JP6245350B2 - GAS DIFFUSIVE POROUS LAYER, GAS DIFFUSIVE LAYER CONTAINING THE SAME, PROCESS FOR PRODUCING THE GAS DIFFUSIVE POROUS LAYER, AND MEMBRANE / ELECTRODE ASSEMBLE - Google Patents

Description

  The present invention relates to a gas diffusion porous layer, a gas diffusion layer including the gas diffusion layer, a method for producing the gas diffusion layer, and a membrane electrode assembly.

  A solid polymer fuel cell using a proton conductive solid polymer membrane operates at a lower temperature than other types of fuel cells such as a solid oxide fuel cell and a molten carbonate fuel cell. For this reason, the polymer electrolyte fuel cell is expected as a stationary power source or a power source for a moving body such as an automobile, and its practical use has been started.

  The polymer electrolyte fuel cell generally has a structure in which an electrolyte membrane-electrode assembly (MEA) is sandwiched between separators. The electrolyte membrane-electrode assembly is formed by sandwiching an electrolyte membrane between a pair of catalyst layers and a pair of gas diffusion layers. In a polymer electrolyte fuel cell, a plurality of single cells having the above-described configuration are generally stacked to form a stack. The electrode is a porous material formed of a mixture of an electrode catalyst and a solid polymer electrolyte, and is also called an electrode catalyst layer. In addition, a porous material is generally used to uniformly supply the reaction gas supplied to the gas diffusion layer to the electrodes.

  In the polymer electrolyte fuel cell, electricity can be taken out through the following electrochemical reaction. First, hydrogen contained in the fuel gas supplied to the fuel electrode (anode) side is oxidized by the catalyst particles to become protons and electrons. Next, the generated protons pass through the solid polymer electrolyte contained in the fuel electrode side electrode catalyst layer and the solid polymer electrolyte membrane in contact with the electrode catalyst layer, and reach the oxygen electrode (cathode) side electrode catalyst layer. . Electrons generated in the fuel electrode side electrode catalyst layer include a conductive carrier constituting the electrode catalyst layer, a gas diffusion layer in contact with a different side of the electrode catalyst layer from the solid polymer electrolyte membrane, a separator, and It reaches the oxygen electrode side electrode catalyst layer through an external circuit. The protons and electrons that reach the oxygen electrode side electrode catalyst layer react with oxygen contained in the oxidant gas supplied to the oxygen electrode side to generate water. Such an electrochemical reaction mainly proceeds at a three-phase interface where catalyst particles, a solid polymer electrolyte, and a reaction gas such as a fuel gas or an oxidant gas are in contact with each other.

  In addition, a solid polymer electrolyte membrane in a fuel cell does not exhibit high proton conductivity unless it is wet. Therefore, it is necessary to make the humidity distribution of the solid polymer electrolyte membrane uniform by humidifying the reaction gas supplied to the solid polymer fuel cell using a gas humidifier or the like.

  Under operating conditions such as high humidification and high current density, the amount of water that moves with the protons that move through the polymer electrolyte membrane from the anode to the cathode, and the water that forms in the oxygen electrode-side electrode catalyst layer The amount of generated water increases. At this time, these produced waters particularly stay in the oxygen electrode-side electrode catalyst layer and cause a flooding phenomenon that closes the pores that have become the reaction gas supply path. As a result, the diffusion of the reaction gas is inhibited, the electrochemical reaction is hindered, and as a result, the battery performance is lowered.

  Therefore, a member for a fuel cell such as a gas diffusion layer is required to have a drainage property for efficiently discharging moisture.

  For this reason, a microporous layer containing carbon and a water repellent is usually formed on at least one surface of the gas diffusion layer. As the water repellent, a fluorine resin such as polytetrafluoroethylene (PTFE) has been mainly used. In Japanese Patent Application Laid-Open No. 2004-221056, a water repellent layer composed of carbon particles as a conductive material and PTFE as a water repellent agent is formed on a carbon paper as a base material. In order to improve the adhesion of the resin, a hydrophilic layer composed of carbon black, carbon fiber, and a perfluoroalkylenesulfonic acid polymer such as Nafion (registered trademark) is interposed between the water repellent layer and the catalyst layer. It is arranged. The reason why fluorine-based resins such as PTFE have been mainly used for the water-repellent layer is that it has water repellency necessary to discharge generated water, heat resistance that can withstand operating conditions, hot water, water vapor, and oxidative degradation There are reasons such as being able to withstand, and not causing catalyst poisoning.

  However, in a system in which a water-repellent layer containing a fluorine-based resin is present as in JP-A-2004-221056, the water-repellent layer is clogged particularly in a high humidity condition or in a high current density region, resulting in gas diffusion performance. There has been a problem that the power generation performance of the fuel cell is lowered.

  Accordingly, an object of the present invention is to provide a gas diffusion porous layer having high gas diffusion performance and improved power generation performance of a fuel cell even under high humidity conditions.

  The present invention is characterized in that the gas diffusion porous layer contains, in addition to carbon particles, a hydrophilic polymer having a surface contact angle of 90 ° or less, and the surface contact angle of the gas diffusion porous layer is 90 ° or less. Have

It is a schematic sectional drawing which shows the basic composition of the polymer electrolyte fuel cell which concerns on one Embodiment of this invention. 1 is a polymer electrolyte fuel cell (PEFC), 2 is a polymer electrolyte membrane, 3 is a catalyst layer, 3a is an anode catalyst layer, 3c is a cathode catalyst layer, 4a is an anode gas diffusion layer, and 4c is a cathode gas diffusion layer 5a is an anode separator, 5c is a cathode separator, 6a is an anode gas flow path, 6c is a cathode gas flow path, 7 is a refrigerant flow path, and 10 is an electrolyte membrane-electrode assembly (MEA). It is an expanded section schematic diagram showing one embodiment of a gas diffusion layer (4a, 4c). Reference numeral 20 denotes a gas diffusion layer substrate, and 21 denotes a gas diffusion porous layer. It is a figure which shows the gas diffusion capability of an Example and a comparative example. It is a schematic diagram which shows the structure of the electric power generation cell using the gas diffusion layer created in the Example and the comparative example. It is a figure which shows the electric power generation evaluation result (current-voltage curve) of an Example and a comparative example.

  One embodiment of the present invention is a gas diffusion porous layer having carbon particles and a hydrophilic polymer having a surface contact angle of 90 ° or less and a surface contact angle of 90 ° or less. The gas diffusion porous layer is used as a member of a fuel cell and a membrane electrode assembly, and is preferably disposed between the catalyst layer and the gas diffusion layer base material and has a function of suppressing a flooding phenomenon.

  Conventionally, in order to suppress the flooding phenomenon, a carbon layer containing a water-repellent fluororesin such as PTFE has been disposed between the gas diffusion layer base material and the catalyst layer as disclosed in Japanese Patent Application Laid-Open No. 2004-221056. It was. However, fluororesins such as PTFE are expensive, which has been a factor in increasing the cost of fuel cells. In addition, the fluorine-based resin needs to be fired at a high temperature after slurry application, and has a disadvantage in terms of energy cost.

