JP7554175B2 - Anode gas diffusion layer substrate - Google Patents

Description

The present invention relates to an anode gas diffusion layer substrate, which is a material used to form an anode gas diffusion layer in a polymer electrolyte fuel cell.

A solid polymer electrolyte fuel cell (hereafter simply referred to as a "fuel cell"), which is widely used as a power source for automobiles and the like, is constructed by stacking multiple fuel cell cells with separators between them. In one single cell, a membrane/electrode assembly is formed by arranging a cathode (+) electrode and an anode (-) electrode, which are composed of a catalyst layer made of a conductive material such as carbon carrying a catalyst such as platinum and an ion exchange resin, and a porous gas diffusion layer arranged on the outside of each catalyst layer, on both sides of a polymer electrolyte membrane that selectively transmits specific ions. Then, on the outside of the gas diffusion layer that constitutes this membrane/electrode assembly, a separator that supplies fuel gas (anode gas) or oxidizing gas (cathode gas) and forms a gas flow path for discharging generated gas and excess gas is arranged, and the membrane/electrode assembly is sandwiched between the separators.

In the fuel cell having the above configuration, the gas diffusion layer constituting the electrode of the single cell battery is arranged to enhance the diffusibility of the reactant gas. Since the gas diffusion layer is responsible for diffusing the fuel gas or oxidizing gas supplied from the gas flow path of the separator to the catalyst layer adjacent to the gas diffusion layer (gas diffusibility), gas permeability is required, and electrical conductivity is also required as a current collecting function that efficiently transfers electrons for the electrochemical reaction. In addition, the gas diffusion layer is required to always keep the polymer electrolyte membrane and catalyst layer in an optimal wet state, while suppressing the flooding phenomenon (the phenomenon in which the pores of the gas diffusion layer are blocked by water) and to maintain stable power generation performance of the battery, and is also required to have water repellency (drainage) to drain excess reaction water and condensation water generated by the electrochemical reaction of hydrogen and oxygen during power generation.

Conventionally, in order to form a gas diffusion layer for a fuel cell, a substrate in the form of a sheet made of conductive fibers such as carbon fibers has been used.
For example, Patent Document 1 discloses a carbon fiber sheet for a gas diffusion layer of a polymer electrolyte fuel cell, which comprises carbon fibers, carbon particles I having a particle diameter (X) of 0.5 to 5 μm on average, and carbon particles II having a particle diameter (Y) of 7 to 20 μm on average, and amorphous carbon bonding the intersections of the carbon fibers, and in which the average particle diameter ratio [(Y)/(X)] of the particle diameter (X) to the particle diameter (Y) is 1.5 to 20, Disclosed is a carbon fiber sheet for use in a gas diffusion layer of a polymer electrolyte fuel cell, in which a mass ratio [(C+D)/(B+C+D)] of the sum of the carbon particle I content (C) and the carbon particle II content (D) to the sum of the carbon particle I content (C) and the elementary particle II content (D) is 0.65 to 0.95, and a mass ratio [(B+C+D)/A] of the sum of the amorphous carbon content (B), the carbon particle I content (C), and the carbon particle II content (D) to the carbon fiber content (A) is 1.50 to 5.00.
Patent Document 2 discloses a gas diffusion layer substrate which is porous and has a predetermined number of pores formed therein, and which includes a conductive substrate made of carbon fiber and a resin carbide which binds the conductive substrate, and in which, when dry nitrogen gas is passed through one surface in the thickness direction of the gas diffusion layer substrate at a flow rate of 10 L/min with a basis weight of 30 g/ ^cm2 , the pressure difference between the front and back of the gas diffusion layer substrate is within a range of 0.01 to 0.3 MPa.
Patent Document 3 discloses a porous gas diffusion layer substrate which is made of a carbon fiber aggregate in which carbon fibers are entangled with one another, contains a carbide binding the carbon fibers of the carbon fiber aggregate, and contains spherical graphite and/or artificial graphite having a median diameter in the range of 40 μm to 120 μm held between the carbon fibers of the carbon fiber aggregate.

JP 2009-289552 A JP 2018-18665 A JP 2020-87826 A

The object of the present invention is to provide an anode gas diffusion layer substrate that is used to form an anode gas diffusion layer for a fuel cell, and that provides a fuel cell with high power generation performance by achieving both gas diffusivity and electrical conductivity.

