JP6746977B2 - Method for producing catalyst ink - Google Patents

Description

The present invention relates to a process for preparing a catalyst ink.

A polymer electrolyte fuel cell generally has a structure in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers each composed of an electrode catalyst layer and a gas diffusion layer laminated on the electrode catalyst layer. The polymer electrolyte fuel cell having such a structure operates at room temperature and has a short start-up time, and thus is expected as an automobile, a stationary power source, and the like (see Patent Documents 1 and 2).
In the electrode catalyst layer, it is important to increase the utilization rate of the catalyst supported on the carbon particles, and for that purpose, a method of increasing the dispersibility of the carbon particles and reducing the particle size of the carbon particles as much as possible is used It is common.

JP, 2002-270187, A JP, 2010-45003, A

However, reducing the particle size of the carbon particles reduces the porosity in the electrode catalyst layer, and as a result, it becomes difficult for the reaction gas to be supplied into the electrode catalyst layer, and the water generated by the reaction is retained. Easier to do. That is, it is important to set the dispersion state and the porosity of the particles in the electrode catalyst layer to appropriate values in order not to reduce the power generation performance and the durability.
Here, Patent Document 1 describes a method of producing an electrode catalyst layer having different porosities by using carbon particles whose median diameter is changed by a bead mill, but the median diameter of carbon particles is changed. The method is not described.

In addition, Patent Document 2 proposes a method of obtaining a large porosity by re-aggregating the carbon particles to increase the particle diameter by applying a large impact during the dispersion of the carbon particles. The impact force required for re-aggregation varies depending on the type of the ink, the composition of the catalyst ink, and the like, and it is difficult to produce the electrode catalyst layer having the desired porosity each time.
The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a catalyst ink that suppresses supply shortage of reaction gas, retention of generated water, or reduction in catalyst utilization rate. And

In order to solve the above problems, a method for producing a catalyst ink according to the present invention is a method for producing a catalyst ink for forming an electrode catalyst layer for a polymer electrolyte fuel cell, wherein the weight ratio of the polymer electrolyte to the carbon particles ( I/C) is 0.6 or more and 1.5 or less, and a polymer electrolyte solution in which a polymer electrolyte is dispersed in water or alcohol is added to the catalyst-supporting carbon particles, and then the dissolver or 0.5 mm is used. A first dispersion step for performing media type dispersion with balls or beads having a larger diameter, and a bead mill using balls or beads having a diameter of 0.1 mm or more and 0.5 mm or less after the first dispersion step. A catalyst ink in which the median diameter of the catalyst-carrying carbon particles is 0.5 μm or more and 5 μm or less is produced by only two steps of the second dispersion step.

According to the method for producing a catalyst ink according to the present invention , it is possible to obtain a catalyst ink that suppresses insufficient supply of reaction gas, retention of generated water, reduction in catalyst utilization rate, and the like.

It is an exploded perspective view showing the internal structure of a polymer electrolyte fuel cell. It is the figure which processed the surface SEM image of an electrode catalyst layer with image processing software for calculation of a porosity.

An embodiment of the manufacturing method of the catalyst ink according to the present invention will be described below with reference to the drawings.

(Polymer fuel cell)
First, as shown in FIG. 1, a polymer electrolyte fuel cell 50 comprises a polymer electrolyte membrane 51, gas diffusion layers 53A and 53F, and separators 54A and 54F on both sides thereof in this order. Become. That is, the pair of gas diffusion layers 53A and 53F are arranged so as to face the pair of electrode catalyst layers 52A and 52F formed on the front and back surfaces of the polymer electrolyte membrane 51, respectively. Further, the separators 54A and 54F are arranged so as to face the pair of gas diffusion layers 53A and 53F.
The electrode catalyst layers 52A and 52F are usually formed by applying the catalyst ink to the polymer electrolyte membrane 51 and drying it, or applying the catalyst ink to a transfer substrate and then transferring it to the polymer electrolyte membrane 51. Manufactured by.

(Method for producing catalyst ink)
The method for producing the catalyst ink of the present embodiment is a method for producing the catalyst ink for forming the electrode catalyst layer 52 for the polymer electrolyte fuel cell 50. Note that the present embodiment is not limited to the embodiments 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. Embodiments are also included in the scope of this embodiment.
The method for producing the catalyst ink of the present embodiment includes a first dispersion step and a second dispersion step.

<First dispersion step>
In the first dispersion step, a polymer electrolyte solution prepared by dispersing a polymer electrolyte in water or alcohol is added to the catalyst-supporting carbon particles, and then a dissolver, or media-type dispersion with balls or beads having a first diameter is performed. This is a process to be performed. Specifically, a polymer electrolyte solution prepared by dispersing a polymer electrolyte in water or alcohol is added to the catalyst-supporting carbon particles, and then a dispersion medium is added to perform the first dispersion. The first dispersion may include performing media type dispersion with a dissolver or balls or beads of a first diameter. Media type dispersion is a general term for ball mills and bead mills.

