Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M4/8605—Porous electrodes
• • 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
• • 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
  • H01M4/8663—Selection of inactive substances as ingredients for catalytic active masses, e.g. binders, fillers
  • H01M4/8668—Binders
• • 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
• • 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
• • 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
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0239—Organic resins; Organic polymers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/02—Details
  • H01M8/0202—Collectors; Separators, e.g. bipolar separators; Interconnectors
  • H01M8/023—Porous and characterised by the material
  • H01M8/0241—Composites
  • H01M8/0243—Composites in the form of mixtures
• • 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
• • 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]
• • 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
  • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
  • H01M2004/8684—Negative electrodes
• • 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
  • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
  • H01M2004/8689—Positive 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
  • H01M2008/1095—Fuel cells with polymeric 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 fuel cell, particularly a gas diffusion electrode used in a polymer electrolyte fuel cell, and a fuel cell including the gas diffusion electrode.
• Each cell consists of an electrode, a catalyst layer, an electrolyte membrane, a catalyst layer, a gas diffusion electrode, and a separator.
• the three-layer part of the catalyst layer, the electrolyte membrane, and the catalyst layer is called the catalyst-coated membrane (CCM), and the five-layer part including the gas diffusion electrodes placed on both sides of the CCM is the membrane. It is called an electrode assembly (MEA: Membrane Electrode Assembly).
• the gas diffusion electrode has high gas diffusivity for diffusing the gas supplied from the separator to the catalyst layer, high drainage for discharging the water generated in the electrochemical reaction to the separator, and A high conductivity is required to extract current. Therefore, a conductive porous substrate made of conductive fibers such as carbon fiber (hereinafter sometimes simply referred to as "substrate") is used, and a microporous layer (MPL: Micro Porous Layer) is formed on the surface. Gas diffusion electrodes are widely used (Patent Documents 1 to 3).
• part of the water generated on the cathode side may permeate the electrolyte membrane and move to the anode side, increasing the humidity on the anode side. Then, when starting up at a low temperature, water droplets may condense and deposit on the anode side to close the separator flow path, thereby hindering the supply of hydrogen. At this time, the cell becomes fuel-starved and cannot continue to generate power. However, since the other cells in the stack other than the cell in question continue to generate power, the fuel-starved cells connected in series with these power-generating cells have a large voltage applied across their electrodes as a load of the fuel cell.
• the reaction (3) is an electrolysis reaction of water
• the reaction (4) is an electrochemical corrosion reaction of carbon.
• the reaction (4) consumes catalyst-supported carbon, which is a constituent material of the anode catalyst layer. Therefore, it causes serious performance deterioration such as detachment of the catalyst and an increase in contact resistance.
• Patent Document 4 iridium oxide or ruthenium oxide with platinum-carrying carbon as an anode catalyst
• the reaction (4) in the CR state proceeds not only in the anode catalyst layer but also in the carbon on the surface of the microporous layer of the anode gas diffusion electrode in contact with the anode catalyst layer. Therefore, the carbon of the anode gas diffusion electrode at the contact interface between the anode catalyst layer and the anode gas diffusion electrode also disappears, the contact resistance at the interface increases, and the power generation performance of the fuel cell deteriorates.
• Patent Document 5 Furthermore, there is also a method of suppressing deterioration by making the carbon used in the catalyst layer highly crystalline (Patent Document 5).
• reaction (4) proceeds in the CR state, so the drop in cell voltage could not be sufficiently suppressed.
• the present invention suppresses the progress of carbon corrosion of the anode gas diffusion electrode even in a CR state caused by a shortage of fuel supplied to the anode gas diffusion electrode of the fuel cell, thereby preventing the power generation performance of the cell from deteriorating.
• An object of the present invention is to provide a gas diffusion electrode that does not
• the gas diffusion electrode of the present invention has a structure in which a microporous layer is formed on a conductive porous substrate. First, the conductive porous substrate will be described.
• porous substrates containing carbon fibers such as carbon fiber fabric, carbon fiber paper, carbon fiber nonwoven fabric, carbon felt, carbon paper, and carbon cloth are used.
