JP2002184414A - Method of manufacturing gas diffusion electrode and method of manufacturing solid polymer fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a gaseous diffusion electrode having long-time stable and superior polarization property and a method of producing a solid polymer fuel cell having superior output property with the gaseous diffusion electrode. SOLUTION: After a catalyst and a fluorine containing ion exchange resin are mixed in a liquid in which the fluorine containing ion exchange resin is soluble or diffusible, a liquid component is removed therefrom to obtain a solid material containing the catalyst and the resin. Then, by cooling and crushing the solid material, a resin coated catalyst powder is produced with the catalyst coated with the fluorine containing ion exchange resin. A dispersion liquid with the obtained powder dispersed in a dispersion medium is prepared and the dispersion liquid is used to form a catalyst layer of the gas diffusion electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a gas diffusion electrode and a method for manufacturing a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell having a polymer electrolyte membrane is expected to be put to practical use as a power source for a mobile vehicle such as an electric vehicle or a small cogeneration system because it is easy to reduce the size and weight. Have been. However, since the polymer electrolyte fuel cell has a relatively low operating temperature and its exhaust heat is difficult to effectively use for auxiliary power, etc., the utilization of anode reaction gas (pure hydrogen, etc.) and cathode Under operating conditions in which the utilization rate of a reaction gas (air or the like) is high, a performance capable of obtaining high power generation efficiency and high power density is required.

The electrode reaction in each of the anode and cathode catalyst layers of a polymer electrolyte fuel cell involves the reaction gas
The reaction proceeds at a three-phase interface where the catalyst and the fluorinated ion exchange resin (electrolyte) are simultaneously present (hereinafter, referred to as a reaction site). Therefore, in a polymer electrolyte fuel cell, a metal catalyst or a metal-supported catalyst (for example, a metal-supported carbon in which a metal catalyst such as platinum is supported on a carbon black carrier having a large specific surface area) or the like is conventionally used as a polymer electrolyte membrane. The number of reaction sites in the catalyst layer is increased by coating it with a fluorine-containing ion exchange resin of the same or different type and using it as a constituent material of the catalyst layer, and by so-called three-dimensional reaction sites in the catalyst layer.

As a method of forming a catalyst layer having such a structure, for example, a catalyst and a fluorinated ion exchange resin are mixed in a predetermined solvent, and the solvent is gradually volatilized from the mixed solution with sufficient stirring. Conventionally, a method of preparing a catalyst coated with a fluorine-containing ion exchange resin (hereinafter referred to as a resin-coated catalyst) and forming a catalyst layer using the catalyst is known.

In order to obtain higher output characteristics of the battery, the coverage of the catalyst particles with the fluorinated ion exchange resin is increased, and pores effective for gas diffusion between the particles of the resin-coated catalyst particles obtained. Various methods have been studied for constructing a structure to ensure sufficient reaction sites in the catalyst layer. In addition, in this specification, the particle | grains of a catalyst show the particle | grains which consist of the aggregate which the secondary particle of these catalysts aggregated.

[0006]

However, when a catalyst layer is formed by the above-mentioned conventional method, it is difficult to coat all the catalyst particles to be used sufficiently and uniformly with a fluorine-containing ion exchange resin. However, since the formed catalyst layer also includes a catalyst that is insufficiently covered with the fluorinated ion exchange resin, it is difficult to sufficiently secure reaction sites that meet all the catalysts contained in the catalyst layer. there were. Therefore, it has been difficult for a polymer electrolyte fuel cell having a catalyst layer formed by a conventional method to obtain a high battery output that meets all the catalysts contained in the catalyst layer.

In this case, the coverage of the catalyst particles with the fluorinated ion exchange resin tends to take a wide range of values, and there is a large variation. The pores formed between the particles of such catalyst particles include, in addition to pores effective for gas diffusion, very small pores disadvantageous for gas diffusion and large pores disadvantageous for effective use of the catalyst. In this regard, it is difficult to obtain a high cell output from the polymer electrolyte fuel cell having the catalyst layer formed by the conventional method.

Further, if a pore structure effective for gas diffusion is not constructed in the catalyst layer as described above, for example, when a battery is operated for a long period of time, humidifying water supplied to each electrode or battery reaction is required. Such as the phenomenon of flooding in which part or all of the pores are blocked by generated water or the like,
It becomes difficult to supply each reaction gas stably and sufficiently to the reaction sites in the catalyst layer, and some of the reaction sites that had contributed to the electrode reaction in the initial stage of operation stopped functioning during operation, and the battery output became low. There has been a problem that it decreases as the operation time elapses.

The present invention has been made in view of the above-mentioned problems of the prior art, and has a method of manufacturing a gas diffusion electrode capable of stably obtaining excellent polarization characteristics for a long period of time, and the method includes the gas diffusion electrode. An object of the present invention is to provide a method for manufacturing a polymer electrolyte fuel cell having high output characteristics.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, it has been described above that the conventional catalyst has a large particle size before coating the resin. I found that it was causing the problem. In particular, in the case of a metal-supported catalyst, it has been found that the coating state of the particles of the catalyst with the resin is greatly affected by the particle size of the catalyst before coating the resin and the pore structure of the carrier such as carbon. . On the other hand, the present inventors have found that by pulverizing the catalyst before being coated with the resin, or the resin-coated catalyst after being coated with the resin, the above-mentioned coating state can be adjusted so as to be enhanced, The present invention has been reached.

That is, the present invention relates to a method for producing a gas diffusion electrode comprising a catalyst layer containing a catalyst and a fluorine-containing ion exchange resin, and a gas diffusion layer disposed adjacent to the catalyst layer. In a liquid that can be dissolved or dispersed,
A mixed liquid preparation step of mixing the catalyst and the resin to obtain a mixed liquid containing the catalyst and the resin, and a liquid component removing step of obtaining a solid containing the catalyst and the resin obtained by removing the liquid components in the mixed liquid A cooling step of cooling the solid to a brittle solid, and pulverizing the solid to obtain a powder; a dispersion preparing step of dispersing the powder in a dispersion medium to prepare a dispersion; and a dispersion. A method for producing a gas diffusion electrode, comprising: applying a gas diffusion electrode as at least one of an anode and a cathode, comprising: The present invention provides a method for producing a polymer electrolyte fuel cell having a polymer electrolyte membrane arranged.

