JP4752216B2 - Membrane electrode composite for tube fuel cell - Google Patents

Description

  The present invention relates to a membrane electrode assembly for a tubular fuel cell formed using multi-walled carbon nanotubes.

  A unit cell, which is a minimum power generation unit of a conventional solid polymer electrolyte fuel cell having a flat plate structure (hereinafter sometimes simply referred to as a fuel cell), generally has a catalyst electrode layer bonded to both sides of the solid electrolyte membrane. A membrane electrode assembly is provided, and gas diffusion layers are disposed on both sides of the membrane electrode assembly. Furthermore, a separator having a gas flow path is arranged outside thereof, and the fuel gas and the oxidant gas supplied to the catalyst electrode layer of the membrane electrode composite are passed through the gas diffusion layer, It works to transmit the current obtained by power generation to the outside.

  In order to reduce the size of the fuel cell and increase the power generation reaction area per unit volume, it is necessary to reduce the thickness of the constituent members of the fuel cell. However, in such a conventional flat-plate structure fuel cell, it is not preferable in terms of function and strength to make the thickness of each component member a certain value or less, and the design limit is approaching. For example, the membrane of Nafion (trade name: Nafion, manufactured by DuPont Co., Ltd.), which is widely used at present, becomes too gas permeable when its thickness is below a certain level, causing gas cross-leakage in the cell and generating voltage. There are problems such as lowering. For this reason, it is structurally difficult to improve the power density per unit volume of a conventional flat plate fuel cell to a certain level or more.

  Therefore, research has been conducted to increase the power density by constructing a fuel cell using a tubular membrane electrode assembly in which hollow fibers or the like are used and an electrolyte membrane, a catalyst electrode layer, etc. are laminated on the inner and outer surfaces thereof. . However, since it is not easy to accurately form a film in a tube shape having an extremely small diameter, there is a case where a problem does not occur in the conventional flat plate structure in the tube-shaped membrane electrode assembly.

  For example, in a tube-type fuel cell, the electric power generated by the power generation reaction flows in the axial direction of the tube and is collected, but for efficient current collection, it is placed inside and outside the tube-shaped solid electrolyte membrane It is necessary to bring the catalyst electrode layer and the current collector into close contact with each other. In a conventional fuel cell having a flat plate structure, since it has a flat plate shape, it is easy to bring the catalyst electrode layer and the current collector into close contact with each other, which is not a problem. However, in a tube-shaped fuel cell, it is particularly difficult to collect current efficiently because it is difficult to bring the current collector inside the tube into close contact with the catalyst electrode layer located outside the tube with pressure. It was.

  Patent Document 1 discloses a solid polymer electrolyte fuel cell in which a solid polymer electrolyte layer and a gas diffusion electrode layer are formed on a hollow gas diffusion electrode layer, and a manufacturing method thereof. However, Patent Document 1 describes that the gas diffusion electrode layer is used not only as a gas flow path but also as a current collector, and it is difficult to efficiently collect current with such a method. Conceivable.

JP 2002-124273 A

  The present invention has been made in view of the above problems, and provides a membrane electrode assembly for a tubular fuel cell that can be miniaturized, has a high output density per unit volume, and has a high current collection efficiency. The main purpose is to do.

  In order to achieve the above object, the present invention provides a membrane electrode assembly for a tubular fuel cell formed using multi-walled carbon nanotubes, which is formed on the inner layer of the multi-walled carbon nanotube and on the outer side of the inner layer. A tube-shaped solid electrolyte membrane is formed between the outer layer and the outer layer, and a catalyst is supported on the inner layer and the outer layer. A membrane electrode assembly for a tube type fuel cell is provided. To do.

  The tube-type membrane electrode assembly can be miniaturized by adopting the above-described configuration of the membrane electrode assembly for a tube-type fuel cell (hereinafter, sometimes simply referred to as a membrane electrode assembly). In addition, since carbon nanotubes have extremely high conductivity, they are also suitable as current collectors, and can efficiently collect power generated by power generation reactions.

