JP2005302665A - Method for producing membrane electrode assembly for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a porosity of a catalyst electrode layer so as to effectively contribute to an improvement in power generation efficiency and to prevent a membrane electrode composite from deteriorating other members such as a catalyst. It aims at providing the manufacturing method of.
To achieve the above object, the present invention has an affinity for a solid electrolyte membrane material, a first solvent for dispersing the solid electrolyte membrane material, and the solid electrolyte membrane material. A coating solution preparing step for preparing a coating solution for forming a catalyst electrode layer having at least a pore-forming polymer that is insoluble in the solvent and soluble in the second solvent, and the catalyst Using the electrode layer forming coating solution, a catalyst electrode layer forming step for forming a catalyst electrode layer on each surface of the solid electrolyte membrane, the catalyst electrode layer formed in the catalyst electrode layer forming step, and the second A method for producing a membrane electrode assembly for a fuel cell, comprising a step of forming a pore in the catalyst electrode layer by removing the pore-forming polymer by contacting with a solvent of provide.
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Description

  The present invention relates to a method for producing a membrane electrode assembly for a fuel cell used in a solid polymer electrolyte fuel cell.

  Fuel cells that generate electricity through the electrochemical reaction of gas have high power generation efficiency, and the exhausted gas is clean and has very little impact on the environment. Applications are expected. Fuel cells can be classified according to their electrolytes. For example, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, solid polymer fuel cells, and the like are known.

  In particular, the polymer electrolyte fuel cell can be operated at a low temperature of about 80 ° C., and therefore it is relatively easy to handle and has a very high output density compared to other types of fuel cells. Therefore, its use is expected. A polymer electrolyte fuel cell is usually a membrane electrode assembly for a fuel cell in which a proton conductive polymer membrane is used as a solid electrolyte membrane, and a pair of catalyst electrode layers respectively serving as a fuel electrode and an air electrode are provided on both sides thereof. (Hereafter, it may be simply referred to as a membrane electrode assembly) is defined as a power generation unit. Then, a fuel gas such as hydrogen or hydrocarbon is supplied to the fuel electrode, and an oxidant gas such as oxygen or air is supplied to the air electrode, and an electrochemical reaction proceeds at the three-phase interface between the gas, the electrolyte, and the electrode. The electricity is taken out by this.

  In such a fuel cell, in order to improve power generation efficiency, it is preferable that the catalyst electrode layer has appropriate pores and a three-phase interface as a reaction field is wide. However, in the conventional method of manufacturing a membrane electrode composite, after applying a coating liquid having carbon black supporting platinum, a solid electrolyte membrane material, and a solvent, and drying and heating to form a catalyst electrode layer Since the membrane electrode composite is manufactured by hot pressing the catalyst electrode layer on both surfaces of the solid electrolyte membrane, the hot pressing will collapse the pores and obtain a sufficient three-phase interface. There was a problem that could not.

In order to solve such problems, several proposals have been made to improve the power generation efficiency by forming holes in the catalyst electrode layer. For example, in Patent Document 1, polymer fine particles are introduced into a catalyst electrode layer using a dispersion plating method, and the polymer particles are decomposed and removed by immersing the polymer fine particles in an acidic solution. A method for forming pores is disclosed. Similarly, Patent Document 2 and Patent Document 3 also show techniques for forming pores in the catalyst electrode layer.
However, these proposals do not necessarily improve only the porosity in the vicinity of the three-phase interface. Therefore, even if the porosity is increased, the conductivity and proton conductivity are reduced, resulting in power generation efficiency. In some cases, it did not lead to improvement. In addition, some of these methods have problems such as deterioration of the catalyst in the pore formation step.

JP-A-8-138715 JP-A-9-199138 JP-A-6-203852

  The present invention has been made in view of the above problems, and can increase the porosity of the catalyst electrode layer so as to effectively contribute to the improvement of the power generation efficiency. The main object is to provide a method for producing a membrane electrode assembly that does not deteriorate.

