JP6801224B2 - Fine porous layer forming paste, gas diffusion layer for fuel cells and fuel cells - Google Patents

Description

The present invention relates to a fine porous layer forming paste.

A fuel cell is a system that can directly convert chemical energy into electrical energy using an electrochemical system, and is expected as next-generation energy because of its high efficiency. In particular, polymer electrolyte fuel cells are being actively developed for automobiles, stationary, and small mobiles.

Generally, in a polymer electrolyte fuel cell, cathode side electrodes and anode side electrodes are formed on both sides of a polymer electrolyte membrane, and these cathode side electrodes and anode side electrodes usually carry a catalyst such as platinum. It is composed of an electrode catalyst layer made of carbon black and an ion exchange resin, and a gas diffusion layer that supplies a reaction gas to the catalyst layer and collects charges generated in the catalyst layer. As the gas diffusion layer, a conductive porous base material having both gas diffusion ability and conductivity is generally used. Specifically, a carbon base material such as carbon cloth or carbon paper is used.

In the gas diffusion layer used in such a polymer electrolyte fuel cell, the electric resistance between the gas diffusion layer and the catalyst layer is lowered, and the electrolyte film is not damaged due to fiber fraying of the gas diffusion layer base material. As an intermediate layer for further preventing water repellency and imparting further water repellency, a carbon powder such as carbon black and a fluororesin dispersion are used as main components on a conductive porous base material constituting a gas diffusion layer. It is known to provide a microporous layer (Micro Porous Layer, hereinafter may be abbreviated as "MPL") (for example, Patent Document 1).

As a method for forming such an MPL, a paste made of carbon powder such as carbon black is prepared using water as a solvent, and the paste is made conductively porous by using a spray method or a printing method, a bar coater, a doctor blade or the like. Examples include a method of coating on a quality substrate.

Conductive porous substrates such as carbon cloth and carbon paper are porous to facilitate the passage of reaction gas and excess water, and therefore use an MPL-forming paste for forming MPL as a substrate. When applied to, part of the paste soaks into the base material, but if the amount of soaked paste is large, the pores in the base material are blocked, and the ability to supply the gas required for the reaction to the catalyst layer and excess There is a risk that the performance of discharging a large amount of water will deteriorate and the battery characteristics will deteriorate.

Further, the MPL formed by applying the MPL forming paste to the base material constitutes a part of the gas diffusion layer, and the gas diffusion layer as a whole is required to have both gas diffusion ability and conductivity. As mentioned above, it goes without saying that MPL is also required to have excellent conductivity as well as gas diffusion ability.

Therefore, as a paste for forming MPL, in order to prevent sagging after coating and permeation into a conductive substrate, Patent Document 2 aims to adjust the viscosity of the water-repellent paste for a gas diffusion layer. Disclosed is a water-repellent paste for a gas diffusion layer, which is a mixture of a carbon black slurry with a fluororesin dispersion, a solvent that is difficult to dissolve in water, and a solvent that is easily soluble in water, and has appropriate permeability to a substrate.

Further, in Patent Document 3, the catalyst layer and the gas diffusion sheet base material have a function of not changing or reducing the electric resistance and a function of securing a gas flow path and improving gas permeability. A fuel cell junction characterized by having a gas diffusion layer obtained by mixing a water-repellent resin and a component containing a vapor-grown carbon fiber having a fiber diameter of 10 to 300 nm and a fiber length of 100 μm or less is provided between the two. It is disclosed.

JP-A-2002-056851 Japanese Unexamined Patent Publication No. 2004-247148 Japanese Unexamined Patent Publication No. 2004-119398

However, in the technique described in Patent Document 2, any of a linear or side chain alcohol having a molecular weight of 70 or more, an ester, a ketone, or an ether is used as a solvent which is hardly soluble in water, and as a solvent which is easily soluble in water. The viscosity of the water-repellent paste for the gas diffusion layer is adjusted by using an ethylene oxide-added surfactant of alcohol with an HLB value of 8 to 13, but there is a problem that the penetration of the paste into the substrate cannot be completely prevented. There was a point. Further, depending on the type of solvent used, there is also a problem that coating unevenness and pinholes occur at the time of coating the water-repellent paste for the gas diffusion layer.

Further, in the technique described in Patent Document 3, is it possible to change the electric resistance by using a gas phase-grown carbon fiber having a fiber diameter of 10 to 300 nm and a fiber length of 100 μm or less as the conductive filler of the MPL forming paste? Or, it has a function to reduce it and a function to secure a gas flow path and improve gas permeability, but it is difficult to stabilize the dispersion of vapor-grown carbon fibers and the particle size cannot be made sufficiently small. There is a problem that coating unevenness and pinholes occur due to the coarse particles in the forming paste. It goes without saying that a fuel cell using a gas diffusion layer with MPL having uneven coating and pinholes is inferior in its power generation performance.

The problems to be solved by the present invention are excellent in flow characteristics (particle size, viscosity, etc.) and coatability on a base material (suppression of penetration amount, generation of pinholes), and gas by increasing pores in MPL. It is an object of the present invention to provide a fine porous layer forming paste suitable for MPL formation that improves diffusivity, and a fuel cell using the same and having good power generation characteristics.

The present inventors have reached the present invention as a result of repeated diligent studies to solve the above problems.

That is, an embodiment of the present invention is a fine porous layer forming paste used for forming a fine porous layer of a fuel cell, which comprises water, a carbon-based conductive filler, a fluorine-based resin dispersion, and a temperature rise. Formation of a microporous layer characterized by containing two types of first and second surfactants having different temperatures, in which 60% of the total mass is reduced when heated at a rate of 10 ° C./min. Regarding paste.

