Electrochemical-based purification of electrolyte solutions, and related systems and methods
Methods and systems for removing impurities from electrolyte solutions having three or more valence states. In some embodiments, a method includes electrochemically reducing an electrolyte solution to lower its valence state to a level that causes impurities to precipitate out of the electrolyte solution and then filtering the precipitate(s) out of the electrolyte solution. In embodiments in which the electrolyte solution is desired to be at a valence state higher than the precipitation valence state, a method of the disclosure includes oxidizing the purified electrolyte solution to the target valence.
1. A method of making a purified electrolyte solution for use in a vanadium redox flow battery, the method comprising:
providing a vanadium-based electrolyte solution having an initial average valence and containing at least one non-vanadium-containing impurity having a precipitation valence below 3.0 and that precipitates out of the vanadium-based electrolyte solution when the valence of the electrolyte solution is at or below the precipitation valence;
reducing the electrolyte solution from the initial average valence to a valence below 3.0 so as to cause the at least one non-vanadium-containing impurity to precipitate out of the electrolyte solution as a solid precipitate; and
while the valance of the electrolyte solution is below 3.0, mechanically separating the solid precipitate out of the electrolyte solution using at least one of 1) a flow-through porous filter and 2) a hydrocyclone so as to make the purified electrolyte solution.
2. The method according to claim 1 , wherein the reducing of the vanadium-based electrolyte solution to an average valence of below 3.0 includes reducing the vanadium-based electrolyte solution to an average valence of less than 2.5.
3. The method according to claim 1 , wherein the reducing of the vanadium-based electrolyte solution to an average valence of below 3.0 includes reducing the vanadium-based electrolyte solution to a valence of substantially 2.0.
4. The method according to claim 1 , wherein the reducing of the vanadium-based electrolyte solution is performed using a hybrid electrochemical cell.
5. The method according to claim 4 , wherein the reducing of the vanadium-based electrolyte solution utilizes hydrogen gas as a reductant.
6. The method according to claim 1 , further comprising oxidizing the purified electrolyte solution to the desired valence prior to installing the purified electrolyte solution into the vanadium redox flow battery.
7. The method according to claim 6 , wherein the desired valence is substantially 3.5.
8. The method according to claim 6 , wherein the desired valence is substantially 4.5.
9. The method according to claim 6 , wherein the desired valence is substantially 2.5.
10. The method according to claim 1 , further comprising, prior to installing the purified electrolyte solution into the vanadium redox flow battery, oxidizing at least a portion of the purified electrolyte solution to each of two valences so as to create a plurality of purified valence-adjusted electrolyte solutions of differing valence.
11. The method according to claim 10 , wherein oxidizing at least a portion of the purified electrolyte solution includes oxidizing a first portion of the purified electrolyte solution to an average valence of greater than 3.5 and oxidizing a second portion of the electrolyte solution to an average valence of less than 3.5.
12. The method according to claim 11 , wherein the oxidizing of a first portion of the purified electrolyte solution to an average valence of greater than 3.5 includes oxidizing the first portion to an average valence of about 4.5 and oxidizing a second portion of the purified electrolyte solution to an average valence of less than 3.5 includes oxidizing the second portion to an average valence of about 2.5.
13. The method according to claim 10 , wherein the oxidizing of at least a portion of the purified electrolyte solution is performed using a hybrid electrochemical reduction cell.
14. The method according to claim 13 , wherein the oxidizing of at least a portion of the purified electrolyte solution utilizes the formation of hydrogen gas from protons.
15. The method according to claim 14 , wherein the reducing of the purified electrolyte solution is performed using a hybrid electrochemical reduction cell.
16. The method according to claim 15 , wherein the reducing of the purified electrolyte solution utilizes hydrogen gas output from the hybrid electrochemical oxidation cell.
17. The method according to claim 10 , wherein the reducing of the vanadium-based electrolyte solution and the oxidizing of at least a portion of the purified electrolyte solution are performed using an electrolyte-only electrochemical cell having a reduction side and an oxidation side with the vanadium-based electrolyte solution on the reduction side and the purified electrolyte solution on the oxidation side.
18. The method according to claim 1 , wherein all vanadium in the vanadium-based electrolyte solution comes substantially only from mixing V 2 O 5 with at least one strong acid.
19. The method according to claim 18 , wherein all the vanadium in the vanadium based electrolyte solution comes substantially from V 2 O 5 and V 2 O 3 , each mixed with at least one strong acid.
20. The method according to claim 1 , wherein the vanadium-based electrolyte solution has a lowest possible valence and the reducing of the vanadium-based electrolyte solution includes reducing the vanadium-based electrolyte solution to about the lowest valence.