WO2020066191A1 - ガス拡散層、膜電極接合体および燃料電池 - Google Patents
ガス拡散層、膜電極接合体および燃料電池 Download PDFInfo
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- WO2020066191A1 WO2020066191A1 PCT/JP2019/025767 JP2019025767W WO2020066191A1 WO 2020066191 A1 WO2020066191 A1 WO 2020066191A1 JP 2019025767 W JP2019025767 W JP 2019025767W WO 2020066191 A1 WO2020066191 A1 WO 2020066191A1
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- gas diffusion
- diffusion layer
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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
- H01M4/88—Processes of manufacture
- H01M4/8803—Supports for the deposition of the catalytic active composition
- H01M4/8807—Gas diffusion layers
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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
- 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
- H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
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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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/90—Selection of catalytic material
- H01M4/92—Metals of platinum group
- H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
- H01M4/926—Metals of platinum group supported on carriers, e.g. powder carriers on carbon or graphite
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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 gas diffusion layer including a carbon sheet and a microporous layer suitably used for a fuel cell, particularly a polymer electrolyte fuel cell, a membrane electrode assembly including the gas diffusion layer, and a fuel including the gas diffusion layer. It relates to batteries.
- a polymer electrolyte fuel cell in which a fuel gas containing hydrogen is supplied to an anode and an oxidizing gas containing oxygen is supplied to a cathode to obtain an electromotive force by an electrochemical reaction occurring at both electrodes, is generally a separator, a gas diffusion It is configured by sequentially stacking a layer, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a separator.
- the gas diffusion layer has a high gas diffusivity for diffusing a gas supplied from the separator to the catalyst layer, and a high drainage property for discharging water generated along with the electrochemical reaction to the separator, and A high conductivity is required for extracting the generated current, and therefore, a gas diffusion layer having a microporous layer formed on a surface thereof using a carbon sheet made of carbon fiber or the like as a base material is widely used.
- a problem with such a gas diffusion layer is a trade-off relationship between conductivity and gas diffusion.
- a typical factor affecting conductivity is a conductive path due to contact between conductive materials such as carbon fibers contained in the gas diffusion layer.
- a typical factor affecting gas diffusivity is the porosity inside the gas diffusion layer, that is, the amount of gas diffusion paths.
- the density of the carbon sheet increases the gas permeation inside the carbon sheet. The number of routes decreases, and gas diffusivity deteriorates.
- Patent Document 1 As a result of suppressing the penetration of the microporous layer precursor into the carbon sheet, a sufficient microporous layer is not formed inside the gas diffusion layer, and the conductivity of the gas diffusion layer is reduced. There is a possibility that the path increases and the conductivity decreases. Further, the inventions described in Patent Literatures 2 and 3 are gas diffusion layers that do not include a microporous layer, and therefore cannot achieve conductivity as high as a gas diffusion layer that includes a microporous layer. In a gas diffusion layer having a microporous layer, it is important to determine where and how much the microporous layer is formed inside the gas diffusion layer. Appropriate control must be performed on the composition and basis weight of the body coating liquid.
- an object of the present invention is to provide a gas diffusion layer that improves the power generation performance of a fuel cell including the gas diffusion layer by improving both gas diffusivity and conductivity in the gas diffusion layer in view of the background of the related art. Is to provide.
- Another object of the present invention is to stably produce a gas diffusion layer having sufficient gas diffusivity and conductivity, which has been difficult to produce by a conventional method.
- Another object of the present invention is to provide a fuel cell including the above gas diffusion layer.
- a gas diffusion layer having a carbon sheet and a microporous layer on at least one surface of the carbon sheet When an arbitrarily selected region having a width of 10 mm and a depth of 3 mm in the gas diffusion layer is compressed at a pressure of 0.5 MPa in a direction perpendicular to the surface from one side of the gas diffusion layer, the inside of the gas diffusion layer is in an in-plane direction.
- A be the “in-plane oxygen transmission coefficient” through which oxygen passes
- the "electrical resistance" when the gas diffusion layer is compressed at 2 MPa in the direction perpendicular to the plane is B
- the number obtained by subtracting the number obtained by multiplying B by 60 from A and adding 310 is referred to as “compatibility index of in-plane oxygen permeability coefficient and electric resistance” C
- C A gas diffusion layer that satisfies the relationship where C is 0 or more.
- the carbon sheet has a region containing carbon fibers occupied by pores having a pore diameter of 10 ⁇ m or more and 100 ⁇ m or less, and a region occupied by pores having a pore diameter of 0.01 ⁇ m or more and less than 10 ⁇ m (hereinafter, internal pores).
- the gas diffusion layer, wherein the internal porous body has an average thickness of 10 ⁇ m or more and 30 ⁇ m or less in a direction perpendicular to the surface of the carbon sheet.
- the present invention due to the difficulty in the conventional art, the in-plane direction of oxygen permeability of the gas diffusion layer and the conductivity of the gas diffusion layer in the direction perpendicular to the plane, the power generation performance when used in a fuel cell.
- a gas diffusion layer that can be improved can be obtained.
- FIG. 2 is a schematic cross-sectional view for illustrating the configuration of the gas diffusion layer of the present invention.
- FIG. 2 is a schematic cross-sectional view illustrating a membrane electrode assembly using the gas diffusion layer of the present invention.
- FIG. 3 is a schematic diagram for explaining a method for measuring the in-plane oxygen permeability coefficient A of the gas diffusion layer of the present invention.
- FIG. 1 is a schematic sectional view showing an example of the gas diffusion layer of the present invention.
- the gas diffusion layer has an internal pore body 4 in a layered form inside the carbon sheet 1 on one surface 2 (plane X) side of the carbon sheet 1, and a fine pore outside the plane X. It has a porous body 5. Having the internal porous body 4 in a layered state inside the carbon sheet 1 means that the internal porous body 4 exists in a layered manner in the void portion of the carbon sheet 1 which is a porous body. The internal porous body will be described later.
- the gas diffusion layer has internal pores 4 in a state of being unevenly distributed inside the carbon sheet 1 on one surface 2 (plane X) side of the carbon sheet 1.
- the microporous body 5 is provided outside X. Having the internal porous body 4 in a state of being non-uniformly distributed inside the carbon sheet 1 means that a portion where the internal porous body 4 exists and a portion where the internal porous body 4 does not exist are mixed in the void portion of the carbon sheet 1 which is a porous body. What you do. In this case, the portion where the internal porous body 4 exists may exist discretely and discontinuously, or may exist continuously in a mesh form.
- FIG. 1B shows a more realistic mode.
- FIG. 2 is an example of a membrane electrode assembly using the gas diffusion layer of the present invention.
- the catalyst layers 6a and 6b are disposed on both sides of the electrolyte membrane 7, and the gas diffusion layers 0a and 0b of the present invention are so arranged that the microporous layers 5a and 5b and the catalyst layers 6a and 6b are in contact with each other. Are laminated.
- the separator is not shown in FIG. 2, the separator is provided on the surface 3 (surface Y) opposite to the surface 2 (surface X) of the carbon sheet 1.
- the gas diffusion layer of the present invention is such that when an arbitrarily selected area of 10 mm in width and 3 mm in depth in the gas diffusion layer is compressed from one side in a direction perpendicular to the plane at 0.5 MPa, the inside of the gas diffusion layer is moved in an in-plane direction.
- the total number is defined as an index C of compatibility between the in-plane oxygen permeability coefficient and the electrical resistance, the relationship that C is 0 or more is satisfied. That is, the gas diffusion layer of the present invention satisfies the following expression: Good power generation performance can be exhibited.
- C (in-plane oxygen transmission coefficient) ⁇ (conductivity in pressurization in the direction perpendicular to the surface) ⁇ 60 + 310 ⁇ 0 It is preferable that C is 10 or more in order to obtain more excellent power generation performance, and it is preferable that C is 20 or more and 200 or less in order to obtain extremely good power generation performance. Note that the direction perpendicular to the plane indicates a direction perpendicular to the plane (thickness direction).
- the gas diffusion layer of the present invention will be described in detail.
- the carbon sheet used in the gas diffusion layer of the present invention can be produced by a process including the production of a porous body containing carbon fibers or a precursor thereof described later, impregnation of a resin composition, heat treatment, and carbonization.
- the impregnation step can be omitted.
- a gas diffusion layer can be produced by laminating a microporous layer on a carbon sheet. At the time of such processing, formation of internal pore bodies and / or water-repellent processing may be performed as necessary.
- the carbon sheet used for the gas diffusion layer 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.
- the binder plays a role in binding carbon fibers.
- the binder contains a carbide of the resin composition. Further, when a water repellent is used for the carbon sheet used for the gas diffusion layer of the present invention, the water repellent is included in the binder.
- a porous body used for producing a carbon sheet will be described.
