Electroconductive sheet and production method therefor

Abstract

Provided is an electroconductive sheet 10 comprising an aromatic polyamide pulp, a fluororesin, a carbon-based electroconductive substance, and an electrode catalyst. Also provided is a production method for the electroconductive sheet, the method comprising: a step X1, in which a slurry X1 including an aromatic polyamide pulp, a fluororesin, a carbon-based electroconductive substance, and an electrode catalyst is prepared and the slurry X1 is formed into a sheet by wet laying to obtain an electroconductive-sheet precursor X1; and a step Y1, in which the electroconductive-sheet precursor X1 is hot-pressed in air at a temperature of 100-350°C and a linear pressure of 10-50 N / m and thereafter fired in an inert gas at 200-500°C. Use may be made of a method in which either one of a slurry X2-1 containing no electrode catalyst and a slurry X2-2 containing the electrode catalyst is formed into a sheet by wet laying to obtain the electroconductive-sheet precursor, and the other slurry is formed into a sheet by wet laying on one surface of the electroconductive-sheet precursor.

Description

Conductive sheet and method of manufacturing the same

[0001] The present disclosure relates to a conductive sheet and a method for manufacturing the same.

[0002] Fuel cells are classified into four types depending on the type of electrolyte used: molten carbonate fuel cells (MCFC), solid oxide fuel cells (SOFC), phosphoric acid fuel cells (PAFC), and polymer electrolyte fuel cells (PEFC).Recently, development of fuel cells that use enzymes or microorganisms as catalysts (biofuel cells) has been progressing.

[0003] A polymer electrolyte fuel cell is composed of a membrane electrode assembly (MEA) that has gas diffusion layers (GDLs) with catalyst layers on both sides of a thin polymer electrolyte membrane. The GDLs with catalyst layers are called gas diffusion electrodes (GDEs).

[0004] The polymer electrolyte membrane is a membrane that can absorb hydrogen ions (H ＋ ) and hydroxide ions (OH － The catalyst layer has a function of selectively conducting ions such as ions of carbon and ions of other metals. The catalyst layer is mainly composed of carbon particles supporting a precious metal catalyst such as platinum, a carbon catalyst, or an enzyme.

[0005] The GDL is required to have gas diffusion properties for guiding fuel gas and air to the catalyst layer and discharging generated gas and excess gas, high electrical conductivity for extracting the generated current to the outside without loss, and resistance to strong acidic and strong basic atmospheres caused by the generated ions. Due to these required properties, carbon fiber sheets such as carbon fiber cloth, carbon fiber felt, and carbon fiber paper, which are lightweight and have excellent mechanical properties, acid resistance, and electrical conductivity, are often used as the material for the GDL.

[0006] Examples of methods for producing carbon fiber sheets include the following: One method produces a carbon fiber sheet by processing carbon fibers such as filament yarns, staple yarns, and cut fibers into a sheet by weaving, papermaking, or the like; another method produces a carbon fiber sheet by processing flame-retardant fibers, which are precursor fibers of carbon fibers, into a sheet in advance and firing the sheet at 1000°C or higher (see, for example, Patent Document 1); and yet another method produces a carbon fiber sheet by mixing carbon fibers and a papermaking binder to form a sheet, impregnating the resulting sheet with a thermosetting resin such as phenol, curing it, and then firing it at a temperature of 1000°C or higher (see, for example, Patent Document 2).

[0007] Furthermore, the gas diffusion layer (GDL) is required to have the function of discharging water generated by the power generation reaction to the separator. For this reason, the carbon fiber sheet constituting the gas diffusion electrode is generally imparted with water repellency. A common method for imparting water repellency to a carbon fiber sheet is to impregnate a conductive sheet such as a carbon fiber sheet with a water-repellent substance such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), and then sinter it at 200 to 500°C (see, for example, Patent Document 3).

[0008] The GDL is also required to have the functions of uniformly diffusing fuel gas into the catalyst layer and controlling the wettability within the MEA. To impart the above functions to the GDL, a microporous layer (MPL) is typically provided on the surface of the carbon fiber sheet. This MPL is composed of carbonaceous particles such as carbon black and a fluororesin, and has pores with an average diameter of approximately several μm. The MPL is formed by spraying or knife coating a slurry containing carbonaceous particles and a fluororesin at an appropriate concentration. The coating method typically involves applying the slurry to the surface of the carbon fiber sheet (see, for example, Patent Document 4).

[0009] As mentioned above, GDEs for polymer electrolyte fuel cells typically use water-repellent conductive sheets manufactured by subjecting carbon fiber sheets to a water-repellent treatment and then forming an MPL. However, as mentioned above, these water-repellent conductive sheets are manufactured through multiple steps, resulting in poor production efficiency. As a result, fuel cells using these conductive sheets as electrode materials are expensive. Furthermore, when manufacturing a GDE in which the GDL functions as a catalyst, it is necessary to coat a catalyst layer on the surface of the GDL obtained through the multiple steps described above (see, for example, Patent Document 5).

[0010] A simple method for producing a GDL has been proposed, which uses a fibrillar material consisting of a conductive carbon material, a water-repellent fluororesin, and an aromatic polyamide binder, disperses these materials in a solvent, forms a paper, and heat-presses the resulting precursor, followed by firing, to obtain a GDL that combines electrical conductivity, water repellency, uniform gas diffusion, and wettability adjustment properties in a simple process (see, for example, Patent Document 6). However, even with this production method, additional steps are required to produce a GDE.

[0011] Patent Document 1: JP 2003-268651 A Patent Document 2: JP 2001-196085 A Patent Document 3: JP 6-203851 A Patent Document 4: JP 7-220734 A Patent Document 5: JP 2015-162279 A Patent Document 6: WO 2012-026498 A

[0012] An object of the present disclosure is to provide a conductive sheet that can be used as a gas diffusion electrode and can be easily produced, and a method for producing the same.

