JP6257443B2 - Microporous layer forming paste composition, method for producing the same, and method for producing a gas diffusion layer for a fuel cell - Google Patents

Description

The present invention relates to a microporous layer that is applied to the surface of a base material made of a conductive porous material such as carbon paper to form a microporous layer (MPL) of a gas diffusion layer (GDL: Gas Diffusion Layer). forming paste composition and a method for producing the same, and relates to a manufacturing method for a gas diffusion layer for a fuel cell employing such a microporous layer forming paste composition.

  In a fuel cell, in particular, a polymer electrolyte fuel cell, a cathode side electrode and an anode side electrode are formed on both sides of a polymer electrolyte membrane. Usually, the cathode side electrode and the anode side electrode are made of platinum or the like. The electrode catalyst layer is made of carbon black supporting a catalyst and an ion exchange resin, and a porous gas diffusion layer disposed outside the electrode catalyst layer.

The gas diffusion layer of the polymer electrolyte fuel cell serves to diffuse anode gas (fuel gas) or cathode gas (oxidizing gas) supplied from the outside of the polymer electrolyte membrane into the catalyst layer adjacent to the gas diffusion layer (gas In order to suppress the flooding phenomenon (a phenomenon in which the pores of the gas diffusion layer are clogged with water), in addition to being required to be conductive so that the electrons used for the reaction can move, Water repellency is required to discharge water generated by the electrochemical reaction of hydrogen and oxygen during power generation.
Such a gas diffusion layer includes a conductive material such as carbon particles for imparting conductivity and a polytetragon for imparting water repellency to a substrate made of a conductive porous material such as carbon cloth or carbon paper. It is known that it can be formed by applying a paste composition for forming a microporous layer containing a water-repellent resin such as fluoroethylene (hereinafter also abbreviated as “PTFE”) as a main component.
In the gas diffusion layer of the fuel cell, as disclosed in Patent Document 1, Patent Document 2, etc., a group in which predetermined pores are formed by using a water-soluble polymer such as polyethylene oxide as a pore-forming agent. Sometimes wood is used.

  Here, in preparation of a microporous layer forming paste composition for forming a gas diffusion layer, in addition to a conductive material such as carbon particles and a water repellent resin such as PTFE, usually a conductive material such as carbon particles. In order to uniformly disperse a water repellent resin such as PTFE fine particles or the like in a solvent such as water, a dispersant is blended. If the conductive material or water-repellent resin is agglomerated without a dispersing agent, resulting in poor dispersion, the stability of the paste is low, and clogging and concentration changes may occur in the piping and pump during application. This is because it adversely affects the film properties. In addition, if there are many aggregates in the film after film formation, the microporous layer lacks homogeneity and adversely affects gas diffusivity and other characteristics, and the surface roughness of the microporous layer increases and contact resistance increases. This is because it becomes difficult to obtain a stable output in the fuel cell.

  A paste composition for forming a microporous layer in which a conductive material, a water-repellent resin and a dispersant are mixed in this manner is applied to the surface of a substrate made of a conductive porous material, and then a dispersant (such as a PTFE emulsion) is applied. The microporous layer of the gas diffusion layer is formed by performing a drying / firing process for decomposing and volatilizing (including a dispersant previously contained in the water-repellent resin). For example, when the paste composition for forming a microporous layer is composed of carbon particles as a conductive material, PTFE emulsion as a water repellent resin, and a nonionic surfactant as a dispersant, it is usually 300 ° C. It can be processed at a moderate drying / firing temperature.

  However, in a coating film (hereinafter sometimes referred to as a microporous layer) formed on the surface of a substrate by applying a paste composition for forming a microporous layer on the surface of the substrate and then drying and firing, the microporous layer If the dispersant contained in the forming paste composition is not sufficiently decomposed and volatilized, moisture is trapped by the hydrophilic group of the dispersant, so the microporous layer of the formed gas diffusion layer is sufficient It is not possible to develop a good water repellency. For this reason, a long drying and firing time is required to ensure that the dispersant in the paste composition is sufficiently decomposed, volatilized and disappeared to ensure water repellency. The drying and firing time associated with the decomposition and volatilization of the agent is further increased. However, if the drying / firing time becomes longer, the length of the tunnel furnace in the continuous production line becomes longer, and the amount of electricity for heating increases, which greatly affects the production cost. Although there is an idea of shortening the drying / firing time by raising the drying / firing temperature, there is a problem that the load on the natural environment increases due to an increase in the drying / firing temperature. In addition, by setting the temperature higher than necessary, the coating film components may deteriorate, cracks may occur due to temperature changes caused by heating, and the fixing power to the substrate may be reduced. is there.

  Here, in Patent Document 3, in a coating liquid containing carbon black and PTFE applied on the base material of the gas diffusion layer, a low temperature pyrolysis type whose mass half-temperature in air is 100 to 300 ° C. The non-ionic surfactant of 300 to 390 ° C. after drying on the base material by adding 0.5 to 10% by mass with respect to the total amount of PTFE and surfactant The gas diffusion layer that can maintain high water repellency for a long time without the surfactant remaining sufficiently thermally decomposed is disclosed.

  Patent Document 4 discloses a catalyst layer, a gas diffusion layer composed of a conductive base material, and a conductive substance, methylcellulose, ethylcellulose, hydroxypropyl, which is located between the catalyst layer and the gas diffusion layer. A fuel cell comprising a thickening agent which is a nonionic cellulose series compound selected from methylcellulose and hydroxypropylethylcellulose and a microporous layer containing a fluorine series resin is disclosed, and a nonionic cellulose series for viscosity adjustment is disclosed It is described that a conductive substance is well dispersed by using a compound.

Japanese Patent Laid-Open No. 2005-267981 JP 2010-062021 A JP 2007-194004 A JP 2006-019300 A

  In the technology of Patent Document 3, the use of a low-temperature pyrolysis-type nonionic surfactant having a mass half-temperature in air of 100 to 300 ° C. is relatively low compared to conventionally known surfactants. The surfactant is completely removed by drying and baking at 300 to 390 ° C., and high water repellency can be maintained. However, the low-temperature pyrolysis-type nonionic surfactant is mainly for suppressing the aggregation and sedimentation of PTFE fine particles and stably dispersing the PTFE fine particles in water. It is difficult to prevent the aggregating material from agglomerating and uniformly disperse. Even if a dispersant for uniformly dispersing a conductive material such as carbon black is added separately, if the amount of the dispersant is large, the drying and firing time associated with the decomposition and volatilization of the dispersant will increase. It is not possible to shorten the drying and baking time. In Patent Document 3, the aqueous dispersion containing PTFE impregnated in the base material of the gas diffusion layer to impart water repellency may contain a polyethylene oxide thickener as necessary. Although it is described as being good, there is no specific specification about the polyethylene oxide thickener, and its technical significance is unknown.

  In the technique of Patent Document 4, the thickener is a nonionic cellulose series compound, and the cellulose-based water-soluble polymer is not completely decomposed at a drying / calcination temperature of about 300 ° C. Since the microporous layer does not exhibit water repellency unless the temperature is increased to about 350 ° C., it is necessary to increase the current drying / firing temperature, which causes a problem of increasing the load of the drying / firing process.

Accordingly, the present invention provides a microporous layer-forming paste composition that can shorten the drying / firing time without increasing the load of the drying / firing process and can reduce the cost, a method for producing the same, and a fuel cell the provision of manufacturing method of the diffusion layer in which an object.

