Substrate for gas diffusion layer in fuel cells and method for manufacturing the same

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

[Technical Field]

[0001] The present invention relates to a gas diffusion layer substrate used for forming a gas diffusion layer in a fuel cell and a method for manufacturing the same. [Background technology]

[0002] Solid polymer fuel cells (hereinafter simply referred to as "fuel cells"), which are widely used as power sources for automobiles and the like, are constructed by stacking multiple fuel cell cells separated by separators. In a single cell, a cathode (+) electrode and an anode (-) electrode are arranged on both sides of a polymer electrolyte membrane that selectively permeates specific ions. These electrodes consist of a catalyst layer made of a conductive material such as carbon supporting a catalyst such as platinum and an ion exchange resin, and a porous gas diffusion layer placed outside each catalyst layer, forming a membrane / electrode assembly. A separator is placed outside the gas diffusion layer that constitutes this membrane / electrode assembly, and has a gas channel for supplying fuel gas (anode gas) or oxidizing gas (cathode gas) and for discharging generated gas and excess gas, with the membrane / electrode assembly sandwiched between the separators.

[0003] In the fuel cell with the above configuration, the gas diffusion layer constituting the electrode of the single cell is arranged to enhance the diffusivity of the reaction gas. It plays a role in diffusing the fuel gas or oxidizing gas supplied from the separator's gas channel to the catalyst layer adjacent to the gas diffusion layer (gas diffusivity), and therefore possesses not only gas permeability but also conductivity as a current collector function that efficiently moves electrons for electrochemical reactions. Furthermore, while the gas diffusion layer maintains the polymer electrolyte membrane and catalyst layer in an optimally moist state at all times, the gas diffusion layer of the cathode electrode in particular requires water repellency (drainage) to discharge excess reaction product water and condensation water generated by the electrochemical reaction of hydrogen and oxygen during power generation in order to suppress the flooding phenomenon (a phenomenon in which the pores of the gas diffusion layer become blocked with water) and stabilize power generation performance.

[0004] Conventionally, a substrate containing conductive carbon fibers and a method for manufacturing the same are known as substrates for forming a gas diffusion layer.

[0005] For example, Patent Document 1 discloses a porous carbon fiber sheet characterized by laminating a carbon fiber layer containing carbon fibers formed on one side and an activated carbon fiber layer containing more activated carbon fibers than the carbon fiber layer, formed on the other side. A method for manufacturing such a porous carbon fiber sheet is disclosed, characterized by preparing a carbon fiber slurry containing carbon fibers and a binder, with the carbon fibers sufficiently dispersed, and an activated carbon fiber slurry containing activated carbon fibers with a larger surface area than the carbon fibers and a binder, with the activated carbon fibers sufficiently dispersed, and sequentially supplying at least the carbon fiber slurry and the activated carbon fiber slurry onto a papermaking screen and papermaking to form a carbon fiber layer on one side of the sheet and an activated carbon fiber layer containing more activated carbon fibers than the carbon fiber layer on the other side, thereby laminating multiple layers. Patent Document 2 discloses a porous carbon sheet containing carbon fibers and a binder, in which, when the carbon sheet is divided into six equal layers in the thickness direction under compression from one surface to the other, the layers obtained are numbered 1, 2, 3, 4, 5, and 6 in order from the layer containing one surface to the layer containing the other surface, the layer with the highest packing density under compression is layer 2, and the relationship of the packing density under compression of layers 2, 3, 4, 5, and 6 is such that layer 2 has the highest packing density and layer 3 has the second highest packing density. It is also disclosed that such a carbon sheet can be manufactured by first producing a porous carbon fiber paper, then impregnating it with a resin composition that will serve as a binder, with the largest amount in layer 2, and further, with layer 3 having the second largest amount among layers 2, 3, 4, 5, and 6, followed by drying and heat treatment (carbonization).

[0006] Patent Document 3 discloses a porous carbon sheet comprising dispersed carbon short fibers bound together with resin carbide, wherein the sheet consists of at least two layers with different pore mode diameters, and when the pore mode diameter of the layer with the largest pore mode diameter is D1 and the pore mode diameter of the layer with the smallest pore mode diameter is D2, the relationship 1.2 ≤ D1 / D2 ≤ 4 is disclosed. A method for producing such a porous carbon sheet is disclosed, comprising a compression step of heating and pressurizing a precursor fiber sheet containing carbon short fibers and a thermosetting resin, and a carbonization step of carbonizing the thermosetting resin contained in the precursor fiber sheet after the compression step, wherein in the compression step, as a first step, the precursor fiber sheet is heated and pressurized, and as a second step, the precursor fiber sheet heated and pressurized in the first step and the precursor fiber sheet before heating and pressurizing are laminated and further heated and pressurized. Furthermore, Patent Document 4 discloses a porous gas diffusion layer substrate comprising a carbon fiber aggregate in which carbon fibers are intertwined, a carbide that binds the carbon fibers of the carbon fiber aggregate, and spheroidal graphite and / or artificial graphite with a median diameter in the range of 40 μm to 120 μm held between the carbon fibers of the carbon fiber aggregate. A method for manufacturing such a gas diffusion layer substrate is disclosed, comprising a papermaking step of forming an aggregate by papermaking together a base carbon fiber, an organic fiber that is burned off in a subsequent heat treatment, and spheroidal graphite and / or artificial graphite with a median diameter in the range of 40 μm to 120 μm; a resin impregnation step of impregnating the aggregate formed in the papermaking step with a carbon precursor resin; a drying step of drying the aggregate impregnated with the carbon precursor resin; and a carbonization and graphitization step of heating and firing the aggregate dried in the drying step in a non-oxidizing atmosphere. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2004-238759 [Patent Document 2] WO2017 / 69014 publication [Patent Document 3] Japanese Patent Publication No. 2009-234851 [Patent Document 4] Japanese Patent Publication No. 2020-87826 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a gas diffusion layer substrate used for forming a gas diffusion layer in a fuel cell that achieves both gas diffusibility and conductivity, and to provide a gas diffusion layer substrate and a method for manufacturing the same that provides a fuel cell with high power generation performance. [Means for solving the problem]

[0009] The inventors have found that by preparing a laminate of graphite particle-containing fiber sheet layers (water-containing laminated sheet) such that the orientation of the fibers in each layer is different from that of the others, and then drying this to obtain a composite sheet, impregnating it with a carbon precursor resin, and subsequently carbonizing it, the resulting gas diffusion layer substrate is suitable for forming a gas diffusion layer in a fuel cell, thus solving the above-mentioned problem.

