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

Abstract

The present invention provides a method for manufacturing a gas diffusion layer substrate that has high normal permeability in the thickness direction, a low contact resistance per unit thickness, and a fuel cell that exhibits high power generation performance. [Solution] The present invention provides a method for manufacturing a gas diffusion layer substrate for fuel cells, comprising, in order: a water-containing sheet manufacturing step, which involves using a slurry containing carbon fibers, graphite particles having a particle diameter of 120 μm or more, fibrillated organic fibers that will be carbonized in a later carbonization step, and water to produce a water-containing sheet containing carbon fibers, graphite particles, and fibrillated organic fibers; a composite sheet manufacturing step, which involves squeezing the water from the water-containing sheet and drying it to produce a composite sheet; a resin impregnation step, which involves impregnating the composite sheet with a carbon precursor resin that will be carbonized in a later carbonization step to produce a resin-impregnated sheet; a compression step, which involves compressing the resin-impregnated sheet to produce a thin-walled sheet; and a carbonization step, which involves heating and firing the thin-walled sheet in a non-oxidizing atmosphere.

Description

Technical Field

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

Background Art

[0002] A solid polymer fuel cell (hereinafter simply referred to as "fuel cell"), which is widely used as a power source for automobiles and the like, is composed of a plurality of fuel cell cells stacked via separators. In one single cell, on both sides of a polymer electrolyte membrane that selectively permeates specific ions, there are a catalyst layer composed of a conductive material such as carbon supporting a catalyst such as platinum and an ion exchange resin, and a porous gas diffusion layer disposed outside each catalyst layer. Cathode (+) side electrodes and anode (-) side electrodes are arranged to form a membrane / electrode assembly. And, outside the gas diffusion layer constituting this membrane / electrode assembly, a separator is arranged that forms a gas flow path for supplying a fuel gas (anode gas) or an oxidizing gas (cathode gas) and discharging the generated gas and excess gas, and the membrane / electrode assembly is sandwiched by the separator.

[0003] In the fuel cell having the above structure, the gas diffusion layer constituting the electrodes of the single cell is arranged to enhance the diffusibility of the reaction gas. And, since it is responsible for the action (gas diffusibility) of diffusing the fuel gas or oxidizing gas supplied from the gas flow path of the separator to the catalyst layer adjacent to the gas diffusion layer, it has not only gas permeability but also conductivity as a current collecting function for efficiently moving electrons for the electrochemical reaction. Further, the gas diffusion layer always keeps the polymer electrolyte membrane and the catalyst layer in an optimal wet state. In particular, in the gas diffusion layer of the cathode electrode, in order to suppress the flooding phenomenon (the phenomenon in which the pores of the gas diffusion layer are blocked by water) and stabilize the power generation performance, water repellency (drainage property) for discharging excess reaction product water and condensed water generated by the electrochemical reaction of hydrogen and oxygen during power generation is required.

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

[0005] For example, Patent Document 1 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.

[0006] Furthermore, Patent Document 2 discloses a carbon fiber sheet in which particles or particle aggregates exist between carbon fibers, characterized in that the particles or particle aggregates include large particles or large particle aggregates having a diameter of 1.5 times or more the average fiber diameter of the carbon fibers, between the carbon fibers in the thickness direction. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2020-87826 [Patent Document 2] Japanese Patent Publication No. 2022-125104 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a gas diffusion layer substrate that has high normal permeability in the thickness direction, a low contact resistance per unit thickness, and a method for manufacturing the same, which provides a fuel cell that exhibits high power generation performance. [Means for solving the problem]

[0009] The inventors have discovered that when manufacturing a gas diffusion layer substrate for fuel cells using carbon fibers, graphite particles, and organic fibers, the above-mentioned problems can be solved by using graphite particles with a particle size exceeding 120 μm in combination with fibrillated organic fibers.