  Accordingly, the present inventors are a system that does not use a fluorine resin such as PTFE, and is equivalent to or better than the case where a fluorine resin such as PTFE is used in terms of gas diffusion performance, battery resistance, and battery performance. The present inventors have sought a layer structure having a slag and have used the hydrophilic polymer to arrive at the structure of the present invention.

  Since the gas diffusion porous layer disposed between the catalyst layer and the gas diffusion layer base material is required to discharge the generated water, a water-repellent material has been conventionally used. However, the present inventors surprisingly have a function of efficiently draining water even when a hydrophilic polymer is used in the porous layer, and in a high-humidity condition, compared with a fluororesin. Rather, it was found that using a hydrophilic polymer has higher drainage and battery performance is improved. Therefore, according to the present invention, by forming a gas diffusion porous layer using a hydrophilic polymer, the gas diffusion property is high and the gas diffusion porous layer has good drainage properties even under high humidity conditions. A diffusion porous layer is obtained.

  The detailed mechanism by which the hydrophilic polymer has such a drainage function is unknown, but is presumed as follows. In addition, this invention is not restrained by the following mechanism at all. When a fluorine resin such as PTFE is used for the gas diffusion porous layer, the water repellency is high and the water repellency is high. However, especially in high-humidity conditions or in a high current density region where a large amount of water is generated, water droplets become large particles due to the water repellency, and the drainage does not work well due to gas diffusion, and the gas diffusion layer becomes It is considered that the battery performance may be lowered due to water blocking. On the other hand, the hydrophilic polymer is compatible with water to some extent, so the diffusion of water is gradual, it can gradually diffuse into the lower layer (separator side), and gradually into the gas diffusion layer substrate with a high porosity. Water can be extruded. Furthermore, in the gas diffusion porous layer using a hydrophilic polymer, since water can also diffuse in the surface direction, even if water is generated in a specific place, a mechanism for discharging water in the entire layer works, Problems such as loss of functions at specific locations are also unlikely to occur.

  For this reason, it is thought that generated water can be drained gradually even under high humidity conditions or in a high current density region, and as a result, water can be drained efficiently.

  In addition, when a hydrophilic polymer is used, high-temperature baking necessary for forming a porous layer using a fluororesin is unnecessary, and it is not necessary to use a heat-resistant coating substrate that can withstand high-temperature baking. . For this reason, the cost at the time of producing a porous layer can be reduced, and also the energy cost at the time of production can be reduced. Further, when a PTFE dispersion is used for forming a porous layer, it is necessary to gently stir the PTFE dispersion so that it does not solidify before use, or when a strong shear is applied when kneading with carbon particles, etc. Since crystallization occurs, it is difficult to input the material once, so that the production efficiency is not good. When forming a porous layer using a hydrophilic polymer, since the material can be input in one step, there is an advantage that productivity is improved.

  Hereinafter, an embodiment of a fuel cell of the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited only to the following embodiments. Each drawing is exaggerated for convenience of explanation, and the dimensional ratio of each component in each drawing may be different from the actual one. Further, in the case where the embodiment of the present invention is described with reference to the drawings, the same reference numerals are given to the same elements in the description of the drawings, and redundant description is omitted.

  In this specification, “X to Y” indicating a range means “X or more and Y or less”. Unless otherwise specified, measurement of operation and physical properties is performed under conditions of room temperature (20 to 25 ° C.) / Relative humidity 40 to 50%.

[Fuel cell]
A fuel cell includes a membrane electrode assembly (MEA), a pair of separators including an anode side separator having a fuel gas flow path through which fuel gas flows and a cathode side separator having an oxidant gas flow path through which oxidant gas flows. Have.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment of the present invention. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (anode gas diffusion layer 4a and cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute a membrane electrode assembly (MEA) 10 in a stacked state. Here, the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c have a gas diffusion porous layer on the catalyst layer (3a, 3c) side.

  In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 1, the separators (5 a, 5 c) are illustrated so as to be positioned at both ends of the illustrated MEA 10. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, gas seal portions (gaskets) are disposed between the separators (5a, 5c) and the solid polymer electrolyte membrane 2 or between the PEFC 1 and another adjacent PEFC. However, these descriptions are omitted in FIG.

  The separators (5a, 5c) are obtained, for example, by forming a concavo-convex shape as shown in FIG. 1 by subjecting a thin plate having a thickness of 0.5 mm or less to a press treatment. The convex part seen from the MEA side of the separator (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, fuel gas (for example, hydrogen) is circulated through the anode gas channel 6a of the anode separator 5a, and oxidant gas (for example, air) is circulated through the cathode gas channel 6c of the cathode separator 5c. Let

  On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  In addition, in embodiment shown in FIG. 1, the separator (5a, 5c) is shape | molded by the uneven | corrugated shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path can be exhibited. Also good.

[Gas diffusion layer]
The gas diffusion layer preferably includes a gas diffusion layer base material in addition to the gas diffusion porous layer.

  FIG. 2 is an enlarged schematic cross-sectional view showing an embodiment of the gas diffusion layers (4a, 4c). In FIG. 2, the gas diffusion layer includes a gas diffusion layer substrate 20 and a gas diffusion porous layer 21 disposed adjacent to the substrate. The gas diffusion porous layer 21 is disposed on the catalyst layer (3a, 3c) side of FIG.

  The gas diffusion layer of the present invention is not limited to the form shown in FIG. 2, and an intermediate layer may be provided between the gas diffusion layer substrate and the gas diffusion porous layer. A form in which a gas diffusion porous layer is directly disposed on top is preferable. That is, it is preferably a gas diffusion layer having a gas diffusion layer base material and a gas diffusion porous layer disposed adjacent to the base material. This is because drainage can be efficiently performed without increasing the resistance of the entire gas diffusion layer, and battery characteristics are improved.

  Further, the gas diffusion porous layer may be provided in either one of the anode gas diffusion layer and the cathode gas diffusion layer, or may be provided in both of them, but at least the cathode is formed because water is generated on the cathode side. Preferably, the gas diffusion porous layer is provided on both gas diffusion layers.

  The gas diffusion layers (anode gas diffusion layer 4a, cathode gas diffusion layer 4c) are catalyst layers (3a, 3c) of gas (fuel gas or oxidant gas) supplied via the gas flow paths (6a, 6c) of the separator. ) And a function as an electron conduction path.

  The material which comprises the base material (gas diffusion layer base material) of a gas diffusion layer (4a, 4c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, carbon paper, carbon cloth formed from carbon fibers such as carbon cloth, paper-like paper body, felt, non-woven sheet material such as non-woven fabric; and wire mesh, foam metal, expanded metal, A punching metal, an etching plate, a precision press working plate, a metal mesh, a metal fine wire sintered body, a metal nonwoven fabric, etc. are mentioned.

  The thickness of the gas diffusion layer substrate may be appropriately determined in consideration of the characteristics of the obtained gas diffusion layer, but may be about 30 to 500 μm. If the thickness of the substrate is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer substrate preferably contains a water repellent. The water repellent is not particularly limited, and is a fluorine-based polymer such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Conventionally known water repellents such as molecular materials, polypropylene, and polyethylene may be used. The water repellent treatment method is not particularly limited, and may be performed using a general water repellent treatment method. For example, after immersing the base material used for a gas diffusion layer in the dispersion liquid of a water repellent agent, the method of heat-drying with oven etc. is mentioned. Alternatively, a sheet body in which a porous body of polytetrafluoroethylene (PTFE) is impregnated with carbon particles and sintered may be used. By using the sheet body, the manufacturing process is simplified, and handling and assembly when the members of the fuel cell 10 are stacked are facilitated.