[0010] The present invention is shown below. [1] A first water-containing sheet manufacturing step, in which a first water-containing sheet is manufactured using a first slurry containing carbon fibers (A1), graphite particles (B1), organic fibers (C1) which are carbonized in a later carbonization step, and water. A water-containing laminated sheet manufacturing step involves 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 to produce a water-containing laminated sheet comprising a first layer derived from the first water-containing sheet and a second layer derived from the second slurry arranged on the surface of the first layer. A composite sheet manufacturing process is performed by squeezing and drying the above-mentioned water-containing laminated sheet to produce a composite sheet, A resin impregnation step is performed to produce a resin-impregnated sheet by impregnating the above composite sheet with a carbon precursor resin that will be carbonized in a later carbonization step, The above resin-impregnated sheet is sequentially subjected to a carbonization process in which it is heated and fired in a non-oxidizing atmosphere. The above-mentioned first water-containing sheet is a sheet in which 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) are interposed between the fibers. A method for manufacturing a gas diffusion layer substrate for a fuel cell, wherein the second layer is a layer in which the carbon fibers (A2) and organic fibers (C2) are randomly oriented in three dimensions, and the graphite particles (B2) are interposed between the fibers. [2] A method for manufacturing a gas diffusion layer substrate for a fuel cell according to item [1] above, wherein a short-wire paper machine or a long-wire paper machine is used in the first water-containing sheet manufacturing step. [3] A method for manufacturing a gas diffusion layer substrate for fuel cells according to item [1] or [2] above, wherein a cylinder wire paper machine is used in the water-containing laminated sheet manufacturing step. [4] A method for manufacturing a gas diffusion layer substrate for a fuel cell 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. [5] A fuel cell gas diffusion layer substrate obtained by the method for manufacturing a fuel cell gas diffusion layer substrate described in item [1] above. [Effects of the Invention]

[0011] 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 achieves both gas diffusibility and conductivity and provides a fuel cell having high power generation performance. In particular, the water-containing laminated sheet obtained in the water-containing laminated sheet production step has carbon fibers (A1) and organic fibers (C1) oriented in a direction substantially parallel to the surface stretching direction, and graphite particles (B1) are interposed between the fibers. On the surface of the first water-containing sheet, the second slurry is laminated such that carbon fibers (A2) and organic fibers (C2) are randomly oriented in three-dimensional directions and graphite particles (B2) are interposed between the fibers. Therefore, the entanglement of the fibers at the interface between the first layer and the second layer becomes sufficient, and the inside of the gas diffusion layer base material obtained after the carbonization step can be made dense. Further, when the production of the water-containing laminated sheet, the production of the composite sheet, the production of the resin-impregnated sheet, and the carbonization are continuously performed using a paper machine, the gas diffusion layer base material for a fuel cell can be produced in a roll shape. However, the ratio (T1 / T2) of the tensile strength T1 in the flow direction (MD) to the tensile strength T2 in the direction perpendicular thereto (TD) is, for example, reduced to 2.0 or less, and cracks and the like during roll-to-roll conveyance can be suppressed. A fuel cell manufactured by using the gas diffusion layer base material for a fuel cell obtained by the present invention as a gas diffusion layer base material for a cathode electrode can be used for a transport fuel cell such as a vehicle or a stationary fuel cell.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic cross-sectional view of the gas diffusion layer base material for a fuel cell obtained by the present invention. [Figure 2] It is an explanatory view showing a region for measuring the material occupancy rate (excluding the void portion) when the gas diffusion layer base material for a fuel cell obtained in [Example] is divided into three equal parts in the thickness direction, and shows the first region F, the second region S, and the third region T set from the side of the first layer derived from the first water-containing sheet. [Figure 3] It is a schematic cross-sectional view of a membrane / electrode assembly manufactured using the gas diffusion layer base material for a fuel cell obtained by the present invention.

Embodiments for Carrying Out the Invention

[0013] The present invention provides a method for manufacturing a gas diffusion layer substrate for fuel cells, comprising, in order, a first water-containing sheet manufacturing step, a water-containing laminated sheet manufacturing step, a composite sheet manufacturing step, a resin impregnation step, and a carbonization step. The present invention also provides a method for manufacturing a gas diffusion layer substrate for fuel cells, which may further include other steps (described later) as needed. In the present invention's method for manufacturing a gas diffusion layer substrate for fuel cells, the water-containing laminated sheet obtained in the water-containing laminated sheet manufacturing step has different fiber orientations in the first layer and the second layer. However, in the gas diffusion layer substrate finally obtained through subsequent processes, the difference in fiber orientation cannot be confirmed by an electron microscope or the like, while excellent battery performance is obtained. In conventional, known manufacturing methods, where a graphite particle-containing fiber aggregate is produced without considering the fiber orientation tendency, followed by resin impregnation, carbonization, etc., naturally, there is no difference in fiber orientation between one side and the other side of the resulting gas diffusion layer substrate. However, the battery performance is inferior to that obtained using the gas diffusion layer substrate according to the present invention.

[0014] Figure 1 is a schematic cross-sectional view showing an example of a fuel cell gas diffusion layer substrate 1 obtained according to the present invention. This fuel cell gas diffusion layer substrate 1 includes a plurality of carbon fibers 2 (derived from carbon fibers (A1) and carbon fibers (A2)), a plurality of graphite particles 4 (derived from graphite particles (B1) and graphite particles (B2)), and a carbonized portion 6 formed by carbonizing organic fibers (C1) contained in the first slurry, organic fibers (C2) contained in the second slurry, and carbon precursor resins contained in the first and second slurries through a carbonization process. The carbonized portion 6 in Figure 1 does not show to be filled with carbides, but rather the carbides bind the graphite particles to each other, or the carbon fibers and graphite particles together, and has voids inside to the extent that it is permeable from one side to the other side of the fuel cell gas diffusion layer substrate 1. The fuel cell gas diffusion layer substrate 1 of the present invention is an article consisting of layers 8 and 9, which are formed by impregnating a composite sheet, which is a dried body of a water-containing laminated sheet containing a first layer derived from fibers contained in a first slurry and a second layer derived from fibers contained in a second slurry, with a carbon precursor resin and then heating and firing it (see Figure 1). As described above, it is difficult to confirm the difference in fiber orientation in each layer using an electron microscope or the like, and normally the interface between layers 8 and 9 cannot be confirmed.

