Classifications

• • D—TEXTILES; PAPER
  • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
  • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
  • D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
  • D04H1/40—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties
  • D04H1/42—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres from fleeces or layers composed of fibres without existing or potential cohesive properties characterised by the use of certain kinds of fibres insofar as this use has no preponderant influence on the consolidation of the fleece
  • D04H1/4326—Condensation or reaction polymers
  • D04H1/4334—Polyamides
  • D04H1/4342—Aromatic polyamides
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H13/00—Pulp or paper, comprising synthetic cellulose or non-cellulose fibres or web-forming material
  • D21H13/10—Organic non-cellulose fibres
  • D21H13/20—Organic non-cellulose fibres from macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
  • D21H13/26—Polyamides; Polyimides
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/20—Macromolecular organic compounds
  • D21H17/33—Synthetic macromolecular compounds
  • D21H17/34—Synthetic macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H17/00—Non-fibrous material added to the pulp, characterised by its constitution; Paper-impregnating material characterised by its constitution
  • D21H17/63—Inorganic compounds
  • D21H17/67—Water-insoluble compounds, e.g. fillers, pigments
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
  • H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
  • H01B1/20—Conductive material dispersed in non-conductive organic material
  • H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/88—Processes of manufacture
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/90—Selection of catalytic material
  • H01M4/92—Metals of platinum group
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/96—Carbon-based electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes

Definitions

• This disclosure relates to a conductive sheet and a method for manufacturing the same.
• 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, fuel cells that use enzymes or microorganisms as catalysts (biobatteries) have been developed.
• MCFC molten carbonate fuel cells
• SOFC solid oxide fuel cells
• PAFC phosphoric acid fuel cells
• PEFC polymer electrolyte fuel cells
• biobatteries fuel cells that use enzymes or microorganisms as catalysts
• a solid 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.
• GDLs gas diffusion layers
• the GDLs with catalyst layers are called gas diffusion electrodes (GDEs).
• the polymer electrolyte membrane has a function of selectively conducting ions such as hydrogen ions (H + ) and hydroxide ions (OH ⁇ ).
• the catalyst layer is mainly composed of carbon particles carrying a precious metal catalyst such as platinum, a carbon catalyst, or an enzyme.
• the GDL is required to have gas diffusion performance for conducting 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.
• the GDL material is often made of 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.
• the following method is exemplified as a method for producing a carbon fiber sheet.
• a method for producing a carbon fiber sheet by processing carbon fibers such as filament yarns, staple yarns, cut fibers, etc., into a sheet by weaving, papermaking, etc.
• a method for producing a carbon fiber sheet by processing flame-retardant fibers, which are precursor fibers of carbon fibers, into a sheet in advance, and baking the sheet at 1000° C. or higher (for example, Patent Document 1).
• thermosetting resin such as phenol
• the gas diffusion layer (GDL) is also required to have the function of discharging water generated by the power generation reaction to the separator. For this reason, the carbon fiber sheet that constitutes the gas diffusion electrode is generally given water repellency.
• a common method of giving water repellency to a carbon fiber sheet is to impregnate a conductive sheet such as a carbon fiber sheet with a water repellent material such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), and then sinter it at 200 to 500°C (see, for example, Patent Document 3).
• PTFE polytetrafluoroethylene
• PVDF polyvinylidene fluoride
• the GDL is also required to have the function of uniformly diffusing fuel gas into the catalyst layer and the function of controlling the wettability within the MEA.
• MPL microporous layer
• This MPL is composed of carbonaceous particles such as carbon black and fluororesin, and has pores with an average diameter of about several ⁇ m.
• the MPL is formed by spraying or knife coating a slurry containing carbonaceous particles and fluororesin at an appropriate concentration.
• the coating method is generally to coat the surface of the carbon fiber sheet (for example, Patent Document 4).
• a GDE for a polymer electrolyte fuel cell generally uses a water-repellent conductive sheet manufactured by subjecting a carbon fiber sheet to a water-repellent treatment and then forming an MPL.
• this water-repellent conductive sheet is produced through many steps, resulting in low production efficiency, and as a result, fuel cells using this conductive sheet as an electrode material are expensive.
• it is necessary to coat a catalyst layer on the surface of the GDL obtained through the above-mentioned many steps for example, Patent Document 5).
• a method for producing a simple GDL in which a fibrillar material made of an electrically conductive carbon material, a water-repellent fluororesin, and an aromatic polyamide as a binder is used, these materials are dispersed in a solvent and paper-formed, the resulting precursor is hot-pressed, and then fired to obtain a GDL that has electrical conductivity, water repellency, uniform gas diffusion, and wettability adjustment properties in a simple process (e.g., Patent Document 6).