• carbon paper refers to a sheet formed by binding a carbon fiber paper body with a resin carbide.
• they have excellent properties of absorbing dimensional changes in the thickness direction of the electrolyte membrane, that is, "springiness". Therefore, it is preferable to use carbon paper.
• carbon fibers examples include polyacrylonitrile (PAN), pitch, and rayon.
• PAN-based carbon fiber and pitch-based carbon fiber are preferably used because of their excellent mechanical strength.
• natural fibers such as rayon fibers, acrylic fibers, and cellulose fibers, and synthetic fibers may be mixed.
• the average diameter of carbon fiber single fibers is preferably 3 to 20 ⁇ m.
• the average diameter is 3 ⁇ m or more, the pore diameter of the conductive porous substrate is increased, the drainage property is improved, and flooding can be suppressed.
• the average diameter is 20 ⁇ m or less, the water vapor diffusibility is reduced, and dryout can be suppressed.
• the average length of carbon fiber single fibers is preferably 3 to 20 mm.
• the average length is 3 mm or more, the mechanical strength, electrical conductivity, and thermal conductivity of the conductive porous substrate are improved.
• the average length is 20 mm or less, the dispersibility of the carbon fibers during papermaking is improved, and a homogeneous conductive porous substrate can be obtained.
• the weight per unit area (basis weight) of the conductive porous substrate is preferably 20 to 50 g/m 2 .
• the basis weight is 20 g/m 2 or more, the mechanical strength and conductivity of the conductive porous substrate are improved.
• the basis weight is 50 g/m 2 or less, the gas diffusibility in the direction perpendicular to the plane of the conductive porous substrate (hereinafter, the direction perpendicular to the plane means the thickness direction) is good, and the power generation performance is improved. do.
• the basis weight of the conductive porous substrate can be adjusted by controlling the amount of carbon fiber, resin carbide, etc., which are constituent materials of the conductive porous substrate.
• a conductive porous substrate that has undergone a water-repellent treatment is preferably used.
• the water-repellent treatment is preferably performed using a water-repellent resin such as a fluorine resin having a fluoroalkyl chain.
• a water-repellent resin such as a fluorine resin having a fluoroalkyl chain.
• the fluororesin include PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PVDF (polyvinylidene fluoride), PVF (polyvinyl fluoride), etc., but PTFE or FEP exhibiting high water repellency is preferred.
• the amount of the water-repellent resin is not particularly limited, it is preferably 0.1 to 20 parts by mass based on 100 parts by mass of the entire conductive porous substrate. Within this range, the water repellent property is sufficiently exhibited, while the water repellent resin can be prevented from clogging pores serving as gas diffusion paths and increasing electrical resistance.
• the method of water-repellent treatment of the conductive porous substrate includes a method of immersing the conductive porous substrate in a water-repellent resin dispersion, as well as a method of applying a water-repellent resin to the conductive porous substrate by die coating, spray coating, etc. can also be applied. Processing by a dry process such as sputtering of fluororesin can also be applied. After the water-repellent treatment, a drying process and a heating process for spreading the water-repellent resin on the substrate may be added as necessary.
• the gas diffusion electrode has high gas diffusivity for diffusing the gas supplied from the separator to the catalyst and high drainage for discharging the water generated in the electrochemical reaction to the separator. sex is required. Therefore, the conductive porous substrate preferably has a pore size peak at 10 to 100 ⁇ m. The pore size and its distribution can be determined by pore size distribution measurement using a mercury porosimeter. In order to obtain the pore size of the conductive porous substrate, only the conductive porous substrate may be measured, or the gas diffusion electrode after forming the microporous layer may be measured.
• each layer structure is confirmed by scanning electron microscope (SEM) observation of the perpendicular cross section (cross section parallel to the thickness direction) of the gas diffusion electrode, and the SEM image is used to determine the conductive porous substrate. Roughly determine the diameter of the pore portion. Subsequently, the pore diameter of the conductive porous substrate is determined while associating multiple pore diameter peaks obtained by a mercury porosimeter with approximate values obtained by the SEM image.