- a high gas diffusivity for diffusing gas supplied from the separator to the catalyst, and for discharging water generated along with the electrochemical reaction to the separator It is important to have a high drainage property and a high conductivity for extracting the generated current. Therefore, it is preferable to use a porous body having conductivity and having an average pore diameter of 10 to 100 ⁇ m. More specifically, in a preferred embodiment, a porous body used for producing a carbon sheet is a porous body containing carbon fibers such as a carbon fiber woven fabric, a carbon fiber paper body, and a carbon fiber nonwoven fabric.
- a porous body containing carbon fibers in order to obtain a carbon sheet because of its excellent corrosion resistance. Further, it absorbs dimensional changes in the direction perpendicular to the plane (thickness direction) of the electrolyte membrane.
- carbon paper obtained by binding a carbon fiber paper body with a carbide as the carbon sheet because of its excellent properties, that is, excellent "spring properties”.
- carbon cloth as a carbon fiber woven fabric and a felt type "carbon nonwoven fabric” as a carbon fiber nonwoven fabric can also be used.
- a carbon fiber paper body will be described as a representative example.
- the carbon sheet obtained by binding the carbon fiber paper body with the binder can also be obtained by impregnating the carbon fiber paper body with the resin composition and carbonizing it, as described later.
- Examples of the carbon sheet used in the gas diffusion layer of the present invention and the carbon fibers in the porous body used to obtain the same include carbon fibers such as polyacrylonitrile (PAN) -based, pitch-based, and rayon-based. Among them, PAN-based carbon fibers and pitch-based carbon fibers are preferably used because of their excellent mechanical strength.
- PAN polyacrylonitrile
- the carbon fibers in the carbon sheet used in the gas diffusion layer of the present invention preferably have an average diameter of single fibers of 3 to 20 ⁇ m, more preferably 5 to 10 ⁇ m.
- a combination of any of the above upper limits and any of the lower limits can be used.
- the average diameter of the single fibers is 3 ⁇ m or more, the pore diameter becomes large and the drainage property is improved.
- the average diameter of the single fiber is 20 ⁇ m or less, when used as a fuel cell, the water vapor diffusion property is reduced, and the water vapor diffusion is reduced.
- the electrolyte it is possible to suppress the problem that the membrane is dried and the proton conductivity is reduced, so that the power generation performance is reduced.
- the average diameter of a single fiber in the carbon fiber is determined by photographing the carbon fiber with a microscope such as a scanning electron microscope at a magnification of 1000 times and randomly selecting 30 different single fibers. Is measured, and the average value is obtained.
- a scanning electron microscope S-4800 manufactured by Hitachi, Ltd. or its equivalent can be used.
- the carbon fiber used in the present invention preferably has an average length of a single fiber of 3 to 20 mm, more preferably 5 to 15 mm.
- the carbon sheet has excellent mechanical strength, electrical conductivity, and thermal conductivity.
- the average length of the single fibers is 20 mm or less, the carbon fibers are excellent in dispersibility during papermaking and a uniform carbon sheet can be obtained.
- Such a carbon fiber having an average length of a single fiber can be obtained by a method of cutting a continuous carbon fiber into a desired length.
- the average length of the single fiber of the carbon fiber is taken by a microscope such as a scanning electron microscope, and the carbon fiber is photographed at a magnification of 50 times, and 30 different single fibers are randomly selected. The length was measured, and the average was calculated.
- a scanning electron microscope S-4800 manufactured by Hitachi, Ltd. or its equivalent can be used.
- the average diameter and average length of a single carbon fiber in a carbon sheet are usually measured by directly observing the carbon fiber as a raw material, but can also be measured by observing the carbon sheet.
- the paper body formed by paper making which is an embodiment of a porous body used to obtain a carbon sheet, has a two-dimensional flat carbon fiber for the purpose of maintaining in-plane conductivity and thermal conductivity isotropically. It is preferably in the form of a sheet randomly dispersed therein.
- the papermaking process of the carbon fiber for obtaining the carbon fiber paper body may be performed only once or may be performed by laminating a plurality of times.
- the carbon fiber paper body preferably has a basis weight of carbon fiber in the range of 10 to 50 g / m 2 , more preferably in the range of 15 to 35 g / m 2 , still more preferably 20 to 50 g / m 2. It is in the range of 30 g / m 2 .
- any of the above upper limits and any of the lower limits may be combined.
- the basis weight of the carbon fibers in the carbon fiber paper is 10 g / m 2 or more, the carbon sheet obtained from the carbon fiber paper has excellent mechanical strength.
- the carbon sheet obtained from the carbon fiber paper has excellent in-plane gas diffusivity and drainage.
- the carbon fiber weight of the carbon fiber paper after bonding is within the above range.
- a porous body containing carbon fibers such as a carbon fiber paper body is impregnated with a resin composition serving as a binder.
- the binder in the carbon sheet is a material that mainly serves to bind the carbon fibers to each other, and a carbide of a resin composition is used as the binder.
- a pre-impregnated carbon sheet obtained by impregnating a porous body containing carbon fibers with a resin composition serving as a binder is referred to as a "pre-impregnated body".
- the carbon sheet used for the gas diffusion layer of the present invention can be obtained from a pre-impregnated body.
- a method for preparing a pre-impregnated body by impregnating a resin composition serving as a binder into a porous body containing carbon fibers a method of immersing the porous body in a solution containing the resin composition, a solution containing the resin composition, Is applied to a porous body, and a method of transferring a film made of a resin composition by overlapping the porous body on the porous body.
- a method of immersing a porous body in a solution containing a resin composition is particularly preferably used because of excellent productivity.
- the resin composition used when preparing the pre-impregnated body is preferably a resin composition which is carbonized at the time of firing in a later step to become a conductive carbide and serves as a binder.
- a resin component to which a solvent or the like is added as necessary can be used as the resin composition used for preparing the pre-impregnated body.
- the resin component includes a resin such as a thermosetting resin, and further includes an additive such as a carbon powder and a surfactant as necessary.
- examples of the resin constituting the resin component in the resin composition used for preparing the pre-impregnated body include thermosetting resins such as phenol resin, epoxy resin, melamine resin and furan resin. Among them, a phenol resin is preferably used because of its high carbonization yield.
- the resin composition can be used as a binder without being carbonized, and a thermoplastic resin such as a fluororesin, an ABS resin, a polyethylene resin, an acrylic resin, a nylon resin, a polypropylene resin, a polyethylene terephthalate resin, and a urethane resin can be used. Can be used.
- Carbon powder can be used as a resin component in the resin composition used when preparing the pre-impregnated body.
- carbon powder carbon black, carbon nanotubes, carbon nanofibers, carbides of fine fibers such as cellulose, chitin and aramid, milled fibers of carbon fibers, graphite, flake graphite and the like can be used.
- carbon nanotubes, carbon nanofibers, carbides of fine fibers such as cellulose, chitin and aramid, and milled fibers of carbon fibers can be preferably used for forming the high void pore portions in the surface layer.
- the resin composition used for preparing the pre-impregnated body may use the above-mentioned resin component as it is, or, if necessary, improve the impregnation property of a porous body such as a carbon fiber paper body with various kinds of resins.
- a solvent can be included.
- the solvent methanol, ethanol, isopropyl alcohol, and the like can be used.
- the resin composition used for preparing the pre-impregnated body is preferably liquid at a temperature of 25 ° C. and 0.1 MPa.
- the resin composition is liquid under the above conditions, the impregnating property of the papermaking body is excellent, and the carbon sheet obtained has excellent mechanical properties, electrical conductivity, and thermal conductivity.
- the resin component is preferably impregnated so as to be 30 to 400 parts by mass, more preferably 50 to 300 parts by mass, based on 100 parts by mass of the carbon fibers in the pre-impregnated body.
- a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the amount of the resin component impregnated with respect to 100 parts by mass of the carbon fibers in the pre-impregnated body is 30 parts by mass or more, the carbon sheet has excellent mechanical properties, electrical conductivity, and thermal conductivity.
- the impregnation amount of the resin component is 400 parts by mass or less, the carbon sheet has excellent gas diffusivity in the in-plane direction and gas diffusivity in the perpendicular direction.
- ⁇ Heat treatment> After forming a pre-impregnated body in which a porous body such as a carbon fiber paper body is impregnated with a resin composition, the pre-impregnated body can be subjected to a heat treatment prior to carbonization.
- the purpose of the heat treatment in the present invention is to thicken and cure the resin composition in the pre-impregnated body.
- Examples of the method of heat treatment include a method of blowing hot air, a method of heating with a hot plate such as a press device, and a method of heating by sandwiching between continuous belts.
- ⁇ Carbonization> in order to carbonize a pre-impregnated body obtained by impregnating a resin composition in a porous body such as a carbon fiber paper body, it is fired in an inert atmosphere.
