JP2014086133A - Gas diffusion layer for fuel cell and production method therefor, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell in which power generation performance can be enhanced furthermore, when using a gas diffusion layer composed of a porous member containing conductive particles and polymer resin, as main components.SOLUTION: A fuel cell includes: an electrolyte membrane; an electrode layer formed on the principal surface of the electrolyte membrane; a gas diffusion layer arranged in contact with the electrode layer and composed of a porous member containing conductive particles and polymer resin, as main components, and having a plurality of holes extending from the principal surface thereof; and a pair of separators arranged on the outside of the gas diffusion layer. The plurality of holes are formed at positions corresponding the passages of the separators.

Description

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

  Conventionally, diffusion layer members (members constituting “electrodes”) such as fuel cells and electric double layer capacitors are manufactured using diffusion films. This diffusion film is known to contain unfired polytetrafluoroethylene, fired polytetrafluoroethylene, and a conductive substance (see, for example, Patent Document 1).

  In addition, a gas diffusion layer for a fuel cell is also known in which a gas diffusion layer of a fuel cell includes a porous member mainly composed of conductive particles and a polymer resin (for example, Patent Document 2). reference). The fuel cell using the gas diffusion layer in Patent Document 2 is operated with a gas humidification dew point of 65 degrees Celsius for the anode, 35 degrees Celsius for the cathode, and a cell temperature of 90 degrees Celsius.

Japanese Patent Laid-Open No. 2003-187809 International Publication No. 2010/050219 (paragraph 0084)

  As described above, in recent years, further improvement in power generation performance has been demanded in a fuel cell including a gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin.

  The present invention has been made in view of the above-described conventional problems, and used in a fuel cell in a gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin. An object of the present invention is to provide a gas diffusion layer for a fuel cell, a method for producing the same, and a fuel cell, which can further improve the power generation performance in the case.

  In order to solve the above-mentioned problems, the gas diffusion layer for a fuel cell, the method for producing the same, and the fuel cell of the present invention each have the following solutions.

  [1] The gas diffusion layer for a fuel cell of the present application is composed of a porous member mainly composed of conductive particles and a polymer resin, and a fuel cell in which a plurality of holes extending from the main surface of the porous member are formed. In the gas diffusion layer for fuel, the main surface of the gas diffusion layer for fuel cell has a plurality of regions, and holes are formed at equal pitch intervals in each of the plurality of regions.

  [2] In the above [1], the porous member is composed of a first layer and a second layer in contact with the first layer and having higher water repellency than the first layer, and the hole penetrates the first layer. Formed.

  [3] In the above [2], the hole is formed so as not to penetrate the second layer.

  [4] A method for producing a gas diffusion layer for a fuel cell according to the present application includes kneading a conductive particle, a polymer resin, and a surfactant with a dispersion solvent to form a kneaded product, and rolling and molding the kneaded product. After forming the sheet-like kneaded product, the sheet-like kneaded product is heat-treated at a first heat treatment temperature to remove the surfactant and the dispersion solvent from the sheet-like kneaded product, thereby forming the first layer. Next, the first layer includes a step of forming a plurality of holes penetrating the first layer. When forming the plurality of holes, a plurality of regions are provided on the main surface of the first layer, and each of the plurality of regions is provided. Holes are formed at equal pitch intervals in the region.

  [5] In the above [4], the conductive particles, the polymer resin, and the surfactant and the dispersion solvent are mixed to form a dispersion, and the dispersion is formed on the first layer before forming a plurality of holes. Is applied and dried to form a dispersion layer thinner than the first layer, and then the first layer on which the dispersion layer is formed is heat-treated at a second heat treatment temperature lower than the first heat treatment temperature. A step of removing the surfactant and the dispersion solvent from the layer to form a second layer having higher water repellency than the first layer on the first layer is included. At this time, when forming a plurality of holes in the first layer, the plurality of holes are formed so as to penetrate the second layer as well.

  [6] In the above [4], the conductive particles, the polymer resin, and the surfactant and the dispersion solvent are mixed to form a dispersion, and the dispersion is formed on the first layer before forming a plurality of holes. Is applied and dried to form a dispersion layer thinner than the first layer, and then the first layer on which the dispersion layer is formed is heat-treated at a second heat treatment temperature lower than the first heat treatment temperature. A step of removing the surfactant and the dispersion solvent from the layer to form a second layer having higher water repellency than the first layer on the first layer is included. At this time, when forming a plurality of holes in the first layer, the plurality of holes are formed so as not to penetrate the second layer.

  [7] The fuel cell of the present application is composed of an electrolyte membrane, an electrode layer formed on the main surface of the electrolyte membrane, and in contact with the electrode layer, and mainly composed of conductive particles and a polymer resin. The gas diffusion layer is formed of a porous member and has a plurality of holes extending from the main surface thereof, and a pair of separators disposed outside the gas diffusion layer. It is formed at a position corresponding to the flow path.

  [8] In the above [7], the gas diffusion layer is composed of a first layer composed of a porous member mainly composed of conductive particles and a polymer resin, and the conductive particles and the polymer resin as main components. And a second layer that is formed in contact with the first layer and has a higher water repellency than the first layer, and the plurality of holes penetrate the first layer. Is formed.

  [9] In the above [8], the plurality of holes are formed so as not to penetrate the second layer.

  With such a configuration, the gas diffusion layer for a fuel cell, the manufacturing method thereof, and the fuel cell of the present application have the effects of the invention described below.

  ADVANTAGE OF THE INVENTION According to this invention, the electric power generation performance at the time of using for a fuel cell the gas diffusion layer comprised with the porous member which has electroconductive particle and polymer resin as a main component can be improved further. In addition, since the holes of the gas diffusion layer are formed at positions corresponding to the flow paths of the separators, the power generation performance of the fuel cell can be further improved. Furthermore, the method for producing the fuel cell gas diffusion layer can also be attributed to the improvement in power generation performance.

Sectional drawing which shows an example of schematic structure of the gas diffusion layer concerning 1st Embodiment The figure which shows the flowchart which shows an example of the manufacturing method of the gas diffusion layer concerning 1st Embodiment. Sectional drawing which shows schematic structure of the membrane electrode gas diffusion layer assembly concerning 1st Example The top view which shows typically schematic structure of the gas diffusion layer concerning 1st Example Sectional drawing which shows an example of schematic structure of the gas diffusion layer concerning 2nd Embodiment The figure which shows the flowchart which shows an example of the manufacturing method of the gas diffusion layer concerning 2nd Embodiment. Sectional drawing which shows schematic structure of the membrane electrode gas diffusion layer assembly concerning 2nd Example The schematic diagram explaining the pitch of the hole in 3rd Embodiment Sectional drawing which shows an example of schematic structure of the gas diffusion layer concerning 4th Embodiment The figure which shows the flowchart which shows an example of the manufacturing method of the gas diffusion layer concerning 4th Embodiment. The schematic diagram explaining the pitch of the hole in 5th Embodiment Cross-sectional schematic diagram illustrating the pitch of holes in the fifth embodiment The schematic diagram showing the relationship between the hole of a gas diffusion layer and the flow path of a separator of the fuel battery cell in 6th-8th Example The schematic diagram showing the relationship between the hole of a gas diffusion layer and the flow path of a separator of the fuel battery cell in the fifth to seventh comparative examples Schematic diagram explaining the fuel cell stack

(Inventors' knowledge about the present invention)
The present inventors have intensively studied to solve the above problems. As a result, the following knowledge was obtained.

  A gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin has a lower air permeability than a gas diffusion layer using a base material such as carbon paper. Therefore, moisture generated in the catalyst layer (electrode) is difficult to diffuse through the gas diffusion layer, and the electrolyte membrane and the catalyst layer are difficult to dry.

  Therefore, the present inventors have found that the gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin has a dew point of the gas supplied to the electrode higher than the temperature of the fuel cell. The knowledge which is suitable for the so-called low humidification operation which operates at a low temperature was obtained. Note that the low humidification operation is preferable in that a humidifier can be dispensed with, and even when a humidifier is required, the size can be reduced.

  As described above, the gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin has low air permeability and the electrolyte membrane is difficult to dry. It has been developed as a premise. However, the present inventors have noticed that in a fuel cell using such a gas diffusion layer, when the operation is repeated under severe conditions such as starting and stopping of the fuel cell, the gas diffusion layer may be deformed. . As a result of examining the cause, it has been found that, for example, when the fuel cell is started from a low temperature of about room temperature, the gas diffusion layer is particularly easily deformed. The reason is considered as follows.

  In the catalyst layer on the cathode side of the fuel cell, a chemical reaction occurs between protons that have passed through the polymer electrolyte membrane from the anode side and oxygen supplied through the gas diffusion layer on the cathode side. By this reaction, fine particles in which a plurality of water molecules are bonded, so-called mist, are generated.

  The mist moves from the catalyst layer to the gas diffusion layer by diffusion. When the temperature of the fuel cell is low, the kinetic energy of the mist is low. For this reason, part of the mist adheres to the gas diffusion layer at the boundary between the catalyst layer and the gas diffusion layer. Using the attached mist as a nucleus, the mist aggregates one after another, and as a result, a region where liquid water is locally accumulated is formed at the boundary between the catalyst layer and the gas diffusion layer. The water accumulation region generates water pressure, and the gas diffusion layer is pushed up by the water pressure, and the gas diffusion layer peels off from the catalyst layer and deforms.

  As the deformation progresses, the gas diffusion layer is broken and the catalyst layer is exposed to the gas flow path, and drying and deterioration of the electrolyte membrane may be accelerated.

  That is, conventionally, when a gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin is used in a fuel cell, a low humidification operation is performed. It has been considered that there is no need to consider the discharge of water generated at the boundary between the catalyst layer and the gas diffusion layer.

  However, even when a low humidification operation is performed according to the study by the present inventors, for example, when the temperature of the fuel cell is as low as about room temperature at start-up, it occurs at the boundary between the catalyst layer and the gas diffusion layer. Water was found to cause problems such as deformation of the gas diffusion layer. The above-mentioned knowledge of the present inventors is a novel knowledge that has not existed before.

  Beginning with such new findings, the present inventors have further studied. As a result, even in a gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin, the gas diffusion layer is formed by forming a plurality of holes extending from the main surface of the gas diffusion layer. It has been found that the possibility of deformation can be reduced.

  The plurality of holes may be holes extending in the thickness direction of the gas diffusion layer. The hole may be a hole extending perpendicularly to the main surface of the gas diffusion layer. The hole may be a hole extending in an oblique direction with respect to the main surface. The hole may penetrate the gas diffusion layer. The hole may not penetrate the gas diffusion layer. The holes facilitate the discharge of water from the boundary between the gas diffusion layer and the catalyst layer.

  Therefore, for example, it is difficult to form a portion where liquid water accumulates at the boundary between the gas diffusion layer and the catalyst layer, and the gas easily diffuses uniformly, thereby improving the power generation performance of the fuel cell.

(About the embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
The gas diffusion layer for a fuel cell according to the first embodiment is composed of a porous member mainly composed of conductive particles and a polymer resin, and a plurality of holes extending from the main surface of the gas diffusion layer for a fuel cell are formed. Yes.

  “Porous member mainly composed of conductive particles and polymer resin” means a structure supported by only conductive particles and polymer resin without using carbon fiber as a base material (so-called self-supporting structure) ).

  When producing a porous member with conductive particles and a polymer resin, for example, a surfactant and a dispersion solvent are used as described later. In this case, during the production process, the surfactant and the dispersion solvent are removed by firing, but they may not be sufficiently removed and may remain in the porous member. Therefore, “a porous member mainly composed of conductive particles and a polymer resin” means that the surface active agent remaining in such a manner is used as long as the structure is supported only by the conductive particles and the polymer resin. It means that a dispersion solvent may be contained in the porous member.

  In addition, within the range in which the object of the present invention can be achieved, the porous member includes materials other than the conductive particles, the polymer resin, the surfactant, and the dispersion solvent (for example, short-fiber carbon fibers). It also means good.

  A flow path may be formed in the gas diffusion layer for a fuel cell. That is, of the two main surfaces of the fuel cell gas diffusion layer, irregularities such as flow paths may be formed on the surface opposite to the catalyst layer side.

  The “porous member” means that the member has an ability to permeate gas (fuel gas, oxidant gas, etc.) to such an extent that the gas diffusion layer can be used for a fuel cell.

  The gas diffusion layer for a fuel cell may be composed of a matrix (substrate) in which conductive particles and a polymer resin are uniformly dispersed in a plane direction. The “plane direction” refers to a direction in which the gas diffusion layer extends. “To be uniformly dispersed in the plane direction” means, for example, a state in which the conductive particles and the polymer resin are substantially uniformly distributed in the plane direction. It may or may not be homogeneous in the thickness direction.

  That is, a plurality of layers stacked in the thickness direction are formed, and within each layer, the conductive particles and the polymer resin are substantially uniformly distributed in the plane direction, and the density between the layers is And the composition may be different. For example, it refers to the case where the conductive particles and the polymer resin are kneaded and then molded, but the production method is not particularly limited.

  More specifically, for example, it means not containing carbon fiber as a base material. Alternatively, for example, it means that carbon fiber is not included as a base material, and that conductive particles and a polymer resin are the main components. Alternatively, for example, it refers to having a structure that does not include carbon fiber as a base material and is supported by conductive particles and a polymer resin. The above points are the same in other embodiments.

  In the fuel cell gas diffusion layer, the holes may be formed so as to penetrate the fuel cell gas diffusion layer.

  The method for producing a gas diffusion layer for a fuel cell according to the first embodiment includes kneading conductive particles, a polymer resin, a surfactant, and a dispersion solvent to obtain a homogeneous kneaded product, and rolling and molding the kneaded product. To obtain a first layer in which the surfactant and the dispersion solvent are removed from the sheet-like kneaded material by heat-treating the sheet-like kneaded material at a first heat treatment temperature. Forming a plurality of holes penetrating the first layer.

[Device configuration]
FIG. 1 is a cross-sectional view showing an example of a schematic configuration of a gas diffusion layer according to the first embodiment. Hereinafter, the gas diffusion layer 100 for a fuel cell according to the first embodiment will be described with reference to FIG.

  As illustrated in FIG. 1, the fuel cell gas diffusion layer 100 includes a first layer 10. 1st Embodiment demonstrates the case where the gas diffusion layer is formed with the single layer.

  The first layer 10 is composed of a porous member mainly composed of conductive particles and a polymer resin. A plurality of holes 12 extending from the main surface of the fuel cell gas diffusion layer 100 are formed in the first layer 10. The hole 12 is formed so as to penetrate the first layer 10.

  The first layer 10 may be composed of a matrix in which conductive particles and a polymer resin are uniformly dispersed in the surface direction of the fuel cell gas diffusion layer 100.

  The fuel cell gas diffusion layer 100 can be formed, for example, as a gas diffusion layer (a so-called substrate-less GDL) that does not use carbon fiber or the like as a substrate.