  In order to solve the above-mentioned problems, the present invention provides a method for producing a membrane electrode assembly for a fuel cell in which a catalyst electrode layer is formed on each surface of a solid electrolyte membrane, the solid electrolyte membrane material, and the solid electrolyte A first solvent for dispersing a membrane material, and for pore making that has an affinity for the solid electrolyte membrane material, is insoluble in the first solvent, and is soluble in the second solvent A catalyst electrode layer is formed on each surface of the solid electrolyte membrane using a coating liquid preparation step of preparing a catalyst electrode layer forming coating liquid having at least a polymer, and the catalyst electrode layer forming coating liquid. The catalyst electrode layer forming step to be formed, the catalyst electrode layer formed in the catalyst electrode layer forming step, and the second solvent are contacted to remove the pore-forming polymer, and the catalyst electrode layer is emptied. And a hole forming step for forming holes. It provides a method for manufacturing a fuel cell membrane electrode assembly.

  In the present invention, since the pore-forming polymer that forms pores in the catalyst electrode layer has an affinity for the solid electrolyte membrane material, it is close to the solid electrolyte membrane material in the catalyst electrode layer. Thus, holes can be formed. Therefore, the membrane electrode assembly obtained in the present invention can effectively increase the three-phase interface in the catalyst electrode layer, and at the same time, can effectively introduce gas and discharge water. When used as a fuel cell, the power generation efficiency can be greatly improved.

In the above invention, the pore-forming polymer is preferably a water-soluble polymer, the first solvent is water at room temperature, and the second solvent is boiling water. If water-soluble polymer is used in this way and water is used as the solvent, the conventional method for producing a membrane electrode assembly can be applied as it is, so there is no trouble in the process and adversely affects other members such as a catalyst. It is because it has the advantage that there is nothing.
The present invention also provides a method for producing a fuel cell, characterized in that the membrane electrode assembly for a fuel cell obtained by the above-described method for producing a membrane electrode assembly for a fuel cell is used. The fuel cell obtained by the present invention can have high power generation efficiency.

  The method for producing a membrane electrode composite of the present invention can effectively increase the three-phase interface in the catalyst electrode layer in the obtained membrane electrode composite, and at the same time, is effective in introducing gas and discharging water. Therefore, when used as a fuel cell, the power generation efficiency can be greatly improved.

  Hereinafter, the manufacturing method of the membrane electrode assembly of the present invention and the manufacturing method of the fuel cell will be described in detail.

A. Method for Producing Membrane Electrode Assembly First, the method for producing the membrane electrode assembly of the present invention will be described. The method for producing a membrane electrode assembly of the present invention is a method for producing a membrane electrode assembly for a fuel cell in which a catalyst electrode layer is formed on each surface of a solid electrolyte membrane, comprising: a solid electrolyte membrane material; and the solid electrolyte A first solvent for dispersing a membrane material, and for pore making that has an affinity for the solid electrolyte membrane material, is insoluble in the first solvent, and is soluble in the second solvent A catalyst electrode layer is formed on each surface of the solid electrolyte membrane using a coating liquid preparation step of preparing a catalyst electrode layer forming coating liquid having at least a polymer, and the catalyst electrode layer forming coating liquid. The catalyst electrode layer forming step to be formed, the catalyst electrode layer formed in the catalyst electrode layer forming step, and the second solvent are contacted to remove the pore-forming polymer, and the catalyst electrode layer is emptied. And a hole forming step for forming a hole. Than it is.

  Hereafter, it divides into a coating liquid preparation process, a catalyst electrode layer formation process, and a void | hole formation process which comprise the manufacturing method of the membrane electrode assembly of this invention, and it explains in full detail, respectively.

1. Coating liquid preparation step The coating liquid preparation step in the present invention has an affinity for the solid electrolyte membrane material, the first solvent for dispersing the solid electrolyte membrane material, and the solid electrolyte membrane material. And a catalyst electrode layer forming coating solution having at least a pore-forming polymer that is insoluble in the solvent and soluble in the second solvent. First, the material used in this step will be described, and then the preparation method will be described.

