KR20230111905A - Method of manufacturing ionomer dispersion using defective ion exchange membrane - Google Patents

Abstract

The present invention relates to a method for preparing an ionomer dispersion using a defective ion exchange membrane and an electrode material manufactured thereby, wherein ionomer is recovered from a defective ion exchange membrane generated during the production process, and the recovered ionomer is used to manufacture an ion exchange membrane or electrode binder having excellent electrochemical properties and durability.

Description

Method of manufacturing ionomer dispersion using defective ion exchange membrane {Method of manufacturing ionomer dispersion using defective ion exchange membrane}

The present invention relates to a method for preparing an ionomer dispersion using a defective ion exchange membrane and an electrode material manufactured thereby, wherein ionomer is recovered from a defective ion exchange membrane generated during the production process, and the recovered ionomer is manufactured. It relates to an ion exchange membrane or electrode binder having excellent electrochemical properties and durability.

Perfluorine-based ion exchange membrane has conductivity for cations such as hydrogen ions (H ⁺ , proton) and is composed of a chemically resistant Teflon main chain, so it has excellent hydrogen ion conductivity and chemical stability. Therefore, it is used in various industrial fields such as polymer electrolyte membrane fuel cell (PEFC), polymer electrolyte membrane water electrolysis, reverse electrodialysis, electrolyte membrane for saline water electrolysis, and electrode binder. It is becoming.

As described above, the perfluorine-based ion exchange membrane is known to have excellent proton conductivity and chemical stability, but when operated in a low humidity state, the proton conductivity rapidly deteriorates due to the spontaneous evaporation of water, and chemical/electrochemical decomposition occurs under severe operating conditions. In order to solve these problems in terms of performance and durability, a concept introduced is a porous support with excellent chemical durability impregnated with a perfluorine/partial fluorine/hydrocarbon-based hydrogen ion conducting ionomer (pore-filling membrane; PFM). Representative commercial perfluorine-based composite films include Gore Select from W.L. Gore & Associates, Nafion XL from Chemours, Aciplex from Asahi Kasei, and Flemion from Asahi Glass.

Perfluorine-based reinforced composite membranes do not meet normal product standards due to reasons such as partial impregnation of ionomer during the production process, failure to control film thickness, failure to control drying/heat treatment process, etc., and are difficult to sell as products when judged to be defective. In the case of manufacturing a membrane electrode assembly (MEA) as a normal product, there is a problem in that unused parts occur due to the difference between the production standards of the manufacturer of the reinforced composite film and the specifications for use by consumers. These unused or defective reinforcing composite membranes are completely discarded or neglected because there is no technology for recovering only the ionomer without loss even if the perfluorine-based ionomer in the membrane is sufficiently reusable. In addition to the reinforced composite membrane, defective pure electrolyte membranes generated in the production process are often discarded as separators because a suitable ionomer recovery technology has not been developed, or are not treated in a timely manner for reasons such as disposal costs.

On the other hand, perfluorinated ionomer is a key material that determines the electrochemical performance and durability of devices, but is currently produced only by a few specific companies abroad, and its price is very high, which is a burden on product production using it. Therefore, there is a need for a technology capable of selectively recovering perfluorine-based ionomer from defective or unused separators generated in the production process, whether it is a reinforced composite membrane or a pure electrolyte membrane.

Korean Patent Publication No. 10-2016-0116194 Korean Patent Publication No. 10-2020-0001419

An object of the present invention is to selectively extract only perfluorine-based ionomer from a defective ion exchange membrane generated during the production process or an unused ion exchange membrane due to a specification difference without damage to produce an ion exchange membrane or an electrode material such as an electrode binder. To provide a method.

In addition, other tasks to be achieved by the present invention are to recover ionomer from defective or unused separators to increase the utilization of perfluorine-based ionomer materials, reduce the manufacturing cost of ion exchange membranes and electrode binders, and reduce environmental problems caused by disposal of separators.

