JP5704094B2 - Fuel cell, gas diffusion layer for fuel cell, and production method thereof - Google Patents

Description

  The present invention relates to a fuel cell, a gas diffusion layer for a fuel cell, and a manufacturing method thereof.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas (for example, hydrogen) and an oxidant gas (for example, oxygen) has attracted attention as an energy source. As this fuel cell, there is a solid polymer fuel cell using a solid polymer membrane as an electrolyte membrane. A polymer electrolyte fuel cell generally includes an electrode (catalyst layer) and a gas diffusion layer in this order on both sides of an electrolyte membrane.

  Conventionally, various techniques for improving the adhesion between the electrode (catalyst layer) and the gas diffusion layer have been proposed. For example, in the technique described in Patent Document 1 below, a binder layer (buffer layer) containing a thickener is provided on a gas diffusion layer, and catalyst particles and a binder layer (buffer layer) are provided on the binder layer (buffer layer). An electrode catalyst layer containing a polymer electrolyte is laminated. That is, in this technique, the gas diffusion layer and the electrode catalyst layer are bonded by the thickener contained in the binder layer. The electrolyte membrane is joined to the electrode catalyst layer laminated on the gas diffusion layer.

JP 2007-317391 A JP-A-2005-294123

  By the way, as described above, the electrode and the gas diffusion layer are bonded not by stacking the electrodes on the gas diffusion, but by a membrane electrode assembly in which the electrodes are bonded to both surfaces of the electrolyte membrane, and the gas diffusion layer. May be performed by preparing and bonding them. In this case, the membrane electrode assembly and the gas diffusion layer are generally joined by hot press joining. And it is possible to use the binder layer described in the said patent document 1 also for the hot press joining of a membrane electrode assembly and a gas diffusion layer.

  However, when a certain amount of heat is applied to the binder layer described in Patent Document 1, the thickener contained in the binder layer is vaporized and reduced. For this reason, when the membrane electrode assembly and the gas diffusion layer are hot-press bonded using the binding layer described in Patent Document 1, the adhesion between the membrane electrode assembly and the gas diffusion layer is reduced. .

  The present invention has been made in order to solve the above-described problems, and in a fuel cell, the membrane electrode assembly and the gas diffusion layer are bonded to each other when hot pressing the membrane electrode assembly and the gas diffusion layer. The purpose is to improve the performance.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A fuel cell,
A membrane electrode assembly formed by bonding electrodes to both surfaces of the electrolyte membrane;
A gas diffusion layer bonded to the surface of the membrane electrode assembly, the gas diffusion layer having a microporous layer formed on the bonding surface with the membrane electrode assembly, and
With
The fine porous layer includes conductive fine particles and an adhesive having water solubility and a heat resistant temperature of 300 (° C.) or higher.
Fuel cell.

  In the fuel cell of Application Example 1, since the adhesive contained in the microporous layer has a heat resistance temperature of 300 (° C.) or higher, the membrane electrode bonding when the membrane electrode assembly and the gas diffusion layer are hot-press bonded. The adhesion between the body and the gas diffusion layer can be improved. In the fuel cell of Application Example 1, since the adhesive contained in the microporous layer is water-soluble, the adhesive force of the adhesive is increased by water generated during power generation, and membrane electrode joining during power generation is performed. The adhesion between the body and the gas diffusion layer can also be improved. The hot press bonding between the membrane electrode assembly and the gas diffusion layer is performed at a heating temperature of less than 300 (° C.).

[Application Example 2]
A fuel cell according to Application Example 1,
The adhesive is a ceramic adhesive,
Fuel cell.

  In the fuel cell of Application Example 2, a heat resistant temperature of 300 (° C.) or more can be secured by using a ceramic adhesive as the adhesive. The ceramic adhesive is an adhesive based on a nonmetallic inorganic solid material.

[Application Example 3]
A fuel cell according to Application Example 1 or 2,
The fine porous layer further includes fine particles made of a fluororesin,
The mixing ratio of the adhesive in the fine porous layer is equal to or less than the mixing ratio of the fine particles made of the fluororesin.
Fuel cell.