The present invention is illustrated below.
[1] A gas diffusion layer substrate for an anode electrode of a fuel cell, comprising (A) carbon fibers and (B) graphite particles, characterized in that the graphite particles (B) contain graphite particles (B1) having a ratio _Dr of the major axis _dL to the minor axis _dS (= _dL / _dS , hereinafter referred to as "aspect ratio Dr") of 5 to 100, where dL is the major axis and _{dS is the} minor axis.
[2] The anode gas diffusion layer substrate according to the above item [1], wherein the graphite particles (B1) have an average particle size d50 of 20 to 80 μm as measured by a laser diffraction method.
[3] The gas diffusion layer substrate for an anode according to item [1] or [2], wherein a content ratio of the graphite particles (B) is 70 to 90 parts by mass per 100 parts by mass of the carbon fibers (A).
[4] The gas diffusion layer substrate for an anode according to any one of the above items [1] to [3], having a basis weight of 40 to 100 g/m2 ^.
[5] The gas diffusion layer substrate for an anode according to any one of the above items [1] to [4], the surface of which is treated to be water repellent.

When the anode gas diffusion layer substrate of the present invention is used to form the anode gas diffusion layer that constitutes the membrane/electrode assembly for a fuel cell, a fuel cell with high power generation performance can be obtained. Therefore, a fuel cell obtained using the anode gas diffusion layer substrate of the present invention is suitable for fuel cells for transportation such as vehicles, stationary fuel cells, etc.

FIG. 1 is a schematic cross-sectional view of an anode gas diffusion layer substrate of the present invention. FIG. 2 is a schematic explanatory diagram for obtaining the aspect ratio of the graphite particles (B1) contained in the anode gas diffusion layer substrate of the present invention. 1 is a schematic cross-sectional view of a membrane/electrode assembly obtained by using an anode gas diffusion layer substrate of the present invention. 1 is a cross-sectional image of the anode gas diffusion layer substrate AS1 obtained in Example 1-1. 1 is a cross-sectional image of the anode gas diffusion layer substrate AS3 obtained in Comparative Example 1-1.

The anode gas diffusion layer substrate of the present invention is, for example, a sheet-like (thin plate-like) material used to form the anode gas diffusion layer 10 in a membrane/electrode assembly 100 shown in FIG. 3, which includes, in order, the anode gas diffusion layer 10, the microporous layer 15, the catalyst layer 40, the electrolyte layer 30, the catalyst layer 50, the microporous layer 25, and the cathode gas diffusion layer 20.

The anode gas diffusion layer substrate of the present invention contains (A) carbon fibers (hereinafter also referred to as "component (A)") and (B) graphite particles (hereinafter also referred to as "component (B)"). The graphite particles (B) contain graphite particles ( _B1 ) (hereinafter also referred to as "component (B1)" or "rod-shaped graphite particles") having a ratio of the length d _L /d _S (aspect ratio Dr) of 5 to 100, where d _L is the major axis length and d S is the minor axis length. The anode gas diffusion layer substrate of the present invention may contain other components (binders, carbides of organic components, additives, etc.) as necessary. The surface of the anode gas diffusion layer substrate of the present invention may be treated to be water repellent.

Figure 1 is a schematic cross-sectional view of the anode gas diffusion layer substrate 1 of the present invention, showing that it contains a plurality of carbon fibers 3 and a plurality of rod-shaped graphite particles 5. The blank areas in Figure 1 are, for example, a phase mainly composed of carbides of organic components that bind the carbon fibers together, the graphite particles together, or the carbon fibers and the graphite particles together. The porosity is low, usually 70% or less.

Component (A) according to the present invention is not particularly limited, and examples thereof include vapor-grown carbon fibers, carbon nanotubes (single-wall, double-wall, multi-wall, cup-laminated, etc.), polyacrylonitrile (PAN)-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, etc. Component (A) contained in the anode gas diffusion layer substrate of the present invention may be one type only, or two or more types.

The average fiber diameter of component (A) is preferably 5 to 15 μm, more preferably 6 to 8 μm, from the viewpoint of gas diffusibility and drainage of the resulting anode gas diffusion layer.
The upper limit of the fiber length of component (A) is usually 12 mm, and the lower limit is usually 2 mm. The average fiber length of component (A) is preferably 2 to 9 mm, more preferably 3 to 6 mm, from the viewpoints of gas diffusivity and drainage of the anode gas diffusion layer to be formed.

Component (B) according to the present invention includes component (B1), i.e., rod-shaped graphite particles (which may have an irregular shape) having an aspect ratio Dr of 5 to 100. Component (B) contained in the anode gas diffusion layer substrate of the present invention may consist of only component (B1), or may consist of a combination of component (B1) and other graphite particles (graphite particles having an aspect ratio Dr outside the above range, such as spherical). In the latter case, the lower limit of the content of component (B1) relative to the total amount of component (B) contained in the anode gas diffusion layer substrate of the present invention is preferably 50 mass%, more preferably 70 mass%.

