WO2016060043A1 - 炭素シート、ガス拡散電極基材および燃料電池 - Google Patents
炭素シート、ガス拡散電極基材および燃料電池 Download PDFInfo
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- WO2016060043A1 WO2016060043A1 PCT/JP2015/078492 JP2015078492W WO2016060043A1 WO 2016060043 A1 WO2016060043 A1 WO 2016060043A1 JP 2015078492 W JP2015078492 W JP 2015078492W WO 2016060043 A1 WO2016060043 A1 WO 2016060043A1
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- 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
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- 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
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/023—Porous and characterised by the material
- H01M8/0234—Carbonaceous material
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- 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
- H01M4/8605—Porous electrodes
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- 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
- H01M4/8647—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites
- H01M4/8657—Inert electrodes with catalytic activity, e.g. for fuel cells consisting of more than one material, e.g. consisting of composites layered
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- 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
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/023—Porous and characterised by the material
- H01M8/0239—Organic resins; Organic polymers
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- 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
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/023—Porous and characterised by the material
- H01M8/0241—Composites
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- 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
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/023—Porous and characterised by the material
- H01M8/0241—Composites
- H01M8/0243—Composites in the form of mixtures
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- 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
- H01M8/02—Details
- H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
- H01M8/023—Porous and characterised by the material
- H01M8/0241—Composites
- H01M8/0245—Composites in the form of layered or coated products
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- 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
- H01M2008/1095—Fuel cells with polymeric electrolytes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
Definitions
- the present invention relates to a carbon sheet suitably used for a fuel cell, particularly a polymer electrolyte fuel cell, a gas diffusion electrode substrate including a microporous layer, and a fuel cell including the gas diffusion electrode substrate.
- a polymer electrolyte fuel cell that supplies a fuel gas containing hydrogen to the anode and an oxidizing gas containing oxygen to the cathode to obtain an electromotive force by an electrochemical reaction occurring at both electrodes is generally a separator, gas diffusion
- the electrode base material, the catalyst layer, the electrolyte membrane, the catalyst layer, the gas diffusion electrode base material, and the separator are laminated in this order.
- the above gas diffusion electrode base material has high gas diffusibility for diffusing the gas supplied from the separator to the catalyst layer, and high drainage for discharging water generated by the electrochemical reaction to the separator.
- high conductivity for taking out the generated current is necessary, and therefore, a gas diffusion electrode base material in which a microporous layer is formed on the surface of a carbon sheet made of carbon fiber or the like is widely used.
- a fuel cell gas diffusion electrode base material whose porosity is controlled on both sides by stacking a plurality of layers using conductive particles having different average particle diameters (patents) Document 1) and gas diffusion electrode base materials for fuel cells (see Patent Document 2) in which pore diameters are controlled on the front and back sides by mixing carbon fibers having different fiber lengths have been proposed.
- Patent Document 3 a method for producing a gas diffusion electrode base material in which the amount of the binder attached is continuously reduced in the direction perpendicular to the surface has been proposed (see Patent Document 3).
- each layer with controlled porosity and pore diameter is produced separately, and a plurality of layers are laminated, so that the entire carbon sheet becomes thick.
- gas diffusibility and drainage became insufficient, and flooding could not be sufficiently suppressed, so power generation performance was still insufficient.
- the object of the present invention is to improve gas diffusibility and drainage significantly in a gas diffusion electrode substrate, thereby being excellent in flooding resistance, at a relatively low temperature, and To provide a carbon sheet that can exhibit high power generation performance even when operated in a high current density region, and that is suitably used for a gas diffusion electrode substrate having excellent mechanical properties, electrical conductivity, and thermal conductivity. It is in.
- Another object of the present invention is to stably produce a thin carbon sheet and a gas diffusion electrode substrate having sufficient gas diffusibility and drainage, which have been difficult to produce by conventional methods.
- Still another object of the present invention is to provide a gas diffusion electrode substrate using the carbon sheet as a substrate, and a fuel cell including the gas diffusion electrode substrate.
- the present invention has the following configuration.
- the first embodiment of the carbon sheet of the present invention is a porous carbon sheet containing carbon fibers and a binder, and the depth distribution in one surface is measured by measuring the depth distribution of the surface.
- the surface layer area ratio X is the ratio of the area of the part of 20 ⁇ m or less
- the surface layer area ratio Y is the ratio of the area of the part whose depth in the measurement area of the other surface is 20 ⁇ m or less.
- the carbon sheet is characterized in that it is larger than the surface layer area ratio Y, and the difference is 3% or more and 12% or less.
- the surface layer area ratio X is 13% or more and 17% or less
- the surface layer area ratio Y is 9% or more and 13% or less.
- the surface having the surface layer area ratio X is the surface X1
- the surface having the surface layer area ratio Y is the surface Y1
- the surface roughness of the surface X1 is smaller than the surface roughness of the surface Y1, and the difference is not less than 1 ⁇ m and not more than 4 ⁇ m.
- the surface having the surface layer area ratio X is the surface X1
- the surface roughness of the surface X1 is 16 ⁇ m or less.
- the second embodiment of the carbon sheet of the present invention is a porous carbon sheet containing carbon fibers and a binder, and the surface on the side having a large coverage with the carbon fibers and the binder is a surface X2.
- the difference in the coverage between the surface X2 and the surface Y2 is not less than 5% and not more than 20%, when the surface on the side having a smaller surface coverage by the carbon fiber and the binder is defined as the surface Y2. It is a carbon sheet.
- the coverage of the surface X2 is 70% or more and 90% or less, and the coverage of the surface Y2 is 50% or more and 75% or less.
- the carbon sheet includes a water repellent material, and has a 50% average fluorine strength closest to one surface.
- the layer obtained by dividing the section into three equal parts in the direction perpendicular to the plane of the carbon sheet, the layer close to one surface and the other Of the layers close to the surface, a layer having a higher average fluorine intensity is layer A, a smaller layer is layer B, and a layer between layers A and B is a layer C. That is, layer A, layer B, and layer C become smaller in this order.
- the water repellent material has a melting point of 200 ° C. or higher and 320 ° C. or lower.
- the sliding angle of water on the surface of the surface Y1 or the surface Y2 is 40 degrees or less.
- the carbon sheet of the present invention 50-100 ⁇ m when the sum of the volume of pores having diameters in the range of 1-100 ⁇ m is 100%.
- the sum of the volumes of pores having diameters in the range of 17 to 50%, and the porosity (( ⁇ t ⁇ b ) / ⁇ t calculated from the bulk density ( ⁇ b ) and the true density ( ⁇ t ) ) Is 75 to 87%.
- the pore diameter (peak diameter) having the largest volume in the pore diameter range of 1 to 100 ⁇ m. It is in the range of 30-50 ⁇ m.
- the third embodiment of the carbon sheet of the present invention has a pore volume having a diameter in the range of 50 to 100 ⁇ m, where the sum of the volumes of pores having a diameter in the range of 1 to 100 ⁇ m is 100%. wherein the sum is 17% to 50% bulk density ([rho b) and the true density ([rho t) porosity calculated from (( ⁇ t - ⁇ b) / ⁇ t) is 75 to 87% It is a carbon sheet.
- the pore diameter (peak diameter) having the maximum volume is in the range of 30 to 50 ⁇ m within the pore diameter range of 1 to 100 ⁇ m. It is.
- the carbon sheet of the present invention can improve power generation performance particularly at a low temperature, and is suitably used for a gas diffusion electrode substrate.
- the schematic diagram of the profile of the ratio for which the area of the part which has the depth with respect to the depth at the time of measuring depth distribution is shown. It is a schematic cross section for demonstrating the structure of the carbon sheet of this invention. It is the schematic which shows how to obtain
- the first embodiment of the carbon sheet of the present invention is a porous carbon sheet containing carbon fibers and a binder, and the depth distribution in one surface is measured by measuring the depth distribution of the surface.
- the surface layer area ratio X is the ratio of the area of the part of 20 ⁇ m or less
- the surface layer area ratio Y is The carbon sheet is larger than the surface layer area ratio Y, and the difference is 3% to 12%.
- the area of the portion having a depth of 20 ⁇ m or less in the measurement area of the surface means a portion having a depth close to the outermost surface side from the outermost surface by measuring the depth distribution of the surface (outermost surface The shallow area close to the side) is accumulated, and the depth until the accumulated area reaches 2% in the entire measurement range is obtained. Based on the depth, the area from the reference to the depth of 20 ⁇ m The area was determined as “the area of the portion having a depth of 20 ⁇ m or less in the measurement area of the surface”. Then, the ratio of the “area of the portion whose depth in the measurement area of the surface is 20 ⁇ m or less” in the measurement area is defined as the surface layer area ratio.
- the surface area ratio is measured by measuring the depth distribution of the surface and accumulating the area ratio of the portion having the depth close to the outermost surface side from the outermost surface (the shallow portion close to the outermost surface side). Depth until the accumulated area ratio becomes 2% in the entire range is obtained, and the area ratio obtained by accumulating a portion from the reference to a depth of 20 ⁇ m is obtained based on the depth.
- the surface area ratio on one surface is different from the surface area ratio on the other surface.
- FIG. 1 shows a schematic diagram of a profile of the ratio (area ratio) of the area occupied by the portion having the depth to the depth when the depth distribution is measured.
- the depth area ratio profile (1) is the ratio (area ratio) of the area having the depth in the entire measurement range, and the total measurement area ratio (4) is the entire depth area of the measurement range.
- the total area ratio is 100%.
- the rightmost point (depth) included in this excluded area ratio (2) is defined as the depth (5) at which the cumulative area ratio is 2%, and this point is defined as the depth reference (0 ⁇ m).
- the area ratio of the portion located in the perpendicular direction range from the reference (0 ⁇ m) to the depth of 20 ⁇ m is accumulated, and the accumulated area ratio is defined as the surface layer area ratio (3).
- the second embodiment of the carbon sheet of the present invention is a porous carbon sheet containing carbon fibers and a binder, and the surface on the side having a large coverage with the carbon fibers and the binder is a surface X2.
- the carbon sheet is a carbon sheet in which the difference in the coverage between the surface X2 and the surface Y2 is not less than 5% and not more than 20% when the surface on the side having a smaller surface coverage by the carbon fiber and the binder is defined as the surface Y2. .
- the carbon sheet includes a water-repellent material, from the surface having the 50% average fluorine strength closest to one surface to the surface having the 50% average fluorine strength closest to the other surface.
- the layer obtained by dividing the section into three equal parts in the direction perpendicular to the surface of the carbon sheet is a layer having a higher average fluorine intensity among the layer close to one surface and the layer close to the other surface. Is the layer A, the smaller layer is the layer B, and the layer between the layer A and the layer B is the layer C, the average fluorine intensity of the layers decreases in the order of the layer A, the layer B, and the layer C.
- the 50% average fluorine intensity refers to a value of 50% of the average value of the fluorine intensity measured along a straight line in a direction perpendicular to the surface of the carbon sheet from one surface of the carbon sheet toward the other surface.
- the “surface having the 50% average fluorine intensity closest to one surface” means the point indicating the 50% average fluorine intensity closest to one surface on the straight line in the perpendicular direction of the carbon sheet in the above measurement. It represents an imaginary plane that includes a set and is substantially parallel to the surface of the carbon sheet, and does not need to be a continuous plane within the carbon sheet.
- the average fluorine intensity of the layers decreases in the order of layer A, layer B, and layer C” means that the average fluorine intensity of each layer is in the relationship of layer A> layer B> layer C.
- FIG. 2 is a schematic cross-sectional view for illustrating and explaining the first embodiment and the second embodiment of the carbon sheet of the present invention, and the preferred mode of the carbon sheet of the present invention.
- the depth (reference depth) (9) at which the cumulative area ratio becomes 2% from one surface (plane X1 or surface X2 (7)) in the direction perpendicular to the surface is measured by measuring the depth distribution of the surface. Determined. A depth (10) of 20 ⁇ m can be obtained from this reference depth with reference to the depth (reference depth) (9) at which the cumulative area ratio is 2%. Similarly, the depth (reference depth) (9) at which the cumulative area ratio is 2% is obtained also on the opposite surface, and the depth (10) of 20 ⁇ m can be obtained from the reference depth.