[0010] The present invention is shown below. [1] A water-containing sheet manufacturing step, which involves using a slurry containing carbon fibers, graphite particles with a particle diameter of 120 μm or more as measured by laser diffraction and scattering (hereinafter, the particle diameter measured by this method is simply referred to as "particle diameter"), and fibrillated organic fibers that are carbonized in a subsequent carbonization step, to produce a water-containing sheet containing the above carbon fibers, the above graphite particles, and the fibrillated organic fibers. A composite sheet manufacturing process is performed by squeezing and drying the above-mentioned water-containing 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, A compression step is performed to compress the above resin-impregnated sheet to produce a thin sheet, A carbonization process in which the thinned sheet is heated and fired in a non-oxidizing atmosphere. A method for manufacturing a gas diffusion layer substrate for fuel cells, comprising the following components in sequence. [2] A method for producing a gas diffusion layer substrate for fuel cells according to item [1], wherein the carbon fiber content in the composite sheet is 20 to 80% by mass. [3] A method for producing a gas diffusion layer substrate for a fuel cell according to item [1], wherein the content ratio of the graphite particles contained in the composite sheet is 5 to 60% by mass. [4] A method for producing a gas diffusion layer substrate for a fuel cell according to item [1], wherein the content of the fibrillated organic fibers contained in the composite sheet is 5 to 60% by mass. [5] A method for producing a gas diffusion layer substrate for a fuel cell according to item [1], wherein the content of the carbon precursor resin contained in the resin-impregnated sheet is 10 to 80% by mass. [6] A method for manufacturing a gas diffusion layer substrate for a fuel cell according to item [1] above, wherein in the compression step above, the graphite particles are crushed and compressed in the planar direction so that the thickness is less than the particle diameter of the graphite particles. [7] A gas diffusion layer substrate for fuel cells obtained by the method for manufacturing a gas diffusion layer substrate for fuel cells described in item [1] above. [8] A fuel cell gas diffusion layer substrate according to item [7] above, wherein graphite is exposed on at least one surface. [9] A carbonization precursor sheet containing carbon fibers, graphite particles larger than 120 μm, fibrillated organic fibers, and impregnated resin is carbonized. A gas diffusion layer substrate having the graphite particles exposed on at least one surface. [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, a gas diffusion layer base material with high normal permeability in the thickness direction can be obtained. After manufacturing a membrane / electrode assembly using this gas diffusion layer base material, a fuel cell with a low contact resistance value per unit thickness of the gas diffusion layer base material can be obtained. That is, according to the present invention, a gas diffusion layer base material suitable as a manufacturing material for a fuel cell that achieves both gas diffusibility and conductivity can be manufactured. According to the present invention, in the water-containing sheet obtained by the water-containing sheet manufacturing process and the composite sheet obtained by the composite sheet manufacturing process, graphite particles having a particle diameter exceeding 120 μm are particularly surely held between fibrillated organic fibers, and compared with the case of using graphite particles having a small particle diameter of 120 μm or less, there will be large voids between adjacent graphite particles. However, thereafter, the graphite particles contained in the resin-impregnated sheet may be crushed by the compression process, and by the carbonization process, a gas diffusion layer base material having voids with air permeability in the thickness direction formed therein can be efficiently obtained. A fuel cell manufactured 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 flowchart showing the flow of the manufacturing method of the present invention. [Figure 2] It is a schematic cross-sectional view of the gas diffusion layer base material for a fuel cell obtained by the present invention. [Figure 3] It is an image showing a cross section of the gas diffusion layer base material for a fuel cell obtained in Example 1.

Embodiments for Carrying Out the Invention

[0013] The method for manufacturing a gas diffusion layer base material for a fuel cell according to the present invention will be described with reference to FIG. 1.

[0014] The manufacturing method of the present invention is a method for manufacturing a gas diffusion layer base material (see Figure 2), which is a manufacturing material for a fuel cell, using a raw material containing carbon fiber C1, graphite particles P1 with a particle diameter exceeding 120 μm, and fibrillated organic fiber R1. As described above, it sequentially includes a water-containing sheet manufacturing step S1, a composite sheet manufacturing step S2, a resin impregnation step S3, a compression step S4, and a carbonization step S5. In addition, the manufacturing method of the gas diffusion layer base material for a fuel cell of the present invention can further include other steps (described later) if necessary.

[0015] The water-containing sheet manufacturing step S1 is a step of manufacturing a water-containing sheet 11 using a slurry containing carbon fiber C1, graphite particles P1 with a particle diameter exceeding 120 μm, and fibrillated organic fiber (hereinafter referred to as "fibrillated organic fiber R1") that is carbonized in a subsequent carbonization step. This slurry may contain other components such as graphite particles P2 with a particle diameter of 120 μm or less (hereinafter referred to as "graphite particles P2") and non-branched organic fibers (hereinafter referred to as "organic fibers R2") if necessary. That is, the raw material for the water-containing sheet used in the water-containing sheet manufacturing step S1 is a slurry containing carbon fiber C1, graphite particles P1, and fibrillated organic fiber R1, and may contain other components such as graphite particles P2 and organic fibers R2 if necessary. Further, the solvent in the above slurry is water or an aqueous solvent. Among these, the aqueous solvent is a mixed solvent of water and a water-soluble organic solvent. Examples of this water-soluble organic solvent include alcohols (such as methanol, ethanol, and isopropanol), ketones (such as acetone and ethyl methyl ketone), ethers (such as dimethyl ether), and acetonitrile. These water-soluble organic solvents may be used alone or in combination of two or more. The content of the water-soluble organic solvent in the aqueous solvent is preferably 50% by mass or less, more preferably 30% by mass or less, and still more preferably 10% by mass or less when the aqueous solvent is 100% by mass.

[0016] The composition (type, size, etc.) of the carbon fiber C1 according to the present invention is not particularly limited. This carbon fiber C1 may be any of the following: vapor-grown carbon fiber, carbon nanotubes (single-wall, double-wall, multi-wall, cup-laminated, etc.), polyacrylonitrile (PAN) carbon fiber, pitch carbon fiber, or rayon carbon fiber.

[0017] The carbon fiber C1 may be in either a straight or curved shape. The average fiber diameter of the carbon fiber C1 is preferably 5 to 15 μm, more preferably 6 to 8 μm, from the viewpoint of the gas diffusion properties and conductivity exhibited by the gas diffusion layer in a fuel cell manufactured using the resulting fuel cell gas diffusion layer substrate. The fiber length of carbon fiber C1 is typically 12 mm at the upper limit and 2 mm at the lower limit. Furthermore, the average fiber length of carbon fiber C1 is preferably 2 to 9 mm, more preferably 3 to 6 mm, from the viewpoint of the gas diffusion properties and conductivity of the gas diffusion layer exhibited by the gas diffusion layer in a fuel cell manufactured using the resulting fuel cell gas diffusion layer substrate.