• Patent Document 6 Even such a fabrication method requires additional steps when fabricating a GDE.
• 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: International Publication No. 2012-026498
• the present disclosure aims to provide a conductive sheet that can be used as a gas diffusion electrode and can be easily manufactured, and a method for manufacturing the same.
• a conductive sheet comprising aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst.
• 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.
• 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.
• the electrode catalyst includes a carbon catalyst containing 0.1 atomic % to 10 atomic % of nitrogen atoms relative to 100 atomic % of carbon atoms.
• the carbon catalyst contains metal atoms in a mass ratio of 0.1 or less to the carbon atoms.
• ⁇ 6> The conductive sheet according to any one of ⁇ 1> to ⁇ 4>, which satisfies the following formula (1): 0 ⁇ M/N ⁇ 1 (1)
• 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
• 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.
• a method for producing the conductive sheet according to any one of ⁇ 1> to ⁇ 5> A step X1 of preparing a slurry X1 containing an aromatic polyamide pulp, a fluororesin, a carbon-based conductive material, and an electrode catalyst, and forming the slurry X1 into a sheet to obtain a conductive sheet precursor X1; a process Y1 of hot pressing the conductive sheet precursor X1 in air at a temperature of 100 to
• a method for producing a conductive sheet comprising the steps of: ⁇ 8> A method for producing the conductive sheet according to ⁇ 6>, A step X2-1 of preparing a slurry X2-1 containing an aromatic polyamide pulp, a fluororesin, and a carbon-based conductive material, and forming the slurry X2-1 into a sheet 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 forming the slurry X2-2 onto one side of the conductive sheet precursor X2-1 to obtain a conductive sheet precursor X2-2; a process Y2 in which the conductive sheet precursor X2-2 is heat-pressed in air at a temperature of 100 to 350° C.
• a method for producing a conductive sheet comprising the steps of: ⁇ 9> A method for producing the conductive sheet according to ⁇ 6>, 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 forming the slurry X2-1 onto one surface of the conductive sheet precursor X2-3 to obtain a conductive sheet precursor X2-4; a process 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/
• the present disclosure provides a conductive sheet that can be used as a gas diffusion electrode and can be easily manufactured, and a method for manufacturing the same.
• FIG. 1 is a schematic diagram showing an example of a configuration of a conductive sheet according to a first embodiment of the present disclosure.
• FIG. 6 is a schematic diagram showing an example of a configuration of a conductive sheet according to a second embodiment of the present disclosure.
• 1 is a schematic diagram showing an example of the configuration of a polymer electrolyte fuel cell to which a conductive sheet according to a first embodiment of the present disclosure is applied.
• 11 is a schematic diagram showing an example of the configuration of a polymer electrolyte fuel cell to which a conductive sheet according to a second embodiment of the present disclosure is applied.
• FIG. 6 is a schematic diagram showing an example of a configuration of a conductive sheet according to a second embodiment of the present disclosure.
• the conductive sheet and the method for manufacturing the conductive sheet according to the present disclosure will be described with reference to the drawings. Note that in the following description, reference numerals may be omitted.
• the term "process” refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.
• the inventors conducted extensive research into a simple method for producing gas diffusion electrodes for use in fuel cells, and discovered that electrode catalysts for use in fuel cells can be made from fibril substances in the same way as other constituent materials, leading to the invention disclosed herein.
• 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.
• a fluororesin is fused to the surface of the aromatic polyamide pulp. This fluororesin provides 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 provides electrical conductivity in the thickness direction of the conductive sheet.
• An electrode catalyst is dispersed between the fibers of the aromatic polyamide pulp. This electrode catalyst also provides catalytic performance to the conductive sheet.
• the conductive sheet having such a structure can be used as a gas diffusion electrode in which the gas diffusion layer and the catalyst layer are integrally formed, and can be easily manufactured.
• FIG. 1 shows a schematic diagram of an example of a conductive sheet according to a first embodiment of the present disclosure (hereinafter, may be referred to as the "first conductive sheet").
• the first conductive sheet 10 has an electrode catalyst 30 dispersed throughout the entire thickness of the sheet.
• 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, as described below.
• the conductive sheet 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 the electrode catalyst per unit area on each side may be different.
• the relationship 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 is N, the relationship may satisfy the following formula (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 off the surface of the conductive sheet and measuring by elemental analysis, or a method of preparing a cross-section of the conductive sheet and measuring by X-ray photoelectron spectroscopy (XPS), electron beam microanalyzer (EPMA), scanning electron microscope energy dispersive X-ray spectroscopy (SEM-EDX), or the like.
