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] A known method for forming an electrolyte layer is the coating and drying method, in which an electrolyte layer-forming ink is applied to the surface of an anode-side catalyst layer or a cathode-side catalyst layer and then dried. The coating and drying method is an effective method in that it allows for continuous formation of an electrolyte layer. However, according to the inventors' investigations, electrolyte membrane-forming inks in which cerium-containing oxide is dispersed tend to have cerium-containing oxide particles that tend to settle, making it difficult to stabilize the composition. For this reason, it is difficult to continuously form an electrolyte layer in which cerium-containing oxide is uniformly dispersed using the coating and drying method.

[0006] The present invention has been made in view of the above circumstances, and aims to provide a method for producing an ink for forming an electrolyte layer of a fuel cell, which contains a cerium-containing oxide but in which the cerium-containing oxide particles are less likely to settle over a long period of time and the composition is stable, thereby contributing to improvement of energy efficiency. [Means for solving the problem]

[0007] The present inventors have found that the above-mentioned problems can be solved by a method in which a cerium-containing oxide powder is crushed into a fine powder, the powder is mixed with water and an ionomer to obtain a first mixed liquid, the first mixed liquid is mixed and stirred with 1-propanol to obtain a second mixed liquid, and the second mixed liquid is then subjected to ultrasonic treatment, and have completed the present invention. Accordingly, the present invention provides the following.

[0008] (1) A method for producing an ink for forming an electrolyte layer of a fuel cell, comprising: a crushing step of crushing 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 liquid; a second mixing step of mixing and stirring the first mixed liquid and 1-propanol to obtain a second mixed liquid; and an ultrasonic treatment step of ultrasonically treating the second mixed liquid.

[0009] According to the method for producing an ink for forming an electrolyte layer of a fuel cell (1), the cerium-containing oxide powder is crushed into a fine powder in the crushing step, and the second mixed liquid is subjected to ultrasonic treatment in the ultrasonic step, so that the cerium-containing oxide particles in the obtained ink for forming an electrolyte layer are fine. As a result, the cerium-containing oxide particles in the obtained ink for forming an electrolyte layer are less likely to settle over a long period of time, and the composition is stable.

[0010] (2) The method for producing an ink for forming an electrolyte layer of a fuel cell according to claim 1, further comprising a shaking treatment step of shaking the second mixed liquid after the ultrasonic treatment step.

[0011] According to the method for manufacturing an ink for forming an electrolyte layer of a fuel cell (2), if particles settle in the second mixed liquid after ultrasonic treatment, the settled particles are redispersed in the shaking process, making the composition of the resulting ink for forming an electrolyte layer more stable.

[0012] (3) The method for producing an ink for forming an electrolyte layer of a fuel cell according to claim 1 or 2, further comprising a classifying step of classifying the cerium-containing oxide fine powder between the crushing step and the first mixing step.

[0013] According to the method for producing an ink for forming an electrolyte layer of a fuel cell described in (3), coarse particles mixed in the cerium-containing oxide fine powder are removed in the classification process, so that the resulting ink for forming an electrolyte layer is less susceptible to particle settling.

[0014] (4) A method for producing 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 relative to the ionomer in the second mixture is in the range of 0.1% by mass or more and 3.0% by mass or less.

[0015] According to the method for producing an ink for forming an electrolyte layer of a fuel cell (4), the content of the cerium-containing oxide is within the above range, and therefore, by using the obtained ink for forming an electrolyte layer, an electrolyte layer that is resistant to deterioration by hydrogen peroxide can be formed. [Effects of the Invention]

[0016] According to the present invention, it is possible to provide a method for producing an ink for forming an electrolyte layer of a fuel cell, which contains a cerium-containing oxide but is less likely to cause the cerium-containing oxide particles to settle over a long period of time, and has a stable composition. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a flow diagram of a method for producing an ink for forming an electrolyte layer of a fuel cell according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] A method for producing an ink for forming an electrolyte layer of a fuel cell according to one embodiment of the present invention will now be described with reference to the accompanying Fig. 1. Fig. 1 is a flow diagram of a method for producing an ink for forming an electrolyte layer of a fuel cell according to one embodiment of the present invention.

