JP2010086859A - Method for forming catalyst layer for fuel cell using catalyst ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To lower viscosity of catalyst ink by eliminating coarse particles and air bubbles in catalyst ink and manufacture uniform catalyst ink. <P>SOLUTION: Catalyst ink materials containing powder comprising catalyst carrying conductive particles, resin having ionic conductivity and a dispersing medium are prepared (S1), shearing force is applied to the catalyst ink materials to disperse each material (S2), the catalyst ink materials are dispersed by cavitation effect produced by applying ultrasonic vibration to the catalyst ink materials (S3), and the catalyst ink obtained is applied to an electrolyte membrane (S4). All coarse particles are crushed in the process S2 and the catalyst carrying conductive particles are uniformly monodispersed, air bubbles are burst by ultrasonic waves in the process S3 to stably manufacture the uniform catalyst ink having stable viscosity, and the catalyst ink is applied to the electrolyte membrane to form an appropriate catalyst layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention manufactures an ink for an electrode catalyst layer (hereinafter referred to as catalyst ink) typified by a polymer electrolyte fuel cell (hereinafter referred to as PEFC), and uses the catalyst ink as an electrolyte membrane. The present invention relates to a manufacturing method for applying and forming a catalyst layer for a fuel cell such as PEFC.

Conventionally, a method for dispersing a catalyst ink suitable for producing a catalyst ink for a fuel cell has been studied. For example, Patent Document 1 lists a plurality of types of dispersion devices used in the dispersion step of the catalyst ink production method.
However, when adopting a plurality of types of dispersion apparatuses, it has not been clarified how to select, how to combine them, and in what order.

By the way, it is desirable that the catalyst ink used as the material of the catalyst layer of the fuel cell has a catalytic ability over the entire catalyst layer. Therefore, the catalyst-carrying conductive particles represented by platinum-carrying carbon particles and the electrolyte having proton conductivity must be uniformly dispersed in the solvent.
Therefore, it is preferable that the catalyst-carrying conductive particles are uniformly suspended in the catalyst ink. And in order to form a catalyst layer uniformly and stably after this suspension, it is preferable that the viscosity, concentration, etc. of the catalyst ink do not change with time.

In order for a fuel cell including a catalyst layer formed using a catalyst ink to exhibit suitable power generation performance, the catalyst-supporting conductive particles are uniformly coated with an electrolyte solution containing an ion conductive resin in the catalyst ink. There is a need. For this purpose, catalyst-carrying conductive particles (hereinafter simply referred to as “particles”) are, for example, pulverized so that the particles fall within a range of about 0.1 μm to 1 μm, and are added to the electrolyte solution so as not to include large particles. It is preferable to disperse.
JP 2004-146165 A

  In view of the above, as a result of intensive studies, the inventor has conducted a dispersion method using shearing force (hereinafter referred to as “shearing force dispersion”) and a dispersion method using cavitation effect (ultrasound) (hereinafter referred to as “ultrasonic dispersion”). The method by the combination with was examined.

  However, according to shear force dispersion, primary particles or secondary particles are given high dispersion energy, so these particles can be suitably pulverized and dispersed. On the other hand, as the shear force increases, particles or particles and media Violently and randomly collide, so that many bubbles are generated in the catalyst ink. The generated air bubbles cause biting in the apparatus during shear dispersion, and the air bubbles act like a cushion, making it difficult to finely disperse the particles. In addition, since the fluctuation of the viscosity and concentration of the catalyst ink is increased by the entrapment of bubbles, it is difficult to stably form the catalyst layer.

  In addition, if bubbles remain in the catalyst ink as they are, the bubbles do not function as a catalyst, but the bubbles inhibit electronic conductivity and ionic conductivity, and the catalyst layer structure becomes brittle, which leads to fuel cell performance. And the durability may be adversely affected.

  On the other hand, according to ultrasonic dispersion, primary particles and secondary particles are pulverized by a strong cavitation force generated at locations where ultrasonic waves intensify in the catalyst ink, and the bubbles are ruptured. However, it is difficult to pulverize large catalyst-carrying conductive particles of about 100 μm, and even if pulverized, it takes a long time until pulverization and lowers the production efficiency. Moreover, if not pulverized, large particles remain as they are, and the catalytic ability is unevenly distributed in the catalyst layer.

