JP2011028867A - Electrode sheet for polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion electrode sheet that achieves superior gas diffusion properties through a porous film, maintains superior cell characteristics, allows uniform gas transmission while having almost no pressure loss and uniformly supplies hydrogen gas and oxygen gas to a catalyst layer. <P>SOLUTION: An electrode sheet for a polymer electrolyte fuel cell is configured such that at least an asymmetric porous resin layer is laminated on one face of a conductive nonwoven fabric. The asymmetric porous resin layer is configured to allow a binder resin to contain a conductive filler and/or conductive fibers. The asymmetric porous resin layer has communicating holes whose pore size on the side contacting with the conductive nonwoven fabric is ≥10 μm and ≤100 μm. The asymmetric porous resin layer also has communicating holes whose pore size on the surface side is ≥0.5 μm and <10 μm. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrode sheet having gas diffusibility (hereinafter abbreviated as an electrode sheet) for a polymer electrolyte fuel cell.

  A fuel cell is a power generation system that continuously supplies fuel and an oxidant, and extracts chemical energy as electric power when the fuel and an oxidant react with each other. Fuel cells using this electrochemical power generation method use the reverse reaction of water electrolysis, that is, a mechanism in which hydrogen and oxygen are combined to produce electrons and water, and have high efficiency and excellent environmental characteristics. In recent years it has been in the spotlight.

  Fuel cells are classified into phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells and solid polymer fuel cells depending on the type of electrolyte. In recent years, solid polymer fuel cells that have advantages such as startup at room temperature and extremely short startup time have attracted attention. The basic structure of a single cell constituting this polymer electrolyte fuel cell is such that a gas diffusion electrode having a catalyst layer is bonded to both sides of a polymer electrolyte membrane, and separators are arranged on both outer surfaces thereof.

  In such a polymer electrolyte fuel cell, first, hydrogen supplied to the fuel electrode side is guided to the gas diffusion electrode through the gas flow path in the separator. Next, the hydrogen is uniformly diffused by the gas diffusion electrode and then led to the catalyst layer on the fuel electrode side, where it is separated into hydrogen ions and electrons by a catalyst such as platinum. Then, the hydrogen ions are guided through the electrolyte membrane to the catalyst layer in the oxygen electrode on the opposite side across the electrolyte membrane. On the other hand, electrons generated on the fuel electrode side are led to a gas diffusion electrode on the oxygen electrode side through a circuit having a load, and further to a catalyst layer on the oxygen side. At the same time, oxygen introduced from the separator on the oxygen electrode side passes through the gas diffusion electrode on the oxygen electrode side and reaches the catalyst layer on the oxygen electrode side. Then, water is generated from oxygen, electrons, and hydrogen ions to complete the power generation cycle. In addition, examples of the fuel other than hydrogen used in the polymer electrolyte fuel cell include alcohols such as methanol and ethanol, and these can be directly used as fuel.

  Conventionally, carbon paper or carbon cloth made of carbon fiber has been used as a gas diffusion electrode of a polymer electrolyte fuel cell. In this carbon paper or carbon cloth, for the purpose of preventing flooding due to humidified water during fuel cell operation or water generated by electrode reaction at the cathode, such as polytetrafluoroethylene (PTFE) is formed on the surface or inside the gap. Water repellent treatment is performed with a water repellent binder. However, since these carbon paper and carbon cloth have a very large pore diameter, water may stay in the pores without obtaining a sufficient water repellent effect.

In order to improve this point, for example, a gas diffusion electrode in which a porous resin containing a conductive filler made of carbon or the like is contained in carbon paper has been proposed (see, for example, Patent Document 1). In general, such a gas diffusion electrode is formed by directly applying a coating material constituting a porous resin containing a conductive filler made of carbon or the like on a carbon paper surface to form a microporous layer. However, since it is made by impregnation, solvent extraction, and drying, many of the gaps in the carbon paper are blocked, so that the gas permeability inside the gaps deteriorates and the battery performance deteriorates. It was.
In addition, the microporous layer is difficult to control the pore size and water repellency due to variations in the opening, roughness, and film thickness of the carbon paper, so the degree of freedom in designing the surface properties according to the operating conditions is low. In addition, there are cases where the strength of the surface is low and carbon particles fall off.

  As another proposal, a solid polymer membrane fuel cell including a gas diffusion electrode in which at least two types of carbon particles having different particle size distribution centers are mixed is described. Graphite is used as the carbon particle having a larger particle size. And the formation of a diffusion layer using carbon particles coated with a fluororesin to impart water repellency is described (for example, see Patent Document 2). However, this solid polymer membrane fuel cell has a problem that the formed diffusion layer has low strength, the porous layer tends to be crushed when the gas diffusion electrode is pressure-bonded to the catalyst phase, and the water repellency of the diffusion layer is not sufficient. was there.

  On the other hand, as described above, the gas diffusion electrode is generally disposed in contact with a separator having a flow path. Since the carbon paper has a rigid plate shape, even if it is installed on the flow path, it is not crushed by the unevenness of the flow path, and is suitably used in combination with such a flow path. Since the flow path design needs to uniformly supply a gas such as hydrogen or oxygen to the gas diffusion electrode, it is necessary to precisely form a complicated flow path pattern, which requires advanced processing technology. Therefore, productivity is low and the use of a separator having a conventional flow path has been a major bottleneck in cost reduction, which is a problem of fuel cells.