(1) Materials used (Porosity polymer)
A feature of the method for producing a membrane electrode assembly of the present invention is that a polymer for pore formation is used. Such a pore-forming polymer used in the present invention is roughly divided into two characteristics.
First, the first feature is that it has an affinity with the solid electrolyte membrane material. In the present invention, by using the pore-forming polymer having an affinity for the solid electrolyte membrane material as described above, when the catalyst electrode layer is formed in the catalyst electrode layer forming step described later, this pore-forming polymer is used. Molecules can be present in close proximity to the solid electrolyte membrane material. For this reason, in the subsequent pore formation step, when the pore-forming polymer is removed to form the pores, the formed pores are formed close to the solid electrolyte membrane material. Specifically, for example, pores are formed in the vicinity of the solid electrolyte membrane material arranged so as to cover the periphery of the carbon particles carrying the platinum catalyst. This makes it possible to effectively increase the three-phase interface in the catalyst electrode layer as compared to the case of randomly forming vacancies as in the conventionally proposed technology. It is possible to effectively discharge the water generated in the water.

  In the present invention, having affinity with a solid electrolyte membrane material is not particularly limited as long as the pore-forming polymer has a property that can be disposed close to the solid electrolyte membrane material. . However, in the present invention, since the solid electrolyte membrane material usually has a polar group such as sulfonic acid that has proton conductivity, the pore-forming polymer also has a polar group. It is preferable to utilize the affinity between polar groups. Therefore, it can be said that the pore-forming polymer used in the present invention preferably has a polar group.

Next, the second characteristic of the pore-forming polymer that can be used in the present invention is that it is insoluble in the first solvent and soluble in the second solvent.
First, the reason why it is insoluble in the first solvent is as follows. That is, in the present invention, the pore-forming polymer is dispersed in the coating solution preparation step together with the first solvent and other materials, specifically, the carbon particles supporting the platinum catalyst and the solid electrolyte membrane material. However, in this case, if it was dissolved in the first solvent, it was mixed with the solid electrolyte membrane material at the molecular level, and when the second solvent was brought into contact in the subsequent pore formation step. This is because elution becomes impossible and pores cannot be formed in the catalyst electrode layer. Therefore, in the present invention, the pore-forming polymer needs to be insoluble in the first solvent. In this case, although not particularly limited, the pore-forming polymer preferably has a solubility in the first solvent in the range of 50 to 100%, particularly in the range of 80 to 100%.
In the present invention, since the first solvent is preferably room temperature water as described later, the pore-forming polymer may have the above-described solubility in water at room temperature. It can be said that it is preferable.

On the other hand, in the pore formation step described later, it is necessary to remove the pore-forming polymer from the catalyst electrode layer by bringing the second solvent into contact therewith. Accordingly, it is required to be soluble in the second solvent. In this case as well, the solubility of the pore-forming polymer in the second solvent is preferably in the range of 50 to 100%, particularly preferably in the range of 80 to 100%.
In the present invention, since the second solvent is preferably boiled water as described later, the pore-forming polymer has the above-described solubility in boiled water. It can be said that it is preferable.

As the pore-forming polymer having these two characteristics, a water-soluble polymer is preferably used. By forming the pore-forming polymer as a water-soluble polymer in this way, water can be used as the second solvent at least in the pore formation step described later. This is because it does not adversely affect the catalyst and the catalyst.
Examples of such a water-soluble polymer include polyvinyl alcohol, polyurethane, acrylic acid polymer, polyethylene oxide, hydroxyethyl cellulose, polyacrylamide and the like. Among them, polyvinyl alcohol is preferable in the present invention. This is because polyvinyl alcohol (hereinafter sometimes referred to as PVA) is inexpensive, versatile, and easy to handle. Moreover, it is because the affinity with the perfluorosulfonic acid polymer used suitably as a solid electrolyte membrane material mentioned later is high.

In the present invention, as described later, it is preferable to use room temperature water as the first solvent and boiled water as the second solvent. It is preferably insoluble and soluble in boiling water. Such solubility in water can be adjusted by changing the molecular weight or using a copolymer with another monomer. In the present invention, although not particularly limited, it is preferable to adjust the solubility characteristics by adjusting the molecular weight. Specifically, the number average molecular weight is in the range of 500 to 20000, particularly 500 to 5000. PVA within the range is preferably used.
As the amount of such a pore-forming polymer added is too large, the porosity in the finally obtained catalyst electrode layer becomes too large, which may cause problems in electronic conductivity, which is not preferable. If the amount is too small, the effects of the present invention cannot be effectively achieved. Therefore, it is usually preferable to add in the range of 10 to 300 parts by weight, particularly 50 to 150 parts by weight with respect to 100 parts by weight of the solid electrolyte membrane material.

