JP2009295342A - Fuel cell and method of manufacturing fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress drop in power generation performance caused by drop in water repellency of a water repellent layer in a fuel cell including a membrane-electrode assembly formed by arranging a catalyst layer, the water repellent layer containing carbon and a water repellent material, and a gas diffusion layer in this order on the surface of an electrolyte membrane. <P>SOLUTION: The fuel cell 100 includes the membrane-electrode assembly 110 formed by arranging the catalyst layer 114, the water repellent layer 116 containing carbon and the water repellent material, and the gas diffusion layer 118 in this order on both sides of the electrolyte membrane 112. In the membrane-electrode assembly 110, the water repellent layer 116 has a region having a bulk density of carbon of 0.010-0.042 (g/mL). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fuel cell and a method for manufacturing the fuel cell.

  A fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen has attracted attention as an energy source. This fuel cell includes a membrane electrode assembly in which a catalyst layer and a gas diffusion layer are bonded to both surfaces of an electrolyte membrane having proton conductivity as a power generator. In this membrane electrode assembly, generated water is generated by the electrochemical reaction during power generation. And when this produced water is not discharged and stays excessively, so-called flooding occurs. Therefore, various techniques have been proposed in the past to improve the drainage of generated water and suppress flooding by interposing a water-repellent layer between the catalyst layer and the gas diffusion layer of the membrane electrode assembly. (For example, refer to Patent Documents 1 to 3 below).

JP 2007-165025 A JP 2007-66805 A JP 2004-119398 A

  By the way, the membrane electrode assembly becomes hot and humid due to heat generated by the electrochemical reaction and generated water during power generation. Then, in the process of improving the fuel cell, when the water repellent layer included in the membrane / electrode assembly contains carbon, the inventor of the present application, when the water repellent layer is exposed to a high temperature and high humidity environment for a long time, Has been found to decrease over time and flooding occurs in the fuel cell. This is presumably because the surface free energy of the carbon contained in the water repellent layer increases as the water repellent layer is exposed to a high temperature and high humidity environment for a long time. However, in the technique described in the above-mentioned patent document, the reduction in power generation performance due to the above-described reduction in water repellency has not been considered.

  The present invention has been made to solve the above-described problems, and on the surface of the electrolyte membrane, a catalyst layer, a water-repellent layer containing carbon and a water-repellent material, and a gas diffusion layer are arranged in this order. In a fuel cell including a membrane electrode assembly, an object is to suppress a decrease in power generation performance due to a decrease in water repellency of a water repellent layer.

  The present invention can be realized as the following forms or application examples in order to solve at least a part of the above-described problems.

  Application Example 1 A fuel cell including a membrane electrode assembly in which a catalyst layer, a water repellent layer containing carbon and a water repellent material, and a gas diffusion layer are arranged in this order on the surface of an electrolyte membrane, The water repellent layer is a fuel cell having a first region in which the carbon has a bulk density of 0.010 to 0.042 (g / mL).

  The present inventor has found that the degree of reduction in water repellency due to exposure of the water-repellent layer to a high-temperature and high-humidity environment has a significant correlation with the bulk density of carbon in the water-repellent layer. It was experimentally found that a decrease in water repellency can be suppressed by setting the density to 0.010 to 0.042 (g / mL). In addition, it is experimental that it is possible to suppress a decrease in power generation performance of a fuel cell by forming a water-repellent layer capable of suppressing the above-described decrease in water repellency in a region where the water-repellent layer is relatively hot and humid. I found it. That is, the fuel cell of Application Example 1 can suppress a decrease in power generation performance due to a decrease in water repellency of the water repellent layer included in the membrane electrode assembly over time. In addition, the lower limit of the bulk density of the carbon is a lower limit of commercially available carbon nanotubes.

  Application Example 2 In the fuel cell according to Application Example 1, the first region includes a peripheral region of the membrane electrode assembly, a region corresponding to the vicinity of the gas outlet, and a gas more than other regions. A fuel cell comprising at least one of a region liable to stay.

  In a membrane / electrode assembly, the peripheral region, the region corresponding to the vicinity of the gas outlet, and the region where gas tends to stay more easily than other regions tend to be hotter and humid than regions other than these regions. Therefore, this application example is effective.

  [Application Example 3] The fuel cell according to Application Example 1 or 2, wherein the water-repellent layer further includes a second region in which a bulk density of the carbon is higher than 0.042 (g / mL). Fuel cell.

