JP2016066510A - Catalyst ink and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst ink used for producing a catalyst layer, which has high dispersion stability, and enables the enhancement in power generation performance of a fuel battery; and a method for manufacturing such a catalyst ink.SOLUTION: A catalyst ink 1 used for producing a catalyst layer formed on a surface of an electrolyte film in a membrane-electrode assembly including the electrolyte film and the catalyst layer laminated on the electrolyte film comprises: carbon 11 with a catalyst supported thereon; an ionomer 12; and a solvent. The solvent consists of water 13.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a catalyst ink and a method for producing the same. More specifically, the present invention relates to a catalyst ink used for producing the catalyst layer formed on the surface of the electrolyte membrane in a membrane-electrode assembly comprising an electrolyte membrane and a catalyst layer laminated on the electrolyte membrane. About.

  In recent years, fuel cells that generate electricity by electrochemical reaction of hydrogen and oxygen are attracting attention as new power sources for automobiles. A fuel cell is preferred in terms of high power generation efficiency because it directly obtains electricity through an electrochemical reaction. In addition, since the fuel cell generates only water during power generation, it is considered preferable from the viewpoint of environmental impact.

  For example, a polymer electrolyte fuel cell has a stack structure in which several tens to several hundreds of fuel cells are stacked. Each fuel cell is configured by sandwiching a membrane-electrode assembly between a pair of separators. The membrane-electrode structure is composed of an anode electrode (cathode), a cathode electrode (anode), and an electrolyte membrane sandwiched between these electrodes, and both electrodes are in contact with the catalyst layer and the catalyst layer. A gas diffusion layer. The separator has a fuel gas channel formed on one surface thereof and an oxidant gas channel formed on the other surface thereof.

  In the polymer electrolyte fuel cell having the above-described configuration, hydrogen as fuel gas is supplied to the anode electrode via the fuel gas flow path. In addition, air as an oxidant gas is supplied to the cathode electrode via the oxidant gas flow path. Then, the hydrogen supplied to the anode electrode is protonated on the catalyst layer, and the generated proton moves to the cathode electrode through the electrolyte membrane. At this time, electrons generated together with protons are taken out to an external circuit and used as electric energy.

  In the production of a polymer electrolyte fuel cell, a catalyst ink containing carbon carrying a catalyst, an ionomer as an ion conductive material, and a solvent is applied to the surface of a water repellent sheet or the like, so that the anode electrode side and A catalyst layer on the cathode electrode side is produced (for example, see Patent Document 1).

JP 2010-192238 A

  By the way, in the catalyst ink used for producing the catalyst layer, the viscosity is adjusted to an appropriate value by using an alcohol having an appropriate viscosity as a solvent, thereby improving the coating workability.

FIG. 9 is a schematic diagram showing the action of a conventional catalyst ink. The ionomer has a large molecular surface area (long molecular end distance) in an alcohol solvent that is a good solvent. As described above, when the intermolecular distance of the ionomer is increased, the dispersion stability of the catalyst ink is lowered, and the coatability is also lowered accordingly.
Furthermore, in conventional catalyst inks, the ionomer has a higher affinity with an alcohol solvent than the carbon on which the catalyst is supported, and thus is difficult to adsorb on the carbon on which the catalyst is supported. As described above, if the ionomer is difficult to adsorb on the carbon on which the catalyst is supported, it is difficult to form a three-phase interface in the catalyst layer, and the power generation performance of the fuel cell is degraded. Note that if the content of a catalyst such as platinum in the catalyst ink is increased, the power generation performance of the fuel cell can be improved. However, if the content of the platinum catalyst in the catalyst is increased, the cost in manufacturing the fuel cell increases.

  The present invention has been made in view of the above problems, and is a catalyst ink used for producing a catalyst layer, which has high dispersion stability and can improve the power generation performance of a fuel cell. An object is to provide an ink and a method for producing the same.

  In order to achieve the above object, the present invention is used to produce the catalyst layer formed on the surface of the electrolyte membrane in a membrane-electrode assembly comprising an electrolyte membrane and a catalyst layer laminated on the electrolyte membrane. A catalyst ink (e.g., catalyst ink 1 described later), a carbon carrying a catalyst (e.g., carbon 11 carrying a catalyst described later), an ionomer (e.g., ionomer 12 described later), a solvent, The solvent provides a catalyst ink composed only of water (for example, water 13).