Further, in the embodiment of the present invention, the two types of surfactants having different temperatures at which 60% of the total mass is reduced are the first surfactant having a high temperature at which 60% of the total mass is reduced and the total mass. The temperature difference between the first surfactant and the second surfactant, which is 60% of the total mass of the first surfactant and the second surfactant, is 5 to 75 ° C. The present invention relates to a fine porous layer-forming paste, which is characterized by being contained.

Further, in the embodiment of the present invention, the first surfactant having a high temperature at which 60% of the total mass is reduced and the second surfactant having a low temperature at which 60% of the total mass is reduced are the total mass. The present invention relates to the fine porous layer-forming paste in which the temperature at which the weight is reduced by 60% is 220 to 350 ° C.

Further, in the embodiment of the present invention, the total amount of the first surfactant and the second surfactant having different temperatures at which 60% of the total mass is reduced is 50 with respect to 100 parts by mass of the carbon-based conductive filler. The present invention relates to the fine porous layer forming paste containing ~ 200 parts by mass.

Further, an embodiment of the present invention relates to a gas diffusion layer for a fuel cell, which comprises the fine porous layer-forming paste on a substrate.

Further, an embodiment of the present invention relates to a fuel cell including the gas diffusion layer for a fuel cell.

According to the present invention, water, a carbon-based conductive filler, a fluororesin-based resin dispersion, and two types of different temperatures in which 60% of the total mass is reduced when heated at a heating rate of 10 ° C./min. With a simple composition containing 1 surfactant and 2nd surfactant as the main components, it has excellent flow characteristics and coatability on the base material, and improves gas diffusion ability by increasing the number of pores in the MPL. It becomes possible to provide a fine porous layer forming paste suitable for MPL formation. This makes it possible to provide a fuel cell having good power generation characteristics.

Hereinafter, the present invention will be described in more detail.
1. 1. Fine Porous Layer Forming Paste 60% of the total mass of the solvent, water, carbon-based conductive filler, and fluorine-based resin dispersion contained in the paste of the present invention when heated at a heating rate of 10 ° C./min. The ratio of the two types of the first surfactant and the second surfactant having different temperatures at which the paste is reduced is not particularly limited and may be appropriately selected within a wide range. The content of the fluorine-based resin dispersion is 15 to 60 parts by mass, preferably 20 to 50 parts by mass, based on 100 parts by mass of the carbon-based conductive filler in the fine porous layer-forming paste. It is preferably 30 to 40 parts by mass. In addition, the sum of the two types of first and second surfactants having different temperatures, in which 60% of the total mass is reduced when heated at a heating rate of 10 ° C./min, is contained in the fine porous layer-forming paste. It is more preferably 50 to 200 parts by mass, preferably 75 to 175 parts by mass, and 100 to 160 parts by mass with respect to 100 parts by mass of the carbon-based conductive filler.

<Carbon-based conductive filler>
Examples of the carbon-based conductive filler which is a constituent component of the fine porous layer-forming paste in the present invention include carbon black powder, carbon nanotube powder, graphite powder and the like.

Examples of the carbon black powder include furnace black, acetylene black, ketjen black, and medium thermal carbon black. Carbon black has various physical properties and costs such as particle size, shape, BET specific surface area, DBP oil absorption, surface acid basicity, surface hydrophilicity, and conductivity depending on the type and manufacturer, so it is suitable for the application and required performance. The optimum material can be selected accordingly. As the DBP oil absorption amount of carbon black, it is preferable that the value measured in accordance with JIS K 6217-4: 2008 is 100 to 250 mL / 100 g.

Commercially available carbon blacks include, for example, Ketjen Black EC-300J and EC-600JD made by Axo; Talker Black # 4300, # 4400, # 4500, and # 5500 made by Tokai Carbon. Black; Furnace Black manufactured by Orion Engineered Carbons Co., Ltd. such as PinteXL; Furnace Black manufactured by Colombian Co., Ltd. Mitsubishi Chemical Furnace Black such as 2400B, # 2600B, # 3050B, # 3030B, # 3230B, # 3350B, # 3400B, and # 5400B; Cabot Corporation such as MONARCH1400, 1300, 1000, 900, VulcanXC-72R, and BlackPearls2000. Furness Black manufactured by TIMCAL such as Ensaco250G, Ensaco260G, Ensaco350G, and SuperP-Li; Denka Black, Denka Black HS-100, FX-35 and other acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. It is not limited to.

The carbon nanotube powder has a shape in which one surface of graphite is wound into a cylindrical shape, and the graphite layer is a single-walled carbon nanotube having a structure in which one layer is wound, and two or more layers are wound. The carbon nanotubes may be mixed, but the multilayer carbon nanotubes are preferable from the viewpoint of cost. Further, it is also possible to use carbon nanotubes having an amorphous structure instead of the graphite structure on the side wall of the carbon nanotube.

The shape of the carbon nanotube may be any form such as a needle shape, a cylindrical tube shape, a fish bone shape (fishbone, cup laminated type), a playing card shape (platelet), and a coil shape. Specific examples thereof include graphite whisker, firamentas carbon, graphite fiber, ultrafine carbon tube, carbon tube, carbon fibril, carbon microtube, carbon nanofiber and the like. As these forms, one type or a combination of two or more types can be used. The present invention preferably has a form other than fish bone shape (fish bone, cup laminated type), playing card shape (platelet), and coil shape.

The carbon nanotubes can be generally produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, a combustion method, or the like, but the present invention may be any carbon nanotube produced by any method. For example, carbon nanotubes can be produced by contact-reacting a hydrocarbon and / or alcohol as a carbon source at 500 to 1000 ° C. in an atmosphere having an oxygen concentration of 1% by volume or less using a catalyst.

