JP2012243656A - Method for producing membrane electrode assembly, and membrane electrode assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce interface resistance between an electrolyte membrane and a catalyst layer, in a membrane electrode assembly used for a solid polymer fuel cell.SOLUTION: Both surfaces of a porous film 12 are coated, respectively, with catalyst inks INKc, INKa, and the porous film 12 is impregnated with a part of ionomer contained in the catalyst inks INKc, INKa thereby an electrolyte membrane 10, a cathode side catalyst layer 20c, and an anode side catalyst layer 20a are simultaneously produced. The size of a catalyst-carrying carbon contained in the catalyst inks INKc, INKa is larger than a pore diameter of the porous film 12.

Description

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

  A fuel cell that generates electricity by an electrochemical reaction between a fuel gas and an oxidant gas 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. A membrane electrode assembly in which electrodes (catalyst layers) are formed on both surfaces of an electrolyte membrane is generally used for a polymer electrolyte fuel cell.

  A membrane electrode assembly is generally manufactured by applying a so-called catalyst ink on both surfaces of an electrolyte membrane. The catalyst ink includes a carrier carrying a catalyst (for example, carbon particles), an ionomer having proton conductivity, and a dispersion medium thereof.

  By the way, conventionally, various techniques for improving the mechanical strength of the membrane electrode assembly have been proposed. As such a technique, an electrolyte membrane is produced by impregnating an electrolyte (ionomer) into a porous body that is a skeleton of the electrolyte membrane, and a catalyst ink is applied to both surfaces of the electrolyte membrane, whereby a membrane electrode assembly is obtained. Is known (see, for example, Patent Document 1 below).

JP 2008-004425 A

  However, in the above-described technique, there is room for further improvement in the bondability between the electrolyte membrane and the catalyst layer and the interface resistance between the electrolyte membrane and the catalyst layer. In addition, the subject about the interface resistance between the electrolyte membrane and catalyst layer in this membrane electrode assembly is a subject common to the membrane electrode assembly manufactured by applying catalyst ink to the electrolyte membrane.

  The present invention has been made to solve the above-described problems, and aims to reduce the interfacial resistance between an electrolyte membrane and a catalyst layer in a membrane electrode assembly used in a polymer electrolyte fuel cell. And

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A method for producing a membrane electrode assembly used in a polymer electrolyte fuel cell,
Preparing a catalyst ink containing catalyst-supporting carbon, which is carbon particles supporting the catalyst, and an ionomer having proton conductivity;
Spreading the catalyst ink into a film;
Solidifying the catalyst ink in a state where the catalyst-supporting carbon is unevenly distributed on one surface of the spread catalyst ink;
The manufacturing method of a membrane electrode assembly provided with this.

  In the method for producing a membrane electrode assembly of Application Example 1, a portion solidified in a state where a large amount of catalyst-carrying carbon on one surface of the catalyst ink spread in a film shape is biased becomes a catalyst layer, and the other side of the catalyst ink The portion solidified with a small amount of catalyst-supporting carbon on the surface becomes an electrolyte membrane (electrolyte layer). For this reason, a clear interface is not formed between the electrolyte membrane and the catalyst layer. Therefore, the interface resistance between the electrolyte membrane and the catalyst layer can be reduced.

  In the method for manufacturing a membrane electrode assembly according to Application Example 1, as a method for unevenly distributing the catalyst-supporting carbon on one surface of the catalyst ink spread in a film shape, for example, the catalyst ink spread in a film shape includes For example, a method in which an external force such as gravity or centrifugal force is applied to the catalyst-supported carbon in a direction perpendicular to the surface of the catalyst ink.

  In Application Example 1 and other application examples described later, carbon particles having various shapes can be applied as the carbon particles constituting the catalyst-supporting carbon. Examples of the carbon particles include carbon black, carbon nanotube, carbon nanohorn, and carbon nanofiber.