The aspect ratio Dr of the component (B1) is preferably 20 to 80, more preferably 30 to 70, since a membrane/electrode assembly constituting a fuel cell having high power generation performance can be obtained.
The method of deriving the aspect ratio Dr is explained with reference to Fig. 2. That is, the major axis (major axis length) _dL of the component (B1) and the minor axis (minor axis length) _dS , which is the maximum length of the component (B1) in a direction perpendicular to the major axis L, are measured, and the ratio of these lengths _dL / _dS (aspect ratio Dr) can be obtained. The aspect ratio Dr of the component (B1) contained in the anode gas diffusion layer substrate can be determined by a method of measuring the component (B1) taken out of the anode gas diffusion layer substrate, or a method of measuring a cross-sectional image of the anode gas diffusion layer substrate.

The average particle size d50 of component (B1) as measured by a laser diffraction method is preferably 20 to 80 μm, more preferably 30 to 50 μm, from the viewpoint of graphite fixation during papermaking.

Component (B) may be either a solid or hollow body, or may be an expanded graphite body. The shape of component (B1) may be any of a plate shape (e.g., a scale shape) or an oval sphere shape, etc., as long as it satisfies the aspect ratio Dr.

The content of component (B) in the anode gas diffusion layer substrate of the present invention is preferably 70 to 90 parts by mass, more preferably 75 to 88 parts by mass, based on 100 parts by mass of component (A), since this provides an anode gas diffusion layer for a membrane/electrode assembly that constitutes a fuel cell with high power generation performance.

As described above, the anode gas diffusion layer substrate of the present invention may further contain other components (binder, carbonized organic component, additives, etc.).
The binder may be derived from polyvinyl alcohol, polyvinyl acetate, polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate, polyacrylonitrile, cellulose, polyethylene oxide, polyacrylamide, phenolic resins, xylenol resins, styrene-butadiene rubber, starch, corn starch, and the like.
The carbonized organic components may be derived from fiber materials such as resin fibers and cellulose fibers, adhesives that bond these fibers together, resins, additives, and the like.

The surface of the anode gas diffusion layer substrate of the present invention may be treated to be water repellent as described above. Examples of water repellent materials include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinyl fluoride (PVF), polyhexafluoropropylene (FEP), etc. In the water repellent treated anode gas diffusion layer substrate, the water repellent material is in the form of a film or is scattered.

The weight per unit area of the anode gas diffusion layer substrate of the present invention is preferably 40 to 100 g/m ² , more preferably 50 to 85 g/m ² , from the viewpoints of gas diffusibility and flexibility.

The anode gas diffusion layer substrate of the present invention is usually in the form of a sheet (thin plate), and its thickness is preferably 100 to 250 μm, more preferably 130 to 200 μm, from the viewpoints of the rigidity of the anode gas diffusion layer to be formed and the power generation performance of the resulting fuel cell.

The method for producing the anode gas diffusion layer substrate of the present invention is not particularly limited. A preferred production method includes an aggregate preparation step for preparing an aggregate containing carbon fibers (hereinafter also referred to as "raw material (a)"), graphite particles containing graphite particles (B1) (hereinafter also referred to as "raw material (b)"), and organic fibers to be carbonized in a subsequent carbonization step, a resin impregnation step for impregnating the aggregate with a carbon precursor resin to be carbonized in a subsequent carbonization step to prepare a resin-impregnated body, and a carbonization step for heating and baking the resin-impregnated body in a non-oxidizing atmosphere, as shown below.

The above-mentioned assembly preparation process is a process for preparing an assembly including a plurality of raw materials (a), a plurality of raw materials (b), and a plurality of organic fibers. Since there is no change in shape or properties of raw materials (a) and (b) before and after the production of the anode gas diffusion layer substrate, the configurations described above as components (A) and (B) are applied to both raw materials (a) and (b).

The raw material (b) may consist of only the above component (B1), or may consist of component (B1) and other graphite particles. In the latter case, however, the upper limit of the content of the other graphite particles is preferably 50% by mass, more preferably 70% by mass. The amount of the raw material (b) used is preferably 70 to 90 parts by mass, more preferably 75 to 88 parts by mass, based on 100 parts by mass of the raw material (a).

The organic fibers may be any fibers that can be carbonized in the subsequent carbonization process, and examples of such fibers include vegetable fibers (wood, cellulose, cotton, bamboo, hemp, and other pulps), animal fibers (wool, etc.), and resin fibers (polylactic acid, polyvinyl alcohol, polyethylene, polyolefin, polypropylene, polyurethane, polyester, polyamide, vinylon, acrylic, aramid, polyacetal, phenolic resin, etc.). When these organic fibers are pyrolyzed and burned by heating in the subsequent carbonization process, the burned areas become pores (pores, air holes) that allow gas and moisture to pass through. Furthermore, the organic fibers also function as binders that capture carbon fibers and bind them together to improve entanglement when preparing an aggregate by, for example, a papermaking method. In the present invention, it is preferable to use vegetable fibers and resin fibers in combination.

