JP6131696B2 - GAS DIFFUSION LAYER, METHOD FOR PRODUCING SAME, MEMBRANE ELECTRODE ASSEMBLY FOR FUEL CELL USING THE SAME, AND FUEL CELL - Google Patents

Description

  The present invention relates to a gas diffusion layer, a method for producing the same, a membrane electrode assembly for a fuel cell using the same, and a fuel cell.

  In recent years, in response to social demands and trends against the background of energy and environmental problems, fuel cells that can operate at room temperature and obtain high output density have attracted attention as power sources for electric vehicles and stationary power sources. A fuel cell is a clean power generation system in which the product of an electrode reaction is water in principle and has almost no adverse effect on the global environment. In particular, a polymer electrolyte fuel cell (PEFC) is expected as a power source for electric vehicles because it operates at a relatively low temperature. The polymer electrolyte fuel cell has a structure in which a plurality of single cells that exhibit a power generation function are stacked. This single cell includes a polymer-electrolyte membrane, a membrane-electrode assembly (MEA) having a pair of catalyst layers and a pair of gas diffusion layers (GDL) that are sequentially formed on both surfaces of the membrane. And MEA which each single cell has is electrically connected with MEA of an adjacent single cell through a separator. Thus, a fuel cell stack is comprised by laminating | stacking a single cell. The fuel cell stack functions as power generation means that can be used for various applications.

  Conventionally, it is disclosed that a microporous layer is formed by applying a paste containing conductive powder, a water repellent and an insulating thermosetting resin to carbon paper (for example, Patent Document 1). According to the said structure, it is described that the crack of a microporous layer can be suppressed.

JP 2009-238388 A

  However, since the carbon paper used as a base material is rigid and weak against bending, there is a problem that the base material itself is cracked during processing.

  Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to provide a flexible gas diffusion electrode layer.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problem can be solved by including conductive carbon in a nonconductive nonwoven fabric or woven fabric.

  According to the present invention, by using a non-conductive nonwoven fabric or woven fabric that can ensure the pore diameter, a continuous porous structure in which pores are continuously present is obtained. Therefore, the ratio of vacancies is higher than in the prior art, and a flexible gas diffusion layer can be provided. For this reason, the fuel cell using a gas diffusion layer is excellent in power generation performance.

It is the schematic which shows the basic composition of the polymer electrolyte fuel cell (PEFC) which concerns on 1st embodiment of this invention. It is a figure which shows the result of having measured the electrical resistance of the thickness direction of the gas diffusion layer of an Example. It is a figure which shows the relationship (experimental result of IV performance) of the current density and cell voltage of the electric power generation cell of an Example.

  The gas diffusion layer of the present invention is characterized in that conductive carbon is held in a nonconductive nonwoven fabric or woven fabric. Since the non-conductive nonwoven fabric or woven fabric is a continuous porous structure in which pores are continuously present, the ratio of the pores is higher than the conventional one. For this reason, a nonelectroconductive nonwoven fabric or a textile fabric is rich in a softness | flexibility. Moreover, the gas diffusion layer using a nonelectroconductive nonwoven fabric or a woven fabric exhibits excellent gas diffusibility. The pores of the non-conductive nonwoven fabric or woven fabric have a size that can pass through the conductive carbon. For this reason, even if the non-woven fabric or the woven fabric is non-conductive, the conductive carbon is continuously arranged in the pores to form a conductive path, so that the gas diffusion layer can ensure sufficient conductivity. Therefore, the fuel cell using the gas diffusion layer is excellent in power generation performance. In addition, since the non-woven fabric or the woven fabric is non-conductive, the range of materials that can be used is widened.

  Moreover, MEA usually has a gas diffusion layer with a fine porous layer (MPL). This gas diffusion layer with a microporous layer (MPL) is baked (heat treated) at a temperature of 300 ° C. or higher for 30 minutes or more after applying the MPL forming ink on the gas diffusion layer substrate (for example, the above-mentioned patent) Reference 1 (see paragraph “0045”). For this reason, the said method had a problem in mass production from a viewpoint of time and energy cost. On the other hand, in this invention, a gas diffusion layer can be manufactured only by immersing and drying a nonelectroconductive nonwoven fabric or a textile fabric in the solution containing low viscosity conductive carbon. For this reason, a gas diffusion layer can be easily produced without requiring baking (heat treatment) at a high temperature as in the prior art. Further, a thickener for controlling the viscosity of the solution or increasing the viscosity is unnecessary, and a special stirrer for increasing the viscosity is not required, so that the range of selection of drying conditions and solvents is widened.

  Embodiments to which the present invention is applied will be described below with reference to the accompanying drawings. In addition, this invention is not restrict | limited only to the following embodiment. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  In the present specification, “X to Y” indicating a range means “X or more and Y or less”, and “weight” and “mass”, “wt%” and “mass%”, “part by weight” and “ “Part by mass” is treated as a synonym. 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%.

  First, a basic configuration of a polymer electrolyte fuel cell to which the gas diffusion layer of this embodiment can be applied will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to a first embodiment of the present invention. The PEFC 1 first has 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.

