JP2009032438A - Manufacturing method for membrane-electrode assembly of fuel battery and membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve battery performance by reducing contact resistance between an electrode and an electrolyte membrane in a solid polymer fuel battery. <P>SOLUTION: A manufacturing method for a membrane-electrode assembly of a fuel battery comprises a first process (step S100) of preparing an electrolyte membrane 20 made of a first solid polymer electrolyte, a second process (step S110) of preparing a plurality of fine particles 29 including a second solid polymer electrolyte, a third process (step S140) of preparing the electrode including a catalyst, and a fourth process (step S150) of joining by overlapping the electrode and the electrolyte membrane 20 via the plurality of fine particles. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a membrane-electrode assembly for a fuel cell and a membrane-electrode assembly.

  One factor affecting the performance of the fuel cell is the contact resistance between the electrolyte membrane and the electrode. Conventionally, as a method of reducing the contact resistance between an electrode and an electrolyte membrane, a resin solution layer having a proton conductivity is sprayed on the electrolyte membrane, and the resin solution layer is dried before the resin solution layer is dried. There has been proposed a method of forming an electrode on an electrolyte membrane via a film. Thus, by forming the electrode before the resin solution layer provided on the electrolyte membrane is dried, the adhesion between the electrode and the electrolyte membrane can be improved and the contact resistance can be reduced (for example, Patent Document 1).

JP 2004-63409 A JP-A-10-189002 JP 2004-281152 A

  However, when a resin solution layer is formed on the electrolyte membrane, the electrolyte membrane swells due to moisture contained in the resin solution layer, and the electrolyte membrane contracts when the electrolyte membrane dries. Therefore, despite the fact that the resin solution layer is provided to improve the adhesion between the electrode and the electrolyte membrane, due to the swelling and shrinkage of the electrolyte membrane, there is a problem between the electrode and the electrolyte membrane. In some cases, the adhesion deteriorated. Therefore, further reduction in contact resistance between the electrode and the electrolyte membrane has been desired.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to improve battery performance by reducing contact resistance between an electrode and an electrolyte membrane in a polymer electrolyte fuel cell. And

In order to achieve the above object, the first method for producing a membrane-electrode assembly for a fuel cell of the present invention comprises:
A first step of preparing an electrolyte membrane comprising a first solid polymer electrolyte;
A second step of preparing a plurality of fine particles containing a second solid polymer electrolyte;
A third step of preparing an electrode including a catalyst;
And a fourth step of superposing and joining the electrode and the electrolyte membrane with the plurality of fine particles interposed therebetween.

  According to the method for manufacturing a membrane-electrode assembly for a fuel cell of the present invention configured as described above, the electrolyte membrane and the electrode are joined to each other through the plurality of fine particles. At this time, excessive water is not supplied to the electrolyte membrane. In addition, since the electrode is prepared separately from the electrolyte membrane in advance and the electrode and the electrolyte membrane are joined together, excessive water supply from the electrode to the electrolyte membrane can be suppressed. Therefore, the electrolyte membrane does not swell due to excessive water supply, or the electrolyte membrane shrinks due to subsequent drying. In this way, by suppressing the swelling and shrinkage of the electrolyte membrane at the time of joining the electrode and the electrolyte membrane, it is possible to suppress a decrease in the adhesion between the electrolyte membrane and the electrode due to the swelling and shrinkage of the electrolyte membrane. Can do.

  In the method for producing a membrane-electrode assembly for a fuel cell of the present invention, the fourth step is heating to a temperature at which at least a part of the second solid polymer electrolyte constituting the fine particles can be softened, The electrolyte membrane and the electrode may be joined. With such a configuration, the adhesion between the electrolyte membrane and the electrode can be enhanced by the softened second solid polymer electrolyte constituting the fine particles.

  In the method for manufacturing a membrane-electrode assembly for a fuel cell according to the present invention, the heating performed in the fourth step is performed without melting at least a part of the plurality of fine particles after joining the electrode and the electrolyte membrane. It is good also as heating on the conditions which maintain particle shape. With such a configuration, it is possible to suppress the occurrence of gas flow inhibition due to liquid water in the vicinity of the electrode.

  In the method for producing a membrane-electrode assembly for a fuel cell of the present invention, the second solid polymer electrolyte is a fluorine-based electrolyte, and the fourth step is performed by heating to a temperature at which the fluorine-based electrolyte is softened. Then, the electrolyte membrane and the electrode may be joined. Fluorine electrolytes have a relatively low glass transition temperature among solid polymer electrolytes. Therefore, by heating to a relatively low temperature, the fine particles can be easily softened, and the adhesion between the electrolyte membrane and the electrode can be ensured.

