JPS6353860A - Diaphragm fro redox flow cell - Google Patents

Abstract

PURPOSE:To reduce metal ion transmission quantity and to increase voltage efficiency as well as Coulomb efficiency by having a specific quantity of pyrrole compound polymer exist on one side of an ion exchange membrance surface. CONSTITUTION:There exists 1X10<-6>-5X10<-1>mg/cm<2> of pyrrole compound polymer on the surface of an ion exchange membrance. This results in an exceedingly low metal ion transmissivity in the change and discharge time of a redox cell. In addition, exceedingly small quantity of pyrrole compound polymer on the membrance surface causes almost no increase of membrance resistance, thus voltage drop in charge and discharge time is reduced.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a diaphragm for redox flow batteries.

Specifically, a redox flow suitable for increasing the voltage efficiency and coulombic efficiency in an iron/chromium-based redox flow battery system in which a specific amount of a polymer of a virol compound is present on at least one surface of an ion exchange membrane. The present invention provides a masking film for batteries.

(Prior art) Conventionally, a diaphragm was used: "91 An anode chamber and a cathode chamber that separated the electrode and cathode, an anode, a solution of iron chloride/hydrochloric acid as the night solution, and a solution of chromium chloride/hydrochloric acid as the catholyte!i, A redox flow battery is known that charges and discharges by circulating gold and redoxing each metal ion to divalent, monovalent, and trivalent ions.As a diaphragm for such a redox flow battery, ■ proton It has excellent permeability and does not contain chromium (Cr) ions or iron (
Fe ) ion permeation is required to be low; - resistance to hydrochloric acid and excellent strength; - low membrane resistance in toilet systems, and low electrical resistance during charging and discharging. For example, anion exchange membranes ( JP-A-53-112431) and a cation exchange membrane (Nozaki et al., Research Report of Electronic Technology Research Institute, No. 201, (1979)) have been proposed. However, in the case of anion exchange membranes, although mixing of metal ions in both electrode chambers can be prevented, the membrane resistance in the system used is large due to the movement of chlorine ions (CC) in the membrane, and the membrane resistance during charging and discharging is large. There is a problem that the voltage drop (IRdrop) becomes large. In addition, in the case of cation exchange membranes, proton ions move through the membrane, which reduces the membrane resistance in the system in use, but since metal ions are mixed, this may cause self-discharge or the activation of metal salts. There is a problem of reducing the solubility and concentration of substances.

To solve the above-mentioned problem, recently, for example, a thin anion exchange layer and a thin cation exchange layer have been developed, and AC resistance in hydrochloric acid is 0.
．． Diaphragm that is 03~2Ω/sub2 (Japanese Patent Application Laid-Open No. 59-2051
No. 65), both surface layers are anion-exchange thin layers, and at least a cation-exchange layer is present as an intermediate layer, and the AC resistance in hydrochloric acid is 0.03 to 2Ω・1M2 (Japanese Patent Application Laid-Open No. No. 60-20462), a diaphragm in which the surface of a cation-exchange membrane is coated with a substance selected from highly cross-linked cation-exchange street fat, highly cross-linked anion-exchange resin, polyamine, and hydrophobic polymer (Unexamined Japanese Patent Publication No. 60-20462); 160560/1982), a diaphragm made of a compound electrochemically produced from a pyrrole compound (Japanese Patent Application Laid-open No. 205491/1983), etc. have been proposed.

(Issues to be Solved by the Invention) However, the diaphragm proposed above does not satisfy all the required functions, and when used as a diaphragm for an industrial redox flow battery, Furthermore, there is a demand for a diaphragm that allows a small amount of metal ions to pass through and has high voltage efficiency and Coulombic efficiency.

(Means for Solving the Problems) As a result of intensive research in view of the above problems, the present inventors found that
We have discovered that by allowing a specific amount of a polymer of a pyrrole compound to exist on at least one surface of an ion exchange membrane, it is possible to obtain a diaphragm for redox flow batteries with a small amount of permeation of metal ions and high voltage efficiency and coulombic efficiency.
This led us to propose the present invention. That is, according to the present invention, on at least one surface of the ion exchange membrane, a polymer of a pyrrole compound is applied on each side in an amount of I.times.10-6 to 5.times.10.
A diaphragm for a redox flow battery is provided in which the present invention has the following characteristics: -'Q/m''.

The ion exchange membrane of the present invention is not limited to organic ion exchange membranes, but also includes inorganic ion exchange membranes themselves such as zirconium phosphate, and those formed by pressurizing and heat molding them with a suitable organic or inorganic binder. is also suitably used. Organic ion exchange membranes include polymeric ion exchange membranes,
A styrene-divinylbenzene copolymer to which ion exchange groups are bonded, and a cation exchange group and/or anion exchange group bonded to an ion exchange membrane such as a condensation membrane are preferably used. As such an organic ion exchange membrane, conventionally known homogeneous or heterogeneous ion exchange membranes can be used, and the base material of the ion exchange membrane can be hydrocarbon-based, buttomized carbon-based, or It is suitably used regardless of the fluorocarbon type.