  In PEFC 1, MEA 10 is further sandwiched between a pair of separators (anode separator 8a and cathode separator 8c). In FIG. 1, the separators (8 a, 8 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, a gas seal portion is disposed between the separators (8a, 8c) and the polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. In 1, these descriptions are omitted.

  The separators (8a, 8c) 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 protrusions seen from the MEA side of the separators (8a, 8c) are in contact with the MEA10. Thereby, the electrical connection with MEA10 is ensured. In addition, 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 (8a, 8c) 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 gas flow path 9a of the anode separator 8a, and oxidant gas (for example, air) is circulated through the gas flow path 9c of the cathode separator 8c.

  On the other hand, the recess viewed from the side opposite to the MEA side of the separators (8a, 8c) serves as a refrigerant flow path 11 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 (8a, 8c) 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.

  The gas diffusion layers (4a, 4c) function as gas diffusion layers. For this reason, a gas diffusion layer (GDL) (gas diffusion layer, microporous layer (MPL)) is not necessarily required separately. However, if necessary, the PEFC 1 may additionally include a microporous layer (MPL) between the gas diffusion layers (4a, 4c) and the catalyst layers (3a, 3c).

[Gas diffusion layer]
The gas diffusion layer has a structure in which conductive carbon is held by a nonconductive nonwoven fabric or woven fabric. Preferably, the gas diffusion layer has a structure in which conductive carbon is held by a nonconductive nonwoven fabric. In this specification, “nonwoven fabric” means a laminate of fibers. For this reason, the carbon paper as described in the said patent document 1 is not included in the nonwoven fabric of this invention. The gas diffusion layer of the present invention may be any of a gas diffusion layer substrate, a microporous layer (MPL), and a gas diffusion layer substrate with a microporous layer (MPL).

  The material which comprises a nonelectroconductive nonwoven fabric or textiles will not be restrict | limited especially if it is nonelectroconductive. For example, glass, polymer resin fiber, cellulose and the like can be mentioned. Of these, glass and polymer resin fibers are preferred. Although it does not restrict | limit especially as a polymeric resin fiber, From a heat resistant and hydrolysis resistant viewpoint, a polypropylene, polyamide, a polyimide, polysulfone, polyphenylene sulfide etc. are mentioned suitably. More preferably, from the viewpoint of cost, the polymer resin fiber is polyamide or polypropylene. The said material may be used individually by 1 type, or may be used with the form of 2 or more types of mixtures. That is, the nonconductive nonwoven fabric or woven fabric is preferably formed from at least one selected from the group consisting of glass, polymer resin fibers, and cellulose.

  Moreover, the magnitude | size of the fiber which comprises a nonelectroconductive nonwoven fabric or a textile fabric is not restrict | limited in particular. Specifically, the thickness (diameter) of the fiber is preferably 0.01 to 100 μm, more preferably 0.1 to 25 μm. If it is such a magnitude | size, a nonelectroconductive nonwoven fabric or textile fabric has a moderate hole size (hole diameter).

The method for producing the nonconductive nonwoven fabric or woven fabric is not particularly limited. For example, the nonconductive nonwoven fabric can be produced by a dry method, a wet papermaking method, a spunbond method, or the like. Moreover, a nonelectroconductive textile fabric can be produced with a well-known weaving method. Here, production conditions of the non-conductive nonwoven fabric or woven fabric is not particularly limited, for example, the basis weight is preferably from 1 to 50 g / ^{m 2,} and more preferably 5 to 25 g / ^{m 2.} The density of the non-conductive nonwoven fabric or woven fabric is preferably 0.05 to 1.0 g / cm ^3, more preferably 0.1 to 0.4 g / cm ^3. Under such conditions, the non-conductive nonwoven fabric or woven fabric can obtain an appropriate porosity (for example, 60 to 97.5%). Here, if the porosity of a nonelectroconductive nonwoven fabric or a woven fabric is the said range, gas diffusibility and electroconductivity can be improved, ensuring intensity | strength (a shape is maintained).

  As described above, it is preferable that the gas diffusion layer has pores having a size that can pass through the conductive carbon. Thereby, even if the non-woven fabric or the woven fabric is non-conductive, the conductive carbon is continuously arranged (in contact with each other) in the pores of the non-conductive non-woven fabric or woven fabric. Since the continuous arrangement of the conductive carbon forms a conductive path, the gas diffusion layer can secure sufficient conductivity. Here, the size of the pores of the non-conductive nonwoven fabric or woven fabric is not particularly limited as long as it is a size that can pass through the conductive carbon. The pore diameter of the non-conductive nonwoven fabric or woven fabric is preferably 1.5 to 100 times, more preferably 2 to 20 times, and particularly preferably 3 to 5 times the average particle diameter of the conductive carbon. . If the pores have such a size, a sufficient amount of conductive carbon can be continuously disposed in the pores (in contact with each other), so that the gas diffusion layer can exhibit sufficient conductivity. In the present specification, “particle diameter of conductive carbon” means the average secondary particle diameter of conductive carbon. Here, for the measurement of the average secondary particle diameter of the conductive carbon, a value calculated as the median value of the particle diameter of the particles observed with a laser diffraction / scattering particle size distribution measuring apparatus is adopted.