The average fiber diameter of the organic fibers is preferably 5 to 20 μm, and more preferably 6 to 8 μm, from the viewpoint of the mechanical strength of the aggregate to be formed.
The upper limit of the fiber length of the organic fiber is usually 15 mm, and the lower limit is usually 1 mm. The average fiber length of the organic fiber is preferably 1 to 10 mm, and more preferably 1 to 5 mm.
The amount of the organic fiber used is preferably 30 to 90 parts by mass, and more preferably 50 to 70 parts by mass, based on 100 parts by mass of the raw material (a).

In the above-mentioned aggregate preparation process, it is preferable to apply a papermaking method. For example, there are a wet papermaking method in which paper is made using a raw material dispersion liquid (slurry) in which multiple raw materials (a), multiple raw materials (b), and multiple organic fibers are dispersed in a dispersion medium (water, organic solvent, etc.), and a dry papermaking method in which a mixture of these raw materials is allowed to fall and accumulate in the air. From the viewpoints of the uniformity, strength, productivity, thickness, and controllability of the basis weight of the raw materials in the aggregate, the wet papermaking method is preferable.

For example, the slurry can be scooped using a separating member such as a mesh member, or vacuum suction or drying to separate the solids and the dispersion medium, and form an aggregate. Specifically, the raw material dispersion is supplied to a wet papermaking machine having wires such as a fourdrinier, short wire, or cylinder wire, dehydrated in a dehydration part, and pressed to squeeze out the water, to obtain an aggregate.
The above-mentioned slurry may contain a binder such as polyvinyl alcohol, polyvinyl acetate, cellulose, polyethylene oxide, styrene-butadiene rubber, starch, or corn starch, a flocculant, a viscosity adjuster, a surfactant, or the like, in order to improve papermaking properties and the binding properties (strength) of the contained components.
The method for preparing the slurry is not particularly limited, and for example, a rotary device such as a pulper can be used.

In the above papermaking method, entanglement treatment such as mechanical entanglement (needle punching, etc.), high-pressure liquid injection (water jet punching, etc.), high-pressure gas injection (steam jet punching, etc.) may be performed.

The aggregate obtained in the above-mentioned aggregate production process has a basis weight of preferably 40 to 100 g/ ^m2 and a thickness of preferably 100 to 500 μm.

The resin impregnation step is a step of impregnating the above-obtained assembly with a carbon precursor resin that will be carbonized in a subsequent carbonization step to produce a resin-impregnated body.
The carbon precursor resin is not particularly limited, but thermosetting resins such as phenol resin, furan resin, epoxy resin, melamine resin, imide resin, urethane resin, aramid resin, urea resin, and unsaturated polyester resin are preferred because they have excellent wettability with the raw material (a), the raw material (b), or the organic fiber, and are likely to form a conductive carbonized material in the subsequent carbonization step. Among these, phenol resin is particularly preferred because it has a high carbonization rate and becomes a highly conductive material after carbonization.
The carbon precursor resin may be used as it is depending on its properties, but may also be used as a solution (resin solution) obtained by dissolving the carbon precursor resin in a solvent, or as a dispersion (resin dispersion) obtained by dispersing the carbon precursor resin in a dispersion medium. In the resin impregnation step, it is preferable to use a liquid containing a carbon precursor resin (hereinafter referred to as a "carbon precursor resin-containing liquid").

When the carbon precursor resin-containing liquid is used, a method of immersing an assembly in the carbon precursor resin-containing liquid, a method of applying the carbon precursor resin-containing liquid to an assembly (kiss coating method, spray method, curtain coating method, roller contact method, etc.), etc., can be applied. Of these, the method of immersing an assembly in the carbon precursor resin-containing liquid is preferred.
When the carbon precursor resin-containing liquid is used, a resin-impregnated body that does not contain a solvent or dispersion medium can be obtained by using a non-contact drying method in which hot air is blown onto the liquid, the liquid is placed in a high-temperature atmosphere, an infrared heater is used, or microwaves are used, or a contact drying method in which the liquid is brought into contact with a heated roll, plate, or the like.

Other methods that do not use the carbon precursor resin-containing liquid include a method in which at least a portion of the surface of the aggregate is covered with a resin film containing the carbon precursor resin, and the carbon precursor resin is dissolved by heating or a solvent and allowed to permeate the entire aggregate.