• XPS X-ray photoelectron spectroscopy
• EPMA electron beam microanalyzer
• SEM-EDX scanning electron microscope energy dispersive X-ray spectroscopy
• FIG. 2 is a schematic diagram showing an example of a conductive sheet according to the second embodiment of the present disclosure (hereinafter, sometimes referred to as the "second conductive sheet").
• the second conductive sheet 20 has a structure in which a catalyst-free layer 20A that does not contain an electrode catalyst 30 and a catalyst-containing layer 20B that contains an electrode catalyst 30 are laminated.
• the electrode catalyst 30 is not present on one surface (first surface) of the second conductive sheet 20, and the electrode catalyst 30 is dispersed on the other surface (second surface).
• the electrode catalyst 30 is usually more expensive than other constituent materials of the conductive sheet.
• the manufacturing cost can be kept low. Note that the content of the electrode catalyst in this conductive sheet may change stepwise or continuously in the thickness direction of the sheet to satisfy formula (1).
• the thickness of the conductive sheets 10 and 20 is not particularly limited, but is preferably 50 to 500 ⁇ m, and more preferably 100 to 400 ⁇ m. If the thickness of the conductive sheets 10 and 20 is 50 ⁇ m or more, high sheet strength is obtained and handling is easy. If the thickness of the conductive sheets 10 and 20 is 500 ⁇ m or less, it is easy to keep the thickness variation low.
• the thickness of the conductive sheets 10 and 20 can be controlled by adjusting the basis weight of the sheet and the temperature and pressure during heat pressing when the conductive sheets are manufactured.
• the thickness of each of the catalyst-free layer 20A and the catalyst-containing layer 20B is preferably 5 ⁇ m or more, and more preferably 10 ⁇ m or more.
• the thickness of the catalyst-containing layer 20B including the electrode catalyst 30 is preferably thinner than the thickness of the catalyst-free layer 20A not including the electrode catalyst 30.
• 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 standpoint of cost reduction, the thickness of the catalyst-containing layer 20B may be 40% or less, or 30% or less of the thickness of the second conductive sheet 20.
• the aromatic polyamide pulp (hereinafter also referred to as "aramid pulp”) used in the present conductive sheet is, for example, an aromatic polyamide pulp having amide bonds 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.
• 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.
• Fibrillation refers to a method of randomly forming minute single fibers on the surface of a fiber.
• fibrillation of aramid pulp is performed by known methods. For example, as described in Japanese Patent Publication Nos. 35-11851 and 37-5752, fibrillation is performed by adding a precipitant to an organic polymer solution and mixing in a system that generates shear force. Alternatively, as described in Japanese Patent Publication No. 59-603, fibrillation is performed by applying mechanical shear force such as beating to a molded product having molecular orientation formed from a polymer solution exhibiting optical anisotropy, thereby randomly imparting minute single fibers.
• the average fiber length of the aramid pulp used in this 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.
• the fluororesin contained in the conductive sheet is preferably fixed to the aromatic polyamide pulp.
• the fluororesin contained in the conductive sheet include polytetrafluoroethylene resin (hereinafter, sometimes referred to as "PTFE"), perfluoroalkoxy resin, tetrafluoroethylene-hexafluoropropylene copolymer resin, tetrafluoroethylene-ethylene copolymer resin, vinylidene fluoride resin, and trifluorochloroethylene.
• PTFE polytetrafluoroethylene resin
• perfluoroalkoxy resin perfluoroalkoxy resin
• tetrafluoroethylene-hexafluoropropylene copolymer resin tetrafluoroethylene-ethylene copolymer resin
• vinylidene fluoride resin vinylidene fluoride resin
• trifluorochloroethylene trifluorochloroethylene
• the carbon-based conductive material contained in the conductive sheet may be, for example, a material having a carbon content of 94 mass% or more and a resistivity of 100 ⁇ cm or less.
• Specific examples of the carbon-based conductive material include carbon fiber, carbon black, graphite particles, carbon nanotubes, carbon milled fiber, carbon nanofiber, carbon nanohorn, and graphene. These carbon-based conductive materials may be used alone or in combination of two or more.
• 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, with PAN-based carbon fibers being particularly preferred.
• the fiber diameter is preferably 3 to 20 ⁇ m, and particularly preferably 5 to 13 ⁇ m.