  Alternatively, the pore diameter of the non-conductive nonwoven fabric or woven fabric is preferably 100 μm or less, more preferably 1 to 50 μm, more preferably 5 to 25 μm, and particularly preferably 5 to 10 μm. . Within such a range, the strength of the gas diffusion layer can be sufficiently secured, and even in a fuel cell stack in which a plurality of MEAs are stacked, no hole is caused by local reverse cell reaction or deterioration. In the present specification, the “pore diameter” of the non-conductive nonwoven fabric or woven fabric is an average pore diameter (μm) calculated from the bubble point. Specifically, after a non-conductive non-woven fabric or woven fabric (sample) is dipped in isopropyl alcohol for 10 minutes or more in advance, it is placed horizontally and attached to a test tank, and isopropyl alcohol is placed in the tank up to a height of 15 mm at the upper end of the sample. pour it up. Next, the air pressure inside the sample is gradually increased from zero, bubbles are first generated from the medium, and the air pressure when the bubbles are continuously generated is read with a manometer. Further increase the air flow rate, measure the air flow rate and air pressure, and continue until the rate of change of the air flow rate becomes almost constant. The relationship between the air flow rate and air pressure is shown in a graph, and the bubble point pressure at the intersection is read from the tangent of the initial slope and the tangent of the final slope. From the obtained intersection bubble point pressure, the average pore diameter is calculated from the following equation.

Here, D represents the average pore diameter (μm); P represents the intersection bubble point pressure (mmH ₂ O).

  The non-conductive nonwoven fabric or woven fabric may be a commercial product. For example, a porous glass (manufactured by Nippon Sheet Glass Co., Ltd., trade name: TGP-015A), a polymer nonwoven fabric (manufactured by Sanki, trade name: Delpore P1001-20B) and the like can be used.

  Moreover, it does not specifically limit as electroconductive carbon, Conventionally well-known materials, such as carbon black, graphite (a granular graphite is included), expanded graphite, can be employ | adopted suitably. Among these, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent conductivity and a large specific surface area. 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; Denka Black manufactured by Denki Kagaku Kogyo Co., and acetylene black such as acetylene black AB-6 manufactured by Denki Kagaku Kogyo. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, furan resin may be used. Moreover, in order to improve corrosion resistance etc., you may process the said carbon particle, such as a graphitization process. In this case, the conductive carbon may be used alone or in the form of a mixture of two or more.

  The particle size of the conductive carbon is not particularly limited. Considering the relationship with the pore size of the non-conductive nonwoven fabric or woven fabric, the particle size (average primary particle size) of the conductive carbon is preferably 2 to 250 nm, and more preferably 10 to 100 nm. Within such a range, the conductive carbon can be efficiently and continuously disposed in the pores of the non-conductive nonwoven fabric or woven fabric to ensure sufficient conductivity. The shape of the conductive carbon is not particularly limited, and may be any structure such as a spherical shape, a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, or a spindle shape, but a granular shape is preferable. Here, the size of the conductive carbon can be measured by a known method. In this specification, an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used unless otherwise specified. 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 visual fields) shall be adopted. The “particle diameter” means the maximum distance among the distances between any two points on the particle outline.

  The content of conductive carbon in the gas diffusion layer is not particularly limited. Considering improvement in conductivity, the content of the conductive carbon is preferably 5 to 40% by volume, more preferably 10 to 25% by volume with respect to the gas diffusion layer.

  The gas diffusion layer is formed by holding conductive carbon in a nonconductive nonwoven fabric or woven fabric, but may further contain other additives. Here, the additive is not particularly limited, and examples thereof include a dispersant, a dispersion aid, a water repellent, and a binding binder. These additives may be used alone or in combination of two or more. Of these, the gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing flooding. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Molecular materials; Thermoplastic resins such as polyethylene and polypropylene; perfluorocarbon sulfonic acids 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.) Polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride -Fluoropolymer electrolytes such as perfluorocarbon sulfonic acid polymers; solvent-soluble fluoropolymers such as fluoroethylene / vinyl ether copolymers (Lumiflon: trade name, manufactured by Asahi Glass), Ryuflon (trade name, manufactured by Dainippon Ink and Chemicals, Inc.) ), Fluoroolefin copolymers such as cerafull coat (trade name, manufactured by Central Glass); solvent-soluble elastomer copolymers (thermoplastic resin), for example, Septon (manufactured by SEPTON, Kuraray); low molecular weight polyolefin wax (heat Plastic resin), for example, high wax (trademark, Mitsui Chemicals) and the like. Of these, fluorine-based polymer materials and fluorine-based polymer electrolytes are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction. As will be described in detail below, from the viewpoint of industrial handling, fluoroethylene vinyl ether copolymer (Lumiflon: trade name, manufactured by Asahi Glass) and Septon (SEPTON) Are more preferably used. When the gas diffusion layer contains a water repellent, the content (addition amount) of the water repellent is not particularly limited. For example, it is preferable to mix the water repellent with about 0.01 to 0.1 parts by weight with respect to 100 parts by weight of the conductive carbon. With such an amount, the gas diffusion layer satisfies both conductivity and water repellency.

