JPS6353861A - Diaphgram for redox flow cell - Google Patents

Abstract

PURPOSE:To reduce metal ion transmission, increase voltage efficiency and Coulomb efficiency, and improve durability by having a specific chain aliphatic compound and a pyrrole compound polymer coexist on one side of a positive ion exchange membrance. CONSTITUTION:A chain aliphatic compound of carbon number between 6 and 30 and a pyrrole compound polymer are made to coexist on at least one side of a positive ion exchange membrance. This results in a diaphragm with higher Coulomb efficiency in particular and superior durability too, compared with a diaphragm having individually either a chain aliphatic compound of carbon number between 6 and 30 or a pyrrole compound polymer. Besides, transmission of metal irons such as those of chromium and iron can be reduced without causing an increase of membrance resistance, and Coulomb efficiency can be increased in addition, by the reaction of the aliphatic compound, in the range of more than in general, 200Angstrom on one side of the membrance and less than 1/3 of the membrance thickness.

Description

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

Specifically, in an iron/chromium-based redox flow battery system in which a polymer of a specific chain aliphatic compound and virol compound is present on at least one surface of a cation exchange membrane, voltage efficiency and coulombic efficiency can be increased. Moreover, the present invention provides a diaphragm for a redox flow battery that has excellent durability.

(Prior art) Conventionally, a solution of iron chloride/hydrochloric acid as an anolyte and a solution of chromium chloride/hydrochloric acid as a catholyte were circulated in an anode chamber and a cathode chamber in which an anode and a cathode were separated by a diaphragm, respectively, to remove each metal ion. Redox flow batteries are known in which charging and discharging are performed by oxidation-reduction of divalent ← → trivalent. The diaphragm for such a redox flow battery should: ■ be excellent in proton permeability and have low permeation of chromium (Cr) ions and iron (Fe) ions; ■ be excellent in hydrochloric acid resistance and strength; ■
It is required that the membrane resistance in the system used is low and the electrical resistance during charging and discharging is low.
Nozaki et al., Research Report of Electronic Technology Research Institute, No. 201, (
1979)) has 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 (Cr-) in the membrane, and during charging and discharging. There is a problem that the voltage drop (IRdrop) 4' increases.

In addition, in the case of cation exchange membranes, proton ions move through the membrane, so the membrane resistance in the system used is reduced, but metal ions may mix and cause self-discharge, or active materials such as metal salts may There is a problem of decreasing the solubility and concentration of

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.
．． A diaphragm having a resistance of 03 to 2Ω・- (JP-A-59-20516
No. 5), a diaphragm in which the image surface layer is composed of an anion exchange membrane layer, and at least a cation exchange layer is present as an intermediate layer, and the AC resistance in hydrochloric acid is 0.03 to 2 Ω.
-20462), a diaphragm in which the surface of a cation exchange membrane is coated with a substance selected from highly cross-linked cation exchange resins, highly cross-linked anion exchange resins, polyamines, and hydrophobic polymers (Japanese Patent Laid-open No. 60-2046) 160560), a diaphragm consisting of a polymer electrochemically prepared from a pyrrole compound (No.
Japanese Unexamined Patent Publication No. 59-205491) and the like have been proposed.

(Problem 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 industrial redox flow batteries, 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
By having a polymer of a specified chain aliphatic compound and pyrrole compound present on at least one surface of the cation exchange membrane, the redox has a small permeation amount of metal ions, high voltage efficiency and coulombic efficiency, and excellent durability. It was discovered that a diaphragm for a flow battery can be obtained, and the present invention was proposed. That is, according to the present invention, there is provided a diaphragm for a redox flow battery in which a polymer of a chain aliphatic compound having 6 to 30 carbon atoms and a pyrrole compound is present on at least one surface of a cation exchange membrane.

The redox flow battery diaphragm of the present invention is characterized in that a polymer of a chain aliphatic compound having 6 to 30 carbon atoms and a pyrrole compound coexists on at least one side of the cation exchange membrane. , a chain aliphatic compound having 6 to 30 carbon atoms, or a polymer of a pyrrole compound, each of which is present alone, has particularly high coulombic efficiency and excellent durability.