  With the fuel cell of Application Example 3, the fine porous layer can function as a water repellent layer. In this application example, the mixing ratio means a weight ratio.

[Application Example 4]
A gas diffusion layer for a fuel cell,
A base material for the fuel cell gas diffusion layer;
A microporous layer formed on the surface of the substrate, the microporous layer comprising conductive fine particles and an adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher;
A gas diffusion layer for a fuel cell comprising:

  In the fuel cell gas diffusion layer of Application Example 4, since the adhesive contained in the microporous layer has a heat resistant temperature of 300 (° C.) or higher, the membrane electrode assembly and the gas diffusion layer are subjected to hot press bonding. The adhesion between the membrane electrode assembly and the gas diffusion layer can be improved. In the fuel cell of Application Example 1, since the adhesive contained in the microporous layer is water-soluble, the adhesive force of the adhesive is increased by water generated during power generation, and membrane electrode joining during power generation is performed. The adhesion between the body and the gas diffusion layer can also be improved. The hot press bonding between the membrane electrode assembly and the gas diffusion layer is performed at a heating temperature of less than 300 (° C.).

[Application Example 5]
A gas diffusion layer for a fuel cell according to Application Example 4,
The adhesive is a ceramic adhesive,
Gas diffusion layer for fuel cells.

  In the gas diffusion layer for a fuel cell of Application Example 5, a heat resistant temperature of 300 (° C.) or more can be secured by using a ceramic adhesive as the adhesive. The ceramic adhesive is an adhesive based on a nonmetallic inorganic solid material.

[Application Example 6]
A fuel cell gas diffusion layer according to Application Example 4 or 5,
The fine porous layer further includes fine particles made of a fluororesin,
The mixing ratio of the adhesive in the fine porous layer is equal to or less than the mixing ratio of the fine particles made of the fluororesin.
Gas diffusion layer for fuel cells.

  With the gas diffusion layer for fuel cells of Application Example 6, the fine porous layer can function as a water repellent layer. In this application example, the mixing ratio means a weight ratio.

[Application Example 7]
A fuel cell manufacturing method comprising:
Preparing a paste comprising conductive fine particles, a thickener, and an adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher;
Applying the paste to the surface of the base material of the fuel cell gas diffusion layer;
Forming the fine porous layer on the surface of the substrate by firing the applied paste at a temperature of 300 (° C.) or higher;
Hot press bonding the microporous layer and a membrane electrode assembly formed by bonding electrodes to both surfaces of the electrolyte membrane;
A method for manufacturing a fuel cell comprising:

  The fuel cell of Application Example 1 can be manufactured by the fuel cell manufacturing method of Application Example 7. In the fuel cell manufacturing method according to Application Example 7, most of the thickener contained in the paste is vaporized and reduced when the paste is fired. However, since the paste contains the adhesive, the adhesiveness between the membrane electrode assembly and the gas diffusion layer can be ensured even if the thickener decreases.

  Further, in the fuel cell manufacturing method of Application Example 7, by adjusting the firing conditions (temperature, time) of the paste, the thickener contained in the paste is completely vaporized to increase the viscosity of the fine porous layer. It is also possible not to include the agent. Since the thickener is generally hydrophilic, the thickener may inhibit the water repellency of the fine porous layer. Therefore, if the thickener contained in the paste is completely vaporized so that the fine porous layer does not contain the thickener, the water repellency of the fine porous layer can be improved.

[Application Example 8]
A method for producing a gas diffusion layer for a fuel cell, comprising:
Preparing a paste comprising conductive fine particles, a thickener, and an adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher;
Applying the paste to the surface of the base material of the fuel cell gas diffusion layer;
Forming the fine porous layer on the surface of the substrate by firing the applied paste at a temperature of 300 (° C.) or higher;
A method for producing a gas diffusion layer for a fuel cell.

