JP2005108770A - Method for producing electrolyte membrane electrode assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the mechanical strength of a polymer electrolyte membrane, to improve battery performance during long-time operation, and to produce an MEA excellent in handling, workability and cost of the polymer electrolyte membrane, which has been regarded as a problem until now I will provide a.
In the production of an electrolyte membrane electrode assembly, a membrane is formed by applying a polymer electrolyte dispersion and drying. At this time, by controlling the removal rate of the liquid component, the crystallinity during film formation can be increased, and the mechanical strength of the film can be improved. Further, the use of a polymer electrolyte having two different EWs improves the mechanical strength of the membrane without using a reinforcing material.
[Selection figure] None

Description

  The present invention relates to a method for producing an electrolyte membrane catalyst layer for a polymer electrolyte fuel cell used in a portable power source, an electric vehicle power source, a household cogeneration system, and the like, and an electrolyte membrane electrode including the electrolyte membrane catalyst layer assembly The present invention relates to a joined body and a fuel cell using the electrolyte membrane electrode joined body.

  A fuel cell using a polymer electrolyte is an electrochemical that generates electric power and heat simultaneously by electrochemically reacting a fuel gas containing hydrogen and an oxidant gas containing oxygen such as air. Device. The basic part of a fuel cell is that a catalytic reaction layer mainly composed of carbon powder carrying a platinum-based metal catalyst is formed on both sides of a polymer electrolyte that selectively transports hydrogen ions, It is obtained by forming a gas diffusion layer having both air permeability and electronic conductivity with respect to the fuel gas on the surface. The gas diffusion layer and the catalytic reaction layer are collectively referred to as an electrode. And what assembled this electrode and polymer electrolyte membrane integrally, or what assembled the catalyst layer and polymer electrolyte membrane integrally is called an electrolyte membrane electrode assembly (Membrane electrode assembly: MEA). .

  Gas seals and gaskets are placed around the electrodes with a polymer electrolyte membrane around the electrodes so that the fuel gas and oxidant gas supplied to the MEA are not leaked to the outside and the two types of gas are not mixed with each other. In addition to mechanically fixing the MEA and the gasket, a conductive separator plate for electrically connecting adjacent MEAs in series with each other is disposed. In the portion of the separator plate that comes into contact with the MEA, a reaction gas is supplied to the electrode surface, and a gas flow path for carrying away the generated gas and surplus gas is formed. Although the gas flow path can be separately provided on the separator plate, it is general to form a gas flow path by providing a groove on the surface of the separator. And a fuel cell is comprised by laminating | stacking many MEA through a separator, and setting it as what is called a laminated battery.

  In order to improve the performance of such fuel cells, various MEA manufacturing methods have been proposed so far. For example, (1) a method in which a catalyst layer is formed on a gas diffusion layer, placed on both sides of a polymer electrolyte membrane, and joined by hot pressing to obtain an MEA (Patent Document 1), (2) a catalyst on a base film A method of obtaining an MEA by forming a layer and then transferring the catalyst layer to the polymer electrolyte membrane with a hot press or hot roller (Patent Document 2), (3) having a catalyst layer on one side of the polymer electrolyte membrane A method of obtaining MEA by forming two sets of each and then joining the surfaces of the polymer electrolyte membranes facing each other (Patent Document 3), and (4) catalyst coating and polymer electrolyte dispersion on a substrate film And a method of obtaining MEA by applying catalyst paints one after the other.

  In general, (1) and (2) are often used from the viewpoint of effective utilization of the catalyst and workability, but each of the above-mentioned MEA production methods has problems. The manufacturing methods of (1) to (3) described above have a step of joining the catalyst layer and the polymer electrolyte membrane with a hot press or a hot roller, and pores that play a role of gas diffusion in the catalyst layer in this step There is a problem that the portion is crushed and the gas diffusibility is lowered, and the performance of the fuel cell is lowered. On the other hand, if the pressure is lowered to retain the pores, the bondability between the catalyst layer and the polymer electrolyte membrane is reduced, and the hydrogen ion migration is hindered, leading to a decrease in fuel cell performance. .