• SEM scanning electron microscope
• the porosity of the conductive porous substrate is preferably 80-95%.
• the porosity is 80% or more, the gas diffusibility increases and the power generation performance improves.
• the porosity is 95% or less, the mechanical strength of the conductive porous substrate increases, and the conductivity also improves. These effects are enhanced when the porosity of the conductive porous substrate is 85 to 90%, which is more preferable.
• the porosity of the conductive porous substrate can be measured using a hydrometer or the like.
• the thickness of the conductive porous substrate of the present invention is preferably 90-180 ⁇ m.
• the thickness of the conductive porous substrate is the thickness when both surfaces are sandwiched under a pressure of 0.15 MPa.
• the gas diffusion electrode can absorb the dimensional change due to the expansion and contraction of the electrolyte membrane during use of the fuel cell due to its high springiness, and the gas diffusion in the in-plane direction is improved, so the power generation performance is improved.
• the thickness of the conductive porous substrate is 180 ⁇ m or less, the gas diffusibility in the perpendicular direction is increased, and the conductive path in the perpendicular direction is shortened, resulting in good conductivity. Better performance. These effects are enhanced when the thickness of the conductive porous substrate is 110 to 150 ⁇ m, which is more preferable.
• the microporous layer has a microporous layer in contact with one surface of the conductive porous substrate. reduction of the interfacial electrical resistance with the conductive porous substrate, suppression of breakage of the electrolyte membrane by the carbon fibers protruding from the conductive porous substrate, and the like.
• the microporous layer is a layer containing fine carbon particles and a fluororesin having a fluoroalkyl chain.
• the specific surface area of the carbon fine particles is A (m 2 /g), the content of the carbon fine particles per unit volume in the microporous layer, and the content of the fluororesin having the fluoroalkyl chain. are B (g/cm 3 ) and C (g/cm 3 ) respectively, the value of A ⁇ 30 ⁇ (C/B) is 10 to 50. It is preferably 10-28, more preferably 10-25.
• the calculation formula “A ⁇ 30 ⁇ (C/B)” is hereinafter referred to as formula X.
• the electrochemical corrosion reaction of the carbon of the anode gas diffusion electrode shown by reaction (4) proceeds.
• the carbon in the vicinity of the catalyst layer is most preferentially reacted. Since the microporous layer of the gas diffusion electrode is in contact with the catalyst layer, the carbon present in the microporous layer, that is, carbon fine particles, corrodes preferentially.
• the inventors discovered that the corrosion reaction of the carbon fine particles in the CR state depends on how much the surface of the carbon fine particles present in the microporous layer is covered with a fluororesin having a fluoroalkyl chain. It has been found that X is an index representing the state of coating of carbon fine particles with a fluororesin having a fluoroalkyl chain.
• the value of formula X is 10 or more, the amount of fluororesin having a fluoroalkyl chain is not too large, so the electrical resistance of the gas diffusion electrode is kept low.
• the value of formula X is 50 or less, the fluororesin having a fluoroalkyl chain covers the surface of the carbon microparticles, suppressing deterioration of the carbon microparticles even in the CR state, thereby suppressing deterioration of power generation performance.
• the value of the formula X is 28 or less, these effects are enhanced, which is more preferable, and the value of the formula X is more preferably 25 or less.
• the carbon microparticles are preferably non-porous carbon microparticles in which pores are not formed inside.
• the specific surface area of carbon fine particles can be measured by the BET method (JIS Z 830, ISO 9277) using nitrogen gas adsorption.
• the specific surface area of commercially available non-porous carbon fine particles measured by the BET method is #3030B: 29 m 2 /g, #3050B: 50 m 2 /g, #3230B: 200 m 2 /g (manufactured by Mitsubishi Chemical Corporation).
