JP2011028849A - Gas diffusion electrode for solid polymer fuel cell, and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve good gas diffusivity through a porous membrane, thereby maintaining good battery characteristics, enabling uniform gas permeation with little pressure loss, and uniform hydrogen gas or oxygen in a catalyst layer. An object of the present invention is to provide a gas diffusion electrode capable of supplying a gas and a method of manufacturing the same.
The gas diffusion electrode for a polymer electrolyte fuel cell according to the present invention is a gas diffusion electrode for a polymer electrolyte fuel cell formed by laminating two or more layers of conductive nonwoven fabric, and is the uppermost conductive layer. The average fiber diameter in the nonwoven fabric and the average fiber diameter in the lowermost conductive nonwoven fabric are different. In addition, such a gas diffusion electrode allows the fiber slurry to flow out from the first flow box onto the inclined traveling portion of the papermaking net that runs obliquely upward, and the inclined line and the flooded line in the first flow box. It can be obtained by pouring the fiber slurry from the second flow box in which the lower part of the flow box is located in the vicinity of the intersection with the part.
[Selection] Figure 1

Description

  The present invention relates to a gas diffusion electrode for a polymer electrolyte fuel cell (hereinafter abbreviated as a gas diffusion electrode) and a method for producing the same.

  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 problems. That is, an object of the present invention is to provide a gas diffusion electrode that can maintain good gas diffusibility through a porous membrane, thereby maintaining good battery characteristics. Another object of the present invention is to provide a gas diffusion electrode capable of uniform gas permeation with little pressure loss and capable of supplying hydrogen gas and oxygen gas uniformly to the catalyst layer. Another object of the present invention is to provide a method for producing the gas diffusion electrode.

The gas diffusion electrode of the present invention that solves the above problems is a gas diffusion electrode for a polymer electrolyte fuel cell in which two or more layers of conductive nonwoven fabric are laminated, and the average fiber diameter in the uppermost conductive nonwoven fabric and The average fiber diameter in the lowermost conductive nonwoven fabric is different.
The average fiber diameter in the uppermost conductive nonwoven fabric is preferably 1 μm or less and the average fiber length is preferably 10 mm or less, and the average fiber diameter in the lowermost conductive nonwoven fabric is 5 μm to 5000 μm. Preferably there is.
The conductive nonwoven fabric is preferably made of carbon fiber, and the carbon fiber is preferably at least one of polyacrylonitrile-based carbon fiber, phenol-based carbon fiber, pitch-based carbon fiber, and carbon nanotube.
Further, the conductive nonwoven fabric is made of conductive fibers in which carbon particles are coated on resin fibers, and the resin component of the resin fibers is polypropylene, polyethylene, polyamide, semi-aromatic polyamide, aromatic polyamide, polyester, polyarylate , Melamine, polyimide, polyamideimide, polyphenylsulfone, polyacetal, polyparaphenylenebenzobisoxazole, polybenzimidazole, polyetheretherketone, and polyketone.

Further, the conductive nonwoven fabric includes a fluorine resin or a mixture of carbon particles and a fluorine resin, the fluorine resin is polyvinylidene fluoride and / or a copolymer thereof, and the fluorine resin is vinylidene fluoride and hexagon. It is preferably a copolymer of fluoropropylene and / or a copolymer of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene.
Moreover, it is preferable that the gas diffusion electrode has a film thickness change rate of 10% or less by pressurization at 120 ° C., 10 MPa for 5 minutes.
In addition, the method for producing a gas diffusion electrode of the present invention allows the fiber slurry to flow from the first flow box onto the inclined traveling portion of the papermaking net that runs obliquely upward, and the submerged line in the first flow box. A non-woven fabric having a plurality of layers is formed by pouring the fiber slurry out of the second flow box in which the lower part of the flow box is positioned in the vicinity of the intersection between the inclined traveling part and the inclined traveling part.