  Although the thickness in particular of a gas diffusion layer is not restrict | limited, It is preferable that it is 5-500 micrometers, and it is more preferable that it is 25-250 micrometers. With such a thickness, a sufficient amount of conductive carbon can be retained, so that sufficient conductivity can be exhibited. It may also be possible to have a gas diffusion function as a gas diffusion layer and appropriate drainage.

  The gas diffusion layer may be provided on at least one of the cathode side and the anode side of the MEA, but is preferably provided on both the cathode and the anode.

(Method for producing gas diffusion layer)
The method for producing the gas diffusion layer is not particularly limited as long as the conductive carbon can be held on the nonconductive nonwoven fabric or woven fabric. For example, a method in which a slurry containing conductive carbon and a solvent is applied to a nonconductive nonwoven fabric or woven fabric and then dried may be used. Here, the application method is not particularly limited, and known methods such as spray coating (spraying method), dip coating (dipping method), spin coating, bar coating, roll coating, and screen printing are similarly modified or appropriately modified. Can be applied. Preferably, an immersion method is applied. The drying conditions are not particularly limited as long as the conductive carbon can be held on the non-conductive nonwoven fabric or woven fabric, but are preferably 250 ° C. or less from the viewpoint of time, energy cost, and mass production. That is, the present invention also includes immersing a non-conductive nonwoven fabric or woven fabric in a slurry containing conductive carbon and a solvent; and heat-treating the non-conductive nonwoven fabric or woven fabric after the immersion at a temperature of 250 ° C. or lower. A method for producing the gas diffusion layer is also provided. Hereinafter, the preferable form of the manufacturing method of the gas diffusion layer of this invention is demonstrated. However, the present invention is not limited to the following form.

  First, a slurry containing conductive carbon and a solvent is prepared. Here, examples of the solvent include water, alcohols such as perfluorobenzene, dichloropentafluoropropane, methanol and ethanol, and petroleum solvents such as toluene. Here, the concentration of the conductive carbon is not particularly limited. Specifically, the concentration of conductive carbon in the slurry is preferably 5 to 25% by weight, more preferably 10 to 20% by weight. If it is such a density | concentration, a sufficient amount of conductive carbon can be hold | maintained to a nonelectroconductive nonwoven fabric or textile fabric at the next immersion process.

  The slurry may contain other additives in addition to the conductive carbon and the solvent. Here, the additive is not particularly limited, and examples thereof include a dispersion aid, a dispersant, a water repellent, and a binder binder. The addition amount of the additive is not particularly limited, and is appropriately selected in consideration of a desired effect (for example, dispersibility and water repellency of conductive carbon). Specifically, the additive is preferably added in an amount of about 1 to 10% by weight with respect to the conductive carbon. If necessary, the slurry may be dispersed while being subjected to ultrasonic treatment (ultrasonic dispersion treatment). In order to lower the viscosity of the slurry by such treatment, when the nonconductive nonwoven fabric or woven fabric is dipped in the next step, the conductive carbon can more efficiently penetrate into the pores of the nonconductive nonwoven fabric or woven fabric.

  Next, the nonconductive nonwoven fabric or woven fabric is immersed in the slurry prepared as described above. Here, the dipping conditions are not particularly limited as long as a sufficient amount of conductive carbon can be held in the non-conductive nonwoven fabric or woven fabric within a range that avoids volatilization and solidification of the solvent used and an increase in viscosity. For example, when water is selected as the solvent, the immersion temperature is preferably 10 to 80 ° C, more preferably 20 to 40 ° C. Further, the immersion time is preferably 5 seconds to 15 minutes, more preferably 10 seconds to 5 minutes (the operation of soaking is light, rather, the operation of tapping with a brush after being soaked (still about 3 minutes) Is more time consuming). In addition, you may repeat the said immersion process as needed (for example, in order to hold | maintain more conductive carbon). In addition, after the dipping process, in order to remove bubbles and promote uniform permeation, vacuum defoaming treatment, jig physical contact with the surface (for example, removal of bubbles by rubbing or hitting with a brush), Ultrasonic treatment or the like may be performed.

  Furthermore, after being immersed in the slurry, the nonconductive nonwoven fabric or woven fabric is dried (heat treated). Here, the drying condition is such that the solvent is removed from the non-conductive nonwoven fabric or woven fabric and the conductive carbon is held on the surface and in the pores, so that a high temperature for baking (firing) is required as in the past. And not. For this reason, it is very preferable in mass production from the viewpoint of time and energy cost. For this reason, the drying temperature should just be the temperature which can remove a solvent, and changes with kinds of solvent to be used. For example, the drying temperature is 250 ° C. or less from the viewpoint of time and energy cost. For example, the drying temperature is preferably 60 to 200 ° C, more preferably 80 to 150 ° C. The drying time is preferably 5 to 20 minutes, more preferably 2 to 10 minutes. The above conditions can be applied particularly suitably when water is selected as the solvent. In consideration of mass production, it is preferable to select water as the solvent. In the drying process, an air flow may be introduced into the drying furnace. By performing such an operation, it is possible to further shorten the drying time. Thus, according to the method of this embodiment, the gas diffusion layer can be produced at a low temperature and in a short time, which is very preferable from an industrial viewpoint. In addition, you may repeat the said drying (heat processing) process as needed (for example, in order to hold | maintain conductive carbon firmly).