  In view of such circumstances, the present invention aims to determine the order by combining the above two dispersion methods in the production of a catalyst ink, and to provide optimum solid concentration conditions in each dispersion method. And

(Aspect of the Invention)
In the present invention, the advantage of ultrasonic dispersion and shear force dispersion is utilized, and the disadvantages are complemented with each other. After sufficient dispersion of shear force, ultrasonic dispersion by cavitation effect (ultrasonic vibration) is performed to produce catalyst ink. To do. As a result, a catalyst ink having excellent uniformity and defoaming can be produced. Furthermore, it is possible to optimize the magnitude relationship of the solid content concentration between the respective dispersion steps, and to further stably disperse the catalyst ink. Various aspects of the production method for forming a catalyst layer for a fuel cell using the catalyst ink according to the present invention, as well as their actions and effects, will be described in detail in the following section of the invention.

  Hereinafter, some aspects of the invention that is recognized as being claimable (hereinafter sometimes referred to as “claimable invention”) will be exemplified and described. As with the claims, each aspect is divided into sections, each section is numbered, and is described in a form that cites the numbers of other sections as necessary. This is for the purpose of facilitating the understanding of the claimable invention, and is not intended to limit the combinations of the constituent elements constituting the claimable invention to those described in the following sections. In other words, the claimable invention should be construed in consideration of the description accompanying each section, the description of the embodiments, etc., and as long as the interpretation is followed, another aspect is added to the form of each section. In addition, an aspect in which constituent elements are deleted from the aspect of each item can be an aspect of the claimable invention. In each of the following items, each of the items (1), (2), (3), and (4) corresponds to each of claims 1, 2, 3, and 4. It corresponds to.

(1) A method for producing an electrode for a fuel cell formed using a catalyst ink, comprising a shearing force dispersion step of applying a shearing force to a catalyst ink material to disperse, and a cavitation in the catalyst ink after the shearing force dispersion step An ultrasonic dispersion step for applying force to disperse the catalyst layer ink, and the catalyst ink after the ultrasonic dispersion step is applied to the electrolyte membrane, or applied to a transfer substrate and then transferred to the electrolyte membrane to thereby transfer the electrolyte to the electrolyte membrane. A method for producing an electrode for a fuel cell, comprising an ink application step for forming a catalyst layer.

According to the production method of this section, shearing and pulverization of large catalyst-carrying conductive particles in the catalyst ink material can be performed by shear force dispersion. This makes it possible to omit the filter processing step (or filter filtration device) for removing coarse particles due to dispersion problems that have been conventionally required.
Also, by ultrasonic dispersion, many bubbles generated in the catalyst ink due to the above-mentioned shear force dispersion can be ruptured, and the catalyst ink can be made uniform. Thus, since the catalyst ink is defoamed by ultrasonic dispersion, the viscosity is constant from the beginning, and as a result, the coating conditions are also constant, so that the coating conditions can be stabilized.

  Preferably, when carrying out the production method, shear force dispersion is performed using a wet jet mill, and then the catalyst layer material ink is subjected to defoaming treatment and homogenization treatment using an ultrasonic vibrator. To do. According to this aspect, since the wet jet mill is media-free, solid-liquid separation processing is unnecessary, and there is no mixing of impurities due to media scraping. In addition, the defoaming treatment and the homogenization treatment can be performed by ultrasonic treatment using the treatment chamber of the wet jet mill. This makes it possible to save labor when manufacturing the catalyst ink.

(2) The method for producing an electrode for a fuel cell according to (1), wherein the catalyst ink material includes a powder composed of catalyst-carrying conductive particles, a resin having ionic conductivity, and a solvent.