Through the pulverizing step, the large particles of the catalyst inside the resin-coated catalyst are also pulverized, and the surface of the pulverized resin-coated catalyst that is not coated with the resin is exposed. Although this catalyst surface has not been used effectively in the past, such a surface is exposed so that during the formation of the catalyst layer, the catalyst surface is coated with particles of another resin-coated catalyst. It is considered that the applied resin comes into contact and is effectively used. as a result,
Since the resin coverage of the catalyst in the catalyst layer becomes sufficiently large as compared with the conventional case, sufficient reaction sites corresponding to the amount of the catalyst can be secured, and the polarization characteristics of the gas diffusion electrode can be improved. It seems that you can do it. In this case, a pore structure having a structure effective for gas diffusion is built in the catalyst layer, and a stable reaction gas can be supplied to the reaction site even if the electrode reaction is continued for a long time. It is considered that a gas diffusion electrode provided with such a catalyst layer can stably maintain high polarization characteristics for a long period of time. Furthermore, if such a gas diffusion electrode is used, it is possible to obtain a high output characteristic, and to constitute a polymer electrolyte fuel cell capable of stably obtaining the high output characteristic for a long period from the initial start-up. Can be.

In the present invention, the temperature at which the resin-coated catalyst is crushed is not particularly limited as long as the fluorinated ion-exchange resin becomes a brittle solid and is easily crushed. It is preferably carried out at a temperature (-196 ° C).

The present invention also provides a method for producing a gas diffusion electrode comprising a catalyst layer containing a catalyst and a fluorinated ion exchange resin, and a gas diffusion layer disposed adjacent to the catalyst layer. A pulverizing step of pulverizing to make the average particle diameter 4 μm or less and substantially not containing particles having a particle diameter of more than 50 μm, and a catalyst pulverized in the pulverizing step in a liquid in which the resin can be dissolved or dispersed. And mixing a resin to obtain a mixed solution containing a catalyst and a resin, and a catalyst layer forming step of applying a mixed solution to form a catalyst layer, and For producing a gas diffusion electrode, and a method for producing a polymer electrolyte fuel cell having an anode, a cathode, and a polymer electrolyte membrane disposed between the anode and the cathode, comprising the gas diffusion electrode as at least one of an anode and a cathode Provide the law.

By covering the aggregate of the catalyst pulverized so as to reduce the particle diameter with a resin, the surface area of the catalyst in contact with the resin can be increased as compared with the conventional case. Accordingly, the resin coverage of the catalyst in the catalyst layer becomes sufficiently large as compared with the conventional case, so that a sufficient reaction site corresponding to the amount of the catalyst is secured, and the polarization characteristics of the gas diffusion electrode are improved. Can be done. In addition, from the same viewpoint as described above, in this case, it is preferable to cool the catalyst before pulverizing the catalyst in the pulverization step. This makes it easier to grind the catalyst to a smaller particle size.

Further, also in this case, a pore structure having a structure effective for gas diffusion is formed in the catalyst layer, so that a stable supply of the reaction gas to the reaction site is possible even if the electrode reaction is continued for a long time. Therefore, the gas diffusion electrode provided with such a catalyst layer can stably maintain high polarization characteristics for a long time. Furthermore, if such a gas diffusion electrode is used,
It is possible to configure a polymer electrolyte fuel cell that can obtain high output characteristics and can stably obtain the high output characteristics for a long period from the initial stage of startup.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the method for manufacturing a gas diffusion electrode and the method for manufacturing a polymer electrolyte fuel cell according to the present invention will be described below in detail.

[First Embodiment] First, a preferred embodiment in which the resin-coated catalyst is cooled and pulverized is described. The method for manufacturing the gas diffusion electrode of the present embodiment, as described above, a mixed liquid preparation step, a liquid component removal step,
The method includes a pulverizing step, a dispersion liquid preparing step, and a catalyst layer forming step.

First, in the mixed liquid preparation step, a resin and a catalyst are mixed in a liquid in which the fluorinated ion exchange resin can be dissolved or dispersed to prepare a mixed liquid containing these. Here, the order of charging the resin and the catalyst into the liquid is not particularly limited. For example, after dissolving or dispersing the resin in the liquid, the catalyst is dispersed in the liquid. At this time, in the liquid, it is considered that the resin comes into contact with the surface of the particles formed of the aggregate of the catalyst and gradually adsorbs.

Here, in the present invention, the catalyst used is not particularly limited, and for example, a noble metal catalyst or a noble metal alloy catalyst may be used. A supported metal supported catalyst or the like may be used. As such a carrier, for example, carbon black, activated carbon, or the like can be used.

However, when a catalyst is selected from the viewpoint of obtaining high polarization characteristics as a gas diffusion electrode, among the above-mentioned catalysts, a group consisting of a platinum group metal and a platinum group alloy on a carbon black carrier having a specific surface area of 300 to 2000 cm ^2. Preferably, the catalyst is a metal-supported catalyst on which metal particles selected from the group consisting of Here, when the specific surface area of the carbon black carrier is less than 300 cm ² , the amount of the catalyst contained in the catalyst layer is insufficient, and a sufficient reaction site cannot be secured, and the polarization characteristics particularly in a high current density region are deteriorated. The tendency increases. On the other hand, the specific surface area of the carbon black carrier is 2
If it exceeds 000 cm ² , the pores of the catalyst become too small, and when the catalyst is brought into contact with the coating resin, a portion where the resin cannot enter sufficiently is easily formed.

In this case, from the viewpoint of using the gas diffusion electrode as an electrode of a polymer electrolyte fuel cell, platinum or a platinum alloy is preferable as the platinum group metal or platinum group alloy.
Further, the supported amount of the metal particles is 1 to the total weight of the supported catalyst.
Preferably it is 0-70%. This loading amount is 10%
If it is less than 3, the amount of the catalyst in the catalyst layer becomes insufficient, so that a sufficient reaction site cannot be secured, and the polarization characteristic particularly in a high current density region tends to decrease. on the other hand,
If this value exceeds 70%, even if a carrier having a large specific surface area is used, the amount of metal carried is high, so that aggregation between metal particles is likely to occur and the activity may be reduced.