• the fiber diameter is the average of the long and short diameters of the fiber cross section. If the fiber diameter is 5 ⁇ m or more, the strength of the single fiber is high, making it easier to improve the strength of the conductive sheet. On the other hand, if the fiber diameter is 20 ⁇ m or less, the outer shape of the carbon single fiber that constitutes the sheet is less likely to rise up on the sheet surface. As a result, irregularities are less likely to form on the sheet surface, the surface smoothness of the sheet is improved, and the contact electrical resistance of the sheet is reduced.
• the average fiber length (cut length) of 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.
• the carbon content of carbon fiber or carbon milled fiber is preferably 94% by mass or more. If the carbon content is 94% by mass or more, the electrical conductivity of the sheet is improved. Furthermore, even if a battery incorporating this conductive sheet is operated for a long period of time, deterioration of the sheet is suppressed.
• carbon black examples include acetylene black and Ketjenblack (registered trademark), which has a hollow shell structure. Ketjenblack is particularly preferred.
• 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.
• the average particle size of the secondary particles is preferably 0.5 to 20 ⁇ m. If the average particle size of the secondary particles is 0.5 ⁇ m or more, further aggregation of the carbon black is suppressed when preparing a carbon black dispersion. If the average particle size is 20 ⁇ m or less, the carbon-based conductive material can easily penetrate into the interior of the sheet, improving the conductivity of the sheet.
• graphite particles examples include flake graphite, flaky graphite, earthy graphite, artificial graphite, expanded graphite, expanded graphite, flake graphite, lump graphite, and spherical graphite.
• graphite in a spherical or flake shape is preferred.
• the average particle size of the graphite particles is preferably 0.05 to 300 ⁇ m.
• the carbon nanofibers may be single fibers or aggregates.
• the average fiber diameter of the carbon nanofibers is, for example, 100 to 1000 nm. If the average fiber diameter of the carbon nanofibers is 100 nm or more, the handling property is good, and if it is 1000 nm or less, the fiber density can be easily increased.
• 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.
• the average fiber length of the carbon nanofibers is preferably 1 ⁇ m or more, and more preferably 10 ⁇ m or more. If the average fiber length is 1 ⁇ m or more, it is possible to suppress the decrease in conductivity, strength, and liquid retention. Furthermore, if the average fiber length is 30 ⁇ m or less, the dispersibility of the carbon fibers is unlikely to be impaired, and the carbon fibers are unlikely to be oriented in the in-plane direction of the conductive sheet. As a result, it is easy 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 ⁇ m, and more preferably 12 to 28 ⁇ m.
• Carbon nanofibers can be produced, for example, by the method disclosed in International Publication No. WO 2020/045243. Specifically, (1) a fiberization step of forming a resin composition comprising a thermoplastic resin and 30 to 150 parts by mass of mesophase pitch per 100 parts by mass of the thermoplastic resin in a molten state to fiberize 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 removing step of removing the thermoplastic resin from the resin-composite stabilized fiber to obtain a stabilized fiber; (4) a carbonization and calcination step of heating the stabilized fiber in an inert atmosphere to carbonize or graphitize the fiber to obtain a carbon fiber aggregate;
• the method for producing the carbon fiber aggregate includes the steps of:
• 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.
• PEFCs polymer electrolyte fuel cells
• PAFCs phosphoric acid fuel cells
• biofuels biofuels.
• the type and content of the electrode catalyst may be selected according to 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.
• the carbon catalyst is a particulate carbon catalyst that is mainly composed of a carbon compound containing carbon atoms and nitrogen atoms, specifically, a carbon compound containing 0.1 atomic % to 10 atomic % of nitrogen atoms relative to 100 atomic % of carbon atoms.
• “mainly composed” means that, among the carbon compounds contained in the carbon catalyst, the proportion (volume fraction) occupied by the carbon compound containing 0.1 atomic % to 10 atomic % of nitrogen atoms relative to 100 atomic % of carbon atoms is the largest.
• the carbon catalyst preferably has a volume fraction of particles having a particle diameter of 20 nm or more and 1 ⁇ m or less of 45% or more.
• the volume fraction of particles refers to a volume fraction obtained by measuring the particle size distribution of the carbon catalyst by a laser diffraction particle size distribution measurement method.
• the nitrogen atom content is 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 will occur, electronic conduction within the catalyst will not be impaired, and a catalyst with high catalytic properties will be obtained.
• the carbon catalyst preferably has a mass ratio of metal atoms to carbon atoms of 0.1 or less.
• 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 the generation of hydrogen peroxide and hydroxyl radicals, are less likely to proceed, and deterioration of the electrolyte of the fuel cell can be suppressed.