[0013] The above-mentioned problems are solved by the following means. <1> A conductive sheet comprising aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst. <2> The conductive sheet according to <1>, wherein the carbon-based conductive material is one or more selected from the group consisting of carbon fiber, carbon black, graphite particles, carbon nanotubes, carbon milled fiber, carbon nanofiber, carbon nanohorn, and graphene. <3> The conductive sheet according to <1> or <2>, wherein the electrode catalyst is one or more selected from the group consisting of a platinum catalyst, an iridium catalyst, a carbon catalyst, and an enzyme. <4> The conductive sheet according to any one of <1> to <3>, wherein the electrode catalyst includes a carbon catalyst containing 0.1 atomic % to 10 atomic % of nitrogen atoms relative to 100 atomic % of carbon atoms. <5> The conductive sheet according to <4>, wherein the carbon catalyst contains metal atoms in a mass ratio to the carbon atoms of 0.1 or less. <6> The conductive sheet according to any one of <1> to <4>, wherein the following formula (1) is satisfied: 0≦M / N<1 (1) (wherein M represents the content of the electrode catalyst in a portion on one side of the conductive sheet from the surface to a depth of 10% of the thickness of the conductive sheet, and N represents the content of the electrode catalyst in a portion on the other side of the conductive sheet from the surface to a depth of 10% of the thickness of the conductive sheet.) <7> A method for producing the conductive sheet according to any one of <1> to <5>, comprising: a step X1 of preparing a slurry X1 containing aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and papermaking the slurry X1 to obtain a conductive sheet precursor X1; and a step Y1 of hot-pressing the conductive sheet precursor X1 in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then firing the conductive sheet precursor X1 in an inert gas at 200 to 500°C.<8> A method for producing the conductive sheet according to <6>, comprising: a step X2-1 of preparing a slurry X2-1 containing an aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material, and papermaking the slurry X2-1 to obtain a conductive sheet precursor X1; a step X2-2 of preparing a slurry X2-2 containing an aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and papermaking the slurry X2-2 onto one side of the conductive sheet precursor X2-1 to obtain a conductive sheet precursor X2-2; and a step Y2 of hot-pressing the conductive sheet precursor X2-2 in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then firing the conductive sheet precursor X2-2 in an inert gas at 200 to 500°C. <9> A method for producing the conductive sheet according to <6>, comprising: a step X2-3 of preparing a slurry X2-2 containing aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and papermaking the slurry X2-2 to obtain a conductive sheet precursor X2-3; a step X2-4 of preparing a slurry X2-1 containing aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material, and papermaking the slurry X2-1 onto one side of the conductive sheet precursor X2-3 to obtain a conductive sheet precursor X2-4; and a step Y3 of hot-pressing the conductive sheet precursor X2-4 in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then firing the conductive sheet precursor X2-4 in an inert gas at 200 to 500°C.

[0014] According to the present disclosure, a conductive sheet that can be used as a gas diffusion electrode and can be easily produced, and a method for producing the same are provided.

[0015] Fig. 1 is a schematic diagram showing an example of the configuration of a conductive sheet according to a first embodiment of the present disclosure; Fig. 2 is a schematic diagram showing an example of the configuration of a conductive sheet according to a second embodiment of the present disclosure; Fig. 3 is a schematic diagram showing an example of the configuration of a polymer electrolyte fuel cell to which the conductive sheet according to the first embodiment of the present disclosure is applied; Fig. 4 is a schematic diagram showing an example of the configuration of a polymer electrolyte fuel cell to which the conductive sheet according to the second embodiment of the present disclosure is applied.

[0016] The conductive sheet and the method for manufacturing the conductive sheet according to the present disclosure will be described below with reference to the drawings. Note that in the following description, reference numerals may be omitted. Furthermore, in the present disclosure, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0017] The inventors conducted extensive research into a simple method for manufacturing a gas diffusion electrode for use in a fuel cell, and discovered that the electrode catalyst for use in a fuel cell can be made into a paper from a fibrillar substance, just like other constituent materials, and thus arrived at the invention disclosed herein.

[0018] [Conductive Sheet] The conductive sheet of the present disclosure (hereinafter, may be referred to as the "conductive sheet") comprises aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst.

[0019] A fluororesin is fused to the surface of the aromatic polyamide pulp. This fluororesin imparts water repellency to the conductive sheet. A carbon-based conductive material is dispersed between the fibers of the aromatic polyamide pulp. This carbon-based conductive material imparts conductivity to the conductive sheet in the thickness direction of the sheet. Furthermore, an electrode catalyst is dispersed between the fibers of the aromatic polyamide pulp. This electrode catalyst also imparts catalytic performance to the conductive sheet. The conductive sheet having this configuration can be used as a gas diffusion electrode in which a gas diffusion layer and a catalyst layer are integrally formed, and can be easily manufactured.

[0020] 1 schematically illustrates an example of a conductive sheet according to a first embodiment of the present disclosure (hereinafter, sometimes referred to as a "first conductive sheet"). The first conductive sheet 10 has an electrode catalyst 30 dispersed throughout the entire thickness of the sheet. As will be described later, the first conductive sheet 10 can be easily manufactured in a single papermaking process using a slurry containing aromatic polyamide pulp, a fluororesin fixed to the aromatic polyamide pulp, a carbon-based conductive material, and an electrode catalyst.

[0021] When the conductive sheet is used as a gas diffusion electrode in a fuel cell, it is sufficient that the electrode catalyst is present on the electrolyte membrane side. Therefore, the amount of electrode catalyst per unit area on each side may be different. That is, when the content of the electrode catalyst in a portion from the surface to a depth of 10% of the thickness of the conductive sheet on one side of the conductive sheet is M, and the content of the electrode catalyst in a portion from the surface to a depth of 10% of the thickness of the conductive sheet on the other side of the conductive sheet is N, the relationship may satisfy the following formula (1): 0≦M / N<1 (1) Methods for measuring the content of the electrode catalyst in a portion from the surface to a depth of 10% of the thickness of the conductive sheet include, for example, a method of scraping the surface of the conductive sheet and measuring it by elemental analysis, or a method of preparing a cross section of the conductive sheet and measuring it by X-ray photoelectron spectroscopy (XPS), electron probe microanalyzer (EPMA), scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX), or the like.

[0022] FIG. 2 schematically illustrates an example of a conductive sheet according to a second embodiment of the present disclosure (hereinafter, sometimes referred to as the "second conductive sheet"). The second conductive sheet 20 has a laminated structure including a catalyst-free layer 20A that does not contain an electrode catalyst 30 and a catalyst-containing layer 20B that does contain an electrode catalyst 30. The electrode catalyst 30 is absent on one surface (first surface) of the second conductive sheet 20, while the electrode catalyst 30 is dispersed on the other surface (second surface). The electrode catalyst 30 is typically more expensive than other constituent materials of the conductive sheet. By disposing the electrode catalyst 30 only on the second surface (catalyst-containing layer 20B) as in the second conductive sheet 20, manufacturing costs can be kept low. The conductive sheet may satisfy formula (1) by varying the content of the electrode catalyst stepwise or continuously across the thickness of the sheet.

[0023] The thickness of the conductive sheets 10, 20 is not particularly limited, but is preferably 50 to 500 μm, and more preferably 100 to 400 μm. A thickness of 50 μm or greater for the conductive sheets 10, 20 provides high sheet strength and ease of handling. A thickness of 500 μm or less for the conductive sheets 10, 20 facilitates keeping thickness variation low. The thickness of the conductive sheets 10, 20 can be controlled by adjusting the sheet basis weight and the temperature and pressure during heat pressing when manufacturing the conductive sheets. In the case of the second conductive sheet 20, from the standpoint of strength, the thickness of each of the catalyst-free layer 20A and the catalyst-containing layer 20B is preferably 5 μm or greater, and more preferably 10 μm or greater. Furthermore, from the standpoint of cost reduction, the thickness of the catalyst-containing layer 20B containing the electrode catalyst 30 is preferably thinner than the thickness of the catalyst-free layer 20A not containing the electrode catalyst 30. Furthermore, in order to satisfy the relationship of the above formula (1), it is preferable that the thickness of each of the catalyst-free layer 20A and the catalyst-containing layer 20B is 10% or more of the total thickness of the second conductive sheet 20, and from the viewpoint of cost reduction, the thickness of the catalyst-containing layer 20B may be 40% or less, or may be 30% or less of the thickness of the second conductive sheet 20.

