Fe—Cr redox flow battery systems including a balance arrangement and methods of manufacture and operation

1. A system, comprising

a redox flow battery system comprising

an anolyte having chromium ions in solution,

a catholyte having iron ions in solution,

a first half-cell comprising a first electrode in contact with the anolyte,

a second half-cell comprising a second electrode in contact with the catholyte, and

a first separator separating the first half-cell from the second half-cell, and

a balance arrangement comprising

a balance electrolyte comprising vanadium ions in solution,

a third half-cell comprising a third electrode in contact with the anolyte or the catholyte,

a fourth half-cell comprising a fourth electrode in contact with the balance electrolyte, and

a reductant in the balance electrolyte or introducible to the balance electrolyte for reducing dioxovanadium ions.

2. The system of claim 1 , further comprising a second separator separating the third half-cell from the fourth half-cell.

3. The system of claim 1 , further comprising a potential source coupled or coupleable to the third and fourth electrodes to provide a potential between the third and fourth electrodes.

4. The system of claim 1 , further comprising

an intermediate electrolyte comprising any combination of either a) V 3+ and V 2+ ions or b) Fe 3+ and Fe 2+ ions;

a fifth half-cell comprising a fifth electrode in contact with intermediate electrolyte,

a second separator between the third half-cell and the fifth half-cell,

a sixth half-cell comprising a sixth electrode in contact with the intermediate electrolyte, and

a third separator between the fourth half-cell and the sixth half-cell.

5. The system of claim 4 , further comprising at least one potential source coupled or coupleable to a) the third and fifth electrodes to provide a potential between the third and fifth electrodes and b) a) the fourth and sixth electrodes to provide a potential between the fourth and sixth electrodes.

6. The system of claim 1 , wherein the third half-cell is in contact with the catholyte.

7. The system of claim 1 , wherein the third half-cell is in contact with the anolyte.

8. The system of claim 1 , wherein the reductant comprises an organic compound.

9. The system of claim 1 , wherein the reductant comprises a sugar, carboxylic acid, aldehyde, or alcohol.

10. The system of claim 1 , wherein the reductant comprises hydrogen gas.

11. The system of claim 1 , wherein the reductant comprises fructose, glucose, or sucrose.

12. The system of claim 1 , wherein the system is configured to operate the balance arrangement continuously during operation of the redox flow battery system.

13. The system of claim 1 , wherein the system is configured to operate the balance arrangement intermittently or periodically during operation of the redox flow battery system.

14. The system of claim 1 , wherein the system is configured to operate the balance arrangement independent of the redox flow battery system.

15. The system of claim 1 , wherein the balance arrangement and the redox flow battery system are integrated and utilize at least one common component.

16. A method of operating the system of claim 1 , the method comprising:

oxidizing the vanadium ions in the balancing electrolyte to dioxovanadium ions to produce hydrogen ions; and

regenerating the vanadium ions by reducing the dioxovanadium ions using the reductant.

17. The method of claim 16 , wherein the reductant comprises an organic compound.

18. The method of claim 16 , wherein the reductant comprises a sugar, carboxylic acid, aldehyde, or alcohol.

19. The method of claim 16 , wherein regenerating the vanadium ions comprises adding the reductant to a balance tank of the balance arrangement, wherein the balance tank contains a portion of the balance electrolyte.

20. The method of claim 16 , wherein regenerating the vanadium ions comprises adding the reductant intermittently or periodically to the balance electrolyte.