JP2024038589A - Gas diffusion layer base material for fuel cell and manufacturing method of the same - Google Patents

Abstract

To provide a manufacturing method of a gas diffusion layer base material which achieves both gas diffusion property and conductivity, is used for formation of a gas diffusion layer of a fuel cell, and gives a fuel cell having high power generation performance.SOLUTION: A manufacturing method of a gas diffusion layer base material for a fuel cell includes: a step of using a first slurry and a second slurry containing carbon fibers, graphite particles, organic fibers and water, and manufacturing a first hydrous sheet in which the carbon fibers and the organic fibers are oriented in a direction approximately parallel to its surface extension direction using the first slurry and the graphite particles are interposed between the fibers; a step of supplying the second slurry to the surface of the first hydrous sheet, forming a layer in which the fibers are randomly oriented in a three-dimensional direction, and the graphite particles are interposed between the fibers, and manufacturing a hydrous laminated sheet; a step of squeezing and drying the hydrous laminated sheet, and manufacturing a composite sheet; a step of impregnating the composite sheet with a carbon precursor resin, and manufacturing a resin-impregnated sheet; and a step of heating, baking and carbonizing the resin-impregnated sheet.SELECTED DRAWING: Figure 1

Description

The present invention relates to a gas diffusion layer base material used for forming a gas diffusion layer of a fuel cell and a method for manufacturing the same.

Polymer electrolyte fuel cells (hereinafter simply referred to as "fuel cells"), which are widely used as a power source for automobiles, are constructed by stacking multiple fuel cells with separators in between. is a polymer electrolyte membrane that selectively transmits specific ions, with a catalyst layer made of a conductive material such as carbon and an ion exchange resin supporting a catalyst such as platinum on both sides, and a porous membrane placed on the outside of each catalyst layer. A cathode (+) side electrode and an anode (-) side electrode constituted by a gas diffusion layer are arranged to form a membrane/electrode assembly. Then, on the outside of the gas diffusion layer that constitutes this membrane/electrode assembly, a gas flow path is formed to supply fuel gas (anode gas) or oxidizing gas (cathode gas) and to discharge generated gas and excess gas. 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 improve the diffusivity of the reactant gas. Since it plays the role of diffusing the fuel gas or oxidizing gas supplied from the gas flow path of the separator into the catalyst layer adjacent to the gas diffusion layer (gas diffusivity), it not only improves gas permeability but also improves the electrochemical reaction. It has conductivity as a current collector to efficiently move electrons. In addition, while the gas diffusion layer always keeps the polymer electrolyte membrane and catalyst layer in an optimally moist state, the gas diffusion layer of the cathode is particularly prone to flooding phenomenon (a phenomenon in which the pores of the gas diffusion layer are clogged with water). ) and stabilize power generation performance, water repellency (drainage properties) is required to drain excess reaction product water and condensation water generated by the electrochemical reaction of hydrogen and oxygen during power generation. .

Conventionally, as a base material for forming a gas diffusion layer, a base material containing carbon fiber, which is a conductive fiber, and a method for manufacturing the same have been known.

For example, Patent Document 1 describes a carbon fiber layer formed on one side and containing carbon fibers, and an activated carbon fiber layer formed on the other side and containing more activated carbon fibers than the carbon fiber layer. A carbon fiber porous sheet characterized by laminating a carbon fiber sheet is disclosed, and as a method for producing such a carbon fiber porous sheet, a carbon fiber porous sheet containing carbon fibers and a binder and sufficiently dispersing the carbon fibers is disclosed. A slurry of carbon fibers, activated carbon fibers with a larger surface area than the carbon fibers, and a slurry of activated carbon fibers containing a binder and sufficiently dispersed in the activated carbon fibers are prepared, and the activated carbon fibers are placed one after another on a paper screen. , by supplying and drawing out at least a carbon fiber slurry and an activated carbon fiber slurry, a carbon fiber layer is formed on one side of the sheet, and the other side contains more activated carbon fiber than the carbon fiber layer. A method for manufacturing a carbon fiber porous sheet is disclosed, which is characterized in that the carbon fiber porous sheet is manufactured by forming an activated carbon fiber layer and laminating a plurality of layers.
Patent Document 2 describes a porous carbon sheet containing carbon fibers and a binding material, in which the carbon sheet is divided into six equal parts in the thickness direction under compression in the section from one surface to the other surface. When the resulting layers are layer 1, layer 2, layer 3, layer 4, layer 5, and layer 6 in order from the layer containing one surface to the layer containing the other surface, the packing ratio under compression is the highest. The largest layer is layer 2, and the relationship between the filling rates under compression of layer 2, layer 3, layer 4, layer 5, and layer 6 is such that the filling rate of layer 2 is the largest, and the filling rate of layer 3 is the second. A large carbon sheet is disclosed. After producing a carbon fiber paper body which is a porous body, such a carbon sheet is further coated with a resin composition serving as a binder such that the amount of the resin composition is the largest in layer 2. It is described that among layer 3, layer 4, layer 5, and layer 6, layer 3 is impregnated in the second largest amount, and then it can be manufactured by drying and heat treatment (carbonization).

Patent Document 3 discloses a single porous carbon sheet in which dispersed short carbon fibers are bound together with a resin carbide, and this sheet is composed of at least two or more layers having different pore mode diameters. Porous carbon characterized in that 1.2≦D1/D2≦4, where D1 is the pore mode diameter of the layer with the largest mode diameter, and D2 is the pore mode diameter of the layer with the smallest mode diameter. A sheet is disclosed, and a method for manufacturing such a porous carbon sheet includes a compression step of heating and pressurizing a precursor fiber sheet containing short carbon fibers and a thermosetting resin, and a precursor fiber sheet that has undergone the compression step. In the compression process, the precursor fiber sheet is heated and pressurized in the first step, and then heated in the first step as the second step. A method for manufacturing a porous carbon sheet is disclosed, which comprises laminating a pressure-treated precursor fiber sheet and a precursor fiber sheet before being subjected to heat and pressure treatment, and further heat and pressure treatment.
Furthermore, Patent Document 4 discloses that carbon fibers are made of a carbon fiber aggregate in which carbon fibers are intertwined with each other, and a carbide that binds the carbon fibers of this carbon fiber aggregate, and a medium that is held between the carbon fibers of the carbon fiber aggregate. A porous gas diffusion layer base material containing spherical graphite and/or artificial graphite having a diameter within the range of 40 μm to 120 μm is disclosed, and as a method for manufacturing such a gas diffusion layer base material, , an aggregate is formed by paper-making a base carbon fiber, an organic fiber that is burnt out in a subsequent heat treatment, and spherical graphite and/or artificial graphite whose median diameter is within the range of 40 μm to 120 μm. a resin impregnation step in which the aggregate formed in the paper making process is impregnated with a carbon precursor resin; a drying step in which the aggregate impregnated with the carbon precursor resin is dried; A method for manufacturing a gas diffusion layer base material is disclosed, which includes a carbonization/graphitization step of heating and firing an aggregate in a non-oxidizing atmosphere.