  The gas diffusion layer substrate may have other additives. Examples of the additive include conductive carbon, a dispersant, and a dispersion aid.

[Gas diffusion porous layer]
The gas diffusion porous layer (also referred to as MPL layer, microporous layer, microporous layer or microporous layer) contains a hydrophilic polymer having a surface contact angle of 90 ° or less and carbon particles.

  Further, the surface contact angle of the gas diffusion porous layer is 90 ° or less. For this reason, the gas diffusion porous layer does not substantially contain a water repellent such as PTFE as described in the column of the gas diffusion layer base material. Therefore, it is considered that the generated water can be drained gradually even under high humidity conditions or in a high current density region, and as a result, water can be drained efficiently. Note that “substantially not containing” excludes a form in which the water repellent is included to the extent that the effects of the present invention are not exerted (for example, contamination of the water repellent in the gas diffusion layer base material). It may contain a small amount of water repellent (for example, 1% by weight or less in the gas diffusion porous layer). The surface contact angle of the gas diffusion porous layer is preferably 75 ° or less. The lower limit of the surface contact angle of the gas diffusion porous layer is not particularly limited, but is usually 5 ° or more.

  The thickness of the gas diffusion porous layer is not particularly limited, and may be appropriately determined in consideration of gas diffusibility and resistance. The thickness of the gas diffusion porous layer is preferably 3 to 500 μm, more preferably 5 to 300 μm. Within such a range, the balance between mechanical strength and permeability such as gas and water can be appropriately controlled.

  The weight ratio of the hydrophilic polymer and the carbon particles is not particularly limited, but considering the mechanical strength and electric resistance of the gas diffusion porous layer, the weight ratio of carbon particles: hydrophilic polymer = 1: 0.1. It is preferable that it is -10, and it is more preferable that it is 1: 0.2-5.

(Carbon particles)
The carbon particles are not particularly limited, and conventionally known materials such as carbon black, fibrous graphite, flaky graphite, graphite such as spherical graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, and acetylene black, scaly for reasons such as excellent electron conductivity, good dispersibility in solvents, and improved gas diffusibility. It is preferable to use flaky graphite, and since the surface area per particle is small and the particle diameter is uniform, the dispersibility in the solvent is better, and therefore acetylene black and flaky graphite are more preferably used.

  A commercially available product can be used for such carbon particles, such as Vulcan XC-72, Vulcan P, Black Pearls 880, Black Pearls 1100, Black Pearls 1300, Black Pearls 2000, Legal 400, and Ketchen manufactured by Lion. Examples include black EC, oil furnace black such as # 3150 and # 3250 manufactured by Mitsubishi Chemical Corporation; acetylene black such as Denka Black HS100 and Denka Black AB6 manufactured by Denki Kagaku Kogyo. In addition to carbon black, the carbon particles may be natural graphite, pitch, coke, polyacrylonitrile, artificial graphite obtained from an organic compound such as phenol resin, furan resin, carbon, or the like. Moreover, in order to improve corrosion resistance etc., you may process the said carbon particle, such as a graphitization process.

  Carbon particles may be used alone or in the form of a mixture of two or more.

  The average particle diameter (diameter) of the carbon particles is not particularly limited, but considering the gas permeability, conductivity, etc., the average particle diameter (average primary particle diameter) of the carbon particles is preferably 2 to 250 nm, More preferably, it is 10-100 nm. Within such a range, the gas diffusion coefficient is improved, high drainage due to capillary force is obtained, and the contact property with the catalyst layer can be improved. Here, the size of the carbon particles can be measured by a known method. In the present specification, unless otherwise specified, an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used. A value calculated as an average value of particle diameters (diameters) of particles observed in a statistically significant number of visual fields (for example, several to several tens of visual fields) shall be adopted. The “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

  The average particle size (average secondary particle size) of the carbon particles is preferably about 0.5 to 25 μm. As a result, the gas diffusion coefficient is improved, high drainage due to capillary force is obtained, and the contact property with the catalyst layer can be improved. Here, the measurement of the average secondary particle diameter of the carbon particles is performed using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The value calculated as the average value of the diameters shall be adopted.

The specific surface area of the carbon particles is preferably 1 to 100 m ² / g and more preferably 5 to 50 m ² / g because the surface area is preferably small.

(Hydrophilic polymer with a surface contact angle of 90 ° or less)
In the present specification, the hydrophilic polymer refers to a polymer having a surface contact angle of 90 ° or less and not a water-soluble polymer as defined below. This is because if the water-soluble polymer is used, the polymer is dissolved by the generated water generated when the battery is operated, and the holding function as a binder is not provided. The lower limit of the surface contact angle of the hydrophilic polymer is preferably 5 ° or more, more preferably 25 ° or more, and more preferably 50 ° or more. Note that Nafion (registered trademark) used in the hydrophilic layer of JP-A-2004-221056 has a surface contact angle of about 100 °. The surface contact angle is a surface contact angle with respect to water, and a value measured by the method described in the following examples is adopted.

  Examples of the hydrophilic polymer include polyamide resins such as nylon 6, nylon 66, nylon 610, nylon 612, nylon 11, nylon 12, and nylon 46, acrylic resins, styrene-acrylic resins, cellulose, and polyethersulfone. It is done. A commercial item can also be used as a hydrophilic polymer.

  Among them, it is preferable to use a soluble polyamide resin as the hydrophilic polymer because the solvent solubility is good and the porous layer can be easily formed.

  The soluble polyamide resin is 1 part by weight or more, preferably 5 parts by weight or more, based on 100 parts by weight of any one of alcohol, a mixture of alcohol and aromatic solvent, or a mixture of alcohol and ketone solvent. Preferably, 10 parts by weight or more of the polyamide is completely soluble. Examples of the alcohol include methanol, ethanol, n-propanol, and isopropyl alcohol. Examples of the aromatic solvent include benzene and toluene. Examples of the ketone solvent include cyclohexanone and 2-butanone. And cyclopentanone. Specific examples of the mixture of alcohol and aromatic solvent include a mixture of isopropyl alcohol and toluene (weight mixing ratio of about 50:50 to 3:97).

  The soluble polyamide resin can be obtained, for example, by solubilizing polyamide. Examples of the solubilization method include a method in which a part of the amide bond hydrogen atom of various polyamides is partially substituted with a methoxymethyl group by an appropriately known method. When a methoxy group is introduced into a polyamide, the hydrogen bonding ability of the amide group is lost, and the crystallinity of the polyamide is inhibited, so that the solubility in a solvent is increased. Examples of the solubilization method include a method of introducing a polyether or polyester into a polyamide molecule before solubilization to obtain a copolymer. Examples of the polyamide before solubilization include nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, and nylon 46.