[0024] The constituent materials and manufacturing method of the conductive sheet will be described below.

[0025] (Aromatic Polyamide Pulp) The aromatic polyamide pulp (hereinafter also referred to as "aramid pulp") used in the present conductive sheet is, for example, an aromatic polyamide pulp in which 85 mol% or more of the amide bonds are formed by dehydration condensation of an aromatic diamine component and an aromatic dicarboxylic acid component. The aramid pulp used in the present conductive sheet preferably has highly fibrillated fibers. Examples of aramids include polyparaphenylene terephthalamide, copolyparaphenylene-3,4'-oxydiphenylene-terephthalamide, polymetaphenylene isophthalamide, polyparabenzamide, poly-4,4'-diaminobenzanilide, polyparaphenylene-2,6-naphthalic amide, copolyparaphenylene / 4,4'-(3,3'-dimethylbiphenylene)terephthalamide, polyorthophenylene terephthalamide, polyparaphenylene phthalamide, and polymetaphenylene isophthalamide.

[0026] Fibrillation refers to a method of randomly forming fine individual fibers on the surface of fibers. In the present disclosure, fibrillation of aramid pulp is carried out by a known method. For example, as described in Japanese Patent Publication Nos. 35-11851 and 37-5752, fibrillation is carried out by adding a precipitant to an organic high molecular weight polymer solution and mixing it in a system that generates shear force. Alternatively, as described in Japanese Patent Publication No. 59-603, fibrillation is carried out by applying a mechanical shear force, such as beating, to a molded product having molecular orientation formed from a high molecular weight polymer solution exhibiting optical anisotropy, thereby randomly imparting fine individual fibers.

[0027] The average fiber length of the aramid pulp used in the present conductive sheet is not particularly limited, but is preferably 0.1 to 100 mm, more preferably 0.5 to 10 mm, and particularly preferably 0.5 to 5 mm.

[0028] (Fluororesin) The fluororesin contained in the conductive sheet is preferably fixed to the aromatic polyamide pulp. Examples of the fluororesin contained in the conductive sheet include tetrafluoroethylene resin (hereinafter sometimes referred to as "PTFE"), perfluoroalkoxy resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-ethylene copolymer resin, vinylidene fluoride resin, and trifluorochloroethylene. PTFE is particularly preferred because of its excellent heat resistance and sliding properties.

[0029] (Carbon-based conductive material) The carbon-based conductive material contained in the conductive sheet may be, for example, a material having a carbon content of 94% by mass or more and a resistivity of 100 Ω cm or less. Specific examples of carbon-based conductive materials include carbon fiber, carbon black, graphite particles, carbon nanotubes, milled carbon fiber, carbon nanofiber, carbon nanohorn, and graphene. These carbon-based conductive materials may be used alone or in combination of two or more.

[0030] Examples of carbon fibers and carbon milled fibers include PAN-based carbon fibers, pitch-based carbon fibers, and phenol-based carbon fibers. Among these, PAN-based carbon fibers and pitch-based carbon fibers are preferred, and PAN-based carbon fibers are particularly preferred.

[0031] When carbon fiber and / or carbon milled fiber is used, the fiber diameter is preferably 3 to 20 μm, and particularly preferably 5 to 13 μm. In the case of carbon fiber with a flat fiber cross section, the average value of the major and minor axes of the fiber cross section is taken as the fiber diameter. If the fiber diameter is 5 μm or more, the strength of the single fiber is high, making it easy to improve the strength of the conductive sheet. On the other hand, if the fiber diameter is 20 μm or less, the outer shape of the carbon single fiber constituting the sheet is less likely to rise to the surface of the sheet. Therefore, irregularities are less likely to form on the sheet surface, improving the surface smoothness of the sheet and reducing the contact electrical resistance of the sheet.

[0032] The average fiber length (cut length) of the carbon fiber or carbon milled fiber is preferably 20 mm or less. If the average fiber length is 20 mm or less, the uniform dispersion of the fibers is improved, and the strength of the sheet is likely to be improved.

[0033] The carbon content of the carbon fiber or carbon milled fiber is preferably 94% by mass or more. A carbon content of 94% by mass or more improves the electrical conductivity of the sheet. Furthermore, deterioration of the sheet is suppressed even when a battery incorporating this conductive sheet is operated for a long period of time.

[0034] Examples of carbon black include acetylene black and Ketjenblack (registered trademark) which has a hollow shell structure. Ketjenblack is particularly preferred.

[0035] The average particle size of the primary particles of carbon black is preferably 1 to 500 nm, more preferably 1 to 200 nm, and even more preferably 10 to 100 nm. Furthermore, when the primary particles of carbon black aggregate, the average particle size of the secondary particles is preferably 0.5 to 20 μm. If the average particle size of the secondary particles is 0.5 μm or more, further aggregation of the carbon black is suppressed when preparing a carbon black dispersion. If the average particle size is 20 μm or less, the carbon-based conductive material can easily penetrate deep into the sheet, improving the conductivity of the sheet.

[0036] Examples of graphite particles include flake graphite, flaky graphite, amorphous graphite, artificial graphite, expanded graphite, expanded graphite, flake graphite, lump graphite, and spherical graphite. Graphite in spherical and flake shapes is particularly preferred. The average particle size of the graphite particles is preferably 0.05 to 300 μm.

[0037] The carbon nanofibers may be single fibers or aggregates. The average fiber diameter of the carbon nanofibers (single fibers or aggregates) is, for example, 100 to 1000 nm. If the average fiber diameter of the carbon nanofibers is 100 nm or more, they are easy to handle, and if it is 1000 nm or less, it is easy to increase the fiber density. The average fiber diameter of the carbon nanofibers is preferably 900 nm or less, more preferably 800 nm or less, even more preferably 600 nm or less, even more preferably 500 nm or less, even more preferably 400 nm or less, and even more preferably 300 nm or less. The average fiber diameter of the carbon nanofibers is preferably 110 nm or more, more preferably 120 nm or more, even more preferably 150 nm or more, even more preferably 200 nm or more, and particularly preferably more than 200 nm.

[0038] Furthermore, the average fiber length of the carbon nanofibers (single fibers or aggregates) is preferably 1 μm or more, and more preferably 10 μm or more. If the average fiber length is 1 μm or more, it is possible to prevent a decrease in conductivity, strength, and liquid retention. Furthermore, if the average fiber length is 30 μm or less, the dispersibility of the carbon fibers is less likely to be impaired, and the carbon fibers are less likely to be oriented in the in-plane direction of the conductive sheet. As a result, it is easier to form a conductive path in the thickness direction of the conductive sheet. The average fiber length of the carbon nanofibers is preferably 10 to 30 μm, and more preferably 12 to 28 μm.

