JP2017022046A - Paste for microporous layer formation and gas diffusion layer for fuel battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem that it is difficult to peel a microporous layer from a conductive porous base material.SOLUTION: A gas diffusion layer 14 for a fuel battery has a microporous layer 15 in which resol type water-dispersible phenol resin as aqueous phenol resin is carbonized by applying microporous layer formation paste to a conductive porous base material 16 of water-repellent carbon paper, and drying and baking this porous base material at predetermined drying and baking temperatures, the paste being obtained by mixing and dispersing: acetylene black as conductive power; PTFE emulsion as water-repellent resin; Triton X-100 as a dispersing agent; resol-type water-dispersant phenol resin as aqueous phenol resin; and ion exchange water as solvent.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas diffusion layer (GDL) used mainly for an electrode of a polymer electrolyte fuel cell (PEFC), and in particular, on the surface of a conductive porous substrate such as carbon paper. The present invention relates to a microporous layer forming paste that is applied to form a microporous layer (MPL) and a gas diffusion layer for a fuel cell that employs the microporous layer forming paste.

In polymer electrolyte fuel cells, which are increasingly used as power sources for automobiles, etc., in general, conductive materials such as carbon carrying a catalyst such as platinum on both sides of a polymer electrolyte membrane that selectively permeates specific ions. A cathode (+) side electrode and an anode (−) side electrode constituted by an electrode catalyst layer made of a material and an ion exchange resin and a porous gas diffusion layer (GDL) arranged outside the electrode catalyst layer are arranged. Thus, a membrane / electrode assembly (MEGA) is formed. In addition, a gas flow path for supplying fuel gas (anode gas) or oxidizing gas (cathode gas) and discharging generated gas and excess gas is formed outside the gas diffusion layer constituting the membrane / electrode assembly. A single cell is formed in which the membrane / electrode assembly is sandwiched between the separators.

In the gas diffusion layer in the polymer electrolyte fuel cell having such a configuration, the function of diffusing the fuel gas or the oxidizing gas supplied from the gas flow path formed in the separator to the catalyst layer adjacent to the gas diffusion layer (gas diffusion) Gas diffusivity is required, and the role of transmitting electrons necessary for the reaction in the catalyst layer and the role of efficiently collecting the generated electricity (charge) in the separator, Conductivity to move electrons is also required. Furthermore, since the gas diffusion layer also serves as a water path, the polymer electrolyte membrane and the catalyst layer are always kept in an optimal wet state, and the flooding phenomenon (a phenomenon in which the pores of the gas diffusion layer are blocked by water) is suppressed. In order to maintain stable power generation performance, water repellency (moisture permeability) is also required to discharge excess reaction product water and condensed water generated by the electrochemical reaction of hydrogen and oxygen during power generation. .

For this reason, in the conventional gas diffusion layer, in order to ensure predetermined gas diffusibility, conductivity (current collection), water repellency, carbon paper made of carbon fiber having gas diffusibility and conductivity, carbon cloth, A conductive porous substrate such as carbon felt is generally used. Further, a water repellent resin such as polytetrafluoroethylene (hereinafter also abbreviated as “PTFE”) for imparting water repellency to the conductive porous substrate, and conductivity (current collecting). Impregnation, application, and the like of a conductive material such as carbon for improvement are performed.

In particular, in recent years, a gas diffusion layer having a multilayer structure in which a coating thin film called a microporous layer (MPL) is formed on a conductive porous substrate has been developed. In addition to bringing the conductive porous substrate side into contact with the separator and bringing the microporous layer side into contact with the catalyst layer and incorporating it into the polymer electrolyte fuel cell, the gas diffusibility and water management are improved. It is known that power generation performance is stabilized. In addition, it is useful in that the controllability of the performance according to the use environment and operating conditions of the battery, which is difficult with a conductive porous substrate, can be obtained by adjusting the components of the microporous layer. In addition, in this gas diffusion layer having a multilayer structure, it is desirable to provide water repellency in order to improve the drainage of water generated during power generation in any layer, and usually both are appropriately subjected to water repellency treatment. The

Such a gas diffusion layer comprising a conductive porous substrate and a microporous layer is, for example, a microporous layer containing a conductive material such as carbon particles, a fluorine-based water repellent resin such as PTFE emulsion, and a dispersant. The forming paste-form mixture is applied to the surface of a conductive porous substrate that has been subjected to a water repellent treatment, and further formed by performing a drying and baking treatment for volatilizing the dispersant and moisture. it can.
In particular, when the microporous layer is formed by using a powdery material such as carbon particles as the conductive material, the surface of the microporous layer is likely to be uniform, the contact resistance with the catalyst layer is reduced, and Since the gas diffusion becomes uniform, the output of the battery can be increased.

However, when using a powdery material such as carbon particles as the conductive material, a mixture of the conductive powder, a fluorine-based water repellent resin, and a dispersant is applied to the conductive porous substrate. However, only by drying and firing, there has been a problem that the coating film that becomes the microporous layer is peeled off from the conductive porous substrate depending on the handling during the operation of bonding to the catalyst layer and assembling to the battery.

Here, Patent Document 1 includes carbon fiber, binder resin, conductive fine particles, and a heat-fusible organic fiber having a specific film thickness and fiber length. There is disclosed a gas diffusion layer in which carbon fibers are bound together by a binder resin together with conductive fine particles in a porous aggregate structure that is formed. In Patent Document 1, the heat-fusible organic fiber has a sheath side resin having a relatively low melting point and a low softening point of 60 to 180 ° C, and a core having a relatively high melting point and a high softening point of 200 to 350 ° C. The heat-fusible organic fibers are mutually heat-melted by applying a temperature higher than the melting point / softening point of the sheath-side resin (described as about 150 ° C. in the embodiment). It is supposed to be worn. In addition, the binder resin adheres to the heat-fusible organic fiber, and the carbon fiber and the conductive fine particles are entangled with each other. It is described that it is fixed by being cured, whereby carbon fibers are entangled with each other and bonded with a binder resin via conductive fine particles. Examples of the binder resin at this time include thermosetting resins such as phenol resins and heat-fusible resins.

Conventionally, a conductive porous substrate of a gas diffusion layer in which carbon fibers are bound with carbon in order to ensure high conductivity has been developed. For example, in Patent Document 2, carbon fibers and carbon powders are developed. As the carbon to be bound, a resin carbide obtained by heating and carbonizing an aqueous phenol resin at a high temperature of 1000 ° C. or higher in an inert atmosphere is disclosed. By binding carbon fiber and carbon powder with this resin carbide, it is said that a strong conductive path can be formed and a good porous electrode substrate can be provided.

JP 2012-190619 A JP 2014-207240 A

Here, in Patent Document 1, heat is obtained by melting and softening a sheath side resin having a melting point and softening point of 60 to 180 ° C. without melting and softening a core resin having a melting point and softening point of 200 to 350 ° C. When a thermosetting resin such as a phenolic resin is used as a binder resin because the welding temperature is applied, the thermosetting resin is dry-cured at that temperature, and the cured thermosetting resin is used for carbon fiber. Is fixed to the heat-fusible organic fiber together with the conductive fine particles. That is, in Patent Document 1, a thermosetting resin such as a phenol-based resin is used for fixing carbon fibers and conductive fine particles to a heat-fusible organic fiber.

Moreover, in patent document 2, although the carbon fiber and carbon powder are bound using the resin carbide which carbonized by heating at a high temperature of 1000 degreeC or more, this is for improving electroconductivity. It is.