  The gas diffusion electrode of the present invention has the functions of gas introduction, gas diffusion, and gas fine dispersion, and has a small pressure loss and allows uniform gas permeation and can supply gas uniformly to the catalyst layer. . Furthermore, as another function, the gas diffusion electrode is excellent in mechanical strength and 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 gas diffusion electrode for polymer electrolyte fuel cells of this invention. It is explanatory drawing which shows the cross-sectional layer structure of the gas diffusion electrode for other polymer electrolyte fuel cells of this invention. It is sectional drawing which shows the structure of the multi-tank inclination type wet paper machine concerning this invention. It is sectional drawing which shows the structure of the other multi-tank inclination type wet paper machine concerning this invention. It is sectional drawing which shows the structure of the other multi-tank inclination type wet paper machine concerning this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The gas diffusion electrode T of the present invention is composed of two or more layers of a conductive nonwoven fabric comprising at least the uppermost conductive nonwoven fabric 2 and the lowermost conductive nonwoven fabric 1 as shown in the cross-sectional layer configuration of FIG. Further, the gas diffusion electrode T of the present invention has an inner conductive nonwoven fabric 3 between the uppermost conductive nonwoven fabric 2 and the lowermost conductive nonwoven fabric 1 as shown in the cross-sectional layer configuration of FIG. May be. The gas diffusion electrode of the present invention is not limited to the stacked configuration of FIG. 1 or FIG.

  In the gas diffusion electrode of the present invention, the average fiber diameter in the uppermost conductive nonwoven fabric and the average fiber diameter in the lowermost conductive nonwoven fabric are different. The average fiber diameter here means an average of fiber diameters at 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. Moreover, the average fiber length in the conductive nonwoven fabric described below refers to the average fiber length of 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. is there.

  The average fiber diameter in the uppermost conductive nonwoven fabric (hereinafter referred to as the uppermost fiber diameter) is preferably 1 μm or less and the average fiber length is preferably 10 mm or less. The pore diameter formed by the uppermost conductive nonwoven fabric is preferably about 1 to 10 μm from the viewpoint of preventing flooding, and when the uppermost fiber diameter is 1 μm or less, the pore diameter range can be easily controlled.

On the other hand, in the present invention, H ₂ or O ₂ gas flows from the uppermost conductive nonwoven fabric to the cross section of the lowermost conductive nonwoven fabric 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 gas diffusion electrode 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 that gas flows into the membrane-electrode assembly (hereinafter referred to as MEA). In addition to the amount being uneven 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 gas diffusion electrode becomes uniform in the surface direction.

  In the gas diffusion electrode of the present invention, the conductive nonwoven fabric constituting each layer such as the uppermost layer, the lowermost layer and the inner layer is formed of carbon fibers or conductive fibers obtained by coating resin particles with carbon particles. It is preferable. 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 present invention is preferably polyvinylidene fluoride (hereinafter referred to as PVdF) and / or a copolymer thereof. In particular, the fluororesin is a copolymer of vinylidene fluoride and hexafluoropropylene. It is preferably a polymer (hereinafter referred to as P (VdF-HFP)) and / or a copolymer of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene (hereinafter referred to as P (TFE-VdF-HFP)).
As the fluororesin in the present invention, those described above capable of achieving both water repellency and adhesiveness are preferably used. However, in the gas diffusion electrode on the anode side and the gas diffusion electrode on the cathode side, various types of water repellency can be used. It can be adjusted by the mixing ratio of the resin. That is, PVdF and P (VdF-HFP) are suitable for fixing the carbon particles to the resin fiber, but P (TFE-VdF-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 gas diffusion electrode may be reduced, and the adhesion with the catalyst layer may be uneven.

In the present invention, a gas diffusion electrode in which the rate of change in film thickness by pressurization at 120 ° C., 10 MPa for 5 minutes is 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 assembling a fuel cell, it is desirable that the gas diffusion electrode and the catalyst layer are pressure-bonded for the purposes of gas supply, electric heating, and current collection. Further, the gas diffusion electrode 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.