[0039] Carbon nanofibers can be produced by, for example, the method disclosed in International Publication No. 2020 / 045243. Specifically, the method includes the following steps: (1) a fiberization step of fiberizing a resin composite fiber by molding, in a molten state, a resin composition comprising a thermoplastic resin and 30 to 150 parts by mass of mesophase pitch relative to 100 parts by mass of the thermoplastic resin, the mesophase pitch, to obtain a resin composite fiber; (2) a stabilization step of stabilizing the resin composite fiber to obtain a resin composite stabilized fiber; (3) a thermoplastic resin removal step of removing the thermoplastic resin from the resin composite stabilized fiber to obtain a stabilized fiber; and (4) a carbonization and calcination step of heating the stabilized fiber in an inert atmosphere to carbonize or graphitize it, thereby obtaining a carbon fiber aggregate.

[0040] (Electrode catalyst) The electrode catalyst contained in the conductive sheet may be a catalyst used in known fuel cells such as polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), and biofuels. The type and content of the electrode catalyst may be selected depending on the application of the conductive sheet, and examples include platinum catalysts, iridium catalysts, carbon catalysts, and enzymes. A carbon catalyst will be described below as a representative example of an electrode catalyst that can be used in the conductive sheet.

[0041] Examples of carbon catalysts include particulate carbon catalysts that are mainly composed of carbon compounds containing carbon atoms and nitrogen atoms, specifically carbon compounds containing 0.1 atomic % to 10 atomic % of nitrogen atoms relative to 100 atomic % of carbon atoms. Here, "mainly composed" means that, among the carbon compounds contained in the carbon catalyst, the proportion (volume fraction) occupied by carbon compounds containing 0.1 atomic % to 10 atomic % of nitrogen atoms relative to 100 atomic % of carbon atoms is the largest. Furthermore, the carbon catalyst preferably has a volume fraction of particles having a particle diameter of 20 nm to 1 μm of 45% or more. The volume fraction of particles refers to the volume fraction obtained by measuring the particle size distribution of the carbon catalyst using a laser diffraction particle size distribution measurement method.

[0042] In order for a carbon catalyst to exhibit its catalytic action, the nitrogen atom content is preferably 0.1 atomic % or more and 10 atomic % or less relative to 100 atomic % of carbon atoms. If the nitrogen atom content is 0.1 atomic % or more relative to 100 atomic % of carbon atoms, the catalytic action is sufficient and the carbon catalyst is useful. On the other hand, if the nitrogen atom content is 10 atomic % or less relative to 100 atomic % of carbon atoms, sufficient graphitization proceeds, electronic conduction within the catalyst is not impaired, and a catalyst with high catalytic properties can be obtained.

[0043] The carbon catalyst preferably has a mass ratio of metal atoms to carbon atoms of 0.1 or less. When a conductive sheet containing a carbon catalyst with such a low metal content is used as an electrode material for a fuel cell, side reactions caused by the metal, such as reactions that generate hydrogen peroxide and hydroxyl radicals, are less likely to proceed, and deterioration of the electrolyte of the fuel cell can be suppressed. Although the lower limit of the metal content is not particularly limited, from the viewpoint of ease of manufacturing the carbon catalyst, the mass ratio of metal atoms to carbon atoms may be 0.001 or more.

[0044] The metal atom may be any of various known metals, and representative examples thereof include iron, cobalt, nickel, copper, tin, manganese, and zinc, which are sometimes added during production to obtain a highly active carbon catalyst.

[0045] The above carbon catalyst can be produced by a known method, for example, the method disclosed in WO 2012 / 161335.

[0046] Examples of the enzyme include bilirubin oxidase, which reduces oxygen, and lactate oxidase, an enzyme that oxidizes lactic acid.

[0047] (Uses of the Present Conductive Sheet) The present conductive sheet is preferably used as an electrode material for electrolysis, flow batteries, and fuel cells, particularly as a gas diffusion electrode material for fuel cells.

[0048] 3 shows a schematic diagram of an example of the configuration of a polymer electrolyte fuel cell employing the first conductive sheet 10 of the present disclosure. A first conductive sheet 12 functioning as an anode is disposed on one side of a thin polymer electrolyte membrane 40, and a first conductive sheet 14 functioning as a cathode is disposed on the other side. Electrode catalysts 32, 34 corresponding to the required functions are dispersed throughout each conductive sheet 12, 14. The electrolyte membrane 40 may be one used in known fuel cells.

[0049] 4 schematically shows an example of the configuration of a polymer electrolyte fuel cell employing the second conductive sheet 20 of the present disclosure. A second conductive sheet 22 functioning as an anode is disposed on one side of a thin polymer electrolyte membrane 40, and a second conductive sheet 24 functioning as a cathode is disposed on the other side. Each conductive sheet 22, 24 is disposed so that the layer (catalyst-containing layer) 22B, 24B containing the electrode catalyst 32, 34 corresponding to the required function is in contact with the electrolyte membrane 40, and the layer (catalyst-free layer) 22A, 24A not containing the electrode catalyst 32, 34 is on the outside.

[0050] There are no particular limitations on the method for manufacturing the conductive sheet, but an example of a method for manufacturing the conductive sheet 10 according to the first embodiment and the conductive sheet 20 according to the second embodiment of the present disclosure will be described below.

[0051] [Method for Manufacturing First Conductive Sheet] The first conductive sheet 10 shown in FIG. 1 can be manufactured, for example, through the following steps X1 and Y1.

[0052] <Step X1> A slurry X1 containing aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst is prepared, and the slurry X1 is paper-formed to obtain a conductive sheet precursor X1.

[0053] (Preparation of Slurry X1) First, a liquid in which aromatic polyamide pulp (aramid pulp) and fluororesin particles are dispersed (hereinafter also referred to as "aramid pulp-fluororesin dispersion") is prepared. The aramid pulp-fluororesin dispersion is prepared by separately preparing a dispersion of aramid pulp and a dispersion of fluororesin particles and mixing these dispersions. Alternatively, aramid pulp may be added to and dispersed in a dispersion of fluororesin particles, or fluororesin particles may be added to and dispersed in an aramid pulp dispersion.

[0054] (Aromatic polyamide pulp dispersion) Aramid pulp dispersion can be prepared by a known method, for example, a dispersion method conventionally used in papermaking of wood pulp. Aramid pulp can be dispersed using various disintegrators (pulpers), various beaters such as a Niagara beater, or various refiners such as a single disc refiner. The dispersion medium in the various dispersions is preferably water such as ion-exchanged water.

[0055] (Fluororesin Dispersion) A fluororesin dispersion can be prepared by a known method, for example, by radical polymerization of raw material monomers of the fluororesin in the presence of a surfactant. Alternatively, a commercially available fluororesin dispersion may be used. Examples of commercially available fluororesin dispersions include Fluon (registered trademark) PTFE Dispersion AD911L (product name) manufactured by AGC Inc. and Polyflon PTFE D-1E (product name) manufactured by Daikin Industries, Ltd.