Therefore, the present invention provides a microporous layer forming paste in which the microporous layer is difficult to peel from the conductive porous substrate, and a gas diffusion layer for a fuel cell in which the microporous layer is difficult to peel from the conductive porous substrate. Providing is an issue.

The paste for forming a microporous layer according to claim 1 comprises a conductive powder, a water-repellent resin, a dispersant, and a solid content of 0.35 to 1.3 parts by weight with respect to 100 parts by weight of the conductive powder. A microporous layer of a gas diffusion layer for a fuel cell is formed by mixing a water-based phenolic resin blended within the range and a solvent, and applying to a conductive porous substrate, followed by drying and firing. At this time, the aqueous phenol resin is carbonized at the drying / firing temperature when it is applied to the conductive porous substrate and dried / fired.
Here, as the aqueous phenol resin, a water-soluble phenol resin or a phenol resin in which the phenol resin is dissolved in water is dispersed without using a solvent (organic solvent) (without diluting with a solvent). Water dispersible phenolic resin products are used.

A fuel cell diffusion layer according to a second aspect is obtained by applying the microporous layer forming paste according to the first aspect to a conductive porous base material, followed by drying and firing.

  According to the paste for forming a microporous layer of the first aspect of the invention, the conductive powder, the water repellent resin, the dispersant, and 0.35 parts by weight to 1 .. The aqueous phenolic resin blended within the range of 3 parts by weight and a solvent are mixed. The aqueous phenol resin is in a carbonized state at the drying / firing temperature when the microporous layer forming paste is applied to the conductive porous substrate and dried / fired.

The present inventors formed a microporous layer forming paste containing a conductive powder, a water repellent resin, a dispersant, and a solvent on a conductive porous substrate, followed by drying and baking. In order to prevent the microporous layer formed on the conductive porous substrate from peeling off from the conductive porous substrate when it is assembled to the fuel cell, we have conducted extensive experimental research. As a result, an aqueous phenol resin was blended in a solid content of 0.35 to 1.3 parts by weight with respect to 100 parts by weight of the conductive powder in the microporous layer forming paste, and the aqueous phenol resin was dried. -Peel strength at which the microporous layer coating film formed on the conductive porous substrate peels off from the conductive porous substrate by becoming a carbonized state after firing (the microporous layer coating film becomes conductive porous It found that the force-load required to peel from the substrate) is significantly improved, in which to complete the present invention based on this finding.

Here, when the amount of the aqueous phenol resin is less than 0.35 parts by weight, the effect of increasing the peel strength of the coating film to be a microporous layer is small and not suitable for practical use. On the other hand, when the amount of the aqueous phenol resin is more than 1.3 parts by weight, the peel strength is lowered.
By making the blending amount of the aqueous phenol resin within the range of 0.35 to 1.3 parts by weight (solid content) with respect to 100 parts by weight of the conductive powder, the microporous layer is surely formed. It becomes difficult to peel from the conductive porous substrate.

According to the gas diffusion layer for a fuel cell of the invention of claim 2, the conductive powder, the water repellent resin, the dispersant, and the solid content is 0.35 to 1.3 weight with respect to 100 parts by weight of the conductive powder. A paste for forming a microporous layer is formed by mixing a water-based phenolic resin blended within the range of a part and a solvent, and applying a microporous layer by applying to a conductive porous substrate and drying and firing. It is applied to a conductive porous substrate, dried and fired. And the said aqueous phenol resin will be in a carbonized state at the drying and baking temperature when apply | coating the said paste for microporous layer formation to the said conductive porous base material, and drying and baking.
The present inventors formed a microporous layer forming paste containing a conductive powder, a water repellent resin, a dispersant, and a solvent on a conductive porous substrate, followed by drying and baking. In order to prevent the microporous layer formed on the conductive porous substrate from peeling off from the conductive porous substrate when it is assembled to the fuel cell, we have conducted extensive experimental research. As a result, an aqueous phenol resin was blended in a solid content of 0.35 to 1.3 parts by weight with respect to 100 parts by weight of the conductive powder in the microporous layer forming paste, and the aqueous phenol resin was dried. -Peel strength at which the microporous layer coating film formed on the conductive porous substrate peels off from the conductive porous substrate by becoming a carbonized state after firing (the microporous layer coating film becomes conductive porous It found that the force-load required to peel from the substrate) is significantly improved, in which to complete the present invention based on this finding.

Here, when the amount of the aqueous phenol resin is less than 0.35 parts by weight, the effect of increasing the peel strength of the coating film to be a microporous layer is small and not suitable for practical use. On the other hand, when the amount of the aqueous phenol resin is more than 1.3 parts by weight, the peel strength is lowered.
By making the blending amount of the aqueous phenol resin within the range of 0.35 to 1.3 parts by weight (solid content) with respect to 100 parts by weight of the conductive powder, the microporous layer is surely formed. It becomes difficult to peel from the conductive porous substrate.
Therefore, the fuel cell diffusion layer using the microporous layer forming paste of the present invention increases the reliability of the fuel cell because the microporous layer does not peel from the conductive porous substrate when assembled to the fuel cell.
In addition, said numerical value is not a strict thing but is approximate, and naturally, it is an approximate value including an error due to measurement or the like, and does not deny an error of several percent.

FIG. 1 is a flowchart showing a manufacturing process of a gas diffusion layer obtained by applying a microporous layer forming paste according to an embodiment of the present invention to a conductive porous substrate, and drying and firing. FIG. 2 is a schematic diagram showing a schematic configuration of a polymer electrolyte fuel cell using a fuel cell gas diffusion layer formed by applying a microporous layer forming paste according to an embodiment of the present invention to a conductive porous substrate. FIG. FIG. 3 is an explanatory diagram for explaining a peeling (tensile) test performed on a gas diffusion layer for a fuel cell formed by applying a microporous layer forming paste according to an embodiment of the present invention to a conductive porous substrate. Yes, (a) is a cross-sectional view showing a state in which an adhesive tape is attached to the surface of a microporous layer of a gas diffusion layer for a fuel cell, and (b) is a cross section showing a state in which the adhesive tape is partially peeled and pulled up and down. FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, the microporous layer forming paste according to the present embodiment will be described.
The microporous layer forming paste of the present embodiment is obtained by mixing a conductive powder, a water repellent resin, a dispersant, a predetermined amount of an aqueous phenol resin, and a solvent.

Examples of the conductive powder include carbon powders such as carbon black powder, graphite powder, and vapor growth carbon powder. One of these can be used alone, or two or more can be used in combination. is there.

In addition, the conductive porous substrate as the application target of the microporous layer forming paste of the present embodiment is a carbon substrate such as carbon paper, carbon cloth, carbon felt, and the like and compatible with these carbon substrates. In view of conductivity, specific surface area, corrosion resistance, electrical resistance, and cost, carbon black is preferable as the conductive powder. Examples of carbon black include acetylene black, ketjen black, furnace black, channel black, thermal black, lamp black and the like. These can be used alone or in combination of two or more. is there.
Among them, acetylene black has high purity and is easy to use, has a large specific surface area, excellent dispersibility, good electronic conductivity and water repellency, high chemical stability, and good thixotropy. Since it is easy to form a film by application, it is suitable for forming a coating film of a microporous layer used for an electrode of a fuel cell.