As the raw material gas as the carbon source of the carbon nanotube, any conventionally known raw material gas can be used. For example, hydrocarbons such as methane, ethylene, propane, butane and acetylene, carbon monoxide, alcohol and the like are used as the gas containing carbon. However, it is desirable to use hydrocarbons or alcohols, especially for ease of use.

The catalyst used for producing carbon nanotubes is, if necessary, activated in a reducing gas atmosphere, or together with the reducing gas, in an atmosphere having an oxygen concentration of 1% by volume or less, as a raw material gas as a carbon source. It is preferable to produce by contact-reacting with. The atmosphere having an oxygen concentration of 1% by volume or less is not particularly limited, but an atmosphere of a rare gas such as argon gas or an inert gas such as nitrogen gas is preferable. As the reducing gas used for activation, hydrogen, ammonia and the like can be used, but hydrogen is particularly preferable.

As the catalyst used for producing carbon nanotubes, various conventionally known metal oxides can be used. For example, a catalyst in which a metal containing an active component such as cobalt, nickel or iron and a metal containing a supporting component such as magnesium or aluminum are combined can be mentioned.

The fiber diameter of the carbon nanotube is preferably 1 to 500 nm, more preferably 5 to 150 nm from the viewpoint of ease of dispersion.

For the fiber diameter of carbon nanotubes, observe the carbon nanotubes with a scanning transmission electron microscope, select any 100 carbon nanotubes in the observation photograph, measure the outer diameter of each, and obtain the average value of the numbers. It can be measured by calculating the average particle size (nm).

The fiber length of the carbon nanotubes is preferably 0.1 to 150 μm, more preferably 1 to 10 μm, from the viewpoint of ease of dispersion.

The carbon purity of the carbon nanotubes is preferably 85% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, based on 100% by mass of the carbon nanotubes.

The carbon nanotube may be a surface-treated one or a carbon nanotube derivative to which a functional group such as a carboxyl group is imparted. Further, carbon nanotubes containing organic compounds, metal atoms, fullerenes and the like can also be used.

Examples of commercially available carbon nanotubes include carbon nanotubes manufactured by Showa Denko Co., Ltd. such as VGCF-H; carbon nanotubes manufactured by Nanocil Co., Ltd. such as NC7000; carbon nanotubes manufactured by CNano Co., Ltd. It is not limited.

Examples of graphite include natural graphite such as artificial graphite, flake graphite, lump graphite, and earth graphite, but they may be used in combination.

<Surfactant>
At least two kinds of surfactants having different temperatures, which are components of the paste for forming a fine porous layer in the present invention, in which 60% of the total mass is reduced when heated at a heating rate of 10 ° C./min, have a total mass. A first surfactant having a high temperature at which 60% of the total mass is lost and a second surfactant having a low temperature at which 60% of the total mass is lost, preferably the difference in temperature at which 60% of the total mass is lost is 5. It is ~ 75 ° C., more preferably 10 to 55 ° C., still more preferably 15 to 35 ° C. The temperature at which 60% of the total mass is reduced in the present specification is a value measured using a differential thermal balance Thermo plus TG8120 manufactured by Rigaku Corporation.

The high temperature first surfactant that loses 60% of the total mass and the low temperature second surfactant that loses 60% of the total mass have a temperature at which 60% of the total mass is lost 220 to 350 to 350. ° C., preferably 225 to 300 ° C., more preferably 230 to 270 ° C.

Examples of such surfactants include nonionic surfactants such as polyoxyalkylene alkyl ether, polyoxyalkylene aryl ether, polyoxyalkylene fatty acid ester, polyalkylene glycol fatty acid ester, glycerin fatty acid ester, and polyoxyethylene polyoxypropylene glycol. Activators can be mentioned. Of these, the polyoxyalkylene alkyl ether is preferable because of the dispersibility of the carbon-based conductive filler and the ability to reduce the load during paste drying and firing. The following is a specific example of a nonionic surfactant having a temperature at which 60% of the total mass is reduced at 220 to 350 ° C. (The values in parentheses represent the temperature at which 60% of the total mass is reduced (° C.)). ..

Examples of the polyoxyalkylene alkyl ether include Emargen 130K (237), 150 (231), 350 (242), 430 (309), 709 (246), 4085 (236), 2025G (250) (above, Kao Corporation). , Nonion S-215 (250), Nonion B-250 (256), Unilube MS-70K (240) (all manufactured by NOF CORPORATION) and the like.

Examples of the polyoxyalkylene aryl ether include Emargen A-500 (330) (above, manufactured by Kao Corporation), Triton X-100 (295) (above, manufactured by Nacalai Tesque, Inc.) and the like.

Examples of the polyoxyalkylene fatty acid ester include Emanone 3199V (245) (above, manufactured by Kao Corporation), Emalmin 862 (242) (above, manufactured by Sanyo Chemical Industries, Ltd.) and the like.

Examples of the glycerin fatty acid ester include Leodor MS-165V (282) (all manufactured by Kao Corporation).

Examples of the polyoxyethylene polyoxypropylene glycol include, but are not limited to, Unilube 70DP-950B (254) (all manufactured by NOF CORPORATION).

<Fluorine-based resin dispersion>
The fluorine-based resin dispersion, which is a constituent component of the fine porous layer-forming paste in the present invention, is used to impart water repellency. For example, an aqueous dispersion of a fluorine-based resin, an alcohol dispersion of a fluorine-based resin, and the like. Can be given. Of these, an aqueous dispersion of a fluororesin is preferable from the viewpoint of ease of exhaust gas treatment during drying.

