Flow battery balancing cells having a bipolar membrane for simultaneous modification of a negative electrolyte solution and a positive electrolyte solution
Parasitic reactions, such as production of hydrogen and oxidation by oxygen, can occur under the operating conditions of flow batteries and other electrochemical systems. Such parasitic reactions can undesirably impact operating performance by altering the pH and/or state of charge of one or both electrolyte solutions in a flow battery. Electrochemical balancing cells can allow rebalancing of electrolyte solutions to take place. Electrochemical balancing cells suitable for placement in fluid communication with both electrolyte solutions of a flow battery can include: a first chamber containing a first electrode, a second chamber containing a second electrode, a third chamber disposed between the first chamber and the second chamber, an ion-selective membrane forming a first interface between the first chamber and the third chamber, and a bipolar membrane forming a second interface between the second chamber and the third chamber.
1. A method comprising:
providing an electrochemical balancing cell comprising:
a first chamber containing a first electrode;
a second chamber containing a second electrode;
a third chamber disposed between the first chamber and the second chamber;
an ion-selective membrane forming a first interface between the first chamber and the third chamber; and
a bipolar membrane forming a second interface between the second chamber and the third chamber;
introducing a first electrolyte solution comprising a first active material into the third chamber;
introducing a second electrolyte solution comprising a second active material into the first chamber and the second chamber:
wherein at least one of the first electrolyte solution and the second electrolyte solution comprises an aqueous electrolyte solution;
applying a potential across the electrochemical balancing cell so as to induce a current therein, such that the second electrode is a positive electrode and the first electrode is a negative electrode; and
converting water into protons and hydroxide ions at the bipolar membrane;
wherein the protons migrate into the first electrolyte solution in the third chamber and the hydroxide ions migrate into the second electrolyte solution in the second chamber;
placing the electrochemical balancing cell in fluid communication with a first half-cell and a second half-cell of a flow battery; and
transferring the first electrolyte solution and the second electrolyte solution between the electrochemical balancing cell and the flow battery.
2. The method of claim 1 , wherein the first electrolyte solution is transferred to a negative half-cell of the flow battery and the second electrolyte solution is transferred to a positive half-cell of the flow battery.
3. The method of claim 1 , wherein the first electrolyte solution is transferred to a positive half-cell of the flow battery and the second electrolyte solution is transferred to a negative half-cell of the flow battery.
4. The method of claim 1 , wherein the first electrolyte solution and the second electrolyte solution each comprise an aqueous electrolyte solution.
5. The method of claim 1 , wherein at least one of the first electrolyte solution and the second electrolyte solution comprises a coordination complex as an active material.
6. A method comprising:
providing an electrochemical balancing cell comprising:
a first chamber containing a first electrode:
a second chamber containing a second electrode;
a third chamber disposed between the first chamber and the second chamber;
an ion-selective membrane forming a first interface between the first chamber and the third chamber; and
a bipolar membrane forming a second interface between the second chamber and the third chamber;
introducing a first electrolyte solution comprising a first active material into the third chamber;
introducing a second electrolyte solution comprising a second active material into the first chamber and the second chamber;
wherein at least one of the first electrolyte solution and the second electrolyte solution comprises an aqueous electrolyte solution:
providing hydrogen peroxide to the second chamber;
applying a potential across the electrochemical balancing cell so as to induce a current therein, such that the second electrode is a positive electrode and the first electrode is a negative electrode:
converting the hydrogen peroxide into protons and oxygen in the second chamber;
and
converting water into protons and hydroxide ions at the bipolar membrane;
wherein the protons formed at the bipolar membrane migrate into the first electrolyte solution in the third chamber and the hydroxide ions formed at the bipolar membrane migrate into the second electrolyte solution in the second chamber.
7. The method of claim 6 , further comprising:
placing the electrochemical balancing cell in fluid communication with a first half-cell and a second half-cell of a flow battery; and
transferring the first electrolyte solution and the second electrolyte solution between the electrochemical balancing cell and the flow battery.
8. The method of claim 7 , wherein the first electrolyte solution is transferred to a positive half-cell of the flow battery and the second electrolyte solution is transferred to a negative half-cell of the flow battery.
9. The method of claim 7 , wherein the first electrolyte solution is transferred to a negative half-cell of the flow battery and the second electrolyte solution is transferred to a positive half-cell of the flow battery.
10. The method of claim 9 , wherein the second active material comprises an iron hexacyanide complex.
11. The method of claim 7 , wherein the hydrogen peroxide is added to the second chamber.
12. The method of claim 7 , wherein the hydrogen peroxide is added to a portion of the second electrolyte solution after being transferred from the flow battery but before entering the second chamber.
13. The method of claim 6 , wherein the first electrolyte solution and the second electrolyte solution each comprise an aqueous electrolyte solution.
14. The method of claim 6 , wherein at least one of the first electrolyte solution and the second electrolyte solution comprises a coordination complex as an active material.