Method for manufacturing ink for forming electrolyte layer of fuel cell

Abstract

To provide a method for manufacturing ink for forming an electrolyte layer of a fuel cell in which particles of cerium-containing oxide are hardly precipitated for over a long time and composition is stabilized while the ink contains cerium-containing oxide.SOLUTION: A method for manufacturing ink for forming an electrolyte layer of a fuel cell includes: a deagglomerating step of deagglomerating cerium-containing oxide powder to obtain cerium-containing oxide fine powder; a first mixing step of mixing and agitating the cerium-containing oxide fine powder, ionomer and water to obtain first liquid mixture; a second mixing step of mixing and agitating the first liquid mixture and 1- propanol to obtain second liquid mixture; and an ultrasonic treatment step of performing ultrasonic treatment to the second liquid mixture.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing ink for forming an electrolyte layer of a fuel cell. [Background technology]

[0002] In recent years, research and development into fuel cells, which contribute to energy efficiency, has been conducted to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. Fuel cells generally have an electrode assembly (MEA) including an anode catalyst layer and a cathode catalyst layer, which are arranged opposite each other with an electrolyte layer interposed between them. In fuel cells, hydrogen ions generated in the anode catalyst layer react with oxygen ions generated in the cathode catalyst layer to produce water. This reaction is known to produce hydrogen peroxide as a by-product. Hydrogen peroxide can cause deterioration of the electrolyte layer. For this reason, it is common to add a hydrogen peroxide scavenger (radical quencher) to the electrolyte layer. Cerium compounds are widely used as hydrogen peroxide scavengers. Water-soluble cerium compounds, such as cerium nitrate, are known as cerium compounds. The use of cerium-containing oxides, such as cerium oxide, has also been investigated (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-64721 Summary of the Invention [Problem to be solved by the invention]

[0004] One of the challenges in fuel cell technology is to extend the life of the electrolyte layer. To achieve this, adding a radical quencher to the electrolyte layer is effective. Cerium-containing oxides are useful as radical quenchers for the electrolyte layer because of their high water resistance.

[0005] As a method for forming an electrolyte layer, a coating-drying method in which an ink for forming an electrolyte layer is applied to the surface of an anode-side catalyst layer or a cathode-side catalyst layer and dried is known. The coating-drying method is an effective method in that it can continuously form an electrolyte layer. However, according to the studies by the present inventors, in an ink for forming an electrolyte membrane in which a cerium-containing oxide is dispersed, the particles of the cerium-containing oxide tend to settle easily and it is difficult to stabilize the composition. For this reason, it is difficult to continuously form an electrolyte layer in which the cerium-containing oxide is uniformly dispersed by the coating-drying method.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing an ink for forming an electrolyte layer of a fuel cell that contains a cerium-containing oxide, but in which the particles of the cerium-containing oxide are difficult to settle over a long period of time and the composition is stable. And by extension, it contributes to the improvement of energy efficiency.

Means for Solving the Problems

[0007] The present inventors have found that the above problems can be solved by a method in which a powder of a cerium-containing oxide is pulverized into fine powder, mixed with water and an ionomer to obtain a first mixed solution, and then the first mixed solution and 1-propanol are mixed and stirred to obtain a second mixed solution, and then ultrasonic treatment is performed on the second mixed solution, and the present invention has been completed. Therefore, the present invention provides the following.

[0008] (1) A pulverization step of pulverizing a cerium-containing oxide powder to obtain a cerium-containing oxide fine powder, a first mixing step of mixing and stirring the cerium-containing oxide fine powder, an ionomer, and water to obtain a first mixed solution, a second mixing step of mixing and stirring the first mixed solution and 1-propanol to obtain a second mixed solution, and an ultrasonic treatment step of performing ultrasonic treatment on the second mixed solution, the method for producing an ink for forming an electrolyte layer of a fuel cell.

[0009] According to the method for manufacturing an ink for forming an electrolyte layer of the fuel cell of (1), since the powder of the cerium-containing oxide is pulverized into fine powder in the pulverization step and ultrasonic treatment is performed on the second mixed solution in the ultrasonic step, the particles of the cerium-containing oxide in the obtained ink for forming an electrolyte layer become fine. For this reason, in the obtained ink for forming an electrolyte layer, the particles of the cerium-containing oxide are less likely to settle over a long period of time, and the composition is stabilized.

[0010] The method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to claim 1, including a shaking treatment step of performing a shaking treatment on the second mixed solution after the ultrasonic treatment step.

[0011] According to the method for manufacturing an ink for forming an electrolyte layer of the fuel cell of (2), when sedimentation of particles occurs in the second mixed solution after the ultrasonic treatment, the sedimented particles are redispersed in the shaking step, so that the composition of the obtained ink for forming an electrolyte layer becomes more stable.