• the mass ratio of metal atoms to carbon atoms may be 0.001 or more.
• the above metal atoms include various known metals, but representative ones include iron, cobalt, nickel, copper, tin, manganese, zinc, etc., which are sometimes added during production to obtain highly active carbon catalysts.
• the above carbon catalyst can be produced by known methods, for example, the method disclosed in WO 2012/161335.
• enzymes examples include bilirubin oxidase, which reduces oxygen, and lactate oxidase, an enzyme that oxidizes lactic acid.
• the conductive sheet is preferably used as an electrode material for electrolysis, flow batteries, and fuel cells, in particular as a gas diffusion electrode material for fuel cells.
• FIG. 3 shows a schematic diagram of an example of the configuration of a polymer electrolyte fuel cell to which the first conductive sheet 10 of the present disclosure is applied.
• a first conductive sheet 12 functioning as an anode is disposed on one surface of a thin polymer electrolyte membrane 40, and a first conductive sheet 14 functioning as a cathode is disposed on the other surface.
• Each of the conductive sheets 12, 14 has an electrode catalyst 32, 34 dispersed throughout the sheet according to the required function.
• the electrolyte membrane 40 may be any of those used in known fuel cells.
• FIG. 4 shows a schematic diagram of an example of the configuration of a polymer electrolyte fuel cell to which the second conductive sheet 20 of the present disclosure is applied.
• a second conductive sheet 22 that functions as an anode is disposed on one side of a thin polymer electrolyte membrane 40, and a second conductive sheet 24 that functions 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 that contains the electrode catalyst 32, 34 according to the required function is in contact with the electrolyte membrane 40, and the layer (catalyst-free layer) 22A, 24A that does not contain the electrode catalyst 32, 34 is on the outside.
• the method for manufacturing the conductive sheet is not particularly limited. Below, an example of a method for manufacturing the conductive sheet 10 according to the first embodiment of the present disclosure and the conductive sheet 20 according to the second embodiment will be described.
• the first conductive sheet 10 shown in FIG. 1 can be manufactured, for example, through the following steps X1 and Y1.
• 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.
• 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 preparing a dispersion of aramid pulp and a dispersion of fluororesin particles, respectively, and mixing these dispersions.
• aramid pulp may be added to and dispersed in a dispersion of fluororesin particles, or fluororesin particles may be added to and dispersed in a dispersion of aramid pulp.
• the dispersion of aramid pulp 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 Niagara beaters, or various refiners such as single disc refiners.
• the dispersion medium in each dispersion liquid is preferably water such as ion-exchanged water.
• the 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.
• 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.
• the average particle size of the fluororesin particles contained in the fluororesin dispersion is preferably 0.01 to 10 ⁇ m, and particularly preferably 0.1 to 1 ⁇ m. If the average particle size is 0.01 ⁇ m 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 ⁇ m or less, it is easy to prepare a stable dispersion of fluororesin particles. As a result, the fluororesin is less likely to be unevenly distributed in the sheet.
• 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 fiber surface of the aramid pulp. An ionic surfactant disperses aggregated fluororesin particles more easily than a nonionic surfactant. However, a dispersion of fluororesin particles dispersed using an ionic surfactant tends to form large flocks of fluororesin particles, making it difficult to obtain a sheet that is uniformly impregnated with fluororesin. On the other hand, when a nonionic surfactant is used, it is difficult to disperse aggregated fluororesin particles.
• aggregated fluororesin particles can be dispersed, fine fluororesin particles can be uniformly deposited on the fiber surface of the aramid pulp. Therefore, a dispersion of fluororesin particles dispersed using a nonionic surfactant is preferably used.
• the aramid pulp-fluororesin dispersion is prepared by mixing the above-mentioned fluororesin particle dispersion with the above-mentioned aramid pulp dispersion. By mixing the aramid pulp dispersion with the fluororesin dispersion, the fluororesin particles aggregate and adhere (deposit) to the surface of the aramid pulp.
• 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. If the aramid pulp/fluororesin ratio is 10/90 or more, the aramid pulp provides a high reinforcing effect for the sheet. On the other hand, if the aramid pulp/fluororesin ratio is 70/30 or less, the fluororesin provides high water repellency.
• the method for preparing the aramid pulp-fluororesin dispersion is not limited to the above method.
• the aramid pulp and the fluororesin particles may be dispersed in a medium at the same time.
• the aramid pulp and the fluororesin particles may also be dispersed using a dispersion of a carbon-based conductive material, a dispersion of an electrode catalyst, or a dispersion of a carbon-based conductive material and an electrode catalyst, which will be described later.