JP 2003-303595 A JP 2001-57215 A

  The present invention has been made for the purpose of improving the above-described problems in conventional gas diffusion electrodes. That is, an object of the present invention is to provide an electrode sheet having gas diffusibility that can maintain good gas diffusibility through a porous film, thereby maintaining good battery characteristics. Another object of the present invention is to provide an electrode sheet that is capable of uniform gas permeation with little pressure loss and that can uniformly supply hydrogen gas and oxygen gas to the catalyst layer.

The electrode sheet of the present invention that solves the above problems is an electrode sheet for a polymer electrolyte fuel cell in which an asymmetric porous resin layer is laminated on at least one side of a conductive nonwoven fabric, and the asymmetric porous resin layer is formed on a binder resin. A conductive filler and / or a conductive fiber, the pore diameter on the side of the asymmetric porous resin layer in contact with the conductive nonwoven fabric is 10 μm or more and 100 μm or less, and the pore diameter on the surface side of the asymmetric porous resin layer Has a communication hole of 0.5 μm or more and less than 10 μm.
The conductive filler and / or conductive fiber is preferably at least one selected from carbon, graphite, and a metal subjected to corrosion resistance treatment.
The binder resin is preferably a fluororesin, and the fluororesin is preferably polyvinylidene fluoride and / or a copolymer thereof.
The conductive nonwoven fabric preferably has a multilayer structure of two or more layers having different fiber diameters, and the fiber diameter in the layer in contact with the asymmetric porous resin layer is preferably smaller than the fiber diameter of another layer. It is preferable that the fiber diameter in the lowermost layer which does not contact | connect an asymmetric porous resin layer is 5 to 5000 micrometers in a basic nonwoven fabric.
The conductive nonwoven fabric is preferably a conductive fiber in which carbon particles or resin fibers are coated with carbon particles.

  The electrode sheet of the present invention has the functions of gas introduction, gas diffusion, and gas fine dispersion, has a small pressure loss, allows uniform gas permeation, and can supply gas uniformly to the catalyst layer. Furthermore, as another function, it is a gas diffusible electrode sheet that is excellent in mechanical strength and has excellent durability, and is excellent in water repellency control, and does not cause flooding or dry-up.

It is explanatory drawing which shows the cross-sectional layer structure of the electrode sheet for solid polymer fuel cells of this invention. It is explanatory drawing shown about the hole diameter of an asymmetric porous resin layer. It is explanatory drawing which shows the cross-sectional layer structure of an electroconductive nonwoven fabric. It is sectional drawing which shows the structure of a multi-tank inclination type wet paper machine. It is sectional drawing which shows the structure of another multi-tank inclination type wet paper machine. It is sectional drawing which shows the structure of another multi-tank inclination type wet paper machine.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The electrode sheet of the present invention is obtained by laminating at least a conductive nonwoven fabric 1 with an asymmetric porous resin layer 2 as shown in the cross-sectional layer configuration of FIG. Further, as shown in FIG. 2, the asymmetric porous resin layer 2 has a communication hole for allowing gas to pass from the side A in contact with the conductive nonwoven fabric to the surface side B, but the side in contact with the conductive nonwoven fabric. The hole diameter in A and the hole diameter on the surface side B are different. Asymmetry in the present invention means that the pore diameter is different between the front and back of the porous resin layer.
Moreover, the preferable form of the conductive nonwoven fabric 1 is formed by laminating two or more layers as shown in the cross-sectional layer configuration of FIG. 3, and the layer 4 on the side in contact with the asymmetric porous resin layer 2 and the asymmetric porous resin. It consists of the lowest layer 3 which does not touch a layer. The conductive nonwoven fabric 1 may not be two or more layers as shown in FIG. 3 but may be a single layer.

The asymmetric porous resin layer 2 must have a communication hole having a pore diameter of 10 μm or more and 100 μm or less on the side A in contact with the conductive nonwoven fabric, and a communication hole having a pore diameter of 0.5 μm or more and less than 10 μm on the surface side B. I must.
The pore diameter referred to here is a value obtained by observing the cross section of the asymmetric porous resin layer with an electron microscope and measuring and averaging the diameters of 30 holes in the vicinity of the surface and the vicinity of the side in contact with the conductive nonwoven fabric. When the hole is not circular but oval or indefinite, the longest diameter is measured as the hole diameter.

  The asymmetric porous resin layer of the present invention is disposed for the purpose of efficiently diffusing fuel gas as an electrode sheet and for preventing flooding due to humidified water during fuel cell operation or water generated by electrode reaction at the cathode. The pore diameter is very important from the viewpoints of the breathability and diffusibility of the fuel gas and the permeability of the generated water. The pore diameter in the asymmetric porous resin layer for balancing these characteristics in a well-balanced manner is such that the pore diameter on the side in contact with the conductive nonwoven fabric is 10 μm or more and 100 μm or less, preferably 15 μm or more and 60 μm or less. Air permeability is poor and power generation efficiency is reduced. When the pore diameter is larger than 100 μm, the strength of the asymmetric porous resin layer is insufficient, and the pores are easily crushed by the pressure applied during operation, resulting in problems such as poor liquid permeability and air permeability and reduced power generation efficiency. Also, having a dense communication hole with a pore diameter on the surface side of 0.5 μm or more and less than 10 μm, preferably 0.5 μm or more and 8 μm or less, allows sufficient diffusion of the fuel gas to supply fuel uniformly to the electrode catalyst. In addition, the hole diameter is important for preventing flooding. If it is less than 0.5 μm, flooding is likely to occur, and if it is 10 μm or more, there is a problem that fuel diffusion is not sufficient.