[0018] In the present invention, graphite particles P1 with a particle diameter exceeding 120 μm are used in a fuel cell manufactured using the resulting fuel cell gas diffusion layer substrate 1, from the viewpoint of gas diffusion properties and drainage properties exhibited by the gas diffusion layer. In the present invention, the composition (type, size, specific surface area, etc.) of the graphite particles P1 is not particularly limited. The graphite particles P1 may consist of either natural graphite or artificial graphite. Furthermore, the shape of the graphite particles P1 can be spherical, ellipsoidal, plate-like, linear, irregular, etc., and in the case of spherical or ellipsoidal shapes, they may be expanded bodies. Moreover, the graphite particles P1 may be aggregates of primary particles. The particle diameter of the graphite particles P1 is preferably 125 to 300 μm, more preferably 130 to 250 μm.

[0019] In the moisture-containing sheet manufacturing step S1 according to the present invention, graphite particles P2 with a particle diameter of 120 μm or less may be used, as long as a moisture-containing sheet 11 that retains them can be obtained. The composition (type, specific surface area, shape, etc.) of graphite particles P2 can be the same as that of graphite particles P1. The particle diameter of graphite particles P2 is preferably 10 to 120 μm.

[0020] The fibril organic fiber R1 according to the present invention is an organic fiber that is carbonized in a subsequent carbonization process, and comprises a stem fiber portion extending in the longitudinal direction of the fiber, and branched fiber portions that branch off from the stem fiber portion and are usually shorter in diameter than the stem fiber portion. The composition (type, size, etc.) of the fibril organic fiber R1 is not particularly limited. Examples of constituent materials for this fibril organic fiber R1 include acrylonitrile polymers, polyvinyl alcohol, polyolefins, polyurethanes, polyesters, polyamides, acrylic resins, aramids, polyacetals, polylactic acid, phenolic resins, cellulose, and the like. Of these, acrylonitrile polymers are preferred.

[0021] The cross-sectional shape of the stem fiber portion, which does not involve branched fibers, constituting the fibril organic fiber R1 is not particularly limited and can be a circle, ellipse, polygon, or a variation thereof. This cross-sectional shape is usually the same throughout the entire length of the fibril organic fiber R1. The average fiber diameter of the stem fiber portion is preferably 5 to 20 μm, more preferably 6 to 8 μm. The length of the stem fiber portion, which is substantially the length of the fibril organic fiber R1, is preferably 1 to 15 mm, more preferably 1 to 10 mm.

[0022] The cross-sectional shape of the branched fiber portion constituting the fibril organic fiber R1 is not particularly limited and can be a circle, ellipse, semicircle, fan-shaped, polygonal, or a variation thereof. This cross-sectional shape may or may not be the same along the entire length of the branched fiber portion.

[0023] The degree of fibrillation of fibril fiber R1 is generally quantified by the degree of water filtration, specific surface area, etc. The Canadian standard water filtration of fibril organic fiber R1 according to the present invention, measured in accordance with JIS P 8121-2, is preferably 50 to 700 mL, more preferably 150 to 600 mL. When fibril organic fiber R1 having a water filtration within the above range is used, the degree of entanglement between multiple types of fibers increases in the water-containing sheet 11 obtained in the water-containing sheet manufacturing step S1 and the composite sheet 12 obtained in the composite sheet manufacturing step S2, and a stable sheet shape can be obtained in which graphite particles P1 with a particle diameter of 120 μm or more, preferably the graphite particles P1 and carbon fibers C1, are suitably held using the branched fiber portions.

[0024] In the water-containing sheet manufacturing step S1 according to the present invention, as described above, unbranched organic fibers R2, i.e., general linear organic fibers, may also be used. The composition of the organic fibers R2 (structure such as cross-sectional shape, size such as fiber diameter and fiber length) is not particularly limited. These organic fibers R2 may be monofilaments or multifilaments. Examples of constituent materials for the organic fibers R2 include acrylonitrile polymers, polyvinyl alcohol, polyolefins, polyurethanes, polyesters, polyamides, acrylic resins, aramids, polyacetals, polylactic acid, phenolic resins, and cellulose. In the water-containing sheet manufacturing step S1 according to the present invention, it is preferable to use both fibril organic fibers R1 and organic fibers R2, and it is particularly preferable to use resin fibers made of polyvinyl alcohol as the organic fibers R2. The organic fibers R2 used may consist of two or more organic fibers containing different resins, for example, a resin fiber mainly composed of a high-melting-point resin and a resin fiber mainly composed of a resin with a lower melting point may be used in combination.

[0025] In the water-containing sheet manufacturing step S1 according to the present invention, the proportion of carbon fiber C1, graphite particles P1, and fibril organic fiber R1 used is not particularly limited. If the total of these is 100% by mass, the proportions of carbon fiber C1, graphite particles P1, and fibril organic fiber R1 used are preferably 20-80% by mass, 5-60% by mass, and 5-60% by mass, and more preferably 30-70% by mass, 10-50% by mass, and 10-50% by mass.