This section defines a powder composed of catalyst-carrying conductive particles, a resin having ionic conductivity, and a solvent as basic starting materials for producing the catalyst ink of (1).
Since the catalyst ink is applied to an electrolyte membrane to form a catalyst layer, catalyst-carrying conductive particles such as platinum-carrying carbon particles are required. This catalyst decomposes hydrogen gas and air (or oxygen gas) into hydrogen ions and electrons and oxygen ions and electrons, respectively. In addition, a resin having ion conductivity such as Nafion (trade name) manufactured by DuPont is required. This promotes the movement of the hydrogen ions, oxygen ions and electrons. Then, water or an alcohol solvent is used as a solvent. This is because the catalyst ink is a liquid, and it is necessary to suspend and disperse the catalyst-carrying conductive particles (powder) and the solid (solid content) of the ion conductive resin in a solvent.
In addition, other materials necessary for the formulation of the catalyst ink, for example, a surface tension adjusting agent and an adhesion improving agent can be added as appropriate.

(3) If the solid content concentration of the catalyst ink obtained in the shearing force dispersion step is X and the solid content concentration of the catalyst ink obtained in the ultrasonic dispersion step is Y, X is equal to Y, or Y is X The value of X and Y is set so that it may become smaller, The manufacturing method of the electrode for fuel cells as described in (1) or (2) characterized by the above-mentioned.

  According to this section, in the ultrasonic dispersion step rather than the shear force dispersion step, the ultrasonic wave from the ultrasonic vibrator is used as a solvent for the catalyst-carrying conductive particles (powder) and the solid content of the ion conductive resin. The solid content is easily dispersed in the solvent by cavitation force, and a large number of bubbles in the catalyst ink are ruptured by cavitation force in the shearing force dispersion step. This is because regarding the solid content, it is considered preferable to increase the solvent content in the latter step because ultrasonic waves are easily transmitted.

(4) A polymer electrolyte fuel cell obtained by the production method according to any one of (1) to (3).

  This section stipulates that the fuel cell to which the above manufacturing method can be suitably applied is a polymer electrolyte fuel cell (PEFC). In addition, since the direct methanol fuel cell (DMFC) is structurally similar to PEFC, the above manufacturing method can be suitably applied in the same manner. However, the catalyst layer ink obtained by the above production method can also be applied to electrolyte membranes other than these fuel cells.

(5) including a shearing force dispersion step of dispersing the catalyst ink material by applying a shearing force, and an ultrasonic dispersion step of dispersing the catalyst layer ink by applying a cavitation force to the catalyst ink after the shearing force dispersion step. A method for producing a fuel cell catalyst ink.

According to the production method of this section, the coarse particles of the catalyst-carrying conductive particles in the catalyst ink material can be pulverized and sheared mainly in the shearing force dispersion step, so that the particle size distribution in the catalyst ink after the dispersion treatment is achieved. The curve can be made steeper and monodispersed. Also, mainly according to the ultrasonic dispersion step, the viscosity is lowered by rupturing a large number of bubbles present in the catalyst ink in the shearing force dispersion step, and a catalyst ink with further excellent uniformity is produced. be able to.
The catalyst ink thus obtained is housed and sealed in a suitable container, and can be manufactured and sold as a catalyst ink for fuel cells.

(6) If the solid content concentration of the catalyst ink obtained in the shearing force dispersion step is X and the solid content concentration of the catalyst ink obtained in the ultrasonic dispersion step is Y, X is equal to Y, or Y is X The method for producing a catalyst ink for a fuel cell according to (5), wherein the values of X and Y are set so as to be smaller.
(7) A polymer electrolyte fuel cell manufactured using the catalyst ink obtained by the manufacturing method according to any one of (5) and (6).

  The effects and other contents of (6) and (7) are the same as the contents described in the section (3), and the description thereof is omitted.

  According to the present invention, it is possible to produce a catalyst ink having a stable viscosity in which a solid content is efficiently monodispersed in a solvent and basically does not contain bubbles.

Hereinafter, an embodiment of the present invention will be described with reference to FIG.
FIG. 1 shows a catalyst ink material preparation step for preparing a catalyst ink material indicated by S1, a shearing force dispersion step indicated by S2, an ultrasonic dispersion step indicated by S3, and a catalyst ink indicated by S4 applied to the electrolyte membrane. It is a manufacturing flow which consists of an ink application | coating process. Hereafter, each process is demonstrated along the flow of this manufacturing flow.