[Application Example 2]
A method for producing a membrane electrode assembly used in a polymer electrolyte fuel cell,
Preparing a porous membrane;
Preparing a catalyst ink comprising a catalyst-carrying carbon, which is a carbon particle carrying a catalyst, the catalyst-carrying carbon having a size larger than the pore diameter of the porous membrane, and an ionomer having proton conductivity;
Applying the catalyst ink to the surface of the porous film, and impregnating the porous film with a part of the ionomer contained in the catalyst ink; and
The manufacturing method of a membrane electrode assembly provided with this.

  In the method for producing a membrane / electrode assembly of Application Example 2, since the size of the catalyst-supporting carbon contained in the catalyst ink is larger than the pore diameter of the porous membrane, in the catalyst ink coating process, part of the ionomer is porous. The pores of the porous membrane are impregnated, but the catalyst-supporting carbon and the remaining part of the ionomer remain on the surface of the porous membrane without being impregnated inside the pores of the porous membrane. Then, the porous membrane impregnated with the ionomer becomes an electrolyte membrane, and the catalyst-supporting carbon and the ionomer remaining on the surface of the porous membrane become the catalyst layer. For this reason, a clear interface is not formed between the electrolyte membrane and the catalyst layer. Therefore, the interface resistance between the electrolyte membrane and the catalyst layer can be reduced.

  The pore diameter of the porous film can be measured using, for example, a scanning electron microscope or a porosimeter. The size of the catalyst-supporting carbon can be measured using, for example, a particle size distribution measuring device. Here, the catalyst-supported carbon exists in an aggregated state in the catalyst ink, and in this specification, the size of the catalyst-supported carbon contained in the catalyst ink means the size of the catalyst-supported carbon aggregated in the catalyst ink. doing.

[Application Example 3]
A membrane electrode assembly used in a polymer electrolyte fuel cell,
An electrolyte membrane obtained by impregnating pores of a porous membrane with an ionomer having proton conductivity;
A catalyst layer formed on the surface of the electrolyte membrane;
With
The catalyst layer is a catalyst-supporting carbon that is a carbon particle supporting a catalyst, and has a catalyst-supporting carbon having a size larger than the pore diameter of the porous membrane.
Membrane electrode assembly.

  In the membrane / electrode assembly of Application Example 5, the catalyst-supporting carbon is not buried in the electrolyte membrane, and the catalyst layer is reliably held on the electrolyte membrane.

  The present invention can be configured as an invention of a membrane electrode assembly manufactured by the above-described manufacturing method, in addition to the configuration as a manufacturing method of the membrane electrode assembly described above. Further, a membrane electrode gas diffusion layer assembly including the membrane electrode assembly, a fuel cell including the membrane electrode assembly or the membrane electrode gas diffusion layer assembly, a fuel cell stack formed by stacking a plurality of the fuel cell It can also be configured as an invention of a moving body such as a fuel cell system including this fuel cell stack and a fuel cell vehicle including this fuel cell system.

It is explanatory drawing which shows the structure of the membrane electrode assembly 100 as 1st Example of this invention. It is explanatory drawing which shows the manufacturing process of the membrane electrode assembly 100 of 1st Example. It is explanatory drawing which shows the manufacturing process of the membrane electrode assembly 100 of 1st Example. It is explanatory drawing which shows the manufacturing process of the membrane electrode assembly 100R of a comparative example. It is explanatory drawing which shows the manufacturing process of 100 A of membrane electrode assemblies of 2nd Example.

Hereinafter, embodiments of the present invention will be described based on examples.
A. First embodiment:
A1. Configuration of membrane electrode assembly:
FIG. 1 is an explanatory view showing a configuration of a membrane electrode assembly 100 as a first embodiment of the present invention. This membrane electrode assembly 100 is used for a polymer electrolyte fuel cell as a power generator. As shown in the figure, the membrane electrode assembly 100 includes an electrolyte membrane 10, an anode side catalyst layer 20a formed on one surface of the electrolyte membrane 10, and a cathode side catalyst layer formed on the other surface of the electrolyte membrane 10. 20c.

A2. Manufacturing process of membrane electrode assembly:
2 and 3 are explanatory views showing a manufacturing process of the membrane electrode assembly 100 of the first embodiment.