[0026] In the present invention, as described above, graphite particles P2 or organic fibers R2 can be used, and the proportion of these materials used is as follows. The upper limit of the amount of graphite particles P2 used is preferably 50 parts by mass, and more preferably 40 parts by mass, assuming that the amount of graphite particles P1 used is 100 parts by mass. Furthermore, when using organic fiber R2, the proportions of carbon fiber C1, graphite particles P1, fibril organic fiber R1, and organic fiber R2 used are preferably 20-80% by mass, 5-60% by mass, 5-60% by mass, and 5-60% by mass, and more preferably 30-70% by mass, 10-40% by mass, 10-40% by mass, and 10-40% by mass.

[0027] The slurry according to the present invention comprises at least carbon fiber C1, graphite particles P1, and fibril organic fiber R1, and may optionally include a binder, carbides of organic materials, additives (such as flocculants, viscosity modifiers, and surfactants).

[0028] The binder can be polyvinyl alcohol, polyvinyl acetate, polyethylene, polyolefins such as polypropylene, polyesters such as polyethylene terephthalate, polyacrylonitrile, cellulose, polyethylene oxide, polyacrylamide, phenolic resin, xylenol resin, styrene-butadiene rubber, starch, corn starch, etc.

[0029] The solid content concentration in the slurry according to the present invention is preferably 0.001 to 2% by mass, and more preferably 0.01 to 0.1% by mass.

[0030] The method for preparing the slurry is not particularly limited, and for example, it can be a method of mixing raw materials using a rotary device such as a pulper.

[0031] In the water-containing sheet manufacturing step S1 and the composite sheet manufacturing step S2 according to the present invention, it is preferable to apply a papermaking method.

[0032] In the moisture-containing sheet manufacturing process S1, paper machines such as cylinder paper machines, long screen paper machines, short screen paper machines, and inclined wire paper machines can be used. The papermaking speed for obtaining the moisture-containing sheet 11 is preferably 4 m / min or more, more preferably 7 m / min or more. The take-up speed is usually the same as the papermaking speed.

[0033] In the present invention, after the water-containing sheet manufacturing step S1, the obtained water-containing sheet 11 can be subjected to entanglement treatment as needed. Examples of entanglement methods include mechanical entanglement (e.g., needle punching), high-pressure liquid injection (e.g., water jet punching), and high-pressure gas injection (e.g., steam jet punching).

[0034] Next, in the composite sheet manufacturing step S2, the water-containing sheet 11 is squeezed and dried to produce the composite sheet 12. In the present invention, the composite sheet 12 may be manufactured using a single-layer water-containing sheet or a laminated water-containing sheet made by stacking multiple single-layer water-containing sheets.

[0035] In the composite sheet manufacturing step S2 according to the present invention, the methods for dewatering and drying the water-containing sheet 11 are not particularly limited. Dewatering can be performed using a suction box for drawing in water, a press roll for compressing and dewatering, 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 12. Depending on the shape and size of the sheet, drying may be performed under reduced pressure. The heating temperature (drying temperature) is not particularly limited as long as it does not deform or deteriorate the fibril organic fibers R1 and organic fibers R2, and is preferably 70°C to 160°C, more preferably 90°C to 130°C.

[0036] The completely dry composite sheet 12 obtained in the composite sheet manufacturing process S2 has a structure in which carbon fibers C1 and graphite particles P1 are held between fibril organic fibers R1 to the extent that they do not easily move within the sheet. Therefore, this composite sheet 12 has a composition in which the proportion of raw materials used in the water-containing sheet manufacturing process S1 is maintained. Furthermore, the basis weight of the obtained composite sheet 12 is preferably 20 to 150 g / m². 2 The thickness is preferably 1.5 to 6 times the thickness of the gas diffusion layer substrate to be manufactured, and is usually 50 to 600 mm.

[0037] The carbon fiber C1 content in the composite sheet 12 according to the present invention is preferably 20 to 80% by mass, more preferably 30 to 70% by mass. The content of graphite particles P1 in the composite sheet 12 is preferably 5 to 60% by mass, more preferably 10 to 50% by mass. Furthermore, the content of fibril organic fibers R1 in the composite sheet 12 is preferably 5 to 60% by mass, more preferably 10 to 50% by mass.

[0038] The composite sheet 12 according to the present invention contains various types of fibers (carbon fiber C1, fibril organic fiber R1, etc.), and the length of each fiber also varies. Therefore, some of the fibers may protrude from the surface of the composite sheet 12 after drying, i.e., it may become fuzzy, and the surface of the composite sheet 12 may not be smooth. In this case, if necessary, before the resin impregnation process, a process may be performed to cut or remove the fibers protruding from the surface of the composite sheet 12, or a process may be performed to push the fibers into the interior of the composite sheet 12.

[0039] Subsequently, in the resin impregnation process S3, a carbon precursor resin that can be carbonized in the carbonization process is impregnated into the composite sheet 12 to produce a resin-impregnated sheet 13. The carbon precursor resin is not particularly limited, but it is preferable to include thermosetting resins such as phenol resins, furan resins, epoxy resins, melamine resins, imide resins, urethane resins, aramid resins, urea resins, and unsaturated polyester resins because they have excellent wettability with carbon fibers C1, fibril organic fibers R1, or other organic fibers R2, and readily form conductive carbides in the subsequent carbonization process. Of these, phenol resins are particularly preferred because they have a high carbonization rate and become excellent conductive materials after carbonization. Depending on the type of thermosetting resin, the carbon precursor resin may also contain a curing accelerator.

