WO2019049934A1 - Gas diffusion layer base material for fuel cells, gas diffusion layer for fuel cells, and fuel cell - Google Patents

Gas diffusion layer base material for fuel cells, gas diffusion layer for fuel cells, and fuel cell Download PDF

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Publication number
WO2019049934A1
WO2019049934A1 PCT/JP2018/033054 JP2018033054W WO2019049934A1 WO 2019049934 A1 WO2019049934 A1 WO 2019049934A1 JP 2018033054 W JP2018033054 W JP 2018033054W WO 2019049934 A1 WO2019049934 A1 WO 2019049934A1
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Prior art keywords
diffusion layer
gas diffusion
fuel cell
carbonaceous
fiber
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PCT/JP2018/033054
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French (fr)
Japanese (ja)
Inventor
貴弘 松村
俊克 円城寺
良平 岩原
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東洋紡株式会社
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Priority to JP2019540997A priority Critical patent/JPWO2019049934A1/en
Publication of WO2019049934A1 publication Critical patent/WO2019049934A1/en

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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
    • 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
    • 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 substrate and the like used in a fuel cell.
  • Fuel cells include solid polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), alkaline fuel cells (AFCs), solid oxide fuel cells (SOFCs), molten carbonate fuel cells (MCFC) are known.
  • PEFC has the advantages of low temperature operation and high power density, and is being applied to portable portable power sources, mobile devices such as notebook computers, and power sources for automotive power.
  • a catalyst or a carbon material having a catalyst is generally disposed on both sides of a proton conductive solid electrolyte membrane, and a gaseous fuel such as gaseous oxygen or hydrogen which is an oxidizing agent is further supplied and the function as an electrode is realized.
  • a gas diffusion layer (GDL) is provided on each catalyst surface.
  • an electrode reaction proceeds at the interface where catalyst / solid electrolyte / gas (oxidant or fuel) contacts.
  • the solid electrolyte needs to be maintained in a wet state in order to develop sufficient proton conductivity. Therefore, the catalyst layer and GDL require gas permeability (gas supply) and moisture retention (wettability maintenance of the solid electrolyte) in the thickness direction, and the water generated at the positive electrode is appropriately discharged to prevent clogging. It is required to have hydrophobicity to
  • Patent Document 1 discloses a fuel cell catalyst layer capable of effectively suppressing both of the dry-up on the anode side electrode and the flooding on the cathode side electrode, and a method of manufacturing the same.
  • a porous material having conductivity is generally used, and in particular, a sheet material such as non-woven fabric or woven fabric made of a carbon material is used from the viewpoint of conductivity and chemical stability.
  • a sheet material such as non-woven fabric or woven fabric made of a carbon material is used from the viewpoint of conductivity and chemical stability.
  • PTFE polytetrafluoroethylene
  • Patent Documents 3 to 5 disclose improvement of drainage characteristics by creating a pattern in which the degree of hydrophobization is changed in the surface direction of GDL, and changing the degree of hydrophobization in the thickness direction. There is.
  • a hydrophilized layer is formed by a sputtering method using at least one selected from the group consisting of metals, metal nitrides, metal carbides and metal oxides as a target, or plating of metals. Methods of forming are disclosed.
  • Japanese Patent Laid-Open Publication No. 2010-165622 Japanese Patent Laid-Open Publication No. 2010-176948 Japanese Patent Laid-Open Publication No. 2011-76739 Japanese Patent Laid-Open Publication No. 2010-61984 Japanese Patent Laid-Open Publication No. 2009-218161 Japanese Patent Laid-Open Publication No. 2010-129393
  • the present invention has been made in view of the above problems, and an object thereof is to provide a fuel cell gas diffusion layer base material or the like which can control moisture retention without raising resistance.
  • the structure of the gas diffusion layer base material for a fuel cell according to the present invention which has solved the above-mentioned problems, is as follows.
  • a gas diffusion layer substrate for a fuel cell characterized by satisfying the following requirements.
  • the particle size of the carbon particle (B) is 20 ⁇ m or less
  • the mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) is 35% or more.
  • the number of bonded oxygen atoms on the surface of the gas diffusion layer substrate for the fuel cell is 1% or more of the total number of carbon atoms on the surface of the gas diffusion layer substrate for the fuel cell.
  • a fuel cell gas diffusion layer comprising the fuel cell gas diffusion layer substrate according to any one of the above 1 to 3. 5. The fuel cell using the gas diffusion layer for fuel cells as described in said 4th.
  • the conductive porous material is rendered hydrophilic and the conductive auxiliary particles are added to provide a gas diffusion layer for fuel cell having good air permeability and hydrophilicity and excellent conductivity.
  • a substrate can be obtained.
  • the present inventors conducted studies using carbon particles in providing a gas diffusion layer base material for a fuel cell, which has air permeability and hydrophilicity and is excellent in conductivity. As a result, it was found that low resistance can be obtained by filling the gaps between the fibers and assisting the conductivity without reducing the steric hindrance and using the carbon particles having a small particle diameter without impairing the air permeability. .
  • carbon particles satisfying the following requirement (1) are adopted as the carbon particles.
  • the particle size of the carbon particles (B) is 20 ⁇ m or less.
  • a binding carbonaceous material that binds both the carbonaceous fiber (A) and the carbon particles (B) is used within the range of the following (2) .
  • the mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) is 35% or more.
  • binding both the carbonaceous fiber (A) and the carbon particle (B) means that the carbonaceous material used in the present invention acts as a binder for the carbonaceous fiber and the carbon particle )
  • the carbonaceous material used in the present invention acts as a binder for the carbonaceous fiber and the carbon particle
  • the carbonaceous material used in the present invention acts as a binder for the carbonaceous fiber and the carbon particle
  • the surface and the inside of the carbonaceous fibers and carbon particles are strongly bound by the carbonaceous material, and the carbon can be viewed as a whole of the gas diffusion layer substrate It means that the surface of the carbon particle is configured to be exposed while the carbonaceous fiber is covered by the quality material.
  • the carbonaceous material after binding is not in the form of a film.
  • does not become a coated state means that the carbonaceous material (C) does not form a webbed state like a total foot (boxok) or a foot between fibers of the carbonaceous fiber (A). In the case of a coated state, the gas permeability deteriorates.
  • the carbonaceous material strongly bonds between the carbonaceous fibers through the carbon particles, thereby forming an efficient conductive path between the carbon particles and the carbonaceous fiber. It is necessary for the formation of the conductive path to increase the content ratio of the carbonaceous material to the total amount of the carbonaceous fiber, the carbon particles and the carbonaceous material, so in the present invention, the above content is 14.5% or more. Do.
  • the gas diffusion layer base material for a fuel cell of the present invention satisfies the following requirement (3).
  • the number of bonded oxygen atoms on the surface of the gas diffusion layer substrate for a fuel cell is 1% or more of the total number of carbon atoms on the surface of the gas diffusion layer substrate for a fuel cell.
  • oxygen atoms can be introduced into the edge surface of carbon and the defect structure portion.
  • the introduced oxygen atom is generated as a reactive group such as a carbonyl group, a quinone group, a lactone group, or a free radical oxide, these reactive groups are water molecules It is possible to obtain the moisture-retaining property of the entire gas diffusion layer.
  • the fuel cell gas diffusion layer substrate of the present invention is configured as described above, a gas diffusion layer substrate having gas permeability and hydrophilicity and excellent conductivity can be obtained.
  • the gas diffusion layer base material for a fuel cell of the present invention is a gas diffusion layer base material comprising a carbonaceous fiber as a base material and supporting carbon particles with a carbonaceous material, and the above (1) to (3) Satisfy the requirements of
  • a carbonaceous fiber is a fiber obtained by heating and carbonizing a precursor of an organic fiber (details will be described later), and means a fiber composed of 90% or more by mass of carbon (JIS L) 0204-2).
  • Precursors of organic fibers as raw materials of carbonaceous fibers include acrylic fibers such as polyacrylonitrile; phenol fibers; PBO fibers such as polyparaphenylene benzobisoxazole (PBO); aromatic polyamide fibers; isotropic pitch, anisotropy Pitch fibers, pitch fibers such as mesophase pitch; cellulose fibers; etc. can be used.
  • acrylic fiber from the viewpoint of being excellent in strength and elastic modulus, acrylic fiber, phenol fiber, cellulose fiber, isotropic pitch fiber and anisotropic pitch fiber are preferable as the organic fiber precursor, and acrylic fiber is more preferable.
  • the acrylic fiber is not particularly limited as long as it contains acrylonitrile as a main component, but the content of acrylonitrile in the raw material monomer forming the acrylic fiber is preferably 95% by mass or more, and 98% by mass or more It is more preferable that
  • the mass average molecular weight of the organic fiber is not particularly limited, but is preferably 10000 or more and 100000 or less, more preferably 15000 or more and 80000 or less, and still more preferably 20000 or more and 50000 or less.
  • the mass average molecular weight can be measured by gel permeation chromatography (GPC), solution viscosity, or the like.
  • the average fiber diameter of the carbonaceous fiber is preferably 0.5 to 40 ⁇ m. If the average fiber diameter is smaller than 0.5 ⁇ m, the air permeability will deteriorate. On the other hand, if the average fiber diameter is larger than 40 ⁇ m, the carbon amount per unit area decreases, and the electrical area resistance increases. It is more preferably 3 to 20 ⁇ m in consideration of the balance between liquid permeability and resistance.
  • the structure of the above-mentioned carbonaceous fiber as a base material, whereby the strength is improved and the handling and the processability become easy.
  • a spun yarn, a filament collected yarn, a nonwoven fabric, a knitted fabric, a woven fabric, a special knitted fabric or carbon described in JP-A-63-200467 etc. which is a sheet-like material comprising carbonaceous fibers
  • the paper etc. which consist of fibers can be mentioned.
  • non-woven fabric made of carbonaceous fiber, knitted fabric, woven fabric, special woven fabric, and paper made of carbon fiber are more preferable from the viewpoint of handling, processability, manufacturability and the like.
  • the average fiber length is preferably 30 to 100 mm.
  • the average fiber length is preferably 5 to 30 mm. By setting it in said range, a uniform fiber structure is obtained.
  • the above-mentioned carbonaceous fiber is obtained by subjecting a precursor of an organic fiber to a carbonization treatment, but it is preferable that the above-mentioned "heat carbonization treatment" includes at least a flameproofing step and a carbonization step.
  • the carbonization step does not necessarily need to be performed after the flameproofing step as described above, and after the graphite particles and the carbonaceous material are attached to the flameproofed fiber as described in the examples described later.
  • a carbonization process may be performed, and in this case, the carbonization process after the oxidization process can be omitted.
  • the above-mentioned flameproofing step means a step of heating the precursor of the organic fiber preferably at a temperature of 180 ° C to 350 ° C in an air atmosphere to obtain a flameproofed organic fiber.
  • the heat treatment temperature is more preferably 190 ° C. or more, and still more preferably 200 ° C. or more.
  • it is preferable that it is 330 degrees C or less, and it is more preferable that it is 300 degrees C or less.
  • the organic fibers may be thermally shrunk and the molecular orientation may collapse during the flameproofing step, and the conductivity of the carbonaceous fibers may be reduced, it is preferable to flameproof the organic fibers under tension or stretching. It is more preferable to flameproof treatment under tension.
  • the flame-resistant organic fiber obtained as described above is preferably heated at a temperature of 1000 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere) to obtain a carbonaceous fiber It means a process.
  • the heating temperature is more preferably 1100 ° C. or more, further preferably 1200 ° C. or more. Moreover, More preferably, it is 1900 degrees C or less.
  • the heating temperature in the carbonization step can be selected according to the type of organic fibers used as the raw material.
  • the heating temperature is preferably 800 ° C. or more and 2000 ° C. or less, and more preferably 1000 ° C. or more and 1800 ° C. or less.
  • the temperature rising rate when raising the temperature from the flameproofing temperature to the carbonization temperature is preferably 20 ° C./min or less, and more preferably. Preferably it is 15 degrees C / min.
