Composite membranes for flow batteries
A composite membrane for use in flow batteries is contemplated. The membrane comprises a hydrogel, such as poly(vinyl alcohol), applied to a polymeric microporous film substrate. This composite is interposed between two half cells of a flow battery. The resulting membrane and system, as well as corresponding methods for making the membrane and making and operating the system itself, provide unexpectedly good performance at a significant cost advantage over currently known systems.
1. A flow battery system comprising:
a positive electrolyte flowing through a positive reaction chamber and a negative electrolyte flowing through a negative reaction chamber, wherein at least one of the positive electrolyte and the negative electrolyte consists of an aqueous solution;
a non-ionomeric membrane comprising hydrogel impregnated into pores of a microporous polymeric substrate, said non-ionomeric membrane: (i) physically separating the positive reaction chamber from the negative reaction chamber so as to prevent any flow of fluid through the pores; (ii) being ionically conductive but resistant to hydraulic crossover; and (iii) not containing any sulfonate or carboxylate ionic groups; and
wherein the hydrogel consists of poly(vinyl alcohol).
2. The flow battery according to claim 1 , wherein the poly(vinyl alcohol) is semi-crystalline and at least 95 wt. % hydrolyzed.
3. The flow battery according to claim 1 , wherein at least one of the positive and negative electrolytes comprise a multi-valent ionic species.
4. The flow battery according to claim 1 , wherein the hydrogel effectively blocks all pores of the microporous polymeric substrate.
5. The flow battery according to claim 1 , wherein the microporous polymeric substrate consists of polyethylene, polypropylene, or combinations thereof.
6. The flow battery according to claim 1 , wherein the polymeric substrate has a void volume between 30% and 80%.
7. The flow battery according to claim 1 , wherein the polymeric substrate has a thickness of between 25 and 200 micrometers prior to being impregnated by the hydrogel.
8. The flow battery according to claim 1 , wherein the aqueous solution has a pH of less than 3.0.
9. The flow battery according to claim 1 , wherein the hydrogel is hydrolyzed and crosslinked.
10. The flow battery according to claim 1 , wherein both the positive and the negative electrolytes comprise separate aqueous solutions.
11. The flow battery according to claim 1 , wherein the non-ionomeric membrane has a conductivity greater than 0.01 S/cm relative to a 1M HCl solution.
12. The flow battery according to claim 1 , wherein the non-ionomeric membrane has a normalized hydraulic permeability of less than or equal to 9×10 −12 cm 2 /cm.
13. The flow battery according to claim 1 , wherein the hydrogel is deposited on at least one side of the substrate at a thickness of 0.1 to 25 micrometers.
14. The flow battery according to claim 1 , wherein the hydrogel is hydrolyzed and has a purity of at least 99 wt. %.
15. The flow battery according to claim 1 , wherein the positive and negative electrolytes each comprise a multi-valent ionic species selected from ferric or ferrous ions.