  In both (1) and (2), a polymer electrolyte membrane which is a solid membrane formed by extrusion melt molding or the like is used. If the film thickness of the polymer electrolyte membrane is reduced for the purpose of improving the performance such as ion conductivity, it is difficult to handle the polymer electrolyte membrane, and wrinkles are likely to occur, and the battery voltage IR due to the increase in the contact resistance between the catalyst layer and the electrolyte membrane. It will lead to a decline due to loss. In addition, the electrode area may be non-uniform due to wrinkles. Furthermore, the mechanical strength of the polymer electrolyte membrane is lowered, and it is not suitable for long-time use. Furthermore, there is a problem in terms of cost when forming a solid film.

Since the manufacturing method of (3) uses the polymer electrolyte in a liquid state, the problem relating to handling when reducing the thickness of the polymer electrolyte membrane is solved. Moreover, the problem of cost is eliminated in terms of film formation. However, there are problems in terms of workability and cost because of the mechanical strength and the large number of processes during MEA creation. In addition, since the production method (4) uses a polymer electrolyte membrane in a liquid state and is continuously laminated with the catalyst layer / polymer electrolyte membrane / catalyst layer, there is a problem in terms of workability and cost. It will be resolved. The problem of mechanical strength is solved by including fibrils of polytetrafluoroethylene (PTFE) as a reinforcing material in the polymer electrolyte membrane. However, inclusion of PTFE fibrils increases the membrane resistance, leading to performance degradation such as ion conductivity. In addition, there is a problem in workability in producing the fibril-containing polymer electrolyte membrane.
Japanese Patent Publication No.2-7398 Japanese Patent Laid-Open No. 10-64574 JP-A-6-176317

  In view of the above prior art, the present invention provides a method for producing an electrolyte membrane electrode assembly that can provide a fuel cell that is excellent in handling and polymer electrolyte membrane handling, MEA creation workability and cost, and good performance, and an electrolyte membrane electrode The object is to obtain a joined body. More specifically, the present invention improves the mechanical strength of the membrane by controlling the liquid component removal rate during the formation of the polymer electrolyte membrane, improves battery performance during long-time operation, and has been problematic until now. It is an object of the present invention to provide an MEA production method excellent in handling of the polymer electrolyte membrane and the workability and cost of creating MEAs.

The present invention is a method for producing an electrolyte membrane electrode assembly for a fuel cell comprising a pair of catalyst layers on both sides of a hydrogen ion conductive polymer electrolyte membrane,
(1) A step of applying a catalyst paint on a substrate;
(2) removing a liquid component from the catalyst paint to form a first catalyst layer;
(3) A step of applying a hydrogen ion conductive polymer electrolyte dispersion on the catalyst layer formed in the step (2),
(4) removing the liquid component of the hydrogen ion conductive polymer electrolyte dispersion to form a polymer electrolyte membrane;
(5) applying a catalyst paint on the polymer electrolyte membrane;
(6) removing the liquid component of the catalyst paint to form a second catalyst layer to obtain a laminate;
(7) It includes a step of heat-treating the laminate at 120 to 200 ° C., and (8) a step of cooling the laminate at a rate of 10 ° C./hour or more. .

In the step (4), it is preferable to remove the liquid component from the dispersion of the hydrogen ion conductive polymer electrolyte at a rate of 25 mg · cm ⁻² · hr− ¹ or less.
Moreover, in the said process (3), it is preferable that the said dispersion liquid contains the at least 2 sort (s) of hydrogen ion conductive polymer electrolyte which has a different ion exchange capacity.
In this case, the hydrogen ion conductive polymer electrolyte comprises a first hydrogen ion conductive polymer electrolyte comprising a perfluorocarbon sulfonate ionomer having a unit weight (EW) per sulfonic acid group of 700 to 900 mg equivalent, and a sulfonic acid. It is preferable that the 2nd hydrogen ion conductive polymer electrolyte which consists of perfluorocarbon sulfonate ionomers of 1000-1500 mg equivalent per unit weight (EW) is included.