• the concentrations of aramid pulp and fluororesin in the aramid pulp-fluororesin dispersion are not particularly limited. From the viewpoint of production costs, it is preferable to set the concentrations as high as possible without impairing the fluidity of the aramid pulp-fluororesin dispersion.
• a flocculant may be added to the dispersion.
• a flocculant may be added 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 according to the type of surfactant used to disperse the fluororesin particles and the specific surface area of the aramid pulp.
• the flocculant used may be a strong acid, a strong electrolyte, or a polymer flocculant such as a polyacrylamide flocculant or polyacrylate.
• the flocculant used may be a base, a strong electrolyte, or a polymer flocculant such as a polyacrylamide flocculant or polymethacrylic acid ester.
• 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.
• 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.
• the above flocculants can also be used in combination.
• the fluororesin particles that are not deposited on the aramid pulp are discharged into the wastewater during papermaking. Discharge of fluororesin into wastewater is undesirable from an economic and environmental standpoint. If fluororesin is discharged into the wastewater, wastewater treatment will be required, increasing production costs. For this reason, it is preferable that substantially all of the fluororesin particles in the aramid pulp-fluororesin dispersion are deposited on the aramid pulp.
• substantially all refers to an amount to which wastewater treatment is not required.
• a carbon-based conductive material and an electrode catalyst are added to the aramid pulp-fluororesin dispersion.
• the order of compounding the carbon-based conductive material and the electrode catalyst is not limited.
• the carbon-based conductive material may be compounded in the aramid pulp-fluororesin dispersion, and then the electrode catalyst may be compounded.
• the electrode catalyst may be compounded, and then the carbon-based conductive material may be compounded.
• the carbon-based conductive material and the electrode catalyst may be compounded simultaneously.
• 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 the 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.
• the blending ratio of aramid pulp to carbon-based conductive material is set appropriately depending on the desired final product.
• the blending ratio of aramid pulp to 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. If the aramid pulp/carbon-based conductive material ratio is 10/90 or more, the conductive sheet produced will have a high reinforcing effect due to the aramid pulp. If the aramid pulp/carbon-based conductive material ratio is 90/10 or less, the conductive sheet produced will have a high conductivity due to the carbon-based conductive material.
• 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 electrode catalyst dispersion into the aramid pulp-fluororesin dispersion, or the electrode catalyst may be blended into the aramid pulp-fluororesin dispersion and then dispersed.
• the type of electrode catalyst and the blending ratio of aramid pulp to electrode catalyst are appropriately set according to the desired final product.
• the blending ratio of aramid pulp to electrode catalyst is, for example, in the range of 100 to 10,000 by mass.
• a slurry X1 (hereinafter simply referred to as "slurry") is obtained that contains aramid pulp, a fluororesin that adheres (deposits) to the aramid pulp, a carbon-based conductive material, and an electrode catalyst.
• the above slurry can also be mixed with a substance that decomposes at or below the firing temperature.
• the substance that decomposes at or below the burning temperature (hereinafter also referred to as "vanishing substance”) is a substance that has a decomposition temperature of less than 500°C in an inert atmosphere and decomposes and vanishes at or below the burning temperature described below.
• the vanishing substance is appropriately selected depending on the burning temperature. Pulp- or fiber-shaped organic matter that has a good yield in the papermaking process and a low decomposition temperature is preferred.
• Examples of vanishing substances include cellulosic pulps such as wood pulp and linter pulp.
• the shape of the vanishing substance is preferably 0.1 to 100 mm in length and 0.1 to 50 ⁇ m in diameter.
• the vanishing substances decompose and disappear during the firing process, forming voids within the conductive sheet.
• the resulting conductive sheet has improved air permeability, drainage properties, and gas diffusion performance.
• the vanishing substance is preferably a substance whose decomposition temperature is at least 30°C lower than the firing temperature. If the substance has a decomposition temperature at least 30°C lower than the firing temperature, the vanishing substance is less likely to remain in the sheet during the firing process, and the sheet's breathability, drainage properties, and gas diffusion properties can be sufficiently increased.
• the blending ratio of aramid pulp to vanishing substance is set appropriately depending on the desired final product.
• the blending ratio of aramid pulp to vanishing substance is preferably 95/5 to 40/60 by mass, and particularly preferably 70/30 to 50/50. If the aramid pulp/vanishing substance ratio is 95/5 or less, the air permeability of the manufactured conductive sheet is high, and the diffusion performance and drainage of fuel gas and fuel liquid are likely to be improved. On the other hand, if the aramid pulp/vanishing substance ratio is 40/60 or more, the aramid pulp provides a high reinforcing effect for the conductive sheet.