Further, the ion exchange membrane used in the present invention is not particularly limited as long as it has generally 0.1 to 15 milliequivalents of ion exchange groups bonded to II of the dried ion exchange membrane. Examples of the ion exchange group include conventionally known cation exchange groups such as sulfonic acid, caldic acid, phosphoric acid, phosphorous acid, sulfonic acid ester, phenolic hydroxyl group, thiol group, and tertiary 4-fluoroalcohol. The anion exchange group used is primary, secondary, tertiary amine,
Onium bases such as quaternary ammonium, tertiary sulfonium, quaternary phosphonium, co-glutiranium and the like are preferred.

In addition, various types of ion exchange membranes such as those in which ion exchange groups are uniformly dispersed in the substrate, those in which ion exchange groups are present biased to one side, and those in which a concentration gradient exists are suitable as the above-mentioned ion exchange membranes. used for. The ion exchange groups present in such an ion exchange membrane include cases where only cation exchange groups are present, cases where only anion exchange groups are present, cases where both ion exchange groups are present at the same time, but especially cation exchange groups are present. Cation exchange membranes composed of ion exchange groups and amphoteric ion exchange membranes composed of amphoteric ion exchange groups are preferred because the effects of the present invention are significant.

When both such ion exchange groups are present at the same time, the two types of ion exchange groups may be present in a layered form over two or more layers, or arbitrarily uniformly present. In addition, if there is a layer in which cation exchange groups exist, if there is a layer in which cation exchange groups and anion exchange groups are arbitrarily distributed, or if there is a layer in which cation exchange groups exist, or if there is a layer in which cation exchange groups exist, or if there is a layer in which cation exchange groups exist, Various types of ion exchange membranes are formed depending on the state of existence of various ion exchange groups, such as when there is a layer having a layer having , or vice versa. It is effectively applied in the method of Note that the above-mentioned cation exchange group and anion exchange group do not mean the same type of cation exchange group and anion exchange group, but rather different field ion exchange groups such as a caldenic acid group and a sulfonic acid group. However, it is often particularly effective when different types are used.

Furthermore, the above-described inorganic ion exchange membranes and organic ion exchange membranes are not limited to those having a single matrix, but a composite of the two may also be suitably used. Specifically, fine powder of an inorganic ion exchanger is molded into an appropriate shape using a thermoplastic organic ion exchanger, or a polymer electrolyte or an inert polymer is dissolved in an appropriate solvent. By dispersing an inorganic ion exchanger therein and scattering the solvent, an ion exchange membrane having a desired shape can be obtained.

In the present invention, the method of making the polymer of the virol compound exist on at least one surface of the ion exchange membrane is not particularly limited, but generally a method of oxidative polymerization of the virol compound in the presence of an oxidizing agent is used.

Virol compounds used in the present invention include virol and substituted virols, such as N-alkylvirol, N-
These include mixtures with at least one selected from aryl virol, monoalkyl- or dialkyl-substituted virol, monohalogen-substituted virol, and dihalogen-substituted virol. In addition, as the oxidizing agent, conventionally known oxidizing agents can be used without particular limitation.
For example, peroxides such as H2O2*(C6H5Co)20□, FeCt5r CuSO4*CuC22, RuC2
, metal salts such as Na2S2O8, Na2SO3゜(N
'H4) Beroxo acids (salts) such as 2S05, NaC2
0.

Examples include oxyacid salts such as NaBr0 and NaClO2.

In other words, cations such as trivalent iron ions, divalent copper ions, trivalent ruthenium ions, organic compounds or metal complex cations whose charge changes depending on the oxidizing element, persulfate ions, superoxides, etc. Oxidizing anions such as elementary ions and perchloric acid are preferably used. These cations and anions are suitable because they undergo ion exchange with the exchange groups of the ion exchange membrane in an oxidized state and are uniformly dispersed within the ion exchange body. Conversely, when it is desired to carry out the oxidative polymerization reaction only in the surface layer of the ion exchanger, a peracid with long-chain alkyl groups or a naphthalene ring that cannot easily enter the pores of the ion exchanger may be used. A compound in which a peracid group is bonded can be used. Furthermore, for example, by using a cationic oxidizing agent for an anion exchanger and an anionic oxidizing agent for a cationic exchanger, each takes advantage of the fact that it is difficult to uniformly contain the oxidizing agent in the ion exchanger. In this way, a monomer that can be oxidatively polymerized can be easily polymerized only on the piece 11.