  The paste composition for forming a microporous layer according to claim 1 is a paste composition containing a conductive material, a water repellent resin, a dispersant, and polyethylene oxide as a dispersion aid, The molecular weight is within the range of 250,000 to 2,200,000, and the conductive material and the water repellent resin are added within the range of 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the total solid content, A microporous layer of a gas diffusion layer for a fuel cell is formed by applying to a substrate, drying and firing.

Here, the specification that the molecular weight of the polyethylene oxide is in the range of 250,000 to 2,200,000 is a result of repeated experiments conducted by the present inventors. As a result, in the case of polyethylene oxide having a molecular weight of less than 250,000, the viscosity is small. In addition, with a small addition amount that does not increase the load of the drying and firing process, the effect of improving the flow characteristics that the paste composition at the time of dispersion cannot be obtained, the amount of dispersant added is reduced to the drying / On the other hand, it is difficult to shorten the baking time. On the other hand, in polyethylene oxide having a molecular weight exceeding 2.2 million, the molecular weight is too large, and the drying and baking time associated with the thermal decomposition of polyethylene oxide becomes long. It was found based on this knowledge that the process load increases.
In addition, although the molecular weight of polyethylene oxide has a viscosity average molecular weight (Mv) and a weight average molecular weight (Mw), in this invention, it is based on a viscosity average molecular weight.

In addition, the inventors of the present invention have repeatedly conducted experimental studies to specify that the polyethylene oxide is added within the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin. As a result, when the addition amount of polyethylene oxide is less than 1 part by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin, the addition amount is too small and the paste composition when dispersed with polyethylene oxide It is difficult to improve the flow characteristics expressed by the product, and it is difficult to reduce the addition amount of the dispersant to shorten the drying and baking time. On the other hand, the addition amount of polyethylene oxide is 2 parts by weight. If the amount exceeds 1, the addition amount is too large, and the drying and baking time associated with the thermal decomposition of polyethylene oxide becomes longer, and on the contrary, the load of the drying and baking process is found to increase. Based those that are set.
Note that the above numerical values are not strict, but are approximate values, and are naturally approximate values including errors due to measurement or the like, and do not deny errors of several percent.

The method for producing a microporous layer-forming paste composition of the invention of claim 2 is a method for dispersing a conductive material, a water repellent resin, a dispersant, and polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000. As an agent, it is added within a range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin, and is mixed and dispersed for a predetermined time.

Method for producing a gas diffusion layer for a fuel cell of the invention of claim 3, claim 2 of the microporous layer conductive porous microporous layer forming paste composition produced by the production method of forming paste composition After applying to the base material made of the material, it is dried and fired.

The paste composition for forming a microporous layer according to the invention of claim 1 comprises a conductive material, a water repellent resin, a dispersant, and a polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 as a dispersion aid. It contains in the range of 1 weight part-2 weight part with respect to 100 weight part of solid content total amount of the said electroconductive material and the said water repellent resin.
Among polyethylene oxides of water-soluble resins that thermally decompose at less than 300 ° C., polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is 1 with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin. Addition within the range of parts by weight to 2 parts by weight improves the flow characteristics of the paste composition, and easily and uniformly disperses paste components such as conductive materials (for example, carbon particles) with a small amount of dispersant. And the amount of dispersant added can be reduced. And even if a predetermined amount of polyethylene oxide as a dispersion aid is added, the amount of the dispersant added is reduced more than the amount of polyethylene oxide added, so that in the drying / firing process performed after application to the substrate, In addition, it is possible to shorten the time required for drying and baking for sufficiently decomposing and volatilizing and dispersing the dispersion aid, and to exhibit sufficient water repellency even with a short drying and baking time.

That is, polyethylene oxide used as a dispersion aid is a water-soluble resin that is thermally decomposed at less than 300 ° C., and has a molecular weight in the range of 250,000 to 2,200,000, and the addition amount is a solid of a conductive material and a water-repellent resin. Since the amount is in the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total amount, the addition of polyethylene oxide reduces the amount of dispersant added without increasing the load in the drying / firing process. By shortening the drying / firing time due to the effect, the power required for drying / firing can be reduced, and the furnace length of the drying / firing furnace can be shortened, so that the manufacturing cost can be reduced.
In this way, without increasing the load of the drying / firing process, the water repellency is expressed in a short drying / firing time, so that the drying / firing time can be shortened and the cost can be reduced. It becomes a paste composition.
Here, polyethylene oxide is basically used in combination with a dispersant as a dispersion aid for assisting a dispersant for efficiently dispersing, but depending on the amount and combination of conductive material and water-repellent resin. Can be used alone as a dispersant, and the drying and firing time can be shortened.

According to a second aspect of the present invention, there is provided a method for producing a microporous layer-forming paste composition comprising: a conductive material, a water-repellent resin, a dispersant, and polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000. As a dispersion aid, it is added within a range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin, and is mixed and dispersed for a predetermined time.
Among polyethylene oxides of water-soluble resins that thermally decompose at less than 300 ° C., polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is 1 with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin. Addition within the range of parts by weight to 2 parts by weight improves the flow characteristics of the paste composition, and easily and uniformly disperses paste components such as conductive materials (for example, carbon particles) with a small amount of dispersant. And the amount of the dispersant can be reduced. The amount of the dispersant is reduced by adding a small amount of the dispersion aid, so that the dispersant and the dispersion aid are sufficiently decomposed and volatilized and disappeared in the drying and baking process performed after application to the substrate. The time can be shortened, and sufficient water repellency can be exhibited even with a short drying and baking time.

  By shortening the drying / firing time in this way, it is possible to reduce the electric power required for drying / firing, and the furnace length of the drying / firing furnace can be shortened, so that the manufacturing cost can be reduced. In this way, a microporous layer forming paste that can reduce the drying and baking time and reduce the cost by exhibiting water repellency in a short drying and baking time without increasing the load of the drying and baking process. It becomes the manufacturing method of a composition.

According to a third aspect of the present invention, there is provided a method for producing a gas diffusion layer for a fuel cell, wherein the microporous layer-forming paste composition produced by the method for producing a microporous layer-forming paste composition of claim 2 is formed from a conductive porous material. After being applied to a base material, it is dried and fired.
As described above, according to the paste composition for forming a microporous layer, the molecular weight is 250,000 within a range of 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin. By adding polyethylene oxide in the range of ˜2.2 million, the flow characteristics of the paste composition are improved, and the paste components are uniformly dispersed with a small amount of dispersant.
For this reason, according to the method for producing a gas diffusion layer obtained by applying the paste composition for forming a microporous layer to a base material made of a conductive porous material, drying and firing, the dispersion amount exceeds the addition amount of the dispersion aid. By reducing the amount of the agent, the dispersant and dispersion aid disappear even in a short drying and baking time and do not remain in the coating film (microporous layer), and the microporous layer of the formed gas diffusion layer The layer sufficiently exhibits water repellency that affects the power generation efficiency of the fuel cell. Therefore, the water generated by the battery reaction is discharged smoothly and the flooding phenomenon is prevented. As a result, deterioration in characteristics such as gas diffusivity is suppressed, and deterioration in battery performance can be prevented. In addition, the addition of polyethylene oxide allows the paste components to be uniformly dispersed with a small amount of dispersant, and shortens the time required for drying and baking to eliminate the dispersant and dispersion aid applied after application to the substrate. Therefore, in the formed microporous layer of the gas diffusion layer, the occurrence of cracks due to non-uniform paste components and long-time heating is prevented, and stable and uniform characteristics such as gas diffusivity can be exhibited. Therefore, a stable output can be obtained, and the polymer electrolyte fuel cell can be suitably used for a membrane electrode assembly that can operate stably for a long period of time.

