Materials for use in an aqueous organic redox flow battery

1. A redox flow battery comprising:

a first redox active material; and

a second redox active material comprising a viologen or a salt thereof, wherein the viologen has formula (VI):

or a salt thereof, wherein:

L 3 and L 4 are each independently selected from the group consisting of bond, C 1 -C 12 alkylenyl, C 1 -C 12 alkenylenyl, C 1 -C 12 alkynylenyl, and C 1 -C 4 alkylenyl-(OCH 2 CH 2 ) m ;

R 11 is selected from the group consisting of, —NO 2 , —OR g , —N(R g ) q , —C(O)R g , —C(O)OR g , —S(O) q , —PO 3 , —S(O) q R g , —S(O) q OR g , —OP(O)(OR g ) 2 , —OCH 3 , —(CR g 2 ) m CN, substituted aryl, and substituted heteroaryl;

R 12 is selected from the group consisting of —CH 3 , —NO 2 , —OR g , —C(O)R g , —C(O)OR g , —S(O) q , —PO 3 , —S(O) q R g , —S(O) q OR g , —OP(O)(OR g ) 2 ; —OCH 3 , —(CR g 2 ) m CN, substituted aryl, and substituted heteroaryl;

R g , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, alkyl-N(R h ) q , alkyl-S(O) q , an oxygen protecting group, and a nitrogen protecting group;

R h , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, an oxygen protecting group, and a nitrogen protecting group; and

q, at each occurrence, is independently 2 or 3.

2. The redox flow battery of claim 1 , wherein the viologen has formula (VI-a):

or a salt thereof, wherein:

R 13 is selected from the group consisting of —N(R g ) q , —S(O) q , —PO 3 , —S(O) q R g , —(OCH 2 CH 2 ) m —OCH 3 , and substituted aryl;

R 14 is selected from the group consisting of —CH 3 , —S(O) q , —PO 3 , —S(O) q R g , —(OCH 2 CH 2 ) m —OCH 3 , and substituted aryl;

R g , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, alkyl-N(R h ) q , alkyl-S(O) q , an oxygen protecting group, and a nitrogen protecting group;

R h , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, an oxygen protecting group, and a nitrogen protecting group;

q, at each occurrence, is independently 2 or 3; and

c, at each occurrence, is independently 0, 1, 2 or 3.

3. The redox flow battery of claim 1 , wherein the viologen has formula (VI-b):

wherein:

R 13 is selected from the group consisting of —N(R g ) q , —S(O) q , —PO 3 , —S(O) q R g , —(OCH 2 CH 2 ) m —OCH 3 , and substituted aryl;

R 14 is selected from the group consisting of —CH 3 , —S(O) q , —PO 3 , —S(O) q R g , —(OCH 2 CH 2 ) m —OCH 3 , and substituted aryl;

R g , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, alkyl-N(R h ) q , alkyl-S(O) q , an oxygen protecting group, and a nitrogen protecting group;

R h , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, an oxygen protecting group, and a nitrogen protecting group;

V, at each occurrence, is independently Na + , K + , Li + , NR i 4 + , F − , Cl − , Br − , I − , SO 4 2− , OH − , CO 3 2− , ClO 4 − , H 2 PO 4 − , HPO 4 2− , PO 4 3− , NO 3 − , N 3 − , CN − , N(CN) 2 − , SCN − or a combination thereof;

R i , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, and heteroaryl;

q, at each occurrence, is independently 2 or 3;

r is 1, 2, 3 or 4;

u is 1, 2, 3 or 4; and

c, at each occurrence, is independently 0, 1, 2 or 3.

4. The redox flow battery of claim 3 , wherein:

R 13 is SO 3 − , —(OCH 2 CH 2 ) m —OCH 3 , or substituted aryl;

R 14 is SO 3 − , —(OCH 2 CH 2 ) m —OCH 3 , or substituted aryl;

V, at each occurrence, is independently Na + , K + , Cl − , Br − or a combination thereof;

r is 2, 3 or 4;

u is 1; and

c, at each occurrence, is independently 1, 2 or 3.

5. The redox flow battery of claim 1 , wherein the viologen is selected from the group consisting of

6. The redox flow battery of claim 1 , wherein the viologen has formula (VII):

or a salt thereof, wherein:

L 5 and L 6 are each independently selected from the group consisting of bond, C 1 -C 12 alkylenyl, C 1 -C 12 alkenylenyl, C 1 -C 12 alkynylenyl; and C 1 -C 4 alkylenyl-(OCH 2 CH 2 ) j ,

R 15 and R 16 are each independently selected from the group consisting of OR j , —C(O)OR j , —S(O) j , —PO 3 , —S(O) j R j , —S(O) j OR j , —OP(O)(OR j ) 2 , —(CR j 2 ) j CN, substituted aryl, and substituted heteroaryl;

R j , at each occurrence, is independently selected from the group consisting of alkyl-S(O) j , and an oxygen protecting group; and

j, at each occurrence, is independently 2 or 3.

7. The redox flow battery of claim 6 , wherein the viologen is selected from the group consisting of

or salts thereof.