[0015] The fuel cell gas diffusion layer substrate obtained by the present invention is a sheet-like (thin plate-like) material used in the manufacture of fuel cells, and can be used, for example, to form the cathode electrode gas diffusion layer 11 in the membrane / electrode assembly 10 shown in Figure 3. A particularly preferred embodiment of the membrane / electrode assembly 10 comprises, in order, a cathode electrode 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 electrode gas diffusion layer 21, and the cathode electrode gas diffusion layer 11 is formed by joining the first surface 1a (the surface on the layer 8 side derived from the first slurry) of the fuel cell gas diffusion layer substrate 1 shown in Figure 1 so as to face the microporous layer 13.

[0016] First, we will explain the first slurry used in the first water-containing sheet manufacturing process and the second slurry used in the water-containing laminated sheet manufacturing process. The first slurry contains carbon fibers (A1), graphite particles (B1), organic fibers (C1), and water. The second slurry also contains carbon fibers (A2), graphite particles (B2), organic fibers (C2), and water. The first and second slurries may contain other components.

[0017] The composition (type, size, etc.) of carbon fiber (A1) and carbon fiber (A2) may be the same or different. These carbon fibers may be any of the following: vapor-grown carbon fibers, carbon nanotubes (single-wall, double-wall, multi-wall, cup-laminated, etc.), polyacrylonitrile (PAN) carbon fibers, pitch carbon fibers, or rayon carbon fibers. The carbon fibers contained in carbon fiber (A1) and carbon fiber (A2) may each consist of only one type or two or more types.

[0018] 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 diffusivity and drainage of the formed gas diffusion layer. Regarding the fiber length of the carbon fibers, the upper limit is usually 12 mm, and the lower limit is usually 2 mm. Furthermore, 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 of the formed gas diffusion layer.

[0019] The composition (type, size, etc.) of graphite particles (B1) and graphite particles (B2) may be the same or different. These graphite particles may be either natural graphite or artificial graphite. The graphite particles contained in graphite particles (B1) and graphite particles (B2) may each consist of only one type or two or more types. The shape of the graphite particles is not particularly limited and can be spherical, ellipsoidal, plate-like, linear, irregular, etc. Furthermore, the graphite particles may be aggregates of primary particles.

[0020] When the graphite particles are spherical, the particle size measured by laser diffraction and scattering is preferably 10 to 200 μm, more preferably 30 to 70 μm, from the viewpoint of gas diffusivity and drainage of the formed gas diffusion layer.

[0021] Organic fibers (C1) and organic fibers (C2) may have the same or different compositions. These organic fibers can be carbonized in a later carbonization process and include resin fibers (derived from polylactic acid, polyvinyl alcohol, polyolefin, polyurethane, polyester, polyamide, acrylic resin, aramid, polyacetal, phenolic resin, cellulose, etc.), plant fibers (derived from wood, cotton, bamboo, hemp, etc.), and animal fibers (derived from wool, etc.). Of these, it is preferable to include resin fibers. Furthermore, using organic fibers can improve entanglement by immobilizing carbon fibers with each other, graphite particles with each other, or carbon fibers and graphite particles together during the production of 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 second water-containing laminated sheet production process using the second slurry. Furthermore, during the carbonization process, when the resin-impregnated sheet is heated and fired, the formed carbides bind carbon fibers together, graphite particles together, or carbon fibers and graphite particles together, while the burnt-out areas become pores (micropores, gas pockets) that allow gas and moisture to pass through, thus obtaining a gas diffusion layer substrate with a suitable structure.

[0022] In the present invention, in order to obtain a composite sheet in a preferred embodiment having a structure in which carbon fibers, graphite particles, and some resin fibers are bonded together by an adhesive during the composite sheet manufacturing process, it is preferable that the organic fibers (C1) and organic fibers (C2) include 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, it is particularly preferable that 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 during the composite sheet manufacturing process (hereinafter referred to as the "drying temperature"), and that the melting point of the high-melting-point resin is higher than this drying temperature. In the present invention, polyvinyl alcohol, which has excellent adhesion to carbon fibers and graphite particles, is preferred as the low-melting-point resin. Acrylic resin is preferred as the high-melting-point resin. The resin fiber may be monofilament, multifilament, or fibril fiber. For example, as an acrylic resin fiber, fibril fiber called "acrylic pulp fiber," which is obtained by beating acrylic fibers to make pulp, can be used.

[0023] The average fiber diameter of the organic fibers is preferably 5 to 20 μm, more preferably 6 to 8 μm, from the viewpoint of the mechanical strength of the resulting water-containing laminated sheet. Regarding the fiber length of the above-mentioned organic fibers, the upper limit is usually 15 mm, and the lower limit is usually 1 mm. Furthermore, the average fiber length of the above-mentioned organic fibers is preferably 1 to 10 mm, more preferably 1 to 5 mm.

[0024] As described above, in a preferred embodiment, the organic fibers (C1) and organic fibers (C2) in the first slurry and the second slurry both contain low-melting-point resin fibers and high-melting-point resin fibers. The content ratios of the low-melting-point resin fibers and high-melting-point resin fibers in the first slurry are preferably 15-32% by mass and 68-85% by mass, and more preferably 18-29% by mass and 71-82% by mass, respectively, when the total of both is 100% by mass. Furthermore, the content ratios of the low-melting-point resin fibers and high-melting-point resin fibers in the second slurry are preferably 12-25% by mass and 75-88% by mass, and more preferably 14-20% by mass and 80-86% by mass, respectively, when the total of both is 100% by mass.

[0025] As described above, the first slurry and the second slurry according to the present invention may contain other components. Examples of other components include binders, carbides of organic materials, and additives (such as flocculants, viscosity modifiers, and surfactants).

[0026] The binder can be derived from polyvinyl alcohol, polyvinyl acetate, polyethylene, polypropylene or other polyolefins, polyester such as polyethylene terephthalate, polyacrylonitrile, cellulose, polyethylene oxide, polyacrylamide, phenolic resin, xylenol resin, styrene-butadiene rubber, starch, corn starch, etc.