• the specific surface area of commercially available porous carbon fine particles measured by the BET method is as follows: "Blackpearls (registered trademark)” 2000: 1475 m 2 /g (manufactured by Cabot Corporation), "Ketjen Black (registered trademark)” EC300J: 800 m 2 /g, “Ketjenblack (registered trademark)” EC600JD: 1200 m 2 /g (manufactured by Lion Specialty Chemicals Co., Ltd.), and the like.
• the specific surface area can be obtained by obtaining the total surface area and mass of all the carbon microparticles.
• a known value may be used, or it may be measured by the BET method described above.
• carbon black, carbon nanofiber, graphene, etc. are used as carbon fine particles.
• carbon black which is inexpensive, is preferably used.
• the carbon fine particles which have been heat-treated at a high temperature in an inert gas to increase the average crystal grain size, are preferable because they are less likely to be oxidized.
• the specific surface area of the carbon fine particles is preferably 20-40 m 2 /g.
• the specific surface area of the carbon fine particles is 20 m 2 /g or more, the dispersibility of the carbon fine particles in the microporous layer coating liquid increases, so that a uniform microporous layer can be formed.
• the moisture retention and drainage properties of the microporous layer are enhanced, power generation performance is improved.
• the specific surface area of the carbon fine particles is 40 m 2 /g or less, the carbon corrosion reaction in the CR state of the gas diffusion electrode is suppressed.
• the content of fluororesin and carbon fine particles having fluoroalkyl chains per unit volume in the microporous layer can be measured by mass spectrometry.
• the content of the fluororesin having a fluoroalkyl chain in the microporous layer is determined by analyzing the degassing components when the microporous layer is heated to 1000° C. in a He atmosphere to decompose and remove the resin component.
• the content of carbon fine particles can be measured from the mass of the residue of the thermal decomposition treatment. By dividing these by the volume of the microporous layer to be measured, the content per unit volume can be obtained. Further, the specific surface area of the carbon fine particles can be determined by analyzing the residue by the BET method.
• fibrous non-porous carbon fine particles such as carbon nanofibers form conductive paths inside the microporous layer, they have the effect of lowering the electrical resistance of the microporous layer.
• PTFE polytetrafluoroethylene; melting point 327°C
• FEP tetrafluoroethylene/hexafluoropropylene copolymer; melting point 260°C
• PFA tetrafluoroethylene/perfluoroalkyl vinyl ether copolymer; melting point 305°C
• ETFE tetrafluoroethylene/ethylene copolymer polymer; melting point 265°C
• PVDF polyvinylidene fluoride; melting point 177°C
• PVF polyvinyl fluoride; melting point 190°C
• the melting point of the fluororesin having a fluoroalkyl chain is preferably 200-300°C.
• the melting point of the fluororesin having a fluoroalkyl chain is 200° C. or higher, the fluororesin having a fluoroalkyl chain is inhibited from moving together with the solvent in the drying process after coating the microporous layer, and the fluororesin having a fluoroalkyl chain is suppressed.
• the fluororesin can be uniformly present inside the microporous layer. Further, when the melting point of the fluororesin having a fluoroalkyl chain is 300° C.
• the fluororesin having a fluoroalkyl chain quickly melts into the microporous layer during the heat treatment after coating and drying the microporous layer. Since it spreads by wetting, the water repellency of the microporous layer is improved. If the melting point of the fluororesin having a fluoroalkyl chain is 230 to 270° C., these effects are enhanced, which is more preferable.
• the melting point of a fluororesin having a fluoroalkyl chain can be obtained by measuring the temperature at which the substance melts when the temperature of the substance is gradually increased. For example, using a differential scanning calorimeter, it is determined by measuring the temperature showing an endothermic peak when the temperature is raised from room temperature to 400° C. at 10° C./min under a nitrogen atmosphere.
• fluororesins having fluoroalkyl chains are insoluble in water and organic solvents. It is preferred to use a dispersion of Examples of dispersions of fluororesin having fine particle-like fluoroalkyl chains include "Polyflon (registered trademark)" D-210C, ND-110 (manufactured by Daikin Industries, Ltd.), 120-JRB, 31-JR (Mitsui Ke Mars Fluoro Products Co., Ltd.), and the like.