  In such a method for producing a membrane-electrode assembly of the present invention, the first solid polymer electrolyte may be a hydrocarbon-based electrolyte. By manufacturing a fuel cell using the membrane-electrode assembly manufactured in this way, the gas cross-leakage between the fuel gas flow path and the oxidizing gas flow path through the electrolyte membrane is compared. It is possible to obtain a fuel cell that does not easily occur. Such a hydrocarbon-based electrolyte has a relatively high glass transition temperature among solid polymer electrolytes. However, in order to ensure adhesion between the electrolyte membrane and the electrode by fine particles comprising a fluorine-based electrolyte, When joining with an electrode, joining can be easily performed without heating to a temperature at which the hydrocarbon-based electrolyte softens.

  In the method for producing a membrane-electrode assembly of the present invention, the third step is a step of applying a catalyst paste containing a catalyst and a solvent on a substrate, and drying the applied catalyst paste. The step 4 may be a step of joining the electrode formed on the substrate and the electrolyte membrane. With such a configuration, the electrode can be formed by a simple method of applying the catalyst paste on the substrate, and the catalyst paste is dried prior to joining, so that the electrode is supplied from the electrode to the electrolyte membrane. It is possible to suppress the amount of moisture.

  In the method of manufacturing a membrane-electrode assembly according to the present invention, the fourth step includes arranging the plurality of fine particles on the surface of one member of the electrode and the electrolyte membrane, and the surface on which the fine particles are arranged and the other side. It is good also as a process of superimposing these members and joining them. With such a configuration, the adhesion between the electrolyte membrane and the electrode can be ensured by a simple process of arranging a plurality of fine particles.

  In the first or second membrane-electrode assembly production method of the present invention, the fine particles may have a particle size of 1 to 100 μm. By setting it as such a structure, the adhesiveness between an electrolyte membrane and an electrode can be ensured favorable.

The membrane-electrode assembly for a fuel cell of the present invention is
An electrolyte membrane comprising a first solid polymer electrolyte;
A fine particle portion formed by a plurality of fine particles including a second solid polymer electrolyte disposed on the electrolyte membrane;
And an electrode provided with a catalyst formed on the electrolyte membrane with the fine particle portion interposed therebetween.

  According to the membrane-electrode assembly of the present invention configured as described above, the adhesion between the electrolyte membrane and the electrode is ensured by the fine particle portion composed of a plurality of fine particles including the second solid polymer electrolyte. be able to. Therefore, by manufacturing a fuel cell using the membrane-electrode assembly of the present invention, the contact resistance between the electrolyte membrane and the electrode can be reduced, and the battery performance can be improved. Further, in the membrane-electrode assembly in which the adhesion between the electrolyte membrane and the electrode is ensured by solid fine particles, such as the membrane-electrode assembly of the present invention, the electrolyte membrane is bonded at the time of joining the electrolyte membrane and the electrode. Therefore, excessive moisture is not supplied. Therefore, in the membrane-electrode assembly, the electrolyte membrane does not swell due to excessive water supply or the electrolyte membrane shrinks due to subsequent drying, and the generation of stress inside the membrane-electrode assembly is suppressed. Has been. Therefore, the durability of the fuel cell can be improved by manufacturing the fuel cell using the membrane-electrode assembly of the present invention.

  The present invention can be realized in various forms other than the above, for example, a membrane-electrode assembly manufactured by the method for manufacturing a membrane-electrode assembly of the present invention, or a fuel including the membrane-electrode assembly of the present invention. It can be realized in the form of a battery or the like.

A. Fuel cell configuration:
FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a single cell 10 constituting a fuel cell as a preferred embodiment of the present invention. The unit cell 10 includes an electrolyte membrane 20, fine particle portions 27 and 28 formed on each surface of the electrolyte membrane 20, an anode 21 and a cathode 22 that are electrodes formed on the fine particle portions 27 and 28, and an electrode. Gas diffusion layers 23 and 24 sandwiching the electrolyte membrane 20 formed with the gas from both sides, and gas separators 25 and 26 disposed further outside the gas diffusion layers 23 and 24.

  The fuel cell of this example is a solid polymer fuel cell, and the electrolyte membrane 20 includes a solid polymer electrolyte that exhibits proton conductivity in a wet state. In the present embodiment, the electrolyte membrane 20 is formed of a hydrocarbon-based solid polymer electrolyte. The fine particle portions 27 and 28 are disposed on the electrolyte membrane 20 and are formed of a plurality of fine particles made of a fluorine-based solid polymer electrolyte. The anode 21 and the cathode 22 include, for example, platinum or a platinum alloy as a catalyst. More specifically, the anode 21 and the cathode 22 include carbon particles supporting the catalyst and a fluorine-based electrolyte similar to the solid polymer electrolyte that forms the fine particle portions 27 and 28. The electrolyte membrane 20, the fine particle portions 27 and 28, the anode 21, and the cathode 22 constitute an MEA (Membrane Electrode Assembly) 30. The detailed configuration and manufacturing process of the MEA 30 will be described in detail later.