In the present invention, in a catalyst ink containing carbon on which a catalyst is supported, an ionomer, and a solvent, the solvent is composed only of water.
Water is a poor solvent for ionomers. Accordingly, in the catalyst ink, the ionomer has a small molecular surface area (short molecular end distance), and thus the catalyst ink has high dispersion stability. Since the catalyst ink has high dispersion stability, the coating property is also high. Further, in the conventional catalyst ink, the ionomer has higher affinity with the carbon on which the catalyst is supported than with water, and thus is adsorbed on the carbon on which the catalyst is supported. When the ionomer is adsorbed on the carbon on which the catalyst is supported, a three-phase interface is easily formed in the catalyst layer formed using the catalyst ink according to the present embodiment. The power generation performance of the fuel cell is improved by forming a three-phase interface in the catalyst layer.

  The total content of the carbon on which the catalyst is supported and the ionomer is preferably 10 to 15% by mass.

  Thereby, the adsorption rate of the ionomer to the carbon carrying the catalyst is further improved. Since the adsorption rate of the ionomer to the carbon on which the catalyst is supported is further improved, a three-phase interface is easily formed in the formed catalyst layer, and the fuel cell performance is further improved.

  The present invention also relates to a catalyst ink (for example, described later) used for forming the catalyst layer on the surface of the electrolyte membrane in a membrane-electrode assembly comprising an electrolyte membrane and a catalyst layer laminated on the electrolyte membrane. A method for producing catalyst ink 1), in which a catalyst is supported on carbon (for example, carbon 11 on which a catalyst described later is supported), an ionomer (for example, ionomer 12 described later) and water as a solvent (for example, water 13). ) Are mixed to obtain a mixed solution (for example, a mixing step S1 to be described later), and a crushing step to crush the carbon on which the catalyst is supported in the mixed solution (for example, a crushing step to be described later) S2), and a method for producing a catalyst ink.

In the present invention, the method for producing a catalyst ink includes a crushing step of crushing carbon carrying a catalyst in a mixed solution in which carbon, an ionomer, and water as a solvent are mixed.
Thereby, it is possible to obtain a catalyst ink having high dispersion stability in which carbon carrying the catalyst is crushed and dispersed. A catalyst ink having a high dispersion stability has a high coating property, and the formed catalyst layer is homogeneous and a three-phase interface is easily formed.

  In the crushing step, the mixed solution is preferably subjected to ultrasonic treatment.

  Thereby, the carbon carrying the catalyst is more easily dispersed. The above effect can be obtained more easily by further dispersing the carbon on which the catalyst is supported.

  ADVANTAGE OF THE INVENTION According to this invention, it can provide the catalyst ink which has high dispersion stability and can improve the electric power generation performance of a fuel cell, and its manufacturing method.

It is a figure which shows the manufacturing method of the catalyst ink which concerns on one Embodiment of this invention. It is a graph which shows the ionomer adsorption rate of the catalyst ink of an Example and a comparative example. It is a graph which shows the ionomer adsorption rate of the catalyst ink of an Example, and is a graph which shows the relationship between solid content concentration of a catalyst ink, and ionomer adsorption rate. It is a graph which shows the relationship between the current density and the cell voltage of the catalyst ink of an Example and a comparative example. It is a graph which shows the relationship between the elapsed days of standing and the median diameter of the carbon by which the catalyst was carry | supported of the catalyst ink of an Example and a comparative example. It is a SEM image of the cross section of the fuel battery cell produced using the catalyst ink of a comparative example. It is a SEM image of the cross section of the fuel battery cell produced using the catalyst ink of an Example. It is a schematic diagram shown about the effect | action of the catalyst ink which concerns on the said embodiment. It is a schematic diagram shown about the effect | action of the conventional catalyst ink.

  Hereinafter, an embodiment of the present invention will be described in detail.

<Membrane-electrode assembly>
The membrane-electrode assembly in the present embodiment includes an electrolyte membrane and a catalyst layer laminated on the electrolyte membrane. More specifically, the membrane-electrode assembly is preferably formed by laminating an electrolyte membrane, a catalyst layer, and a gas diffusion layer in this order.
The electrolyte membrane is, for example, a solid polymer electrolyte membrane composed of perfluorosulfonic acid. As this solid polymer electrolyte membrane, a commercially available product can be used. For example, “Nafion” manufactured by DuPont can be used.