In addition, it is preferable that the median diameter (primary particle diameter) of electroconductive powder exists in the range of 20 nm-150 nm from a uniform dispersible viewpoint.
Incidentally, according to the definition of terms in the text and explanation of JIS Z 8901 “Test Powder and Test Particles”, the median diameter is the number (or mass) larger than a certain particle diameter in the particle size distribution of the powder. ) is the particle diameter when occupying 50% of its Zenkonatai (diameter), i.e., a particle size of oversized 50%, usually expressed as the median diameter or 50% particle size and good D _50. By definition, the size of the particle group is expressed by the average particle diameter and the median diameter, but here, it is a value measured by the display of the product description and the laser diffraction / scattering method.
The “median diameter measured by the laser diffraction / scattering method” is a particle whose cumulative weight part is 50% in the particle size distribution obtained by the laser diffraction / scattering method using a laser diffraction particle size distribution measuring apparatus. This refers to the diameter (D ₅₀ ).
The above numerical values are not strict, but are approximate, and are naturally approximate values including errors due to measurement and the like, and do not deny errors of several percent. From the point of view of this error, the difference from the average particle size is closer as the distribution is closer to the normal distribution. The average particle size is about the median diameter, and the average particle size can be regarded as the median size.

In addition, when the content of the conductive powder is too small, the conductivity is insufficient. On the other hand, when the content is too large, the pores of the microporous layer are reduced and the gas permeability is decreased. The total solid content in the porous layer-forming paste is preferably 50 to 95% by weight.

As the water-repellent resin, a water-repellent resin can exhibit water repellency in the coating film of the microporous layer to be formed, and at least a part thereof is softened and melted by baking to form a conductive material (conductive powder of the microporous layer or conductive porous material). Any material can be used as long as it functions as a resin binder that binds a conductive material such as carbon fiber of the base material. For example, polytetrafluoroethylene (PTFE), tetrafluoroethylene / hexafluoropropylene copolymer (FEP) ), Perfluoroalkoxy fluororesin (PFA), polychlorotrifluoroethylene (PCTFE), ethylene / tetrafluoroethylene copolymer (ETFE), ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinylidene fluoride (PVdF) ) And the like, and silicone resins can be used. These can be used singly or in appropriate combination of two or more. Since water repellents such as fluororesins do not disperse in water as they are, those dispersed in water with an appropriate dispersant (surfactant), for example, water repellents such as fluororesins are emulsified. An emulsion or a dispersion in which a water repellent such as a fluorine-based resin is dispersed 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.

The average molecular weight of the water repellent resin is preferably in the range of 50,000 to 1,000,000. Those having an average molecular weight that is too low have a low binding property as a binder for binding a conductive material (conductive powder such as a conductive powder of a microporous layer or carbon fiber of a conductive porous substrate), while the average If the molecular weight is too large, the fiber tends to become dispersible due to mixing and the stability of the paste is lowered, or the fiber is solidified by shearing force in the manufacturing process such as coating, and clogging occurs in pipes and pumps. It causes density change and causes poor coating. Incidentally, when the water-repellent resin is a fluoropolymer, the fluoropolymer is difficult to dissolve in a solvent, and therefore it is difficult to measure the average molecular weight with melt viscosity. For this reason, the specific gravity method which calculates | requires an average molecular weight from the relationship between specific gravity and a number average molecular weight is applied.
On the other hand, when the content of the water repellent resin is too small, the water repellency is insufficient, or the binder effect is small and high film strength and bonding strength cannot be obtained. On the other hand, when there is too much content, the void | hole of a microporous layer will decrease and gas permeability will fall. Therefore, it is desirable that the water repellent resin has a content in the range of 5 to 50% by weight with respect to the total solid content in the microporous layer forming paste.

Incidentally, an emulsion (also referred to as an “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 in the liquid (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), it is generally used in a broader sense in this specification. The term “emulsion” is used herein as “a solid or liquid particle dispersed in a liquid”.

Dispersing agents include polyoxyethylene alkylphenyl ether (Triton X-100, etc.), nonionic surfactants such as polyoxyethylene lauryl ether, polyoxyethylene distyrenated phenyl ether, polyoxyethylene alkylene alkyl ether, polyethylene Nonionic dispersants such as glycol alkyl ethers, cationic dispersants such as alkyltrimethylammonium salts, dialkyldimethylammonium chlorides, and alkylpyridium chlorides, anionic dispersants such as polyoxyethylene fatty acid esters and acid group-containing structure-modified polyacrylates These can be used alone or in combination of two or more. For example, when carbon black is used as the conductive powder and PTFE emulsion is used as the water repellent resin, in order to improve the wettability and improve the dispersibility of these conductive powder and water repellent resin fine particles, a nonionic interface is used. An activator dispersant is preferred. In some cases, the water repellent resin is mixed in a state containing a dispersant.

By blending the dispersant, the conductive powder and the water-repellent resin can be prevented from agglomerating and uniformly dispersed in the solvent. As a result, the stability of the paste is increased, and clogging and concentration change are prevented from occurring in the piping, pump, etc. during application, and good film forming properties can be obtained. Furthermore, it is possible to obtain characteristics such as good gas diffusibility as a microporous layer that is homogeneous and has less surface undulations. In addition, the contact resistance with the catalyst layer is reduced, and a stable output can be obtained in the fuel cell.
The dispersant is contained in the microporous layer forming paste in an amount of 0.1% by weight or more in order to ensure dispersibility. However, if the content is too large, the paste is liable to foam and is dried and fired. Since the time is increased and a burden is imposed, the content is preferably 5% by weight or less.

Here, as a result of accumulating extensive experimental research, the present inventors formulated a predetermined amount of aqueous phenolic resin in a microporous layer forming paste containing these conductive powder, water repellent resin, and dispersant. Then, the peel strength from the conductive porous substrate of the microporous layer obtained by applying the microporous layer forming paste to the conductive porous substrate of the carbon substrate, drying and firing, that is, the conductive porous substrate It has been found that the bonding strength (adhesion) to the material is remarkably improved.
This is because a microporous layer-forming paste containing a predetermined amount of aqueous phenolic resin is applied to a conductive porous substrate, and then dried and fired to form a microporous layer. The aqueous phenolic resin is carbonized at a drying / firing temperature lower than the decomposition temperature of the resin, and the carbonized component is bound in the microporous layer and the interface between the microporous layer and the conductive porous substrate. It is presumed to work as a binding component that promotes

It is further inferred that water-based phenolic resins tend to bind carbon when carbonized compared to other water-based resins, so that carbon components such as carbon black as a conductive powder and conductive porous substrates can be used. The bond strength with the contained carbon component is increased. This effectively binds the conductive powder and conductive porous substrate of the microporous layer, effectively strengthens the microporous layer, and increases the peel strength between the conductive porous substrate and the microporous layer. Can do. Moreover, it is possible to prevent the conductive powder from dropping from the microporous layer. Here, when the decomposition temperature of the aqueous phenol resin is 400 ° C. to 500 ° C., there are many components remaining in a carbonized state (high carbonization rate) at a drying / calcination temperature 250 ° C. to 350 ° C. described later, and the efficiency is high. A material having such a decomposition temperature is suitable having a low weight average molecular weight (Mw), but a material having a very low molecular weight is not suitable for the film strength of the microporous layer or the peel strength between the conductive porous substrate and the microporous layer. Not suitable for improvement. Therefore, an aqueous phenol resin having a residual carbon ratio of 40% or more is suitable. In addition, the ratio of the carbonization state (residual carbon ratio) to the content of the aqueous phenol resin is determined by the type of the aqueous phenol resin used, the content and the drying / calcination temperature, and when all of the contained aqueous phenol resin is carbonized. The carbonization rate is 100%.