  The shape, number, size, arrangement, and the like of the holes 12 are not particularly limited. The hole 12 may have, for example, a substantially linear shape (cylindrical shape with a constant diameter). The hole 12 is formed so as to penetrate the first layer 10. That is, in the present embodiment, the hole 12 is a through hole that penetrates the first layer 10.

  The hole 12 may have a circular shape, an elliptical shape, a triangular shape, a quadrangular shape, or the like. The hole 12 may penetrate the first layer 10 obliquely, for example. For example, the opening 12 on one surface of the first layer 10 may be larger than the opening on the other surface of the first layer 10. The hole 12 may have a tapered shape, for example.

  The longest part of the opening of the hole 12 may be, for example, 30 μm or more and 500 μm or less, 50 μm or more and 250 μm or less, or 100 μm or more and 230 μm or less.

  When the opening of the hole 12 is substantially circular, the diameter may be, for example, 30 μm or more and 500 μm or less, 50 μm or more and 250 μm or less, or 100 μm or more and 230 μm or less.

  By setting the total area of the openings of the holes 12 to 5% or less of the area of the first layer 10, the moisture retention and strength of the fuel cell gas diffusion layer 100 can be made suitable. By setting the total area of the openings of the holes 12 to 1% or less of the area of the first layer 10, the moisture retention and strength of the fuel cell gas diffusion layer 100 can be further improved. The area of the first layer 10 refers to the area of the main surface of the first layer 10.

  The holes 12 may be distributed, for example, in a grid alignment in which the periods of adjacent rows coincide with each other, or in a zig-zag alignment in which the periods of adjacent rows are shifted by half. Also good. The hole 12 is not necessarily formed on the entire surface of the first layer 10, and may be formed only on a part of the main surface of the first layer 10. The arrangement direction of the holes 12 is not necessarily parallel or perpendicular to the gas flow path. For example, the distance between the adjacent holes 12 (the distance between the centers of the holes 12) may be 0.3 mm or more and 10 mm or less. The distance may be 0.5 mm or more and 5 mm or less. The distance may be 1 mm or more and 3 mm or less.

The formation method of the hole 12 is not specifically limited. Specifically, for example, the hole 12 may be formed by piercing a needle made of metal or the like. Alternatively, for example, the holes 12 may be formed using a laser such as a UV laser or a CO ₂ laser. Alternatively, for example, a penetrating member may be provided in a mold used when the first layer 10 is molded, and the hole 12 may be formed by pouring a material into the mold. That is, the hole 12 may be formed simultaneously with the formation of the first layer 10 or may be formed after the first layer 10 is formed.

  The thickness of the 1st layer 10 can be 100 micrometers or more and 1000 micrometers or less, for example. If the thickness of the 1st layer 10 is 100 micrometers or more, the mechanical strength of the 1st layer 10 will become large. If the thickness of the 1st layer 10 is 1000 micrometers or less, the electrical resistance of the 1st layer 10 will become small.

  For example, carbon fine powder can be used as the conductive particles. Examples of the carbon fine powder include carbon materials such as graphite, carbon black, activated carbon, and carbon fiber fine powder. Examples of carbon black include acetylene black (AB), furnace black, ketjen black, and vulcan. Examples of the carbon fiber fine powder include vapor grown carbon fiber (VGCF), milled fiber, cut fiber, and chop fiber. As the conductive particles, these materials may be used alone, or a plurality of materials may be used in combination. The raw material form of the carbon material may be any shape such as powder, fiber, and granule.

  When carbon black and carbon fiber are mixed, the manufacturing cost, electrical conductivity, and strength of the gas diffusion layer can be improved. Furthermore, when acetylene black is used as carbon black, the impurity content can be reduced and the electrical conductivity can be further improved.

  As the polymer resin, for example, a fluororesin can be used. Fluororesin includes PTFE (polytetrafluoroethylene), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), PVDF (polyvinylidene fluoride), ETFE (tetrafluoroethylene / ethylene copolymer), PCTFE (polyethylene). Chlorotrifluoroethylene), PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer), and the like.

  When PTFE is used as the fluororesin, the heat resistance, water repellency, and chemical resistance can be improved. Examples of the raw material of PTFE include a dispersion and a powdery shape. When the dispersion is used, workability can be improved.

  The polymer resin may have a function as a binder that binds the conductive particles. When the content of the polymer resin in the first layer 10 is 5% by weight or more, the polymer resin effectively functions as a binder. A rolling process may be employed to make the first layer 10 uniform thickness. When the content of the polymer resin in the first layer 10 is 50% by weight or less, the conditions during the rolling process can be simplified. When the content of the polymer resin in the first layer 10 is 30% by weight or less, the conditions during the rolling process can be further simplified.

  The first layer 10 may have an air resistance of 100 seconds or more when the hole 12 is not formed. The air resistance is a time required for permeation of a predetermined volume (100 mL) of air per unit area and unit pressure difference. The air resistance in the present specification is determined by the Gurley method based on JIS-P8177: 2009. JIS-P8177: 2009 is the same as ISO5636-5: 2003 except that the range of applicable air resistance is not limited. Of the above standards, a B-type device is used, and the measurement starts when the first 50 ml mark is passed.

  The first layer 10 may be a porous member mainly composed of conductive particles and a polymer resin. The first layer 10 may be composed of a porous member containing conductive particles and a polymer resin as main components and carbon fibers having a weight less than that of the polymer resin added as conductive particles. The porous member may contain 2.0% by weight or more and 7.5% by weight or less of carbon fiber. The porous member may contain 10 wt% or more and 17 wt% or less of the polymer resin. The 1st layer 10 can be set as the structure which does not contain a base material.

  In this specification, “a porous member mainly composed of conductive particles and a polymer resin” means a structure that is supported only by conductive particles and a polymer resin without using carbon fiber as a base material ( It means a porous member having a so-called self-supporting structure. When producing a porous member with conductive particles and a polymer resin, for example, a surfactant and a dispersion solvent are used as described later.

  In this case, during the production process, the surfactant and the dispersion solvent are removed by firing, but they may not be sufficiently removed and may remain in the porous member. Therefore, “a porous member mainly composed of conductive particles and a polymer resin” means that the surface active agent remaining in such a manner is used as long as the structure is supported only by the conductive particles and the polymer resin. It means that a dispersion solvent may be contained in the porous member.

  In addition, within the range in which the object of the present invention can be achieved, the porous member includes materials other than the conductive particles, the polymer resin, the surfactant, and the dispersion solvent (for example, short-fiber carbon fibers). It also means good.

  The porosity of the first layer 10 may be 42% or more and 60% or less.

  Hereinafter, the measurement method (calculation method) of the porosity of the gas diffusion layer in this specification will be described. First, the apparent true density of the manufactured gas diffusion layer is calculated from the true density and composition ratio of each material constituting the gas diffusion layer. Next, the weight, thickness, vertical and horizontal dimensions of the manufactured gas diffusion layer are measured, and the density of the manufactured gas diffusion layer is calculated. Next, the porosity is calculated by substituting the calculated density of the gas diffusion layer and the apparent true density into the formula of porosity = (density of the gas diffusion layer) / (apparent true density) × 100. As described above, the porosity of the produced gas diffusion layer can be measured.

  The first layer 10 may contain a dispersion solvent, a surfactant, and the like in addition to the polymer resin and the conductive particles. Examples of the dispersion solvent include water, alcohols such as methanol and ethanol, and glycols such as ethylene glycol. Examples of the surfactant include nonionic surfactants such as polyoxyethylene alkyl ether, and zwitterionic surfactants such as alkylamine oxide.

  The content of the dispersion solvent and the surfactant in the first layer 10 can be appropriately selected depending on the types of the conductive particles and the polymer resin constituting the first layer 10, the blending ratio of the polymer resin and the conductive particles, and the like. . In general, the higher the content of the dispersion solvent and the surfactant, the easier the polymer resin and conductive particles are uniformly dispersed. When the content of the dispersion solvent and the surfactant is set to a certain value or less, the fluidity does not become too high, and sheeting can be facilitated.

  The first layer 10 may contain materials other than the conductive particles, the polymer resin, the surfactant, and the dispersion solvent (for example, short-fiber carbon fibers).

  The fuel cell gas diffusion layer 100 may include layers other than the first layer 10.

  The fuel cell gas diffusion layer 100 may be used as a cathode-side gas diffusion layer, as an anode-side gas diffusion layer, or as both a cathode-side and anode-side gas diffusion layer. Good. The water generated by the power generation reaction is mainly generated on the cathode side, but the water passes through the electrolyte membrane. Therefore, drainage through the holes 12 can be realized on either the cathode or anode side by appropriately selecting the flow path configuration, gas dew point, and the like.

  The present embodiment includes an electrolyte membrane, an anode electrode layer in contact with one main surface of the electrolyte membrane, a cathode electrode layer in contact with the other main surface of the electrolyte membrane, and an electrolyte membrane side of the main surfaces of the anode electrode layer, An anode side gas diffusion layer in contact with a main surface on a different side, and a cathode side gas diffusion layer in contact with a main surface on a different side from the electrolyte membrane side among the main surfaces of the cathode electrode layer. At this time, at least one of the anode side gas diffusion layer and the cathode side gas diffusion layer is composed of a porous member mainly composed of conductive particles and a polymer resin, and a plurality of holes extending from the main surface of the gas diffusion layer are provided. It may be implemented as a membrane electrode gas diffusion layer assembly formed and formed so that the hole penetrates the gas diffusion layer.

  The present embodiment includes an electrolyte membrane, an anode electrode layer in contact with one main surface of the electrolyte membrane, a cathode electrode layer in contact with the other main surface of the electrolyte membrane, and an electrolyte membrane side of the main surfaces of the anode electrode layer, An anode side gas diffusion layer in contact with a main surface on a different side, and a cathode side gas diffusion layer in contact with a main surface on a different side from the electrolyte membrane side among the main surfaces of the cathode electrode layer. At this time, at least one of the anode side gas diffusion layer and the cathode side gas diffusion layer is composed of a porous member mainly composed of conductive particles and a polymer resin, and a plurality of holes extending from the main surface of the gas diffusion layer are provided. It may be implemented as a fuel cell formed and formed so that the hole penetrates the gas diffusion layer.

  The polymer electrolyte membrane is preferably a polymer membrane having hydrogen ion conductivity. Although the shape of a polymer electrolyte membrane is not specifically limited, For example, it can be set as a substantially rectangular shape. The material of the polymer electrolyte membrane is not particularly limited as long as it selectively moves hydrogen ions.

  Examples of the polymer electrolyte membrane include a fluorine-based polymer electrolyte membrane made of perfluorocarbon sulfonic acid (for example, Nafion (registered trademark) manufactured by DuPont, USA, Aciplex (registered trademark), manufactured by Asahi Kasei Corporation, Asahi Glass Co., Ltd. Flemion (registered trademark), etc.) and various hydrocarbon electrolyte membranes can be used.

  The electrode layer is preferably a layer containing a catalyst for the redox reaction of hydrogen or oxygen. The electrode layer is not particularly limited as long as it has conductivity and has a catalytic ability for a redox reaction of hydrogen and oxygen. Although the shape of an electrode layer is not specifically limited, For example, it can be set as a substantially rectangular shape.

  The electrode layer is made of, for example, a porous member mainly composed of carbon powder carrying a platinum group metal catalyst and a polymer material having proton conductivity. The proton conductive polymer material used for the electrode layer may be the same as or different from the polymer electrolyte membrane.

  The fuel cell gas diffusion layer 100 is preferably used for the low humidification operation, but may be used for the high humidification operation. That is, the fuel cell system using the fuel cell gas diffusion layer 100 may or may not be provided with a humidifier that humidifies the gas supplied to the fuel cell.

  Since the first layer 10 is composed of a porous member mainly composed of conductive particles and a polymer resin, the air resistance of the first layer 10 in portions other than the holes 12 is low. It is difficult for the gas containing mist present in the catalyst layer on the cathode side of the fuel cell to pass through the fuel cell gas diffusion layer 100 as in the case where the holes 12 are not present. Therefore, even when the dew point of water vapor contained in the gas supplied to the fuel cell is lower than the temperature of the fuel cell, the fuel cell including the fuel cell gas diffusion layer 100 does not dry the polymer electrolyte membrane. It can generate electricity properly while preventing it.

  On the other hand, since excess moisture is appropriately discharged through the holes 12, the possibility that a region in which liquid water accumulates locally at the boundary between the catalyst layer and the first layer 10 is reduced. Therefore, the possibility that the gas diffusion layer is pushed up by the water pressure at which the water accumulation region is generated is reduced, and the possibility that the gas diffusion layer is separated from the catalyst layer and deformed is reduced.

[Production method]
FIG. 2 is a flowchart showing an example of a method for producing a gas diffusion layer according to the first embodiment. Hereinafter, the manufacturing method of the fuel cell gas diffusion layer 100 of the first embodiment will be described with reference to FIG.

  The first layer 10 can be produced by kneading, extruding, rolling, and firing a mixture containing a polymer resin and conductive particles.

  Specifically, for example, first, the kneaded product is obtained by kneading the conductive particles, the polymer resin, the surfactant, and the dispersion solvent (step S101). The content of the conductive particles in the kneaded product can be, for example, 10% by weight or more and 50% by weight or less. The content of the polymer resin in the kneaded product can be, for example, 1% by weight or more and 20% by weight or less.

  Examples of the dispersion solvent used as a raw material for the kneaded product include water, alcohols such as methanol and ethanol, and glycols such as ethylene glycol. Among these, when water is used, cost can be reduced and environmental load can also be reduced.

  The content of the dispersion solvent in the kneaded product can be, for example, 30% by weight or more and 88% by weight or less.

  Examples of the surfactant used as a raw material for the kneaded product include an anionic surfactant, a cationic surfactant, an amphoteric surfactant, and a nonionic surfactant. Specific examples include nonionics such as polyoxyethylene alkyl ethers and zwitterionics such as alkylamine oxides. From the viewpoint of removing the surfactant and preventing catalyst poisoning by metal ions, it is preferable to use a nonionic surfactant as the surfactant. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkylphenol ether, alkyl glucoside, polyoxyethylene fatty acid ester, sucrose fatty acid ester, sorbitan fatty acid ester, and fatty acid alkanolamide.

  The content of the surfactant in the kneaded product can be, for example, 0.1% by weight or more and 5% by weight or less.

  The contents of the dispersion solvent and the surfactant in the kneaded product can be appropriately selected depending on the types of the conductive particles and the polymer resin, the blending ratio of the polymer resin and the conductive particles, and the like. In general, the higher the content of the dispersion solvent and the surfactant, the easier the polymer resin and conductive particles are uniformly dispersed. When the content of the dispersion solvent and the surfactant is set to a certain value or less, the fluidity does not become too high, and sheeting can be facilitated.