8. The redox flow battery of claim 1 , wherein the first redox active material comprises − [Fe(CN) 6 ] 3+/2+ , I 3 − /I − , Br 2 /Br − , S 4 − /S 2 , KBr, NaBr, NH 4 Br, KI, NaI, NH 4 I, FeCl 2 , FeBr 2 , Ce 4+3+ , Mn 3+/2+ , PbO 2 /PbSO 4 , quinines, anthraxquinines, K 4 [Fe(CN) 6 ], N 4 [Fe(CN) 6 ], (NH 4 ) 4 [Fe(CN) 6 ], V 5+4+ , (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl (TEMPO), a derivative of TEMPO, or a combination thereof.

9. The redox flow battery of claim 8 , wherein the derivative of TEMPO has formula (VIII-a):

wherein:

R 19 , R 20 , R 21 , R 22 and R 23 are each independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, —CN, —NO 2 , —OR k , —SR k , -alkyl-N(R k ) w , —N(R k ) w , —C(O)R k , —C(O)OR k , —S(O) w R k , —S(O) w OR k , and —OP(O)(OR k ) 2 ;

R k , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, alkyl-N(R l ) w , an oxygen protecting group, and a nitrogen protecting group;

R l , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, an oxygen protecting group, and a nitrogen protecting group;

X 2 − is Cl − , Br − , I − , SO 4 2− , —NO 3 − or a combination thereof;

n 2 is 1, 2, 3, 4, or 5; and

w, at each occurrence, is independently 2 or 3.

10. The redox flow battery of claim 8 , wherein the derivative of TEMPO has formula (VIII-b):

wherein:

R 24 , R 25 , R 26 , R 27 and R 28 are each independently selected from the group consisting of hydrogen, halogen, alkyl, cycloalkyl, heterocyclyl, alkylaryl, aryl, heteroaryl, —CN, —NO 2 , —OR m , —SR m , -alkyl-N(R m ) q , —N(R m ) q , —C(O)R m , —C(O)OR m , —S(O) q R m , —S(O) q OR m , and —OP(O)(OR m ) 2 ;

R m , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, alkyl-N(R n ) q , an oxygen protecting group, and a nitrogen protecting group;

R n , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, heteroaryl, an oxygen protecting group, and a nitrogen protecting group;

X 3 + is H + , Li + , Na + , K + , NH 4 + or a combination thereof;

n 3 is 1, 2, 3, 4, or 5; and

w, at each occurrence, is independently 2 or 3.

11. The redox flow battery of claim 8 , wherein the derivative of TEMPO is selected from the group consisting of 4-trimethylammonium-(2,2,6,6-Tetramethylpiperidin-1-yl)oxy (4-N Me -TEMPO), 4-dimethyl(propyl-3-N,N,N,-trimethylammonium)-(2,2,6,6-Tetramethylpiperidin-1-yl)oxy ((4-N NPr -TEMP 0), 4-hyoxyl-ammonium-(2,2,6,6-Tetramethylpiperidin-1-yl)oxy (4-OHTEMPO), 4-sulfonate-(2,2,6,6-Tetramethylpiperidin-1-yl)oxy (4-S03-TEMPO), 4-amino-(2,2,6,6-Tetramethylpiperidin-1-yl)oxy (4-NH 2 -TEMPO), and a combination thereof.

12. The redox flow battery of claim 1 , further comprising:

a first aqueous electrolyte;

a second aqueous electrolyte; and

a separator between the first and second aqueous electrolytes.

13. The redox flow battery of claim 1 , wherein the second redox active material is present in the second aqueous electrolyte at a concentration of ≥0.1 M.

14. The redox flow battery of claim 12 , further comprising a first electrode in contact with the first aqueous electrolyte and a second electrode in contact with the second aqueous electrolyte.

15. The redox flow battery of claim 12 , wherein the separator is a porous separator.

16. The redox flow battery of claim 12 , wherein the separator is an anion exchange membrane or a cation exchange membrane.

17. The redox flow battery of claim 12 , wherein the first and second aqueous electrolytes each independently comprise a salt having the formula (IV):

A-B  (IV),

wherein:

A is Na + , K + , Li + , NR c 4 + , pyridinium, pyrrolidium, or imidazolium;

R c , at each occurrence, is independently selected from the group consisting of hydrogen, alkyl, cycloalkyl, heterocyclyl, aryl, and heteroaryl; and

B is halide anion, SO 4 2− , OH − , CO 3 2− , ClO 4 − , H 2 PO 4 − , HPO 4 2− , PO 4 3− , NO 3 − , N 3 − , CN − , —N(CN) 2 − , or SCN − .

18. The redox flow battery of claim 12 , wherein the first and second electrolytes each independently comprise NaCl, KCl, or NH 4 Cl.

19. The redox flow battery of claim 18 , wherein the first and second aqueous electrolytes each independently comprise between about 0.5 M to about 5 M NaCl, KCl, or NH 4 Cl.

20. The redox flow battery of claim 12 , further comprising:

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

a second circulation loop comprising a second storage tank containing the second aqueous electrolyte, piping for transporting the second aqueous electrolyte, a chamber in which the 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.

21. A method of storing energy, comprising applying a potential difference across the first and second electrode of the redox flow battery of claim 14 , wherein the first redox active material is oxidized.

22. A method of releasing energy, comprising applying a potential difference across the first and second electrode of the redox flow battery of claim 14 , wherein the first redox active material is reduced.