(Solid electrolyte membrane material)
The solid electrolyte membrane material used in the present invention is not particularly limited as long as it is a material having proton conductivity, and materials generally used as solid electrolyte membranes can be used. Specifically, a perfluorosulfonic acid polymer (trade name: Nafion, manufactured by DuPont Co., Ltd.) or the like is preferably used.

(First solvent)
The first solvent used in the present invention is not particularly limited as long as the pore-forming polymer can be appropriately dispersed in the catalyst electrode layer-forming coating solution as described above. .
As described above, the first solvent and the second solvent in the present invention are insoluble in the pore-forming polymer and the second solvent is soluble. Thus, the method for changing the solubility in the pore-forming polymer is not particularly limited, and the first solvent and the second solvent may be different from each other, or the mixed solvent may be used as a mixed solvent. The solubility may be changed by changing the ratio, or the solubility may be changed by changing the temperature using the same solvent.

In the present invention, as described above, a water-soluble polymer is preferably used as the pore-forming polymer. In this case, it is preferable to use relatively low temperature water as the first solvent. . This is because even a water-soluble polymer is insoluble in water at a low temperature, and it is preferable to use low-temperature water to obtain appropriate dispersibility. This is because the use of as a first solvent does not adversely affect other materials such as a catalyst and a solid electrolyte membrane material.
Here, the low temperature water is usually room temperature water, and specifically, water within a range of 10 ° C. to 50 ° C., particularly 15 ° C. to 40 ° C. is preferably used.

(Other)
A conductive component and a catalyst are added as other essential components to the coating solution for forming a catalyst electrode layer used in the present invention. Specifically, carbon particles on which a platinum catalyst is supported are added. Moreover, you may add other additives, such as viscosity modifiers, such as polyethyleneglycol, as needed.
The addition amount of the material other than the pore-forming polymer can be the same as that of the coating solution for forming a catalyst electrode layer usually used for forming a catalyst electrode layer.

(2) Adjustment method The coating solution for forming a catalyst electrode layer used in the present invention is obtained by stirring the above-described materials. Depending on the stirring conditions, pores in the catalyst electrode layer finally obtained are obtained. The power generation characteristics of the obtained membrane electrode composites are different. That is, it differs greatly depending on the affinity with the first solvent, the pore-forming polymer, and the solid electrolyte membrane material, but when the degree of stirring is low, the degree of dispersion of the pore-forming polymer is low. The diameter of the pores in the finally obtained catalyst electrode layer becomes large, the three-phase interface cannot be effectively increased for the porosity, and the power generation efficiency cannot be improved. There is a case. On the other hand, if stirring is performed excessively, the dispersion becomes too good, and there is a possibility that the pore-forming polymer cannot be completely removed in the pore formation step described later, resulting in improved power generation efficiency. I can't.
In the present invention, it is preferable that optimum stirring conditions are examined according to the formulation of each catalyst electrode layer forming coating solution, and the catalyst electrode layer forming coating solution is prepared according to the conditions.

2. Catalyst electrode layer forming step Next, the catalyst electrode layer forming step in the present invention will be described. The catalyst electrode layer forming step in the present invention is a step of forming a catalyst electrode layer on each surface of the solid electrolyte membrane using the catalyst electrode layer forming coating solution.
In the present invention, the method for forming the catalyst electrode layer on the solid electrolyte membrane is not particularly limited. For example, the catalyst electrode layer forming coating solution is formed on a polytetrafluoroethylene sheet. It may be a method in which the surface is smoothened by using a doctor blade method or the like, heated and dried, and thermally transferred onto a solid electrolyte membrane by a method such as hot pressing, and bonded. The catalyst electrode layer-forming coating solution may be directly applied onto the solid electrolyte membrane by a spray method, a printing method, or the like, and dried to form the solid electrolyte membrane.

3. Hole forming step Finally, the hole forming step in the present invention will be described. In the pore forming step in the present invention, the catalyst electrode layer formed in the catalyst electrode layer forming step and the second solvent are brought into contact with each other to remove the pore-forming polymer, and the pores are formed in the catalyst electrode layer. This is a step of forming holes.
As described above, the second solvent used in this step is a solvent capable of eluting the pore-forming polymer in the catalyst electrode layer when contacting with the catalyst electrode layer formed in this step as described above. If it is, it will not specifically limit.

