KR20030076057A - Polymer composite electrolyte membrane for fuel battery and method for preparing the same - Google Patents

Abstract

PURPOSE: Provided is a composite polymer electrolyte membrane for a fuel cell, which has high ion conductivity, low methanol permeability, excellent mechanical property and uniformly dispersed hydrophilic micropores. CONSTITUTION: The electrolyte membrane(2) for a fuel cell is characterized by comprising a polymer film containing the pores having the maximum size of 50 nm and the porosity of 15 to 60 volume%. In particular, the polymer film is composed of 40 to 80 wt% of a polymer selected from the group consisting of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, polyacrylonitrile and a mixture thereof, and 20 to 60 wt% of a hydrophilic mineral powders. The polymer film preferably has the thickness of 5 to 500 micrometers.

Description

Composite Polymer Electrolyte Membrane for Fuel Cell and Manufacturing Method Thereof {POLYMER COMPOSITE ELECTROLYTE MEMBRANE FOR FUEL BATTERY AND METHOD FOR PREPARING THE SAME}

The present invention relates to an electrolyte membrane, and more particularly, to an electrolyte membrane for a fuel cell, a manufacturing method thereof, and a fuel cell to which the same is applied.

There are five types of fuel cells: phosphoric acid (PAFC), molten carbonate (MCFC), solid electrolyte (SOFC), polymer electrolyte (PEMFC), and direct methanol fuel cell (DMFC), depending on the type of electrolyte used. Among them, DMFC is known to be the most suitable form for ultra-miniaturization and portable. In recent years, PEMFC and DMFC, which is the most active research and one step closer to commercialization, are the core material of polymer electrolyte, which is a carrier of hydrogen ion between anode and cathode, and Nafion electrolyte, which is a fluorine-based electrolyte, is in the spotlight now. have.

Fuel cells are strongly acidic because of the presence of hydrogen ions in the electrolyte, and oxygen and hydrogen ions react at the cathode, so a polymer electrolyte having excellent thermal and oxidation stability that can withstand such an oxidizing atmosphere is required. Currently, polymers that can withstand these reaction conditions are fluorine-based electrolyte membranes having stronger C-F bonds than C-H bonds. In addition, in order to prevent the movement of methanol, which is a fuel, an electrolyte must be composed of a material having little or no affinity with methanol.

Nafion refers to a proton conducting membrane developed by Dupont, and the chemical name of Nafion is perfluorosulphonic acid. The molecular structure of the Nafion membrane is shown in the following formula (1).

[Formula 1]

As shown in Formula 1, the Nafion membrane structure has a form in which polytetrafluoroethylene (hereinafter referred to as PTFE) forms a skeleton and sulfonic acid is attached to the end of a side chain. Due to its very unique characteristics.

This Nafion membrane has both hydrophilic and hydrophobic properties. PTFE has a hydrophobicity to discharge water supplied to the membrane to prevent flooding in the structure, and to maintain physically strong and chemically stable conditions due to the strong bonding force between fluorine and carbon. This is very excellent. On the other hand, when looking at sulfonic acid functional groups, SO ^{3 −} and H ⁺ ions are strongly bound by ionic bonds. However, because sulfonic acid is hydrophilic, it attracts water and eventually forms a dilute acid region having a very high water content in the overall structure. This hydration (hydration) is to significantly reduce the binding force between the H ⁺ ions and sulfone anions and finally to be able to move the H ⁺ ions. Indeed, this structure enables high ion conductivity of about 0.1 S / cm 2 below 100 ° C. This mechanism of proton conducting is shown in Scheme 1 below.

Scheme 1

Currently, Nafion membrane is divided into Nafion 117, Nafion 115 and Nafion 112 according to the thickness and commercialized. However, the Nafion membrane has the biggest disadvantage that the price is too expensive in spite of various advantages, acting as the biggest obstacle to the commercialization of fuel cells.

In addition, Nafion has a disadvantage in that it is difficult to be used directly for methanol fuel cells due to the cross-over phenomenon of the fuel in addition to the high price. Basically, Nafion becomes conductive only after hydration. As the fuel of the direct methanol fuel cell, an aqueous solution in which methanol is diluted to about 3 to 15% by weight is used. At this time, water and methanol penetrate into the structure of Nafion to hydrate the membrane. The phenomenon is cross-over. When methanol is diffused toward the anode, a negative potential is generated between Pt, an anode catalyst, and the OCV (Open Cuicuit Voltage) of the cathode and the anode has a smaller value than the theoretical value. Therefore, it plays a role of reducing the performance of the fuel cell as a whole.

That is, the Nafion electrolyte has a problem in that the manufacturing cost is high and methanol, a fuel, is transmitted to the anode through the electrolyte. Therefore, there is a need for the development of new polymer electrolyte membranes which are low in production cost and have no or very low methanol permeation.