  In the said invention, it is preferable that the said multi-walled carbon nanotube is formed of two layers. By using a multi-walled carbon nanotube having two layers and forming a solid electrolyte membrane between the inner layer and the outer layer, layers other than the two layers prevent the flow of gas and generated water, etc. It is because a malfunction can be prevented.

  The present invention is advantageous in that it is possible to obtain a membrane electrode assembly for a tube-type fuel cell that can be miniaturized, has a high output density per unit volume, and has high current collection efficiency.

Hereinafter, the membrane electrode assembly for a tube type fuel cell of the present invention will be described in detail.
The membrane electrode composite of the present invention is a membrane electrode composite for a tube type fuel cell formed using multi-walled carbon nanotubes, and includes an inner layer of the multi-walled carbon nanotubes and an outer side formed outside the inner layer. A tube-shaped solid electrolyte membrane is formed between the inner layer and the outer layer, and a catalyst is supported on the inner layer and the outer layer.

  The membrane electrode composite of the present invention is a membrane electrode composite having the size of a multi-walled carbon nanotube, and can be arranged at a very high density in a narrow space. Therefore, by forming a fuel cell using the membrane electrode assembly, the power generation reaction area per unit volume can be greatly improved, and a fuel cell with a high output density per unit volume can be obtained. Further, since the power density per unit volume can be improved, a high output can be obtained even with a small fuel cell, and the fuel cell can be miniaturized. Furthermore, the catalyst is supported on the inner layer and the outer layer of the multi-walled carbon nanotube, and a solid electrolyte membrane is formed between the inner layer and the outer layer, and it is necessary to provide a member corresponding to the conventional catalyst electrode layer Therefore, the membrane electrode assembly can have a simple structure.

  In addition, in the membrane electrode assembly of the present invention, since the multi-walled carbon nanotube as a carrier functions as a current collector, the generated electrons need to move through the catalyst electrode layer to the current collector as in the past. In addition, loss due to movement of electrons can be reduced. Furthermore, since the multi-walled carbon nanotube has extremely high conductivity, the current collecting efficiency can be improved by using the multi-walled carbon nanotube as a current collector.

First, the structure of the membrane electrode assembly of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic structural diagram showing an example of the membrane electrode assembly of the present invention. As shown in FIG. 1, the membrane electrode assembly 1 of the present invention uses multi-walled carbon nanotubes, and includes an inner layer 2 positioned inside and an outer layer 3 positioned outside the inner layer 2. A solid electrolyte membrane 4 is formed therebetween.

  In the present invention, one layer other than the outermost layer of the multi-walled carbon nanotube is defined as an inner layer, and one layer positioned outside the inner layer is defined as an outer layer. For example, when the multi-walled carbon nanotube is formed of three layers, the innermost layer may be the inner layer, the outermost layer may be the outer layer, the innermost layer may be the inner layer, and the middle layer may be the outer layer. Alternatively, the middle layer may be an inner layer and the outermost layer may be an outer layer.

  The number of the multi-walled carbon nanotubes used in the membrane electrode assembly of the present invention is not particularly limited as long as it is two or more. preferable. By using a multi-walled carbon nanotube having two layers and forming a solid electrolyte membrane between the inner layer and the outer layer, problems other than the above-mentioned two layers such as obstructing the flow of gas or generated water This is because it can be prevented. When the multi-walled carbon nanotube is formed of two layers as described above, the inner layer is the inner layer and the outer layer is the outer layer.

  The outer diameter of the multi-walled carbon nanotube as described above is not particularly limited, but is preferably in the range of 10 to 1000 nm, and more preferably in the range of 100 to 500 nm. If the outer diameter is less than the above range, it may be too small to form a membrane electrode assembly with high accuracy. On the other hand, multi-walled carbon nanotubes having an outer diameter exceeding the above range may be difficult to manufacture.

