JP2005294121A - Gas diffusion layer and fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas diffusion layer ensuring a gas passage without increasing the number of constitution members of a fuel cell even when a smooth surface separator is used, and to provide the fuel cell using the gas diffusion layer. <P>SOLUTION: The gas diffusion layer 4 is arranged between the separator 6 and a membrane electrode assembly 3, and has a partition 7 forming the gas passage inside the gas diffusion layer, and the fuel cell uses the gas diffusion layer. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gas diffusion layer having a gas flow path formed therein and a fuel cell using the same.

  As shown in FIG. 3, a unit cell, which is the minimum power generation unit of a solid polymer electrolyte fuel cell, generally has a membrane electrode assembly 3 having catalyst electrodes 2 bonded to both sides of an electrolyte membrane 1, and this membrane electrode Gas diffusion layers 4 are arranged on both sides of the composite 3. Further, a separator 6 having a gas flow path 5 is disposed outside thereof, and a fuel gas and an oxidant gas supplied to the catalyst electrode 2 of the membrane electrode assembly 3 through the gas diffusion layer 4 are passed. In addition to current flow, it works to transmit the current obtained by power generation to the outside.

  In power generation using a fuel cell, water is generated by the reaction of hydrogen and oxygen. If the water generated during this reaction remains in the gas diffusion layer 4 without being drained, so-called flooding occurs, and the supply of fuel gas to the catalyst electrode 2 is hindered by the accumulated water, resulting in a decrease in fuel cell performance. It will lead to. Therefore, the role of the gas flow path is great not only for the supply of fuel gas and oxidant gas but also as a drainage path for water generated by the reaction.

  In the conventional fuel cell, since the gas flow path is provided on the separator surface, it is necessary to perform processing for forming the gas flow path in the separator. In addition, a gas channel groove is formed on the separator surface, and the thickness of the separator needs to be increased accordingly.

  In particular, when the separator is made of metal, a gold plating process on the surface is necessary to prevent corrosion. However, when the gas flow path is formed on the surface, the shape of the surface of the separator becomes complicated, and there is a problem that it is not easy to uniformly perform gold plating on the surface of such a complicated shape. . For this reason, a method of using a separator having a smooth surface and securing a gas flow path is required.

  Patent Document 1 discloses a method for securing a gas flow path by disposing carbon paper cut into a pattern between a separator and a gas diffusion layer. However, according to this method, the number of constituent members is increased as compared with the conventional fuel cell, and the thin carbon paper cut into a pattern is easily damaged, and requires careful handling for handling. there were.

JP 2000-123850 A JP 2000-299113 A

  The present invention has been made in view of the above problems, and even when a separator having a smooth surface is used, a gas diffusion layer capable of ensuring a gas flow path without increasing the number of components of the fuel cell, and The main object is to provide a fuel cell using the same.

  In order to achieve the above object, the present invention has a gas diffusion layer disposed between a separator and a membrane electrode assembly in a fuel cell, and has a partition wall that forms a gas flow path in the gas diffusion layer. A gas diffusion layer is provided.

  In the gas diffusion layer of the present invention, the flow of water generated by the fuel gas, the oxidant gas, or the reaction can be formed by the gas flow path formed by the partition walls described above. Therefore, it is not necessary to form a gas flow path for the separator used with this gas diffusion layer, and a separator having a smooth surface can be used.

  In the said invention, it is preferable that the said partition is comprised from resin which has water repellency. This is because the partition walls preferably have water repellency in order to smoothly drain water generated during power generation.

  The present invention also provides a fuel cell comprising the gas diffusion layer described above, and a separator surface in contact with the gas diffusion layer being a flat surface. By using the gas diffusion layer in which the gas flow path is formed in the fuel cell, a separator having a smooth surface on the gas diffusion layer side can be used. Therefore, it is not necessary to form a gas flow path in the separator as in the prior art, so that the separator can be made thinner by that amount, and a miniaturized fuel cell can be obtained.

  Even when a separator having a smooth surface is used, the gas diffusion layer of the present invention can secure a gas flow path without increasing the number of constituent members, and has the effects of downsizing the fuel cell and reducing costs.