  More specifically, the conductive particles, the dispersion solvent, and the surfactant are put into a stirring kneader, kneaded, pulverized, and granulated to disperse the conductive particles in the dispersion solvent. Next, the polymer resin is further dropped into a stirring kneader and stirred and kneaded to disperse the conductive particles and the polymer resin in the dispersion solvent. By such a method, a kneaded product is obtained.

  Next, the kneaded material obtained is rolled and molded to obtain a sheet-like kneaded material (step S102). The sheet-like kneaded product refers to a kneaded product that has been rolled and formed so as to have a sheet-like shape. For rolling and forming, for example, a roll press or a flat plate press can be used. The thickness of the sheet-like kneaded product can be adjusted as appropriate so that the thickness of the first layer becomes a desired value.

  Next, the obtained sheet-like kneaded material is heat-treated to remove the dispersion solvent and the surfactant, thereby obtaining the first layer 10 (step S103). The heat treatment of the sheet-shaped kneaded material can be performed, for example, in a firing furnace, an electric furnace, a gas furnace, or the like. Hereinafter, the heating temperature in the heat treatment of the sheet-shaped kneaded material is referred to as a first heat treatment temperature.

  The first heat treatment temperature can be set to 260 degrees Celsius or higher. By setting the first heat treatment temperature to 260 degrees Celsius or higher, it becomes easy to remove the surfactant from the sheet-like kneaded material at a speed that can ensure mass productivity.

  The 1st heat processing temperature can be made below into melting | fusing point of the polymer resin used as the raw material of a kneaded material. By setting the first heat treatment temperature to be equal to or lower than the melting point of the polymer resin that is the raw material of the kneaded product, the polymer resin is hardly melted, the strength as a structure is difficult to be lowered, and the sheet shape is not easily collapsed.

  When PTFE is used as the polymer resin, the melting point of the polymer resin may be 330 degrees Celsius or more and 350 degrees Celsius or less, and the temperature in the heat treatment at the first heat treatment temperature may be 260 degrees Celsius or more and 330 degrees Celsius or less.

  The heating temperature and the heating time in the heat treatment may be set to a temperature and a time at which the surfactant and the dispersion solvent are sufficiently removed from the sheet-like kneaded product and the crystallization of the polymer resin proceeds. The remaining amount of the surfactant and the dispersion solvent can be measured by an analysis result such as TG / DTA (differential heat / thermogravimetric simultaneous measurement device). The remaining amount may be 1 wt% or less with respect to the total weight of the first layer 10. The remaining amount can be appropriately controlled by adjusting the thickness of the first layer 10, the heat treatment temperature, and the time.

Next, a plurality of holes 12 penetrating the first layer 10 are formed in the first layer 10 (step S104). The formation method of the hole 12 is not specifically limited. Specifically, for example, the hole 12 may be formed by piercing a needle made of metal or the like. Alternatively, for example, the holes 12 may be formed using a laser such as a UV laser or a CO ₂ laser. Alternatively, for example, a penetrating member may be provided in a mold used when the first layer 10 is molded, and the hole 12 may be formed by pouring a material into the mold. That is, the hole 12 may be formed simultaneously with the formation of the first layer, or may be formed after the first layer is formed. In other words, step S104 may be executed simultaneously with step S102 and step S103.

[First embodiment]
In the first example, a membrane electrode gas diffusion layer assembly using the gas diffusion layer of the first embodiment was produced and a power generation test was performed.

  FIG. 3 is a cross-sectional view showing a schematic configuration of the membrane electrode gas diffusion layer assembly according to the first embodiment. As shown in FIG. 3, in the membrane electrode gas diffusion layer assembly of the first embodiment, the cathode catalyst layer 18 is provided on the cathode-side main surface of the polymer electrolyte membrane 20, and the anode side of the polymer electrolyte membrane 20 is provided. The anode catalyst layer 22 is provided on the main surface of the cathode catalyst layer, the gas diffusion layer 100 for the fuel cell is provided on the main surface of the cathode catalyst layer 18 opposite to the polymer electrolyte membrane 20, and the polymer of the anode catalyst layer 22 is provided. A layer 24 is provided on the main surface opposite to the electrolyte membrane 20.

  The fuel cell gas diffusion layer 100 has a first layer 10 composed of a porous member mainly composed of conductive particles and a polymer resin, and penetrates the first layer 10 through the first layer 10. A plurality of holes 12 are formed. The layer 24 is composed of a porous member mainly composed of conductive particles and a polymer resin, and no holes are formed in the layer 24.

  In the first example, a membrane electrode assembly was produced by the following method.

  That is, a catalyst-supporting carbon (TEC10E50E manufactured by Tanaka Kikinzoku Kogyo Co., Ltd., 50 mass% is Pt) obtained by supporting platinum particles as an electrode catalyst on carbon powder, and a polymer electrolyte solution having hydrogen ion conductivity ( An ink for forming a cathode catalyst layer was prepared by dispersing Aquivion, D79-20BS, manufactured by Solvay Solexis Co., Ltd., in a mixed dispersion medium (mass ratio 1: 1) of ethanol and water. The polymer electrolyte was added so that the mass of the polymer electrolyte in the catalyst layer after coating formation was 0.4 times the mass of the catalyst-supported carbon.

The obtained ink for forming a cathode catalyst layer was applied to one surface of a polymer electrolyte membrane (GSII manufactured by Japan Gore-Tex Co., Ltd., 150 mm × 150 mm) by a spray method, so that the platinum loading was 0.3 mg / The cathode catalyst layer was formed so as to be cm ² .

  At the time of applying the catalyst layer, a substrate (PET) punched out to 140 mm × 140 mm was used as a mask.

  Next, a catalyst-supported carbon (manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) in which platinum ruthenium alloy (platinum: ruthenium = 1: 1.5 molar ratio (substance ratio)) particles as electrode catalysts are supported on carbon powder. TEC61E54, 50% by mass of a Pt—Ru alloy) and a polymer electrolyte solution having hydrogen ion conductivity (Aquivion, D79-20BS, manufactured by Solvay Solexis Co., Ltd.), a mixed dispersion medium of ethanol and water ( An ink for forming an anode catalyst layer was prepared by dispersing in a mass ratio of 1: 1). The polymer electrolyte was added so that the mass of the polymer electrolyte in the catalyst layer after coating formation was 0.4 times the mass of the catalyst-supported carbon.

The obtained ink for forming an anode catalyst layer was applied to the other surface of the polymer electrolyte membrane opposite to the surface on which the cathode catalyst layer was formed by a spray method, and had a single layer structure and a platinum carrying amount. The anode catalyst layer was formed so as to be 0.2 mg / cm ² .

  The shape of the mask and the method of use were the same as in the preparation of the cathode catalyst layer.

  In the first example, a gas diffusion layer was produced by the following method.

  50 g of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo), 80 g of graphite (manufactured by Wako Pure Chemical Industries), 3 g of VGCF (manufactured by Showa Denko, fiber diameter 0.15 μm), 4 g of surfactant (Triton X), 200 g of water was put into a mixer and kneaded. Subsequently, 25 g of PTFE dispersion (manufactured by Asahi Glass Co., Ltd., AD911, solid content ratio: 60 wt%) was added to the mixer, and the mixture was further stirred for 5 minutes to obtain a kneaded product. 20 g of the obtained kneaded material was taken out from the mixer, and a sheet-like kneaded material having a thickness of 600 μm was obtained using a stretching roll machine (gap 600 μm). Thereafter, the sheet-like kneaded product was heat-treated at 300 ° C. for 2 hours in a baking furnace to remove the surfactant and water in the kneaded product. The sheet-like kneaded product from which the surfactant and water have been removed is taken out of the firing furnace, and rolled again with a drawing roll machine (gap 400 μm) to adjust the thickness and reduce the thickness variation, and then cut into a 14 cm square. did. Thus, a rubber-like first layer having a thickness of 400 μm was produced.

  It was 850 second as a result of measuring the air resistance of the 1st layer with the B type device of the Gurley test machine method (Gurley method) based on JIS-P8177: 2009.

  For the cathode gas diffusion layer, a through hole having a diameter of 230 μm was formed by completely piercing a needle made of Kanthal wire (iron, chromium, aluminum alloy) into the first layer obtained by the above method.

  FIG. 4 is a plan view schematically showing a schematic configuration of the gas diffusion layer according to the first embodiment. As shown in FIG. 4, the gas diffusion layer of the first example was formed in the first layer 10 such that the holes 12 were arranged in a zig-zag alignment.

The pitch of the through holes was about 3 mm, and the distance to adjacent through holes was about 3 mm. The density of the through holes was 11 per 1 cm ² . The opening area of the through hole, the area 1 cm ² per the first layer was 0.0046cm ^2. The total area of the openings of the through holes was 0.46% of the area of the first layer.

  For the anode gas diffusion layer, the first layer was used as it was without forming a through hole.

The cathode gas diffusion layer and anode gas diffusion layer produced as described above were brought into contact with the membrane electrode assembly produced by the above method, and hot-pressed at 120 ° C. and 6 kgf / cm ² for 5 minutes, By joining the catalyst layer and the gas diffusion layer, a membrane electrode gas diffusion layer assembly of the first example was obtained.

[First comparative example]
In the first comparative example, a membrane electrode gas diffusion layer assembly using a gas diffusion layer including carbon cloth was produced, and a power generation test was performed.

  In the first comparative example, a membrane electrode assembly was produced by the same method as in the first example.

  In the first comparative example, a gas diffusion layer was produced by the following method.

  A carbon cloth having a thickness of 270 μm (SK-1 manufactured by Mitsubishi Chemical Corporation) is impregnated into a fluororesin-containing aqueous dispersion (ND-1 manufactured by Daikin Industries, Ltd.) and then dried to dry the carbon. The cloth was given water repellency (water repellency treatment). Subsequently, a water repellent carbon layer was formed on one surface (entire surface) of the carbon cloth after the water repellent treatment. Conductive carbon powder (Denka Black (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd.) and an aqueous solution (D-1 manufactured by Daikin Industries, Ltd.) in which fine powder of polytetrafluoroethylene (PTFE) is dispersed. By mixing, an ink for forming a water-repellent carbon layer was prepared. This water repellent carbon layer forming ink was applied to one surface of the carbon cloth after the water repellent treatment by a doctor blade method (Doctor Blade Technique) to form a water repellent carbon layer. Thereafter, the carbon cloth after the water-repellent treatment and the formation of the water-repellent carbon layer was baked at 350 ° C. for 30 minutes to obtain a gas diffusion layer including the carbon cloth.

  The gas resistance of the gas diffusion layer including the carbon cloth was measured by a Gurley method B type apparatus based on JIS-P8177: 2009, and the result was 0.4 second.

  In the first comparative example, the cathode gas diffusion layer and the anode gas diffusion layer were produced by the same method.

The cathode gas diffusion layer and anode gas diffusion layer produced as described above were brought into contact with the membrane electrode assembly produced by the above method, and hot-pressed at 120 ° C. and 6 kgf / cm ² for 5 minutes, The membrane electrode gas diffusion layer assembly of the first comparative example was obtained by bonding the catalyst layer and the gas diffusion layer.

[Second Comparative Example]
In the second comparative example, a gas diffusion layer was produced without forming a through hole in the first layer obtained by the same method as in the first example, and a membrane electrode gas diffusion layer assembly was produced using this. A power generation test was conducted.

  In the second comparative example, a membrane electrode assembly was produced by the same method as in the first example.

  In the second comparative example, the first layer was produced by the same method as in the first example.

  It was 777 seconds as a result of measuring the air resistance of the 1st layer with the B-type apparatus of the Gurley test method (Gurley method) based on JIS-P8177: 2009.

  In the second comparative example, both the cathode gas diffusion layer and the anode gas diffusion layer used the first layer as it was without forming a through hole.

The cathode gas diffusion layer and anode gas diffusion layer produced as described above were brought into contact with the membrane electrode assembly produced by the above method, and hot-pressed at 120 ° C. and 6 kgf / cm ² for 5 minutes, By joining the catalyst layer and the gas diffusion layer, the membrane electrode gas diffusion layer assembly of the second example was obtained.

[Power generation test]
A fuel cell was fabricated using the membrane electrode gas diffusion layer assembly obtained in each of the first example, the first comparative example, and the second comparative example. The membrane electrode gas diffusion layer assembly is sandwiched between a separator having a gas flow path for supplying fuel gas and a cooling water flow path and a separator having a gas flow path for supplying oxidant gas, and a cathode and an anode between both separators. A gasket made of fluororubber was placed around, and a unit cell having an effective electrode (anode or cathode) area of 196 cm ² was obtained.

  The temperature of the unit cell obtained for each of the first example, the first comparative example, and the second comparative example is maintained at 65 degrees Celsius, and hydrogen gas and carbon dioxide as fuel gas are supplied to the gas flow path on the anode side. A mixed gas (75% hydrogen gas, 25% carbon dioxide) was supplied, and air was supplied to the gas flow path on the cathode side. The hydrogen gas utilization rate was 70%, and the air utilization rate was 40%. The fuel gas and air were both humidified so that the dew point was about 65 degrees Celsius, and then supplied to the unit cell.

First, aging (activation process) of the unit cells was performed by generating each unit cell with a current density of 0.2 A / cm ² for 12 hours.

Then, room temperature start-up was performed as follows. First, power generation was stopped for each unit cell, and the temperature of the unit cell was lowered to room temperature (about 25 degrees Celsius). Thereafter, the dew point of the fuel gas is supplied to the anode with a dew point of about 65 degrees Celsius, and the air is supplied to the cathode in a dry state without dehumidification (dew point = 45 degrees Celsius [minus] 45 degrees Celsius). Power generation was started (started up) at a current density of 0.25 A / cm ² . Furthermore, the temperature of the unit cell was raised to 65 degrees Celsius after the start of power generation. Such a process is called room temperature startup because the temperature of the cell at the start of power generation is at room temperature.

  After the first room temperature startup, power generation was continued for 4 hours, and then the voltage was measured. Further, after starting the room temperature 100 times, the power generation test was completed, the fuel cell was disassembled, and the number of locations where the cathode-side gas diffusion layer was separated from the catalyst layer was confirmed. In addition, the part which has peeled refers to the part from which the gas diffusion layer has floated from the catalyst layer a little. In any sample, no portion where the gas diffusion layer was peeled off was found on the anode side.

  Table 1 shows the results of the power generation test.

  As shown in Table 1, in the first example, the first comparative example, and the second comparative example, the cell voltages are 748 mV, 720 mV, and 749 mV, respectively. The voltage was almost equal and higher than that of the first comparative example. This is because the first example and the second comparative example having the first layer composed of a porous member mainly composed of conductive particles and a polymer resin than the first comparative example using the carbon cloth. This is because the electrolyte membrane can be more effectively prevented from drying, and the power generation efficiency is improved.

