JP2006049184A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell equipped with a water repellent layer suppressing the elution of a water repellent. <P>SOLUTION: The water repellent layer 23 increasing water repellency is installed between a catalyst layer 21 of an anode or a cathode of the fuel cell and a gas diffusion layer 22, and the water repellent layer 23 prevents the elution of the water repellent 34 by laminating a first layer 33 comprising conductive particles 32 and the water repellent 34 attached to the conductive particles 32 and a second layer 33 comprising conductive particles, and making a vacancy size between the conductive particles of the second layer 33 smaller than the particle size of the water repellent 34. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell provided with a water repellent layer.

  In a fuel cell that generates hydrogen by supplying hydrogen to the fuel electrode (anode) and supplying air or oxygen to the oxidant electrode (cathode), water is generated at the cathode. Especially in high humidification and high current density operation where water is easily generated, the generated water of the cathode accumulates in the electrolytic layer, and is blocked by the generated water, so that the reactant is not sufficiently supplied to the electrode, and the battery output is reduced. A phenomenon occurs. Therefore, in order to increase the output of the fuel cell, it is necessary to discharge water from the cathode.

Conventionally, a water repellent layer is provided between the cathode catalyst layer and the gas diffusion layer to drain water from the cathode, and the water repellent weight of the water repellent layer is inclined to improve water repellency. It is disclosed in Document 1.
Japanese Patent Laid-Open No. 2003-092112

  However, a phenomenon occurs that the water repellent in the water repellent layer is eluted to the gas flow path or the catalyst layer due to the influence of the generated water accumulated by the long operation of the fuel cell. As a result, the water repellent effect of the water repellent layer is reduced, and a flattening phenomenon is likely to occur. In particular, when the water repellent weight of the water repellent layer is inclined as in the above-described invention, the portion where the water repellent weight is large has a large pore diameter between the carbon particles provided with the water repellent, and the water repellent. The portion having a small weight has a small pore diameter. For this reason, when water repellent particles in a portion having a large water repellent weight are eluted, pores spread, and the water repellent begins to elute from the water repellent layer one after another, resulting in poor durability of the water repellent layer. is there.

  The present invention has been invented to solve such problems, and aims to suppress elution of the water repellent from the water repellent layer.

  In the present invention, in a fuel cell having a water-repellent layer disposed between the anode or cathode catalyst layer and the gas diffusion layer of the fuel cell and improving the drainage of the fuel cell, the water-repellent layer is composed of conductive particles and conductive layers. The first layer composed of the water repellent adhered to the conductive particles and the second layer composed of the conductive particles are laminated.

  According to the present invention, the water repellent layer provided to enhance drainage from the fuel cell is composed of the first layer having a water repellent and the second layer having no water repellent. Even when the agent deviates from the first layer, it is possible to suppress the elution of the water repellent by the second layer not having the water repellent.

  A configuration of a fuel cell system including the fuel cell 1 according to the first embodiment of the present invention will be described with reference to the schematic diagram of FIG. This fuel cell system includes a fuel cell 1, a hydrogen cylinder 3 that supplies hydrogen to the anode 2 of the fuel cell 1, and a compressor 5 that supplies air to the cathode 4. In addition, current collectors 6 that take out the electric power generated by the fuel cell 1 are provided at both ends of the fuel cell 1, and the electric power generated by the fuel cell 1 is consumed by the load 7.

  Hydrogen supplied from the hydrogen cylinder 3 to the anode 2 via the hydrogen supply manifold 8 is consumed by the fuel cell 1, and residual hydrogen not consumed by the fuel cell 1 is discharged as hydrogen through the hydrogen discharge manifold 9 to the fuel cell. 1 is discharged. A shutoff valve 10 is provided between the hydrogen cylinder 3 and the hydrogen supply manifold 8 to selectively switch the hydrogen supply to the anode 2, and discharge of discharged hydrogen from the anode 2 to the outside is provided downstream of the hydrogen discharge manifold 9. A shut-off valve 11 is provided for selectively switching between. When the fuel cell 1 is stopped, the shutoff valves 10 and 11 are closed to fill the anode 2 with hydrogen, thereby preventing air from entering the anode 2 from the outside. Since no air is mixed into the anode 2, the fuel cell 1 can be started without reacting hydrogen and oxygen in the air at the anode 2 at the next start-up, and deterioration of the fuel cell 1 can be prevented. . Moreover, the pressure of the anode 2 can be controlled by controlling the shutoff valves 10 and 11.