[0012] The method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to claim 1 or 2, including a classification step of classifying the cerium-containing oxide fine powder between the pulverization step and the first mixing step.

[0013] According to the method for manufacturing an ink for forming an electrolyte layer of the fuel cell of (3), since coarse particles mixed in the cerium-containing oxide fine powder are removed in the classification step, sedimentation of particles is less likely to occur in the obtained ink for forming an electrolyte layer.

[0014] The method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to claim 1 or 2, wherein the content of the cerium-containing oxide fine powder with respect to the ionomer in the second mixed solution is in the range of 0.1% by mass or more and 3.0% by mass or less.

[0015] According to the method for manufacturing an ink for forming an electrolyte layer of the fuel cell of (4), since the content of the cerium-containing oxide is within the above range, an electrolyte layer less likely to be deteriorated by hydrogen peroxide can be formed by using the obtained ink for forming an electrolyte layer.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a method for manufacturing an ink for forming an electrolyte layer of a fuel cell that contains a cerium-containing oxide, but in which the particles of the cerium-containing oxide are difficult to settle over a long period of time and the composition is stable.

Brief Description of the Drawings

[0017]

Figure 1

Embodiments for Carrying Out the Invention

[0018] Hereinafter, a method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to an embodiment of the present invention will be described with reference to the attached FIG. 1. FIG. 1 is a flowchart of a method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to an embodiment of the present invention.

[0019] As shown in FIG. 1, the ink for forming an electrolyte layer of a fuel cell according to the present embodiment includes a crushing step S1, a classification step S2, a first mixing step S3, a second mixing step S4, an ultrasonic treatment step S5, and a shaking treatment step S6.

[0020] The crushing step S1 is a step of crushing a cerium-containing oxide powder to obtain a cerium-containing oxide fine powder. As the cerium-containing oxide powder, cerium oxide (CeO2) powder can be used. The cerium oxide powder may be doped with a transition metal oxide such as zirconium oxide. The crushing of the cerium-containing oxide powder may be performed wet or dry. As the crushing device, for example, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a mortar and a pestle can be used.

[0021] The classification step S2 is a step of classifying the cerium-containing oxide fine powder obtained in the crushing step S1 to remove coarse cerium-containing oxide particles. By removing the coarse cerium-containing oxide particles, sedimentation of the particles of the electrolyte layer-forming ink becomes less likely to occur. The classification of the cerium-containing oxide fine powder may be performed by a wet method or a dry method. Examples of the classification device that can be used include a sieve and an air classifier.

[0022] The cerium-containing oxide fine powder after the classification step S2 may be one that passes through a sieve with an opening of 32 μm, for example.

[0023] The first mixing step S3 is a step of mixing and stirring a cerium-containing oxide fine powder, an ionomer, and water to obtain a first mixed solution. The order of mixing the cerium-containing oxide fine powder, the ionomer, and the water is not particularly limited. The cerium-containing oxide fine powder may be mixed with a mixed solution of the ionomer and water, or the water may be mixed with a mixture of the cerium-containing oxide fine powder and the ionomer, or the ionomer may be mixed with a mixture of the cerium-containing oxide fine powder and water, or the cerium-containing oxide fine powder, the ionomer, and the water may be mixed simultaneously. A magnetic stirrer or a propeller mixer can be used as the stirring device.

[0024] The second mixing step S4 is a step of mixing and stirring the first mixed solution with 1-propanol to obtain a second mixed solution. By mixing the first mixed solution with 1-propanol in the second mixing step S4, the ionomer is more easily dispersed than when the cerium-containing oxide fine powder, the ionomer, water, and 1-propanol are mixed. A magnetic stirrer or a propeller mixer can be used as the stirring device.

[0025] The content rate of the cerium-containing oxide with respect to the ionomer in the second mixture may be, for example, within the range of 0.1 mass% or more and 3.0 mass%. The content rate of 1-propanol with respect to the ionomer in the second mixture may be, for example, within the range of 40 mass% or more and 80 mass%. The content rate of water with respect to the ionomer in the second mixture may be, for example, within the range of 5 mass% or more and 30 mass%.

[0026] The ultrasonic treatment step S5 is a step of performing ultrasonic treatment on the second mixture. By the ultrasonic treatment, the aggregated particles aggregated in the second mixture are crushed, and the cerium-containing oxide becomes primary particles or fine particles close to them. Therefore, sedimentation of the particles is less likely to occur. As the ultrasonic treatment device, an ultrasonic bath or an ultrasonic homogenizer can be used.

