Rebalancing electrolytes in redox flow battery systems

Abstract

Embodiments of redox flow battery rebalancing systems include a system for reacting an unbalanced flow battery electrolyte with a rebalance electrolyte in a first reaction cell. In some embodiments, the rebalance electrolyte may contain ferrous iron (Fe 2+ ) which may be oxidized to ferric iron (Fe 3+ ) in the first reaction cell. The reducing ability of the rebalance reactant may be restored in a second rebalance cell that is configured to reduce the ferric iron in the rebalance electrolyte back into ferrous iron through a reaction with metallic iron.

1 - 9 . (canceled) 
     
     
         10 . A flow battery system, comprising:
 a first flow battery reaction cell comprising:
 a first liquid filled half-cell chamber in fluid communication with a first liquid electrolyte with a first concentration of a first dissolved ionic species at a first oxidation state; 
 a second half-cell chamber in fluid communication with a second liquid electrolyte with a second concentration of a second dissolved ionic species at a second oxidation state; and 
 a first separator membrane separating the first half-cell chamber of the first flow battery reaction cell from the second half-cell chamber of the first flow battery reaction cell; 
   a first rebalance reaction cell comprising:
 a first liquid filled half-cell chamber in fluid communication with the first liquid electrolyte; 
 a second liquid filled half-cell chamber in fluid communication with a liquid mediator electrolyte with a third concentration of a third dissolved ionic species at a third oxidation state; and 
 a second separator membrane separating the first half-cell chamber of the first rebalance reaction cell from the second half-cell chamber of the first rebalance reaction cell; and 
   a second rebalance reaction cell in fluid communication with the second source of liquid mediator electrolyte, the second rebalance reaction cell comprising a replenishable reactant,   wherein:
 the first rebalance reaction cell has a configuration that supports an electrochemical reaction in which the first dissolved ionic species in the first liquid electrolyte is reduced to a first lower oxidation state that is lower than the first oxidation state of the first ionic species while oxidizing a quantity of the third dissolved ionic species in the liquid mediator electrolyte to a third higher oxidation state that is higher than the third oxidation state of the third dissolved ionic species; and 
 the second rebalance reaction cell has a configuration that supports an electrochemical reaction in which a quantity of the third dissolved ionic species in the liquid mediator electrolyte is reduced from the third higher oxidation state to the third oxidation state of the third dissolved ionic species while a quantity of the replenishable reactant is oxidized. 
   
     
     
         11 . The flow battery system of  claim 10 , wherein the second rebalance reaction cell comprises a galvanic cell. 
     
     
         12 . The flow battery system of  claim 10 , wherein the second rebalance reaction cell comprises an electrolytic cell. 
     
     
         13 . The flow battery system of  claim 10 , wherein the second rebalance reaction cell comprises a chemical reaction chamber. 
     
     
         14 . The flow battery system of  claim 13 , wherein:
 the chemical reaction chamber contains metallic iron chips; and   the chemical reaction chamber has a configuration such that the liquid mediator electrolyte directly contacts the metallic iron chips.   
     
     
         15 . The flow battery system of  claim 13 , wherein the chemical reaction chamber has a configuration that supports a restoring reaction in the mediator electrolyte inside a mediator electrolyte tank. 
     
     
         16 . The flow battery system of  claim 10 , wherein the second rebalance cell comprises a reactor comprising a column of solid chips of the replenishable reactant over which the mediator electrolyte is capable of flowing. 
     
     
         17 . The flow battery system of  claim 16 , wherein an outlet of the reactor is bifurcated with a first branch returning to a mediator electrolyte tank and a second branch directing a portion of the mediator electrolyte to be removed from the system. 
     
     
         18 . The flow battery system of  claim 16 , wherein an outlet of the reactor is coupled to a cooling coil and to a crystallization chamber containing seed crystals. 
     
     
         19 . The flow battery system of  claim 10 , wherein the replenishable reactant comprises metallic iron. 
     
     
         20 . The flow battery system of  claim 10 , wherein at least one of: the first rebalance reaction cell; and the second rebalance reaction cell comprises a catalyst. 
     
     
         21 . The flow battery system of  claim 10 , wherein the first ionic species at the first oxidation state in the first liquid electrolyte comprises Fe3+. 
     
     
         22 . The flow battery system of  claim 10 , wherein the third ionic species at the third oxidation state in the liquid mediator electrolyte comprises Fe2+. 
     
     
         23 . The flow battery system of  claim 10 , wherein at least one of the first rebalance reaction cell and the second rebalance reaction cell has a configuration comprising a flow-through reaction cell. 
     
     
         24 . The flow battery system of  claim 10 , further comprising:
 a reservoir containing the liquid mediator electrolyte; and   a pump configured to circulate the liquid mediator electrolyte between the reservoir, the second half-cell of the first rebalance reaction cell and the second rebalance reaction cell.   
     
     
         25 . The flow battery system of  claim 24 , wherein the second rebalance reaction cell is located inside the reservoir.