FIG. 1 is a schematic configuration diagram of a polymer electrolyte fuel cell having a gas diffusion layer for a fuel cell that uses the paste composition for forming a microporous layer according to an embodiment of the present invention.

Embodiments of the present invention will be described below.
In the embodiment, the numerical values described in the same column of Table 1 and Table 2 indicate the magnitude of the quantity, and basically there is no difference in the material, and therefore, a duplicate description is omitted here.

First, the microporous layer forming paste composition according to the present embodiment will be described.
The microporous layer forming paste composition of the present embodiment is a paste-like mixture containing a conductive material, a water repellent resin, a dispersant, and polyethylene oxide as a dispersion aid.

  Examples of the conductive material that can be used include powdered conductive materials such as carbon black powder, graphite powder, and vapor-grown carbon powder, and fibrous conductive materials such as carbon fibers (carbon nanotubes). Among them, carbon black is preferable from the viewpoint of compatibility with the carbon base material to be coated, and examples of the carbon black include carbon particles such as acetylene black, ketjen black, furnace black, channel black, and lamp black. Since acetylene black is excellent in electron conductivity, has a large specific surface area, has a high purity and is easy to use, it is suitable for forming a coating layer used for an electrode of a fuel cell. These can be used singly or in appropriate combination of two or more.

  Any water-repellent resin may be used as long as it can exhibit water repellency in the coating layer to be formed and functions as a resin binder. For example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene Copolymer (FEP), perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), A fluororesin such as polyvinylidene fluoride (PVdF), a silicone resin, or the like can be used. Among them, a fluorine-based polymer material excellent in water repellency, corrosion resistance during electrode reaction, and the like is preferable, and in particular, an emulsion of PTFE is preferably used. PTFE may be a tetrafluoroethylene homopolymer, derived from halogenated olefins such as chlorotrifluoroethylene and hexafluoropropylene, and other fluorine-based monomers such as perfluoro (alkyl vinyl ether). It may be a modified PTFE containing units. These can be used singly or in appropriate combination of two or more.

  Emulsion (also referred to as “emulsion”) is also called an emulsion, and the original meaning is that the liquid particles form a milky form as colloidal particles or coarser particles (dispersed system). Although it is (Saburo Nagakura et al., “Iwanami Rikagaku Dictionary (5th edition)” page 152, published by Iwanami Shoten Co., Ltd. on February 20, 1998), in this specification and claims, it is more general. As used herein, the term “emulsion” is used herein as “in which solid or liquid particles are dispersed in a liquid”.

Polyethylene oxide as a dispersion aid is a water-soluble resin that thermally decomposes at less than 300 ° C. Mainly used for preventing aggregation of conductive materials such as carbon black and facilitating uniform dispersion, but in addition to this, water repellent resins such as PTFE fine particles can be easily dispersed uniformly, It can also be used to dissolve in a solvent.
Here, the reason why polyethylene oxide is used as a dispersion aid will be described below. Polyethylene oxide has the effect of increasing the viscosity of the paste composition for forming a microporous layer by its addition. Due to this thickening effect, the water-repellent resin and the conductive material can be efficiently dispersed in the microporous layer-forming paste composition, and the amount of dispersant added can be reduced.
At this time, if the dispersant and the dispersion aid remain in the microporous layer forming the gas diffusion layer, the characteristics such as water repellency in the microporous layer and further battery performance are adversely affected. For this reason, dispersants and dispersion aids need to be thermally decomposed in a drying / firing process in which drying / firing is carried out, but polyethylene oxide has a low decomposition temperature, and a difference in decomposition temperature depending on molecular weight is also small. Therefore, even if the molecular weight is increased, the drying / baking temperature is less than 300 ° C., so that the pyrolysis is not necessary. However, depending on the molecular weight and addition amount of polyethylene oxide, the drying / firing time associated with the thermal decomposition of polyethylene oxide becomes longer, increasing the load of the drying / firing process. In the present invention, the molecular weight is 250,000- Polyethylene oxide within the range of 2,200,000 is added within the range of 1 to 2 parts by weight of solid content with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin. .

  In the case of polyethylene oxide having a molecular weight of less than 250,000, the effect of thickening is small, and with a small addition amount that does not increase the load of the drying / firing process, the microporous layer forming paste composition can be efficiently dispersed to the region where it is dispersed. Since the effect of improving the flow characteristics cannot be obtained, it is difficult to reduce the addition amount of the dispersant to shorten the drying / firing time. On the other hand, in the case of polyethylene oxide having a molecular weight exceeding 2.2 million, the molecular weight is too large, and the drying and firing time associated with the thermal decomposition of polyethylene oxide becomes long. That is, the load of the drying / firing process is increased, and it is difficult to ensure sufficient water repellency in a desired short drying / firing time.

  Moreover, when the addition amount of polyethylene oxide is less than 1 part by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin, the addition amount is too small, and the paste for forming a microporous layer by polyethylene oxide The effect of improving the flow characteristics of the composition is difficult to obtain, and in order to sufficiently disperse the conductive material and the water-repellent resin, it is difficult to greatly reduce the addition amount of the dispersant. That is, approximately the same amount of dispersant is required regardless of whether or not polyethylene oxide is added, and the effect of adding polyethylene oxide is difficult to obtain. On the other hand, when the amount exceeds 2 parts by weight, the amount added is too large, and the drying and firing time associated with the thermal decomposition of polyethylene oxide becomes long. That is, the load of the drying / firing process is increased, and it is difficult to ensure sufficient water repellency in a desired short drying / firing time.

On the other hand, polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is in the range of 1 to 2 parts by weight in terms of solid content with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin. When added inside, the viscosity of the paste composition for forming a microporous layer can be increased to facilitate dispersion. By using polyethylene oxide as a dispersion aid that facilitates dispersion when the paste component of the microporous layer forming paste composition is dispersed in this manner, the amount of dispersant added can be reduced, and the load during drying and firing is reduced. This makes it possible to shorten the drying and baking time without increasing the temperature.
Examples of such polyethylene oxide include commercially available products sold by Sumitomo Seika Co., Ltd. (trade name: PEO), Meisei Chemical Industry Co., Ltd. (trade name: Alcox), and the like. Can be used.

  Examples of the dispersing agent include nonionic surfactants such as polyoxyethylene alkylphenyl ether (Triton X-100) and polyoxyethylene lauryl ether, polyoxyethylene distyrenated phenyl ether, and polyoxyethylene alkylene alkyl ether. , Nonionic dispersants such as polyethylene glycol alkyl ethers, cationic dispersants such as alkyltrimethylammonium salts, dialkyldimethylammonium chlorides and alkylpyridinium chlorides, anionic systems such as polyoxyethylene fatty acid esters and acid group-containing structurally modified polyacrylates Examples thereof include a dispersant, and one of these can be used alone or two or more of them can be used. For example, when carbon black is used as the conductive material and PTFE emulsion is used as the water repellent resin, a nonionic surfactant dispersant is used. In some cases, the water repellent resin is mixed in a state containing a dispersant.

Thus, the microporous layer forming paste composition of the present embodiment has a conductive material such as carbon black, a water-repellent resin such as PTFE emulsion, a dispersant, and a molecular weight in the range of 250,000 to 2,200,000. A certain amount of polyethylene oxide is blended as a dispersion aid at a predetermined ratio. When this microporous layer forming paste composition is applied to a fuel cell gas diffusion layer 14 (see FIG. 1) described later, A microporous layer-forming paste composition is obtained by mixing and dispersing in a solvent such as exchange water.
As described above, the present invention is a paste composition for forming a microporous layer in which polyethylene oxide is used in combination with a dispersant other than polyethylene oxide as a dispersion aid.
Polyethylene oxide may be used alone as a dispersing agent, not as a dispersing aid.