  When the water repellency of the water-repellent layer of the membrane / electrode assembly decreases, flooding is likely to occur, but if a water-repellent layer capable of suppressing the above-described decrease in water repellency is formed in a region that is not likely to be relatively hot and humid, dry-up The power generation performance may be reduced. In this application example, a water-repellent layer having a carbon bulk density higher than 0.042 (g / mL) is formed in a region where the water-repellent layer is unlikely to be relatively hot and humid. Can be suppressed. As a result, the power generation distribution in the membrane electrode assembly can be made uniform.

  Application Example 4 In the fuel cell according to any one of Application Examples 1 to 3, the water-repellent layer is formed on at least the cathode side of the anode side and the cathode side in the membrane electrode assembly. A fuel cell.

  In the membrane / electrode assembly, generated water is generated by a cathode reaction, and therefore, the cathode side is more likely to be hot and humid than the anode side. Therefore, this application example can suppress a decrease in water repellency of at least the cathode-side water-repellent layer in the membrane electrode assembly.

  The present invention can be configured as an invention of the above-described fuel cell manufacturing method in addition to the above-described configuration of the fuel cell. Moreover, it can also be comprised as invention of the membrane electrode assembly used for the above-mentioned fuel cell, and its manufacturing method.

Hereinafter, embodiments of the present invention will be described based on examples.
A. Fuel cell:
FIG. 1 is an explanatory view schematically showing a schematic cross-sectional structure of a fuel cell 100 as one embodiment of the present invention. As shown in the figure, the fuel cell 100 is configured by sandwiching both surfaces of a membrane electrode assembly 110 with an anode-side separator 120 and a cathode-side separator 130. The membrane electrode assembly 110 is obtained by joining an anode and a cathode to both surfaces of an electrolyte membrane having proton conductivity. The membrane electrode assembly 110 will be described in detail later.

  As shown in the figure, the surface of the anode separator 120 on the side in contact with the anode has a concave-convex shape including a groove 122. The groove 122 includes hydrogen as a fuel gas and an anode off-gas discharged from the anode. A gas flow path through which the gas flows is formed. Moreover, the surface of the cathode-side separator 130 on the side in contact with the cathode also has a concave-convex shape including a groove portion 132, and the groove portion 132 includes air containing oxygen as an oxidant gas (humidified air). And a gas flow path through which the cathode off-gas discharged from the cathode flows. In this embodiment, each of these gas flow paths is a serpentine type gas flow path, and is formed such that the gas flows in a direction facing each other with the membrane electrode assembly 110 interposed therebetween.

  Although not shown, the anode-side separator 120 and the cathode-side separator 130 are also formed with flow paths for flowing cooling water. As materials for the anode-side separator 120 and the cathode-side separator 130, various conductive materials such as carbon and metal can be used.

  As shown in FIG. 1, the membrane electrode assembly 110 has a catalyst layer 114 on one side of the electrolyte membrane 112, and carbon and a water repellent material (for example, PTFE: polytetrafluoroethylene on the surface in contact with the catalyst layer 114). It is configured by joining a gas diffusion layer 118 on which a water repellent layer 116 containing (fluoroethylene) is formed. In this embodiment, a solid polymer electrolyte membrane such as Nafion (registered trademark) is used as the electrolyte membrane 112. As the electrolyte membrane 112, another electrolyte membrane may be used. In this embodiment, a carbon cloth is used as the gas diffusion layer 118. As the gas diffusion layer 118, other materials having gas diffusibility and conductivity such as carbon paper may be used. The water repellent layer 116 is for effectively discharging generated water generated by an electrochemical reaction between hydrogen and oxygen during power generation and suppressing flooding.

  By the way, in general, the membrane / electrode assembly becomes hot and humid due to heat generated by the electrochemical reaction and generated water during power generation. Then, in the process of improving the fuel cell, when the water repellent layer included in the membrane / electrode assembly contains carbon, the inventor of the present application, when the water repellent layer is exposed to a high temperature and high humidity environment for a long time, Has been found to decrease over time and flooding occurs in the fuel cell. This is presumably because the surface free energy of the carbon contained in the water repellent layer increases as the water repellent layer is exposed to a high temperature and high humidity environment for a long time. Therefore, in this embodiment, the water repellent layer 116 included in the membrane electrode assembly 110 is improved in order to suppress a decrease in water repellency due to prolonged exposure to a high temperature and high humidity environment.