[0056] The average particle size of the fluororesin particles contained in the fluororesin dispersion is preferably 0.01 to 10 μm, and particularly preferably 0.1 to 1 μm. If the average particle size is 0.01 μm or more, the fluororesin particles are likely to deposit on the aramid pulp surface. On the other hand, if the average particle size is 10 μm or less, a stable dispersion of the fluororesin particles can be easily prepared. As a result, the fluororesin is less likely to be unevenly distributed in the sheet.

[0057] A surfactant may be added to the dispersion of fluororesin particles as appropriate. Fluororesin particles may aggregate. Adding a surfactant can disperse the aggregated fluororesin particles and promote uniform deposition on the aramid pulp fiber surface. Ionic surfactants are more effective at dispersing aggregated fluororesin particles than nonionic surfactants. However, dispersions of fluororesin particles dispersed using ionic surfactants tend to form large flocs of fluororesin particles, making it difficult to obtain a sheet uniformly impregnated with fluororesin. On the other hand, nonionic surfactants make it difficult to disperse aggregated fluororesin particles. If aggregated fluororesin particles can be dispersed, fine fluororesin particles can be uniformly deposited on the aramid pulp fiber surface. Therefore, dispersions of fluororesin particles dispersed using nonionic surfactants are preferably used.

[0058] The aramid pulp-fluororesin dispersion is prepared by mixing the aramid pulp dispersion with the fluororesin dispersion, and the fluororesin particles aggregate and adhere (deposit) to the surface of the aramid pulp.

[0059] The blending ratio of aramid pulp to fluororesin is appropriately selected depending on the desired final product. The aramid pulp / fluororesin (mass ratio) is preferably in the range of 10 / 90 to 70 / 30, and particularly preferably in the range of 20 / 80 to 60 / 40. When the aramid pulp / fluororesin ratio is 10 / 90 or more, a high reinforcing effect of the sheet due to the aramid pulp can be obtained. On the other hand, when the aramid pulp / fluororesin ratio is 70 / 30 or less, high water repellency due to the fluororesin can be obtained.

[0060] The method for preparing the aramid pulp-fluororesin dispersion is not limited to the above method, and for example, the aramid pulp and the fluororesin particles may be dispersed simultaneously in a medium. Alternatively, the aramid pulp and the fluororesin particles may be dispersed using a dispersion of a carbonaceous conductive material, a dispersion of an electrode catalyst, or a dispersion in which a carbonaceous conductive material and an electrode catalyst are dispersed, as described below.

[0061] The concentrations of the aramid pulp and the fluororesin in the aramid pulp-fluororesin dispersion are not particularly limited, but from the viewpoint of production costs, it is preferable to set the concentrations as high as possible within a range that does not impair the fluidity of the aramid pulp-fluororesin dispersion.

[0062] In order to efficiently fix the fluororesin particles to the surface of the aramid pulp, a flocculant may be added to the dispersion. By adding a flocculant to the aramid pulp-fluororesin dispersion, the fluororesin particles are more likely to be deposited in particulate form on the fiber surface of the aramid pulp. The type and amount of flocculant added are determined appropriately depending on the type of surfactant used to disperse the fluororesin particles and the specific surface area of ​​the aramid pulp.

[0063] When the fluororesin particles in the aramid pulp-fluororesin dispersion are dispersed using an anionic surfactant, a strong acid, a strong electrolyte, or a polymer flocculant such as a polyacrylamide flocculant or a polyacrylate is used as the flocculant.

[0064] When the fluororesin particles in the aramid pulp-fluororesin dispersion are dispersed using a cationic surfactant, a base, a strong electrolyte, or a polymer flocculant such as a polyacrylamide flocculant or a polymethacrylic acid ester is used as the flocculant.

[0065] When the fluororesin particles in the aramid pulp-fluororesin dispersion are dispersed using a nonionic surfactant, a strong electrolyte or a polyacrylamide polymer flocculant is used as the flocculant.

[0066] When adding a flocculant to the aramid pulp-fluororesin dispersion, it is preferable to add an alkaline component such as calcium hydroxide or ammonia to adjust the pH of the aramid pulp-fluororesin dispersion to a range of 3.5 to 6.0.

[0067] The above flocculants may also be used in combination.

[0068] The fluororesin particles that are not deposited on the aramid pulp are discharged into the wastewater during papermaking. Discharge of the fluororesin into the wastewater is undesirable from the viewpoints of economy and the environment. Discharge of the fluororesin into the wastewater necessitates wastewater treatment, which increases production costs. Therefore, it is preferable that substantially all of the fluororesin particles in the aramid pulp-fluororesin dispersion are deposited on the aramid pulp. Here, "substantially all" refers to an amount such that wastewater treatment is not required.

[0069] A carbon-based conductive material and an electrode catalyst are added to the aramid pulp-fluororesin dispersion. The order in which the carbon-based conductive material and the electrode catalyst are mixed is not limited. The carbon-based conductive material may be mixed into the aramid pulp-fluororesin dispersion, and then the electrode catalyst may be mixed therein. The carbon-based conductive material may be mixed into the aramid pulp-fluororesin dispersion, and then the electrode catalyst may be mixed therein. The carbon-based conductive material and the electrode catalyst may be mixed at the same time.

[0070] The carbon-based conductive material may be added before or after the fluororesin particles are deposited on the aramid pulp. The method of blending the carbon-based conductive material into the aramid pulp-fluororesin dispersion may involve blending a dispersion of the carbon-based conductive material into the aramid pulp-fluororesin dispersion, or blending the carbon-based conductive material into the aramid pulp-fluororesin dispersion and then dispersing it.

[0071] The blending ratio of the aramid pulp to the carbon-based conductive material is appropriately set depending on the desired final product. The blending ratio of the aramid pulp to the carbon-based conductive material (aramid pulp / carbon-based conductive material) is preferably in the range of 90 / 10 to 10 / 90 by mass, and particularly preferably in the range of 85 / 15 to 15 / 85. When the aramid pulp / carbon-based conductive material ratio is 10 / 90 or more, the produced conductive sheet can obtain a high reinforcing effect due to the aramid pulp. When the aramid pulp / carbon-based conductive material ratio is 90 / 10 or less, the produced conductive sheet can obtain high conductivity due to the carbon-based conductive material.

[0072] The electrode catalyst may be added before or after the fluororesin particles are deposited on the aramid pulp. The method of blending the electrode catalyst into the aramid pulp-fluororesin dispersion may involve blending the dispersion of the electrode catalyst into the aramid pulp-fluororesin dispersion, or the electrode catalyst may be blended into the aramid pulp-fluororesin dispersion and then dispersed.