The present invention also provides an electrolyte membrane electrode assembly for a fuel cell comprising a pair of catalyst layers on both sides of a hydrogen ion conductive polymer electrolyte membrane,
The hydrogen ion conductive polymer electrolyte membrane comprises a first hydrogen ion conductive polymer electrolyte comprising a perfluorocarbon sulfonic acid ionomer having a unit weight (EW) of 700 to 900 mg equivalent per sulfonic acid group; The present invention also relates to an electrolyte membrane electrode assembly comprising a second hydrogen ion conductive polymer electrolyte comprising perfluorocarbon sulfonic acid ionomer having a unit weight (EW) of 1000 to 1500 mg equivalent.
Furthermore, the present invention also relates to a polymer electrolyte fuel cell including the electrolyte membrane electrode assembly.

  According to the present invention, the liquid component removal rate at the time of forming the polymer electrolyte membrane is controlled to improve the mechanical strength of the membrane, improve the battery performance during long-time operation, It is possible to provide an MEA manufacturing method excellent in handling of the molecular electrolyte membrane, workability of MEA creation, and cost.

  According to the method of manufacturing an electrolyte membrane electrode assembly according to the present invention, a polymer electrolyte membrane having a thin film thickness (20 microns or less) can be easily prepared and used, and workability with a thin membrane is eliminated. The In addition, by forming a film using a polymer electrolyte in a liquid state, it is possible to reduce the cost as compared with a manufacturing method using a solid film from the beginning.

  In particular, the polymer electrolyte membrane preferably includes at least two types of hydrogen ion conductive polymer electrolytes having different ion exchange capacities, and specifically, the hydrogen ion conductive polymer electrolyte is per sulfonic acid group. First hydrogen ion conductive polymer electrolyte comprising 700 to 900 mg equivalent of perfluorocarbonsulfonic acid ionomer, and perfluorocarbon sulfone having a unit weight (EW) of 1000 to 1500 mg equivalent per unit sulfonic acid group Preferably, a second hydrogen ion conducting polymer electrolyte comprising an acid ionomer is included.

  This is because, when a solid film is formed from a polymer electrolyte in a liquid state, it is possible to impart mechanical strength using the crystallinity of the polymer electrolyte. In general, when liquid components are removed rapidly when creating a polymer electrolyte membrane that is a solid membrane, the polymer electrolyte unit fragments (molecular chains or polymer chains) are arranged in the resulting polymer electrolyte membrane. Is not regular and sufficient molecular orientation cannot be obtained.

  On the other hand, according to the method for manufacturing an electrolyte membrane electrode assembly according to the present invention, by reducing the removal rate of the liquid component, the arrangement of the unit pieces of the polymer electrolyte is sufficient, and the crystals in the solid membrane are And the problem of mechanical strength can be solved. Furthermore, by using two types of polymer electrolytes having different ion exchange capacities, the resulting polymer electrolyte membrane can be obtained as compared with the case of using a polymer electrolyte having one type of ion exchange capacities while maintaining ionic conductivity. It is possible to increase the mechanical strength.

  That is, the first hydrogen ion conductive polymer electrolyte having a small EW mainly serves to maintain and improve the hydrogen ion conductivity, and the second hydrogen ion conductive polymer electrolyte having a large EW is added to the hydrogen ion conductivity. This is mainly because the mechanical strength can be maintained and improved. As the first polymer electrolyte, one having an EW of less than 700 mg equivalent is not preferable because the strength of the obtained polymer electrolyte membrane is lowered. As for the second hydrogen ion conductive polymer electrolyte, it is said that the crystallinity of the polymer electrolyte increases as EW increases. If the EW is less than 1000 mg equivalent, the mechanical strength cannot be improved, and if it exceeds 1500 mg, the ionic conductivity decreases, which is not preferable.