Next, the manufacturing method of the paste composition for microporous layer formation of this invention is demonstrated. As a method of mixing and dispersing a conductive material, a water-repellent resin, a dispersant, and polyethylene oxide as a dispersion aid in a solvent, an ordinary mixer such as a disper can be used. It is desirable to disperse by using collision energy generated by contact (collision) between materials and contact with the inner wall of the stirring vessel (collision) without using force. It is preferable to mix and disperse using a planetary stirring / defoaming device or the like that can be set to 1. As a result, the conductive material can be dispersed while maintaining the three-dimensional structure of the conductive material without causing the destruction of the three-dimensional structure of the conductive material. A structure can be formed, and sufficient coating strength can be obtained. Further, by using a planetary agitation / defoaming device, since such an apparatus does not have a stirring blade or the like, it does not take time for cleaning, and the yield is improved, so that the cost can be reduced. .
In addition, a solvent is a solvent for mixing each component of a conductive material, a water-repellent resin, a dispersant, and polyethylene oxide to form a paste, and disappears after drying and baking.

And after apply | coating the paste composition for microporous layer formation prepared in this way to the base material 16 (refer FIG. 1) which consists of an electroconductive porous material, the coating film becomes microporous by drying and baking. A surface layer 15 as a layer is formed, and a gas diffusion layer 14 for a fuel cell in which a surface layer 15 (see FIG. 1) as a microporous layer is formed on a substrate 16 is formed.
That is, the gas diffusion layer 14 for a fuel cell according to the present embodiment is a simple work process in which a paste composition for forming a microporous layer is applied to a base material 16 made of a conductive porous material, and then dried and fired. And can be finished into an arbitrary shape depending on the shape of the substrate 16.

  Here, the structure of the polymer electrolyte fuel cell (single cell) to which the fuel cell gas diffusion layer 14 using the microporous layer forming paste composition according to the present embodiment is applied is schematically shown in FIG. This will be described with reference to the drawings.

  As shown in the figure, in the fuel cell 1 in which the microporous layer forming paste composition according to the present embodiment is used, an oxidizing gas such as oxygen gas reacts on one surface of an electrolyte membrane 11 that becomes the core of a single cell. The cathode electrode 12A is disposed on the surface of the cathode electrode 12A of the membrane-electrode assembly 10 and the membrane-electrode assembly 10 in which an anode electrode 12B on which the fuel gas such as hydrogen gas reacts is disposed on the other surface. The cathode-side separator 20A and the anode-side separator 20B disposed on the surface of the anode electrode 12B of the membrane-electrode assembly 10 are configured. The membrane-electrode assembly 10 is also called a membrane-electrode assembly, and an oxidizing gas and a fuel gas react with each other, and electric power is taken out between the cathode side separator 20A and the anode side separator 20B.

  The electrolyte membrane 11 composed of an ion exchange group and a polymer membrane has a property of binding firmly to specific ions and selectively transmitting cations or anions. The electrodes 12 (cathode electrode 12A and anode electrode 12B) formed on both surfaces of the electrolyte membrane 11 are a catalyst layer 13 (cathode side catalyst layer 13A and anode side catalyst layer 13B) and a gas diffusion layer 14 (cathode side). 14A and anode side diffusion layer 14B).

The catalyst layer 13 (cathode-side catalyst layer 13A or anode-side catalyst layer 13B) with which the oxidizing gas or the fuel gas reacts is a catalyst-supporting carbon in which a noble metal catalyst such as platinum, gold or palladium is supported by carbon, and this catalyst-supporting carbon. And a resin that adheres to the electrolyte membrane 11.
The gas diffusion layer 14 (cathode side diffusion layer 14A or anode side diffusion layer 14B) having gas permeability and water permeability is formed on the surface of the catalyst layer 13 (cathode side catalyst layer 13A or anode side catalyst layer 13B). Is done.

  The gas diffusion layer 14 (cathode side diffusion layer 14A or anode side diffusion layer 14B) includes a base material 16 (cathode side base material 16A or anode side base material 16B) and a surface layer 15 as a microporous layer (microporous layer). (The cathode side surface layer 15A or the anode side surface layer 15B), and the surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B) as a microporous layer is the catalyst layer 13 (cathode side catalyst layer 13A or The base material 16 (cathode side base material 16A or anode side base material 16B) is disposed on the surface of the surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B) in contact with the surface of the anode side catalyst layer 13B). Is done.

  With such a configuration, when an oxidizing gas is supplied from the outside to the oxidizing gas channel 21A of the cathode side separator 20A, a part of the oxidizing gas flowing along the oxidizing gas channel 21A is a gas diffusion layer on the cathode side. It penetrates into the inside from the surface of the substrate 16A side of 14A. Other unreacted oxidizing gas flows along the oxidizing gas channel 21 </ b> A and is discharged to the outside of the fuel cell 1. Similarly, when fuel gas is supplied from the outside to the fuel gas passage 21B of the anode separator 20B, a part of the fuel gas flowing along the fuel gas passage 21B is based on the anode-side gas diffusion layer 14B. The material 16B enters the inside from the surface. Other unreacted fuel gas flows along the fuel gas flow path 21B as it is, and is discharged to the outside of the fuel cell 1.

In the present embodiment, the microporous layer forming paste composition is applied to the base material 16 (cathode side base material 16A or anode side base material 16B) made of a conductive porous material, and then dried and fired. Thus, a surface layer 15 (cathode side surface layer 15A or anode side surface layer 15B) as a microporous layer is formed, and the gas diffusion layer 14 having gas permeability and water permeability is formed between the surface layer 15 and the base material 16. (Cathode side diffusion layer 14A or anode side diffusion layer 14B) is formed.
At this time, the surface layer 15 (cathode-side surface layer 15A or anode-side surface layer 15B) is made conductive by a conductive material such as carbon black contained in the microporous layer forming paste composition according to the present embodiment. Furthermore, water repellency is imparted by a water repellent resin such as PTFE emulsion. Incidentally, the water-repellent resin melts after drying and firing, and is in a state of adhering to the carbon on the surface of the base material 16 or the carbon of the surface layer 15. It is firmly bound to the surface carbon.

In the present embodiment, the base material 16 (cathode side base material 16A or anode side base material 16B) made of a conductive porous material is a gas of a conventional fuel cell (in particular, a polymer electrolyte fuel cell). A material composed of any material having gas permeability and conductivity generally used in a diffusion layer can be used, for example, carbon materials such as graphite and expanded graphite, and these nanocarbon materials, A conductive inorganic material such as stainless steel, molybdenum, or titanium that is formed in the form of fibers, particles, woven fabric, or nonwoven fabric can be used. More specifically, carbon paper, carbon cloth, carbon felt (carbon nonwoven fabric) and the like are preferably used. Furthermore, the base material 16 made of a conductive porous material such as carbon paper or carbon cloth is preferably subjected to a water repellent treatment in order to further improve the water repellency of the gas diffusion layer 14.
Further, the application of the paste composition for forming the microporous layer on the substrate 16 is performed by brush coating, brush coating, roll coater coating, bar coater coating, die coater coating, screen printing, spray coating, doctor blade coating, wire bar coating, It can be performed by a method such as applicator application.