[0027] In the present invention, a preferred first slurry 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 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 of organic fibers (C1) is preferably 4 to 40 parts by mass, more preferably 8 to 24 parts by mass, when the content of carbon fibers (A1) is 100 parts by mass. The water content is usually adjusted so that the total content of carbon fibers (A1), graphite particles (B1), and organic fibers (C1) is preferably 0.001 to 2%, more preferably 0.01 to 0.1%, relative to the total amount of the first slurry.

[0028] Furthermore, the preferred second slurry 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 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 fibers (A2) is 100 parts by mass. The content of organic fibers (C2) is preferably 4 to 40 parts by mass, more preferably 8 to 24 parts by mass, when the content of carbon fibers (A2) is 100 parts by mass. The content of water is usually adjusted so that the total content of carbon fibers (A2), graphite particles (B2), and organic fibers (C2) is preferably 0.001 to 2%, more preferably 0.01 to 0.1%, relative to the total amount of the second slurry.

[0029] The method for preparing the first slurry and the second slurry is not particularly limited, and for example, it may involve mixing the raw materials using a rotary device such as a pulper.

[0030] The first water-containing sheet manufacturing step is a step in manufacturing a sheet (first water-containing sheet) in which 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. In the present invention, since continuous mass production of the gas diffusion layer substrate is possible, it is preferable to manufacture the first slurry using a short-wire paper machine or a long-wire paper machine (hereinafter, these may be collectively referred to as the "first paper machine"). Conventional paper machines known to exist can be used as both short-screen and long-screen paper machines. The papermaking conditions are not particularly limited, but preferably the thickness at oven-drying is 100-400 μm, more preferably 200-300 μm, or the basis weight at oven-drying is preferably 10-100 g / m². 2 , comfortable 30~60g / m 2 The first water-containing sheet is prepared in such a manner.

[0031] When using a short-wire paper machine, the papermaking speed is preferably 4 to 40 m / min, more preferably 7 to 24 m / min. When using a long-screen paper machine, the papermaking speed is preferably 4 to 40 m / min, more preferably 7 to 24 m / min.

[0032] The first moist sheet obtained in the first moist sheet manufacturing process is a moist material of a fiber aggregate containing graphite particles, in which carbon fibers (A1) and organic fibers (C1) are oriented in all directions almost perpendicular to the thickness direction of the first moist sheet, and graphite particles (B1) are interposed between the fibers. Furthermore, in the subsequent process of manufacturing the water-containing laminated sheet, the first water-containing sheet is used. The first water-containing sheet obtained in the first water-containing sheet manufacturing process can be used as is, but a water-containing sheet obtained by processing with a press roll or the like to adjust the sheet thickness, moisture content, etc., may also be used.

[0033] The water-containing laminated sheet manufacturing process involves supplying a second slurry to the surface of a first water-containing sheet to form a second layer on the surface of the first layer derived from the first water-containing sheet, thereby manufacturing a water-containing laminated sheet. In the present invention, since it is possible to continuously mass-produce gas diffusion layer substrates when a first paper machine is used in the first water-containing sheet manufacturing process, it is preferable to use a cylinder wire paper machine to manufacture the second slurry on the surface of the first water-containing sheet. Conventional papermaking machines can be used as the cylinder screen papermaking machine. The papermaking conditions are not particularly limited, but the thickness (total thickness) when completely dry is preferably 100 to 400 μm, more preferably 200 to 300 μm, or the basis weight when the water-containing laminated sheet is completely dry is preferably 10 to 100 g / m². 2 , comfortable 30~60g / m 2 A water-containing laminated sheet is prepared in such a manner. In this case, the papermaking speed is preferably 4 to 40 m / min, more preferably 7 to 24 m / min.

[0034] A first slurry and a second slurry are used to prepare a water-containing laminated sheet. The ratio (B1 / B2) of the amount of graphite particles (B1) in the first layer derived from the first slurry to the amount of graphite particles (B2) in the second layer derived from the second slurry is preferably 1.0 or more, more preferably 1.2 or more, even more preferably 1.2 to 2.0, and particularly preferably 1.2 to 1.6.

[0035] The water-containing laminated sheet obtained in the water-containing laminated sheet manufacturing process is a water-containing laminate consisting of a first layer containing graphite particles (B1) with low fiber orientation and a second layer containing graphite particles (B2) with greater fiber orientation than the first layer. By using a cylinder paper machine, it is possible to form a second layer with excellent interlocking properties with the fibers constituting the first layer at the interface with the first layer, while suppressing delamination between the layers.

[0036] In the present invention, after the water-containing laminated sheet manufacturing process, the obtained water-containing laminated sheet can be subjected to entanglement treatment as needed. Examples of entanglement methods include mechanical entanglement (such as needle punching), high-pressure liquid injection (such as water jet punching), and high-pressure gas injection (such as steam jet punching).

[0037] Next, in the composite sheet manufacturing process, the water-containing laminated sheet is dewatered and dried to produce the composite sheet. The methods for dewatering and drying the water-containing laminated sheet are not particularly limited. Dewatering can be performed using a suction box to draw in water, a press roll to compress and dewater, etc. After dewatering, the sheet can be transferred to, for example, a drum-shaped Yankee dryer with a mirror-finished surface and heated to obtain a dried composite sheet. Depending on the shape and size of the sheet, drying may be performed under reduced pressure. The lower limit of the drying temperature is preferably 70°C, more preferably 90°C, and the upper limit is usually 160°C. If the organic fibers contained in the water-containing laminated sheet include the above-mentioned high-melting-point resin fibers and low-melting-point resin fibers, preferably, only the low-melting-point resin fibers can be melted at the above-mentioned drying temperature to obtain a composite sheet in which carbon fibers, graphite particles and high-melting-point resin fibers are bound together. For composite sheets in a completely dry state, the basis weight is preferably 20 to 150 g / m². 2 The thickness is preferably 200 to 600 μm.

[0038] If entanglement treatment is not performed after the water-containing laminated sheet manufacturing process, entanglement treatment can be performed on the resulting composite sheet after the composite sheet manufacturing process, if necessary.

[0039] Because the composite sheet contains various types of fibers of varying lengths, some fibers may protrude from the surface of the composite sheet after drying, resulting in a rough, uneven surface. In the subsequent resin impregnation process, a smooth surface can be formed by embedding the fibers with a carbon precursor resin. Alternatively, before the resin impregnation process, the protruding fibers may be cut or removed, or the fibers may be pushed back into the composite sheet.