  In addition, although a gas diffusion layer can be manufactured as described above, in order to improve the water repellency of the gas diffusion layer, the non-conductive nonwoven fabric or woven fabric after the immersion may be subjected to a water repellent treatment. Here, the water repellent treatment method is not particularly limited, but is preferably immersed in a solution containing the water repellent as described above from the viewpoint of ease of operation. The solvent that can be used to prepare the water repellent solution is not particularly limited as long as it can dissolve the water repellent, and can be appropriately selected depending on the type of the water repellent. Examples thereof include water, alcohols such as perfluorobenzene, dichloropentafluoropropane, methanol and ethanol, and petroleum solvents such as toluene. Here, the concentration of the water repellent is not particularly limited. Specifically, the concentration (solid content concentration) of the water repellent in the water repellent solution is preferably 0.1 to 25% by weight, more preferably 1 to 5% by weight. With such a concentration, sufficient water repellency can be imparted to the gas diffusion layer.

  Further, the immersion conditions in the water repellent solution are not particularly limited as long as a sufficient amount of water repellency can be imparted to the gas diffusion layer, but in order to prevent volatilization of the solvent used for immersion, the immersion condition is 20 It is preferable to carry out at a temperature that is lower than ° C. and does not cause thickening or coagulation of the solution. For example, the immersion temperature when an alcohol solution of a perfluorosulfonic acid polymer is used is preferably 10 to 60 ° C, more preferably 20 to 40 ° C. The immersion time is preferably 2 seconds to 15 minutes, more preferably 5 seconds to 10 minutes. In addition, it is preferable to remove the air bubbles inside the gas diffusion layer by ultrasonic treatment or reduced pressure defoaming treatment during the immersion step. In addition, you may repeat the said immersion process as needed (for example, in order to provide more water repellency).

  Further, after being immersed in the water repellent solution, the gas diffusion layer is dried (heat treatment). That is, preferably, after the immersion and before the heat treatment, the nonconductive nonwoven fabric or woven fabric after the immersion is subjected to a water repellent treatment. As a result, a water-repellent gas diffusion layer is obtained. Here, the drying condition may be that the solvent is removed. Specifically, the drying temperature may be any temperature at which the solvent can be removed, and varies depending on the type of solvent used. For example, from the viewpoint of time and energy cost, the drying temperature is 250 ° C. or lower, preferably 80 to 200 ° C., more preferably 80 to 150 ° C. In consideration of mass production, the drying time is preferably 30 seconds to 20 minutes, more preferably 3 minutes to 15 minutes. In addition, you may repeat the said drying (heat processing) process as needed (for example, in order to hold | maintain electroconductive carbon firmly or to provide water repellency more efficiently). Thus, according to the method of this embodiment, the gas diffusion layer can be produced at a low temperature and in a short time, which is very preferable from an industrial viewpoint.

[Solid polymer electrolyte membrane]
The solid polymer electrolyte membrane 2 allows protons generated on the anode side (anode gas diffusion layer or anode catalyst layer) during operation of the PEFC 1 to flow toward the cathode side (cathode gas diffusion layer or cathode catalyst layer) along the film thickness direction. It has a function of selectively transmitting. 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 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 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 layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance of strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

[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 used in the present application. 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 included in the catalyst ink 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. The conductive carrier may have any 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. Preferably there is. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. In the present invention, “the main component is carbon” refers to containing a carbon atom as a main component, and is a concept including both a carbon atom only and a substantially carbon atom. 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. Is good. When the specific surface area is in the above range, the catalyst component and the polymer electrolyte are sufficiently dispersed on the conductive support to obtain sufficient power generation performance, and the catalyst component and the polymer electrolyte can be sufficiently effectively used. .

  Further, the size of the conductive carrier is not particularly limited, but from the viewpoint of controlling the ease of loading, the 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 carrier, the supported amount of the catalyst component is preferably 10 to 80% by weight, more preferably 30 to 70% by weight with respect to the total amount of the electrode catalyst. Good. 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 electrolyte layer mentioned above 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. 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, and the description thereof 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 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.

  In the method of the present invention, a catalyst layer is formed by applying a catalyst ink comprising the electrode catalyst, polymer electrolyte and solvent as described above to the surface of the polymer electrolyte membrane. 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, water, lower alcohols such as cyclohexanol, ethanol 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 oxidation reaction of hydrogen (anode side) and the reduction reaction of oxygen (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 catalyst ink of the present invention may contain a thickener. The use of a thickener is effective when the catalyst ink cannot be successfully applied onto a transfer mount. The thickener that can be used in this case is not particularly limited, and a known thickener can be used. Examples thereof include glycerin, ethylene glycol (EG), polyvinyl alcohol (PVA), and propylene glycol (PG). Of these, propylene glycol (PG) is preferably used. The use of propylene glycol (PG) increases the boiling point of the catalyst ink and decreases the solvent evaporation rate. For this reason, for example, when a catalyst layer is formed on an electrolyte membrane by a transfer method, the solvent evaporation rate in the applied catalyst ink is suppressed by adding PG to the catalyst ink, and the catalyst after the drying process is suppressed. It is possible to suppress / prevent the occurrence of cracks in the layer. By transferring the catalyst layer with few cracks to the film in this way, mechanical stress concentration on the film is alleviated, and as a result, the durability of the MEA can be improved. The amount of the thickener added when using the thickener is not particularly limited as long as it does not interfere with the above effect of the present invention, but is preferably 5 to 20 with respect to the total weight of the catalyst ink. % By weight.