  The catalyst layer is laminated on both surfaces of the electrolyte membrane. The catalyst layer can be produced, for example, by coating the catalyst ink on a water-repellent sheet such as a PET sheet made of a PET film. The method for applying the catalyst ink to the water repellent sheet or the like is not particularly limited, and a conventionally known application method can be used. Examples of conventionally known coating methods include brush coating, brush coating, bar coater coating, knife coater coating, doctor blade method, screen printing, and spray coating.

  Subsequently, after sandwiching the electrolyte membrane with the catalyst layer produced on the PET sheet and hot pressing, the PET sheet is peeled off to laminate the anode catalyst layer on one surface of the electrolyte membrane and the cathode on the other surface. A catalyst layer is laminated. The catalyst ink for producing the catalyst layer will be described in detail later.

  The gas diffusion layers are laminated on the outer surfaces of the pair of catalyst layers. The gas diffusion layer can be produced by applying a slurry in which carbon black and PTFE (polytetrafluoroethylene) particles are uniformly dispersed to carbon paper and drying the slurry. An anode gas diffusion layer is disposed on the outer surface of the anode catalyst layer, and a cathode gas diffusion layer is disposed on the outer surface of the cathode catalyst layer. In this state, hot pressing is performed. Thereby, a membrane-electrode assembly is produced.

A fuel cell is produced by laminating a pair of separators on the membrane-electrode assembly.
The separator is laminated on the outer surface of the pair of gas diffusion layers. The separator can be produced by forming a metal thin plate into a corrugated plate by press molding. Specifically, a metal thin plate is formed by drawing with a conventionally known press forming apparatus to form a corrugated plate having irregularities. As the metal thin plate, for example, a steel plate, a stainless steel plate, an aluminum plate, or the like is used. The separator is not limited to a metal separator, and may be a carbon separator, for example.

  A fuel gas (hydrogen) flow path is formed between the anode gas diffusion layer and one separator, and an oxidant gas (oxygen) flow path is formed between the cathode gas diffusion layer and the other separator. The Hydrogen supplied to the fuel gas channel diffuses in the anode gas diffusion layer and is protonated on the anode catalyst layer, and the generated proton moves to the cathode electrode side through the electrolyte membrane. At this time, electrons generated together with protons are taken out to an external circuit and used as electric energy.

<Catalyst ink>
The catalyst ink according to the present embodiment includes carbon on which a catalyst is supported, an ionomer, and a solvent.
The carbon on which the catalyst is supported is an electrode catalyst in which catalytic metal particles as a catalyst are supported on carbon as a conductive carrier.

  The carbon supporting the catalyst metal particles is not particularly limited as long as it has conductivity and moderate corrosion resistance. It is desirable to have. Carbon not only supports the catalyst metal particles but also functions as a current collector for taking out electrons to the external circuit or taking them in from the external circuit. If the electric resistance of carbon is high, the internal resistance of the battery increases, and the performance of the battery decreases. For this reason, the electronic conductivity of carbon contained in the catalyst ink must be sufficiently high. Therefore, a carbon material having fine pores is preferably used as the carbon supporting the catalyst metal particles. Examples of the carbon material having developed pores include carbon black and activated carbon. Examples of carbon black include channel black, furnace black, thermal black, and acetylene black. Activated carbon is obtained by carbonizing and activating materials containing various carbon atoms.

  The catalytic metal particles supported on the conductive carrier are not particularly limited as long as they have catalytic activity, and examples thereof include platinum and platinum alloys. If a platinum alloy is used, the stability and activity of the electrode catalyst can be imparted. Platinum alloys include platinum group metals other than platinum (ruthenium, rhodium, palladium, osmium, iridium), cobalt, iron, titanium, gold, silver, chromium, manganese, molybdenum, tungsten, aluminum, silicon, rhenium, zinc, Further, an alloy of platinum and one or more metals selected from the group consisting of tin and platinum is preferable, and the platinum alloy may contain an intermetallic compound of platinum and a metal to be alloyed.