The resin-impregnated body obtained by the resin impregnation step may contain the carbon precursor resin used as is, or, in the case where the carbon precursor resin is a curable resin, may be a cured resin formed by, for example, an operation (heating, etc.) for removing the solvent or dispersion medium as described above.
In order to obtain a resin-impregnated body in which the raw materials (a), (b) and organic fibers contained in the above-mentioned aggregate are bound by a cured resin, and which has a desired thickness and is free of raw materials (a), (b) or organic fibers and has excellent structural stability, a hot press (hydraulic press, hot press, belt press, roll press, etc.) can be performed with the carbon precursor resin in contact with the aggregate.

In the resin impregnation step, the amount of carbon precursor resin applied to the assembly is not particularly limited. From the viewpoint of the electrical conductivity and strength of the finally obtained anode gas diffusion layer substrate, the mass proportions of the assembly and the carbon precursor resin in the resin impregnated body are preferably 50 to 90 mass% and 10 to 50 mass%, more preferably 60 to 80 mass% and 20 to 40 mass%, respectively, when the total of the two is taken as 100 mass%.

The carbonization step is a step of heating and baking the resin-impregnated body in a non-oxidizing atmosphere, which may be an atmosphere containing an inert gas such as argon gas or helium gas, or nitrogen gas.
The heating temperature of the resin-impregnated body is preferably 1800° C. to 2500° C., more preferably 1900° C. to 2200° C., in order not to cause a deterioration in the strength of the raw material (a) and to facilitate the carbonization of the resin fiber and the carbon precursor resin. Note that the carbonization step can be performed using a multi-stage heating method in which a heat treatment is performed at a temperature lower than the preferred carbonization temperature.
The heating time for the resin-impregnated body varies depending on the size of the resin-impregnated body, but is usually 1 minute or more.

The carbonization step carbonizes the resin fibers derived from the aggregate and the carbon precursor resin contained in the resin-impregnated body, and the carbon fibers are bound to each other, the graphite particles are bound to each other, or the carbon fibers and the graphite particles are bound to each other by the formed charcoal, thereby obtaining an anode gas diffusion layer substrate having the structure shown in FIG. 1.
The resulting anode gas diffusion layer substrate has a strong conductive path due to the phase mainly composed of carbide, and since the carbide is derived from a resin, it has elasticity and has high dimensional absorption when bonded to an electrolyte layer or a catalyst layer during the manufacture of a fuel cell. Furthermore, when a fuel cell manufactured using this anode gas diffusion layer substrate is operated, the diffusion of water vapor is slowed (water vapor is difficult to escape) in the anode gas diffusion layer containing graphite particles made of component (B1), drying is suppressed, and water retention is maintained, so that it is believed to exhibit high power generation performance.

In addition, when manufacturing an anode gas diffusion layer substrate having a water-repellent surface (hereinafter referred to as a "water-repellent gas diffusion layer substrate for anode"), a water-repellent step of attaching a water-repellent material to the anode gas diffusion layer substrate after the carbonization step can be further included. In this water-repellent step, for example, a method can be applied in which the anode gas diffusion layer substrate is contacted with a solution or dispersion of the water-repellent material, and then heat-treated as necessary.
It is preferable that the water-repellent material is mainly composed of a fluororesin such as polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA), or tetrafluoroethylene-ethylene copolymer (ETFE).

When manufacturing a fuel cell, the anode gas diffusion layer substrate of the present invention (including the above-mentioned water-repellent anode gas diffusion layer substrate) may be applied as is to the gas diffusion layer electrode, but it is preferable to use a laminate (anode gas diffusion layer laminate) in which a microporous layer is formed on one side. When a fuel cell obtained using the anode gas diffusion layer laminate equipped with this microporous layer is operated, flooding caused by large water droplets generated by condensation of water vapor can be suppressed.

The microporous layer is preferably a finely porous layer containing a conductive material and a water-repellent resin and having a thickness of up to about 100 μm.
Examples of the conductive material include carbon black, carbon nanotubes, carbon nanofibers, chopped carbon fibers, graphene, and graphite.
As the water-repellent resin, the above-mentioned fluororesin is preferably used.

The membrane/electrode assembly 100 shown in FIG. 3 can be manufactured using an anode gas diffusion layer substrate (including the above-mentioned water-repellent gas diffusion layer substrate for the anode) with a microporous layer on one side, a cathode gas diffusion layer substrate with a microporous layer on one side, and a laminate in which catalyst layers are formed on both sides of an electrolyte membrane (polymer electrolyte membrane) that selectively allows specific ions to pass through. A fuel cell (single cell) can be manufactured using this membrane/electrode assembly 100 and separators (anode side and cathode side).