[0040] Subsequently, in the resin impregnation process, a carbon precursor resin that can be carbonized in the carbonization process is impregnated into the composite sheet to produce a resin-impregnated sheet. While the carbon precursor resin is not particularly limited, thermosetting resins such as phenolic resins, furan resins, epoxy resins, melamine resins, imide resins, urethane resins, aramid resins, urea resins, and unsaturated polyester resins are preferred because they exhibit excellent wettability with carbon fibers or organic fibers and readily form conductive carbides in the subsequent carbonization process. Among these, phenolic resins are particularly preferred because they have a high carbonization rate and become excellent conductive materials after carbonization. In the resin impregnation process, the carbon precursor resin can be used as is depending on its properties. However, since the composite sheet is a fiber aggregate containing graphite particles, it is preferable to use a liquid containing the carbon precursor resin (hereinafter referred to as "carbon precursor resin-containing liquid") in order to thoroughly impregnate the composite sheet by filling all the voids between the fibers with the carbon precursor resin. This carbon precursor resin-containing liquid may consist only of liquid carbon precursor resin, but is preferably a solution obtained by dissolving the carbon precursor resin in a solvent (resin solution) or a dispersion obtained by dispersing the carbon precursor resin in a dispersion medium (resin dispersion).

[0041] When using a carbon precursor resin-containing liquid, methods such as immersing the composite sheet in the carbon precursor resin-containing liquid or coating the composite sheet with the carbon precursor resin-containing liquid (kiss coat method, spray method, curtain coat method, roller contact method, etc.) can be applied. Of these, the method of immersing the composite sheet in the carbon precursor resin-containing liquid is preferred.

[0042] The drying state of the resin-impregnated sheet that is heated and fired in the carbonization process is not particularly limited. Therefore, when a carbon precursor resin-containing liquid is brought into contact with the composite sheet in the resin impregnation process, a dry resin-impregnated body free of solvents or dispersion media can be obtained by using a non-contact drying method in which hot air is blown onto the liquid-attached sheet, the liquid-attached sheet is placed in a high-temperature atmosphere, or the liquid-attached sheet is dried using an infrared heater or microwave, or by using a contact drying method in which the liquid-attached sheet is brought into contact with a heated roll, plate, etc.

[0043] Other methods for impregnating a composite sheet with carbon precursor resin without using a carbon precursor resin-containing liquid include contacting a resin film containing carbon precursor resin with at least a portion of the surface of the composite sheet, dissolving the carbon precursor resin by heating, solvent spraying, etc., and allowing it to permeate the entire composite sheet.

[0044] In the obtained resin-impregnated sheet, when the total of the completely dry composite sheet and the impregnated carbon precursor resin is taken as 100% by mass, the content of the carbon precursor resin is preferably 10 to 80% by mass, more preferably 30 to 60% by mass.

[0045] In the present invention, the resin-impregnated sheet obtained by the resin impregnation process may be subjected to a heating press using a hydraulic press, hot press, belt press, roll press, etc., as necessary, for purposes such as thickness adjustment, before being subjected to the carbonization process.

[0046] The carbonization process involves 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 or helium, or nitrogen gas. The heating temperature for the resin-impregnated sheet is preferably 1800°C to 2500°C, more preferably 1900°C to 2200°C, in order to avoid degrading the strength of the carbon fibers and to facilitate the carbonization of the organic fibers and carbon precursor resin. In addition, a multi-stage heating method may be applied in the carbonization process, in which the resin-impregnated sheet is heated at a temperature lower than the above preferred carbonization temperature before being raised. Furthermore, the heating time for the resin-impregnated sheet varies depending on its size, but is usually one minute or more.

[0047] In the carbonization process, organic fibers derived from the composite sheet and carbon precursor resin contained in the resin-impregnated sheet are carbonized, and the resulting carbides bind the carbon fibers together, the graphite particles together, or the carbon fibers and graphite particles together, thereby obtaining a fuel cell gas diffusion layer substrate. The fuel cell gas diffusion layer substrate used in the production of membrane / electrode assemblies, which are manufacturing components of fuel cells, can be obtained by this carbonization process, but if necessary, the process may further include a smoothing process to smooth the surface, a water-repellent process to make the surface water-repellent, etc.

[0048] In the water-repellent treatment process, a method can be applied in which the gas diffusion layer substrate 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, and can be polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), etc.

[0049] The gas diffusion layer substrate for fuel cells obtained by the present invention has a phase mainly composed of carbides (carbide portion 6), and the carbon fibers 2 and graphite particles 4 contained in the phase have strong conductive paths. Furthermore, because the carbides are derived from resin, the gas diffusion layer substrate has elasticity, and dimensional absorption is improved when it is joined with the electrolyte layer forming material or catalyst layer forming material during the manufacture of the fuel cell. Moreover, when the gas diffusion layer substrate 1 for fuel cells shown in Figure 1 is used as a gas diffusion layer substrate for the cathode electrode, and the surface on the layer 8 side (first surface 1a) formed using the first slurry is joined to face the microporous layer 13 to form the gas diffusion layer 11 for the cathode electrode, and the membrane / electrode assembly 10 shown in Figure 3 is fabricated and used in a fuel cell, the water generated during power generation can be efficiently drained out of the system (outside the cathode electrode gas diffusion layer 11 on the side where the microporous layer 13 is not located), and the decrease in power generation performance due to flooding can be suppressed, so it is expected that high power generation performance will be achieved.

[0050] When manufacturing a membrane / electrode assembly, the fuel cell gas diffusion layer substrate of the present invention may be applied directly to the gas diffusion layer electrode, but it is preferable to use a laminate (gas diffusion layer laminate) obtained by forming a microporous layer on one side. When a fuel cell equipped with a membrane / electrode assembly made using this gas diffusion layer laminate with a microporous layer is driven, flooding caused by large water droplets formed by the condensation of water vapor can be suppressed.

[0051] The above-mentioned microporous layer is preferably a microporous layer with an upper limit of about 100 μm in thickness, containing a conductive material and a water-repellent resin. Examples of conductive materials 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.