  The electrode sheet of the present invention is required to have high conductivity, and therefore the asymmetric porous resin layer is obtained by containing a conductive filler and / or conductive fiber in a binder resin. As the material of the conductive filler and / or conductive fiber, any material having high conductivity can be used, but carbon, graphite, a metal subjected to corrosion resistance treatment, and a mixture thereof are preferable. Examples of the carbon filler include carbon black, acetylene black, carbon nanotube, carbon nanohorn, fullerene and the like. Examples of the carbon fiber include pan-based carbon fiber and pitch-based carbon fiber. Examples of graphite include natural graphite such as massive graphite, scale-like graphite, and earth-like graphite, and artificial graphite. These materials have high conductivity and high corrosion resistance and are preferably used. On the other hand, when a metal is used as a conductive material, it is necessary to perform a corrosion resistance treatment. Any metal can be used as long as it has conductivity, and examples include stainless steel, aluminum, and iron. Stainless steel is preferred from the viewpoint of conductivity, strength, and corrosion resistance. Even in the case of using stainless steel, the surface needs to be subjected to a corrosion resistance treatment, and a noble metal plating is a main example of the method. A conductive polymer can be raised as another conductive material, but it is not preferable in terms of durability under high acidic conditions in the fuel cell.

  In the present invention, a binder resin is necessary as a main constituent material of the asymmetric porous resin layer in order to bind the conductive filler and / or conductive fiber. The binder resin must have heat resistance, flexibility, toughness, corrosion resistance, chemical resistance, etc. with a melting point of 120 ° C. or higher. Among them, fluororesin is corrosion resistance, strength and water repellency to prevent flooding. It is preferably used to combine these functions. In the case of using a resin material other than the fluorine-based resin, it is not preferable because it is difficult to select a resin for satisfying the above characteristics, and a material for imparting a water repellency effect for preventing flooding is further required. The fluororesin is preferably polyvinylidene fluoride and / or a copolymer thereof. Specific examples of the fluorine resin include tetrafluoroethylene resin (PTFE), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer resin (PFA), and tetrafluoroethylene-hexafluoropropylene copolymer resin (FEP). , Ethylene tetrafluoride-ethylene copolymer resin (ETFE), polyvinylidene fluoride resin (PVdF), vinylidene fluoride-tetrafluoroethylene copolymer resin (P (VdF-TFE)), vinylidene fluoride-hexafluoropropylene And a copolymer resin (P (VdF-HFP)), vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer resin (P (VdF-TFE-HFP)), and the like.

Next, a method for producing the asymmetric porous resin layer of the present invention will be described.
Known methods such as a dry method and a wet method can be widely used as a method for producing the asymmetric porous resin layer. As an example of the dry method, in a solution in which a resin is dissolved, a solvent that does not dissolve a resin having a higher boiling point than the dissolved solvent, that is, a poor solvent is appropriately added and mixed, cast on a substrate, and then dried stepwise. By this method, an asymmetric porous film can be produced. In addition, as an example of the wet method, a solution in which a resin is dissolved is cast on a base material, and after drying to such an extent that a solvent only on the surface is removed as necessary, the resin is not dissolved but the resin is dissolved. An asymmetric porous film can be produced by immersing in a poor solvent that is uniformly mixed with a solvent and pulling and drying the whole substrate when the solvent is sufficiently substituted. In the present invention, an asymmetric porous resin layer can be easily obtained by using these production methods as they are or by application. In the present invention, in the procedure for producing a solution for dissolving the resin, the conductive filler and / or It is necessary to disperse and mix the conductive fibers. In this case, the pore diameter can be more strictly controlled by using a surfactant, a viscosity modifier and the like.
In this invention, it is possible to laminate | stack an asymmetric porous resin layer on the surface of a conductive nonwoven fabric directly using the conductive nonwoven fabric as a base material in the said preparation procedures. On the other hand, it is also possible to produce an asymmetric porous resin layer on a releasable substrate and laminate it with a conductive nonwoven fabric by thermocompression bonding. When thermocompression bonding, it is necessary to control the heat and pressure so that the porous layer is not crushed. Therefore, it is simpler and more efficient to laminate the asymmetric porous resin layer directly on the surface of the conductive nonwoven fabric. It is preferable.

The conductive nonwoven fabric in the present invention may be a single-layer nonwoven fabric, but has a multilayer structure of two or more layers having different fiber diameters, and the fiber diameter in the layer in contact with the asymmetric porous resin layer is larger than the fiber diameter of another layer. A thin one is also preferred.
The fiber diameter here refers to an average of fiber diameters in 100 fibers obtained by sampling the fibers of the conductive nonwoven fabric with an electron microscope and sampling the fibers in the confirmed visual field. In addition, the fiber length in the conductive nonwoven fabric described below refers to the average fiber length of 100 fibers obtained by sampling the fibers in the conductive nonwoven fabric with an electron microscope and sampling the fibers in the confirmed visual field. .