Japanese Patent Application Publication No. 2004-238759 WO2017/69014 publication JP2009-234851A JP2020-87826A

An object of the present invention is to provide a method for manufacturing a gas diffusion layer base material used for forming a gas diffusion layer of a fuel cell, which has both gas diffusivity and electrical conductivity, and provides a gas diffusion layer base material that provides a fuel cell with high power generation performance. An object of the present invention is to provide a diffusion layer base material and a method for manufacturing the same.

The present inventors produced a laminate of graphite particle-containing fiber sheet layers (water-containing laminate sheet) so that the orientation of the fibers in each layer was different from each other, and dried this to create a composite sheet containing a carbon precursor. It has been found that the gas diffusion layer base material obtained is suitable for forming a gas diffusion layer of a fuel cell by impregnating it with a body resin and then carbonizing it, and that it solves the above problems.

The invention is illustrated below.
[1] A first water-containing sheet is produced using a first slurry containing carbon fibers (A1), graphite particles (B1), organic fibers (C1) to be carbonized in a subsequent carbonization step, and water. A first water-containing sheet production step,
Supplying a second slurry containing carbon fibers (A2), graphite particles (B2), organic fibers (C2) to be carbonized in a subsequent carbonization step, and water to the surface of the first water-containing sheet, A water-containing laminate sheet production step of producing a water-containing laminate sheet comprising a first layer derived from the first water-containing sheet, and a second layer derived from the second slurry disposed on the surface of the first layer;
A composite sheet production step of producing a composite sheet by squeezing and drying the water-containing laminated sheet;
a resin impregnation step of producing a resin-impregnated sheet by impregnating the composite sheet with a carbon precursor resin that will be carbonized in a subsequent carbonization step;
sequentially comprising a carbonization step of heating and baking the resin-impregnated sheet in a non-oxidizing atmosphere;
The first water-containing sheet has the carbon fibers (A1) and the organic fibers (C1) oriented in a direction substantially parallel to the surface stretching direction of the first water-containing sheet, and the graphite particles (B1) is a sheet interposed between fibers,
The second layer is a layer in which the carbon fibers (A2) and the organic fibers (C2) are randomly oriented in a three-dimensional direction, and the graphite particles (B2) are interposed between the fibers. A method for manufacturing a gas diffusion layer base material for fuel cells.
[2] The method for producing a gas diffusion layer substrate for a fuel cell according to item [1] above, wherein a short wire paper machine or a Fourdrinier paper machine is used in the first water-containing sheet production step.
[3] The method for producing a gas diffusion layer base material for a fuel cell according to item [1] or [2] above, wherein a cylinder paper machine is used in the step of producing the water-containing laminate sheet.
[4] Production of the gas diffusion layer base material for fuel cells according to item [1] above, wherein the mass ratio (B1/B2) of the graphite particles (B1) and the graphite particles (B2) is 1.2 or more. Method.
[5] A gas diffusion layer base material for a fuel cell obtained by the method for manufacturing a gas diffusion layer base material for a fuel cell as described in the above item [1].

According to the method for manufacturing a gas diffusion layer base material for a fuel cell of the present invention, it is possible to efficiently manufacture a gas diffusion layer base material that provides a fuel cell that has both gas diffusivity and conductivity and has high power generation performance. In particular, in the water-containing laminate sheet obtained in the water-containing laminate sheet manufacturing process, the carbon fibers (A1) and the organic fibers (C1) are oriented in a direction substantially parallel to the surface stretching direction, and the graphite particles (B1 ) is applied between the fibers, and the second slurry is applied to the surface of the first water-containing sheet in which the carbon fibers (A2) and the organic fibers (C2) are randomly oriented in a three-dimensional direction, and the graphite particles (B2) are Since the fibers are laminated so as to be interposed between the fibers, the intertwining of the fibers at the interface between the first layer and the second layer is sufficient, and the inside of the gas diffusion layer base material obtained after the carbonization process is can be made dense. Furthermore, if the production of a water-containing laminated sheet, composite sheet production, resin-impregnated sheet production, and carbonization are performed continuously using a paper machine, the gas diffusion layer base material for fuel cells can be produced in roll form; For example, by reducing the ratio (T1/T2) of the tensile strength T1 in the direction (MD) to the tensile strength T2 in the direction (TD) perpendicular thereto to 2.0 or less, cracks etc. during roll-to-roll conveyance can be prevented. can be suppressed.
A fuel cell manufactured using the gas diffusion layer base material for fuel cells obtained according to the present invention as a gas diffusion layer base material for a cathode electrode can be used for transportation fuel cells such as vehicles, stationary fuel cells, etc. Can be done.

1 is a schematic cross-sectional view of a gas diffusion layer base material for fuel cells obtained according to the present invention. FIG. 2 is an explanatory diagram showing the regions where the material occupancy rate (excluding voids) is measured when the gas diffusion layer base material for fuel cells obtained in [Example] is divided into three equal parts in the thickness direction; It is a figure which shows the 1st area|region F, the 2nd area|region S, and the 3rd area|region T set from the 1st layer originating in the 1st water-containing sheet. 1 is a schematic cross-sectional view of a membrane/electrode assembly produced using a gas diffusion layer base material for fuel cells obtained according to the present invention.

The method for producing a gas diffusion layer substrate for fuel cells of the present invention sequentially includes a first water-containing sheet production process, a water-containing laminated sheet production process, a composite sheet production process, a resin impregnation process, and a carbonization process. Note that the method for producing a gas diffusion layer base material for a fuel cell of the present invention may further include other steps (described later), if necessary.
In the method for producing a gas diffusion layer substrate for fuel cells of the present invention, the water-containing laminate sheet obtained in the water-containing laminate sheet production step is characterized by the orientation of the fibers (carbon fibers and organic fibers) in the first layer and the orientation of the fibers ( Although the orientation of the fibers (carbon fibers and organic fibers) is different, in the gas diffusion layer base material finally obtained through subsequent steps, it is not possible to confirm the difference in fiber orientation using an electron microscope, etc. Battery performance can be obtained. Even in the case of a conventionally known production method in which a graphite particle-containing fiber aggregate is produced without considering the orientation tendency of the fibers, and then impregnated with resin, carbonized, etc., the resulting gas diffusion layer base material naturally has 1 Although there is no difference in fiber orientation between the one side and the other side, the battery performance is inferior to the case where the gas diffusion layer base material obtained according to the present invention is used.