Catalyst ink material preparation step (S1) : In this step, a starting material (catalyst ink material) is prepared. The catalyst ink material is basically a powder made of catalyst-carrying conductive particles, a resin having ionic conductivity, and a dispersion medium.
The catalyst-carrying conductive particles are preferably platinum-carrying carbon particles, platinum / ruthenium-carrying carbon particles, nickel-carrying carbon particles, and the like. Examples of the resin having ion conductivity include a resin having an ion exchange group such as a sulfonic acid group in a perfluoro skeleton represented by Nafion (registered trademark) manufactured by DuPont. The dispersion medium is preferably water or alcohols such as methanol, propanol, and butyl alcohol. Other materials and ink preparation methods necessary for ink production are determined according to a conventional method according to the viscosity and concentration of the target ink.

Shearing force dispersion step (S2) : In this step, kneading is carried out by dispersing and pulverizing with a continuous biaxial kneader, batch kneader, pressure homogenizer, bead mill, high shear mill, sand mill, wet jet mill, etc. A mill or grinder is used as the shear force device. Among these, it is preferable to use a wet jet mill.
The wet jet mill has high pulverization / dispersion efficiency because the catalyst-carrying conductive particles collide with each other with great energy without using any pulverizing media, and pulverization is performed. Further, since the pulverization / dispersion is performed in the chamber of the wet jet mill, it is possible to prevent impurities from being mixed into the catalyst ink material from the material of the pulverization medium.

  That is, for other pulverizers, solid-liquid separation between the catalyst ink, shearing and pulverizing media, kneading rods, etc. is essential, but according to the wet jet mill, solid-liquid separation is unnecessary, and the process Can be simplified and labor-saving, and the material of the media and the kneading rod is not mixed as impurities in the catalyst ink.

  Further, after the catalyst ink material is processed in the chamber of the wet jet mill in this step, when the bubbles contained therein are ruptured and removed in the next step, the catalyst ink is not transferred to another device. This can be done by sonication in the same chamber.

Ultrasonic dispersion step (S3) : In this step, ultrasonic vibration is applied to the catalyst ink produced by the shearing force dispersion step. By this ultrasonic vibration, the bubbles contained in the catalyst-carrying conductive particle slurry (catalyst ink) produced in the shearing force dispersion process are ruptured and defoamed, and the catalyst-carrying conductive material that has become secondary particles. Particles can be decomposed into primary particles.

  However, in ultrasonic vibration, the place where the ultrasonic waves intensify is fixed at a fixed position (focal point), so the chamber is always satellite-rotated, eccentrically rotated, and / or ultrasonic waves during processing. It is preferable to move the vibrator in the chamber or along the chamber wall. In this way, the cavitation effect (ultrasonic dispersion treatment) by ultrasonic vibration is applied to the entire catalyst-supporting conductive particle slurry.

  Note that it is desirable to perform ultrasonic dispersion by attaching an ultrasonic vibrator (ultrasonic vibration device) in the chamber or wall of the wet jet mill. This is because, as described above, the manufacturing cost can be reduced and the mixing of impurities can be avoided by simplifying and saving labor.

Furthermore, in order to improve the production efficiency of the catalyst ink, the solid content concentration (vol%) (solid content) of the catalyst ink material before being processed in each of the shearing force dispersion step (S2) and the ultrasonic dispersion step (S3). Is preferably X ≧ Y, where X and Y are the catalyst-carrying conductive particles).
The production method for forming a catalyst layer for a fuel cell using the catalyst ink according to the present invention stops at the ultrasonic dispersion step (S3), and the catalyst ink of the intermediate product is stored in a sealed container and manufactured and sold. Is possible.

Ink applying step (S4): a catalyst ink obtained by the ultrasonic dispersion process (S3), a doctor blade method, a spray method, a screen printing method, a gravure coating method, die coating method, coating and inkjet method (coating) By the method, it is applied to the electrolyte membrane with a certain thickness. Any coating method may be used, but it is desirable to adjust the viscosity of the catalyst ink before coating so as to obtain a suitable viscosity by adding or evaporating the solvent of the catalyst ink according to the coating method.