  First, the porous membrane 12 that serves as the skeleton of the electrolyte membrane 10 is prepared (step S100). The porous membrane 12 functions as a reinforcing member for improving the mechanical strength of the electrolyte membrane 10 and the membrane electrode assembly 100. In this embodiment, the porous membrane 12 is made of PTFE (polytetrafluoroethylene) which is a fluororesin.

  The porous membrane 12 is produced, for example, by a PTFE fine powder (powder in which PTFE fine particles are aggregated) by paste extrusion and rolling, and a tape-like member is produced. It is produced by performing a stretching / firing process. In this example, the pore diameter of the porous membrane 12 was less than 0.1 (μm), and the porosity was about 60 (%). These values can be measured using, for example, a scanning electron microscope or a porosimeter. The pore diameter of the porous film 12 is designed to be smaller than the size of catalyst-carrying carbon contained in the catalyst ink described later. Moreover, the porosity of the porous membrane 12 is appropriately changed according to, for example, the mechanical strength required for the porous membrane 12.

  Next, two types of catalyst inks INKa and INKc are prepared (step S110). The catalyst ink INKa is used to form the anode side catalyst layer 20a on the surface of the electrolyte membrane 10. The catalyst ink INKc is used to form the cathode side catalyst layer 20 c on the surface of the electrolyte membrane 10.

  These catalyst inks INKa and INKc are produced by mixing and stirring a catalyst-supporting carbon, an ionomer having proton conductivity, and a dispersion medium (pure water and ethanol) with a homogenizer. . In this example, carbon black carrying platinum particles was used as the catalyst-carrying carbon. In these catalyst inks INKa and INKc, the catalyst-carrying carbon exists in an aggregated state. In this embodiment, the particle diameter of the agglomerated catalyst-carrying carbon in the catalyst ink (hereinafter simply referred to as “catalyst-carrying carbon”). The particle diameter ”is 0.1 to 0.3 (μm). That is, the size of the catalyst-supporting carbon is larger than the pore diameter of the porous membrane 12. The particle size of the catalyst-supporting carbon can be measured using, for example, a particle size distribution measuring device. In this example, a perfluorosulfonic acid resin that is a fluorine ionomer is used as the ionomer. In this example, in the catalyst ink INKa, the ratio I / C between the ionomer weight I and the carbon black weight C was 2-10. In the catalyst ink INKc, the ratio I / C between the weight I of the ionomer and the weight C of the carbon black was 1.5 to 5.

  Next, the catalyst ink INKc is applied to one surface of the porous film 12 (step S120). In this embodiment, as shown in FIG. 3A, the catalyst ink INKc is ejected from the slit of the die head, and the catalyst ink INKc is die-coated on one surface of the porous film 12. At this time, since the size of the catalyst-supporting carbon contained in the catalyst ink INKc is larger than the pore diameter of the porous film 12, some of the ionomer contained in the catalyst ink INKc is inside the pores of the porous film 12. Although impregnated, the catalyst-supporting carbon and the remaining part of the ionomer remain on the surface of the porous membrane 12 without being impregnated inside the pores of the porous membrane 12. When the catalyst ink INKc is dried, the porous membrane 12 impregnated with the ionomer becomes the electrolyte membrane 10, and the catalyst-supporting carbon and the ionomer remaining on the surface of the porous membrane 12 are exchanged with the cathode-side catalyst layer 20c. Become. Thus, a clear interface is not formed between the cathode side catalyst layer 20c formed by impregnating the porous membrane 12 with a part of the ionomer contained in the catalyst ink INKc and the electrolyte membrane 10.

  Next, the catalyst ink INKa is applied to the other surface of the porous film 12 (step S130). In this embodiment, as shown in FIG. 3B, the catalyst ink INKa is ejected from the slit of the die head, and the catalyst ink INKa is die-coated on the other surface of the porous film 12. At this time, since the size of the catalyst-supporting carbon contained in the catalyst ink INKa is larger than the pore diameter of the porous film 12, some of the ionomer contained in the catalyst ink INKa is inside the pores of the porous film 12. Although impregnated, the catalyst-supporting carbon and the remaining part of the ionomer remain on the surface of the porous membrane 12 without being impregnated inside the pores of the porous membrane 12. When the catalyst ink INKa is dried, the porous membrane 12 impregnated with the ionomer becomes the electrolyte membrane 10, and the catalyst-supporting carbon and the ionomer remaining on the surface of the porous membrane 12 are exchanged with the anode-side catalyst layer 20a. Become. Thus, a clear interface is not formed between the anode catalyst layer 20a formed by impregnating the porous membrane 12 with a part of the ionomer contained in the catalyst ink INKa and the electrolyte membrane 10.