  The fuel cell gas diffusion layer of Application Example 4 can be manufactured by the method of manufacturing the fuel cell gas diffusion layer of Application Example 8. In addition, in the manufacturing method of the fuel cell gas diffusion layer of Application Example 8, most of the thickener contained in the paste is vaporized and reduced when the paste is fired. However, since the paste contains the adhesive, the adhesiveness between the membrane electrode assembly and the gas diffusion layer can be ensured even if the thickener decreases.

  Further, in the method for producing a gas diffusion layer for a fuel cell of Application Example 8, by adjusting the firing conditions (temperature, time) of the paste, the thickener contained in the paste is completely vaporized, and the fine porous The layer can also be free of thickeners. Since the thickener is generally hydrophilic, the thickener may inhibit the water repellency of the fine porous layer. Therefore, if the thickener contained in the paste is completely vaporized so that the fine porous layer does not contain the thickener, the water repellency of the fine porous layer can be improved.

  Note that the various additional elements described above can also be applied to the fuel cell manufacturing method of Application Example 7 and the fuel cell gas diffusion layer manufacturing method of Application Example 8.

It is explanatory drawing which shows schematic structure of the fuel cell 100 as one Example of this invention. 5 is an explanatory view showing a manufacturing process of the fuel cell 100. FIG. It is explanatory drawing for demonstrating the effect of the fuel cell 100 of an Example.

Hereinafter, embodiments of the present invention will be described in the following order based on examples.
A. Fuel cell configuration:
FIG. 1 is an explanatory diagram showing a schematic configuration of a fuel cell 100 as one embodiment of the present invention. FIG. 1A schematically shows a cross-sectional structure of the fuel cell 100. FIG. 1B schematically shows the structure of the fine porous layer 24.

  As shown in FIG. 1A, the fuel cell 100 is prepared by separately preparing a membrane electrode assembly 10 and a gas diffusion layer 20, and bonding the gas diffusion layer 20 to both surfaces of the membrane electrode assembly 10. Become. The membrane electrode assembly 10 is formed by joining a catalyst layer 14 as an electrode to both surfaces of an electrolyte membrane 12. The gas diffusion layer 20 is formed by forming a microporous layer 24 on the surface of a gas diffusion layer base material 22.

  In this embodiment, Nafion (registered trademark) is used as the electrolyte membrane 12. As the electrolyte membrane 12, another solid polymer membrane having proton conductivity may be used. The catalyst layer 14 includes an ionomer (for example, Nafion) and a carrier (for example, carbon black) carrying a catalyst (for example, platinum). In this example, carbon paper (manufactured by Toray Industries, Inc .: TGP-60) is used as the gas diffusion layer base material 22. As the gas diffusion layer base material 22, other materials having gas diffusibility and conductivity such as carbon cloth may be used.

  The microporous layer 24 includes carbon black 24a as conductive fine particles and an adhesive 24b. In this example, acetylene black manufactured by Denki Kagaku Kogyo Co., Ltd. was used as the carbon black 24a. Other materials may be used as the conductive fine particles. In this example, “Resbond 919” manufactured by Kotronics, USA was used as the adhesive 24b. “Resbond 919” is a ceramic adhesive having water solubility, and is based on magnesia and has a heat resistant temperature of about 1530 (° C.). As the adhesive 24b, another adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher may be used. In this embodiment, the average particle size of the adhesive 24b is 1/5 to 1/10 of the average particle size of the carbon black 24a. The average particle diameter of the adhesive 24b and the average particle diameter of the adhesive 24b are measured by, for example, a dynamic light scattering method. The average particle diameter of acetylene black (carbon black 24a) is about 35 (nm), and the average particle diameter of the adhesive 24b is about 3.5 to 7 (nm).

  As shown in FIG. 1B, in the microporous layer 24, the adhesive 24b enters and adheres to the voids on the surface of the carbon black 24a to form a continuous structure. And since this structure has a spring property, when it joins with the membrane electrode assembly 10, the fine porous layer 24 and the membrane electrode assembly 10 become more familiar, and it has the effect | action which increases an anchor effect.