- the section (17) up to the plane having the 50% average fluorine intensity closest to the plane Y2 (8) (plane BB (13))
- the section is obtained by equally dividing the section into three in the direction perpendicular to the plane of the carbon sheet.
- the layer having the highest average fluorine intensity is selected.
- a (14), a layer close to the other surface (surface Y1 or surface Y2 (8)) and having a layer whose average fluorine intensity is smaller than layer A (14) is layer B (16), and layers A (14) and B
- the layer between (16) is layer C (15)
- the average fluorine intensity of the layer is A (14), a layer B (16)
- a preferred embodiment of the carbon sheet (6) of the present invention is composed of the layer A (14), the layer B (16), the layer C (15), and the layer (10) having an average fluorine intensity of less than 50%. ing.
- a gas diffusion electrode substrate can be obtained by providing a microporous layer on the surface X1 or the surface X2 (7).
- the third embodiment of the carbon sheet of the present invention is a porous carbon sheet containing carbon fibers and a binder, and the sum of the volumes of pores having a diameter in the range of 1 to 100 ⁇ m is 100%. Sometimes, the sum of the volumes of pores having diameters in the range of 50 to 100 ⁇ m is 17 to 50%, and the porosity calculated from the bulk density ( ⁇ b) and the true density ( ⁇ t) (( ⁇ t ⁇ b) / ⁇ t) is a carbon sheet having 75 to 87%.
- the carbon sheet of the present invention is prepared by a porous body containing carbon fibers described later, impregnation with a resin composition, bonding and heat treatment performed as necessary, carbonization, and water repellent processing as necessary. Can do.
- the carbon sheet of the present invention refers to a porous sheet containing carbon fibers and a binder, and can be water-repellent processed as necessary.
- the binder represents a component other than carbon fibers in the carbon sheet. Therefore, the binder includes a carbide of a resin composition that is a material that serves to bond carbon fibers together. Further, when a water repellent material is used for the carbon sheet of the present invention, the water repellent material is included in the binder.
- the carbon sheet of the present invention is porous. Since the carbon sheet is porous, both excellent gas diffusibility and drainage can be achieved. In order to make the carbon sheet porous, it is preferable to use a porous body as a material used for producing the carbon sheet.
- porous body used for producing a porous carbon sheet will be described.
- the porous carbon sheet of the present invention has a high gas diffusibility for diffusing the gas supplied from the separator into the catalyst, and a high drainage property for discharging water generated with the electrochemical reaction to the separator. It is preferable to have high conductivity for taking out the generated current. For this reason, in order to obtain a porous carbon sheet, it is preferable to use a porous body having conductivity. More specifically, the porous body used to obtain the porous carbon sheet is preferably a porous body containing carbon fibers such as a carbon fiber papermaking body, a carbon fiber woven fabric, and a felt type carbon fiber nonwoven fabric. It is an aspect.
- the carbon fiber papermaking body should be used as the porous body because of its excellent property of absorbing the dimensional change of the electrolyte membrane in the direction perpendicular to the surface, that is, "spring property". Is preferred.
- a carbon fiber papermaking body will be described as a representative example.
- a base material formed by binding carbon fiber papermaking bodies with a binder can also be obtained by impregnating a carbon fiber papermaking body with a resin and carbonizing.
- Examples of the carbon sheet of the present invention and the carbon fiber in the porous body used to obtain the carbon sheet include polyacrylonitrile (PAN) -based, pitch-based and rayon-based carbon fibers.
- PAN polyacrylonitrile
- PAN-based carbon fibers and pitch-based carbon fibers are preferably used because of their excellent mechanical strength.
- the average diameter of the single fibers is preferably in the range of 3 to 20 ⁇ m, more preferably in the range of 5 to 10 ⁇ m.
- the average diameter of the single fibers is 3 ⁇ m or more, the pore diameter is increased, drainage is improved, and flooding can be suppressed.
- the average diameter of the single fibers is 20 ⁇ m or less, the water vapor diffusion is reduced.
- the electrolyte membrane is dried and the proton conductivity is reduced. Can be suppressed (hereinafter referred to as dry-up).
- the average diameter of the single fiber in the carbon fiber is taken with a microscope such as a scanning electron microscope, the carbon fiber is magnified 1000 times, a photograph is taken, and 30 different single fibers are selected at random. Is measured and the average value is obtained.
- a microscope such as a scanning electron microscope
- S-4800 manufactured by Hitachi, Ltd. or its equivalent can be used.
- the carbon fibers used in the present invention preferably have an average single fiber length in the range of 3 to 20 mm, more preferably in the range of 5 to 15 mm.
- the carbon sheet has excellent mechanical strength, electrical conductivity, and thermal conductivity.
- the average length of the single fiber is 20 mm or less, the carbon fiber is excellent in dispersibility during papermaking and a homogeneous carbon sheet can be obtained.
- the carbon fiber having such an average length of single fibers is obtained by a method of cutting continuous carbon fibers into a desired length.
- the average length of the carbon fiber single fiber is taken with a microscope such as a scanning electron microscope, the carbon fiber is magnified 50 times, a photo is taken, and 30 different single fibers are selected at random. The length is measured and the average value is obtained.
- a microscope such as a scanning electron microscope
- S-4800 manufactured by Hitachi, Ltd. or its equivalent can be used as the scanning electron microscope.
- the average diameter and average length of single fibers in the carbon fiber are usually measured by directly observing the carbon fiber as a raw material, but can also be measured by observing the carbon sheet.
- a carbon fiber papermaking body formed by papermaking which is an embodiment of a porous body used to obtain a carbon sheet, is intended to keep the in-plane conductivity and thermal conductivity isotropic when made into a carbon sheet.
- the carbon fiber is preferably in the form of a sheet in which it is randomly dispersed in a two-dimensional plane.
- the carbon fiber papermaking for obtaining the carbon fiber papermaking body can be performed only once or can be performed by laminating a plurality of times. In the present invention, it is desirable to perform papermaking at a time in order to stably produce a thin carbon sheet that is easy to obtain not only productivity but also high power generation performance.
- the average diameter of the single fibers of the carbon fiber is such that the ratio of the average diameter of the single fibers of the carbon fiber obtained from one surface of the carbon sheet and the average diameter of the single fibers of the carbon fiber obtained from the other surface is 0. It is preferably 5 or more and 1 or less. When the average diameter is the same, the ratio is 1, and when the average diameter is different, the ratio is “small average diameter / large average diameter”. Moreover, it is preferable that the difference is 0 mm or more and 10 mm or less about the average length of the single fiber of the carbon fiber calculated
- the carbon fiber papermaking body preferably has a carbon fiber basis weight in the range of 10 to 50 g / m 2 , more preferably in the range of 15 to 35 g / m 2 , and still more preferably in the range of 20 to It is within the range of 30 g / m 2 .
- the basis weight of the carbon fiber in the carbon fiber papermaking body is 10 g / m 2 or more
- the carbon sheet obtained from the carbon fiber papermaking body has excellent mechanical strength.
- the basis weight of the carbon fiber in the carbon fiber papermaking body is 50 g / m 2 or less
- the carbon sheet obtained from the carbon fiber papermaking body is excellent in in-plane gas diffusibility and drainage.
- a carbon fiber papermaking body is obtained by laminating a plurality of papermaking bodies, it is preferable that the carbon fiber basis weight of the carbon fiber papermaking body after the lamination is in the above range.
- the basis weight of the carbon fiber in the carbon sheet is a residue of the carbon fiber paper body cut out in 10 cm square in a nitrogen atmosphere in an electric furnace at a temperature of 450 ° C. for 15 minutes to remove organic matter. It can be determined by dividing the mass by the area of the carbon fiber papermaking body (0.01 m 2 ).
- a porous composition containing carbon fibers such as a carbon fiber papermaking body is impregnated with a resin composition serving as a binder.
- the binder in the carbon sheet refers to a component other than the carbon fibers in the carbon sheet, and mainly serves to bind the carbon fibers together.
- the material that plays a role in binding carbon fibers include a resin composition impregnated in a porous body or a carbide thereof.
- a porous body containing carbon fibers impregnated with a resin composition serving as a binder may be referred to as a “pre-impregnated body”.
- a method of impregnating a porous body containing carbon fibers with a resin composition as a binder a method of immersing the porous body in a resin composition to which a solvent is added, or a resin composition to which a solvent is added is applied to the porous body. And a method of forming a layer made of a resin composition on a peeling film and transferring the layer made of the resin composition to a porous body. Especially, since productivity is excellent, the method of immersing a porous body in the resin composition which added the solvent is used especially preferable.
- the binder By attaching the resin composition to the entire pre-impregnated body, the binder can be attached to the entire carbon sheet to be obtained, so that the strength of the carbon sheet can be further improved.
- the surface area ratio or coverage of the other surface differs from the surface area ratio or coverage of one surface of the carbon sheet ( Details will be described later).
- This can be obtained by distributing a large amount of the resin composition on one surface when the porous body is impregnated with the resin composition serving as the binder in the carbon sheet. That is, in the carbon sheet, it can be obtained by distributing a large amount of the binder on one surface. More specifically, after the resin composition is uniformly impregnated in a porous body such as a papermaking body containing carbon fibers by dipping or the like, the resin composition excessively adhered from one side is removed before drying. Thus, the surface area ratio or the coverage of one surface and the other surface of the obtained carbon sheet can be controlled to different values.
- a carbon fiber papermaking body is dipped in a solution containing a resin composition to obtain a pre-impregnated body, and then dried by sucking the solution containing the resin composition from one surface before drying.
- Resin in the vicinity of one surface of carbon fiber papermaking body (surface Y1 or surface Y2 to be described later when it becomes a carbon sheet) by pressing the squeeze roll only on one surface of the fiberpaper body
- the adhesion amount of the composition can be reduced with respect to the adhesion amount of the resin composition in the vicinity of the other surface (the surface on the side that becomes the surface X1 or the surface X2 described later when the carbon sheet is formed).
- the resin composition can be attached to the entire carbon fiber papermaking body, the binder is present on the entire carbon sheet obtained as a result, and the mechanical strength can be maintained.
- an additional resin composition is added only to one surface of the carbon fiber papermaking body.
- the surface area ratio or coverage of one surface and the other surface of the carbon sheet can also be controlled to different values by applying with a spray or a gravure roll.
- by drying the carbon fiber papermaking body after immersing it in a solution containing the resin composition by attaching a large amount of the resin composition on one side by gravity applied to the resin composition or hot air drying from one side, The surface area ratio or the coverage of one surface of the carbon sheet and the other surface can be controlled to different values.
- two carbon fiber paper bodies are immersed in a solution containing a resin composition in a state where the two surfaces Y1 or Y2 are overlapped and dried, and the two carbon fiber paper bodies are stacked and dried.
- the amount of the binder adhering to the surface Y1 or the surface Y2 side can be reduced compared to the surface X1 or the surface X2 side.
- the third embodiment of the carbon sheet of the present invention is prepared by a method of additionally applying a resin composition only to one surface of the carbon fiber papermaking body, as in the first embodiment and the second embodiment. Can do. Also, the pores formed inside the carbon sheet are impregnated with a resin composition containing particles that disappear at a high temperature of 400 ° C. or higher on at least one surface of the carbon fiber papermaking body, and the particles are eliminated in the carbonization step described later. It is also possible to control the size of. At this time, the disappearing particles may be impregnated from only one surface, or a portion having large pores can be formed unevenly by applying in a pattern.
- the resin composition used when preparing the pre-impregnated body is obtained by adding a solvent or the like to the resin component as necessary.
- the resin component includes a resin such as a thermosetting resin or a thermoplastic resin, and further includes an additive such as a carbon powder or a surfactant as necessary.
- the carbonization yield of the resin component contained in the resin composition is preferably 40% by mass or more.
- the carbonization yield is 40% by mass or more, the carbon sheet tends to be excellent in mechanical properties, electrical conductivity, and thermal conductivity.
- the carbonization yield of the resin component contained in a resin composition it is about 60 mass% normally.