[0052] A membrane / electrode assembly 10 shown in Figure 3 can be manufactured using a gas diffusion layer substrate for an anode electrode having a microporous layer on one side (which may be water-repellent), a gas diffusion layer substrate for a cathode electrode having a microporous layer on one side (which may be water-repellent), and a laminate in which catalyst layers are formed on both sides of an electrolyte membrane (polymer electrolyte membrane) that selectively permeates specific ions. A fuel cell (single cell) can be manufactured using this membrane / electrode assembly 10 and separators (anode side and cathode side).

[0053] In a fuel cell with this configuration, when oxidizing gas is supplied from an external source to the oxidizing gas channel of the cathode-side separator, a portion of the oxidizing gas flowing along this channel enters the interior of the cathode electrode gas diffusion layer. The remaining unreacted oxidizing gas that does not enter flows along the oxidizing gas channel and is discharged to the outside of the fuel cell. Similarly, when fuel gas is supplied from an external source to the fuel gas channel of the anode-side separator, a portion of the fuel gas flowing along this channel enters the interior of the anode electrode gas diffusion layer. The remaining unreacted fuel gas that does not enter flows along the fuel gas channel and is discharged to the outside of the fuel cell. Then, as the oxidizing gas and fuel gas react, electricity is extracted between the cathode-side separator and the anode-side separator. [Examples]

[0054] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples unless it exceeds the spirit of the invention.

[0055] 1. Raw materials for manufacturing gas diffusion layer substrates The manufacturing raw materials used in the examples and comparative examples are as follows:

[0056] 1-1. Carbon Fiber Teijin carbon fiber (fiber length: 3 mm, fiber diameter: 7 μm) was used.

[0057] 1-2. Organic Fibers (1) Resin fibers (high melting point resin fibers) Acrylic pulp fibers (fiber length: 2 mm) manufactured by Toyobo Co., Ltd. were used. (2) Resin fibers (low melting point resin fibers) We used vinylon fibers manufactured by Kuraray Co., Ltd. (fiber length: 3 mm, fiber diameter: 11 μm).

[0058] 1-3. Graphite particles The graphite powder used was "CGB-50" (product name) manufactured by Nippon Graphite Industries Co., Ltd. The particles were spherical, and the average particle size d50, determined by laser diffraction, was 50 μm.

[0059] 2. Preparation of slurry Five types of slurries (S1, S2, S3, S4, and S5) were prepared by mixing the above carbon fibers, high-melting-point resin fibers, low-melting-point resin fibers, and graphite particles with water using a pulper, according to the mixing ratios shown in Table 1. The proportion of graphite particles relative to the total amount of carbon fibers, high-melting-point resin fibers, low-melting-point resin fibers, and graphite particles was 10% by mass, 20% by mass, 30% by mass, 40% by mass, and 50% by mass, respectively. Table 1 shows the proportion of carbon fibers, high-melting-point resin fibers, low-melting-point resin fibers, and graphite particles contained in each slurry. The proportion of the total amount of carbon fibers, high-melting-point resin fibers, low-melting-point resin fibers, and graphite particles relative to the total amount of slurry was 0.001 to 0.1% by mass. [Table 1]

[0060] 3. Manufacturing of gas diffusion layer substrate A roll-shaped gas diffusion layer substrate for fuel cells was manufactured by continuous papermaking using the slurries S1 to S5 described above.

[0061] Example 1 Slurry S3 was used as the first slurry, and slurry S1 was used as the second slurry. First, a short-wire paper machine was used to produce a first water-containing sheet from slurry S3 (first slurry). At this time, the thickness of the first water-containing sheet was approximately 250 μm, and the basis weight when completely dry was approximately 24 g / m². 2The papermaking speed was set to 7 m / min. While the first water-containing sheet was in a conveying state, papermaking was carried out using a cylinder mold papermaking machine while supplying slurry S1 (the second slurry) to the surface of the first water-containing sheet, and a water-containing laminated sheet composed of a first layer derived from the first water-containing sheet and a second layer derived from the second slurry was obtained. At this time, the thickness of the water-containing laminated sheet was about 200 μm, and the basis weight of the composite sheet at absolute dryness was about 24 g / m 2 The papermaking speed was set to 7 m / min so as to be as follows. Next, using a press roll, the water-containing laminated sheet was dehydrated at a pressure of 6 kgf / cm 2 and further dried at 130 °C by a Yankee dryer to obtain a composite sheet. Thereafter, a solution of a phenolic resin, which is a carbon precursor resin, was dip-coated on this composite sheet and dried at 120 °C using a hot air dryer, and a resin-impregnated sheet having an adhesion amount of 25 parts by mass of the phenolic resin with respect to 100 parts by mass of the composite sheet was obtained. Then, heat pressing (250 °C, 1 minute) was performed by a double belt press. The thickness was 200 μm. Next, this resin-impregnated sheet was heat-treated for 1 minute in a graphitization furnace having an internal temperature of 2000 °C and a nitrogen gas atmosphere to carbonize the phenolic resin, the high melting point resin fiber, and the low melting point resin, and a carbon fiber sheet supporting graphite particles (hereinafter referred to as "fuel cell gas diffusion layer base material GD1") in which graphite particles are included and carbides such as resin bind the carbon fiber and the graphite particles was obtained (see Table 2). The thickness of the obtained fuel cell gas diffusion layer base material GD1 was 200 μm.

[0062] Example 2 As the first slurry, slurry S3 was used, and as the second slurry, slurry S2 was used. First, in the same manner as in Example 1, papermaking of slurry S3 (the first slurry) was carried out using a Fourdrinier papermaking machine to obtain a first water-containing sheet having a thickness of 250 μm. While the first water-containing sheet was in a conveying state, papermaking was carried out using a cylinder mold papermaking machine while supplying slurry S2 (the second slurry) to the surface of the first water-containing sheet to obtain a water-containing laminated sheet. At this time, the thickness of the water-containing laminated sheet was 450 μm, and the basis weight of the composite sheet at absolute dryness was about 48 g / m 2To achieve this, the papermaking speed was set to 7 m / min. Next, in the same manner as in Example 1, the water-containing laminated sheet was dewatered using a press roll and dried using a Yankee dryer in sequence to obtain a composite sheet. Subsequently, a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer substrate GD2") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer substrate GD2 was 200 μm.

