JP6569251B2 - Catalyst ink for forming electrode catalyst layer of polymer electrolyte fuel cell and method for producing the same - Google Patents

Description

  The present invention relates to a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell and a method for producing the same.

A polymer electrolyte fuel cell having a structure in which a polymer electrolyte membrane is sandwiched between a cathode electrode catalyst layer and an anode electrode catalyst layer operates at room temperature and has a short start-up time. Has been.
Usually, the electrode catalyst layer is manufactured by a method of applying and drying a catalyst ink to a polymer electrolyte membrane, a method of applying a catalyst ink to a transfer substrate, and then transferring the catalyst ink to a polymer electrolyte membrane.
The catalyst ink used in the above production is usually one in which carbon particles carrying a catalyst and a polymer electrolyte are dissolved in alcohol. However, in this case, there is a risk of ignition due to the activity of the catalyst due to direct contact between the catalyst and the alcohol during ink production.

As a measure for preventing the danger, Patent Document 1 uses a method in which only water is used as a dispersion medium without using alcohol. However, when the water content increases, the dispersibility of the catalyst ink decreases, and cracks and pinholes are generated in the catalyst layer during coating and drying, leading to a decrease in power generation performance. Further, when applied to a transfer film having water repellency, the application becomes impossible due to repelling of the catalyst ink.
In addition, there is a method of preventing ignition by a method in which the catalyst is dissolved in water in advance and alcohol is added thereto, but this method also causes the above problem because a large amount of water is required. To deal with this problem, Patent Document 2 describes a method using t-butanol and 1-butanol as dispersion media. However, since t-butanol becomes a solid at room temperature, it is difficult to handle, and 1-butanol has a high boiling point, and it is necessary to set the drying temperature to a high temperature. May be reduced.

JP 2004-139899 A JP 2012-182153 A

  The present invention can reduce the risk of ignition during the production of a catalyst ink, and can be used to form an electrode catalyst layer of a polymer electrolyte fuel cell that can reduce the occurrence of cracks and pinholes during the coating and drying process. It is an object of the present invention to provide a catalyst ink and a method for producing the same.

In order to solve the above problems, a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell according to an aspect of the present invention is a water-dispersed polymer obtained by dispersing a polymer electrolyte having ion conductivity in water. It includes an electrolyte solution, catalyst-supporting carbon particles obtained by supporting a catalyst on a carbon particle carrier, and a dispersion medium.
In addition, in order to solve the above problems, a method for producing a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell according to one embodiment of the present invention comprises dispersing a polymer electrolyte having ion conductivity in water. A step of obtaining a water-dispersed polymer electrolyte solution, a step of mixing a catalyst-supporting carbon particle having a catalyst supported on a carbon particle carrier and the water-dispersed polymer electrolyte solution to obtain a slurry, and the slurry using a dispersion medium Diluting and mixing with the dispersion medium.

  According to the present invention, a water-dispersed polymer electrolyte solution obtained by dispersing a polymer electrolyte in water is obtained, and a slurry is obtained by adding the water-dispersed polymer electrolyte solution to catalyst-carrying carbon particles. A catalyst ink is produced by diluting with a dispersion medium and mixing with the dispersion medium. Therefore, it is possible to reduce the risk of ignition during production with a small amount of water compared to the conventional case. Furthermore, since the amount of water can be reduced, it is possible to suppress a decrease in the dispersibility of the catalyst ink due to an increase in water concentration. As a result, it is possible to reduce the occurrence of cracks and pinholes when applying and drying the catalyst ink.

It is a disassembled perspective view which shows an example of the internal structure of the polymer electrolyte fuel cell which concerns on embodiment of this invention. It is a figure which shows the manufacturing process of the catalyst ink which concerns on embodiment of this invention.

Embodiments of the present invention will be described below with reference to the drawings.
The present embodiment is not limited to the embodiment described below, and modifications such as design changes based on the knowledge of those skilled in the art can be added, and such modifications have been added. The embodiment is also included in the scope of the present embodiment.
(Structure of polymer electrolyte fuel cell)
FIG. 1 is an exploded perspective view showing an example of the internal structure of the polymer electrolyte fuel cell according to the present embodiment.