  In the conductive nonwoven fabric, the fiber diameter (hereinafter referred to as the fiber diameter of the uppermost layer) in the layer in contact with the asymmetric porous resin layer is 1 μm or more and 10 μm or less, and the average fiber length is 10 mm or less. Is desirable. The pore diameter formed by the uppermost conductive nonwoven fabric is preferably about 10 μm to 100 μm from the viewpoint of preventing flooding, and when the fiber diameter of the uppermost layer is 1 μm or more and 10 μm or less, it is easy to control the pore diameter range.

On the other hand, in the present invention, H ₂ or O ₂ gas flows from the lowermost layer not in contact with the asymmetric porous resin layer toward the cross section of the layer on the side in contact with the asymmetric porous resin layer at a substantially right angle. The average fiber diameter of the lowermost conductive nonwoven fabric is preferably 5 μm to 5000 μm. When the average fiber diameter is less than 5 μm, the gap formed by the overlapping of the fibers becomes narrow, and when the gas flow rate of H ₂ or O ₂ is large, the inflow resistance increases and the pressure difference in the surface direction becomes large. As a result, the in-plane variation of the gas flow rate increases. On the other hand, when the average fiber diameter is larger than 5000 μm, the pressure loss in the surface direction is reduced even if the gas flow rate is large, and the variation in the gas flow rate in the surface direction of the electrode sheet is reduced, but the fiber diameter is increased. As a result, the unevenness of the surface becomes excessive and the pressure on the inner layer becomes non-uniform. As a result, the pressure on the uppermost layer becomes non-uniform, so the amount of gas flowing into the membrane-electrode assembly (hereinafter referred to as MEA) In addition to the non-uniformity in the surface direction, the MEA may be locally compressed and damaged, which may cause in-plane variation in power generation performance, which is not preferable.

  As described above, in the present invention, by increasing the porosity by thickening the fibers forming the lowermost layer portion as described above, and providing a rigid layer having high compression resistance, it is Since the pressure loss is small and the internal pressure is constant in any part of the lowermost layer, the gas flow rate in the electrode sheet is uniform in the surface direction.

  Moreover, in the electrode sheet of this invention, it is preferable that the fiber which comprises each layer of an electroconductive nonwoven fabric is formed with the carbon fiber or the electroconductive fiber by which the resin particle coated carbon particles. In the present invention, both can be suitably used, and both may be mixed and used. The carbon fiber is preferably composed of at least one of polyacrylonitrile-based carbon fiber, phenol-based carbon fiber, pitch-based carbon fiber, and carbon nanotube, but is not necessarily limited thereto. In addition, the resin component of the resin fiber coating the carbon particles includes polypropylene, polyethylene, polyamide, semi-aromatic polyamide, aromatic polyamide, polyester, polyarylate, melamine, polyimide, polyamideimide, polyphenylsulfone, polyacetal, poly Although at least 1 or more types of paraphenylene benzobisoxazole, polybenzimidazole, polyetheretherketone, and polyketone are mentioned, it is not necessarily limited to these.

  In the present invention, it is possible to control conductivity and water repellency by applying a fluorine-based resin or a mixture of carbon particles and a fluorine-based resin to a conductive nonwoven fabric. As carbon particles, what is called conductive carbon black with a relatively large specific surface area is suitable for improving the initial performance, but acetylene black with appropriate water repellency is compatible with both conductivity and durability. Therefore, it is more preferably used.

The fluororesin used in the conductive nonwoven fabric used in the present invention is preferably PVdF and / or a copolymer thereof, and in particular, the fluororesin is P (VdF-HFP) and / or P (VdF-TFE). -HFP) is preferred.
As the fluororesin used for the conductive nonwoven fabric in the present invention, those mentioned above capable of achieving both water repellency and adhesiveness are preferably used. In the electrode sheet on the anode side and the electrode sheet on the cathode side, Can be adjusted by the mixing ratio of various fluororesins. That is, PVdF or P (VdF-HFP) is suitable for fixing the carbon particles to the resin fiber, but P (VdF-TFE-HFP) is preferable for improving water repellency. By optimizing the mixing ratio of the plurality of resins, it becomes possible to control the fixing of the carbon particles to the resin fibers and the water repellency of the anode and the cathode, respectively. Moreover, it is preferable that the said fluorine resin has the mass mean molecular weight in the range of 100,000 to 1,200,000. If the mass average molecular weight is less than 100,000, the strength may be low. On the other hand, if it exceeds 1,200,000, the solubility in a solvent is poor, making it difficult to form a paint, and uneven viscosity of the paint occurs. As a result, the thickness accuracy of the final electrode sheet may be reduced, and the adhesion with the catalyst layer may be uneven.