  The catalyst ink of the present invention is not particularly limited in its preparation method as long as an electrode catalyst, an electrolyte and a solvent, and if necessary, a water-repellent polymer and / or a 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 (for example, DuPont Nafion solution: Nafion dispersed / suspended at a concentration of 5 wt% in 1-propanol) in which the electrolyte is previously prepared in the above other solvent is used as it is. May be used in the method.

  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 application 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 g / 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 g / 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 g / cm ² or more. More preferably, the platinum content is 0.05 to 0.20 g / cm ² . In this specification, inductively coupled plasma emission spectroscopy (ICP) is used for the measurement (confirmation) of the “catalyst (platinum) content (g / cm ² ) per unit catalyst application area”. A person skilled in the art can easily carry out a method of making the desired “catalyst (platinum) content per unit catalyst coating area (g / 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. However, the thickness of the cathode catalyst layer and the anode catalyst layer may be the same or different.

[Microporous layer (MPL)]
The membrane electrode assembly (MEA) may have a microporous layer (MPL) between the catalyst layer and the gas diffusion layer, if necessary. Here, the microporous layer (MPL) is not particularly limited, but preferably has a large gas diffusion coefficient. By using such a microporous layer (MPL), the gas permeability can be further improved, and the power generation performance under dry and wet conditions can be more effectively achieved. Such a microporous layer (MPL) is not particularly limited, but can be an aggregate of carbon particles containing a water repellent if necessary. Here, the carbon particles are not particularly limited, and conventionally known materials such as carbon black, graphite (including granular graphite), expanded graphite and the like can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. 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, and acetylene black such as Denka Black manufactured by Denki Kagaku Kogyo. In addition to carbon black, artificial graphite or carbon obtained from organic compounds such as natural graphite, pitch, coke, polyacrylonitrile, phenol resin, furan resin may be used. Moreover, in order to improve corrosion resistance etc., you may process the said carbon particle, such as a graphitization process. In this case, the above materials may be used alone or in the form of a mixture of two or more.

  The particle size of the carbon particles is preferably about 10 to 100 nm. 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. The shape of the carbon particles is not particularly limited, and may take any structure such as a spherical shape, a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, and a spindle shape. In the present specification, “particle diameter of carbon particles” is an average secondary particle diameter of conductive carrier particles. Here, the measurement of the average secondary particle diameter of the conductive carrier particles is performed by using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and particles observed in several to several tens of fields. The value calculated as the average value of the particle diameters of the particles shall be adopted.

  The microporous layer (MPL) preferably contains a water repellent for the purpose of further improving the water repellency and preventing the flooding phenomenon. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, thermoplastic resins such as polyethylene and polypropylene. Of these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction. In the microporous layer (MPL), the mixing ratio of the carbon particles to the water repellent may not be as good as the water repellent as expected when there are too many carbon particles. Conductivity may not be obtained. Considering these, the mixing ratio of the carbon particles and the water repellent in the microporous layer (MPL) is preferably about 90:10 to 40:60 in terms of weight ratio.

  In the fine porous layer (MPL), carbon particles may be bound by a binder. Examples of the binder that can be used here include fluorine-based polymer materials such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP). And thermosetting resins such as phenol resin, melamine resin and polyamide resin, and thermoplastic resins such as polypropylene and polyethylene. Note that the above-described water repellent and binder partially overlap. Therefore, a binder having water repellency is preferably used. Among these, fluorine-based polymer materials are preferably used because of their excellent water repellency and corrosion resistance during electrode reaction, and polytetrafluoroethylene (PTFE) is particularly preferable. By using a binder having water repellency, water repellency is imparted to the pores (between carbon particles) in the microporous layer (MPL), and water drainage can be improved. In addition, these binders may be used individually by 1 type, or may be used together 2 or more types. Moreover, polymers other than these may be used.

  What is necessary is just to adjust suitably content of the binder in a microporous layer (MPL) so that the space | gap structure in a microporous layer (MPL) may become a desired characteristic. Specifically, the binder content is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and still more preferably 12 to 40% by weight with respect to the total weight of the microporous layer (MPL). A range is preferred. If the blending ratio of the binder is 5% by weight or more, the particles can be bonded well, and if it is 60% by weight or less, an increase in the electrical resistance of the microporous layer (MPL) can be prevented.