Here, there are two types of phenolic resins, water-based ones and water-insoluble solvent-based ones (solvent dilution type). In the present invention, aqueous phenolic resins are used, and solvents (organic solvents) are used. Phenol resin products (including emulsions (emulsions) and dispersions) that are dissolved and dispersed in water without being diluted (without being diluted with a solvent) are used. When an organic solvent is used, when mixed with the microporous layer forming paste, the dispersion state of the water repellent resin such as PTFE emulsion becomes difficult to be stabilized by the organic solvent, and the water repellent resin such as PTFE emulsion is separated. This is because the film formability is deteriorated and the characteristics such as water repellency are deteriorated, so that high battery performance cannot be obtained.

As such an aqueous phenol resin, for example, commercially available products such as Sumitrite Resin manufactured by Sumitomo Bakelite Co., Ltd., Phenolite manufactured by DIC Co., Ltd., Shounol manufactured by Showa Denko Co., Ltd., etc. should be used. Can do.
In addition, it is preferable to use what does not use a metal catalyst or an alkali catalyst for this aqueous phenol resin in the case of a synthesis | combination. If ions such as sodium and calcium are present in the aqueous phenolic resin, these metal ions may cause a decrease in proton conductivity of the solid polymer electrolyte membrane constituting the fuel cell, thereby reducing the battery performance. is there.

Moreover, it is preferable to mix | blend aqueous phenolic resin in the range of 0.35 weight part-1.3 weight part by solid content (resin content) with respect to 100 weight part of electroconductive powder.
It is because the effect which raises the peeling strength of a microporous layer and an electroconductive porous base material is small from the test result mentioned later when the mixing | blending of aqueous phenol resin is outside this range.

In the present embodiment, in addition to the conductive powder such as carbon black described above, the water repellent resin such as PTFE emulsion, the dispersant, and the aqueous phenol resin within the specified amount range, ion-exchanged water or the like as a solvent. The blended materials are mixed and dispersed to obtain a microporous layer forming paste (step S1 in FIG. 1).

The solvent is a solvent for mixing and dispersing each component of conductive powder, water repellent resin, dispersant, and aqueous phenol resin to form a paste, and disappears after drying and baking. When an aqueous solvent such as ion-exchanged water is used as the solvent, the water-repellent resin such as PTFE emulsion is more dispersible and the water-repellent resin such as PTFE emulsion is separated than when an organic solvent is used. Therefore, good film formability can be obtained. In addition, workability during coating and firing is good, and there is no risk of ignition. Furthermore, it can be manufactured at low cost without causing environmental load.

Here, the mixing / dispersing treatment of the blended material can be performed by using a mixer such as a general disper or planetary, or a bead mill, but without using a shearing force by a stirring blade or the like. It is desirable to disperse using collision energy generated by contact (collision) or contact of the material with the inner wall of the stirring vessel (collision). For example, planetary agitation / removal can be set to a specific value for revolution and rotation. It is preferable to mix and disperse using a foaming device or the like. As a result, the conductive powder can be dispersed while maintaining the three-dimensional structure of the conductive particles without destroying the three-dimensional structure of the conductive particles such as carbon. 3D bonds can be formed and the film strength can be improved. In addition, if high shear stress is applied during dispersion, the resin content in the conductive powder and the water-repellent resin emulsion aggregates to form aggregates, resulting in clogging of the filter during coating and loss of the coating film. By using an agitation / defoaming device, the resin content in the conductive powder and water-repellent resin emulsion is prevented from agglomerating to prevent agglomeration, preventing clogging of the filter during coating and loss of the coating film. Is done. Furthermore, 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, when implementing this invention, it is also possible to mix | blend other additives as needed. For example, a fibrous conductive material such as carbon fiber (carbon nanotube) can be used to increase conductivity and strength. However, if the fibrous conductive material is large, the microporous layer of the conductive porous substrate and the microporous layer constituting the gas diffusion layer comes into contact with the catalyst layer, so that the fiber pierces the polymer film. There is a risk that the polymer film is deteriorated and the power generation performance is lowered. Further, since unevenness is likely to be generated on the surface by the fiber, the contact area with the catalyst layer is reduced, and the contact resistance is increased, so that there is a possibility that sufficient conductivity and drainage cannot be obtained. For this reason, addition in the range which does not produce such a malfunction is preferable.

Next, a gas diffusion layer for a fuel cell formed by using the microporous layer forming paste of this embodiment will be described.
In the production of the gas diffusion layer for a fuel cell referred to as the present embodiment, the paste for forming the microporous layer obtained through the mixing and dispersing step in step S1 in FIG. 1 is applied to the coating step in step S2 in FIG. And apply to the conductive porous substrate.

As the conductive porous substrate, a porous material having gas permeability and conductivity generally used in gas diffusion layers of conventional fuel cells (particularly, polymer electrolyte fuel cells) is used. It contains a carbon component having good binding properties with the carbonized component contained in the microporous layer formed by the microporous layer forming paste of the present invention. For example, conductive materials of carbon materials (including nanocarbon materials) such as graphite and expanded graphite are porous such as fibers, particles, woven fabrics, nonwoven fabrics, meshes, lattices, punched bodies, foams, etc. What was comprised by the form of the body can be used. In particular, from the viewpoint of gas permeability, carbon fibers are preferable, and more specifically, carbon paper, carbon cloth, carbon felt (carbon nonwoven fabric), and the like are preferably used. These are selected in consideration of the use state of the fuel cell, operating conditions, and the like.

Incidentally, carbon cloth and carbon felt (carbon non-woven fabric) are structurally highly gas permeable and suitable for use in high humidity conditions. Carbon paper is obtained by binding carbon fibers with a binder, and its pore size distribution is smaller than that of carbon cloth or carbon felt (carbon non-woven fabric), so it has low gas permeability and is suitable for use in low humidity conditions. Compared to carbon cloth and carbon felt (carbon non-woven fabric), carbon paper has high dimensional stability in the surface direction and thickness direction, excellent molding processability, and high bending rigidity. / Excellent handling when stacking electrode assemblies. Furthermore, since carbon paper can be made thinner and easier to mold than carbon cloth or carbon felt (carbon nonwoven fabric), it is easy to reduce the stack size. In addition, the dimensional stability after cutting during the process of cutting the gas diffusion layer to a predetermined dimension is also good, and it is advantageous for mass production of fuel cells because it is excellent in easy chucking and easy mobility in the transfer process by the robot. is there.

In addition, conductive porous substrates such as carbon paper and carbon cloth are subjected to water repellent treatment in order to improve the water repellency of the gas diffusion layer and improve the power generation performance and durability of the fuel cell. The In addition, if the conductive porous substrate is subjected to water repellent treatment (step S11 in FIG. 1), when the microporous layer forming paste is applied to the conductive porous substrate, a part of the conductive porous substrate is electrically conductive. It is prevented that the porous porous substrate soaks (permeates) and clogs the space. That is, the microporous layer forming paste can be formed without soaking into the conductive porous substrate, and gas diffusivity is not hindered. As a result, the porosity of the conductive porous substrate is kept large, the pressure loss is reduced, the uniform gas supply and the good discharge of the reaction product water can be performed, and the output of the solid polymer fuel cell is increased. Can be achieved.