- thermosetting resins such as phenol resin, epoxy resin, melamine resin, and furan resin.
- a phenol resin is preferably used because of high carbonization yield.
- carbon powder can be used for the purpose of improving the mechanical properties, conductivity and thermal conductivity of the carbon sheet.
- carbon powder carbon black such as furnace black, acetylene black, lamp black and thermal black
- graphite such as scaly graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite and flake graphite, carbon nanotube, Carbon nanofibers, carbon fiber milled fibers, and the like can be used.
- the resin composition can use the above-described resin components as they are, and can contain various solvents as necessary for the purpose of improving the impregnation property into a porous body such as a carbon fiber papermaking body.
- methanol, ethanol, isopropyl alcohol, or the like can be used as the solvent.
- the resin composition is preferably in a liquid state at 25 ° C. and 0.1 MPa.
- the resin composition is liquid, the impregnation property into a porous body such as a carbon fiber papermaking body is excellent, and the resulting carbon sheet is excellent in mechanical properties, electrical conductivity, and thermal conductivity.
- the resin composition When impregnated, the resin composition is preferably impregnated so that the resin component is 30 to 400 parts by mass with respect to 100 parts by mass of the carbon fibers in the pre-impregnated body, and is 50 to 300 parts by mass. It is more preferable to impregnate.
- the carbon sheet has excellent mechanical properties, electrical conductivity and thermal conductivity when the impregnation amount of the resin component is 30 parts by mass or more, more preferably 50 parts by mass or more with respect to 100 parts by mass of the carbon fibers in the pre-impregnated body. It becomes.
- the impregnation amount of the resin component with respect to 100 parts by mass of the carbon fiber in the pre-impregnated body is 400 parts by mass or less, more preferably 300 parts by mass or less, the carbon sheet has in-plane direction gas diffusibility and perpendicular direction.
- the gas diffusivity is excellent.
- a plurality of pre-impregnated bodies can be bonded together for the purpose of making the carbon sheet have a predetermined thickness.
- a plurality of pre-impregnated bodies having the same properties can be bonded together, or a plurality of pre-impregnated bodies having different properties can be bonded together.
- a plurality of pre-impregnated bodies having different carbon fiber diameters, carbon fiber lengths, the weight of carbon fibers of a porous body such as a carbon fiber papermaking body used for obtaining a pre-impregnated body, and the amount of resin component impregnated are different. It can also be pasted together.
- discontinuous surfaces are formed in the perpendicular direction by bonding, and internal isolation may occur. Therefore, in the present invention, only one sheet without bonding a porous body such as a carbon fiber papermaking body. It is desirable to perform heat treatment on this.
- the pre-impregnated body can be heat-treated for the purpose of thickening and partially cross-linking the resin composition in the pre-impregnated body.
- a heat treatment method a method of blowing hot air, a method of heating with a hot plate such as a press apparatus, a method of heating with a continuous belt, etc. can be used.
- a porous material such as a carbon fiber papermaking body is impregnated with a resin composition to obtain a pre-impregnated material, and then fired in an inert atmosphere in order to carbonize the resin component.
- a batch type heating furnace can be used, or a continuous type heating furnace can be used.
- the inert atmosphere can be obtained by flowing an inert gas such as nitrogen gas or argon gas in the furnace.
- the maximum firing temperature is preferably in the range of 1300 to 3000 ° C, more preferably in the range of 1700 to 3000 ° C, and still more preferably in the range of 1900 to 3000 ° C.
- the maximum temperature is 1300 ° C. or higher, the carbonization of the resin component in the pre-impregnated body proceeds, and the carbon sheet has excellent conductivity and thermal conductivity.
- the maximum temperature is 3000 ° C. or lower, the operating cost of the heating furnace is lowered.
- carbon fiber fired body what is carbonized after impregnating a resin composition into a porous body such as a carbon fiber papermaking body
- the carbon sheet means a carbon fiber fired body, and both the carbon fiber fired body before the water repellent process and the carbon fiber fired body after the water repellent process correspond to the carbon sheet.
- the carbon fiber fired body is subjected to water repellent finishing.
- the carbon sheet of the present invention preferably contains a water repellent material.
- the water repellent finish can be performed by applying a water repellent material to the carbon fiber fired body and heat-treating it.
- the water-repellent material is included in the carbon sheet as a binder.
- the water repellent material it is preferable to use a fluorine-based polymer because of its excellent corrosion resistance.
- fluorine-based polymer examples include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).
- PTFE polytetrafluoroethylene
- FEP tetrafluoroethylene-hexafluoropropylene copolymer
- PFA tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer
- the sliding angle of water on the surface Y1 or the surface Y2 is preferably 40 degrees or less.
- the gas diffusion electrode substrate of the present invention can be obtained.
- the surface Y1 or surface Y2 of the carbon sheet is on the separator side, but by making the sliding angle of water on the surface Y1 or surface Y2 40 degrees or less, Good drainage to the separator can be obtained.
- the sliding angle of water on the surface Y1 or the surface Y2 means a sliding angle obtained by measurement from the surface Y1 or the surface Y2 side of the carbon sheet.
- the sliding angle on the surface Y1 or the surface Y2 is preferably as low as possible, and the best drainage can be obtained at 1 degree.
- a method for controlling the sliding angle of water on the surface Y1 or the surface Y2 to be 40 degrees or less a method of performing water repellent processing can be mentioned.
- the water repellent material melts and has a low viscosity, so that the water repellent material can be uniformly attached to the surface of the carbon fibers in the carbon sheet, and the sliding angle of water is 40.
- the water repellency of the carbon sheet can be improved.
- the sliding angle of water on one side of the carbon sheet is 40 degrees or less, and that side is opposite to the side forming the microporous layer.
- a surface is preferred.
- the conductivity with the separator can be improved by thinly adhering the water repellent material to the surface of the baked carbon sheet.
- the water repellent material used in the water repellent process has a melting point of 200 ° C. or higher and 320 ° C. or lower.
- the water repellent material satisfying this include FEP or PFA.
- the water repellent material has a melting point of 200 ° C. or higher, the water repellent material is hardly thermally decomposed during the heat treatment in the water repellent processing step, and a carbon sheet with high water repellency can be obtained.
- the drainage of the carbon sheet having the structure of the present invention can be greatly increased, and the accumulation of water inside the water-repellent carbon sheet can be reduced. The characteristics can be greatly improved.
- the adhesion amount of the water repellent material is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass with respect to 100 parts by mass of the carbon fiber fired body.
- a carbon sheet will become the thing excellent in drainage as the adhesion amount of a water repellent material is 1 mass part or more.
- the adhesion amount is 50 parts by mass or less, the carbon sheet has excellent conductivity.
- the carbon fiber fired body corresponds to a “carbon sheet”. As described above, the carbon fiber fired body is subjected to water-repellent processing as necessary. In the present invention, the carbon fiber fired body subjected to water-repellent processing also corresponds to the “carbon sheet”. The carbon fiber fired body which is not subjected to water repellent treatment naturally corresponds to a “carbon sheet”.
- the density of the carbon sheet is preferably in the range of 0.20 to 0.40 g / cm 3 , more preferably in the range of 0.22 to 0.35 g / cm 3 , and still more preferably. It is within the range of 0.24 to 0.30 g / cm 3 .
- the density is 0.20 g / cm 3 or more, the water vapor diffusibility is small, and dry-up can be suppressed.
- the mechanical strength of the carbon sheet is improved, and the electrolyte membrane and the catalyst layer can be sufficiently supported.
- the conductivity is high and the power generation performance is improved.
- the density is 0.40 g / cm 3 or less, drainage performance is improved and flooding can be suppressed.
- the carbon sheet having such a density is obtained by controlling the basis weight of the carbon fiber, the blending amount of the resin component with respect to the carbon fiber, and the thickness of the carbon sheet, as will be described later in the carbon sheet manufacturing method.
- the density of the carbon sheet is obtained by dividing the basis weight (mass per unit area) of the carbon sheet weighed using an electronic balance by the thickness of the carbon sheet when pressed with a surface pressure of 0.15 MPa. Can do.
- the thickness of the carbon sheet of the present invention is preferably 50 to 230 ⁇ m, more preferably 70 to 180 ⁇ m, and still more preferably 90 to 130 ⁇ m.
- the thickness of the carbon sheet is 230 ⁇ m or less, more preferably 180 ⁇ m or less, and even more preferably 130 ⁇ m or less, the gas diffusibility is likely to increase, and the generated water is also easily discharged. Further, the size of the fuel cell as a whole can be easily reduced.
- the thickness of the carbon sheet is 50 ⁇ m or more, more preferably 70 ⁇ m or more, and even more preferably 90 ⁇ m or more, gas diffusion in the in-plane direction inside the carbon sheet is efficiently performed, and power generation performance is easily improved.
- the thickness of the carbon sheet of the present invention is obtained by the following method. That is, the difference in height between when the measured object is present and when it is not measured with a pressure of 0.15 MPa is measured by placing the carbon sheet and the gas diffusion electrode substrate on a smooth surface plate. Sampling is performed at 10 different locations, and the average of the measured height differences is taken as the thickness.
- the surface layer area ratio on one surface is different from the surface layer area ratio on the other surface.
- the surface area ratio is obtained by obtaining the depth distribution of the surface of the carbon sheet with a shape analysis laser microscope.
- the randomly selected carbon sheets are each fixed to a surface plate so that the range of 5 mm square does not float, and the surface depth distribution of the randomly selected portion is measured using a laser microscope.
- the surface depth distribution is calculated. Then, after performing planar automatic tilt correction on the obtained data, the surface depth distribution is calculated. Then, a profile of the ratio (area ratio) of the area of the portion having the depth to the depth shown in FIG. 1 is created. Then, the area ratio of the shallow part near the outermost surface is accumulated, and the part where the accumulated area ratio becomes 2% is set as the excluded area ratio. Further, using the depth at which the cumulative area ratio becomes 2% as a reference, the cumulative area ratio from the reference depth to a depth of 20 ⁇ m is obtained. The cumulative area ratio thus obtained is the surface area ratio. The surface area ratio is the average of the values obtained in this way.
- the surface area ratio physically represents the area ratio of the substance existing in the surface layer, and the surface area ratio increases when a large amount of carbon fiber and binder are present in a relatively shallow portion of the surface.
- This surface area ratio can be controlled by depositing a large amount of the binder near the surface of the carbon sheet by depositing a large amount of the resin composition near the surface when preparing the pre-impregnated body.
- a laser microscope Keyence VK-X100
- 10 times as an objective lens is used.
- Surface depth distribution data in the range of 5 mm square can be obtained by measuring 5 rows vertically and 4 columns horizontally and connecting the resulting images.
- the liquid water in the carbon sheet has a large opening from the surface X1 side where the surface layer area ratio is large.
- the surface Y1 side where the surface area ratio Y is small liquid water can be efficiently drained from the carbon sheet to the separator. This not only improves drainage, but also prevents the carbon sheet from being clogged with water and improves gas diffusibility. For this reason, flooding can be suppressed even in power generation in a high current density region where a large amount of liquid water is generated.
- the difference in the surface area ratio between the surface X1 and the surface Y1 is preferably 3% or more.
- the difference in the surface layer area ratio is 12% or less.
- 4.0% to 9.6% is preferable, and 4.7% to 7.0% is more preferable.
- the surface layer area ratio X in order to control the diffusion of water vapor by the surface layer area ratio, is preferably 13% or more, and 17% or less in order to ensure the diffusion of the fuel gas and the oxidizing gas. It is preferable. Furthermore, considering the balance with mechanical strength, 14.8% or more and 16.0% or less are preferable.
- the surface area ratio Y is preferably 9% or more in order to maintain the mechanical strength.
- the surface layer area ratio Y is 13% or less. Preferably there is. In consideration of gas diffusibility, 9.1% or more and 10.3% or less is more preferable.
- the surface roughness of the surface X1 is preferably smaller than the surface roughness of the surface Y1.