- a batch-type heating furnace can be used, or a continuous-type heating furnace can be used.
- An inert atmosphere can be obtained by flowing an inert gas such as a nitrogen gas or an argon gas into 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.
- a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the maximum temperature is 1300 ° C. or higher, the carbonization of the resin component in the pre-impregnated body proceeds, and the carbon sheet becomes excellent in electrical conductivity and thermal conductivity.
- the maximum temperature is 3000 ° C. or lower, energy consumption accompanying the operation of the heating furnace can be reduced.
- a porous body such as a carbon fiber paper body that has been impregnated with a resin composition and then carbonized may be referred to as a “fired carbon fiber body”. That is, the carbon sheet usually means a fired carbon fiber body, and the fired carbon fiber body corresponds to a carbon sheet regardless of whether or not a water-repellent treatment is performed.
- the water repellent treatment of the carbon sheet is performed for the purpose of improving the drainage property, and can be performed by subjecting the carbon fiber fired body to the water repellent treatment.
- the water repellent process can be performed by applying a water repellent to the carbon fiber fired body and performing heat treatment.
- As another method of water-repellent treatment of a carbon sheet there is a method of not directly performing a water-repellent treatment on a carbon sheet. After applying the layer precursor coating liquid to the carbon sheet, a heat treatment is performed to move the water repellent contained in the coating liquid into the carbon sheet.
- the carbon sheet containing the water repellent as a binder can be obtained by performing a water repellent process.
- the water repellent may be included in the carbon sheet as a binder.
- the water repellent 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-perfluoroalkylvinyl ether copolymer (PFA).
- both the water repellency and the conductivity with the conductive separator are improved by thinly attaching the water-repellent to the surface of the fired carbon sheet.
- Can be The melting point of the water repellent used in the water repellent process is preferably 150 ° C. or more and 400 ° C. or less, so that the melting of the resin and the drying of the carbon sheet after the resin adhesion can be performed efficiently, more preferably.
- By setting the temperature to 200 ° C. or more and 320 ° C. or less it is possible to make the spread of the resin wet to the carbon fiber paper body uniform when the resin is melted.
- a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- Examples of such a water repellent include FEP and PFA.
- the amount of the water repellent applied is preferably 1 to 50 parts by mass, more preferably 2 to 40 parts by mass, per 100 parts by mass of the carbon fiber fired body. Note that a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the application amount of the water repellent is 1 part by mass or more, the carbon sheet has excellent drainage properties.
- the coating amount is 50 parts by mass or less, the carbon sheet has excellent conductivity.
- the heat treatment of the carbon fiber fired body can be performed after applying the water repellent to the carbon fiber fired body and further applying the precursor coating liquid for the microporous layer.
- the coating liquid also contains a water repellent.
- the water repellent in the microporous layer precursor coating liquid is applied to the carbon sheet.
- the amount of the water repellent that the carbon sheet has after the heat treatment is performed, the water repellent included in the carbon sheet before the application of the coating liquid, and the water repellent included in the coating liquid, the carbon sheet Is determined on the basis of the total amount of the movement.
- the microporous layer precursor coating liquid is applied to the carbon sheet, a phenomenon occurs in which the water repellent in the coating liquid moves to the carbon sheet. At this time, since the water repellent is diffused by the concentration gradient, the concentration of the water repellent at the moving destination is kept uniform.
- the amount of the water repellent on the carbon fibers on the surface Y can be reduced, and as an index for controlling the conductivity of the carbon sheet, The amount of water repellent that adheres to the carbon sheet can be used.
- the ratio of the number of fluorine elements to the carbon element on the carbon sheet can be used as an index of the amount of the water repellent attached to the carbon sheet. The range is preferably from 0.002 to 0.030, more preferably from 0.003 to 0.030.
- microporous layer which is one of the components of the present invention will be described.
- the carbon sheet used for the gas diffusion layer of the present invention can be used as a gas diffusion layer by forming a microporous layer on one surface.
- the gas diffusion layer of the present invention has a microporous layer on at least the surface X of the carbon sheet.
- the basis weight of the microporous layer is preferably in the range of 10 to 30 g / m 2 .
- the basis weight of the microporous layer is 10 g / m 2 or more, when the precursor coating liquid for the microporous layer is applied to the carbon sheet, the coating liquid easily penetrates from the surface of the carbon sheet in a direction perpendicular to the surface.
- a microporous layer is formed inside the carbon sheet, and this microporous layer becomes an internal porous body.
- the basis weight of the microporous layer is 30 g / m 2 or less, excessive penetration of the coating liquid into the carbon sheet can be suppressed.
- the microporous layer is formed in a range up to an appropriate position in the direction.
- the basis weight of the microporous layer including the internal porous body should be in the range of 10 to 20 g / m 2. Is more preferred. Note that a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the microporous layer preferably contains conductive particles.
- the conductive particles further preferably include carbon powder.
- a porous body containing linear carbon and a water repellent can be used for the microporous layer.
- the carbon powder includes carbon black such as furnace black, acetylene black, lamp black and thermal black, and graphite such as flaky graphite, flaky graphite, earthy graphite, artificial graphite, expanded graphite, and flake graphite. And CNTs and other carbon powders.
- carbon black is more preferably used, and acetylene black is most preferably used because of a small amount of impurities.
- the porosity of the internal pore body is preferably in the range of 80% or more and 95% or less. More preferably, it is 85% or more and 95% or less.
- the porosity of the microporous layer is 85% or more, gas diffusion in the in-plane direction is promoted, so that gas diffusibility can be improved and drainage from the gas diffusion layer can be improved.
- the porosity of the microporous layer is 95% or less, reverse diffusion of gas is promoted. Therefore, when the fuel cell is operated at a relatively high temperature condition of 80 ° C. or more, the electrolyte membrane is dried and proton The problem that the conductivity is reduced can be suppressed.
- the microporous layer contains a water repellent.
- a fluorine-based polymer as the water repellent because of its excellent corrosion resistance.
- the fluorine-based polymer include polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and tetrafluoroethylene-perfluoroalkylvinyl ether copolymer (PFA).
- the microporous layer can be formed by applying a conductive particle-containing coating liquid containing the above-described conductive particles to the surface of the carbon sheet.
- the conductive particle-containing coating liquid may contain a dispersion medium such as water or an organic solvent, and may also contain a dispersing aid such as a surfactant.
- a dispersing aid such as a surfactant.
- Water is preferred as the dispersion medium, and a nonionic surfactant is preferably used as the dispersion aid.
- various carbon powders and water repellents as described above can be contained.
- the conductive particle-containing coating liquid can be applied to the carbon sheet using various commercially available coating apparatuses.
- an application method such as screen printing, rotary screen printing, spray spraying, intaglio printing, gravure printing, die coater application, bar application, and blade application can be used.
- the application method described above is merely an example, and is not necessarily limited thereto.
- the coating liquid After applying the conductive particle-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 applied material is put into a dryer 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 microcracks on the surface. After the coated material is dried, it is put into a muffle furnace, a baking oven or a high-temperature dryer, and is preferably heated at a temperature of 300 to 380 ° C. for 5 to 20 minutes to melt the water repellent and to remove carbon powder or the like. It is preferable to form a microporous layer as a binder between the conductive particles.
- an internal porous body 4 having a pore diameter of 0.01 ⁇ m or more and less than 10 ⁇ m is provided near the inner surface on the surface 2 (plane X) side of the carbon sheet 1. In a preferred embodiment, it is included as a layered region having an average thickness represented by reference numeral 12. As another preferred embodiment, as shown in FIG. 1B, an internal pore body having a pore diameter of 0.01 ⁇ m or more and less than 10 ⁇ m is provided near the inner surface on the surface 2 (face X) side of the carbon sheet 1. 4 may be included in a non-uniformly distributed state.
- a value obtained by averaging a range in which the internal porous body is filled in the vicinity of the surface on the surface 2 (plane X) side of the carbon sheet 1 is defined as an average internal porous body thickness 12.
- a region composed of carbon fibers mainly has pores having a pore diameter of 10 ⁇ m or more and 100 ⁇ m or less, while the internal pore body has the above pore diameter. It is important that the internal pores exist in a range from the surface of the carbon sheet to an appropriate position in a direction perpendicular to the surface.
- the average thickness 12 is preferably in a range of 10 ⁇ m to 30 ⁇ m in a direction perpendicular to the surface of the carbon sheet, more preferably 12 to 25 ⁇ m, and further preferably 15 to 25 ⁇ m.
- a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the range is 10 ⁇ m or more, the number of conductive paths inside the carbon sheet increases, and the conductivity improves.
- the range is 30 ⁇ m or less, a gas permeation path is favorably formed inside the carbon sheet, and gas diffusibility is improved.