  Through the above manufacturing steps, the membrane electrode assembly 100 is completed as shown in FIG.

A3. Advantages of the membrane electrode assembly of the example:
The effect of the membrane electrode assembly 100 manufactured through the manufacturing process of the first embodiment described above is the same as that of the fuel cell using the membrane electrode assembly 100R manufactured through the manufacturing process of the comparative example described later and the first embodiment. It confirmed by comparing the interface resistance between an electrolyte membrane and a catalyst layer about the fuel cell using the membrane electrode assembly 100 manufactured through the manufacturing process of an example.

  FIG. 4 is an explanatory view showing a manufacturing process of the membrane electrode assembly 100R of the comparative example. In the manufacturing process of the membrane electrode assembly 100R of the comparative example, as shown in FIG. 4A, first, the ionomer dispersion liquid DLio is discharged from the slit of the die head, and the die coating is performed on the surface of the porous film 12. . The ionomer dispersion liquid DLio contains the same ionomer as that contained in the catalyst inks INKa and INKc described above, and a dispersion medium. Then, the ionomer contained in the ionomer dispersion liquid DLio is impregnated inside the pores of the porous membrane 12 to produce the electrolyte membrane 10R.

  Next, as shown in FIG. 4B, the catalyst ink INKrc is ejected from the slit of the die head, the catalyst ink INKrc is die-coated on one surface of the electrolyte membrane 10R, and the cathode side catalyst layer 20Rc is formed. Form. A clear interface is formed between the cathode catalyst layer 20Rc thus formed and the electrolyte membrane 10R. The catalyst-carrying carbon contained in the catalyst ink INKrc is the same as the catalyst-carrying carbon contained in the catalyst ink INKc. The thickness of the cathode side catalyst layer 20Rc is the same as the thickness of the cathode side catalyst layer 20c. Further, the catalyst amount per unit volume in the cathode side catalyst layer 20Rc is the same as the catalyst amount per unit volume in the cathode side catalyst layer 20c.

  Next, as shown in FIG. 4C, the catalyst ink INKra is ejected from the slit of the die head, the catalyst ink INKra is die-coated on the other surface of the electrolyte membrane 10R, and the anode side catalyst layer 20Ra is formed. Form. A clear interface is formed between the anode-side catalyst layer 20Ra and the electrolyte membrane 10R thus formed. The catalyst-carrying carbon contained in the catalyst ink INKra is the same as the catalyst-carrying carbon contained in the catalyst ink INKa. The thickness of the anode side catalyst layer 20Ra is the same as the thickness of the anode side catalyst layer 20a. Further, the catalyst amount per unit volume in the anode side catalyst layer 20Ra is the same as the catalyst amount per unit volume in the anode side catalyst layer 20a.

  Gas diffusion is performed on both surfaces of the membrane electrode assembly 100R manufactured through the manufacturing process of the comparative example described above and the membrane electrode assembly 100 manufactured through the manufacturing process of the first embodiment described above. The layers were joined to produce a membrane electrode gas diffusion layer assembly, and fuel cells using these were produced. For each fuel cell, the interface resistance between the electrolyte membrane and the catalyst layer was measured. As a result, in the fuel cell using the membrane electrode assembly 100 manufactured through the manufacturing process of the first embodiment, the electrolyte membrane is more effective than the fuel cell using the membrane electrode assembly 100R manufactured through the manufacturing process of the comparative example. The interface resistance between the catalyst layer and the catalyst layer was 21 (%) low. This is clear in the membrane electrode assembly 100R manufactured through the manufacturing process of the comparative example, between the electrolyte membrane 10R and the cathode side catalyst layer 20Rc, and between the electrolyte membrane 10R and the anode side catalyst layer 20Ra. In contrast, in the membrane / electrode assembly 100 manufactured through the manufacturing process of the first embodiment, the interface between the electrolyte membrane 10 and the cathode side catalyst layer 20c and between the electrolyte membrane 10 and the anode side catalyst are formed. This is because a clear interface is not formed with the layer 20a.