  Here, in the present embodiment, the polyethylene oxide that thermally decomposes at a molecular weight of less than 300 ° C. within the range of 250,000 to 2.2 million is based on 100 parts by weight of the total solid content of the conductive material and the water repellent resin. It is added within the range of 1 to 2 parts by weight. For this reason, it is possible to reduce the addition amount of a dispersant used mainly for preventing and uniformly dispersing a conductive material such as carbon black, that is, the addition amount in the paste composition for forming a microporous layer. The time required for drying and baking to decompose and volatilize and disperse the dispersant and polyethylene oxide performed after applying the paste composition to 16, in other words, drying and baking to develop water repellency by the water-repellent resin Can reduce the time it takes. That is, even when the drying and baking time is short, high water repellency can be expressed without the dispersant and polyethylene oxide completely disappearing and remaining.

In other words, in this embodiment, by specifying the molecular weight and addition amount of polyethylene oxide to be added, the drying and baking time associated with the thermal decomposition of polyethylene oxide rather than the drying and baking time associated with the decomposition and volatilization of the dispersant. Will not be long. In addition, since polyethylene oxide is thermally decomposed at a low temperature of less than 300 ° C., the drying / firing temperature is not increased compared to when polyethylene oxide is not used, and the load of the drying / firing process is increased. There is nothing. And since the addition amount of a dispersing agent can be reduced more than the addition amount of a polyethylene oxide, in this Embodiment, it applies when apply | coating the paste composition for microporous layer formation to the base material 16, and forming a microporous layer. The time required for drying and baking can be shortened, and the electric power required for drying and baking can be reduced. Furthermore, the length of the drying / firing furnace can be shortened. Therefore, manufacturing cost can be reduced.
Further, the polyethylene oxide having a molecular weight within the range of 250,000 to 2,200,000 is added within the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin. By adding a small amount, the flow characteristics of the paste composition for forming a microporous layer are dramatically improved and the dispersibility of paste components such as conductive materials is increased, so that the amount of dispersant added can be increased more than the amount of polyethylene oxide added. Since the amount of the dispersant can be reduced and the amount of the dispersant added can be reduced as compared with the prior art, the material cost can be reduced.
Therefore, the cost of the fuel cell can be reduced.

Furthermore, since the electric power required for drying and baking is reduced by shortening the drying and baking time, the amount of CO ₂ emission can be reduced and the burden on the environment can be reduced. In addition, production efficiency can be increased by shortening the drying and baking time.

In the fuel cell in which the gas diffusion layer 14 is formed by applying the microporous layer forming paste composition of the present embodiment to the base material 16, even if the drying and firing time is short, the dispersant and the dispersion aid The polyethylene oxide as the agent disappears and does not remain in the microporous layer, and the water repellency, which is an important characteristic of the gas diffusion layer 14 that affects the power generation efficiency of the fuel cell, is maintained well for a long time. Thereby, the water generated by the battery reaction is smoothly discharged, the flooding phenomenon is also prevented, and the deterioration of the battery performance due to the deterioration of the characteristics such as gas diffusibility is suppressed.
Further, by containing a specific molecular weight and a specific addition amount of polyethylene oxide in the microporous layer-forming paste composition, the conductive material and the repellent properties can be contained in the microporous layer-forming paste composition even if the amount of the dispersant is reduced. Since the aqueous resin is homogeneously dispersed and stabilized and a paste composition for forming a microporous layer with good dispersion stability is obtained, there is no clogging or concentration change in pipes or pumps during coating, and the base It is also possible to suppress poor application to the material 16.
Furthermore, the occurrence of cracks in the surface layer 15 due to non-uniformity (bias due to aggregation) of the paste component, that is, the conductive material and the water-repellent resin, and cracks due to long-time heating can be prevented, and uniform gas in the microporous layer. Characteristics such as diffusivity can be obtained.
In addition, since the paste composition for forming a microporous layer contains polyethylene oxide having a specific molecular weight and a specific addition amount, the paste composition has good flow characteristics, so that it can be smoothly applied to the substrate 16. Uniform application is possible and gas diffusion can be made uniform.
Therefore, characteristics such as stable gas diffusibility are exhibited in the gas diffusion layer 14, and a stable output as a fuel cell can be obtained. Therefore, the production quality can be made uniform, and the polymer electrolyte fuel cell can be suitably used for a membrane electrode assembly capable of operating stably for a long period of time.

In the present embodiment, the flow characteristics of the microporous layer-forming paste composition are improved by adding a small amount of polyethylene oxide and not using polyethylene oxide, thereby improving the coating properties of the paste. Increases production efficiency.
In addition, about polyethylene oxide, the molecular weight is in the range of 250,000 to 2,200,000, and within the range of 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin. If it is an addition amount, it becomes possible to adjust the viscosity characteristic of the paste composition for microporous layer formation to the viscosity characteristic according to coating conditions by adjusting molecular weight and addition amount in those ranges.

  Next, each example will be described by specifically showing the blending content and blending amount of each component of the paste composition for forming a microporous layer according to the embodiment of the present invention.

[Example]
The paste composition for forming a microporous layer according to Example 1 includes 75.0 g of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd .: trade name “DENKA BLACK”) as a conductive material, and a PTFE emulsion as a water repellent resin. (Daikin Kogyo Co., Ltd .: POLYFLON PTFE D-210C [solid content (resin content) 61%]) 41.7 g (solid content 25.4 g, moisture content 16.3 g), Triton X-100 as a dispersant 2.4 g, 379.4 g of ion-exchanged water as a solvent, and polyethylene oxide having a molecular weight of about 1.1 million as a dispersion aid (manufactured by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) E-60” The polyethylene oxide has a molecular weight distribution. Therefore, the polyethylene oxide of Examples and Comparative Examples is included. Id molecular weight is described as “about” with the molecular weight being the average (arithmetic average) molecular weight of the maximum molecular weight and the minimum molecular weight in the molecular weight distribution.
In Example 1, such a blended material was mixed and dispersed and defoamed for 3 minutes using a planetary agitation and defoaming device (Kurashinbo Co., Ltd .: trade name “Mazerustar KK-1000W”) set at a revolution of 800 rpm and a rotation of 900 rpm. Thus, a microporous layer forming paste composition according to Example 1 was prepared.

  In Example 2, polyethylene oxide having a molecular weight of about 1.1 million (manufactured by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) E-60” was reduced to 1.0 g compared to Example 1. The microporous layer forming paste composition according to Example 2 was prepared under the same conditions as in Example 1 except that the amount of ion-exchanged water as a solvent was increased to 379.9 g.

  In Example 3, the amount of polyethylene oxide having a molecular weight of about 1.1 million (made by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) E-60” was increased from Example 1 to 2.0 g. A microporous layer forming paste composition according to Example 3 was prepared under the same conditions as in Example 1 except that the amount of ion-exchanged water as a solvent was reduced to 378.9 g.

  In Example 4, 1.5 g of polyethylene oxide having a molecular weight of about 270,000 (manufactured by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark); R-1000”) was added, and the molecular weight was higher than that of Example 1. A microporous layer-forming paste composition according to Example 4 was prepared under the same conditions as in Example 1 except that a small polyethylene oxide was used.

  In Example 5, 1.5 g of polyethylene oxide having a molecular weight of about 1.8 million (manufactured by Sumitomo Seika Co., Ltd .: trade name “PEO (registered trademark); PEO-8”) was added, and the molecular weight was higher than that of Example 1. A microporous layer-forming paste composition according to Example 5 was prepared under the same conditions as in Example 1 except that a large polyethylene oxide was used.