FIG. 1 is a schematic cross-sectional view showing an example of a gas diffusion layer base material 1 for fuel cells obtained according to the present invention, and this gas diffusion layer base material 1 for fuel cells has a plurality of carbon fibers 2 (carbon (derived from graphite particles (A1) and carbon fibers (A2)), a plurality of graphite particles 4 (derived from graphite particles (B1) and graphite particles (B2)), and organic matter contained in the first slurry through the carbonization process. The fiber (C1), the organic fiber (C2) contained in the second slurry, and the carbonized portion 6 formed by carbonizing the carbon precursor resin contained in the first slurry and the second slurry are included. The carbonized portion 6 in FIG. 1 does not indicate that it is filled with carbide, but the carbide binds graphite particles to each other or carbon fibers and graphite particles. It has a void inside it to the extent that it has air permeability from one side to the other side.
The gas diffusion layer base material 1 for fuel cells of the present invention is a water-containing laminate sheet including a first layer derived from fibers contained in a first slurry and a second layer derived from fibers contained in a second slurry. This is an article consisting of layer 8 and layer 9, which is obtained by impregnating a composite sheet, which is a dried product of carbon precursor resin, with a carbon precursor resin and then heating and baking it (see FIG. 1). As mentioned above, it is difficult to confirm the orientation difference of fibers in each layer using an electron microscope or the like, and it is also usually impossible to confirm the interface between layers 8 and 9.

The gas diffusion layer base material for fuel cells obtained by the present invention is a sheet-like (thin plate-like) material used in the production of fuel cells, and is used, for example, as a cathode electrode in the membrane/electrode assembly 10 shown in FIG. It can be used to form the gas diffusion layer 11. A particularly preferred embodiment of the membrane/electrode assembly 10 includes a cathode gas diffusion layer 11, a microporous layer 13, a catalyst layer 15, an electrolyte layer 31, a catalyst layer 25, a microporous layer 23, and an anode gas diffusion layer 21. , the gas diffusion layer 11 for the cathode electrode is prepared such that the first surface 1a (the surface on the layer 8 side derived from the first slurry) of the gas diffusion layer base material 1 for a fuel cell shown in FIG. They are joined so that they face each other.

First, the first slurry used in the first water-containing sheet production process and the second slurry used in the water-containing laminate sheet production process will be described.
The first slurry contains carbon fibers (A1), graphite particles (B1), organic fibers (C1), and water. Moreover, the second slurry contains carbon fibers (A2), graphite particles (B2), organic fibers (C2), and water. The first slurry and the second slurry may contain other components.

The configurations (type, size, etc.) of the carbon fibers (A1) and the carbon fibers (A2) may be the same or different. These carbon fibers include vapor-grown carbon fibers, carbon nanotubes (single wall, double wall, multi-wall, cup laminated type, etc.), polyacrylonitrile (PAN) carbon fibers, pitch carbon fibers, and rayon carbon fibers. But that's fine. The carbon fibers contained in the carbon fibers (A1) and the carbon fibers contained in the carbon fibers (A2) may each be of one type or two or more types.

The average fiber diameter of the carbon fibers is preferably 5 to 15 μm, more preferably 6 to 8 μm, from the viewpoint of gas diffusion and drainage properties of the gas diffusion layer to be formed.
Regarding the fiber length of carbon fiber, the upper limit is usually 12 mm, and the lower limit is usually 2 mm. Further, the average fiber length of the carbon fibers is preferably 2 to 9 mm, more preferably 3 to 6 mm, from the viewpoint of gas diffusivity and drainage performance of the gas diffusion layer to be formed.

The structures (type, size, etc.) of the graphite particles (B1) and the graphite particles (B2) may be the same or different from each other. These graphite particles may be either natural graphite or artificial graphite. The number of graphite particles contained in the graphite particles (B1) and the graphite particles contained in the graphite particles (B2) may be one type or two or more types.
The shape of the graphite particles is not particularly limited, and may be spherical, ellipsoidal, plate-like, linear, amorphous, or the like. Further, the graphite particles may be aggregates of primary particles.

When the graphite particles are spherical, the particle diameter measured by the laser diffraction/scattering method is preferably 10 to 200 μm, more preferably 30 to 70 μm, from the viewpoint of the gas diffusion and drainage properties of the gas diffusion layer formed.

The organic fiber (C1) and the organic fiber (C2) may have the same structure or different structures. Any of these organic fibers may be carbonized in the subsequent carbonization step, and resin fibers (polylactic acid, polyvinyl alcohol, polyolefin, polyurethane, polyester, polyamide, acrylic resin, aramid, polyacetal, phenolic resin, Examples include those derived from cellulose, etc.), vegetable fibers (derived from wood, cotton, bamboo, hemp, etc.), and animal fibers (derived from wool, etc.). Among these, it is preferable to include resin fibers. In addition, when organic fibers are used, when manufacturing the first water-containing sheet in the first water-containing sheet production process using the first slurry, and during the production of the water-containing laminated sheet in the water-containing laminated sheet production process using the second slurry, carbon Entanglement can be improved by fixing fibers, graphite particles, or carbon fibers and graphite particles. In addition, in the carbonization process, when the resin-impregnated sheet is heated and fired, the formed carbide binds carbon fibers, graphite particles, or carbon fibers and graphite particles, while the burnt residue remains behind gas and The pores (pores, pores) allow moisture to pass through, and a gas diffusion layer base material having a suitable structure can be obtained.

In the present invention, in the composite sheet manufacturing process, organic fibers (C1) and organic The fibers (C2) preferably contain both resin fibers made of a low-melting point resin (low-melting point resin fibers) and resin fibers made of a high-melting point resin having a higher melting point (high-melting point resin fibers). In this case, the melting point of the low melting point resin is lower than the temperature at which the water-containing laminated sheet is squeezed and dried in the composite sheet manufacturing process (hereinafter referred to as "drying temperature"), and the melting point of the high melting point resin is It is particularly preferred that the temperature is higher than that. In the present invention, polyvinyl alcohol, which has excellent adhesiveness to carbon fibers and graphite particles, is preferred as the low melting point resin. Further, as the high melting point resin, acrylic resin is preferable.
The resin fibers may be monofilament, multifilament, or fibril fibers. For example, as the acrylic resin fiber, fibrillar fiber called "acrylic pulp fiber", which is obtained by beating acrylic fiber into a pulp form, can be used.

The average fiber diameter of the organic fibers is preferably 5 to 20 μm, more preferably 6 to 8 μm, from the viewpoint of mechanical strength of the obtained water-containing laminate sheet.
Regarding the fiber length of the organic fiber, the upper limit is usually 15 mm, and the lower limit is usually 1 mm. Further, the average fiber length of the organic fiber is preferably 1 to 10 mm, more preferably 1 to 5 mm.