  As described above, according to the method for manufacturing the membrane electrode assembly 100 of the first embodiment, the size of the catalyst-supporting carbon contained in the catalyst inks INKc and INKa is larger than the pore diameter of the porous membrane 12 respectively. Therefore, a part of the ionomer contained in the catalyst inks INKc and INKa is impregnated inside the pores of the porous film 12, but the catalyst-supporting carbon and the remaining part of the ionomer are part of the porous film 12. It remains on the surface of the porous membrane 12 without being impregnated inside the pores. The porous membrane 12 impregnated with the ionomer becomes the electrolyte membrane 10, and the catalyst-supporting carbon and the ionomer remaining on the surface of the porous membrane 12 become the cathode side catalyst layers 20c and 20a. For this reason, a clear interface is not formed between the electrolyte membrane 10 and the cathode side catalyst layer 20c and between the electrolyte membrane 10 and the anode side catalyst layer 20a. Therefore, in the membrane electrode assembly 100, the interface resistance between the electrolyte membrane 10 and the cathode side catalyst layer 20c and the interface resistance between the electrolyte membrane 10 and the anode side catalyst layer 20a can be reduced.

  In addition, according to the method of manufacturing the membrane electrode assembly 100 of the first embodiment, the electrolyte membrane 10, the cathode side catalyst layer 20 c, and the anode side catalyst layer 20 a can be produced at the same time. Further, the number of steps can be reduced and the manufacturing cost can be reduced as compared with the manufacturing method of the membrane electrode assembly 100R of the comparative example for producing the cathode side catalyst layer 20Rc and the anode side catalyst layer 20Ra.

B. Second embodiment:
FIG. 5 is an explanatory view showing a manufacturing process of the membrane electrode assembly 100A of the second embodiment. In the manufacturing process of the membrane electrode assembly 100A of the second embodiment, as shown in FIG. 5A, first, for example, the catalyst ink INK is spread in a film shape on a sheet made of PTFE. This catalyst ink INK also contains catalyst-supporting carbon, an ionomer, and a dispersion medium, like the catalyst inks INKa and INKc in the first embodiment. In FIG. 5A, the catalyst-supporting carbon contained in the catalyst ink INK is indicated by dots. However, the catalyst ink INK in this embodiment is prepared so that the catalyst-supported carbon precipitates and the layers are more easily separated than the catalyst inks INKa and INKc.

  Next, the catalyst ink INK is solidified in a state where the catalyst-carrying carbon contained in the catalyst ink INK is precipitated by gravity on one surface of the catalyst ink INK spread in a film shape and is unevenly distributed. At this time, as shown in black in FIG. 5 (b), the portion solidified in a state where the catalyst-carrying carbon on one side of the catalyst ink INK is unevenly present becomes the catalyst layer 20A, and the other side of the catalyst ink INK The portion of the surface solidified with a small amount of catalyst-supporting carbon becomes the electrolyte layer 10L. In this embodiment, two sheets of this sheet-like member are produced.

  Then, as shown in FIG. 5C, the sheet-like member is overlapped and joined so that the electrolyte layer 10L and the electrolyte layer 10L face each other. By joining the electrolyte layer 10L and the electrolyte layer 10L, an electrolyte membrane 10A is obtained. In this embodiment, the same ionomer as the ionomer contained in the catalyst ink INK and an ionomer dispersion containing a dispersion medium are used as an adhesive for joining the electrolyte layer 10L and the electrolyte layer 10L.

  Through the above steps, as shown in FIG. 5D, the membrane electrode assembly 100A including the catalyst layers 20A on both surfaces of the electrolyte membrane 10A is completed.

  Even in the manufacturing process of the membrane electrode assembly 100A of the second embodiment described above, a clear interface is not formed between the electrolyte membrane 10A and the catalyst layer 20A. Accordingly, the interface resistance between the electrolyte membrane 10A and the catalyst layer 20A can be reduced in the membrane / electrode assembly 100A in the same manner as the membrane / electrode assembly 100 manufactured by the manufacturing process of the first embodiment.

