JP2009043553A - Manufacturing method of catalyst ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress poisoning of noble metal catalyst in manufacturing catalyst ink. <P>SOLUTION: This manufacturing method of catalyst ink comprises: a process (step S100, step S110) of manufacturing a first dispersion solution prepared by dispersing particulate noble metal catalyst in water; a process (step S115) of defoaming bubbles adhering to surfaces of the noble metal catalyst included in the first dispersion solution; a process (step S120, step S130) of manufacturing a suspension liquid prepared by mixing an aqueous electrolyte solution in the first dispersion solution; and a process (step S140) of mixing a nonionic and fluorine-based surface active agent in the suspension liquid. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a catalyst ink for forming a catalyst electrode in a membrane electrode assembly including a solid polymer electrolyte membrane.

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas (for example, hydrogen) and an oxidant gas (for example, oxygen) has attracted attention as an energy source. As this fuel cell, there is a solid polymer fuel cell using a solid polymer membrane as an electrolyte membrane. The polymer electrolyte fuel cell includes a membrane electrode assembly formed by bonding gas diffusion electrodes (anode and cathode) to both surfaces of a solid polymer membrane having proton conductivity. Each of the anode and the cathode includes a catalyst layer (catalyst electrode) for promoting the electrochemical reaction.

  Conventionally, so-called catalyst ink is often used to form a catalyst layer on an electrolyte membrane. This catalyst ink is generally produced by dispersing carbon black carrying a noble metal catalyst such as platinum or a polymer electrolyte (for example, Nafion (registered trademark)) in a solvent such as water or an organic solvent.

  Incidentally, when carbon black carrying a noble metal catalyst is used in the catalyst layer, it is known that carbon oxidation occurs in the catalyst layer during operation depending on the operating conditions of the fuel cell. When carbon oxidation occurs in the catalyst layer, the noble metal catalyst supported on the carbon black is aggregated to reduce the surface area of the catalyst layer, resulting in a decrease in catalyst performance, that is, electrode performance.

  Therefore, in recent years, it has been proposed to form the catalyst layer without using carbon black when manufacturing a membrane electrode assembly. Various techniques for producing a catalyst ink used for forming such a catalyst layer have been proposed (see, for example, Patent Documents 1 to 3 below). For example, in the following Patent Document 1, the temperature of a mixed liquid composed of a polymer electrolyte and a fluorine compound is adjusted to 40 to 70 ° C., and platinum black is added to the mixed liquid. A method is described.

JP 2006-185855 A JP 2002-15088 A JP 2005-294264 A

  However, in the technique described in the above-mentioned patent document, there is no consideration about the catalyst ink containing an organic solvent and the noble metal catalyst (platinum black) is poisoned by the organic solvent and the catalytic performance is lowered. It wasn't.

  The present invention has been made to solve the above-described problems, and an object thereof is to suppress poisoning of a noble metal catalyst when a catalyst ink is produced.

  The present invention can be realized as the following forms or application examples in order to solve at least a part of the above-described problems.

  [Application Example 1] A method for producing a catalyst ink for forming a catalyst electrode in a membrane electrode assembly having a solid polymer electrolyte membrane, in which a particulate noble metal catalyst and an electrolyte material are dispersed in water A suspension preparation step for preparing a liquid, and a surfactant mixing step for mixing a non-ionic and fluorine-based surfactant into the suspension.

  In the production method of Application Example 1, when producing the suspension, an organic solvent is not used as a solvent for the particulate noble metal catalyst and the electrolyte material. Therefore, when the catalyst ink is manufactured, poisoning of the noble metal catalyst can be suppressed. As a result, by making a membrane electrode assembly using the catalyst ink, it is possible to suppress a decrease in electrode performance in the membrane electrode assembly. Examples of the electrolyte material include polymer electrolytes such as Nafion (registered trademark) and Flemion (registered trademark).

  In the manufacturing method of this application example, a surfactant is mixed in the suspension (catalyst ink). Therefore, when the catalyst ink is applied onto the electrolyte membrane and dried, the particulate noble metal catalyst can be prevented from aggregating due to surface tension. In the production method of this application example, a nonionic and fluorine surfactant is used as the surfactant. By using such a surfactant, it is possible to suppress a decrease in electrode performance in the membrane electrode assembly.

  [Application Example 2] The manufacturing method according to Application Example 1, wherein the suspension preparation step includes a step of dispersing the noble metal catalyst in water to prepare a first dispersion solution, and the first dispersion. Defoaming bubbles adhering to the surface of the noble metal catalyst contained in the solution, and mixing the second dispersion solution in which the electrolyte material is dispersed in water with the defoamed first dispersion solution; And a step of producing the suspension.