Further, the fluorinated ion exchange resin contained in each of the catalyst layers in the present invention is preferably a perfluorocarbon polymer having a sulfonic acid group (hereinafter referred to as a sulfonic acid type perfluorocarbon polymer). The sulfonic acid type perfluorocarbon polymer enables chemically stable and rapid proton conduction for a long time in the catalyst layer.

Further, a sulfonic acid type perfluorocarbon _{polymer, CF 2 = CF- (OCF 2} CFX) m -O p -
(CF ₂ ) _n —SO ₃ H A polymerization unit based on a fluorovinyl compound represented by the formula (where m is an integer of 0 to 3, n is 1 to 3)
An integer of 12, p is 0 or 1, and X is F or CF ₃ ) and a polymer unit based on tetrafluoroethylene is preferred. Preferred examples of the fluorovinyl compound include the following compounds (i) to (iii). However, in the following formula, q is an integer of 1 to 8, r
Represents an integer of 1 to 8, and t represents an integer of 1 to 3. _{CF 2 = CFO (CF 2)} q SO 3 H ... (i) CF 2 = CFOCF 2 CF (CF 3) O (CF 2) r SO 3 H ... (ii) CF 2 = CF (OCF 2 CF (CF 3 )) _T O (CF ₂ ) ₂ SO ₃ H ... (iii)

In the above-mentioned copolymer, if the polymerization units based on a fluorinated olefin such as hexafluoropropylene or perfluoro (alkyl vinyl ether) are 25% by mass or less of the polymerization units based on tetrafluoroethylene, It may be contained in place of a polymerization unit based on ethylene.

The ion exchange capacity (hereinafter referred to as A _R ) of the fluorinated ion exchange resin in the present invention is 0.5.
~ 2.0 meq / g dry resin (hereinafter referred to as meq./g). A _{R of the} fluorinated ion exchange resin is 0.5 meq. If it is less than / g, the number of reaction sites decreases, and it tends to be difficult to obtain sufficient polarization characteristics. On the other hand, A _R of the fluorinated ion exchange resin is 2.0 meq. If it exceeds / g, the density of ion-exchange groups in the fluorinated ion exchange resin increases, and the gas diffusion property or drainage property in the catalyst layer decreases, and flooding easily occurs. A _R of fluorinated ion exchange resin contained in the catalyst layer, from the same viewpoint as above, 0.8.
5meq. / G is more preferable.

Further, regarding the contents of the catalyst and the fluorinated ion exchange resin contained in the catalyst layer in the present invention,
The range of the ratio (mass ratio) between the catalyst and the fluorinated ion exchange resin is as follows: mass of the catalyst: mass of the ion exchange resin = 40: 60.
９５95: 5, particularly preferably 60:40 to 80:20. Therefore, in the mixed solution process, the catalyst and the fluorinated ion exchange resin are each adjusted to an amount corresponding to the above range of the ratio, and the fluorinated ion exchange resin is introduced into the dissolvable or dispersible liquid. .

Here, if the content of the catalyst with respect to the fluorinated ion exchange resin is lower than the ratio of the mass of the catalyst to the mass of the fluorinated ion exchange resin = 40: 60, the amount of the catalyst is insufficient and the number of reaction sites is reduced. Tend. Further, the thickness of the coating layer of the fluorinated ion exchange resin that coats the catalyst tends to increase, and the diffusion rate of the reaction gas in the resin tends to decrease. Further, pores required for diffusion of the reaction gas may be blocked by the resin, and a so-called flooding phenomenon may easily occur. On the other hand, when the content of the catalyst with respect to the fluorinated ion exchange resin exceeds the ratio of mass of the catalyst: mass of the fluorinated ion exchange resin = 95: 5, the amount of the ion exchange resin coating the catalyst with respect to the catalyst is reduced. Insufficiently, the number of reaction sites decreases, and the polarization characteristics tend to decrease. Further, the fluorinated ion exchange resin also functions as a binder of the catalyst layer and an adhesive between the catalyst layer and the polymer electrolyte membrane, but the function thereof becomes insufficient and the tendency of the catalyst layer structure to be unable to be stably maintained increases. . In addition, in the case of a supported catalyst, the catalyst here includes the mass of the carrier.

Further, in the liquid containing the catalyst and the fluorinated ion exchange resin in the mixed liquid preparation step, the concentration of the solid component obtained by combining the catalyst and the fluorinated ion exchange resin is as follows:
It is preferably from 0.1 to 30% by mass, more preferably from 1 to 20% by mass, based on the total mass of the mixture.
When the concentration of the solid component is less than 0.1% by mass, the dispersion prepared in the dispersion preparation step described below is applied to a predetermined member by a method such as spraying, coating, filtration and transfer in the catalyst layer forming step. If the number of these operations is not repeated when forming the catalyst layer by heating, a gas diffusion electrode having a predetermined thickness cannot be obtained, and the production efficiency of the catalyst layer tends to deteriorate.
If the solid component concentration exceeds 30% by mass, the viscosity of the mixed solution may be too high.

Furthermore, in the present invention, the liquid in which the fluorinated ion exchange resin can be dissolved or dispersed includes a liquid having 1 to 1 carbon atoms.
It is preferable to use at least one compound selected from the group consisting of an alcohol having 6 carbon atoms, an ether having 2 to 6 carbon atoms, and a dialkyl sulfoxide having 2 to 6 carbon atoms.
Further, preferred specific examples of the organic solvent include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1,4-dioxane, n-propyl ether, dimethyl sulfoxide and the like.

