Materials for use with aqueous redox flow batteries and related methods and systems

1. A redox flow battery comprising:

a first aqueous electrolyte comprising a first type of redox active material;

a second aqueous electrolyte comprising a second type of redox active material;

wherein the first type of redox active material comprises a quinoxaline moiety, a salt of the quinoxaline moiety, or a mixture thereof;

wherein the quinoxaline moiety is selected from the group consisting of a quinoxaline dimer, a quinoxaline trimer, a quinoxaline tetramer, a quinoxaline polymer, and a quinoxaline dendrimer, or a combination thereof.

2. The battery of claim 1 , further comprising a first electrode in contact with the first aqueous electrolyte and a second electrode in contact with the second aqueous electrolyte.

3. A method of storing energy, comprising applying a potential difference across the first and second electrode of a flow battery of claim 2 , wherein the first active material is reduced.

4. A method of releasing energy, comprising applying a potential difference across the first and second electrode of a flow battery of claim 2 , wherein the first type of active material is oxidized.

5. The battery of claim 1 , further comprising a separator between the first aqueous electrolyte and second aqueous electrolyte.

6. The battery of claim 5 , wherein the separator comprises a porous separator.

7. The battery of claim 5 , wherein the separator comprises a cation exchange membrane.

8. The battery of claim 7 , wherein the cation exchange membrane is a sulfonate containing fluoropolymer.

9. The battery of claim 5 , wherein the separator comprises a cation conducting ceramic, cation conducting zeolite, or cation conducting glass.

10. The battery of claim 1 , wherein the first aqueous electrolyte has a pH between about 7 and about 10, or between about 10 and about 12, or between about 12 and about 14.

11. The battery of claim 1 , wherein the first type of redox active material is present in the first aqueous electrolyte in a concentration of between about 0.5 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.

12. The battery of claim 1 , wherein the quinoxaline moiety comprises a quinoxaline dimer or quinoxaline trimer.

13. The battery of claim 1 , wherein the quinoxaline moiety comprises Formula (II):

or a salt thereof, wherein:

each R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is independently hydrogen, halogen, optionally substituted alkyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —CN, —NO 2 , —OR a , —N(R a ) 2 , —C(═O)R a , —C(═O)OR a , —S(═O) 2 R a , or —S(═O) 2 OR a ;

and optionally the two R 2 groups are joined together to be L 1 ;

and each L 1 is independently a direct bond, an optionally substituted alkyl chain, optionally substituted heteroalkyl chain, optionally substituted carbocyclyl ring, optionally substituted heterocyclyl ring, optionally substituted aryl ring, or optionally substituted heteroaryl ring.

14. The battery of claim 1 , wherein the quinoxaline moiety comprises Formula (III-A):

or a salt thereof, wherein:

each R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is independently hydrogen, halogen, optionally substituted alkyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —CN, —NO 2 , —OR a , —N(R a ) 2 , —C(═O)R a , —C(═O)OR a , —S(═O) 2 R a , or —S(═O) 2 OR a ;

and optionally the two R 2 groups are joined together to be L 1 ;

and each L 1 is independently a direct bond, an optionally substituted alkyl chain, optionally substituted heteroalkyl chain, optionally substituted carbocyclyl ring, optionally substituted heterocyclyl ring, optionally substituted aryl ring, or optionally substituted heteroaryl ring.

15. The battery of claim 1 , wherein the quinoxaline moiety comprises Formula (III-A):

or a salt thereof, wherein:

each R 1 , R 2 , R 3 , R 4 , R 5 , and R 6 is independently hydrogen, halogen, optionally substituted alkyl, optionally substituted carbocyclyl, optionally substituted heterocyclyl, optionally substituted aryl, optionally substituted heteroaryl, —CN, —NO 2 , —OR a , —N(R a ) 2 , —C(═O)R a , —C(═O)OR a , —S(═O) 2 R a , or —S(═O) 2 OR a ;

L 2 is an optionally substituted alkyl chain, optionally substituted heteroalkyl chain, optionally substituted carbocyclyl ring, optionally substituted heterocyclyl ring, optionally substituted aryl ring, or optionally substituted heteroaryl ring,

and optionally any two R 2 groups are joined to form a direct bond, an optionally substituted alkyl chain, optionally substituted heteroalkyl chain, optionally substituted carbocyclyl ring, optionally substituted heterocyclyl ring, optionally substituted arylene ring, or optionally substituted heteroaryl ring linker.

16. The battery of claim 1 , wherein the second type of redox active material comprises a hexacyanoiron complex, a quinone, a hydroquinone, or an organic dye, a salt of any one of these compounds, or a mixture thereof.

17. The battery of claim 16 , wherein the second type of redox active material comprises ferrocyanide, ferricyanide, 1,2-dihydroxy-3,5-benzenedisulfonate, 1,2,4-trihydroxy-3,5-benzenedisulfonate, or indigo carmine, a salt of any one of these compounds, or a mixture thereof.

18. The battery of claim 1 , further comprising:

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

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

control hardware and software.

19. The battery of claim 12 , wherein the second type of redox active material comprises a hexacyanoiron complex, a quinone, a hydroquinone, or an organic dye, a salt of any one of these compounds, or a mixture thereof.

20. A method of storing energy, comprising applying a potential difference across the first and second electrode of a flow battery of claim 19 , wherein the first active material is reduced.

21. The battery of claim 1 , wherein the quinoxaline moiety is a quinoxaline tetramer or a salt thereof.

22. The battery of claim 1 , wherein the quinoxaline moiety is a quinoxaline polymer or a salt thereof.

23. The battery of claim 1 , wherein the quinoxaline moiety is a quinoxaline dendrimer or a salt thereof.