As described above, in a preferred embodiment, the organic fibers (C1) and the organic fibers (C2) both contain low melting point resin fibers and high melting point resin fibers in the first slurry and the second slurry. The content ratio of the low melting point resin fiber and the high melting point resin fiber in the first slurry is preferably 15 to 32% by mass and 68 to 85% by mass, more preferably 18% by mass, respectively, when the total of both is 100% by mass. -29% by weight and 71-82% by weight. Further, the content ratio of the low melting point resin fiber and the high melting point resin fiber in the second slurry is preferably 12 to 25% by mass and 75 to 88% by mass, more preferably 75 to 88% by mass, respectively, when the total of both is 100% by mass. are 14-20% by weight and 80-86% by weight.

As mentioned above, the first slurry and second slurry according to the present invention can contain other components. Other components include binders, carbides of organic materials, additives (flocculants, viscosity modifiers, surfactants, etc.), and the like.

Examples of binders include polyolefins such as polyvinyl alcohol, polyvinyl acetate, polyethylene, and polypropylene, polyesters such as polyethylene terephthalate, polyacrylonitrile, cellulose, polyethylene oxide, polyacrylamide, phenol resin, xylenol resin, styrene-butadiene rubber, starch, corn starch, etc. It can be derived from.

A preferred first slurry in the present invention contains carbon fibers (A1), graphite particles (B1), organic fibers (C1) consisting of low melting point resin fibers and high melting point resin fibers, and water. The content ratio of graphite particles (B1) is preferably 10 to 150 parts by mass, more preferably 30 to 90 parts by mass, when the content of carbon fibers (A1) is 100 parts by mass. The content ratio of the organic fiber (C1) is preferably 4 to 40 parts by mass, more preferably 8 to 24 parts by mass, when the content of carbon fiber (A1) is 100 parts by mass. The content ratio of water is usually such that the total content ratio of carbon fibers (A1), graphite particles (B1) and organic fibers (C1) is preferably 0.001 to 2% with respect to the total amount of the first slurry, More preferably, it is adjusted to 0.01 to 0.1%.

Further, the second slurry preferable in the present invention contains carbon fibers (A2), graphite particles (B2), organic fibers (C2) consisting of low melting point resin fibers and high melting point resin fibers, and water. The content ratio of graphite particles (B2) is preferably 10 to 50 parts by mass, more preferably 10 to 20 parts by mass, when the content of carbon fiber (A2) is 100 parts by mass. The content ratio of the organic fiber (C2) is preferably 4 to 40 parts by mass, more preferably 8 to 24 parts by mass, when the content of carbon fiber (A2) is 100 parts by mass. The water content is usually such that the total content of carbon fibers (A2), graphite particles (B2), and organic fibers (C2) is preferably 0.001 to 2% with respect to the total amount of the second slurry. More preferably, it is adjusted to 0.01 to 0.1%.

The method for preparing the first slurry and the second slurry is not particularly limited, and may be, for example, a method of mixing raw materials using a rotary device such as a pulper.

In the first water-containing sheet production step, carbon fibers (A1) and organic fibers (C1) are oriented in a direction substantially parallel to their surface stretching direction, and graphite particles (B1) are interposed between the fibers. This is a step of producing a sheet (first water-containing sheet). In the present invention, since continuous mass production of the gas diffusion layer base material is possible, a short wire paper machine or a Fourdrinier paper machine (hereinafter, these may be collectively referred to as "first paper machine") It is preferable to use the first slurry for paper making.
As both the short wire paper machine and the fourdrinier paper machine, conventionally known paper machines can be used. Paper-making conditions are not particularly limited, but the thickness when bone dry is preferably 100 to 400 μm, more preferably 200 to 300 μm, or the basis weight when bone dry is preferably 10 to 100 g/m. ² , more preferably 30 to 60 g/m ² , the first water-containing sheet is produced.

When using a short wire paper machine, the paper making speed is preferably 4 to 40 m/min, more preferably 7 to 24 m/min.
When using a fourdrinier paper machine, the paper making speed is preferably 4 to 40 m/min, more preferably 7 to 24 m/min.

The first water-containing sheet obtained in the first water-containing sheet manufacturing step is a hydrated fiber aggregate containing graphite particles, and the carbon fibers (A1) and organic fibers (C1) are distributed in the thickness direction of the first water-containing sheet. The sheet is oriented in all directions, almost perpendicular to the fibers, and has graphite particles (B1) interposed between the fibers.
In addition, the first water-containing sheet is used in the subsequent water-containing laminated sheet production process, and the first water-containing sheet obtained in the first water-containing sheet production process can be used as it is, but the thickness of the sheet may be adjusted. , a water-containing sheet obtained by processing using a press roll or the like may be used for moisture adjustment and the like.

The step of producing a water-containing laminated sheet is a step of supplying the second slurry to the surface of the first water-containing sheet to form a second layer on the surface of the first layer originating from the first water-containing sheet, thereby producing a water-containing laminated sheet. It is. In the present invention, when the first paper machine is used in the first water-containing sheet production process, it is possible to continuously mass-produce the gas diffusion layer base material. It is preferable to form the second slurry on the surface of the first water-containing sheet.
As the cylinder paper machine, a conventionally known paper machine can be used. Paper-making conditions are not particularly limited, but the absolute dry thickness (total thickness) is preferably 100 to 400 μm, more preferably 200 to 300 μm, or when the water-containing laminated sheet is in an absolutely dry state. The water-containing laminated sheet is prepared so that the basis weight is preferably 10 to 100 g/m ² , more preferably 30 to 60 g/m ² . The papermaking speed in this case is preferably 4 to 40 m/min, more preferably 7 to 24 m/min.

The first slurry and the second slurry are used before producing the water-containing laminate sheet, but in the water-containing laminate sheet, the content of graphite particles (B1) in the first layer, which originates from the first slurry, and the content of graphite particles (B1), which originates from the second slurry, The ratio (B1/B2) to the content of graphite particles (B2) in the second layer is preferably 1.0 or more, more preferably 1.2 or more, still more preferably 1.2 to 2.0, Particularly preferably, the first slurry and the second slurry are used so that the ratio is 1.2 to 1.6.

The water-containing laminated sheet obtained in the water-containing laminated sheet manufacturing process includes a first layer containing graphite particles (B1) and having a low fiber orientation, and a first layer containing graphite particles (B2) and having a low fiber orientation compared to the first layer. It is a hydrated product of a laminate consisting of a second layer with high properties. When using a cylinder paper machine, it is possible to form a second layer that has excellent entanglement with the fibers constituting the first layer at the interface with the first layer while suppressing delamination from the first layer. can.