  The thickness of the microporous layer (MPL) is not particularly limited and may be appropriately determined in consideration of the characteristics of the gas diffusion layer. The thickness of the microporous layer (MPL) is preferably 3 to 500 μm, more preferably 5 to 300 μm, still more preferably 10 to 150 μm, and particularly preferably 20 to 100 μm. Within such a range, the balance between mechanical strength and permeability such as gas and water can be appropriately controlled.

[Gas diffusion layer substrate]
The membrane electrode assembly (MEA) may have a gas diffusion layer base material between the gas diffusion layer and the separator, if necessary. Here, as a gas diffusion layer base material, it does not specifically limit but a well-known thing can be used similarly. For example, carbon paper, carbon cloth such as carbon paper, carbon-made woven fabric, paper-like paper body, felt, non-woven sheet-like material having conductivity and porosity; and metal mesh, expanded metal, etching The thing which uses a plate as a base material etc. are mentioned. The thickness of the substrate is not particularly limited and may be appropriately determined in consideration of desired characteristics, but may be about 30 to 500 μm. With such a thickness, sufficient mechanical strength and permeability such as gas and water can be secured. In addition, the gas diffusion layer base material may contain a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. Although it does not specifically limit as said water repellent, It is fluorine-type, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, tetrafluoroethylene-hexafluoropropylene copolymer (FEP). Examples thereof include polymer materials, polypropylene, and polyethylene. Here, the water repellent treatment method is not particularly limited, and a general water repellent treatment method may be used. For example, after immersing the gas diffusion layer base material in a water repellent dispersion, a method of heating and drying in an oven or the like can be used. In particular, a sheet body in which a porous body of polytetrafluoroethylene (PTFE) is impregnated with carbon particles and sintered can be used. By using the sheet body, the manufacturing process is simplified, and handling and assembly when the members of the fuel cell are stacked are facilitated. Further, depending on the drainage characteristics of MEA and the surface properties of the separator, the gas diffusion layer substrate may not be subjected to water repellent treatment or may be subjected to hydrophilic treatment.

  Moreover, you may use what combined the gas diffusion layer base material and the microporous layer. At this time, the method for forming the fine porous layer on the gas diffusion layer substrate is not particularly limited. For example, a slurry is prepared by dispersing carbon particles, a water repellent, and the like in a solvent such as water, alcohol solvents such as perfluorobenzene, dichloropentafluoropropane, methanol, and ethanol. Next, the slurry may be applied on a gas diffusion layer substrate and dried, or the slurry may be dried and pulverized to form a powder, which may be applied onto the gas diffusion layer. Then, it is preferable to heat-process at about 250-400 degreeC using a muffle furnace or a baking furnace. Or you may use the commercial item by which the fine porous layer was previously formed on the gas diffusion layer base material.

[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 method of joining a gas diffusion layer to a catalyst layer that is transferred or applied to an electrolyte membrane by hot pressing and then dried can be used. In addition, an anode catalyst layer and a cathode catalyst layer are applied in advance to the anode microporous layer side of the anode gas diffusion layer and to the cathode gas diffusion layer (cathode microporous layer if a cathode microporous layer is provided), respectively. A method of producing two gas diffusion electrodes by drying and bonding the gas diffusion electrodes to both surfaces of the electrolyte membrane by hot pressing can also be used. Application and joining conditions such as hot pressing may be appropriately adjusted depending on the type of electrolyte (perfluorosulfonic acid type or hydrocarbon type) in the electrolyte membrane or the catalyst layer.

[Separator]
The separator has a function of electrically connecting cells 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. In addition, an alkaline fuel cell, a direct methanol fuel is used. Examples include batteries and micro fuel cells. 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 stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. However, the fuel cell is particularly useful for an automobile application in which system start / stop and output fluctuation frequently occur. It can be particularly preferably used.

  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 gas diffusion layer having excellent gas diffusibility and conductivity. Therefore, the PEFC and the membrane electrode assembly exhibit excellent power generation performance.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples. In the examples, “parts” or “%” is used, but “parts by weight” or “% by weight” is indicated unless otherwise specified. Unless otherwise specified, each operation is performed at room temperature (25 ° C.).

Example 1
(Production of gas diffusion layer)
Conductive carbon (acetylene black AB-6, average primary particle size = 50 nm, manufactured by Denki Kagaku Kogyo Co., Ltd.) 25.6 g, Emulgen (San Nopco Co., Ltd., trade name: thickener) 1.4 g as dispersion aid, and water 120 g Was added. This mixture was stirred with a propeller stirrer for 10 minutes to obtain a paste-like ink. The paste-like ink was subjected to a dispersion treatment with an ultrasonic disperser for 60 minutes to prepare a carbon ink. By the ultrasonic dispersion treatment, the carbon ink has a low viscosity, and has properties suitable for the porous body impregnation in the next step. When this carbon ink was measured with a laser diffraction / scattering particle size distribution analyzer (Microtrap MT3000), a dispersion having a median value (average secondary particle diameter of conductive carbon) of 2.2 μm was obtained.