In order to solve the above technical problem, the present invention provides a method for preparing an ionomer dispersion using a defective ion exchange membrane, including the following steps.

(S1) preparing an ion exchange membrane determined to be defective during a production process;

(S2) dispersing the defective ion exchange membrane in a solvent at a temperature of 100° C. or higher and a pressure of 1 MPa or higher; and

(S3) cooling and separating the dispersion from which the ionomer was extracted through the dispersion process.

At this time, the ion exchange membrane determined to be defective is a perfluorine-based ion exchange membrane, and may include, for example, defective products due to partial impregnation of ionomer, failure to control film thickness, failure to control drying or heat treatment processes, or unused products due to differences in specifications.

In addition, the present invention provides an ion exchange membrane or an electrode binder prepared using an ionomer dispersion recovered from a defective ion exchange membrane and a membrane electrode assembly including the same.

According to the present invention, an ion exchange membrane prepared using a perfluorine-based ionomer recovered through a supercritical dispersion method from a defective perfluorine-based ion exchange membrane, such as a defective membrane generated during the production process or an unused membrane due to a specification difference, was manufactured as a membrane electrode assembly (MEA) and evaluated. As a result, it was confirmed that the electrochemical properties of PEFC were excellent. In addition, it was confirmed that the electrochemical characteristics of the electrode using the perfluorine-based ionomer recovered as described above as an electrode binder were also improved. The recovered ionomer according to the present invention exhibited excellent ion exchange membrane properties by securing high hydrogen ion conductivity and hydrogen gas barrier properties through the unique dispersion characteristics obtained through the supercritical dispersion process, and excellent properties as an electrode binder with improved mass transfer characteristics. When introduced as an ion exchange membrane and electrode binder, the electrochemical performance of PEFC can be improved.

As such, the present invention can selectively recover the perfluorine-based ionomer from the defective separation membrane during the process without loss of the perfluorine-based ionomer, and can adjust the state of the dispersion to suit the required use, such as an ion exchange membrane and an electrode binder.

In addition, through ionomer recovery technology, it is possible to alleviate supply and demand issues for perfluorinated ionomer materials, and it is possible to save manufacturing cost by manufacturing ion exchange membranes and electrode binders through ionomer recovery without a separate synthesis process, and environmental problems caused by waste generated through total disposal can be prevented. However, the effects of the invention are not limited to the effects mentioned above.

In addition, the ion exchange membrane and electrode binder prepared using the recovered perfluorine-based ionomer according to the present invention can be applied to various industrial fields such as a cation exchange membrane for reverse electrodialysis, a polymer electrolyte membrane water electrolysis membrane, and an electrode binder in addition to polymer electrolyte fuel cells.

1 is a flow chart showing a process for preparing an ionomer dispersion using a defective ion exchange membrane according to the present invention.
2 is a graph showing current-voltage curves of membrane-electrode assemblies introduced with ion exchange membranes manufactured according to Examples and Comparative Examples of the present invention at 65 °C.
3 is a graph showing current-voltage curves of membrane-electrode assemblies to which an ionomer prepared according to Examples and Comparative Examples of the present invention is applied as a binder at 65 °C.

Hereinafter, the present invention will be described in more detail with reference to the drawings and examples.

According to the present invention, only perfluorine-based ionomer can be selectively extracted from defective ion exchange membranes generated during the production process and recovered in the form of a dispersion, and the recovered ionomer dispersion can be used in the manufacture of ion exchange membranes and electrode binders.

Specifically, the method for preparing an ionomer dispersion using a defective ion exchange membrane according to the present invention includes the following steps:

(S1) preparing an ion exchange membrane determined to be defective during a production process;

(S2) dispersing the defective ion exchange membrane in a solvent at a temperature of 100° C. or higher and a pressure of 1 MPa or higher; and

(S3) cooling and separating the dispersion from which the ionomer was extracted through the dispersion process.