  The gas diffusion layers 23 and 24 can be formed of a conductive member having gas permeability, such as carbon paper or carbon cloth, metal mesh, or foam metal. The gas diffusion layers 23 and 24 of the present embodiment are both formed as flat plate members. Such a gas diffusion layer 24 serves as a flow path for a gas used for an electrochemical reaction and collects current.

  The gas separators 25 and 26 are formed of a gas impermeable conductive member, for example, a member made of compressed carbon or stainless steel. Each of the gas separators 25 and 26 has a predetermined uneven shape. Due to this uneven shape, an in-cell fuel gas channel 47 through which a fuel gas containing hydrogen flows is formed between the gas separator 25 and the gas diffusion layer 23. In addition, due to the uneven shape, an in-single cell oxidizing gas channel 48 through which an oxidizing gas containing oxygen flows is formed between the gas separator 26 and the gas diffusion layer 24.

  Further, a sealing member such as a gasket is disposed on the outer peripheral portion of the single cell 10 in order to ensure gas sealing performance in the single-cell fuel gas flow channel 47 and the single-cell oxidizing gas flow channel 48 (FIG. Not shown). In addition, the fuel cell of this embodiment has a stack structure in which a plurality of single cells 10 are stacked. The outer periphery of the stack structure is parallel to the stacking direction of the single cells 10 and is fuel gas or oxidation. A plurality of gas manifolds through which gas flows are provided (not shown). The fuel gas flowing through the fuel gas supply manifold among the plurality of gas manifolds is distributed to each single cell 10 and passes through each single cell fuel gas flow channel 47 while being subjected to an electrochemical reaction. Collect in the gas exhaust manifold. Similarly, the oxidizing gas flowing through the oxidizing gas supply manifold is distributed to each single cell 10 and passes through each single cell oxidizing gas flow path 48 while being subjected to an electrochemical reaction, and then gathers in the oxidizing gas discharge manifold. To do.

B. Configuration and manufacturing method of MEA 30:
FIG. 2 is an explanatory diagram schematically showing an enlarged view of the state of the cathode side of the MEA 30, that is, the electrolyte membrane 20, the fine particle portion 28, and the cathode 22. In FIG. 2, unlike FIG. 1, the MEA 30 is shown in a direction in which the film surface is horizontal. In FIG. 2, the region enclosed by a square in the drawing is further enlarged. As described above, the fine particle portions 27 and 28 are layers formed by a plurality of fine particles 29 made of a solid polymer electrolyte disposed between the electrolyte membrane 20 and the anode 21 or the cathode 22. As will be described later, the MEA 30 is formed by arranging fine particles 29 on the electrolyte membrane 20 and then superimposing electrodes produced separately from the electrolyte membrane 20 and hot-pressing them. Therefore, in FIG. 2, a part of the plurality of fine particles 29 constituting the fine particle portions 27 and 28 is shown so as to enter the inside from the surface of the electrolyte membrane 20 and each electrode. In FIG. 2, only the configuration on the cathode side of the MEA 30 is shown, but the MEA 30 of the present embodiment also has the same configuration on the anode side. Below, the manufacturing method of such MEA30 is demonstrated.

  FIG. 3 is a process diagram showing a method for manufacturing the MEA 30. When manufacturing the MEA 30, first, a membrane made of a solid polymer electrolyte to be the electrolyte membrane 20 is prepared (step S100). In this embodiment, as described above, a hydrocarbon-based solid polymer film is used.

  Separately from the electrolyte membrane 20, fine particles 29 made of a solid polymer electrolyte are produced (step S110). In this embodiment, the fine particles 29 are formed of a perfluorosulfonic acid electrolyte that is a fluorine-based solid polymer electrolyte. As a method for producing the fine particles 29 made of such an electrolyte, for example, a spray drying method can be used. Specifically, a solution containing the above-described fluorine-based solid polymer electrolyte is prepared, and the electrolyte solution is granulated by a spray dryer to produce the fine particles 29. When the spray drying method is used, particles having a desired particle diameter can be granulated by appropriately selecting the granulation conditions. Adjustable granulation conditions include the amount of solvent (water, alcohol, etc.) with respect to the electrolyte (solid content) in the electrolyte solution used, the nozzle temperature (inlet temperature) and spray pressure when spray drying, or the electrolyte The spray amount of a solution can be mentioned. By using the spray drying method, substantially spherical particles can be easily produced as the fine particles 29. The particle size of the fine particles 29 made of such a solid polymer electrolyte can be set to 1 to 100 μm, for example. In producing the fine particles 29, a method other than the spray drying method may be used. For example, the fine particles 29 may be formed by a freeze drying method.

  Next, the fine particles 29 prepared in step S110 are arranged on the electrolyte membrane 20 prepared in step S100 (step S120), and a layer made of the fine particles 29 to be the fine particle portions 27 and 28 is formed on the electrolyte membrane 20. To do. The fine particles 29 arranged on the electrolyte membrane 20 are configured to improve the adhesion between the electrolyte membrane 20 and the electrodes, as will be described later. Therefore, in the present embodiment, the fine particles 29 are arranged over the entire region where the electrolyte membrane 20 and the electrode overlap on the electrolyte membrane 20.