  Moreover, in the manufacturing method of the electrolyte membrane electrode assembly which concerns on this invention, the crystallinity of a polymer electrolyte membrane is improved by performing heat processing of MEA in process (7) and (8). Annealing is performed by heat treatment at a temperature of 120 to 200 ° C., and further, the unit rate of the polymer electrolyte unit pieces in the solid film is sufficiently performed by setting the cooling rate to 10 ° C./hour or more. Strength is improved.

Below, the manufacturing method of the electrolyte membrane electrode assembly which concerns on this invention is demonstrated in detail.
First, in the step (1), a catalyst layer is formed on a substrate such as a substrate film or a porous conductive substrate. The MEA obtained when using the base film is an MEA having a structure of catalyst layer / polymer electrolyte membrane / catalyst layer. In addition, the MEA obtained when a porous conductive substrate is used has an electrode (gas diffusion layer + catalyst layer) / polymer electrolyte membrane / electrode (catalyst) because the porous conductive substrate becomes a gas diffusion layer. MEA having a structure of “layer + gas diffusion layer”.

  The base film is required to have chemical resistance, heat resistance, peelability of the catalyst layer, and the like. As a material to be used, a film made of a hydrocarbon resin such as polypropylene (PP), polyethylene terephthalate (PET), polyethylene (PE), a film obtained by treating the surface of the film with Si or fluorine, polytetrafluoroethylene ( PTFE) and other fluororesin films.

  A preferable material for the porous conductive substrate is a carbon diffusing substrate such as carbon paper made of carbon fiber or carbon cloth. A carbon layer having water repellency composed of carbon particles and PTFE for water management of the electrode may be disposed on the porous conductive substrate in advance. In this case, the penetration of the catalyst layer into the porous substrate can be suppressed.

The catalyst paint may be prepared by adding and mixing the catalyst powder, the polymer electrolyte, and the dispersion medium.
As the catalyst powder, a catalyst powder made of carbon particles carrying platinum or a platinum alloy may be used. As the carbon particles, it is preferable to use acetylene black, Vulcan or Ketjen black having a specific surface area of 50 to 1000 m ² / g. The loading ratio of the platinum catalyst or platinum alloy catalyst to the carbon particles is preferably 25 to 60% by weight. That is, it is sufficient that 25 to 60% by weight of the catalyst-supporting carbon particles is a catalyst. When these are used, the catalyst activity is high, and the catalyst is highly dispersed and a stable power generation reaction can be maintained.

  As the polymer electrolyte used for the catalyst coating, it is preferable to use a polymer having an acidic functional group having excellent heat resistance and chemical resistance. In general, a perfluorosulfonic acid ionomer represented by Nafion (DuPont) or Flemion (Asahi Glass Co.) dispersed in an alcoholic organic solvent or water may be used. As the dispersion medium, an alcoholic organic solvent or water is used. Or you may use the mixed solvent which used these 2 or more types at least. Since the platinum catalyst has high activity, if a low boiling alcohol solvent is used, it may cause ignition. Therefore, it is preferable to use water as the dispersion medium.

The concentration of the catalyst paint may be appropriately adjusted according to the target thickness platinum catalyst amount. Preferably it is 10 to 30% by weight.
As a method for applying the catalyst paint to the substrate film or the porous conductive substrate, spraying, bar coating, doctor blade, die coating, screen printing, or the like may be used.

  Next, in the step (2), the applied catalyst paint is dried to remove the liquid component, thereby obtaining a catalyst layer. The drying method includes a method of removing heat by applying heat, such as a hot plate, and a method of gradually removing the solvent component while keeping the vapor pressure constant. In the method of gradually removing these solvents, the crystallinity of the polymer electrolyte can be improved, and the connectivity between the polymer electrolytes in the catalyst layer can be improved.

  In the step (3), as the hydrogen ion conductive polymer electrolyte, a polymer having an acidic functional group excellent in heat resistance and chemical resistance is used as in the case of the catalyst paint. In general, it is preferable to use a perfluorosulfonic acid ionomer typified by Nafion (manufactured by DuPont) and Flemion (manufactured by Asahi Glass Co., Ltd.) in an alcoholic organic solvent or water.