  • the lower limit of the temperature rising rate is preferably 5 ° C./min or more in consideration of mechanical properties and the like.
  • Carbon particle (B) The carbon particles in the present invention are useful for improving the conductivity and realizing low resistance.
  • the present invention in order to secure air permeability, one satisfying the above (1) was used.
  • the particle size of the carbon particles used in the present invention is 20 ⁇ m or less, preferably 1 ⁇ m or less, as defined in the above (1). If the particle size exceeds 20 ⁇ m, the carbon particles can not be well dispersed in the carbonaceous material attached near the intersection of the fiber intersections, and the conductivity can not be improved.
  • the “particle size” means an average particle size (D50) at a median 50% diameter in a particle size distribution obtained by a dynamic light scattering method or the like. Commercially available carbon particles may be used, and in that case, the particle size described in the catalog can be adopted.
  • the carbon particles used in the present invention are not particularly limited as long as they have conductivity, and known or commercially available materials can be used.
  • carbon black such as channel black, furnace black, ketjen black, acetylene black, lamp black, etc .; graphite; activated carbon etc. may be mentioned. These can be used alone or in combination of two or more.
  • the fuel cell gas diffusion layer of the present invention can improve the conductivity of the fuel cell gas diffusion layer by containing such conductive carbon particles.
  • the content of carbon particles used in the present invention is 5% or more by mass ratio to the total amount of the above-mentioned carbonaceous fiber (A), carbon particle (B) and carbonaceous material (C) described later
  • 10% or more is more preferable.
  • the carbon particles become bound with the carbonaceous material, and the resistance is reduced.
  • the upper limit is preferably about 90% or less.
  • content of the carbonaceous fiber (A) used for calculation of said content is content of the said structure, when using structures, such as a nonwoven fabric, as a base material.
  • the mass ratio of the carbonaceous material (C) described later to the carbon particles (B) is preferably 0.2 or more and 5.0 or less, and more preferably equivalent.
  • the carbon particles are frequently detached, and the carbon particles are not sufficiently bound to the carbonaceous material.
  • the above ratio exceeds 5.0, the carbon particles are not connected to each other, and the conductivity can not be improved.
  • the carbonaceous material is added as a binding agent (binder) for strongly binding the carbonaceous fiber which can not be bound originally and the carbon particles other than the graphite particles.
  • the content of the carbonaceous material (C) used in the present invention is the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) described above as defined in (3) above. 35% or more by mass ratio with respect to, and 38% or more is more preferable.
  • the upper limit thereof is preferably about 90% or less in consideration of air permeability and the like.
  • the type of the carbonaceous material (C) used in the present invention may be any type as long as it can bind the carbonaceous fiber (A) and the carbon particles (B).
  • the fuel cell gas of the present invention It is not particularly limited as long as it exhibits binding property at the time of carbonization at the time of preparation of the diffusion layer base material.
  • pitches such as coal tar pitch and coal pitch
  • phenol resin benzoxazine resin, epoxide resin, furan resin, vinyl ester resin, melanin-formaldehyde resin, urea-formaldehyde resin, resorcinol-formaldehyde Resins such as resins, cyanate ester resins, bismaleimide resins, polyurethane resins, polyacrylonitrile, etc .
  • furfuryl alcohol rubbers such as acrylonitrile-butadiene rubber and the like.
  • a commercial item may be used for these.
  • pitches such as coal tar pitch and coal-based pitch which are easily crystalline are preferable because the target carbonaceous material (C) can be obtained at a low firing temperature.
  • a phenolic resin is also preferably used because the degree of increase and decrease in crystallinity is small depending on the calcination temperature and the crystallinity can be easily controlled.
  • polyacrylonitrile resin is also preferably used because the target carbonaceous material (C) can be obtained by raising the firing temperature. Particularly preferred are pitches.
  • pitches which are particularly preferably used will be described in detail.
  • the content of the mesophase phase liquid crystal phase
  • the content of the mesophase phase can be controlled by the temperature and time of the infusibilization treatment. If the content of the mesophase is small, a relatively low temperature melts or a liquid state at room temperature is obtained. On the other hand, if the content of the mesophase phase is high, it melts at high temperature and a carbonization yield is high.
  • the content of the mesophase phase is preferably high (ie, the carbonization ratio is high), for example, 30% or more is preferable, and 50% or more is more preferable.
  • the upper limit thereof is preferably, for example, 90% or less in consideration of expression of binding property and the like.
  • the melting point of the pitch is preferably 100 ° C. or more, and more preferably 200 ° C. or more.
  • the upper limit thereof is preferably, for example, 350 ° C. or less in consideration of expression of binding property and the like.
  • the number of bonded oxygen atoms on the surface of the fuel cell gas diffusion layer substrate satisfies 1% or more of the total number of carbon atoms on the surface of the fuel cell gas diffusion layer substrate.
  • the ratio of the number of bonded oxygen atoms to the total number of carbon atoms may be abbreviated as O / C.
  • O / C can be measured by surface analysis such as X-ray photoelectron spectroscopy (XPS) or X-ray fluorescence analysis.
  • the O / C of which is controlled to 1% or more the hydrophilicity is enhanced, and a water flow rate (preferably 0.5 mm / sec or more) described later can be secured.
  • the fuel cell gas diffusion layer base material having a low oxygen concentration with an O / C of less than 1% is used, the hydrophilicity of the fuel cell gas diffusion layer base material surface becomes small, and the generated water can flow Can not raise. As a result, when incorporated into a cell, problems such as flooding occur.
  • the fuel cell gas diffusion layer substrate of the present invention is excellent in hydrophilicity.
  • the hydrophilicity can be confirmed by the water flow rate when a water droplet is dropped after dry oxidation treatment of the fuel cell gas diffusion layer substrate.
  • the water flow rate of the fuel cell gas diffusion layer substrate according to the present invention is preferably 0.5 mm / sec or more. Thereby, it can be judged that it has sufficient affinity to generated water.
  • the water flow rate of the fuel cell gas diffusion layer substrate is preferably as high as possible, more preferably 1 mm / sec or more, still more preferably 5 mm / sec or more, and still more preferably 10 mm / sec or more.
  • the weight per unit area of the gas diffusion layer base material for fuel cells of the present invention is preferably 50 to 500 g / m 2 and more preferably 100 to 400 g / m 2 when used in 0.3 to 3 mm when assembled in a cell. .
  • non-woven fabric or paper which has been flat-processed on one side as the gas diffusion layer substrate for a fuel cell of the present invention.
  • any known method can be applied, for example, a method of applying and drying a slurry on one side of a carbonaceous fiber; and a method of impregnating and drying on a smooth film such as PET.
  • the gas diffusion layer base material for a fuel cell of the present invention comprises a carbon fiber, a carbonization step, a graphitization step, oxidation after attaching carbon particles and a precursor of carbon material (before carbonization) to a carbonaceous fiber (base material). It can be manufactured through processing steps. In each step, known methods can be optionally applied.
  • Step of attaching carbon particles and precursor of carbonaceous material to carbonaceous fiber First, carbon particles and a precursor of a carbonaceous material are attached to the carbonaceous fiber.
  • any known method can be adopted.
  • the above-mentioned carbonaceous material precursor may be heated and melted, graphite particles may be dispersed in the obtained melt, the carbonaceous fiber may be immersed in the melt dispersion, and then cooled to room temperature.
  • the above-mentioned carbonaceous material precursor and carbon particles are added to a solvent such as water or alcohol to which a binder (temporary adhesive) which disappears upon carbonization, such as polyvinyl alcohol, is added.
  • a method of heating and drying can be used.
  • excess liquid among the above-mentioned melt dispersion liquid and dispersion liquid in which the carbonaceous fiber is immersed is squeezed out excess dispersion liquid when immersed in the dispersion liquid by passing it through a nip roller provided with a predetermined clearance,
  • the surface of excess dispersion when immersed in the dispersion with a doctor blade or the like can be removed by a method such as scraping.
  • the carbonization step is carried out to calcine the product after attachment obtained in the above step. As a result, the carbonaceous fibers are bound via the carbon particles.
  • it is preferable to sufficiently remove the decomposition gas at the time of carbonization and for example, it is preferable to heat at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere).
  • the heating temperature is more preferably 1000 ° C. or higher, still more preferably 1200 ° C. or higher, still more preferably 1300 ° C. or higher, and further preferably 1500 ° C. or lower, even more preferably 1400 ° C. or lower.
  • the treatment corresponding to the carbonization step may be performed after the stabilization of the fibers, but the carbonization treatment performed after the stabilization of the fibers may be omitted. That is, the method of producing the gas diffusion layer substrate for a fuel cell of the present invention is roughly classified into the following method 1 and method 2.
  • Method 1 Flame resistance of fiber ⁇ carbonization of fiber ⁇ adhesion of graphite particles and carbonaceous material ⁇ carbonization ⁇ graphitization ⁇ oxidation ⁇
  • Method 2 flame resistance of fiber ⁇ carbon particles other than graphite particles and carbon material Attachment ⁇ carbonization ⁇ graphitization ⁇ oxidation According to method 1 above, although processing cost increases because carbonization is performed twice, the sheet used as a gas diffusion layer base material for fuel cells is affected by the difference in volume contraction ratio Since it is hard to be received, there is an advantage that the obtained sheet is hard to be deformed (warpage occurrence).
  • the processing cost can be reduced because the carbonization step may be performed once, the sheet obtained is easily deformed due to the difference in volume contraction ratio at the time of carbonization of each material.
  • Which one of the above methods 1 and 2 is adopted may be appropriately determined in consideration of these.
  • the graphitization step is a step carried out to sufficiently enhance the crystallinity of the carbonaceous material, to improve the electron conductivity, and to improve the oxidation resistance to the oxidation-reduction reaction in the fuel cell and the like.
  • heating is preferably performed at a temperature of 1300 ° C. or more in an inert atmosphere (preferably under a nitrogen atmosphere), more preferably 1500 ° C. or more.
  • the upper limit thereof is preferably 2000 ° C. or less in consideration of providing the carbonaceous material with high electrolytic solution affinity.
  • an oxidation treatment step is further carried out to form an oxygen functional group such as a hydroxyl group, a carbonyl group, a quinone group, a lactone group, and a free radical oxide on the surface of the gas diffusion layer base material for fuel cells. Will be introduced. As a result, the above-mentioned O / C ratio O1% can be achieved. These oxygen functional groups greatly contribute to the water flow rate.
  • the dry oxidation treatment step means a step of heating (oxidation treatment) in an air atmosphere, for example, at 500 ° C. or more and 900 ° C. or less.
  • the heating temperature is more preferably 600 ° C. or more, and still more preferably 650 ° C. or more, in order to effectively exert the effect of the introduction of the oxygen functional group.
  • 800 degrees C or less is more preferable, and 750 degrees C or less is further more preferable.
  • the mass yield of the fuel cell gas diffusion layer substrate before and after oxidation treatment is 90% or more and 96% or less. It is preferable to adjust. This can be adjusted, for example, by a method such as adjusting the processing time and temperature of dry air oxidation appropriately.
  • Mass Content In the following Examples and Comparative Examples, the mass content was roughly calculated as follows. (i) Only the base material is fired to determine its mass. (ii) A carbonaceous material and carbon particles are attached to a base material, and the mass after firing is determined. (iii) Subtract (i) from (ii) to determine the attached mass of carbonaceous material and carbon particles. (iv) The attachment mass of (iii) is distributed by the ratio of the mass of the carbonaceous material and the carbon particles in the attachment liquid used for the attachment of (iii). (v) The mass content is determined from (i) and (iv). However, when the carbonaceous material and carbon particles lose their mass in firing, the ratio in (iv) is changed accordingly.