  The gas diffusion electrode of the present invention may further contain a filler other than the above carbon material. 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 affects 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. However, in consideration of the environment inside the gas diffusion electrode in the fuel cell, inorganic fillers can be used. Fine particles are 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 gas diffusion electrode 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 gas diffusion electrode 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 gas diffusion electrode is preferably 5 μm to 5000 μm, more preferably 10 μm to 4000 μm, and still more 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 in the gas diffusion electrode 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 thickness of the gas diffusion electrode 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 the above. It is preferable for the reason.
Density (g / cm ³ ) = mass per unit area / (film thickness × unit area) (2)

  The pore diameter is preferably in the range of 0.5 μm to 10 μm, more preferably 3 μm or more, and even more preferably 5 μm 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 gas diffusion electrode of this invention is explained in full detail.
With respect to the method for producing the gas diffusion electrode of the present invention, various nonwoven fabric production methods are used. In particular, a 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 the uppermost layer and the lowermost layer of the conductive nonwoven fabric used in the present invention are integrally formed. As a manufacturing method for integrally forming such layers, the gas diffusion electrode manufacturing method of the present invention is such that the fiber slurry is poured out from the first flow box onto the inclined traveling portion of the papermaking net traveling obliquely upward. At the same time, a plurality of layers of non-woven fabric is formed by pouring the fiber slurry from the second flow box in which the lower part of the flow box is located in the vicinity of the intersection of the floodline and the inclined traveling part in the first flow box. A production method is preferred.

The gas diffusion electrode manufacturing method of the present invention uses the multi-tank inclined wet paper machine shown in FIG. In the multi-tank inclined wet paper machine of FIG. 3, 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, the flow box has two stages in the example of FIG. 3, but it may have a number of flow boxes of three or more stages including the third flow box 20 as shown in FIG.

In the present invention, a gas diffusion electrode is manufactured using the multi-tank inclined 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. 3 and is inclined with the water 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. The sheet taken out after drying and obtained after peeling off the polyethylene terephthalate film becomes the gas diffusion electrode of the present invention.

  In the gas diffusion electrode manufacturing method of the present invention, the nonwoven fabric is formed so that the inner diameter decreases continuously toward the uppermost layer by continuously decreasing the fiber diameter from the lowermost layer toward the uppermost layer. Is possible. This makes it possible to reduce the flow resistance of the gas flowing in from the bottom layer by making the path to the top layer continuously small and uniform, thereby reducing the flow resistance of the gas from the top layer of the gas diffusion electrode toward the catalyst phase. Therefore, it is possible to supply a very uniform gas with little variation in the surface direction. Further, by using such a manufacturing method, the fibers of the uppermost layer and the other layers are entangled so that the interface between the two layers is substantially eliminated, or the fibers of the uppermost layer are entangled with the fibers of the other layers at the interface. Thus, it becomes possible to bind the interface between both layers without a binder by the anchor effect.

Moreover, the multi-tank inclination type wet paper machine shown in FIG. 5 may be used for the manufacturing method of the gas diffusion electrode of the present invention. In the multi-tank inclined wet paper machine shown in FIG. 5, 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, by the manufacturing method of the present invention, fibers and nonwoven fabrics made of different materials are entangled with each other from the lowermost layer to the uppermost layer, so that the pore size continuously decreases from the lowermost layer to the uppermost layer. In addition, since it can be formed in one step, it can contribute to improvement in productivity.

Further, if both the lowermost layer and the inner layer portion located immediately above are formed of an existing non-woven fabric and wet-made with two unwinding rolls in the same manner as described above, four layers can be formed. It is also possible to form a three-layered non-woven fabric once, and similarly form an inner layer portion and an uppermost layer portion thereon, so as to form an inclined structure with a more gradual change in pore diameter.
The present invention will be described more specifically with reference to examples. A gas diffusion electrode was prepared as follows, and then a polymer electrolyte fuel cell in which the gas diffusion electrode was disposed on both the fuel electrode side and the oxygen electrode side was prepared and evaluated.

In the multi-tank wet type wet paper machine shown in FIG. 5, a polyarylate nonwoven fabric having an average fiber diameter of 20 μm (basis weight 50 g / m ² ) was disposed on the unwinding roll 30 as the lowermost layer. In addition, a slurry of polyarylate fibers having an average fiber diameter of 5 μm is introduced as the fiber slurry 16 in the first flow box 14, and an average fiber diameter of 0.3 μm and an average fiber length as the fiber slurry 17 in the second flow box 15. A slurry of 3 mm MF aramid fibers was introduced. And the papermaking sheet | seat 1 which integrated three types of fiber so that the nonwoven fabric of polyarylate fiber might become a basic weight of 30 g / m < ² >, and the nonwoven fabric of MF aramid fiber might become a basic weight of 10 g / m < ² > was obtained.

