JP2008282646A - Fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the variation of a pressure loss in a flow passage at each laminated body assembly in a fuel cell having a gas diffusion layer formed by using carbon nanotubes, and to effectively generate electric power in the fuel cell. <P>SOLUTION: The fuel cell 100 has the gas diffusion layer 30 formed between an electrolyte/electrode assembly 20 and a separator 40 so as to make the carbon nanotubes 34 orientate toward the electrode assembly 20 from the separator 40. Elastic members 32 for reducing the variation of the thickness of the gas diffusion layer 30 caused by the swelling of the electrolyte layer 23 forming the electrolyte/electrode assembly 20 are arranged on the gas diffusion layer 30 at equal intervals. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fuel cell, and more particularly to a fuel cell using carbon nanotubes in a gas diffusion layer.

  A fuel cell is generally configured by laminating a plurality of laminate assemblies formed by sandwiching both surfaces of an electrolyte with an electrode layer, a gas diffusion layer, and a separator. In the case of a solid polymer fuel cell, for example, carbon paper or carbon non-woven fabric, which is a good conductor, is used for the electrode layer and the gas diffusion layer. When such a carbon-based gas diffusion layer is used, the laminated assembly is strongly clamped from both ends so that the contact surface between the electrolyte and the electrode layer and the contact resistance between the gas diffusion layer and the separator do not increase. By tightening, the contact surface is pressed and the contact resistance is lowered to improve the power generation efficiency.

  Thus, tightening the laminate assembly with a large external force is not preferable from the viewpoint of the durability of the electrolyte. Therefore, fuel cells using carbon nanotubes for electrode layers and gas diffusion layers have been developed. A carbon nanotube is a fibrous material in which a six-membered ring network made of carbon is a single layer or a multilayer coaxial tube. In the case of a single layer, the minimum fiber diameter is about 1 nm. By using such fine fibers, it is possible to increase the above-described contact area and improve power generation efficiency without tightening with a large external force. As a fuel cell using carbon nanotubes as described above, for example, the technique of the following patent document is known.

JP 2005-203332 A JP-A-2005-004967 JP 2005-302305 A

  However, in the above-described fuel cell using carbon nanotubes, the rigidity of the carbon nanotubes is small, so that the electrolyte swells with water during operation of the fuel cell, or the temperature of the fuel cell rises and the separator expands. If so, the carbon nanotubes are deformed accordingly, and the thickness of the gas diffusion layer is reduced. When such a phenomenon occurs in each laminated body assembly, the flow path pressure loss of each laminated body assembly varies.

  In such a fuel cell, in order to achieve a certain level of power generation performance in each laminate assembly, it is necessary to supply a fuel gas and an oxidizing gas corresponding to the laminate assembly having a gas diffusion layer having a large flow path pressure loss. There is. Therefore, there has been a problem that the excessive supply rate of the fuel gas and the oxidizing gas is increased.

  In light of the above problems, the problem to be solved by the present invention is to reduce fluctuations in flow path pressure loss for each laminate assembly in a fuel cell having a gas diffusion layer formed using carbon nanotubes. It is to generate electricity.

The fuel cell of the present invention that solves the above problems is
A fuel cell,
An electrolyte-electrode assembly comprising an electrolyte layer having ion conductivity and an electrode layer having catalytic ability;
A separator that functions as a partition wall for a reaction gas provided for a fuel cell reaction in the fuel cell;
Between the separator and the electrolyte / electrode assembly, a gas diffusion layer formed by orienting carbon nanotubes in a direction substantially perpendicular to a surface of the separator and the electrolyte / electrode assembly facing each other;
And an elastic member that is disposed in the gas diffusion layer and relaxes a change in the thickness of the gas diffusion layer caused by expansion of the member of the fuel cell caused by operation of the fuel cell. .

  The fuel cell having such a structure is an elastic member disposed in the gas diffusion layer even when a force that changes the thickness of the gas diffusion layer acts as the fuel cell member expands as the fuel cell is operated. Relaxes the change in the thickness of the gas diffusion layer. Therefore, fluctuations in flow path pressure loss for each laminate assembly can be mitigated, and efficient power generation can be performed while suppressing an excessive supply rate of fuel gas and oxidizing gas.

  In the fuel cell having such a configuration, the elastic member may be a coil spring. With such a configuration, the elastic member does not occupy a large volume in the gas diffusion layer. Therefore, it is possible to sufficiently relieve the change in the thickness of the gas diffusion layer while suppressing the deterioration of the function of the gas diffusion layer, and to mitigate fluctuations in the flow path pressure loss for each laminate assembly.

  In the fuel cell having such a configuration, the carbon nanotube may have a single-layer structure. With such a configuration, the single-walled carbon nanotube has a very small diameter, so that a sufficient contact area between the gas diffusion layer and the electrolyte / electrode assembly or separator can be secured to reduce the contact resistance. . Therefore, efficient power generation can be performed.