  Since the dispersion of the hydrogen ion conductive polymer electrolyte is applied on the catalyst layer, it is preferable to use water as the dispersion medium in order to prevent ignition by the catalyst. The concentration is preferably 5 to 30% by weight, and may be appropriately adjusted according to the required thickness of the polymer electrolyte membrane. It is also possible to apply a plurality of times according to the required thickness. The coating method may be a bar coating, a doctor blade, a die coating or the like, and a uniform polymer electrolyte membrane can be created by using these.

  At this time, two types of polymer electrolytes having different ion exchange capacities are used. A first polymer electrolyte having a unit weight (EW) per sulfonic acid group of 700 to 900 mg equivalent is used. Those having an EW of less than 700 mg equivalent are not preferable because they cause a decrease in strength when the film is formed. As the second hydrogen ion conductive polymer electrolyte, one having an EW of 1000 to 1500 mg equivalent is used. It is said that the crystallinity of the polymer electrolyte increases as the EW increases. However, if the EW is less than 1000 mg equivalent, the mechanical strength cannot be improved, which is not preferable. Exceeding 1500 mg equivalent is not preferable because it causes a decrease in ionic conductivity.

  In step (4), after applying a dispersion of hydrogen ion conductive polymer electrolyte, the liquid component (solvent component) is removed to obtain a solid film. There are a method for removing liquid components by applying heat, such as a hot plate, and a method for gradually removing liquid components with a constant vapor pressure. In the present invention, the latter is used to improve the mechanical strength and hydrogen ion conductivity of the solid membrane by improving the crystallinity of the hydrogen ion conductive polymer electrolyte. When two types of hydrogen ion conductive polymer electrolytes having different ion exchange capacities are used, polymer electrolytes having the same crystallinity are easily bonded to each other in the solid membrane, and mechanical strength is obtained without using a reinforcing material. Can be improved.

At this time, the removal rate of the liquid component is preferably 25 mg · cm ⁻² · hr− ¹ or less. If it is larger than 50 mg · cm ⁻² · hr− ¹ , sufficient mechanical strength cannot be obtained, and when the fuel cell is operated for a long period of time, a performance deterioration that is considered to be a deterioration of the membrane occurs at an early stage.
Steps (5) and (6) may be performed in the same manner as the above steps (1) and (2), and the second catalyst layer may be formed in the same manner as the first catalyst layer.

In steps (7) and (8), after the electrolyte membrane electrode assembly is formed, heat treatment is performed in an oven or the like. 120-200 degreeC is the temperature range below the decomposition temperature below the softening temperature of a polymer electrolyte. This heat treatment can improve the crystallinity of the polymer electrolyte membrane in the electrolyte membrane electrode assembly. At this time, the cooling rate after heating is preferably 10 ° C. · cm ⁻² · hour ⁻¹ or less. When the temperature exceeds 10 ° C · cm ^-2 · hour ^-1 , the change in membrane strength due to the difference in crystallinity of the two different polymer electrolytes causes deterioration of the membrane when the fuel cell is operated for a long time. It is thought that the performance of the fuel cell is lowered, which is not preferable.
Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

-Preparation of catalyst paint A catalyst obtained by supporting platinum particles having an average particle diameter of about 3 nm on Ketjen Black (manufactured by AKZO Chemie, The Netherlands) having an average particle diameter of 30 nm and a specific surface area of 800 m ² / g. Used as supported particles (50 wt% platinum).
5 g of the catalyst-supporting particles, 25 g of a polymer electrolyte dispersion (Flemion water dispersion manufactured by Asahi Glass Co., Ltd., 10 wt% polymer electrolyte, EW 900 mg equivalent) and 7.5 g of water are mixed and ultrasonically dispersed. Thus, a catalyst paint was prepared.