In the diaphragm of the present invention, the polymer of a chain aliphatic compound having 6 to 30 carbon atoms and a pyrrole compound is -a
5 x 10-' to 5 x 10-' each on one side
'mg/crA range is desirable, especially 5 mg/crA.
The thickness is preferably in the range of X 10-' to 5 X 10-'' mg/cj. The thickness is generally several hundred, and preferably 1]3 or less of the total thickness of the film.

It is desirable that the presence of ′ on the film surface be in the form of homogeneous mixture or block-like mixture, and for this purpose,
It is preferable that 10 to 30% of a chain aliphatic compound having 6 to 30 carbon atoms is first bonded to the functional group on the membrane surface, and then 10 to 30% of a pyrrole compound polymer is present. By doing so, a polymer of a cation exchange group, a chain aliphatic compound having 6 to 30 carbon atoms, and a pyrrole compound is present on the membrane surface.

The method for producing the diaphragm of the present invention is not particularly limited, but generally a chain aliphatic compound having 6 to 30 carbon atoms is chemically bonded to at least one side of a cation exchange membrane, and then a pyrrole compound is bonded to at least one surface of the cation exchange membrane. A method in which a polymer is present is preferably used.

The method of chemically bonding a chain aliphatic compound having 6 to 30 carbon atoms to the surface of the above-mentioned cation exchange membrane is not particularly limited, but generally a membrane-like compound having an acid halide group or (and) an acid anhydride group is used. After reacting the polymer with a chain aliphatic compound having 6 to 30 carbon atoms and having a reactive functional group, a cation exchange group can be introduced if necessary to produce a good product.

Examples of the acid halide group or acid anhydride group of the above-mentioned film-like polymer include sulfonic acid halide groups such as sulfonyl chloride, sulfonyl fluoride, sulfonyl bromide, and sulfonyl iodide, as well as carboxylic acid and phosphoric acid groups. and (and) acid anhydride groups such as sulfonic acid anhydride, carboxylic acid anhydride, and phosphoric acid anhydride. These acid halide groups or/
The functional groups of the acid anhydride and the acid anhydride may be present uniformly or non-uniformly in the film-like polymer compound as required, or may be bonded only to the surface.

In addition to the above-mentioned functional groups, the film-like polymer has other functional groups,
For example, sulfonic acid group, carboxylic acid group, phosphoric acid group, phosphorous acid group, sulfuric acid ester group, phosphoric acid ester group, phosphite group, arsenic acid group, silicate group, fluoro tertiary alcohol group, phenolic hydroxyl group , a thiol group, a chelating functional group, an organic solvent, a functional group that can become negatively charged in a water-organic solvent mixture system, etc. may be bonded to one or more types of functional groups. The polymer compound with such functional groups bonded to it may be made of only components of known ion exchange resins, such as styrene-divinylbenzene polymers, but there are other components that maintain the strength of the ion exchange membrane. Other polymeric or low-molecular compounds may be present within the cough polymeric compound in order to provide a reaction site or to provide a reaction site. Furthermore, in order to maintain the strength of the ion exchange membrane, conventionally known woven fabrics, nets, knitted fabrics,
In many cases, it is desirable to include nonwoven fiber chops, etc.

Next, a chain aliphatic group having at least a reactive functional group capable of reacting with the acid halide group or acid anhydride group is bonded to the film-like polymer having an acid halide group or an acid anhydride group as described above. By reacting compounds, carbon number 6
A membrane in which ~30 chain aliphatic compounds are bonded can be obtained. Such a chain aliphatic compound is preferably a saturated straight chain aliphatic compound from the viewpoint of reaction rate;
Even unsaturated or branched aliphatic compounds are effective. Therefore, in order to obtain a good diaphragm for a redox flow battery as desired in the present invention, it is necessary that the chain length (C, 1, 1) of the chain aliphatic compound be 6 to 30, particularly 8 to 20 carbon atoms. (n) is preferred. In other words, when an aliphatic compound with a chain length shorter than 6 is used, it has a poor ability to form a hydrophobic atmosphere and polymeric micelles in the surface layer of the resulting diaphragm, resulting in poor selective permeation of protons in the resulting membrane. However, if an aliphatic compound with a chain length of 30 or more is used, the hydrophobic atmosphere becomes too strong.
The resistance of the resulting membrane increases. Examples of reactive functional groups bonded to such chain aliphatic compounds include amino groups, alcohols, thiols, activated methylene,
It is not particularly limited as long as it is a reactive functional group that forms a bond that shares electrons in a conventionally known chemical reaction, such as active methine, active methyl, epoxy group, or aromatic ring. As such a chain aliphatic compound, for example, tetradecyl epoxide and dioctylamine are preferably used.