  As the carbon on which the catalyst is supported, a prepared carbon may be used, or a commercially available carbon may be used. When preparing carbon carrying a catalyst, the preparation method is not particularly limited, and a conventionally known method can be used. As a conventionally known method for preparing a catalyst, for example, a platinum compound solution or suspension is added to a carrier powder, evaporated to dryness, insolubilized with an acid or alkali, and then subjected to a reduction treatment to activate the supported component. And the like.

  The ionomer conducts ions used or generated in the electrode reaction in the catalyst layer. Examples of the ionomer include a fluorine-based polymer in which at least a part of the polymer skeleton is fluorinated, or a hydrocarbon-based polymer that does not contain fluorine in the polymer skeleton, and includes an ion exchange group. And the like. Moreover, the kind of this ion exchange group is not specifically limited, It can select arbitrarily according to a use. Examples of the ion exchange group include sulfonic acid, carboxylic acid, and phosphonic acid.

  In the catalyst ink, the total content of carbon and ionomer on which the catalyst is supported is preferably 10 to 15% by mass. When the total content of carbon and ionomer on which the catalyst is supported is less than 10% by mass, the adsorption rate of the ionomer on the carbon on which the catalyst is supported tends to decrease. When the adsorption rate of the ionomer on the carbon on which the catalyst is supported is lowered, the three-phase interface is hardly formed in the formed catalyst layer, so that the fuel cell performance is lowered. Even if the total content of carbon and ionomer on which the catalyst is supported exceeds 15% by mass, the adsorption rate of the ionomer on the carbon on which the catalyst is supported is difficult to improve, and the coating property of the catalyst ink decreases. There is a tendency.

  The solid mass ratio of the catalyst-supported carbon and the ionomer (the solid mass of the carbon on which the catalyst is supported / the solid content of the ionomer) is preferably 30/70 to 70/30. If the solid content mass ratio between the carbon on which the catalyst is supported and the ionomer is out of the above range, it is difficult to form a three-phase interface in the formed catalyst layer, and the fuel cell performance tends to be lowered.

The solvent is composed only of water. Water is a poor solvent for ionomers.
FIG. 8 is a schematic diagram showing the action of the catalyst ink 1 according to this embodiment. The ionomer 12 has a small molecular surface area (a short molecular end distance) in the poor solvent water 13. Further, in the conventional catalyst ink, since the ionomer 12 has a higher affinity with the carbon 11 on which the catalyst is supported than with water, the ionomer 12 is adsorbed on the carbon 11 on which the catalyst is supported.

<Method for producing catalyst ink>
Subsequently, a method for producing a catalyst ink according to the present embodiment will be described.
FIG. 1 is a schematic diagram for explaining a method for producing the catalyst ink 1 according to the present embodiment. As shown in FIG. 1, the manufacturing method of the catalyst ink 1 includes a mixing step S1 for obtaining a mixed solution by mixing the carbon 11 supporting the catalyst, the ionomer 12 and water 13 as a solvent, and the mixed solution. A crushing step S2 for crushing the carbon 11 on which the catalyst is supported.

  In the mixing step S1, it is sufficient that the carbon 11 supporting the catalyst, the ionomer 12 and the water 13 as a solvent can be mixed, and the mixing method in the mixing step S1 is not particularly limited. However, in order to prevent excessive agglomeration of the carbon 11 and the ionomer 12 on which the catalyst is supported, it is preferable to perform the mixing in the procedure described later in the mixing step S1.

First, the carbon 11 carrying the catalyst is placed in a container 2 such as a beaker (S11).
Subsequently, water 13 as a solvent is added to the container 2 containing the carbon 11 carrying the catalyst (S12).
Subsequently, the carbon 11 carrying the catalyst in the container and the water 13 are mixed (S13). At this time, the mixing method is not particularly limited. Examples of the mixing method include manual mixing using a glass rod and the like, and mixing using a stirrer such as a magnetic stirrer.

Subsequently, an aqueous dispersion of ionomer 12 is added to the container 2 containing a mixture 14 of carbon 11 and water 13 on which a catalyst is supported (S14).
Subsequently, the carbon 11 on which the catalyst is supported, the ionomer 12 and the water 13 as a solvent are mixed together to obtain a mixed solution 15 (S15). At this time, the mixing method is not particularly limited. As a mixing method, the same method as in S13 can be mentioned.