A glass porous body of 80 cm × 80 cm (non-conductive nonwoven fabric, 57.7 mg) was immersed in the carbon ink prepared above for 1 minute, and then pulled up. In addition, as a glass porous body used, Nippon Sheet Glass Co., Ltd., brand name: TGP-015A (thickness = 160 μm (when loaded with 19.6 kPa), pore diameter = 7.8 μm, basis weight = 22 g / m ² , Density = 0.136 g / m ³ ) was used.
The glass porous body was hit with a brush to remove bubbles adhering to the surface, and then dried at 120 ° C. for 8 minutes to obtain a carbon particle / porous composite.

  10 g of electrolyte solution DE2020 (manufactured by DuPont, solid concentration = 21 wt%) was diluted with 100 g of ethanol to prepare a water repellent solution (solid concentration = 2 wt%). In this water repellent solution, the carbon particle / porous body composite prepared in the previous step is immersed, and ultrasonic waves are irradiated for 2 minutes while the carbon particle / porous body composite is continuously immersed in the water repellent solution. Air bubbles were removed. The carbon particle / porous body composite thus subjected to water repellency treatment was dried (heat treatment) at 120 ° C. for 10 minutes to obtain a gas diffusion layer (165 mg, 0.46 cc). The content of conductive carbon in the gas diffusion layer thus obtained was about 13% by volume.

When the Gurley air permeability of the gas diffusion layer thus obtained was measured under the above conditions, it was about 1.23 × 10 ⁻⁴ m ² . For the Gurley air permeability, a Gurley air permeability measuring instrument defined in JIS P8117: 2009 was used, and a sample held by a clamping plate having a circular hole with an outer diameter of 28.6 mm was 100 cc (0.1 dm ³ ) Was measured as the permeability (air permeability, unit: m ² ) normalized by the thickness.

The gas diffusion layer thus obtained was measured for electric resistance by the following method, and the result is shown in FIG. That is, the measurement was performed by energizing both surfaces of a gas diffusion layer having an area of 0.95 cm ² between gold foils and applying a load. The current value was 1 A, up to 5 MPa was taken as one cycle, and the value at 1 MPa in the second cycle was measured. As a result, the electric resistance at 1 MPa in the second cycle was about 11 mΩ / cm ² , indicating a sufficiently low electric resistance.

(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 TEC10E50E (platinum carrying amount = 50%) was used.

This catalyst ink was applied to both surfaces of the electrolyte membrane to form a cathode catalyst layer (dry film thickness = 8 μm) and an anode catalyst layer (dry film thickness = 8 μm), thereby producing an MEA having an active area of 2 cm × 5 cm. As the electrolyte membrane, an electrolyte membrane (Nafion (registered trademark) NR211, manufactured by DuPont, film thickness = 25 μm) was used. The amount of platinum in the cathode catalyst layer so that the 0.363 g / cm ^2, so that the amount of platinum in the anode catalyst layer is 0.063 g / cm ^2, was prepared.

  The gas diffusion layer cut out to the same size as the active area (2 cm × 5 cm) was arranged on the MEA thus produced so as to overlap each catalyst layer, and a power generation cell was assembled.

The power generation cell thus obtained was subjected to power generation test evaluation under the following conditions. Under the following conditions, the load current density was swept in the range of 0 to 1.9 A / cm ² to obtain an IV curve, and the result is shown in FIG.

  From FIG. 3, it can be seen that the MEA using the gas diffusion layer of the present invention can exhibit sufficient power generation performance.

1 Polymer electrolyte fuel cell (PEFC),
2 solid polymer electrolyte membrane,
3a anode catalyst layer,
3c cathode catalyst layer,
4a Anode gas diffusion layer,
4c cathode gas diffusion layer,
8a anode separator,
8c cathode separator,
9a Anode gas flow path,
9c cathode gas flow path,
10 MEA,
11 Refrigerant flow path.

Claims (8)

Conductive carbon kept nonconductive nonwoven or woven fabric Ri Na,
A gas diffusion layer in which the pore diameter of the non-conductive nonwoven fabric or woven fabric is 3 to 5 times the average secondary particle diameter of the conductive carbon .   The gas diffusion layer according to claim 1, wherein the non-conductive nonwoven fabric or woven fabric is formed of at least one selected from the group consisting of glass, polymer resin fibers, and cellulose. The gas diffusion layer according to claim 1 or 2 , wherein the non-conductive nonwoven fabric or woven fabric has a pore diameter of 100 µm or less. The gas diffusion according to any one of claims 1 to 3, further comprising a water repellent, wherein the water repellent is contained in an amount of 0.01 to 0.1 parts by weight with respect to 100 parts by weight of the conductive carbon. layer.   The non-conductive nonwoven fabric or woven fabric is immersed in a slurry containing conductive carbon and a solvent; and the non-conductive nonwoven fabric or woven fabric after the immersion is heat-treated at a temperature of 250 ° C or lower. 2. A method for producing a gas diffusion layer according to item 1.   The method according to claim 5, further comprising water-repellent treatment of the non-conductive nonwoven fabric or fabric after the immersion and before the heat treatment.   The membrane electrode assembly for fuel cells which has a gas diffusion layer of any one of Claims 1-4.   A fuel cell comprising the membrane electrode assembly for a fuel cell according to claim 7.

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