  FIG. 2 is an explanatory view showing the water repellent layer 116 of the present embodiment. FIG. 2A schematically shows the gas flow on the cathode side surface of the membrane electrode assembly 110 when the membrane electrode assembly 110 is viewed from the anode side. FIG. 2B shows the configuration of the water-repellent layer 116 on the cathode side of the membrane electrode assembly 110. Here, only the configuration of the water-repellent layer 116 on the cathode side of the membrane electrode assembly 110 will be described. In this embodiment, the water-repellent layer 116 on the anode side is the same as the water-repellent layer 116 on the cathode side. The configuration is applied.

  As shown in FIG. 2A, gas (humidified air and cathode off-gas) meanders and flows on the cathode side surface of the membrane electrode assembly 110. Then, water (generated water and moisture in the humidified air) tends to stay in the gas meandering region and the region near the cathode offgas outlet at the periphery of the membrane electrode assembly 110. For this reason, the gas meandering region and the region near the cathode offgas outlet at the periphery of the membrane electrode assembly 110 are more likely to be hot and humid than other regions, and the water repellency of the water repellent layer is likely to be reduced. Become.

  Therefore, in the present embodiment, as shown in FIG. 2B, the gas meandering region or the region near the cathode offgas outlet (region A), that is, the high temperature and high temperature, at the periphery of the membrane electrode assembly 110. A water-repellent layer having a carbon bulk density of 0.035 (g / mL) is formed in a region where the water-repellent layer is likely to be wet and the water-repellent layer is likely to be lowered. A water repellent layer having a carbon bulk density of 0.15 (g / mL) was formed in a region that is less likely to be hot and humid than the region A. The region A and the region B in the water repellent layer 116 correspond to the first region and the second region in the present invention, respectively. The reason why the water repellent layer 116 is configured as described above is based on the experimental results described below.

B. Experiment:
A sample in which a water repellent layer (water repellent layer 1 to water repellent layer 4 described later) having different carbon bulk densities was formed on a carbon cloth constituting the gas diffusion layer 118 was prepared, and a high-temperature and high-humidity environment in a fuel cell was created. As a simulation, the contact angle of water when the hot water treatment at 80 (° C.) was performed on these, that is, the change in water repellency was examined. The bulk density of carbon in the water repellent layer 1 is 0.042 (g / mL), the bulk density of carbon in the water repellent layer 2 is 0.035 (g / mL), and the carbon in the water repellent layer 3 is carbon. The bulk density is 0.24 (g / mL), and the bulk density of carbon in the water repellent layer 4 is 0.15 (g / mL).

  FIG. 3 is an explanatory diagram showing a change in the contact angle of water when the hydrothermal treatment is performed on the water repellent layer 1 to the water repellent layer 4 having different carbon bulk densities. FIG. 4 is an explanatory diagram showing the relationship between the bulk density of carbon in the water repellent layer and the decrease from the initial contact angle when the hot water treatment is performed for 45 hours.

As can be seen from FIGS. 3 and 4, this experiment shows that there is a significant difference between the degree of reduction in water repellency in the water repellent layer when exposed to a high temperature and high humidity environment and the bulk density of carbon in the water repellent layer. It was found that the higher the bulk density of carbon in the water-repellent layer, the greater the degree of reduction in water repellency. Moreover, it turned out that the fall of water repellency can be suppressed by making the carbon bulk density in a water repellent layer into 0.035-0.042 (g / mL). The relationship between the degree of water repellency reduction in the water-repellent layer and the specific surface area of carbon in the water-repellent layer when exposed to a high-temperature and high-humidity environment was also investigated, but there was no correlation between these. (For example, the specific surface area of carbon in the water repellent layer 1 is 13 (m ² / g), the specific surface area of carbon in the water repellent layer 2 is 50 (m ² / g), and the water repellent layer 3 The specific surface area of carbon is 69 (m ² / g), and the specific surface area of carbon in the water repellent layer 4 is 800 (m ² / g).

  From the above experimental results, as described above, the water repellent layer 2 having the smallest degree of decrease in water repellency was applied to the region A (see FIG. 2) in the water repellent layer 116. For example, the water repellent layer 1 may be applied to the region A in the water repellent layer 116 instead of the water repellent layer 2. In this embodiment, the reason why the water-repellent layer 4 having the lowest water repellency is applied to the region B (see FIG. 2) in the water-repellent layer 116 is to suppress dry-up in the region B. For example, the water repellent layer 3 may be applied to the region B in the water repellent layer 116 instead of the water repellent layer 4.