  Air supplied from the compressor 5 to the cathode 4 via the air supply manifold 12 is consumed by the fuel cell 1, and residual air not consumed by the fuel cell 1 is discharged as air via the air discharge manifold 13. Discharged from. A shutoff valve 14 for selectively switching the air supply is provided between the compressor 5 and the air supply manifold 12, and the discharge of the exhaust air from the cathode 4 to the outside is selectively switched downstream of the air discharge manifold 13. A shutoff valve 15 is provided. By controlling the shutoff valves 14 and 15, the pressure of the cathode 4 can be controlled.

  Furthermore, a flow rate controller 16 that controls the flow rate of hydrogen from the startup state of the fuel cell 1 and a controller 60 that controls the compressor 5 that controls the air flow rate and controls the shut valves 10, 11, 14, 15 are provided.

  The fuel cell 1 will now be described with reference to the schematic diagram of FIG. The fuel cell 1 is configured by stacking unit cells 500. The unit cell 50 includes a polymer electrolyte membrane 20 (hereinafter referred to as an electrolyte membrane), an anode 2 provided on one surface of the electrolyte membrane 20, a cathode 4 provided on the other surface of the electrolyte membrane 20, and hydrogen. A separator 28 having a flowing hydrogen channel 29 and a separator 31 having an air channel 30 through which air flows are configured. In addition, in the separators 28 and 30 of FIG. 2, the hydrogen flow path 29 or the air flow path 31 is provided on one surface, but the surface opposite to the surface provided with the hydrogen flow path 29 or the air flow path 31 is also provided. A channel through which hydrogen or air flows may be provided.

  The anode 2 is configured by stacking a catalyst layer 21 such as platinum, a gas diffusion layer 22 for diffusing hydrogen in the catalyst layer 21, and a water repellent layer 23 between the catalyst layer 21 and the gas diffusion layer 22. By providing the water repellent layer 23 between the catalyst layer 21 and the gas diffusion layer 22, for example, even when water generated by the cathode 4 penetrates the anode 2 through the electrolyte membrane 20, the drainage of the permeated water is improved. It is possible to improve and prevent flatting. Further, even when hydrogen is humidified to prevent the electrolyte membrane 20 from drying, the electrolyte membrane 20 can be uniformly humidified.

  The cathode 4 is formed by stacking a catalyst layer 25 such as platinum, a gas diffusion layer 26 for diffusing hydrogen in the catalyst layer 25, and a water-repellent layer 27 between the catalyst layer 25 and the gas diffusion layer 26. By providing the water repellent layer 27 between the catalyst layer 25 and the gas diffusion layer 26, the drainage of the water generated at the cathode 4 can be improved.

  Next, the water-repellent layers 23 and 27 of this embodiment will be described in detail with reference to the schematic diagram of FIG. 3 is a schematic view of the water repellent layer 23 of the anode 2, but the water repellent layer 27 of the cathode 4 has the same configuration.

  The water repellent layer 23 provided between the catalyst layer 21 and the gas diffusion layer 22 includes a carbon layer (second layer) 33 composed of only carbon particles (conductive particles) 32, a water repellent 34, and carbon particles. A carbon water-repellent layer (first layer) 35 composed of 32 is laminated. Here, carbon black is used as the carbon particles 32 and PTFE is used as the water repellent 34, but other materials may be used.