  As shown in Table 1, in the first example, the first comparative example, and the second comparative example, the number of peeled portions is 8, 0, and 67, respectively, and the first example and the first comparative example are The number of peeled portions was substantially smaller than that of the second comparative example. This is because the first embodiment having a through-hole having a high air permeability resistance and the air resistance having a through-hole are compared to the second comparative example having the high air-resistance resistance and having no through-hole. In the first comparative example having a lower temperature, a region where liquid water is locally accumulated is less likely to be generated at the boundary between the catalyst layer and the gas diffusion layer, and the gas diffusion layer is pushed up by the water pressure at which the water accumulation region is generated. This is thought to be because it became difficult to be done.

  In summary, in the first example, the voltage was as good as that of the second comparative example, and the number of peeled portions was as good as that of the first comparative example. That is, the gas diffusion layer of the first embodiment generates power appropriately while preventing drying of the polymer electrolyte membrane, and the gas diffusion layer peels off from the catalyst layer and deforms in a combination of low humidification operation and room temperature startup. It turned out that the conflicting problem of reducing the possibility can be solved simultaneously.

(Second Embodiment)
The gas diffusion layer for a fuel cell according to the second embodiment is a gas diffusion layer for a fuel cell according to the first embodiment and its modifications, and is composed of a porous member mainly composed of conductive particles and a polymer resin. A first layer formed of a porous member mainly composed of conductive particles and a polymer resin, formed so as to be in contact with the first layer, and having a higher water repellency than the first layer; The hole is formed so as to penetrate the first layer and the second layer.

  The manufacturing method of the gas diffusion layer for fuel cells of 2nd Embodiment is a manufacturing method of the gas diffusion layer for fuel cells of 1st Embodiment and its modification. Specifically, the conductive particles, the polymer resin, the surfactant, and the dispersion solvent are mixed to obtain a homogeneous dispersion, and the dispersion is applied and dried on the first layer before forming the pores. To form a dispersion layer thinner than the first layer. Next, the first layer on which the dispersion layer is formed is heat-treated at a second heat treatment temperature lower than the first heat treatment temperature to remove the surfactant and the dispersion solvent from the dispersion layer, and A second layer having a higher water repellency than the first layer is obtained. At this time, when the hole is formed in the first layer, the hole is formed so that the hole also penetrates the second layer.

  The second layer has higher water repellency than the first layer. The mist generated by the power generation reaction is unlikely to adhere to the second layer. For this reason, the mist in the second layer can move more smoothly than in the first layer. The presence of the second layer between the catalyst layer and the first layer promotes the movement of mist in a direction (plane direction) parallel to the main surface of the polymer electrolyte membrane in the second layer. The amount of mist that moves from the catalyst layer to the boundary between the first layer and the second layer or to the first layer is reduced.

  When the temperature of the fuel cell is low, such as during startup, the kinetic energy of the mist is low. Therefore, a part of the mist moving in the second layer is likely to adhere to the first layer at the boundary between the first layer and the second layer. The mist present near the boundary between the first layer and the second layer is aggregated one after another using the mist adhering to the first layer as a nucleus, and as a result, locally at the boundary between the first layer and the second layer. A region where water accumulates is formed. The gas diffusion layer of the second embodiment has a hole penetrating the first layer and the second layer. Since the water present in the region can be discharged to the outside of the gas diffusion layer through the holes, the possibility that the gas diffusion layer is deformed by water pressure can be further reduced.

[Device configuration]
FIG. 5 is a cross-sectional view showing an example of a schematic configuration of the gas diffusion layer according to the second embodiment. Hereinafter, the gas diffusion layer 200 for a fuel cell according to the second embodiment will be described with reference to FIG.

  As illustrated in FIG. 5, the fuel cell gas diffusion layer 100 includes a first layer 10 and a second layer 14. That is, 2nd Embodiment demonstrates the case where the gas diffusion layer is formed with two layers.

  The fuel cell gas diffusion layer 200 can be formed, for example, as a gas diffusion layer (a so-called substrate-less GDL) that does not use carbon fiber or the like as a substrate.

  The first layer 10 can be the same as that of the first embodiment except that the sign of the hole penetrating the first layer 10 is changed from 12 to 16. Therefore, detailed description is omitted.

  The second layer 14 is composed of a porous member mainly composed of conductive particles and a polymer resin, is formed so as to be in contact with the first layer 10, and has higher water repellency than the first layer 10.

  The second layer 14 may be a porous member mainly composed of conductive particles and a polymer resin. The second layer 14 may be composed of a porous member containing conductive particles and a polymer resin as main components and carbon fibers having a weight less than that of the polymer resin added as conductive particles. The porous member may contain 2.0% by weight or more and 7.5% by weight or less of carbon fiber. The porous member may contain 10 wt% or more and 17 wt% or less of the polymer resin. The 2nd layer 14 can be set as the structure which does not contain a base material.

  The porosity of the second layer 14 may be 42% or more and 75% or less.

  When the fuel cell gas diffusion layer 200 is used in a fuel cell, the second layer 14 can be disposed in contact with the catalyst layer. The first layer can be disposed in contact with the separator.

  Since the conductive particles and the polymer resin can be the same as those in the first embodiment, detailed description thereof is omitted.

  The water repellency can be evaluated based on the contact angle of water droplets when liquid water is dropped on the surface. That is, the greater the contact angle, the higher the water repellency. When the contact angle = 180 °, there is no wetting and the water repellency is maximized. When the contact angle = 0 °, the film is completely wetted and the water repellency is minimized. As factors affecting water repellency, the hydrophobicity-hydrophilicity of the material constituting the layer and the porosity (surface area) of the material constituting the layer are considered. If the material constituting the layer is hydrophobic, the water repellency is considered to increase. If the porosity of the material forming the layer is large, the water repellency is considered to be large. Thus, water repellency is an indicator of whether or not mist is likely to move through the interior of the layer.

  The water repellency can be adjusted by changing the content of the polymer resin contained in each layer and the porosity (surface area) of the material constituting each layer. For example, the content of the polymer resin in the second layer 14 is made larger than that in the first layer 10, and the second layer 14 is made of a material having a larger porosity (surface area) than the first layer 10. For example, the water repellency of the second layer 14 can be made higher than that of the first layer 10.

  The second layer 14 may be thinner than the first layer 10. The thickness of the second layer 14 can be, for example, 10 μm or more and 100 μm or less. If the thickness of the 2nd layer 14 is 10 micrometers or more, it will become easier to ensure the adhesive strength with a catalyst layer. If the thickness of the second layer 14 is 100 μm or less, the surfactant can be removed at a speed that can ensure mass productivity even at a low heat treatment temperature.

  The composition of the conductive particles and the polymer resin constituting the second layer 14 may be different from the composition of the conductive particles and the polymer resin constituting the first layer 10.

  The polymer resin content of the second layer 14 may be higher than the polymer resin content of the first layer 10. By increasing the content of the polymer resin in the second layer 14, the water repellency of the second layer 14 is increased, and the mist generated by the power generation reaction is less likely to adhere to the second layer 14. Therefore, the mist can move more smoothly in the second layer 14 than in the first layer 10.

  The second layer 14 may contain a dispersion solvent, a surfactant, and the like in addition to the polymer resin and the conductive particles. Examples of the dispersion solvent include water, alcohols such as methanol and ethanol, and glycols such as ethylene glycol. Examples of the surfactant include nonionic surfactants such as polyoxyethylene alkyl ether, and zwitterionic surfactants such as alkylamine oxide.

  The content of the dispersion solvent and the surfactant in the second layer 14 can be appropriately selected depending on the types of the conductive particles and the polymer resin constituting the second layer 14, the blending ratio of the polymer resin and the conductive particles, and the like. . In general, the higher the content of the dispersion solvent and the surfactant, the easier the polymer resin and conductive particles are uniformly dispersed. However, when the content of the dispersion solvent and the surfactant is set to a certain value or less, the fluidity does not become too high, and sheeting can be facilitated.

  The second layer 14 may include materials other than the conductive particles, the polymer resin, the surfactant, and the dispersion solvent (for example, short-fiber carbon fibers).

  The hole 16 is formed so as to penetrate the first layer 10 and the second layer 14. That is, in the present embodiment, the hole 16 is a through hole that penetrates the first layer 10 and the second layer 14. Other points, for example, the shape, number, size, arrangement, formation method, and the like can be the same as those of the hole 12 of the first embodiment. Therefore, detailed description is omitted.

[Production method]
FIG. 6 is a flowchart showing an example of a method for producing a gas diffusion layer according to the second embodiment. Hereinafter, a method for manufacturing the fuel cell gas diffusion layer 200 of the second embodiment will be described with reference to FIG.

  Since steps S201 to S203 can be the same as steps S101 to S103 of the first embodiment, detailed description thereof will be omitted.

  When the first layer 10 is obtained in step S203, the second layer 14 is formed by the following method.

  First, a dispersion liquid is obtained by mixing conductive particles, a polymer resin, a surfactant, and a dispersion solvent (step S204). More specifically, for example, a dispersion treatment is added to a mixture of a surfactant and a dispersion solvent, and then a fine carbon powder and a fluororesin are added to the dispersion treatment. Note that all the materials including the surfactant may be dispersed at the same time without previously performing the surfactant dispersion treatment.

  As the material for the conductive particles used as the raw material for the dispersion, the same materials as those exemplified above as the material for the conductive particles used as the raw material for the first layer 10 can be used. The conductive particles used as the raw material for the kneaded product and the conductive particles used as the raw material for the dispersion may be the same or different. The content of the conductive particles in the dispersion can be, for example, 1% by weight or more and 30% by weight or less.

  As the material of the polymer resin that becomes the raw material of the dispersion, the same materials as those exemplified above as the material of the polymer resin that becomes the raw material of the first layer 10 can be used. The material of the polymer resin that is the raw material of the kneaded product and the material of the polymer resin that is the raw material of the dispersion may be the same or different. The content of the polymer resin in the dispersion can be, for example, 0.1% by weight or more and 10% by weight or less.

  As the surfactant material used as the raw material of the dispersion, the same materials as those exemplified above as the surfactant material used as the raw material of the kneaded material of the first layer 10 can be used. The surfactant used as the raw material for the kneaded product and the surfactant used as the raw material for the dispersion may be the same or different. The content of the surfactant in the dispersion is desirably, for example, 0.1% by weight or more and 5% by weight or less.

  As the material for the dispersion solvent that becomes the raw material of the dispersion liquid, the same materials as those exemplified above as the material for the dispersion solvent that becomes the raw material of the first layer 10 can be used. In addition, the material of the dispersion solvent used as the raw material of the kneaded product and the material of the dispersion solvent used as the raw material of the dispersion may be the same or different. The content of the dispersion solvent in the dispersion is desirably 55% by weight or more and 98% by weight or less, for example.

  Next, the dispersion liquid is applied and dried on the first layer 10 to form a dispersion liquid layer thinner than the first layer (step S205). For the coating of the dispersion, known printing and coating techniques such as spray coating, screen printing, and die coating can be used. As a drying method, for example, drying by a hot plate and drying by a drying furnace can be applied.

  Next, the first layer 10 and the dispersion liquid layer are heat-treated to remove the surfactant and the dispersion solvent, and a laminated structure of the first layer 10 and the second layer 14 is obtained (step S206).

  The heat treatment of the dispersion layer formed on the first layer 10 can be performed in, for example, an electric furnace, a gas furnace, a far infrared heating furnace, or the like. Hereinafter, the heating temperature in the heat treatment of the dispersion layer is referred to as a second heat treatment temperature.

  The second heat treatment temperature can be equal to or higher than the decomposition temperature of the surfactant that is the raw material of the dispersion. For example, the second heat treatment temperature can be set to 220 degrees Celsius or higher. By setting the second heat treatment temperature to 220 degrees Celsius or higher, it becomes easy to remove the surfactant from the dispersion layer at a speed that can ensure mass productivity.

  The second heat treatment temperature can be set to 240 degrees Celsius or higher. By setting the second heat treatment temperature to Celsius: 240 ° C. or more, it becomes easy to remove the surfactant to 1% by weight or less of the carbon layer.

  The second heat treatment temperature can be set to less than 260 degrees Celsius. By setting the second heat treatment temperature to less than 260 degrees Celsius, a decrease in the adhesion of the carbon layer surface is suppressed, and a high adhesive force can be obtained in the adhesion to the catalyst layer.

  The heat treatment may be performed in air. In the heat treatment of the dispersion layer, for example, the material, thickness, temperature, time, etc. are sufficient to remove the surfactant and prevent the adhesion with the catalyst layer from being reduced by crystallization of the polymer resin. May be set. The second layer 14 is formed by the heat treatment.

  Note that the heating temperature and heating time in the heat treatment for forming the second layer 14 are lower than the heat treatment temperature for producing the first layer 10, and the surfactant and the dispersion solvent are sufficiently removed from the dispersion layer. In addition, the temperature and time may be set so that the crystallization of the polymer resin does not proceed easily. That is, the second heat treatment temperature can be lower than the first heat treatment temperature. The remaining amount of the surfactant and the dispersion solvent can be measured by an analysis result such as TG / DTA (differential heat / thermogravimetric simultaneous measurement device). The remaining amount may be 1 wt% or less with respect to the total weight of the second layer 14. The remaining amount can be appropriately controlled by adjusting the thickness of the second layer 14, the heat treatment temperature, and the time.

  By producing in this way, the porosity (surface area) of the second layer 14 can be made higher than the porosity (surface area) of the first layer 10. By increasing the porosity (surface area) of the second layer, the wettability of water in the second layer 14 decreases, and the mist generated by the power generation reaction becomes difficult to adhere to the second layer 14. Therefore, the mist can move more smoothly in the second layer 14 than in the first layer 10. Thus, it can be said that increasing the porosity (surface area) of the second layer 14 has the same effect as increasing the amount of the polymer resin of the second layer 14.

Next, a plurality of holes 16 penetrating the first layer 10 and the second layer 14 are formed to obtain a gas diffusion layer (step S207). The method for forming the holes 16 is not particularly limited. Specifically, for example, the hole 16 may be formed by piercing a needle made of metal or the like. Alternatively, for example, the holes 16 may be formed using a laser such as a UV laser or a CO ₂ laser. Alternatively, for example, a penetrating member may be provided in a mold used when the first layer 10 and the second layer 14 are molded, and the hole 16 may be formed by pouring a material into the mold. That is, the hole 16 may be formed simultaneously with the formation of the first layer 10 and the second layer 14, or may be formed after the second layer 14 is formed. In other words, step S207 may be executed simultaneously with steps S102 to S206.

[Second Embodiment]
In the second example, a membrane electrode gas diffusion layer assembly using the gas diffusion layer of the second embodiment was produced and a power generation test was performed.

  FIG. 7: is sectional drawing which shows schematic structure of the membrane electrode gas diffusion layer assembly concerning 2nd Example. As shown in FIG. 7, in the membrane electrode gas diffusion layer assembly of the second embodiment, the cathode catalyst layer 18 is provided on the cathode-side main surface of the polymer electrolyte membrane 20, and the anode side of the polymer electrolyte membrane 20 The anode catalyst layer 22 is provided on the main surface of the cathode catalyst layer, the gas diffusion layer 200 for the fuel cell is provided on the main surface of the cathode catalyst layer 18 opposite to the polymer electrolyte membrane 20, and the polymer of the anode catalyst layer 22 is provided. A fuel cell gas diffusion layer 250 is provided on the main surface opposite to the electrolyte membrane 20.