The present invention is designed to utilize defective ion exchange membranes that cannot be commercialized due to defects found during the manufacturing process. Perfluorine-based separators widely used in fuel cells or water electrolysis devices, in particular, perfluorine-reinforced composite membranes, do not meet normal product standards due to reasons such as partial impregnation of ionomer during the production process, failure to control film thickness, and failure to control drying/heat treatment processes. Many cases are judged to be defective. In addition, even when there is no problem in quality, when manufacturing a membrane electrode assembly (MEA), there is a problem in that unused parts occur due to the difference between the production standard of the reinforced composite membrane manufacturer and the consumer use standard. In this way, abnormal products generated due to process control failure and unused products generated due to differences in manufacturing standards and usage standards in the process of manufacturing MEA are left as they are or discarded as separators, causing environmental problems. Therefore, the technology for recovering the perfluorine-based ionomer from the separation membrane according to the present invention can be said to be economical as well as highly useful from an environmental point of view.

The present invention selectively extracts a perfluorinated ionomer from a defective ion exchange membrane due to partial impregnation of the ionomer, failure to control the film thickness, failure to control the drying or heat treatment process, or an unused ion exchange membrane due to a difference in specification, and then recycles the ion exchange membrane or electrode binder. It relates to a method. The defective ion exchange membrane that can be used for the ionomer extraction of the present invention can be either a reinforced composite membrane including a support or a pure electrolyte membrane without the support, and there is no particular limitation whether it is a commercially available ion exchange membrane or an ion exchange membrane directly prepared using an ionomer.

Examples of the ionomer constituting the perfluorine-based ion exchange membrane in the present invention include poly(perfluorosulfonic acid), poly(perfluorocarboxylic acid), copolymers of tetrafluoroethylene and fluorovinyl ether containing a sulfonic acid group, and mixtures thereof. It may include a mixture of, but is not particularly limited thereto.

In addition, even when the membrane judged to be defective used in the present invention is a reinforced composite membrane including a support, the ionomer can be extracted and used as an electrode material. Examples of the support constituting the reinforced composite film include polyterafluoroethylene, polyvinyldifluoroethylene, polyethylene, polypropylene, polyethylene terephthalate, polyimide and polyamide. As described above, a reinforced composite membrane impregnated with a perfluorine-based ionomer in a porous support is widely used because of its high process efficiency, low hydrogen permeability, and improved mechanical strength and hydrogen ion conductivity.

On the other hand, separate pretreatment is not necessarily required before extracting the ionomer from the ion exchange membrane, but in the case of using a defective ion exchange membrane that has been neglected for a long time, it is preferable to perform an acid treatment process in advance to remove impurities that would have been contaminated due to an inadequate storage environment.

The acid treatment is performed for the purpose of converting the terminal functional group of the perfluorinated ionomer in the ion exchange membrane from a salt state such as sodium salt (SO ₃ ^- Na ⁺ ) to an acid (SO ₃ ^- H ⁺ ) form capable of hydrogen ion transfer. At this time, the type of acid (acid) that can be used is not particularly limited, but it is suitable to use one of strong acids such as sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), phosphoric acid (H ₃ PO ₄ ), hydrochloric acid (HCl), and the concentration of the acid (acid) is suitable in the range of 0.1 to 10 M. When the concentration is less than 0.1 M, complete conversion to the acid (SO ₃ ^- H ⁺ ) form may not be achieved, and when it exceeds 10 M, it is undesirable from an economic point of view because it is introduced in excess of the amount that can be converted to the acid (SO ₃ ^- H ⁺ ) form. Acid treatment of the ion exchange membrane is generally performed by treating the acid in a boiling state for 30 minutes to 6 hours. Afterwards, it is more preferable to boil in ultrapure water again for 30 minutes to 6 hours in order to remove acid residues that may be excessively adhered to the surface of the ion exchange membrane.