In a fuel cell configured as described above, when oxidizing gas is supplied from the outside to the oxidizing gas flow path of the cathode separator, a portion of the oxidizing gas flowing along this oxidizing gas flow path penetrates into the cathode gas diffusion layer. The remaining unreacted oxidizing gas that does not penetrate flows along the oxidizing gas flow path and is discharged to the outside of the fuel cell. Similarly, when fuel gas is supplied from the outside to the fuel gas flow path of the anode separator, a portion of the fuel gas flowing along this fuel gas flow path penetrates into the anode gas diffusion layer. The remaining unreacted fuel gas that does not penetrate flows along the fuel gas flow path and is discharged to the outside of the fuel cell.
As a result of the reaction between the oxidizing gas and the fuel gas, electric power is generated between the cathode side separator and the anode side separator.

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples as long as they do not depart from the spirit of the present invention.

1. Raw Materials for the Anode Gas Diffusion Layer Substrate The raw materials used in the examples and comparative examples are as follows.

1-1. Carbon fiber Carbon fiber manufactured by Teijin Ltd. (fiber length: 3 mm, fiber diameter: 7 μm) was used.

1-2. Pulp fiber Pulp fiber manufactured by Toyobo Co., Ltd. (fiber length: 2 mm, freeness: 550 ml) was used.

1-3. Resin fiber Vinylon fiber (fiber length: 3 mm, fiber diameter: 11 μm) manufactured by Kuraray Co., Ltd. was used.

1-4. Graphite particles (1) Graphite particles G1
Graphite powder "CMX-40" (product name) manufactured by Nippon Graphite Industries Co., Ltd. was used. The minor axis (thickness) of the particles was 0.9 to 1.2 μm, the average particle diameter d50 measured by the laser diffraction method was 45.46 μm, and the aspect ratio was 45.9.
(2) Graphite particles G2
Graphite powder "CGB-50" (product name) manufactured by Nippon Graphite Industries Co., Ltd. was used. The particles were spherical, with a minor axis (thickness) of 30 to 50 μm, an average particle diameter d50 measured by laser diffraction method of 59.94 μm, and an aspect ratio of 1.6.

2. Production of anode gas diffusion layer substrate Anode gas diffusion layer substrate was produced using the above-mentioned production raw materials.

Example 1-1
30 parts by mass of carbon fiber, 13 parts by mass of pulp fiber, 3 parts by mass of resin fiber, and 25 parts by mass of graphite particles G1 were mixed and continuously papered using a cylinder papermaking machine to obtain a roll-shaped raw material sheet in which the carbon fiber, pulp fiber, and resin fiber were entangled and the graphite particles G1 were sandwiched in the gaps between the fibers.
The rolled sheet was then impregnated with a binder solution and dried to obtain a graphite particle-attached sheet in which the carbon fibers, pulp fibers, resin fibers and graphite particles G1 were bound by the binder. The amount of the binder attached was 25 parts by mass per 100 parts by mass of the graphite particle-attached sheet.
Thereafter, this graphite particle-attached sheet was pressed with a double belt press (pressure: 1 MPa, temperature: 250° C.) to obtain a compressed sheet having a thickness of 200 μm.
Next, this compressed sheet was heat-treated (time: 1 minute) in a graphitization furnace with an internal temperature of 2000°C and a nitrogen gas atmosphere to carbonize the binder, pulp fibers, and resin fibers, thereby obtaining a graphite particle-supported carbon fiber sheet in which graphite particles G1 were encapsulated and the resin carbide bonded the carbon fibers together. The basis weight was 70 g/ ^m2 and the thickness was about 170 μm. Hereinafter, this graphite particle-supported carbon fiber sheet is referred to as "anode gas diffusion layer substrate AS1".
A cross section of the obtained anode gas diffusion layer substrate AS1 was photographed with an electron microscope, obtaining the image shown in Fig. 4. As can be seen from Fig. 4, flake-like graphite with a large aspect ratio is filled between the carbon fibers.

Example 1-2
The same operations as in Example 1-1 were carried out except that the amounts of the carbon fibers, pulp fibers, resin fibers and graphite particles G1 used were changed to 36 parts by mass, 15 parts by mass, 3 parts by mass and 31 parts by mass, respectively, to obtain an "anode gas diffusion layer substrate AS2" having a basis weight of 85 g/m ² and a thickness of approximately 190 μm.

Comparative Example 1-1
The same procedure as in Example 1-1 was carried out except that graphite particles G2 were used instead of graphite particles G1, to obtain an "anode gas diffusion layer substrate AS3" having a basis weight of 92 g/m ² and a thickness of approximately 200 μm.
A cross section of the resulting anode gas diffusion layer substrate AS3 was photographed with an electron microscope, and the image shown in FIG. 5 was obtained.