Here, the first diameter is preferably larger than 0.5 mm. If the first diameter is less than 0.5 mm, the collision force sufficient to crush the carbon particles is insufficient and the desired particle size may not be obtained, so the first dispersion step is required. Becomes Further, as the catalyst-supporting carbon particles, it is preferable to use platinum-supported carbon black.
Moreover, as the above-mentioned polymer electrolyte, a polymer material having proton conductivity, for example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte is used.
Examples of the dispersion medium include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, isobutyl alcohol, tert-butyl alcohol, pentanole and the like. It is desirable to be selected from the above alcohols. Further, it is possible to use a solvent in which two or more of the above-mentioned solvents are mixed.

<Second dispersion step>
The second dispersion step is a dispersion step using a bead mill using balls or beads having a second diameter smaller than the first diameter after the first dispersion step. Specifically, the catalyst ink that has been subjected to the first dispersion is subjected to the second dispersion using a bead mill disperser. The final particle size of the carbon particles is influenced by the ball size used for the bead mill dispersion. The smaller the ball, the smaller the particle size, and the larger the ball, the larger the particle size. In this embodiment, the median diameter of the carbon particles is in the range of 0.4 μm to 5 μm by setting the ball diameter used to be 0.1 mm to 0.5 mm.

Since the polymer electrolyte plays a role of a dispersant in the first dispersion step and the second dispersion step, if the weight ratio (I/C) of the polymer electrolyte to the carbon particles is too small, the dispersion will proceed. As a result, the particle size does not decrease, and the porosity of the electrode catalyst layer 52 increases. Further, if the weight ratio (I/C) of the polymer electrolyte to the carbon particles is too large, the polymer electrolyte closes the pores and the porosity becomes small, so the weight ratio of the polymer electrolyte to the carbon particles (I/C). Is preferably in the range of 0.6 to 1.5, and particularly preferably in the range of 0.9 to 1.4.

<Method for producing electrode catalyst layer>
A method of applying the catalyst ink prepared by the above method to a transfer substrate and drying it to transfer it to the polymer electrolyte membrane 51, or applying the catalyst ink directly to the polymer electrolyte membrane 51 and drying the electrode catalyst Layer 52 can be manufactured. At this time, as a coating method, a die coating method, a doctor blade method, a dipping method, a screen printing method, a roll coating method, a spray method or the like can be used, but a die coating method is preferable.
The transfer base material is a sheet made of a material capable of peeling the electrode catalyst layer 52. For example, fluorine such as ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer (PFA), and polytetrafluoroethylene (PTFE). In addition to resin, polystyrene heat resistant film or the like can be used.

The polymer electrolyte membrane 51 is a polymer membrane having proton conductivity, and as the material of the polymer electrolyte membrane 51, for example, a fluorine-based polymer electrolyte or a hydrocarbon-based polymer electrolyte can be used. Examples of the fluorine-based polymer electrolyte include NAFION (registered trademark) manufactured by DuPont, FLEXION (registered trademark) manufactured by Asahi Glass Co., Ltd., ACPLEX (registered trademark) manufactured by Asahi Kasei Co., Ltd., and GORE-SELECT (registered trademark) manufactured by Gore. As the hydrocarbon-based polymer electrolyte that can be used, electrolytes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used.

The porosity of the surface of the electrode catalyst layer obtained by applying the catalyst ink produced by the above method to the transfer substrate or the polymer electrolyte membrane and drying it is in the range of 10% to 35%. If so, it is possible to prevent the supply rate of the catalyst from being significantly reduced, and to suppress the supply shortage of the reaction gas and the retention of the produced water.
As described above, according to the present embodiment, by optimizing the ball diameter and the weight ratio of the polymer electrolyte to the carbon particles, the porosity of the catalyst layer can be produced at an appropriate value, and power generation can be performed. It is possible to suppress deterioration of performance.

(Example 1)
Examples of the present invention will be described below.
<Catalyst Ink Manufacturing Method>
A water-dispersed polymer electrolyte solution was added to the catalyst-supporting carbon particles carrying 50 wt% of platinum, then 1-propanol was added, and dispersion was performed by a dissolver. At this time, the weight ratio (I/C) of the polymer electrolyte to the carbon particles was 1.0.
Next, the catalyst ink dispersed by the dissolver was dispersed using a bead mill disperser. At this time, a zirconia ball having a ball diameter of 0.2 mm was used as the ball.

<Method for producing electrode catalyst layer>
Then, 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 at a temperature of 80° C. for 5 minutes to obtain an electrode catalyst layer 52.
(Measurement of particle size and porosity)
As a result of measuring the particle diameter of the catalyst-supporting carbon particles in the catalyst ink, the median diameter was 0.6 μm. In addition, as shown in FIG. 2, the image of the surface of the electrode catalyst layer before transfer which was applied to the transfer substrate was photographed with a scanning electron microscope, and the image processing software (ImageJ) was used to obtain pores As a result of measuring the rate, it was 30%. As a result of transferring this electrode catalyst layer to an electrolyte membrane to produce a membrane electrode assembly and evaluating the power generation performance, it was confirmed that good results were obtained.