In the present invention, an electrode sheet having a rate of change in film thickness by pressure of 120 ° C., 10 MPa, and 5 minutes within 10% is preferable. The film thickness change rate here is obtained from the following formula (1).
Film thickness change rate (%) = 1-film thickness after pressurization / film thickness before pressurization × 100 (1)
In the assembly of a fuel cell, it is desirable that the electrode sheet and the catalyst layer are pressure-bonded for the purposes of gas supply, electric heating, and current collection. Further, the electrode sheet is required to have a structure that can withstand changes in internal pressure during operation of the fuel cell. In the present invention, the film thickness change rate is preferably within 10% under the above conditions. When the film thickness changes in a range exceeding 10%, there are problems in gas permeability and drainage, and in long-term durability.

  In the electrode sheet of this invention, fillers other than said carbon material may further be contained. By adding this filler, it becomes possible to control the discharge of gas / water, the pore diameter of the porous membrane, and the dispersion of the carbon material, which will affect the fuel cell performance. As the filler other than the carbon material, those having hydrophilicity are preferable, and any of inorganic fine particles or organic fine particles can be used. In consideration of the environment inside the electrode sheet in the fuel cell, inorganic fine particles are used. Is preferred. The pore size of the porous membrane by adding a hydrophilic filler to the fluororesin having water repellency, microscopically intermingling the water repellent part and the hydrophilic part, and forming an aggregate with the carbon material This is because gas and water can be discharged well by expanding the ratio. As a result, it is possible to prevent a decrease in battery performance due to the flooding phenomenon. As the hydrophilic filler, inorganic oxide fine particles such as titanium dioxide and silicon dioxide are preferable. This is because they can withstand the environment inside the gas diffusion electrode in the fuel cell and have sufficient hydrophilicity. Any particle size of the filler can be used. However, when the particle size is very small, dispersion in the paint becomes difficult. When the particle size is very large, porous voids are used. The problem of blocking the hole occurs. Therefore, generally, a particle size range comparable to the particle size of the particulate carbon material, that is, a range of 10 nm to 100 nm is used.

In the present invention, when extreme water repellency is required, polytetrafluoroethylene particles may be added as a filler other than the carbon material. At this time, the electrode sheet of the present invention functions as a super water-repellent film.
The mass ratio of the filler to the fluororesin is preferably 3 parts by mass or less of the filler with respect to 1 part by mass of the fluororesin. More preferably, it is 1.5 parts by mass or less. When the blending amount of the filler is more than 3 parts by mass, the inside of the electrode sheet is excessively filled, which causes a decrease in gas diffusion capacity and a decrease in conductivity. As a result, the fuel cell performance is likely to be deteriorated.

  In the present invention, the thickness of the electrode sheet is preferably 5 μm to 5000 μm, more preferably 10 μm to 4000 μm, and further preferably 15 μm to 3000 μm. If the thickness is smaller than 5 μm, the water retention effect is not sufficient, and if it is larger than 5000 μm, it is too thick and the gas diffusing capacity and drainage capacity are lowered, and the battery performance tends to be lowered.

The porosity of the electrode sheet of the present invention is preferably in the range of 60% to 95%, more preferably 70% or more, and particularly preferably 80% or more. If the porosity is less than 60%, the gas diffusing capacity and water discharge are insufficient, and if it exceeds 95%, the mechanical strength is remarkably lowered, and the fuel cell is easily damaged in the process until it is assembled.
Further, the density can be determined by the film thickness of the electrode sheet and the mass per unit area as shown in the following formula (2), and the range of 0.10 g / cm ^{3 to} 0.65 g / cm ³ is the same as above. It is preferable for the reason.
Density (g / cm ³ ) = mass per unit area / (film thickness × unit area) (2)

  Moreover, the hole diameter of an electrode sheet has the suitable range of 0.5 micrometer-10 micrometers, More preferably, it is 3 micrometers or more, More preferably, it is 5 micrometers or more. When the pore diameter is 0.5 μm or less, gas diffusing capacity and water discharge are insufficient. Here, the pore diameter means an average pore diameter by the bubble point method.

Next, the manufacturing method of the electroconductive nonwoven fabric in this invention is explained in full detail.
As for the method for producing the conductive nonwoven fabric of the present invention, various nonwoven fabric production methods are used. In particular, the wet papermaking method is preferably used from the viewpoint of ensuring uniformity such as formation and film thickness control. In particular, it is desirable that each layer of the conductive nonwoven fabric used in the present invention is formed integrally. As a manufacturing method for integrally forming each layer as described above, the fiber slurry is poured out from the first flow box onto the inclined traveling portion of the papermaking net traveling obliquely upward, and the inside of the first flow box is A production method in which a plurality of layers of non-woven fabric is formed by pouring the fiber slurry out of the second flow box where the lower part of the flow box is located in the vicinity of the intersection between the flooded line and the inclined traveling part is preferable.