Next, in the liquid component removing step, a solid containing the resin and the catalyst is obtained by removing the liquid component from the mixed solution containing the resin and the catalyst. It is considered that the particles of the catalyst contained in the solid material are at least partially coated with the resin. Here, the removal of the liquid component
It is preferably carried out until the content of the liquid component contained in the solid matter of the obtained resin-coated catalyst becomes 5% by mass or less based on the total mass of the solid matter, and it is more preferable to completely remove the solid matter. Thereby, in the dispersion liquid preparation step described later, peeling and elution of the resin from the resin-coated catalyst can be effectively prevented. Further, from the viewpoint of further strengthening the coating of the resin on the catalyst, it is preferable to further dry the resin-coated catalyst after removing the liquid component. Further, it is preferable that the operation of removing the liquid component is performed by heating in a temperature range where the resin is not thermally degraded. For example, when heating is performed under normal pressure, it is preferable to perform heating in a temperature range of 180 ° C. or lower. Moreover, when heating under reduced pressure using an evaporator etc., 40-70 degreeC
It is preferable to carry out in the temperature range of Further, when the solvent contains a flammable component, it is preferable that the operation of removing the solvent is performed under an atmosphere of an inert gas such as nitrogen.

Next, in the pulverizing step, a brittle solid containing a resin and a catalyst is obtained by cooling as described above, and this is pulverized. At this time, it is preferable that the powder obtained after the pulverization has an average particle diameter of 4 μm or less and does not substantially contain particles having a particle diameter of more than 50 μm. Here, in the present invention, the state of “substantially not containing particles having a particle size of more than 50 μm” refers to a state in which the ratio of particles having a particle size of 50 μm to all particles of the resin-coated catalyst is 5% or less. The particle diameter of the fine particles of the resin-coated catalyst obtained after the pulverization in the present invention is a value measured by a natural sedimentation method using a particle size distribution analyzer (trade name: LPA3000 / 3100) manufactured by Otsuka Electronics.

Here, when the average particle size of the resin-coated catalyst obtained after the pulverization exceeds 4 μm, the amount of the catalyst not coated with the resin increases, so that the catalyst utilization when the catalyst layer is formed tends to decrease. When the resin-coated catalyst obtained after the pulverization substantially contains particles having a particle size of 50 μm, when the resin-coated catalyst is dispersed in a dispersion medium in a dispersion liquid preparation step described below, the resin-coated catalyst in the dispersion medium may be used. The tendency for catalyst dispersion stability to be lost increases. Furthermore, the average particle size of the particles of the resin-coated catalyst obtained after freeze-pulverization is more preferably 0.1 to 3 μm. When the average particle size is less than 0.1 μm, in the catalyst layer forming step described below, when a catalyst layer is formed by applying a dispersion liquid in which a catalyst is dispersed, the layer structure becomes too dense and gas diffusion occurs. And the output performance when a fuel cell is configured is reduced.

Next, in the dispersion preparation step, a dispersion in which the resin-coated catalyst obtained in the pulverization step is dispersed in a dispersion medium as described above is prepared. Here, from the viewpoint of preventing the fluorine-containing ion-exchange resin in the resin-coated catalyst from being redissolved or peeling off, a dispersion medium that does not easily dissolve the fluorine-containing ion-exchange resin is preferable. Further, from the viewpoint of ensuring good dispersibility of the fine particles of the resin-coated catalyst in the dispersion, it is preferable to use a dispersion medium in which the fluorinated ion exchange resin is easily swollen by mixing with the fluorinated ion exchange resin. As such a dispersion medium, it is preferable to use at least one selected from the group consisting of saturated hydrocarbons, aromatic hydrocarbons, fluorinated alcohols, fluorinated ethers, and fluorinated alkanes. Among these, it is more preferable to use at least one selected from the group consisting of fluorinated alcohols, fluorinated ethers and fluorinated alkanes.

Examples of the above-mentioned saturated hydrocarbon include chain hydrocarbons such as hexane, heptane, nonane and decane, and examples of the aromatic hydrocarbon include benzene, toluene and xylene. Further, as the fluorinated alcohol, 2,2,2-trifluoroethanol,
2,2,3,3,3-pentafluoro-1-propanol, 2,2,3,4,4,4-hexafluoro-1-butanol, 1,1,1,3,3,3-hexafluoro −
2-propanol and the like. Further, as the fluorine-containing alkane, 1,3-dichloro-1,1,2,2,3
-Pentafluoropropane, 3,3-dichloro-1,
1,1,2,2-pentafluoropropane, 1,1,
1,2,2,3,4,5,5,5-decafluoropentane, 1,1,1-trichloro-2,2,3,3,3-pentafluoropropane, heptafluorocyclopropane, and the like. . Also, as the fluorine-containing ether,
2,2,3,3,3-pentafluoropropyl methyl ether, 2,2,3,3,3-pentafluoropropyl fluoromethyl ether, 1,1,3,3,3-pentafluoro-2-trifluoro Methylpropyl methyl ether, 1,1,1,2,2,3,3,4,4-nonafluorobutyl methyl ether, 1,1,1,2,2,3,
3,4,4-nonafluorobutylethyl ether and the like.

Here, among the above-mentioned saturated hydrocarbons, aromatic hydrocarbons, fluorinated alcohols, fluorinated ethers and fluorinated alkanes, from the viewpoint of swelling the fluorinated ion exchange resin, 2,2,3,3 3,3-pentafluoro-1-propanol, 1,1,1,2,2
3,4,5,5,5-decafluoropentane, heptafluorocyclopentane, 1,1,1,2,2,3,3
4,4-nonafluorobutyl methyl ether, 1,1,
1,2,2,3,3,4,4-nonafluorobutyl ethyl ether, 3,3-dichloro-1,1,1,2,2-
Pentafluoropropane or 1,3-dichloro-1,
It is particularly preferable to use 1,2,2,3-pentafluoropropane and the like.

Further, a water repellent such as polytetrafluoroethylene (hereinafter, referred to as PTFE) may be contained in the dispersion as required. However, since the water-repellent agent is an insulator, its amount is preferably as small as possible.
It is preferably 0% by mass.

When it is difficult to disperse other additives such as a resin-coated catalyst and a water repellent in a dispersion medium, a dispersant may be further used. As such dispersants, commonly used dispersants can be used, and cationic surfactants such as amine salts, quaternary ammonium salts, pyridinium salts, sulfonium salts, phosphonium salts, and polyethylene polyamines, amino acids, betaines, amino sulfates And amphoteric surfactants such as sulfobetaine, and nonionic surfactants such as alkyl polyoxyethylene and polyhydric alcohol. Further, a thickener, a diluent, a pore-forming agent such as alumina and silica, and other components such as water may be added to the dispersion.