C. Fuel cell manufacturing process:
The fuel cell 100 described above is manufactured by a manufacturing process described below. FIG. 5 is an explanatory view showing the manufacturing process of the fuel cell 100.

  First, the membrane electrode assembly 110 is produced (step S100). In this step, the catalyst layer 114 is formed by applying and drying the catalyst ink on both surfaces of the electrolyte membrane 112 (step S100). Next, a solution prepared by mixing carbon, a water repellent material, and a solvent is applied to the region A and the region B on the surface of the gas diffusion layer base material (for example, carbon cloth) constituting the gas diffusion layer 118, respectively. The water-repellent layer 116 is formed by drying (Step S104). Then, these are superposed and hot press bonded so that the water repellent layer 116 is interposed between the catalyst layer 114 and the gas diffusion layer 118 (step S106). Then, the fuel cell 100 can be manufactured by sandwiching both surfaces of the membrane electrode assembly 110 thus manufactured between the anode side separator 120 and the cathode side separator 130.

D. Effects of Comparative Examples and Examples:
FIG. 6 is an explanatory diagram showing power generation characteristics after performing an endurance test on the fuel cell 100 of this example and the fuel cell of the comparative example. The structure of the fuel cell of Comparative Example 1 and Comparative Example 2 is the same as the structure of the fuel cell 100 of the present example except that the structure of the water repellent layer provided in the membrane electrode assembly is different from that of the present example. is there. That is, in the fuel cell of Comparative Example 1, the bulk density of carbon applied to the region B of the water repellent layer 116 in the fuel cell 100 of this example is applied to the entire surface of the water repellent layer. In the fuel cell of Comparative Example 2, the bulk density of carbon applied to the region A of the water repellent layer 116 in the fuel cell 100 of this example is applied to the entire surface of the water repellent layer.

  As can be seen from the figure, the fuel cell of Comparative Example 2 is superior to the fuel cell of Comparative Example 1 in power generation characteristics after the durability test. Further, the fuel cell 100 of this example is superior in the power generation characteristics after the durability test to the fuel cell of Comparative Example 2. The reason why the fuel cell of Comparative Example 2 is more excellent in power generation characteristics than the fuel cell of Comparative Example 1 is that the decrease in water repellency of the water-repellent layer was suppressed in the fuel cell of Comparative Example 2. In addition, the fuel cell 100 of this example is superior in power generation characteristics to the fuel cell of Comparative Example 2 in the fuel cell 100 of this example, and the dry-up in the region B of the water repellent layer 116 is suppressed. It was because it was done.

  As described above, according to the fuel cell 100 of the present embodiment, it is possible to suppress a decrease in power generation performance due to a decrease in water repellency of the water repellent layer 116 included in the membrane electrode assembly 110 over time.

E. Variations:
Although the embodiments of the present invention have been described above, the present invention is not limited to such embodiments, and can be implemented in various modes without departing from the scope of the present invention. For example, the following modifications are possible.

E1. Modification 1:
FIG. 7 is an explanatory view showing the water-repellent layer 116A in the membrane electrode assembly 110A provided in the fuel cell of the modification. FIG. 7A schematically shows the gas flow on the cathode side surface of the membrane electrode assembly 110A when the membrane electrode assembly 110A is viewed from the anode side. FIG. 7B shows the configuration of the water-repellent layer 116A on the cathode side of the membrane electrode assembly 110A.

  The configuration of the fuel cell of the modification is almost the same as the configuration of the fuel cell 100 described above. However, in the fuel cell of the modified example, unlike the fuel cell 100, gas flow paths are formed in the anode-side separator and the cathode-side separator so that the gas flows straight on the surface of the membrane electrode assembly 110A. (See FIG. 7 (a)). Accordingly, as shown in FIG. 7B, the arrangement of the region A and the region B in the water repellent layer 116A is different from that of the water repellent layer 116. Then, in the region A and the region B in the water repellent layer 116A, a water repellent layer having the same carbon bulk density as the region A and the region B in the water repellent layer 116 is formed, respectively.

  Even in the fuel cell of the modified example described above, similarly to the fuel cell 100 of the above-described example, the power generation performance is reduced due to the temporal decrease in the water repellency of the water repellent layer 116A included in the membrane electrode assembly 110A. Can be suppressed.