Preparation of hydrogen ion conductive polymer electrolyte dispersion 10% by weight of aqueous dispersion containing 10% by weight of hydrogen ion conductive polymer electrolyte with EW of 900 mg equivalent and 10% by weight of isoionic conductive polymer electrolyte with EW of 1200 mg equivalent The aqueous dispersion is mixed at a ratio of 1 to 1 (weight ratio) and ultrasonically dispersed, and then the concentration is adjusted to 20% by weight with an evaporator to obtain a mixed dispersion of hydrogen ion conductive polymer electrolyte. It was.

-Preparation of electrolyte membrane electrode assembly On the polypropylene base film, the above-mentioned catalyst paint is applied by the doctor blade method and gradually dried in an oven at 50 ° C, and the amount of platinum catalyst is 0.5 mg / cm. ^Two first catalyst layers were formed. At this time, the size of the catalyst layer was set to 60 mm × 60 mm by masking.
Next, the mixed aqueous dispersion of the hydrogen ion conductive polymer electrolyte was applied onto the first catalyst layer by a doctor blade method so that the solid content was 6 mg / cm ² . At this time, the size of the polymer electrolyte membrane was set to 120 mm × 120 mm by masking.

After applying the mixed dispersion, the substrate film is placed in an oven, adjusted so that the removal rate of the liquid component is 25 mg · cm ⁻² · hr ⁻¹ and gradually dried to obtain a polymer electrolyte membrane Formed. At this time, the thickness of the obtained polymer electrolyte membrane was 30 microns.
Next, on the polymer electrolyte membrane, the catalyst paint was applied by a doctor blade method, an oven, was gradually dried at a 50 ° C., the as platinum catalyst amount is 0.5 mg / cm ² 2 The catalyst layer was formed. At this time, the size of the second catalyst layer was set to 60 mm × 60 mm by masking.

Subsequently, the laminate of the first catalyst layer / polymer electrolyte membrane / second catalyst layer was heat-treated in an oven at 120 ° C. for 1 hour. Thereafter, cooling was gradually performed at a rate of 10 ° C./hour to obtain MEA-1 according to the present invention.
Further, the liquid component removal rate after coating the mixed dispersion of the hydrogen ion conductive polymer electrolyte, except that the 12 mg · cm ^-2 · hr ^-1 is, MEA-2 in the same manner as in MEA-1 It was created.

Comparative example

The liquid component removal rate after coating the mixed dispersion of the hydrogen ion conductive polymer electrolyte, except for using 50 or 150 mg · cm ^-2 · hr ^-1, compared in the same manner as in Example 1 MEA-1 And comparative MEA-2 was made.
Further, Comparative MEA-3 was prepared in the same manner as in Example 1 except that only a hydrogen ion conductive polymer electrolyte having an EW of 900 mg equivalent was used.

Further, Comparative MEA-4 was prepared in the same manner as in Example 1 except that only a hydrogen ion conductive polymer electrolyte having an EW of 1200 mg equivalent was used.
Moreover, after heating to 120 degreeC in oven, comparative MEA-5 was produced by the method similar to an Example except having cooled the cooling rate at 10 degree-C / min.

[Characteristic evaluation]
Since the MEA obtained in the above-described Examples and Comparative Examples is in a state of being laminated on the base film, the base film was peeled off. Thereafter, a pair of gas diffusion layers was disposed on both sides of each MEA. The gas diffusion layer is composed of a conductive carbon fiber non-woven fabric (TGP-H-120 manufactured by Toray Industries, Inc.) having an outer dimension of 6 cm × 6 cm and a thickness of 360 μm, and an aqueous dispersion containing fluororesin (manufactured by Daikin Industries, Ltd.). Was obtained by impregnating with neoflon ND1), drying and heating at 380 ° C. for 30 minutes. This treatment was performed to impart water repellency.
Further, a water repellent layer was formed on one surface of the carbon nonwoven fabric by applying an ink obtained by mixing a dispersion of conductive carbon powder and PTFE fine powder using a screen printing method. .