In the dispersion, the concentration of the solid component including the resin-coated catalyst and other additional components is preferably 0.1 to 20% by mass relative to the total mass of the mixture. It is more preferable that the content be 15 to 15% by mass. When the concentration of the solid component is less than 0.1% by mass, the dispersion prepared in the dispersion preparation step is applied to a predetermined member by a method such as spraying, coating, or filtration transfer in the catalyst layer forming step described below. If the number of these operations is not repeated when forming the catalyst layer by heating, a gas diffusion electrode having a predetermined thickness cannot be obtained, and the production efficiency of the catalyst layer tends to deteriorate. Also,
If the solid component concentration exceeds 20% by mass, the viscosity of the mixed solution may be too high.

Further, in this dispersion liquid preparation step, when the particle diameter distribution of the particles of the resin-coated catalyst dispersed in the dispersion liquid is observed, it is determined that the particle diameters of all the particles are distributed within a range of 1 μm or less. Preferably, the particles are dispersed, and more preferably, the particles are dispersed so that the particle diameter of all the particles is in the range of 0.1 to 0.8 μm. In the dispersion preparation step of the present invention, the particle size distribution of the particles of the resin-coated catalyst dispersed in the dispersion is measured using a particle size distribution analyzer (trade name: LPA3000 / 3100) manufactured by Otsuka Electronics Co., Ltd. The values obtained by infinitely diluting the dispersion with water are measured by a laser scattering method (dynamic light scattering method). Therefore, this value is not a direct measurement of the particle size distribution of the resin-coated catalyst particles in the dispersion, but rather an indirect comparison of the degree of the particle size distribution of the resin-coated catalyst particles in the dispersion. Is to be observed.

Here, if the resin-coated catalyst in the dispersion contains particles having a particle size exceeding 1 μm, the dispersion stability of the fine particles of the resin-coated catalyst in the dispersion is likely to be reduced. In this case, the utilization of the catalyst tends to decrease when the catalyst layer is formed. In addition, the particle diameter of the resin-coated catalyst in the dispersion is set to 0.1.
When the fine particles having a particle size of less than 1 μm are included, the fine particles are included in pores serving as gas diffusion paths formed between the particles of the resin-coated catalyst when the catalyst layer is formed, and the gas diffusion of the catalyst layer is performed. There is a possibility that the properties may be reduced and the electrode characteristics may be reduced.

Next, in the catalyst layer forming step, using the dispersion prepared in the dispersion preparing step, a catalyst layer is formed on the gas diffusion layer, the polymer electrolyte membrane or the support plate so as to have a uniform thickness. At this time, a catalyst layer is first formed on the gas diffusion layer, the polymer electrolyte membrane or the support plate in a state containing a volatile component such as an organic solvent, and the volatile component is removed by performing a predetermined heat treatment on the catalyst layer. A catalyst layer having the structure described above is formed. Here, the method of forming the catalyst layer in a state containing a volatile component on the gas diffusion layer, the polymer electrolyte membrane, or the support plate is not particularly limited, and for example, a method such as spraying, coating, filtration, and transfer may be used. However, from the viewpoint of simplicity of operation, a method by coating is preferable. The method of the heat treatment is not particularly limited. For example, the heat treatment may be performed in the air, and then hot pressing may be performed under a predetermined pressure and temperature.

As described above, the gas diffusion electrode can be manufactured by forming the catalyst layer on the gas diffusion layer in the catalyst layer forming step. When the catalyst layer is formed on the polymer electrolyte membrane in the catalyst layer forming step, the gas diffusion layer is formed such that the catalyst layer is disposed between the gas diffusion layer and the polymer electrolyte membrane. Is disposed adjacent to the catalyst layer to produce a gas diffusion electrode in which the catalyst layer is bonded to the polymer electrolyte membrane. At this time, the gas diffusion layer and the catalyst layer may be further thermally bonded by performing heat treatment such as hot pressing as needed. Further, when the catalyst layer is formed on the support plate in the catalyst layer formation step in the catalyst layer formation step, for example, a gas diffusion layer is prepared, and the catalyst layer is disposed between the gas diffusion layer and the support plate. The gas diffusion layer may be disposed adjacent to the catalyst layer such that the support plate is peeled off and transferred onto the gas diffusion layer. For example, the catalyst layer is first formed on the polymer electrolyte membrane in the same manner as described above. Then, the gas diffusion layer may be arranged such that the catalyst layer is arranged between the gas diffusion layer and the polymer electrolyte membrane.

Here, as a constituent material of the gas diffusion layer,
For example, a porous body having electron conductivity (for example, carbon cloth or carbon paper) is used. Further, the polymer electrolyte membrane is not particularly limited as long as it is an ion exchange membrane showing good ion conductivity under a wet state. As a solid polymer material constituting the polymer electrolyte membrane, for example, a perfluorocarbon polymer having a sulfonic acid group, a polysulfone resin, a perfluorocarbon polymer having a phosphonic acid group or a carboxylic acid group, or the like can be used. Among them, a sulfonic acid type perfluorocarbon polymer is preferable. The polymer electrolyte membrane may be made of the same resin as the fluorinated ion exchange resin contained in the catalyst layer, or may be made of a different resin. Further, as the support plate, for example, a plate formed of PTFE, polyethylene terephthalate, or the like may be used. Further, the thickness of the formed catalyst layer may be the same as that of a normal gas diffusion electrode, and is preferably 1 to 200 μm, and more preferably 10 to 100 μm.

Next, a polymer electrolyte fuel cell is manufactured by using the gas diffusion electrode manufactured by the above method as at least one of an anode and a cathode. Here, in the polymer electrolyte fuel cell, the activation overvoltage of the oxygen reduction reaction of the cathode is usually very large as compared with the activation overvoltage of the hydrogen oxidation reaction of the anode. Ensuring the reaction site and improving the polarization characteristics of the cathode are effective in improving the output characteristics of the battery. Therefore, it is particularly preferable to use the gas diffusion electrode as a cathode.