As described above, when the impurity removal from the ion exchange membrane is completed, the ion exchange membrane is dispersed under supercritical conditions of a temperature of 100° C. or higher and a pressure of atmospheric pressure or higher to extract the ionomer in a dispersed liquid phase.

Supercritical fluids above the critical point are characterized by liquid-like solvency, very low surface tension, and gas-like permeability, and the density of the supercritical fluid has the advantage of improving dissolution performance. Since the solute has a low viscosity in a supercritical fluid, mass transfer can be accelerated, so that the perfluorinated ionomer can exhibit high solute diffusivity.

The solubility of these specific solutes can be further improved by introducing mixed solvents. In an embodiment of the present invention, water and alcohol were used as a co-solvent to improve the polarity and solvation strength of the supercritical fluid through the formation of hydrogen bonds. Meanwhile, the mixed solvent used for supercritical dispersion for ionomer recovery preferably has an alcohol content higher than that of water in order to induce rapid volatilization of the solvent when preparing an ion exchange membrane and using an electrode binder later. For example, the volume ratio of alcohol:water is preferably in the range of 55:45 to 99:1.

Alcohols usable in the present invention include, for example, methanol, ethanol, 1-propanol, isopropyl alcohol, butanol, isobutanol, 2-butanol, tert-butanol, n-pentanol, isopentyl alcohol, 2-methyl-1-butanol, neopentyl alcohol, diethyl ketinol, methyl propyl ketinol, methyl isopropyl carbinol, dimethyl ethyl carbinol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2-methyl-2-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-3-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl -1-butanol, 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol and 4-heptanol, and mixtures thereof, but are not particularly limited thereto.

The temperature of the supercritical condition for recovering the perfluorinated ionomer of the present invention is in the range of 100 to 350 ° C, the pressure is in the range of 1 to 17.0 MPa, the temperature for extracting the ionomer in a high concentration is in the range of 130 to 350 ° C, and the pressure is preferably in the range of 4 to 17.0 MPa. When the temperature is less than 100 ° C. or the reaction pressure is less than 1 MPa, it is difficult for the recovered ionomer dispersion to have uniform dispersion characteristics in a partially dispersed state, and on the contrary, when the temperature exceeds 350 ° C. or 17.0 MPa, the reaction conditions of high temperature and high pressure must be maintained, resulting in low economic efficiency. In the present invention, the specific temperature and pressure range for the supercritical dispersion of the ionomer may vary depending on the type and ratio of the ionomer and alcohol to be recovered, and the concentration of the ionomer dispersion can be adjusted according to the purpose of use, so the utilization is very high. The ionomer dispersion supercritically dispersed according to the present invention exhibits unique dispersion characteristics, and can contribute to improving the electrochemical performance of a battery or water electrolysis device incorporating an ion exchange membrane and an electrode binder prepared thereon.

On the other hand, the perfluorine-based ionomer dispersion extracted into the mixed solvent using the supercritical dispersion method is cooled and filtered to separate from the support fibers. The ionomer dispersion can be easily separated using a general filter paper, and it is preferable to use a paper filter paper having an average pore size of 0.45 to 10 μm. It is okay to use other filters or separation devices other than paper filter paper, and there is no particular limitation. Meanwhile, the dispersion that has passed through the filter paper or the filtering device is a dispersion obtained by extracting the ionomer in a mixed solvent of alcohol and water, and may contain a small amount of water-soluble substances such as antioxidants. Since additives such as antioxidants are components used for manufacturing ion exchange membranes or electrode binders, the ionomer dispersion containing a small amount of water-soluble substances such as antioxidants may be used as it is for manufacturing ion exchange membranes or electrode binders.