In the present invention, after the step of producing a water-containing laminate sheet, the obtained water-containing laminate sheet can be subjected to an entanglement treatment, if necessary. Examples of the entangling method include a mechanical entangling method (needle punching method, etc.), a high pressure liquid injection method (water jet punching method, etc.), a high pressure gas injection method (steam jet punching method, etc.).

Next, in the composite sheet production step, the water-containing laminated sheet is squeezed and dried to produce a composite sheet. The method for squeezing and drying the water-containing laminate sheet is not particularly limited. Water extraction can be performed using a suction box that sucks water, a press roll that compresses and dewaters, or the like. Thereafter, a dried composite sheet can be obtained by transferring the water-squeezed sheet to, for example, a drum-shaped Yankee dryer with a mirror-finished surface and heating it. Note that depending on the shape, size, etc. of the sheet, it may be dried under reduced pressure conditions. The lower limit of the drying temperature is preferably 70°C, more preferably 90°C, and the upper limit is usually 160°C. When the organic fibers contained in the water-containing laminate sheet include the above-mentioned high-melting point resin fibers and low-melting point resin fibers, preferably, only the low-melting point resin fibers are melted at the above drying temperature, and the carbon fibers, graphite particles, and high-melting point resin fibers are melted at the above-mentioned drying temperature. A composite sheet formed by binding melting point resin fibers can be obtained.
In the case of a completely dry composite sheet, the basis weight is preferably 20 to 150 g/m ² and the thickness is preferably 200 to 600 μm.

If the entangling treatment is not performed after the step of producing a water-containing laminated sheet, the resulting composite sheet can be subjected to an entanglement treatment, if necessary, after the step of producing the composite sheet.

Since there are many types of fibers contained in a composite sheet and their lengths also vary, the fibers may protrude from the surface of the composite sheet after drying, that is, become fluffy, and the surface of the composite sheet may not be smooth. In the subsequent resin impregnation step, a smooth surface can be formed by embedding with a carbon precursor resin, but as another method, before the resin impregnation step, a smooth surface can be formed by A process of cutting or removing the fibers, or a process of pushing the fibers into the interior of the composite sheet may be performed.

Thereafter, in the resin impregnation step, the composite sheet is impregnated with a carbon precursor resin that can be carbonized in the carbonization step to produce a resin-impregnated sheet.
The carbon precursor resin is not particularly limited, but since it has excellent wettability with carbon fibers or organic fibers and easily forms conductive carbide in the subsequent carbonization process, it may include phenol resin, furan resin, epoxy resin, melamine resin, Thermosetting resins such as imide resins, urethane resins, aramid resins, urea resins, and unsaturated polyester resins are preferred. Among these, phenol resin is particularly preferred because it has a high carbonization rate and becomes an excellent conductive material after carbonization.
In the resin impregnation process, the carbon precursor resin can be used as it is depending on its properties, but since the composite sheet is a fiber aggregate containing graphite particles, the entire void between the fibers is filled with the carbon precursor resin. In order to sufficiently impregnate the resin while filling the resin, it is preferable to use a liquid containing a carbon precursor resin (hereinafter referred to as a "carbon precursor resin-containing liquid"). This carbon precursor resin-containing liquid may be only a liquid carbon precursor resin, but preferably a solution (resin solution) in which the carbon precursor resin is dissolved in a solvent, and a solution in which the carbon precursor resin is dispersed in a dispersion medium. This is a dispersion liquid (resin dispersion liquid).

When using a carbon precursor resin-containing liquid, there are two methods: immersing the composite sheet in the carbon precursor resin-containing liquid, applying the carbon precursor resin-containing liquid to the composite sheet (kiss coating method, spray method, curtain coating method, roller contact method). Act, etc.) can be applied. Among these methods, the method of immersing the composite sheet in a carbon precursor resin-containing liquid is preferred.

The dry state of the resin-impregnated sheet heated and fired in the carbonization process is not particularly limited, so when the composite sheet is brought into contact with the carbon precursor resin-containing liquid in the resin impregnation process, hot air may be blown onto the liquid-adhering sheet, or the liquid-adhering sheet may be A non-contact drying method in which the sheet is placed in a high-temperature atmosphere or the liquid-adhered sheet is dried using an infrared heater or microwave, or a contact method in which the liquid-adhered sheet is brought into contact with a heated roll, plate, etc. A dry resin-impregnated body containing no solvent or dispersion medium can be obtained using a drying method.

Another method for impregnating a composite sheet with a carbon precursor resin without using a carbon precursor resin-containing liquid is to bring a resin film containing a carbon precursor resin into contact with at least a portion of the surface of the composite sheet, heat it, Examples include a method of dissolving the carbon precursor resin by solvent spraying or the like and allowing it to permeate the entire composite sheet.

In the obtained resin-impregnated sheet, when the total of the bone-dry composite sheet and the impregnated carbon precursor resin is 100% by mass, the content ratio of the carbon precursor resin is preferably 10 to 80% by mass, More preferably, it is 30 to 60% by mass.

In the present invention, before subjecting the resin-impregnated sheet obtained by the resin impregnation process to the carbonization process, a hydraulic press, hot press, belt press, It can be subjected to heat pressing using a roll press or the like.

The carbonization step is a step of heating and firing the resin-impregnated sheet in a non-oxidizing atmosphere. The non-oxidizing atmosphere can be an atmosphere containing an inert gas such as argon gas or helium gas, nitrogen gas, or the like.
The heating temperature of the resin-impregnated sheet is preferably 1800° C. to 2500° C., more preferably 1900° C. to 2200° C., in order to smoothly carbonize the organic fibers and carbon precursor resin without causing strength deterioration of the carbon fibers. be. In the carbonization step, a multi-stage heating method may be applied in which the resin-impregnated sheet is heat-treated at a temperature lower than the above-mentioned preferred carbonization temperature and then heated.
The heating time for the resin-impregnated sheet depends on its size, but is usually 1 minute or more.

In the carbonization process, the organic fibers originating from the composite sheet and the carbon precursor resin contained in the resin-impregnated sheet are carbonized, and the formed carbide causes carbon fibers to form together, graphite particles to form together, or carbon fibers and graphite particles to form. By binding, a gas diffusion layer base material for fuel cells can be obtained. The gas diffusion layer base material for fuel cells used for manufacturing membrane/electrode assemblies, which are manufacturing components of fuel cells, can be obtained by this carbonization process, but the surface may be smoothed as necessary. The surface may further include a smoothing process to make the surface water repellent, a water repellent process to make the surface water repellent, and the like.