Then, the paste composition for microporous layer formation of the comparative example 1 thru | or the comparative example 6 produced for the comparison is demonstrated.
[Comparative example]
In Comparative Example 1, a microporous layer forming paste composition was prepared without using polyethylene oxide.
That is, in Comparative Example 1, 75.0 g of carbon particles acetylene black (trade name “DENKA BLACK” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material and PTFE emulsion (Daikin Industries, Ltd.) as a water-repellent resin. ): POLYFLON PTFE D-210C [solid content (resin content) 61%]) 41.7 g (solid content 25.4 g, moisture content 16.3 g), Triton X-1002.4 g as a dispersant, solvent And mixed with 30.9 minutes of planetary agitation and defoaming device (Kurashita Boshoku Co., Ltd .: trade name “Mazerustar KK-1000W”) set at 800 rpm for revolution and 900 rpm for rotation. A paste composition for forming a microporous layer according to Comparative Example 1 was prepared by foaming. That is, it produced on the conditions similar to Example 1 except not having used polyethylene oxide.

  In Comparative Example 2, the amount of Triton X-100 added as a dispersant was increased to 6 g, which is 2.5 times the amount of Comparative Example 1, and the amount of ion-exchanged water as a solvent was reduced to 377.3 g. A paste composition for forming a microporous layer according to Comparative Example 2 was prepared under the same conditions as in Comparative Example 1.

  In Comparative Example 3, 1.5 g of polyethylene oxide having a molecular weight of about 220,000 (manufactured by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) R-400”) was added, and the molecular weight was smaller than that of Example 4. A paste composition for forming a microporous layer according to Comparative Example 3 was prepared under the same conditions as in Example 1 except that polyethylene oxide was used.

  In Comparative Example 4, 1.5 g of polyethylene oxide having a molecular weight of about 2.3 million (manufactured by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) E-75”) was added, and the molecular weight was larger than that of Example 5. A paste composition for forming a microporous layer according to Comparative Example 4 was prepared under the same conditions as in Example 1 except that polyethylene oxide was used.

  In Comparative Example 5, polyethylene oxide having a molecular weight of about 1.1 million (manufactured by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) E-60” was reduced to 0.5 g from that in Example 2. Thus, a microporous layer forming paste composition according to Comparative Example 5 was prepared under the same conditions as in Example 1 except that the amount of ion-exchanged water as a solvent was increased to 380.4 g.

  In Comparative Example 6, the amount of polyethylene oxide having a molecular weight of about 1.1 million (made by Meisei Chemical Industry Co., Ltd .: trade name “Alcox (registered trademark) E-60” was increased from that of Example 3 to 2.5 g. The microporous layer forming paste composition according to Comparative Example 6 was prepared under the same conditions as in Example 1 except that the amount of ion-exchanged water as a solvent was reduced to 378.4 g.

  The composition of these examples is shown in the upper part of Table 1, and the composition of Comparative Example is shown in the upper part of Table 2.

  Here, the dispersibility of the paste component was observed and evaluated for the microporous layer forming paste compositions of each Example and each Comparative Example, and when the microporous layer forming paste composition was applied to the substrate 16 A water repellency evaluation test of the coated surface (surface layer 15 as a microporous layer) was performed. The evaluation results will be described with reference to the lower part of Table 1 and the lower part of Table 2.

  Regarding the dispersibility of the paste component in the paste composition for forming a microporous layer, the paste composition for forming a microporous layer prepared by mixing and dispersing with a mixer was used for a stainless steel plate with an applicator of 7.5 mm in length and 6 mm in width. The dispersion state of the carbon particles of acetylene black as a conductive material was visually confirmed after being applied to a thickness of 150 μm. The case where the aggregation of the carbon particles was not confirmed was evaluated as “good”, and the case where the aggregate of the carbon particles was observed was evaluated as “poor”.

In the water repellency evaluation test, first, the microporous layer forming paste composition was transferred onto carbon paper as the base material 16 with a thin film coating tool (die head) at a moving speed of 1.0 m / min and a basis weight of 5.0 mg / cm. ² applied. After coating, the gas diffusion layer 14 (cathode side diffusion layer 14A or anode side diffusion layer 14B) in which a microporous layer is formed on the surface layer 15 by drying and baking for 10 minutes, 30 minutes, and 60 minutes at 300 ° C. Produced. And in the produced gas diffusion layer 14, in order to confirm the water repellency of the surface layer 15 as a microporous layer, the produced gas diffusion layer 14 is set up vertically, and the surface of the gas diffusion layer 14 on the surface layer 15 side Then, 3 g of ion-exchanged water was sprayed in five times by spraying, and a test was conducted to determine whether the water droplets would fall. Water droplets that have fallen without remaining on the coated surface of the gas diffusion layer 14 (surface of the surface layer 15 as a microporous layer) are judged to have good water repellency. Those that remained attached to the surface of the coated surface were judged to be poor in water repellency and evaluated as x. In addition, evaluation is started from 10 minutes for drying and baking time. For those for which water repellency cannot be confirmed by drying and baking for 10 minutes, drying and baking are performed with a new test product with a drying and baking time of 30 minutes. Evaluation was conducted. For those for which water repellency could not be confirmed by drying and baking for 30 minutes, drying and baking were carried out with a new test product at a drying and baking time of 60 minutes, and water repellency was evaluated.

  Dispersibility in the paste composition for forming a microporous layer prepared by the composition of each example and each comparative example, and the paste composition for forming a microporous layer was applied to the substrate 16, dried and baked. The evaluation results of the water repellency of the surface layer 15 (microporous layer) in the gas diffusion layer 14 are as shown in the lower part of Tables 1 and 2.

As can be seen from the evaluation results, polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is 1 weight with respect to 100 parts by weight of the total solid content of acetylene black as a conductive material and PTFE emulsion as a water repellent resin. The paste compositions for forming the microporous layer of Examples 1 to 6 added within the range of 2 parts by weight to 2 parts by weight have flow characteristics having viscosity suitable for dispersion, and the amount of the dispersant added is 2.4 g. Even in a small amount, there was no aggregate of carbon particles of acetylene black and it was uniformly dispersed. Further, the surface layer 15 (microporous layer) of the gas diffusion layer 14 formed by applying the microporous layer forming paste composition of Examples 1 to 6 to the base material 16 and drying and baking the paste composition. Sufficient water repellency was expressed by drying and baking in a short time of 10 minutes.
That is, in Examples 1 to 6, polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is added to 100 parts by weight of the total solid content of acetylene black as a conductive material and PTFE emulsion as a water repellent resin. On the other hand, when it is added in the range of 1 to 2 parts by weight, the flow characteristics of the microporous layer forming paste composition are improved, and even if the amount of the dispersant added is small, carbon that is a paste component The particles were uniformly dispersed. And it was confirmed that sufficient water repellency was expressed even if drying and baking for a short time of 10 minutes by reducing the addition amount of a dispersing agent.

On the other hand, in Comparative Example 1, although the blending amounts of acetylene black as a conductive material, PTFE emulsion as a water repellent resin, and Triton X-100 as a dispersant are the same as those in Example 1, polyethylene oxide is added. The composition is not.
In Comparative Example 1, polyethylene oxide was not added, and the amount of dispersant added was as small as 2.4 g. Thus, in the prepared paste composition for forming a microporous layer, the dispersion characteristics were poor, and agglomeration of carbon particles was confirmed. It was found that it was not suitable for practical use. In addition, about the paste composition for microporous layer formation, since it was not suitable for practical use, the water-repellent evaluation test was not implemented.

In Comparative Example 2, polyethylene oxide was not added as in Comparative Example 1, but the amount of dispersant added was larger than that in Comparative Example 1, and corresponds to the conventional example.
In Comparative Example 2, although polyethylene oxide was not added, carbon particles were not agglomerated in the prepared microporous layer-forming paste composition by increasing the amount of dispersant added to 6.0 g. It was uniformly dispersed. However, the surface layer 15 (microporous layer) of the gas diffusion layer 14 formed by applying the paste composition for forming the microporous layer to the substrate 16 and drying and baking is dried for 30 minutes for 10 minutes. -The water repellency was insufficient in firing, and the desired water repellency was confirmed by drying and firing for a long time of 60 minutes. That is, high water repellency was not obtained by drying and baking for a short time. This is because the amount of the dispersant added is large, and the dispersant having a hydrophilic group does not completely disappear and remains in the microporous layer after drying and baking for a short time.