First, single cells were assembled using MEA-1, MEA-2, comparative MEA-1 and comparative MEA-2, respectively, hydrogen gas was supplied to the fuel electrode, and air was supplied to the air electrode. The battery temperature was 70 ° C., the fuel gas utilization rate (Uf) was 70%, and the air utilization rate (Uo) was 40%. Gas humidification was performed using a bubbler, the fuel gas was humidified to have a dew point of 70 ° C., and the air was humidified to have a dew point of 70 ° C. Under the above conditions, a fuel cell using hydrogen and air as fuel was operated at a current density of 0.2 A / cm ² for 2000 hours to evaluate the characteristics. The results are shown in Table 1.

As shown in Table 1, it was found that the deterioration of the battery characteristics due to long-time operation of the unit cell is reduced by setting the liquid component removal rate in step (3) to 25 mg · cm ⁻² · hour ⁻¹ or less. . This is considered due to the difference in mechanical strength of the film due to crystal growth in the polymer electrolyte film. When forming a film by removing the liquid component, the removal rate of the liquid component is slowed down to 25 mg · cm ^-2 · hr- ¹ or less, so that the same EW of two types of polymer electrolytes with different EWs can be used. It became easy for the macromolecules having a regular arrangement to each other, and the crystallinity increased. As a result, the mechanical strength of the membrane was improved, and the battery voltage change (deterioration rate) when the unit cell was operated for a long time could be suppressed with a very small decrease of 10 mV / 1000 hours or less.

On the other hand, if the removal rate of the liquid component exceeds 25 mg · cm ^-2 · hr ^-1 , the film is formed in a state where two different types of EW polymers are randomly entangled, so that the crystallinity is sufficient. The film strength could not be increased. The battery voltage change (deterioration rate) during the long-time operation of the unit cell showed a large value of 100 mV / 1000 hours or more. Based on the above, the battery performance during long-time operation can be achieved by setting the liquid component removal rate to 25 mg · cm ^-2 · hr ^-1 or less when using a polymer electrolyte dispersion to form a polymer electrolyte membrane. It was shown that it is possible to improve.
Here, Table 2 shows the results of the battery characteristics of the single cells manufactured in the same manner as described above, using MEA-1, Comparative MEA-3, and Comparative MEA-4 prepared in Example 1, Comparative Examples 3 and 4, respectively. Indicated.

  In Comparative Example 3, the battery voltage up to the initial 100 hours is higher than that in Example and Comparative Example 2. This is an excellent ion conductivity effect due to the low EW of the polymer electrolyte, that is, the large number of ion exchange groups. However, since the crystallinity is lowered due to the small EW, the mechanical strength of the film is insufficient, and the battery characteristics are remarkably deteriorated during long-time operation. In Comparative Example 2, since EW was large, the ionic conductivity was lower than that of Example and Comparative Example 1, and the battery voltage was low. However, when EW is large, the crystal growth property is improved, so that the mechanical strength of the film is improved, and the change in battery voltage during long-time operation is as low as 10 mV / 1000 hours or less.

It was shown from Table 2 that the characteristics of the polymer electrolyte having the small EW and the polymer electrolyte having the large EW were exhibited in the examples.
From the above, when forming a film using a dispersion of a polymer electrolyte, the mechanical strength of the film is improved by using at least two different types of polymer electrolytes of EW instead of a single EW. It was found that battery characteristics can be improved during operation.
Next, Table 3 shows the results of battery characteristics of single cells using MEA-1 and Comparative MEA-5 prepared in Example and Comparative Example 5, respectively.

  From the results of Table 3, it was found that the battery performance affects the cooling rate after the electrolyte membrane electrode assembly is heat-treated. This shows that the same effect as that obtained by improving the mechanical strength of the film by controlling the crystal growth property by the removal rate of the liquid component during film formation can be obtained by the cooling rate. In other words, the crystal membrane electrode assembly was heat-treated (annealed) to promote crystal alignment, and the cooling rate was controlled to promote crystal growth, thereby improving the mechanical strength of the membrane. As shown in Comparative Example 5, when the cooling rate after annealing is high, sufficient crystal growth in the film cannot be performed, so that sufficient mechanical strength that can withstand operation for a long time cannot be obtained. On the other hand, in the examples, since the cooling rate was a time sufficient for crystal growth, the mechanical strength of the film was improved, and a relatively stable battery performance of 10 mV / 1000 hours or less could be maintained even when operated for a long time.