  Specific examples of the soluble polyamide include Zytel 61 (manufactured by DuPont), Versalon (manufactured by General Mills), Amilan CM4000, CM4001, CM8000 (manufactured by Toray Industries, Inc.), PA-100 (manufactured by Fuji Kasei Kogyo Co., Ltd.), Examples include Toresin (manufactured by Nagase ChemteX Corporation).

  In addition, as other soluble polyamides, products obtained by reaction of dimer acid based dimer acid, for example, dimer acid of fatty acid such as soybean oil and tung oil, and alkyl diamine such as ethylenediamine and diethylenetriamine The soluble polyamide resin which is a thing can be mentioned. Specific examples thereof include Macromelt 6212, 6217, 6238, 6239 (manufactured by Henkel), DPX927, 1175, 1196 (manufactured by Henkel).

  The said soluble polyamide resin may be used individually by 1 type, and may be used together 2 or more types.

  The polymer in the hydrophilic polymer is sufficient if it is a polymer of monomers, and the weight average molecular weight of the hydrophilic polymer is not particularly limited, but is usually in the range of 500 to 5,000,000. The weight average molecular weight (Mw) is measured by gel permeation chromatography (GPC) using polystyrene as a standard substance.

  What is necessary is just to adjust suitably content of the hydrophilic polymer in a gas diffusion porous layer so that the space | gap structure in a gas diffusion porous layer may become a desired characteristic. Specifically, the content of the hydrophilic polymer is preferably 1 to 90% by weight, more preferably 2 to 70% by weight, based on the total weight of the gas diffusion porous layer. If the blending ratio of the hydrophilic polymer is 1% by weight or more, the particles can be bonded well, and if it is 90% by weight or less, an increase in electric resistance of the gas diffusion porous layer can be prevented.

[Production method of gas diffusion porous layer]
One preferred embodiment of the method for producing a gas diffusion porous layer is a step (1) of mixing a hydrophilic polymer, carbon particles and a solvent to obtain a mixture, and applying the mixture onto a coated substrate, followed by drying. And (2) forming a gas diffusion porous layer on the coated substrate. Furthermore, the process (3) which peels a gas diffusion porous layer from an application | coating base material is usually included after a process (2).

(Process (1))
In step (1), a hydrophilic polymer, carbon particles and a solvent are mixed to obtain a mixture.

  Since the types of the hydrophilic polymer and carbon particles used in the step (1) are the same as described above, the description thereof is omitted here.

  What is necessary is just to select suitably as a solvent used in a process (1) with the hydrophilic polymer used. Specifically, alcohol solvents such as water, methanol, ethanol, 1-propanol, 2-propanol, pentane, hexane, heptane, octane, nonane, n-decane, n-dodecane, n-tridecane, tetradecane, cyclohexane, Petroleum solvents such as aliphatic hydrocarbon solvents such as cyclopentane and aromatic hydrocarbon solvents such as benzene, toluene, xylene and 2-methylnaphthalene, ethyl acetate, methyl acetate, butyl acetate, butyl propionate, butyl butyrate Ester solvents such as chloroform, bromoform, methylene chloride, carbon tetrachloride, 1,2-dichloroethane, 1,1,1-trichloroethane, chlorobenzene, 2,6-dichlorotoluene, hexafluoroisopropanol, and other halogenated hydrocarbons Solvent, acetone, methyl ether Ketone solvents such as ruketone, methyl isobutyl ketone, methyl butyl ketone, N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), N, N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA) ), Aprotic polar solvents such as propylene carbonate, trimethyl phosphoric acid, 1,3-dimethyl-2-imidazolidinone, sulfolane, carboxylic acid solvents such as formic acid, acetic acid, propionic acid, butyric acid, lactic acid, anisole, diethyl ether , Tetrahydrofuran, diisopropyl ether, dioxane, diglyme, dimethoxyethane, and other ether solvents or mixtures thereof. Of these, non-aqueous solvents such as alcohol solvents, ether solvents, ketone solvents, and petroleum solvents are preferably used. In addition, when a soluble polyamide resin, which is the preferred hydrophilic polymer, is used, it is more preferable to use an alcohol-based solvent, an ether-based solvent, or a ketone-based solvent because a dispersion aid is unnecessary.

  In addition, the mixture may contain additives such as a dispersion aid such as a surfactant, a pore-forming agent, and a viscosity modifier.

  In this step, the order of addition of the hydrophilic polymer, the carbon particles, and the solvent is not particularly limited, and all the components are mixed together; after mixing any of the above components, the remaining portion is added; Either of the components may be mixed sequentially. Preferably, it is preferable to dissolve the hydrophilic polymer in a solvent and then add the carbon particles to the obtained solution. Thereby, the hydrophilic polymer can be easily and uniformly dissolved in the solvent.

  In the step (1), the solid content concentration in the mixture is preferably 5 to 50% by weight, and more preferably 10 to 25% by weight. By setting the solid content concentration in the mixture within the above range, it is preferable because the polymer is uniformly dispersed and the coating thickness is easily secured.

  Further, the mixing ratio of the hydrophilic polymer and the carbon particles in the mixture of the step (1) is appropriately set in consideration of the content weight ratio of both of the obtained gas diffusion porous layers. It is preferable that it is 1: 0.1-10, and it is more preferable that it is 1: 0.2-5.

  After mixing the hydrophilic polymer, the carbon particles, and the solvent as described above, if necessary, defoaming treatment, stirring (stirring) treatment, and grinding treatment may be performed for the purpose of homogenization and pulverization. The defoaming process, the stirring (stirring) process, and the pulverizing process may be performed in any one or in combination of two or more. Among these, the machine used for the stirring (kneading) treatment is not limited to the following, but is a self-revolving stirring defoaming mixer, vacuum stirring defoaming mixer, variable speed stirring defoaming mixer, stirrer (stirrer), ultra A sonic disperser or the like can be used. In addition, the machine used for the pulverization is not limited to the following, but is a milling device that gives impact with a spherical media such as a ball mill or a bead mill, a device that applies a shear stress in a roller gap such as a two-roll or three-roll, a homogenizer A device that rotates stirring blades such as a mixer or a jet mill device that collides the objects to be crushed can be used. What is necessary is just to set grinding | pulverization conditions (rotation speed, time, etc.) suitably.

  Moreover, you may filter for the purpose of removing a coarse particle, after performing the said deaeration process, stirring (stirring) process, or a grinding | pulverization process. The filtration method may be natural filtration performed at normal pressure, suction filtration, pressure filtration, or centrifugal filtration.

(Process (2))
In the step (2), the mixture obtained in the step (1) is applied on the coated substrate and then dried to form a porous layer on the coated substrate.

  It is considered that, after the mixture is applied to the coating substrate, the hydrophilic polymer is adsorbed on the carbon particles and the solvent in the slurry is volatilized, whereby the inside of the layer becomes porous.

  The coating substrate used is not particularly limited. In a system using conventional PTFE, it is necessary to use a base material (for example, a polyimide film) that can withstand high-temperature baking in a subsequent process, which contributes to high cost. Since the hydrophilic polymer used in the present invention does not require high-temperature baking, any resin that can withstand drying and hot pressing can be widely used. Specific examples of the coating substrate include polypropylene films, polyethylene films; polyester films such as PTFE (polytetrafluoroethylene) films and PET (polyethylene terephthalate) films; polyimide films, polysulfone sheets, and the like. Especially, since it is cheap, it is preferable to use a polypropylene film, a polyethylene film, a PET (polyethylene terephthalate) film, etc. as an application | coating base material.