• the vanishing substance may be mixed into the slurry by mixing a dispersion of the vanishing substance into the slurry, or the vanishing substance may be mixed into the slurry and then dispersed.
• Fillers and additives such as graphite and bronze powder can also be added to the slurry to improve the performance of the resulting sheet or to impart other properties.
• conductive sheet precursor X1 (hereinafter, also simply referred to as "conductive sheet precursor").
• the paper-formation can be performed by a known method, for example, using a fourdrinier or cylinder-type paper-former.
• the obtained conductive sheet precursor is dehydrated and dried as necessary.
• 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.
• the inert gas include nitrogen gas and argon gas.
• the conductive sheet precursor X1 obtained in step X1 is heat-pressed in air.
• the heat-pressing imparts electrical 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 line pressure during the 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 in either a continuous or batch manner.
• the hot-pressed conductive sheet precursor is given electrical conductivity in the thickness direction of the sheet by the carbon-based conductive material.
• the fluororesin in this hot-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.
• the hot-pressed conductive sheet precursor is fired in an inert gas.
• the baking temperature is 200 to 500° C., preferably 230 to 430° C. If the baking temperature is 200° C. or higher, the fluororesin particles deposited on the aramid pulp melt, and the water repellency of the resulting sheet becomes sufficient. If the baking temperature is 500° C. or lower, it is possible to prevent the fluororesin from being decomposed to generate hydrofluoric acid.
• the baking time is, for example, 10 to 120 minutes, preferably 30 to 90 minutes.
• the conductive sheet may be fired while applying 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, etc.
• the firing process causes the fluororesin particles deposited on the aramid pulp to melt and fuse to the surface of the aramid pulp. As a result, a first conductive sheet 10 containing an electrode catalyst and having water repellency is obtained.
• the second conductive sheet 20 shown in FIG. 2 can be manufactured, for example, through the following steps X2-1, X2-2, and Y2.
• 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.
• the slurry X2-1 in the 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.
• the slurry X2-1 is paper-formed to obtain a conductive sheet precursor X2-1.
• the slurry X2-1 is used to perform paper-formation in the same manner as in the step X1 of the first embodiment to obtain a conductive sheet precursor X2-1.
• 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.
• the slurry X2-2 in the step X2-2 is similar to the slurry X1 in the first embodiment, and can be prepared in the same manner as the slurry X1.
• the prepared slurry X2-2 is applied to one surface of the conductive sheet precursor X2-1 to obtain the conductive sheet precursor X2-2.
• the slurry X2-2 can be produced in the same manner as the conductive sheet precursor X1 in the first embodiment, except that the slurry X2-2 is produced on one surface of the conductive sheet precursor X2-1.
• 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 a temperature of 200 to 500°C.
• the hot pressing in the step Y2 can be performed in the same manner as the hot pressing in the first embodiment, except that the conductive sheet precursor X2-2 is used.
• One side of the hot-pressed conductive sheet precursor X2-2 is given catalytic performance by an electrode catalyst.
• the hot-pressed conductive sheet precursor 2-2 is fired in an inert gas. Except for using the conductive sheet precursor 2-2, firing can be performed in the same manner as in the first embodiment. The firing causes the fluororesin particles deposited on the aramid pulp to melt and fuse to the surface of the aramid pulp, resulting in a second conductive sheet 20 containing an electrode catalyst on one side and having water repellency.
• the second conductive sheet 20 may be manufactured, for example, by a procedure in which slurry X2-2 is first paper-formed, and then slurry X2-1 is paper-formed. That is, slurry X2-2 is paper-formed to obtain conductive sheet precursor X2-3, and then slurry X2-1 is paper-formed onto one side of conductive sheet precursor X2-3 to obtain conductive sheet precursor X2-4, which is then hot-pressed and fired under the same conditions as in step Y2.
• N/C ratio nitrogen/carbon atom ratio
• ⁇ 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 by an electron probe microanalyzer (EPMA, EPMA-1400 manufactured by Shimadzu Corporation). The elemental analysis by EPMA was performed using the obtained powder of the particulate carbon catalyst processed into a pellet shape without using a binder. The molar ratio of iron atoms to carbon atoms (iron/carbon atom ratio, sometimes abbreviated as Fe/C ratio) was calculated as a percentage from the obtained composition of carbon and iron elements.