  Further, apart from the electrolyte membrane 20 and the fine particles 29, a catalyst paste for forming the anode 21 and the cathode 22 which are electrodes is prepared (step S130). The catalyst paste contains carbon particles carrying platinum and a fluorine-based solid polymer electrolyte similar to the fine particles 29. For example, carbon particles comprising platinum are dispersed in a platinum compound solution (for example, a tetraammine platinum salt solution, a dinitrodiammine platinum solution, a platinum nitrate solution, or a chloroplatinic acid solution). It is produced by an impregnation method, a coprecipitation method, or an ion exchange method. The platinum-supported carbon particles thus prepared are dispersed in an appropriate solvent composed of water and an organic solvent, and an electrolyte solution containing the above-described fluorine-based solid polymer electrolyte (for example, Nafion solution, manufactured by Aldrich) ) Is further mixed to obtain a catalyst paste.

  Next, the catalyst paste is applied to a predetermined base material, and an electrode to be the anode 21 or the cathode 22 is formed on the base material (step S140). As a base material to which the catalyst paste is applied, for example, a base material made of polyethylene terephthalate (PET) or polytetrafluoroethylene (PTFE) can be used. The application of the catalyst paste onto the substrate can be performed by, for example, a spray method, screen printing, a doctor blade method, or an ink jet method. By using these methods, the catalyst paste can be applied to a desired thickness. After applying the catalyst paste as described above, the applied catalyst paste is dried to form a porous electrode having fine pores inside. The applied catalyst paste is dried in step S140 as long as it removes at least a part of the solvent contained in the applied catalyst paste. However, as the degree of drying increases, the electrode and the electrolyte membrane described later are increased. The amount of water supplied from the electrode to the electrolyte membrane at the time of bonding can be suppressed.

  Thereafter, the electrode produced on the substrate in step S140 is hot-pressure transferred onto the electrolyte membrane 20 in which the fine particles 29 are arranged in step S120 (step S150), and then the substrate is peeled off and removed, thereby removing the MEA 30. Is completed. That is, the MEA 30 in which the fine particle portions 27 and 28 made of the fine particles 29 are formed on the electrolyte membrane 20 and the anode 21 or the cathode 22 is further formed on the fine particle portions 27 and 28 is completed. The temperature at the time of joining as one of the conditions for performing the thermal pressure transfer in step S150 may be a temperature at which at least a part of the solid polymer electrolyte constituting the fine particles 29 is softened. As described above, the softening of the fine particles 29 brings the electrolyte membrane 20 and the electrode into close contact via the fine particle portions 27 and 28 formed of the fine particles 29. That is, the fine particle portions 27 and 28 function as an adhesive layer that improves the adhesion between the electrolyte membrane 20 and the electrode. In this embodiment, since the fine particles 29 are formed of a fluorine-based electrolyte, the temperature at which the thermal pressure transfer is performed may be a temperature at which the fine particles 29 made of the fluorine-based electrolyte are softened, for example, 80 to 160 ° C. Can be done. The pressure as another condition when performing the heat-pressure transfer is a pressure that can sufficiently bring the electrolyte membrane 20 and the electrode into close contact via the fine particle portions 27 and 28 including the softened electrolyte as described above. For example, it may be 1 to 10 MPa. The conditions for performing the hot-pressure transfer can be set as a combination of temperature, pressure, and time. The conditions at the time of the transfer are the fine particle portions 27 and 28 between the electrolyte membrane 20 and the electrodes joined by the transfer. It is desirable to maintain the particle shape without melting at least part of the fine particles 29.

  Note that the process of step S120 or step S150 in FIG. 3 need not be performed simultaneously on the anode side and the cathode side. After the steps S120 to S150 are performed on one side of the anode side and the cathode side to join the electrolyte membrane and the electrode, the same steps may be repeated on the other side.

  According to the method of manufacturing the MEA 30 included in the fuel cell of the present embodiment configured as described above, a plurality of fine particles 29 are disposed between the electrolyte membrane 20 and the electrode, and then the electrolyte membrane 20 and the electrode are joined. As a result, fine particle portions 27 and 28 are formed between the electrolyte membrane 20 and the electrodes. Therefore, excessive moisture is not supplied to the electrolyte membrane 20 when forming the fine particle portions 27 and 28 that function as adhesive layers that improve the adhesion between the electrolyte membrane 20 and the electrodes. Further, since the electrode is prepared separately from the electrolyte membrane 20 and dried in advance, excessive water is not supplied from the electrode to the electrolyte membrane 20. Therefore, swelling of the electrolyte membrane 20 due to excessive water supply and shrinkage of the electrolyte membrane 20 due to subsequent drying do not occur. By suppressing the swelling and shrinkage of the electrolyte membrane 20, it is possible to suppress a decrease in adhesion between the electrolyte membrane 20 and the electrode during the production of the fuel cell due to the swelling and shrinkage of the electrolyte membrane 20. Further, by suppressing the swelling and shrinkage of the electrolyte membrane 20, the generation of stress inside the MEA 30 due to the swelling and shrinkage of the electrolyte membrane 20 is suppressed, and the electrolyte membrane 20 and the electrode in the process of generating power by the fuel cell It is possible to suppress a decrease in adhesion between the two.

