Electrolyte balancing strategies for flow batteries

1. A redox flow battery comprising at least one electrochemical cell in fluid communication with a balancing cell, said balancing cell comprising:

a first and second half-cell chamber separated by a membrane,

wherein the first half-cell chamber comprises a first electrode in contact with an aqueous electrolyte of the at least one electrochemical cell;

wherein the second half-cell chamber comprises a second electrode, the second electrode abutting the membrane, and the second electrode comprising a catalyst for the generation of O 2 ;

wherein the second half-cell chamber does not contain an added electrolyte;

wherein the catalyst for the generation of O 2 is in fluid communication with water transported across the membrane from the aqueous electrolyte of the redox flow battery, and

wherein the balancing cell is configured to maintain a state of charge of the aqueous electrolyte of the electrochemical cell, and

wherein the aqueous electrolyte has a pH in a range of from 9 to 14.

2. The flow battery of claim 1 , wherein the aqueous electrolyte comprises a negative working electrolyte of the redox flow battery.

3. The flow battery of claim 1 , further comprising a porous medium located near or adjacent to the membrane in the first half-cell chamber.

4. The flow battery of claim 1 , wherein the membrane comprises a sulfonated perfluorinated polymer or co-polymer.

5. The flow battery of claim 4 , wherein the membrane comprises a sulfonated perfluorinated polymer or co-polymer of tetrafluoroethylene, optionally comprising perfluorovinyl ether.

6. The flow battery of claim 1 , wherein the membrane comprises an ionomer membrane.

7. The flow battery of claim 6 , wherein the ionomer membrane comprises a short side chain (SSC) copolymer of tetrafluoroethylene and a sulfonyl fluoride vinyl ether (SFVE) F 2 C═CF—O—CF 2 CF 2 —SO 2 F.

8. The flow battery of claim 7 , wherein the ionomer membrane is modified by precipitating particles therewithin, the particles comprising a metal, metal oxide, organometallic, polymeric material, or a combination thereof.

9. The flow battery of claim 1 , wherein the membrane comprises a bipolar membrane.

10. The flow battery of claim 9 , wherein the bipolar membrane comprises at least one cation exchange ionomer membrane and one anion exchange ionomer membrane.

11. The flow battery of claim 10 , wherein the bipolar membrane further comprises a metal oxide film sandwiched between the at least one cation exchange ionomer membrane and one anion exchange ionomer membrane, the metal oxide film being capable of catalyzing the dissociation of water upon the application of an electric potential thereto.

12. The flow battery of claim 1 , wherein the second electrode comprises a catalyst suitable for the electrochemical generation of oxygen from water.

13. The flow battery of claim 12 , wherein catalyst comprises a metal oxide.

14. The flow battery of claim 13 , wherein the metal oxide comprises an oxide of cobalt, iridium, iron, manganese, nickel, ruthenium, indium, tin, or a combination thereof.

15. The flow battery of claim 14 , wherein the second electrode comprises an oxide of iridium, an oxide of nickel, or an oxide of a nickel-iron alloy.

16. The flow battery of claim 12 , wherein the catalyst comprises an allotrope of carbon.

17. The flow battery of claim 2 , wherein the negative working electrolyte of the flow battery comprises a compound comprising Al, Ca, Ce, Co, Cr, Fe, Mg, Mn, Mo, Si, Sn, Ti, V, W, Zn, or Zr.

18. The flow battery of claim 17 , wherein the negative working electrolyte of the flow battery comprises a coordination compound of titanium.

19. The flow battery of claim 1 , wherein the first half-cell chamber is configured as a flow-through cell.

20. An energy storage system comprising the flow battery of claim 1 .