Polyoxometalate active charge-transfer material for mediated redox flow battery

1. A redox flow battery comprising:

a half-cell electrode chamber coupled to an electrode, wherein the half-cell electrode chamber comprises a first redox-active mediator and a second redox-active mediator, wherein the first redox-active mediator and the second redox-active mediator are circulated through the half-cell electrode chamber into a container comprising an active charge-transfer material, wherein the active charge-transfer material comprises a redox potential between a redox potential of the first redox-active mediator and a redox potential of the second redox-active mediator, and wherein the active charge-transfer material is a polyoxometalate or derivative thereof; and

a separator coupled to the half-cell electrode chamber.

2. The redox flow battery of claim 1 , wherein the active charge-transfer material comprises an additional metal to tune the redox potential of the active charge-transfer material.

3. The redox flow battery of claim 2 , wherein the additional metal is selected from metals in group 3B, 4B, 5B, or 6B.

4. The redox flow battery of claim 1 , wherein the first, second, or first and second redox-active mediator is selected from redox-active, electrochemically reversible, cyclic or heterocylic organic compounds.

5. The redox flow battery of claim 1 , wherein the first, second or first and second redox-active mediator has a structure corresponding to one of formula 1-6 below:

wherein the aromatic or cyclic structures in each formula are optionally substituted with electron withdrawing or donating groups.

6. The redox flow battery of claim 5 , wherein the electron withdrawing or donating groups are present and are selected from the group consisting of:

groups having the formula —XR n , wherein X is O, S, or N, wherein each R is independently selected from a linear, branched, cyclic, aromatic alkyl group having 1-50 carbon atoms, or hydrogen, and R is optionally functionalized with a functional group including a halogen, O, S, or N; and n ranges from 0 up to a valence of 3;

—NO 2 , —CN, —CO 2 R, -halogens, halogenated hydrocarbons, —CF 3 , —COH, —SO 3 R, —NH 3-n R n , —O 2 CR, amide, —OR, —NH 2-m R m , and saturated or unsaturated linear, branched, cyclic or aromatic alkyl groups, wherein R and n are as defined above, and m ranges from 0 to 2; and combinations thereof.

7. The redox flow battery of claim 1 , wherein the active charge-transfer material is in particulate form in a packed bed in the container.

8. The redox flow battery of claim 1 , wherein the redox potential of the active charge-transfer material is within 200 mV of the redox potentials of the first and second redox-active mediators.

9. The redox flow battery of claim 1 , wherein the volumetric capacity of the half-cell is 90 Ah/L to 400 Ah/L.

10. The redox flow battery of claim 1 , wherein the half-cell electrode chamber is a cathode cell chamber and the electrode is a cathode, and the battery further comprising an anode.

11. The redox flow battery of claim 1 , wherein the half-cell electrode chamber is an anode cell chamber and the electrode is an anode, and the battery further comprising a cathode.

12. The redox flow battery of claim 1 , wherein a voltage of a single cell of the battery ranges from 1 to 5 volts.

13. A method for storing, releasing, or storing and releasing electrical energy by mediating electrochemical reactions in at least one of a first or second cycle, the method comprising:

in the first cycle:

circulating a first redox-active mediator and a second redox-active mediator through a half-cell electrode chamber into a container comprising an active charge-transfer material;

reducing the first redox-active mediator in the container and oxidizing the active charge-transfer material;

circulating the reduced first redox-active mediator and the second redox-active mediator through the container comprising the active charge-transfer material to the half-cell electrode chamber; and

oxidizing the reduced first redox-active mediator and reducing an electrode surface; and

in the second cycle:

circulating the first redox-active mediator and the second redox-active mediator through the half-cell electrode chamber into the container comprising the active charge-transfer material;

oxidizing the second redox-active mediator in the container and reducing the active charge-transfer material;

circulating the first redox-active mediator and the oxidized second redox-active mediator through the container comprising the active charge-transfer material to the half-cell electrode chamber; and

reducing the oxidized second redox-active mediator and oxidizing the electrode surface in the electrode chamber, wherein the active charge-transfer material comprises a redox potential between a redox potential of the first redox-active mediator and a redox potential of the second redox-active mediator, and wherein the active charge-transfer material is a polyoxometalate or derivative thereof.

14. The method of claim 13 , wherein the method is performed in a battery cell, and a single cell of the battery has a voltage of 1 to 5 volts.

15. The method of claim 13 , further comprising selecting the first, second, or first and second redox-active mediator from those having a structure corresponding to one of formula 1-6 below:

wherein the aromatic or cyclic structures in each formula are optionally substituted with electron withdrawing or donating groups.

16. A method of making a redox flow battery, the method comprising:

pre-determining a redox potential of a battery half-cell, the voltage being selected from a range of 0 to 5 volts versus Li/Li + ;

based on the predetermined redox potential of the battery half-cell, selecting an active charge-transfer material that comprises a polyoxometalate;

selecting a first redox-active mediator and a second redox-active mediator, the redox potential of the active charge-transfer material being between a redox potential of the first redox-active mediator and a redox potential of the second redox-active material; and

assembling the battery half-cell comprising:

a half-cell electrode chamber coupled to an electrode;

a separator membrane coupled to the half-cell electrode chamber;

a container coupled to the half-cell electrode chamber, the container comprising the active charge-transfer material; and

the half-cell electrode chamber comprising the first redox-active mediator and the second redox-active mediator.

17. The method of claim 16 , wherein the half-cell electrode chamber is a cathode cell chamber and the electrode is a cathode, and further comprising assembling an anode cell chamber coupled to an anode electrode and the separator.

18. The method of claim 16 , wherein the half-cell electrode chamber is an anode cell chamber and the electrode is an anode, and further comprising assembling a cathode cell chamber coupled to a cathode electrode and the separator.

19. The method of claim 16 , wherein the electron withdrawing or donating groups are present and are selected from the group consisting of:

groups having the formula —XR n , wherein X is O, S, or N, wherein each R is independently selected from a linear, branched, cyclic, aromatic alkyl group having 1-50 carbon atoms, or hydrogen, and R is optionally functionalized with a functional group including a halogen, O, S, or N; and n ranges from 0 up to a valence of 3;

—NO 2 , —CN, —CO 2 R, -halogens, halogenated hydrocarbons, —CF 3 , —COH, —SO 3 R, —NH 3-n R n , —O 2 CR, amide, —OR, —NH 2-m R m , and saturated or unsaturated linear, branched, cyclic or aromatic alkyl groups, wherein R and n are as defined above, and m ranges from 0 to 2; and combinations thereof.