Apparatus and method for determining state of charge in a redox flow battery via limiting currents

Patent metadata

Field	Value
Publication number	US-11929528-B2
Application number	US-202016997403-A
Country	US
Kind code	B2
Filing date	Aug 19, 2020
Priority date	Nov 1, 2013
Publication date	Mar 12, 2024
Grant date	Mar 12, 2024

Abstract

The present invention relates to methods and apparatuses for determining the ratio of oxidized and reduced forms of a redox couple in solution, each method comprising: contacting first and second stationary working electrodes and first and second counter electrode to the solution; applying a first potential at the first stationary working electrode and a second potential at the second stationary working electrode relative to the respective counter electrodes and measuring first and second constant currents for the first and second stationary working electrodes, respectively; wherein the first and second constant currents have opposite signs and the ratio of the absolute values of the first and second constant currents reflects the ratio of the oxidized and reduced forms of the redox couple in solution. When used in the context of monitoring/controlling electrochemical cells, additional embodiments include those further comprising oxidizing or reducing the solution.

First claim

What is claimed:

1. A method of determining the ratio of the oxidized and reduced forms of a redox couple in solution, said method comprising:
(a) contacting a first stationary working electrode and a first counter electrode to the solution;
(b) contacting a second stationary working electrode and a second counter electrode to the solution;
(c) applying a first potential at the first stationary working electrode relative to the first counter electrode and measuring a first constant current for the first stationary working electrode; and
(d) applying a second potential at the second stationary working electrode relative to the second counter electrode and measuring a second constant current for the second stationary working electrode;
wherein the first and second constant currents have opposite signs; and
wherein the ratio of the absolute values of the first and second constant currents reflects the ratio of the oxidized and reduced forms of the redox couple in solution.

2. The method of claim 1 , wherein the first and second potentials are applied simultaneously.

3. The method of claim 1 , wherein the first and second potentials are of substantially the same magnitude but opposite in sign.

4. The method of claim 1 , wherein the first and second stationary working electrodes and the first and second counter electrodes each have a surface area contacting the solution, and each of the first and second stationary working electrode surface areas is less than that of the first and second counter electrodes.

5. The method of claim 4 , wherein the surface areas of the first and second stationary working electrodes are each less than about 20% of the surface areas of the first and second counter electrodes, respectively.

6. The method of claim 1 , wherein the first and second stationary working electrodes and the first and second counter electrodes each have a surface area contacting the solution, and each surface area of the first and second stationary working electrodes is substantially the same.

7. The method of claim 1 , wherein the ratio of the oxidized and reduced forms of the redox couple are in a range of from about 5:95 to 95:5.

8. The method of claim 1 , wherein the ratio of the oxidized and reduced forms of the redox couple are in a range of from about 20:80 to 80:20.

9. The method of claim 1 , wherein the redox couple comprises a metal or metalloid of Groups 2-16, including the lanthanide and actinide elements, or a coordination compound thereof.

10. The method of claim 1 , wherein the redox couple is a reversible redox couple.

11. The method of claim 1 , wherein the redox couple is a quasi-reversible redox couple.

12. The method of claim 1 , wherein the solution is an aqueous solution.

13. The method of claim 1 , wherein the solution is a non-aqueous solution.

14. The method of claim 1 , wherein the solution is moving.

15. The method of claim 1 , wherein at least one of the stationary working electrodes or at least one of the counter electrodes comprises an allotrope of carbon.

16. The method of claim 1 , wherein a constancy of at least one of the first or second constant currents is characterized by a change of less than 0.1% over one second or less than 1% over ten seconds.

17. The method of claim 1 , wherein the solution is contained within a half-cell fluidic loop of an operating flow battery cell or other operating electrochemical cell, said operating electrochemical cell generating or storing electrical energy.

18. The method of claim 1 , wherein the ratio of oxidized and reduced forms of the redox couple in solution based on the ratio of the absolute values of the first and second constant currents is determined by applying an experimentally derived correction factor.

19. A method of maintaining an electrochemical cell, said cell having at least one half-cell comprising oxidized and reduced forms of a redox couple in solution, said method comprising:
determining the ratio of the oxidized and reduced forms of a redox couple in solution according to claim 1 ; and
(e) oxidizing or reducing the solution, so as to alter a balance of the oxidized and reduced forms of the redox couple in solution, to a degree dependent on the ratio of the absolute values of the first and second constant currents.

20. The method of claim 19 , wherein the first and second potentials are applied simultaneously.

21. The method of claim 19 , wherein the first and second potentials are of substantially the same magnitude but opposite in sign.

22. The method of claim 21 , wherein the surface areas of the first and second stationary working electrodes are each less than about 20% of the surface areas of the first and second counter electrodes, respectively.

23. The method of claim 19 , wherein the first and second stationary working electrodes and the first and second counter electrodes each have a surface area contacting the solution, and each of the first and second stationary working electrode surface areas is less than that of the first and second counter electrodes.

24. The method of claim 19 , wherein the first and second stationary working electrodes and the first and second counter electrodes each have a surface area contacting the solution, and each surface area of the first and second stationary working electrodes is substantially the same.

25. The method of claim 19 , wherein the ratio of the oxidized and reduced forms of the redox couple are in a range of from about 5:95 to 95:5.

26. The method of claim 19 , wherein the ratio of the oxidized and reduced forms of the redox couple are in a range of from about 20:80 to 80:20.

27. The method of claim 19 , wherein the redox couple comprises a metal or metalloid of Groups 2-16, including the lanthanide and actinide elements, or a coordination compound thereof.

28. The method of claim 19 , wherein the redox couple is a reversible redox couple.

29. The method of claim 19 , wherein the redox couple is a quasi-reversible redox couple.

30. The method of claim 19 , wherein the solution is an aqueous solution.

31. The method of claim 19 , wherein the solution is a non-aqueous solution.

32. The method of claim 19 , wherein the solution is moving.

33. The method of claim 19 , wherein at least one of the stationary working electrodes or at least one of the counter electrodes comprises an allotrope of carbon.

34. The method of claim 19 , wherein a constancy of at least one of the first or second constant currents is characterized by a change of less than 0.1% over one second or less than 1% over ten seconds.

35. The method of claim 19 , wherein the solution is contained within a half-cell fluidic loop of an operating flow battery cell or other operating electrochemical cell, said operating electrochemical cell generating or storing electrical energy.

36. The method of claim 19 , wherein oxidizing or reducing the solution is performed electrochemically.

37. The method of claim 36 , wherein oxidizing or reducing the solution takes place in a rebalancing sub-system within a half-cell fluidic loop of an electrochemical cell.

38. The method of claim 19 , wherein the ratio of oxidized and reduced forms of the redox couple in solution ba

Assignees

• Lockheed Martin Energy Llc

Inventors

• King Evan R
• Duffey Kean
• Morris-Cohen Adam
• Goeltz John
• Reece Steven Y

Classifications

• H01M8/04194 Primary

  Concentration measuring cells · CPC title

• H01M4/96

  Carbon-based electrodes · CPC title

• H01M8/04201

  Reactant storage and supply, e.g. means for feeding, pipes · CPC title

• H01M8/0444

  Concentration; Density (H01M8/04492 takes precedence) · CPC title

• H01M8/04791

  Concentration; Density (H01M8/04828 takes precedence) · CPC title