  The fuel cell gas diffusion layer 200 includes a first layer 10 composed of a porous member mainly composed of conductive particles and a polymer resin, and a porous layer composed mainly of conductive particles and a polymer resin. It is formed of a member, is formed so as to be in contact with the first layer 10, has a second layer 14 having higher water repellency than the first layer 10, and has a hole 16 so as to penetrate the first layer 10 and the second layer 14. Is formed. The second layer 14 is in contact with the cathode catalyst layer 18.

  The fuel cell gas diffusion layer 250 includes a layer 24 composed of a porous member mainly composed of conductive particles and a polymer resin, and a porous member composed mainly of a conductive particle and a polymer resin. And a layer 26 having a higher water repellency than the layer 24, and no holes are formed in the layer 24 and the layer 26. Layer 26 is in contact with anode catalyst layer 22.

  In the second example, a membrane electrode assembly was produced in the same manner as in the first example.

  In the second example, the first layer was produced by the same method as in the first example.

  Next, a second layer was produced by the following method.

151 g of water and 1 g of a surfactant (Triton X) were put into a container, and the surfactant was dispersed in a self-revolving stirring deaerator. Subsequently, 10 g of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and 5.5 g of PTFE dispersion (Asahi Glass, AD911, solid content ratio: 60% by weight) were put into a container, and a revolving stirring deaerator. Then, acetylene black and PTFE were dispersed. Furthermore, after removing coarse particles using a filter (made by SUS, 200 mesh), a dispersion was obtained by performing a defoaming treatment using a self-revolving stirring deaerator. The obtained dispersion was applied by spraying to one side of the first layer placed on a hot plate. A dispersion layer was prepared by removing almost all of the dispersion by drying with a hot plate (60 ° C.). More specifically, the weight of the dispersion layer after drying was adjusted to 2.0 mg / cm ² . Thereafter, the carbon sheet on which the dispersion layer is formed is heat-treated at 240 ° C. for 2 hours in a firing furnace to remove the surfactant in the dispersion layer, thereby forming a second layer, A laminate in which the second layer was laminated on one layer was obtained.

  It was 853 second as a result of measuring the air-permeable resistance of the obtained laminated body with the B type | mold apparatus of the Gurley method (Gurley method) based on JIS-P8177: 2009.

  With respect to the cathode gas diffusion layer, a through hole having a diameter of 230 μm was formed by completely piercing a needle made of Kanthal wire (iron, chromium, aluminum alloy) into the laminate obtained by the above method.

  Similarly to the first example, the gas diffusion layer of the second example was formed in the stack so that the through holes were arranged in a zig-zag alignment.

The pitch of the through holes was about 3 mm, and the distance to adjacent through holes was about 3 mm. The density of the through holes was 11 per 1 cm ² . The opening area of the through hole, the area 1 cm ² per the first layer was 0.0046cm ^2. The total area of the openings of the through holes was 0.46% of the area of the first layer.

  For the gas diffusion layer for the anode, the laminate was used as it was without forming a through hole.

The cathode gas diffusion layer and anode gas diffusion layer produced as described above were brought into contact with the membrane electrode assembly produced by the above method, and hot-pressed at 120 ° C. and 6 kgf / cm ² for 5 minutes, By joining the catalyst layer and the gas diffusion layer, the membrane electrode gas diffusion layer assembly of the second example was obtained.

  The water repellency can be evaluated using a known wettability measurement technique. Specifically, the evaluation was performed using a wettability evaluation apparatus (DropMaster 100, manufactured by Kyowa Interface Science Co., Ltd.). First, a gas diffusion layer having a first layer and a second layer is cut out to 3 × 5 cm and left in a vacuum vessel for 1 hour in a state where the gas diffusion layer is immersed in a beaker containing distilled water. After sufficiently impregnating with water, it was dried at 80 ° C. for 4 hours to make the wet state constant. Next, the dried gas diffusion layer is cut into 1 cm squares, set on a measurement stage of a wettability evaluation apparatus, and a liquid mixture for wet tension test using a microsyringe (wet tension 27.3 mN / m, Wako Pure Chemical Industries, Ltd.) 4 μL of each was added dropwise to the surface of each of the first layer and the second layer. Furthermore, the contact angle of the liquid mixture for wet tension test was measured 3 minutes after the dropping. As a result, the contact angle of the liquid mixture in the first layer is 72 degrees, the contact angle of the liquid mixture in the second layer is 130 degrees, and the contact angle of the liquid mixture in the second layer is larger than that of the first layer, resulting in water repellency. Was higher in the second layer than in the first layer.

[Third comparative example]
In the third comparative example, a gas diffusion layer was produced without forming a through hole in the laminate obtained by the same method as in the second example, and a membrane electrode gas diffusion layer assembly was produced using this. A power generation test was conducted.

  In the third comparative example, a membrane electrode assembly was produced by the same method as in the first example.

  In the third comparative example, a laminate was produced by the same method as in the second example.

  It was 802 second as a result of measuring the air resistance of a laminated body by the B type | mold apparatus of the Gurley method (Gurley method) based on JIS-P8177: 2009.

  In the third comparative example, both the cathode gas diffusion layer and the anode gas diffusion layer were used as they were without forming through holes.

The cathode gas diffusion layer and anode gas diffusion layer produced as described above were brought into contact with the membrane electrode assembly produced by the above method, and hot-pressed at 120 ° C. and 6 kgf / cm ² for 5 minutes, By joining the catalyst layer and the gas diffusion layer, the membrane electrode gas diffusion layer assembly of the second example was obtained.

[Power generation test]
A power generation test was conducted using the membrane electrode gas diffusion layer assembly obtained in each of the second example and the third comparative example. Since the method of the power generation test is the same as that of the first embodiment, the first comparative example, and the second comparative example, detailed description is omitted.

  Table 2 shows the results of the power generation test.

  As shown in Table 2, in the second example, the first comparative example, and the third comparative example, the cell voltages are 744 mV, 720 mV, and 744 mV, respectively, and the second example and the third comparative example are Equally, the voltage was higher than in the first comparative example. This is because the second example and the third comparative example having the first layer composed of the porous member mainly composed of the conductive particles and the polymer resin than the first comparative example using the carbon cloth. This is because the electrolyte membrane can be more effectively prevented from drying, and the power generation efficiency is improved.

  As shown in Table 2, in the second example, the first comparative example, and the third comparative example, the number of peeled portions is 0, 0, and 39, respectively, and the second example and the first comparative example are Equally zero, and the number of peeled portions was significantly smaller than in the third comparative example. This is because the first embodiment having a first layer having a high air permeability resistance and having a through hole has a first layer having a high air permeability resistance and having no through hole, and the first embodiment having the through hole. In the first comparative example having a low resistance, a region where liquid water is locally accumulated is less likely to be generated at the boundary between the catalyst layer and the gas diffusion layer, and the gas diffusion layer is generated by the water pressure at which the water accumulation region is generated. This is thought to be because it became difficult to push up.

  In the second example, the number of peeled portions was further reduced as compared with the first example. This is because the main surface of the polymer electrolyte membrane in the second layer having the second layer having high water repellency is more in the second layer than in the first example having no second layer having high water repellency. This is considered to be because the movement of mist in the direction parallel to the direction was promoted and the amount of mist moving from the catalyst layer to the first layer was reduced. That is, in the second embodiment, compared to the first embodiment, a region where liquid water is locally accumulated is less likely to be generated at the boundary between the catalyst layer and the gas diffusion layer, and a region where water is accumulated is generated. This is probably because the possibility that the gas diffusion layer is pushed up by the water pressure is further reduced.

  In summary, in the second example, the voltage is as good as that in the third comparative example, and the number of peeled portions is the same as that in the first comparative example, which is better than the first example. Showed a good result. That is, the gas diffusion layer of the second embodiment generates power appropriately while preventing drying of the polymer electrolyte membrane, and the gas diffusion layer peels off from the catalyst layer and deforms in a combination of low humidification operation and room temperature startup. It has been found that the conflicting problem of reducing the possibility can be solved more effectively.

(Third embodiment)
The gas diffusion layer for a fuel cell according to the third embodiment is a gas diffusion layer for a fuel cell according to the first embodiment, the second embodiment, and modifications thereof, and the opening area of the hole is a gas diffusion layer for a fuel cell. It is 0.1% or more and 1.2% or less of the area of the main surface.

  In the fuel cell gas diffusion layer, the opening area of the holes may be not less than 0.3% and not more than 1.1% of the area of the main surface of the fuel cell gas diffusion layer.

  In the fuel cell gas diffusion layer, the opening area of the holes may be not less than 0.5% and not more than 1.0% of the area of the main surface of the fuel cell gas diffusion layer.

[Examination in the third embodiment]
The present inventors diligently studied to improve the power generation efficiency of a fuel cell using a fuel cell gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin. As a result, the following knowledge was obtained.

  That is, the fuel cell under study has a low gas permeability of the gas diffusion layer, so that the polymer electrolyte membrane is dried even when the dew point of the supplied gas is lower than the temperature of the fuel cell. We were able to generate electricity properly while preventing it. However, it has been found that the fuel cell to be studied has a problem that the gas diffusion layer is deformed when power generation is started from a state where the temperature of the fuel cell is low.

  This is because a region where water is locally accumulated is formed at the boundary between the catalyst layer and the gas diffusion, the gas diffusion layer is pushed up by the water pressure generated in the region, and the gas diffusion layer is separated from the catalyst layer.

  On the other hand, by providing a hole in the gas diffusion layer, it was conceived that the accumulated water is drained from the hole. As a result, the catalyst layer is in contact with the outside air just below the hole, so that the pressure is close to atmospheric pressure, and even if water pressure is generated around the hole, water flows into the low-pressure hole, reducing the increase in water pressure due to stagnation. can do.

  However, as a result of further studies, when the through hole is provided in the gas diffusion layer, if the opening area of the hole is too large, the catalyst layer and the electrolyte membrane may be dried and the life of the fuel cell may be shortened. It has been found. The following mechanism was considered as the cause.

  That is, when the hole is provided, the catalyst layer is directly exposed to the relatively dry oxidant gas or fuel gas inside the hole. For this reason, drying of the catalyst layer is accelerated, and the electrochemical reaction on the catalyst is not smoothly performed. As a result, the generation amount of radicals increases and the amount of generated water that flushes radicals decreases, and the chemical decomposition of the electrolyte membrane is accelerated.

  In the part facing the separator flow path, the gas diffusion layer is not fixed by the rib of the separator, and deformation is likely to occur. In the part facing the separator flow path, the gas concentration is high, and the chemical deterioration of the electrolyte membrane due to drying tends to be accelerated. For example, by appropriately providing holes in the gas diffusion layer along the flow path of the separator, it is possible to reduce chemical deterioration of the electrolyte membrane while reducing deformation of the gas diffusion layer.

[Device configuration]
The gas diffusion layer for a fuel cell according to this embodiment can have the same configuration as the gas diffusion layer for a fuel cell according to the first and second embodiments and their modifications, except for the opening area of the holes. Therefore, a detailed description other than the opening area of the hole is omitted.

  In the present embodiment, the opening area of the holes (holes 12 and 16, hereinafter referred to as “holes”) is 0.1% or more and 1.2% or less of the area of the main surface of the fuel cell gas diffusion layer. The opening area of the holes may be 0.3% or more and 1.1% or less of the area of the main surface of the fuel cell gas diffusion layer. The opening area of the holes may be not less than 0.5% and not more than 1.0% of the area of the main surface of the fuel cell gas diffusion layer.

  When the hole is formed, the effect of reducing the deformation of the gas diffusion layer can be obtained even if the opening area of the hole is small. Therefore, the lower limit of the opening area of the hole can be appropriately set to a predetermined value larger than 0 with reference to the following experimental example.

  When the opening area of the hole increases, chemical degradation of the electrolyte membrane easily proceeds. Therefore, the upper limit of the opening area of the hole can be appropriately set with reference to the following experimental example.

  In the present embodiment, the hole diameter may be not less than 30 μm and not more than 300 μm. The diameter of the hole may be 50 μm or more and 275 μm or less. The hole diameter may be not less than 80 μm and not more than 250 μm.

  In the present embodiment, the pitch of the holes may be 0.8 mm or greater and 3.2 mm or less. 1 mm or more and 3 mm or less may be sufficient as the pitch of a hole. The pitch of the holes is the pitch x in the direction parallel to the gas flow path (distance from the center of the hole to the center of the adjacent hole, the same applies hereinafter) and the pitch y in the direction perpendicular to the gas flow path (parallel to the gas flow path). When the holes are formed in a row so as to line up with each other, the distance between lines passing through the centers of the holes in adjacent rows (the same applies hereinafter) may be different.

  FIG. 8 is a schematic diagram for explaining the pitch of holes in the third embodiment. In the example shown in FIG. 8, the holes are arranged in a staggered pattern (a configuration in which the rows of holes 12 adjacent to each other in a direction perpendicular to the gas flow path 30 are shifted by half a cycle), and in a direction parallel to the gas flow path 30. The pitch x is larger than the pitch y in the direction perpendicular to the gas flow path 30. In the present embodiment, no gas flow path is formed in the gas diffusion layer itself. The gas flow path 30 shown in FIG. 8 shows the direction of the gas flow path (part) formed in the separator used when incorporating the gas diffusion layer into the fuel cell. For example, the gas flow path can be configured so that the width of the flow path is 1 mm, the pitch of the flow paths is 2 mm, and the adjacent five flow paths are folded as a unit at the end of the gas diffusion layer without a gap.

  In the present embodiment, the holes are not necessarily formed at regular intervals. For example, the pitch of the holes may be different depending on the position of the main surface of the gas diffusion layer. A hole may be formed only in a part of the main surface of the gas diffusion layer.

  The gas diffusion layer of the third embodiment can be modified in the same manner as in the first and second embodiments.

[Production method]
The manufacturing method of the fuel cell gas diffusion layer of the present embodiment can be the same as the manufacturing method of the fuel cell gas diffusion layer of the first and second embodiments and their modifications. Therefore, detailed description is omitted. Also in the manufacturing method of the gas diffusion layer of the third embodiment, the same modifications as those of the first embodiment and the second embodiment are possible.

[Third comparative example]
The sample of the third comparative example did not form a hole. Specifically, a sample of the membrane electrode gas diffusion layer assembly was produced in the same manner as in the third comparative example of the second embodiment.

[Third embodiment]
In the third example, the gas diffusion layer was fabricated by setting the opening area of the holes to 0.52% of the area of the main surface of the gas diffusion layer. In the third example, similarly to the second embodiment, the second layer was formed on the first layer, and the hole was formed so as to penetrate both the first layer and the second layer.