Examples of the present invention will be described below in comparison with comparative examples. However, the present invention is not limited to the following examples.
In addition, the viscosity of the catalyst ink is measured with a B-type viscometer manufactured by Toki Sangyo, and the particle size distribution in the catalyst ink is measured by laser diffraction to measure the particle size distribution including not only primary particles but also secondary particles. A possible Nikkiso Microtrack MT3300EX (trade name) was used.

<Example 1>
Carbon black (carbon particles) with 50% platinum particles supported on carbon black, DuPont Nafion electrolyte solution (ionic conductive resin solution), water, ethanol (Dispersion medium) is prepared, the ratio of carbon to the electrolyte component in the electrolyte solution is 1: 1, the solid content concentration is 10.7%, and the carbon concentration (carbon concentration in carbon black) is 3.6%. The prepared solution was prepared so that the total amount was 3 L.

In Example 1, the dispersion treatment was performed on the preparation solution in the order of a wet jet mill and ultrasonic vibration.
The wet jet mill was dispersed for 15 minutes under a low pressure of 3 MPa, followed by a dispersion treatment for 30 minutes under a high pressure of 150 MPa. Thereafter, ultrasonic dispersion treatment was carried out for 20 minutes (the above preparation solution formulation and dispersion treatment conditions were also adopted in Examples 2 and 3).
And as shown in FIG. 2, the viscosity (mPa * s) of the preparation solution with respect to the elapsed time of a dispersion process was measured. Moreover, as shown in FIG. 3, the relationship between a particle size (micrometer) and volume frequency (%) was measured.

<Comparative Example 1>
In Comparative Example 1, the preparation solution was subjected to a rough dispersion treatment for 15 minutes under a low pressure of 3 MPa only by a wet jet mill, and then a dispersion treatment for 50 minutes under a high pressure of 150 MPa. . Then, as shown in FIG. 2, the viscosity of the preparation solution with respect to the elapsed time of the dispersion treatment was measured in the same manner as in the example, as a relationship between the particle size (μm) and the volume frequency (%).

<Comparative example 2>
In Comparative Example 2, the preparation solution was subjected to an ultrasonic dispersion process for 65 minutes using only an ultrasonic vibrator. As shown in FIG. 3, the particle size distribution (relationship between particle size (μm) and volume frequency (%)) of the catalyst ink subjected to ultrasonic dispersion treatment was measured.

<Example 2>
After the shearing force dispersion, water and ethanol were added and diluted so that the solid content concentration was 9.4%, and the dispersion treatment was performed under the same conditions as in Example 1. Then, as shown in FIG. 3, the particle size distribution (the relationship between the particle size (μm) and the volume frequency (%)) was measured in the same manner.
<Comparative Example 3>
The method for dispersing the catalyst ink was the same as in Example 1. After dispersing the shearing force, ultrasonic dispersion was performed by adding water and ethanol to dilute so that the solid content concentration was 12.5%. Then, as shown in FIG. 3, the particle size distribution (the relationship between the particle size (μm) and the volume frequency (%)) was measured in the same manner.

<Evaluation>
The line graph in FIG. 2 shows the change over time in the viscosity measured for the catalyst inks obtained in Example 1 and Comparative Example 1. The catalyst ink of Example 1 obtained by carrying out the shearing force dispersion treatment and the ultrasonic dispersion treatment in this order had a constant viscosity even after 30 hours had passed since the viscosity measurement was started. On the other hand, the catalyst ink of Comparative Example 1 obtained by carrying out only the shearing force dispersion treatment had a viscosity about three times lower than that of the catalyst ink of Example 1 at the time of starting the viscosity measurement. And after 15 hours, it almost coincided with the viscosity of the catalyst ink of Example 1.
This is because in Comparative Example 1, many bubbles s were present in the catalyst ink obtained by the shearing force dispersion treatment, and the viscosity thereof was increased. After 15 hours, the bubbles naturally formed from the catalyst ink. This is thought to be due to the fact that it gradually floated and burst and became the same viscosity as in Example 1.
From this result, since the catalyst ink according to Example 1 has a certain viscosity from the beginning, it is applied to the electrolyte membrane immediately after production, and a stable quality and excellent durability catalyst layer is formed on the electrolyte membrane. I found out that This also contributes to shortening of the manufacturing time, thereby making it possible to reduce the manufacturing cost.