On the other hand, polyvinylidene fluoride (PVdF) is known as a polymer having thermal stability, chemical and electrochemical stability, and mechanical strength. Such PVdF is easy to process and has already been used as a binder in a lithium secondary battery, and thus has characteristics and performances and has various advantages such as thin film manufacturing. In fact, PVdF has been developed as a separator in a lithium polymer secondary battery (LiPB), which is compatible with ceramic powder and can produce a thin and uniform separator in which the ceramic powder is uniformly dispersed.

Examples of the composite of PVdF and inorganic powder to make an electrolyte and applied to a battery include US Pat. Nos. 5,296,318, 5,456,000, and 5,643,689. This method is to prepare a uniform and flexible film by mixing inorganic powder in PVdF and plasticizer added to it, extracting the plasticizer using the extraction solvent from the film to make uniform fine pores and impregnated organic electrolyte in the pores (swelling) ) As a polymer electrolyte of a lithium secondary battery.

In addition, WO 99/44245 prepared an ion conductive electrolyte by combining PVdF with a hydrophilic inorganic powder. The method for producing a film is to prepare a uniform slurry using a low boiling point solvent and a high boiling point solvent having a high volatilization temperature. It was coated on and dried at room temperature for 24 hours to make a transparent film. In this film, a solvent having a high volatilization temperature was extracted and dissolved in water to form fine pores. The film was impregnated with an acid, alkali, or salt solution, and used as an ion conductive electrolyte. The limitation of this method is that it takes a long time to manufacture the film because it needs to be dried at room temperature, and it is also difficult to apply commercially because it takes a long time to extract the hot volatile solvent contained in the film. There is a possibility to affect.

However, the film produced by the above methods is not applied to the DMFC, and if the pores are not properly formed, the permeation of methanol, which is a very important fuel in the DMFC, or the ionic conductivity is low, so there is a problem in applying to the fuel cell.

SUMMARY OF THE INVENTION In view of the problems of the prior art, an object of the present invention is to provide an electrolyte membrane for a fuel cell and a method for producing the same, which maintain a high ion conductivity and have a very low permeability of fuel methanol.

Another object of the present invention is to provide a polymer composite electrolyte membrane for a fuel cell having excellent mechanical strength and uniformly dispersed fine hydrophilic pores, and a method of manufacturing the same.

1 is a schematic diagram of a MEA (Membrane Electrode Assembly) of a fuel cell manufactured by thermally compressing a composite electrolyte membrane and an electrode of the present invention.

2 is a graph comparing ionic conductivity and methanol permeability according to porosity of the composite polymer electrolyte membrane of Example 5. FIG.

3 is a conceptual diagram illustrating that the pores of the composite electrolyte membrane of the present invention are reduced by thermal pressure.

Reference numeral 1 is an anode having a catalyst powder of Pt-Ru (50%: 50%), 2 is a composite electrolyte membrane, 3 is a cathode having a Pt-Black catalyst powder, and a is a pore. The ionic conductivity value according to the figure, b is the permeation amount of methanol according to the porosity, and the hatched area of FIG. 2 shows the appropriate porosity with excellent performance.

In order to achieve the above object, the present invention provides a fuel cell electrolyte membrane,

An electrolyte membrane for a fuel cell comprising a polymer film containing pores having a pore size of up to 50 nm and a porosity of 15 to 60% by volume.

The polymer film

a) polyvinylidene fluoride (PVdF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), and 40 to 80% by weight of a polymer selected from the group consisting of mixed polymers by a combination thereof; And

b) 20 to 60% by weight of hydrophilic inorganic powder

It is preferable to include.

In addition, the present invention is a method of manufacturing an electrolyte membrane for a fuel cell,

It provides a method for producing an electrolyte membrane for a fuel cell comprising the step of producing a membrane containing pores having a pore size of up to 50 nm, porosity of 15 to 60% by volume by thermally pressing a polymer film containing pores.

In another aspect, the present invention provides a fuel cell comprising the electrolyte membrane for the fuel cell.

Hereinafter, the present invention will be described in detail.

The present invention provides a composite polymer electrolyte of a new concept that compensates for the shortcomings of the polymer electrolyte used in the conventional fuel cell, a method for producing the same, and a fuel cell including the same as an electrolyte membrane.

The present invention provides a polymer electrolyte that can dramatically reduce the methanol methanol's permeability (Methanol Crossover) while maintaining high ionic conductivity when applied to a fuel cell, and a method for commercially producing the same. In particular, the size of the pores and the number of pores are controlled, and hydrophilic pores are formed to provide an electrolyte membrane having a high ion conductivity and an extremely low permeation rate of methanol.