3. Manufacture and evaluation of fuel cells The surface of the above-mentioned anode gas diffusion layer substrate AS1, AS2 or AS3 was subjected to a water repellent treatment to obtain a water repellent gas diffusion layer substrate for the anode electrode, and then a microporous layer forming paste was applied to one side of the obtained water repellent gas diffusion layer substrate for the anode electrode to produce a gas diffusion layer laminate for the anode electrode having a microporous layer (15). On the other hand, the surface of the cathode gas diffusion layer substrate CS1 was subjected to a water repellent treatment, and then a microporous layer forming paste was applied to one side of the obtained gas diffusion layer substrate for the anode electrode to produce a gas diffusion layer laminate for the cathode electrode having a microporous layer (25). Thereafter, a membrane/electrode assembly (100) shown in FIG. 3 was produced using these gas diffusion layer laminates and a fuel cell electrode membrane having catalyst layers (40, 50) made of 50 mass % Pt/C and having a Pt loading of 0.5 mg/ ^cm2 on both sides of an electrolyte layer (30) made of a Nafion (registered trademark) series electrolyte membrane "NRE-212" (product name). This membrane/electrode assembly (100) sequentially comprises an anode gas diffusion layer (10) derived from a water-repellent gas diffusion layer substrate for an anode that has been subjected to a water-repellent treatment, a microporous layer (15), a catalyst layer (40), an electrolyte layer (30), a catalyst layer (50), a microporous layer (25), and a cathode gas diffusion layer (20).
Next, a JARI standard cell was produced using this membrane/electrode assembly (100) together with a separator, a current collector, etc., and this was assembled into a single cell for fuel cell evaluation, and the power generation performance was evaluated.

Example 2-1
(1) Manufacture of anode gas diffusion layer laminate A 40 μm thick polyethylene film was placed on both sides of the anode gas diffusion layer substrate AS1, and the film laminate was pressed at a surface pressure of 1.5 MPa to remove free fluff from the carbon fibers. Next, this film laminate was impregnated with Daikin's PTFE dispersion and subjected to heat treatment (temperature: 200° C., pass time: 5 minutes) to obtain a water-repellent anode gas diffusion layer substrate in which 0.5 parts by mass of PTFE was spread on 100 parts by mass of the anode gas diffusion layer substrate AS1.
Thereafter, a paste for forming a microporous layer containing carbon black, fluororesin and water was applied to one side of the water-repellent gas diffusion layer substrate for the anode electrode, and heat treatment was performed (temperature: 320°C, pass time: 5 minutes) to obtain a gas diffusion layer laminate AB1 for the anode electrode in which 3 parts by mass of the microporous layer was spread per 100 parts by mass of the water-repellent gas diffusion layer substrate for the anode electrode.

(2) Production of gas diffusion layer laminate for cathode 28 parts by mass of carbon fiber, 10 parts by mass of pulp fiber, 2 parts by mass of resin fiber, and 10 parts by mass of graphite particles G2 were mixed and continuously papered using a cylinder paper machine to obtain a roll-shaped raw material sheet in which the carbon fiber, pulp fiber, and resin fiber were entangled with each other and graphite particles were interposed in the gaps between the fibers.
The rolled sheet was then impregnated with a binder solution and dried to obtain a graphite particle-attached sheet in which the carbon fibers, pulp fibers, resin fibers and graphite particles G2 were bound by the binder. The amount of the binder attached was 25 parts by mass per 100 parts by mass of the graphite particle-attached sheet.
Thereafter, this graphite particle-attached sheet was pressed with a double belt press (pressure: 1 MPa, temperature: 250° C.) to obtain a compressed sheet having a thickness of 200 μm.
Next, this compressed sheet was heat-treated (time: 1 minute) in a graphitization furnace with an internal temperature of 2000°C and a nitrogen gas atmosphere to carbonize the binder, pulp fibers, and resin fibers, thereby obtaining a graphite particle-supported carbon fiber sheet in which graphite particles G1 were encapsulated and the resin carbide bonded the carbon fibers together. The basis weight was 50 g/ ^m2 and the thickness was about 150 μm. Hereinafter, this graphite particle-supported carbon fiber sheet is referred to as "cathode gas diffusion layer substrate CS1".
Thereafter, in the same manner as for the anode gas diffusion layer substrate AS1, the cathode gas diffusion layer substrate CS1 was subjected to a water repellent treatment, and then a microporous layer was formed on one surface thereof to obtain a cathode gas diffusion layer laminate CB1.