- the position and thickness of the internal porous body can be determined by taking a photograph of a cross section of the carbon sheet or the gas diffusion layer, taken at a high magnification, and observing the photograph.
- the internal pore body Since the internal pore body has a small pore diameter, it has an effect of improving the conductivity between carbon fibers, and can reduce the electric resistance of the gas diffusion layer.
- This internal pore body can be formed by applying a precursor coating liquid for the internal pore body to the side to be the surface X of the carbon sheet before the firing step during the production process of the carbon sheet. Since the internal pores are formed before the porous layer precursor coating liquid is applied to the carbon sheet, it is possible to suppress a phenomenon in which the microporous layer precursor coating liquid excessively permeates the carbon sheet. As a result, the gas permeability in the carbon sheet can be improved.
- the carbon fiber fired body including the internal pore body when the internal pore body precursor is formed before carbonization of the carbon sheet, the carbon fiber fired body including the internal pore body also corresponds to the “carbon sheet”.
- the internal pore body may be formed by applying a precursor coating liquid for the internal pore body after the production of the carbon sheet.
- the microporous layer precursor coating liquid may be formed as a precursor for the internal pore body. It can also be used as a coating liquid.
- the basis weight of the porous body inside the carbon sheet is preferably in the range of 3 g / m 2 to 15 g / m 2 , and more preferably 5 g / m 2 to 12 g / m 2 . Note that a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the internal pore body precursor coating liquid is composed of a material that becomes conductive particles after firing and a resin mixture that becomes a binder after firing.
- a resin composition can be used, and as a material that becomes conductive particles after firing, carbon black, carbon nanotubes, carbon nanofibers, fine fibers such as cellulose or chitin or aramid or carbides thereof, milled fibers of carbon fibers, graphite, Flake graphite or the like can be used.
- carbon nanotubes, carbon nanofibers, carbides of fine fibers such as cellulose, chitin, and aramid, and milled fibers of carbon fibers can be preferably used to form the internal pores forming high voids.
- the density of the surface layer of the carbon sheet is 0.34 g / cm 3 or more.
- the upper limit is preferably 0.80 g / cm 3 or less.
- the density of the entire carbon sheet is preferably in the range of 0.29 / cm 3 or more and 0.33 g / cm 3 or less. That is, in a preferred embodiment of the carbon sheet used in the present invention, it is important that the density of the surface layer of the carbon sheet is higher than the density of the entire carbon sheet.
- the pore diameter of the carbon sheet tends to decrease, so that the thickness of the internal pore body existing inside the carbon sheet in the direction perpendicular to the plane is controlled to a range described later. can do. Further, this allows the microporous layer to cover the surface of the carbon sheet, suppressing the possibility that the carbon fibers protrude from the microporous layer, and improving the surface quality. In addition, the conductivity is high, and the power generation performance is improved at both high and low temperatures.
- the density of the entire carbon sheet is 0.29 g / cm 3 or more, a conductive path is formed in the carbon sheet, and the conductivity of the gas diffusion layer using the carbon sheet is improved.
- the density of the entire carbon sheet is 0.33 g / cm 3 or less, appropriate voids are formed in the carbon sheet, and the gas diffusion property of the gas diffusion layer using the carbon sheet is improved.
- the carbon sheet having such a density controls the carbon fiber basis weight in the pre-impregnated body, the blending amount of the resin component with respect to the carbon fiber, and the thickness of the carbon sheet.
- 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 at a surface pressure of 0.15 MPa. Can be.
- the thickness of the carbon sheet used for the gas diffusion layer of the present invention is preferably 50 to 230 ⁇ m, more preferably 70 to 180 ⁇ m, and further preferably 90 to 130 ⁇ m. Note that a preferable range may be a combination of any one of the above upper limits and any one of the lower limits.
- the thickness of the carbon sheet is 230 ⁇ m or less, more preferably 180 ⁇ m or less, and still more preferably 130 ⁇ m or less, the diffusivity of the gas is easily increased, and the generated water is easily discharged. Further, the size of the whole fuel cell can be easily reduced.
- the thickness of the carbon sheet is 50 ⁇ m or more, more preferably 70 ⁇ m or more, and still more preferably 90 ⁇ m or more, gas diffusion in the in-plane direction inside the carbon sheet is efficiently performed, and the power generation performance is easily improved.
- the thickness of the carbon sheet used for the gas diffusion layer of the present invention is determined by the following method. That is, the carbon sheet and the gas diffusion layer are placed on a flat surface plate, and the thickness is measured under a pressure of 0.15 MPa. Sampling is performed at 10 different locations, and the average of the measured values is defined as the thickness.
- the cross section of the gas diffusion layer is formed by ion cutting, and the position of the surface X of the carbon sheet is determined by observing the cross section with an SEM.
- the area from the surface X to a depth of 20 ⁇ m is defined as the surface layer
- the area of the material-filled region in the surface layer is determined
- the filled area is divided by the area of the surface layer.
- Ask for. The value obtained by multiplying the filling rate by the density of the substance to be filled is defined as the surface density.
- a membrane electrode assembly can be formed by joining the above-mentioned gas diffusion layer to a solid polymer electrolyte membrane via a catalyst layer. At that time, by disposing the microporous gas diffusion layer on the catalyst layer side, the reverse diffusion of the generated water is more likely to occur, and the contact area between the catalyst layer and the gas diffusion layer increases, and the contact electric resistance increases. Can be reduced.
- the fuel cell of the present invention includes the gas diffusion layer of the present invention, and has separators on both sides of the above-mentioned membrane electrode assembly. That is, a fuel cell is constituted by disposing separators on both sides of the above-mentioned membrane electrode assembly. Usually, a polymer electrolyte fuel cell is constituted by laminating a plurality of such membrane electrode assemblies sandwiched between separators via gaskets on both sides.
- the catalyst layer is composed of a layer containing a solid polymer electrolyte and carbon carrying a catalyst. Usually, platinum is used as the catalyst.
- 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-based polymer material having high proton conductivity, oxidation resistance, and heat resistance. The configuration itself of such a fuel cell unit or fuel cell is well known.
- gas diffusion layer of the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.
- Toray's polyacrylonitrile-based carbon fiber “Treca” (registered trademark) T300 (average carbon fiber diameter: 7 ⁇ m) was cut into an average length of 12 mm, dispersed in water, and continuously made by a wet papermaking method. . Furthermore, a 10 mass% aqueous solution of polyvinyl alcohol was applied and dried on the paper as the binder, the carbon fiber areal weight was produced paper of 25 g / m 2. The attached amount of polyvinyl alcohol was 22 parts by mass based on 100 parts by mass of the carbon fiber paper body.
- the carbon fiber paper body cut into a size of 15 cm ⁇ 12.5 cm was horizontally immersed in a resin composition filled in an aluminum vat, sandwiched between rolls, and impregnated. At this time, two rolls were arranged horizontally with a certain clearance, and the carbon fiber paper body was vertically pulled up to adjust the total amount of adhered resin.
- One side is a smooth metal roll with a structure that removes excess resin using a doctor blade, the other side is sandwiched between gravure rolls with irregularities, and the resin composition is squeezed to reduce the difference in resin adhesion amount on the front and back. Can be adjusted.
- the impregnation it was dried by heating at a temperature of 100 ° C. for 5 minutes to prepare a pre-impregnated body.
- a heat treatment was performed at a temperature of 180 ° C. for 5 minutes while pressing with a flat plate press.
- a spacer was arranged outside the end of the pre-impregnated body in the thickness direction by a flat plate press to adjust the interval between the upper and lower press face plates.
- a step of applying the microporous layer precursor coating liquid to the carbon sheet or a step of applying the internal pore precursor coating liquid to the carbon sheet A water repellent treatment was performed on the carbon sheet by moving the fluorine-based polymer into the carbon sheet using the microporous layer precursor coating solution or the internal pore body precursor coating solution containing the fluorine-based polymer.
- -Solvent F methanol-Dispersion medium
- G purified water
- the above materials were mixed using a dispersing machine with the composition shown in Table 1, and the microporous layer precursor coating liquid 1 and the internal pore body precursor coating were mixed. Liquids 2 to 4 were prepared. Further, an internal pore precursor coating liquid was applied on a carbon sheet using a slit die coater, and carbonization was performed as necessary. A microporous layer precursor coating solution was applied to the carbon sheet to form a planar microporous layer.
- the coating liquid used here carbon powder, a water repellent, a surfactant, and purified water were added so as to have a composition of a conductive particle-containing coating liquid in which the blending amount was described in parts by mass as shown in Table 1.
- the adjusted one was used.
- the compounding amount of the FEP resin shown in Table 1 represents not the compounding amount of the aqueous dispersion of the FEP resin but the compounding amount of the FEP resin itself.