  The microporous layer 24 also includes fine particles (not shown) made of a fluororesin and functions as a water repellent layer. In this embodiment, polytetrafluoroethylene (PTFE) is used as the fluororesin. As the fluororesin, for example, a fluororesin other than PTFE such as PFA may be used. However, since the microporous layer 24 is formed by baking a paste described later at a temperature of 300 (° C.) or higher, it is preferable to use a fluororesin having a melting point of 300 (° C.) or higher.

B. Fuel cell manufacturing process:
FIG. 2 is an explanatory view showing a manufacturing process of the fuel cell 100. First, a paste (hereinafter referred to as MPL paste) for forming a microporous layer (MPL) is prepared (step S100). The MPL paste is prepared by mixing carbon black 24a, PTFE dispersion (a dispersion in which PTFE fine particles are dispersed), a thickener, an adhesive 24b, and pure water. In this example, “31J” manufactured by Mitsui DuPont Fluorochemical Co., Ltd. was used as the PTFE dispersion. Further, as the adhesive 24b, the solvent (water) of “Resbond 919” is evaporated to make only a solid component, and this is dissolved so that the average particle diameter of the carbon black 24a is 1/5 to 1/10. Used by crushing. Examples of the thickener include styrene-butadiene rubber (SBR) latex, polytetrafluoroethylene (PTFE) aqueous dispersion, polyolefins, polyimide, PTFE powder, fluoro rubber, thermosetting resin, polyurethane, and polyethylene oxide (PEO). ), Polyaniline (PAN), polyvinylidene fluoride (PVdF), propylene fluoride (HFP), polyvinyl ether / methyl methacrylate (PVE / MMA), casein, starch, ammonium alginate, polyvinyl alcohol (PVA), and poly Ammonium acrylate or the like can be used.

  Next, an MPL paste is applied to the surface of the gas diffusion layer base material 22 (step S110), and the applied MPL paste is baked (step S120). In this example, the MPL paste was fired at a temperature of 300 (° C.). At this time, most of the thickener contained in the MPL paste is evaporated by heat and decreases. Through the above manufacturing process, the fine porous layer 24 is formed on the surface of the gas diffusion layer base material 22, and the gas diffusion layer 20 used in the fuel cell 100 is manufactured.

  Then, the microporous layer 24 in the gas diffusion layer 20 and the membrane electrode assembly 10 are hot-press bonded (Step S130). In this example, the microporous layer 24 and the membrane electrode assembly 10 were hot press bonded at a heating temperature of 130 (° C.) and a pressure of 3 (MPa). The fuel cell 100 is manufactured by the above manufacturing process.

C. Effects of the embodiment:
FIG. 3 is an explanatory diagram for explaining the effect of the fuel cell 100 of the embodiment. Membrane / electrode assembly 10 and gas diffusion layer 20 in fuel cells (Examples 1 to 12 and Comparative Examples 1 to 3) manufactured by changing the addition amount of the adhesive 24b in the MPL paste and the firing temperature of the MPL paste The results of a 90-degree peel test on the adhesive strength of the are shown. This 90 degree peel test is a peel test in which the angle between the membrane electrode assembly 10 and the gas diffusion layer 20 is always kept at 90 degrees.

  In each MPL paste, the mixing ratio (weight ratio) of carbon black 24a and PTFE was 80:20, respectively. The amount of adhesive 24b added was set with the total weight of carbon black 24a and PTFE being 100. The MPL paste was prepared with pure water as a solvent so that the mixing ratio (weight ratio) of the solid components (carbon black 24a, PTFE, adhesive 24b) was 20 (%).

  FIG. 3A shows the test results when the firing temperature of the MPL paste is 300 (° C.). In all the fuel cells of Examples 1 to 4 in which the adhesive addition amount was 0.1 (%), 1.0 (%), 5.0 (%), and 10.0 (%), the adhesive addition amount The peel strength was larger than that of the fuel cell of Comparative Example 1 in which 0 was set to 0 (%). That is, the adhesion between the membrane electrode assembly 10 and the gas diffusion layer 20 was improved by adding the adhesive 24b to the MLP paste.