To this end, the present invention is excellent in chemical and electrochemical, thermal and dimensional stability, it is possible to manufacture a thin film, such as polyvinylidene fluoride (PVdF) that can not easily penetrate fuel due to affinity with methanol as a raw material A polymer is used, and a hydrophilic inorganic powder is added and compounded therein to prepare a composite film. Pores are formed in the film to prepare a composite electrolyte membrane, followed by thermocompression. The electrolyte membrane thus prepared has a high ion conductivity and a small amount of methanol permeation, which not only improves the battery performance when applied to fuel cells such as DMFC, but also improves the high temperature performance of the battery.

The composite polymer electrolyte membrane of the present invention is a film (film) in which a polymer and an inorganic powder are mixed, and the polymer serves as a support for enclosing the inorganic powder and maintains the mechanical strength of the film. The inorganic powder has hydrophilicity and imparts hydrophilicity to the composite polymer electrolyte membrane. In addition, the micropores of the powder and the micropores formed in the membrane has a characteristic of maintaining a high ion conductivity by supporting a lot of electrolyte solution.

When the composite electrolyte membrane of the present invention is applied directly to a methanol fuel cell, and the characteristics of the cell are evaluated, the performance of the cell is equal to or higher than that of a battery using a conventional Nafion electrolyte, and in particular, the methanol permeability is low. Have

The ionic conductivity of the electrolyte to which the composite electrolyte membrane of the present invention is applied is made by the liquid electrolyte solution impregnated with the composite polymer electrolyte membrane. That is, the ion conduction of the electrolyte membrane of the present invention is caused by the movement of acid, base, and salt solution. Therefore, the composite polymer electrolyte should be able to impregnate a lot of liquid electrolyte. The impregnation amount of the liquid electrolyte depends on the micropores in the composite polymer electrolyte membrane. The more pores, the more the impregnation of the liquid electrolyte increases and the ionic conductivity increases. However, since polymers such as PVdF are hydrophobic, hydrophilic inorganic powders are added to impart hydrophilicity to them. In addition to improving the mechanical strength of the membrane, the inorganic powder can also support the electrolyte at high temperatures, thereby maintaining the ionic conductivity at high temperatures, thereby improving the high temperature characteristics of the battery.

If the pore size of the electrolyte membrane of the fuel cell is larger than a certain size, the permeability of methanol increases rapidly. Therefore, it is important to finely control the pore size, to uniformly control the pore distribution, and to make the pores hydrophilic in the composite polymer electrolyte membrane. Therefore, the present invention is to control the size of the pores finely and uniformly dispersed in the preparation of the electrolyte membrane and to make the pores become hydrophilic. In addition, since the electrolyte membrane can be used as a separator of a fuel cell by stacking a plurality of films, the porosity of the electrolyte membrane can be adjusted to an appropriate range by thermocompression bonding.

The polymer that serves as a support for the composite polymer electrolyte membrane of the present invention and provides mechanical strength is chemically, electrochemically and thermally stable and has compatibility in aqueous solution. Examples thereof include polyvinylidene fluoride (PVdF) and poly A copolymer of vinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), or a mixed polymer thereof. The electrolyte membrane contains 40 to 80% by weight.

In addition, the inorganic powder is hydrophilic, the type is aluminum oxide (Al ₂ O ₃ ), fumed silica (zemed), zeolite (Zeolite), titanium oxide (TiO ₂ ) -based, barium titanate (BaTiO ₃ ) And at least one selected from the group consisting of inorganic powders having a molecular sieve structure. The size of the powder is 5 to 500 nanometers (nm), and the specific surface area is preferably 10 to 500 m 2 / g.

The composite polymer electrolyte membrane of the present invention contains micropores in the membrane, and in order to prevent the permeation of methanol in the fuel cell, the porosity is preferably 15 to 60% by volume and the size of the micropores is at most 50 nm. More preferably, the pore size is 3 to 20 nm, and the porosity is 15 to 30% by volume. These micropores are filled with a solution of acids, bases, and salts that exhibit ionic conductivity.

The composite polymer electrolyte membrane of the present invention preferably has a thickness of 5 to 500 micrometers (µm), and this membrane can be used as an electrolyte membrane of a fuel cell by laminating a plurality of films.

Hereinafter, the manufacturing method of the composite polymer electrolyte membrane of the present invention will be described.

The composite polymer electrolyte membrane of the present invention is prepared by using a so-called solvent casting method for making a slurry from a solvent, coating it on a release paper, and drying the solvent, and an extrusion method for extruding a film raw material in an extruder. Can be.