Examples of the fluorine-based resin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and the like. Of these, PTFE is preferable because it has excellent water repellency. Examples of commercially available fluororesin dispersions include PTFE aqueous dispersions manufactured by Daikin Industries, Ltd. such as Polyflon PTFE D-210C; and Mitsui DuPont Fluorochemicals such as Teflon (registered trademark) PTFE dispersion 31-JR and 34-JR. Fluoron PTFE dispersion AD911E and other PTFE aqueous dispersions manufactured by Asahi Glass Co., Ltd., but are not limited thereto.

<Other constituents of the fine porous layer forming paste>
Additives such as thickeners, defoamers, and organic solvents may be mixed with the fine porous layer-forming paste as long as the effects of the present invention are not impaired.

<Thickener>
Examples of the thickener include cellulose-based water-soluble polymers such as methyl cellulose and ethyl cellulose, and urethane-associated thickeners such as nonionic polyurethane.

<Defoamer>
Examples of the defoaming agent include silicone-based surfactants, nonions, anions, cationic surfactants, and dimethylpolysiloxane.

<Organic solvent>
Examples of the organic solvent include a water-soluble organic solvent having a high affinity with water. Alcohol can be preferably used as the water-soluble organic solvent. Examples of the alcohol include monohydric or polyhydric alcohols. Alcohol having a boiling point of 80 to 200 ° C. is preferable, and alcohol having 4 or less carbon atoms is preferable. Specific examples thereof include 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol and the like. As the monohydric alcohol, 2-propanol, 1-butanol and t-butanol are preferable. These organic solvents can be used alone or in admixture of two or more.

<Method for producing microporous layer-forming paste of the present invention>
Next, a method for producing the fine porous layer-forming paste of the present invention will be described. As a device for dispersing a carbon-based conductive filler, which is a component of a fine porous layer-forming paste, in water with a surfactant and mixing it with a fluorine-based resin dispersion liquid, it is a dispersion usually used for pigment dispersion and the like. The machine can be used. For example, mixers such as disposables, homomixers, planetary mixers, homogenizers (M-Technique's "Clearmix", PRIMIX's "Fillmix", Sugino's "Abramix", etc.), paint conditioners ( Red Devil), ball mill, sand mill (Simmal Enterprises "Dyno Mill" etc.), Atwriter, Pearl Mill (Eirich "DCP Mill" etc.), media type disperser such as Coball Mill, wet jet mill (Genus) Medialess disperser such as "Genus PY" manufactured by Sugino Machine Limited, "Star Burst" manufactured by Sugino Machine Limited, "Nanomizer" manufactured by Nanomizer, etc.), "Claire SS-5" manufactured by M-Technique, "MICROS" manufactured by Nara Machinery Co., Ltd. , Other roll mills, etc., but are not limited to these. Further, as the disperser, only one type may be used, or a plurality of types of devices may be used in combination.

2. 2. Gas Diffusion Layer for Fuel Cell Next, the gas diffusion layer for fuel cell using the fine porous layer forming paste of the present invention described above will be described.

<Manufacturing method of gas diffusion layer for fuel cells>
A gas diffusion layer for a fuel cell can be obtained by applying the fine porous layer forming paste of the present invention on a base material and then firing the paste. The method for applying the fine porous layer-forming paste is not particularly limited, and a known method can be used. Specific examples thereof include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a spray coating method, a gravure coating method, and a screen printing method.

Firing after applying the microporous layer-forming paste on the substrate completely removes the surfactant, so that the temperature atmosphere is 250 to 400 ° C., and further, the temperature atmosphere is 300 to 380 ° C. It is preferable to bake. The firing time varies depending on the firing temperature, but may be 30 to 120 minutes from the viewpoint of the time required for completely removing the surfactant.

<Base material>
The base material is not particularly limited, but a conductive porous base material capable of allowing fuel or an oxidizing agent to permeate and having conductivity is preferable. Generally, a metal material, a carbon material or the like is selected as the material, but from the viewpoint of durability, price and the like, carbon paper made of carbon fiber, carbon cloth, carbon felt, carbon non-woven fabric and the like are preferable. The thickness of the base material is not particularly limited, and may be within a range generally adopted as a gas diffusion layer for a fuel cell. Specifically, it is usually about 50 to 1000 μm, preferably about 100 to 400 μm.

3. 3. Fuel cell A fuel cell can be obtained by forming a catalyst layer on a gas diffusion layer for a fuel cell coated with the fine porous layer forming paste of the present invention obtained as described above and using it as an anode and a cathode.

<Catalyst layer>
The catalyst layer for a fuel cell is not particularly limited as long as it is generally used for a fuel cell, and is generally a catalyst-supported carbon particle (carbon particle carrying a catalyst) and a hydrogen ion conductive polymer. Those containing are used. The content ratio of the catalyst-supported carbon particles and the hydrogen ion-conducting polymer is about 10 to 300 parts by mass, preferably about 20 to 250 parts by mass, with respect to 100 parts by mass of the catalyst-supported carbon particles. do it.

<Catalyst-supported carbon particles>
The catalyst-supported carbon particles are carbon particles on which a catalyst is supported, and known or commercially available ones can be used. The carbon particles constituting the catalyst-supported carbon particles are not particularly limited, and examples thereof include carbon black such as channel black, furnace black, thermal black, acetylene black, and lamp black, graphite, activated carbon, carbon fibers, and carbon nanotubes. .. The catalyst carried on the carbon particles is not particularly limited as long as it causes a battery reaction at the fuel electrode or the air electrode of the fuel cell, but a catalyst composed of platinum and a transition metal is preferable, and the transition metal is iron or cobalt. , Nickel, chromium, copper, manganese, titanium, zirconium, vanadium, zinc and the like.