In the water-repellent step, a method can be applied in which the gas diffusion layer base material is brought into contact with a solution or dispersion of a water-repellent material, and then, if necessary, heat-treated to fix the water-repellent material.
The water-repellent material is preferably a fluororesin, such as polytetrafluoroethylene (PTFE), tetrafluoroethylene/hexafluoropropylene copolymer (FEP), tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer (PFA), or tetrafluoroethylene/hexafluoropropylene copolymer (FEP). Fluoroethylene/ethylene copolymer (ETFE) or the like can be used.

The gas diffusion layer base material for fuel cells obtained according to the present invention has a strong conductive path due to the phase mainly composed of carbide (carbonized portion 6) and the carbon fibers 2 and graphite particles 4 contained in this phase. In addition, since the carbide is derived from resin, the gas diffusion layer base material has elasticity and has high dimensional absorption when joined with the electrolyte layer forming material or catalyst layer forming material during fuel cell manufacturing. Become. Further, the fuel cell gas diffusion layer base material 1 of FIG. 1 is used as a cathode gas diffusion layer base material, and the surface on the layer 8 side (first surface 1a) formed using the first slurry is made microporous. When the membrane/electrode assembly 10 shown in FIG. 3 is fabricated as the cathode gas diffusion layer 11 by joining it so as to face the layer 13, and the membrane/electrode assembly 10 shown in FIG. Water can be efficiently drained out of the system (outside the cathode gas diffusion layer 11 on the side where the microporous layer 13 is not arranged), and the deterioration in power generation performance due to flooding can be suppressed. It is expected that high power generation performance will be exhibited.

When producing a membrane/electrode assembly, the fuel cell gas diffusion layer base material of the present invention may be applied as it is to the gas diffusion layer electrode, but it is possible to form a microporous layer on one side. It is preferable to use the obtained laminate (gas diffusion layer laminate). When driving a fuel cell equipped with a membrane/electrode assembly produced using a gas diffusion layer laminate having this microporous layer, flooding caused by large water droplets produced by condensation of water vapor can be suppressed. Can be done.

The microporous layer is preferably a microporous layer containing a conductive material and a water-repellent resin and having an upper limit of thickness of 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 fluororesins are preferably used.

An anode gas diffusion layer base material (which may be made water repellent) with a microporous layer on one side, and a cathode gas diffusion layer base material (which may be water repellent) with a microporous layer on one side. The membrane/electrode junction shown in FIG. A fuel cell (single cell) can be manufactured using this membrane/electrode assembly 10 and separators (anode side and cathode side).

In a fuel cell with such a configuration, when oxidizing gas is supplied from the outside to the oxidizing gas flow path of the cathode-side separator, a portion of the oxidizing gas flowing along the oxidizing gas flow path flows into the gas diffusion layer for the cathode electrode. Infiltrate inside. Other unreacted oxidizing gas that does not enter 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-side separator, a portion of the fuel gas flowing along the fuel gas flow path enters the inside of the anode electrode gas diffusion layer. Other unreacted fuel gas that does not enter flows along the fuel gas flow path and is discharged to the outside of the fuel cell.
Then, as the oxidizing gas and the fuel gas react, electric power is extracted between the cathode-side separator and the anode-side separator.

Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples unless the gist of the present invention is exceeded.

1. Raw Materials for Manufacturing Gas Diffusion Layer Base Materials Raw materials for manufacturing gas diffusion layer base materials used in Examples and Comparative Examples are as follows.

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

1-2. Organic fiber (1) Resin fiber (high melting point resin fiber)
Acrylic pulp fibers manufactured by Toyobo Co., Ltd. (fiber length: 2 mm) were used.
(2) Resin fiber (low melting point resin fiber)
Vinylon fiber manufactured by Kuraray Co., Ltd. (fiber length: 3 mm, fiber diameter: 11 μm) was used.

1-3. Graphite particles Graphite powder "CGB-50" (trade name) manufactured by Nippon Graphite Industries Co., Ltd. was used. It is spherical and has an average particle diameter d50 of 50 μm as measured by laser diffraction.

2. Preparation of Slurry The above carbon fibers, high melting point resin fibers, low melting point resin fibers and graphite particles are mixed together with water using a pulper in the proportions shown in Table 1. Five types of slurries (S1, S2, S3, S4 and S5) in which the content ratio of graphite particles to the total graphite particles are 10% by mass, 20% by mass, 30% by mass, 40% by mass and 50% by mass, respectively. Prepared. Table 1 shows the content ratios of carbon fibers, high melting point resin fibers, low melting point resin fibers, and graphite particles contained in each slurry. Note that the ratio of the total amount of carbon fibers, high melting point resin fibers, low melting point resin fibers, and graphite particles to the entire slurry is 0.001 to 0.1% by mass.

3. Manufacture of gas diffusion layer base material A roll-shaped gas diffusion layer base material for a fuel cell was manufactured by continuous paper making using the above slurries S1 to S5.

Example 1
Slurry S3 was used as the first slurry, and slurry S1 was used as the second slurry.
First, slurry S3 (first slurry) was made into paper using a short wire paper machine to obtain a first water-containing sheet. At this time, the paper making speed was set to 7 m/min so that the thickness of the first water-containing sheet was about 250 μm and the basis weight when completely dry was about 24 g/m ² . Then, while the first water-containing sheet is in a conveying state, paper making is performed using a cylinder paper machine while supplying slurry S1 (second slurry) to the surface of the first water-containing sheet. A water-containing laminated sheet consisting of one layer and a second layer derived from the second slurry was obtained. At this time, the papermaking speed was set to 7 m/min so that the thickness of the water-containing laminated sheet was about 200 μm and the basis weight of the composite sheet when completely dry was about 24 g/m ² .
Next, the water-containing laminated sheet was dehydrated using a press roll at a pressure of 6 kgf/cm ² and further dried at 130° C. using a Yankee dryer to obtain a composite sheet.
Thereafter, this composite sheet was dip-coated with a solution of phenolic resin, which is a carbon precursor resin, and dried at 120°C using a hot air dryer, so that the amount of phenol resin adhered to 100 parts by mass of the composite sheet was 25 parts by mass. A resin-impregnated sheet was obtained. Then, heat pressing (250° C., 1 minute) was performed using a double belt press. The thickness was 200 μm.
Next, this resin-impregnated sheet was heat-treated for 1 minute in a graphitization furnace with an internal temperature of 2000°C and a nitrogen gas atmosphere to carbonize the phenol resin, high-melting resin fibers, and low-melting resin, and form graphite particles. A graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer base material GD1") in which carbon fibers such as resin were encapsulated and carbon fibers and graphite particles were bound together was obtained (see Table 2). . The thickness of the obtained fuel cell gas diffusion layer base material GD1 was 200 μm.