  The masses of the carbon 11 supporting the catalyst, the ionomer 12 and the water 13 as the solvent mixed in the mixing step S1 are appropriately adjusted. These masses are preferably adjusted so that the solid content of the catalyst ink 1 and the contents of the carbon 11 and the ionomer 12 on which the catalyst is supported are in the above range.

  In the crushing step S2, it is only necessary to crush the carbon 11 on which the catalyst is supported, and the crushing method is not particularly limited. However, in order to crush the carbon 11 on which the catalyst is supported and prevent aggregation, it is preferable to ultrasonically treat the mixed solution 15 in the crushing step S2.

  The ultrasonic treatment in the crushing step S2 is performed using, for example, an ultrasonic homogenizer. In the crushing step S <b> 2, the tip of the horn 3 that emits ultrasonic waves of an ultrasonic homogenizer is immersed in the mixed solution 15 in the container 2. During the ultrasonic treatment, it is preferable that the container 2 is immersed in the cold bath 4 so that the temperature of the mixed liquid 15 (catalyst ink 1) is 60 ° C. or lower.

  The condition of the ultrasonic treatment in the crushing step S2 is not particularly limited, but the amplitude of the ultrasonic wave (crushing intensity) is 60 to 180 μm, and the treatment time (time during which the ultrasonic wave is irradiated) is 30 to 240 minutes. It is preferable.

  Through the above steps, the catalyst ink 1 according to this embodiment can be obtained.

According to this embodiment, the following effects are produced.
In the present embodiment, in the catalyst ink containing the carbon on which the catalyst is supported, the ionomer, and the solvent, the solvent is composed only of water.
Water is a poor solvent for ionomers. Accordingly, in the catalyst ink, the ionomer has a small molecular surface area (short molecular end distance), and thus the catalyst ink has high dispersion stability (FIG. 8). Since the catalyst ink has high dispersion stability, the coating property is also high. Furthermore, in the conventional catalyst ink, the ionomer has higher affinity with the carbon on which the catalyst is supported than with water, so that the ionomer is adsorbed on the carbon on which the catalyst is supported (FIG. 8). When the ionomer is adsorbed on the carbon on which the catalyst is supported, a three-phase interface is easily formed in the catalyst layer formed using the catalyst ink according to the present embodiment. The power generation performance of the fuel cell is improved by forming a three-phase interface in the catalyst layer.

In the catalyst ink according to the present embodiment, the total content of carbon carrying the catalyst and the ionomer is 10 to 15% by mass.
Thereby, the adsorption rate of the ionomer to the carbon carrying the catalyst is further improved. Since the adsorption rate of the ionomer to the carbon on which the catalyst is supported is further improved, a three-phase interface is easily formed in the formed catalyst layer, and the fuel cell performance is further improved.

Further, in the method for producing a catalyst ink according to the present embodiment, the production method includes a crushing step of crushing carbon carrying the catalyst in a mixed solution in which carbon, an ionomer, and water as a solvent are mixed. It was supposed to be prepared.
Thereby, it is possible to obtain a catalyst ink having high dispersion stability in which carbon carrying the catalyst is crushed and dispersed. A catalyst ink having a high dispersion stability has a high coating property, and the formed catalyst layer is homogeneous and a three-phase interface is easily formed.

In the method for producing the catalyst ink according to the present embodiment, the mixed solution was subjected to ultrasonic treatment in the crushing step.
Thereby, the carbon carrying the catalyst is more easily dispersed. The above effect can be obtained more easily by further dispersing the carbon on which the catalyst is supported.

It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.
In the above embodiment, the method for producing a catalyst ink includes the crushing step S2. However, it is not essential for the catalyst ink according to the present invention to undergo a crushing step in the production process.

  In the catalyst ink according to the present invention, the solvent is composed only of water. Here, “consisting only of water” does not mean that the present invention excludes a catalyst ink containing an organic solvent such as alcohol which is unintentionally mixed. A catalyst ink containing a trace amount of an organic solvent within a range where the effects of the present invention can be obtained is also included in the present invention.