E2. Modification 2:
In the above embodiment, in the water repellent layer 116, the water repellent layer, which is relatively less likely to decrease water repellency, is applied to the region A where the water repellency is relatively less likely to be exposed to a high temperature and high humidity environment. Although the water repellent layer in which the water repellency is relatively likely to be lowered is applied to the region B that is not easily lowered, the present invention is not limited to this. In the present invention, the water repellent layer 116 generally has only to have a region where the bulk density of carbon is 0.010 to 0.042 (g / mL). If not, a water-repellent layer capable of suppressing a decrease in water repellency may also be formed in the region B.

E3. Modification 3:
In the above embodiment, the water-repellent layer of the present invention is applied to both the anode-side water-repellent layer 116 and the cathode-side water-repellent layer 116. However, the present invention is not limited to this. However, the generated water is generated on the cathode side, and the cathode side is more likely to be hot and humid than the anode side. Therefore, it is preferable to apply at least the cathode side.

E4. Modification 4:
In the above embodiment, the water-repellent layer 116 is formed on the surface of the gas diffusion layer 118 in the manufacturing process of the membrane electrode assembly 110 in the manufacturing process of the fuel cell 100. However, the present invention is not limited to this. . Instead of forming the water repellent layer 116 on the surface of the gas diffusion layer 118, the water repellent layer 116 may be formed on the surface of the catalyst layer 114, or the surface of the catalyst layer 114 and the surface of the gas diffusion layer 118 The water repellent layer 116 may be formed on both of them.

It is explanatory drawing which shows typically the general | schematic cross-section of the fuel cell 100 as one Example of this invention. It is explanatory drawing shown about the water repellent layer 116 of a present Example. It is explanatory drawing which shows the change of the contact angle of water when performing a hot water process with respect to the water repellent layer 1 thru | or the water repellent layer 4 from which the bulk density of carbon differs, respectively. It is explanatory drawing which shows the relationship between the bulk density of carbon in a water repellent layer, and the fall from the initial contact angle when a hot-water process is performed for 45 hours. 5 is an explanatory view showing a manufacturing process of the fuel cell 100. FIG. It is explanatory drawing which shows the electric power generation characteristic after performing an endurance test with respect to the fuel cell 100 of a present Example, and the fuel cell of a comparative example. It is explanatory drawing shown about the water-repellent layer 116A in the membrane electrode assembly 110A with which the fuel cell of a modification is provided.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... Fuel cell 110,110A ... Membrane electrode assembly 112 ... Electrolyte membrane 114 ... Catalyst layer 116, 116A ... Water-repellent layer 118 ... Gas diffusion layer 120 ... Anode side separator 122 ... Groove part 130 ... Cathode side separator 132 ... Groove part

Claims (5)

A fuel cell comprising a membrane electrode assembly in which a catalyst layer, a water repellent layer containing carbon and a water repellent material, and a gas diffusion layer are arranged in this order on the surface of the electrolyte membrane,
The water repellent layer has a first region in which the carbon has a bulk density of 0.010 to 0.042 (g / mL).
Fuel cell. The fuel cell according to claim 1, wherein
The first region includes at least one of a peripheral region of the membrane electrode assembly, a region corresponding to the vicinity of a gas outlet, and a region in which gas is likely to stay than other regions.
Fuel cell. The fuel cell according to claim 1 or 2,
The water repellent layer further has a second region in which the bulk density of the carbon is higher than 0.042 (g / mL).
Fuel cell. A fuel cell according to any one of claims 1 to 3,
The water repellent layer is formed on at least the cathode side of the anode side and the cathode side in the membrane electrode assembly,
Fuel cell. A fuel cell manufacturing method comprising:
Producing a membrane electrode assembly;
Sandwiching both surfaces of the membrane electrode assembly with a separator, and
The step of producing the membrane electrode assembly includes
A catalyst layer forming step of forming a catalyst layer on the surface of the electrolyte membrane;
A water repellent layer forming step of forming a water repellent layer containing carbon and a water repellent material on at least one of the surface of the gas diffusion layer substrate constituting the gas diffusion layer and the surface of the catalyst layer;
A bonding step of overlapping and bonding each member so that the water repellent layer is interposed between the catalyst layer and the gas diffusion layer,
The water repellent layer forming step includes
Forming a water repellent layer having a bulk density of carbon of 0.010 to 0.042 (g / mL) in at least a part of the region;
Production method.

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