• the microporous layer of the present invention may contain a water-repellent resin such as a fluororesin having no fluoroalkyl chain or a silicone resin having a siloxane bond.
• a thermosetting resin may be contained. Thermosetting resins include phenolic resins, epoxy resins, acrylate resins, furan resins, and the like.
• the microporous layer may contain fine particles of iridium oxide, ruthenium oxide, titanium oxide, etc. that promote electrolysis of water in a reverse potential (CR) state during hydrogen deficiency.
• fine particles such as cerium oxide and manganese oxide may be contained for inactivating hydroxide radicals generated at the anode electrode.
• the microporous layer of the present invention preferably has a basis weight of 10 to 35 g/m 2 .
• the basis weight of the microporous layer is 10 g/m 2 or more, the carbon fibers protruding from the surface of the conductive porous substrate are covered, so that damage to the electrolyte membrane by the carbon fibers can be suppressed, which is preferable.
• the microporous layer has a basis weight of 35 g/m 2 or less, because the drainage property is improved.
• the surface of the microporous layer of the present invention preferably has few irregularities, cracks, pinholes, and the like. When these defects are few and the surface is smooth, the durability of the microporous layer is improved, and the electrical resistance and thermal resistance of the interface between the microporous layer and the electrolyte membrane with the catalyst layer are lowered. In addition, since the carbon fine particles in the microporous layer are less likely to come into contact with water, the progress of the corrosion reaction of the carbon fine particles is suppressed.
• the arithmetic mean roughness (Ra), which is an index of smoothness of the surface of the microporous layer, is preferably 7 ⁇ m or less. Ra can be measured using a laser microscope.
• the unevenness profile at a length of 5 mm at an arbitrary location on the surface is measured, and the average value can be calculated as Ra.
• Ra is 1 ⁇ m or more, the generated water is likely to be trapped in the recesses present on the surface of the microporous layer, and the interface of the catalyst layer in contact with the surface of the microporous layer is moistened to increase the catalytic activity, which is preferable.
• the thickness of the gas diffusion electrode of the present invention is preferably 90-200 ⁇ m.
• the thickness of the gas diffusion electrode is the thickness when both surfaces are sandwiched by a pressure of 0.15 MPa.
• the thickness of the gas diffusion electrode is 90 ⁇ m or more, the mechanical strength is maintained and the handling in the manufacturing process is easy.
• the thickness of the gas diffusion electrode is 200 ⁇ m or less, the gas diffusibility is enhanced and the electrical resistance is reduced, thereby improving the power generation performance of the fuel cell.
• the thickness of the gas diffusion electrode can be adjusted by appropriately adjusting the thickness of each of the conductive porous substrate and the microporous layer.
• carbon fiber bundles cut to a predetermined length are loosened in water, uniformly dispersed to produce a carbon fiber dispersion liquid, which is then drawn up and dried to produce a paper body of carbon fibers.
• the carbon fiber dispersion may contain a surfactant, a thickener, and an antifoaming agent. good too.
• Polyvinyl alcohol, polyvinyl acetate, or the like is used as the water-soluble resin.
• the speed of the papermaking wire can be increased to orient the carbon fibers in the longitudinal direction, increasing the elastic modulus in the direction of carbon fiber orientation.
• arranging the carbon fiber orientation direction of the gas diffusion electrode and the separator flow path at right angles prevents the gas diffusion electrode from being pushed into the grooves of the flow path, thereby improving drainage.
• the carbon fiber paper body obtained above may be used as the conductive porous substrate of the present invention, but in order to improve mechanical strength and reduce electrical resistance, the intersections of the carbon fibers are bound with resin carbide. is preferred.
• a method of impregnating a carbon fiber paper body with a resin composition solution and then heat-treating it to carbonize the resin component in the resin composition can be applied.
• Thermosetting resins such as phenolic resins, epoxy resins, melamine resins, and furan resins are examples of resins used in the resin composition solution.