The water-repellent treatment (step S11 in FIG. 1) applied to the conductive porous substrate is, for example, a fluorine-based material such as PTFE (polytetrafluoroethylene) or tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA). It can be carried out by immersing the conductive porous substrate in a dispersion liquid (PTFE dispersion or the like) in which a water-repellent resin such as a resin is dispersed, and then impregnating it by drying. Immersion and drying may be repeated until a desired amount of fluororesin is impregnated. According to this method, the uniformity of the amount of impregnation in the in-plane direction and the thickness direction is high. In addition, an impregnation treatment by a spray method or the like that sprays a dispersion liquid in which a water-repellent resin is dispersed is also possible. The water repellent used for the water repellent treatment can be performed using the same water repellent resin that can be used for the above-mentioned microporous layer forming paste.
From the viewpoint of ensuring water repellency, it is desirable that the water-repellent agent is 1% by weight or more in the conductive porous substrate. However, if the water-repellent agent is excessive, gas diffusibility and drainage will be reduced. Therefore, the content is preferably 30% by weight or less.

The thickness of the conductive porous substrate is set in consideration of the operating conditions of the fuel cell and the required performance, but if the conductive porous substrate is too thin, the strength is insufficient and a stable gas The performance of the gas diffusion layer such as diffusibility, drainage, conductivity, etc. cannot be obtained, or the handleability is deteriorated and the displacement with respect to the catalyst layer is caused, leading to a decrease in battery performance. Moreover, even if the conductive porous substrate is too thick, the gas diffusibility is lowered or the internal resistance value is increased, so that high battery performance cannot be obtained. For this reason, the inside of the range of 2 micrometers-500 micrometers is preferable. In general, the thickness of the conductive porous substrate is larger than the thickness of the microporous layer.

Application of the microporous layer forming paste to the conductive porous substrate is brush coating, brush coating, roll coater method, bar coater method, die coater method, blade method, knife coater method, spin coater method, screen printing, curtain coating method, dip A coater method, a spray coater method, a gravure coater method, an applicator or the like can be used.

At this time, the coating thickness of the microporous layer forming paste is set in consideration of the operating conditions of the fuel cell and the required performance, but the dry film thickness (microporous layer thickness) of the coating film after drying and baking is It is preferably set to be in the range of 1 μm to 300 μm.
If the dry film thickness is too thin, the effect of absorbing the irregularities of the conductive porous substrate or preventing the fibers of the conductive porous substrate from sticking into the electrolyte membrane cannot be obtained. On the other hand, if the coating film thickness is too thick, the surface smoothness tends to decrease due to shrinkage due to drying and baking, and the contact resistance with the catalyst layer increases. Moreover, when the dry film thickness is thick, the electrical resistance in the thickness direction increases.

When the dry film thickness is in the range of 1 μm to 300 μm, a microporous layer with high surface smoothness can be obtained, and good gas permeability and electrical resistance performance can be ensured. Further, it is desirable that the thickness of the microporous layer is 50% or less with respect to the thickness of the conductive porous substrate. If the difference in thickness is within an appropriate range, the shrinkage stress between the conductive porous substrate and the microporous layer due to drying and firing is small, and high bonding strength is obtained. Further, the smoothness of the entire diffusion layer is increased, and the contact resistance with the catalyst layer is reduced.

The conductive porous substrate to which the microporous layer forming paste is applied in the application process in step S2 in FIG. 1 is dried and fired in the drying and firing process in step S3 in FIG.
By this drying and baking, the dispersant and moisture in the coating film by the microporous layer forming paste applied to the conductive porous substrate are removed, voids (pores) are formed, and the water-repellent resin is used. Water repellency is exhibited. Furthermore, the aqueous phenolic resin blended in the present embodiment becomes carbonized, thereby reinforcing the microporous layer and preventing the conductive powder from falling off the microporous layer, and the microporous layer and the conductive porous substrate. It becomes possible to improve the adhesiveness.

Therefore, the drying / baking temperature is a temperature at which the dispersant and moisture can be removed, and the water repellent resin can be softened and melted to exhibit water repellency by the water repellent resin. Is a temperature at which can be bound to the conductive powder of the microporous layer or the conductive porous substrate. The temperature enabling these is usually set in the range of 250 ° C to 350 ° C.

If the drying / firing temperature is too low, the dispersant remains and water is trapped by the hydrophilic groups of the dispersant, so that sufficient water repellency cannot be expressed in the gas diffusion layer and is practical when applied to a fuel cell. Can not get a good drainage. In addition, the binder effect due to the water-repellent resin and the binding force due to the carbonized component of the aqueous phenol resin are small, making it difficult to ensure high mechanical strength of the microporous layer and bonding strength (peel strength) with the conductive porous substrate. Become. On the other hand, if the drying / firing temperature is too high, the components of the microporous layer are deteriorated, the deformation of the microporous layer is increased due to a high temperature change, the smoothness is lowered, or cracks are generated, It becomes difficult to form a microporous layer having desired performance. Furthermore, the load in the drying / firing process from drying to baking and the load on the natural environment are increased, and the manufacturing cost is increased.
If the drying / firing temperature is in the range of 250 ° C to 350 ° C, the dispersing agent and moisture are not completely decomposed and volatilized and lost and remain, which is an important characteristic of the diffusion layer that greatly affects the power generation efficiency. Water repellency can be ensured, and formation of a desired microporous layer and good bonding with a conductive porous substrate can be ensured.

Thus, the fuel in which the microporous layer is formed on the conductive porous substrate by drying and firing the conductive porous substrate coated with the microporous layer forming paste in the drying / firing process of step S3. It becomes a gas diffusion layer for a battery.

In this way, the microporous layer forming paste formed by mixing the conductive powder, the water repellent resin, the dispersant, a predetermined amount of the aqueous phenol resin, and the solvent is applied to the conductive porous substrate. In the gas diffusion layer of the present embodiment obtained by drying and firing, the conductive powder in the microporous layer formed by the microporous layer forming paste and the carbon fiber constituting the conductive porous substrate Conductivity is exhibited by a conductive material such as PT, and water repellency is exhibited by a water repellent resin such as PTFE. Moreover, micropores smaller than the voids (pores) of the conductive porous substrate are formed in the microporous layer, and gas diffusibility and drainage can be ensured. Characteristically, the microporous layer becomes stronger and stronger than the case of not containing the aqueous phenol resin due to the carbonized component of the aqueous phenol resin newly developed in the microporous layer when the microporous layer is formed. It is difficult to peel from the porous porous substrate. For this reason, the diffusion layer of the present embodiment is improved in reliability and durability.

Next, a polymer electrolyte fuel cell (single unit) in which a microporous layer formed using the microporous layer forming paste according to the present embodiment and a gas diffusion layer for a fuel cell made of a conductive porous substrate are incorporated. The structure of the cell) will be described with reference to the schematic configuration diagram of FIG. In the figure, the anode side is A and the cathode side is K.
As shown in the figure, the fuel cell gas diffusion layer 14 (cathode side diffusion layer 14K or anode side diffusion layer 14A) of the present embodiment has a catalyst layer 13 (cathode side catalyst layer 13K or The electrode 12 (cathode electrode 12K and anode electrode 12A) is integrally joined to the anode side catalyst layer 13A), and is disposed on both surfaces of the electrolyte membrane 11 serving as the core of the single cell together with the catalyst layer 13. The membrane / electrode assembly 10 is configured. The membrane / electrode assembly 10 includes a cathode separator 20K provided with an oxidizing gas passage 21K for supplying an oxidizing gas as an oxidizing agent outside the cathode gas diffusion layer 14K, and an anode gas diffusion layer 14A. A single cell of the fuel cell 1 is formed by being sandwiched by a cathode-side separator 20A provided with a fuel gas passage 21A for supplying fuel gas to the outside.