The curve in FIG. 3 shows the particle size distribution in the catalyst inks obtained in Example 1 and Comparative Example 2. Focusing on the particle size distribution of Comparative Example 2, the particle size distribution is divided into two peaks, and pulverization / dispersion treatment was not performed on particles close to 100 μm only by ultrasonic dispersion. On the other hand, the coarse particle side crest did not exist in the particle size distribution of Example 1.
From this result, since only the ultrasonic dispersion as in Comparative Example 1 leaves coarse particles, a filtration filter treatment may be necessary as in the prior art (see Patent Document 1). In Example 1 which concerns on this, it turned out that it becomes unnecessary.

  The curves in FIG. 4 show the particle size distributions in the catalyst inks obtained in Example 1, Example 2 and Comparative Example 3, and the solid content concentrations are 10.7% and 9 in order as described above. 4% and 12.5%. The solid content concentrations (vol%) of the catalyst ink material before the treatment in the shearing force dispersion step (S2) and the ultrasonic dispersion step (S3) are X = 10.7% and Y = 12.5, respectively. In Comparative Example 3 in which X ≦ Y was set as%, not only the coarse particles found in Comparative Example 2 were present, but also the particle size distribution was broad. On the other hand, in Example 2 where X = 10.7% and Y = 9.4% and X ≧ Y was set, such coarse particles did not exist, and the particle size distribution became steeper. Thus, it is considered that a more uniform catalyst ink is produced when the solid content concentration is set as X ≧ Y.

  In addition, the manufacturing method of the catalyst layer for polymer electrolyte fuel cells (PEFC) which forms the catalyst layer based on this invention in an electrolyte membrane is not limited to above-described embodiment, It deviates from the summary of this invention. Of course, various modifications can be made within the range not to be performed. For example, the manufacturing method can be applied to a catalyst ink for a catalyst layer of a direct methanol fuel cell (DMFC).

FIG. 1 is a manufacturing process flow of a catalyst ink for a solid molecular fuel cell according to the present invention and a method for manufacturing a catalyst layer formed using the ink. FIG. 2 is a graph showing the change over time in the viscosity of the catalyst inks obtained in Example 1 and Comparative Example 1. FIG. 3 is a curve showing the particle size distribution of platinum-supported carbon particles in the catalyst inks obtained in Example 1 and Comparative Example 2. FIG. 4 is a curve showing the particle size distribution of platinum-supported carbon particles in the catalyst inks obtained in Example 1, Example 2, and Comparative Example 2.

Explanation of symbols

S1: Catalyst ink material preparation step, S2: Shear force dispersion step, S3: Ultrasonic dispersion step, S4: Catalyst ink application step

Claims (4)

A method for producing a fuel cell electrode formed using a catalyst ink, comprising:
A shearing force dispersing step for dispersing the catalyst ink material by applying a shearing force;
An ultrasonic dispersion step of dispersing the catalyst layer ink by applying a cavitation force to the catalyst ink after the shearing force dispersion step;
An ink application step of forming a catalyst layer on the electrolyte membrane by applying the catalyst ink after the ultrasonic dispersion step to the electrolyte membrane, or applying the catalyst ink to a transfer substrate and then transferring the catalyst ink to the electrolyte membrane. A method for manufacturing an electrode for a fuel cell.   2. The method for producing an electrode for a fuel cell according to claim 1, wherein the catalyst ink material includes a powder composed of catalyst-carrying conductive particles, a resin having ionic conductivity, and a solvent.   If the solid content concentration (vol%) of the catalyst ink obtained in the shearing force dispersion step is X and the solid content concentration (vol%) of the catalyst ink obtained in the ultrasonic dispersion step is Y, X and Y are equal or The method for producing a fuel cell electrode according to claim 1 or 2, wherein the values of X and Y are set so that X is larger than Y.   The polymer electrolyte fuel cell obtained by the manufacturing method of any one of Claims 1-3.

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