(1) Example:
Examples of the present invention will be described. FIG. 1 is an explanatory diagram showing a configuration of a fuel cell 100 as an embodiment of the present invention. The fuel cell 100 is a solid polymer fuel cell. The fuel cell 100 is configured by laminating a plurality of laminate assemblies formed by sandwiching the gas diffusion layer 30 and the separator 40 on both sides of the electrolyte / electrode assembly 20. FIG. 1 shows a part of the stacked layers.

  The electrolyte / electrode assembly 20 is a portion where an electrochemical reaction of the fuel cell is performed, and is composed of an anode electrode layer 22, an electrolyte layer 23, and a cathode electrode layer 24. The electrolyte layer 23 is a proton conductive ion exchange membrane made of a solid polymer material, and exhibits good electrical conductivity in a wet state. In this example, a fluororesin was used.

  The anode electrode layer 22 and the cathode electrode layer 24 are formed by supporting a catalyst on a conductive carrier. In this embodiment, an electrode paste is prepared using carbon particles carrying a platinum catalyst and an electrolyte made of the same material as the electrolyte constituting the electrolyte layer 23, and this electrode paste is applied to the electrolyte layer 23 and dried.・ Used one that was fixed.

  The gas diffusion layer 30 serves as a flow path for a reactive gas (a fuel gas containing hydrogen or an oxidizing gas containing oxygen) used for an electrochemical reaction in the electrolyte / electrode assembly 20 and collects current. It is. In general, the gas diffusion layer 30 can be formed of a conductive member having gas permeability, such as carbon paper, carbon cloth, or carbon nanotube. In this embodiment, the gas diffusion layer 30 is formed by the carbon nanotubes 34 and the elastic member 32.

  The carbon nanotubes 34 used in this example are formed by aligning single-walled carbon nanotubes having a minimum diameter of about 1 nm from the separator 40 toward the electrode assembly 20. The carbon nanotube 34 is a good conductor and has a small minimum diameter, and can increase the contact area with the cathode electrode layer 24 and the separator 40 as compared with the above-described carbon paper. Therefore, it is possible to ensure electrical contact without strongly tightening from both ends of the fuel cell 100, to reduce contact resistance, and to improve power generation efficiency. Of course, the carbon nanotube 34 is not limited to a single-layer structure, and may be a multi-layer structure. Such a carbon nanotube 34 has low rigidity, and even when subjected to bending stress, the carbon nanotube 34 is deformed while taking a wavy structure.

  The carbon nanotube 34 is an arc discharge method, a laser vapor deposition method, a CVD method in which a catalyst metal for generating a carbon nanotube is used and a hydrocarbon gas or a hydrogen gas is supplied thereto, and a high temperature / high pressure condition. It can be produced by using a known synthesis method such as HiPco method in which carbon monoxide is disproportionated (CO + CO → C + CO2).

  The elastic member 32 is a coil spring provided between the cathode electrode layer 24 and the separator 40, and stainless steel is used in this embodiment. As the fuel cell 100 is operated, the elastic member 32 causes the electrolyte layer 23 to swell with water, or the separator 40 to thermally expand due to a temperature rise, thereby deforming the carbon nanotube 34 with low rigidity, When a force acts in the direction of decreasing the thickness of the gas diffusion layer 30, the change in the thickness of the gas diffusion layer 30 is relaxed against the force.

  In this embodiment, the elastic member 32 has 15 coil springs arranged at equal intervals per gas diffusion layer 30, but the number and installation locations of the elastic members 32 are the size of the electrolyte / electrode assembly 20, and the like. What is necessary is just to set suitably according to the material of the electrolyte layer 23, the bias | inclination of the swelling condition of the electrolyte layer 23 etc. which are assumed. In addition, when the layer thickness of the gas diffusion layer 30 is small, for example, 100 μm, the elastic member 32 may be a minimal spring manufactured by micromachine technology.

  In this embodiment, a linear characteristic spring is used. However, a non-linear characteristic spring such as a tapered coil spring or an unequal pitch coil spring may be used. In this way, even if the degree of swelling of the electrolyte layer 23 is uneven depending on the location, the layer thickness of the gas diffusion layer 30 can be effectively increased by using a nonlinear characteristic spring in which the spring constant increases according to the amount of displacement. Change can be mitigated.

  In this embodiment, a coil spring is used as the elastic member 32. However, various types of springs such as a leaf spring and a disc spring can be used. Needless to say, the elastic body is not limited to a spring, and may be various elastic bodies that relieve changes in the thickness of the gas diffusion layer 30, such as a resin system such as urethane or steel wool. The reason why the elastic body is used in this way is to prevent a large stress from being applied to the electrolyte layer 23 against the force acting in the direction of reducing the thickness of the gas diffusion layer 30. When a material with high rigidity is used for the electrolyte layer 23, the support member is not limited to an elastic body and may be a support member that restricts the thickness of the gas diffusion layer 30. If the elastic member 32 is made of a highly conductive material such as a copper alloy, the resistance can be reduced.

  In this embodiment, the gas diffusion layer 30 is composed of the carbon nanotubes 34 and the elastic member 32 on both the anode electrode layer 22 side and the cathode electrode layer 24 side. It may be configured.