That is, the single cell of the fuel cell 1 using the fuel cell gas diffusion layer 14 according to the present embodiment includes the cathode side catalyst layer 1313K and the cathode on which one surface of the electrolyte membrane 11 reacts with an oxidizing gas such as oxygen gas. The cathode electrode 12K constituted by the side diffusion layer 14K is arranged, and the anode electrode 12A constituted by the anode side catalyst layer 13A and the anode side diffusion layer 14A on which the fuel gas such as hydrogen gas reacts is arranged on the other surface. The membrane-electrode assembly 10 constituting the power generation unit, the cathode-side separator 20K disposed on the surface of the cathode electrode 12K of the membrane-electrode assembly 10 and the surface of the anode electrode 12A of the membrane-electrode assembly 10 Anode side separator 20A.
When assembling the fuel cell 1, the catalyst layer 13 and the gas diffusion layer 14 may be joined to form the electrode 12, and the electrode 12 may be joined to the electrolyte membrane 11. The step of transferring the layer 13 to the electrolyte membrane 11 and joining the gas diffusion layer 14 to the catalyst layer 13 joined to the electrolyte membrane 11 may be taken.

  Here, as described above, the gas diffusion layer 14 for a fuel cell incorporated in the fuel cell 1 having such a configuration includes a conductive powder, a water repellent resin, a dispersant, and a predetermined amount. Since the microporous layer forming paste formed by mixing an aqueous phenol resin and a solvent is applied to the conductive porous substrate 16 and dried and fired, the film strength of the microporous layer 15 is increased. In addition, the bonding strength (adhesiveness) and peel strength between the microporous layer 15 and the conductive porous substrate 16 are high.

That is, in the fuel cell gas diffusion layer 14 of the present embodiment, an aqueous phenol resin having a decomposition temperature higher than the drying and firing temperature is added to the microporous layer forming paste, which is a material for forming the microporous layer 15. Therefore, the aqueous phenol resin is carbonized by drying and baking when the microporous layer 15 is formed, and the microporous layer 15 newly includes a carbonized component resulting from the aqueous phenol resin. This carbonized component exerts the action of binding the conductive powder of the microporous layer 15 and the conductive porous substrate 16, prevents the conductive powder from falling off the microporous layer 15, and the film strength of the microporous layer 15. , And the bonding strength (adhesion) and peel strength between the microporous layer 15 and the conductive porous substrate 16 are improved. The carbonized component of the aqueous phenol resin further has an effect of increasing the conductivity of the microporous layer 15 depending on the carbonization rate.

Therefore, the microporous layer 15 formed on the conductive porous substrate 16 becomes a strong film, and has high bonding strength and peel strength with the conductive porous substrate 16, so that the microporous layer 15 is assembled to the fuel cell 1. The conductive powder forming the layer 15 is difficult to fall off (misses), and the microporous layer 15 is difficult to peel off from the conductive porous substrate 16, thereby improving handling.
Further, after assembly of the fuel cell, the microporous layer 15 is missing even if an external force is applied to the electrolyte membrane 11 due to the operation of the fuel cell, for example, due to expansion or contraction, or due to the pressure of the separator during stacking ( It is difficult to peel off, has excellent durability, and the conductive powder forming the microporous layer 15 is flowed to block the pores of the conductive porous substrate 16 and the gas flow path 21, thereby reducing output due to clogging. There is no fear of causing it.
Therefore, the performance of the fuel cell diffusion layer 14 is stabilized.

In addition, since the bonding of the conductive material (conductive powder of the microporous layer 15 or the conductive material such as carbon fiber of the conductive porous substrate 16) by the water repellent resin is flexible, only the binding by the water repellent resin is possible. Then, when incorporated in the fuel cell 1, the pores of the microporous layer 15 may be crushed by being pinched by the separator 20.
However, in this embodiment, since the carbonized component of the aqueous phenol resin increases the binding component of the microporous layer 15, the microporous layer 15 becomes appropriately hard and is sandwiched between the separators 20 when incorporated in the fuel cell. Even if this is done, the pores of the icoroporous layer 15 are hardly crushed and held, and stable performances such as gas diffusibility and drainage can be secured.

By the way, the diffusion layer 14 in which the microporous layer 15 is formed on the conductive porous substrate 16 absorbs the undulations of the conductive porous substrate 16 by the microporous layer 15 to obtain a smooth surface. Even if the carbon fiber of the conductive porous substrate 16 is frayed or fluffed, the carbon fiber of the conductive porous substrate 16 can be prevented from coming into contact with the catalyst layer 13. The occurrence of a short circuit caused by the catalyst layer 13 can be prevented. Here, if the film strength and peel strength of the microporous layer 15 of the diffusion layer 14 are weak, the microporous layer 15 is partially conductive porous substrate during assembly of the fuel cell 1 or during use of the fuel cell 1. When peeling from 16 occurs, the smoothness at the contact surface of the diffusion layer 14 with the catalyst layer 13 is lost, resulting in a decrease in power generation efficiency due to an increase in contact resistance, and a conductive porous group with the catalyst layer 13. There is a concern about short circuit due to the contact of the carbon fiber of the material 16.

However, when the microporous layer 15 of the present embodiment is interposed between the catalyst layer 13 and the conductive porous substrate 16, the microporous layer 15 has a strong film strength due to the expression of the carbonized component by the aqueous phenol resin, and is electrically conductive. Since the peel strength from the conductive porous substrate 16 is also strong, the microporous layer 15 can be prevented from peeling from the conductive porous substrate 16, and there is no risk of an increase in contact resistance or occurrence of a short circuit (short circuit). Increases nature.
When the fuel cell gas diffusion layer 14 of this embodiment is integrated with the catalyst layer 13 to form the electrode 12 (anode and cathode) of the fuel cell 1 and incorporated in the fuel cell 1. In addition, it is possible to make the production quality uniform, and it is possible to obtain stable characteristics such as gas diffusibility of the gas diffusion layer 14, the ability to remove generated water (drainage), and conductivity for a long period of time. Battery 1 is obtained.

Next, the content of each component of the microporous layer forming paste according to the embodiment of the present invention is specifically shown, and the microporous layer forming paste and the fuel produced using the microporous layer forming paste Examples of the battery gas diffusion layer 14 will be described.

Three types of microporous layer forming pastes according to Examples 1 to 3 were prepared with the mixing contents shown in Table 1 as the mixing composition of the microporous layer forming paste according to the present embodiment. For comparison, pastes for forming a microporous layer according to Comparative Examples 1 to 3 were also produced. The composition of each Example and each Comparative Example is shown in the upper part of Table 1.

In the paste for forming a microporous layer according to Examples and Comparative Examples, acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd .: trade name “Denka Black”) is used as the conductive powder, and PTFE emulsion (Daikin Industries, Ltd.) is used as the water repellent resin. ): POLYFLON PTFE D-210C [solid content (resin content) 61%]), Triton X-100 as a dispersant, and ion-exchanged water as a solvent. In addition, as an aqueous phenolic resin, a resol-type water-dispersible phenolic resin (manufactured by Sumitomo Bakelite Co., Ltd .: trade name “Sumilite Resin PR-50607B” [solid content (resin content) 65%], residual carbon ratio 46% / 800 C. (JIS K2270) was used.

