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;
a negative electrolyte flowing through a negative reaction chamber;
a non-ionomeric membrane comprising a hydrogel physically separating the positive reaction chamber from the negative reaction chamber; and
wherein the membrane is ionically conductive but resistant to hydraulic crossover and wherein at least one of the positive and negative electrolytes comprises an aqueous solution.
2 . A flow battery according to claim 1 , wherein the hydrogel comprises poly(vinyl alcohol).
3 . (canceled)
4 . A flow battery according to claim 1 , wherein at least one of the positive and negative electrolytes comprise a multi-valent ionic species.
5 . A flow battery according to claim 1 , wherein the hydrogel is selected from: poly(vinyl alcohol), poly(acrylic acid), poly(ethylene glycol), and combinations thereof.
6 . A flow battery according to claim 5 , wherein the hydrogel effectively blocks all pores of a polymeric substrate so as to prevent any flow of fluid through the pores.
7 . A flow battery according to claim 1 , wherein the polymeric substrate is microporous.
8 . A flow battery according to claim 7 , wherein the polymeric substrate consists of polyethylene, polypropylene, and combinations thereof.
9 . A flow battery according to claim 1 , wherein the polymeric substrate has a void volume between 30% and 80%.
10 . A flow battery according to claim 1 , wherein the polymeric substrate has a void volume exceeding 80%.
11 . A flow battery according to claim 1 , wherein the membrane consists of hydrogel.
12 . A flow battery according to claim 1 , wherein the pH of the positive and negative electrolytes is less than 3.0.
13 . A flow battery according to claim 1 , wherein the hydrogel is at least one of: hydrolyzed, crystalline, semi-crystalline, and crosslinked.
14 . A method of making a composite membrane that is ionically conductive and resistant to hydraulic crossover, the method comprising:
providing a substrate having a plurality of pores forming a void volume;
impregnating the pores with a hydrogel;
treating the hydrogel to create a non-ionomeric membrane; and
wherein the hydrogel is selected from: poly(vinyl alcohol), poly(acrylic acid), poly(ethylene glycol), and combinations thereof.
15 . The method according to claim 14 , wherein the treating the hydrogel includes at least one of thermal crosslinking, chemical crosslinking, photochemical crosslinking, and hydrolyzing the hydrogel.
16 . The method according to claim 14 , wherein the impregnating the pores comprises at least one of film casting, roll-to-roll casting, infiltration, and dip coating.
17 . The method according to claim 14 , wherein the impregnating the pores results in a layer of hydrogel deposited on at least one side of the substrate at a thickness of 0.1 to 25 micrometers.
18 . The method according to any preceding method claim 17 , further comprising, prior to the impregnating the pores, at least one of: cleaning the pores and removing air from the pores.
19 . The method according to claim 14 , further comprising submerging the substrate in alcohol.
20 . The method according to any preceding method claim 14 , wherein the hydrogel comprises poly(vinyl alcohol) selected to have a purity of at least 99 wt. %.
21 . The method according to claim 14 , wherein at least 95 wt. % of the hydrogel is hydrolyzed.
22 . The method according to any preceding method claim 14 , wherein a plurality of layers of hydrogel are successively impregnated on the substrate.
23 . A flow battery according to claim 4 , wherein the multi-valent species include at least one of: vanadium (2 + ) ions, vanadium (3 + ) ions, vanadium (4 + ) ions, vanadium (5 + ) ions, cuprous ions, cupric ions, ferric ions, and ferrous ions.