- the surface roughness of the surface X1 is smaller than the surface roughness of the surface Y1, the penetration of the filler-containing coating liquid into the carbon sheet is reduced, and the gas diffusibility of the gas diffusion electrode substrate can be increased. It is desirable that there is a certain difference in surface roughness between the surface X1 and the surface Y1, and the difference is preferably 1 ⁇ m or more and 4 ⁇ m or less.
- the surface roughness of the surface X1 means the surface roughness measured from the surface X1 side of the carbon sheet
- the surface roughness of the surface Y1 means the surface roughness measured from the surface Y1 side of the carbon sheet.
- the surface roughness of the surface X1 is preferably 16 ⁇ m or less, more preferably 11 ⁇ m or more and 16 ⁇ m or less, and further preferably 13 ⁇ m or more and 15 ⁇ m or less.
- the surface roughness of the surface Y1 is preferably 12 ⁇ m or more and 20 ⁇ m or less, and more preferably 14 ⁇ m or more and 19 ⁇ m or less.
- the surface roughness of the surface having a smaller surface roughness is preferably 16 ⁇ m or less, more preferably 11 ⁇ m or more and 16 ⁇ m or less. More preferably, it is 13 ⁇ m or more and 15 ⁇ m or less.
- the surface roughness of the surface having a larger surface roughness is preferably 12 ⁇ m or more and 20 ⁇ m or less, and more preferably 14 ⁇ m or more and 19 ⁇ m or less.
- the surface coverage by the carbon fiber and the binder on one surface of the surface X2 and the surface Y2 described above, and the carbon fiber and the binder on the other surface are bonded. It is important that the coverage of the surface with the dressing is different.
- the coverage is represented by the ratio of the portion of the entire surface (the entire portion including the void portion and the portion where the carbon fiber and the binder exist) covered by the carbon fiber and the binder.
- This coverage can be obtained by numerically processing an image obtained by observing the surface of the carbon sheet with a scanning electron microscope. That is, it is possible to obtain the area ratio by separating the void portion on the surface and the portion where the carbon fiber and the binder are present.
- the surface of the carbon sheet is magnified 50 times, and an image is taken by using the attached automatic adjustment function for contrast of light and dark.
- the image processing program “J-trim” the obtained image is divided into 256 levels of brightness and maximum and minimum of brightness, and binarization is performed with the minimum to 70 steps as a threshold. Do. Of the entire area, the ratio of the binarized bright area is defined as the coverage [%].
- the surface on the side with the larger coverage is defined as surface X2
- the surface on the smaller side is defined as surface Y2.
- the liquid water in the carbon sheet is opened from the side of the surface X having a large coverage.
- liquid water can be efficiently drained from the carbon sheet to the separator. This not only improves drainage, but also prevents the carbon sheet from being clogged with water and improves gas diffusibility. For this reason, flooding can be suppressed even in power generation in a high current density region where a large amount of liquid water is generated.
- the difference in coverage between the surface X2 and the surface Y2 is 5% or more. This is very important.
- the difference in coverage is too large, the uneven distribution of the binder in the layer becomes excessive and the mechanical strength tends to be insufficient. For this reason, it is important that the difference in coverage is 20% or less.
- it is preferably 6.5% or more and 15.0% or less, and more preferably 7.5% or more and 12.0% or less.
- the coverage of the surface X2 in order to control the diffusion of water vapor by the coverage, is preferably 70% or more, and 90% or less in order to ensure the diffusion of fuel gas and oxygen gas. Is preferred. Moreover, when considering the balance between efficient drainage and gas diffusivity, it is preferably 75.0% or more and 81.4% or less.
- the coverage of the surface Y2 is preferably 50% or more, while the coverage is 75% or less in order to effectively discharge liquid water. It is preferable that Further, if considering the balance between efficient drainage and gas diffusibility, 68.0% to 75.0% is preferable.
- the carbon sheet of the present invention contains a water repellent material, and it is preferable that the average fluorine strength of the layers A, B, and C decreases in the order of layer A, layer B, and layer C.
- the average fluorine intensity of the layer C is smaller than the average fluorine intensity of the layer A, the generated water generated by power generation moves quickly from the layer A to the layer C. Moreover, since the average fluorine intensity
- the fluorine intensity so that the average fluorine intensity decreases in the order of layer A, layer B, and layer C in this way, the flooding resistance is improved compared to the case where layer A> layer C> layer B. It becomes possible to do.
- the average fluorine intensity of the layer for improving the flooding resistance is preferably within the range of 1.30 to 9.00 when the average fluorine intensity of the layer B is 1.
- the average fluorine intensity of the layer C is in the range of 0.10 to 0.90.
- the average fluorine intensity of layer C is more preferably 0.30 to 0.80, and further preferably 0.50 to 0.70, when the average fluorine intensity of layer B is 1. .
- the average fluorine intensity of layer B is 1, the average fluorine intensity of layer C is 0.90 or less, more preferably 0.80 or less, and even more preferably 0.70 or less. Is significantly improved, and the power generation performance is easily improved.
- the layer C with respect to the average fluorine intensity of the layer B is 0.10 or more, more preferably 0.30 or more, and further preferably 0.50 or more
- the layer C has a certain level or more of water repellency. As a result, the generated water is hardly accumulated in the layer C, and flooding is suppressed.
- the average fluorine intensity of layer A is more preferably 1.40 to 8.00, and further preferably 1.50 to 7.00, when the average fluorine intensity of layer B is 1. .
- the average fluorine intensity of the layer A relative to the average fluorine intensity of the layer B is 1.30 or more, more preferably 1.40 or more, and further preferably 1.50 or more, the generated water is discharged from the layer A to the layer B side. It becomes easy to be done.
- the average fluorine intensity of the layer B is 1, the average fluorine intensity of the layer A is 9.00 or less, more preferably 8.00 or less, and still more preferably 7.00 or less. It has water repellency above a certain level, and the generated water is less likely to accumulate in the portion of the layer B in contact with the separator rib portion, and flooding is suppressed.
- the fiber diameter and density of the carbon fibers constituting the carbon sheet and the distribution of the binder are controlled in the perpendicular direction.
- the fluorine intensity of the carbon sheet can be measured using a scanning electron microscope (SEM) -energy dispersive X-ray analysis (EDX) apparatus. If a carbon sheet that has been subjected to water repellent treatment is not available, use a sample for observing the cross section in the thickness direction of the carbon sheet in the gas diffusion electrode base material or the carbon sheet in the membrane electrode assembly. Can be requested.
- SEM scanning electron microscope
- EDX EDX-ray analysis
- the diameter is in the range of 50 to 100 ⁇ m.
- the sum of the volume of the pores possessed is 17 to 50%, and the porosity (( ⁇ t ⁇ b) / ⁇ t) calculated from the bulk density ( ⁇ b) and the true density ( ⁇ t) is 75 to 87%.
- the pore diameter (peak diameter) having the maximum volume is 30 to 50 ⁇ m within the pore diameter range of 1 to 100 ⁇ m. It is more preferable that it is in the range.
- the sum of the volumes of pores having a diameter in the range of 50 to 100 ⁇ m, where the sum of the volumes of pores having a diameter in the range of 1 to 100 ⁇ m is 100%, is hereinafter referred to as a diameter of 50 to 100 ⁇ m. It may be described as a pore volume ratio.
- the third embodiment of the carbon sheet of the present invention is a porous carbon sheet containing carbon fibers and a binder, and the sum of the volumes of pores having a diameter in the range of 1 to 100 ⁇ m is 100%.
- the sum of the volumes of pores having diameters in the range of 50 to 100 ⁇ m is 17 to 50%
- the porosity calculated from the bulk density ( ⁇ b) and the true density ( ⁇ t) (( ⁇ t ⁇ b) / ⁇ t) is a carbon sheet characterized by 75 to 87%.
- the volume ratio of pores having a diameter of 50 to 100 ⁇ m is preferably 25 to 35%.
- the porosity (( ⁇ t ⁇ b ) / ⁇ t ) is preferably 77 to 85%.
- the pores having a diameter in the range of 50 to 100 ⁇ m have an important role in controlling water and water vapor during power generation. Further, the pore volume ratio with a diameter of 50 to 100 ⁇ m is also related to the uniformity of the carbon sheet such as uneven formation. If the pore volume ratio of the carbon sheet having a diameter of 50 to 100 ⁇ m is 17% or more, drainage can be improved and flooding can be suppressed. Further, if the pore volume ratio of the carbon sheet having a diameter of 50 to 100 ⁇ m is 50% or less, the water vapor diffusibility is small and the dry-up can be suppressed, and the carbon sheet made of paper or the like has uneven formation. Therefore, mechanical properties such as tension can be improved.
- the porosity of the carbon sheet is 75% or more, drainage is improved and flooding can be suppressed.
- the carbon sheet can be made flexible, the carbon sheet can be easily processed without problems such as breaking of the carbon sheet or wrinkling during the process. Further, since a process using a roll having a small diameter can be adopted, it becomes easy to save space and reduce the cost of the processing machine.
- the porosity of the carbon sheet is 87% or less, dry-up can be suppressed.
- the carbon sheet made of paper or the like can be uniformly produced without uneven formation, the mechanical strength such as tensile strength can be improved. This facilitates stable processing without breakage of the sheet when passing through the process.
- the third embodiment of the carbon sheet of the present invention has a pore diameter range of 1 to 100 ⁇ m, and the pore diameter (peak diameter) having the maximum volume is in the range of 30 to 50 ⁇ m. Is more preferable, and is more preferably in the range of 35 to 45 ⁇ m. If the peak diameter of the carbon sheet is in the range of 30 to 50 ⁇ m, flooding and dry-up can be more effectively suppressed.
- a carbon sheet having a peak diameter in the range of 30 to 50 ⁇ m can be obtained by controlling the basis weight and thickness of the carbon sheet, the amount of the binder attached to the carbon fiber, and the coverage of the front and back surfaces of the carbon sheet.
- the pore size distribution of carbon sheets was obtained by the mercury intrusion method.
- Three sample pieces of about 12 mm ⁇ 20 mm square are cut out from the carbon sheet, put into a measuring cell so as not to overlap after precise weighing, and mercury is injected under reduced pressure. And it measures on the conditions shown below.
- Measurement pressure range Pressure at the start of measurement 6 kPa (pore diameter 400 ⁇ m) to pressure at the end of measurement 414 MPa (pore diameter 30 nm) ⁇ Measurement cell mode: Pressurization process in the above pressure range ⁇ Cell volume: 5 cm 3 ⁇ Surface tension of mercury: 485 dyn / cm ⁇ Contact angle of mercury: 130 ° As a measuring device, an autopore 9520 manufactured by Shimadzu Corporation or an equivalent thereof can be used. From the pore diameter distribution thus obtained, the sum of the volumes of pores having a diameter in the range of 1 to 100 ⁇ m and the sum of the volumes of pores having a diameter in the range of 50 to 100 ⁇ m are obtained. Calculate the pore volume ratio.
- the diameter (peak diameter) of the pore having the maximum volume in the range of the pore diameter of 1 to 100 ⁇ m is obtained from this pore diameter distribution.
- the porosity is calculated from the bulk density ⁇ b (g / cm 3 ) and the true density ⁇ t (g / cm 3 ) measured by the following method.
- the bulk density ⁇ b is a thickness t b (cm) of a carbon sheet obtained using a micrometer in a state where the surface pressure is 0.15 MPa, and a mass M b measured by cutting into a 10 cm square. Calculated from (g / 100 cm 2 ) by the following equation.
- ⁇ b (g / cm 3 ) (M b / t b ) / 100
- the true density ⁇ t is calculated from the following equation using the true volume V t (cm 3 ) measured by the pycnometer method and the mass M t (g) of the sample used for the measurement.
- ⁇ b (g / cm 3 ) M t / V t
- a quantometer manufactured by Quantachrome, MicroUltrapyc 1200e, or an equivalent thereof can be used.
- as true volume V t to the cell volume is 10% or more, filling the sample in the cell.
- the bulk density ⁇ b of the carbon sheet is preferably in the range of 0.2 to 0.4 g / cm 3 , more preferably in the range of 0.22 to 0.35 g / cm 3 .