  • Example 1 First, 1.8% by mass of Leodol TW-L120 (non-ionic surfactant) manufactured by Kao Corporation, 1.8% by mass of polyvinyl alcohol (temporary adhesive material) in ion exchange water, MCP 250 (carbon manufactured by JFE Chemical Co., Ltd.) 14% by mass, and 9.8% by mass of graphite particles having a particle diameter of 9 ⁇ m as carbon particles were added, and the mixture was stirred for 1 hour with a mechanical stirrer to obtain a dispersion.
  • Leodol TW-L120 non-ionic surfactant
  • polyvinyl alcohol temporary adhesive material
  • MCP 250 carbon manufactured by JFE Chemical Co., Ltd.
  • carbon paper (CFP-030-PE, manufactured by Nippon Polymer Industries, 30 g / m 2 , 0.51 mm thickness) made of polyacrylonitrile fiber (average fiber diameter 10 ⁇ m) is immersed After passing, it was passed through a nip roller to remove excess dispersion. Next, it was dried at 150 ° C. for 20 minutes in an air atmosphere, and then calcined (carbonized) at 1000 ° C. for 1 hour and further at 2000 ° C. for 1 hour in a nitrogen atmosphere. After firing, oxidation treatment was performed at 700 ° C. for 20 minutes in an air atmosphere to obtain a fuel cell gas diffusion layer substrate having a thickness of 0.51 mm and a basis weight of 149.0 g / m 2 .
  • Example 1 A gas diffusion layer substrate for a fuel cell having a thickness of 0.50 mm and a basis weight of 153.0 g / m 2 is obtained in the same manner as in Example 1 except that graphite particles having a particle diameter of 24 ⁇ m are used as carbon particles.
  • Example 1 is the same as Example 1 except that 3 mass% of MCP 250 (carbonaceous material) manufactured by JFE Chemical Co., Ltd. and 2.1 mass% of graphite particles having a particle diameter of 9 ⁇ m as carbon particles are added.
  • Example 3 A gas diffusion layer base material for a fuel cell having a thickness of 0.56 mm and a basis weight of 160.0 g / m 2 was obtained in the same manner as in Example 1 except that the oxidation treatment after firing was not performed in Example 1.
  • Table 1 shows the measurement results of various items in Example 1 and Comparative Examples 1 to 3 above.
  • Example 1 is a gas diffusion layer base material for a fuel cell satisfying the requirements of the present invention, and a gas diffusion layer base material for a fuel cell having water permeability and low resistance was obtained.
  • Comparative Example 1 the carbon particles were too large to be well dispersed in the carbonaceous material attached near the intersection of the fiber intersections because the carbon particles were too large, and the conductivity could not be improved. .
  • the comparative example 2 is an example with little content of carbon particles other than graphite, and resistance increased. It is considered that the electron conduction path becomes insufficient as the content of the carbon particles decreases.
  • Comparative Example 3 is an example in which the ratio of O / C is small, and water was not passed. This is considered to be due to the fact that the amount of oxygen functional group is small and the affinity with generated water is lower than in Example 1.
  • a fuel cell gas diffusion layer substrate capable of controlling the moisture retention without raising the resistance by imparting hydrophilicity to the conductive porous material and adding the conductive auxiliary particles
  • the fuel cell gas diffusion layer base material of the present invention is suitably used not only for fuel cells, but also for carbon monoxide sensors utilizing the structure of fuel cells, NOx decomposition filters, and the like.

Abstract

This gas diffusion layer base material for fuel cells is composed of (A) carbonaceous fibers, (B) graphite particles, and (C) a carbonaceous material that bonds the carbonaceous fibers and the graphite particles with each other, and satisfies the following requirements. (1) The carbon particles (B) have a particle diameter of 20 μm or less. (2) The mass content of the carbonaceous material (C) relative to the total mass of the carbonaceous fibers (A), the carbon particles (B) and the carbonaceous material (C) is 35% or more. (3) The number of bonded oxygen atoms in the surface of this gas diffusion layer base material for fuel cells is 1% or more of the total number of carbon atoms in the surface of this gas diffusion layer base material for fuel cells.

Description

燃料電池用ガス拡散層基材、燃料電池用ガス拡散層、燃料電池Fuel cell gas diffusion layer base material, fuel cell gas diffusion layer, fuel cell
　本発明は、燃料電池で用いられるガス拡散層基材等に関する。 The present invention relates to a gas diffusion layer substrate and the like used in a fuel cell.
　近年、エネルギー効率および排出ガスの観点から燃料電池を用いた発電方法が注目されている。燃料電池には、固体高分子電解質型燃料電池（ＰＥＦＣ）、リン酸型燃料電池（ＰＡＦＣ）、アルカリ型燃料電池（ＡＦＣ）、固体酸化物型燃料電池（ＳＯＦＣ）、溶融炭酸塩型燃料電池（ＭＣＦＣ）など複数の方法が知られている。このうちＰＥＦＣは、低温作動と高出力密度という利点を有しており、可搬式のポータブル電源、ノートコンピューターなどのモバイル機器、自動車の動力用電源などへの適用が進められている。 In recent years, a power generation method using a fuel cell has attracted attention from the viewpoint of energy efficiency and exhaust gas. Fuel cells include solid polymer electrolyte fuel cells (PEFCs), phosphoric acid fuel cells (PAFCs), alkaline fuel cells (AFCs), solid oxide fuel cells (SOFCs), molten carbonate fuel cells ( Several methods such as MCFC) are known. Among them, PEFC has the advantages of low temperature operation and high power density, and is being applied to portable portable power sources, mobile devices such as notebook computers, and power sources for automotive power.
　ＰＥＦＣは一般的にプロトン導電性の固体電解質膜の両面に、触媒または触媒を有した炭素材料を配置し、さらに酸化剤である気体酸素、水素等の気体燃料を供給するとともに電極としての機能を有したガス拡散層（ＧＤＬ）が各々の触媒面に配置されている。 In PEFC, a catalyst or a carbon material having a catalyst is generally disposed on both sides of a proton conductive solid electrolyte membrane, and a gaseous fuel such as gaseous oxygen or hydrogen which is an oxidizing agent is further supplied and the function as an electrode is realized. A gas diffusion layer (GDL) is provided on each catalyst surface.
　ＰＥＦＣにおいては、触媒／固体電解質／ガス（酸化剤または燃料）が接触する界面で電極反応が進行する。固体電解質は十分なプロトン伝導性を発現するため湿潤状態を維持することが必要である。したがって触媒層やＧＤＬには厚み方向への気体透過性（ガス供給）及び保湿性（固体電解質の湿潤性維持）が必要であり、さらには正極で生じた水分を適度に排出し、閉塞を防止するための疎水性を有することが求められる。 In PEFC, an electrode reaction proceeds at the interface where catalyst / solid electrolyte / gas (oxidant or fuel) contacts. The solid electrolyte needs to be maintained in a wet state in order to develop sufficient proton conductivity. Therefore, the catalyst layer and GDL require gas permeability (gas supply) and moisture retention (wettability maintenance of the solid electrolyte) in the thickness direction, and the water generated at the positive electrode is appropriately discharged to prevent clogging. It is required to have hydrophobicity to
　例えば特許文献１には、アノード側電極におけるドライアップとカソード側電極におけるフラッティングの双方を効果的に抑制することのできる燃料電池用触媒層とその製造方法が開示されている。 For example, Patent Document 1 discloses a fuel cell catalyst layer capable of effectively suppressing both of the dry-up on the anode side electrode and the flooding on the cathode side electrode, and a method of manufacturing the same.
　ＧＤＬは一般的に導電性を有する多孔質材料が用いられ、特に導電性や化学的な安定性の観点から炭素材料からなる不織布、織物などのシート状物が用いられる。これらの多孔質材料に疎水性を与えるために、特許文献２には、ポリテトラフルオロエチレン（ＰＴＦＥ）ディスパージョンを多孔質材料に浸透させた後に熱分解により界面活性剤を除去するとともに溶融固着させる方法が開示されている。 As GDL, a porous material having conductivity is generally used, and in particular, a sheet material such as non-woven fabric or woven fabric made of a carbon material is used from the viewpoint of conductivity and chemical stability. In order to impart hydrophobicity to these porous materials, according to Patent Document 2, after the polytetrafluoroethylene (PTFE) dispersion is infiltrated into the porous material, the surfactant is removed by thermal decomposition and the melt fixing is carried out. A method is disclosed.
　また、特許文献３～５には、ＧＤＬの面方向において疎水化度を変化させたパターンを作成すること、厚み方向に対して疎水化度を変化させることにより、排水特性の向上が開示されている。 Further, Patent Documents 3 to 5 disclose improvement of drainage characteristics by creating a pattern in which the degree of hydrophobization is changed in the surface direction of GDL, and changing the degree of hydrophobization in the thickness direction. There is.
　ＧＤＬの基材となる導電性多孔質材料への疎水性を与える技術は数多く発表されているものの、保湿性すなわち親水性を与える技術は数が少ない。 Although a large number of techniques have been disclosed to impart hydrophobicity to the conductive porous material that is the basis of GDL, there are few techniques to impart moisture retention or hydrophilicity.
　ここで、特許文献６には、金属、金属窒化物、金属炭化物及び金属酸化物よりなる群から選択される１種以上をターゲットとするスパッタ法、または、金属のメッキ処理によって、親水化層を形成する方法が開示されている。 Here, in Patent Document 6, a hydrophilized layer is formed by a sputtering method using at least one selected from the group consisting of metals, metal nitrides, metal carbides and metal oxides as a target, or plating of metals. Methods of forming are disclosed.
日本国特許公開公報「特開２０１０－１６５６２２号」Japanese Patent Laid-Open Publication No. 2010-165622 日本国特許公開公報「特開２０１０－１７６９４８号」Japanese Patent Laid-Open Publication No. 2010-176948 日本国特許公開公報「特開２０１１－７６７３９号」Japanese Patent Laid-Open Publication No. 2011-76739 日本国特許公開公報「特開２０１０－６１９８４号」Japanese Patent Laid-Open Publication No. 2010-61984 日本国特許公開公報「特開２００９－２１８１６１号」Japanese Patent Laid-Open Publication No. 2009-218161 日本国特許公開公報「特開２０１０－１２９３９３号」Japanese Patent Laid-Open Publication No. 2010-129393
　しかし、スパッタ法では拡散による回りこみが発生しないため、シート表面近傍が親水化されるのみである。またメッキ法では、貴金属を使用しコストが高くなる懸念がある。 However, in the sputtering method, since wraparound due to diffusion does not occur, only the vicinity of the sheet surface is hydrophilized. In addition, in the plating method, there is a concern that the use of a noble metal may increase the cost.
　上記したように、燃料電池の普及を進めるためには、更なる低抵抗化及び気体透過性及び保湿性が必要である。 As described above, in order to promote the spread of fuel cells, it is necessary to further reduce resistance and gas permeability and moisture retention.
　本発明は上記課題に鑑みてなされたものであり、その目的は、抵抗を上昇させることなく、保湿性を制御することが可能な燃料電池用ガス拡散層基材等を提供することにある。 The present invention has been made in view of the above problems, and an object thereof is to provide a fuel cell gas diffusion layer base material or the like which can control moisture retention without raising resistance.
　上記課題を解決し得た本発明に係る燃料電池用ガス拡散層基材の構成は以下のとおりである。 The structure of the gas diffusion layer base material for a fuel cell according to the present invention, which has solved the above-mentioned problems, is as follows.
１．炭素質繊維（Ａ）と、炭素粒子（Ｂ）と、これらを結着する炭素質材料（Ｃ）と、からなり、
　下記の要件を満足することを特徴とする燃料電池用ガス拡散層基材。
（１）前記炭素粒子（Ｂ）の粒径は２０μｍ以下、
（２）前記炭素質繊維（Ａ）、前記炭素粒子（Ｂ）、および前記炭素質材料（Ｃ）の合計量に対する前記炭素質材料（Ｃ）の質量含有率は３５％以上、
（３）燃料電池用ガス拡散層基材表面の結合酸素原子数が燃料電池用ガス拡散層基材表面の全炭素原子数の１％以上
２．前記炭素粒子（Ｂ）に対する前記炭素質材料（Ｃ）の質量比が０．２～５．０である上記１に記載の燃料電池用ガス拡散層基材。
３．水滴を垂らした時の通水速度が０．５ｍｍ/ｓｅｃ以上である上記１または２に記載の燃料電池用ガス拡散層基材。
４．上記１～３のいずれかに記載の燃料電池用ガス拡散層基材を用いた燃料電池用ガス拡散層。
５．上記４に記載の燃料電池用ガス拡散層を用いた燃料電池。 1. It consists of a carbonaceous fiber (A), carbon particles (B), and a carbonaceous material (C) binding these,
A gas diffusion layer substrate for a fuel cell characterized by satisfying the following requirements.