As shown in FIG. 1, a polymer electrolyte membrane 51 constituting a solid polymer fuel cell 50 has a pair of electrode catalyst layers 52A and 52F facing each other across the polymer electrolyte membrane 51 on both sides. Has been placed.
A gas diffusion layer 53A is provided on the surface of the electrode catalyst layer 52A opposite to the surface facing the polymer electrolyte membrane 51, and a gas diffusion layer 53A is provided on the surface of the electrode catalyst layer 52F opposite to the surface opposite to the polymer electrolyte membrane 51. The diffusion layer 53F is disposed so as to face each other across the polymer electrolyte membrane 51 and the pair of electrode catalyst layers 52A and 52F.

The surface of the gas diffusion layer 53A opposite to the surface facing the electrode catalyst layer 52A is provided with a gas flow channel 55A for reaction gas flow on the surface facing this surface, and cooling for circulating cooling water on the opposite main surface. A separator 54A having a water passage 56A is disposed.
Further, the surface of the gas diffusion layer 53F opposite to the surface facing the electrode catalyst layer 52F is provided with a gas flow channel 55F for reaction gas flow on the surface facing this surface, and the coolant flow is provided on the opposite main surface. A separator 54F having a cooling water passage 56F is disposed.
Hereinafter, when it is not necessary to distinguish, the electrode catalyst layers 52A and 52F may be simply referred to as “electrode catalyst layer 52”.

(Method for producing catalyst ink)
Next, a method for producing a catalyst ink for forming an electrode catalyst layer 52 (an electrode catalyst layer for a polymer electrolyte fuel cell) of the polymer electrolyte fuel cell 50 according to the present embodiment will be described with reference to FIG. . FIG. 2 is a diagram illustrating a manufacturing process of the catalyst ink according to the present embodiment.
As shown in FIG. 2, first, a polymer electrolyte is dispersed in water to obtain a water-dispersed polymer electrolyte solution. Subsequently, a slurry (hereinafter may be referred to as “polymer electrolyte slurry”) is obtained by adding and mixing the water-dispersed polymer electrolyte solution to the catalyst-supporting carbon particles. Thus, by adding the polymer electrolyte in water dispersion to the catalyst-supporting carbon particles, the risk of ignition can be reduced with a smaller amount of water than the method of adding water alone. For mixing, for example, a planetary mixer, a dissolver, a kneader or the like can be used. In this embodiment, as an example of the catalyst-supporting carbon particles, carbon black (platinum-supporting carbon particles) in which platinum is supported as a catalyst on a carbon particle support is used.

The concentration of the water-dispersed polymer electrolyte solution used in the present embodiment is such that the water concentration in the finally provided catalyst ink is in the range of 10% by mass to 35% by mass, preferably 15% by mass to 30% by mass. Prepare to be in the range. If the water concentration is too low, the risk of ignition increases. If the water concentration is too high, the dispersibility of the catalyst ink decreases, and cracks and pinholes are likely to occur during coating and drying.
The dry mass value (equivalent weight; EW (Equivalent Weight)) per mole of the proton-donating group of the polymer electrolyte used for the production of the catalyst ink is 500 (g / eq) or more and 800 (g / eq) or less. Here, the dry mass value (equivalent weight; EW) per mole of the proton donating group is the mass of the proton conducting material per unit mole of the introduced proton donating group, and the smaller the value, the proton conducting material. It indicates that the ratio of proton donating groups is high.

As the polymer electrolyte, a polymer material having proton conductivity, for example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte is used.
Commercially available aqueous dispersions of polymer electrolytes can also be used, but if the dispersion medium contains a small amount of alcohol, the catalyst-carrying carbon particles are pre-moistened with water to prevent ignition. Risk can be reduced.
If the ratio of the polymer electrolyte to the carbon particle carrier is too small, the proton transport resistance increases, causing a decrease in power generation performance, and the strength of the coating film becomes weak at the time of coating, which causes cracks. On the other hand, if the ratio of the polymer electrolyte to the carbon particle carrier is too large, the gas permeability may be reduced, or the water generated by power generation may be prevented from being discharged and the power generation performance may be reduced.
From the above, in this embodiment, the weight ratio, which is the ratio of the polymer electrolyte to the carbon particle carrier, is set in the range of 0.9 to 1.5.