- the bulk density [rho b is at 0.2 g / cm 3 or more, the water vapor diffusion resistance is reduced, it is possible to suppress the dry-up. Further, the mechanical properties of the carbon sheet are improved, and the electrolyte membrane and the catalyst layer can be sufficiently supported. In addition, the conductivity is high, and the power generation performance is improved at both high and low temperatures.
- the bulk density [rho b is at 0.4 g / cm 3 or less, it is possible to drainage is improved, to suppress flooding.
- the carbon sheet from the gas diffusion electrode base material and measure the surface layer area ratio and coverage, the pore volume ratio of 50 to 100 ⁇ m in diameter, the porosity, and the peak diameter.
- a gas diffusion electrode substrate is heated in the atmosphere at 600 ° C. for 30 minutes to oxidatively decompose the resin composition contained in the microporous layer in the gas diffusion electrode substrate, and then subjected to ultrasonic treatment in a solvent such as ethanol.
- the carbon sheet can be taken out by removing the residue of the microporous layer.
- the gas diffusion electrode substrate of the present invention can be produced by forming a microporous layer described later on the above-described carbon sheet.
- microporous layer that is one of the components of the present invention will be described.
- the carbon sheet of the present invention can be used as a gas diffusion electrode substrate by forming a microporous layer on one surface.
- the gas diffusion electrode base material of this invention has a microporous layer in the surface X1 or the surface X2 side of a carbon sheet, when using 1st embodiment or 2nd embodiment of a carbon sheet.
- a microporous layer may be formed on any surface of the carbon sheet, but a carbon sheet prepared by a method in which the pores on one side are reduced is used. When used, it is desirable to form a microporous layer on a surface with small pores.
- the microporous layer can be formed by one application, but can also be formed by a plurality of applications. Thereby, surface defects can be significantly reduced, and durability can be improved.
- the basis weight of the microporous layer is preferably in the range of 10 to 35 g / m 2 , more preferably 30 g / m 2 or less, and even more preferably 25 g / m 2 or less. Further, the basis weight is more preferably 14 g / m 2 or more, and further preferably 16 g / m 2 or more.
- the basis weight of the microporous layer is 10 g / m 2 or more, one surface of the carbon sheet can be covered with the microporous layer, the back diffusion of the generated water is further promoted, and the drying of the electrolyte membrane is further suppressed. Can do. Further, when the basis weight of the microporous layer is 35 g / m 2 or less, the drainage performance is further improved, and flooding can be further suppressed.
- the microporous layer preferably contains a filler.
- carbon powder is preferable.
- Carbon powders include carbon black such as furnace black, acetylene black, lamp black and thermal black, graphite such as scaly graphite, scaly graphite, earthy graphite, artificial graphite, expanded graphite, and flake graphite, carbon nanotube, carbon nano Examples thereof include fiber and carbon fiber milled fiber.
- carbon black is more preferably used as the filler carbon powder, and acetylene black is most preferably used because it has few impurities.
- a porous body containing linear carbon and a water repellent material can be used for the microporous layer from the viewpoint of improving conductivity and drainage.
- the microporous layer contains carbon powder, the carbon powder is linear carbon, and the aspect ratio of the linear carbon is 30 to 5000, whereby the filler-containing coating that is a precursor of the microporous layer is used. Since the penetration of the liquid into the carbon sheet can be moderately suppressed and the gas diffusibility and drainage in the in-plane direction can be improved, flooding can be suppressed, and moreover, sufficient on the surface of the carbon sheet. Since a microporous layer having a thickness is formed and the reverse diffusion of the generated water is promoted, dry-up can be suppressed.
- the microporous layer preferably includes a water repellent material.
- a fluorine-type polymer as a water repellent material.
- the fluorine-based polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA).
- the filler-containing coating liquid may contain a dispersion medium such as water or an organic solvent, or may contain a dispersion aid such as a surfactant.
- a dispersion medium water is preferable, and a nonionic surfactant is preferably used as a dispersion aid.
- fillers and water repellent materials such as various carbon powders as described above can also be contained.
- the microporous layer can be formed by applying a filler-containing coating liquid containing the filler described above to one side of a carbon sheet.
- the coating of the filler-containing coating liquid on the carbon sheet can be performed using various commercially available coating apparatuses.
- coating methods such as screen printing, rotary screen printing, spray spraying, intaglio printing, gravure printing, die coater coating, bar coating, and blade coating can be used.
- the coating methods exemplified above are merely examples, and are not necessarily limited thereto.
- the coating liquid After applying the filler-containing coating liquid to the carbon sheet, it is preferable to dry the coating liquid at a temperature of 80 to 180 ° C. That is, the coated material is put into a drier set at a temperature of 80 to 180 ° C. and dried in a range of 5 to 30 minutes. The amount of drying air can be determined as appropriate, but rapid drying may induce surface microcracks. After the coated material is dried, it is put into a muffle furnace, a baking furnace or a high-temperature dryer, and preferably heated at a temperature of 300 to 380 ° C. for 5 to 20 minutes to melt the water repellent material, and a filler such as carbon powder. It is preferable to form a microporous layer by using a binder between them.
- a membrane electrode assembly can be formed by bonding the gas diffusion electrode base material described above to at least one surface of a solid polymer electrolyte membrane having catalyst layers on both surfaces. At that time, by arranging the microporous layer of the gas diffusion electrode substrate on the catalyst layer side, the back diffusion of the generated water is more likely to occur, and the contact area between the catalyst layer and the gas diffusion electrode substrate is increased. The contact electrical resistance can be reduced.
- the fuel cell of the present invention includes the gas diffusion electrode base material of the present invention, that is, has a separator on both sides of the membrane electrode assembly described above. That is, a fuel cell is configured by arranging separators on both sides of the membrane electrode assembly.
- a polymer electrolyte fuel cell is constructed by laminating a plurality of such membrane electrode assemblies on both sides sandwiched by separators via gaskets.
- the catalyst layer is composed of a layer containing a solid polymer electrolyte and catalyst-supporting carbon. As the catalyst, platinum is usually used.
- a fuel cell in which a reformed gas containing carbon monoxide is supplied to the anode side it is preferable to use platinum and ruthenium as the catalyst on the anode side.
- the solid polymer electrolyte it is preferable to use a perfluorosulfonic acid polymer material having high proton conductivity, oxidation resistance, and heat resistance.
- thermosetting resin / carbon powder / solvent 10 parts by mass / 5 parts by mass / 85 parts by mass, and these were mixed and stirred for 1 minute using an ultrasonic dispersing device to uniformly disperse the resin An impregnating solution of the composition was obtained.
- the carbon fiber paper body cut into 15 cm ⁇ 12.5 cm was immersed in a resin composition filled with aluminum bat and then squeezed by sandwiching it between two horizontally disposed rolls.
- the amount of the resin composition attached to the carbon fiber papermaking body was adjusted by changing the clearance between two horizontally disposed rolls.
- one of the two rolls was a smooth metal roll having a structure capable of removing excess resin with a doctor blade, and the other roll was a roll having a configuration of an uneven gravure roll.
- One surface side of the carbon fiber paper body is sandwiched between metal rolls, the other surface side is sandwiched between gravure rolls, and the resin composition on one surface and the other surface of the carbon fiber paper body is squeezed out by squeezing the impregnating solution of the resin composition.
- the pre-impregnated body was produced by heating and drying at a temperature of 100 ° C. for 5 minutes. Next, heat treatment was performed for 5 minutes at a temperature of 180 ° C. while pressing with a flat plate press. Spacers were arranged on the flat plate press during pressurization to adjust the distance between the upper and lower press face plates.
- the base material heat-treated with this pre-impregnated body was introduced into a heating furnace having a maximum temperature of 2400 ° C. maintained in a nitrogen gas atmosphere in a heating furnace, and a carbon sheet having a thickness of 220 ⁇ m made of a carbon fiber fired body was obtained. It was.
- ⁇ Water repellent finish> An aqueous dispersion of PTFE resin ("Polyflon” (registered trademark) PTFE Dispersion D-1E (manufactured by Daikin Industries, Ltd.)) or an FEP resin ("Neofluon”) is produced by using the carbon sheet prepared above as a water repellent material.
- the carbon fiber fired body was impregnated with a water-repellent material by immersing it in an aqueous dispersion of “(registered trademark) FEP dispersion ND-110 (manufactured by Daikin Industries, Ltd.). Thereafter, a dryer having a temperature of 100 ° C.
- the carbon sheet was heated and dried in a furnace for 5 minutes to produce a water-repellent carbon sheet, and when drying, the carbon sheet was placed vertically and the vertical direction was changed every minute.
- the aqueous dispersion of the water material was used after being diluted to an appropriate concentration so that 5 parts by mass of the water repellent material was applied to 95 parts by mass of the carbon sheet after drying.
- Carbon powder A Acetylene black “Denka Black” (registered trademark) (manufactured by Denki Kagaku Kogyo Co., Ltd.)
- Carbon powder B Linear carbon: Vapor growth carbon fiber “VGCF” (registered trademark) (manufactured by Showa Denko KK)
- Material C Water repellent material PTFE resin (using “Polyflon” (registered trademark) PTFE dispersion D-1E (produced by Daikin Industries), which is an aqueous dispersion containing 60 parts by mass of PTFE resin)
- Material D Surfactant “TRITON” (registered trademark) X-100 (manufactured by Nacalai Tesque).
- the above materials were mixed using a disperser to prepare a filler-containing coating liquid.
- This filler-containing coating solution is applied in a planar shape on one surface of a water-repellent carbon sheet using a slit die coater, and then heated at a temperature of 120 ° C. for 10 minutes and at a temperature of 380 ° C. for 10 minutes. did. In this way, a microporous layer was formed on the water-repellent carbon sheet to produce a gas diffusion electrode substrate.
- Carbon powder, water repellent material, surfactant and purified water are used for the filler-containing coating liquid used here, and the blending amount shown in the table is adjusted to be the composition of the filler-containing coating liquid described in parts by mass. What was done was used.
- the blending amount of the material C (PTFE resin) shown in the table represents the blending amount of the PTFE resin itself, not the blending amount of the aqueous PTFE resin dispersion.
- ⁇ Evaluation of power generation performance of polymer electrolyte fuel cells > 1.00 g of platinum-supported carbon (produced by Tanaka Kikinzoku Kogyo Co., Ltd., platinum support: 50% by mass), 1.00 g of purified water, “Nafion” (registered trademark) solution (“Nafion” (registered trademark) manufactured by Aldrich) 5.0 mass%) 8.00 g and isopropyl alcohol (manufactured by Nacalai Tesque) 18.00 g were sequentially added to prepare a catalyst solution.
- a catalyst solution was applied to 9001 (manufactured by Nichias Co., Ltd.) by spraying and dried at room temperature to prepare a PTFE sheet with a catalyst layer having a platinum amount of 0.3 mg / cm 2 .
- a solid polymer electrolyte membrane “Nafion” (registered trademark) NRE-211CS (manufactured by DuPont) cut to 8 cm ⁇ 8 cm is sandwiched between two PTFE sheets with a catalyst layer and pressed to 5 MPa with a flat plate press.
- the catalyst layer was transferred to a solid polymer electrolyte membrane by pressing at a temperature of 130 ° C. for 5 minutes. After pressing, the PTFE sheet was peeled off to produce a solid polymer electrolyte membrane with a catalyst layer.
- the solid polymer electrolyte membrane with a catalyst layer is sandwiched between two gas diffusion electrode substrates cut into 5 cm ⁇ 5 cm, pressed at a temperature of 130 ° C. for 5 minutes while being pressurized to 3 MPa with a flat plate press, and the membrane electrode A joined body was produced.
- the gas diffusion electrode substrate was arranged so that the surface having the microporous layer was in contact with the catalyst layer side.
- the obtained membrane electrode assembly was incorporated into a single cell for fuel cell evaluation, and the voltage when the current density was changed was measured.
- a serpentine type separator having a single flow path of 1.0 mm was used for the groove width, groove depth, and rib width. Further, evaluation was performed by supplying non-pressurized hydrogen to the anode side and non-pressurized air to the cathode side.
- both hydrogen and air were humidified using a humidification pot set at a temperature of 40 ° C. The humidity at this time was 100%.