In this case, it is more preferable to use the gas diffusion electrode as an anode of a polymer electrolyte fuel cell. This makes it possible to increase the number of reaction sites on the anode in addition to the cathode, thereby improving the battery output and improving the gas diffusivity that can maintain the high battery output even when operating for a long time. Can be achieved more reliably.

The method for manufacturing the polymer electrolyte fuel cell is not particularly limited as long as the polymer electrolyte membrane is disposed between the gas diffusion electrode serving as the anode and the gas diffusion electrode serving as the cathode. As described above, if necessary, the anode and cathode catalyst layers and the polymer electrolyte membrane are joined by heat treatment, or the anode and cathode catalyst layers and the gas diffusion layer are joined, and the unit cell is heated. The so-called electrode
It may be manufactured as a membrane assembly. The joining by the above heat treatment may be performed by, for example, a hot press or a roll press. At this time, as described in Japanese Patent Application Laid-Open No. 7-220741, the bonding may be performed using a special adhesive.

[Second Embodiment] Next, a preferred embodiment in the case where a catalyst before coating with a resin is pulverized will be described. As described above, the method for manufacturing a gas diffusion electrode of the present embodiment mainly includes a pulverizing step, a mixed liquid preparation step, and a catalyst layer forming step.

First, in the pulverizing step, the average particle diameter of the pulverized catalyst obtained by pulverizing the catalyst is set to 4 μm or less, and substantially no particles exceeding 50 μm are contained. The operation in the pulverizing step and the various conditions for advancing the operation are the same as in the pulverizing step in the first embodiment except that a catalyst before coating with a resin is used instead of the resin-coated catalyst. Further, as described above, it is preferable to cool the catalyst before the catalyst is pulverized in the pulverization step.

Here, if the average particle size of the catalyst obtained after the pulverization exceeds 4 μm, the amount of the catalyst that is not covered with the resin in the mixed liquid preparation step described later increases, so that the catalyst utilization when forming the catalyst layer is reduced. Easy to get low. Further, when the catalyst obtained after the pulverization substantially contains particles having a particle diameter of 50 μm, the catalyst is difficult to be stably dispersed in the liquid in a mixed liquid preparation step described later. The average particle size of the catalyst particles obtained after the pulverization is more preferably 0.1 to 3 μm. When the average particle size is less than 0.1 μm,
When dispersing the catalyst in the liquid in the mixed liquid preparation step described below, simultaneously with the progress of the coating of the resin on the catalyst particles, the progress of agglomeration of the catalyst particles also more easily progressed, forming a catalyst layer. The catalyst utilization at the time tends to decrease. In this case, the fine particles of the catalyst are contained in the pores formed in the catalyst layer, and the gas diffusibility of the catalyst layer may be reduced.

Next, in the mixed liquid preparation step, the resin after the pulverization obtained in the pulverization step and the resin are mixed in a liquid in which the resin can be dissolved or dispersed. The operation in the mixed liquid preparation step and the various conditions for advancing the operation are the same as in the mixed liquid preparation step in the first embodiment except that the crushed catalyst is used.

Next, in the catalyst layer forming step, a catalyst layer is formed using the above-mentioned mixed solution. Specifically, this mixed liquid is mixed with the dispersion medium used in the dispersion liquid preparation step in the first embodiment to prepare a coating liquid for forming a catalyst layer. At this time, additives such as the above-described water repellent may be further added to the coating liquid. Here, in the catalyst layer forming step of the present embodiment, it is preferable to remove the solvent in which the resin can be dissolved or dispersed, as in the case of the freezing step in the first embodiment. It is more preferable to dry the solvent, but it is also possible to keep the state of the liquid containing the catalyst and the resin without removing the solvent, and to directly use this liquid in the dispersion medium. A dispersion in which the resin-coated catalyst is dispersed in a dispersion medium is prepared. The operation for removing the solvent in this manner and the conditions for proceeding with the operation are the same as the dispersion preparation step in the first embodiment except that the production process of the resin-coated catalyst charged into the dispersion medium is different. The same is true. Also, other operations in the catalyst layer forming step and various conditions for advancing the operations are the same as those in the first embodiment except that the production process of the resin-coated catalyst charged in the dispersion medium to be used is different. This is the same as the formation process.

Although the preferred embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments. For example, in the first embodiment of the present invention, a mixed liquid preparation step before shifting to a dispersion liquid preparation step,
The three steps of the liquid component removing step and the pulverizing step may be continuously and repeatedly performed as necessary.

Also, in the second embodiment of the present invention, when the liquid component is removed from the mixed solution in the catalyst layer forming step, the solid material containing the resin and the catalyst obtained after removing the liquid component is removed. May be further pulverized to obtain a resin-coated catalyst powder. Further, in the case where the liquid component is removed from the mixed solution in the second embodiment, the pulverizing step and the mixed liquid preparation step may be repeated a plurality of times using a solid containing the obtained resin and catalyst. . However, even when the pulverizing step and the resin coating step are repeatedly performed in this manner, in the final resin coating step, the liquid state including the catalyst and the resin is maintained without removing the liquid component, and described later. In the dispersion liquid preparation step, this liquid may be directly introduced into the dispersion medium and used.

Further, in the above-described embodiment of the present invention, a method for manufacturing a polymer electrolyte fuel cell in the case where a gas containing hydrogen as a main component is used as an anode reaction gas has been described, but the present invention is not limited to this. Is not
For example, the present invention may be applied to a polymer electrolyte fuel cell having a configuration in which methanol gas is directly introduced into the anode as an anode reaction gas.

[0056]

EXAMPLES Hereinafter, the method for producing a gas diffusion electrode and the method for producing a polymer electrolyte fuel cell according to the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Not something.