  Although it does not specifically limit as thickness of an application | coating base material, Usually, it is about 5-500 micrometers.

  The coated substrate used is preferably formed by coating a water-soluble polymer on the surface of the substrate. Since the hydrophilic polymer has a high surface energy, it easily adheres firmly to the coated substrate. For this reason, by using a coated substrate coated with a water-soluble polymer, the porous layer can be easily peeled off from the coated substrate by washing the coated substrate with water when joining to the gas diffusion layer substrate later. it can.

  The water-soluble polymer refers to a polymer having a dissolution amount of 0.25 g or more, preferably 2.5 g or more, more preferably 25 g or more when dissolved in 100 g of water at 20 ° C. Specific examples of the water-soluble polymer include polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably 1000 to 3000, and saponification degree is preferably 80 mol% or more (up to 100 mol). %), More preferably 90 mol% or more (upper limit of 100 mol%)) and a modified product thereof (ethylene / vinyl acetate = 2/98 to 30/70 mol ratio of copolymer 1 to 1 of vinyl acetate units) 80 mol% saponification product, 1-50 mol% partial acetalization product of polyvinyl alcohol, etc., starch and modified products thereof (oxidized starch, phosphate esterified starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxy) Propyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl pyro Don, gelatin, polyacrylic acid (salt), polyethylene glycol, acrylic resin (acrylic acid-acrylonitrile copolymer, potassium acrylate-acrylonitrile copolymer, vinyl acetate-acrylic ester copolymer, acrylic acid- Acrylic ester copolymer, etc.), styrene acrylic resin (styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylic ester copolymer, styrene-α-methylstyrene-acrylic) Acid copolymer, styrene-α-methylstyrene-acrylic acid-acrylic acid ester copolymer, etc.), styrene-sodium styrenesulfonate copolymer, styrene-2-hydroxyethyl acrylate copolymer, styrene-2-hydroxy Ethyl acrylate-styrene sulfone Potassium copolymer, styrene-maleic acid copolymer, styrene-maleic anhydride copolymer, vinyl naphthalene-acrylic acid copolymer, vinyl naphthalene-maleic acid copolymer, vinyl acetate copolymer (vinyl acetate- Maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer, vinyl acetate-acrylic acid copolymer, etc.), casein, soybean protein, synthetic protein, agar and mannangalactan derivatives. Particularly preferred examples include polyvinyl alcohol, polyvinyl pyrrolidone, and gelatin. These water-soluble polymers may be used alone or in combination of two or more. A commercial item may be used for the said water-soluble polymer, and the product containing water-soluble polymers, such as a laundry paste, may be used.

  Although the application | coating thickness of a water-soluble polymer is not specifically limited, It is preferable that it is 1-10 micrometers by the thickness after drying, and it is more preferable that it is 2-5 micrometers.

  The method for applying the water-soluble polymer is not particularly limited, and conventionally known methods such as spray coating, spin coating, and bar coating can be used.

  After applying the water-soluble polymer, it is preferably dried. The drying conditions may be set as appropriate, but the drying temperature is preferably 10 to 50 ° C., and the drying time is preferably 0.1 to 1 hour.

  The method of applying the mixture to the coating substrate (preferably coated with a water-soluble polymer) is not particularly limited, and conventionally known methods such as spray coating, spin coating, and bar coating can be used.

  Although the application | coating thickness of a mixture is not specifically limited, It is preferable that it is 10-150 micrometers by the thickness after drying, and it is more preferable that it is 20-60 micrometers.

  After the mixture is coated on the coated substrate, it is preferably dried. The drying conditions are not particularly limited as long as the solvent in the mixture volatilizes, but for example, 10 to 50 ° C. is preferable, and the drying time is preferably 0.1 to 1 hour.

  Here, it is preferable to further heat-press after applying and drying the mixture on the coated substrate. Hot pressing is preferable because the carbon particles are easily bonded to each other and the toughness of the porous layer is increased.

  The conditions for the hot press are not particularly limited, and may be set as appropriate in consideration of the type of the coated substrate, the hydrophilic polymer, the carbon particle content, and the like. For example, the hot press temperature is preferably from room temperature to the base material deformation temperature, and more preferably 100 to 150 ° C. Moreover, it is preferable that it is 0.2-2 Mpa, and, as for a hot press pressure, it is more preferable that it is 0.5-1 Mpa. The hot press time is preferably 0.2 to 1 minute, and more preferably 0.3 to 0.5 minute.

  Further, in the present invention, since the hydrophilic polymer is used for the gas diffusion porous layer, the firing after the base material coating and drying necessary when the PTFE solution is used becomes unnecessary. If firing is necessary, it is disadvantageous in terms of energy costs. Therefore, in this invention, it is preferable not to include a baking process in a process (2). Here, a baking process refers to the process processed for 0.4 to 0.6 hours at the temperature of 250-400 degreeC. That is, the preferred form of the gas diffusion porous layer of the present invention is a non-fired gas diffusion porous layer.

(Process (3))
Step (3) is a step of peeling the gas diffusion porous layer formed from the coated substrate.

  The peeling method is not particularly limited, but when the coating substrate is in a form in which a water-soluble polymer is coated on the mixture coated surface, it is preferable to peel with an aqueous solvent. That is, a preferred embodiment is formed from a coated substrate by forming a porous layer on a coated substrate obtained by coating a water-soluble polymer on a substrate, and then removing the water-soluble polymer with an aqueous solvent. The method for producing a gas diffusion porous layer further includes a step of peeling the gas diffusion porous layer.

  The method for removing the water-soluble polymer is not particularly limited as long as the water-soluble polymer is dissolved in an aqueous solvent and the gas diffusion porous layer can be peeled from the coated substrate. For example, a method of immersing in an aqueous solvent, peeling by being exposed to vapor of an aqueous solvent, peeling in a heated state, and the like can be mentioned. In addition, it is preferable to warm the aqueous solvent for the purpose of promoting the elution (removal) of the water-soluble polymer. The temperature of the aqueous solvent used is preferably 20 to 50 ° C. Moreover, it is preferable that immersion time is 3 to 10 minutes, for example.

  The aqueous solvent used is not particularly limited as long as it dissolves only the water-soluble polymer and does not dissolve the hydrophilic polymer, but water is preferably used.

  After the gas diffusion porous layer is peeled from the coated substrate using an aqueous solvent, a drying step is usually included. The drying conditions at this time are not particularly limited, but the drying temperature is preferably 20 to 40 ° C., and the drying time is preferably 0.1 to 0.5 hours.

  In addition, as a peeling method, it is physically peeled by hand or using a machine, and after being immersed in water, by applying reduced pressure treatment or ultrasonic vibration, bubbles are generated between the gas diffusion porous layer and the substrate, and physical For example, the method of exfoliating automatically.

  The gas diffusion porous layer thus obtained can be made into a gas diffusion layer by bonding to the gas diffusion layer substrate. The joining method of the gas diffusion layer base material and the gas diffusion porous layer is not particularly limited, and examples thereof include press joining.