According to the present invention, since the perfluorinated ionomer dispersion obtained from the defective separation membrane during the process has no difference in performance and quality from the ionomer dispersion prepared by dispersing the ionomer or the commercially available ionomer dispersion, the ion exchange membrane can be manufactured using a general membrane manufacturing method. For example, a perfluorine-based ionomer dispersion obtained from an ion exchange membrane according to the present invention may be cast on a substrate, dried, and heat treated to prepare an ion exchange membrane, and the concentration of the dispersion may be adjusted or mixed with other ionomer dispersions. Any conventional separator manufacturing method may be applied. Even when the perfluorine-based ionomer dispersion obtained from the ion exchange membrane according to the present invention is used as an electrode binder, there is no particular limitation as in the case of using a commercially available ionomer dispersion.

Meanwhile, it was confirmed that the unit cell performance of the ion exchange membrane-based membrane electrode assembly prepared using the ionomer dispersion recovered from the ion exchange membrane through the supercritical dispersion method according to the present invention was excellent, and the membrane electrode assembly was applied as an electrode binder. Unit cell performance was also very good. Therefore, it can be confirmed that the ionomer can be extracted from the defective separator during the process according to the present invention without performance loss.

The present invention will be described in more detail through the following examples. However, the following examples are presented by way of example to aid understanding of the present invention and should not be construed as limiting the scope of the present invention thereto.

<Example 1>

In this example, the perfluorine-based separator was extracted from the perfluorine-based separator, which was defective during the manufacturing process, and recovered as a dispersion composed of an alcohol-water mixed solvent, and the recovered ionomer dispersion was used to re-manufacture the ion exchange membrane.

For this experiment, an ion exchange membrane was prepared in the form of a reinforced composite membrane in which Nafion ionomer (Chemours, USA) was filled in the pores of a porous PTFE support, and a poor separator caused by partial impregnation of the ionomer during the manufacturing process was used. 1-propanol was selected as an alcohol solvent for supercritical dispersion for recovering the perfluorinated ionomer in the ion exchange membrane, and was purchased from Aldrich Chemical Co., USA, and prepared without further purification.

During the process, a defective perfluorinated ion exchange membrane (weight, 25 g) was added to a glass liner containing 124 g of 1-propanol and 101 g of ultrapure water (55:45 weight ratio). A high-pressure/high-temperature reactor (4560 Mini-Bench Reactor System, PARR, USA) was fitted with a glass liner, then the reaction mixture in the reactor was heated to 270 °C at a heating rate of 4.25 °C min ^-1 , and when the pressure reached 7 MPa, the reaction was maintained for 2 h. After cooling slowly under atmospheric pressure (101.3 kPa), a dispersion was obtained. Finally, the recovered ionomer dispersion was separated from the support fibers and filtered using a paper filter having an average pore size of 5 to 10 μm.

The ionomer dispersion recovered as described above was immersed in a porous PTFE support to prepare an ion exchange membrane in the form of a reinforced composite membrane through a dip-coating method. The film was solidified in a vacuum oven set at 50 degrees for 1 hour and heat-treated at 210 degrees for 2 hours to prepare a film. Thereafter, the membrane was prepared by treating in a boiling 0.5 MH ₂ SO ₄ aqueous solution for 2 hours and boiling in ultrapure water for 2 hours to remove excessive H ₂ SO ₄ on the surface of the film sample.

To evaluate the electrochemical performance of a polymer electrolyte fuel cell, an electrode slurry containing a certain amount of a commercially available 40 wt % Pt/C catalyst (Johnson Matthey, England) was transferred to both sides corresponding to an active area of 25 cm ² on the prepared ion exchange membrane to prepare a membrane electrode assembly. At this time, the amount of the catalyst to be loaded was prepared to be 0.4 mg cm ^-2 .

<Example 2>

In this embodiment, the perfluorine-based separator was extracted from the perfluorine-based separator, which was defective during the manufacturing process, and recovered as a dispersion composed of an alcohol-water mixed solvent, and an electrode binder was prepared using the recovered ionomer dispersion.

In this experiment, a reinforced composite membrane (Comparative Example 2) in which Nafion ionomer (Chemours, USA) was partially impregnated in the pores of a porous PTFE support was used as a poor separator, and 1-propanol was selected as an alcohol solvent for supercritical dispersion. It was purchased from Aldrich Chemical Co., USA and prepared without further purification.