- the microporous layer precursor coating liquid was applied to the carbon sheet using a die coater, and then heated at a temperature of 120 ° C. for 10 minutes and subsequently at a temperature of 380 ° C. for 10 minutes to form a microporous layer.
- ⁇ Measurement of basis weight of microporous layer> The basis weight [g / m 2 ] of the carbon sheet and the gas diffusion layer was determined by dividing the mass of a sample cut into a square of 10 cm by the area of the sample (0.01 m 2 ). The value obtained by subtracting the weight of the carbon sheet from the weight of the gas diffusion layer was used as the weight of the microporous layer.
- ⁇ Measurement of thickness and density> The carbon sheet and the gas diffusion layer were placed on a flat surface plate, and the thickness under a pressure of 0.15 MPa was measured. Sampling was performed at 10 different locations, and the average of the measured values was defined as the thickness. In addition, the density [g / cm 3 ] was obtained by dividing the basis weight by the thickness.
- a gas diffusion layer (28) is set on a sealing material (32) having a width of 10 mm and a depth of 3 mm provided between a gas chamber A (27) and a gas chamber B (29), and by pressing the sealing material, The gas diffusion layer was compressed so that a region having a width of 10 mm and a depth of 3 mm was pressurized at 0.5 MPa.
- the valve A (23) was closed, the valve B (25) was opened, and nitrogen gas was allowed to flow through the pipe B (26).
- the nitrogen gas flowing into the gas chamber A (27) moves to the gas chamber B (29) through the gap of the gas diffusion layer (28), passes through the pipe C (30), and further passes through the gas flow meter (31). Released and released into the atmosphere.
- the gas flow rate (cc / min) flowing through the gas flow meter (31) was measured, and the value of 90.9% of the measured value was changed to the in-plane oxygen permeability coefficient A [cc / min] of the compression region having a width of 10 mm and a depth of 3 mm. ].
- the electric resistance of the gas diffusion layer is such that the gas diffusion layer cut to 2.0 cm ⁇ 2.0 cm is sandwiched between two gold-plated plates, and a uniform surface pressure of 2.0 MPa is applied to the gas diffusion layer in the thickness direction of the gas diffusion layer.
- the electric resistance when a current of 1.0 A was applied was measured and obtained as a value obtained by multiplying the electrode area by 4 cm 2 .
- the porosity of the internal pore body was determined as follows. First, using a S-3500 manufactured by Hitachi, Ltd. as a scanning electron microscope, 20 different internal pores inside the carbon sheet were randomly selected in a section perpendicular to the surface of the gas diffusion layer, and 2000 The photograph was taken at about twice the magnification. Next, for each of the 20 images obtained by the photographing, the gap portion and the non-gap portion are separated, and the area ratio of the gap portion to the total area of the gap portion and the non-gap portion is defined as the porosity of each image. did.
- the above-mentioned individual porosity was averaged for 20 images to obtain an average value of the porosity.
- an ion milling apparatus IM4000 manufactured by Hitachi High-Technologies Corporation was used. Even if the structure of the microporous layer is not uniform, if the above method is performed, it is possible to obtain an averaged internal pore volume porosity [%] by taking an average of 20 samples at random. it can. Also, at this time, by determining the area of the existence region of the internal pore body, it is possible to determine the thickness assuming that the internal pore body is uniformly present inside the carbon sheet. The average thickness of the body (reference numeral 12 in FIG. 1) was used.
- the basis weight of the internal porous body was determined by the product of the density of the internal porous body and the average thickness.
- the density of the internal pore body is determined by using the porosity of the internal pore body and the true density 2.1 g / cm 3 of the substance forming the internal pore body used in Examples and Comparative Examples. It is obtained by the following equation.
- the average thickness the value determined in the above ⁇ Measurement of porosity and average thickness of internal pore body> is used.
- ⁇ Evaluation of power generation performance of polymer electrolyte fuel cells > 1.00 g of platinum-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., platinum supported amount: 50% by mass), 1.00 g of purified water, "Nafion” (registered trademark) solution (“Nafion” (registered trademark) manufactured by Aldrich) 5.00% by mass) and 18.00 g of isopropyl alcohol (manufactured by Nacalai Tesque) were added in this order to prepare a catalyst solution.
- “Naflon” (registered trademark) PTFE tape “TOMBO” (registered trademark) No. 5 cm ⁇ 5 cm was cut.
- a catalyst liquid was applied to 9001 (manufactured by Nichias Corporation) 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 into 8 cm ⁇ 8 cm is sandwiched between two PTFE sheets with a catalyst layer, and is pressed to 5 MPa by a flat plate press.
- Pressing was performed at a temperature of 130 ° C. for 5 minutes to transfer the catalyst layer to the solid polymer electrolyte membrane. 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 was sandwiched between two gas diffusion layers prepared in each of Examples and Comparative Examples, each of which was cut into a size of 5 cm ⁇ 5 cm.
- a membrane electrode assembly was produced.
- the gas diffusion layer was arranged such that the surface having the microporous layer was in contact with the catalyst layer side.
- the obtained membrane electrode assembly was assembled in a single cell for fuel cell evaluation, and the output voltage at a current density of 2.0 A / cm 2 was measured.
- a separator a serpentine type separator having a single flow channel having a groove width, a groove depth, and a rib width of 1.0 mm was used.
- non-pressurized hydrogen was supplied to the anode side, and non-pressurized air was supplied to the cathode side for evaluation.
- Example 1 After performing a water-repellent treatment by impregnating the carbon sheet with a water-repellent agent according to the above ⁇ Preparation of carbon sheet>, apply the microporous layer precursor coating liquid according to the method described in ⁇ Preparation of gas diffusion layer>. A gas diffusion layer having internal pores was obtained by using the same. As a result, compatibility between gas diffusion properties and conductivity was good, and power generation performance was good. Table 2 shows the results.
- Example 2 A gas diffusion layer was obtained in the same manner as in Example 1, except that the basis weight of the microporous layer was 20 g / m 2 and the thickness of the internal porous body was 11 ⁇ m. By further optimizing the average thickness, the number of gas permeation paths was increased, and gas diffusibility was improved as compared with Example 1. In addition, compatibility between gas diffusivity and conductivity was good, and power generation performance was good. Table 2 shows the results.
- Example 3 The method is the same as that of Example 1, except that the basis weight of the microporous layer is 5 g / m 2 , the coating clearance of the microporous layer precursor coating solution is reduced, and the thickness of the internal porous body is 20 ⁇ m.
- the gas diffusion layer was obtained by the method, the gas diffusion property was improved as compared with Example 1 by further optimizing the basis weight of the internal pores. The compatibility between gas diffusivity and conductivity was good, and the power generation performance was good. Table 2 shows the results.
- Example 4 A gas diffusion layer was obtained in the same manner as in Example 1, except that the basis weight of the microporous layer was 10 g / m 2 and the average thickness of the internal pores was 10 ⁇ m. And the compatibility of the conductivity were even better, and the power generation performance was even better. Table 2 shows the results.
- Example 5 A method similar to that of Example 4 was performed, except that the amount of the water repellent used in the water repellent treatment of the carbon sheet was reduced to obtain a gas diffusion layer in which the fluorine / carbon ratio on the surface Y fiber was 0.020. Since the conductivity was improved by further optimizing the amount of the water repellent, the compatibility between the gas diffusion property and the conductivity was further better, and the power generation performance was further better. Table 2 shows the results.
- Example 6 This is the same method as in Example 5, except that the amount of the water repellent used in the water repellent treatment of the carbon sheet was further reduced to obtain a gas diffusion layer having a fluorine / carbon ratio on the back fiber of 0.015.
- the conductivity was further improved by further optimizing the amount of the liquid agent, the compatibility between gas diffusion and conductivity was extremely good, and the power generation performance was extremely good. Table 2 shows the results.
- Example 7 A method similar to that of Example 6, except that the carbon sheet is not impregnated with a water-repellent agent and the carbon sheet is subjected to water-repellent treatment with a microporous layer precursor coating solution, so that the fluorine / carbon ratio on the back fiber is reduced to 0.
- a gas diffusion layer of .0050 was obtained, the compatibility between gas diffusion and conductivity was extremely good, and the power generation performance was extremely good. Table 2 shows the results.
- Example 8 In the method described in ⁇ Preparation of gas diffusion layer>, the same procedure as in Example 7 was carried out except that the internal pore precursor coating liquid 2 was applied to the carbon sheet, and the microporous layer precursor coating liquid 1 was applied after drying.
- the gas diffusivity was improved due to an increase in the porosity.
- the compatibility between gas diffusivity and conductivity was very good, and the power generation performance was very good. Table 2 shows the results.