  The above-described poisoning of the noble metal catalyst by the organic solvent occurs when the noble metal catalyst, the organic solvent, and oxygen are present. And the said electrolyte dispersion solution may contain a trace amount organic solvent.

  The production method of Application Example 2 includes a step of defoaming bubbles (air containing oxygen) adhering to the surface of the noble metal catalyst contained in the first dispersion solution. Therefore, a trace amount of organic solvent is contained in the electrolyte dispersion solution. Even in such a case, poisoning of the noble metal catalyst can be suppressed.

  [Application Example 3] The production method according to Application Example 1 or 2, wherein the surfactant is an oligomer containing a perfluoroalkylethylene oxide adduct, a perfluoroalkyl group, and a hydrophilic group, or a perfluoroalkyl group. A production method comprising an oligomer containing a fluoroalkyl group, a hydrophilic group, and a lipophilic group.

  In addition to the constitution as the method for producing the catalyst ink described above, the present invention provides a catalyst ink produced by the production method described above, a membrane electrode assembly produced using the catalyst ink, and further, this membrane electrode assembly. It can also be configured as an invention of the fuel cell used. In addition, in each aspect, it is possible to apply the various additional elements shown above.

Hereinafter, embodiments of the present invention will be described based on examples.
A. First embodiment:
FIG. 1 is an explanatory view showing the production process of the catalyst ink of the first embodiment. This catalyst ink is for forming a catalyst electrode in a membrane electrode assembly having a solid polymer electrolyte membrane. And this membrane electrode assembly is used for a polymer electrolyte fuel cell.

  First, a particulate noble metal catalyst is mixed with water (step S100), and stirring as preliminary dispersion is performed (step S110). In this example, platinum black having an average primary particle diameter of 2 to 20 (nm) was used as the particulate noble metal catalyst. The average particle diameter of the primary particles of the noble metal catalyst can be arbitrarily set as desired. Moreover, it is good also as what uses another noble metal catalyst instead of platinum black. In this example, in step S100, the precious metal catalyst and water were weighed and mixed so that the weight ratio was 1: 10-20. The weight ratio between the noble metal catalyst and water can be arbitrarily set as desired. In this example, in step S110, stirring was performed for 5 minutes using an ultrasonic homogenizer. The stirring time by the ultrasonic homogenizer can be arbitrarily set as desired. The dispersion solution thus prepared corresponds to the first dispersion solution in the present invention.

  Next, an aqueous electrolyte solution is mixed with the first dispersion solution (step S120). The aqueous electrolyte solution is a dispersion solution in which a polymer electrolyte such as Nafion (registered trademark) or Flemion (registered trademark) is dispersed in water, and does not contain VOC (volatile organic compound) or alcohols. In this example, mixing was performed so that the weight of the polymer electrolyte contained in the aqueous electrolyte solution with respect to the weight of the noble metal catalyst was 5 to 15 (%). The weight of the polymer electrolyte contained in the aqueous electrolyte solution relative to the weight of the noble metal catalyst can be arbitrarily set as desired. The aqueous electrolyte solution corresponds to the second dispersion solution in the present invention.

  Next, the mixed solution of the first dispersion solution and the aqueous electrolyte solution (second dispersion solution) is stirred (step S130). In this example, the mixture was stirred for 5 to 15 minutes using an ultrasonic homogenizer. At this time, in the particle size distribution, the value of D50 of the secondary particles of the noble metal catalyst was set to 1 (μm) or less, and the value of D90 was set to 2 (μm) or less. These values can be arbitrarily set as desired. Through the above steps, the suspension in the present invention is produced.

  Next, a nonionic and fluorosurfactant is mixed in the suspension and stirred (step S140). In this example, “FC-4432 (manufactured by 3M)” was used as the surfactant. In this example, this surfactant was mixed in 0.1 (wt%) with respect to the water in the suspension. This value can be arbitrarily set as desired. In place of “FC-4432”, an oligomer containing a perfluoroalkylethylene oxide adduct, a perfluoroalkyl group, and a hydrophilic group, or a perfluoroalkyl group, a hydrophilic group, and a lipophilic group. It is also possible to use other nonionic and fluorine-based surfactants including oligomers containing. Further, the amount of the surfactant mixed is determined when the contact angle between the electrolyte membrane and the catalyst ink when the catalyst ink is spray-coated on the electrolyte membrane during the production of the membrane electrode assembly does not mix the surfactant. It is preferable to set it to be half or less of the above. With the above steps, the catalyst ink manufacturing process is completed.