- the utilization rates of hydrogen and oxygen in the air were 70 mol% and 40 mol%, respectively.
- An output voltage with a current density of 1.5 A / cm 2 was measured and used as an indicator of flooding resistance.
- both hydrogen and air were humidified using a humidification pot set at a temperature of 80 ° C. The humidity at this time was 42%.
- the utilization rates of hydrogen and oxygen in the air were 80 mol% and 67 mol%, respectively, and the output voltage at a current density of 1.5 A / cm 2 was measured and used as an indicator of dry-up resistance.
- the average diameter of carbon fibers (carbon fiber diameter) varies randomly at 30 times with a microscope such as a scanning electron microscope. Select a single fiber of the book, measure its diameter, and use the average value. Moreover, it calculates
- S-4800 manufactured by Hitachi, Ltd. or its equivalent can be used as the scanning electron microscope. Table shows the average diameter obtained from the surface X1 or surface X2 and the surface Y1 or surface Y2 of the carbon sheet.
- carbon fiber diameter (surface X1 / surface Y1) in the table means the average diameter of carbon fiber single fibers determined from the surface X1 side and the average diameter of carbon fiber single fibers determined from the surface Y1 side. Show.
- the melting point of the water repellent material was measured by differential scanning calorimetry. Using a DSC6220 manufactured by Seiko Instruments Inc. (SII), the apparatus was changed from 30 ° C. to 400 ° C. at a temperature rising rate of 2 ° C./min in nitrogen, and the endothermic peak at that time was observed. The endothermic peak at a temperature of 150 ° C. or higher was defined as the melting point of the water repellent material.
- the surface roughness of the carbon sheet was measured using a laser microscope.
- the measuring apparatus used VK-X100 (manufactured by Keyence Corporation) to scan a 5 mm square range with an objective lens having a magnification of 10, and determined the arithmetic average roughness (Ra) at 5 mm square. Ten measurement points were taken, and the average of the arithmetic average roughness was defined as the surface roughness.
- the result obtained by measuring from the surface X1 side of the carbon sheet was defined as the surface roughness of the surface X1
- the result obtained by measuring from the surface Y1 side of the carbon sheet was defined as the surface roughness of the surface Y1.
- the sliding angle of the carbon sheet was determined by a sliding method using an automatic contact angle meter.
- an automatic contact angle meter DM-501 manufactured by Kyowa Interface Science Co., Ltd. was used as an apparatus. After fixing the surface Y of the water-repellent carbon sheet on the apparatus stage with the upper side (measurement side), a droplet of 10 ⁇ L of ion-exchanged water is deposited on the carbon sheet that has been water-repellent and waited for 1 second.
- the carbon sheet treated with water repellency along with the device stage was tilted, and the tilt angle of the device stage when the liquid droplet started to slide down the surface of the carbon sheet treated with water repellency was defined as the sliding angle.
- the fluorine strength of the carbon sheet was determined as follows. Hereinafter, a description will be given with reference to FIG. First, after temporarily determining one surface of the carbon sheet (6) as the surface X1 or surface X2 (7) and the other surface as the surface Y1 or surface Y2 (8), the carbon sheet (6) is randomly selected with a sharp blade. 50) samples for cross-sectional observation in the perpendicular direction were prepared. Using a scanning electron microscope (SEM) -energy dispersive X-ray analysis (EDX) apparatus, a line scan is performed on the cross section of the 50 carbon sheets (6) in the direction perpendicular to the surface of the carbon sheet (6).
- SEM scanning electron microscope
- EDX -energy dispersive X-ray analysis
- fluorine intensity fluorine signal intensity
- the fluorine intensity was measured under the conditions of an acceleration voltage of 7 kV, an enlargement magnification of 300 times, and a line width of 20 ⁇ m.
- a 50% value (20) of the average value (19) of the fluorine intensity measured along the straight line in the direction perpendicular to the surface of the carbon sheet (6) from one surface of the carbon sheet (6) to the other surface is obtained.
- the 50% average fluorine closest to the temporarily determined surface Y1 or surface Y2 is a layer obtained by equally dividing the carbon sheet (6) into three in the direction perpendicular to the surface.
- the layer obtained by equally dividing the carbon sheet (6) into three in the direction perpendicular to the surface is a layer including the surface AA (12).
- Temporarily determined as A (14) a layer including the surface BB (13) is temporarily determined as a layer B (16), and a central layer sandwiched between the layers A (14) and B (16) is defined as a layer C (15). ).
- the average value of fluorine intensity in layer A of each of the 50 carbon sheets was calculated to obtain 50 “average value of fluorine intensity in layer A”.
- the average value of the obtained 50 “average value of fluorine intensity in layer A” was defined as the average fluorine intensity of layer A.
- the average fluorine intensity was calculated in the same manner.
- the layer with the higher average fluorine intensity is the layer A
- the smaller layer is the layer B
- the surface on the layer A side of the carbon sheet is the surface X1 or surface X2
- the surface on the layer B side was defined as surface Y1 or surface Y2.
- the fluorine intensity can be determined by the method described above.
- the above method takes an average of 50 samples prepared at random. Since it is averaged including the continuous part, the fluorine intensity can be obtained.
- Example 1 In accordance with the methods described in ⁇ Preparation of Carbon Sheet>, ⁇ Water Repellent Processing>, and ⁇ Preparation of Gas Diffusion Electrode Base>, a porous carbon sheet having a thickness of 220 ⁇ m with different surface area ratios was used. A gas diffusion electrode substrate was obtained. As a result of evaluating the power generation performance of this gas diffusion electrode substrate, the flooding resistance was very good, with the output voltage being 0.4 V or higher and the dry-up resistance being 0.35 V or higher. The results are shown in Table 1.
- Example 2 In accordance with the methods described in ⁇ Preparation of Carbon Sheet>, ⁇ Water Repellent Processing>, and ⁇ Preparation of Gas Diffusion Electrode Base>, a porous carbon sheet having a thickness of 150 ⁇ m with different surface area ratios was used. A gas diffusion electrode substrate was obtained. As a result of evaluating the power generation performance of this gas diffusion electrode substrate, the flooding resistance was very good, with the output voltage being 0.4 V or higher and the dry-up resistance being 0.35 V or higher. The results are shown in Table 1.
- Example 3 In accordance with the methods described in ⁇ Preparation of Carbon Sheet>, ⁇ Water Repellent Processing>, and ⁇ Preparation of Gas Diffusion Electrode Base>, a porous carbon sheet having a thickness of 100 ⁇ m with different surface area ratios was used. A gas diffusion electrode substrate was obtained. As a result of evaluating the power generation performance of this gas diffusion electrode substrate, the flooding resistance is very good when the output voltage is 0.4 V or higher, and the dry-up resistance is 0.3 V or higher although it does not reach 0.35 V. It was a good result. The results are shown in Table 1.
- Example 4 In accordance with the methods described in ⁇ Preparation of Carbon Sheet>, ⁇ Water Repellent Processing>, and ⁇ Preparation of Gas Diffusion Electrode Base>, a porous carbon sheet having a thickness of 150 ⁇ m with different surface area ratios was used. A gas diffusion electrode substrate was obtained. At this time, by attaching a doctor blade to the roll in contact with the surface Y1 or the surface Y2 to reduce the resin composition adhering to the surface Y1 or the surface Y2 and removing a large amount of the binder on the surface Y1 or the surface Y2, the surface X1 or The difference in the amount of the binding resin between the surface X2 and the surface Y1 or the surface Y2 was largely changed from that in Example 2.
- Example 5 According to the methods described in ⁇ Preparation of carbon sheet>, ⁇ Water repellent finish> and ⁇ Preparation of gas diffusion electrode base material>, the porous surface layer having a surface area ratio of 150 ⁇ m having different surface area on the front and back sides is shown in Table 1.
- a gas diffusion electrode substrate using a carbon sheet was obtained. At this time, the clearance between the two rolls to be sandwiched was made larger than that in Example 2, so that the amount of the binder on both the surface X and the surface Y was larger than that in Example 2.
- the flooding resistance was very good, with an output voltage of 0.4 V or higher and a dry-up resistance of 0.35 V or higher. The results are shown in Table 1.
- Example 6 Similar to Example 4 except that the amount of the resin composition was increased as compared to Example 4 in accordance with the methods described in ⁇ Preparation of Carbon Sheet>, ⁇ Water Repellent Processing>, and ⁇ Preparation of Gas Diffusion Electrode Base>. It was made. A porous carbon sheet having a thickness of 150 ⁇ m with different surface area ratios was obtained, and a gas diffusion electrode substrate was further obtained. The flooding resistance was good at an output voltage of 0.35 V or higher. Further, the dry-up resistance was 0.35 V or more, which was very good.
- Example 7 The results are shown in Table 1 (Example 7) According to the methods described in ⁇ Preparation of Carbon Sheet>, ⁇ Water Repellent Processing>, and ⁇ Preparation of Gas Diffusion Electrode Substrate>, the water repellent processing of the carbon sheet is performed using a tetrafluoroethylene-hexafluoropropylene copolymer (FEP). It was produced in the same manner as in Example 2 except that the change was made. As a result, a porous carbon sheet composed of 150 ⁇ m having different surface area ratios on the front and back sides was obtained, and a gas diffusion electrode substrate was further obtained.
- FEP tetrafluoroethylene-hexafluoropropylene copolymer
- the anti-flooding resistance was 0.45V or higher and the dry-up resistance was 0.35V or higher, both of which were extremely good.
- the carbon sheet was uniformly repelled by water repellency by FEP having a low melting point, and the sliding angle was 25 degrees, which was much lower than 40 degrees. Thus, a significant improvement in water repellency was confirmed. For this reason, the drastic improvement in flooding resistance was confirmed by the synergistic effect of the drainage improvement by the difference in surface area ratio between the front and back surfaces of the present invention and the improvement in water repellency. The results are shown in Table 1.
- Example 8 In the configuration shown in Table 2, a carbon sheet and a gas diffusion electrode substrate were obtained in the same manner as in Example 2 except that the composition of the filler-containing coating liquid for forming the microporous layer was different. As a result of evaluating the power generation performance of this gas diffusion electrode base material, the flooding resistance greatly exceeded the output voltage of 0.4 V, and the dry-up resistance was 0.35 V or more, both of which were extremely good. This is presumably because the use of a high aspect ratio filler in the microporous layer resulted in a high porosity microporous layer and improved gas diffusibility. From this, it was confirmed that the flooding resistance was greatly improved by the synergistic effect of the improvement in gas diffusibility by increasing the porosity of the microporous layer and the drainage performance of the present invention. The results are shown in Table 2.
- Example 9 A polyacrylonitrile long fiber was subjected to a flameproofing treatment at a temperature of 200 ° C. for 10 minutes, a nonwoven fabric was produced by hydroentanglement treatment, and roll pressing was performed. This was introduced into a heating furnace at a temperature of 2000 ° C. to obtain a carbon sheet made of a carbon fiber fired body of 150 ⁇ m thick nonwoven fabric.
- a binder and water repellent material an impregnating solution was prepared by dispersing carbon powder A and PTFE resin of material C as a solid content in a dispersant and water so that the mass ratio of the solid content was 1: 1.
- Example 2 It was produced in the same manner as in Example 2 according to the method described in ⁇ Production of Gas Diffusion Electrode Base Material> on the surface X with a large amount of binder. As shown in Table 2, a gas diffusion electrode substrate using a porous carbon sheet having a thickness of 150 ⁇ m with different surface area ratios on the front and back sides was obtained. The anti-flooding resistance was extremely good with an output voltage of 0.4 V or higher and a dry-up resistance of 0.35 V or higher. The results are shown in Table 2.
- Example 2 Other methods were the same as those in Example 3, to obtain a porous carbon sheet having a thickness of 250 ⁇ m, and further to obtain a gas diffusion electrode substrate.
- the flooding resistance was significantly lower than the output voltage 0.35V, and the dry-up resistance was much lower than 0.3V. This is because the carbon sheet becomes thick due to the lamination method, and the gas diffusibility and drainage are insufficient.
- Table 2 The results are shown in Table 2.