• the resin composition solution may contain carbon powder, a surfactant, and the like in addition to the resin component and the solvent. Carbon powders include carbon black, graphite, graphite, carbon nanotubes, carbon nanofibers, and the like.
• Methods for impregnating the resin composition solution include immersion, spraying, blade coating, die coating, and transfer methods. By adjusting the impregnation method, a gradient distribution of the amount of the resin composition in the thickness direction of the substrate may be imparted.
• the substrate impregnated with the resin composition solution is dried in air at a temperature of 80°C to 150°C. Subsequently, by heating in the air at a temperature of 200° C. to 300° C., the thermosetting resin is cured and the surfactant and the like are decomposed and removed. At this time, the flatness of the substrate may be improved and the thickness thereof may be adjusted by pressing both surfaces of the substrate with a flat plate.
• the resin composition in order to increase the conductivity of the base material and improve long-term durability, it is preferable to carbonize the resin composition after curing at a temperature of 1000°C to 2400°C in an inert atmosphere such as nitrogen.
• an inert atmosphere such as nitrogen.
• pre-carbonization is performed at a temperature of 300° C. to 1000° C. in an inert atmosphere before carbonization to decompose and remove impurities to bring the crystal structure closer to that of graphite, the crystallinity during carbonization can be improved. is increased, and the above performance is enhanced, which is preferable.
• the base material thus obtained can have sufficient conductivity as a conductive porous base material for gas diffusion electrodes of fuel cells.
• a water-repellent treatment may be applied to improve the drainage of the conductive porous substrate.
• the water-repellent treatment is performed by immersing the base material in a liquid containing a water-repellent resin, drying it, and applying a heat treatment to wet and spread the water-repellent resin inside the base material. A adhered conductive porous substrate is obtained.
• the water-repellent resin the same fluororesin contained in the microporous layer can be used. Further, it is also possible to use a liquid containing a water-repellent resin obtained by diluting a dispersion liquid of a water-repellent resin in the form of fine particles to a predetermined concentration.
• the conductive porous substrate of the present invention can be obtained.
• the microporous layer can be formed by applying a coating liquid obtained by dispersing carbon fine particles and a fluororesin having a fluoroalkyl chain in a solvent such as water onto the conductive porous substrate, followed by heat treatment.
• a coating liquid obtained by dispersing carbon fine particles and a fluororesin having a fluoroalkyl chain in a solvent such as water
• a dispersant a thickener, or the like
• a dispersant a nonionic surfactant is preferable because it has a small amount of metal components.
• a polyoxyalkylene aryl ether that increases the dispersion stability of the coating liquid and improves the surface smoothness of the resulting microporous layer.
• System “Triton (registered trademark)" X-100 manufactured by Nacalai Tesque Co., Ltd.) and the like are preferable.
• thickener for example, methylcellulose-based, polyethylene glycol-based, polyvinyl alcohol-based, and the like are preferably used.
• the same substance may have two functions, or materials suitable for each function may be selected.
• the thickener and the dispersant are selected separately, it is preferable to select a thickener that does not impair the dispersibility of the carbon fine particles and the fluororesin having a fluoroalkyl chain.
• fine particles such as iridium oxide, ruthenium oxide, and titanium oxide are added to promote electrolysis of water, and fine particles such as cerium oxide and manganese oxide are added to inactivate radicals.
• the above mixture is kneaded using a homogenizer, a planetary mixer, an ultrasonic disperser, or the like to obtain a coating liquid for forming a microporous layer.
• the application of the coating liquid for forming the microporous layer to the conductive porous substrate can be performed using various commercially available coating devices.
• a coating method screen printing, rotary screen printing, intaglio printing, gravure printing, spray coating, die coating, bar coating, blade coating, roll knife coating, and the like can be used.