[Catalyst layer]
The catalyst layers (the anode catalyst layer 3a and the cathode catalyst layer 3c) are layers in which the cell reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer 3a, and the reduction reaction of oxygen proceeds in the cathode catalyst layer 3c.

  The catalyst layer includes a catalyst component, a conductive catalyst carrier (conductive carrier) that supports the catalyst component, and an electrolyte. Hereinafter, a composite in which a catalyst component is supported on a catalyst carrier is also referred to as an “electrode catalyst”.

  The catalyst component used in the anode catalyst layer is not particularly limited as long as it has a catalytic action in the oxidation reaction of hydrogen, and a known catalyst can be used in the same manner. The catalyst component used in the cathode catalyst layer is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, it may be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. .

  Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. Although the composition of the alloy depends on the type of metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be sufficient. At this time, the catalyst component used in the anode catalyst layer and the catalyst component used in the cathode catalyst layer can be appropriately selected from the above. In the present specification, unless otherwise specified, descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both. Therefore, they are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer and the cathode catalyst layer do not have to be the same, and can be appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be adopted. For example, the catalyst component may be granular, scale-like, or layered, but is preferably granular. At this time, the average particle diameter of the catalyst particles is preferably 1 to 30 nm, more preferably 1 to 10 nm, still more preferably 1 to 5 nm, and particularly preferably 2 to 4 nm. When the average particle diameter of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. The “average particle diameter of the catalyst particles” in the present invention is the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction, or the particle diameter of the catalyst component determined by a transmission electron microscope (TEM). It can be measured as an average value of.

  The catalyst component described above is preferably contained in the catalyst layer as an electrode catalyst supported on a conductive carrier.

  The conductive carrier functions as a carrier for supporting the above-described catalyst component and an electron conduction path involved in the transfer of electrons between the catalyst component and another member. Any conductive carrier may be used as long as it has a specific surface area for supporting the catalyst particles in a desired dispersed state and has sufficient electronic conductivity as a current collector. The main component is carbon. Is preferred. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. In addition, being substantially composed of carbon atoms means that mixing of impurities of about 2 to 3% by weight or less is allowed.

The BET specific surface area of the conductive carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. Good. When the specific surface area is in the above range, the catalyst component and the polymer electrolyte are sufficiently dispersed in the conductive support to obtain sufficient power generation performance, and the catalyst component and the polymer electrolyte can be used sufficiently effectively.

  In addition, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, catalyst utilization, and the thickness of the electrode catalyst layer within an appropriate range, the average particle size is 5 to 200 nm, The thickness is preferably about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the conductive support, the supported amount of the catalyst component is preferably 10 to 80% by weight, more preferably 30 to 70% by weight, based on the total amount of the electrode catalyst. . When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst support and the catalyst performance can be appropriately controlled. The amount of the catalyst component supported can be examined by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, the ion exchange resin which comprises the following electrolyte layer can be added to a catalyst layer as a polymer electrolyte.

  The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. Polymer electrolytes are roughly classified into fluorine-based polymer electrolytes and hydrocarbon-based polymer electrolytes depending on the type of ion exchange resin that is a constituent material. In addition, since the specific description of the fluorine-based polymer electrolyte and the hydrocarbon-based polymer electrolyte is the same as the description of the solid polymer electrolyte membrane below, the description is omitted here. Among these, the polymer electrolyte preferably contains a fluorine atom because it is excellent in heat resistance, chemical stability, and the like. Particularly preferred are fluorine-based electrolytes such as Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like.

  The content of the polymer electrolyte in the catalyst layer is not particularly limited, but the weight ratio of the polymer electrolyte to carbon in the electrode catalyst is preferably 0.3 to 1.2.

  The catalyst component can be supported on the conductive carrier by a known method. For example, known methods such as impregnation method, liquid phase reduction support method, evaporation to dryness method, colloid adsorption method, spray pyrolysis method, reverse micelle (microemulsion method) can be used. Alternatively, a commercially available electrode catalyst may be used.

  The method for forming the catalyst layer is not particularly limited, but preferably a method for forming the catalyst layer by applying a catalyst ink comprising the electrode catalyst, polymer electrolyte and solvent as described above to the surface of the polymer electrolyte membrane. Is mentioned. In this case, the solvent is not particularly limited, and usual solvents used for forming the catalyst layer can be used in the same manner. Specifically, lower alcohols such as water, cyclohexanol, ethanol, 1-propanol, and 2-propanol can be used. Further, the amount of the solvent used is not particularly limited, and a known amount can be used. In the catalyst ink, the electrocatalyst is used in any amount as long as it can sufficiently exhibit the desired action, that is, the action of catalyzing the hydrogen oxidation reaction (anode side) and the oxygen reduction reaction (cathode side). May be. It is preferable that the electrode catalyst is present in the catalyst ink in an amount of 5 to 30% by weight, more preferably 9 to 20% by weight.

  The preparation method of the catalyst ink is not particularly limited as long as the electrode catalyst, the electrolyte and the solvent, and if necessary, the water-repellent polymer and / or the thickener are appropriately mixed. For example, a catalyst ink can be prepared by adding an electrolyte to a polar solvent, heating and stirring the mixed solution to dissolve the electrolyte in the polar solvent, and then adding an electrode catalyst thereto. Alternatively, after the electrolyte is once dispersed / suspended in a solvent, the dispersion / suspension may be mixed with an electrode catalyst to prepare a catalyst ink. In addition, a commercially available electrolyte solution in which the electrolyte is previously prepared in the above-mentioned other solvent (for example, Nafion solution manufactured by DuPont: for example, Nafion dispersed / suspended at a concentration of 5 wt% in 1-propanol) You may use for the said method as it is.

  Each catalyst layer is formed by applying the catalyst ink as described above on the polymer electrolyte membrane or the gas diffusion layer. At this time, the conditions for forming the cathode / anode catalyst layer on the polymer electrolyte membrane are not particularly limited, and can be used in the same manner as known methods or appropriately modified. For example, the catalyst ink is applied onto the polymer electrolyte membrane so that the thickness after drying becomes a desired thickness, and is 25 to 150 ° C., more preferably 60 to 120 ° C. in a vacuum dryer or under reduced pressure. And drying for 5 to 30 minutes, more preferably for 10 to 20 minutes. In addition, in the said process, when the thickness of a catalyst layer is not enough, the said application | coating and drying process is repeated until it becomes desired thickness.

Further, the catalyst content per unit catalyst coating area (mg / cm ² ) is not particularly limited, but in view of sufficient dispersion of the catalyst on the carrier, power generation performance, etc., 0.01 to 1.0 mg / cm ² . However, when the catalyst contains platinum or a platinum-containing alloy, the platinum content per unit catalyst coating area is preferably 0.5 mg / cm ² or less. The use of expensive noble metal catalysts typified by platinum (Pt) and platinum alloys has become a high cost factor for fuel cells. Therefore, it is preferable to reduce the amount of expensive platinum used (platinum content) to the above range and reduce the cost. The lower limit is not particularly limited as long as power generation performance is obtained, and is, for example, 0.01 mg / cm ² or more. In this specification, inductively coupled plasma emission spectroscopy (ICP) is used for measurement (confirmation) of “catalyst (platinum) content per unit catalyst application area (mg / cm ² )”. A person skilled in the art can easily carry out a method of making the desired “catalyst (platinum) content per unit catalyst coating area (mg / cm ² )”, and control the ink composition (catalyst concentration) and coating amount. You can adjust the amount.

