Method and system to maintain electrolyte stability for all-iron redox flow batteries
Methods and systems are provided which maintain the positive and negative electrolyte pH and stability of a redox flow battery through the use of electrochemical rebalancing cells. The electrochemical cells may be activated by applying an electrical load to affect changes to the pH of the electrolytes. The use of the electrochemical cells improves long term performance stability redox flow batteries by decreasing and/or eliminating Fe(OH) 3 precipitation formation.
1. A method for maintaining stability of an electrolyte in a hybrid flow battery, comprising:
while the hybrid flow battery is charging:
supplying an electrical current to at least one electrochemical cell based on a pH of an electrolyte; and
producing H + in the electrochemical cell to maintain the pH of the electrolyte within a desired range, wherein an equilibrium of production of the H + changes as the electrical current changes;
wherein the electrochemical cell is a positive electrochemical cell coupled to a positive electrode compartment either in line or in parallel.
2. The method of claim 1 , further comprising:
supplying the electrolyte to a cathode of the at least one electrochemical cell; and
supplying hydrogen gas to an anode of the at least one electrochemical cell.
3. The method of claim 1 , further comprising a negative electrochemical cell coupled to a negative electrode compartment either in line or in parallel.
4. The method of claim 1 , where the electrical current is delivered from external loads, and wherein a residual current of the electrical current is used to power auxiliary components in an overall IFB system.
5. The method of claim 1 , wherein the electrical current is supplied when a pH of a positive electrolyte is greater than a first set point.
6. The method of claim 5 , wherein, for an all-iron redox battery, the first set point of the pH of the positive electrolyte is in a range of pH 1 to 1.8.
7. The method of claim 1 , wherein the electrical load is applied when a pH of a negative electrolyte is greater than a third set point.
8. The method of claim 7 , wherein, for an all-iron redox battery, the third set point of the pH of the negative electrolyte is in a range of pH 3.5 to 4.5.
9. The method of claim 1 , further comprising stopping the electrical current based on the pH of the electrolyte.
10. The method of claim 9 , wherein the electrical current is turned off when a pH of a positive electrolyte is lower than a second set point or a pH of a negative electrolyte is lower than a fourth set point.
11. The method of claim 10 , wherein the electrical current for the positive electrochemical cell is supplied during battery charge only and an electrical current for a negative electrochemical cell is applied during battery charge or discharge.
12. A method for maintaining stability of an electrolyte in an all-iron redox flow battery, comprising:
flowing a positive electrolyte to a cathode of a first electrochemical cell;
flowing a negative electrolyte to a cathode of a second electrochemical cell;
supplying hydrogen gas from a head space of an electrolyte source to an anode of the first electrochemical cell and an anode of the second electrochemical cell via eductors or pumps;
supplying a first electrical current to the first electrochemical cell responsive to electrolyte pH set points;
supplying a second electrical current to the second electrochemical cell responsive to pH set points; and
producing H + in the electrochemical cell to maintain the pH of the electrolyte within a desired range.
13. The method of claim 12 , further comprising:
applying the first electrical load during a charge cycle of the all-iron redox flow battery.
14. The method of claim 12 , further comprising;
stopping the first electrical current responsive to a positive electrolyte pH lower than a second set point; and
stopping the second electrical current responsive to a negative electrolyte pH lower than a fourth set point.