Specifically, as described above, since a water-soluble polymer is suitably used as the pore-forming polymer, water is preferably used, and particularly high-temperature water is preferably used. This is because water will not adversely affect the catalyst, the solid electrolyte membrane, etc. even when it is brought into contact with the membrane electrode assembly. In addition, as described above, high-temperature water is used as the first solvent because low-temperature water is preferably used, and therefore, there is a need to provide a difference in solubility between the high-temperature water and the high-temperature water. It was.
The high-temperature water in the present invention is not particularly limited as long as it is higher than the water used in the first solvent, but is usually 30 ° C., preferably 50 ° C. than the water used in the first solvent. High temperature water is used. Specifically, it is in the range of 60 ° C. to 100 ° C., particularly in the range of 80 ° C. to 100 ° C., and particularly boiling water is preferably used.

In the present invention, when water is used as the first solvent and the second solvent, there is no particular limitation as long as water is the main component. Specifically, the content of water in the solvent is preferably 30% by mass or more, particularly preferably 50% by mass or more, and most preferably 100% by weight water.
In the present invention, the catalyst electrode layer and the second solvent are brought into contact with each other as long as the pore-forming polymer in the catalyst electrode layer is removed by the second solvent. It is not limited. Specific examples include a method of immersing the membrane electrode assembly on which the catalyst electrode layer is formed in a second solvent, a method of applying the second solvent on the catalyst electrode layer in a mist form, and the like.
The contact time between the second solvent and the catalyst electrode layer is the time until the pore-forming polymer in the catalyst electrode layer is removed. A method of determining the time is taken.

B. Next, a method for manufacturing a fuel cell according to the present invention will be described. The fuel cell manufacturing method of the present invention is characterized by using the membrane electrode composite obtained by the manufacturing method described in the above-mentioned section “A. Manufacturing method of membrane electrode composite”.

  Since the fuel cell manufacturing method of the present invention uses the membrane electrode composite obtained by the above-described manufacturing method of the membrane electrode composite as described above, the advantages of the method of manufacturing the membrane electrode composite, that is, It was possible to effectively increase the three-phase interface in the catalyst electrode layer in the obtained membrane electrode assembly, and at the same time, it was possible to effectively introduce gas and discharge water, and used as a fuel cell. Sometimes, the power generation efficiency can be greatly improved.

  The diffusion layer and the separator forming step in the method for manufacturing a fuel cell of the present invention can be performed by a method generally used for manufacturing a fuel cell, and thus description thereof is omitted here. As the diffusion layer and separator used in the present invention, those usually used in fuel cells can be used, and specifically, the diffusion layer formed by molding carbon fiber or the like is preferably used. The separator can be a carbon type, a metal type, or the like.

The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
For example, in the above description, the material for forming the pores has been described as the polymer for pore formation. However, in the present invention, the polymer is not necessarily a polymer, and the two characteristics of the polymer for pore formation described above are included. That is, even a low molecular weight material can be used as long as it has an affinity for the solid electrolyte membrane material, is insoluble in the first solvent, and is soluble in the second solvent. Can do.

Claims (3)

A method for producing a membrane electrode assembly for a fuel cell in which a catalyst electrode layer is formed on each surface of a solid electrolyte membrane,
A solid electrolyte membrane material, a first solvent for dispersing the solid electrolyte membrane material, an affinity for the solid electrolyte membrane material, insoluble in the first solvent, and in the second solvent A coating solution preparation step of preparing a coating solution for forming a catalyst electrode layer having at least a pore-forming polymer that is soluble;
Using the catalyst electrode layer forming coating solution, a catalyst electrode layer forming step of forming a catalyst electrode layer on each surface of the solid electrolyte membrane;
A pore forming step of contacting the catalyst electrode layer formed in the catalyst electrode layer forming step with the second solvent to remove the pore-forming polymer and forming pores in the catalyst electrode layer; A method for producing a membrane electrode assembly for a fuel cell, comprising: The pore-forming polymer is a water-soluble polymer, the first solvent is room temperature water, and the second solvent is boiling water. A method for producing a membrane electrode assembly for a fuel cell. A method for producing a fuel cell, comprising using the membrane electrode assembly for a fuel cell obtained by the method for producing a membrane electrode assembly for a fuel cell according to claim 1 or 2.