• the coating liquid is dried at a temperature of 60 ° C. to 150 ° C., and then heated at a temperature of 250 ° C. to 380 ° C. to add a dispersant or a thickener. It promotes the decomposition and removal of additives such as fluororesin and the melting of the fluororesin having a fluoroalkyl chain. At this time, not only the fluororesin having a fluoroalkyl chain in the microporous layer but also the water-repellent resin adhering to the conductive porous substrate melts, and these are other constituent materials such as carbon fibers and resins. Wet and spread on the surface of carbides, carbon fine particles, etc. As a result, the drainage properties of the conductive porous substrate and the microporous layer are enhanced, and the performance of the fuel cell using this is improved.
• the gas diffusion electrode of the present invention is particularly preferably used as an anode electrode.
• the microporous layer side surface of the gas diffusion electrode of the present invention was joined to one side surface of an electrolyte membrane (CCM) having catalyst layers on both sides, and a separately prepared cathode gas diffusion electrode microporous layer was attached to the surface opposite to the CCM.
• a membrane-electrode assembly (MEA) is produced by joining with the surface on the porous layer side.
• the gas diffusion electrode of the present invention may also be used in the cathode gas diffusion electrode.
• the obtained MEA is sandwiched from both sides by two separators for the anode and the cathode in which gas flow paths are formed to fabricate a fuel cell.
• the size of the MEA is set so that it is one size smaller than the circumference of the two separators, and a gasket is arranged so as to surround the outside of the MEA.
• the MEA is fixed in a compressed state to a moderate thickness. Since the thickness of the MEA in the power generation cell can be controlled by adjusting the thickness of the gasket, the performance can be optimized according to the power generation purpose.
• an inlet/outlet for supplying hydrogen is provided on the anode side, and an inlet/outlet for supplying air is provided on the cathode side.
• the separator is made of a conductive material such as stainless steel or carbon, it is possible to supply and withdraw electricity by connecting electrical wiring. Furthermore, by providing a passage through which circulating water can be supplied inside the separator, the cell can be maintained at a predetermined temperature.
• a high voltage such as 40 kV to 200 kV can be generated. It can be used as a power source for automobiles and the like.
• ⁇ Method for producing conductive porous substrate Polyacrylonitrile-based carbon fiber “Torayca (registered trademark)” T300 (average fiber diameter: 7 ⁇ m) manufactured by Toray Industries, Inc. was cut into lengths of 12 mm and dispersed in water for continuous papermaking. A mass % aqueous solution was spray-coated and dried to obtain a long paper sheet made of carbon fibers and having a basis weight of 20 g/m 2 . The adhered amount of polyvinyl alcohol was 20 parts by mass with respect to 100 parts by mass of the paper body.
• a composition solution was prepared. Then, the resin composition solution is continuously spray-coated on the carbon fiber paper body so that the total of the phenolic resin and the scale-like graphite is 130 parts by mass with respect to 100 parts by mass of the carbon fibers in the base material. It was applied and dried at 100° C. for 5 minutes.
• the base material to which the resin composition was adhered was sandwiched between upper and lower hot plates by a press molding machine, and subjected to heat compression treatment at 180°C for 5 minutes.
• release paper is placed between the base material and the hot plate so that the hot plate and the base material do not adhere to each other. made adjustments.
• it was carbonized by heating at 2400° C. in a nitrogen atmosphere in a heating furnace.
• a water-repellent resin dispersion obtained by mixing 5 parts by mass of PTFE fine particle dispersion (“Polyflon (registered trademark)” D-210C manufactured by Daikin Industries, Ltd.) and 95 parts by mass of ion-exchanged water was spray-coated. C. for 5 minutes to obtain a conductive porous substrate having a thickness of 150 ⁇ m at 0.15 MPa and a basis weight of 40 g/m 2 .
• Arithmetic mean roughness (Ra) at a length of 5 mm on the microporous layer side surface of the gas diffusion electrode was measured using a laser microscope "VK-X3000" (manufactured by KEYENCE CORPORATION). Ra was measured at arbitrary four points on a 30 mm ⁇ 30 mm test piece, and the average value was calculated.