Specifically, the first manufacturing method of the electrolyte membrane for a fuel cell by the solvent casting method

a) in solvent

Iii) polyvinylidene fluoride (PVdF), copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), and 40 to 80 parts by weight of a polymer selected from the group consisting of mixed polymers combined therefrom;

Ii) Aluminum oxide (Al ₂ O ₃ ) -based, fumed silica-based, zeolite-based, titanium oxide (TiO ₂ ) -based, barium titanate (BaTiO ₃ ) -based, and molecular sieve structures 20 to 60 parts by weight of at least one hydrophilic inorganic powder selected from the group consisting of inorganic powders; And

Iii) 8 to 120 parts by weight of plasticizer

Adding, mixing and dissolving to prepare a slurry;

b) coating the slurry of step a) on a release paper and drying to form a film;

c) extracting the plasticizer by impregnating the film of step b) in the extraction solvent; And

d) thermopressing the film of step c)

To prepare an electrolyte membrane for a fuel cell, including.

In addition, the second manufacturing method of the electrolyte membrane for a fuel cell by the extrusion method

a) polyvinylidene fluoride (PVdF), copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN) 40 to 80 parts by weight of a polymer selected from the group consisting of, and mixed polymers combined therefrom;

Ii) Aluminum oxide (Al ₂ O ₃ ) -based, fumed silica-based, zeolite-based, titanium oxide (TiO ₂ ) -based, barium titanate (BaTiO ₃ ) -based, and molecular sieve 20 to 60 parts by weight of a hydrophilic inorganic powder selected from the group consisting of inorganic powders having a structure; And

Iii) 8 to 120 parts by weight of plasticizer

Mixing;

b) injecting the mixture of step a) into an extruder and extruding at a temperature of 120 to 170 ℃ forming a film;

c) extracting the plasticizer by impregnating the film of step b) in the extraction solvent; And

d) thermopressing the film of step c)

It includes.

In the solvent casting method, a polymer, a hydrophilic inorganic powder, and a plasticizer are mixed and dissolved and dispersed in a solvent to prepare a slurry, the slurry is coated on a release paper, dried to form a film, and then the plasticizer in the film is extracted with an extraction solvent. The pores are extracted to form a composite polymer electrolyte membrane. The drying temperature may vary depending on the type of polymer and solvent used, but 80 to 95 ° C. is preferred. The solvent used in the solvent casting method is preferably acetone, dimethylformamide (DMF), dimethylacetamide (DMAC), N-methylpyrrolidone (NMP), tetrahydrofuran (THF), methylethyl-ketone (MEK), or a mixed solvent thereof. .

In the extrusion method, a polymer, a hydrophilic inorganic powder, and a plasticizer are mixed, and the mixture is introduced into an extruder, extruded, and molded into a film, followed by extracting the plasticizer in the film with an extraction solvent to form pores to form a composite polymer electrolyte membrane. Manufacture. The extrusion temperature may vary depending on the type of polymer, but 120 to 170 ° C. is preferred.

The electrolyte membrane prepared in this way is commonly used to extract the plasticizer contained in the film to form micropores. That is, the film is prepared by containing 20 to 150% by weight of a plasticizer relative to the weight of the polymer used in the film raw material, and then the plasticizer is extracted with the extraction solvent. Types of plasticizers include dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), dioctyl phthalate (DOP), dialkyl phthalate (DAP), ethylene carbonate (EC), and propylene carbonate (PC). , Dimethyl adipate (DMA) and the like and combinations thereof. As the extraction solvent, a solvent that can dissolve and extract a plasticizer such as methanol or diethylether may be used.

The composite polymer electrolyte membrane thus prepared is hot pressed to reduce pores to a size such that methanol cannot be permeated. For example, the pore size of the membrane before thermocompression is 10 to 50 nm, but the pore size after thermocompression is reduced to 3 to 10 nm, and the pore size becomes smaller as shown in FIG. Therefore, as the pore size decreases, the ionic conductivity of protons is maintained, but methanol permeation is drastically reduced. The thermocompression temperature is preferably 80 to 160 ° C., and the pressure may be slightly different depending on the thickness of the membrane, but the range of 5 Kg / cm 2 to 10 ton / cm 2 is a condition for obtaining a pore size that reduces methanol permeation. In the thermo-pressure method, the films may be laminated and pressed in a heating press, or may be pressed by passing a lamination roller.

The composite polymer electrolyte membrane of the present invention can be made of a laminated film in which a plurality of films are laminated. Such laminations are made by laminating and hot pressing multiple films before or after plasticizer extraction, including lamination of ones of the same composition or of different compositions with each other. Preferably, two or more films are laminated before plasticizer extraction, thermocompression-bonded to integrate the film, and then the plasticizer is extracted to form pores, and the laminated film on which the pores are formed is manufactured by thermopressing again. The temperature for thermocompression bonding the film is preferably 80 to 160 ℃, the pressure may be slightly different depending on the thickness of the film, but the range of 5 Kg / ㎠ to 10 ton / ㎠. In the thermo-pressure method, the films may be laminated and pressed in a heating press, or may be pressed by passing a lamination roller.