  Next, a catalyst ink is manufactured by diluting and mixing the polymer electrolyte slurry manufactured by the said process with a dispersion medium. Examples of the dispersion medium used for dilution / mixing include alcohols (organic solvents) such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, and pentanol. Any one of these can be selected and used. Moreover, it is possible to use the solvent with which 2 or more types was mixed among the solvents mentioned above. For mixing, for example, a planetary mixer, a dissolver, a bead mill, and the like can be used. Among them, it is preferable to use a bead mill.

(Effect of this embodiment)
According to the present embodiment, the following effects can be obtained.
At the time of production of the catalyst ink, a polymer electrolyte slurry is obtained by adding a water-dispersed polymer electrolyte solution in which a polymer electrolyte is dispersed in water to catalyst-carrying carbon particles having a catalyst supported on a carbon particle carrier. I made it. Thereby, compared with the conventional method of adding water alone, it becomes possible to reduce the risk of ignition during production with a small amount of water. Furthermore, since the amount of water to be added can be made small, it is possible to suppress a decrease in the dispersibility of the catalyst ink due to an increase in water concentration. As a result, it is possible to reduce the occurrence of cracks and pinholes when applying and drying the catalyst ink, and it is possible to reduce the occurrence of appearance defects due to cracks and pinholes.

In addition, since the concentration of the water-dispersed polymer electrolyte solution is set to a concentration in which the final catalyst ink has a water concentration in the range of 10% by mass to 35% by mass, it is possible to obtain a catalyst ink having a good dispersion state. Thus, cracks and pinholes during application and drying can be further reduced.
In addition, since a dispersion medium composed of one or more solvents belonging to alcohols is used as a dispersion medium for diluting and mixing the polymer electrolyte slurry, the polymer electrolyte can be sufficiently dissolved and the catalyst is supported. It becomes possible to ensure a relatively good dispersibility of the carbon particles. Moreover, since alcohol has a low boiling point, it becomes possible to reduce energy required in the drying step.
In addition, since the weight ratio, which is the ratio of the polymer electrolyte to the carbon particle carrier, is in the range of 0.9 to 1.5, the gas permeability is reduced when the weight ratio is too small and the coating at the time of coating is performed. It is possible to suppress a decrease in film strength. In addition, it is possible to suppress a decrease in gas permeability and a decrease in power generation performance caused by an excessively large weight ratio.

Example 1
Embodiment 1 of the present invention will be described below.
(Production of catalyst-supported carbon particles and polymer electrolyte slurry)
A water-dispersed polymer electrolyte solution prepared so that the final water concentration in the catalyst ink is 25% is added to catalyst-supported carbon particles (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Co., Ltd.) supporting 50 wt% platinum. It mixed with the Lee mixer. At this time, the mass ratio of the polymer electrolyte to carbon (corresponding to the weight ratio of the above embodiment) (I / C) was 1.0. The equivalent weight of the polymer electrolyte was 700 (g / eq).

(Manufacture of catalyst ink)
1-Propanol was added to the slurry produced by the above method and mixed with a bead mill to obtain a catalyst ink.
(Film formation process)
Next, the above catalyst ink was applied to a transfer sheet by a die coating method, and the catalyst ink applied on the transfer sheet was dried in an air atmosphere at a temperature of 80 ° C. for 5 minutes to obtain an electrode catalyst layer 52. . At this time, the thickness of the electrode catalyst layer 52 was adjusted so that the supported amount of the catalyst substance was 0.3 mg / cm ² . The catalyst ink of Example 1 did not ignite during the production process, and the electrode catalyst layer obtained by coating and drying was satisfactory without defects such as cracks and pinholes.

(Example 2)
Next, a second embodiment of the present invention will be described.
The catalyst of Example 2 was the same as Example 1 except that the final water concentration in the catalyst ink was 20% and the mass ratio (I / C) of the polymer electrolyte to carbon was 1.2. Ink was obtained. The catalyst ink of Example 2 did not ignite during the production process, and the electrode catalyst layer obtained by coating and drying was satisfactory without defects such as cracks and pinholes.
(Example 3)
Next, a third embodiment of the present invention will be described.
The catalyst ink of Example 3 was obtained in the same manner as in Example 1 except that the final water concentration in the catalyst ink was 15% and 1-butanol was used as a dispersion medium for diluting the slurry. The catalyst ink of Example 3 did not ignite during the production process, and the electrode catalyst layer obtained by coating and drying was satisfactory without defects such as cracks and pinholes.