  The thickness of the catalyst layer is preferably 0.5 to 30 μm, more preferably 1 to 20 μm, and still more preferably 1 to 10 μm. In addition, the said thickness is applied to both a cathode catalyst layer and an anode catalyst layer. The thickness of the cathode catalyst layer and the anode catalyst layer may be the same or different.

[Solid polymer electrolyte membrane]
The solid polymer electrolyte membrane 2 has a function of selectively allowing protons generated in the anode catalyst layer 3a during operation of the PEFC 1 to permeate the cathode catalyst layer 3c along the film thickness direction. The solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The solid polymer electrolyte membrane 2 is roughly classified into a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of improving power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. A membrane is used.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon-based polymer electrolyte membranes have manufacturing advantages such as low cost raw materials, simple manufacturing processes, and high material selectivity.

  In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

  The thickness of the solid polymer electrolyte membrane may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte membrane is usually about 5 to 100 μm. When the thickness of the electrolyte membrane is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[Production method of membrane electrode assembly]
A method for producing the membrane electrode assembly is not particularly limited, and a conventionally known method can be used. For example, a catalyst layer is transferred or applied to a solid polymer electrolyte membrane with a hot press and dried, and a gas diffusion layer is bonded to the dried one, or a catalyst layer is applied in advance to the gas diffusion porous layer surface of the gas diffusion layer. Then, two gas diffusion electrodes (GDE) are prepared by drying and the gas diffusion electrodes are bonded to both surfaces of the solid polymer electrolyte membrane by hot pressing. Application and joining conditions such as hot pressing may be appropriately adjusted according to the type of polymer electrolyte in the solid polymer electrolyte membrane or catalyst layer (perfluorosulfonic acid type or hydrocarbon type).

[Separator]
The separator has a function of electrically connecting each cell in series when a plurality of single cells of a fuel cell such as a polymer electrolyte fuel cell are connected in series to form a fuel cell stack. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the separators is preferably provided with a gas flow path and a cooling flow path. As a material constituting the separator, conventionally known materials such as dense carbon graphite, carbon such as a carbon plate, and metal such as stainless steel can be appropriately employed without limitation. The thickness and size of the separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The type of the fuel cell is not particularly limited. In the above description, the polymer electrolyte fuel cell (PEFC) has been described as an example. However, in addition to the above, an alkaline fuel cell and a direct methanol fuel cell are used. And a micro fuel cell. Among them, a polymer electrolyte fuel cell is preferable because it is small in size, and can achieve high density and high output. The fuel cell is useful as a power source for stationary vehicles as well as a power source for a moving body such as a vehicle in which a mounting space is limited. Particularly, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be used suitably.

  The manufacturing method of the fuel cell is not particularly limited, and conventionally known knowledge can be appropriately referred to in the field of the fuel cell.

  The fuel used when operating the fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

  Furthermore, a fuel cell stack having a structure in which a plurality of membrane electrode assemblies are stacked and connected in series via a separator may be formed so that the fuel cell can exhibit a desired voltage. The shape of the fuel cell is not particularly limited, and may be determined as appropriate so that desired battery characteristics such as voltage can be obtained.

  The PEFC and membrane electrode assembly described above use a member that can achieve both dryout resistance and flooding resistance. Therefore, the PEFC and the membrane electrode assembly exhibit excellent power generation performance that is not easily affected by fluctuations in humidity.

  The effects of the present invention will be described using the following examples and comparative examples. Unless otherwise specified, each operation is performed at room temperature (25 ° C.).

Example 1
4 parts by weight of a polyamide resin (manufactured by Henkel, Macromelt 6212) was added to 100 parts by weight of 1-propanol, and the mixture was stirred while heating at 80 ° C. to obtain a solution.

On the other hand, acetylene black (manufactured by Denki Kagaku, Denka Black AB6, average primary particle size 40 nm, specific surface area 37 m ² / g) was added (polyamide resin: acetylene black = 30.8: 69.2 (weight ratio)). Then, pulverization was performed for 15 min at 13500 rpm / min with a homogenizer (manufactured by IKA, model: ULTRA TURRAX T25-basic). The obtained ink composition was filtered through a 150 μm mesh to remove coarse particles to obtain an ink (solid content concentration: 9.9% by weight).

  Subsequently, a laundry paste (Uehara Chemical Co., Ltd .; Kuranol (registered trademark)) containing polyvinyl alcohol is applied on a polypropylene sheet (thickness: 100 μm) with a wet thickness of 30 μm using an applicator, followed by natural drying (room temperature (25 ° C.)). 0.5 hours) to prepare a coated substrate (dry thickness: 3 μm).

  The ink prepared earlier was applied on a polyvinyl alcohol-coated surface of a polypropylene sheet coated with polyvinyl alcohol with an applicator at a wet thickness of 250 μm, and air-dried at room temperature (25 ° C.) for 0.5 hour (dry) Thickness 40 μm).

  The dried product was hot-pressed (hot press pressure 0.8 MPa, 120 ° C., 0.4 minutes) and thermally cured. The pressed sheet was immersed in water (30 ° C. to 40 ° C.) for 10 minutes to dissolve polyvinyl alcohol and peel the coating film from the coated substrate. The water adhering to the coating film was wiped off and air-dried at room temperature (25 ° C.) for 20 minutes.

(Example 2)
A sample was prepared in the same procedure as in Example 1 except that the ratio of the polyamide resin and acetylene black in the ink was polyamide resin: acetylene black = 50: 50 (weight ratio).

(Example 3)
The ratio of polyamide resin, scaly graphite (average particle size 15 μm, specific surface area 6 m ² / g), and acetylene black in the ink was determined as polyamide resin: flaky graphite: acetylene black = 30.8: 51.9: 17.3. A sample was prepared in the same procedure as in Example 1 except that (weight ratio) was used.

(Comparative Example 1)
To 100 parts by weight of 1-propanol, 2 parts by weight of polyamide resin (manufactured by Henkel, Macromelt 6212) and 2 parts by weight of PTFE (D-210C (trade name) made by Daikin) are added and stirred while heating to 80 ° C. did. However, PTFE was not dispersed and a gas diffusion porous layer could not be produced.

(Production of gas diffusion layer)
As the gas diffusion layer substrate, commercially available carbon paper (model number: 25BA, manufactured by SGL, thickness 190 μm, hydrophobized with 5 wt% PTFE) was used, and the gas obtained in Examples 1 to 3 on the substrate. The diffusion porous layer was press-bonded (pressing pressure * 2 Mpa) to prepare a gas diffusion layer test piece. Hereinafter, the gas diffusion layers having the gas diffusion porous layers obtained in Examples 1 to 3 are referred to as Samples 1 to 3.

  As a reference comparative example, a commercially available gas diffusion layer member (25BCH, manufactured by SGL, MPL layer: containing 5 wt% PTFE) in which MPL ink was applied to the same carbon paper was used.