Example 2
Slurry S3 was used as the first slurry, and slurry S2 was used as the second slurry.
First, slurry S3 (first slurry) was made into paper using a short wire paper machine in the same manner as in Example 1 to obtain a first water-containing sheet with a thickness of 250 μm. Then, while the first water-containing sheet was in a conveying state, paper was made using a cylinder paper machine while supplying slurry S2 (second slurry) to the surface of the first water-containing sheet, to obtain a water-containing laminated sheet. At this time, the papermaking speed was set to 7 m/min so that the thickness of the water-containing laminated sheet was 450 μm and the basis weight of the composite sheet when completely dry was about 48 g/m ² .
Next, in the same manner as in Example 1, the water-containing laminated sheet was dehydrated using a press roll and dried using a Yankee dryer in order to obtain a composite sheet.
Thereafter, a graphite particle-supporting carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer base material GD2") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material GD2 was 200 μm.

Example 3
Slurry S5 was used as the first slurry, and slurry S1 was used as the second slurry.
First, slurry S5 (first slurry) was made into paper using a short wire paper machine to obtain a first water-containing sheet. At this time, the paper making speed was set to 7 m/min so that the thickness of the first water-containing sheet was about 250 μm and the basis weight when completely dry was about 24 g/m ² . Then, while the first water-containing sheet is in a conveying state, paper making is performed using a cylinder paper machine while supplying slurry S1 (second slurry) to the surface of the first water-containing sheet. A water-containing laminated sheet consisting of one layer and a second layer derived from the second slurry was obtained. At this time, the papermaking speed was set to 7 m/min so that the thickness of the water-containing laminated sheet was about 200 μm and the basis weight of the composite sheet when completely dry was about 24 g/m ² .
Next, in the same manner as in Example 1, the water-containing laminated sheet was dehydrated using a press roll and dried using a Yankee dryer in order to obtain a composite sheet.
Thereafter, a carbon fiber sheet carrying graphite particles (hereinafter referred to as "fuel cell gas diffusion layer base material GD3") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material GD3 was 200 μm.

Comparative example 1
Slurry S3 (first slurry) is made into paper using a short wire paper machine, dehydrated using a press roll, and further dried at 130°C to form a single layer sheet (hereinafter referred to as "single layer sheet") having a thickness of 250 μm. A layer sheet MS1) was obtained. Next, this single layer sheet MS1 was dip coated with a phenolic resin solution and dried at 120°C using a hot air dryer to obtain a resin in which the amount of phenol resin adhered to 100 parts by mass of the single layer sheet was 25 parts by mass. An impregnated sheet (hereinafter referred to as "resin-impregnated sheet RS1") was obtained.
On the other hand, slurry S1 (second slurry) was made into paper using a cylinder paper machine, dehydrated using a press roll, and further dried at 130°C to form a single layer sheet (hereinafter referred to as A "monolayer sheet MS2") was obtained. Next, in the same manner as above, a phenolic resin solution was applied to the single-layer sheet MS2 and dried, and a resin-impregnated sheet (hereinafter referred to as "resin An impregnated sheet RS2) was obtained.
Next, using a double belt press, heat pressing (250°C, 1 minute) was performed with these resin-impregnated sheets RS1 and RS2 stacked on top of each other, and graphite particle-supported carbon fiber sheets (hereinafter referred to as "fuel cell gas A diffusion layer base material GD11") was obtained (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material GD11 was 200 μm.

Comparative example 2
Slurry S3 was used as the first slurry, and slurry S1 was used as the second slurry.
Slurry S3 (first slurry) was hand-made to obtain a first water-containing sheet with a thickness of about 200 μm. Next, a slurry S1 (second slurry) was hand-made on the surface of the first water-containing sheet to obtain a water-containing laminated sheet. Thereafter, the water-containing laminated sheet was dehydrated using a press roll at a pressure of 6 kgf/cm ² and further dried using a Yankee dryer to obtain a composite sheet having a thickness of 400 μm.
Next, the same operation as in Example 1 was performed to obtain a graphite particle-supporting carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer base material GD12") (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material ED1 was 200 μm.

Comparative example 3
Slurry S4 was made into paper using a short wire paper machine to obtain a water-containing sheet. At this time, the papermaking speed was set to 7 m/min so that the thickness of the water-containing sheet was about 450 μm and the basis weight when completely dry was about 48 g/m ² .
Next, in the same manner as in Example 1, the water-containing sheet was sequentially dehydrated using a press roll and dried using a Yankee dryer to obtain a single-layer sheet.
Thereafter, a graphite particle-supporting carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer base material GD13") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material GD13 was 200 μm.

Comparative example 4
Slurry S4 was made into paper using a cylinder paper machine to obtain a water-containing sheet. At this time, the papermaking speed was set to 7 m/min so that the thickness of the water-containing sheet was about 400 μm and the basis weight when completely dry was about 48 g/m ² .
Next, in the same manner as in Example 1, the water-containing sheet was sequentially dehydrated using a press roll and dried using a Yankee dryer to obtain a single-layer sheet.
Thereafter, a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer base material GD14") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material GD14 was 200 μm.

4. Evaluation of Gas Diffusion Layer Base Materials The above gas diffusion layer base materials GD1 to GD3 and GD11 to GD14 for fuel cells were evaluated. The results are also listed in Table 2.

4-1. Evaluation of filling properties of materials in gas diffusion layer base material for fuel cells The obtained gas diffusion layer base material for fuel cells was cut perpendicularly to the thickness direction, divided into three equal parts in the thickness direction, and divided into the first region F. , a second region S and a third region T were set, and the filling rate of the material in each region was measured using a high-resolution X-ray microscope "nano3DX" (model name) manufactured by Rigaku Corporation. Note that the first region F and the third region T are a combination (J1) of carbon fibers and graphite particles contained in the first slurry and carbide after the carbonization step, and a combination (J1) of carbon fibers and graphite particles contained in the first slurry, and a combination (J1) of carbon fibers and graphite particles contained in the first slurry. The combination (J2) is mainly a combination of carbon fibers, graphite particles, and carbide after the carbonization process. Moreover, the second region S is derived from these combinations (J1) and (J2).
A cross-sectional image (two-dimensional observation image) is taken, and in order to analyze the presence and absence of material in each region of the first region F, second region S, and third region T, a threshold value is set using image processing software. 128, and the area ratio of the white part, which is the material existing part, was taken as the "filling rate". Therefore, the filling rates in the first region F, second region S, and third region T were defined as _AF , A _S , and _AT, respectively.