- Example 9 In the method described in ⁇ Preparation of gas diffusion layer>, the same procedure as in Example 7 was carried out except that the internal pore precursor coating liquid 3 was applied to the carbon sheet, and the microporous layer precursor coating liquid 1 was applied after drying. Using a similar method, a gas diffusion layer having an internal porosity of 90% was obtained. As a result, the porosity increased, while the average thickness of the internal porosity increased. Although the gas diffusivity did not improve, the conductivity improved. The compatibility between gas diffusivity and conductivity was very good, and the power generation performance was very good. Table 2 shows the results.
- Example 10 In the method described in ⁇ Preparation of gas diffusion layer>, except that the microporous layer precursor coating liquid 1 is applied after the internal pore precursor coating liquid 4 is applied to the carbon sheet, dried and carbonized. Using a method similar to that of Example 7, a gas diffusion layer having an internal pore volume porosity of 91% was obtained. As a result, the surface layer density was slightly reduced, and the gas diffusion property was improved as compared with Example 9. . The compatibility between gas diffusivity and conductivity was very good, and the power generation performance was very good. Table 2 shows the results.
- Example 11 The carbon sheet manufacturing method was changed. First, long fibers of polyacrylonitrile were subjected to a flameproofing treatment at a temperature of 200 ° C. for 10 minutes, a nonwoven fabric was produced by a hydroentanglement treatment, and roll pressing was performed. It was introduced into a heating furnace at a temperature of 2000 ° C. to obtain a carbon sheet made of a non-woven carbon fiber fired body having a thickness of 150 ⁇ m. Next, when a gas diffusion layer was obtained using the carbon sheet in the same manner as in Example 1, the compatibility between the gas diffusion property and the conductivity was good, and the power generation performance was good. Table 2 shows the results.
- Example 12 A gas diffusion layer was obtained in the same manner as in Example 9 except that the same nonwoven fabric as that used in Example 11 was used as the carbon sheet, and that the basis weight of the internal pores was 5 g / m 2 . However, compatibility between gas diffusivity and conductivity was very good, and power generation performance was very good. Table 2 shows the results.
- Example 13 A gas diffusion layer was obtained in the same manner as in Example 1 except that the weight of the internal porous body was 5 g / m 2 and the weight of the microporous layer was 5 g / m 2 , and high gas diffusivity was obtained. On the other hand, the conductivity slightly decreased due to the decrease in the basis weight of the microporous layer. The compatibility between gas diffusivity and conductivity was good, and the power generation performance was good. Table 2 shows the results.
- Example 14 This is the same method as in Example 2, except that the basis weight of the microporous layer was increased to 25 g / m 2 , while the clearance in the process of applying the microporous layer precursor was increased, and the average thickness of the internal porous body was reduced to 30 ⁇ m.
- the obtained gas diffusion layer was obtained, the compatibility between the gas diffusion property and the conductivity was good, and the power generation performance was good. Table 2 shows the results.
- Example 15 The method is the same as that of Example 14, except that the coating clearance of the microporous layer precursor coating liquid is reduced and the gas diffusion layer in which the average thickness of the internal pores is increased to 26 ⁇ m, as compared with Example 14. As a result, the compatibility between the gas diffusion property and the conductivity was good, and the power generation performance was good. Table 2 shows the results.
- Example 1 A gas diffusion layer was obtained in the same manner as in Example 1 except that the coating clearance of the microporous layer precursor coating liquid was reduced and the average thickness of the internal pores was set to 33 ⁇ m, as compared with Example 1. The compatibility between gas diffusivity and conductivity was poor, and the power generation performance was low. Table 2 shows the results.
- Example 2 (Comparative Example 2) Compared with Example 1, a gas diffusion layer was obtained in the same manner as in Example 1 except that a carbon sheet having a high density was set at a carbon fiber weight of 29 g / m 2 in the production of the carbon sheet. The compatibility of the conductivity was poor, and the power generation performance was low. Table 2 shows the results.
- Example 3 (Comparative Example 3) Compared with Example 1, the microporous layer precursor coating liquid was applied to release paper at a basis weight of 13 g / m 2 and dried at a temperature of 100 ° C. to obtain a dried microporous layer precursor. The dried microporous layer precursor was placed on a carbon sheet and pressed, and the release paper was peeled off at a temperature of 120 degrees to transfer the dried microporous layer precursor onto the carbon sheet. The mixture was heated at a temperature for 10 minutes to obtain a gas diffusion layer. By this method, the average thickness of the internal pore body was reduced to 3 ⁇ m. Otherwise, when a gas diffusion layer was obtained in the same manner as in Example 1, the compatibility between gas diffusion and conductivity was poor, and the power generation performance was low. Table 2 shows the results.