  Next, 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 and mixed. A solvent was obtained. Next, 45 parts by mass of diethylene glycol was mixed and stirred to obtain paint 1.

  Next, the paint 1 is cast on a polyethylene terephthalate film, and the papermaking sheet 1 obtained by the above operation is laid down on the paint 1 before being put into the drying process, so that the paint 1 soaks into the whole papermaking sheet. The paint 1 and the papermaking sheet were integrated with each other and dried in an oven. It took out after drying, peeled off the polyethylene terephthalate film, and obtained the gas diffusion electrode 1 of this invention.

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, the gas diffusion electrode 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. 5, a nonwoven fabric in which a polyacrylonitrile carbon fiber having an average fiber diameter of 30 μm and a polyarylate fiber having an average fiber diameter of 20 μm are mixed at a mass ratio of 6: 4 to an unwinding roll 30 as the lowermost layer (Basis weight 50 g / m ² ) was arranged. Further, a slurry of polyacrylonitrile-based carbon fiber having an average fiber diameter of 5 μm is introduced as the fiber slurry 16 in the first flow box 14, and an average fiber diameter of 0.2 μm and an average is obtained as the fiber slurry 17 in the second flow box 15. A slurry of MF aramid fiber having a fiber length of 2 mm was introduced. And the papermaking sheet | seat 2 which integrated three types of fibers so that the nonwoven fabric of polyacrylonitrile-type carbon fiber may become a basic weight of 30 g / m < ² >, and the nonwoven fabric of MF-ized aramid fiber may become a basic weight of 10 g / m < ² > was obtained.
Next, the coating material 1 obtained in Example 1 was cast on a polyethylene terephthalate film, and the papermaking sheet 2 obtained by the above operation was laid down on the coating material 1 before being put into the drying process. The paint 1 and the papermaking sheet were integrated so that the paint 1 soaked into the paper, and then dried in an oven. It took out after drying, peeled off the polyethylene terephthalate film, and obtained the gas diffusion electrode 3 of this invention.

  A gas diffusion electrode 4 of the present invention was obtained in the same manner as in Example 3, except that the paint 2 obtained in Example 2 was used instead of the paint 1.

[Comparative Example 1]
In Example 1, instead of the polyarylate nonwoven fabric having an average fiber diameter of 20 μm (basis weight 50 g / m ² ) disposed on the unwinding roll 30 as the lowermost layer, an average fiber diameter of 0.3 μm (basis weight 50 g / m ² ) A comparative gas diffusion electrode 5 was obtained in the same manner except that a polyethylene nonwoven fabric was used.

(Thickness change rate)
In order to confirm the degree of void collapse by hot pressing per unit area of the gas diffusion electrodes obtained in Examples 1 to 4 and Comparative Example 1, hot pressing (120 ° C., 10 MPa, 5 minutes) was performed to change the film thickness. (%) Was measured. The results are shown in Table 1.

(Solid polymer fuel cell)
(1) Production of polymer electrolyte fuel cell As the gas diffusion electrode for the fuel cell 1, one 50 mm square gas diffusion electrode 1 and one gas diffusion electrode 2 of the present invention obtained above were prepared. Further, as the gas diffusion electrode for the fuel cell 2, one 50 mm square gas diffusion electrode 3 and one gas diffusion electrode 4 of the present invention obtained above were prepared. Two gas diffusion electrodes 5 of 50 mm square for comparison obtained above were prepared as gas diffusion electrodes for the fuel cell 3. A catalyst paint composed of carbon and ion conductive resin carrying a platinum catalyst and a mixed solvent of water and ethanol is applied to the surface of the uppermost layer side of the gas diffusion electrode and dried to form a catalyst layer. A gas diffusion electrode was obtained. The amount of each platinum catalyst was 0.3 mg / cm ² . Next, the gas diffusion electrode with the catalyst layer is arranged so that the catalyst layer surface is in contact with the electrolyte membrane (manufactured by DuPont, trade name: Nafion 117), and the gas with the catalyst layer is formed by hot pressing (120 ° C., 10 MPa, 10 minutes). The diffusion electrode and the electrolyte membrane were joined to obtain a membrane-electrode assembly. A graphite separator having a smooth surface was disposed on both sides of the obtained membrane-electrode assembly, and the fuel cells 1 to 3 for evaluation were produced by incorporating the separator into a single cell. In the fuel cell 1, the gas diffusion electrode 1 is disposed on the fuel electrode side, and the gas diffusion electrode 2 is disposed on the air electrode side. In the fuel cell 2, the gas diffusion electrode 3 is disposed on the fuel electrode, and the gas diffusion electrode 4 is disposed on the air electrode side. In the fuel cell 3, the gas diffusion electrode 5 was used for both the fuel electrode side and the air electrode side.