The pores of the electrolyte membrane of the present invention can be adjusted by the amount of plasticizer to prepare a membrane having a controlled porosity, and the pores can be adjusted according to temperature and pressure in the process of hot pressing the membrane. Basically, the pore size is adjusted to 50 nm or less, preferably 3 to 20 nm, and the porosity is adjusted to 15 to 60% by volume, particularly 15 to 30% by volume, which shows excellent characteristics in the fuel cell. The size of the micropores of the present invention is measured by applying the specific surface area measurement method of the BET method (Brunauer, Emmett, Teller Method) using the nitrogen adsorption amount obtained from the single molecule adsorption layer of nitrogen. In other words, it is assumed that the specific surface area is formed as a part of the walls of all the micropores, and in a simple geometric calculation, the average pore radius is converted to twice the pore volume divided by the surface area.

The electrolyte membrane of the present invention should be impregnated with an electrolyte solution in the acid solution to show the ionic conductivity, the acid concentration in the acid solution is preferably 0.1 to 5 M, the acid type of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, super acid (CF ₃ (CF ₂ ) _n SO ₃ H, HO ₃ S (CF ₂ ) _n SO ₃ H), or mixed acids combined therefrom are used.

In the electrolyte membrane, the acid solution is impregnated into the micropores. Higher porosity results in higher ion conductivity but higher methanol permeability, while lower porosity results in lower ion conductivity but lower methanol permeability. Therefore, porosity in the membrane is important and must be adjusted in a complementary way.

When the composite polymer electrolyte membrane of the present invention is applied to a fuel cell, the thermocompressed micropore-controlled electrolyte membrane is placed in the center and the cathode and the cathode are respectively placed on both sides of the membrane to be thermally compressed to be assembled into a battery cell (Cell; full cell). have.

Each of the above electrodes can be prepared similarly to the preparation of the electrolyte membrane of the present invention. For example, the polymer and the inorganic powder are the same, and the composition of each component is 70 to 90% by weight of the noble metal catalyst (for example, Pt-Ru alloy for the cathode and Pt-black for the anode) and 10 to 20 polymers. It is preferable to contain the weight% and the inorganic powder 0-15 weight%. In the manufacturing method of the electrode may include both a method of making a slurry made of a solvent and coating it and an extrusion method.

The composite polymer electrolyte membrane of the present invention has a high ion conductivity, and at the same thickness, methanol has a lower permeability than a conventional Nafion electrolyte membrane, which is very suitable for use in fuel cells. In addition, when the composite polymer electrolyte membrane is directly applied to a methanol fuel cell, the cell performance is equal to or higher than that of a conventional Nafion electrolyte, and the manufacturing process is simple and very economical.

Due to these advantages, the composite polymer electrolyte of the present invention and a direct methanol fuel cell using the same may be used as a power source for medium and large household appliances, and also as a power source for electric vehicles.

The present invention will be described in more detail with reference to the following examples and comparative examples. However, an Example is for illustrating this invention and is not limited only to these.

EXAMPLE

Example 1

(Production of Composite Polymer Electrolyte Membrane)

The composite polymer electrolyte membrane was prepared by preparing a slurry in a dry room having a relative humidity of less than 1% and coating a film to prevent moisture from being absorbed in the manufacturing process of the polymer and the inorganic powder.

As a polymer, a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP) was used.

Inorganic powder was used as the fumed silica (SiO ₂ ) as follows.

1) AE200 (AEROSIL manufactured by DAGUSSA): Specific surface area 200 ㎡ / g

2) AE300 (AEROSIL manufactured by DAGUSSA): Specific surface area 380 ㎡ / g

3) M-5 (CAB-O-SIL manufactured by CABOT): Specific surface area 200 m 2 / g

4) H-5 (CAB-O-SIL manufactured by Cabot Co., Ltd.): specific surface area 300 m 2 / g

5) EH-5 (CAB-O-SIL manufactured by Cabot Co., Ltd.): specific surface area 380 m 2 / g

The plasticizer used dibutyl phthalate (DBP).

As a solvent, a mixed solvent obtained by mixing acetone and an NMP solvent was used. The mixing ratio was used in the range of acetone / NMP = 0.5 to 4 by volume, in the present embodiment mainly used acetone amount of 50 to 70% by volume in the total solution. The amount of solvent used is 70 to 85 ml based on 10 g of the powder sample.

Slurry preparation is first put an appropriate amount of inorganic powder in a container, and when the powder is completely dispersed in a solvent, the appropriate amount of polymer is added and dispersed again. Place the plasticizer in a well dispersed solution and allow the plasticizer to be sufficiently dispersed in the slurry.

The uniformly dispersed slurry was prepared by coating in an automated Hirano Corporation (Japan) coater of Doctor blade type. The slurry was coated to a suitable thickness on a silicon-release paper (silicon-release paper) on the surface and immediately dried to prepare a film. The drying temperature was adjusted to 80 to 95 ℃ and in this example mainly dried at 85 to 90 ℃ 15 minutes.