The conditions for reacting the above-mentioned film-like polymer having an acid halide group or an acid anhydride group with a chain aliphatic compound having 6 to 30 carbon atoms and having a reactive group are under reduced pressure, normal pressure, or increased pressure, and at a temperature. Generally, there is no particular restriction as long as the temperature is from -20°C to a temperature at which decomposition and deterioration of the polymer compound does not occur. However, when reacting only the surface layer of the film-like polymer,
It is preferable to carry out the reaction at a relatively high temperature for a short period of time so that the reaction proceeds according to the diffusion rate of the predetermined chain aliphatic compound.In this case, if the chain aliphatic compound is liquid under the reaction conditions, It can be reacted as it is or dissolved in an appropriate solvent. After the reaction, excess unreacted compounds are removed using a solvent that dissolves the chain aliphatic compound used, and the remaining unreacted acid halide groups or acid anhydride groups in the membrane polymer are removed. can be converted into a cation exchange group. The exchange means for such an ion exchange group is
Conventionally known hydrolysis reactions can be used without any restriction. For example, aqueous solutions of alkali metals, alkaline earth metals, hydroxide ion type organic amines, water-organic solvent mixed systems at room temperature,
It is sufficient to hydrolyze the polymer compound by immersing it under heating. Most commonly, aqueous solutions such as sodium hydroxide and potassium hydroxide, alcoholic solutions, alcoholic aqueous solutions, etc. are used. A solvent that can swell the polymer chain may be appropriately selected depending on the type.

The membrane bonded with chain aliphatic compounds having 6 to 30 carbon atoms thus obtained has a thickness selected from a range of 0.01 to 2 mm depending on the purpose, and an exchange capacity of 0.3 to 6 mm. .0
Most widely used in the milliequivalent/gram dry membrane (Na type) range. In addition, such a film has an electrical resistance of 1 when measured in 0.5 N-HCl compared to a film in which no aliphatic compound is bonded to the film-like polymer compound serving as the starting material.
．． It is desirable that the range does not exceed twice that. moreover,
A given chain aliphatic compound is typically 200 Å on one side of the membrane.
As mentioned above, by reacting below 173 of the film thickness,
The increase in electrical resistance of the membrane is small, the passage of metal ions such as chromium and iron ions is small, and the Coulombic efficiency is high.

Next, the diaphragm of the present invention is obtained by allowing a polymer of a pyrrole compound to exist in the membrane to which a chain aliphatic compound having 6 to 30 carbon atoms is bonded as described above.

Although there are no particular restrictions on the method of making the polymer of the pyrrole compound present in the membrane to which the chain aliphatic compound having 6 to 30 carbon atoms is bonded, a method of oxidative polymerization of the pyrrole compound is generally preferred.

The oxidizing agent used in the above oxidative polymerization method is not particularly limited as long as it is a conventionally known oxidizing agent.

For example, H2O2, peroxides such as (C, lI, CO) 20□, FeCj! 3, CuSO4, CuCl2
, RuCe, etc., NazSzOs, Na
Beroxo acids such as tSOs, (Nils)zsOs (
salt), oxyacid salts such as NaCjO, NaBr01NaCIQ, and the like. In other words, metal ions whose charge changes by redox, such as trivalent iron ions, divalent copper ions, and trivalent ruthenium ions, and cations such as organic compounds or metal complex cations whose charge changes by redox. Ions and oxidizing anions such as persulfate ions and perchlorate ions 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. In addition, when it is desired to carry out the oxidative polymerization reaction of the present invention only in the surface layer of the ion exchange membrane, a peracid bonded with a long-chain alkyl group or a naphthalene ring that can easily enter the pores of the ion exchange membrane can be used. It is possible to use a compound in which a peracid group is bonded to a compound that does not have a peracid group. In addition, when an anionic oxidizing agent is used, it is difficult to uniformly contain the oxidizing agent in the cation exchange membrane.
Utilizing this, a pyrrole compound can be easily polymerized only on one side.