The non-woven fabric manufacturing method uses the multi-tank inclined wet paper machine shown in FIG. In the multi-tank inclined type wet paper machine shown in FIG. 4, the papermaking net 10 is run in the direction of arrow α by a plurality of guide rollers. The inclined paper making net 10 between the guide roller 11 and the guide roller 12 is referred to as an inclined traveling unit 13. In the present invention, the lower part of the second flow box 15 is located in the vicinity A of the intersection of the floodline WL and the inclined traveling part 13 in the first flow box 14. In the vicinity A of the intersection, the fiber slurry 16 in the first flow box 14 and the fiber slurry 17 in the second flow box 15 are adjacent to each other with a partition wall 18 therebetween.
There is a gap between the partition wall 18 and the inclined running part 13 in the vicinity A of the intersection, and the fiber slurry 16 that has flowed out of the first flow box 14 along with the running of the papermaking net 10 passes through this gap. The fiber slurry 17 in the second flow box 15 is mixed.
In the present invention, in the example of FIG. 4, the flow box has two stages. However, as shown in FIG. 5, a plurality of flow boxes having three or more stages including the third flow box 20 may be provided.

In this invention, a nonwoven fabric is manufactured using said multi-tank inclination type wet paper machine. That is, the fiber slurry 16 flows out from the first flow box 14 onto the inclined traveling portion 13 of the papermaking net 10 that runs obliquely upward in FIG. 4, and is inclined with the flooding line WL in the first flow box 14. By flowing the fiber slurry 17 out of the second flow box 15 where the lower part of the flow box is located in the vicinity A of the intersection with the traveling unit 13, it is possible to form a papermaking sheet made of a plurality of layers of non-woven fabric.
Since the fiber slurry 16 of the first flow box 14 and the fiber slurry 17 of the second flow box 15 are mixed in a wet state in the vicinity A of the intersection, the fibers are entangled and the obtained papermaking sheet is laminated between , Delamination hardly occurs. It is preferable that the floodline WL in the first flow box 14 in the vicinity A of the intersection is not brought into contact with the inclined traveling portion 13 of the papermaking net 10. When the water line WL is brought into contact with the inclined traveling unit 13, when the fiber slurry 16 flows out to the inclined traveling unit 13, moisture is absorbed inside the papermaking net, and the fiber slurry 17 of the second flow box 15 It will be difficult to obtain sufficient entanglement between the fibers.

The said fiber slurry mixes the fiber which comprises the said conductive nonwoven fabric in liquids, such as water. Specifically, cut fiber, low beating fiber, or the like is used as the fiber slurry 16 of the first flow box 14. Further, as the fiber slurry 17 of the second flow box 15, microfibrillated fiber or the like is used.
Next, a PVdF resin, P (TFE-VdF-HFP), etc. are mixed and dissolved and dispersed in the carbon particles to prepare a paint. The solvent is an amide solvent, and is mixed with a stirrer to form a paint. The paint is cast on a polyethylene terephthalate film, and the papermaking sheet obtained by the above operation is laid down on the paint before being put into the drying step, so that the paint and the papermaking sheet are soaked into the whole papermaking sheet. After integration, it is dried in an oven. A sheet obtained after drying and removing the polyethylene terephthalate film becomes a conductive nonwoven fabric.

  In the conductive nonwoven fabric of the present invention, the fiber diameter continuously decreases from the lowermost layer not in contact with the asymmetric porous resin layer toward the layer in contact with the asymmetric porous resin layer, so that the inner diameter is directed toward the uppermost layer. Thus, the nonwoven fabric can be formed so as to be continuously smaller. This makes it possible to reduce the gas flow resistance of the gas flowing in from the lowermost layer by making the path to the layer on the side in contact with the asymmetric porous resin layer continuously small and uniform. It is possible to supply a very uniform gas with little variation in the surface direction toward the catalyst phase from the layer in contact with the porous resin layer. Further, by using such a production method, the layer on the side in contact with the asymmetric porous resin layer and the fibers of the other layers are entangled, so that the interface between the two layers is substantially eliminated or the asymmetric porous resin is formed at the interface. The fibers in the layer on the side in contact with the layers are entangled with the fibers in the other layers, so that the interface between the two layers can be bound without a binder due to the anchor effect.

Moreover, the manufacturing method of the electroconductive nonwoven fabric of this invention may use the multi-tank inclination type wet paper machine shown in FIG. In the multi-tank inclined wet paper machine shown in FIG. 6, a nonwoven fabric 31 is fed from an unwinding roll 30 on which a nonwoven fabric is wound in advance on the inclined traveling portion 13 of the papermaking net 10 that is traveled in the direction of arrow α by a plurality of guide rollers. To run. And the fiber slurry 16 in the 1st flow box 14 and the fiber slurry 17 in the 2nd flow box 15 are poured out on the run nonwoven fabric 31, and the layer which consists of two layers of nonwoven fabrics is formed. The
As described above, fibers and nonwoven fabrics made of different materials are entangled with each other from the lowest layer not in contact with the asymmetric porous resin layer to the layer in contact with the asymmetric porous resin layer. It is possible to reduce the size continuously from the lowermost layer not in contact with the resin layer toward the layer in contact with the asymmetric porous resin layer, and it can be formed in one step, which contributes to improvement in productivity. It becomes possible.
The present invention will be described more specifically with reference to examples. An electrode sheet was prepared as follows, and then a polymer electrolyte fuel cell in which the electrode sheet was disposed on both the fuel electrode side and the oxygen electrode side was prepared and evaluated.