4-2. Tensile strength and transport resistance As the roll-shaped gas diffusion layer base material for fuel cells was manufactured as described above, test pieces (size: 15 mm x 100 mm) for measuring tensile strength were used in the machine direction (MD) and perpendicular to it. Two test pieces in the same direction (TD) were prepared, and the tensile strength was measured by a method according to JIS P 8113.
Then, the T1/T2 ratio was calculated when the tensile strength in the MD direction and the tensile strength in the TD direction were respectively defined as T1 and T2, and the transport resistance was evaluated based on the following criteria.
〇: T1/T2≦2
×: T1/T2>2

4-3. Cell Characteristics The above gas diffusion layer base materials GD1 to GD3 and GD11 to GD14 for fuel cells were processed in the following manner to produce water-repellent gas diffusion layer base materials for cathode electrodes, and then the resulting cathode A microporous layer was formed on one side of the water-repellent gas diffusion layer base material for an electrode to produce a gas diffusion layer laminate for a cathode electrode.

A polyethylene film with a thickness of 40 μm was placed on both sides of the gas diffusion layer base material for a fuel cell, and free fluff of the carbon fibers was removed by applying pressure at a surface pressure of 1.5 MPa. Next, this film laminate is impregnated with a PTFE dispersion manufactured by Asahi Glass Co., Ltd. and heat-treated at 200°C, so that 10 parts by mass of PTFE (fabric weight: 0.45 mg/cm ² ) to obtain a water-repellent gas diffusion layer base material for a cathode electrode.
Next, a paste for forming a microporous layer is applied to the surface of the obtained water-repellent gas diffusion layer base material for a cathode electrode and dried, thereby producing a gas diffusion layer laminate for a cathode electrode including a microporous layer. did.

In addition, a water-repellent gas diffusion layer laminate for an anode electrode was produced by the following method.
The above slurry containing carbon fibers, high melting point resin fibers, low melting point resin fibers, graphite particles and water was subjected to paper making, then impregnated with resin and heat treated at 2000°C to obtain a gas diffusion layer base for an anode electrode. The surface of the material was subjected to the same water-repellent treatment as above to obtain a water-repellent gas diffusion layer base material for an anode electrode, and then, on one side of the obtained water-repellent gas diffusion layer base material for an anode electrode, A water-repellent gas diffusion layer laminate for an anode electrode including a microporous layer was prepared by applying a microporous layer-forming paste and drying it.

Next, the obtained water-repellent gas diffusion layer laminate for the cathode, the water-repellent gas diffusion layer laminate for the anode, and the Nafion (registered trademark) series electrolyte membrane "NRE-212" (trade name) ^As shown in FIG. The membrane/electrode assembly 10 shown was manufactured. This membrane/electrode assembly 10 includes a cathode gas diffusion layer 11 derived from a water-repellent cathode gas diffusion layer base material, a microporous layer 13, a catalyst layer 15, and an electrolyte layer. 31, a catalyst layer 25, a microporous layer 23, and an anode gas diffusion layer 21 are sequentially provided.
Thereafter, this membrane/electrode assembly 10 was used as a separator, a current collector plate, etc. to produce a JARI standard cell, which was incorporated into a single cell for fuel cell evaluation, and using a fuel cell evaluation device manufactured by Enoa, The voltage was measured when power was generated at 40° C. and 2 A/cm ² . With reference to the voltage value (0.60 V) in Comparative Example 3, battery performance was determined based on the following criteria (see Table 2).
◎: The voltage value was 0.63V or more.
○: The voltage value was 0.61V or more and less than 0.63V.
Δ: The voltage value was 0.59V or more and less than 0.61V.
×: The voltage value was less than 0.59V.

The following can be seen from Table 2.
Examples 1 to 3 are examples of the manufacturing method according to the present invention, and both the tensile strength T1 in the flow direction and the tensile strength T2 in the direction perpendicular to the flow direction of the obtained gas diffusion layer base material for fuel cells are high, In addition, T1/T2 was less than 2, and transportability was good. Moreover, the cell performance of the fuel cells obtained by forming the gas diffusion layer for the fuel cell for the cathode using these gas diffusion layer base materials for the fuel cell was very good compared to the comparative example.

It should be noted that the present invention is not limited to those shown in the above-described specific embodiments, but can be modified in various ways within the scope of the present invention depending on the purpose and use.

The fuel cell gas diffusion layer base material obtained according to the present invention is suitable as a material for forming a cathode gas diffusion layer constituting a membrane/electrode assembly included in a fuel cell. Therefore, a fuel cell including such a cathode gas diffusion layer has high power generation performance and can be used for transportation fuel cells such as vehicles, stationary fuel cells, and the like.

1: Gas diffusion layer base material for fuel cells 2: Carbon fiber 4: Graphite particles 6: Carbonized part 10: Membrane/electrode assembly 11: Gas diffusion layer for cathode 13: Microporous layer 15: Catalyst layer 21: Anode electrode gas diffusion layer 23: microporous layer 25: catalyst layer 31: electrolyte layer F: first region S: second region T: third region

Claims (5)

A first water-containing sheet is produced using a first slurry containing carbon fibers (A1), graphite particles (B1), organic fibers (C1) to be carbonized in a subsequent carbonization step, and water. Sheet manufacturing process,
Supplying a second slurry containing carbon fibers (A2), graphite particles (B2), organic fibers (C2) to be carbonized in a subsequent carbonization step, and water to the surface of the first water-containing sheet, a step of producing a water-containing laminate sheet comprising a first layer derived from the first water-containing sheet and a second layer originating from the second slurry disposed on the surface of the first layer;
a composite sheet production step of producing a composite sheet by squeezing and drying the water-containing laminated sheet;
a resin impregnation step of producing a resin-impregnated sheet by impregnating the composite sheet with a carbon precursor resin that will be carbonized in a subsequent carbonization step;
a carbonization step of heating and firing the resin-impregnated sheet in a non-oxidizing atmosphere;
In the first water-containing sheet, the carbon fibers (A1) and the organic fibers (C1) are oriented in a direction substantially parallel to the surface stretching direction of the first water-containing sheet, and the graphite particles (B1) is a sheet interposed between fibers,
The second layer is a layer in which the carbon fibers (A2) and the organic fibers (C2) are randomly oriented in a three-dimensional direction, and the graphite particles (B2) are interposed between the fibers. A method for manufacturing a gas diffusion layer base material for fuel cells. The method for producing a gas diffusion layer base material for a fuel cell according to claim 1, wherein a short wire paper machine or a fourdrinier paper machine is used in the first water-containing sheet production step. The method for producing a gas diffusion layer substrate for a fuel cell according to claim 1 or 2, wherein a cylinder paper machine is used in the step of producing the water-containing laminated sheet. The method for producing a gas diffusion layer base material for a fuel cell according to claim 1, wherein the mass ratio (B1/B2) of the graphite particles (B1) and the graphite particles (B2) is 1.2 or more. A gas diffusion layer base material for a fuel cell obtained by the method for producing a gas diffusion layer base material for a fuel cell according to claim 1.

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