Pyrrole compounds used in the present invention include pyrrole and its derivatives, such as N-methylolpyrrole, 2-
Known ones such as ethylpyrrole and N-arylpyrrole are not particularly limited.

There is no particular restriction on the method of oxidatively polymerizing a pyrrole compound to form a pyrrole compound in the diaphragm bonded with the chain aliphatic compound having 6 to 30 carbon atoms, but in general, A method for polymerizing a pyrrole compound in a diaphragm containing a pyrrole compound. A method for polymerizing a pyrrole compound by bringing it into contact with the pyrrole compound in a diaphragm. A method in which an oxidizing agent is transferred from one side through the diaphragm and the other side is polymerized. Methods such as transferring the pyrrole compound from the side and polymerizing the pyrrole compound in the diaphragm are particularly preferably used. Method (2) generally involves dissolving a pyrrole compound in an organic solvent such as acetonitrile, ethyl alcohol, or an inorganic solvent such as water using a membrane containing an oxidizing agent.
Alternatively, it may be immersed in a dispersed solution. 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. Further, in the polymerization, the concentration of the pyrrole compound is not particularly limited, and generally ranges from 0.01% to a saturated solution, and the polymerization may be carried out in a suspended state. The polymerization time varies depending on the type of pillow compound and the type of membrane mentioned above, and can be carried out by selecting an appropriate time generally from 1 minute to 72 hours. In addition, in method (2), generally, a liquid in which an oxidizing agent is dissolved or dispersed in an inorganic solvent is transferred from one side through a membrane, and a pyrrole compound is transferred to an organic or inorganic solvent from the other side. Polymerization of the pyrrole compound in the membrane is achieved by moving the dissolved or dispersed liquid. The polymerization conditions at this time are the same as in (2).

By doing this, the diaphragm for redox flow batteries of the present invention can be obtained. To specifically explain the method for producing the diaphragm of the present invention, for example, a cation exchange membrane crosslinked with styrene-divinylbenzene is mixed with iron chloride. After immersing it in an aqueous solution to make it into an iron ion form, it is thoroughly washed with water and immersed in an aqueous solution containing pyrrole, whereupon the pyrrole undergoes cation exchange and simultaneously polymerizes. The membrane thus obtained is thoroughly washed with water, thoroughly conditioned with 1N hydrochloric acid and 0.5N saline to remove Fe44, and a cation exchange membrane crosslinked with styrene-divinylbenzene. is placed in a cell divided into two chambers, an aqueous solution of iron chloride is placed on one side, an aqueous solution containing pyrrole is placed on the other side, and each method is transferred.

The membrane thus obtained is preferably thoroughly washed with water and thoroughly conditioned with 1N hydrochloric acid and 0.5N saline to remove PE++, thereby obtaining the diaphragm of the present invention.

(Functions and Effects) The diaphragm for redox flow batteries of the present invention has a thin layer made of a polymer of a chain aliphatic compound having 6 to 30 carbon atoms and a pyrrole compound on the surface, thereby achieving low resistance and high coulombic efficiency. It also exhibits high voltage efficiency and excellent durability. The reason why the diaphragm of the present invention retains such a special function is not necessarily clear, but the coexistence of long-chain alkyl groups and virol compound polymers on the membrane surface makes it particularly suitable for iron/chromium-based redox flow batteries. It is presumed that the permeation of iron and chromium ions in the positive and catholyte fluids is extremely reduced during charging and discharging, and that protons are selectively permeated.

(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 90 parts of styrene, 10 parts of divinylbenzene with a purity of about 55%
A paste mixture obtained by mixing 20 parts of dioctyl phthalate, 70 parts of polyvinyl chloride fine powder, and 2 parts of benzoyl peroxide was applied to a polyvinyl chloride cloth, deaerated, and both sides covered with cellophane. ) Polymerization was carried out by heating at 0'C for 4 hours to obtain a polymer film having a thickness of about 0.120. This was immersed in a 1:1 mixture of 98% concentrated sulfuric acid and chlorosulfonic acid with a purity of 90% or more at 40° C. for 60 minutes to convert about 40% sulfonyl chloride and 60% sulfonic acid groups.