(Evaluation method)
1. Measurement of gas permeability in thickness direction Samples 1 to 3 and a reference comparative example were measured by the following method.

Gurley Air Permeability Using Gurley Air Permeability Measurement stipulated in JIS P8117: 2009, a sample is fixed to a fastening plate having a circular hole with an outer diameter of 28.6 mm so that the gas diffusion porous layer surface is on the upper surface and 100 cc ( The time (second) through which 0.1 dm ³ ) air permeated was measured, and the Gurley air permeability was measured. Using this value, Permeability (unit: m ² ) normalized by thickness was calculated. The higher this value, the better the gas diffusibility.

  The results are shown in FIG.

  From the results of FIG. 3, it was found that the gas diffusion layers having the gas diffusion porous layers of Examples 1 to 3 have the same gas diffusibility as the gas diffusion layer of the reference comparative example.

2. Measurement of electric resistance in thickness direction The electric resistance values in the thickness direction of Samples 1 to 3 and the reference comparative example were measured by the following method.

In the measurement, both sides of a test piece having an area of 0.95 cm ² were sandwiched between gold foils, set in a penetration electric resistance measuring device (TER-2000SS: manufactured by ULVAC-RIKO), and measured by energizing under a load. The current value was 1 A, and 0.5 MPa to 5 MPa was taken as one cycle, and the values at 1 MPa in the second cycle were compared.

  The results are shown in Table 1.

  From the results of Table 1, it was found that the gas diffusion layers having the gas diffusion porous layers of Examples 1 to 3 have the same electrical resistance value as that of the gas diffusion layer of the reference comparative example.

3. Measurement of contact angle on gas diffusion porous layer surface The contact angle on the gas diffusion porous layer surface of Examples 1 to 3 and the reference comparative example was measured as follows.

  In the measurement, the gas diffusion porous layer was fixed to the glass plate with a double-sided tape, and 3 μl of pure water was dropped with a contact angle measuring device (Auto Dispenser AD-31, DropMaster 700, manufactured by Kyowa Interface Chemical Co., Ltd.), and the elliptical fitting method was used. The contact angle 20 seconds after the pure water was dropped was measured.

  The results are shown in Table 2.

  Further, a layer composed of 100% polymer was formed as a smooth film on a glass plate, and the surface contact angle was measured in the same manner. The surface contact angle of the polyamide resin used in Examples 1 to 3 was 70.4 °, and the surface contact angle of PTFE used in the reference comparative example was 116 °.

4). Power generation test (production of small power generation cells)
A solution containing platinum-supported carbon as an electrode catalyst and 20 wt% Nafion (registered trademark) as an electrolyte resin binder (DE2020, manufactured by DuPont) has a solid weight ratio of platinum / electrolyte resin binder of 1.1. The catalyst ink was prepared by mixing the electrode catalyst / electrolyte resin binder so that the solid weight ratio was 0.55. Here, as platinum carrying carbon, Tanaka Kikinzoku Kogyo Co., Ltd. make, TEC10E50E (platinum carrying amount = 50 weight%) was used.

The catalyst ink is applied to both surfaces of the electrolyte membrane and dried to form a cathode catalyst layer (dry film thickness = 10 μm) and an anode catalyst layer (dry film thickness = 5 μm), and a CCM (Catalyst Coated) having an active area of 5 cm × 2 cm. Membrane; electrolyte membrane-catalyst layer assembly) was prepared. As the electrolyte membrane, an electrolyte membrane (Nafion (registered trademark) NR211, manufactured by DuPont, film thickness = 25 μm) was used. Moreover, it adjusted so that the platinum amount in an anode catalyst layer might be 0.05 mg / cm < ² > so that the platinum amount in a cathode catalyst layer might be 0.35 mg / cm < ² >.

  The gas diffusion porous layer obtained in Example 1 was press-bonded to a commercially available carbon paper base material (model number: 25BA, manufactured by SGL) (pressing pressure * 2 Mpa), and the size was cut out to 5.2 cm × 6.3 cm. Thus, a gas diffusion layer was created.

  The member is arranged so that the porous surface of the gas diffusion layer is in contact with the cathode surface of the cathode of the CCM produced in this way, and carbon paper (25BA, manufactured by SGL) is arranged on the outside thereof. Similarly, carbon paper (25BCH, manufactured by SGL) coated with the MPL layer was also arranged on the side, and the cell was assembled to obtain a test cell (FIG. 4). This sample is designated as test cell 1.

  Moreover, as a comparative example, instead of the gas diffusion layer having the gas diffusion porous layer obtained in the example, carbon paper (25BCH, manufactured by SGL) coated with the MPL layer was disposed on the cathode side for testing. A comparative test cell 1 was assembled in the same manner as the cell 1.

(Test conditions)
Using the power generation cell obtained by the above procedure, H ₂ / Air, 80 ° C., the cell gas pressure is set to 200 KPa, and the relative humidity of the anode and cathode is set to 100% (current-voltage curve) ) Is shown in FIG.

  From the result of FIG. 5, the cell using the gas diffusion porous layer of the present invention was excellent in power generation performance even under high humidity conditions.

  The technical scope of the present invention is not limited to the above-described embodiments.

  This application is based on Japanese Patent Application No. 2014-60810 filed on March 24, 2014, the disclosure of which is referred to and incorporated in its entirety.

Claims (9)

A gas diffusion layer substrate;
A gas diffusion layer comprising carbon particles and a soluble polyamide resin as a hydrophilic polymer having a surface contact angle of 90 ° or less and a gas diffusion porous layer having a surface contact angle of 90 ° or less.   The gas diffusion layer according to claim 1, wherein the gas diffusion porous layer is disposed adjacent to the gas diffusion layer base material. A step (1) of obtaining a mixture by mixing a soluble polyamide resin, carbon particles and a solvent as a hydrophilic polymer;
The method for producing a gas diffusion layer according to claim 1, further comprising a step (2) of applying the mixture onto a coated substrate and then drying to form a porous layer on the coated substrate.   The manufacturing method according to claim 3, wherein in the step (2), the mixture is applied on a coating substrate, dried, and then further hot-pressed.   The manufacturing method of Claim 3 or 4 with which a water-soluble polymer is apply | coated to the surface of the said application | coating base material.   The membrane electrode assembly which has a gas diffusion layer of Claim 1 or 2. A method for producing a gas diffusion porous layer having carbon particles and a hydrophilic polymer having a surface contact angle of 90 ° or less and having a surface contact angle of 90 ° or less,
A step (1) of mixing a hydrophilic polymer, carbon particles and a solvent to obtain a mixture;
Applying the mixture onto a coated substrate having a surface coated with a water-soluble polymer, and then drying to form a porous layer on the substrate (2). Production method.   The manufacturing method according to claim 7, wherein, in the step (2), the mixture is applied onto a coated substrate, dried, and then further hot-pressed. A gas diffusion layer substrate;
The carbon particles and the surface contact angle are not less than 50 ° and not more than 90 °, and are not water-soluble polymers (here, the water-soluble polymer is dissolved in 100 g of water at 20 ° C. so that its dissolution amount is 0.00). A gas diffusion layer having a hydrophilic polymer and a gas diffusion porous layer having a surface contact angle of 90 ° or less.