(1) The particle size of the carbon particle (B) is 20 μm or less,
(2) The mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) is 35% or more.
(3) The number of bonded oxygen atoms on the surface of the gas diffusion layer substrate for the fuel cell is 1% or more of the total number of carbon atoms on the surface of the gas diffusion layer substrate for the fuel cell. The fuel cell gas diffusion layer substrate according to the above 1, wherein the mass ratio of the carbonaceous material (C) to the carbon particles (B) is 0.2 to 5.0.
3. 3. The gas diffusion layer substrate for a fuel cell according to the above 1 or 2, wherein the water flow rate when dripping water droplets is 0.5 mm / sec or more.
4. A fuel cell gas diffusion layer comprising the fuel cell gas diffusion layer substrate according to any one of the above 1 to 3.
5. The fuel cell using the gas diffusion layer for fuel cells as described in said 4th.
　本発明の上記構成により、導電性多孔質材料に親水性を付与し、導電補助粒子を加えることで、良好な通気性と親水性を有し、かつ導電性に優れた燃料電池用ガス拡散層基材を得ることができる。 According to the above configuration of the present invention, the conductive porous material is rendered hydrophilic and the conductive auxiliary particles are added to provide a gas diffusion layer for fuel cell having good air permeability and hydrophilicity and excellent conductivity. A substrate can be obtained.
　本発明者らは、通気性と親水性とを有し、かつ導電性に優れた燃料電池用ガス拡散層基材を提供するに当たり、炭素粒子を用いて検討を行なった。その結果、粒径が小さい炭素粒子を用いれば立体的な障害も少なく、通気性を損なうことなく、繊維間の空隙を埋めて導電性を補助することで、低抵抗が得られることが判明した。 The present inventors conducted studies using carbon particles in providing a gas diffusion layer base material for a fuel cell, which has air permeability and hydrophilicity and is excellent in conductivity. As a result, it was found that low resistance can be obtained by filling the gaps between the fibers and assisting the conductivity without reducing the steric hindrance and using the carbon particles having a small particle diameter without impairing the air permeability. .
　具体的には本発明では、炭素粒子として、下記（１）の要件を満足する炭素粒子を採用した。
（１）炭素粒子（Ｂ）の粒径は２０μｍ以下である。
　上記（１）のように粒径の小さい炭素粒子を用いると、通気性を損なうことなく、導電補助の効果から低抵抗化が可能である。 Specifically, in the present invention, carbon particles satisfying the following requirement (1) are adopted as the carbon particles.
(1) The particle size of the carbon particles (B) is 20 μm or less.
When carbon particles with a small particle size are used as in the above (1), the resistance can be reduced from the effect of conductivity support without impairing the air permeability.
　更に本発明では炭素質材料（Ｃ）として、炭素質繊維（Ａ）と炭素粒子（Ｂ）との両方を結着する結着性の炭素質材料を、下記（２）の範囲内で用いた。
（２）炭素質繊維（Ａ）、炭素粒子（Ｂ）、および炭素質材料（Ｃ）の合計量に対する前記炭素質材料（Ｃ）の質量含有率は３５％以上である。
　ここで「炭素質繊維（Ａ）と炭素粒子（Ｂ）との両方を結着する」（換言すれば、本発明に用いられる炭素質材料は炭素質繊維と炭素粒子の結着剤として作用する）とは、当該炭素質材料によって炭素質繊維および炭素粒子の表面および内部（炭素質繊維間、炭素粒子同士を含む）が強く結着されて、ガス拡散層基材全体としてみた場合に当該炭素質材料により炭素質繊維が被覆されつつ、炭素粒子の表面が露出しているように構成されていることを意味する。
　但し、結着後の炭素質材料は被膜状態にならないことが好ましい。ここで「被膜状態にならない」とは、炭素質繊維(Ａ)の繊維間において炭素質材料(Ｃ)が全蹼足（ボクソク）や蹼足のような水かき状態を形成しないことを意味する。被膜状態になる場合、ガスの通気性が悪化する。 Furthermore, in the present invention, as the carbonaceous material (C), a binding carbonaceous material that binds both the carbonaceous fiber (A) and the carbon particles (B) is used within the range of the following (2) .
(2) The mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) is 35% or more.
Here, “bind both the carbonaceous fiber (A) and the carbon particle (B)” (in other words, the carbonaceous material used in the present invention acts as a binder for the carbonaceous fiber and the carbon particle ) Means that the surface and the inside of the carbonaceous fibers and carbon particles (including between the carbonaceous fibers and the carbon particles) are strongly bound by the carbonaceous material, and the carbon can be viewed as a whole of the gas diffusion layer substrate It means that the surface of the carbon particle is configured to be exposed while the carbonaceous fiber is covered by the quality material.
However, it is preferable that the carbonaceous material after binding is not in the form of a film. Here, "does not become a coated state" means that the carbonaceous material (C) does not form a webbed state like a total foot (boxok) or a foot between fibers of the carbonaceous fiber (A). In the case of a coated state, the gas permeability deteriorates.
　炭素質材料は炭素粒子を介して炭素質繊維間などを強く結着するため、炭素粒子と炭素質繊維の効率的な導電パスを形成する。炭素質繊維と炭素粒子と炭素質材料との合計量に対する炭素質材料の含有比率を多くすることが導電パスの形成には必要であり、そのため本発明では上記含有率を１４．５％以上とする。 The carbonaceous material strongly bonds between the carbonaceous fibers through the carbon particles, thereby forming an efficient conductive path between the carbon particles and the carbonaceous fiber. It is necessary for the formation of the conductive path to increase the content ratio of the carbonaceous material to the total amount of the carbonaceous fiber, the carbon particles and the carbonaceous material, so in the present invention, the above content is 14.5% or more. Do.
　更に本発明の燃料電池用ガス拡散層基材は下記（３）の要件を満足する。
（３）燃料電池用ガス拡散層基材表面の結合酸素原子数が燃料電池用ガス拡散層基材表面の全炭素原子数の１％以上である。
　これにより、炭素のエッジ面や欠陥構造部に酸素原子を導入することができる。その結果、ガス拡散層基材の表面では、導入された酸素原子がカルボニル基、キノン基、ラクトン基、フリーラジカル的な酸化物などの反応基として生成されるため、これらの反応基が水分子と親和性を示し、ガス拡散層全体として保湿性を得ることが出来る。 Furthermore, the gas diffusion layer base material for a fuel cell of the present invention satisfies the following requirement (3).
(3) The number of bonded oxygen atoms on the surface of the gas diffusion layer substrate for a fuel cell is 1% or more of the total number of carbon atoms on the surface of the gas diffusion layer substrate for a fuel cell.
As a result, oxygen atoms can be introduced into the edge surface of carbon and the defect structure portion. As a result, on the surface of the gas diffusion layer substrate, since the introduced oxygen atom is generated as a reactive group such as a carbonyl group, a quinone group, a lactone group, or a free radical oxide, these reactive groups are water molecules It is possible to obtain the moisture-retaining property of the entire gas diffusion layer.
　本発明の燃料電池用ガス拡散層基材は上記のように構成されているため、通気性と親水性とを有し、かつ導電性に優れたガス拡散層基材が得られる。 Since the fuel cell gas diffusion layer substrate of the present invention is configured as described above, a gas diffusion layer substrate having gas permeability and hydrophilicity and excellent conductivity can be obtained.
　本発明を構成要件ごとに詳細に説明する。 The present invention will be described in detail for each component.
　前述したとおり本発明の燃料電池用ガス拡散層基材は、炭素質繊維を基材とし、炭素粒子を炭素質材料で坦持するガス拡散層基材であり、上記（１）～（３）の要件を満足する。 As described above, the gas diffusion layer base material for a fuel cell of the present invention is a gas diffusion layer base material comprising a carbonaceous fiber as a base material and supporting carbon particles with a carbonaceous material, and the above (1) to (3) Satisfy the requirements of
［炭素質繊維（Ａ）］
　本発明において炭素質繊維は、有機繊維のプレカーサーを加熱炭素化処理（詳細は後述）して得られる繊維であって、質量比で９０％以上が炭素で構成される繊維を意味する（ＪＩＳ　Ｌ　０２０４－２）。炭素質繊維の原料となる有機繊維のプレカーサーとしては、ポリアクリロニトリル等のアクリル繊維；フェノール繊維；ポリパラフェニレンベンゾビスオキサゾール（ＰＢＯ）等のＰＢＯ繊維；芳香族ポリアミド繊維；等方性ピッチ、異方性ピッチ繊維、メソフェーズピッチ等のピッチ繊維；セルロース繊維；等を使用することができる。中でも、強度・弾性率に優れる等の観点から、有機繊維のプレカーサーとしては、アクリル繊維、フェノール繊維、セルロース繊維、等方性ピッチ繊維、異方性ピッチ繊維が好ましく、アクリル繊維がより好ましい。アクリル繊維は、アクリロニトリルを主成分として含有するものであれば特に限定されないが、アクリル繊維を形成する原料単量体中、アクリロニトリルの含有量が９５質量％以上であることが好ましく、９８質量％以上であることがより好ましい。 [Carbonaceous fiber (A)]
In the present invention, a carbonaceous fiber is a fiber obtained by heating and carbonizing a precursor of an organic fiber (details will be described later), and means a fiber composed of 90% or more by mass of carbon (JIS L) 0204-2). Precursors of organic fibers as raw materials of carbonaceous fibers include acrylic fibers such as polyacrylonitrile; phenol fibers; PBO fibers such as polyparaphenylene benzobisoxazole (PBO); aromatic polyamide fibers; isotropic pitch, anisotropy Pitch fibers, pitch fibers such as mesophase pitch; cellulose fibers; etc. can be used. Among them, from the viewpoint of being excellent in strength and elastic modulus, acrylic fiber, phenol fiber, cellulose fiber, isotropic pitch fiber and anisotropic pitch fiber are preferable as the organic fiber precursor, and acrylic fiber is more preferable. The acrylic fiber is not particularly limited as long as it contains acrylonitrile as a main component, but the content of acrylonitrile in the raw material monomer forming the acrylic fiber is preferably 95% by mass or more, and 98% by mass or more It is more preferable that
　有機繊維の質量平均分子量は、特に限定されないが、１００００以上、１０００００以下であることが好ましく、１５０００以上、８００００以下であることがより好ましく、２００００以上、５００００以下であることがさらに好ましい。質量平均分子量は、ゲルパーミエーションクロマトグラフィー（ＧＰＣ）や溶液粘度などの方法によって測定することができる。 The mass average molecular weight of the organic fiber is not particularly limited, but is preferably 10000 or more and 100000 or less, more preferably 15000 or more and 80000 or less, and still more preferably 20000 or more and 50000 or less. The mass average molecular weight can be measured by gel permeation chromatography (GPC), solution viscosity, or the like.
　炭素質繊維の平均繊維径は０．５～４０μｍであることが好ましい。平均繊維径が０．５μｍより小さいと通気性が悪化してしまう。一方、平均繊維径が４０μｍよりも大きいと目付あたりの炭素量が低下し、電気面積抵抗が高くなってしまう。通液性および抵抗のバランスを考慮すると、より好ましくは３～２０μｍである。 The average fiber diameter of the carbonaceous fiber is preferably 0.5 to 40 μm. If the average fiber diameter is smaller than 0.5 μm, the air permeability will deteriorate. On the other hand, if the average fiber diameter is larger than 40 μm, the carbon amount per unit area decreases, and the electrical area resistance increases. It is more preferably 3 to 20 μm in consideration of the balance between liquid permeability and resistance.