[0073] The type of electrode catalyst and the blending ratio of the aramid pulp to the electrode catalyst are appropriately set depending on the desired final product. The blending ratio of the aramid pulp to the electrode catalyst (aramid pulp / electrode catalyst) is, for example, in the range of 100 to 10,000 in mass ratio.

[0074] As a result, a slurry X1 (hereinafter also simply referred to as "slurry") containing aramid pulp, a fluororesin adhered (deposited) to the aramid pulp, a carbon-based conductive material, and an electrode catalyst is obtained.

[0075] The slurry may also contain a substance that decomposes at a temperature equal to or lower than the firing temperature.

[0076] (Substances that decompose at or below the firing temperature) Substances that decompose at or below the firing temperature (hereinafter also referred to as "vanishing substances") are substances that have a decomposition temperature of less than 500°C in an inert atmosphere and that decompose and disappear at or below the firing temperature described below. The vanishing substance is appropriately selected depending on the firing temperature. Pulp-shaped or fibrous organic substances that have good retention in the papermaking process and a low decomposition temperature are preferred. Examples of vanishing substances include cellulosic pulps such as wood pulp and linter pulp. The shape of the vanishing substance preferably has a length of 0.1 to 100 mm and a diameter of 0.1 to 50 μm.

[0077] The vanishing substance decomposes and disappears during the firing process, forming voids within the conductive sheet. When the conductive sheet is manufactured by incorporating the vanishing substance, the resulting conductive sheet has improved air permeability, drainage properties, and gas diffusion properties.

[0078] The eliminable substance is preferably a substance whose decomposition temperature is at least 30° C. lower than the firing temperature. If the eliminable substance has a decomposition temperature at least 30° C. lower than the firing temperature, the eliminable substance is less likely to remain in the sheet during the firing step, and the air permeability, drainage property, and gas diffusibility of the sheet can be sufficiently increased.

[0079] The blending ratio of the aramid pulp to the vanishing substance is appropriately set depending on the desired final product. The blending ratio of the aramid pulp to the vanishing substance (aramid pulp / vanishing substance) is preferably 95 / 5 to 40 / 60 by mass, and particularly preferably 70 / 30 to 50 / 50. When the aramid pulp / vanishing substance ratio is 95 / 5 or less, the air permeability of the manufactured conductive sheet is increased, and the diffusion performance and drainage performance of fuel gas and fuel liquid are likely to be improved. On the other hand, when the aramid pulp / vanishing substance ratio is 40 / 60 or more, a high reinforcing effect of the aramid pulp on the conductive sheet is obtained.

[0080] The method of blending the vanishing substance into the slurry may involve blending a dispersion of the vanishing substance into the slurry, or the vanishing substance may be blended into the slurry and then dispersed.

[0081] Fillers and additives such as graphite and bronze powder may also be added to the slurry to improve the performance of the resulting sheet or to impart other properties.

[0082] (Papermaking) Next, the slurry is paper-made to obtain a conductive sheet precursor X1 (hereinafter also simply referred to as "conductive sheet precursor"). Papermaking can be performed using a known method, for example, a fourdrinier or cylinder paper-making machine. The obtained conductive sheet precursor is dehydrated and dried as necessary.

[0083] <Step Y1> The conductive sheet precursor X1 obtained by papermaking is heat-pressed in air at a temperature of 100 to 350° C. and a linear pressure of 10 to 50 N / m, and then fired in an inert gas at 200 to 500° C. Examples of the inert gas that can be used include nitrogen gas and argon gas.

[0084] (Heat Pressing) The conductive sheet precursor X1 obtained in step X1 is heat pressed in air. The heat pressing imparts conductivity to the conductive sheet precursor. The heat pressing temperature is 100 to 350°C, preferably 200 to 340°C, and particularly preferably 250 to 330°C. The linear pressure during heat pressing is 10 to 50 N / m, preferably 15 to 45 N / m, and particularly preferably 20 to 40 N / m. The heat pressing may be performed either continuously or batchwise.

[0085] The heat-pressed conductive sheet precursor is provided with conductivity in the thickness direction of the sheet by the carbon-based conductive material, but the fluororesin in this heat-pressed conductive sheet precursor is merely deposited in the form of particles on the aramid pulp, and in this state, the water repellency is insufficient.

[0086] (Firing) Next, the hot-pressed conductive sheet precursor is fired in an inert gas. The firing temperature is 200 to 500°C, preferably 230 to 430°C. If the firing temperature is 200°C or higher, the fluororesin particles deposited on the aramid pulp melt, and the resulting sheet has sufficient water repellency. If the firing temperature is 500°C or lower, it is possible to prevent the fluororesin from decomposing and generating hydrofluoric acid.

[0087] The baking time is, for example, 10 to 120 minutes, preferably 30 to 90 minutes.

[0088] The conductive sheet may be fired while being subjected to a surface pressure. The surface pressure is, for example, 1.0 kPa or less, and preferably 0.1 to 0.5 kPa. The surface pressure is applied using, for example, a batch press, an intermittent press, a calendar press, a belt press, a roller, or the like.

[0089] The firing melts the fluororesin particles deposited on the aramid pulp and fuses them to the surface of the aramid pulp, resulting in a first conductive sheet 10 that contains an electrode catalyst and has water repellency.

[0090] [Method for Manufacturing Second Conductive Sheet] The second conductive sheet 20 shown in FIG. 2 can be manufactured, for example, through the following steps X2-1, X2-2, and Y2.

[0091] <Step X2-1> A slurry X2-1 containing aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material is prepared, and the slurry X2-1 is paper-formed to obtain a conductive sheet precursor X2-1.

[0092] (Preparation of Slurry X2-1) The slurry X2-1 in step X2-1 is the same as the slurry X1 in the first embodiment except that it does not contain an electrode catalyst, and can be prepared in the same manner as the slurry X1 except that no electrode catalyst is added.

[0093] (Papermaking) Conductive sheet precursor X2-1 is obtained by papermaking from slurry X2-1. Using slurry X2-1, conductive sheet precursor X2-1 can be obtained by papermaking in the same manner as in step X1 of the first embodiment.

[0094] <Step X2-2> A slurry X2-2 containing aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst is prepared, and the slurry X2-2 is applied to one side of the conductive sheet precursor X2-1 to obtain a conductive sheet precursor X2-2.

[0095] (Preparation of Slurry X2-2) The slurry X2-2 in step X2-2 is the same as the slurry X1 in the first embodiment, and can be prepared in the same manner as the slurry X1.

[0096] (Papermaking) The prepared slurry X2-2 is paper-formed onto one side of the conductive sheet precursor X2-1 to obtain the conductive sheet precursor X2-2. The papermaking of the slurry X2-2 can be performed in the same manner as the papermaking of the conductive sheet precursor X1 in the first embodiment, except that the slurry X2-2 is paper-formed onto one side of the conductive sheet precursor X2-1.

[0097] <Step Y2> The conductive sheet precursor X2-2 is heat-pressed in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then fired in an inert gas at 200 to 500°C.