The method of making a polymer of a pyrrole compound exist on at least one surface of an ion exchange membrane by the above-mentioned oxidative polymerization is not particularly limited, but in general: ■ A method of bringing an oxidizing agent into contact with an ion exchange membrane containing a virol compound to polymerize the virol compound in the ion exchange membrane;
A method in which the virol compound is polymerized in the ion exchange membrane by moving an oxidizing agent from one side and moving the virol compound from the other side, etc.
Particularly preferred are methods (1) and (2).

In method (2), the ion exchange membrane is generally immersed in an oxidizing agent solution, then washed with water, and then dried. The virol compound may be dissolved or dispersed in water and immersed therein. The immersion is carried out under cooling to the extent that the solvent does not freeze, or under heating to the extent that the solvent does not boil. In addition, method (2) generally involves transferring a solution in which an oxidizing agent is dissolved or dispersed in an inorganic solvent from one side through an ion exchange membrane.
Polymerization of the virol compound is achieved in the ion exchange membrane by transferring a liquid in which the virol compound is dissolved or dispersed in an organic or inorganic solvent from the other side. In the polymerization method described above, the concentration of the -role compound is not particularly limited and is generally 0. Saturation 1 from OIJ
or may be polymerized in a suspended state. Polymerization time varies depending on the type of virol compound and ion exchange membrane, etc.
Generally, it can be carried out by selecting an appropriate time from 1 minute to 72 hours. Then, it is generally washed with water.

After washing with methanol, etc., conditioning is performed if necessary.

In the redox flow battery diaphragm of the present invention, the amount of the pyrrole compound polymer present on the surface of the ion exchange membrane is also very important, and varies depending on the type of ion exchange membrane, charge, etc., but at least 1 x 10 to 5 ×10 ■
/2, especially 5 x 10-5 x 10-2 /2 is preferred. If the amount is less than 1 x 1o-'mp/-2, the amount of metal ion permeation will be large and the Coulombic efficiency will be reduced, and if it is larger than 5 x 10-'rn9/crn2, the In either case, the object of the present invention cannot be satisfactorily achieved if I Rdrop is large.

(Functions and Effects) As explained above, according to the diaphragm for redox flow batteries of the present invention in which a specific amount of a polymer of a pyrrole compound is present on the surface of an ion exchange membrane, the diaphragm for redox flow batteries of the present invention can be used particularly for iron/chromium-based redox flow battery systems. It is possible to increase the voltage efficiency and coulomb efficiency. Although the detailed mechanism by which the diaphragm of the present invention exhibits such excellent performance is not clear,
The present inventors estimate as follows. That is, the pyrrole compound used in the present invention is mechanically and chemically strong;
In addition, since a polymer of pyrrole compounds, which has excellent permeability to proton ions and blocks the permeation of highly charged ionic species and ionic species with a small radius of water-containing ions, is present on the surface of the ion exchange membrane, charging and discharging in redox flow batteries is possible. Since the permeation of metal ions is extremely small and the amount of the pyrrole compound polymer present on the membrane surface is extremely small, there is almost no increase in membrane resistance. Therefore, the voltage drop during charging and discharging becomes smaller.

(Examples) Hereinafter, the present invention will be described in detail based on Examples, but the present invention is not particularly limited to the following Examples.

Example 1 and Comparative Example 1 Benzoyl/4' was added to a paste-like mixture obtained by adding fine powder of polyvinyl chloride to a mixture of 100 parts of styrene, 10 o'1 of 4-vinylzeridine, and 30 parts of divinylbenzene with a purity of about 55. - Oxide was added, applied to a nonwoven fabric made of propylene, heated and polymerized to form a film.

This was immersed in 97% sulfuric acid and gently sulfonated for 3 days. Next, this was immersed in 0.1N caustic soda for one hour, and then immersed in a bath consisting of hexane and methyl iodide to alkylate the pyridine ring.

The anion exchange capacity of the amphoteric ion exchange membrane thus obtained was 1.42 meq/g dry membrane, and the anion exchange capacity was 0.61 meq/g dry membrane.

The following two treatments were performed using this amphoteric ion exchange membrane.

(,) The membrane was immersed in an aqueous solution of ruthenium trichloride to convert it into ruthenium ion bottles, then washed with water and dried, and then immersed in a 2% aqueous solution of 1 roll, and the surface of the amphoteric ion exchange membrane was impregnated with virol. Polymerized. After that, it was washed with water and methanol.

(b) After being immersed in a 5% aqueous solution of sodium persulfate to form a persulfate ion form, the roll was immersed in a 3% aqueous solution of virol, and one roll was impregnated and polymerized on the surface of the amphoteric ion exchange membrane. Next, it was washed with water and methanol.

Each membrane was immersed in 1N hydrochloric acid solution to synthesize the diaphragm of the present invention.