<Hydrogen ion conductive polymer>
Examples of the hydrogen ion conductive polymer include a fluorine ion exchange resin such as a perfluorosulfonic acid type, an olefin resin having a strongly acidic functional group such as a sulfo group introduced therein, and a polyimide resin. For example, by introducing a fluorine atom having a high electronegativity, it is chemically very stable, the dissociation degree of the sulfo group is high, and high ionic conductivity can be realized. Specific examples of such hydrogen ion conductive polymers include "Nafion" manufactured by DuPont, "Flemion" manufactured by Asahi Glass Co., Ltd., "Aciplex" manufactured by Asahi Kasei Co., Ltd., and "Gore" manufactured by Gore. "Gore Select" and the like can be mentioned. Usually, the hydrogen ion conductive polymer is used as an aqueous alcohol solution containing 5 to 30% by mass of the polymer. As the alcohol, for example, methanol, propanol, ethanol diethyl ether and the like are used.

<Paste for forming catalyst layer>
Examples of the catalyst layer forming paste include those obtained by mixing catalyst-supported carbon particles, a hydrogen ion conductive polymer, and a viscosity adjusting solvent. The proportions of the catalyst-supporting carbon particles, the hydrogen ion conductive polymer, and the viscosity adjusting solvent contained in the catalyst layer forming paste are not limited, and can be appropriately selected within a wide range. As the catalyst-supported carbon particles and the hydrogen ion conductive polymer, those described above can be used. Examples of the method for forming the catalyst layer include a method of applying and drying the catalyst layer forming paste on the gas diffusion layer for a fuel cell to which the fine porous layer forming paste is applied.

<Solvent for adjusting viscosity>
Examples of the viscosity adjusting solvent include water and a water-soluble organic solvent having a high affinity with water. Alcohol can be preferably used as the water-soluble organic solvent. Examples of the alcohol include monohydric or polyhydric alcohols. Alcohol having a boiling point of 80 to 200 ° C. is preferable, and alcohol having 4 or less carbon atoms is preferable. Specific examples thereof include 1-propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol and the like. As the monohydric alcohol, 2-propanol, 1-butanol and t-butanol are preferable. As the polyhydric alcohol, propylene glycol and ethylene glycol are preferable, and propylene glycol is more preferable, from the viewpoint of compatibility with the hydrogen ion conductive polymer and the problem of drying efficiency when the catalyst ink composition is used. These viscosity adjusting solvents can be used alone or in admixture of two or more.

<Method of preparing paste for forming catalyst layer>
The method for preparing the paste for forming the catalyst layer is also not particularly limited. In the preparation, each component may be dispersed at the same time, or the catalyst-supported carbon particles may be dispersed and then the hydrogen ion-conducting polymer component may be added. The catalyst-supported carbon particles to be used, the hydrogen ion-conducting polymer, and the viscosity may be added. It can be optimized by the adjusting solvent type. However, if the catalyst-supported carbon particles are dispersed first and the hydrogen ion conductive polymer is added afterwards to prepare a paste for forming a catalyst layer, the dispersion time can be shortened and the cost can be greatly reduced.

<Method of forming catalyst layer>
The catalyst layer for a fuel cell may be formed by directly applying and drying the paste for forming the catalyst layer to the gas diffusion layer for the fuel cell to which the paste for forming the fine porous chamber layer is applied, or forming the catalyst layer. A catalyst layer transfer sheet formed by applying and drying a paste for use on a peelable transfer sheet (base material) such as a Teflon (registered trademark) sheet is produced, and then transferred to a solid polymer electrolyte membrane. May be good.

The catalyst layer for a fuel cell is a fuel obtained by applying the catalyst layer forming paste to a transfer sheet (such as a Teflon (registered trademark) sheet) or applying the catalyst layer forming paste to the fine porous layer forming paste. When it is produced by directly applying it to the gas diffusion layer for a battery and then drying it, a usual coating method can be used as the coating method. The coating method is not particularly limited, and for example, general methods such as knife coater, bar coater, blade coater, spray, dip coater, spin coater, roll coater, die coater, curtain coater, and screen printing can be used. Applicable.

A coating film (catalyst layer for a fuel cell) is formed by applying and drying. The drying temperature is usually 40 to 120 ° C, preferably 75 to 95 ° C. The drying time is usually 5 minutes to 2 hours, preferably 30 minutes to 1 hour, although it depends on the drying temperature. The thickness of the catalyst layer for a fuel cell after coating and drying is usually 5 to 80 μm, preferably 10 to 70 μm.

The pressurization level when the above catalyst layer for a fuel cell is transferred to the solid polymer electrolyte membrane is usually 0.5 to 20 MPa, preferably 1 to 10 MPa in order to avoid transfer failure. Further, during this pressurization operation, it is preferable to heat the pressurizing surface in order to avoid transfer defects. The heating temperature is usually 200 ° C. or lower, preferably 120 to 150 ° C., in order to avoid damage, denaturation, etc. of the solid polymer electrolyte membrane.

<Membrane electrode assembly>
The membrane electrode assembly for a fuel cell is formed by adhering a catalyst layer for a fuel cell on one side or both sides of a hydrogen ion conductive solid polymer electrolyte membrane, and further, the fine porous material is formed on one side or both sides thereof. It means a fuel cell gas diffusion layer coated with a layer-forming paste in close contact with the gas diffusion layer.