  A schematic view of the carbon layer 33 as viewed from above is shown in FIG. The carbon layer 33 is disposed so that the adjacent carbon particles 32 are in contact with each other, and has a hole 36 between the adjacent carbon particles 32. The carbon particles 32 are not limited to the arrangement shown in FIG.

  Similarly to FIG. 4, the carbon water repellent layer 35 is also arranged so that the carbon particles 32 having the water repellent 34 are in contact with each other, that is, the water repellent 34 is in contact with each other. The particle size of the water repellent 34 is larger than the pores 36 constituted by the carbon particles 32 of the carbon layer 33. Thus, for example, when the water repellent 34 is separated from the carbon particles 32 when the fuel cell 1 is started for a long time, it is possible to prevent the water repellent 34 from being eluted from the holes 36. Here, the carbon layer 33 is laminated so as to be in contact with the catalyst layer 21 and the gas diffusion layer 22. That is, both ends of the water-repellent layer 23 in the stacking direction are carbon layers 33 so that the carbon water-repellent layer 35 is not in direct contact with the catalyst layer 21 and the gas diffusion layer 22. This can prevent the water repellent 34 from eluting from the water repellent layer 23. The carbon layers 33 and the carbon water repellent layers 35 are desirably laminated alternately or at a predetermined interval. As a result, the movement of the water repellent 34 deviated from the carbon particles 32 can be restricted, the uneven distribution of the water repellent 34 can be reduced, and the electrical resistance of the fuel cell 1 can be reduced.

  As a method for producing the water repellent layer 23, a slurry containing carbon particles 32 is applied to the gas diffusion layer 22 and dried, and then a slurry containing carbon particles 32 and a water repellent 34 is applied and dried. By repeating these steps, the water repellent layer 23 is formed. Finally, a slurry made of carbon particles 32 is applied. As a result, the layer in contact with the catalyst layer 21 becomes the carbon layer 33 and the water repellent 34 and elution can be prevented. A layer other than the layer in contact with the catalyst layer 21 and the layer in contact with the gas diffusion layer 22 may be the carbon water repellent layer 31, or the carbon layer 33 and the carbon water repellent layer 35 may be alternately stacked at a predetermined stacking interval. . As the coating device, a coater device such as a bar coater is used. Moreover, you may spray the powder which grind | pulverized after drying the slurry.

  The effect of 1st Embodiment of this invention is demonstrated.

  The water-repellent layers 23 and 27 when the present invention is not used will be described with reference to FIG. FIG. 5 is a schematic view of the water repellent layer 23 of the anode 2. Here, the water-repellent layer 23 provided between the catalyst layer 21 and the gas diffusion layer 22 is not provided with the carbon layer 33 made of only the carbon particles 32, but the carbon water-repellent layer 35 made of the carbon particles 32 and the water-repellent agent 34. A water repellent layer 23 is formed. Since the carbon particles 32 have the water repellent 34, the distance between the carbon particles 32 becomes long. Therefore, when the water repellent 34 is separated from the carbon particles 32, the water repellent 34 may pass between the carbon particles 32 and be eluted from the water repellent layer 23. Further, when the electrical resistance of the water repellent 34 is large, if the eluted water repellent 34 is unevenly distributed, the electrical resistance of the water repellent layer 23, that is, the electrical resistance of the fuel cell 1 may be increased. There is a possibility of reducing the power generation efficiency of the battery 1.

  In this embodiment, the water repellent layer 23 is formed by laminating a carbon layer 33 made of carbon particles 32 and a carbon water repellent layer 35 made of carbon particles 32 having a water repellent 34. Since the pores 36 between the carbon particles 32 are smaller than the water repellent 34 in the carbon layer 33, the water repellent 34 is prevented from eluting from the water repellent layer 23 even when the water repellent 34 is separated from the carbon particles 32. be able to. In addition, the uneven distribution of the water repellent 34 can be prevented, the electrical resistance of the fuel cell 1 can be prevented from increasing, and the power generation efficiency of the fuel cell 1 can be prevented from being lowered.