[0040] In the resin impregnation step S3 according to the present invention, if the carbon precursor resin is in liquid form, it can be used as is. Alternatively, a solution (resin solution) obtained by dissolving the liquid carbon precursor resin in a solvent, or a dispersion (resin dispersion) obtained by dispersing the carbon precursor resin in a dispersion medium may be used. If the carbon precursor resin is solid, it is preferable to use a solution (resin solution) obtained by dissolving the carbon precursor resin in a solvent. In the resin impregnation step S3, using a resin solution or resin dispersion allows for efficient penetration into the composite sheet 12, which is a fiber aggregate containing carbon fibers C1, graphite particles P1, fibril organic fibers R1, and other organic fibers R2, and has voids.

[0041] When preparing the resin-impregnated sheet 13, if a carbon precursor resin-containing liquid is used, methods such as immersing the composite sheet 12 in the carbon precursor resin-containing liquid or applying the carbon precursor resin-containing liquid to the composite sheet 12 (kiss coat method, spray method, curtain coat method, roller contact method, etc.) can be applied. Of these, the method of immersing the composite sheet 12 in the carbon precursor resin-containing liquid is preferred.

[0042] The drying state of the resin-impregnated sheet used in the carbonization process S5 is not particularly limited. Therefore, when the composite sheet 12 is brought into contact with the carbon precursor resin-containing liquid in the resin-impregnation process S3, a dry resin-impregnated sheet 13 free of solvent or dispersion medium can be obtained by using a non-contact drying method, such as blowing hot air onto the liquid-attached sheet, placing the liquid-attached sheet in a high-temperature atmosphere, or using an infrared heater or microwave to dry the liquid-attached sheet, or by using a contact drying method, such as bringing the liquid-attached sheet into contact with a heated roll, plate, etc.

[0043] As described above, using a carbon precursor resin-containing liquid in the resin impregnation process S3 allows the liquid to efficiently penetrate into the composite sheet. However, other methods for impregnating the composite sheet 12 with carbon precursor resin without using a carbon precursor resin-containing liquid include methods such as contacting and adhering a resin film containing carbon precursor resin to at least a portion of the surface of the composite sheet 12, and then dissolving the adhering carbon precursor resin by heating, solvent spraying, etc., to allow it to penetrate the entire composite sheet 12.

[0044] In the resin impregnation step S3 according to the present invention, it is preferable to contact the carbon precursor resin-containing liquid, etc., such that the carbon precursor resin-containing liquid is 10 to 80% by mass, and more preferably 20 to 70% by mass, when the total amount of the completely dry composite sheet 12 and the carbon precursor resin (pure content) is 100% by mass. When the carbon precursor resin-containing liquid is 25 to 50% by mass, the permeability in the thickness direction of the gas diffusion layer substrate 1 of the present invention obtained by the carbonization step S5 is suitable.

[0045] Next, in the compression step S4, the resin-impregnated sheet 13 obtained in the resin-impregnation step S3 is compressed to form a thinned sheet 14. The degree of compression is not particularly limited, but it is done so that graphite particles P1 used as the manufacturing raw material or small pieces derived therefrom are exposed on the surface of at least one side. Furthermore, even if the obtained thinned sheet 14 is subjected to the subsequent carbonization step S5, its thickness does not change, so the thickness of the thinned sheet 14 obtained in this compression step is substantially the same as the thickness of the gas diffusion layer substrate 1 of the present invention.

[0046] In the compression step S4 according to the present invention, depending on the size of the graphite particles P1 contained in the resin-impregnated sheet 13, a thinned sheet 14 thinner than the particle diameter can be obtained. For example, when producing a thinned sheet 14 with a thickness less than the particle diameter of the graphite particles P1, the resin-impregnated sheet 13 is compressed while crushing the graphite particles P1. Even in such cases, the carbon precursor resin contained in the resin-impregnated sheet 13 prevents the graphite particles P1 or their crushed material from detaching, ensuring reliable compression of the resin-impregnated sheet 13. Furthermore, a thinned sheet thinner than the particle diameter of the graphite particles P1 will contain crushed graphite particles P1. On the other hand, when producing a thinned sheet 14 with a thickness greater than or equal to the particle diameter of the graphite particles P1, it is usually possible to obtain a thinned sheet 14 in which the shape of the graphite particles P1 is maintained. However, if the graphite particles P1 in the composite sheet 12 are in the above-mentioned preferred content ratio, some of the graphite particles P1 tend to be exposed on at least one side of the thinned sheet 14.

[0047] In the compression step S4 according to the present invention, a hydraulic press, belt press, roll press, etc., can be used. The compression conditions (pressure, time, etc.) are not particularly limited. Depending on the type of carbon precursor resin, the resin-impregnated sheet 13 may be compressed while heating. If the carbon precursor resin contains a thermosetting resin, compressing the resin-impregnated sheet 13 while heating will yield a thin sheet whose shape is fixed by a cured resin that readily forms conductive carbides in the subsequent carbonization step S5.

[0048] The thickness of the thinned sheet 14 according to the present invention is preferably 50 to 500 μm, more preferably 50 to 300 μm.