The acetylene black as the conductive powder, the PTFE emulsion as the water repellent resin, the Triton X-100 as the dispersant, the ion exchange water as the solvent, and the resol type water dispersible phenol resin as the aqueous phenol resin, respectively. Mixing and dispersing and defoaming for 3 minutes using a planetary agitation and defoaming device (manufactured by Kurashiki Boseki Co., Ltd .: trade name “Mazerustar KK-1000W”) blended in the blending amount shown in 1 and set at 800 rpm for revolution and 900 rpm for rotation Thus, a microporous layer forming paste according to Examples and Comparative Examples was obtained.

In Examples and Comparative Examples, as shown in Table 1, all the contents other than the resol-type water-dispersible phenol resin as the aqueous phenol resin and the ion-exchanged water as the solvent are the same, and the resol-type water-dispersibility. The blending ratio of the phenol resin to acetylene black was changed, and the blending amount of ion-exchanged water was adjusted according to the increase / decrease.

That is, in this example and comparative example, 75.0 g of conductive powder acetylene black, 41.7 g of PTFE emulsion of water repellent resin (solid content 25.4 g), and Triton X-100 as a dispersant are 7. The acetylene black, PTFE emulsion, and Triton X-100 are unified in the same amount in all of the examples and comparative examples, and the total amount (total amount) of the present examples and comparative examples is all 500 g. Unified.
Then, between the examples and comparative examples, the resol-type water-dispersible phenol resin was blended by changing the blending ratio with respect to acetylene black and blended with ion-exchanged water as a solvent so that the total amount became 500 g according to the change. The amount was adjusted.

That is, in Example 1, the blending amount of the resol-type water-dispersible phenol resin with respect to the blending amount of acetylene black is 0.53% by weight, and the resol-type water-dispersible phenol resin is in a solid content blending ratio with respect to acetylene black. It is blended at a ratio of 0.35% by weight. That is, the resol-type water-dispersible phenol resin is blended at a solid content of 0.35 parts by weight with respect to 100 parts by weight of acetylene black.

In Example 2, the blending amount of the resol-type water-dispersible phenol resin with respect to the blending amount of acetylene black is 1.1% by weight, and the resol-type water-dispersible phenol resin has a solid content blending ratio of 0.1% with respect to acetylene black. It is blended at a ratio of 7% by weight. That is, the resol-type water-dispersible phenol resin is blended at a ratio of 0.7 parts by weight in solid content to 100 parts by weight of acetylene black.

In Example 3, the blending amount of the resol-type water-dispersible phenol resin with respect to the blending amount of acetylene black is 2.0% by weight, and the resol-type water-dispersible phenol resin is 1. It is blended at a rate of 3% by weight. That is, the resol-type water-dispersible phenol resin is blended at a ratio of 0.7 parts by weight in solid content to 100 parts by weight of acetylene black.

In Comparative Example 1, since no resol type water dispersible phenol resin is blended, the blending amount is 0% by weight.

In Comparative Example 2, the amount of the resol-type water-dispersible phenol resin based on the amount of acetylene black is 0.27% by weight, and the amount of the resol-type water-dispersible phenol resin relative to acetylene black is 0. It is blended at a ratio of 17% by weight. That is, the resol-type water-dispersible phenol resin is blended at a solid content of 0.17 parts by weight with respect to 100 parts by weight of acetylene black.

Furthermore, in Comparative Example 3, the blending amount of the resol-type water-dispersible phenol resin with respect to the blending amount of acetylene black is 3.1% by weight, and the resol-type water-dispersible phenol resin is in a solid content blending ratio with respect to acetylene black. It is blended at a ratio of 2.0% by weight. That is, the resol-type water-dispersible phenol resin is blended at a ratio of 2.0 parts by weight in solid content with respect to 100 parts by weight of acetylene black.

And the diffusion layer 14 for fuel cells was produced using the paste for microporous layer formation concerning Example 1 thru | or Example 3 and Comparative Example 1 thru | or Comparative Example 3 which were obtained by mix | blending in this way.
Specifically, a PTFE emulsion (made by Daikin Industries, Ltd .: POLYFLON PTFE D-210C [solid content (resin content) 61%]) is impregnated to a basis weight of 1 mg / cm ² and dried to remove moisture. With respect to the carbon paper as the conductive porous substrate 16 subjected to the water repellent treatment, a moving speed of 1.0 m / min and a basis weight of 5.0 mg / cm are used on one side using a thin film coating tool (die head). ^The microporous layer-forming paste was applied under the conditions of ² , and then dried and fired at 300 ° C. for 30 minutes.
Thus, the fuel cell according to Examples 1 to 3 and Comparative Examples 1 to 3 in which the microporous layer 15 was formed on the conductive porous substrate 16 made of carbon paper subjected to water repellent treatment. Gas diffusion layer 14 was obtained.

Here, with respect to the gas diffusion layers 14 for fuel cells according to Examples 1 to 3 and Comparative Examples 1 to 3 obtained, an evaluation test (peeling test) of peeling (tensile) strength was performed. In this peeling (tensile) test, JIS K6854-2 was referred.
Specifically, first, the gas diffusion layer 14 was cut into a width of 30 mm, and an adhesive tape T having the same width as the gas diffusion layer 14 was attached to the surface of the microporous layer 15 as shown in FIG. . Next, as shown in FIG. 3B, a part of the adhesive tape T attached to the microporous layer 15 is peeled off, and the end A of the adhesive tape T peeled off from the microporous layer 15 and the adhesive tape T The end B of the gas diffusion layer 14 on the side from which the film is peeled off is sandwiched between holding parts of a tensile tester (autograph) and pulled in a 180 ° direction at a pulling (peeling) speed of 100 mm / min. The peel strength (tensile strength) when peeled from the conductive porous substrate 16 was measured. The measurement results are as shown in the lower part of Table 1.

As shown in Table 1, the peel strength was 15 N / m in the comparative example 1 of the conventional example in which no resol type water dispersible phenol resin was added.
In Comparative Example 2 in which the resol-type water-dispersible phenol resin was blended at a blending ratio of 0.17 parts by weight in solid content with respect to 100 parts by weight of acetylene black, the peel strength was slightly increased as compared with Comparative Example 1. The value was 17 N / m.
On the other hand, in Comparative Example 3 in which the resol-type water-dispersible phenol resin was blended at a blending ratio of 2.0 parts by weight with respect to 100 parts by weight of acetylene black, the peel strength was lower than that in Comparative Example 1, and the value Was 12 N / m.

On the other hand, Example 1 thru | or Example 3 which mix | blended the resol type water-dispersible phenol resin with the compounding ratio in the range of 0.35 weight part-1.3 weight part by solid content with respect to 100 weight part of acetylene black. Then, the peel strength was significantly higher than those of Comparative Examples 1 to 3, and the value thereof was in the range of 29 N / m to 38 N / m.

From this, a resol-type water-dispersible phenol resin was added in a solid content to 100 parts by weight of acetylene black in a microporous forming paste containing a predetermined amount of acetylene black, PTFE emulsion, Triton X-100, and ion-exchanged water. By blending at a blending ratio within the range of .35 parts by weight to 1.3 parts by weight, the peel strength is significantly increased as compared with Comparative Example 1 in which no resol type water-dispersible phenol resin is disposed.

