HIGH SOLUBILITY IRON HEXACYANIDES

• US 20140051003A1
• Filed: 05/06/2013
• Published: 02/20/2014
• Est. Priority Date: 08/15/2012
• Status: Active Grant

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Sun Catalytix Corporation (Martin Marietta Corporation)
• Inventors: ESSWEIN, ARTHUR J., GOELTZ, JOHN, AMADEO, DESIREE
• Granted Patent: US 9,929,425 B2
• Time in Patent Office: Days
• US Class Current: 429/452
• CPC Class Codes: H01M 2300/0002 Aqueous electrolytes
• CPC Class Codes: H01M 8/08 Fuel cells with aqueous electrolytes
• CPC Class Codes: H01M 8/188 by recharging of redox couples containing fluids; Redox flow type batteries
• CPC Class Codes: H01M 8/20 Indirect fuel cells, e.g. fuel cells with redox couple being irreversible H01M8/18 takes precedence
• CPC Class Codes: H01M 8/222 Fuel cells in which the fuel is based on compounds containing nitrogen, e.g. hydrazine, ammonia
• CPC Class Codes: Y02E 60/36 Hydrogen production from non-carbon containing sources, e.g. by water electrolysis
• CPC Class Codes: Y02E 60/50 Fuel cells

Abstract

Stable solutions comprising high concentrations of charged coordination complexes, including iron hexacyanides are described, as are methods of preparing and using same in chemical energy storage systems, including flow battery systems. The use of these compositions allows energy storage densities at levels unavailable by other iron hexacyanide systems.

Claims

1. An aqueous solution, comprising:

(a) an iron hexacyanide complex; and

(b) at least two different alkali metal counterions;

the concentration of said iron hexacyanide complex, at a given temperature, being higher than can be obtained when said iron hexacyanide complex is in the presence of any single one of the at least two different alkali metal counterions.

2. The solution of claim 1, wherein the solution is stable to precipitation at a temperature in the range of from about −

10°

C. to about 60°

C.

3. The solution of claim 1, wherein the at least two different alkali metal counterions include Na⁺ and K⁺.

4. The solution of claim 1, wherein two of the at least two different alkali metal counterions are present at a molar ratio in the range of from about 1:

10 to about 10;

1, with respect to one another.

5. The solution of claim 4, wherein the different alkali metal cations are Na⁺ and K⁺ cations, present in a ratio of Na⁺:

K⁺ in the range of from about 1;

5 to about 5;

1.

6. The solution of claim 1, wherein the solution is alkaline.

7. The solution of claim 1, wherein the concentration of the iron hexacyanide complex is at least about 0.8 M.

8. The solution of claim 1, wherein the concentration of the iron hexacyanide complex is at least about 1 M,

9. The solution of claim 1, wherein the concentration of the iron hexacyanide complex is at least about 1.2 M.

10. The solution of claim 1, wherein the concentration of said iron hexacyanide complex in the solution is at least 25% higher than can be obtained when said iron hexacyanide complex is in the presence of any single one of the at least two different counterions.

11. A method of preparing an aqueous solution of claim 1 comprising iron(II) hexacyanide (Fe(CN)₆⁴⁻

), said method comprising dissolving sufficient amounts of Na₄[Fe(CN)₆] and K₄[Fe(CN)₆] in an amount of aqueous solvent, so as to provide a concentration of Fe(CN)₆⁴⁻

in said solution, at a given temperature, that exceeds the concentration of Fe(CN)₆⁴⁻

in either a saturated solution of Na₄[Fe(CN)₆] or a saturated solution of K₄[Fe(CN)₆], at the same temperature.

12. The method of claim 11, wherein the aqueous solution is alkaline.

13. The solution of claim 1 comprising iron(II) hexacyanide [Fe(CN)₆⁴⁻

], the concentration of Fe(CN)₆⁴⁻

in said solution, at a given temperature and pH, being higher than the concentration of Fe(CN)₆⁴⁻

in either a saturated aqueous alkaline solution of Na₄[Fe(CN)₆] or a saturated aqueous alkaline solution of K₄[Fe(CN)₆], at the same temperature and pH.

14. The solution of claim 1, further comprising a viscosity modifier or a wetting agent.

15. The solution of claim 1, further comprising a buffering agent and/or a supporting electrolyte.

16. The solution of claim 1, further comprising another species which is redox active over a range of from about −

0.8 V to about 1.8 V, vs. RHE.

17. The solution of claim 1 consisting essentially of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 20 A-h/L.

18. The solution of claim 17 consisting essentially of an alkaline solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 30 A-h/L.

19. An electrochemical cell having at least one half-cell comprising a solution of claim 1.

20. The electrochemical cell of claim 19, wherein the at least one half-cell comprises a solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 20 A-h/L.

21. The electrochemical cell of claim 20, wherein the at least one half-cell consists essentially of an alkaline solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 20 A-h/L.

22. The electrochemical cell of claim 19, wherein the at least one half-cell comprises a solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 30 A-h/L.

23. The electrochemical cell of claim 22, wherein the at least one half-cell consists essentially of an alkaline solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 30 A-h/L.

24. The electrochemical cell of claim 19, wherein the cell is a flow battery cell.

25. An energy storage system comprising a series array of electrochemical cells, wherein at least one electrochemical cell is an electrochemical cell of claim 19.

26. The energy storage system of claim 25, wherein the at least one half-cell comprises a solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 20 A-h/L.

27. The energy storage system of claim 26, wherein the at least one half-cell consists essentially of an alkaline solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 20 A-h/L.

28. The energy storage system of claim 25, wherein the at least one half-cell comprises a solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 30 A-h/L.

29. The energy storage system of claim 28, wherein the at least one half-cell consists essentially of an alkaline solution of iron(II) hexacyanide, iron(III) hexacyanide, or a mixture of iron(II) hexacyanide and iron(III) hexacyanide capable of exhibiting a theoretical charge/discharge density of at least about 30 A-h/L.

30. The energy storage system of claim 25, wherein at least one of the electrochemical cells is a flow battery cell.