  The separator 40 described above is a portion that forms the wall surface of the gas diffusion layer 30 serving as a reaction gas flow path. In this embodiment, stainless steel is used, but a gas-impermeable conductive member such as carbon is used. It may be dense carbon that has been compressed and gas-impermeable, or calcined carbon. In addition, the separator 40 includes a cooling water passage 42 for adjusting the operating temperature of the fuel cell. In this embodiment, as the separator 40, a flat separator provided on the anode electrode layer 22 side, a flat separator provided on the cathode electrode layer 24 side, a cooling flow path disposed between them, Although the three-layer separator integrated with the intermediate plate in which the through hole having a predetermined shape is formed is used, the present invention is not limited to this. For example, various separators such as a separator having two layers and a separator having irregularities on the surface can be used.

  Further, between the separators 40, the outer periphery of the electrolyte / electrode assembly 20 and the gas diffusion layer 30 is provided with a seal portion 50 for ensuring sealing performance in the gas flow path in the cell. It is provided integrally with the joined body 20. In this example, fluororubber was used.

  The separator 40 and the seal portion 50 described above are provided with through holes, and these communicate with each other to form an oxidizing gas supply manifold 44 and an oxidizing gas discharge manifold 46. As shown in the drawing, the oxygen as the oxidizing gas supplied to the oxidizing gas supply manifold 44 is supplied to the gas diffusion layer 30 through the inside of the separator 40 and used for the fuel cell reaction at the cathode electrode layer 24. Then, the exhaust gas (cathode exhaust gas) is discharged from the gas diffusion layer 30 to the oxidizing gas discharge manifold 46 through the inside of the separator 40. Although explanation is omitted, fuel gas and cooling water are also supplied to the anode electrode layer 22 or the cooling water passage 42 through manifolds formed in the separator 40 and the seal portion 50 in other cross sections (not shown). Discharged.

  The fuel cell 100 having such a configuration deforms the carbon nanotube 34 having a low rigidity by the electrolyte layer 23 containing water and swelling due to the operation of the fuel cell 100, or by the thermal expansion of the separator 40 due to the temperature rise. Even if a force acts in the direction of decreasing the thickness of the gas diffusion layer 30, the elastic member 32 counters the force and relaxes the change in the layer thickness of the gas diffusion layer 30. Therefore, the flow path pressure loss of each laminate assembly constituting the fuel cell 100 is made uniform, so that the excessive supply rate of the reaction gas can be suppressed.

  Further, since the fuel cell 100 configured as described above uses a coil spring for the elastic member 32, the elastic member 32 does not occupy a large volume in the gas diffusion layer 30. Therefore, it is possible to suppress the functional degradation of the gas diffusion layer 30.

(2) Modification:
In this embodiment, the anode electrode layer 22 and the cathode electrode layer 24 are formed using a material different from carbon nanotubes (electrode paste of carbon particles carrying a catalyst), but may be formed using carbon nanotubes. . In this case, the anode electrode layer 22 and the cathode electrode layer 24 may be formed as a carbon nanotube layer formed on the electrolyte layer 23. Or you may make it function as the anode electrode layer 22 and the electrolyte layer 23 by making a catalyst carry | support to the front-end | tip part by the side of the electrolyte-electrode assembly 20 of the carbon nanotube 34 shown in the Example. In these cases, the elastic member 32 shown in the embodiment may be installed between the electrolyte layer 23 and the separator 40.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an example, and it is needless to say that the present invention can be implemented in various modes without departing from the gist of the present invention. For example, the fuel cell of the present invention is not limited to the polymer electrolyte fuel cell shown in the examples. As long as it has a gas diffusion layer using carbon nanotubes, it can be configured as another type of fuel cell.

It is explanatory drawing which shows schematic structure of the fuel cell 100 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Electrolyte / electrode assembly 22 ... Anode electrode layer 23 ... Electrolyte layer 24 ... Cathode electrode layer 30 ... Gas diffusion layer 32 ... Elastic member 34 ... Carbon nanotube 40 ... Separator 42 ... Cooling water flow path 44 ... Oxidizing gas supply manifold 46 ... Oxidizing gas discharge manifold 50 ... Seal part 100 ... Fuel cell

Claims (3)

A fuel cell,
An electrolyte-electrode assembly comprising an electrolyte layer having ion conductivity and an electrode layer having catalytic ability;
A separator that functions as a partition wall for a reaction gas provided for a fuel cell reaction in the fuel cell;
Between the separator and the electrolyte / electrode assembly, a gas diffusion layer formed by orienting carbon nanotubes in a direction substantially perpendicular to a surface of the separator and the electrolyte / electrode assembly facing each other;
A fuel cell comprising: an elastic member that is disposed in the gas diffusion layer and that relaxes a change in the layer thickness of the gas diffusion layer caused by expansion of the member of the fuel cell caused by operation of the fuel cell.   The fuel cell according to claim 1, wherein the elastic member is a coil spring.   The fuel cell according to claim 1, wherein the carbon nanotube has a single-layer structure.

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