30 parts by mass of PVdF and 10 parts by mass of P (TFE-VdF-HFP) are dissolved in 600 parts by mass of 1-methyl-2-pyrrolidone, and 100 parts by mass of acetylene black having an average primary particle size of 40 nm is dispersed to obtain a mixed solvent. It was. Subsequently, 60 mass parts diethylene glycol was mixed and stirred, and the coating material 1 was obtained.
The applicator 1 is coated on a conductive nonwoven fabric 1 (basis weight 50 g / m ² ) obtained by mixing a polyacrylonitrile-based carbon fiber having a fiber diameter of 30 μm and a polyarylate fiber having an average fiber diameter of 20 μm at a mass ratio of 6: 4. And dried at 100 ° C. for 1 minute, and then impregnated in a water bath to replace the solvent. This was pulled up and dried at 50 ° C. for 24 hours to obtain an electrode sheet 1 of the present invention in which an asymmetric porous film was laminated on a conductive nonwoven fabric.

A paint 2 was obtained in the same manner as the paint 1 except that the paint 1 in Example 1 was changed to 20 parts by mass of PVdF and 20 parts by mass of P (TFE-VdF-HFP).
Next, an electrode sheet 2 of the present invention was obtained in the same manner as in Example 1 except that the paint 2 was used instead of the paint 1.

In the multi-tank wet type wet paper machine shown in FIG. 4, polyacrylonitrile-based carbon fibers having a fiber diameter of 30 μm and polyarylate fibers having a fiber diameter of 20 μm are mixed at a mass ratio of 6: 4 as the fiber slurry 16 in the first flow box 14. In addition, a slurry of polyacrylonitrile-based carbon fiber having an average fiber diameter of 5 μm was introduced as the fiber slurry 17 in the second flow box 15. And the conductive nonwoven fabric 2 which integrated three types of fiber was obtained.
Next, in Example 1, the electrode sheet 3 of the present invention was obtained in the same manner except that the conductive nonwoven fabric 2 was used instead of the conductive nonwoven fabric 1.

  In Example 3, an electrode sheet 4 of the present invention was obtained in the same manner except that the paint 2 obtained in Example 2 was used instead of the paint 1.

30 parts by mass of PVdF and 10 parts by mass of P (TFE-VdF-HFP) are dissolved in 600 parts by mass of 1-methyl-2-pyrrolidone, 80 parts by mass of 5 μm fiber-based polyacrylonitrile-based carbon fiber is dispersed, and the mixed solvent is added. Obtained. Subsequently, 60 mass parts diethylene glycol was mixed and stirred, and the coating material 3 was obtained.
Next, the coating material 3 was applied on the conductive nonwoven fabric 2 used in Example 3 using an applicator, dried at 100 ° C. for 1 minute, and then impregnated in a water bath to replace the solvent. This was pulled up and dried at 50 ° C. for 24 hours to obtain an electrode sheet 5 of the present invention in which an asymmetric porous film was laminated on a conductive nonwoven fabric.

A coating material 4 was obtained in the same manner as the coating material 3 except that the coating material 3 of Example 5 was changed to 20 parts by mass of PVdF and 20 parts by mass of P (TFE-VdF-HFP).
Next, an electrode sheet 6 of the present invention was obtained in the same manner as in Example 5 except that the paint 4 was used instead of the paint 3.

[Comparative Example 1]
40 parts by mass of PVdF was dissolved in 600 parts by mass of 1-methyl-2-pyrrolidone, and 100 parts by mass of acetylene black having an average primary particle diameter of 40 nm was dispersed to obtain a mixture. Next, 45 parts by mass of diethylene glycol was mixed and stirred to obtain paint 5.
The coating material 5 is applied using an applicator on a conductive nonwoven fabric (basis weight 50 g / m ² ) obtained by mixing polyacrylonitrile-based carbon fiber having a fiber diameter of 30 μm and polyarylate fiber having a fiber diameter of 20 μm at a mass ratio of 6: 4. And it dried at 180 degreeC for 5 minute (s), and obtained the electrode sheet 7 for a comparison by which an isotropic porous film was laminated | stacked on the electroconductive nonwoven fabric.

(Measurement of pore diameter of porous resin layer)
In order to measure the pore diameter of the porous resin layer of the electrode sheets obtained in Examples 1 to 6 and Comparative Example 1, each electrode sheet was cut with a microtome, and the cross section was observed with an electron microscope. Thirty holes were arbitrarily selected for the hole on the side in contact with the conductive nonwoven fabric and the hole on the surface side, and the hole diameter was measured. The diameter was measured when the hole was close to a perfect circle, and the longest distance was measured as the hole diameter when the hole was elliptical or indefinite. Table 1 shows the average value of the 30 pore diameters as the pore diameter on the side in contact with the conductive nonwoven fabric and the pore diameter on the surface side.

  As shown in Table 1, the pore diameter of the porous resin layer of the electrode sheet of the present invention is different between the conductive nonwoven fabric side and the surface side, and the asymmetric porosity is in the relationship of pore diameter on the conductive nonwoven fabric side> pore diameter on the surface side. It was confirmed that the resin layer was a porous resin layer. On the other hand, the pore diameter of the porous resin layer of Comparative Example 1 was almost equal between the conductive nonwoven fabric side and the surface side, and it was confirmed that the porous resin layer was an isotropic porous resin layer.