In Comparative Example 3, although the blending amounts of acetylene black as a conductive material, PTFE emulsion as a water repellent resin, Triton X-100 as a dispersant and polyethylene oxide are the same as those in Example 1, the molecular weight is about 220,000. This is a composition using polyethylene oxide.
In Comparative Example 3, since the added polyethylene oxide has a small molecular weight, the produced microporous layer-forming paste composition has little effect of improving the flow characteristics of the paste composition. The particles could not be uniformly dispersed, and aggregation of carbon particles was confirmed. In addition, about the paste composition for microporous layer formation, since it was not suitable for practical use, the water-repellent evaluation test was not implemented.

In Comparative Example 4, although the blending amounts of acetylene black as a conductive material, PTFE emulsion as a water repellent resin, Triton X-100 as a dispersant and polyethylene oxide are the same as those in Example 1, the molecular weight is about 2.3 million. This is a composition using polyethylene oxide.
In Comparative Example 4, the carbon particles were uniformly dispersed without agglomeration in the prepared microporous layer forming paste composition. However, the surface layer 15 (microporous layer) of the gas diffusion layer 14 formed by applying the paste composition for forming a microporous layer, drying and baking, has no water repellency when dried and fired for 10 minutes. It was sufficient, and sufficient water repellency was confirmed by performing drying and baking for 30 minutes. That is, high water repellency could not be obtained in the desired drying and baking for a short period of 10 minutes. This is because the polyethylene oxide has a large molecular weight, and after drying and baking for a short time, the polyethylene oxide remains without being completely thermally decomposed, and the water repellency is hindered by the presence of the polyethylene oxide. As a result, the drying and firing time associated with the thermal decomposition of polyethylene oxide becomes longer than the drying and firing time associated with the decomposition and volatilization of the dispersant, and the load in the drying and firing process is increased by the addition of polyethylene oxide. I understood that.

Comparative Example 5 is a polyethylene having a molecular weight of about 1.1 million, although the blending amounts of acetylene black as a conductive material, PTFE emulsion as a water repellent resin, and Triton X-100 as a dispersant are the same as those in Example 1. In this composition, the amount of oxide added is 0.5 parts by weight with respect to 100 parts by weight of the total solid content of acetylene black as the conductive material and PTFE emulsion as the water-repellent resin.
In Comparative Example 5, since the amount of polyethylene oxide added is small, the produced microporous layer-forming paste composition has little effect of improving the flow characteristics, and a small amount of dispersant can uniformly disperse the carbon particles. It was not possible to agglomerate carbon particles. In addition, about the paste composition for microporous layer formation, since it was not suitable for practical use, the water-repellent evaluation test was not implemented.

Comparative Example 6 is a polyethylene having a molecular weight of about 1.1 million, although the blending amounts of acetylene black as a conductive material, PTFE emulsion as a water repellent resin, and Triton X-100 as a dispersant are the same as those in Example 1. In this composition, the amount of oxide added is 2.5 parts by weight with respect to 100 parts by weight of the total solid content of acetylene black as a conductive material and PTFE emulsion as a water repellent resin.
In Comparative Example 6, carbon particles were uniformly dispersed without agglomeration in the prepared paste composition for forming a microporous layer. However, the surface layer 15 (microporous layer) of the gas diffusion layer 14 formed by applying the paste composition for forming a microporous layer, drying and baking, has no water repellency when dried and fired for 10 minutes. It was sufficient, and sufficient water repellency was confirmed by performing drying and baking for 30 minutes. That is, high water repellency could not be obtained in the desired drying and baking for a short period of 10 minutes. This is because the amount of polyethylene oxide added is large, and in a short period of drying and baking, polyethylene oxide remains without being completely thermally decomposed, and the water repellency is hindered by the remaining polyethylene oxide. As a result, the drying and firing time associated with the thermal decomposition of polyethylene oxide becomes longer than the drying and firing time associated with the decomposition and volatilization of the dispersant, and the load in the drying and firing process is increased by the addition of polyethylene oxide. I understood that.

  From the above evaluation results, in the microporous layer forming paste composition according to this example, polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is used as acetylene black as a conductive material and as a water repellent resin. The viscosity of the paste composition for forming a microporous layer is less than when no polyethylene oxide is added by being added within the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the PTFE emulsion. As can be seen from the comparison with Comparative Example 1, the flow characteristics suitable for dispersion were obtained, and the carbon particles of acetylene black as a paste component were uniformly dispersed even when the amount of the dispersant added was small. . In particular, as can be seen from the comparison with the comparative example 2 which is the conventional example, in this example, even if the additive amount of the dispersant is reduced by 60% compared to the conventional example, the carbon particles are uniformly dispersed. I was able to. And in Comparative Example 2 of the conventional example, 60 minutes of drying and baking time was required to develop sufficient water repellency, whereas in this example, drying and baking for an extremely short time of 10 minutes were required. Thus, it was revealed that sufficient water repellency was exhibited, and that the drying and firing time necessary for developing the water repellency by eliminating the polyethylene oxide of the dispersant and dispersion aid could be greatly shortened.

  In addition, from the evaluation results of this example and Comparative Examples 3 and 4, when the molecular weight of the polyethylene oxide to be added is less than 250,000, the addition amount does not increase the load of the drying / firing process. The effect of improving the flow characteristics of the paste composition cannot be obtained. On the other hand, when the molecular weight exceeds 2.2 million, polyethylene oxide can be thermally decomposed at a drying and baking temperature of 300 ° C. It has been clarified that the firing time becomes long and sufficient water repellency cannot be secured with a desired drying and firing time of 10 minutes.

  Furthermore, from the evaluation results of this example and Comparative Examples 5 and 6, the polyethylene oxide was used for 100 parts by weight of the total solid content of acetylene black as the conductive material and PTFE emulsion as the water repellent resin. When the addition amount is less than 1 part by weight, the addition amount is too small to obtain the effect of improving the flow characteristics due to polyethylene oxide. On the other hand, when the addition amount of polyethylene oxide exceeds 2 parts by weight, polyethylene oxide is added. Although it can be thermally decomposed at a drying and baking temperature of 300 ° C., the drying and baking time associated with the thermal decomposition of polyethylene oxide becomes longer, and it is clear that sufficient water repellency cannot be ensured with the desired short drying and baking time of 10 minutes. It became.

  Accordingly, the polyethylene oxide blended in the microporous layer forming paste composition has a molecular weight in the range of 250,000 to 2,200,000, and uses acetylene black as a conductive material and PTFE emulsion as a water repellent resin. By adding within a range of 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the total solid content, the flow characteristics of the microporous layer forming paste composition are reliably improved, and the amount of dispersant added is At least, the paste component is uniformly dispersed. Further, the addition of polyethylene oxide does not increase the load of the drying / firing process, and sufficient water repellency can be expressed by the desired short drying / firing of 10 minutes.

  Thus, in this example, the molecular weight added in the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of acetylene black as the conductive material and PTFE emulsion as the water repellent resin is 25 parts by weight. By including polyethylene oxide in the range of 10,000 to 2,200,000 as a dispersion aid, the viscosity of the paste composition for forming a microporous layer is adjusted to a viscosity suitable for dispersion, and as a result, the amount of dispersant added is small. However, the paste component is uniformly dispersed. And since there are few addition amounts of a dispersing agent and a dispersing aid, drying and baking time required in order to make a dispersing agent and a dispersing aid disappear and to express water repellency are shortened. And since the time required for drying / firing is shortened in this way, the electric power required for drying / firing is reduced, and the furnace length of the drying / firing furnace can be shortened. Cost reduction can be achieved.