  FIG. 3B shows the test results when the firing temperature of the MPL paste is 310 (° C.). In all the fuel cells of Examples 5 to 8 in which the adhesive addition amount was 0.1 (%), 1.0 (%), 5.0 (%), and 10.0 (%), the adhesive addition amount The peel strength was larger than that of the fuel cell of Comparative Example 2 in which is set to 0 (%). That is, the adhesiveness between the membrane electrode assembly 10 and the gas diffusion layer 20 was improved by adding the adhesive 24b to the MPL paste. Further, in the fuel cells of Examples 1 to 8, even when the firing temperature of the MPL paste was changed, the peeling force did not change. On the other hand, the peel strength of the fuel cell of Comparative Example 2 was lower than that of the fuel cell of Comparative Example 1. This is because, in the fuel cell of Comparative Example 2, the firing temperature of the MPL paste is higher than that of the fuel cell of Comparative Example 1, and thus the thickener contained in the microporous layer 24 is reduced by evaporation.

  FIG. 3 (c) shows the test results for the fuel cells (Examples 9 to 12 and the fuel cell of Comparative Example 3) immediately after the power is generated by the fuel cells of Examples 5 to 8 and Comparative Example 2. Indicated. The power generation conditions are as follows.

<Power generation conditions>
Cooling water temperature: 60 (° C)
Load current density: 0.8 (A / cm ² ) constant Air stoichiometric ratio: 1.5
Hydrogen stoichiometric ratio: 1.2
Retention time: 8 hours

  In the fuel cell of Comparative Example 3 in which the amount of adhesive added was 0 (%), the peeling force did not change before and after power generation. On the other hand, in all the fuel cells of Examples 9 to 12 in which the adhesive addition amount was 0.1 (%), 1.0 (%), 5.0 (%), 10.0 (%) However, it increased about twice as much as the fuel cell of Examples 5-8 before power generation. This is probably because the adhesive 24b is water-soluble, and the adhesive force of the adhesive 24b is increased by water generated by power generation.

  In the fuel cell 100 of the present embodiment described above, since the adhesive 24b included in the fine porous layer 24 has a heat resistance temperature of 300 (° C.) or more, the thickener contained in the fine porous layer 24 is reduced. However, the adhesion between the membrane electrode assembly 10 and the gas diffusion layer 20 when the membrane electrode assembly 10 and the gas diffusion layer 20 are hot-press bonded can be improved. In the fuel cell 100 of the present embodiment, the adhesive 24b included in the microporous layer 24 is water-soluble, so that the adhesive force of the adhesive 24b is increased by the water generated during power generation, and power generation is in progress. The adhesion between the membrane electrode assembly 10 and the gas diffusion layer 20 can also be improved.

  Further, in the fuel cell 100 of the present embodiment, since a ceramic adhesive is used as the adhesive 24b, a heat resistant temperature of 300 (° C.) or more can be secured.

  Further, in the fuel cell 100 of the present embodiment, the MPL paste, the microporous layer 24 contains fine particles made of PTFE, and the mixing ratio (weight ratio) of the adhesive 24b is equal to or less than the mixing ratio (weight ratio) of PTFE. The fine porous layer 24 can function as a water repellent layer.

  Further, in the manufacturing process of the gas diffusion layer 20 and the manufacturing process of the fuel cell 100 of this embodiment, the thickener contained in the MPL paste is completely adjusted by adjusting the firing conditions (temperature, time) of the MPL paste. The fine porous layer 24 can be made to contain no thickener. Since the thickener is generally hydrophilic, the thickener may inhibit the water repellency of the fine porous layer 24. Therefore, if the thickener contained in the MPL paste is completely vaporized so that the fine porous layer 24 does not contain the thickener, the water repellency of the fine porous layer 24 can be improved.