(Example 2)
A catalyst ink and an electrode catalyst layer 52 were obtained in the same manner as in Example 1 except that the balls used in the second dispersion step were 0.5 mm zirconia balls. At this time, the median diameter of the catalyst-supporting particles in the catalyst ink was 1.2 μm. Further, the porosity on the surface of the electrode catalyst layer was 35%, and it was confirmed that the power generation performance of the membrane electrode assembly obtained by transferring the electrode catalyst layer 52 to the polymer electrolyte membrane 51 was good.

(Example 3)
A catalyst ink and an electrode catalyst layer 52 were obtained in the same manner as in Example 1 except that the weight ratio (I/C) of the polymer electrolyte to the carbon particles was 1.4. At this time, the median diameter of the catalyst-supporting particles in the catalyst ink was 0.5 μm. Further, the porosity of the surface of the electrode catalyst layer 52 was 20%, and it was confirmed that the power generation performance of the membrane electrode assembly obtained by transferring the electrode catalyst layer 52 to the polymer electrolyte membrane 51 was good.

(Comparative Example 1)
A catalyst ink and an electrode catalyst layer were obtained in the same manner as in Example 1 except that the first dispersion step was not performed and the dispersion treatment was performed only by bead mill dispersion using zirconia balls of 0.1 mm. At this time, the median diameter of the catalyst-supporting particles in the catalyst ink was 10 μm or more, and the dispersion did not proceed, and it was confirmed that cracks and aggregates of carbon particles remained in the electrode catalyst layer produced by applying and drying this ink. .. The membrane-electrode assembly in which the electrode catalyst layer was transferred to the electrolyte membrane did not provide good power generation performance, and particularly during operation at low humidification, a large reduction in power generation performance occurred.

(Comparative example 2)
A catalyst ink and an electrode catalyst layer were obtained in the same manner as in Example 1 except that the dispersion treatment was performed by a ball mill dispersion using 3 mm zirconia balls in the second dispersion step. At this time, the median diameter of the catalyst-bearing particles in the catalyst ink was 10 μm or more, and it was confirmed that the electrode catalyst layer produced by applying and drying this ink had cracks and residual carbon particle aggregates. The membrane-electrode assembly in which the electrode catalyst layer was transferred to the electrolyte membrane did not provide good power generation performance, and particularly during operation at low humidification, a large reduction in power generation performance occurred.

(Comparative example 3)
A catalyst ink and an electrode catalyst layer were obtained in the same manner as in Example 1 except that the weight ratio (I/C) of the polymer electrolyte to the carbon particles was 1.7. At this time, the median diameter of the catalyst-supporting particles in the catalyst ink was 0.4 μm. Further, the porosity of the surface of the electrode catalyst layer was 8%, and in the membrane electrode assembly in which the electrode catalyst layer was transferred to the electrolyte membrane, flooding occurred due to water clogging of the generated water, resulting in deterioration of power generation performance. It was

As is clear from the evaluation results of Examples 1 to 3, according to the present invention, the porosity of the electrode catalyst layer can be controlled, and a good power generation performance can be obtained with the electrode catalyst layer, the electrode catalyst layer, and A polymer electrolyte fuel cell can be obtained. That is, by controlling the porosity of the electrode catalyst layer, insufficient supply of reaction gas caused by a decrease in the porosity, retention of generated water, or decrease in catalyst utilization rate due to an increase in the porosity, etc. It is possible to provide a method for producing a catalyst ink that suppresses the above, an electrode catalyst layer, and a polymer electrolyte fuel cell.

50... Solid polymer fuel cell 51... Polymer electrolyte membrane 52 (52A, 52F)... Electrode catalyst layer 53 (53A, 53F)... Gas diffusion layer 54 (54A, 54F)... Separator

Claims (4)

In a method for producing a catalyst ink for forming an electrode catalyst layer for a polymer electrolyte fuel cell,
A polymer electrolyte solution obtained by dispersing the polymer electrolyte in water or alcohol is used as the catalyst-supporting carbon particles so that the weight ratio (I/C) of the polymer electrolyte to the carbon particles is 0.6 or more and 1.5 or less. After the addition, a first dispersion step of performing media type dispersion with a dissolver or balls or beads having a diameter larger than 0.5 mm;
A second dispersion step using a bead mill using balls or beads having a diameter of 0.1 mm or more and 0.5 mm or less after the first dispersion step ;
The method for producing a catalyst ink, wherein the catalyst ink in which the median diameter of the catalyst-supporting carbon particles is 0.5 μm or more and 5 μm or less is produced by only the two steps . The method for producing a catalyst ink according to claim 1, wherein the weight ratio (I/C) in the first dispersion step is 0.9 or more and 1.4 or less . The method for producing a catalyst ink according to claim 1 , wherein the diameter of the balls or the beads in the second dispersion step is 0.2 mm or more and 0.5 mm or less . Method for producing a catalyst ink according to any one of claims 1 3, wherein the median diameter of the catalyst-carrying carbon particles by the two steps is 0.5μm or more 1.2μm or less.

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