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Abstract
Description
本発明の炭素シートは、後述する炭素繊維を含む多孔体の作製、樹脂組成物の含浸、必要に応じて行われる貼り合わせと熱処理、炭化および必要に応じて撥水加工する工程により作製することができる。本発明の炭素シートは、炭素繊維及び結着材を含む多孔質のものをいい、必要に応じて撥水加工することもできる。
多孔質の炭素シートを製造するために用いる多孔体について説明する。本発明の多孔質の炭素シートは、セパレータから供給されるガスを触媒へと拡散するための高いガス拡散性と、電気化学反応に伴って生成する水をセパレータへ排出するための高い排水性、および発生した電流を取り出すための高い導電性を有することが好ましい。このため多孔質の炭素シートを得るためには、導電性を有する多孔体を用いることが好ましい。より具体的には、多孔質の炭素シートを得るために用いる多孔体は、例えば、炭素繊維抄紙体、炭素繊維織物およびフェルトタイプの炭素繊維不織布などの炭素繊維を含む多孔体を用いることが好ましい態様である。中でも、多孔体を多孔質の炭素シートとした際に、電解質膜の面直方向の寸法変化を吸収する特性、すなわち「ばね性」に優れていることから炭素繊維抄紙体を多孔体として用いることが好ましい。以下、炭素繊維抄紙体を代表例として説明する。
本発明の炭素シートを得る際においては、炭素繊維抄紙体などの炭素繊維を含む多孔体などに結着材となる樹脂組成物が含浸される。
<貼り合わせと熱処理>
本発明においては、炭素繊維抄紙体などの多孔体に樹脂組成物を含浸した予備含浸体を形成した後、炭化を行うに先立って、予備含浸体を貼り合わせたり予備含浸体に熱処理を行うことができる。
本発明において、炭素繊維抄紙体などの多孔体に樹脂組成物を含浸して予備含浸体とした後、樹脂成分を炭化するために、不活性雰囲気下で焼成を行なう。この焼成は、バッチ式の加熱炉を用いることもできるし、連続式の加熱炉を用いることもできる。また、不活性雰囲気は、炉内に窒素ガスやアルゴンガスなどの不活性ガスを流すことにより得ることができる。
本発明において、排水性を向上させる目的で、炭素繊維焼成体に撥水加工を施すことが好ましい態様である。つまり本発明の炭素シートは、撥水材を含むことが好ましい。撥水加工は、炭素繊維焼成体に撥水材を塗布し熱処理することにより行なうことができる。なお、撥水材を用いて撥水加工した場合、前記撥水材は結着材として炭素シートに含まれる。
ここで、撥水材としては、耐腐食性が優れることから、フッ素系のポリマーを用いることが好ましい。フッ素系のポリマーとしては、ポリテトラフルオロエチレン(PTFE)、テトラフルオロエチレン-ヘキサフルオロプロピレン共重合体(FEP)、およびテトラフルオロエチレン-パーフルオロアルキルビニルエーテル共重合体(PFA)などが挙げられる。
以上のような工程により得られた本発明の炭素シートの特徴について、次に説明する。
本発明において、炭素シートの密度は0.20~0.40g/cm3の範囲内であることが好ましく、より好ましくは0.22~0.35g/cm3の範囲内であり、さらに好ましくは0.24~0.30g/cm3の範囲内である。密度が0.20g/cm3以上であると、水蒸気拡散性が小さく、ドライアップを抑制することができる。また、炭素シートの機械強度が向上し、電解質膜と触媒層を十分に支えることができる。加えて、導電性が高く発電性能が向上する。一方、密度が0.40g/cm3以下であると、排水性が向上し、フラッディングを抑制することができる。
また、本発明の炭素シートの厚さは50~230μmであることが好ましく、70~180μmであることがより好ましく、90~130μmであることがさらに好ましい。炭素シートの厚さが230μm以下、より好ましくは180μm以下、さらに好ましくは130μm以下であることにより、ガスの拡散性が大きくなりやすく、また生成水も排出されやすくなる。さらに、燃料電池全体としてサイズも小さくしやすくなる。一方、炭素シートの厚さが50μm以上、より好ましくは70μm以上、さらに好ましくは90μm以上であることにより、炭素シート内部の面内方向のガス拡散が効率よく行われ、発電性能が向上しやすくなる。
・測定セルモード:上記圧力範囲の昇圧過程
・セル容積:5cm3
・水銀の表面張力:485dyn/cm
・水銀の接触角:130°
測定装置としては、島津製作所製オートポア9520、あるいはその同等品を用いることができる。こうして得られた細孔径分布から、1~100μmの範囲に径を有する細孔の容積の和と50~100μmの範囲に径を有する細孔の容積の和を求めて、径50~100μmの細孔容積割合を算出する。
次に、真密度ρtは、ピクノメータ法で測定された真の容積Vt(cm3)と、測定に用いた試料の質量Mt(g)から以下の式より算出される。
真の容積Vt(cm3)の測定装置としては、Quantachrome製のピクノメータ、MicroUltrapyc 1200e、あるいはその同等品を用いることができる。なお、測定の際、セル容積に対する真の容積Vtが10%以上となるように、試料をセル内に充填する。
次に、本発明のガス拡散電極基材について説明する。
次に、本発明の構成要素の一つであるマイクロポーラス層について説明する。
[膜電極接合体]
本発明において、前記したガス拡散電極基材を、両面に触媒層を有する固体高分子電解質膜の少なくとも片面に接合することにより、膜電極接合体を形成することができる。その際、触媒層側にガス拡散電極基材のマイクロポーラス層を配置することにより、より生成水の逆拡散が起こりやすくなることに加え、触媒層とガス拡散電極基材の接触面積が増大し、接触電気抵抗を低減させることができる。
本発明の燃料電池は、本発明のガス拡散電極基材を含むものであり、つまり上述の膜電極接合体の両側にセパレータを有するものである。すなわち、上述の膜電極接合体の両側にセパレータを配することにより燃料電池を構成する。通常、このような膜電極接合体の両側にガスケットを介してセパレータで挟んだものを複数個積層することによって固体高分子型燃料電池を構成する。触媒層は、固体高分子電解質と触媒担持炭素を含む層からなる。触媒としては、通常、白金が用いられる。アノード側に一酸化炭素を含む改質ガスが供給される燃料電池にあっては、アノード側の触媒としては白金およびルテニウムを用いることが好ましい。固体高分子電解質は、プロトン伝導性、耐酸化性および耐熱性の高い、パーフルオロスルホン酸系の高分子材料を用いることが好ましい。このような燃料電池ユニットや燃料電池の構成自体は、よく知られているところである。
・厚さ220μmの炭素シートの作製
東レ(株)製ポリアクリルニトリル系炭素繊維“トレカ”(登録商標)T300(平均炭素繊維径:7μm)を平均長さ12mmにカットし、水中に分散させて湿式抄紙法により連続的に抄紙した。さらに、バインダーとしてポリビニルアルコールの10質量%水溶液を当該抄紙に塗布して乾燥させ、炭素繊維目付が44.0g/m2の抄紙体を作製した。ポリビニルアルコールの付着量は、炭素繊維抄紙体100質量部に対して22質量部であった。
炭素繊維の目付を30.0g/m2とし、平板プレスでの熱処理において上下プレス面板の間隔を調整したこと以外は、上記した厚さ220μmの炭素シートの作製に記載した方法に従って、厚さが150μmの炭素シートを作製した。
炭素繊維の目付を22.0g/m2とし、平板プレスでの熱処理において上下プレス面板の間隔を調整したこと以外は、上記した厚さ220μmの炭素シートの作製に記載した方法に従って、厚さが100μmの炭素シートを作製した。
上記にて作製した炭素シートを、撥水材として、PTFE樹脂(“ポリフロン”(登録商標)PTFEディスパージョンD-1E(ダイキン工業(株)製))の水分散液、ないしはFEP樹脂(“ネオフロン”(登録商標)FEPディスパージョンND-110(ダイキン工業(株)製)の水分散液に浸漬することにより、炭素繊維焼成体に撥水材を含浸した。その後、温度が100℃の乾燥機炉内で5分間加熱して乾燥し、撥水加工された炭素シートを作製した。なお、乾燥する際は、炭素シートを垂直に配置し、1分毎に上下方向を変更した。また、撥水材の水分散液は、乾燥後で炭素シート95質量部に対し、撥水材が5質量部付与されるように適切な濃度に希釈して使用した。
[材料]
・炭素粉末A:アセチレンブラック“デンカ ブラック”(登録商標)(電気化学工業(株)製)
・炭素粉末B:線状カーボン:気相成長炭素繊維“VGCF”(登録商標)(昭和電工(株)製) アスペクト比70
・材料C:撥水材 PTFE樹脂(PTFE樹脂を60質量部含む水分散液である“ポリフロン”(登録商標)PTFEディスパージョンD-1E(ダイキン工業(株)製)を使用)
・材料D:界面活性剤“TRITON”(登録商標)X-100(ナカライテスク(株)製)。
白金担持炭素(田中貴金属工業(株)製、白金担持量:50質量%)1.00gと、精製水1.00g、“Nafion”(登録商標)溶液(Aldrich社製“Nafion”(登録商標)5.0質量%)8.00gと、イソプロピルアルコール(ナカライテスク社製)18.00gとを順に加えることにより、触媒液を作製した。
炭素シートおよびガス拡散電極基材の目付は、10cm四方に切り取ったサンプルの質量を、サンプルの面積(0.01m2)で除して求めた。
炭素シートおよびガス拡散電極基材を平滑な定盤にのせ、圧力0.15MPaをかけた状態での測定物がある場合からない場合の高さの差を測定した。異なる部位にて10箇所サンプリングを行い、高さの差の測定値を平均したものを厚さとした。
炭素繊維の単繊維の平均直径(炭素繊維径)は、走査型電子顕微鏡などの顕微鏡で、炭素シートの一方の表面の炭素繊維を1000倍に拡大して写真撮影を行い、無作為に異なる30本の単繊維を選んでその直径を計測し、その平均値とする。また、炭素シートの他方の表面の炭素繊維の単繊維についても同様に求める。走査型電子顕微鏡としては、(株)日立製作所製S-4800あるいはその同等品を用いることができる。表に、炭素シートの面X1または面X2と面Y1または面Y2から求めた平均直径を示す。
本発明において、撥水材の融点は示差走査熱量測定により行った。装置はセイコーインスツル株式会社(SII社)製DSC6220を用いて、窒素中にて昇温速度2℃/分で、30℃から400℃の温度まで変化させ、その際の吸発熱ピークを観察し、150℃以上の温度での吸熱ピークを撥水材の融点とした。
炭素シートの表面粗さはレーザー顕微鏡を用いて行った。測定装置はVK-X100(キーエンス(株)製)を用いて倍率10の対物レンズにて5mm角の範囲をスキャンして測定し、5mm角での算術平均粗さ(Ra)を求めた。測定箇所10箇所をとり、算術平均粗さの平均を表面粗さとした。ここで、炭素シートの面X1側から測定して得られた結果を面X1の表面粗さとして、炭素シートの面Y1側から測定して得られた結果を面Y1の表面粗さとした。
炭素シートの滑落角は、自動接触角計を用いた滑落法により求めた。装置としては、協和界面科学(株)製の自動接触角計DM-501を用いた。撥水加工された炭素シートの面Yを上側(測定側)にして装置ステージに固定し、イオン交換水10μLの液滴を撥水加工された炭素シートに着滴させ、1秒間待機させた後、装置ステージとともに撥水加工された炭素シートを傾斜させ、液滴が撥水加工された炭素シート表面を滑落し始めたときの装置ステージの傾斜角度を滑落角とした。