As a method for manufacturing a membrane electrode assembly for a fuel cell, a fuel cell catalyst layer previously formed on a fuel cell gas diffusion layer coated with the fine porous layer forming paste is formed on one side of a solid polymer electrolyte membrane. Alternatively, a fuel cell membrane electrode assembly may be produced by heat-bonding on both sides, or a fuel cell catalyst layer previously formed on the transfer substrate may be formed on the solid polymer electrolyte membrane by transfer. The fuel cell membrane electrode assembly may be produced by heat-bonding the fuel cell gas diffusion layer coated with the fine porous layer forming paste. At this time, as the gas diffusion layer for a fuel cell to which the fine porous layer forming paste to be used is applied, a fuel cell catalyst layer may be formed in advance.

In the above membrane electrode assembly for fuel cells, the pressure level when the gas diffusion layer for fuel cells coated with the fine porous layer forming paste, the catalyst layer for fuel cells, and the solid polymer electrolyte membrane are thermally pressure-bonded. Is usually 0.1 to 100 MPa, preferably 1 to 20 MPa. The heating temperature is usually 200 ° C. or lower, preferably 120 to 150 ° C., in order to avoid damage and denaturation of the solid polymer electrolyte membrane.

<Solid polymer electrolyte membrane>
Examples of the solid polymer electrolyte membrane include a perfluorosulfonic acid-based fluorine ion exchange resin and the like. By introducing a fluorine atom having a high electronegativity, it is chemically very stable, the dissociation degree of the sulfo group is high, and high ionic conductivity can be realized. Specific examples of such hydrogen ion conductive polymer electrolytes include "Nafion" manufactured by DuPont, "Flemion" manufactured by Asahi Glass, "Aciplex" manufactured by Asahi Kasei, and "Gore Select" manufactured by Gore. Examples thereof include a film formed by using the above. The film thickness of the electrolyte membrane is usually 20 to 250 μm, preferably 20 to 80 μm.

<Transfer substrate>
The transfer base material is a film base material for forming a catalyst layer for a fuel cell by applying a catalyst layer forming paste and transferring the catalyst layer on the transfer base material to a solid polymer electrolyte membrane such as Nafion. .. As the transfer base material, an inexpensive and easily available polymer film is preferable, and polytetrafluoroethylene, polyimide, polyethylene terephthalate and the like are more preferable. The thickness of the transfer base material is usually 6 to 100 μm, preferably 10 to 50 μm, and more preferably 15 to 30 μm from the viewpoint of handleability and economy.

<Fuel cell>
Compared with the conventional fuel cell, the fuel cell of the present invention uses the gas diffusion layer for a fuel cell coated with the fine porous layer forming paste, so that the resistance of the gas diffusion layer, which is usually in a trade-off relationship, is low. High diffusion can be achieved at the same time, and performance is improved.

An example of a method for evaluating the performance of a fuel cell is shown below. A fuel cell membrane electrode assembly is used as a 4 cm square sample, two gaskets are sandwiched from both sides, then two separators, which are graphite plates, are sandwiched, and two current collector plates are mounted from both sides to prepare a single cell. .. Humidified oxygen gas is supplied from the cathode (air electrode) side, and humidified hydrogen gas is supplied from the anode (fuel electrode) side to measure the battery characteristics.

As described above, the microporous layer-forming paste of the present invention can be produced with a simple composition, and by improving the flow characteristics, the microporous layer-forming paste on the conductive porous substrate can be produced. There is an advantage that the amount of the paste can be controlled and the production efficiency at the time of coating on the base material can be improved. Further, an MPL having many pores can be produced by applying the fine porous layer forming paste to the base material and then drying it. As a result, the gas diffusion layer for a fuel cell coated with the fine porous layer forming paste of the present invention can achieve both low resistance and high diffusion of the gas diffusion layer, which usually have a trade-off relationship. Therefore, the fuel cell produced by using the fine porous layer forming paste of the present invention and the gas diffusion layer for a fuel cell has an advantage that it is superior in power generation performance as compared with a conventional fuel cell.

Next, the present invention will be specifically described with reference to Examples, but the present invention is not particularly limited to the Examples. In each example, unless otherwise specified, "parts" means parts by mass and "%" means% by mass.

(Preparation of fine porous layer forming paste and gas diffusion layer)
[Example 1]
100 parts of carbon black A, at least two kinds of surfactants with different temperatures that lose 60% of the total mass: 80 parts of the high temperature first surfactant A that loses 60% of the total mass and 60% of the total mass After mixing and dispersing 80 parts of the second surfactant B (the temperature difference of 60% of the total mass is 15 ° C.) and 780 parts of water, which have a low temperature to be reduced, using a homogenizer, the fluororesin dispersion A58 is further added. The mixture was partially added and stirred for 10 minutes to obtain a fine porous layer-forming paste. The obtained fine porous layer-forming paste was applied to carbon paper (manufactured by Toray Industries, Inc., TGP-H090, thickness 280 μm) as a base material using an applicator so as to have a grain size of 20 g / m ² after drying. Then, it was dried and calcined at 340 ° C. for 10 minutes to prepare a gas diffusion layer.

In the present invention, the temperature at which 60% of the total mass of the surfactant is reduced was measured using a thermo-plus TG8120 differential heat balance manufactured by Rigaku Corporation. The measurement conditions were flow gas type air, flow gas flow rate 500 mL / min, sample volume 10 mg, heating rate 10 ° C./min, and temperature range room temperature to 400 ° C.

[Examples 2 to 10, Comparative Examples 1 to 4]
A fine porous layer-forming paste and a gas diffusion layer were prepared in the same manner as in Example 1 except that the types and compositions of the materials constituting the fine porous layer-forming paste were changed as shown in Table 1.
However, in the present specification, the pastes of Examples 2, 4, 5 and 9 and the gas diffusion layer and the fuel cell using them are reference examples.