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 various aspects 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 ionomers contained in the catalyst inks INKc and INKa are each a perfluorosulfonic acid resin. However, the present invention is not limited to this. As said ionomer, it is good also as what uses other fluorine-type ionomers other than perfluorosulfonic acid resin. Moreover, as said ionomer, it is good also as what uses other ionomers other than fluorine-type ionomers, such as a hydrocarbon-type ionomer, for example. Further, the ionomer contained in the catalyst ink INKc and the ionomer contained in the catalyst ink INKa may be the same or different.

C2. Modification 2:
In the first embodiment, the porous membrane 12 is made of PTFE, but the present invention is not limited to this. The porous membrane 12 may be made of a fluororesin other than PTFE. The porous film 12 may be made of a material other than a fluororesin such as a hydrocarbon resin.

C3. Modification 3:
In the first embodiment, in the catalyst ink INKc, the ratio I / C between the ionomer weight I and the carbon black weight C is 1.5 to 5, and in the catalyst ink INKa, the ionomer weight I is The ratio I / C with respect to the weight C of the carbon black is 2 to 10, but the present invention is not limited to this. In the catalyst inks INKc and INKa, the ratio I / C between the ionomer weight I and the carbon black weight C can be changed as appropriate.

C4. Modification 4:
In the first embodiment, the anode side catalyst layer 20a is formed after the cathode side catalyst layer 20c is formed. However, the present invention is not limited to this. The cathode side catalyst layer 20c may be formed after the anode side catalyst layer 20a is formed.

C5. Modification 5:
In the first embodiment, the catalyst inks INKc and INKa are applied to the surface of the porous film 12 by die coating. However, the present invention is not limited to this. Instead of die coating, other coating methods such as applicator coating may be applied.

C6. Modification 6:
In the above embodiment, carbon black is used as the carbon particles constituting the catalyst-supporting carbon contained in the catalyst ink. However, the present invention is not limited to this. As the carbon particles constituting the catalyst-supporting carbon, for example, carbon particles having other shapes such as carbon nanotubes, carbon nanohorns, and carbon nanofibers may be used.

DESCRIPTION OF SYMBOLS 100,100R, 100A ... Membrane electrode assembly 10, 10R, 10A ... Electrolyte membrane 10L ... Electrolyte layer 12 ... Porous membrane 20a, 20Ra ... Anode side catalyst layer 20c, 20Rc ... Cathode side catalyst layer 20A ... Catalyst layer INKc, INKa , INKrc, INKra, INK ... catalyst ink DLio ... ionomer dispersion

Claims (3)

A method for producing a membrane electrode assembly used in a polymer electrolyte fuel cell,
Preparing a catalyst ink containing catalyst-supporting carbon, which is carbon particles supporting the catalyst, and an ionomer having proton conductivity;
Spreading the catalyst ink into a film;
Solidifying the catalyst ink in a state where the catalyst-supporting carbon is unevenly distributed on one surface of the spread catalyst ink;
The manufacturing method of a membrane electrode assembly provided with this. A method for producing a membrane electrode assembly used in a polymer electrolyte fuel cell,
Preparing a porous membrane;
Preparing a catalyst ink comprising a catalyst-carrying carbon, which is a carbon particle carrying a catalyst, the catalyst-carrying carbon having a size larger than the pore diameter of the porous membrane, and an ionomer having proton conductivity;
Applying the catalyst ink to the surface of the porous film, and impregnating the porous film with a part of the ionomer contained in the catalyst ink; and
The manufacturing method of a membrane electrode assembly provided with this. A membrane electrode assembly used in a polymer electrolyte fuel cell,
An electrolyte membrane obtained by impregnating pores of a porous membrane with an ionomer having proton conductivity;
A catalyst layer formed on the surface of the electrolyte membrane;
With
The catalyst layer is a catalyst-supporting carbon that is a carbon particle supporting a catalyst, and has a catalyst-supporting carbon having a size larger than the pore diameter of the porous membrane.
Membrane electrode assembly.

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