(Comparative Example 1)
A catalyst ink of Comparative Example 1 was obtained in the same manner as in Example 1 except that the final water concentration in the catalyst ink was 5%. In the production process of the catalyst ink of Comparative Example 1, good catalyst-carrying carbon particles and a polymer electrolyte slurry could not be obtained, and when a dispersion medium was added for dilution, heat generation was confirmed.
(Comparative Example 2)
A catalyst ink of Comparative Example 2 was obtained in the same manner as in Example 1 except that the mass ratio (I / C) of the polymer electrolyte to carbon was 0.6. The catalyst ink of Comparative Example 2 did not ignite during the production process, but cracks and pinholes were confirmed in the electrode catalyst layer obtained by coating and drying.
(Comparative Example 3)
A catalyst ink of Comparative Example 3 was obtained in the same manner as in Example 1 except that the equivalent weight of the polymer electrolyte was 1000 (g / eq). The catalyst ink of Comparative Example 3 did not ignite during the production process, but cracks and pinholes were confirmed in the electrode catalyst layer obtained by coating and drying.

DESCRIPTION OF SYMBOLS 50 ... Solid polymer fuel cell 51 ... Polymer electrolyte membrane 52A, 52F ... Electrode catalyst layer 53A, 53F ... Gas diffusion layer 54A, 54F ... Separator 55A, 55F ... Gas flow path 56A, 56F ... Cooling water path

Claims (9)

A catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell,
A water-dispersed polymer electrolyte solution obtained by dispersing a polymer electrolyte having ion conductivity in water;
A catalyst-carrying carbon particles consisting by supporting a catalyst on a carbon particle carrier, a dispersion medium, only including,
The dispersion medium is at least one selected from the group consisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanol,
The catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell, wherein the concentration of the water in the catalyst ink is adjusted to 20% by mass or more .   2. The polymer electrolyte fuel cell according to claim 1, wherein the concentration of the water-dispersed polymer electrolyte solution is adjusted such that the water concentration in the catalyst ink is greater than 30% by mass. Catalyst ink for forming an electrode catalyst layer. The polymer electrolyte has a dry mass value (equivalent weight; EW (Equivalent Weight)) per mole of proton donating groups of 500 (g / eq) to 800 (g / eq). Item 3. A catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell according to Item 1 or 2 . The water-dispersible polymer electrolyte solution according to any one of claims 1 to 3, the weight ratio of the carbon particle carrier is characterized in that it consists of 0.9 to 1.5 polyelectrolytes Catalyst ink for forming an electrode catalyst layer of a solid polymer fuel cell. A method for producing a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell, comprising:
A step of dispersing a polymer electrolyte having ion conductivity in water to obtain a water-dispersed polymer electrolyte solution;
Mixing a catalyst-supporting carbon particle obtained by supporting a catalyst on a carbon particle carrier and the water-dispersed polymer electrolyte solution to obtain a slurry;
A method for producing a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell, comprising the steps of diluting the slurry with a dispersion medium and mixing with the dispersion medium. In the step of obtaining the water-dispersed polymer electrolyte solution, the concentration of the water-dispersed polymer electrolyte solution is adjusted so that the water concentration in the catalyst ink is in the range of 10% by mass to 35% by mass. A method for producing a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell according to claim 5 . The method for producing a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell according to claim 5 or 6 , wherein the dispersion medium comprises one or more solvents belonging to alcohols. The dry mass value (equivalent weight; EW (Equivalent Weight)) per mole of the proton-donating group of the polymer electrolyte is 500 (g / eq) or more and 800 (g / eq) or less. The method for producing a catalyst ink for forming an electrode catalyst layer of a polymer electrolyte fuel cell according to any one of claims 5 to 7 . Solid high according to any one of claims 8 from claim 5, wherein the weight ratio of the carbon particle carrier of the polymer electrolyte in the catalyst ink is 0.9 to 1.5 A method for producing a catalyst ink for forming an electrode catalyst layer of a molecular fuel cell.

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