  Next, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

[Example 1]
The catalyst ink of Example 1 was produced as follows.
First, carbon carrying a platinum catalyst (TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) was put in a container. Subsequently, water as a solvent was added to a container containing carbon on which a catalyst was supported. Subsequently, carbon carrying the catalyst in the container and water were mixed. Further, an ionomer aqueous dispersion (Nafion, DuPont) was added to the container. Finally, the liquid to which the ionomer was added was mixed. The masses of carbon, ionomer and water carrying the catalyst were adjusted so that the total content of carbon and ionomer carrying the catalyst (solid content of the catalyst ink) was 15% by mass. Further, the solid content mass ratio between the carbon carrying the catalyst and the ionomer (the solid mass of the carbon carrying the catalyst / the solid mass of the ionomer) was adjusted to be 1/1.
The mixed liquid thus obtained was used as the catalyst ink of Example 1.

[Example 2]
The catalyst ink of Example 2 was obtained by ultrasonically treating the mixed liquid in which the catalyst-supported carbon, ionomer and water obtained through the same steps as in Example 1 were mixed.

The conditions for ultrasonic treatment in the crushing step in Example 2 are shown below. In order to suppress the temperature of the catalyst ink to 60 ° C. or lower during the ultrasonic treatment, the container containing the catalyst ink was immersed in an ice bath.
Ultrasonic homogenizer: “BRANSON 450D” (manufactured by Emerson Japan)
Horn: φ13mm
Ultrasound amplitude (crushing strength): 120 μm
Operation: Ultrasonic ON 0.5 second-Ultrasonic OFF 0.5 second cycle processing time: 180 minutes (Ultrasonic ON time: 90 minutes)

[Example 3]
A catalyst ink of Example 3 was obtained in the same manner as in Example 2, except that the total content of carbon and ionomer on which the catalyst was supported was adjusted to 10% by mass.

[Example 4]
A catalyst ink of Example 4 was obtained in the same manner as in Example 2, except that the total content of carbon and ionomer on which the catalyst was supported was adjusted to 5% by mass.

[Comparative example]
A catalyst ink of a comparative example was obtained by the same process as in Example 2, except that a mixed solvent of water and 1-propanol (volume ratio: water / propanol = 2/8) was used as the solvent.

<Ionomer adsorption characteristics>
About the catalyst ink of Examples 1-4 and a comparative example, the ionomer which is not adsorb | sucking to the carbon with which the catalyst was carry | supported was quantified using ¹⁹ F-NMR. From the mass of the ionomer used for the production of the catalyst ink and the mass of the ionomer not adsorbed on the carbon carrying the catalyst, the mass of the ionomer adsorbed on the carbon carrying the catalyst was determined. For each catalyst ink, the adsorption rate of the ionomer to carbon carrying the catalyst was determined.
The results are shown in FIGS.

<Power generation performance>
Fuel cell cells were produced using the catalyst inks of Examples 1 and 2 and Comparative Example. Specifically, the fuel cell was produced as follows.
First, the catalyst ink was applied on a PET sheet by screen printing. Subsequently, the polymer electrolyte membrane (Nafion, manufactured by DuPont) was sandwiched and hot-pressed by the PET sheet coated with the catalyst ink, and then the PET sheet was peeled off. The gas diffusion layer was prepared by applying a slurry in which carbon black and PTFE (polytetrafluoroethylene) particles were uniformly dispersed to carbon paper and drying. Subsequently, diffusion layers were disposed on both sides of the polymer electrolyte membrane on which the catalyst layer was formed, and hot pressing was performed. A metal separator formed into a corrugated plate shape was disposed on the surfaces of both diffusion layers.

  About the produced fuel cell, the cell voltage was measured and the relationship between a current density and a cell voltage was investigated. The results are shown in FIG.

<Dispersion stability>
The catalyst inks of Example 2 and Comparative Example were allowed to stand, and the median diameter (D50) of the carbon on which the catalyst was supported was measured over a predetermined number of elapsed days. A laser diffraction particle size distribution analyzer SALD-2200 (manufactured by Shimadzu Corporation) was used for measuring the median diameter.
The results are shown in FIG.

<Cross sectional structure of catalyst layer>
A cross section of the fuel cell used in the measurement of the power generation performance was taken with a SEM (manufactured by Hitachi High-Technologies Corporation).
The results are shown in FIGS. FIG. 6 is a cross section of a fuel cell produced using the catalyst ink of the comparative example, and FIG. 7 is a cross section of a fuel cell produced using the catalyst ink of Example 2. The enlargement ratios of the images in FIGS. 6 and 7 are substantially the same.