During the process, a defective perfluorinated ion exchange membrane (weight, 12 g) was added to a glass liner containing 124 g of 1-propanol and 101 g of ultrapure water (55:45 weight ratio). A high-pressure/high-temperature reactor (4560 Mini-Bench Reactor System, PARR, USA) was fitted with a glass liner, then the reaction mixture in the reactor was heated to 290 °C at a heating rate of 4.25 °C min ^-1 , and when the pressure reached 5 MPa, the reaction was maintained for 1 hour. After cooling slowly under atmospheric pressure (101.3 kPa), a dispersion was obtained. Finally, the recovered ionomer dispersion was separated from the support fibers using a paper filter having an average pore size of 5 to 10 μm to obtain an electrode binder.

To evaluate the electrochemical performance of a polymer electrolyte fuel cell, a commercially available 40 wt % Pt/C catalyst (Johnson Matthey, UK) was mixed with ultrapure water and isopropyl alcohol (IPA, Sigma-Aldrich, USA) using a homogenizer (VCX130, Sonics & Materials Inc., USA). Then, 5 wt % of the ionomer electrode binder prepared as described above was added to the ink slurry and mixed for 30 minutes. A 7 cm × 7 cm Nafion membrane (NR211, Chemours, USA) was prepared, and the prepared ink slurry was applied on the cathode-side membrane corresponding to an active area of 25 cm ² at 0.4 mg cm ⁻² . sprayed.

<Comparative Example 1>

For comparison, an ion exchange membrane in the form of a reinforced composite membrane in which Nafion ionomer is normally filled in the pores of a porous PTFE support without any defects (ionomer partial impregnation, failure to control thickness, failure to control drying/heat treatment conditions, etc.) was prepared and used. In addition, for unit cell performance evaluation, an MEA was manufactured and prepared in the same manner as in Example 1 above.

<Comparative Example 2>

For comparison, an ion exchange membrane in the form of a reinforced composite membrane in which Nafion ionomer is partially impregnated in the pores of a porous PTFE support was prepared and used as a poor separation membrane during the process. In addition, for unit cell performance evaluation, an MEA was manufactured and prepared in the same manner as in Example 1 above.

<Comparative Example 3>

To compare the performance of the electrode binder, a commercially available Nafion binder (D521, Chemours, USA) was prepared, and an MEA was prepared in the same manner as in Example 2.

<Comparative Example 4>

During the process, a defective perfluorinated ion exchange membrane (weight, 25 g) was added to a glass liner containing 124 g of 1-propanol and 101 g of ultrapure water (weight ratio 55:45), and the ionomer was dispersed in the same manner as in Example 1, except that the temperature of the reactor (4560 Mini-Bench Reactor System, PARR, USA) was reacted at 80 ° C and atmospheric pressure. As such, when the ion exchange membrane was dispersed under temperature and pressure conditions outside the supercritical range, extraction of the ionomer from the membrane hardly occurred, and even a small amount of extracted ionomer at a low concentration was not uniformly dispersed in the solvent, resulting in poor dispersion characteristics. Therefore, it was confirmed that the ionomer dispersion obtained in this experiment had too low a concentration and poor dispersion characteristics, and thus was not suitable for manufacturing an ion exchange membrane or an electrode binder.

<Experimental Example> Unit cell performance comparison test

2 is a graph showing current-voltage curves of Example 1 and Comparative Examples 1 and 2 according to the present invention at 65 °C. Looking at the results, it can be confirmed that Example 1 exhibits better unit cell performance than Comparative Examples 1 and 2 at the same current density. The membrane properties, which were deteriorated due to the partial impregnation of the ionomer generated during the manufacturing process, are remanufactured and restored through recovery technology, and the change in the dispersion characteristics of the ionomer during supercritical dispersion results in effective hydrogen ion conduction and gas barrier properties on the ion exchange membrane.

