Fe—Cr redox flow battery systems and methods of manufacture and operation
A redox flow battery system includes an anolyte having chromium ions in solution; a catholyte having iron ions in solution, where a molar ratio of chromium in the anolyte to iron in the catholyte is at least 1.25; a first electrode in contact with the anolyte; a second electrode in contact with the catholyte; and a separator separating the anolyte from the catholyte.
1. A redox flow battery system, comprising
an anolyte comprising chromium ions in solution;
a catholyte comprising iron ions in solution, wherein a molar ratio of chromium in the anolyte to iron in the catholyte is at least 1.25, wherein the redox flow battery system, at a state of charge of 0%, has a molarity of H + in the anolyte that is at least 10% less than a molarity of H + in the catholyte;
a first electrode in contact with the anolyte;
a second electrode in contact with the catholyte; and
a separator separating the anolyte from the catholyte.
2. The redox flow battery system of claim 1 , wherein the anolyte further comprises iron ions in the solution and the catholyte further comprises chromium ions in the solution.
3. The redox flow battery system of claim 2 , wherein a molarity of the iron ions in the anolyte is within 25% of a molarity of iron ions in the catholyte and a molarity of the chromium ions in the anolyte is within 25% of a molarity of chromium ions in the catholyte.
4. The redox flow battery system of claim 1 , wherein a volume of the anolyte is at least 1.25 times a volume of the catholyte.
5. The redox flow battery system of claim 4 , wherein a molarity of the chromium ions in the anolyte is equal to a molarity of the iron ions in the catholyte.
6. The redox flow battery system of claim 1 , wherein a volume of the anolyte is at least 1.43 times a volume of the catholyte.
7. The redox flow battery system of claim 1 , wherein a volume of the anolyte is at least 1.67 times a volume of the catholyte.
8. The redox flow battery system of claim 1 , wherein the molar ratio of chromium ions in the anolyte to iron ions in the catholyte is at least 1.43.
9. The redox flow battery system of claim 1 , wherein the molar ratio of chromium ions in the anolyte to iron ions in the catholyte is at least 1.67.
10. The redox flow battery system of claim 1 , wherein the anolyte comprises chromium chloride to provide the chromium ions.
11. The redox flow battery system of claim 1 , wherein the catholyte comprises iron chloride to provide the iron ions.
12. The redox flow battery system of claim 1 , wherein the anolyte and catholyte both further comprise hydrochloric acid.
13. The redox flow battery system of claim 1 , wherein utilization of chromium in the anolyte is limited by the amount of iron in the catholyte.
14. The redox flow battery system of claim 13 , wherein the utilization of chromium in the anolyte is limited to no more than 80% by the amount of iron in the catholyte.
15. The redox flow battery system of claim 1 , wherein the redox flow battery system does not comprise a homogenous catalyst.
16. The redox flow battery system of claim 1 , wherein the redox flow battery system does not comprise a metallic catalyst.
17. The redox flow battery system of claim 1 , wherein the redox flow battery system, at a state of charge of 0%, has a molarity of H + in the anolyte that is at least 20% less than a molarity of H + in the catholyte.
18. The redox flow battery system of claim 1 , wherein the redox flow battery system, at a state of charge of 0%, has a molarity of H + in the anolyte that is at least 25% less than a molarity of H + in the catholyte.
19. The redox flow battery system of claim 1 , wherein the redox flow battery system, at a state of charge of 0%, has a molarity of H + in the anolyte that is at least 50% less than a molarity of H + in the catholyte.
20. The redox flow battery system of claim 1 , wherein the redox flow battery system is configured so that, at a state of charge of 50%, a molarity of H + in the anolyte is equal to a molarity of H + in the catholyte.