In the sample of the third example, a hole was formed using a needle. The hole diameter is almost equal to the needle diameter (about 230 μm). As for the pitch of the holes, the pitch x in the direction parallel to the gas flow path was 3.0 mm, and the pitch y in the direction perpendicular to the gas flow path was 2.6 mm. The holes were arranged in a zigzag shape (a configuration in which a row of holes adjacent to each other in a direction perpendicular to the gas flow path is shifted by a half cycle). The shape of the gas diffusion layer was a 140 mm × 140 mm square. The area of the main surface of the gas diffusion layer is 19600mm ^2, 1 single area hole is 0.042 mm ^2, a number of holes 2450 pieces, the opening area of the holes is 102 mm ^2. Therefore, the opening area of the hole in the third embodiment is 0.52% of the area of the main surface of the fuel cell gas diffusion layer. About the other structure, it was set as the 2nd Example of 2nd Embodiment, and the membrane electrode gas diffusion layer assembly was obtained.

[Fourth embodiment]
In the fourth example, the gas diffusion layer was fabricated by setting the opening area of the holes to 0.97% of the area of the main surface of the gas diffusion layer. In the fourth example, similarly to the second embodiment, the second layer was formed on the first layer, and the hole was formed so as to penetrate both the first layer and the second layer.

In the sample of the fourth example, holes were formed using a UV laser. The pore diameter was about 100 μm. As for the pitch of the holes, the pitch x in the direction parallel to the gas flow path was 1.8 mm, and the pitch y in the direction perpendicular to the gas flow path was 1.2 mm. The holes were arranged in a zigzag shape (a configuration in which a row of holes adjacent to each other in a direction perpendicular to the gas flow path is shifted by a half cycle). The shape of the gas diffusion layer was a 140 mm × 140 mm square. The area of the main surface of the gas diffusion layer is 19600 mm ² , the area of one hole is 0.0079 mm ² , the number of holes is 24300, and the opening area of the holes is 191 mm ² . Therefore, the opening area of the hole in the fourth embodiment is 0.97% of the area of the main surface of the fuel cell gas diffusion layer. About the other structure, it was set as the 2nd Example of 2nd Embodiment, and the membrane electrode gas diffusion layer assembly was obtained.

[Fourth Comparative Example]
In the fourth comparative example, the gas diffusion layer was fabricated with the opening area of the holes being 1.56% of the area of the main surface of the gas diffusion layer. In the fourth comparative example, as in the second embodiment, the second layer was formed on the first layer, and the hole was formed so as to penetrate both the first layer and the second layer.

In the sample of the fourth comparative example, holes were formed using a UV laser. The pore diameter was about 100 μm. As for the pitch of the holes, the pitch x in the direction parallel to the gas flow path was 1 mm, and the pitch y in the direction perpendicular to the gas flow path was 1.2 mm. The holes were arranged in a zigzag shape (a configuration in which a row of holes adjacent to each other in a direction perpendicular to the gas flow path is shifted by a half cycle). The shape of the gas diffusion layer was a 140 mm × 140 mm square. The area of the main surface of the gas diffusion layer is 19600 mm ² , the area of one hole is 0.0079 mm ² , the number of holes is 39,050, and the opening area of the holes is 307 mm ² . Therefore, the opening area of the hole in the fourth comparative example is 1.56% of the area of the main surface of the fuel cell gas diffusion layer. About the other structure, it was set as the 2nd Example of 2nd Embodiment, and the membrane electrode gas diffusion layer assembly was obtained.

[Power generation test]
About a 3rd comparative example, 3rd Example, 4th Example, and a 4th comparative example, a power generation test is performed using the sample of the obtained membrane electrode gas diffusion layer assembly, and the elution amount of fluoride ion is measured. At the same time, the deformation locations of the gas diffusion layer were counted. The contents of the test are as follows.

About each sample, the fuel cell was produced using the separator in which the flow path was formed. That is, the membrane electrode gas diffusion layer assembly is sandwiched between a separator having a gas flow path for supplying a fuel gas and a cooling water flow path and a separator having a gas flow path for supplying an oxidant gas, and around the cathode and the anode. A single cell was obtained by arranging a gasket made of fluoro rubber. The effective electrode (anode or cathode) area is 196 cm ² .

Regarding the elution amount of fluoride ions, first, the temperature of the single cell produced for each of the third comparative example, the third example, the fourth example, and the fourth comparative example is maintained at 65 degrees Celsius, A mixed gas of hydrogen gas and carbon dioxide (75% hydrogen gas and 25% carbon dioxide) was supplied as a fuel gas to the gas flow path on the anode side, and air was supplied to the gas flow path on the cathode side. The hydrogen gas utilization rate was 70%, and the air utilization rate was 40%. The fuel gas and air were both humidified so that the dew point was about 65 degrees Celsius, and then supplied to the unit cell. Each cell was subjected to power generation at a current density of 0.2 A / cm ² for 12 hours, thereby aging the cell (activation process).

Then, room temperature start-up with low humidification was performed as follows. First, power generation was stopped for each unit cell, and the temperature of the unit cell was lowered to room temperature (about 25 degrees Celsius). After that, the dew point of the fuel gas is supplied to the anode with a dew point of 65 degrees Celsius, and the air is supplied without being humidified and dried air (dew point = 45 degrees Celsius [minus] 45 degrees) is supplied to the cathode. Power generation was started (started up) at a density of 0.25 A / cm ² . Furthermore, the temperature of the unit cell was raised to 65 degrees Celsius after the start of power generation. This process is called room temperature low humidification start-up because the temperature of the unit cell at the start of power generation is room temperature and the air supplied to the cathode is not humidified.

  After repeating the room temperature low humidification start about 500 times, the concentration of fluoride ions in the liquid discharged from the gas flow paths on the cathode side and the anode side is measured using liquid chromatography, so that the electrolyte during power generation The elution amount of fluoride ions discharged from the membrane was evaluated. Regarding the elution amount of fluoride ions, the membrane electrode gas diffusion layer assembly, particularly the electrolyte membrane, reaches the total elution amount that leads to membrane rupture using the amount of fluoride ions eluted over time at a predetermined film thickness. The period until the time was calculated and evaluated based on whether or not this exceeded the desired life required for the fuel cell.

About each sample after repeating room temperature low humidification start about 500 times as mentioned above, room temperature start by high humidification was performed as follows. First, power generation was stopped for each unit cell, and the temperature of the unit cell was lowered to room temperature (about 25 degrees Celsius). Thereafter, the dew point of the fuel gas is supplied to the anode at 60 degrees Celsius, and the air is humidified and supplied to the cathode so that the dew point is 65 degrees Celsius. For each unit cell, the current density is 0.25 A / cm ² . Power generation was started (started up). Furthermore, the temperature of the unit cell was raised to 65 degrees Celsius after the start of power generation. This process is called room temperature high humidification start-up because the temperature of the unit cell at the start of power generation is room temperature and the air supplied to the cathode is humidified.

  After the room temperature high humidification start-up was repeated about 100 times, the fuel cell was disassembled, and the number of locations where the cathode-side gas diffusion layer was peeled off from the membrane electrode assembly was counted. Note that the peeled portion refers to a portion where the gas diffusion layer is slightly lifted from the membrane electrode assembly. In any sample, no portion where the gas diffusion layer was peeled off was found on the anode side.

  Table 3 shows the results of the power generation test.

  As shown in Table 3, the elution amount of fluoride ions failed to satisfy the desired life in the fourth comparative example, but was inferior, but desired in the third comparative example, the third example, and the fourth example. It was small enough to meet the lifespan. On the other hand, the number of peeled portions was 0 in the fourth example and the fourth comparative example, 3 in the third example, and 76 in the third comparative example.

  That is, the fourth comparative example had a large amount of fluoride ion elution, and the third comparative example had a large number of peeled portions. On the other hand, in the third example and the fourth example, both the elution amount of fluoride ions and the number of peeled portions were suitable.

  From the above results, by setting the ratio of the opening area of the hole and the area of the main surface of the gas diffusion layer for the fuel cell within a suitable range, the chemical deterioration of the electrolyte membrane can be achieved while reducing the deformation of the gas diffusion layer. It was also confirmed that it can be reduced.

(Fourth embodiment)
The fuel cell gas diffusion layer of the fourth embodiment is the fuel cell gas diffusion layer of the first embodiment and its modifications, and the holes are formed so as not to penetrate the fuel cell gas diffusion layer. .

  In the gas diffusion layer for a fuel cell, a first layer composed of a porous member mainly composed of conductive particles and a polymer resin, and a porous member composed mainly of conductive particles and a polymer resin And a second layer having higher water repellency than the first layer, and the hole may be formed so as to penetrate the first layer.

  In the gas diffusion layer for a fuel cell, the hole may be formed so as not to penetrate the second layer.

  A fuel cell according to a fourth embodiment includes an electrolyte membrane, an electrode layer in contact with the main surface of the electrolyte membrane, and the gas diffusion layer for a fuel cell arranged so that the second layer is in contact with the electrode layer. None of the anode electrode layer, the cathode electrode layer, or the electrolyte membrane is exposed inside.

  The manufacturing method of the fuel cell gas diffusion layer of the fourth embodiment is the manufacturing method of the fuel cell gas diffusion layer of the first embodiment and its modifications. That is, conductive particles, a polymer resin, a surfactant, and a dispersion solvent are mixed to obtain a homogeneous dispersion, and the dispersion is applied and dried on the first layer after the pores are formed. A dispersion layer thinner than one layer is formed. The first layer on which the dispersion layer is formed is heat-treated at a second heat treatment temperature lower than the first heat treatment temperature to remove the surfactant and the dispersion solvent from the dispersion layer, and on the first layer. Obtaining a second layer having a higher water repellency than the first layer.

[Examination in Fourth Embodiment]
The present inventors diligently studied to improve the power generation efficiency of a fuel cell using a fuel cell gas diffusion layer composed of a porous member mainly composed of conductive particles and a polymer resin. As a result, the following knowledge was obtained.

  That is, the fuel cell under study has a low gas permeability of the gas diffusion layer, so that the polymer electrolyte membrane is dried even when the dew point of the supplied gas is lower than the temperature of the fuel cell. We were able to generate electricity properly while preventing it. However, it has been found that the fuel cell to be studied has a problem that the gas diffusion layer is deformed when power generation is started from a state where the temperature of the fuel cell is low.

  This is because a region where water is locally accumulated is formed at the boundary between the catalyst layer and the gas diffusion, the gas diffusion layer is pushed up by the water pressure generated in the region, and the gas diffusion layer is separated from the catalyst layer.

  On the other hand, by providing a hole in the gas diffusion layer, it was conceived that the accumulated water is drained from the hole. As a result, the catalyst layer is in contact with the outside air just below the hole, so that the pressure is close to atmospheric pressure, and even if water pressure is generated around the hole, water flows into the low-pressure hole, reducing the increase in water pressure due to stagnation. can do.

  However, as a result of further studies, when a hole is formed in the gas diffusion layer, if the hole is formed so as to penetrate the gas diffusion layer, the voltage may decrease or the catalyst and the electrolyte membrane may deteriorate. There was found. The following mechanism was considered as the cause.

  That is, when a hole is formed so as to penetrate the gas diffusion layer, the water repellency of the catalyst layer is lower than that of the gas diffusion layer, so liquid water aggregates on the catalyst layer with low water repellency exposed inside the hole. Easier to flood (flooding). In particular, when the fuel cell system is started, the saturated vapor pressure is lowered because of the low temperature. Therefore, liquid water is more likely to stay in and around the hole. If liquid water stays on the surface of the catalyst layer in and around the pores, gas diffusion to the relevant site is hindered, the battery reaction does not proceed smoothly, and the voltage decreases.

  In addition, when a hole is formed so as to penetrate the gas diffusion layer, since there is no gas diffusion layer inside the hole, current collection from the surface of the catalyst layer (power collection) cannot be performed. In the vicinity of the hole formed in the gas diffusion layer on the cathode side, the catalyst is oxidized in a state where electrons are insufficient in the catalyst contained in the catalyst layer, the reaction does not proceed smoothly, and a high voltage is applied. It will be exposed to the agent gas. As a result, aggregation of the catalyst may progress, or radicals may be generated to accelerate deterioration of the electrolyte membrane.

  In response to this problem, the present inventors have found that the voltage can be improved or the deterioration of the catalyst and the electrolyte membrane can be reduced by forming the holes so as not to penetrate the gas diffusion layer.

  In particular, if a second layer with high water repellency is provided and the holes are formed so as not to penetrate the second layer, liquid water is less likely to stay in and around the holes, and the voltage at start-up also increases. I found. The second layer has a function of transporting mist generated in the catalyst to the first layer without aggregating on the catalyst surface (interface between the catalyst layer and the gas diffusion layer). The second layer also has a current collecting function.

[Device configuration]
FIG. 9 is a cross-sectional view illustrating an example of a schematic configuration of a gas diffusion layer according to the fourth embodiment. Hereinafter, the fuel cell gas diffusion layer 300 of the fourth embodiment will be described with reference to FIG.

  As illustrated in FIG. 9, the fuel cell gas diffusion layer 300 includes a first layer 10 and a second layer 15. That is, hereinafter, a case where the gas diffusion layer is formed of two layers will be described. The gas diffusion layer may include a layer other than the first layer and the second layer. The gas diffusion layer may be composed of only the first layer.

  The fuel cell gas diffusion layer 300 can be formed, for example, as a gas diffusion layer (so-called substrate-less GDL) that does not use carbon fiber or the like as a substrate.

  The first layer 10 has the same material, size, shape, manufacturing method, and the like as the first layer 10 of the first embodiment, except that the sign of the hole penetrating the first layer 10 is changed from 12 to 17. can do. The material, size, shape, manufacturing method, and the like of the second layer 15 can be the same as those of the second layer 14 of the second embodiment, except that no hole is formed.

  That is, the fuel cell gas diffusion layer of the present embodiment is the same as the fuel cell gas diffusion layer of the first and second embodiments and their modifications, except that the holes do not penetrate the gas diffusion layer. It can be set as the same structure. Therefore, detailed description of the configuration other than the holes 17 is omitted.

  In the present embodiment, the holes 17 are formed so as not to penetrate the fuel cell gas diffusion layer 300.

  In the example shown in FIG. 9, the hole 17 penetrates the first layer 10 and does not penetrate the second layer 15. In the example shown in FIG. 9, the hole 17 is not formed at all in the second layer 15, but the hole 17 may be formed in the second layer 15 as long as it does not penetrate the second layer 15. The material constituting the second layer 15 may enter a part of the hole 17 penetrating the first layer 10.

  In the example shown in FIG. 9, the hole 17 penetrates the first layer 10, but the hole 17 does not have to penetrate the first layer 10. Specifically, for example, the second layer 15 may be formed so as to extend in the thickness direction from the main surface opposite to the second layer 15 so that the second layer 15 is not exposed inside the hole 17.