[0063] Example 3 Slurry S5 was used as the first slurry, and slurry S1 was used as the second slurry. First, a short-wire paper machine was used to produce a paper sheet from slurry S5 (first slurry) to obtain a first water-containing sheet. At this time, the thickness of the first water-containing sheet was approximately 250 μm, and the basis weight when completely dry was approximately 24 g / m². 2 To achieve this, the papermaking speed was set to 7 m / min. Then, while the first water-containing sheet was being transported, papermaking was performed using a cylinder paper machine, supplying slurry S1 (second slurry) to the surface of the first water-containing sheet, thereby obtaining a water-containing laminated sheet consisting of a first layer derived from the first water-containing sheet and a second layer derived from the second slurry. At this time, the thickness of the water-containing laminated sheet was approximately 200 μm, and the basis weight of the composite sheet when completely dry was approximately 24 g / m². 2 To achieve this, the papermaking speed was set to 7 m / min. Next, in the same manner as in Example 1, the water-containing laminated sheet was dewatered using a press roll and dried using a Yankee dryer in sequence to obtain a composite sheet. Subsequently, a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer substrate GD3") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer substrate GD3 was 200 μm.

[0064] Comparative Example 1 Using a short-wire paper machine, slurry S3 (first slurry) was used for papermaking, dewatered using a press roll, and then dried at 130°C to obtain a single-layer sheet (hereinafter referred to as "single-layer sheet MS1") with a thickness of 250 μm. Next, this single-layer sheet MS1 was dip-coated with a phenol resin solution and dried at 120°C using a hot-air dryer to obtain a resin-impregnated sheet (hereinafter referred to as "resin-impregnated sheet RS1") in which the amount of phenol resin adhering to 100 parts by mass of the single-layer sheet was 25 parts by mass. On the other hand, a cylinder paper machine was used to make paper from slurry S1 (second slurry), which was then dewatered using a press roll and dried at 130°C to obtain a single-layer sheet (hereinafter referred to as "single-layer sheet MS2") with a thickness of 200 μm. Next, in the same manner as above, a phenolic resin solution was applied to the single-layer sheet MS2 and dried to obtain a resin-impregnated sheet (hereinafter referred to as "resin-impregnated sheet RS2") in which the amount of phenolic resin attached to 100 parts by mass of the single-layer sheet was 25 parts by mass. Next, using a double belt press, the resin-impregnated sheets RS1 and RS2 were stacked and subjected to a heat press (250°C, 1 minute) to obtain a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer substrate GD11") (see Table 2). The thickness of the obtained fuel cell gas diffusion layer substrate GD11 was 200 μm.

[0065] 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-formed to obtain a first water-containing sheet with a thickness of approximately 200 μm. Next, slurry S1 (second slurry) was hand-formed onto the surface of the first water-containing sheet to obtain a water-containing laminated sheet. Subsequently, the water-containing laminated sheet was pressed using a press roll at a pressure of 6 kgf / cm². 2 The material was dehydrated and then dried using a Yankee dryer to obtain a composite sheet with a thickness of 400 μm. Next, the same procedure as in Example 1 was performed to obtain a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer substrate GD12") (see Table 2). The thickness of the obtained fuel cell gas diffusion layer substrate ED1 was 200 μm.

[0066] Comparative Example 3 Using a short-wire paper machine, slurry S4 was used to produce a water-containing sheet. At this time, the thickness of the water-containing sheet was approximately 450 μm, and the basis weight when completely dry was approximately 48 g / m². 2 To achieve this, the papermaking speed was set to 7 m / min. Next, in the same manner as in Example 1, the water-containing sheet was dewatered using a press roll and dried using a Yankee dryer in sequence to obtain a single-layer sheet. Subsequently, a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer substrate GD13") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer substrate GD13 was 200 μm.

[0067] Comparative Example 4 A cylinder screen paper machine was used to produce a paper sheet from slurry S4, yielding a water-containing sheet. The water-containing sheet had a thickness of approximately 400 μm and a basis weight of approximately 48 g / m² when completely dry. 2 To achieve this, the papermaking speed was set to 7 m / min. Next, in the same manner as in Example 1, the water-containing sheet was dewatered using a press roll and dried using a Yankee dryer in sequence to obtain a single-layer sheet. Subsequently, a graphite particle-supported carbon fiber sheet (hereinafter referred to as "fuel cell gas diffusion layer substrate GD14") was obtained in the same manner as in Example 1 (see Table 2). The thickness of the obtained fuel cell gas diffusion layer substrate GD14 was 200 μm.

[0068] 4. Evaluation of gas diffusion layer substrate The fuel cell gas diffusion layer substrates GD1-GD3 and GD11-GD14 described above were evaluated. The results are shown in Table 2.

[0069] 4-1. Evaluation of the packing properties of materials in gas diffusion layer substrates for fuel cells. The obtained fuel cell gas diffusion layer substrate was cut perpendicular to the thickness direction and divided equally into three regions in the thickness direction to define the first region F, the second region S, and the third region T. The material packing density in each region was measured using a Rigaku high-resolution X-ray microscope "nano3DX" (model name). The first region F and the third region T mainly consist of a combination of carbon fibers and graphite particles contained in the first slurry and carbides after the carbonization process (J1), and a combination of carbon fibers and graphite particles contained in the second slurry and carbides after the carbonization process (J2), respectively. The second region S is derived from these combinations (J1) and (J2). Cross-sectional images (2D observation images) were taken, and in order to analyze the areas where material is present and absent in each of the first region F, second region S, and third region T, the images were binarized using image processing software with a threshold of 128, and the area ratio of the white areas where material is present was defined as the "filling rate". Therefore, the filling rates in the first region F, second region S, and third region T were defined as A, respectively. F , A S and A T That's what I decided.

[0070] 4-2. Tensile strength and transport resistance As described above, since a roll-shaped fuel cell gas diffusion layer substrate was manufactured, two test specimens (size: 15 mm x 100 mm) were prepared for measuring tensile strength: one in the flow direction (MD) and one perpendicular to it (TD). The tensile strength was measured according to the method conforming to JIS P 8113. Then, the T1 / T2 ratio was calculated, with the tensile strength in the MD direction and the tensile strength in the TD direction being T1 and T2, respectively, and the transport resistance was evaluated according to the following criteria. 〇: T1 / T2≦2 ×:T1 / T2>2

[0071] 4-3. Battery Characteristics The above fuel cell gas diffusion layer substrates GD1 to GD3 and GD11 to GD14 were processed by the following method to produce water-repellent gas diffusion layer substrates for cathode electrodes. Subsequently, a microporous layer was formed on one side of the obtained water-repellent gas diffusion layer substrates for cathode electrodes to produce a laminated gas diffusion layer for cathode electrodes.