[0049] Subsequently, in carbonization step S5, the thinned sheet 14 is heated and fired in a non-oxidizing atmosphere to obtain the fuel cell gas diffusion layer substrate 1 of the present invention. The non-oxidizing atmosphere can be an atmosphere containing an inert gas such as argon gas or helium gas, or nitrogen gas. The heating and firing method is not particularly limited and can be a method using a high-temperature furnace, a method using laser irradiation, etc.

[0050] When heating and firing the thinned sheet 14, the heating temperature 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 C1 and to facilitate the carbonization of the organic fibers and carbon precursor resin. When using a high-temperature furnace for heating and firing, a multi-stage heating method may be applied in which the thinned sheet 14 is heated at a temperature lower than the above preferred temperature before being raised. Furthermore, the heating time for the thinned sheet 14 is usually 1 minute or more, although this depends on its size.

[0051] When irradiating the thinned sheet 14 with a laser, either a continuous-wave laser or a pulsed-wave laser may be used. Specific methods for irradiating with a laser include irradiating the thinned sheet 14 while it is fixed, moving the thinned sheet 14 while irradiating it with a laser at a predetermined position, and, if necessary, repeatedly spot-irradiating the thinned sheet 14 using multiple laser light sources, or irradiating the thinned sheet 14 with a laser while scanning the laser or widening the irradiation area through a diffusion lens.

[0052] In the carbonization process S5 according to the present invention, the organic fibers and carbon precursor resin contained in the thinned sheet 14 are carbonized, forming voids inside that have suitable permeability in the thickness direction, and further, the formed carbides bind the carbon fibers C1 together, the graphites together, or the carbon fibers C1 and graphite together, thereby obtaining a fuel cell gas diffusion layer substrate 1 (see Figure 2).

[0053] The fuel cell gas diffusion layer substrate 1 used in the fabrication of a membrane / electrode assembly, which is a manufacturing component of a fuel cell, can be obtained by the carbonization process S5 according to the present invention. However, the fuel cell gas diffusion layer substrate manufacturing method of the present invention may further include, if necessary, a smoothing process to smooth the surface, a water-repellent process to make the surface water-repellent, and so on.

[0054] 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.

[0055] Figure 2 is a schematic cross-sectional view showing a preferred embodiment of the 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 C1, a plurality of graphite portions 4 (derived from graphite particles P1 or their crushed material), and a carbonized portion 6 made of carbides formed by carbonizing organic fibers contained in a water-containing sheet and carbon precursor resin contained in a thinned sheet through a carbonization process. The structure is such that the graphite portions 4 are exposed on at least one surface of the gas diffusion layer substrate. The carbonized portion 6 in Figure 2 does not indicate that the area excluding the carbon fibers C1 and graphite portions 4 is filled with carbides. Rather, the carbides bind the graphite portions to each other, or to the carbon fibers C1 and graphite portions 4, and voids (not shown) are formed from one side to the other of the fuel cell gas diffusion layer substrate 1, i.e., inside the carbonized portion 6, to the extent that it is permeable in the thickness direction of the gas diffusion layer substrate.

[0056] The fuel cell gas diffusion layer substrate 1 of the present invention is a thin plate-like material with a thickness preferably of 55 to 600 μm, more preferably of 70 to 350 μm.

[0057] The fuel cell gas diffusion layer substrate 1 of the present invention can be used, for example, to form a gas diffusion layer for the cathode electrode or anode electrode in a membrane / electrode assembly. A particularly preferred embodiment of a membrane / electrode assembly (not shown) comprises, in order, a cathode electrode gas diffusion layer, a microporous layer, a catalyst layer, an electrolyte layer, a catalyst layer, a microporous layer, and an anode electrode gas diffusion layer, all formed using the fuel cell gas diffusion layer substrate 1 of the present invention.

[0058] The fuel cell gas diffusion layer substrate 1 obtained by the present invention has a strong conductive path due to the carbide-based phase (carbide portion 6) and the carbon fibers C1 and graphite portion 4 contained in the phase. Furthermore, because the carbide is derived from organic fibers and carbon precursor resin, the gas diffusion layer substrate has elasticity, and its dimensional absorption is enhanced 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 fuel cell gas diffusion layer substrate of the present invention is used as a cathode electrode gas diffusion layer substrate to produce a membrane / electrode assembly, and this is used to drive a fuel cell, the water generated during power generation can be efficiently drained out of the system (outside the cathode electrode gas diffusion layer on the side where the microporous layer is not placed), thereby suppressing the decrease in power generation performance due to flooding, and thus high power generation performance can be achieved.

[0059] 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.

[0060] 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.

[0061] A membrane / electrode assembly can be manufactured using a laminate comprising an anode electrode gas diffusion layer substrate (which may be water-repellent) having a microporous layer on one side, a cathode electrode gas diffusion layer substrate (which may be water-repellent) having a microporous layer on one side, and a catalyst layer formed on both sides of an electrolyte membrane (polymer electrolyte membrane) that selectively permeates specific ions. A fuel cell (single cell) can then be manufactured using this membrane / electrode assembly and separators (anode side and cathode side).

[0062] 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.

[0063] The gas diffusion layer substrate 1 of the present invention is a carbonized precursor sheet containing carbon fibers C1, graphite particles P1 larger than 120 μm, fibrillated organic fibers R1, and impregnated resin, which is carbonized, and the graphite particles 4 are exposed on at least one surface. The configuration of the gas diffusion layer substrate 1 of the present invention can be adapted to the configuration of the gas diffusion layer substrate 1 for fuel cells described above.