　本発明では、上記炭素質繊維の構造体を基材として用いることが好ましく、これにより、強度が向上し、取扱いや加工性が容易になる。上記構造体として、具体的には、炭素質繊維よりなるシート状物である紡績糸、フィラメント集束糸、不織布、編物、織物、特開昭６３－２００４６７号公報などに記載の特殊編織物または炭素繊維からなる紙などを挙げることができる。これらのうち、炭素質繊維よりなる不織布、編物、織物、特殊織編物、及び炭素繊維からなる紙が、取り扱いや加工性、製造性等の点からより好ましい。 In the present invention, it is preferable to use the structure of the above-mentioned carbonaceous fiber as a base material, whereby the strength is improved and the handling and the processability become easy. As the above-mentioned structure, specifically, a spun yarn, a filament collected yarn, a nonwoven fabric, a knitted fabric, a woven fabric, a special knitted fabric or carbon described in JP-A-63-200467 etc., which is a sheet-like material comprising carbonaceous fibers The paper etc. which consist of fibers can be mentioned. Among these, non-woven fabric made of carbonaceous fiber, knitted fabric, woven fabric, special woven fabric, and paper made of carbon fiber are more preferable from the viewpoint of handling, processability, manufacturability and the like.
　ここで不織布、編物、織物などを用いる場合、平均繊維長は３０～１００ｍｍが好ましい。また炭素繊維からなる紙を用いる場合、平均繊維長は５～３０ｍｍが好ましい。上記の範囲内とすることで、均一な繊維構造体が得られる。 When non-woven fabric, knitted fabric, woven fabric or the like is used here, the average fiber length is preferably 30 to 100 mm. When a paper made of carbon fiber is used, the average fiber length is preferably 5 to 30 mm. By setting it in said range, a uniform fiber structure is obtained.
　前述したように上記炭素質繊維は、有機繊維のプレカーサーを加熱炭素化処理して得られるが、上記「加熱炭素化処理」は、少なくとも、耐炎化工程、および炭素化工程を含むことが好ましい。但し、これらのうち炭素化工程は、必ずしも上記のように耐炎化工程の後に行う必要はなく、後記する実施例に記載のように耐炎化された繊維に黒鉛粒子および炭素質材料を添着した後に炭素化工程を行っても良く、この場合は耐炎化工程後の炭素化工程を省略することができる。 As described above, the above-mentioned carbonaceous fiber is obtained by subjecting a precursor of an organic fiber to a carbonization treatment, but it is preferable that the above-mentioned "heat carbonization treatment" includes at least a flameproofing step and a carbonization step. However, among these, the carbonization step does not necessarily need to be performed after the flameproofing step as described above, and after the graphite particles and the carbonaceous material are attached to the flameproofed fiber as described in the examples described later. A carbonization process may be performed, and in this case, the carbonization process after the oxidization process can be omitted.
　このうち上記耐炎化工程は、空気雰囲気下、有機繊維のプレカーサーを好ましくは１８０℃以上３５０℃以下の温度で加熱し、耐炎化有機繊維を得る工程を意味する。加熱処理温度は、１９０℃以上であることがより好ましく、２００℃以上であることがさらに好ましい。また、３３０℃以下であることが好ましく、３００℃以下であることがさらに好ましい。上記温度範囲で加熱することにより、有機繊維が熱分解することなく炭素質繊維の形態を保持したまま有機繊維中の窒素、水素の含有率を低減し、炭素化率を向上することができる。耐炎化工程の際、有機繊維が熱収縮し分子配向が崩壊して、炭素質繊維の導電性が低下する場合があることから、有機繊維を緊張下ないし延伸下で耐炎化処理することが好ましく、緊張下で耐炎化処理することがより好ましい。 Among the above, the above-mentioned flameproofing step means a step of heating the precursor of the organic fiber preferably at a temperature of 180 ° C to 350 ° C in an air atmosphere to obtain a flameproofed organic fiber. The heat treatment temperature is more preferably 190 ° C. or more, and still more preferably 200 ° C. or more. Moreover, it is preferable that it is 330 degrees C or less, and it is more preferable that it is 300 degrees C or less. By heating in the above temperature range, the content of nitrogen and hydrogen in the organic fiber can be reduced while maintaining the form of the carbonaceous fiber without the organic fiber being thermally decomposed, and the carbonization rate can be improved. Since the organic fibers may be thermally shrunk and the molecular orientation may collapse during the flameproofing step, and the conductivity of the carbonaceous fibers may be reduced, it is preferable to flameproof the organic fibers under tension or stretching. It is more preferable to flameproof treatment under tension.
　上記炭素化工程は、不活性雰囲気下（好ましくは窒素雰囲気下）、上記のようにして得られた耐炎化有機繊維を好ましくは１０００℃以上２０００℃以下の温度で加熱し、炭素質繊維を得る工程を意味する。加熱温度は、１１００℃以上であることがより好ましく、１２００℃以上であることがさらに好ましい。また、より好ましくは１９００℃以下である。上記温度範囲で炭素化工程を行うことにより、有機繊維の炭素化が進行し、擬黒鉛結晶構造を有する炭素質繊維を得ることができる。 In the carbonization step, the flame-resistant organic fiber obtained as described above is preferably heated at a temperature of 1000 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere) to obtain a carbonaceous fiber It means a process. The heating temperature is more preferably 1100 ° C. or more, further preferably 1200 ° C. or more. Moreover, More preferably, it is 1900 degrees C or less. By performing the carbonization step in the above temperature range, carbonization of the organic fiber proceeds and a carbonaceous fiber having a pseudo-graphite crystal structure can be obtained.
　有機繊維は、それぞれ異なる結晶性を有するため、炭素化工程における加熱温度は、原料とする有機繊維の種類に応じて選択することができる。例えば、有機繊維としてアクリル樹脂（好ましくはポリアクリロニトリル）を使用する場合、加熱温度は８００℃以上２０００℃以下であることが好ましく、１０００℃以上１８００℃以下であることがさらに好ましい。 Since the organic fibers have different crystallinity, the heating temperature in the carbonization step can be selected according to the type of organic fibers used as the raw material. For example, when using an acrylic resin (preferably polyacrylonitrile) as the organic fiber, the heating temperature is preferably 800 ° C. or more and 2000 ° C. or less, and more preferably 1000 ° C. or more and 1800 ° C. or less.
　前述した耐炎化処理工程および炭素化工程は、連続的に行うことが好ましく、耐炎化温度から炭素化温度へ昇温するときの昇温速度は、２０℃／分以下であることが好ましく、より好ましくは１５℃分／以下である。昇温速度を上記範囲とすることにより、有機繊維の形状を保持し、かつ機械的性質に優れた炭素質繊維を得ることができる。なお上記昇温速度の下限は、機械的性質などを考慮すると、５℃／分以上であることが好ましい。 It is preferable to carry out the above-mentioned flameproofing step and carbonization step continuously, and the temperature rising rate when raising the temperature from the flameproofing temperature to the carbonization temperature is preferably 20 ° C./min or less, and more preferably. Preferably it is 15 degrees C / min. By setting the heating rate within the above range, it is possible to maintain the shape of the organic fiber and obtain a carbonaceous fiber excellent in mechanical properties. The lower limit of the temperature rising rate is preferably 5 ° C./min or more in consideration of mechanical properties and the like.
［炭素粒子（Ｂ）］
　本発明においての炭素粒子は、導電性を向上させ低抵抗を実現するために有用である。本発明では、通気性確保のため、上記（１）を満足するものを用いた。 [Carbon particle (B)]
The carbon particles in the present invention are useful for improving the conductivity and realizing low resistance. In the present invention, in order to secure air permeability, one satisfying the above (1) was used.
　まず本発明に用いられる炭素粒子の粒径は上記（１）に規定するように２０μｍ以下であり、１μｍ以下が好ましい。粒径が２０μｍを超えると、繊維交差部の交点近傍に付着した炭素質材料中に炭素粒子を良好に分散させることができず、導電性を向上させることが出来ない。ここで「粒径」とは、動的光散乱法などで得られた粒径分布におけるメジアン５０％径での平均粒径（Ｄ５０）を意味する。炭素粒子は市販品を用いてもよく、その場合、カタログ記載の粒径を採用できる。 First, the particle size of the carbon particles used in the present invention is 20 μm or less, preferably 1 μm or less, as defined in the above (1). If the particle size exceeds 20 μm, the carbon particles can not be well dispersed in the carbonaceous material attached near the intersection of the fiber intersections, and the conductivity can not be improved. Here, the “particle size” means an average particle size (D50) at a median 50% diameter in a particle size distribution obtained by a dynamic light scattering method or the like. Commercially available carbon particles may be used, and in that case, the particle size described in the catalog can be adopted.
　本発明に用いられる炭素粒子としては、導電性を有する炭素材であれば特に限定されず、公知又は市販の材料を使用できる。例えば、チャンネルブラック、ファーネスブラック、ケッチェンブラック、アセチレンブラック、ランプブラック等のカーボンブラック；黒鉛；活性炭等が挙げられる。これらは、１種単独又は２種以上で用いることができる。本発明の燃料電池用ガス拡散層はこのような導電性炭素粒子を含有することにより、燃料電池用ガス拡散層の導電性を向上させることができる。 The carbon particles used in the present invention are not particularly limited as long as they have conductivity, and known or commercially available materials can be used. For example, carbon black such as channel black, furnace black, ketjen black, acetylene black, lamp black, etc .; graphite; activated carbon etc. may be mentioned. These can be used alone or in combination of two or more. The fuel cell gas diffusion layer of the present invention can improve the conductivity of the fuel cell gas diffusion layer by containing such conductive carbon particles.
　本発明に用いられる炭素粒子の含有量は、前述した炭素質繊維（Ａ）、炭素粒子（Ｂ）、および後記する炭素質材料（Ｃ）の合計量に対する質量比率で５％以上であることが好ましく、１０％以上がより好ましい。これにより、炭素粒子が炭素質材料で結着されるようになり、抵抗が低下するようになる。但し、炭素粒子（Ｂ）の量が過剰になると、炭素質材料による結着性が不十分となり粒子の脱落が発生し、また充填密度の向上により通気性が悪化する。そのため、上限はおおむね９０％以下であることが好ましい。なお上記含有量の算出に用いる炭素質繊維（Ａ）の含有量は、基材として不織布などの構造体を用いる場合は当該構造体の含有量である。 The content of carbon particles used in the present invention is 5% or more by mass ratio to the total amount of the above-mentioned carbonaceous fiber (A), carbon particle (B) and carbonaceous material (C) described later Preferably, 10% or more is more preferable. Thereby, the carbon particles become bound with the carbonaceous material, and the resistance is reduced. However, when the amount of the carbon particles (B) is excessive, the binding property by the carbonaceous material is insufficient, and the particles fall off, and the air permeability is deteriorated due to the improvement of the packing density. Therefore, the upper limit is preferably about 90% or less. In addition, content of the carbonaceous fiber (A) used for calculation of said content is content of the said structure, when using structures, such as a nonwoven fabric, as a base material.
　本発明において、炭素粒子（Ｂ）に対する後記する炭素質材料（Ｃ）の質量比は、０．２以上５．０以下であることが好ましく、同等であることがより好ましい。上記の比が０．２未満では、炭素粒子の脱落が多くなり、当該炭素粒子が炭素質材料に十分結着されなくなる。一方、上記の比が５．０を超えると、炭素粒子同士のつながりがなくなり、導電性向上に寄与できない。 In the present invention, the mass ratio of the carbonaceous material (C) described later to the carbon particles (B) is preferably 0.2 or more and 5.0 or less, and more preferably equivalent. When the above ratio is less than 0.2, the carbon particles are frequently detached, and the carbon particles are not sufficiently bound to the carbonaceous material. On the other hand, when the above ratio exceeds 5.0, the carbon particles are not connected to each other, and the conductivity can not be improved.