D. Variation:
As mentioned above, although several embodiment of this invention was described, this invention is not limited to such embodiment at all, and implementation in various aspects is possible within the range which does not deviate from the summary. It is. For example, the following modifications are possible.

D1. Modification 1:
In the said Example, although the baking temperature of MPL paste was 300 (degreeC) or 310 (degreeC), this invention is not limited to this. The firing temperature of the MPL paste is a temperature of 300 (° C.) or higher, and may be a temperature within a range in which the gas diffusion layer base material 22 and the fine porous layer 24 are not altered by heat. For example, in the above embodiment, PTFE as a fluororesin is contained in the microporous layer 24 and the MPL paste, and therefore the firing temperature of the MPL paste is set to less than 327 (° C.) which is the melting point of PTFE.

D2. Modification 2:
In the above embodiment, the fine porous layer 24 and the MPL paste include fine particles made of fluororesin (PTFE), but the present invention is not limited to this. The fine porous layer 24 and the MPL paste may not include fine particles made of a fluororesin.

D3. Modification 3:
In the above embodiment, in the fuel cell 100, the gas diffusion layer 20 is bonded to both surfaces of the membrane electrode assembly 10, but the present invention is not limited to this. The gas diffusion layer 20 may be bonded to one surface of the membrane electrode assembly 10.

DESCRIPTION OF SYMBOLS 100 ... Fuel cell 10 ... Membrane electrode assembly 12 ... Electrolyte membrane 14 ... Catalyst layer 20 ... Gas diffusion layer 22 ... Gas diffusion layer base material 24 ... Fine porous layer 24a ... Carbon black 24b ... Adhesive

Claims (8)

A fuel cell,
A membrane electrode assembly formed by bonding electrodes to both surfaces of the electrolyte membrane;
A gas diffusion layer bonded to the surface of the membrane electrode assembly, the gas diffusion layer having a microporous layer formed on the bonding surface with the membrane electrode assembly, and
With
The fine porous layer includes conductive fine particles and an adhesive having water solubility and a heat resistant temperature of 300 (° C.) or higher.
Fuel cell. The fuel cell according to claim 1, wherein
The adhesive is a ceramic adhesive,
Fuel cell. The fuel cell according to claim 1 or 2,
The fine porous layer further includes fine particles made of a fluororesin,
The mixing ratio of the adhesive in the fine porous layer is equal to or less than the mixing ratio of the fine particles made of the fluororesin.
Fuel cell. A gas diffusion layer for a fuel cell,
A base material for the fuel cell gas diffusion layer;
A microporous layer formed on the surface of the substrate, the microporous layer comprising conductive fine particles and an adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher;
A gas diffusion layer for a fuel cell comprising: A gas diffusion layer for a fuel cell according to claim 4,
The adhesive is a ceramic adhesive,
Gas diffusion layer for fuel cells. A gas diffusion layer for a fuel cell according to claim 4 or 5,
The fine porous layer further includes fine particles made of a fluororesin,
The mixing ratio of the adhesive in the fine porous layer is equal to or less than the mixing ratio of the fine particles made of the fluororesin.
Gas diffusion layer for fuel cells. A fuel cell manufacturing method comprising:
Preparing a paste comprising conductive fine particles, a thickener, and an adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher;
On the surface of the base material of the fuel cell gas diffusion layer, a step of applying said paste,
Forming the fine porous layer on the surface of the substrate by firing the applied paste at a temperature of 300 (° C.) or higher;
Hot press bonding the microporous layer and a membrane electrode assembly formed by bonding electrodes to both surfaces of the electrolyte membrane;
A method for manufacturing a fuel cell comprising: A method for producing a gas diffusion layer for a fuel cell, comprising:
Preparing a paste comprising conductive fine particles, a thickener, and an adhesive having water solubility and a heat resistance temperature of 300 (° C.) or higher;
Applying the paste to the surface of the base material of the fuel cell gas diffusion layer;
Forming the fine porous layer on the surface of the substrate by firing the applied paste at a temperature of 300 (° C.) or higher;
A method for producing a gas diffusion layer for a fuel cell.

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