[0027] The shaking treatment step S6 is a step of performing a shaking treatment on the second mixture after the ultrasonic treatment. In the second mixture after the ultrasonic treatment, sedimentation of particles may occur. In this case, the sedimented particles are redispersed by the shaking treatment. The shaking treatment may be performed manually or using a shaker. The shaking treatment step S6 may be performed immediately before use as the ink for forming the electrolyte layer of the fuel cell.

[0028] Even if several hours have passed after the shaking treatment, sedimentation of particles is less likely to occur in the second liquid after the shaking treatment, and the stability of the composition is high. Therefore, it can be advantageously used as the ink for forming the electrolyte layer of the fuel cell. By using the second liquid as the ink for forming the electrolyte layer, the electrolyte layer can be formed continuously for several hours.

[0029] According to the method for manufacturing the ink for forming the electrolyte layer of the present embodiment configured as described above, it is possible to manufacture an ink for forming the electrolyte layer of a fuel cell in which particles of the cerium-containing oxide are less likely to sediment over a long period of time and the composition is stable.

[0030] The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments and can be appropriately changed.

[0031] For example, in the present embodiment, the classification step S2 is performed after the crushing step S1. However, in the crushing step S1, if the cerium-containing oxide powder is sufficiently crushed, the classification step S2 may be omitted. Further, the shaking step S6 is performed after the ultrasonic treatment step S5. However, if no particle sedimentation is observed in the second mixed solution after the ultrasonic treatment, the shaking step S6 may be omitted.

Example

[0032] [Example 1] As the cerium-containing oxide powder, CeO2 powder was prepared. The CeO2 powder was crushed using an agate mortar and pestle. Next, the obtained crushed product was classified using a sieve with an opening of 32 μm to obtain CeO2 fine powder.

[0033] 118.8 parts by mass of an ionomer and 13.3 parts by mass of water were mixed to prepare a mixed solution. 0.14 part by mass of the above CeO2 fine powder was added to this mixed solution, and using a propeller mixer, it was mixed at a rotational speed of 650 rpm for 15 minutes to obtain a first mixed solution. Next, 67.9 parts by mass of 1-propanol was added to the first mixed solution, and using a propeller mixer, it was further mixed at a rotational speed of 650 rpm for 15 minutes to obtain a second mixed solution.

[0034] The above second mixed solution was ultrasonically treated for 30 minutes using an ultrasonic bath. A small amount of white particles had slightly sedimented in the second mixed solution after the ultrasonic treatment. Next, the second mixed solution after the ultrasonic treatment was shaken to disperse the white particles and obtain a CeO2 dispersion. The obtained CeO2 dispersion was placed in a transparent container and allowed to stand for 3 hours. When the CeO2 dispersion after standing was visually observed, no sedimentation of white particles was seen. Therefore, this CeO2 dispersion can be advantageously used as an ink for forming the electrolyte layer of a fuel cell.

[0035] [Example 2] Except that ZrO₂-doped CeO₂ powder was used as the cerium-containing oxide powder and the addition amount of the ZrO₂-doped CeO₂ fine powder to the mixed solution of the ionomer and water was 0.7 parts by mass, a ZrO₂-doped CeO₂ dispersion was obtained in the same manner as in Example 1. The obtained ZrO₂-doped CeO₂ dispersion was placed in a transparent container and allowed to stand for 3 hours. When the ZrO₂-doped CeO₂ dispersion after standing was visually observed, no sedimentation of white particles was seen. Therefore, this ZrO₂-doped CeO₂ dispersion can be advantageously used as an ink for forming the electrolyte layer of a fuel cell.

Claims

1. A pulverization step of pulverizing a cerium-containing oxide powder to obtain a cerium-containing oxide fine powder, a first mixing step of mixing and stirring the cerium-containing oxide fine powder, an ionomer, and water to obtain a first mixed solution, a second mixing step of mixing and stirring the first mixed solution and 1-propanol to obtain a second mixed solution, and an ultrasonic treatment step of performing ultrasonic treatment on the second mixed solution. A method for manufacturing an ink for forming an electrolyte layer of a fuel cell, comprising:

2. The method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to claim 1, further comprising a shaking treatment step of performing a shaking treatment on the second mixed solution after the ultrasonic treatment step.

3. The method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to claim 1 or 2, further comprising a classification step of classifying the cerium-containing oxide fine powder between the pulverization step and the first mixing step.

4. The method for manufacturing an ink for forming an electrolyte layer of a fuel cell according to claim 1 or 2, wherein the content of the cerium-containing oxide fine powder with respect to the ionomer in the second mixed solution is in the range of 0.1% by mass or more and 3.0% by mass or less.

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