• ⁇ Polymer Viscosity Measurement> The relative viscosity ( ⁇ rel ) at 30° C. of a sample solution having a polymer concentration of 0.5 g/dL prepared using N-methyl-2-pyrrolidone (NMP) as a solvent was determined, and the reduced viscosity ⁇ sp /C was calculated based on this value according to the following formula.
• ⁇ sp /C ( ⁇ rel ⁇ 1)/C (In the above formula, ⁇ sp /C represents the reduced viscosity, ⁇ rel represents the relative viscosity, and C represents the polymer concentration in the solution.)
• NMP was added so that the concentration of the resulting polyacrylonitrile became 0.5 g/dL to prepare a sample solution, and the reduced viscosity ( ⁇ sp /C) measured by the above-mentioned method was 1.34 dL/g.
• 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 to obtain an infusible polyacrylonitrile particle.
• Iron (II) chloride tetrahydrate was supported on the obtained infusible particle so that the composition contained 0.3 mass% of iron atoms, and the obtained infusible polyacrylonitrile-iron (II) chloride tetrahydrate composition was heat-treated at 600°C for 5 hours under a nitrogen stream, and then subjected to a dispersion treatment using a ball mill.
• a heat treatment (activation treatment) was performed at 800°C for 1 hour under an ammonia stream and at 1000°C for 1 hour under an ammonia stream to obtain 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
• the iron/carbon mass ratio of the obtained particulate carbon catalyst was 0.011 by EPMA measurement.
• the freeness of aromatic polyamide pulp was measured in accordance with the Canadian standard freeness method of JIS P8121-2:2012 "Testing method for freeness of pulp.”
• Carbon-Based Conductive Material Dispersion "C-1" 0.2 g of carbon black (Ketjen Black (registered trademark) EC600JD: product name, manufactured by Lion Corporation, primary particle size: 34 nm) was added to 100 ml of ion-exchanged water and stirred to prepare carbon black dispersion C-1.
• carbon black Ketjen Black (registered trademark) EC600JD: product name, manufactured by Lion Corporation, primary particle size: 34 nm
• Carbon-Based Conductive Material Dispersion "C-2" 0.2 g of carbon nanofibers (PotenCia (registered trademark): product of Teijin Limited, average fiber diameter 120 nm, average fiber length 3 ⁇ m) was added to 100 ml of ion-exchanged water and stirred to prepare a carbon nanofiber dispersion C-2.
• Carbon-Based Conductive Material Dispersion "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 ⁇ m) was added to 100 ml of ion-exchanged water and stirred to prepare a carbon nanofiber dispersion C-3.
• Example 1 (Preparation of conductive sheet containing oxygen reduction catalyst) ⁇ Process X1> Dispersions A-1 and B-1 were mixed according to the composition shown in Table 1 to obtain flocculated liquid 1 in which fluororesin particles were flocculated and adhered to the aramid pulp. Furthermore, each of the dispersions C-1, C-2, and D-1 was mixed according to the composition shown in Table 1, and the mixture was added to the coagulation liquid 1 to obtain a slurry 1. This slurry 1 was subjected to wet papermaking to obtain a conductive sheet precursor having the composition shown in Table 1.
• 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, and then baked at 400° C. for 60 minutes in a nitrogen atmosphere to obtain a conductive sheet containing an oxygen reduction catalyst (carbon catalyst).
• carbon catalyst an oxygen reduction catalyst
• Dispersions A-1 and B-1 were mixed according to the composition shown in Table 1 to obtain flocculated liquid 2-1 in which fluororesin particles were flocculated and adhered to the aramid pulp. Furthermore, each of the dispersions C-1 and C-2 was mixed according to the composition shown in Table 1, and the mixture was added to the coagulation liquid 2-1 to obtain a slurry 2-1. The slurry 2-1 was subjected to wet papermaking to obtain a conductive sheet precursor (catalyst-free layer X2-1) not containing a catalyst and having the composition shown in Table 1.
• Dispersions A-1 and B-1 were mixed according to the composition shown in Table 1 to obtain flocculated liquid 2-2 in which fluororesin particles were flocculated and adhered to the aramid pulp. Furthermore, each of the dispersions C-1, C-2, and D-1 was mixed according to the composition in Table 1, and the mixture was added to the flocculation liquid 2-2 to obtain a slurry 2-2. This slurry 2-2 was applied to one side of the conductive sheet precursor obtained in the step X2-1 by wet papermaking, thereby obtaining a conductive sheet precursor containing a carbon catalyst having the composition of the catalyst-containing layer X2-2 shown in Table 1 on one side.
• 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 to obtain 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.
• 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.
• 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.

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