[0098] (Heat Pressing) The heat pressing in the step Y2 can be performed in the same manner as the heat pressing in the first embodiment, except that the conductive sheet precursor X2-2 is used.

[0099] One surface of the hot-pressed conductive sheet precursor X2-2 is provided with catalytic properties by an electrode catalyst.

[0100] (Firing) Next, the hot-pressed conductive sheet precursor 2-2 is fired in an inert gas. Firing can be performed in the same manner as in the first embodiment, except that the conductive sheet precursor 2-2 is used. Firing causes the fluororesin particles deposited on the aramid pulp to melt and fuse to the aramid pulp surface. As a result, a second conductive sheet 20 containing an electrode catalyst on one side and having water repellency is obtained.

[0101] The second conductive sheet 20 may be produced, for example, by a procedure in which the slurry X2-2 is first paper-formed and then the slurry X2-1 is paper-formed. That is, the slurry X2-2 is paper-formed to obtain a conductive sheet precursor X2-3, the slurry X2-1 is then paper-formed onto one side of the conductive sheet precursor X2-3 to obtain a conductive sheet precursor X2-4, and the conductive sheet precursor X2-4 is then hot-pressed and fired under the same conditions as in step Y2.

[0102] The conductive sheet and the manufacturing method thereof according to the present disclosure will be specifically described below using examples, although the scope of the present disclosure is not limited to the following examples.

[0103] In the examples, analyses and measurements were carried out by the following methods.

[0104] <Elemental Analysis of Carbon Catalyst> Measurement was performed using a 2400II manufactured by Perkin Elmer Co. From the obtained composition of carbon, hydrogen, and nitrogen elements, the molar ratio of nitrogen atoms to carbon atoms (which may be abbreviated as nitrogen / carbon atom ratio, or N / C ratio) was calculated in percentage.

[0105] <EPMA analysis of carbon catalyst> The molar ratio of iron atoms to carbon atoms in the carbon catalyst was obtained from the results of elemental analysis using an electron probe microanalyzer (EPMA, EPMA-1400 manufactured by Shimadzu Corporation). The elemental analysis using EPMA was carried out using the obtained powder of the particulate carbon catalyst processed into pellets without using a binder. From the obtained composition of carbon and iron elements, the molar ratio of iron atoms to carbon atoms (iron / carbon atom ratio, or may be abbreviated as Fe / C ratio) was calculated in percentage.

[0106] <Measurement of Polymer Viscosity> A sample solution with a polymer concentration of 0.5 g / dL prepared using N-methyl-2-pyrrolidone (NMP) as a solvent was measured for relative viscosity (η ｒｅｌ ) was calculated, and the reduced viscosity η was calculated using the following formula based on this. ｓｐ / C was calculated. ｓｐ / C = (η ｒｅｌ -1) / C (In the above formula, η ｓｐ / C is the reduced viscosity, η ｒｅｌ represents the relative viscosity, and C represents the polymer concentration in the solution.

[0107] Reference Example 1 (Synthesis of Polyacrylonitrile) Under a nitrogen stream, 56.35 parts by mass of acrylonitrile was added to a flask containing 280 ml of toluene and dissolved, and then 0.75 parts by mass of 2,2'-azobisisobutyronitrile was added. The mixture was heated to 65°C and stirred, and reacted for 3.5 hours. After confirming the generation of a white precipitate, the reaction was terminated. Tetrahydrofuran was added to the reaction mixture, and the mixture was filtered. The filter cake was washed with tetrahydrofuran, filtered, and dried to obtain polyacrylonitrile. NMP was added so that the concentration of the obtained polyacrylonitrile became 0.5 g / dL to prepare a sample solution, and the reduced viscosity (η ｓｐ / C) was 1.34 dL / g.

[0108] Reference Example 2 (Preparation of Carbon Catalyst) The polyacrylonitrile particles obtained in Reference Example 1 were gradually heated from 190°C and heat-treated at 230°C for 1 hour in air, thereby obtaining an infusible polyacrylonitrile particle. Iron (II) chloride tetrahydrate was supported on the obtained infusible polyacrylonitrile so that the iron atom content was 0.3 mass %, and the obtained infusible polyacrylonitrile-iron (II) chloride tetrahydrate composition was heat-treated at 600°C for 5 hours in a nitrogen stream, and then subjected to a dispersion treatment using a ball mill. Next, heat treatment (activation treatment) was performed at 800°C for 1 hour in an ammonia stream and at 1000°C for 1 hour in an ammonia stream, thereby obtaining a particulate carbon catalyst. The nitrogen / carbon atom ratio (N / C ratio) of the obtained particulate carbon catalyst was 3.22% by elemental analysis, the iron / carbon atom ratio (Fe / C ratio) of the obtained particulate carbon catalyst was 0.24% by EPMA measurement, and the iron / carbon mass ratio of the obtained particulate carbon catalyst was 0.011 by EPMA measurement.

[0109] Reference Example 3 Preparation of Each Dispersion Preparation of Aromatic Polyamide Pulp Dispersion "A-1" Twaron (registered trademark) pulp (product name, manufactured by Teijin Aramid B.V., BET specific surface area: 13.5 m) was used as a fibrillated para-aromatic polyamide pulp. ２ 0.2 g (dry mass) of cellulose acylate (cellulose acetate stearate, ...

[0110] The freeness of the aromatic polyamide pulp was measured in accordance with the Canadian standard freeness method of JIS P8121-2:2012 "Testing method for freeness of pulp."

[0111] <Preparation of fluororesin dispersion liquid "B-1"> As a PTFE dispersion liquid, 0.33 g (solid content: 0.2 g) of AD911E (manufactured by AGC Inc., average PTFE particle size: 250 μm, PTFE content: 61% by mass) was added to 100 ml of ion-exchanged water and stirred to prepare fluororesin PTFE dispersion liquid B-1.

[0112] <Preparation of Carbon-Based Conductive Material Dispersion Liquid "C-1"> 0.2 g of carbon black (Ketjenblack (registered trademark) EC600JD: product name, manufactured by Lion Corporation, primary particle diameter: 34 nm) was added to 100 ml of ion-exchanged water and stirred to prepare carbon black dispersion liquid C-1.

[0113] <Preparation of Carbon-Based Conductive Material Dispersion Liquid "C-2"> 0.2 g of carbon nanofibers (PotenCia (registered trademark): product of Teijin Limited, average fiber diameter 120 nm, average fiber length 3 μm) were added to 100 ml of ion-exchanged water and stirred to prepare carbon nanofiber dispersion liquid C-2. <Preparation of Carbon-Based Conductive Material Dispersion Liquid "C-3"> 0.2 g of carbon nanofibers (PotenCia (registered trademark): product of Teijin Limited, average fiber diameter 260 nm, average fiber length 13.5 μm) were added to 100 ml of ion-exchanged water and stirred to prepare carbon nanofiber dispersion liquid C-3. <Preparation of Carbon-Based Conductive Material Dispersion Liquid "C-4"> 0.2 g of carbon nanofibers (PotenCia (registered trademark): product of Teijin Limited, average fiber diameter 260 nm, average fiber length 16.9 μm) was added to 100 ml of ion-exchanged water and stirred to prepare carbon nanofiber dispersion liquid C-4.