Here, as described above, the factor of the peel strength improvement due to the blending of the aqueous phenol resin is that the aqueous phenol resin becomes carbonized at a drying and firing temperature lower than the decomposition temperature of the aqueous phenol resin, and the carbonized component is It is presumed that this is because it acts as a binding component that promotes binding in the microporous layer and binding at the interface between the microporous layer 15 and the conductive porous substrate 16. This is due to the experimental research conducted by the present inventors, in which the coating film before the microporous layer forming paste is applied to the conductive porous substrate 16 and fired, and the coating film of the microporous layer 15 after firing. When the resistance value was measured, it was confirmed that the resistance value changed greatly before and after firing.

That is, with respect to the coating film before firing, in which the microporous layer forming paste is applied to the conductive porous substrate 16, the electrical resistance value is measured with a digital low resistance meter model 3566 manufactured by Tsuruga Electric Co., Ltd. Further, regarding the coating film of the microporous layer 15 after firing (300 ° C., 20 minutes), the electrical resistance value was measured with the same device, as shown in Table 1, before firing. In Examples 1 to 3 in which an aqueous phenol resin was blended, the resistance value was 16.2 to 19.1 (mΩ · cm ₂ ), and the resistance value of Comparative Example 1 in which no aqueous phenol resin was added. It is significantly higher than 5.8 (mΩ · cm ₂ ). However, after firing, in Comparative Example 1 where no aqueous phenol resin is added, the resistance value is 5.4 (mΩ · cm ₂ ), which is a little lower than before firing, whereas the aqueous phenol resin is The resistance values of the blended Examples 1 to 3 are 5.1 to 5.4 (mΩ · cm ₂ ), which is significantly smaller than that before firing and equal to or less than that of Comparative Example 1 in which no aqueous phenol resin is added. It has become.

Here, the resin component in the uncarbonized state does not have conductivity, but when the resin component is in the carbonized state, current is passed and the resistance value is lowered.
Therefore, in Example 1 thru | or Example 3 which mix | blended the aqueous phenol resin, since the resistance value after baking has decreased significantly compared with before baking, the aqueous phenol resin is carbonized by drying and baking. I guess that. Then, since the aqueous phenol resin is in a carbonized state by drying and firing, the carbonized component is bound in the microporous layer 15 and bound at the interface between the microporous layer 15 and the conductive porous substrate 16. It is considered that the peel strength is improved by acting as a binder component that promotes the adhesion.

By the way, when Examples 1 to 3 are compared with Comparative Example 2 and Comparative Example 3, the resol-type water-dispersible phenolic resin is less than 0.35 parts by weight in solid content with respect to 100 parts by weight of acetylene black. In some cases, and exceeding 1.3 parts by weight, the peel strength was reduced, and it was found that there was an appropriate range for the amount of the resol-type water-dispersible phenol resin. This is because when the amount of the resol-type water-dispersible phenol resin is less than 0.35 parts by weight, the amount of the binder component is not sufficient to exert a sufficient effect on peeling. It is presumed that the binder component in the porous layer 15 becomes too much and is easily broken.

As shown in Examples 1 to 3, the resol-type water-dispersible phenol resin is blended in a predetermined range of 0.35 to 1.3 parts by weight in solid content with respect to 100 parts by weight of acetylene black. If so, the blending of the resol-type water-dispersible phenol resin with respect to acetylene black is within an appropriate range, and the microporous layer is excellent in both the adhesive strength (adhesive strength) to the conductive porous substrate 16 and the film strength of the microporous layer 15. Layer 15 is formed.
Therefore, in the fuel cell gas diffusion layer 14 formed by applying the microporous layer forming paste according to Examples 1 to 3 to the conductive porous substrate 16 and drying and firing, the fuel cell 1 is formed. At the time of assembly, the microporous layer 15 is not easily broken and is not easily peeled off from the conductive porous substrate 16.

As described above, the microporous layer forming paste according to the present example is composed of acetylene black as a conductive powder, PTFE emulsion as a water repellent resin, Triton X-100 as a dispersant, and acetylene black 100. A resol-type water-dispersible phenol resin as an aqueous phenol resin having a solid content of 0.35 to 1.3 parts by weight with respect to parts by weight and ion-exchanged water as a solvent are mixed and dispersed. Then, the microporous layer forming paste is applied to the conductive porous substrate 16 of carbon paper subjected to water repellent treatment, dried and fired at a predetermined drying and firing temperature (300 ° C. in the example), The resol-type water-dispersible phenolic resin as the aqueous phenolic resin in the porous layer forming paste becomes carbonized.

The gas diffusion layer 14 for a fuel cell according to this example is composed of acetylene black as a conductive powder, PTFE emulsion as a water repellent resin, Triton X-100 as a dispersant, and 100 parts by weight of acetylene black. A microporous layer obtained by mixing and dispersing 0.35 parts by weight to 1.3 parts by weight of a resol-type water-dispersible phenol resin as an aqueous phenol resin and ion-exchanged water as a solvent. The forming paste is applied to the conductive porous base material 16 of carbon paper that has been subjected to water repellent treatment, and dried and baked at a predetermined drying and baking temperature (300 ° C. in the embodiment), thereby forming an aqueous phenolic resin. The resole type water-dispersible phenol resin has a microporous layer 15 in a carbonized state.

In practicing the present invention, the structure, composition, components, blending amount, material, and other manufacturing processes of the microporous layer forming paste and other parts of the gas diffusion layer 14 for a fuel cell formed using the same However, the present invention is not limited to this embodiment.
Note that the numerical values given in the embodiments and examples of the present invention do not indicate critical values but indicate appropriate values suitable for implementation, so even if the numerical values are slightly changed, implementation is denied. Not what you want.

1 Fuel Cell 11 Electrolyte Membrane 10 Membrane / Electrode Assembly 12 Electrode (Cathode Electrode 12K, Anode Electrode 12A)
13 catalyst layer (cathode side catalyst layer 13K, anode side catalyst layer 13A)
14 Gas diffusion layer (cathode side diffusion layer 14K, anode side diffusion layer 14A)
15 Microporous layer 16 Conductive porous substrate

Claims (2)

A conductive powder, a water-repellent resin, a dispersant, an aqueous phenol resin blended in a range of 0.35 to 1.3 parts by weight in solid content with respect to 100 parts by weight of the conductive powder, and a solvent. A paste for forming a microporous layer, which is formed by mixing, forming a microporous layer of a gas diffusion layer for a fuel cell by applying to a conductive porous substrate, drying and firing,
For forming a microporous layer, the aqueous phenolic resin is carbonized at a drying / firing temperature when the microporous layer forming paste is applied to the conductive porous substrate and dried / fired. paste. A conductive powder, a water-repellent resin, a dispersant, an aqueous phenol resin blended in a range of 0.35 to 1.3 parts by weight in solid content with respect to 100 parts by weight of the conductive powder, and a solvent. Apply a microporous layer forming paste that forms a microporous layer by mixing, applying to a conductive porous substrate, drying and baking, and then drying and baking to a conductive porous substrate. A fuel cell gas diffusion layer comprising:
The aqueous phenolic resin is in a carbonized state at a drying / firing temperature when the microporous layer forming paste is applied to the conductive porous substrate and then dried / firing. layer.

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