［炭素質材料（Ｃ）］
　本発明において炭素質材料は、本来、結着し得ない炭素質繊維と、黒鉛粒子以外の炭素粒子とを強く結着させるための結着剤（バインダー）として添加されるものである。本発明に用いられる炭素質材料（Ｃ）の含有量は、上記（３）に規定するように前述した炭素質繊維（Ａ）、炭素粒子（Ｂ）、および炭素質材料（Ｃ）の合計量に対する質量比率で３５％以上であり、３８％以上がより好ましい。このように炭素質材料の含有率を多くすることによって炭素質繊維および炭素粒子の両方を十分結着することができ、炭素質材料添加による結着作用が有効に発揮される。なお、その上限は、通気性などを考慮すると、概ね９０％以下であることが好ましい。 [Carbonaceous material (C)]
In the present invention, the carbonaceous material is added as a binding agent (binder) for strongly binding the carbonaceous fiber which can not be bound originally and the carbon particles other than the graphite particles. The content of the carbonaceous material (C) used in the present invention is the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) described above as defined in (3) above. 35% or more by mass ratio with respect to, and 38% or more is more preferable. Thus, by increasing the content of the carbonaceous material, both the carbonaceous fiber and the carbon particles can be sufficiently bonded, and the binding action by the addition of the carbonaceous material is effectively exhibited. The upper limit thereof is preferably about 90% or less in consideration of air permeability and the like.
　本発明に用いられる炭素質材料（Ｃ）の種類は、炭素質繊維（Ａ）および炭素粒子（Ｂ）を結着し得るものであれば良く、具体的には、本発明の燃料電池用ガス拡散層基材作製時における炭化時に結着性を示すものであれば特に限定されない。このような例として、例えば、コールタールピッチ、石炭系ピッチ等のピッチ類；フェノール樹脂、ベンゾオキサジン樹脂、エポキシド樹脂、フラン樹脂、ビニルエステル樹脂、メラニン－ホルムアルデヒド樹脂、尿素－ホルムアルデヒド樹脂、レソルシノール－ホルムアルデヒド樹脂、シアネートエステル樹脂、ビスマレイミド樹脂、ポリウレタン樹脂、ポリアクリロニトリル等の樹脂；フルフリルアルコール；アクリロニトリル－ブタジエンゴム等のゴムなどが挙げられる。これらは市販品を用いても良い。 The type of the carbonaceous material (C) used in the present invention may be any type as long as it can bind the carbonaceous fiber (A) and the carbon particles (B). Specifically, the fuel cell gas of the present invention It is not particularly limited as long as it exhibits binding property at the time of carbonization at the time of preparation of the diffusion layer base material. Such examples include pitches such as coal tar pitch and coal pitch; phenol resin, benzoxazine resin, epoxide resin, furan resin, vinyl ester resin, melanin-formaldehyde resin, urea-formaldehyde resin, resorcinol-formaldehyde Resins such as resins, cyanate ester resins, bismaleimide resins, polyurethane resins, polyacrylonitrile, etc .; furfuryl alcohol; rubbers such as acrylonitrile-butadiene rubber and the like. A commercial item may be used for these.
　これらのうち、特に易結晶性であるコールタールピッチ、石炭系ピッチ等のピッチ類は、低い焼成温度で目的とする炭素質材料（Ｃ）が得られるため好ましい。また、フェノール樹脂も焼成温度によって結晶性の増減が少なく、結晶性の制御がし易いため、好ましく用いられる。また、ポリアクリロニトリル樹脂も、焼成温度を上げれば目的とする炭素質材料（Ｃ）が得られるため、好ましく用いられる。特に好ましいのはピッチ類である。 Among these, pitches such as coal tar pitch and coal-based pitch which are easily crystalline are preferable because the target carbonaceous material (C) can be obtained at a low firing temperature. In addition, a phenolic resin is also preferably used because the degree of increase and decrease in crystallinity is small depending on the calcination temperature and the crystallinity can be easily controlled. In addition, polyacrylonitrile resin is also preferably used because the target carbonaceous material (C) can be obtained by raising the firing temperature. Particularly preferred are pitches.
　ここで、特に好ましく用いられるピッチ類について詳述する。前述したコールタールピッチや石炭系ピッチは、不融化処理の温度や時間によって、メソフェーズ相（液晶相）の含有率をコントロールすることができる。メソフェーズ相の含有量が少なければ、比較的低温で溶融、または室温で液体状態のものが得られる。一方、メソフェーズ相の含有率が高ければ、高温で溶融し、炭化収率の高いものが得られる。ピッチ類を炭素質材料（Ｃ）に適用する場合、メソフェーズ相の含有率が高い（すなわち炭化率が高い）ことが好ましく、例えば３０％以上が好ましく、５０％以上がより好ましい。これにより、溶融時の流動性を抑え、黒鉛粒子の表面を過剰に被覆することなく、黒鉛粒子を介して炭素質繊維間を結着することができる。なお、その上限は、結着性の発現などを考慮すると、例えば９０％以下であることが好ましい。 Here, pitches which are particularly preferably used will be described in detail. In the coal tar pitch and the coal pitch described above, the content of the mesophase phase (liquid crystal phase) can be controlled by the temperature and time of the infusibilization treatment. If the content of the mesophase is small, a relatively low temperature melts or a liquid state at room temperature is obtained. On the other hand, if the content of the mesophase phase is high, it melts at high temperature and a carbonization yield is high. When pitches are applied to the carbonaceous material (C), the content of the mesophase phase is preferably high (ie, the carbonization ratio is high), for example, 30% or more is preferable, and 50% or more is more preferable. Thereby, the fluidity at the time of melting can be suppressed, and the carbonaceous fibers can be bonded via the graphite particles without excessively covering the surface of the graphite particles. The upper limit thereof is preferably, for example, 90% or less in consideration of expression of binding property and the like.
　上記と同様の観点から、ピッチ類の融点は、１００℃以上であることが好ましく、２００℃以上であることがより好ましい。これにより、上記効果が得られる他、添着加工時の臭気を抑えることができ、加工性の面でも好ましい。なお、その上限は、結着性の発現などを考慮すると、例えば３５０℃以下であることが好ましい。 From the same viewpoint as above, the melting point of the pitch is preferably 100 ° C. or more, and more preferably 200 ° C. or more. Thus, the above-mentioned effects can be obtained, and in addition, the odor at the time of attachment processing can be suppressed, which is preferable also from the viewpoint of processability. The upper limit thereof is preferably, for example, 350 ° C. or less in consideration of expression of binding property and the like.
（燃料電池用ガス拡散層基材）
　本発明の燃料電池用ガス拡散層基材は、燃料電池用ガス拡散層基材表面の結合酸素原子数が燃料電池用ガス拡散層基材表面の全炭素原子数の１％以上を満足する。以下、上記全炭素原子数に対する結合酸素原子数の比をＯ／Ｃで略記する場合がある。Ｏ／Ｃは、Ｘ線光電子分光法（ＸＰＳ）や蛍光Ｘ線分析法などの表面分析にて測定できる。 (Gas diffusion layer base material for fuel cell)
In the fuel cell gas diffusion layer substrate of the present invention, the number of bonded oxygen atoms on the surface of the fuel cell gas diffusion layer substrate satisfies 1% or more of the total number of carbon atoms on the surface of the fuel cell gas diffusion layer substrate. Hereinafter, the ratio of the number of bonded oxygen atoms to the total number of carbon atoms may be abbreviated as O / C. O / C can be measured by surface analysis such as X-ray photoelectron spectroscopy (XPS) or X-ray fluorescence analysis.
　Ｏ／Ｃが１％以上に制御した燃料電池用ガス拡散層基材を用いることにより、親水性が高められ、後記する通水速度（好ましくは０．５ｍｍ/ｓｅｃ以上）を確保することができる。これに対し、Ｏ／Ｃが１％未満の酸素濃度の低い燃料電池用ガス拡散層基材を用いると、燃料電池用ガス拡散層基材表面の親水性が小さくなり、生成水の通液性を高めることはできない。その結果、セルに組み込んだ際フラッディングなどの問題が生ずる。 By using a gas diffusion layer base material for fuel cells, the O / C of which is controlled to 1% or more, the hydrophilicity is enhanced, and a water flow rate (preferably 0.5 mm / sec or more) described later can be secured. . On the other hand, when the fuel cell gas diffusion layer base material having a low oxygen concentration with an O / C of less than 1% is used, the hydrophilicity of the fuel cell gas diffusion layer base material surface becomes small, and the generated water can flow Can not raise. As a result, when incorporated into a cell, problems such as flooding occur.
　本発明の燃料電池用ガス拡散層基材は親水性に優れている。親水性は、燃料電池用ガス拡散層基材を乾式酸化処理後、水滴を垂らした時の通水速度によって確認することができる。本発明に係る燃料電池用ガス拡散層基材の通水速度は、０．５ｍｍ/ｓｅｃ以上であることが好ましい。これにより、生成水に対する十分な親和性を有すると判断できる。燃料電池用ガス拡散層基材の通水速度は大きい程良く、より好ましくは１ｍｍ/ｓｅｃ以上、更に好ましくは５ｍｍ/ｓｅｃ以上、更により好ましくは１０ｍｍ/ｓｅｃ以上である。 The fuel cell gas diffusion layer substrate of the present invention is excellent in hydrophilicity. The hydrophilicity can be confirmed by the water flow rate when a water droplet is dropped after dry oxidation treatment of the fuel cell gas diffusion layer substrate. The water flow rate of the fuel cell gas diffusion layer substrate according to the present invention is preferably 0.5 mm / sec or more. Thereby, it can be judged that it has sufficient affinity to generated water. The water flow rate of the fuel cell gas diffusion layer substrate is preferably as high as possible, more preferably 1 mm / sec or more, still more preferably 5 mm / sec or more, and still more preferably 10 mm / sec or more.
　本発明の燃料電池用ガス拡散層基材の目付量は、セルに組んだ時の０．３～３ｍｍで使用する場合、５０～５００ｇ／ｍ２が好ましく、１００～４００ｇ／ｍ２がより好ましい。目付を上記範囲内に制御することで、通気性を確保しつつ、固体電解質膜の破損を防止することができる。特に、近年では低抵抗化の観点から、固体電解質膜の厚みは薄くなる傾向にあり、固体電解質膜へのダメージを軽減する処置及び使用方法は極めて重要である。また上記の観点から、本発明の燃料電池用ガス拡散層基材として、片面に平坦加工が施された不織布や紙を使用することもより好ましい。平坦加工方法は、公知の任意の方法を適用でき、例えばスラリーを炭素質繊維の片面に塗布、乾燥する方法；ＰＥＴなどの平滑なフィルム上で含侵、乾燥するなどの手法が挙げられる。 The weight per unit area of the gas diffusion layer base material for fuel cells of the present invention is preferably 50 to 500 g / m 2 and more preferably 100 to 400 g / m 2 when used in 0.3 to 3 mm when assembled in a cell. . By controlling the fabric weight within the above range, damage to the solid electrolyte membrane can be prevented while ensuring air permeability. In particular, the thickness of the solid electrolyte membrane tends to be reduced from the viewpoint of resistance reduction in recent years, and a treatment and a method for reducing damage to the solid electrolyte membrane are extremely important. From the above point of view, it is more preferable to use non-woven fabric or paper which has been flat-processed on one side as the gas diffusion layer substrate for a fuel cell of the present invention. As the flattening method, any known method can be applied, for example, a method of applying and drying a slurry on one side of a carbonaceous fiber; and a method of impregnating and drying on a smooth film such as PET.