  The gas diffusion layer and fuel cell of the present invention will be described in detail below.

A. Gas diffusion layer The gas diffusion layer of the present invention is a gas diffusion layer disposed between a separator and a membrane electrode assembly in a fuel cell, and has a partition wall that forms a gas flow path in the gas diffusion layer. It is characterized by. In the present invention, the portion of the gas diffusion layer other than the partition walls may be referred to as a gas diffusion layer body.

In the gas diffusion layer of the present invention, the flow of the fuel gas and the oxidant gas can be created by the gas flow path formed inside the gas diffusion layer by the partition walls described above. By creating such a gas flow, these gases can move smoothly without staying at a specific location, and the flow of water generated by the reaction is also smoothed to prevent flooding. And it can suppress that the power generation efficiency of a fuel cell falls. Further, since a gas flow path is provided in the gas diffusion layer, it is not necessary to form a gas flow path as a separator used with the gas diffusion layer, and a separator having a smooth surface can be used. Thereby, the thickness of a separator can be made thin, and when a separator is a metal, surface plating can be performed easily.
Hereinafter, the gas diffusion layer of the present invention will be described by dividing it into a partition wall and a gas diffusion layer body.

1. Partition (1) Shape of Partition The shape of the partition formed in the gas diffusion layer of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of a gas diffusion layer of the present invention. As illustrated in FIG. 1, the partition wall 7 is formed so as to be embedded in the gas diffusion layer 4. In this example, the upper surface of the partition wall 7 is formed on the same plane as the upper surface of the gas diffusion layer 4, and the lower surface of the partition wall 7 reaches about half of the thickness of the gas diffusion layer 4. Here, the vertical length of the partition wall 7 in the figure is the height “a”, and the horizontal length is the width “b”.

  The shape of the partition wall, which is a feature of the gas diffusion layer of the present invention, is not particularly limited as long as the gas flow path can be formed, but the separator side surface of the partition wall is the separator side surface of the gas diffusion layer. It is preferable that the same surface. By forming in this way, the surface of the gas diffusion layer on the separator side can be made smooth, so that the adhesiveness when joining the separator as a constituent member of the fuel cell can be kept good.

The height a of the partition wall is not particularly limited as long as it is high enough to form a gas flow path, but the depth is such that the partition wall does not reach the surface of the gas diffusion layer on the catalyst electrode side. Is preferred. Among these, it is more preferable that the partition reaches about half of the thickness of the gas diffusion layer. When the partition wall reaches the surface on the catalyst electrode side and is in contact with the catalyst electrode, the area where the gas diffusion layer body formed of a material having good conductivity such as carbon and the catalyst electrode is in contact with the catalyst electrode decreases. This is because the current collection efficiency of the generated electricity may be reduced.
The height a of the partition wall is preferably in the range of 0.1 to 0.8, and more preferably in the range of 0.7 to 0.8, where the thickness of the gas diffusion layer is 1.

  The width b of the partition wall is not particularly limited as long as the gas flow path can be formed in the gas diffusion layer in a state where gas does not permeate. Specifically, it is preferably in the range of 100 to 1000 μm, and more preferably in the range of 500 to 1000 μm.

  The width of the gas flow path formed by the partition walls is not particularly limited as long as the gas can form a flow. The width of the gas flow path varies greatly depending on the water repellency of the partition walls, the amount of gas to flow, etc., but specifically, it is in the range of 0.5 to 2 mm, particularly in the range of 0.5 to 1 mm. It is preferable. If the width of the gas flow path is less than the above range, the width may not be sufficient with respect to the amount of gas flowing, and if it exceeds the above range, the gas will not flow over the entire surface of the gas flow path, This is because flooding may occur.

  The gas channel pattern formed by the partition walls is not particularly limited, and can be formed in the same manner as the gas channel pattern formed in the conventional separator. Examples of such gas flow path patterns include a straight type and a serpentine type.

(2) Substance constituting the partition The substance that can be used to form the partition as described above is not particularly limited, but it is preferable to use a substance having low gas permeability such as resin or metal. preferable. This is because when the partition walls are formed using a material having high gas permeability such as a porous body, the gas permeates the partition walls and cannot serve as the partition walls forming the gas flow path.