  In the membrane electrode assembly of the present invention, the catalyst is opposite to the inner surface of the inner layer and the outer surface of the outer layer of the multi-walled carbon nanotube, that is, the surface where the inner layer and the outer layer are in contact with the solid electrolyte membrane. It is carried on the side surface. In the conventional membrane electrode assembly, the catalyst is generally arranged in contact with the electrolyte material. However, in the membrane electrode assembly of the present invention, the catalyst and the electrolyte material are not in contact. The reason is as follows.

  Each layer of the multi-walled carbon nanotube does not have carbon arranged in a perfect arrangement, and usually has fine pores that are defects everywhere. Such fine holes are too small to allow gas to pass through, but are so large that ions can pass through. The catalyst is supported on the inside and outside of the inner layer having such characteristics, and the gas contacts the catalyst by passing the fuel gas and the oxidant gas through the inside and outside of the inner layer, respectively. Since it becomes ions, it can pass through the fine holes. That is, the fuel gas comes into contact with the catalyst to become protons, and the protons pass through fine holes in the inner layer or the outer layer and reach the solid electrolyte membrane. In addition, the oxidant gas comes into contact with the catalyst to become oxygen ions, and reacts with protons conducted by the solid electrolyte membrane.

  The catalyst supported on the inner side of the inner layer and the outer side of the outer layer is not particularly limited. For example, a catalyst usually used in a fuel cell such as platinum or a platinum alloy can be used. The supporting method is not particularly limited.

  Moreover, in the membrane electrode assembly of the present invention, a tube-shaped solid electrolyte membrane is formed between the inner layer and the outer layer of the multi-walled carbon nanotube. The electrolyte material for forming such a solid electrolyte membrane is not particularly limited as long as a layer can be formed between the inner layer and the outer layer, and among them, an electrolyte material capable of forming a monomolecular film is preferable. . Examples of such electrolyte materials include fluorine-based resins such as Nafion (trade name: Nafion, manufactured by DuPont), and organic materials such as hydrocarbon resins such as amide resins. Alternatively, inorganic materials such as those containing silicon oxide as the main component can be used, and among them, those containing silicon oxide as the main component are preferable.

  The thickness of the solid electrolyte membrane, that is, the distance between the inner layer and the outer layer of the multi-walled carbon nanotube is not particularly limited, but is in the range of 5 to 50 nm, particularly in the range of 10 to 20 nm. It is preferable. If the thickness of the solid electrolyte membrane is less than the above range, it may be too thin to form the solid electrolyte membrane accurately and uniformly. On the other hand, when the thickness of the solid electrolyte membrane, that is, the distance between the inner layer and the outer layer exceeds the above range, it may be difficult to produce such multi-walled carbon nanotubes.

  In the membrane electrode assembly of the present invention, the inner layer and the outer layer of the multi-walled carbon nanotube function as a current collector, so that the electric power generated by the power generation reaction is collected through the inner layer and the outer layer. The method for extracting power from these inner and outer layers is not particularly limited. For example, the inner layer and the outer layer may be formed with different lengths in the axial direction, and power may be supplied from their ends. Can be taken out.

  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.

It is a schematic block diagram which shows an example of the membrane electrode assembly of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Membrane electrode complex 2 ... Inner layer 3 ... Outer layer 4 ... Solid electrolyte membrane

Claims (2)

A membrane electrode composite for a tubular fuel cell formed using multi-walled carbon nanotubes,
A tube-shaped solid electrolyte membrane is formed between the inner layer of the multi-walled carbon nanotube and the outer layer formed outside the inner layer,
A membrane electrode assembly for a tube type fuel cell, wherein a catalyst is supported on the inner layer and the outer layer. 2. The membrane electrode assembly for a tube type fuel cell according to claim 1, wherein the multi-walled carbon nanotube is formed of two layers.

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