  By providing a carbon layer 33 with high conductivity on a part of the water repellent layer 23, the electrical resistance of the water repellent layer 31 can be reduced, and the power generation efficiency of the fuel cell 1 can be improved.

  Moreover, elution of the water repellent 34 can be reliably prevented by using the carbon layer 33 as the layer in contact with the catalyst layer 21 or the gas diffusion layer 22.

  Next, a second embodiment of the present invention will be described using the schematic diagram of FIG. 6 is a schematic view of the water repellent layer 23 of the anode 2, but the water repellent layer 27 of the cathode 4 has the same configuration. In this embodiment, in the water repellent layer 23, a minute carbon layer 38 composed of minute carbon particles 37 having a small particle diameter is provided on the layer in contact with the catalyst layer 21 or the gas diffusion layer 22. As a result, the pores 39 between the minute carbon particles 37 become smaller. Therefore, elution of the water repellent 34 can be further prevented. Since other configurations are the same as those in the first embodiment, description thereof is omitted here. The fine carbon layer 38 may be provided in addition to the catalyst layer 21 or the layer in contact with the gas diffusion layer 22.

  As a method for producing the water repellent layer 23, a slurry composed of small carbon particles 37 having a small particle diameter is applied to the gas diffusion layer 22, and then a slurry composed of the carbon particles 32 and the water repellent 34 is applied. Then, the application of the slurry composed of the carbon particles 32 or the slurry composed of the carbon particles 32 and the water repellent 34 is repeated. Finally, a slurry made of fine carbon particles 37 is applied again to form the water repellent layer 23. As a result, the catalyst layer 21 or the layer in contact with the gas diffusion layer 22 becomes the fine carbon layer 38, and the elution of the water repellent 34 can be further prevented. Note that a coater such as a bar coater is used as the coating device. Moreover, you may spray the powder which grind | pulverized after drying the slurry.

  The effect of 2nd Embodiment of this invention is demonstrated.

  In this embodiment, in addition to the effects of the first embodiment, the layer in contact with the catalyst layer 21 or the gas diffusion layer 22 becomes a small carbon layer 38 with a small particle diameter, and the pores 39 between the small carbon layers 38 become small, The elution of the water repellent 34 can be further prevented. Further, the contact resistance with the catalyst layer 21 or the gas diffusion layer 22 can be reduced, and the power generation efficiency of the fuel cell 1 can be improved.

  It goes without saying that the present invention is not limited to the above-described embodiments, and includes various modifications and improvements that can be made within the scope of the technical idea.

  It can be used in various fields equipped with fuel cells.

It is the schematic of the fuel cell system using the fuel cell of this invention. It is the schematic of the fuel cell of this invention. It is the schematic of the water repellent layer of 1st Embodiment of this invention. It is a top view of the carbon layer of the present invention. It is the schematic of a water repellent layer when not using this invention. It is the schematic of the water repellent layer of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 Anode 3 Cathode 23 Water repellent layer 27 Water repellent layer 32 Carbon particle (particle)
33 Carbon layer (second layer)
34 Water repellent 35 Carbon water repellent layer (first layer)
36 pores 37 minute carbon particles 39 pores

Claims (4)

In a fuel cell comprising a water repellent layer disposed between a catalyst layer and a gas diffusion layer of an anode or a cathode of the fuel cell and enhancing the drainage of the fuel cell,
The water repellent layer is
A first layer composed of conductive particles and a water repellent adhering to the conductive particles;
A fuel cell comprising: a second layer composed of the conductive particles.   2. The fuel cell according to claim 1, wherein a pore diameter between the conductive particles of the second layer is smaller than a particle diameter of the water repellent.   3. The fuel cell according to claim 1, wherein layers positioned at both ends of the water repellent layer in the stacking direction are the second layers.   4. The fuel according to claim 3, wherein the conductive particles of the layers located at both ends in the stacking direction of the second layer have a smaller particle size than the conductive particles of the other second layer. battery.

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