  As described above, the microporous layer-forming paste composition according to the present example is a microporous layer-forming paste composition having a conductive material, a water-repellent resin, and a dispersant, and includes polyethylene oxide. Is a paste composition for forming a microporous layer in which is used as a dispersion aid. Here, the polyethylene oxide has a molecular weight in the range of 250,000 to 2,200,000, and is added in the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin. It is what is done.

  Then, the conductive material, the water repellent resin, the dispersant, polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 as a dispersion aid, and the total solid content of the conductive material and the water repellent resin are 100 weights. It can also be set as the manufacturing method of the paste composition for microporous layer formation added within the range of 1 weight part-2 weight part with respect to a part, and mixing and dispersing for predetermined time.

Thus, among polyethylene oxide, polyethylene oxide having a molecular weight in the range of 250,000 to 2,200,000 is 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin. By adding within this range, the viscosity of the paste composition for forming a microporous layer is increased, and the flow characteristics are improved up to a region where it is easy to disperse. This viscosity improving effect makes it possible to easily and uniformly disperse the conductive material and the water-repellent resin, and the amount of the dispersant added can be reduced to be more than the amount of polyethylene oxide added. As a result, the time required for drying and baking can be shortened, and sufficient water repellency can be exhibited even with a short drying and baking time.
The polyethylene oxide used is a water-soluble resin that is thermally decomposed at less than 300 ° C., has a molecular weight in the range of 250,000 to 2,200,000, and an addition amount of acetylene black as a conductive material and water repellent resin. Since it is in the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the PTFE emulsion, the load in the drying and baking process due to the addition of polyethylene oxide is not increased. And by shortening drying and baking time, the electric power concerning drying and baking can be reduced, and since the furnace length of a baking and drying furnace can be shortened, manufacturing cost can be reduced. As a result, the cost of the fuel cell can be reduced.

  Thus, the present invention provides a microporous layer-forming paste composition that can shorten the drying / firing time without increasing the load of the drying / firing process and can reduce the cost, and a method for producing the same.

Then, the gas diffusion layer 14 for the fuel cell is formed by applying this microporous layer forming paste composition to the base material 16 made of a conductive porous material such as carbon paper, followed by drying and baking.
According to the gas diffusion layer 14 for a fuel cell obtained by applying a paste composition for forming a microporous layer to a base material 16 made of a conductive porous material, followed by drying and firing, the dispersant can be used even in a short drying and firing time. In addition, the water repellency that affects the power generation efficiency of the fuel cell is sufficiently exhibited without the dispersion aid disappearing and remaining. Therefore, the water generated by the battery reaction is smoothly discharged and the flooding phenomenon is prevented. Accordingly, it is possible to suppress a decrease in characteristics such as gas diffusibility and to prevent a decrease in battery performance.
In addition, the addition of polyethylene oxide allows the conductive material and the water-repellent resin paste component to be uniformly dispersed with a small amount of dispersant, thereby reducing the time required for drying and baking performed after application to the substrate 16. In the microporous layer of the gas diffusion layer 14, the occurrence of cracks due to non-uniform paste components and long-time heating is prevented, and stable and uniform characteristics such as gas diffusivity can be exhibited. Therefore, a stable output can be obtained, and the polymer electrolyte fuel cell can be suitably used for a membrane electrode assembly that can operate stably for a long period of time.

The gas diffusion layer for a fuel cell according to the above example is formed by applying a paste composition for forming a microporous layer to a base material made of a conductive porous material, and drying and firing.
As described above, according to the paste composition for forming a microporous layer, the molecular weight is 250,000 within a range of 1 part by weight to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin. By adding polyethylene oxide in the range of ˜2.2 million as a dispersion aid, the flow characteristics of the paste composition are improved, and the paste components are uniformly dispersed with a small amount of dispersant.
Therefore, according to the gas diffusion layer formed by applying the paste composition for forming a microporous layer to a base material made of a conductive porous material, and drying and firing, a short drying time due to a small amount of dispersant and dispersion aid. -Since the dispersant and the dispersion aid do not disappear and remain in the coating film (microporous layer) even during the firing time, the water repellency that affects the power generation efficiency of the fuel cell is sufficiently expressed. Therefore, the water generated by the battery reaction is discharged smoothly and the flooding phenomenon is prevented. As a result, deterioration in characteristics such as gas diffusivity is suppressed, and deterioration in battery performance can be prevented. In addition, since the paste component is uniformly dispersed with a small amount of dispersant and dispersion aid, the time taken for drying and baking to eliminate the dispersant and dispersion aid performed after coating on the substrate is shortened. In the formed microporous layer of the gas diffusion layer, the occurrence of cracks due to non-uniform paste components and long-time heating is prevented, and stable and uniform characteristics such as gas diffusivity can be exhibited. Therefore, a stable output can be obtained, and the polymer electrolyte fuel cell can be suitably used for a membrane electrode assembly that can operate stably for a long period of time.

In carrying out the present invention, the microporous layer forming paste composition, the composition of other portions of the diffusion layer for fuel cells, the components, the blending amount, the material, and other manufacturing processes are described in the present embodiment. It is not limited.
In addition, the numerical values listed in the embodiment of the present invention do not indicate critical values but indicate appropriate values suitable for implementation, and therefore, even if the numerical values are slightly changed, the implementation is denied. is not.

DESCRIPTION OF SYMBOLS 1 Fuel cell 11 Electrolyte membrane 10 Membrane-electrode assembly 12 Electrode (cathode electrode 12A, anode electrode 12B)
13 catalyst layer (cathode side catalyst layer 13A, anode side catalyst layer 13B)
14 diffusion layer (cathode side diffusion layer 14A, anode side diffusion layer 14B)
15 surface layers (cathode side surface layer 15A, anode side surface layer 15B)
16 base materials (cathode side base material 16A, anode side base material 16B)

Claims (3)

A paste composition containing a conductive material, a water repellent resin, a dispersant, and polyethylene oxide as a dispersion aid,
The polyethylene oxide has a molecular weight in the range of 250,000 to 2,200,000, and is added in the range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water-repellent resin. And
A paste composition for forming a microporous layer, wherein the blending amount of the polyethylene oxide is in the range of 42 to 83 parts by weight with respect to 100 parts by weight of the dispersing agent.   Conductive material, water repellent resin, dispersant, molecular weight of 250,000 to within a range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin Polyethylene oxide is added as a dispersion aid within the range of 2.2 million, and the blending amount of the polyethylene oxide is within the range of 42 to 83 parts by weight with respect to 100 parts by weight of the dispersing agent. A method for producing a paste composition for forming a microporous layer, comprising mixing and dispersing for a predetermined time.   Conductive material, water repellent resin, dispersant, molecular weight of 250,000 to within a range of 1 to 2 parts by weight with respect to 100 parts by weight of the total solid content of the conductive material and the water repellent resin Polyethylene oxide is added as a dispersion aid within the range of 2.2 million, and the blending amount of the polyethylene oxide is within the range of 42 to 83 parts by weight with respect to 100 parts by weight of the dispersing agent. A gas diffusion layer for a fuel cell, characterized in that a microporous layer-forming paste composition produced by mixing and dispersing for a predetermined time is applied to a substrate made of a conductive porous material, and then dried and fired. Manufacturing method.

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