[0019] As shown in FIG. 1, the process for preparing the ink for forming an electrolyte layer of a fuel cell according to this 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 the 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. Crushing of the cerium-containing oxide powder may be performed wet or dry. Examples of crushing devices that can be used include a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, and a mortar and pestle.

[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 of the cerium-containing oxide relative to the ionomer in the second mixed liquid may be, for example, in the range of 0.1% by mass to 3.0% by mass. The content of 1-propanol relative to the ionomer in the second mixed liquid may be, for example, in the range of 40% by mass to 80% by mass. The content of water relative to the ionomer in the second mixed liquid may be, for example, in the range of 5% by mass to 30% by mass.

[0026] The ultrasonic treatment step S5 is a step of subjecting the second mixed liquid to ultrasonic treatment. The ultrasonic treatment breaks down the aggregated particles in the second mixed liquid, and the cerium-containing oxide becomes primary particles or fine particles close to primary particles. This makes it difficult for the particles to settle. An ultrasonic bath or an ultrasonic homogenizer can be used as the ultrasonic treatment device.

[0027] The shaking step S6 is a step of shaking the second mixed solution after the ultrasonic treatment. The second mixed solution after the ultrasonic treatment may contain particles that have settled. In this case, the settling particles are redispersed by the shaking step. The shaking step may be performed manually or using a shaker. The shaking step S6 may be performed immediately before the ink is used as an electrolyte layer-forming ink for a fuel cell.

[0028] The second liquid after shaking is less likely to experience particle settling even after several hours of shaking, and has a highly stable composition. Therefore, it can be advantageously used as an ink for forming an electrolyte layer in a fuel cell. By using the second liquid as an ink for forming an electrolyte layer, an electrolyte layer can be formed continuously for several hours.

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

[0030] Although the preferred embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and can be modified as appropriate.

[0031] For example, in this embodiment, the classification step S2 is performed after the crushing step S1, but the classification step S2 may be omitted if the cerium-containing oxide powder is sufficiently crushed in the crushing step S1. Also, the shaking step S6 is performed after the ultrasonic treatment step S5, but the shaking step S6 may be omitted if no sedimentation of particles is observed in the second mixed liquid after the ultrasonic treatment. [Example]

[0032] [Example 1] CeO2 powder was prepared as the cerium-containing oxide powder. The CeO2 powder was crushed using an agate mortar and pestle. The crushed material was then classified using a sieve with 32 μm openings to obtain fine CeO2 powder.

[0033] A mixed solution was prepared by mixing 118.8 parts by mass of ionomer and 13.3 parts by mass of water. 0.14 parts by mass of the CeO2 fine powder was added to this mixed solution, and the mixture was mixed for 15 minutes at a rotation speed of 650 rpm using a propeller mixer to obtain a first mixed solution. Next, 67.9 parts by mass of 1-propanol was added to the first mixed solution, and the mixture was mixed for another 15 minutes at a rotation speed of 650 rpm using a propeller mixer to obtain a second mixed solution.

[0034] The second mixture was sonicated for 30 minutes using an ultrasonic bath. After sonication, a small amount of white particles had settled in the second mixture. The sonicated second mixture was then immersed in a container to disperse the white particles, yielding a CeO2 dispersion. The resulting CeO2 dispersion was placed in a transparent container and allowed to stand for 3 hours. Visual observation of the CeO2 dispersion after standing revealed no sedimentation of the white particles. Therefore, this CeO2 dispersion can be advantageously used as an ink for forming an electrolyte layer in a fuel cell.

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

Claims

1. a crushing step of crushing the 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 with 1-propanol to obtain a second mixed solution; an ultrasonic treatment step of subjecting the second mixed liquid to ultrasonic treatment.

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

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

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

Images