[0072] A 40 μm thick polyethylene film was placed on both sides of the fuel cell gas diffusion layer substrate and pressed with a surface pressure of 1.5 MPa to remove loose carbon fiber fuzz. Next, this film laminate was impregnated with PTFE dispersion manufactured by Asahi Glass Co., Ltd. and heat-treated at 200°C, resulting in a concentration of 10 parts by mass (basis weight: 0.45 mg / cm³) of PTFE per 100 parts by mass of the cathode electrode gas diffusion layer substrate. 2 A substrate for a cathode electrode with a water-repellent gas diffusion layer, which is then applied to the substrate, was obtained. Next, a paste for forming a microporous layer was applied to the surface of the obtained water-repellent gas diffusion layer substrate for the cathode electrode and dried to produce a laminated structure for a gas diffusion layer for a cathode electrode that includes a microporous layer.

[0073] Furthermore, a water-repellent gas diffusion layer laminate for the anode electrode was fabricated using the following method. A slurry containing the above-mentioned carbon fibers, high-melting-point resin fibers, low-melting-point resin fibers, graphite particles, and water was subjected to papermaking, then impregnated with resin, and heat-treated at 2000°C to obtain an anode electrode gas diffusion layer substrate. The surface of the substrate obtained was subjected to the same water-repellent treatment as above to obtain an anode electrode water-repellent gas diffusion layer substrate. Next, a paste for forming a microporous layer was applied to one side of the obtained anode electrode water-repellent gas diffusion layer substrate and dried to produce an anode electrode water-repellent gas diffusion layer laminate with a microporous layer.

[0074] Next, on both sides of the obtained cathode electrode water-repellent gas diffusion layer laminate, the anode electrode water-repellent gas diffusion layer laminate, and the electrolyte layer 31 consisting of the Nafion® series electrolyte membrane "NRE-212" (product name), a Pt-supported material made of 50% Pt / C with a Pt load of 0.5 mg / cm³ is applied. 2A membrane / electrode assembly 10, as shown in Figure 3, was manufactured using a fuel cell electrode membrane comprising catalyst layers 15 and 25. This membrane / electrode assembly 10 sequentially comprises a cathode electrode gas diffusion layer 11 derived from a water-repellent treated cathode electrode water-repellent gas diffusion layer substrate, a microporous layer 13, a catalyst layer 15, an electrolyte layer 31, a catalyst layer 25, a microporous layer 23, and an anode electrode gas diffusion layer 21. Subsequently, this membrane / electrode assembly 10 was used with a separator, current collector plate, etc. to fabricate a JARI standard cell, which was then incorporated into a single cell for fuel cell evaluation. Using an ENOA fuel cell evaluation device, it was tested at 40°C and 2A / cm². 2 The voltage generated was measured. Based on the voltage value (0.60V) in Comparative Example 3, the battery performance was determined according to the following criteria (see Table 2). ◎: The voltage value was 0.63V or higher. ○: The voltage value was between 0.61V and less than 0.63V. △: The voltage value was between 0.59V and less than 0.61V. ×: The voltage value was less than 0.59V.

[0075] [Table 2]

[0076] From Table 2, the following can be seen. Examples 1 to 3 are examples of the manufacturing method according to the present invention. The resulting fuel cell gas diffusion layer substrates exhibited high tensile strength T1 in the flow direction and high tensile strength T2 in the direction perpendicular to it, and T1 / T2 was less than 2, resulting in good transportability. Furthermore, the battery performance of the fuel cell obtained by forming a cathode fuel cell gas diffusion layer using these fuel cell gas diffusion layer substrates was significantly better than that of the comparative examples.

[0077] Furthermore, the present invention is not limited to the specific embodiments shown above, and various modified embodiments can be made within the scope of the present invention depending on the purpose and application. [Industrial applicability]

[0078] The fuel cell gas diffusion layer substrate obtained by the present invention is suitable as a material for forming the cathode electrode gas diffusion layer that constitutes the membrane / electrode assembly contained in the fuel cell. Therefore, a fuel cell equipped with such a cathode electrode gas diffusion layer has high power generation performance and can be used in transport fuel cells for vehicles, stationary fuel cells, and the like. [Explanation of Symbols]

[0079] 1: Substrate for gas diffusion layer in fuel cells 2: Carbon fiber 4: Graphite particles 6: Carbonized part 10: Membrane / electrode assembly 11: Gas diffusion layer for cathode electrode 13: Microporous layer 15: Catalyst layer 21: Gas diffusion layer for anode electrode 23: Microporous layer 25: Catalyst layer 31: Electrolyte layer F:First area S:Second area T:Third area

Claims

1. A first water-containing sheet manufacturing step involves using a first slurry containing carbon fibers (A1), graphite particles (B1), organic fibers (C1) that will be carbonized in a later carbonization step, and water to produce a first water-containing sheet. A water-containing laminated sheet manufacturing step involves supplying a second slurry containing carbon fibers (A2), graphite particles (B2), organic fibers (C2) to be carbonized in a later carbonization step, and water to the surface of the first water-containing sheet to produce a water-containing laminated 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 manufacturing step involves squeezing and drying the aforementioned water-containing laminated sheet to produce a composite sheet, A resin impregnation step is performed to produce a resin-impregnated sheet by impregnating the composite sheet with a carbon precursor resin that will be carbonized in a later carbonization step, The process is to sequentially include a carbonization step in which the resin-impregnated sheet is heated and fired in a non-oxidizing atmosphere, The first water-containing sheet is a sheet in which 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) are interposed between the fibers. A method for manufacturing a gas diffusion layer substrate for a fuel cell, wherein 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.

2. The method for manufacturing a gas diffusion layer substrate for a fuel cell according to claim 1, wherein in the first water-containing sheet manufacturing step, a short-wire paper machine or a long-wire paper machine is used.

3. A method for manufacturing a gas diffusion layer substrate for a fuel cell according to claim 1 or 2, wherein a cylinder wire paper machine is used in the water-containing laminated sheet manufacturing step.

4. A method for manufacturing a gas diffusion layer substrate 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.

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