These membranes were assembled into a liquid flow type single cell cell of 10α2 type with a carden cross electrode on each of the anode and the coated plate, and a 4N cell containing 1.5M chromium and 1.5M iron was used. Hydrochloric acid aqueous solution, temperature 40℃, current density 40
Charge/discharge experiments were conducted at mA/cm2.

The results are shown in Table 1.

Table 1 On the other hand, an amphoteric ion exchange membrane obtained by alkylation treatment was used as a comparative membrane.

Example 2 and Comparative Example 2 100 parts of styrene, 80 parts of N,N'-zooctylacinomethylstyrene, novinylbenzene with a purity of about 55 °C 2
Add azoisobutyronitrile to a paste mixture obtained by adding fine powder of polyvinyl chloride to a mixture of 0 parts of 0 parts and 10 parts of dioctyl phthalate, apply this to a cloth made of polyvinyl chloride, and polymerize it by heating to form a film. It was made into a shape. This is 95
% or more of sulfuric acid and was gently sulfonated for 2 days. Next, this was immersed in a 0.1 normal force sorter, and then immersed in a liquid consisting of n-hebutane and butyl bromide for alkylation treatment.

The cation exchange capacity of the amphoteric ion exchange membrane thus obtained was 1.21 meq/g dry membrane and the anion exchange capacity 0.85 milJ equiv/g dry membrane.

Using this amphoteric ion exchange membrane, the following three treatments were performed.

(,) When the membrane was immersed in a 5% aqueous solution of ferric chloride to ion-exchange iron ions to the cation exchange group, and after washing with water, it was immersed in a 2% ethanol solution of pyrrole.
Pyrrole polymerized on the membrane surface where cation exchange groups existed. Then, it was washed with water and methanol.

(b) The membrane was immersed overnight in an aqueous solution in which 1 roll of 5T was dispersed, stirred at room temperature for 4 hours, then immersed in an aqueous solution of 10T of ammonium persulfate to polymerize the virol, and then washed with water and methanol.

(c) The membrane was assembled into a cell divided into two chambers, and a 5-thi aqueous solution of ferric chloride was placed in one chamber for equilibrium to form a ferric ion type cell. A 2% aqueous solution of virol was then introduced into the other chamber and allowed to polymerize on one surface of the membrane. After that, it was washed with water and methanol.

Both of these membranes were immersed in 1N hydrochloric acid to synthesize the diaphragm of the present invention.

On the other hand, the amphoteric ion exchange membrane obtained in Example 2 was used as a comparative membrane.

Charge/discharge experiments were conducted on these films in the same manner as in Example 1. The results are shown in Table 2.

Table 2 Example 3 and Comparative Example 3 50 parts of styrene, 30 parts of butanoene, and N, N'-
50 parts of trimethylvinylbenzylamine! A block copolymer was synthesized by J-ping anionic polymerization. This was cast onto a flat plate to form a film. This film was sulfonated with sulfuric acid to introduce sulfonic acid groups, then substituted with methanol, and then treated with methyl iodide to introduce quaternary ammonium groups.

The membrane thus obtained was immersed in an aqueous solution of iron trichloride to exchange iron ions with cation exchange groups.

Next, this was immersed in an acetonitrile solution of pyrrole to impregnate it with pyrrole and oxidatively polymerized. Thereafter, it was washed with water and methanol, and further immersed in 1N hydrochloric acid to obtain a diaphragm of the present invention.

On the other hand, for comparison, the membrane of Example 3, which had not been oxidized and polymerized, was used as a comparative bite.

A charging/discharging experiment was conducted on this film in the same manner as in Example 1 below. The results are shown in Table 3.

Table 3 Example 4 A cation exchange membrane having an ion exchange capacity of 2.3 mEfk/Durham dry membrane with sulfonic acid groups bound thereto was
It was immersed in an aqueous solution of iron and equilibrated to form the fJ2 iron ion type.

Next, two rolls were immersed in the aqueous solution and stirred. 3
After 0 minutes, it was taken out, washed with water and ethanol, and then immersed in 1N hydrochloric acid, and the hydrochloric acid was replaced repeatedly. Fluorescent X
When we looked at the absorption of iron using the wire, we found that iron had been removed from the membrane. In this way, the diaphragm of the present invention was obtained.

On the other hand, for comparison, the cation exchange membrane of Example 4 was used as a comparative membrane.

Hereinafter, charging and discharging experiments were conducted in the same manner as in Example 1. The results are shown in Table 4.

Table 4

Claims (1)

[Claims] 1) On at least one surface of the ion exchange membrane, apply a polymer of pyrrole compound from 1×10^-^6 to 5×10^-^1
A diaphragm for redox flow batteries in which mg/cm^2 is present.