  Further, in the present embodiment, at the time of bonding performed by arranging a plurality of fine particles 29 between the electrolyte membrane 20 and the electrode, at least a part of the solid polymer electrolyte constituting the fine particles 29 is softened, so that the electrolyte The adhesion between the film 20 and the electrode is further increased. Therefore, by ensuring the adhesion between the electrolyte membrane 20 and the electrode in this way, the contact resistance between the electrolyte membrane 20 and the electrode can be reduced and the battery performance can be improved. Durability can be improved.

  Here, in this embodiment, the fine particles 29 are made of a solid polymer electrolyte, specifically, a fluorine-based solid polymer electrolyte similar to the electrolyte provided in the electrode. Thus, since the fine particles 29 have proton conductivity, the movement of protons between the electrolyte membrane 20 and the electrode is not hindered by the fine particles 29, and the battery performance resulting from the provision of the fine particle portions 27 and 28 is provided. Can be suppressed.

  Further, like the fuel cell of the present embodiment, a fuel cell using an electrolyte membrane made of a hydrocarbon-based electrolyte has a gas between a fuel gas channel and an oxidizing gas channel with the electrolyte membrane interposed therebetween. The cross-leakage is relatively unlikely to occur, and the hydrocarbon electrolyte has excellent features such as a lower manufacturing cost than the fluorine electrolyte. However, the hydrocarbon-based electrolyte has a property that the glass transition temperature is high (about 220 ° C.) and the glass transition temperature is close to the decomposition temperature of the electrolyte. Therefore, if the electrolyte membrane and the electrode are joined by, for example, increasing the temperature of the electrolyte membrane to near the glass transition temperature to soften the electrolyte membrane and then thermocompression bonding with the electrode, the electrolyte membrane is decomposed. There was a problem that it was difficult to control the temperature for joining the electrolyte membrane and the electrode while suppressing deterioration. In this embodiment, since the fine particle 29 made of a fluorine-based electrolyte is disposed between the electrolyte membrane 20 made of such a hydrocarbon-based electrolyte and the electrode, the decomposition temperature of the hydrocarbon-based electrolyte is lower. Then, the hot-pressure bonding can be performed by raising the temperature to a temperature at which the fluorine-based electrolyte is softened. Therefore, it is possible to facilitate the process of securing the adhesion between the electrolyte membrane 20 and the electrode by hot-pressure bonding.

  In addition, when the electrolyte membrane 20 is formed of a hydrocarbon-based electrolyte and the fine particles 29 are formed of a fluorine-based electrolyte, the above advantages are obtained, but different configurations may be employed. Various combinations are possible for the electrolyte included in the electrolyte membrane 20, the fine particles 29, and the electrode.

  In the embodiment, the fine particles 29 are composed only of the solid polymer electrolyte, but may be configured differently. The fine particles 29 can be softened to improve the adhesion between the electrolyte membrane 20 and the electrodes, and at least a part of the solid polymer electrolyte that can ensure proton conductivity in the fine particle portions 27 and 28. It should just contain. As a result, it is possible to improve the initial performance of the fuel cell by improving the adhesion between the electrolyte membrane and the electrode, and to suppress the excessive water supply to the electrolyte membrane and to increase the durability of the fuel cell. In the case where the fine particles 29 further contain a substance other than the solid polymer electrolyte, the fine particles 29 are disposed if the other substances than the electrolyte have conductivity, catalytic activity, or proton conductivity. It is possible to suppress a decrease in the battery reaction due to. Examples of the configuration in which the fine particles include a substance other than the solid polymer electrolyte include a configuration in which the fine particles further include catalyst particles such as platinum and particles made of a conductive material such as carbon. In order to produce such fine particles, for example, as a fine particle material, in addition to the solid polymer electrolyte, a dispersion containing the above catalyst particles and conductive particles may be used in a spray dryer and granulated.

  In step S120, the fine particles 29 are arranged to form the fine particle portions 27 and 28 in the entire contact region, which is a region where the electrolyte membrane 20 and the electrode overlap, but a different configuration may be used. Even if the region where the fine particle part is formed is a part of the contact region, in the part where the fine particle part is provided, the deterioration of durability due to the water supply to the electrolyte membrane is suppressed, and the electrolyte membrane and the electrode A similar effect for improving adhesion can be obtained. For example, in the contact area, the fine particle part may be provided only in the vicinity of the outer peripheral part. However, in order to ensure an even adhesion between the electrolyte membrane and the electrode in the entire contact area, the fine particles are formed substantially uniformly in the entire contact area, as in the embodiment. Is desirable.