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Abstract
Description
(1)炭素シートと、前記炭素シートの少なくとも片面に微多孔層と、を有するガス拡散層であって、
前記ガス拡散層における幅10mmかつ奥行き3mmの任意に選択される領域を、前記ガス拡散層の片側から面直方向に0.5MPaの圧力で圧縮したときに、ガス拡散層内部を面内方向に酸素が透過する「面内酸素透過係数」をAとし、
前記ガス拡散層の面直方向を2MPaで圧縮したときの「電気抵抗」をBとし、
Aから、Bに60を乗じた数を減じ、310を加えた数を、「面内酸素透過係数と電気抵抗の両立性指標」Cとしたとき、
Cが0以上となる関係を満たす、ガス拡散層。
(2)炭素シートと、前記炭素シートの少なくとも片面に微多孔層と、を有するガス拡散層であって、
前記炭素シートは、細孔径10μm以上100μm以下の細孔体で占められる、炭素繊維を含む領域と、細孔径0.01μm以上10μm未満の細孔体(以下、内部細孔体)で占められる領域とを有し、
内部細孔体は、前記炭素シート表面から面直方向に10μm以上30μm以下の平均厚さで存在する、ガス拡散層。
さらに良好な発電性能を得るためにはCが10以上であることが好ましく、きわめて良好な発電性能を得るためにはCが20以上200以下であることが好ましい。なお、面直方向とは面に対して垂直な方向(厚さ方向)を表すものである。
以下に本発明のガス拡散層の詳細を述べる。
本発明のガス拡散層に用いられる炭素シートは、後述する炭素繊維またはその前駆体を含む多孔体の作製、樹脂組成物の含浸、熱処理、炭化を含む工程により作製することができる。ここで樹脂組成物を含まない場合は含浸の工程を削除することもできる。また、炭素シートは、微多孔層を積層することでガス拡散層を作製することができる。かかる加工の際に必要に応じて内部細孔体の形成及び/又は撥水加工を行ってもよい。
本発明のガス拡散層に用いられる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ことが好ましい。
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た予備含浸体を、炭化するために、不活性雰囲気下で焼成を行う。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、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不活性雰囲気とすることができる。
本発明において、炭素シートの撥水加工は、排水性を向上させる目的で行うものであり、炭素繊維焼成体に撥水加工を施すことで実施可能である。この場合、撥水加工は、炭素繊維焼成体に撥水剤を塗布し熱処理することにより行うことができる。炭素シートの撥水加工のもう一つの方法として、炭素シートに直接的に撥水加工を行わない方法があり、これは、前記焼成体に撥水剤を塗布するのではなく、例えば、微多孔層前駆体塗液を炭素シートに塗布した後、熱処理を行うことで、前記塗液に含まれる撥水剤を炭素シート内に移動させて行う方法を採ることができる。炭素シートに直接的に撥水剤を塗布する場合は、撥水加工することにより、結着材として撥水剤を含む炭素シートとすることができる。なお、撥水剤を用いて撥水加工した場合、前記撥水剤は結着材として炭素シートに含まれ得る。
<微多孔層の形成>
次に、本発明の構成要素の一つである微多孔層について説明する。
本発明のガス拡散層に用いられる炭素シートは、一方の表面に微多孔層を形成することで、ガス拡散層として用いることができる。そして本発明のガス拡散層は、炭素シートの少なくとも面Xの上に微多孔層を有するものである。
本発明においては、図1(a)に示すように、炭素シート1の表面2(面X)側の内部の表面近傍に、0.01μm以上10μm未満の細孔径を有する内部細孔体4が符号12で表される平均厚さを有する層状の領域として含まれることが好ましい態様である。また、別の好ましい態様として、図1(b)に示すように炭素シート1の表面2(面X)側の内部の表面近傍に、0.01μm以上10μm未満の細孔径を有する内部細孔体4が不均一に分布した状態で含まれる態様が挙げられる。かかる態様を採る場合は、炭素シート1の表面2(面X)側の内部の表面近傍において内部細孔体が充填する範囲を平均化した値を内部細孔体の平均厚さ12と定義する。炭素シートにおいて、炭素繊維からなる領域が主として10μm以上100μm以下の細孔径の空隙を有するのに対し、この内部細孔体は上記の細孔径を有する。この内部細孔体は炭素シート表面から面直方向に適切な位置までの範囲に存在することが重要である。平均厚さ12は、前記炭素シートの表面から面直方向に10μm以上30μm以下の範囲であることが好ましく、さらに好ましくは12~25μmであり、さらに好ましくは15~25μmである。なお、好ましい範囲としては、上記の上限値のいずれかと下限値のいずれかの組み合わせとすることもできる。前記範囲が10μm以上であると、前記炭素シート内部の導電経路が増加し、導電性が向上する。また、前記範囲が30μm以下であると、前記炭素シート内部にガス透過経路が良好に形成され、ガス拡散性が向上する。なお、内部細孔体の存在位置および厚みは、炭素シートまたはガス拡散層の面直断面を高倍率で写真撮影し、前記写真を観察することで決定することができる。
以上のような工程により得られた本発明のガス拡散層に用いられる炭素シートの特徴について、説明する。
本発明において、前記したガス拡散層を、触媒層を介して固体高分子電解質膜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層の微多孔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、触媒層とガス拡散層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、本発明のガス拡散層を含むものであり、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が構成される。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。
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25g/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。
上記にて作製した炭素シートを、撥水剤として、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剤を含浸した。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。また、撥水剤の水分散液は、乾燥後で炭素シート100~95質量部に対し、撥水剤が0~5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。
また、炭素シートに対し直接的に上記撥水加工を行わない場合は、微多孔層前駆体塗液を炭素シートに塗布する過程、または内部細孔体前駆体塗液を炭素シートに塗布する過程において、フッ素系ポリマーを含む微多孔層前駆体塗液または内部細孔体前駆体塗液を用い、フッ素系ポリマーを炭素シート内に移動させることで、炭素シートに撥水加工を行った。
<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:“VGCF(登録商標)”(昭和電工(株)製)アスペクト比70
・材料C:撥水剤:FEP樹脂(FEP樹脂を25質量部含む水分散液である“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)を使用)
・材料D:ノボラック型フェノール樹脂“タマノル(登録商標)”759(荒川化学工業(株)製)
・材料E:界面活性剤“TRITON(登録商標)”X-100(ナカライテスク(株)製)。
・溶媒F:メタノール
・分散媒G:精製水
上記の各材料を、表1に示した組成で分散機を用いて混合し、微多孔層前駆体塗液1、および内部細孔体前駆体塗液2~4を調製した。また、スリットダイコーターを用いて炭素シート上に内部細孔体前駆体塗液を塗布し、必要に応じて炭化処理を行った。この炭素シートに微多孔層前駆体塗液を塗布して面状の微多孔層を形成した。ここで用いた塗液には、炭素粉末、撥水剤、界面活性剤および精製水を、表1に示すように配合量を質量部で記載した導電性粒子含有塗液の組成となるように調整したものを用いた。なお、表1に示すFEP樹脂の配合量は、FEP樹脂の水分散液の配合量ではなく、FEP樹脂自体の配合量を表す。ダイコーターを用いて炭素シートに微多孔層前駆体塗液を塗布後、120℃の温度で10分間、続いて380℃の温度で10分間加熱し、微多孔層を形成した。
<微多孔層の目付の測定>
炭素シートおよびガス拡散層の目付[g/m2]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。また、ガス拡散層の目付けから、炭素シートの目付けを減じた値を微多孔層の目付けとした。
炭素シートおよびガス拡散層を平滑な定盤にのせ、圧力0.15MPaをかけた状態での厚さを測定した。異なる部位にて10箇所サンプリングを行い、測定値を平均したものを厚さとした。また、目付を厚さで除して密度[g/cm3]を求めた。
西華産業(株)製水蒸気ガス水蒸気透過拡散評価装置(MVDP-200C)を用いた。図3に示すような配管系において、最初にバルブA(23)のみ開いて、バルブB(25)を閉じた状態にしておいて、窒素ガス33を一次側配管A(22)に流した。マスフローコントローラー(21)に所定量(190cc/分)のガスが流れ、圧力コントローラー(24)にガス圧力が大気圧に対して5kPaかかるように調整した。ガス室A(27)とガス室B(29)の間に設置した幅10mm、奥行き3mmのシール材(32)の上にガス拡散層(28)をセットし、シール材を加圧することで、ガス拡散層における幅10mm、奥行き3mmの領域が0.5MPaで加圧されるように圧縮した。次いで、バルブA(23)を閉じ、バルブB(25)を開いて、配管B(26)に窒素ガスが流れるようにした。ガス室A(27)に流入する窒素ガスは、ガス拡散層(28)の空隙を通ってガス室B(29)に移動し、配管C(30)を通過、さらにガス流量計(31)を通過して大気中に放出された。このときのガス流量計(31)を流れるガス流量(cc/分)を測定し、その値の90.9%の値を幅10mm奥行き3mmの圧縮領域の面内酸素透過係数A[cc/min]とした。
ガス拡散層の電気抵抗は、2.0cm×2.0cmにカットしたガス拡散層を2枚の金メッキ板の間に挟んで2.0MPaの一様な面圧をかけつつガス拡散層の厚さ方向に1.0Aの電流を流したときの電気抵抗を測定して、電極面積4cm2をかけた数値として求めた。
ガス拡散層のガス拡散性と導電性の両立性を評価するにあたり、上記方法で算出した面内酸素透過係数Aと、上記方法で算出した加圧時の電気抵抗Bを用いて、Aから、Bに60乗じた数を減じ、310を加えた数Cを算出した。