（燃料電池用ガス拡散層基材の製造方法）
　次に、本発明の燃料電池用ガス拡散層基材を製造する方法について説明する。本発明の燃料電池用ガス拡散層基材は、炭素質繊維（基材）に炭素粒子および炭素質材料の前駆体（炭化前のもの）を添着した後、炭素化工程、黒鉛化工程、酸化処理工程を経て製造することができる。各工程では、公知の方法を任意に適用することができる。 (Method of producing gas diffusion layer base material for fuel cell)
Next, a method of producing the gas diffusion layer substrate for a fuel cell of the present invention will be described. The gas diffusion layer base material for a fuel cell of the present invention comprises a carbon fiber, a carbonization step, a graphitization step, oxidation after attaching carbon particles and a precursor of carbon material (before carbonization) to a carbonaceous fiber (base material). It can be manufactured through processing steps. In each step, known methods can be optionally applied.
　以下、各工程について説明する。 Each step will be described below.
（炭素質繊維に炭素粒子、および炭素質材料の前駆体を添着する工程）
　まず、炭素質繊維に炭素粒子および炭素質材料の前駆体を添着させる。炭素質繊維に炭素粒子及び炭素質材料の前駆体を添着させるには、公知の方法を任意に採用できる。例えば上記の炭素質材料前駆体を加熱して溶融させ、得られた溶融液中に黒鉛粒子を分散させ、この溶融分散液に炭素質繊維を浸漬した後、室温まで冷却する手法が挙げられる。或は、後記する実施例に示すように、上記の炭素質材料前駆体と炭素粒子を、ポリビニルアルコールなどのように炭化時に消失するバインダー（仮接着剤）を添加した水やアルコールなどの溶媒に分散させ、この分散液に炭素質繊維を浸漬した後、加熱して乾燥する手法を用いることができる。ここで、炭素質繊維を浸漬した上記溶融分散液や分散液のうち余分な液は、所定のクリアランスを設けたニップローラーに通すことで分散液に浸漬した際の余分な分散液を絞ったり、或は、ドクターブレード等で分散液に浸漬した際の余分な分散液の表面をかきとったり等の方法で除去することができる。 (Step of attaching carbon particles and precursor of carbonaceous material to carbonaceous fiber)
First, carbon particles and a precursor of a carbonaceous material are attached to the carbonaceous fiber. In order to attach the carbon particle and the precursor of the carbonaceous material to the carbonaceous fiber, any known method can be adopted. For example, the above-mentioned carbonaceous material precursor may be heated and melted, graphite particles may be dispersed in the obtained melt, the carbonaceous fiber may be immersed in the melt dispersion, and then cooled to room temperature. Alternatively, as shown in the examples described later, the above-mentioned carbonaceous material precursor and carbon particles are added to a solvent such as water or alcohol to which a binder (temporary adhesive) which disappears upon carbonization, such as polyvinyl alcohol, is added. After dispersing and immersing the carbonaceous fiber in the dispersion, a method of heating and drying can be used. Here, excess liquid among the above-mentioned melt dispersion liquid and dispersion liquid in which the carbonaceous fiber is immersed is squeezed out excess dispersion liquid when immersed in the dispersion liquid by passing it through a nip roller provided with a predetermined clearance, Alternatively, the surface of excess dispersion when immersed in the dispersion with a doctor blade or the like can be removed by a method such as scraping.
　その後、空気雰囲気下、例えば８０～１５０℃で乾燥する。 Thereafter, it is dried at, for example, 80 to 150 ° C. in an air atmosphere.
（炭素化工程）
　炭素化工程は、上記工程で得られた添着後の製造物を焼成するために行なわれる。これにより、炭素粒子を介して炭素質繊維間が結着されるようになる。炭素化工程では、炭化時の分解ガスを十分に除去することが好ましく、例えば、不活性雰囲気下（好ましくは窒素雰囲気下）、８００℃以上２０００℃以下の温度で加熱することが好ましい。加熱温度は１０００℃以上がより好ましく、１２００℃以上がさらに好ましく、１３００℃以上がさらにより好ましく、また、１５００℃以下がより好ましく、１４００℃以下がさらに好ましい。 (Carbonization process)
The carbonization step is carried out to calcine the product after attachment obtained in the above step. As a result, the carbonaceous fibers are bound via the carbon particles. In the carbonization step, it is preferable to sufficiently remove the decomposition gas at the time of carbonization, and for example, it is preferable to heat at a temperature of 800 ° C. or more and 2000 ° C. or less under an inert atmosphere (preferably under a nitrogen atmosphere). The heating temperature is more preferably 1000 ° C. or higher, still more preferably 1200 ° C. or higher, still more preferably 1300 ° C. or higher, and further preferably 1500 ° C. or lower, even more preferably 1400 ° C. or lower.
　なお前述したとおり、上記炭素化工程に対応する処理を、繊維の耐炎化後にも行っても良いが、繊維の耐炎化後に行われる炭素化処理は省略しても良い。すなわち、本発明の燃料電池用ガス拡散層基材を製造する方法は、下記方法１と方法２に大別される。
・方法１：繊維の耐炎化→繊維の炭素化→黒鉛粒子および炭素質材料の添着→炭素化→黒鉛化→酸化
・方法２：繊維の耐炎化→黒鉛粒子以外の炭素粒子および炭素質材料の添着→炭素化→黒鉛化→酸化
　上記方法１によれば、炭素化を２回行うため加工コストが上昇するものの、燃料電池用ガス拡散層基材として使用するシートは体積収縮比率の差による影響を受け難いため、得られるシートが変形（反り発生）し難いという利点がある。一方、上記方法２によれば、炭素化工程を１回行えば良いため加工コストを低減できるものの、各材料の炭素化時における体積収縮比率の差により得られるシートが変形し易くなる。上記方法１、２のいずれを採用するかは、これらを勘案して適宜決定すれば良い。 As described above, the treatment corresponding to the carbonization step may be performed after the stabilization of the fibers, but the carbonization treatment performed after the stabilization of the fibers may be omitted. That is, the method of producing the gas diffusion layer substrate for a fuel cell of the present invention is roughly classified into the following method 1 and method 2.
Method 1: Flame resistance of fiber → carbonization of fiber → adhesion of graphite particles and carbonaceous material → carbonization → graphitization → oxidation → Method 2: flame resistance of fiber → carbon particles other than graphite particles and carbon material Attachment → carbonization → graphitization → oxidation According to method 1 above, although processing cost increases because carbonization is performed twice, the sheet used as a gas diffusion layer base material for fuel cells is affected by the difference in volume contraction ratio Since it is hard to be received, there is an advantage that the obtained sheet is hard to be deformed (warpage occurrence). On the other hand, according to the method 2, although the processing cost can be reduced because the carbonization step may be performed once, the sheet obtained is easily deformed due to the difference in volume contraction ratio at the time of carbonization of each material. Which one of the above methods 1 and 2 is adopted may be appropriately determined in consideration of these.
（黒鉛化工程）
　黒鉛化工程は、炭素質材料の結晶性を十分に高め、電子伝導性の向上ならびに燃料電池セル中の酸化還元反応などに対する耐酸化性を向上させるために行なわれる工程である。上記炭素化工程の後、さらに不活性雰囲気下（好ましくは窒素雰囲気下）で１３００℃以上の温度で加熱することが好ましく、１５００℃以上がより好ましい。なお、その上限は、炭素質材料に高い電解液親和性を付与することを考慮すると、２０００℃以下が好ましい。 (Graphitization process)
The graphitization step is a step carried out to sufficiently enhance the crystallinity of the carbonaceous material, to improve the electron conductivity, and to improve the oxidation resistance to the oxidation-reduction reaction in the fuel cell and the like. After the carbonization step, heating is preferably performed at a temperature of 1300 ° C. or more in an inert atmosphere (preferably under a nitrogen atmosphere), more preferably 1500 ° C. or more. In addition, the upper limit thereof is preferably 2000 ° C. or less in consideration of providing the carbonaceous material with high electrolytic solution affinity.
（酸化処理工程）
　上記黒鉛化工程の後、さらに酸化処理工程を行うことにより、燃料電池用ガス拡散層基材表面に、ヒドロキシル基、カルボニル基、キノン基、ラクトン基、フリーラジカル的な酸化物などの酸素官能基が導入されるようになる。その結果、前述したＯ／Ｃ比≧１％を達成することができる。これらの酸素官能基は水の通水速度に大きく寄与する。 (Oxidation treatment process)
After the above graphitization step, an oxidation treatment step is further carried out to form an oxygen functional group such as a hydroxyl group, a carbonyl group, a quinone group, a lactone group, and a free radical oxide on the surface of the gas diffusion layer base material for fuel cells. Will be introduced. As a result, the above-mentioned O / C ratio O1% can be achieved. These oxygen functional groups greatly contribute to the water flow rate.
　酸化処理工程は、例えば湿式の化学酸化、電解酸化、乾式酸化などの各種処理工程を適用できるが、加工性、製造コストの観点から乾式酸化処理工程が好ましい。乾式酸化処理工程は、空気雰囲気下、例えば５００℃以上、９００℃以下で加熱（酸化処理）する工程を意味する。上記酸素官能基の導入による効果を有効に発揮させるためには、上記加熱温度は、６００℃以上がより好ましく、６５０℃以上がさらに好ましい。また、８００℃以下がより好ましく、７５０℃以下がさらに好ましい。 For the oxidation treatment step, various treatment steps such as wet chemical oxidation, electrolytic oxidation and dry oxidation can be applied, but a dry oxidation treatment step is preferable from the viewpoint of processability and production cost. The dry oxidation treatment step means a step of heating (oxidation treatment) in an air atmosphere, for example, at 500 ° C. or more and 900 ° C. or less. The heating temperature is more preferably 600 ° C. or more, and still more preferably 650 ° C. or more, in order to effectively exert the effect of the introduction of the oxygen functional group. Moreover, 800 degrees C or less is more preferable, and 750 degrees C or less is further more preferable.
　更に乾式酸化処理工程では、燃料電池用ガス拡散層基材の機械的強度を維持する観点から、酸化処理前後の燃料電池用ガス拡散層基材の質量収率を９０％以上、９６％以下に調整することが好ましい。これは、例えば、乾式空気酸化の処理時間や温度を適宜調整するなどの方法により調整することができる。 Furthermore, in the dry oxidation treatment step, from the viewpoint of maintaining the mechanical strength of the fuel cell gas diffusion layer substrate, the mass yield of the fuel cell gas diffusion layer substrate before and after oxidation treatment is 90% or more and 96% or less. It is preferable to adjust. This can be adjusted, for example, by a method such as adjusting the processing time and temperature of dry air oxidation appropriately.
　以下に実施例及び比較例を挙げて、本発明をより詳細に説明する。なお、本発明は、以下の実施例に限定されるものではない。 The present invention will be described in more detail with reference to the following Examples and Comparative Examples. The present invention is not limited to the following examples.
　本実施例では、以下の項目を測定した。測定方法の詳細は以下の通りである。 The following items were measured in this example. Details of the measurement method are as follows.
（１）ＸＰＳ表面分析によるＯ／Ｃの測定
　ＥＳＣＡまたはＸＰＳと略称されているＸ線光電子分光法の測定には、アルバック・ファイ５８０１ＭＣの装置を用いた。
　まず、試料をサンプルホルダー上にＭｏ板で固定し、予備排気室にて十分に排気した後、測定室のチャンバーに投入した。線源にはモノクロ化ＡｌＫα線を用い、出力は１４ｋＶ、１２ｍＡ、装置内真空度は１０-8ｔｏｒｒとした。
　全元素スキャンを行って表面元素の構成を調べ、検出された元素および予想される元素についてナロースキャンを実施し、存在比率を評価した。
　全表面炭素原子数に対する表面結合酸素原子数の比を百分率（％）で算出し、Ｏ／Ｃを算出した。 (1) Measurement of O / C by XPS Surface Analysis For measurement of X-ray photoelectron spectroscopy abbreviated as ESCA or XPS, an apparatus of ULVAC-PHI 5801 MC was used.
First, the sample was fixed on a sample holder with a Mo plate, fully evacuated in the preliminary evacuation chamber, and then introduced into the chamber of the measurement chamber. A monochromated AlKα ray was used as a radiation source, the output was 14 kV, 12 mA, and the degree of vacuum in the apparatus was 10 −8 torr.