  In the embodiment, the fine particles 29 are arranged on the electrolyte membrane 20 and the electrodes are stacked thereon to produce the MEA. However, a different configuration may be used. For example, the MEA may be manufactured by disposing the fine particles 29 on the electrode formed on the base material, and superposing the electrolyte membrane 20 on the electrode 29, followed by hot pressure bonding. Alternatively, the fine particles 29 are arranged on the electrodes, the electrolyte membrane 20 is overlaid thereon, the fine particles 29 are further arranged on the electrolyte membrane 20, and the electrodes are further overlaid thereon, and then the whole is subjected to hot-pressure bonding. Thus, the MEA can be manufactured.

  In the embodiment, the fine particle 29 is used to provide the fine particle portions 27 and 28 on both sides of the electrolyte membrane 20, but the fine particle portion may be provided only on either the anode side or the cathode side. If the electrolyte membrane and the electrode are bonded to each other on at least one surface of the electrolyte membrane with the fine particles in between, the durability deterioration due to the water supply to the electrolyte membrane is reduced on the side where the fine particle portion is formed. While suppressing, the same effect which improves the adhesiveness of an electrolyte membrane and an electrode can be acquired.

C. Evaluation results of fuel cells of Examples:
The fuel cells of Experimental Examples 1 to 4 were manufactured according to the above-described Examples, and the performance was evaluated together with the fuel cell of the Comparative Example. Each fuel cell differs only in the MEA configuration. The production conditions for the MEA provided in each fuel cell are as follows. In addition, as a manufacturing condition of MEAs other than Experimental Example 1, only the parts different from Experimental Example 1 are described.

Experimental example 1:
In step S100, as described above, the electrolyte membrane 20 made of a hydrocarbon-based electrolyte was prepared. In step S110, a Nafion solution (manufactured by DuPont, solid content 20%) diluted with a solvent to a solid content of 10% was used as the electrolyte solution. A powder having a particle size distribution peak of 5 to 10 μm was prepared from such an electrolyte solution using a spray dryer, and the particles 29 were obtained. In step S120, a predetermined amount of the fine particles 29 are arranged on the electrolyte membrane 20 so as to be substantially uniform through a sieve. At that time, the basis weight was 0.2 mg / cm ² .

In step S130, platinum-carrying carbon particles having a platinum loading of 50 wt%, water, and an electrolyte solution similar to that used in step S110 are mixed, and the mixture is dispersed by ultrasonic waves to obtain a catalyst paste. Produced. In step S140, such a catalyst paste was applied onto a polytetrafluoroethylene (PTFE) base material with a bar coater and dried on a hot plate at 120 ° C. to form an electrode. When the amount of platinum per unit area contained in the obtained electrode was calculated, it was about 1 mg / cm ² .

  In step S150, the electrode formed on the substrate was superposed on the surface of the electrolyte membrane 20 on which the fine particles 29 were disposed, and was transferred onto the electrolyte membrane by heat and pressure. The hot-pressure transfer was performed under the conditions of a temperature of 100 ° C., a pressure of 3 MPa, and a time of 50 minutes.

Experimental Example 2 (fine particle portions 27 and 28 are thick):
In Experimental Example 2, the same process as in Experimental Example 1 was performed except that the basis weight when placing the fine particles 29 on the electrolyte membrane 20 so as to be substantially equal in Step S120 was 0.4 mg / cm ^2. Manufactured.

Experimental Example 3 (Particle 29 has a large particle size):
In Experimental Example 3, it was manufactured in the same process as in Experimental Example 1 except that when the fine particles 29 were prepared using a spray dryer in Step S110, the peak of the particle size distribution was changed to 40 to 50 μm.

Experimental example 4 (temperature at the time of joining is high):
In Experimental Example 4, it was manufactured by the same process as in Experimental Example 1 except that the temperature was changed to 150 ° C. when performing the thermal pressure transfer in Step S150.

Comparative Example 1 (using an electrolyte solution instead of the fine particles 29):
In Comparative Example 1, an electrolyte solution was disposed instead of the powdery fine particles 29 between the electrolyte membrane 20 and the electrode. That is, instead of step S110, a process of preparing an electrolyte solution (solid content 10%) similar to that used in step S110 is performed, and instead of step S120, the electrolyte solution 20 is applied by spraying the electrolyte solution. Above, it was arranged so as to have a basis weight of 0.2 mg / cm ² . The other steps S100, S130, and S140 are performed in the same manner as in Example 1. In step S150, the electrode was subjected to hot-pressure transfer before the electrolyte solution disposed on the electrolyte membrane 20 was dried. .