(Thickness change rate)
In order to confirm the degree of void collapse by hot pressing per unit area of the electrode sheets obtained in Examples 1 to 6 and Comparative Example 1, hot pressing (120 ° C., 10 MPa, 5 minutes) was performed to change the film thickness ( %). The results are shown in Table 2.

(Solid polymer fuel cell)
(1) Manufacture of a polymer electrolyte fuel cell As the electrode sheet for the fuel cell 1, one 50 mm square electrode sheet 1 and one electrode sheet 2 of the present invention obtained above were prepared. In addition, as the electrode sheet for the fuel cell 2, one 50 mm square electrode sheet 3 and one electrode sheet 4 of the present invention obtained above were prepared. As the electrode sheet for the fuel cell 3, one 50 mm square electrode sheet 5 and one electrode sheet 6 of the present invention obtained above were prepared. As the electrode sheet for the fuel cell 4, two 50mm square electrode sheets 7 for comparison obtained above were prepared. A catalyst coating comprising a carbon catalyst-supported platinum catalyst and a mixed solvent of water and ethanol is applied to the surface of the electrode sheet on the porous resin layer side and dried to form a catalyst layer. A layered electrode sheet was obtained. The amount of each platinum catalyst was 0.3 mg / cm ² . Next, the electrode sheet with the catalyst layer is arranged so that the catalyst layer surface is in contact with the electrolyte membrane (trade name: Nafion 117, manufactured by DuPont), and the electrode sheet with the catalyst layer is subjected to hot press (120 ° C., 10 MPa, 10 minutes). And the electrolyte membrane were joined to obtain a membrane-electrode assembly. A graphite separator having a smooth surface was arranged on both sides of the obtained membrane-electrode assembly, and the fuel cells 1 to 4 for evaluation were produced by incorporating the separator into a single cell. In the fuel cell 1, the electrode sheet 1 is disposed on the fuel electrode side, and the electrode sheet 2 is disposed on the air electrode side. In the fuel cell 2, the electrode sheet 3 is disposed on the fuel electrode, and the electrode sheet 4 is disposed on the air electrode side. In the fuel cell 3, the electrode sheet 5 is disposed on the fuel electrode, and the electrode sheet 6 is disposed on the air electrode side. In the fuel cell 4, the electrode sheet 7 was used for both the fuel electrode side and the air electrode side.

(2) Evaluation of solid polymer fuel cell The power generation characteristics of the fuel cells 1 to 4 were evaluated in the following manner. As the supply gas for the fuel cell, hydrogen gas was used on the fuel electrode side and oxygen gas on the oxygen electrode side. Hydrogen gas was supplied at a humidification temperature of 85 ° C. so as to be 500 mL / min and 0.1 MPa, and oxygen gas was supplied so as to be 1000 mL / min and 0.1 MPa at a humidification temperature of 70 ° C. Under this condition, the voltage at a current density of 1 A / cm ² was measured. The results are shown in Table 3.

As shown in Table 3, the polymer electrolyte fuel cells provided with the electrode sheets obtained in Examples 1 to 6 have a higher voltage at a current density of 1 A / cm ² than that of Comparative Example 1, and excellent power generation characteristics. It was. In addition, although the fuel cells 1 to 3 were able to generate power up to a current density of 1.8 A / cm ² without problems, the fuel cell 4 was flooded around 1.1 A / cm ² because the isotropic porous resin layer had a small diameter. Produced.

1 conductive nonwoven fabric 2 asymmetric porous resin layer

Claims (7)

  An electrode sheet for a polymer electrolyte fuel cell in which an asymmetric porous resin layer is laminated on at least one surface of a conductive nonwoven fabric, wherein the asymmetric porous resin layer contains a conductive filler and / or conductive fibers in a binder resin, The asymmetric porous resin layer has a communication hole with a diameter of 10 μm or more and 100 μm or less on the side in contact with the conductive nonwoven fabric, and a surface of the asymmetric porous resin layer has a communication hole with a diameter of 0.5 μm or more and less than 10 μm. An electrode sheet for a solid polymer fuel cell.   2. The electrode sheet for a polymer electrolyte fuel cell according to claim 1, wherein the conductive filler and / or the conductive fiber is at least one selected from carbon, graphite, and a metal subjected to corrosion resistance treatment. .   The electrode sheet for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the binder resin is a fluororesin.   The electrode sheet for a polymer electrolyte fuel cell according to claim 3, wherein the fluororesin is polyvinylidene fluoride and / or a copolymer thereof.   2. The conductive nonwoven fabric has a multilayer structure of two or more layers having different fiber diameters, and the fiber diameter in the layer in contact with the asymmetric porous resin layer is smaller than the fiber diameter of another layer. 5. The electrode sheet for a polymer electrolyte fuel cell according to any one of 4 to 4.   6. The electrode sheet for a polymer electrolyte fuel cell according to claim 1, wherein the conductive nonwoven fabric has a fiber diameter of 5 to 5000 [mu] m in a lowermost layer not in contact with the asymmetric porous resin layer. .   The electrode sheet for a polymer electrolyte fuel cell according to any one of claims 1 to 6, wherein the conductive nonwoven fabric is a conductive fiber in which carbon particles or resin fibers are coated with carbon particles.

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