A total element scan was performed to determine the composition of the surface elements, and a narrow scan was performed for the detected element and the expected element to evaluate the abundance ratio.
The ratio of the number of surface-bound oxygen atoms to the total number of surface carbon atoms was calculated as a percentage (%) to calculate O / C.
（２）質量含有率
　以下の実施例、比較例では、質量含有率は次のように概算で求めた。
(i)基材のみを焼成しその質量を求める。
(ii)基材に炭素質材料及び炭素粒子を添着させて焼成後の質量を求める。
(iii)(ii)から(i)を減算し、炭素質材料及び炭素粒子の添着質量を決定する。
(iv)(iii)の添着に用いた添着液中の炭素質材料と炭素粒子との質量の比率にて、(iii)の添着質量を分配する。
(v)(i)と(iv)とから質量含有率を求める。
ただし、炭素質材料、炭素粒子が焼成において質量が減る場合には、それに応じて(iv)での比率を変更する。 (2) Mass Content In the following Examples and Comparative Examples, the mass content was roughly calculated as follows.
(i) Only the base material is fired to determine its mass.
(ii) A carbonaceous material and carbon particles are attached to a base material, and the mass after firing is determined.
(iii) Subtract (i) from (ii) to determine the attached mass of carbonaceous material and carbon particles.
(iv) The attachment mass of (iii) is distributed by the ratio of the mass of the carbonaceous material and the carbon particles in the attachment liquid used for the attachment of (iii).
(v) The mass content is determined from (i) and (iv).
However, when the carbonaceous material and carbon particles lose their mass in firing, the ratio in (iv) is changed accordingly.
（３）水の通水試験
　燃料電池用ガス拡散層基材からの高さ５ｃｍの地点において、３ｍｍφのピペットから１滴のイオン交換水を燃料電池用ガス拡散層基材上に落とし、垂らした水滴が浸透するまでの時間を計測して、水の通水速度を算出した。 (3) Water passing test At a point 5 cm high from the fuel cell gas diffusion layer substrate, 1 drop of ion exchanged water was dropped from a 3 mmφ pipette onto the fuel cell gas diffusion layer substrate and dropped The time until the water droplet penetrated was measured to calculate the water flow rate.
（４）電気面積抵抗値
　２枚の５０ｍｍ角(厚さ１０ｍｍ)の金メッキした電極で、燃料電池用ガス拡散層基材を電極が全面接触するように挟み、荷重１０ｋＰａをシートの厚さ方向に掛けたときの厚さ方向の電気面積抵抗値を測定した。 (4) Electric area resistance value Two 50 mm square (10 mm thick) gold-plated electrodes sandwich the gas diffusion layer base material for fuel cell so that the electrodes are in full contact, and load 10 kPa in the sheet thickness direction The electrical area resistance value in the thickness direction was measured.
（実施例１）
　まず、イオン交換水中に、花王社製レオドールＴＷ－Ｌ１２０（非イオン系界面活性剤）を１．８質量％、ポリビニルアルコール（仮接着材）を１．８質量％、ＪＦＥケミカル社製ＭＣＰ２５０（炭素質材料）を１４質量％、炭素粒子として粒径９μｍの黒鉛粒子を９．８質量％となるように加え、メカニカルスターラーで１時間撹拌して分散液とした。 Example 1
First, 1.8% by mass of Leodol TW-L120 (non-ionic surfactant) manufactured by Kao Corporation, 1.8% by mass of polyvinyl alcohol (temporary adhesive material) in ion exchange water, MCP 250 (carbon manufactured by JFE Chemical Co., Ltd.) 14% by mass, and 9.8% by mass of graphite particles having a particle diameter of 9 μm as carbon particles were added, and the mixture was stirred for 1 hour with a mechanical stirrer to obtain a dispersion.
　このようにして得られた分散液中に、ポリアクリロニトリル繊維（平均繊維径１０μｍ）からなるカーボンペーパー（日本ポリマー産業社製ＣＦＰ－０３０－ＰＥ、目付３０ｇ／ｍ２、厚み０．５１ｍｍ）を浸漬した後、ニップローラーに通して余分な分散液を除去した。次に、空気雰囲気下、１５０℃で２０分間乾燥した後、窒素雰囲気下、１０００℃で１時間、さらに２０００℃で１時間焼成（炭化）した。焼成後、空気雰囲気下、７００℃で２０分間酸化処理して、厚み０．５１ｍｍ、目付１４９．０ｇ／ｍ2の燃料電池用ガス拡散層基材を得た。 In the dispersion thus obtained, carbon paper (CFP-030-PE, manufactured by Nippon Polymer Industries, 30 g / m 2 , 0.51 mm thickness) made of polyacrylonitrile fiber (average fiber diameter 10 μm) is immersed After passing, it was passed through a nip roller to remove excess dispersion. Next, it was dried at 150 ° C. for 20 minutes in an air atmosphere, and then calcined (carbonized) at 1000 ° C. for 1 hour and further at 2000 ° C. for 1 hour in a nitrogen atmosphere. After firing, oxidation treatment was performed at 700 ° C. for 20 minutes in an air atmosphere to obtain a fuel cell gas diffusion layer substrate having a thickness of 0.51 mm and a basis weight of 149.0 g / m 2 .
（比較例１）
　実施例１において、炭素粒子として粒径２４μｍの黒鉛粒子を用いたこと以外は実施例１と同様にして厚み０．５０ｍｍ、目付１５３．０ｇ／ｍ2の燃料電池用ガス拡散層基材を得た。 (Comparative example 1)
A gas diffusion layer substrate for a fuel cell having a thickness of 0.50 mm and a basis weight of 153.0 g / m 2 is obtained in the same manner as in Example 1 except that graphite particles having a particle diameter of 24 μm are used as carbon particles. The
（比較例２）
　実施例１において、ＪＦＥケミカル社製ＭＣＰ２５０（炭素質材料）を３質量％、炭素粒子として粒径９μｍの黒鉛粒子を２．１質量％となるように加えた以外は実施例１と同様にして厚み０．５６ｍｍ、目付８０．０ｇ／ｍ2の燃料電池用ガス拡散層基材を得た。 (Comparative example 2)
Example 1 is the same as Example 1 except that 3 mass% of MCP 250 (carbonaceous material) manufactured by JFE Chemical Co., Ltd. and 2.1 mass% of graphite particles having a particle diameter of 9 μm as carbon particles are added. A fuel cell gas diffusion layer base material having a thickness of 0.56 mm and a basis weight of 80.0 g / m 2 was obtained.
（比較例３）
　実施例１において、焼成後の酸化処理を行わなかった以外は実施例１と同様にして厚み０．５６ｍｍ、目付１６０．０ｇ／ｍ2の燃料電池用ガス拡散層基材を得た。 (Comparative example 3)
A gas diffusion layer base material for a fuel cell having a thickness of 0.56 mm and a basis weight of 160.0 g / m 2 was obtained in the same manner as in Example 1 except that the oxidation treatment after firing was not performed in Example 1.
　表１に、実施例１、上記比較例１～３における各種項目の測定結果を示す。 Table 1 shows the measurement results of various items in Example 1 and Comparative Examples 1 to 3 above.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　実施例１は、本発明の要件を満足する燃料電池用ガス拡散層基材であり、水の通液性があり低抵抗な燃料電池用ガス拡散層基材が得られた。 Example 1 is a gas diffusion layer base material for a fuel cell satisfying the requirements of the present invention, and a gas diffusion layer base material for a fuel cell having water permeability and low resistance was obtained.
　これに対し、比較例１は、炭素粒子が大きすぎたため繊維交差部の交点近傍に付着した炭素質材料に炭素粒子を良好に分散させることができず、導電性を向上させることが出来なかった。 On the other hand, in Comparative Example 1, the carbon particles were too large to be well dispersed in the carbonaceous material attached near the intersection of the fiber intersections because the carbon particles were too large, and the conductivity could not be improved. .
　比較例２は、黒鉛以外の炭素粒子の含有量が少ない例であり、抵抗が増加した。上記炭素粒子の含有量の低下に伴って電子伝導パスが不十分になるためと考えられる。 The comparative example 2 is an example with little content of carbon particles other than graphite, and resistance increased. It is considered that the electron conduction path becomes insufficient as the content of the carbon particles decreases.
　比較例３は、Ｏ／Ｃの比が小さい例であり、通水しなかった。これは、酸素官能基量が少ないため実施例１に比べて生成水との親和性が低下したためと考えられる。 Comparative Example 3 is an example in which the ratio of O / C is small, and water was not passed. This is considered to be due to the fact that the amount of oxygen functional group is small and the affinity with generated water is lower than in Example 1.
　本発明によれば、導電性多孔質材料に親水性を付与し、導電補助粒子を加えることで、抵抗を上昇させることなく、保湿性を制御することが可能な燃料電池用ガス拡散層基材を提供できる。本発明の燃料電池用ガス拡散層基材は、燃料電池はもちろんのこと、燃料電池の仕組みを利用した一酸化炭素センサーや、ＮＯｘ分解フィルターなどに好適に用いられる。
  According to the present invention, a fuel cell gas diffusion layer substrate capable of controlling the moisture retention without raising the resistance by imparting hydrophilicity to the conductive porous material and adding the conductive auxiliary particles Can provide The fuel cell gas diffusion layer base material of the present invention is suitably used not only for fuel cells, but also for carbon monoxide sensors utilizing the structure of fuel cells, NOx decomposition filters, and the like.

Claims (5)

  1. 　炭素質繊維（Ａ）と、炭素粒子（Ｂ）と、これらを結着する炭素質材料（Ｃ）と、からなり、
    　下記の要件を満足することを特徴とする燃料電池用ガス拡散層基材。
    （１）前記炭素粒子（Ｂ）の粒径は２０μｍ以下、
    （２）前記炭素質繊維（Ａ）、前記炭素粒子（Ｂ）、および前記炭素質材料（Ｃ）の合計量に対する前記炭素質材料（Ｃ）の質量含有率は３５％以上、
    （３）燃料電池用ガス拡散層基材表面の結合酸素原子数が燃料電池用ガス拡散層基材表面の全炭素原子数の１％以上     It consists of a carbonaceous fiber (A), carbon particles (B), and a carbonaceous material (C) binding these,
    A gas diffusion layer substrate for a fuel cell characterized by satisfying the following requirements.
    (1) The particle size of the carbon particle (B) is 20 μm or less,
    (2) The mass content of the carbonaceous material (C) with respect to the total amount of the carbonaceous fiber (A), the carbon particles (B), and the carbonaceous material (C) is 35% or more.
    (3) The number of bonded oxygen atoms on the surface of the gas diffusion layer substrate for fuel cells is 1% or more of the total number of carbon atoms on the surface of the gas diffusion layer substrate for fuel cells
  2. 　前記炭素粒子（Ｂ）に対する前記炭素質材料（Ｃ）の質量比が０．２～５．０である請求項１に記載の燃料電池用ガス拡散層基材。 The fuel cell gas diffusion layer substrate according to claim 1, wherein a mass ratio of the carbonaceous material (C) to the carbon particles (B) is 0.2 to 5.0.
  3. 　水滴を垂らした時の通水速度が０．５ｍｍ/ｓｅｃ以上である請求項１または２に記載の燃料電池用ガス拡散層基材。 The gas diffusion layer substrate for a fuel cell according to claim 1 or 2, wherein a water flow rate when dripping a water drop is 0.5 mm / sec or more.
  4. 　請求項１～３のいずれかに記載の燃料電池用ガス拡散層基材を用いた燃料電池用ガス拡散層。 A fuel cell gas diffusion layer using the fuel cell gas diffusion layer substrate according to any one of claims 1 to 3.
  5. 　請求項４に記載の燃料電池用ガス拡散層を用いた燃料電池。
          A fuel cell using the fuel cell gas diffusion layer according to claim 4.
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