Comparative example 2 (electrolyte membrane and electrode are directly joined):
In Comparative Example 2, the electrode formed on the base material in Step S140 was directly bonded onto the electrolyte membrane 20 prepared in Step S100 without performing Step S110 and Step S120 related to the fine particles 29. In step S150, hot-pressure transfer was performed at a temperature of 130 ° C. while supplying water to the interface between the electrolyte membrane and the electrode. As a method of supplying water to the interface between the electrolyte membrane and the electrode, a method of supplying liquid water, specifically, a method of pre-wetting the electrolyte membrane surface with water was used.

Using each MEA produced as described above, a fuel cell was produced in a single cell state as shown in FIG. 1 and connected to a load to generate power. FIG. 4 shows the measured value of the output voltage when the temperature is kept at 80 ° C. and the output current density is kept at 0.2 A / cm ² for each fuel cell. At this time, hydrogen and oxygen are excessively large for the anode and cathode of each fuel cell (the so-called stoichiometry, which is the ratio of the actual supply amount to the theoretically required amount, is 1.2 to 6. Hydrogen gas or air was supplied to 0), and the supplied hydrogen gas and air were humidified using a bubbler.

  As shown in FIG. 4, any of the fuel cells of Experimental Examples 1 to 4 showed an output voltage equivalent to that of Comparative Example 1. That is, when the electrolyte membrane 20 and the electrode are joined via the fine particles 29 made of the electrolyte, the initial performance is equivalent to that obtained when the electrolyte membrane and the electrode are joined using the electrolyte solution. It was. As shown in this example, when using a powdery solid adhesive layer as in the example, as in the case of using a liquid adhesive layer, the gap between the electrolyte membrane and the electrode is shown. It was confirmed that the contact resistance was sufficiently small. Therefore, when a powdery adhesive layer is used as in the examples, it is considered that the adhesion between the electrolyte membrane and the electrode is enhanced as in the case of using the liquid adhesive layer. As described above, in Experimental Examples 1 to 4, the basis weight of the fine particles 29, the particle size of the fine particles 29, or the bonding temperature is different, but the initial performance greatly decreases due to the difference in these conditions. I couldn't see it.

  FIG. 5 shows the results of examining the durability of the electrolyte membrane by causing each fuel cell to generate power for the load under a temperature condition of 80 ° C. and repeatedly turning on and off the connection with the load at regular time intervals. Is shown. The durability of the electrolyte membrane was examined based on the amount of hydrogen leakage from the fuel gas channel side to the oxidizing gas channel side through the electrolyte membrane. Specifically, the hydrogen concentration in the cathode offgas discharged from the cathode side of the fuel cell is measured, and the time until the hydrogen concentration in the cathode offgas exceeds a predetermined reference value is defined as the endurance time. The battery durability time was compared. Here, the reference value is set to 1 / 100th of the lower limit of hydrogen explosion, and the time until the hydrogen concentration in the cathode off-gas exceeds the reference value, that is, the power generation of the fuel cell that is repeatedly turned on and off. The elapsed time from the start of the process was defined as the durability time. When measuring the endurance time, hydrogen gas or air is supplied to the anode and cathode of each fuel cell so that the stoichiometric ratio is 1.2 to 6.0. Gas and air were humidified using a bubbler.

  As shown in FIG. 5, all the fuel cells of Experimental Examples 1 to 4 showed significantly longer endurance time than the fuel cells of Comparative Example 1 and Comparative Example 2. As described above, when an adhesive layer made of fine electrolyte particles is provided, the durability of the fuel cell is improved compared to the case where a method is used in which moisture is supplied to the electrolyte membrane when joining the electrolyte membrane and the electrode. Confirmed to do. As a result, when an adhesive layer made of electrolyte fine particles is provided, deformation (dimension change) of the electrolyte membrane caused by excessive water supply to the electrolyte can be suppressed. It is considered that the deterioration of the electrolyte membrane that progresses with time is suppressed.

  In addition to the results shown in FIG. 4 and FIG. 5, changes in output voltage (so-called IV characteristics) when the output current was changed were examined for the fuel cells of each experimental example and comparative example. The IV characteristic of a fuel cell generally shows that the output voltage increases until the output current increases to a certain degree (high load), but the output voltage gradually decreases when the output current increases to a certain degree. As one of the factors for lowering the output voltage in such a high load region, flooding (inhibition of gas flow caused by liquid water) due to water generated by an electrochemical reaction can be cited. Since the amount of generated water increases as the amount of power generation increases, the degree of voltage drop due to flooding increases in a high load region. When the IV characteristics of the fuel cells of each experimental example and comparative example are examined, in experimental example 2 and experimental example 4, together with comparative example 1, the degree of voltage drop in the high load region as compared with experimental example 1 and experimental example 3 Was obtained (data not shown). That is, in Experimental Example 2 and Experimental Example 4, it is considered that the degree of occurrence of flooding in the high load region is greater in Comparative Example 1 than in Experimental Example 1 and Experimental Example 3. The reason for this is considered to be that the amount of water retained in the MEA increased in the experimental example 2 because the basis weight of the fine particles 29 was larger than that in the first example, and the electrolytic mass in the MEA increased. Further, in Experimental Example 4, the basis weight of fine particles (electrolytic mass in the MEA) is the same as that in Experimental Example 1, except that the bonding temperature with the electrode is high. When the bonding temperature is high, more fine particles 29 are melted at the time of bonding, and the fine particle portions 27 and 28 are not aggregates of fine particles but are in a state close to an adhesive layer made of an electrolyte solution included in Comparative Example 1. it is conceivable that. Therefore, based on the above results, when providing an adhesive layer having a structure that maintains the shape as an aggregate of fine particles as in Example 1 and Example 3, the adhesive layer is formed by using a molten electrolyte. It is thought that the occurrence of flooding can be suppressed.