ガス拡散層において、微多孔層を形成した面と反対側の表面の炭素繊維上から無作為に異なる10点を選び、走査型電子顕微鏡で7kVの加速電圧で2000倍に拡大して顕微鏡で観測し、フッ素元素数と炭素元素数を点分析で測定し、炭素元素数に対するフッ素元素数の比率を10点で平均した値を炭素繊維上のフッ素元素/炭素元素比率とした。なお、走査型電子顕微鏡としては、(株)日立製作所製S-3500Nを用い、エネルギー分散型X線分析装置としては、(株)堀場製作所EX-370を用いた。
内部細孔体の空隙率は、次のようにして求めた。まず、走査型電子顕微鏡として(株)日立製作所製S-3500を用い、ガス拡散層の面直断面において、炭素シート内部に存在する内部細孔体を、無作為に異なる20箇所を選び、2000倍程度で拡大して写真撮影を行った。次に、撮影により得られた20枚の画像それぞれに対し、空隙部と非空隙部を分離して、空隙部と非空隙部の合計面積に対する空隙部の面積比を個々の画像の空隙率とした。最後に、上記の個々の空隙率を20枚の画像について平均して空隙率の平均値を求めた。面直断面の作製に際しては、(株)日立ハイテクノロジーズ製イオンミリング装置IM4000を用いた。微多孔層の構造が不均一である場合でも、上述の方法を行えば、無作為に20箇所のサンプルの平均を取ることで平均化された内部細孔体空隙率[%]を求めることができる。また、この際、内部細孔体の存在領域面積を求めることで、内部細孔体が炭素シート内部に均一に存在すると仮定した場合の厚さを求めることができ、この厚さを内部細孔体の平均厚さ(図1における符号12)とした。
内部細孔体の目付は、内部細孔体の密度と平均厚さの積によって求めた。ここで、内部細孔体の密度は、内部細孔体の空隙率と、実施例・比較例で用いた内部細孔体を形成する物質の真密度2.1g/cm3を用いて、次の式により求められる。平均厚さは、上記<内部細孔体の空隙率と平均厚さの測定>で求めた値を用いる。
内部細孔体密度[g/cm3]=2.1[g/cm3]×(1-内部細孔体の空隙率[%]÷100)
<表層密度の算出方法>
まず、ガス拡散層の面直断面を無作為に20個選び、SEMを用いてそれぞれの断面を200倍程度で拡大して観察した。次に、観察したそれぞれの領域において、炭素シート表面から垂直に20μmの位置までの領域について、炭素繊維や内部細孔体を形成する物質により充填された部分の面積の合計を抽出した。この際、内部細孔体形成領域の物質充填率は、内部細孔体の存在領域の面積に空隙率を掛けることで求めることができる。次に、表層領域に対する物質充填率に対して、充填物質の密度2.1g/cm3をかけた数値を求め、この値を20箇所について平均したものを表層密度とした。
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とをこの順に加えることにより、触媒液を作製した。
上記の<炭素シートの作製>に従って、炭素シートに撥水剤を含侵させて撥水処理を行った後、<ガス拡散層の作製>に記載した方法に従って、微多孔層前駆体塗液を用いて内部細孔体を形成したガス拡散層を得たところ、ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
実施例1と同様の方法であるが、微多孔層の目付を20g/m2、内部細孔体の厚みを11μmとした点のみ異なる方法によりガス拡散層を得たところ、内部細孔体の平均厚さのさらなる適正化によりガス透過経路が増加し、実施例1よりもガス拡散性が向上した。また、ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
実施例1と同様の方法であるが、微多孔層の目付を5g/m2とし、微多孔層前駆体塗液の塗布クリアランスを低減し、内部細孔体の厚みを20μmとした点のみ異なる方法によりガス拡散層を得たところ、内部細孔体目付のさらなる適正化により実施例1よりもガス拡散性が向上した。ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
実施例1と同様の方法であるが、微多孔層の目付を10g/m2、内部細孔体の平均厚さを10μmとした点のみ異なる方法によりガス拡散層を得たところ、ガス拡散性と導電性の両立性はさらに良好であり、発電性能はさらに良好であった。結果を表2に示す。
実施例4と同様の方法であるが、炭素シートの撥水処理で用いる撥水剤の量を減らし、面Yの繊維上フッ素/炭素比率を0.020としたガス拡散層を得たところ、撥水剤量のさらなる適正化により導電性が向上したため、ガス拡散性と導電性の両立性はさらに良好であり、発電性能はさらに良好であった。結果を表2に示す。
実施例5と同様の方法であるが、炭素シートの撥水処理で用いる撥水剤の量をさらに減らし、裏面繊維上フッ素/炭素比率を0.015としたガス拡散層を得たところ、撥水剤量のさらなる適正化によるさらなる導電性向上があり、ガス拡散性と導電性の両立性はきわめて良好であり、発電性能はきわめて良好であった。結果を表2に示す。
実施例6と同様の方法であるが、炭素シートを撥水剤に含侵させず、微多孔層前駆体塗液によって炭素シートを撥水処理することで、裏面繊維上フッ素/炭素比率を0.0050としたガス拡散層を得たところ、ガス拡散性と導電性の両立性はきわめて良好であり、発電性能はきわめて良好であった。結果を表2に示す。
<ガス拡散層の作製>に記載した方法において、炭素シートに内部細孔体前駆体塗液2を塗布し、乾燥後に微多孔層前駆体塗液1を塗布すること以外は、実施例7と同様の方法を用い、内部細孔体空隙率を80%としたガス拡散層を得たところ、空隙率の増大によりガス拡散性が向上した。ガス拡散性と導電性の両立性はきわめて良好であり、発電性能はきわめて良好であった。結果を表2に示す。
<ガス拡散層の作製>に記載した方法において、炭素シートに内部細孔体前駆体塗液3を塗布し、乾燥後に微多孔層前駆体塗液1を塗布すること以外は、実施例7と同様の方法を用い、内部細孔体空隙率を90%としたガス拡散層を得たところ、空隙率が増大した一方、内部細孔体の平均厚さが増大したために、実施例8と比べ、ガス拡散性は向上しなかったが、導電性が向上した。ガス拡散性と導電性の両立性はきわめて良好であり、発電性能はきわめて良好であった。結果を表2に示す。
<ガス拡散層の作製>に記載した方法において、炭素シートに内部細孔体前駆体塗液4を塗布し乾燥および炭化を行ったのち微多孔層前駆体塗液1を塗布すること以外は、実施例7と同様の方法を用いた上で、内部細孔体空隙率を91%としたガス拡散層を得たところ、表層密度が若干低下し、実施例9よりもガス拡散性が向上した。ガス拡散性と導電性の両立性はきわめて良好であり、発電性能はきわめて良好であった。結果を表2に示す。
炭素シート作製方法の変更を行った。まず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、厚み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。次に、この炭素シートを用いて実施例1と同様の方法でガス拡散層を得たところ、ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
炭素シートとして、実施例11で用いたものと同じ不織布を用い、かつ内部細孔体の目付を5g/m2としたこと以外、実施例9と同様の方法を用いてガス拡散層を得たところ、ガス拡散性と導電性の両立性はきわめて良好であり、発電性能はきわめて良好であった。結果を表2に示す。
実施例1と同様の方法であるが、内部細孔体の目付を5g/m2、微多孔層の目付を5g/m2としてガス拡散層を得たところ、高いガス拡散性が得られた一方、微多孔層目付低減により導電性がわずかに低下した。ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
実施例2と同様の方法であるが、微多孔層の目付を25g/m2に増やした一方、微多孔層前駆体塗布過程でのクリアランスを拡大し、内部細孔体の平均厚さを30μmとしたガス拡散層を得たところ、ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
実施例14と同様の方法であるが、実施例14と比べ、微多孔層前駆体塗液の塗布クリアランスを低減し、内部細孔体の平均厚さを26μmに増大させたガス拡散層を得たところ、ガス拡散性と導電性の両立性は良好であり、発電性能は良好であった。結果を表2に示す。
実施例1と比べ、微多孔層前駆体塗液の塗布クリアランスを低減し、内部細孔体の平均厚さを33μmとしたこと以外は実施例1と同じ方法でガス拡散層を得たところ、ガス拡散性と導電性の両立性は悪く、発電性能は低かった。結果を表2に示す。
実施例1と比べ、炭素シートの作製において炭素繊維目付けを29g/m2として、密度の高い炭素シート作製したこと以外は実施例1と同じ方法でガス拡散層を得たところ、ガス拡散性と導電性の両立性は悪く、発電性能は低かった。結果を表2に示す。
実施例1と比べ、微多孔層前駆体塗液を離型紙に目付け13g/m2で塗布し100℃の温度内で乾燥して得た微多孔層前駆体乾燥物を得た。その微多孔層前駆体乾燥物側を炭素シートに重ねて加圧し、120度の温度で離型紙を剥離することで微多孔層前駆体乾燥物を炭素シート上に転写し、大気中380℃の温度で10分間加熱してガス拡散層を得た。この方法により、内部細孔体の平均厚さは3μmと小さくなった。その他は実施例1と同じ方法でガス拡散層を得たところ、ガス拡散性と導電性の両立性は悪く、発電性能は低かった。結果を表2に示す。
1、1a、1b: 炭素シート
2: 面X(微多孔層側)
3: 面Y(セパレータ側)
4: 内部細孔体
5、5a、5b: 微多孔層
6、6a,6b: 触媒層
7: 電解質膜
11: 炭素シートの厚さ
12: 内部細孔体の厚さ
13: 微多孔層の厚さ
21: マスフローコントローラー
22: 配管A
23: バルブA
24: 圧力コントローラー
25: バルブB
26: 配管B
27: ガス室A
28: ガス拡散層
29: ガス室B
30: 配管C
31: ガス流量計
32: シール材
33: 窒素ガス
W: 幅方向
D: 奥行き方向
Claims (8)
- 炭素シートと、前記炭素シートの少なくとも片面に微多孔層と、を有するガス拡散層であって、
前記ガス拡散層における幅10mmかつ奥行き3mmの任意に選択される領域を、前記ガス拡散層の片側から面直方向に0.5MPaの圧力で圧縮したときに、ガス拡散層内部を面内方向に酸素が透過する「面内酸素透過係数」をAとし、
前記ガス拡散層の面直方向を2MPaで圧縮したときの「電気抵抗」をBとし、
Aから、Bに60を乗じた数を減じ、310を加えた数を「面内酸素透過係数と電気抵抗の両立性指標」Cとしたとき、
Cが0以上となる関係を満たす、ガス拡散層。 - 炭素シートと、前記炭素シートの少なくとも片面に微多孔層と、を有するガス拡散層であって、
前記炭素シートは、
細孔径10μm以上100μm以下の空隙を有する炭素繊維からなる領域と、
細孔径0.01μm以上10μm未満の内部細孔体で占められる領域とを有し、
内部細孔体は、前記炭素シート表面から面直方向に10μm以上30μm以下の平均厚さで存在する、請求項1に記載のガス拡散層。 - 前記内部細孔体の目付が3g/m2以上15g/m2以下である、請求項1または2に記載のガス拡散層。
- 前記炭素シートはフッ素系の撥水剤を含み、かつ、片面のみに微多孔層を有し、その逆側の面において、表面の炭素繊維上の、炭素元素数に対するフッ素元素数の比が0.002以上0.030以下である、請求項2または3に記載のガス拡散層。
- 前記内部細孔体の空隙率が80%以上95%以下である、請求項1~4のいずれかに記載のガス拡散層。
- 前記炭素シートの微多孔層を有する面から面直方向に20μmの位置までの範囲を表層としたとき、前記炭素シートの表層の密度が0.34g/cm3以上であり、かつ炭素シート全体の密度は0.29g/cm3以上0.33g/cm3以下である、請求項1~5のいずれかに記載のガス拡散層。
- 請求項1~6のいずれかに記載のガス拡散層を含む膜電極接合体。
- 請求項7に記載の膜電極接合体を含む燃料電池。
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