The prepared electrolyte membrane was put in an extraction solvent to extract a plasticizer. Methanol or diethylether was used as an extraction solvent, and it was supported for more than 1 hour, extracted, and dried. This process was repeated three times and washed in fresh solution to ensure complete extraction.

Porosity (porosity; porosity) of the electrolyte membrane is defined as the ratio of the pore volume (V _p ) and the total volume (V _t ) according to Equation 1 below. That is, the pore volume is obtained by subtracting the volume occupied by the particle (V _p ) from the total volume V _t .

[Equation 1]

In Equation 1,

V _p is the volume of the particles and V _t is the total volume.

In the present invention, the porosity (porosity) calculation of the electrolyte membrane was performed based on the following basis. The total volume (V _t ) of the film was obtained from the size and thickness of the film, and the volume occupied by the particles was obtained from the composition of the film by the weight of each powder in the total weight of the film. Since PCM uses PVdF and SiO ₂ , the volume (V _p ) occupied by the particles was calculated from the weight and density of each of them. The total volume (V _t ) of the film minus the volume (V _p ) at which particles are filled is the pore volume, and from these values, the porosity of the electrolyte membrane was determined using Equation 1 above.

The pore and mechanical strength of the electrolyte membrane according to the slurry composition is shown in Table 1 below. Here, the amount of plasticizer is fixed and manufactured in the same manner while changing the amount of PVdF and the type and amount of SiO ₂ .

Composition, Porosity and Mechanical Strength of Electrolyte Membrane division Silica Type and Amount (g) Amount of PVdF (g) Amount of plasticizer (g) Mechanical strength Porosity (%) Composition 1 M-5: 2 8 10 Very good 32 to 35 Composition 2 H-5: 2 8 10 Very good 34-37 Composition 3 EH-5: 2 8 10 Very good 35 to 39 Composition 4 M-5: 3 7 10 Very good 38-42 Composition 5 H-5: 3 7 10 Very good 39-43 Composition 6 EH-5: 3 7 10 Good 40-44 Composition 7 M-5: 4 6 10 Bad 42 to 45 Composition 8 H-5: 4 6 10 Bad 43-45 Composition 9 EH-5: 4 6 10 Very bad 44-46

Good in mechanical strength is the use of electrolyte membranes in batteries, bad is uneven or not easy to use membranes, and very bad is a uniform membrane not well made or difficult to use.

Inorganic powder does not affect the influence of SiO ₂ depending on the manufacturer (DAGUSSA, or CABOT) and affects the surface area of the powder. As the surface area increased to 200 m 2 / g, 300 m 2 / g, and 380 m 2 / g, the porosity increased but the mechanical strength of the membrane decreased.

Inorganic powder SiO ₂ is prepared using M-5 (200 m 2 / g) and adjusting the amount of plasticizer (DBP) to 2 to 20 g based on the combined amount of polymer and inorganic powder of 10 g in the same composition. The comparison is shown in Table 2.

Influence of Plasticizers in the Composition of Electrolyte Membranes division Silica Type and Amount (g) Amount of PVdF (g) Amount of plasticizer (g) Mechanical strength Porosity (%) Composition 10 M-5: 3 7 2 Very good 28-32 Composition 11 M-5: 3 7 5 Very good 30 to 33 Composition 12 M-5: 3 7 7.5 Very good 38-41 Composition 13 M-5: 3 7 10 Very good 39-42 Composition 14 M-5: 3 7 15 Bad 40-44 Composition 15 M-5: 3 7 20 Very bad 42-44

As the amount of plasticizer increased, the porosity increased but the mechanical strength decreased. The amount of plasticizer in the range of 7.5 to 10 g (compositions 12 and 13) showed no significant change in porosity and excellent mechanical strength of the membrane.

Example 2

An electrolyte membrane was prepared and tested in the same manner as in Example 1 except that the polymer was changed to polyvinylidene fluoride (PVdF).

Test results were similar to Example 1 above. Polyvinylidene fluoride (PVdF), a homopolymer, has a degree of crystallinity compared to a copolymer of polyvinylidene fluoride-hexafluoropropylene, a copolymer (PVdF-HFP copolymer: PVD-HFP). (crystalinity) is high. In the fuel cell, the electrolyte membrane is preferably low in crystallinity because of its high flexibility.

Example 3

(Ion conductivity measurement)

Since the ionic conductivity of the electrolyte membrane is caused by the acid solution impregnated in the micropores, the electrolyte membrane must first be impregnated with the acid solution. In the present invention, sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, super acidic acid (CF ₃ (CF ₂ ) _n SO ₃ H, HO ₃ S (CF ₂ ) _n SO ₃ H) or a mixed acid thereof is used in the case of using sulfuric acid It has the best ionic conductivity.

In the ion conductivity measurement, the electrolyte membrane was immersed in a 3 molar acid solution for 5 hours, and then the ac impedance was measured.