[0064] Furthermore, the carbonization precursor sheet forming the gas diffusion layer substrate 1 of the present invention is not particularly limited as long as it is a sheet-like material containing carbon fibers C1, graphite particles P1 larger than 120 μm, fibrillated organic fibers R1, and impregnating resin.Specific examples of the carbonization precursor sheet include the water-containing sheet 11, composite sheet 12, resin-impregnated sheet 13, and thinned sheet 14 used in the above-mentioned manufacturing method of the gas diffusion layer substrate 1 for fuel cells.

[0065] The gas diffusion layer substrate 1 of the present invention can be used, for example, in the manufacture of a fuel cell, as described above, as a material for forming the cathode electrode gas diffusion layer or the anode electrode gas diffusion layer in a membrane / electrode assembly that sequentially includes a cathode electrode gas diffusion layer, a microporous layer, a catalyst layer, an electrolyte layer, a catalyst layer, a microporous layer, and an anode electrode gas diffusion layer. Furthermore, the gas diffusion layer substrate 1 of the present invention can be cut or otherwise processed to produce electrode material for secondary batteries of a predetermined size, or as a raw material for manufacturing electrode layers for redox flow batteries. [Examples]

[0066] 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.

[0067] 1. Raw materials for manufacturing gas diffusion layer substrates The manufacturing raw materials used in the examples and comparative examples are as follows:

[0068] 1-1. Carbon fiber C1 Teijin carbon fiber (fiber length: 3 mm, fiber diameter: 7 μm)

[0069] 1-2. Graphite particles P1 (G1) Graphite particles "PAG-80" manufactured by Nippon Graphite Co., Ltd. (product name, particle size: 220 μm as determined by laser diffraction / scattering method) (G2) Graphite particles "PAG-120" manufactured by Nippon Graphite Co., Ltd. (product name, particle size: 130 μm as determined by laser diffraction / scattering method) (G3) Graphite particles "CGB-90" manufactured by Nippon Graphite Co., Ltd. (product name, particle size: 90 μm as determined by laser diffraction / scattering method) (G4) Graphite particles "PAG-C" manufactured by Nippon Graphite Co., Ltd. (product name, particle size 50 μm as determined by laser diffraction / scattering method) (G5) Graphite particles "HAG-10W" manufactured by Nippon Graphite Co., Ltd. (product name, particle size: 20 μm as determined by laser diffraction / scattering method)

[0070] 1-3. Fibril Organic Fiber R1 Acrylic pulp fibers manufactured by Toyobo Co., Ltd. (fiber length: 2 mm, average fiber diameter of the main fiber section: 15 μm, Canadian standard filtration rate: 550 mL)

[0071] 1-4. Linear organic fiber R2 Kuraray's vinylon fiber (fiber length: 3mm, fiber diameter: 11μm)

[0072] 2. Manufacturing and evaluation of gas diffusion layer substrates Each of the above raw materials was prepared in a predetermined ratio and mixed with water using a pulper to prepare a slurry. The obtained slurry was then subjected to papermaking, and subsequently dried to form a composite sheet 12. This composite sheet 12 was impregnated with phenolic resin, and then the resulting resin-impregnated sheet 13 was compressed and subjected to carbonization treatment to obtain a fuel cell gas diffusion layer substrate 1. The normal air permeability and contact resistance values ​​were then measured for this fuel cell gas diffusion layer substrate 1.

[0073] Example 1 A slurry was prepared by mixing 47 parts by mass of carbon fiber, 20 parts by mass of graphite particles G1, 17 parts by mass of acrylic pulp fiber, 16 parts by mass of vinylon fiber, and 5000 parts by mass of water. This slurry was further diluted 200 times to prepare a papermaking slurry, which was then used to continuously papermake a cylinder paper machine (average papermaking speed: 7 m / min) to obtain a water-containing sheet in which the carbon fiber, acrylic pulp fiber, and vinylon fiber were intertwined, and the graphite particles G1 were interposed in the gaps between the fibers. Next, using a press roll, the water-containing sheet is subjected to a pressure of 6 kgf / cm². 2The material was dehydrated and then dried at 130°C using a Yankee dryer to obtain a composite sheet. Subsequently, a solution of phenolic resin, a carbon precursor resin, was dip-coated onto this composite sheet, and it was dried at 120°C using a hot air dryer to obtain a resin-impregnated sheet in which the amount of phenolic resin attached was 25 parts by mass per 100 parts by mass of the composite sheet. Then, a heat press (250°C, 10 seconds) was performed using a double belt press to obtain a thinned sheet containing graphite that was crushed and deformed or partially crushed. The thickness was 120 μm. Next, this thinned sheet was heat-treated (for 1 minute) in a furnace with an internal temperature of 2000°C and a nitrogen gas atmosphere to obtain a gas diffusion layer substrate for fuel cells (hereinafter referred to as "gas diffusion layer substrate S1"). The basis weight of this gas diffusion layer substrate S1 is 30 g / m². 2 The thickness was 120 μm (see Table 1).