3 is a graph showing current-voltage curves of MEA prepared by introducing Example 2 and Comparative Example 3 according to the present invention as an electrode binder into a cathode under an oxygen condition at 65 °C. Looking at the results, it can be seen that Example 2 (1.57 A/cm ² @0.6 V) exhibits better unit cell performance than commercial Comparative Example 3 (1.28 A/cm ² @0.6 V). The expression of unique dispersion characteristics obtained through the supercritical dispersion process for recovery leads to effective hydrogen ion conduction and gas permeation characteristics in the electrode layer, which is considered to be an effect due to improved PEFC performance.

Claims (14)

A method for preparing an ionomer dispersion using a defective ion exchange membrane, comprising the following steps:
(S1) preparing an ion exchange membrane determined to be defective during a production process;
(S2) dispersing the defective ion exchange membrane in a solvent at a temperature of 100 °C or higher and a pressure of 1 MPa or higher; and
(S3) cooling and separating the dispersion from which the ionomer was extracted through the dispersion process. According to claim 1,
The method for producing an ionomer dispersion, characterized in that the ion exchange membrane determined to be defective is a defective product due to partial impregnation of the ionomer, failure to control the film thickness, failure to control the drying or heat treatment process, or an unused product due to a difference in specifications. According to claim 1,
The ion exchange membrane is a method for producing an ionomer dispersion, characterized in that the perfluorine-based separation membrane. According to claim 1,
The method for producing an ionomer dispersion, characterized in that the ion exchange membrane is a reinforced composite membrane including a support or a pure electrolyte membrane without a support. According to claim 1,
The step (S1) of preparing the ion exchange membrane determined to be defective during the production process comprises the step of treating the ion exchange membrane with an acid to remove impurities. According to claim 5,
The acid is a method for preparing an ionomer dispersion, characterized in that at least one selected from sulfuric acid (H ₂ SO ₄ ), nitric acid (HNO ₃ ), phosphoric acid (H ₃ PO ₄ ), and hydrochloric acid (HCl). According to claim 5,
The method for preparing an ionomer dispersion, further comprising the step of treating the ion exchange membrane with acid and then boiling it in ultrapure water to remove acid residues. According to claim 1,
The method of preparing an ionomer dispersion, characterized in that the solvent is a mixed solution of alcohol and water. According to claim 8,
The alcohol is methanol, ethanol, 1-propanol, isopropyl alcohol, butanol, isobutanol, 2-butanol, tert-butanol, n-pentanol, isopentyl alcohol, 2-methyl-1-butanol, neopentyl alcohol, diethyl ketinol, methyl propyl ketinol, methyl isopropyl carbinol, dimethyl ethyl carbinol, 1-hexanol, 2-hexanol, 3-hexanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 4-methyl-1-pentanol, 2-methyl-2-pentanol, 3-methyl-2-pentanol, 4-methyl-2-pentanol, 2-methyl-3-pentanol, 3-methyl-3-pentanol, 2,2-dimethyl-1-butanol, 2,3-dimethyl-1-butanol, At least one selected from the group consisting of 2,3-dimethyl-2-butanol, 3,3-dimethyl-1-butanol, 2-ethyl-1-butanol, 1-heptanol, 2-heptanol, 3-heptanol and 4-heptanol Method for producing an ionomer dispersion, characterized in that. According to claim 8,
The method for producing an ionomer dispersion, characterized in that the alcohol and water are in the range of 55:45 to 99:1 by volume. According to claim 1,
The dispersion temperature in step (S2) is in the range of 100 to 350 ° C, and the pressure is in the range of 1 to 17.0 MPa. An ion exchange membrane prepared using the ionomer dispersion prepared according to claim 1. An electrode binder prepared using the ionomer dispersion prepared according to claim 1. A membrane electrode assembly comprising the ion exchange membrane according to claim 12 or the electrode binder according to claim 13.