Example 4

Methanol Permeability Measurement

Methanol permeability was measured using a diffusion cell. The electrolyte membrane was placed in the center of the cell, 100% methanol was charged in one cell, and pure water was charged in the other, and then the amount of methanol movement was measured over time. At this time, the detector used a refractometer.

Example 5

(Manufacture of composite polymer electrolyte membrane for battery)

In the composite polymer electrolyte membrane for batteries, a film of composition 13 of Example 1 having a thickness of 60 μm was used and four sheets were laminated. Lamination process was carried out at a temperature of 130 to 160 ℃ by cutting the film prepared by coating to an appropriate size. There was no significant effect on the temperature, but in the present embodiment, the production was mainly performed at 140 to 145 ° C. In the case of lamination of several sheets, two sheets were laminated first, followed by second lamination. These laminated multilayer films are integrated because they are bonded together at temperatures above the melting point of PVdF.

Example 6

(Control of Porosity of Composite Polymer Electrolyte Membrane)

The membrane of the composition 13 of Example 1 was laminated in the same manner as in Example 5 to prepare a multilayer membrane, and then the plasticizer was removed using an extraction solvent to prepare an electrolyte membrane. The porosity of this membrane is on the order of 38 to 42% by volume. The pore size was measured by the BET method (Brunauer, Emmett, Teller Method) using the nitrogen adsorption amount obtained from the monomolecular adsorbent layer of nitrogen (using ASAP 2010 by micromeritics) and showed a distribution of 10 to 50 nm.

If the porosity is high, the ion conductivity is high, but at the same time the methanol permeability is also high, so porosity is controlled by thermocompression. Here, the thermocompression temperature 80 to 160 ℃, the pressure was used to adjust the compression conditions in the range of 5 Kg / ㎠ to 10 ton / ㎠ to have a porosity of 15 to 30% by volume. The performance of the cell was best in the range of 18 to 25% by volume porosity as shown in FIG. In addition, the influence of the ion conductivity and the methanol permeability on the pore size of the membrane was relatively high permeability of methanol when the pore size exceeded 50 nm, and relatively low when the pore size was less than 3 nm. Therefore, the size of the membrane pores is preferably 50 nm or less, especially 3 to 20 nm was more excellent.

Example 7

(Electrode manufacture)

The composition of the electrode was set in the range of 70 to 90% by weight of the noble metal catalyst, 10 to 20% by weight of the polymer, 0 to 15% by weight of the inorganic powder. In this embodiment, the negative electrode has a composition of Pt-Ru alloy powder (Pt: Ru = 50% by weight: 50% by weight, Johnson Matthey Co.) 0.85g, PVdF powder (KF-2801 manufactured by elf atochem) 0.1g, 0.05 g of SiO ₂ powder (CAB-O-SIL manufactured by CABOT; M-5); 0.80 g of Pt-Black powder (Pt Black, Johnson Matthey Co.) as a catalyst, PVdF powder (elf atochem, KF- 2801) 0.13 g, SiO ₇ powder (CABOT, CAB-O-SIL, M-5) 0.07 g.

The electrode is prepared by spray coating a diffusion layer (carbon paper) by preparing a slurry, and the slurry is prepared in the same manner as in Example 1. The amount of loading of the catalyst was calculated by weight measurement while drying.

The solvent used the same mixed solvent as Example 1, and the composition of the solvent is the same. After drying the electrode was cut to a certain size and used in the assembly process, the next step.

Example 8

(Battery assembly)

Batteries were prepared by thermocompression bonding at a temperature between 80 and 100 ° C. using the composite polymer electrolyte membrane and electrode for batteries prepared in Examples 5 and 6, respectively. The cell was thermocompressed with an electrolyte membrane in the center and a cathode and an anode on both sides of the membrane. In this example, the temperature was at 90 ° C. and the pressure was adjusted to suit the application.

Example 9

(Battery evaluation)

Battery evaluation was performed after the battery prepared in Example 8 was loaded at 80 ° C. for 12 hours in 3M sulfuric acid solution. The fuel was tested with varying concentrations of sulfuric acid in a 0.5-4 M methanol solution in the 1-4 M range. The results are shown in Table 3 below.

Battery Performance Comparison According to Sulfuric Acid and Methanol Concentration (Unit: mW / ㎠) Methanol Concentration 0.5 M 1.0 M 2.0 M 3.0 M 4.0 M 1 M 70 100 125 120 100 2 M 80 120 140 140 120 3 M 90 130 160 160 130 4 M 90 130 160 160 130

The concentration of sulfuric acid in the raw material solution is the most excellent in the concentration of 2 to 3 M methanol at 2 M. The concentration of sulfuric acid was much lower at a lower temperature below 0.5 M, and there was no difference in performance above 3 M. The concentration of methanol was deteriorated at 4 M and above, but also at 1.0 M and below.