  In the manufacturing process of the catalyst ink of the first embodiment described above, no organic solvent is used as a solvent for the particulate noble metal catalyst and the electrolyte material when the suspension is prepared. Therefore, when the catalyst ink is manufactured, poisoning of the noble metal catalyst can be suppressed. As a result, by making a membrane electrode assembly using the catalyst ink, it is possible to suppress a decrease in electrode performance in the membrane electrode assembly.

  In the production process of this example, a surfactant is mixed in the suspension. Therefore, when the catalyst ink is applied onto the electrolyte membrane and dried, the particulate noble metal catalyst can be prevented from aggregating due to surface tension. In addition, since a nonionic and fluorosurfactant is used as the surfactant, it is possible to suppress a decrease in electrode performance in the membrane electrode assembly.

  Note that the catalyst ink produced by the above production process has a relatively small secondary particle size of the noble metal catalyst and contains a surfactant, so that the catalyst ink is used during the production of the membrane electrode assembly. When spray coating is performed on the electrolyte membrane, clogging of the spray can be suppressed, which is preferable.

B. Second embodiment:
FIG. 2 is an explanatory view showing the production process of the catalyst ink of the second embodiment. This manufacturing process is a degassing process that degass bubbles (air containing oxygen) adhering to the surface of the noble metal catalyst between steps S110 and S120 in the manufacturing process of the catalyst ink of the first embodiment shown in FIG. A foaming process is provided (step S115). In this example, vacuum defoaming was performed under a vacuum environment of 0.02 (MPa) or less. The conditions for vacuum defoaming (degree of vacuum, time, etc.) can be arbitrarily set within a range where bubbles attached to the surface of the noble metal catalyst can be sufficiently defoamed. Other than this, the process is the same as that of the catalyst ink of the first embodiment.

  Also in the production process of the catalyst ink of the second embodiment described above, as in the production process of the catalyst ink of the first embodiment, the fine particulate noble metal catalyst and the electrolyte solvent are used during the preparation of the suspension. No organic solvent is used. Therefore, when the catalyst ink is manufactured, poisoning of the noble metal catalyst can be suppressed.

  In addition, since there is a defoaming step for defoaming bubbles adhering to the surface of the noble metal catalyst between Step S110 and Step S120 in the production process of the catalyst ink of the first embodiment, a trace amount is added to the aqueous electrolyte dispersion solution. Even when the organic solvent is contained, poisoning of the noble metal catalyst can be suppressed. This is because poisoning of the noble metal catalyst with the organic solvent occurs when the noble metal catalyst, the organic solvent, and oxygen are present.

C. Variations:
As mentioned above, although several embodiment of this invention was described, this invention is not limited to such embodiment at all, and implementation in a various aspect is possible within the range which does not deviate from the summary. It is. For example, the following modifications are possible.

C1. Modification 1:
In the first embodiment, the first dispersion solution is prepared, and then the aqueous electrolyte solution (second dispersion solution) is mixed to prepare the suspension. Not limited. In step 100 of FIG. 1, the particulate noble metal catalyst, water, and the aqueous electrolyte solution may be mixed simultaneously.
C2. Modification 2:
In the second embodiment, vacuum degassing is performed in step S115 of FIG. 2, but the present invention is not limited to this. For example, you may make it apply other defoaming methods, such as stirring defoaming.

It is explanatory drawing which shows the manufacturing process of the catalyst ink of 1st Example. It is explanatory drawing which shows the manufacturing process of the catalyst ink of 2nd Example.

Claims (3)

A method for producing a catalyst ink for forming a catalyst electrode in a membrane electrode assembly comprising a solid polymer electrolyte membrane,
A suspension preparation step for preparing a suspension in which a fine particle precious metal catalyst and an electrolyte material are dispersed in water;
A non-ionic and surfactant-containing step of mixing a fluorine-containing surfactant into the suspension,
A manufacturing method comprising: The manufacturing method according to claim 1,
The suspension preparation step includes
Dispersing the noble metal catalyst in water to produce a first dispersion;
Defoaming bubbles adhering to the surface of the noble metal catalyst contained in the first dispersion;
Mixing the defoamed first dispersion solution with a second dispersion solution in which the electrolyte material is dispersed in water to produce the suspension; and
Manufacturing method. The manufacturing method according to claim 1 or 2,
The surfactant is an oligomer containing a perfluoroalkyl ethylene oxide adduct, a perfluoroalkyl group, and a hydrophilic group, or an oligomer containing a perfluoroalkyl group, a hydrophilic group, and a lipophilic group. including,
Production method.

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