(2) Evaluation of polymer electrolyte fuel cell The power generation characteristics of the fuel cells 1 to 3 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 2.

As shown in Table 2, the fuel cells 1 and 2 provided with the gas diffusion electrodes obtained in Examples 4 to 4 have a current density of 1 A than the fuel cell 3 provided with the gas diffusion electrodes obtained in Comparative Example 1. The voltage at / cm ² was high, and the power generation characteristics were excellent. In the fuel cell 3, since the lowermost nonwoven fabric was polyethylene and the change in the film thickness due to compression was large, the porosity was low and the power generation performance was low.

DESCRIPTION OF SYMBOLS 1 Bottom layer conductive nonwoven fabric 2 Top layer conductive nonwoven fabric 3 Inner layer conductive nonwoven fabric T Gas diffusion electrode for polymer electrolyte fuel cell

Claims (12)

  A gas diffusion electrode for a polymer electrolyte fuel cell formed by laminating two or more conductive nonwoven fabrics, wherein the average fiber diameter in the uppermost conductive nonwoven fabric is different from the average fiber diameter in the lowermost conductive nonwoven fabric A gas diffusion electrode for a polymer electrolyte fuel cell.   2. The gas diffusion electrode for a polymer electrolyte fuel cell according to claim 1, wherein the uppermost conductive nonwoven fabric has an average fiber diameter of 1 μm or less and an average fiber length of 10 mm or less.   3. The gas diffusion electrode for a polymer electrolyte fuel cell according to claim 1, wherein the lowermost conductive nonwoven fabric has an average fiber diameter of 5 μm to 5000 μm.   The gas diffusion electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the conductive nonwoven fabric is made of carbon fiber.   The gas diffusion for a polymer electrolyte fuel cell according to claim 4, wherein the carbon fiber is at least one of polyacrylonitrile-based carbon fiber, phenol-based carbon fiber, pitch-based carbon fiber, and carbon nanotube. electrode.   The gas diffusion electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the conductive non-woven fabric is made of conductive fibers obtained by coating resin particles with carbon particles.   The resin component of the resin fiber is polypropylene, polyethylene, polyamide, semi-aromatic polyamide, aromatic polyamide, polyester, polyarylate, melamine, polyimide, polyamideimide, polyphenylsulfone, polyacetal, polyparaphenylenebenzobisoxazole, poly The gas diffusion electrode for a polymer electrolyte fuel cell according to claim 6, comprising at least one of benzimidazole, polyetheretherketone, and polyketone.   The gas diffusion electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the conductive nonwoven fabric contains a fluorine resin or a mixture of carbon particles and a fluorine resin.   The gas diffusion electrode for a polymer electrolyte fuel cell according to claim 8, wherein the fluororesin is polyvinylidene fluoride and / or a copolymer thereof.   9. The fluororesin is a copolymer of vinylidene fluoride and hexafluoropropylene and / or a copolymer of tetrafluoroethylene, vinylidene fluoride and hexafluoropropylene. Gas diffusion electrode for polymer electrolyte fuel cells.   The gas diffusion electrode for a polymer electrolyte fuel cell according to any one of claims 1 to 10, wherein the rate of change in film thickness at 120 ° C, 10 MPa, and pressurization for 5 minutes is within 10%.   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 flow box is disposed in the vicinity of the intersection of the floodline and the inclined traveling portion in the first flow box. A method for producing a gas diffusion electrode for a polymer electrolyte fuel cell, comprising forming a plurality of layers of nonwoven fabric by pouring a fiber slurry from a second flow box having a lower portion.

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