[0114] <Preparation of Carbon Catalyst Dispersion Liquid "D-1"> 0.96 mg of the carbon catalyst produced in Reference Example 2 was added to 10 ml of ion-exchanged water, and then the mixture was stirred to prepare a carbon catalyst dispersion liquid D-1.

[0115] Example 1 (Production of conductive sheet containing oxygen reduction catalyst) <Step X1> Dispersions A-1 and B-1 were mixed according to the composition shown in Table 1 to obtain agglomerate 1 in which fluororesin particles were aggregated and attached to aramid pulp. Furthermore, dispersions C-1, C-2, and D-1 were mixed according to the composition shown in Table 1, and the mixture was added to agglomerate 1 to obtain slurry 1. This slurry 1 was subjected to wet papermaking to obtain a conductive sheet precursor having the composition shown in Table 1.

[0116] <Step Y1> This conductive sheet precursor was passed through a metal-metal calendar roll under conditions of a temperature of 300° C. and a linear pressure of 32.4 N / m, followed by a baking treatment at 400° C. for 60 minutes in a nitrogen atmosphere, thereby obtaining a conductive sheet containing an oxygen reduction catalyst (carbon catalyst).

[0117] Example 2 (Preparation of a conductive sheet containing an oxygen reduction catalyst on one side)

[0118] <Step X2-1> Dispersions A-1 and B-1 were mixed according to the composition shown in Table 1 to obtain agglomerate 2-1 in which fluororesin particles were aggregated and attached to aramid pulp. Furthermore, dispersions C-1 and C-2 were mixed according to the composition shown in Table 1, and the mixture was added to agglomerate 2-1 to obtain slurry 2-1. A conductive sheet precursor (catalyst-free layer X2-1) containing no catalyst and having the composition shown in Table 1 was obtained by wet papermaking from this slurry 2-1.

[0119] <Step X2-2> Dispersions A-1 and B-1 were mixed according to the composition shown in Table 1 to obtain a coagulated liquid 2-2 in which fluororesin particles were coagulated and attached to aramid pulp. Furthermore, dispersions C-1, C-2, and D-1 were mixed according to the composition shown in Table 1, and the mixture was added to coagulated liquid 2-2 to obtain slurry 2-2. This slurry 2-2 was applied to one surface of the conductive sheet precursor obtained in step X2-1 by wet papermaking, to obtain a conductive sheet precursor containing, on one surface thereof, a carbon catalyst having the composition of catalyst-containing layer X2-2 shown in Table 1.

[0120] <Step Y2> This conductive sheet precursor was passed through a metal-metal calendar roll under conditions of a temperature of 300°C and a linear pressure of 32.4 N / m. Thereafter, a baking treatment was performed at 400°C for 60 minutes in a nitrogen atmosphere, thereby obtaining a conductive sheet containing an oxygen reduction catalyst (carbon catalyst). The obtained conductive sheet had the carbon catalyst present on only one side, and satisfied the above-mentioned formula (1) 0≦M / N<1.

[0121]

[0122] Example 3 A conductive sheet was produced in the same manner as in Example 2, except that the carbon-based conductive material dispersion liquid C-2 was changed to C-3, and the sheet could be produced without any problems.

[0123] Example 4 A conductive sheet was produced in the same manner as in Example 2, except that the carbon-based conductive material dispersion liquid C-2 was changed to C-4, and the sheet could be produced without any problems.

[0124] When a fuel cell was constructed using the conductive sheets obtained in Examples 1 to 4 as a gas diffusion layer, power generation was possible without any problems.

[0125] The disclosures of Japanese Patent Application No. 2023-137521 filed on August 25, 2023 and Japanese Patent Application No. 2024-77513 filed on May 10, 2024 are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated herein by reference.

[0126] 10, 12, 14 Conductive sheets 20, 22, 24 Conductive sheets 30, 32, 34 Electrode catalyst 40 Electrolyte membrane

Claims

1. A conductive sheet comprising aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst.

2. The conductive sheet according to claim 1, wherein the carbon-based conductive material is one or more selected from the group consisting of carbon fibers, carbon black, graphite particles, carbon nanotubes, carbon milled fibers, carbon nanofibers, carbon nanohorns, and graphene.

3. The conductive sheet according to claim 1, wherein the electrode catalyst is one or more selected from the group consisting of platinum catalysts, iridium catalysts, carbon catalysts, and enzymes.

4. The conductive sheet according to claim 1, wherein the electrode catalyst comprises a carbon catalyst containing 0.1 atomic % or more and 10 atomic % or less of nitrogen atoms relative to 100 atomic % of carbon atoms.

5. The conductive sheet according to claim 4, wherein the carbon catalyst contains metal atoms in a mass ratio to the carbon atoms of 0.1 or less.

6. The conductive sheet according to claim 1, which satisfies the following formula (1): 0≦M / N<1 (1) (wherein M represents the content of the electrode catalyst in a portion on one side of the conductive sheet that is from the surface to a depth of 10% of the thickness of the conductive sheet, and N represents the content of the electrode catalyst in a portion on the other side of the conductive sheet that is from the surface to a depth of 10% of the thickness of the conductive sheet.) 7. A method for producing the conductive sheet according to any one of claims 1 to 5, comprising: a step X1 of preparing a slurry X1 containing aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and paper-forming the slurry X1 to obtain a conductive sheet precursor X1; and a step Y1 of hot-pressing the conductive sheet precursor X1 in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then firing the conductive sheet precursor X1 in an inert gas at a temperature of 200 to 500°C.

8. A method for producing the conductive sheet according to claim 6, comprising: a step X2-1 of preparing a slurry X2-1 containing an aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material, and paper-forming the slurry X2-1 to obtain a conductive sheet precursor X2-1; a step X2-2 of preparing a slurry X2-2 containing an aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and paper-forming the slurry X2-2 onto one side of the conductive sheet precursor X2-1 to obtain a conductive sheet precursor X2-2; and a step Y2 of hot-pressing the conductive sheet precursor X2-2 in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then firing the conductive sheet precursor X2-2 in an inert gas at a temperature of 200 to 500°C.

9. A method for producing the conductive sheet according to claim 6, comprising: a step X2-3 of preparing a slurry X2-2 containing an aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and paper-forming the slurry X2-2 to obtain a conductive sheet precursor X2-3; a step X2-4 of preparing a slurry X2-1 containing an aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material, and paper-forming the slurry X2-1 onto one side of the conductive sheet precursor X2-3 to obtain a conductive sheet precursor X2-4; and a step Y3 of hot-pressing the conductive sheet precursor X2-4 in air at a temperature of 100 to 350°C and a linear pressure of 10 to 50 N / m, and then firing the conductive sheet precursor X2-4 in an inert gas at a temperature of 200 to 500°C.

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