  As exemplified in the first embodiment, when the gas diffusion layer is formed of a single layer, the holes extend, for example, in the thickness direction from one main surface of the single layer, and It can be formed so as not to reach the other main surface.

  As exemplified in the second embodiment, when the gas diffusion layer is composed of the first layer and the second layer, the hole may be formed so as to penetrate the first layer, for example. Furthermore, the hole may be formed so as not to penetrate the second layer. That is, the hole extends from the main surface of the first layer in the thickness direction from the main surface opposite to the second layer, and extends through the first layer into the second layer; and The main surface of the second layer can be formed so as not to reach the main surface opposite to the first layer.

  In this embodiment, the fuel cell includes an electrolyte membrane, an electrode layer provided so as to be in contact with the main surface of the electrolyte membrane, and the gas diffusion layer provided so that the second layer is in contact with the main surface of the electrode layer. And the anode electrode layer, the cathode electrode layer, and the electrolyte membrane are not exposed inside the hole.

  In the present embodiment, the holes are not necessarily formed at regular intervals. For example, the pitch of the holes may be different depending on the position of the main surface of the gas diffusion layer. A hole may be formed only in a part of the main surface of the gas diffusion layer.

  Also in the gas diffusion layer of the fourth embodiment, the same modifications as those of the first embodiment, the second embodiment, and the third embodiment are possible.

[Production method]
FIG. 10 is a flowchart showing an example of a method for producing a gas diffusion layer according to the fourth embodiment. Hereinafter, the manufacturing method of the gas diffusion layer of the fourth embodiment will be described with reference to FIG.

  Since steps S301 to S303 can be the same as steps S101 to S103 of the first embodiment, detailed description thereof is omitted.

When the first layer 10 is obtained in step S303, a plurality of holes 17 penetrating the first layer 10 are formed (step S304). The formation method of the hole 17 is not specifically limited. Specifically, for example, the hole 17 may be formed by piercing a needle made of metal or the like. Alternatively, for example, the holes 17 may be formed using a laser such as a UV laser or a CO ₂ laser. Alternatively, for example, a penetrating member may be provided in a mold used when the first layer 10 is molded, and the hole 17 may be formed by pouring a material into the mold. That is, the hole 17 may be formed simultaneously with the formation of the first layer, or may be formed after the first layer is formed.

  Next, the second layer 15 is formed by the following method.

  First, a dispersion liquid is obtained by mixing conductive particles, a polymer resin, a surfactant, and a dispersion solvent (step S305). Since step S305 can be the same as step S204 of the second embodiment, detailed description thereof is omitted.

  Next, the dispersion liquid is applied and dried on the first layer 10 to form a dispersion liquid layer thinner than the first layer (step S306). Since step S306 can be the same as step S205 of the second embodiment, a detailed description thereof will be omitted.

  Next, the first layer 10 and the dispersion layer are heat-treated to remove the surfactant and the dispersion solvent, and a fuel cell gas diffusion layer having a laminated structure of the first layer 10 and the second layer 15 is formed. Is obtained (step S307). Since step S307 can be the same as step S206 of the second embodiment, detailed description thereof is omitted.

  The penetrating member may be provided in a mold used when the first layer 10 is molded, and the hole 17 may be formed by pouring a material into the mold. That is, the holes 17 may be formed simultaneously with the formation of the first layer 10 or may be formed after the first layer 10 is formed. In other words, step S304 may be executed simultaneously with steps S303 to S307.

  Also in the gas diffusion layer manufacturing method of the fourth embodiment, the same modifications as those of the first embodiment, the second embodiment, and the third embodiment are possible.

[Second Embodiment]
In the second example, a hole was formed in the gas diffusion layer having the first layer and the second layer so as to penetrate both the first layer and the second layer. Specifically, a sample of the membrane electrode gas diffusion layer assembly was produced in the same manner as in the second example of the second embodiment. The number of samples in the second embodiment is two.

[Fifth embodiment]
In the fifth example, a hole was formed in the gas diffusion layer having the first layer and the second layer so as to penetrate only the first layer. Specifically, the sample of the fifth example was produced by the following method. The number of samples in the fifth embodiment is five.

  A membrane electrode assembly was produced in the same manner as in the first example.

  A first layer was produced in the same manner as in the first example.

About the obtained 1st layer, the hole was formed by the method similar to 1st Example. The holes were formed so as to be arranged in a zig-zag alignment. The pitch of the holes was about 3 mm, and the distance to adjacent holes was about 3 mm. The density of the holes was 11 per cm ² . The opening area of the holes, the area 1 cm ² per the first layer was 0.0046cm ^2. The total area of the openings of the holes was 0.46% of the area of the first layer.

  About the 1st layer in which the hole was formed, the 2nd layer was formed by the same method as the 2nd example, and the layered product in which the 2nd layer was laminated on the 1st layer was obtained.

  For the anode gas diffusion layer, the laminate obtained by the same method as in the first embodiment was used as it was without forming holes.

  About the other structure, it was set as the 2nd Example of 2nd Embodiment, and the membrane electrode gas diffusion layer assembly was obtained.

[Third comparative example]
In the fifth embodiment, no hole is formed in the gas diffusion layer having the first layer and the second layer. Specifically, a sample of the membrane electrode gas diffusion layer assembly was produced in the same manner as in the third comparative example of the second embodiment. In addition, about the 3rd experiment example, the measurement of a voltage was not performed but only the number of peeling locations was measured.

[Power generation test]
About 2nd Example, 5th Example, and a 3rd comparative example, a power generation test was performed using the sample of the obtained membrane electrode gas diffusion layer assembly, voltage measurement, and counting of deformation locations of the gas diffusion layer Went. The contents of the test are as follows.

About each sample, the fuel cell was produced using the separator in which the flow path was formed. That is, the membrane electrode gas diffusion layer assembly is sandwiched between a separator having a gas flow path for supplying a fuel gas and a cooling water flow path and a separator having a gas flow path for supplying an oxidant gas, and around the cathode and the anode. A single cell was obtained by arranging a gasket made of fluoro rubber. The effective electrode (anode or cathode) area is 196 cm ² . For each example and comparative example, a stack in which four unit cells were connected in series was produced one by one, and a power generation test was conducted.

Regarding voltage measurement, first, the stack temperature was controlled to 65 degrees Celsius for each of the second embodiment, the fifth embodiment, and the third comparative example, and hydrogen gas as a fuel gas was supplied to the anode-side gas flow path. A gas mixture of hydrogen and carbon dioxide (hydrogen gas 75%, carbon dioxide 25%) was supplied, and air was supplied to the gas flow path on the cathode side. The hydrogen gas utilization rate was 70%, and the air utilization rate was 40%. The fuel gas and air were both humidified so that the dew point was about 65 degrees Celsius before being supplied to the stack. Each stack was subjected to power generation at a current density of 0.2 A / cm ² for 12 hours, thereby aging the stack (activation process).

Then, room temperature start-up with low humidification was performed as follows. First, power generation was stopped for each stack, and the temperature of the stack was further lowered to room temperature (about 25 degrees Celsius). After that, the fuel gas dew point is supplied to the anode at 65 degrees Celsius, and the air is dried without supplying air (dew point = 45 degrees Celsius [minus] 45 degrees Celsius). Power generation was started (activated) at 0.25 A / cm ² . Furthermore, the stack temperature was raised to 65 degrees Celsius after the start of power generation. Such a process is called room temperature low humidification start-up because the temperature of the stack at the start of power generation is room temperature and the air supplied to the cathode is not humidified.

  At about 30 minutes after startup, liquid water stays on the surface of the catalyst due to power generation at a low temperature, and the voltage decreases most. When 4 hours have elapsed after startup, the inside of the cell is dried, and the liquid water on the catalyst surface almost disappears. As a result, the voltage rises and stable power generation with little voltage fluctuation becomes possible. Therefore, after completion of aging, room temperature low humidification start-up was executed again, and the voltage after 30 lapses after start-up was compared with the voltage after 4 hours lapse after start-up. The voltage was individually measured for each of the four unit cells constituting the stack.

About each sample after performing the room temperature low humidification start-up as mentioned above and measuring a voltage, the room temperature start-up with high humidification was performed as follows. First, power generation was stopped for each stack, and the stack temperature was further lowered to room temperature (about 25 degrees Celsius). Thereafter, the fuel gas is supplied to the anode at a dew point of 60 degrees Celsius, the air is humidified so that the dew point is 65 degrees Celsius, and supplied to the cathode, and each stack generates power at a current density of 0.25 A / cm ² Was started (activated). Furthermore, the stack temperature was raised to 65 degrees Celsius after the start of power generation. Such a process is called room temperature high humidification start-up because the temperature of the stack at the start of power generation is room temperature and the air supplied to the cathode is humidified.

  After the room temperature high humidification start-up was repeated about 100 times, the fuel cell was disassembled, and the number of locations where the cathode-side gas diffusion layer was peeled off from the membrane catalyst layer assembly was counted. Note that the peeled portion refers to a portion where the gas diffusion layer is slightly lifted from the membrane-catalyst layer assembly. In any sample, no portion where the gas diffusion layer was peeled off was found on the anode side.

  Table 4 shows the results of the power generation test.

  As shown in Table 4, the voltage after 30 minutes from the start-up was 738 ± 2 mV in the second example, whereas it was remarkably high at 750 ± 3 mV in the fifth example. The voltage difference is about 12 mV, which corresponds to 1.6% of the average voltage of 738 mV in the second embodiment. That is, when the hole does not penetrate the second layer (fifth embodiment), after 30 minutes have passed since the start-up, compared with the case where the hole penetrates the second layer (second embodiment). The voltage was about 1.6% higher.

  On the other hand, the voltage after 4 hours and 30 minutes after the start-up was 756 ± 1 mV in the second example, whereas it was almost the same as 752 ± 1 mV in the fifth example. That is, when the hole does not penetrate the second layer (fifth embodiment), 4 hours and 30 minutes have elapsed since the start-up, compared with the case where the hole penetrates the second layer (second embodiment). The voltage after the test was similar.

  In the third comparative example, the number of peeled portions was 30 or more for all four unit cells, but in the second and fifth examples, the number of peeled portions was zero for all four unit cells. In both cases, it was found that the deformation of the gas diffusion layer could be appropriately reduced.

  From the above results, it was confirmed that by forming the holes so as not to penetrate the gas diffusion layer, it is possible to improve the starting voltage while reducing the deformation of the gas diffusion layer.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. Details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

(Fifth embodiment)
The fuel cell of the fifth embodiment is a fuel cell using the gas diffusion layer described in the first to fourth embodiments, and all the holes of the gas diffusion layer are located at positions corresponding to the flow path portions of the separator. Is formed. The apparatus configuration and manufacturing method will be described below.

[Device configuration]
1. Fuel cell:
FIG. 15 is a schematic view of a general fuel cell.

  This fuel cell is a polymer electrolyte fuel cell, in which a plurality of fuel cells, which are basic units, are stacked and fastened with a predetermined load from both sides by a current collecting plate 61, an insulating plate 62, and an end plate 63 It is. The current collecting plate 61 is provided with a current extraction terminal portion, from which current is extracted during power generation. The insulating plate 62 insulates between the current collecting plate 61 and the end plate 63 and may be provided with a gas or cooling water inlet / outlet (not shown). The end plate 63 fastens and holds a plurality of stacked fuel cells 60, a current collecting plate 61, and an insulating plate 62 with a predetermined load by a pressing means (not shown).

  The fuel cell 60 is obtained by sandwiching a membrane electrode gas diffusion layer assembly 55 between two separators 56. The separator 56 may be any gas-impermeable conductive material. For example, a material obtained by cutting a resin-impregnated carbon material into a predetermined shape, or a material obtained by molding a mixture of carbon powder and a resin material is generally used.

  In the portion of the separator 56 that comes into contact with the membrane electrode gas diffusion layer assembly 55, a gas flow path for supplying fuel gas or oxidant gas to the electrode surface and carrying away excess gas is formed. The gas flow path formed on the surface of the separator 56 is, for example, formed in a serpentine shape so that one or more paths (gas flow paths) are arranged in a plurality of directions from the inlet toward the outlet. . The serpentine-like gas flow path has a continuous structure in which the ends of the forward path and the return path that are linearly formed in parallel with each other are connected by a turn portion.

  A cooling water channel is formed on the surface of the separator 56 opposite to the gas channel. Further, a fuel gas inlet manifold, a fuel gas outlet manifold, an oxidant gas inlet manifold, and an oxidant gas outlet manifold are provided on the side surface of the separator 56 for supplying and discharging fuel gas and oxidant gas to and from the fuel cell 60. Is formed.

  Therefore, in a fuel cell in which a plurality of fuel cells 60 are stacked, the fuel gas inlet manifold, the fuel gas outlet manifold, the oxidant gas inlet manifold, and the oxidant gas outlet manifold communicate with each other in all the fuel cells. In addition, the separator 56, the current collector plate 61, the insulating plate 62, and the end plate 63 are provided with seal members (not shown) to prevent the fuel gas and the oxidant gas from being mixed or leaking to the outside. doing.

2. “Membrane electrode assembly” and “Gas diffusion layer”:
The membrane electrode gas diffusion layer assembly 55 forms a catalyst layer 52 mainly composed of carbon powder carrying a platinum-ruthenium alloy catalyst on the anode surface side of the polymer electrolyte membrane 51 that selectively transports hydrogen ions. A catalyst layer 53 composed mainly of carbon powder carrying a platinum catalyst is formed on the cathode surface side, and a fuel cell having both air permeability of fuel gas or oxidant gas and electronic conductivity on the outer surface of the catalyst layer. The gas diffusion layer 54 is disposed.

  The polymer electrolyte membrane 51 is usually composed of a polymer membrane having ion exchange groups such as sulfonic acid groups and carboxylic acid groups in the side chain. The polymer electrolyte membrane 51 has a property of being firmly bonded to specific ions and selectively transmitting cations or anions.

  Examples of the polymer electrolyte membrane 51 include a membrane made of perfluorosulfonic acid polymer, Gore Select (registered trademark) of Japan Gore-Tex Co., Ltd., Nafion (DuPont) of Nafion, (Registered trademark), Aciplex (registered trademark) of Asahi Kasei Corporation, Flemion (registered trademark) of Asahi Glass Co., Ltd., and various hydrocarbon electrolyte membranes can be used. In the present embodiment, protons move in the polymer electrolyte membrane 51 with water molecules. The film thickness of the polymer electrolyte membrane 51 is, for example, in the range of 5 μm to 50 μm, preferably 10 μm to 30 μm. When the film thickness of the polymer electrolyte membrane becomes thinner than 5 μm, the mechanical strength becomes weak, and the polymer electrolyte membrane deteriorates due to mechanical stress due to power generation, resulting in poor durability of the fuel cell. On the other hand, when the thickness of the polymer electrolyte membrane is greater than 50 μm, the proton transfer resistance increases and the battery voltage decreases.