• This MEA was assembled into a fuel cell single cell, hydrogen was supplied to the anode side and air was supplied to the cathode side at a cell temperature of 70° C., and a power generation state was maintained for 3 hours at a current density of 1 A/cm 2 .
• the fuel utilization efficiency was 70%
• the air utilization efficiency was 40%
• the dew points of hydrogen on the anode side and air on the cathode side were 59°C (relative humidity: 60%) and 60°C, respectively. introduced inside.
• the voltage value after 3 hours was read as the power generation voltage and used as an index of the power generation performance.
• Example 1 Using carbon fine particles A as the carbon fine particles, PTFE as the fluororesin having a fluoroalkyl chain, polyoxyalkylene aryl ether-based “Triton (registered trademark)” X-100 (manufactured by Nacalai Tesque Co., Ltd.) as the dispersant, and a dispersion medium.
• a microporous layer-forming coating liquid was prepared so that the content of the total amount was 23% by mass.
• a dispersion of PTFE particles in water "Polyflon (registered trademark)" D-210C (manufactured by Daikin Industries, Ltd.) was used as a source of PTFE.
• the microporous layer-forming coating liquid is applied onto the conductive porous substrate manufactured according to ⁇ Method for manufacturing conductive porous substrate> using a die coater, and dried at 100° C. for 10 minutes. After that, the mixture was heated at 350° C. for 10 minutes to promote the adhesion between the fluororesin having a fluoroalkyl chain and the carbon fine particles and to decompose and remove the dispersant and the like, thereby producing a gas diffusion electrode.
• the coating amount was adjusted so that the fabric weight of the microporous layer after heating was 20 g/cm 2 . Note that the fluororesin having a fluoroalkyl chain is not decomposed by heating at 350° C. for 10 minutes.
• the arithmetic mean roughness of the surface of the microporous layer of the obtained gas diffusion electrode was 6 ⁇ m.
• the power generation performance was evaluated, and it was 0.58V. Further, CRT evaluation showed that the retention time was 50 hours.
• Examples 2 to 14, Comparative Examples 1 to 6 A microporous layer-forming coating liquid was prepared in the same manner as in Example 1 except that the types and parts by mass of each component were as shown in Tables 1 to 3, and applied on the conductive porous substrate. A gas diffusion electrode was obtained. In Examples 11 to 14 and Comparative Examples 5 to 6, a dispersion of FEP particles in water "Polyflon" (registered trademark) ND-110 (manufactured by Daikin Industries, Ltd.) was used as the source of FEP. Using the obtained gas diffusion electrode, power generation performance evaluation and CRT evaluation were performed, and the results are shown in Tables 1 to 3. For Comparative Example 2, Example 1 of Patent Document 1 was referred to. For Comparative Example 3, Example 1 of Patent Document 2 was referred to, and for Comparative Example 4, Comparative Example 1 of Patent Document 3 was referred to.
• Carbon fine particles C are used as carbon fine particles
• PTFE is used as a fluororesin having a fluoroalkyl chain
• polyoxyalkylene alkyl ether-based "Emulgen” 430 (manufactured by Kao Corporation) is used as dispersant A
• "Unileave (registered)" is used as dispersant B.
• the microporous layer-forming coating liquid is applied onto the conductive porous substrate manufactured according to ⁇ Method for manufacturing conductive porous substrate> using a die coater, and dried at 100° C. for 10 minutes. After that, the mixture was heated at 350° C. for 10 minutes to promote the adhesion between the fluororesin having a fluoroalkyl chain and the carbon fine particles and to decompose and remove the dispersant and the like, thereby producing a gas diffusion electrode.
• the coating amount was adjusted so that the fabric weight of the microporous layer after heating was 20 g/cm 2 . Note that the fluororesin having a fluoroalkyl chain is not decomposed by heating at 350° C. for 10 minutes.
• the arithmetic mean roughness of the surface of the microporous layer of the obtained gas diffusion electrode was 8 ⁇ m.
• the power generation performance was evaluated, and it was 0.60V. Further, CRT evaluation showed that the retention time was 38 hours.

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