Electrochemical energy storage systems and methods featuring large negative half-cell potentials
The invention concerns flow batteries comprising: a first half-cell comprising: (i) a first aqueous electrolyte comprising a first redox active material; and a first carbon electrode in contact with the first aqueous electrolyte; (ii) a second half-cell comprising: a second aqueous electrolyte comprising a second redox active material; and a second carbon electrode in contact with the second aqueous electrolyte; and (iii) a separator disposed between the first half-cell and the second half-cell; the first half-cell having a half-cell potential equal to or more negative than about −0.3 V with respect to a reversible hydrogen electrode; and the first aqueous electrolyte having a pH in a range of from about 8 to about 13, wherein the flow battery is capable of operating or is operating at a current density at least about 25 mA/cm 2 .
1. A flow battery comprising:
a first half-cell comprising:
a first aqueous electrolyte comprising a first redox active material at a concentration in a range of from 0.75 M to about 2.5 M, and a first carbon electrode in contact with the first aqueous electrolyte, the first electrolyte having a pH in the range of from 8 to 13;
a second half-cell comprising:
a second aqueous electrolyte comprising a second redox active material, and a second carbon electrode in contact with the second aqueous electrolyte; and
a separator disposed between the first half-cell and the second half-cell;
wherein the first half-cell has a half-cell potential ranging between −0.3 V and −0.7 V with respect to a reversible hydrogen electrode, and
the first redox active material exhibits substantially reversible electrochemical kinetics; wherein
the half-cell potential is the average measured potential of forward and reverse peaks of a cyclic voltammogram of the first aqueous electrolyte, when measured using an ex-situ apparatus using a flat glassy carbon disc electrode at a scan rate of 100 mV/s; and wherein
substantially reversible electrochemical kinetics refers to a condition in which the first aqueous electrolyte exhibits a voltage difference between the anodic and cathodic peaks of less than 0.3 V, when measured by cyclic voltammetry using an ex-situ apparatus using a flat glassy carbon disc electrode at a scan rate of 100 mV/s.
2. The flow battery of claim 1 , wherein the flow battery is capable of operating at a current density ranging between 25 mA/cm 2 and 500 mA/cm 2 .
3. The flow battery of claim 2 , wherein the flow battery is capable of operating with a current efficiency of at least 50% at a current density ranging between 50 mA/cm 2 and 500 mA/cm 2 .
4. The flow battery of claim 2 , wherein the flow battery is capable of operating with a current efficiency of at least 85% at a current density ranging between 50 mA/cm 2 and 500 mA/cm 2 .
5. The flow battery of claim 1 , wherein the flow battery is capable of operating with a current efficiency of at least 50%.
6. The flow battery of claim 1 , wherein the flow battery is capable of operating with a current efficiency of at least 85%.
7. The flow battery of claim 1 , wherein the flow battery has an open circuit voltage ranging between 1.48 V and 1.95 V, when the flow battery exists at a 50% state-of-charge.
8. The flow battery of claim 1 , wherein the redox active materials do not plate onto the carbon electrodes during operation of the flow battery.
9. The flow battery of claim 1 , wherein at least the first redox active material is a metal ligand coordination compound.
10. The flow battery of claim 9 , wherein both the first redox active material and the second redox active material are metal ligand coordination compounds.
11. The flow battery of claim 9 , wherein the first redox active material is a metal ligand coordination compound comprising titanium.
12. The flow battery of claim 11 , wherein the second redox active material is a hexacyanide metal ligand coordination compound.
13. The flow battery of claim 1 , wherein the separator comprises an ionomer.
14. The flow battery of claim 1 , wherein the second half-cell has a potential ranging between +1.10 V and +2.0 V versus a reversible hydrogen electrode.
15. The flow battery of claim 1 , wherein each redox active material exhibits substantially reversible electrochemical kinetics.
16. A system comprising the flow battery of claim 1 , and further comprising:
a first chamber containing the first aqueous electrolyte and a second chamber containing the second aqueous electrolyte;
at least one electrolyte circulation loop in fluidic communication with each chamber, the at least one electrolyte circulation loop comprising storage tanks and piping for containing and transporting the first and second aqueous electrolytes; and
a power conditioning unit.
17. The flow battery of claim 1 , wherein the first redox active material at a concentration in a range of from 1 M to about 2.5 M.
18. The flow battery of claim 1 , wherein the first half-cell has a half-cell potential ranging between −0.35 V and −0.7 V with respect to a reversible hydrogen electrode, and the first redox active material does not substantially plate onto the carbon electrode during operation of the flow battery.
19. The flow battery of claim 1 , wherein the first half-cell has a half-cell potential ranging between −0.4 V and −0.7 V with respect to a reversible hydrogen electrode, and the first redox active material does not substantially plate onto the carbon electrode during operation of the flow battery.
20. The flow battery of claim 1 , wherein the first half-cell has a half-cell potential ranging between −0.5 V and −0.7 V with respect to a reversible hydrogen electrode, and the first redox active material does not substantially plate onto the carbon electrode during operation of the flow battery.