  The catalyst layers 52 and 53 are made of, for example, a porous member mainly composed of carbon powder supporting a platinum group metal catalyst and a polymer material having proton conductivity. The proton conductive polymer material used for the electrode layer may be the same as or different from the polymer electrolyte membrane.

  Examples of carbon used in the catalyst layer include ketjen black, furnace black, channel black, thermal black, and acetylene black.

  In addition to the perfluorosulfonic acid solid polymer electrolyte, the resin used in the catalyst layer includes polytetrafluoroethylene, tetrafluoroethylene / hexafluoropropylene copolymer, polyvinylidene fluoride, tetrafluoroethylene Any polymer containing fluorine atoms, such as an ethylene copolymer, polychlorotrifluoroethylene, and tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer may be used. Alternatively, these copolymers, copolymers of these monomer units and other monomers such as ethylene and styrene, and blends thereof can be used. The film thickness of the catalyst layers 52 and 53 is, for example, in the range of 1 μm to 100 μm, preferably 5 μm to 20 μm.

  The fuel cell gas diffusion layer 54 is disposed on the surfaces of the catalyst layers 52 and 53. As the fuel cell gas diffusion layer 54, the gas diffusion layer described in the first to third embodiments, in which only the arrangement of the holes is changed as follows, is used. Therefore, descriptions other than the changes are omitted.

  The holes formed in the fuel cell gas diffusion layer 54 are preferably formed at positions corresponding to the flow path portions of the separator in order to quickly discharge water generated in the catalyst layer to the outside of the gas diffusion layer. Therefore, the hole pattern needs to be changed depending on the flow path pattern of the separator.

3. Fuel cell (relationship between gas diffusion layer and separator):
FIG. 11 shows an example of a separator channel and through-hole pattern.

  Fig.11 (a) is a schematic diagram of the flow path pattern of a separator. An area where the flow paths are formed in parallel is A, an area where the flow path is turned is B, and a pitch of the flow paths is a. Next, a pattern of holes in the gas diffusion layer (a flow path of the separator is also illustrated) is shown in FIG.

  The holes 12 of the gas diffusion layer are defined as follows. In the region A, the y-direction pitch is b, the x-direction pitch is c, the region B is the y-direction pitch d, and the x-direction pitch is e. The pitch b of the hole 12 is such that b = a, the pitch d in the y direction in the region B is d = a, and the pitch e in the x direction in the region B is e = a. Form. Here, the pitch c in the x direction of the region A may be a distance that allows the water locally accumulated at the boundary between the first layer and the catalyst layer of the gas diffusion layer to be discharged.

  By forming the holes 12 as shown in FIG. 11B, all of the holes 12 can be formed at positions corresponding to the flow paths of the separator as shown in the sectional view of FIG.

  The fuel cell gas diffusion layer 100 may be used as a cathode-side gas diffusion layer, as an anode-side gas diffusion layer, or as both a cathode-side and anode-side gas diffusion layer. good. The water generated by the power generation reaction is mainly generated on the cathode side, but the water passes through the electrolyte membrane. Therefore, drainage through the holes 12 can be realized on either the cathode or anode side by appropriately selecting the flow path configuration, gas dew point, and the like.

  The structure of the fuel cell using the above gas diffusion layer will be described. The fuel cell of the present embodiment includes an electrolyte membrane, an anode electrode layer in contact with one main surface of the electrolyte membrane, a cathode electrode layer in contact with the other main surface of the electrolyte membrane, and a main surface of the anode electrode layer, An anode side gas diffusion layer in contact with the main surface on the side different from the electrolyte membrane side, and a cathode side gas diffusion layer in contact with the main surface on the side different from the electrolyte membrane side among the main surfaces of the cathode electrode layer. At this time, at least one of the anode side gas diffusion layer and the cathode side gas diffusion layer is composed of a porous member mainly composed of conductive particles and a polymer resin, and a plurality of holes extending from the main surface of the gas diffusion layer are provided. The holes are formed so as to penetrate the gas diffusion layer, and all the holes are configured to coincide with the flow path portion of the separator.

With this fuel cell, the air permeation resistance in the portions other than the holes of the gas diffusion layer is low during the low humidification operation, so that it is possible to appropriately generate power while preventing the polymer electrolyte membrane from drying.
On the other hand, during low temperature start-up and high humidification operation, excess water is appropriately discharged to the separator flow path through the holes of the gas diffusion layer, so that liquid is locally generated at the boundary between the catalyst layer and the gas diffusion layer. The possibility of creating water accumulation areas is reduced. Therefore, the possibility that the gas diffusion layer is pushed up by the water pressure at which the water accumulation region is generated is reduced, and the possibility that the gas diffusion layer is separated from the catalyst layer and deformed is reduced.

[Production method]
4). Manufacturing method of gas diffusion layer:
The manufacturing method of the gas diffusion layer of this embodiment is the same as that of 1st-4th embodiment except the formation method of a hole, gas diffusion layer size, and electrode size. Therefore, only the method for forming holes in the gas diffusion layer will be described.

(1) Method for forming holes in the gas diffusion layer:
A method for forming the holes 12 in the gas diffusion layer will be described. The formation method of the hole 12 is not specifically limited. Specifically, for example, the hole 12 may be formed by piercing a needle made of metal or the like. Alternatively, the hole 12 may be formed using a laser such as a UV laser or a CO ₂ laser. Alternatively, for example, a penetrating member may be provided in a mold used when the first layer 10 is molded, and the hole 12 may be formed by pouring a material into the mold.

  That is, the hole 12 may be formed simultaneously with the formation of the first layer, or may be formed after the first layer is formed.

  When a needle or a laser is used, the hole forming position is programmed in the processing machine in accordance with the hole pattern previously determined according to the flow path shape of the separator, and the hole pattern is formed in the gas diffusion layer. Further, when a large number of needles are used, the needles are arranged in a hole pattern determined according to the flow path shape of the separator, and the hole pattern is formed by batch or block division.

[Sixth to eighth embodiments]
In this example, a membrane electrode assembly was produced in the same manner as in the first, second and fifth examples.

  Next, a method for producing the cathode gas diffusion layer used in the sixth to eighth embodiments will be described.

  In the sixth example, a cathode gas diffusion layer was produced in the same manner as in the first example except for the hole pattern.

  In the seventh example, a cathode gas diffusion layer was produced in the same manner as in the second example except for the hole pattern.

  In the eighth example, a cathode gas diffusion layer was produced in the same manner as in the fifth example except for the hole pattern.

  Formation of the hole pattern in the gas diffusion layer was performed as follows.

  A hole pattern is formed in the gas diffusion layer using a cemented carbide punch having a diameter of 160 μm. The hole pattern is determined from the flow path pattern of the separator. As shown in FIG. 13, the separator used in this example has a channel width of 1 mm, a rib width of 1 mm, and a channel pitch of 2 mm, and the number of channels is three and has four turn portions. Therefore, except for the turn portion, the holes have a Y direction pitch of 2 mm and an X direction pitch of 1.5 mm, and the turn portions have a pitch of 2 mm in both the X direction and the Y direction.

  As a result of measuring the hole diameter after forming the hole, it was confirmed that the diameter was 160 μm ± 30 μm.

The shape of the gas diffusion layer was a square of 32 mm × 32 mm. The area of the main surface of the gas diffusion layer is 1024 mm ² , the area of one hole is 0.020 mm ² , the number of holes is 315, and the opening area of the holes is 6.33 mm ² . Therefore, the opening area of the holes in the sixth to eighth embodiments is 0.62% of the area of the main surface of the fuel cell gas diffusion layer.

  As the gas diffusion layer used for the anode, a layer in which the first layer and the second layer were formed was used in the same manner as the cathode gas diffusion layer used in Example 2, except that no hole was provided. .

  The cathode and anode gas diffusion layers produced as described above were brought into contact with the membrane electrode assembly produced in this example, and hot pressing was performed at 120 ° C. and 6 kgf / cm 2 for 5 minutes, By joining the gas diffusion layer, a membrane electrode gas diffusion layer assembly was obtained.

This membrane electrode gas diffusion layer assembly is sandwiched between the anode side and the cathode side by the separator shown in FIG. 11, and a fluororubber gasket is arranged around the cathode and the anode between both separators, so that the effective electrode area is 10 A fuel cell having a size of 24 cm ² was obtained.

[Fifth to eighth comparative examples]
Only differences from the fourth to sixth embodiments will be described.

  Only the hole pattern of the cathode gas diffusion layer was changed with respect to the fourth to sixth examples. As shown in FIG. 14, the hole pattern of the gas diffusion layer has an entire surface x-direction pitch of 1.5 mm and a y-direction pitch of 1.5 mm.

The shape of the gas diffusion layer was a square of 32 mm × 32 mm. The area of the main surface of the gas diffusion layer is 1024 mm ² , the area of one hole is 0.020 mm ² , the number of holes is 441, and the opening area of the holes is 8.82 mm ² . Accordingly, the opening area of the holes in the sixth to eighth embodiments is 0.87% of the area of the main surface of the fuel cell gas diffusion layer.

  In the fifth comparative example, fuel cells were obtained in the same manner as in the fourth example except for the hole pattern.

  In the sixth comparative example, a fuel cell was obtained in the same manner as in the fifth example except for the hole pattern.

  In the seventh comparative example, fuel cells were obtained in the same manner as in the sixth example except for the hole pattern.

[Power generation test]
5. Power generation test contents:
A power generation test was performed using the fuel cells obtained in the sixth to ninth examples and the fifth to eighth comparative examples. Since the method of the power generation test is the same as that of the first embodiment, detailed description thereof is omitted.

  Table 5 shows the results of the power generation test.

  As described above, in the fuel cells of the fourth to sixth examples, the gas diffusion layer was not peeled off because the through hole of the gas diffusion layer was formed on the flow path of the separator. This is because excessive moisture is appropriately discharged to the separator flow path through the holes of the gas diffusion layer at the time of low temperature startup and high humidification operation, so that liquid is locally applied at the boundary between the catalyst layer and the gas diffusion layer. Therefore, the possibility that the gas diffusion layer is pushed up by the water pressure generated by the water accumulation region is reduced, and the gas diffusion layer may be detached from the catalyst layer and deformed. This is because of the reduction.

  On the other hand, in the fuel cells of the fifth to seventh comparative examples, the gas diffusion layer was peeled off mainly in the region where the holes of the gas diffusion layer were not formed on the separator flow path. This is because water generated by the cathode catalyst at room temperature startup moves to the separator side through the holes in the gas diffusion layer, but if the holes in the gas diffusion layer are in the ribs of the separator, discharge of the generated water is hindered and gas diffusion occurs. This is because peeling of the layer occurs.

  From the foregoing description, many modifications and other embodiments of the present invention are obvious to one skilled in the art. Accordingly, the foregoing description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the invention. Details of the structure and / or function may be substantially changed without departing from the spirit of the invention.

  The gas diffusion layer for fuel cell and the fuel cell of the present invention further improve the power generation performance when the gas diffusion layer composed of a porous member mainly composed of conductive particles and polymer resin is used for the fuel cell. It is useful as a gas diffusion layer for a fuel cell and a fuel cell that can be improved.

DESCRIPTION OF SYMBOLS 10 1st layer 12 hole 14,15 2nd layer 16,17 hole 18 cathode catalyst layer 20 polymer electrolyte membrane 22 anode catalyst layer 24,26 layer 30 gas flow path 51 polymer electrolyte membrane 52,53 catalyst layer 54,100 , 200, 250, 300 Gas diffusion layer for fuel cell 55 Membrane electrode gas diffusion layer assembly 56 Separator 60 Fuel cell 61 Current collecting plate 62 Insulating plate 63 End plate

Claims (9)

In the gas diffusion layer for a fuel cell, which is composed of a porous member mainly composed of conductive particles and a polymer resin, and a plurality of holes extending from the main surface of the porous member are formed,
The main surface of the fuel cell gas diffusion layer has a plurality of regions,
The gas diffusion layer for a fuel cell, wherein the holes are formed at equal pitch intervals in each of the plurality of regions. The porous member is composed of a first layer and a second layer in contact with the first layer and having higher water repellency than the first layer,
The hole is formed through the first layer;
The gas diffusion layer for fuel cells according to claim 1. The gas diffusion layer for a fuel cell according to claim 2, wherein the hole is formed so as not to penetrate the second layer. Kneaded conductive particles, polymer resin, and surfactant with a dispersion solvent to produce a kneaded product,
After rolling and forming the kneaded material into a sheet-like kneaded material,
The sheet-like kneaded material is heat-treated at a first heat treatment temperature to form the first layer by removing the surfactant and the dispersion solvent from the sheet-like kneaded material,
Forming a plurality of holes penetrating the first layer in the first layer,
When forming the plurality of holes, a plurality of regions are provided on the main surface of the first layer, and the holes are formed at equal pitch intervals in each of the regions.
A method for producing a gas diffusion layer for a fuel cell. Conductive particles, polymer resin, and a surfactant and a dispersion solvent are mixed to produce a dispersion,
After forming the dispersion layer thinner than the first layer by applying and drying the dispersion on the first layer before forming the plurality of holes,
The first layer on which the dispersion layer is formed is heat-treated at a second heat treatment temperature lower than the first heat treatment temperature to remove the surfactant and the dispersion solvent from the dispersion layer, and Forming a second layer having higher water repellency than the first layer on one layer;
5. The method of manufacturing a fuel cell gas diffusion layer according to claim 4, wherein when the plurality of holes are formed in the first layer, the plurality of holes are formed so as to also penetrate the second layer. Conductive particles, polymer resin, and a surfactant and a dispersion solvent are mixed to produce a dispersion,
After forming the dispersion layer thinner than the first layer by applying and drying the dispersion on the first layer before forming the plurality of holes,
The first layer on which the dispersion layer is formed is heat-treated at a second heat treatment temperature lower than the first heat treatment temperature to remove the surfactant and the dispersion solvent from the dispersion layer, and Forming a second layer having higher water repellency than the first layer on one layer;
5. The method for producing a fuel cell gas diffusion layer according to claim 4, wherein, when the plurality of holes are formed in the first layer, the plurality of holes are formed so as not to penetrate the second layer. An electrolyte membrane;
An electrode layer formed on the main surface of the electrolyte membrane;
A gas diffusion layer that is disposed in contact with the electrode layer and is composed of a porous member mainly composed of conductive particles and a polymer resin, and in which a plurality of holes extending from the main surface are formed;
A pair of separators disposed outside the gas diffusion layer,
The plurality of holes are formed at positions corresponding to the flow paths of the separator;
A fuel cell characterized by. The gas diffusion layer is
A first layer composed of a porous member mainly composed of conductive particles and a polymer resin;
It is composed of a porous member mainly composed of conductive particles and a polymer resin, and has a second layer formed in contact with the first layer and having higher water repellency than the first layer. ,
The fuel cell according to claim 7, wherein the plurality of holes are formed so as to penetrate the first layer. The fuel cell according to claim 8, wherein the plurality of holes are formed so as not to penetrate the second layer.

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