2 is a schematic cross-sectional view illustrating a schematic configuration of a single cell 10. FIG. It is explanatory drawing which expands and shows the mode of the cathode side of MEA30 typically. 5 is a process diagram illustrating a method for manufacturing MEA 30. FIG. It is explanatory drawing showing the result of having investigated initial performance about the fuel cell of an experiment example and a comparative example. It is explanatory drawing showing the result of having investigated durability about the fuel cell of an experiment example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Single cell 20 ... Electrolyte membrane 21 ... Anode 22 ... Cathode 23, 24 ... Gas diffusion layer 25, 26 ... Gas separator 27, 28 ... Fine particle part 29 ... Fine particle 30 ... MEA
47 ... Fuel gas flow path in single cell 48 ... Oxidation gas flow path in single cell

Claims (13)

A method for producing a membrane-electrode assembly for a fuel cell, comprising:
A first step of preparing an electrolyte membrane comprising a first solid polymer electrolyte;
A second step of preparing a plurality of fine particles containing a second solid polymer electrolyte;
A third step of preparing an electrode including a catalyst;
A fourth step of superposing and joining the electrode and the electrolyte membrane with the plurality of fine particles in between, and a method for producing a membrane-electrode assembly. A method for producing a membrane-electrode assembly for a fuel cell according to claim 1,
In the fourth step, the electrolyte membrane and the electrode are joined by heating to a temperature at which at least a part of the second solid polymer electrolyte constituting the fine particles can be softened. Production method. A method for producing a membrane-electrode assembly for a fuel cell according to claim 2,
The heating performed in the fourth step is heating under a condition that maintains the particle shape without melting at least a part of the plurality of fine particles after bonding the electrode and the electrolyte membrane. Production method. A method for producing a membrane-electrode assembly for a fuel cell according to claim 2,
The second solid polymer electrolyte is a fluorine-based electrolyte,
The fourth step is a method of manufacturing a membrane-electrode assembly in which the electrolyte membrane and the electrode are joined by heating to a temperature at which the fluorine-based electrolyte is softened. A method for producing a membrane-electrode assembly for a fuel cell according to claim 4,
The first solid polymer electrolyte is a hydrocarbon electrolyte. A method for producing a membrane-electrode assembly. A method for producing a membrane-electrode assembly for a fuel cell according to any one of claims 1 to 5,
The third step is a step of applying a catalyst paste containing a catalyst and a solvent on a substrate and drying the applied catalyst paste,
The fourth step is a step of joining the electrode formed on the substrate and the electrolyte membrane. A method for producing a membrane-electrode assembly. A method for producing a membrane-electrode assembly for a fuel cell according to any one of claims 1 to 6,
The fourth step is a step in which the plurality of fine particles are arranged on the surface of one member of the electrode and the electrolyte membrane, and the surface on which the fine particles are arranged and the other member are overlapped to perform bonding. A method for producing a membrane-electrode assembly. A method for producing a membrane-electrode assembly for a fuel cell according to any one of claims 1 to 7,
The method for producing a membrane-electrode assembly, wherein the fine particles have a particle size of 1 to 100 μm. A fuel cell membrane-electrode assembly comprising:
An electrolyte membrane comprising a first solid polymer electrolyte;
A fine particle portion formed by a plurality of fine particles including a second solid polymer electrolyte disposed on the electrolyte membrane;
A membrane-electrode assembly comprising: an electrode comprising a catalyst formed on the electrolyte membrane with the fine particle portion interposed therebetween. A membrane-electrode assembly for a fuel cell according to claim 9,
The second solid polymer electrolyte is a fluorine-based electrolyte. Membrane-electrode assembly. A membrane-electrode assembly for a fuel cell according to claim 10,
The first solid polymer electrolyte is a hydrocarbon electrolyte. Membrane-electrode assembly. A fuel cell membrane-electrode assembly according to any one of claims 9 to 11,
The fine particle has a particle size of 1 to 100 μm. A fuel cell,
A fuel cell comprising the membrane-electrode assembly according to any one of claims 9 to 12.

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