Next, this was immersed in tetradecyl epoxide at room temperature for 24 hours, thoroughly washed with methanol, and then immersed in a 2N aqueous solution of caustic soda for hydrolysis.

Next, it was immersed in a 5% aqueous solution of ferric chloride to equilibrate it to form a ferric ion type. Then, it was immersed in a 2% aqueous solution of pyrrole and stirred. After 12 hours, it was taken out and washed with water and ethanol. Thereafter, the membrane was immersed in 1N hydrochloric acid to remove iron and obtain a diaphragm of the present invention. The abundance of long-chain alkyl groups and pyrrole compounds on this membrane surface is 9 X 10-'mg/c++l and 2
On the other hand, for comparison, the membrane sulfonated in Example 1 was hydrolyzed to obtain a comparative intestinal ion exchange membrane.

This membrane was assembled into a liquid flow type unit cell having an electrode area of 10 cIA and having carbon cloth electrodes on each of the anode and cathode, and was heated in a 4N hydrochloric acid aqueous solution containing 1.5M chromium and 1.5M iron at temperature. 40℃, current density 40
Charge/discharge experiments were conducted at mA/crA.

Further, in order to further investigate the durability, a charging/discharging experiment was conducted under the above conditions for one month.

The results are shown in Tables 1 and 2.

Example 2 and Comparative Example 2 100 parts of styrene, 20 parts of chloromethylstyrene, 20 parts of acrylonitrile, 10 parts of dioctyl phthalate, 20 parts of finely powdered polyvinyl chloride, and 15 parts of divinylbenzene with a purity of 80% were heated and mixed, and the monomers were mixed. 3 parts of benzoyl peroxide was added to the solution, which was applied to a polyvinyl chloride cloth, and then heated and polymerized to obtain a polymer film. The resulting polymer film was mixed with chlorosulfonic acid and sulfuric acid.
:1 immersion treatment at 40° C. for 1 hour. Then,
This membrane was immersed in a 5% (isopropyl ether) solution of dioctylamine for 8 hours, and then immersed in a 2N aqueous solution of caustic soda for 2 hours.

Next, this membrane was assembled into a cell divided into two chambers, and one chamber was filled with a 5% aqueous solution of ruthenium trichloride to change the exchange group to the ruthenium ion type.
0% ethyl alcohol? G? e) and allowed to react for 4 hours. Then, it was taken out and washed with water and methanol. Furthermore, the membrane of the present invention was obtained by immersing it in 1N hydrochloric acid to remove ruthenium ions. The amounts of long-chain alkyl groups and pyrrole compounds on this membrane surface were 8 x 10-3 mg/- and 6 x 10-'' on each side, respectively.
mg/cIa.

On the other hand, for comparison, the cation exchange membrane reacted with dioctylamine in Example 2 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 3.4.

Table 3, Table 4 Results after one month Patent applicant Tokuyama Soda Co., Ltd. Procedural amendment October 2, 1986 Commissioner of the Patent Office Black 1) Mr. Akio (1)
, Indication of the case Japanese Patent Application No. 1987-195576 2, Title of the invention: Diaphragm for redox flow battery 3, Person making the amendment Relationship with the case Patent applicant Address: 1-1, Mikage-cho, Yamaguchi Prefecture 1) Column 5 of the “Detailed Description of the Invention” of the specification, contents of amendment (1〉page 9 of page 9) of the specification, “reactive 6f functional group”
"reactive functional group".

(2) On page 14, line 19, written by the Ministry of Specification, between ``membrane'' and ``weathered iron'', it says ``soaked in a mixture of concentrated sulfuric acid and chlorosulfonic acid, washed with sulfonyl chloride, and then washed with methanol.
Hydrolyze in aqueous caustic soda solution. Furthermore, this membrane.”
Insert.

3) Insert "bonded with a chain aliphatic compound" between "shita" and "cation exchange membrane" on page 15, line 6 of the specification.

that's all

Claims (1)

[Claims] (1) A diaphragm for a redox flow battery in which a polymer of a chain aliphatic compound having 6 to 30 carbon atoms and a pyrrole compound is present on at least one surface of a cation exchange membrane.