(Example 1) The unit cell of Example 1 was manufactured by the procedure described below. First, 3.0 g of a platinum-supported catalyst (trade name: TECIOE50E, manufactured by Tanaka Kikinzoku Co., Ltd.) in which 50% by weight of platinum was supported on carbon black powder.
With a freeze grinder (made by US SPEX Industries Inc., trade name:
The mixture was ground in liquid nitrogen for 10 minutes using a freezer mill 6700). The particle size distribution of the obtained and pulverized catalyst was measured using a particle size distribution analyzer (trade name: LP, manufactured by Otsuka Electronics Co., Ltd.).
A3000 / 3100), the average particle size was 2.5 μm, and the ratio of particles having a particle size of 50 μm to all particles was 1%.

Next, 2.6 g of the crushed catalyst was sufficiently dispersed in 25 g of ethanol. Then, a polymerized unit based on tetrafluoroethylene and CF ₂ ＣＦCFOCF _{2 are} added thereto.
8. A copolymer (A _R = 1.1 meq./g) comprising a polymerized unit based on CF (CF ₃ ) OCF ₂ CF ₂ SO ₃ H
A mixed solution containing a catalyst and a copolymer (hereinafter, referred to as a mixed solution 1) was prepared by adding 12.4 g of a 0% by mass ethanol solution, and sufficiently stirred.

Next, the liquid mixture 1 was treated with an evaporator in which the temperature of a hot water bath was set at 50 ° C. to remove liquid components and obtain solids. Next, 3.7 g of this solid material was added to 2,2,3,3,3
-Pentafluoro-1-propanol was added to 33.3 g and mixed well to obtain a dispersion of the resin-coated catalyst (hereinafter referred to as dispersion 1). Here, the particle size distribution of the fine particles of the resin-coated catalyst dispersed in the dispersion was measured using the particle size distribution analyzer (trade name: LPA3000 / 3100) manufactured by Otsuka Electronics Co., Ltd. by the method described above. The particle size of all the particles was distributed in the range of 0.1 to 0.5 μm.

Next, as a gas diffusion layer, a water-repellent carbon cloth (fiber woven fabric) was filled with a water-repellent carbon powder layer (a mixture of carbon black and PTFE) to a thickness of 300.
μm was prepared. Also, as a polymer electrolyte membrane,
Ion exchange membrane made of a sulfonic acid type perfluorocarbon polymer (trade name: Flemion S, manufactured by Asahi Glass Co., A _R =
1.0 meq. / G, dry film thickness 50 μm).

Next, the above-mentioned dispersion liquid was added to the above-mentioned polymer electrolyte membrane.
Layer thickness 30 μm on both sides, platinum content 0.3 mg / c
m^Two, Apply once with an applicator so that
And dried at 120 ° C. for 1 hour in the air. Finish drying
Later, gas is applied to both sides of the joined body of the polymer electrolyte membrane and the catalyst layer.
The water-repellent carbon powder layer is in contact with the catalyst diffusion layer
At a temperature of 160 ° C. and a pressure of 3M.
Hot pressing was performed for 5 minutes under the condition of Pa. next,
The prepared electrode / membrane assembly has an effective electrode area of 10 cm. ^TwoWhen
An electrode-membrane assembly was produced.

Example 2 First, a mixture 2 was prepared in the same manner as in preparation of the mixture 1 in Example 1, except that 2.6 g of the same catalyst as in Example 1 was used without pulverization. next,
The liquid mixture 2 was treated with an evaporator at a water bath temperature of 50 ° C. to remove the liquid components to obtain 3.7 g of a solid, which was pulverized under the same conditions as in Example 1. The particle size distribution of the pulverized powder was measured in the same manner as in Example 1. Table 1 shows the results. Then, the procedure thereafter is described in Example 1.
A dispersion having a particle size distribution shown in Table 1 was prepared in the same manner as described above, and an electrode / membrane assembly was further obtained.

(Example 3) First, 2.6 g of a platinum-supported catalyst (trade name: TECIOE40E, manufactured by Tanaka Kikinzoku Co., Ltd.) in which 40% by weight of platinum was supported on carbon black powder was sufficiently dispersed in 25 g of ethanol. Next, polymerized units based on tetrafluoroethylene and CF ₂ ＣＦCFO
Copolymer consisting of CF ₂ CF (CF ₃ ) OCF ₂ CF ₂ SO ₃ H and polymerized units (A _R = 1.1 meq./g)
Then, 6.2 g of a 9.0% by mass ethanol solution was added to prepare a mixed solution containing the catalyst and the copolymer (hereinafter, referred to as a mixed solution 3), and the mixed solution was sufficiently stirred.

Next, the mixed solution 3 was treated with an evaporator in which the temperature of a hot water bath was set at 50 ° C. to remove liquid components to obtain 3.1 g of a solid. This was ground in the same manner as in Example 1. The particle size distribution of the pulverized powder was measured in the same manner as in Example 1. Table 1 shows the results.

Next, the pulverized powder was mixed with the copolymer (A)
_R = 1.1 meq. / G) in 6.2 g of a 9.0% by mass ethanol solution to prepare a mixed solution (hereinafter, referred to as a mixed solution 4) containing the resin-coated catalyst after pulverization and the above copolymer. 4 was sufficiently stirred, and the pulverized resin-coated catalyst was further coated with the above copolymer.

Next, the mixed solution 4 was treated with an evaporator in which the temperature of a hot water bath was set at 50 ° C. to remove the solvent, and the solid substance 3.1 was obtained.
g was obtained. The subsequent procedure was the same as in Example 1 to prepare a dispersion 2 having a particle size distribution shown in Table 1, and further obtained an electrode-membrane assembly.

(Comparative Example 1) The same catalyst 2.6 as in Example 1
g and pulverized mixture were prepared in the same manner as in Example 1 except that the mixture was used without pulverization.
A membrane assembly was obtained. In Comparative Example 1, the average particle diameter of the catalyst in a non-pulverized state and a particle diameter of 50
Table 1 shows the proportion of particles exceeding μm.