(3) Production and Evaluation of Fuel Cell An anode gas diffusion layer substrate AS1 was abutted against one side of the fuel cell electrode membrane so that the microporous layer of the anode gas diffusion layer substrate AS1 faced, and a cathode gas diffusion layer substrate CS1 was abutted against the other side of the fuel cell electrode membrane so that the microporous layer of the cathode gas diffusion layer substrate CS1 faced, and these were stacked and pressed (pressure: 1 MPa, temperature: 100° C.) using a double belt press device to obtain a membrane/electrode assembly (MEA) 100 having a thickness of 360 μm (see FIG. 3 ).
Next, a JARI standard cell was produced using this membrane/electrode assembly 100, a serpentine separator with one flow channel having a flow channel width of 1.0 mm, a rib width of 1.0 mm, and a groove depth of 1.0 mm, and a current collector plate, and this was incorporated into a single cell for fuel cell evaluation, and power generation performance evaluation (cell voltage measurement) was performed under conditions of a current density of 1.0 A/cm ² , a cell temperature of 80° C., an anode side dew point temperature of 77° C., and a cathode side dew point temperature of 60° C. The results are shown in Table 1.

Example 2-2
An anode gas diffusion layer laminate AB2 was produced in the same manner as in Example 2-1, except that an anode gas diffusion layer substrate AS2 was used instead of an anode gas diffusion layer substrate AS1. A JARI standard cell and a single cell for fuel cell evaluation were then produced in the same manner as in Example 2-1, using this anode gas diffusion layer laminate AB2 together with the cathode gas diffusion layer substrate CS1 in Example 2-1, and the power generation performance was evaluated (see Table 1).

Comparative Example 2-1
An anode gas diffusion layer laminate AB3 was produced in the same manner as in Example 2-1, except that an anode gas diffusion layer substrate AS3 was used instead of an anode gas diffusion layer substrate AS1. A JARI standard cell and a single cell for fuel cell evaluation were then produced in the same manner as in Example 2-1 using this anode gas diffusion layer laminate AB3 together with the cathode gas diffusion layer substrate CS1 in Example 2-1, and the power generation performance was evaluated (see Table 1).

Examples 2-1 and 2-2 are examples in which an anode gas diffusion layer substrate containing graphite particles according to the present invention was used. Compared to Comparative Example 2-1, which used an anode gas diffusion layer substrate containing graphite particles with an aspect ratio of less than 2, a higher cell voltage was obtained and the resistance values in the thickness direction and surface direction were reduced. From these results, it can be seen that the anode gas diffusion layer substrate of the present invention is suitable for manufacturing a fuel cell that combines gas diffusibility and electrical conductivity, efficiently discharges water generated during power generation to the outside of the system, and suppresses deterioration of power generation performance.

The present invention is not limited to the specific examples shown above, and various modifications may be made within the scope of the present invention depending on the purpose and application.

The anode gas diffusion layer substrate of the present invention is suitable as a material for forming an anode gas diffusion layer constituting a membrane/electrode assembly included in a fuel cell. Therefore, a fuel cell including such an anode gas diffusion layer has high power generation performance and can be used as a fuel cell for transportation such as a vehicle, a stationary fuel cell, etc.
The anode gas diffusion layer substrate of the present invention can also be used for electromagnetic shielding materials, conductive sheets, carbonaceous cushioning materials, furnace wall insulating materials for high-temperature vacuum furnaces, and the like.

1: Anode gas diffusion layer substrate 3: Carbon fiber 5: (rod-shaped) graphite particles 7: (spherical) graphite particles 10: Anode gas diffusion layer 15: Microporous layer 20: Cathode gas diffusion layer 25: Microporous layer 30: Electrolyte layer 40: Catalyst layer 50: Catalyst layer 100: Membrane/electrode assembly

Claims (5)

(A) carbon fibers;
(B) graphite particles;
A gas diffusion layer substrate for an anode electrode of a fuel cell, comprising:
The graphite particles (B) include rod-shaped graphite particles ( _B1 ) having a ratio Dr (= _dL / _dS ) of the major axis _dL to the minor axis dS of 20 to 100, where dL is a major axis and _dS is a minor _axis . The anode gas diffusion layer substrate according to claim 1, wherein the graphite particles (B1) have an average particle diameter d50 of 20 to 80 μm as measured by a laser diffraction method. The anode gas diffusion layer substrate according to claim 1 or 2, wherein the content of the graphite particles (B) is 70 to 90 parts by mass when the content of the carbon fibers (A) is 100 parts by mass. The gas diffusion layer substrate for an anode according to any one of claims 1 to 3, having a basis weight of 40 to 100 g/ ^m2 . The gas diffusion layer substrate for an anode electrode according to any one of claims 1 to 4, the surface of which has been treated to be water repellent.

Images