  In the above embodiment, a platinum catalyst is used for the electrode. However, a similar result can be obtained by using a platinum-metal alloy catalyst such as a platinum-ruthenium catalyst used when a city gas reformed gas or the like is used for the fuel. Obtained. In addition, perfluorosulfonic acid ionomer is used for the polymer electrolyte, but not limited thereto, polymer electrolytes having acidic functional groups such as sulfonic acid, carboxylic acid, and phosphonic acid, such as polythiophenylene sulfonic acid and polyaniline. Composite polymer, polydiphenylamine, polyphenylene derivative (poly (4-phenoxybenzoyl-1,4-phenylene), poly (benzimidazole) -butanesulfonic acid, poly (silamine), styrene / ethylene-butylene / styrene triblock copolymer, poly Ether ether ketone or the like may be used.

  According to the present invention, it is possible to obtain an electrolyte membrane electrode assembly having a good balance between ion conductivity and mechanical strength. The electrolyte membrane electrode assembly is a portable power source, an electric vehicle power source, and a home cogeneration system. For example, it can be suitably used for a polymer electrolyte fuel cell used in the above.

Claims (6)

A method for producing a fuel cell electrolyte membrane electrode assembly comprising a pair of catalyst layers on both sides of a hydrogen ion conductive polymer electrolyte membrane,
(1) A step of applying a catalyst paint on a substrate;
(2) removing a liquid component from the catalyst paint to form a first catalyst layer;
(3) A step of applying a hydrogen ion conductive polymer electrolyte dispersion on the catalyst layer formed in the step (2),
(4) removing the liquid component of the hydrogen ion conductive polymer electrolyte dispersion to form a polymer electrolyte membrane;
(5) applying a catalyst paint on the polymer electrolyte membrane;
(6) removing the liquid component of the catalyst paint to form a second catalyst layer to obtain a laminate;
(7) A method for producing an electrolyte membrane electrode assembly, comprising: a step of heat-treating the laminate at 120 to 200 ° C .; and (8) a step of cooling the laminate at a rate of 10 ° C./hour or more. In the step (4), the liquid component is removed from the dispersion of the hydrogen ion conductive polymer electrolyte at a rate of 25 mg · cm ⁻² · hr− ¹ or less. .   The method for producing an electrolyte membrane electrode assembly according to claim 1, wherein, in the step (3), the dispersion contains at least two types of hydrogen ion conductive polymer electrolytes having different ion exchange capacities.   The hydrogen ion conductive polymer electrolyte comprises a first hydrogen ion conductive polymer electrolyte comprising a perfluorocarbon sulfonic acid ionomer having a unit weight (EW) of 700 to 900 mg equivalent per sulfonic acid group; 4. The method for producing an electrolyte membrane electrode assembly according to claim 3, comprising a second hydrogen ion conductive polymer electrolyte comprising a perfluorocarbonsulfonic acid ionomer having a unit weight (EW) of 1000 to 1500 mg equivalent. 5. A fuel cell electrolyte membrane electrode assembly comprising a pair of catalyst layers on both sides of a hydrogen ion conductive polymer electrolyte membrane,
The hydrogen ion conductive polymer electrolyte membrane comprises a first hydrogen ion conductive polymer electrolyte comprising a perfluorocarbon sulfonic acid ionomer having a unit weight (EW) of 700 to 900 mg equivalent per sulfonic acid group; An electrolyte membrane electrode assembly comprising a second hydrogen ion conductive polymer electrolyte comprising a perfluorocarbonsulfonic acid ionomer having a unit weight (EW) of 1000 to 1500 mg equivalent.   A polymer electrolyte fuel cell comprising the electrolyte membrane electrode assembly according to claim 5.