mm on each side of the cell. A cation exchange membrane (620PE, supplier: fumatech) was used to separate the positive and negative electrolytes. The membrane was conditioned in 0.5 M Base (KOH/NaOH=50 mol %/50 mol %) for at least 150 h prior to each test. An anolyte volume of 25 mL was used for every experiment while the pH of the anolyte solution was adjusted using a 1:1 mixture of KOH/NaOH or solely KOH. The catholyte composition is listed in table 1 and the catholyte was always employed in at least 1.05 fold stoichiometric excess in order to obtain charge limitation solely due to the phenazine electrolyte (see table 1). The catholyte volume for (IV) is 60 mL (0.4 M KOH; 0.4 M NaOH), for (III) 30 mL (0.2 M KOH and 0.2 M NaOH), and for (I) 20 mL (0.3 M KOH and 0.3 M NaOH). Alternatively, 25 mL of 0.5 M Phenazine (0.25M NaOH, 0.25M KOH) solution is used on the negative half-cell and 37 mL of a catholyte (0.34 M K.sub.4Fe(CN).sub.6, 0.34 M Na.sub.4Fe(CN).sub.6, 0.125 M NaOH, 0.125 M KOH) is used on the positive half-cell. The electrolytes were circulated by peristaltic pumps (Drifton BT100-1 L, Cole Parmer Ismatec MCP and BVP Process IP 65) at a rate of 72 mL/min, respectively. The electrolyte reservoirs were purged with N.sub.2 gas for 1 h before start of charging and the inert atmosphere was maintained during the experiments.

Electrochemical Tests:

[0580] Electrochemical testing was performed on a BaSyTec (BaSyTec GmbH, 89176 Asselfingen, Germany) or a Bio-Logic (Bio-Logic Science Instruments, Seyssinet-Pariset 38170, France) battery test system. For galvanostatic cycling, the cell was charged at a current density of or 20 mA/cm.sup.2 and discharged at the same current density with the in table 1 listed voltage cut-offs. A full potentiostatic cycle with voltage limitations of 1.7 (up to 1.7 V) or 1.5 V for charging and 1.0 or 0.8 or 0.7 V for discharging with <1.5 mA/cm.sup.2 current limitation was conducted in order to get maximum electrolyte exploitation and to calculate the accessible maximum charge per volume of used Phenazine electrolyte. The results are summarized in table 1.

TABLE-US-00001 OCV Used Charge [V] at voltage plateau Discharge RTE SOC = cut-offs Anolyte Phenazine [V] plateau [V] [%] 100% [V] Catholyte composition composition DHPS 1.47-1.60 1.31-1.15 75 1.52 1.7-1.0 0.54M K.sub.2Na.sub.2Fe(CN).sub.6 0.50M Phenazine pH = 13.1 pH = 13. IV 1.15-1.25 1.05-0.90 76 1.19 1.5-0.7 0.2M K.sub.4Fe(CN).sub.6 0.5M Phenazine 0.2M Na.sub.4Fe(CN).sub.6 2M KOH pH = 13.9 pH > 14 III 1.20-1.45 1.30-0.90 84 1.48 1.7-0.8 0.25M K.sub.4Fe(CN).sub.6 0.5M Phenazine 0.25M Na.sub.4Fe(CN).sub.6 0.75M NaOH pH = 13.6 0.75M KOH pH > 14 II 1.45-1.60 1.37-1.15 84 1.51 1.7-1.0 0.2M K.sub.4Fe(CN).sub.6 0.5M Phenazine 0.2M Na.sub.4Fe(CN).sub.6 0.25M NaOH pH = 13.9 0.25M KOH II 1.42-1.55 1.46-1.28 91 1.60 1.7-1.0 1.00M 0.87M Phenazine K.sub.1.6Na.sub.2.4Fe(CN).sub.6 pH = 13.9 pH = 14.0 I 1.30-1.41 1.26-1.14 82 1.45 1.5-0.7 0.3M K.sub.4Fe(CN).sub.6 0.7M Phenazine 0.3M Na.sub.4Fe(CN).sub.6 1.0M KOH pH = 13.8 1.0M NaOH pH = 14
Table 1: Cell tests of Phenazines Flow-Through Cells. RTE=Round Trip Efficiency, OCV=Open Circuit Voltage, SOC=State-of-charge.

[0581] The difference in plateaus [V] (range defined by (i) and (ii) as the lower and upper value: (i) difference of the upper (ultimate) charging value and initial discharging value (and (ii): initial charging value and the ultimate discharging value)) for DHPS is 0.29-0.32, which is advantageously low. Even lower “difference in plateaus” range values are observed for compounds (IV), (III), (II), and (I), respectively, all exhibiting a lower difference in plateaus of the following value ranges: 0.20-0.25 (IV), 0.15-0.30 (III) (which is characterized by a broader range due to its character as a mixture of structurally different compounds), 0.09-0.14 (II), 0.15-0.16 (I). The lower the value for the “difference in plateaus” range, the higher the energetic efficiency of the redox-active compound. The advantageous properties of the tested compounds, in particular of compounds (I), (II), (III) and (IV), is also represented by an RTE value of at least 75%. The RTE value is even higher for compounds (I), (II), (III), and (IV) than for DHPS.

[0582] The results of the flow cell experiments by using phenazine compound (II) and phenazine compound (III) are depicted by FIG. 1 (phenazine compound (III)), FIG. 2 and FIG. 3 (phenazine compound (II)). By these figures the initial charge plateau and the subsequent discharge plateau is presented.