[0074] Furthermore, the normal air permeability and contact resistance values ​​of the obtained gas diffusion layer substrate S1 were measured using the following method, and the results, along with the calculated values ​​per unit thickness, are shown in Table 1. (1) Normal air permeability (Pa·s) Nitrogen gas was supplied to the substrate in the direction normal to the gas, and the differential pressure of the gas that passed through was converted to obtain the normal air permeability. (2) Contact resistance value (mΩ·cm) 2 ) The electronic resistance was measured while both sides of the substrate were pressurized at 0.8 MPa with a metal block.

[0075] Figure 2 is a cross-sectional image of the gas diffusion layer substrate S1 taken with an electron microscope, showing that some of the graphite, which has been deformed by heating and pressing using a double-belt press, is exposed on both sides. In Figure 2, the carbides of acrylic pulp fibers (fibril organic fibers R1), vinylon fibers (linear organic fibers R2), and phenolic resin due to the heat treatment of the thinned sheet are not clearly visible, but since the substrate has a stable shape and the normal air permeability was measured as described above, it is presumed that the carbides bind the carbon fibers together or the carbon fibers together with the graphite while allowing air permeability in the cross-sectional direction.

[0076] Examples 2-4 and Comparative Examples 1-4 Using carbon fibers, graphite particles, acrylic pulp fibers, and vinylon fibers in the proportions shown in Table 1, and further mixing a predetermined amount of water with the total amount of these materials in the same manner as in Example 1, the same procedure as in Example 1 was performed to obtain a fuel cell gas diffusion layer substrate, except that the resulting slurry was used. Hereinafter, the fuel cell gas diffusion layer substrates obtained in Examples 2 to 4 will be referred to as "gas diffusion layer substrate S2," "gas diffusion layer substrate S3," and "gas diffusion layer substrate S4," respectively, and the fuel cell gas diffusion layer substrates obtained in Comparative Examples 1 to 4 will be referred to as "gas diffusion layer substrate SS1," "gas diffusion layer substrate SS2," "gas diffusion layer substrate SS3," and "gas diffusion layer substrate SS4," respectively. In Example 4, although not shown in the figure, graphite particles G2 having a particle diameter shorter than the thickness of the thinned sheet and gas diffusion layer substrate were included, and it was confirmed that the graphite particles G2 were exposed on one side of the obtained gas diffusion layer substrate S4. Subsequently, the normal air permeability and contact resistance values ​​were measured in the same manner as in Example 1, and the results are shown in Table 1.

[0077] [Table 1]

[0078] From Table 1, the following can be seen: Examples 1-4 are examples of the manufacturing method of the present invention. The normal air permeability of the obtained fuel cell gas diffusion layer substrate is high, at 750,000 Pa·s·μm or higher, and the contact resistance value per unit thickness is 34 mΩ·cm. 2 The density was less than ) / μm. Thus, the fuel cell gas diffusion layer substrates of Examples 1 to 4 have superior gas permeability and conductivity in the thickness direction compared to the fuel cell gas diffusion layer substrates of Comparative Examples 1 to 4, and can therefore be suitably used as manufacturing materials for fuel cells that exhibit high power generation performance.

[0079] 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]

[0080] 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 can exhibit high power generation performance and can be used in transport fuel cells for vehicles, stationary fuel cells, and the like. [Explanation of Symbols]

[0081] 1: Substrate for gas diffusion layer in fuel cells C1: Carbon fiber 4: Graphite section 6: Carbonized part

Claims

1. A water-containing sheet manufacturing step involves using a slurry containing carbon fibers, graphite particles with a particle size exceeding 120 μm as measured by laser diffraction / scattering, and fibrillated organic fibers that are carbonized in a subsequent carbonization step to produce a water-containing sheet containing the carbon fibers, the graphite particles, and the fibrillated organic fibers. A composite sheet manufacturing process in which the water-containing sheet is water-extracted and dried 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, A compression step is performed to compress the resin-impregnated sheet to produce a thin sheet, A carbonization step in which the thinned sheet is heated and fired in a non-oxidizing atmosphere. A method for manufacturing a gas diffusion layer substrate for fuel cells, comprising the following components in sequence.

2. A method for producing a gas diffusion layer substrate for a fuel cell according to claim 1, wherein the carbon fiber content in the composite sheet is 20 to 80% by mass.

3. A method for producing a gas diffusion layer substrate for a fuel cell according to claim 1, wherein the content ratio of the graphite particles contained in the composite sheet is 5 to 60% by mass.

4. A method for producing a gas diffusion layer substrate for a fuel cell according to claim 1, wherein the content ratio of the fibrillated organic fibers in the composite sheet is 5 to 60% by mass.

5. A method for producing a gas diffusion layer substrate for a fuel cell according to claim 1, wherein the content ratio of the carbon precursor resin contained in the resin-impregnated sheet is 10 to 80% by mass.

6. A method for manufacturing a gas diffusion layer substrate for a fuel cell according to claim 1, wherein in the compression step, the graphite particles are crushed and compressed in the planar direction so that the thickness is less than the particle diameter of the graphite particles.

7. A fuel cell gas diffusion layer substrate obtained by the method for manufacturing a fuel cell gas diffusion layer substrate according to claim 1.

8. The fuel cell gas diffusion layer substrate according to claim 7, wherein graphite is exposed on at least one surface.

9. A carbonization precursor sheet containing carbon fibers, graphite particles exceeding 120 μm, fibrillated organic fibers, and impregnated resin is carbonized. A gas diffusion layer substrate having the graphite particles exposed on at least one surface.

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