The materials used in the examples are listed below.
<Carbon-based conductive filler>
Carbon Black A: Denka Black HS-100 manufactured by Denki Kagaku Kogyo Co., Ltd.
Carbon Black B: Ketjen Black EC-300J, manufactured by Lion Specialty Chemicals
Carbon Black C: Made by Cabot, REGAL99R

<Carbon nanotube>
Carbon Nanotube D: Showa Denko VGCF-H
Carbon Nanotube E: Flotube 9000 manufactured by Canon

<Non-carbon conductive filler>
Non-carbon conductive filler F: manufactured by Ishihara Sangyo Co., Ltd., FT-3000

<Surfactant>
Surfactant A: Kao Corporation, Emargen 709, temperature at which 60% of the total mass is reduced at 246 ° C.
Surfactant B: Kao Corporation, Emargen 150, temperature at which 60% of the total mass is reduced at 231 ° C.
Surfactant C: manufactured by Kao Corporation, Leodor MS-165V, temperature at which 60% of the total mass is reduced at 282 ° C.
Surfactant D: Kao Corporation, Emargen 2025G, temperature at which 60% of the total mass is reduced at 250 ° C.
Surfactant E: Kao Corporation, Emanone 3199V, temperature at which 60% of the total mass is reduced at 245 ° C.
Surfactant F: Kao Corporation, Emargen 430, temperature at which 60% of the total mass is reduced at 309 ° C.
Surfactant G: NOF Corporation, Unilube 70DP-950B, temperature at which 60% of the total mass is reduced at 254 ° C.
Surfactant H: Kao Corporation, Emargen 4085, temperature at which 60% of the total mass is reduced at 236 ° C.
Surfactant I: Sanyo Chemical Industries, Ltd., Emulmin 862, temperature at which 60% of the total mass is reduced at 242 ° C.
Surfactant J: Kao Corporation, Emargen A-500, temperature at which 60% of the total mass is reduced at 330 ° C.
Surfactant K: manufactured by Nacalai Tesque, Triton X-100, temperature at which 60% of the total mass is reduced at 295 ° C.
Surfactant L: manufactured by NOF CORPORATION, Unilube MS-70K, temperature at which 60% of the total mass is reduced at 240 ° C.

<Fluorine-based resin dispersion>
Fluorine-based resin dispersion A: Daikin Corporation, Polyflon PTFE D-210C Solid content 60%
Fluorine-based resin dispersion B: Mitsui / DuPont Fluorochemical Co., Ltd., PTFE dispersion 31-JR solid content 60%

<Measurement of particle size of fine porous layer forming paste>
Table 1 shows the measurement results of the particle size of the fine porous layer-forming paste obtained in each of the above Examples and Comparative Examples. The measurement was carried out by the method specified in JIS K5600-2-5 using a 100 μm grain gauge. The better the dispersion, the lower the particle size.

<Measurement of viscosity of fine porous layer forming paste>
The viscosity of the microporous layer-forming paste obtained in each of the above Examples and Comparative Examples was measured by the method specified in JIS Z 8803: 2011. The viscosity at 6 rpm at 25 ° C. was measured with a single cylindrical rotational viscometer (manufactured by Toki Sangyo Co., Ltd., model number: TVB10M). The results are shown in Table 1.

As is clear from Table 1, when two types of surfactants having different temperatures at which 60% of the total mass is reduced are used (Examples 1 to 10), and when one type of surfactant is used (Comparative Example). Compared with 1 to 3), it was clarified that the particle size was small and sufficient dispersion was possible, and the flow characteristics were excellent. In Comparative Example 3, the gas diffusion layer could not be prepared because the fine porous layer-forming paste gelled and could not be applied to the base material.

<Evaluation when the fine porous layer forming paste is applied to the base material>
When the fine porous layer-forming paste obtained in the above Examples and Comparative Examples is applied to carbon paper to prepare a gas diffusion layer, the coatability, the presence or absence of pinholes on the coated surface, and the penetration into the base material Was determined based on the following criteria. The results are shown in Table 2.

<Applicability of fine porous layer forming paste>
◯: A uniform coating film (layer) can be produced, and no shading (uneven coating) is observed on the coating film (good).
Δ: A uniform coating film (layer) can be produced, but shading (coating unevenness) with a stripe length of less than 5 mm is observed in 1 to 3 places on the coating film (no problem in practical use).
X: A uniform coating film (layer) cannot be produced, and four or more shades (uneven coating) with a stripe length of less than 5 mm are observed on the coating film, or one shade with a stripe length of 5 mm or more is observed. Observed more than one place (defective).

<Presence or absence of pinholes on the painted surface>
◯: No pinhole is observed (good).
Δ: Pinholes with a diameter of less than 1 mm are observed at 1 to 3 places (defective).
X: Four pinholes with a diameter of less than 1 mm are observed, or one or more pinholes with a diameter of 1 mm or more are observed (extremely defective).

<Penetration of microporous layer-forming paste into the substrate>
5: There is no bleeding from the coated part, and the paste does not adhere even if the back surface of the coated part is rubbed with a finger (very good).
4: Bleeding from the coated part is seen within 2 mm from the edge of the coated part, but the paste does not adhere even if the back surface of the coated part is rubbed with a finger (good).
3: Bleeding from the coated part is seen within 2 mm from the edge of the coated part, and when the back surface of the coated part is rubbed with a finger, the paste adheres (there is no problem in practical use).
2: Bleeding from the coated part is observed from the edge of the coated part to a range of more than 2 mm and less than 4 mm, and the paste adheres to the back surface of the coated part just by touching it with a finger (defective).
1: Bleeding from the coated part spreads to 4 mm or more from the edge of the coated part, and a large amount of paste adheres to the back surface of the coated part just by touching it with a finger (extremely defective).