炭素シートのフッ素強度は、次のようにして求めた。以下、図3を用いて説明する。まず、炭素シート(6)の一方の表面を面X1または面X2(7)、他方の表面を面Y1または面Y2(8)と仮決めした後、鋭利な刃物により無作為に炭素シート(6)の面直方向断面観察用サンプルを50個作製した。前記50個の炭素シート(6)の断面に対して、走査型電子顕微鏡(SEM)-エネルギー分散形X線分析(EDX)装置を用いて、炭素シート(6)の面直方向にラインスキャンを行い、フッ素強度(フッ素のシグナル強度)の分布(18)を求めた。フッ素強度の測定は加速電圧7kV、拡大倍率300倍、ライン幅20μmの条件で行った。炭素シート(6)の一方の表面から他方の表面に向かう、炭素シート(6)の面直方向の直線に沿って測定したフッ素強度の平均値(19)の50%の値(20)を求め、仮決めした面X1または面X2(7)に最も近い50%平均フッ素強度を有する面(面AA(12))から、仮決めした面Y1または面Y2(8)に最も近い50%平均フッ素強度を有する面(面BB(13))までの区間(17)において、前記炭素シート(6)を面直方向に3等分して得られる層について、面AA(12)を含む層を層A(14)と仮決めし、面BB(13)を含む層を層B(16)と仮決めし、層A(14)と層B(16)に挟まれる中央の層を層C(15)とした。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、表層面積率が表裏で異なる厚さ220μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。このガス拡散電極基材の発電性能を評価した結果、耐フラッディング性は出力電圧が0.4V以上、耐ドライアップ性は0.35V以上であり、ともに極めて良好であった。結果を表1に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、表層面積率が表裏で異なる厚さ150μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。このガス拡散電極基材の発電性能を評価した結果、耐フラッディング性は出力電圧が0.4V以上、耐ドライアップ性は0.35V以上であり、ともに極めて良好であった。結果を表1に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、表層面積率が表裏で異なる厚さ100μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。このガス拡散電極基材の発電性能を評価した結果、耐フラッディング性は出力電圧が0.4V以上で極めて良好であり、耐ドライアップ性は0.35Vには及ばないものの0.3V以上であり良好な結果であった。結果を表1に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、表層面積率が表裏で異なる厚さ150μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。この際、面Y1または面Y2に接するロールにドクターブレードを取り付けることで面Y1または面Y2に付着する樹脂組成物を減じることで面Y1または面Y2の結着材を多く取り除くことによって面X1または面X2と面Y1または面Y2での結合樹脂量の差を実施例2に対して大きく変更した。このガス拡散電極基材の発電性能を評価した結果、耐フラッディング性は出力電圧0.45V以上、耐ドライアップ性は0.35V以上であり、ともに極めて良好であった。となり大幅な向上しており、これは表層面積率の差が大きく、排水性が改善したためと考えられる。結果を表1に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、表1に示す、表層面積率が表裏で異なる厚さ150μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。この際、はさむ2本のロール間のクリアランスを実施例2に比べ大きくすることで面Xと面Yともに結着材量を、実施例2に対して多くした。耐フラッディング性は出力電圧が0.4V以上、耐ドライアップ性は0.35V以上であり、ともに極めて良好であった。結果を表1に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、樹脂組成物量を実施例4に比べ大きくしたこと以外は、実施例4と同様にして作製した。表層面積率が表裏で異なる厚さ150μmからなる多孔質の炭素シートを得て、さらにガス拡散電極基材を得た。耐フラッディング性は出力電圧0.35V以上で良好であった。また、耐ドライアップ性は0.35V以上であり極めて良好であった。結果を表1に示す
(実施例7)
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法に従って、炭素シートの撥水加工をテトラフルオロエチレン-ヘキサフルオロプロピレン共重合体(FEP)に変更したこと以外は、実施例2と同様にして作製した。この結果、表層面積率が表裏で異なる150μmからなる多孔質の炭素シートを得て、さらにガス拡散電極基材を得た。耐フラッディング性は出力電圧0.45V以上、耐ドライアップ性は0.35V以上であり、ともに極めて良好であった。低融点のFEPによる撥水で均一に炭素シートが撥水され、滑落角も25度を示し40度を大きく下回ったことから、大幅な撥水性の向上が確認できた。このため、本発明の表裏の表層面積率の差と撥水性の向上とによる排水性向上での相乗効果で大幅な耐フラッディング性の向上が確認できた。結果を表1に示す。
表2に示す構成にて、マイクロポーラス層を形成するためのフィラー含有塗液の組成が異なること以外は実施例2同様にして炭素シートおよびガス拡散電極基材を得た。このガス拡散電極基材の発電性能を評価した結果、耐フラッディング性は出力電圧0.4Vを大きく上回り、耐ドライアップ性は0.35V以上であり、ともに極めて良好であった。これはマイクロポーラス層に高アスペクト比のフィラーを用いたことで高空隙のマイクロポーラス層となりガスの拡散性が向上したためと考えられる。このことからマイクロポーラス層の高空隙率化によるガス拡散性向上と本発明の排水性向上との相乗効果で大幅な耐フラッディング性の向上が確認できた。結果を表2に示す。
ポリアクリロニトリルの長繊維を200℃の温度で10分間の耐炎化処理を行い、水流交絡処理により不織布を作製し、ロールプレスを行った。2000℃の温度の加熱炉に導入し、厚さ150μmの不織布の炭素繊維焼成体からなる炭素シートを得た。結着材兼撥水材として、固形分として炭素粉末Aと材料CのPTFE樹脂を固形分の質量比1:1となるように分散剤と水に分散させた含浸液を作製した。この含浸液に耐炎化処理不織布を含浸した後、一定のクリアランスをあけて水平に2本配置したロール(2本のうちの一方のロールはドクターブレードを有する平滑な金属ロール、他方のロールは凹凸のついたグラビアロール)に挟んで絞り含浸させ、表裏での付着量を調整した。その後、加熱炉内で380℃の温度で10分間の加熱を行った。その結果、固形分量で5質量%の結着材兼撥水材で結合ざれた撥水加工済み炭素シートを得た。結着材の多い面Xに、上記の<ガス拡散電極基材の作製>に記載した方法に従って、実施例2と同様にして作製した。表2に示す、表層面積率が表裏で異なる厚さ150μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。耐フラッディング性は出力電圧が0.4V以上、耐ドライアップ性は0.35V以上でともに極めて良好であった。結果を表2に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法において、樹脂組成物を含浸させた炭素繊維抄紙体を両面から同じ形状のロールで挟み液を絞り、結着材を付着させ撥水加工を行った。それ以外は、実施例2と同様に作製した。その結果、表2に示すとおり、両面とも近い結着材量が付着することによって、表面の表層面積率も5%以下の差の値となった。厚さ150μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。耐フラッディング性は出力電圧が0.35Vを下回り、耐ドライアップ性は0.3Vを大きく下回る、いずれも不十分な性能であった。結果を表2に示す。
上記の<炭素シートの作製>、<撥水加工>および<ガス拡散電極基材の作製>に記載した方法において、炭素繊維抄紙体に樹脂組成物を含浸させる際に、片面からグラビア塗布により樹脂組成物を付着させたこと以外は、実施例2と同様に作製した。その結果、表2に示すとおり、表面の表層面積率は13%以上の差となった。厚さ150μmからなる多孔質の炭素シートを用いたガス拡散電極基材を得た。耐フラッディング性は出力電圧が0.35Vを下回り、耐ドライアップ性も0.3Vを大きく下回る、いずれも不十分な性能であった。結果を表2に示す。
上記の<炭素シートの作製>において実施例3と同様の炭素繊維抄紙体に比較例1と同じ方法で樹脂組成物を含浸させ予備含浸体を作製した。一方、平均直径が3μm、平均長さが2mmの炭素繊維を用いて、その他は実施例3と同様の方法で炭素繊維抄紙体を得て、比較例1と同じ方法で樹脂組成物を含浸させ予備含浸体を作製した。これら2枚の予備含浸体を重ねて加熱加圧を行い積層した。その他の方法は実施例3と同じ方法で、厚さ250μmからなる多孔質の炭素シートを得て、さらにガス拡散電極基材を得た。このガス拡散電極基材の発電性能を評価した結果、耐フラッディング性は出力電圧0.35Vを大きく下回り、耐ドライアップ性も0.3Vを大きく下回る、いずれも不十分な性能であった。これは、積層方式を行ったため炭素シートが厚くなり、ガス拡散性と排水性が不足したためである。結果を表2に示す。
2:除外面積率
3:表層面積率
4:全測定面積率
5:累積面積率が2%となる深さ
6:炭素シート
7:面X1または面X2
8:面Y1または面Y2
9:累積面積率が2%となる深さ(基準深さ)
10:基準深さから20μmの深さ
11:50%平均フッ素強度未満の層
12:面AA
13:面BB
14:層A
15:層C
16:層B
17:区間
18:フッ素強度の分布
19:フッ素強度の平均値
20:フッ素強度の平均値の50%の値
Claims (15)
- 炭素繊維および結着材を含む多孔質の炭素シートであって、表面の深さ分布を測定して、一方の表面の測定面積における深さが20μm以下の部分の面積の割合を表層面積率Xとし、他方の表面の測定面積における深さが20μm以下の部分の面積の割合を表層面積率Yとした場合に、前記表層面積率Xが前記表層面積率Yに比べて大きく、その差が3%以上12%以下であることを特徴とする炭素シート。
- 表層面積率Xが13%以上17%以下であり、表層面積率Yが9%以上13%以下である、請求項1記載の炭素シート。
- 表層面積率Xである表面を面X1とし、表層面積率Yである表面を面Y1としたとき、前記面X1の表面粗さが前記面Y1の表面粗さよりも小さく、その差が1μm以上4μm以下である、請求項1または2記載の炭素シート。
- 表層面積率Xである表面を面X1としたとき、面X1の表面粗さが16μm以下である、請求項1~3のいずれかに記載の炭素シート。
- 炭素繊維および結着材を含む多孔質の炭素シートであって、炭素繊維と結着材による表面の被覆率の大きい側の表面を面X2とし、炭素繊維と結着材による表面の被覆率の小さい側の表面を面Y2としたとき、前記面X2と前記面Y2の前記被覆率の差が5%以上20%以下であることを特徴とする炭素シート。
- 前記面X2の被覆率が70%以上90%以下であり、前記面Y2の被覆率が50%以上75%以下である、請求項5に記載の炭素シート。
- 炭素シートが撥水材を含み、一方の表面に最も近い50%平均フッ素強度を有する面から、他方の表面に最も近い50%平均フッ素強度を有する面までの区間において、前記区間を炭素シートの面直方向に3等分して得られる層について、一方の表面に近い層と他方の表面に近い層のうち、層の平均フッ素強度がより大きい層を層A、より小さい層を層Bとし、前記層Aと前記層Bの間の層を層Cとすると、層の平均フッ素強度が、層A、層B、層Cの順に小さくなる、請求項1~6のいずれかに記載の炭素シート。
- 撥水材の融点が、200℃以上320℃以下である、請求項7記載の炭素シート。
- 面Y1又は面Y2の表面における水の滑落角が40度以下である、請求項3~8のいずれかに記載の炭素シート。
- 1~100μmの範囲に径を有する細孔の容積の和を100%としたときに、50~100μmの範囲に径を有する細孔の容積の和が17~50%であり、
嵩密度(ρb)と真密度(ρt)から算出される空隙率((ρt-ρb)/ρt)が75~87%である、請求項1~9のいずれかに記載の炭素シート。 - 1~100μmの細孔の径の範囲で、最大の容積を有する細孔の径(ピーク径)が30~50μmの範囲内にある、請求項10に記載の炭素シート。
- 表面面積率Xである表面を面X1としたとき、請求項1~11のいずれかに記載の炭素シートの面X1又は面X2側に、マイクロポーラス層を有する、ガス拡散電極基材。
- 請求項12記載のガス拡散電極基材を含む燃料電池。
- 炭素繊維および結着材を含む多孔質の炭素シートであって、
1~100μmの範囲に径を有する細孔の容積の和を100%としたときに、50~100μmの範囲に径を有する細孔の容積の和が17~50%であり、
嵩密度(ρb)と真密度(ρt)から算出される空隙率((ρt-ρb)/ρt)が75~87%であることを特徴とする炭素シート。 - 1~100μmの細孔の径の範囲で、最大の容積を有する細孔の径(ピーク径)が30~50μmの範囲内にある、請求項14に記載の炭素シート。
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