  Moreover, it is preferable that the partition used for this invention has the water repellency on the surface. When the surface of the partition wall forming the gas flow path is not water-repellent, water generated by the power generation reaction may adhere to the partition wall, which may cause water to accumulate in the gas flow path and block the gas flow path. Because. As a method for imparting water repellency to the surface of the partition wall, there are a method of treating the surface of the partition wall with water repellency and a method of forming the partition wall with a water repellent material. It is preferable to form a partition wall. This is because the partition wall can be easily formed.

  As the substance having water repellency as described above, it is preferable to use a fluororesin. It is because it has acid resistance and high water repellency. Examples of such fluorine-based resins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride, polyvinyl fluoride, polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene. -Chlorotrifluoroethylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, perfluorocyclopolymer, vinyl ether-fluoroolefin copolymer, vinyl ester-fluoroolefin copolymer, tetrafluoroethylene-vinyl ether copolymer, chlorotrifluoroethylene-vinyl ether copolymer, Tetrafluoroethylene urethane crosslinked product, tetrafluoroethylene epoxy Hashitai, tetrafluoroethylene acrylic crosslinked body, there may be mentioned polymers containing tetrafluoroethylene melamine crosslinked body and the like fluoro groups, it is more preferred to use among them PTFE.

(3) Formation method of partition The method for forming the partition as described above is not particularly limited as long as it can be accurately formed into the shape described above. Examples of such a method include forming a partition wall in a pattern using a solid substance in advance and embedding it in the gas diffusion layer body, or forming a gas diffusion layer body on the partition wall, and A method of impregnating this directly into the gas diffusion layer using a coating liquid containing a material for forming the partition walls and solidifying it can be mentioned.

  Among the above, when a solid substance is used, for example, a partition wall is previously formed in a pattern on a separator, and a gas diffusion layer body such as carbon fiber is formed so as to cover the partition wall. The method of forming a partition can be mentioned.

  On the other hand, as the coating liquid in the case of using the coating liquid, a coating liquid in which a resin forming a partition wall is dissolved or dispersed in a solvent, a coating liquid composed of a monomer of a thermosetting resin, or a thermoplastic resin is used. Examples include a coating solution in a melted state. In the present invention, it is preferable to use a coating solution composed of a monomer of a thermosetting resin. This is because the viscosity of the coating liquid can be kept low, and by applying heat, the partition walls can be easily formed without trouble such as drying.

  The method for impregnating the diffusion layer body with such a coating liquid in a pattern is not particularly limited as long as it can form the partition walls with high accuracy. A method in which a head having a discharge port formed in the same shape is used, and this is brought into contact with the surface of the diffusion layer to discharge the coating liquid from the discharge port. A pattern in which a thin nozzle having a discharge port at the tip is formed as a partition wall For example, a method of discharging while moving along an ink jet, a method of using an ink jet method, and the like can be given.

2. Gas diffusion layer body The gas diffusion layer body forming the partition walls as described above is not particularly limited as long as it has gas permeability and can collect the generated electricity. Gas diffusion layers that have been used in batteries can be used. In general, a porous body such as carbon cloth or carbon paper made of carbon fiber is preferably used.
The thickness of the gas diffusion layer main body is not particularly limited as long as the above-described partition can be formed and the function as a conventional gas diffusion layer can be achieved.

B. Fuel Cell Next, the fuel cell of the present invention will be described.
The fuel cell of the present invention is characterized by using the gas diffusion layer described above.
Such a configuration of the fuel cell of the present invention will be described with reference to the drawings. FIG. 2 is a schematic cross-sectional view showing an example of a fuel cell that is the minimum unit of the fuel cell of the present invention. A catalyst electrode 2 is joined to both sides of the electrolyte membrane 1 disposed at the center of the fuel cell (membrane electrode assembly 3), and a gas having a partition wall 7 forming a gas flow path 5 on both sides thereof. The diffusion layer 4 is further provided with separators 6 having smooth surfaces on both sides thereof. Although not shown, gas supply devices for supplying fuel gas and oxidant gas to the catalyst electrodes 2 on both sides of the electrolyte membrane 1 are connected to the separators 6 on the corresponding sides.