<Coating film thickness after drying>
The coating film thickness of MPL was measured when the fine porous layer-forming paste obtained in the above Examples and Comparative Examples was applied to carbon paper to a basis weight of 20 g / m ² after drying to prepare a gas diffusion layer. The results are shown in Table 2. The measurement was carried out by a method specified in JIS K5600-1-7: 2014 using a Nikon Digimicro Head MH-15M. The thicker the film thickness, the larger the value, which means that there are many pores in the MPL.

As is clear from Table 2, in Examples 1 to 10 using two types of surfactants having different temperatures in which 60% of the total mass is reduced, practically no problem was obtained in all the items. On the other hand, in Comparative Examples 1 and 2, there was no problem in practical use in terms of coatability, but pinholes were observed on the coated surface, and the penetration into the base material was also poor.

As is clear from Table 2, the coating film thickness after drying is 10 μm or more in Examples 1 to 10 using two types of surfactants having different temperatures in which 60% of the total mass is reduced. It became a thick film. On the other hand, in Comparative Examples 1 and 2, the thin film was thinner than 10 μm.

<Preparation of paste for forming catalyst layer for fuel cells>
The method for producing the catalyst layer for the fuel cell used for producing the membrane electrode assembly for the fuel cell will be described below. 4 parts by mass of platinum catalyst-supported carbon (manufactured by Tanaka Kikinzoku Co., Ltd., platinum amount 46%), 56 parts by mass of butanol (manufactured by Kishida Chemical Co., Ltd.) as a solvent, and 20 parts by mass of water with a disper (manufactured by Primix, TK homodisper). It was prepared by stirring and mixing. Next, 20 parts by mass of a 20 mass% Nafion solution (hydrogen ion conductive polymer, manufactured by DuPont, solvent: water and 1-propanol) was added, and the mixture was prepared with a disper (Primix, TK homodisper). A paste for forming a catalyst layer (a paste for forming a catalyst layer having a solid content concentration of 8% by mass and a paste for forming a catalyst layer of 100% by mass) was prepared by stirring and mixing.

<Preparation of catalyst layer for fuel cell>
The above catalyst layer forming paste was applied onto a Teflon (registered trademark) film so that the amount of platinum catalyst-supported carbon was 0.46 mg / cm ² , and dried in an air atmosphere at 95 ° C. for 15 minutes. , A catalyst layer for a fuel cell was prepared.

<Manufacturing of membrane electrode assembly for fuel cells>
The catalyst layer for a fuel cell is brought into close contact with both sides of a solid polymer electrolyte membrane (DuPont, Nafion212, film thickness 50 μm), held at 150 ° C. and 5 MPa, and then a Teflon (registered trademark) film is applied. It peeled off. Next, the gas diffusion layer with MPL formed by the fine porous layer forming paste of the present invention is further adhered from both sides, and the electrode membrane junction for a fuel cell of the present invention (gas diffusion layer / catalyst layer / solid polymer electrolyte) is further adhered. Membrane / catalyst layer / gas diffusion layer) was prepared.

<Manufacturing of fuel cell (single cell)>
The electrode film joint for a fuel cell obtained above is used as a 4 cm square sample, sandwiched between two gaskets from both sides, then two separators which are graphite plates, and two current collector plates are attached from both sides to fuel. It was manufactured as a battery (single cell). The measurement was carried out with the Auto PEM series "PEFC evaluation system" (manufactured by Toyo Corporation). Humidified oxygen gas was supplied from the cathode (air electrode) side, and humidified hydrogen gas was supplied from the anode (fuel electrode) side to measure the battery characteristics.

The battery characteristics were evaluated by measuring the current-voltage characteristics of the small single cell obtained as described above. The battery characteristics were determined by a relative value with the maximum current density of the small single cell manufactured using Comparative Example 1 as 1.00. If a difference of 0.10 or more is observed in this evaluation, it can be said that there is a clearly remarkable difference in battery characteristics. The results are shown in Table 3.

As is clear from Table 3, a small single cell prepared by using the fine porous layer-forming paste of Examples 1 to 10 using at least two kinds of surfactants having different temperatures at which 60% of the total mass is reduced. Was found to exhibit significantly better battery characteristics than any of the comparative examples. In Comparative Example 4 using the non-carbon conductive filler, the cell resistance was large and no power was generated.

Claims (3)

A fine porous layer forming paste used for forming a fine porous layer of a fuel cell when heated with water, a carbon-based conductive filler, a fluorine-based resin dispersion, and a heating rate of 10 ° C./min. Contains two types of surfactants with different temperatures, which reduces the weight by 60% of the total mass .
The two types of surfactants having different temperatures at which 60% of the total mass is lost are the first surfactant having a high temperature at which 60% of the total mass is lost and the first surfactant having a low temperature at which 60% of the total mass is lost. A temperature difference of 5 to 75 ° C., which contains a second surfactant and is reduced by 60% of the total mass of the first surfactant and the second surfactant, is included in the temperature range of the first surfactant. The temperature at which 60% of the total mass of the second surfactant is lost is 230-270 ° C.
With respect to 100 parts by mass of the carbon-based conductive filler, the total of the first surfactant and the second surfactant having different temperatures at which 60% of the total mass is reduced contains 120 to 200 parts by mass. A fine porous layer-forming paste characterized by this. A gas diffusion layer for a fuel cell, comprising the fine porous layer-forming paste according to claim 1 on a substrate. A fuel cell comprising the gas diffusion layer for a fuel cell according to claim 2 .