[Battery Characteristics Test] Examples 1 to 3 above
A separator having a gas flow path was attached to each unit cell (electrode / membrane assembly) of Comparative Example 1 to form a measurement cell, and an electronic load and a DC power supply (FK400L and EX750L, manufactured by Takasago Seisakusho) were used. A current-voltage characteristic test of the measurement cell was performed. Measurement conditions were: hydrogen inlet pressure; 0.2 MPa,
Air inlet pressure; 0.2 MPa; operating temperature of measuring cell;
At 70 ° C., the open-circuit voltage before operation was measured, and then the output current density (A / cm ² ) of each measurement cell when the voltage between terminals was maintained at 0.6 V was measured over time. The output current density of each measuring cell was 5
The values at 00 hours and 1000 hours were measured. Under these operating conditions, the hydrogen utilization rate is 70% and the air utilization rate is 40%.
% And the flow rates of hydrogen gas and air were adjusted.

[Platinum Utilization Measurement Test of Electrode] Using each measurement cell including each unit cell (electrode / membrane assembly) of Examples 1 to 3 and Comparative Example 1 used in the above battery characteristic test,
The cyclic voltammogram of the anode and the cathode of each measurement cell was measured by the procedure shown below, and the platinum utilization of the anode and the cathode of each unit cell of Examples 1 to 3 and Comparative Example 1 was measured based on this. . Table 1 shows the results.

First, the temperature of the measuring cell was maintained at 80 ° C., and the water content of the catalyst layer of each electrode and the polymer electrolyte membrane was set to a level equivalent to that when each measuring cell was operating at a steady state and generating power. Adjusted to be. Next, of the anode and the cathode, the electrode for evaluating the platinum utilization was used as a working electrode, and the other electrode was used as a counter electrode. Then, nitrogen gas was introduced into the working electrode, hydrogen gas was introduced into one counter electrode, and the counter electrode was used also as a hydrogen reference electrode.

The measurement by cyclic voltammetry of the above-mentioned bipolar system was performed by connecting a working electrode and a counter electrode to a potentiostat connected to a function generator. Specifically, the potential of the working electrode with respect to the reference electrode is changed from 70 mV to 120 mV.
Swept in a range of 0 mV, it was determined the surface area S _H of the resulting cyclic voltammogram of active platinum which can be regarded as the quantity of electricity Q based on hydrogen adsorption peak is utilized during cell operation. The _SH was obtained from the area of hydrogen adsorption and the potential sweep rate to determine the quantity of electricity Q of hydrogen adsorbed on the platinum surface, using the following equation (1). In the following equation (1),
The value of 0.21 × 10 ⁻³ corresponds to the amount of electricity flowing when hydrogen is adsorbed and desorbed per 1 cm ² of the surface of polycrystalline platinum.
On the other hand, CO. The total surface area S _{A of} platinum was estimated using the MSA value (Pt surface area by the CO adsorption method), and the platinum utilization factor U was obtained using the following equation (2). S _H = Q / (0.21 × 10 ⁻³ ) (1) U = 100 × S _H / S _A (2)

[0072]

[Table 1]

[Table 2]

[0073]

As described above, according to the present invention,
Gas diffusion that can stably obtain excellent polarization characteristics over a long period of time because it is possible to stably secure sufficient reaction sites for the amount of catalyst contained in the catalyst layer of the electrode for a long period of time. It is possible to provide a method for manufacturing an electrode and a method for manufacturing a polymer electrolyte fuel cell having excellent output characteristics provided with the gas diffusion electrode.

Claims (6)

[Claims] 1. A method for manufacturing a gas diffusion electrode, comprising: a catalyst layer containing a catalyst and a fluorine-containing ion exchange resin; and a gas diffusion layer disposed adjacent to the catalyst layer, wherein the resin is dissolved. Or in a dispersible liquid, mixing the catalyst and the resin, a mixed liquid preparation step of obtaining a mixed liquid containing the catalyst and the resin, and the liquid component obtained by removing the liquid component in the mixed liquid A liquid component removing step of obtaining a solid containing a catalyst and the resin, a cooling step of cooling the solid to a brittle solid, and a pulverizing step of pulverizing the solid to obtain a powder; A method for producing a gas diffusion electrode, comprising: a dispersion liquid preparing step of preparing a dispersion liquid by dispersing the dispersion liquid into a catalyst layer; and a catalyst layer forming step of applying the dispersion liquid to form a catalyst layer. 2. The powder obtained in the pulverizing step has an average particle size of 4 μm or less and substantially has a particle size of 5 μm.
The method for producing a gas diffusion electrode according to claim 1, wherein the method does not include particles exceeding 0 μm. 3. A method for producing a gas diffusion electrode, comprising: a catalyst layer containing a catalyst and a fluorinated ion exchange resin; and a gas diffusion layer disposed adjacent to the catalyst layer, wherein the catalyst is pulverized. And a pulverizing step of reducing the average particle diameter to 4 μm or less, and substantially not including particles having a particle diameter of more than 50 μm, in a liquid in which the resin can be dissolved or dispersed, and pulverized in the pulverizing step. A mixed solution preparation step of mixing the catalyst and the resin to obtain a mixed solution containing the catalyst and the resin; a catalyst layer forming step of applying the mixed solution to form a catalyst layer; A method for producing a gas diffusion electrode, comprising: 4. The catalyst has a specific surface area of 300 to 200.
The gas diffusion electrode according to any one of claims 1 to 3, wherein the metal diffusion catalyst is a metal-supported catalyst in which metal particles selected from the group consisting of a platinum group metal and a platinum group alloy are supported on a carbon black carrier of 0 cm ^2. Manufacturing method. 5. The resin according to claim 1, wherein the resin is a copolymer comprising a polymerization unit based on a perfluorovinyl compound represented by the following formula (A) and a polymerization unit based on tetrafluoroethylene. The method for producing a gas diffusion electrode according to any one of claims 1 to 4. _{CF 2 = CF- (OCF 2 CFX} ) m -O p - in _{(CF 2) n -SO 3 H} ... (A) [ Formula (A), m represents an integer of 0 to 3, n is from 1 to 12
And p represents 0 or 1, and X represents a fluorine atom or a trifluoromethyl group. ] 6. A method for manufacturing a polymer electrolyte fuel cell, comprising: an anode and a cathode each comprising a gas diffusion electrode; and a polymer electrolyte membrane disposed between the anode and the cathode. A method for manufacturing a polymer electrolyte fuel cell, wherein at least one of the cathodes is manufactured by the method for manufacturing a gas diffusion electrode according to claim 1.