The electrolyte membrane for a fuel cell prepared by the new method of the present invention is easy to produce, economical in process, and excellent in ionic conductivity, low methanol permeability and mechanical strength in terms of performance.

Claims (20)

In the electrolyte membrane for a fuel cell, Polymer film containing pores having a pore size of up to 50 nm and a porosity of 15 to 60% by volume Electrolyte membrane for fuel cell comprising a. The method of claim 1, The film is a) polyvinylidene fluoride (PVdF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), and 40 to 80% by weight of a polymer selected from the group consisting of mixed polymers by a combination thereof; b) 20 to 60% by weight hydrophilic inorganic powder; And Electrolyte membrane for fuel cell comprising a. The method of claim 1, The pores have a pore size of 3 to 20 nm, porosity of 15 to 30% by volume electrolyte membrane for a fuel cell. The method of claim 1, An electrolyte membrane for a fuel cell having a thickness of 5 to 500 μm. The method of claim 1, The electrolyte membrane is a fuel cell electrolyte membrane is a laminated membrane in which at least two membranes are laminated. The method of claim 2, The inorganic powder of b) may be aluminum oxide (Al ₂ O ₃ ), fumed silica, zeolite, titanium oxide (TiO ₂ ), barium titanate (BaTiO ₃ ), and powder Electrolyte membrane for fuel cell selected from the group consisting of inorganic powders of a molecular sieve structure. The method of claim 1, The inorganic powder of b) has a particle size of 5 to 500 nm and a specific surface area of 10 to 500 m 2 / g electrolyte membrane for fuel cells. In the method for producing an electrolyte membrane for a fuel cell, A method of manufacturing an electrolyte membrane for a fuel cell, the method comprising: preparing a membrane comprising pores having a pore size of up to 50 nm and a porosity of 15 to 60% by volume by thermally pressing a polymer film containing pores. The method of claim 8, a) providing a polymer film comprising a polymer, a hydrophilic inorganic powder, and a plasticizer; b) impregnating the polymer film of step a) into an extraction solvent to extract a plasticizer to produce a polymer film containing pores; And c) thermopressing the polymer film of step b) Method for producing an electrolyte membrane for a fuel cell comprising a. The method of claim 9, The polymer film of step a) is a method for producing an electrolyte membrane for a fuel cell is a laminated film in which at least two films are laminated. The method of claim 9, The method of claim 1, wherein the polymer film of step a) comprises 40 to 80 parts by weight of polymer, 20 to 60 parts by weight of hydrophilic inorganic powder, and 8 to 120 parts by weight of plasticizer. The method of claim 9, The polymer film of step a) Coating a polymer slurry comprising a polymer, a hydrophilic inorganic powder, a plasticizer, and a solvent on a release paper and drying to form a film Method for producing an electrolyte membrane for a fuel cell prepared by the method comprising a. The method of claim 9, The polymer film of step a) Injecting a mixture containing a polymer, a hydrophilic inorganic powder, and a plasticizer in an extruder and extruding at a temperature of 120 to 170 ℃ forming a film Method for producing an electrolyte membrane for a fuel cell prepared by the method comprising a. The method of claim 9, The polymer of step a) is polyvinylidene fluoride (PVdF), copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF-HFP copolymer: PVDHFP), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), and a method for producing an electrolyte membrane for a fuel cell selected from the group consisting of mixed polymers combined therefrom. The method of claim 9, The hydrophilic inorganic powder of step a) is aluminum oxide (Al ₂ O ₃ ) -based, fumed silica (zemed), zeolite (Zeolite), titanium oxide (TiO ₂ ) -based, barium titanate (BaTiO ₃ ) -based, And at least one member selected from the group consisting of inorganic powders having a molecular sieve structure. The method of claim 12, The solvent is acetone, dimethylformamide (DMF; dimethylformamide), dimethylacetamide (DMAC; dimethylacetamide), N-methylpyrrolidone (NMP; N-methylpyrrolidone), tetrahydrofuran (THF; tetrahydrofuran), methyl ethyl ketone ( MEK; methylethylketone), and a method for producing an electrolyte membrane for a fuel cell selected from the group consisting of mixed solvents thereof. The method of claim 8, The thermal pressure is a manufacturing method of an electrolyte membrane for a fuel cell is carried out under the conditions of the compression temperature of 80 to 160 ℃, and the pressing pressure of 5 Kg / ㎠ to 10 ton / ㎠. The method of claim 8, The thermal pressure is a method for producing an electrolyte membrane for a fuel cell in which the polymer film is carried out by a hot press or a lamination roll. The method of claim 8, The method for producing an electrolyte membrane for a fuel cell is a polymer film containing the pores is a laminated film in which at least two films are laminated. A fuel cell comprising the electrolyte membrane of claim 1.