From the results shown in FIG. 2, it was found that the catalyst ink of Example 1 had a significantly higher ionomer adsorption rate than the catalyst ink of the comparative example. From this result, it was confirmed that the ionomer adsorption rate in the catalyst ink is increased by constituting the solvent used in the catalyst ink only with water.
In addition, the results shown in FIG. 2 indicate that the ionomer adsorption rate of the catalyst ink of Example 2 is higher than that of the catalyst ink of Example 1. From this result, it was confirmed that in the production of the catalyst ink, the ionomer adsorption rate in the catalyst ink is further increased by ultrasonically treating the mixed liquid of carbon, ionomer and water.

  From the results shown in FIG. 3, it was found that the ionomer adsorption rate of the catalyst inks of Examples 2 and 3 was higher than that of the catalyst ink of Example 4. From this result, it was confirmed that the ionomer adsorption rate in the catalyst ink is increased by setting the total content of carbon and ionomer on which the catalyst is supported in the catalyst ink to 10 to 15% by mass. Even if the total content of carbon and ionomer on which the catalyst is supported in the catalyst ink is more than 15% by mass, the ionomer adsorption rate does not increase, and the coating property of the catalyst ink tends to decrease.

From the results shown in FIG. 4, it was found that the fuel cell produced from the catalyst ink of Example 1 was superior in power generation performance to the fuel cell produced from the catalyst ink of the comparative example. From this result, it was confirmed that the power generation performance of the produced fuel cell is improved by configuring the solvent used for the catalyst ink only with water.
Further, from the results shown in FIG. 4, it was found that the fuel battery cell produced from the catalyst ink of Example 2 was superior in power generation performance to the fuel battery cell produced from the catalyst of Example 1. From this result, it was confirmed that in the production of the catalyst ink, the power generation performance of the produced fuel cell is improved by ultrasonically treating the mixed liquid of carbon, ionomer and water.
These results are thought to be due to the fact that the three-phase interface tends to be formed in the catalyst layer by increasing the ionomer adsorption rate in the catalyst ink (FIGS. 2 and 4).

  From the results shown in FIG. 5, it was found that the dispersion stability of the catalyst ink of Example 2 was higher than that of the catalyst ink of Comparative Example. From this result, it was confirmed that the dispersion stability of the catalyst ink is enhanced by constituting the solvent used in the catalyst ink with only water.

From the results shown in FIGS. 6 and 7, the catalyst ink of Example 2 has fewer large aggregates in the formed catalyst layer (“electrode” in FIGS. 6 and 7) than the catalyst ink of the comparative example. It was found to be a homogeneous structure. From this result, the catalyst ink which can form the catalyst layer of a homogeneous structure by comprising the solvent used for a catalyst ink only with water, and ultrasonically processing the liquid mixture of carbon, ionomer, and water in manufacture of a catalyst ink. It was confirmed that
In addition, when there are many aggregates in the catalyst layer, deterioration of the electrolyte membrane (PEM in FIGS. 6 and 7) tends to proceed.

DESCRIPTION OF SYMBOLS 1 ... Catalyst ink 11 ... Carbon on which the catalyst was supported 12 ... Ionomer 13 ... Water 15 ... Mixture S1 ... Mixing process S2 ... Crushing process

Claims (4)

In a membrane-electrode assembly comprising an electrolyte membrane and a catalyst layer laminated on the electrolyte membrane, a catalyst ink used for producing the catalyst layer formed on the surface of the electrolyte membrane,
A catalyst-supported carbon, an ionomer, and a solvent;
The solvent is a catalyst ink composed only of water.   2. The catalyst ink according to claim 1, wherein the total content of carbon carrying the catalyst and the ionomer is 10 to 15% by mass. In a membrane-electrode assembly comprising an electrolyte membrane and a catalyst layer laminated on the electrolyte membrane, a method for producing a catalyst ink used for forming the catalyst layer on the surface of the electrolyte membrane,
A mixing step of obtaining a mixed solution by mixing carbon as a catalyst, ionomer, and water as a solvent;
A crushing step of crushing carbon on which the catalyst is supported in the mixed solution.   The method for producing a catalyst ink according to claim 3, wherein in the crushing step, the mixed solution is subjected to ultrasonic treatment.