The fuel cell of the present invention is characterized in that a gas flow path is formed in the gas diffusion layer, not in the separator. Since the gas diffusion layer has the gas flow path as described above, it is not necessary to form the gas flow path in the separator in the present invention. Therefore, it is possible to smooth the surface of the separator on which the gas flow path has been conventionally formed, and to easily perform the plating process on the surface of the separator. Furthermore, since the portion of the separator where the conventional gas flow path is formed is not necessary, the thickness of the separator can be reduced, and the fuel cell can be reduced in size.
Hereinafter, the fuel cell of the present invention will be described for each component.

(1) Electrolyte membrane The electrolyte membrane used in the present invention is not particularly limited as long as it is made of a material that is excellent in ion (proton) permeability and does not flow current. Examples of materials that are currently widely used include perfluorosulfonic acid polymers (trade name: NafionTM, manufactured by DuPont).

(2) Catalytic electrode The catalytic electrode used in the present invention is not particularly limited, and conventional ones that have been conventionally used can be used. For example, a catalyst in which platinum or an alloy of platinum is dispersed on carbon powder can be used. Further, the catalyst electrode can be formed by forming the catalyst on the electrolyte membrane surface as it is or by mixing it with a binder or the like.

(3) Gas Diffusion Layer The gas diffusion layer used in the fuel cell of the present invention has a partition that forms a gas flow path as described above. Such a gas diffusion layer is the same as that described in “A. Gas Diffusion Layer” above, and thus description thereof is omitted here.

(4) Separator A separator having a smooth surface is used for the fuel cell of the present invention. This is because it is not necessary to provide a gas flow path unlike the conventional separator by using it with the gas diffusion layer which has the partition which forms a gas flow path as mentioned above. Since the separator used in the present invention may have a smooth surface, the manufacturing process of the separator can be greatly simplified. In particular, when the separator is a metal, the surface is smooth, so that the plating process can be easily performed. Furthermore, since the gas flow path portion that has been conventionally provided is unnecessary, there is an advantage that the thickness can be reduced accordingly.

  The material of the separator used in the present invention is not particularly limited, and conventionally used carbon or metal can be used. Among them, it is preferable to use a metal in the present invention. When the separator is made of metal, it is necessary to apply a plating treatment to the surface of the separator to prevent corrosion. However, if the separator surface is smooth, the plating treatment is easy and the effect of the present invention is further exhibited. Because it becomes.

(5) Others The method for producing the fuel cell of the present invention is not particularly limited. That is, the fuel cell of the present invention can be manufactured by a conventional method using a conventional electrolyte membrane and catalyst electrode, a gas diffusion layer and a separator manufactured by the above-described materials, shapes, methods, and the like.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  For example, even when the partition in the diffusion layer is formed integrally with the separator, it is included in the scope of the present invention. That is, for example, a partition layer may be formed integrally with the separator on the separator surface in advance, and a diffusion layer body may be formed on the separator surface, thereby forming a diffusion layer having a flow path therein. This is because a diffusion layer having a flow path inside and having a high current collecting effect can be obtained.

It is a schematic sectional drawing which shows an example of the gas diffusion layer of this invention. It is a schematic sectional drawing which shows an example of the structure of the cell which is the minimum unit of the fuel cell of this invention. It is a schematic sectional drawing which shows an example of the structure of the cell which is the minimum unit of the conventional fuel cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Electrolyte membrane 2 ... Catalyst electrode 3 ... Membrane electrode composite 4 ... Gas diffusion layer 5 ... Gas flow path 6 ... Separator 7 ... Partition

Claims (3)

A gas diffusion layer disposed between a separator and a membrane electrode assembly in a fuel cell, wherein the gas diffusion layer has a partition wall forming a gas flow path in the gas diffusion layer. The gas diffusion layer according to claim 1, wherein the partition wall is made of a resin having water repellency. A fuel cell comprising the gas diffusion layer according to claim 1 or 2, wherein a separator surface in contact with the gas diffusion layer is a flat surface.

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