JP2012048836A - Method of manufacturing membrane electrode assembly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve power generation performance by improving the bondability of an interface between an electrolyte film and a catalyst layer formed by vapor deposition.SOLUTION: The method of manufacturing the membrane electrode assembly includes the processes of: i) manufacturing a catalyst layer formation body having the catalyst layer formed by vapor-depositing a catalyst on a surface of a porous film; and (ii) bonding the electrolyte film and the catalyst layer of the catalyst layer formation body together.

Description

  The present invention relates to a membrane electrode assembly used in a solid polymer electrolyte fuel cell, and more particularly to a method for producing a membrane electrode assembly having a catalyst layer formed by depositing a catalyst.

A fuel cell is a device that generates electricity by an electrochemical reaction between hydrogen as a fuel gas and oxygen as an oxidizing gas. Hereinafter, the fuel gas and the oxidizing gas may be simply referred to as “reaction gas” or “gas” without particular distinction. A fuel cell is usually configured by stacking a plurality of fuel cells via a separator. One fuel cell includes a catalyst electrode layer (hereinafter also simply referred to as “catalyst layer”) on both sides of a solid polymer electrolyte membrane having proton (H ⁺ ) conductivity (hereinafter also simply referred to as “electrolyte membrane”) and In many cases, a gas diffusion layer (GDL: Gas Diffusion Layer) is used in the structure. This structure is called a membrane electrode assembly (MEA) or a membrane electrode gas diffusion layer assembly (MEGA).

  In order to reduce the cost of fuel cells, there is a demand for a reduction in the catalyst used for the production of MEA, for example, platinum. As a manufacturing method therefor, a method is known in which a catalyst layer is formed by vapor-depositing a catalyst on a gas diffusion layer, and the catalyst layer of the gas diffusion layer is bonded to an electrolyte membrane.

  However, the MEA produced by the above method has a problem in that the bonding property at the interface between the electrolyte membrane and the deposited catalyst layer is poor, and the power generation performance of the fuel cell using this is low.

JP 2007-056064 A Japanese Patent Application Laid-Open No. 08-213027

  Therefore, an object of the present invention is to provide a technique capable of improving the bondability at the interface between the electrolyte membrane and the deposited catalyst layer and improving the power generation performance.

  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,
i) producing a catalyst layer forming body in which a catalyst layer is formed by depositing a catalyst on the surface of the porous film;
ii) joining the electrolyte membrane and the catalyst layer of the catalyst layer forming body;
A method for producing a membrane electrode assembly, comprising:
According to the production method of Application Example 1, the catalyst layer formed body in which the catalyst layer is vapor-deposited on the surface of the porous film is more flexible than the conventional case where the catalyst layer is vapor-deposited on the surface of the gas diffusion layer. have. For this reason, when the catalyst layer and the electrolyte membrane of the catalyst layer forming body are joined, it is possible to improve the bondability at the interface between the catalyst layer and the electrolyte membrane, and the fuel using the produced membrane electrode assembly It is possible to improve the power generation performance of the battery cell.

  The present invention can be realized in various forms. For example, not only a method for producing a membrane electrode assembly, but also a membrane electrode assembly produced by this production method, and this membrane electrode assembly are used. The present invention can be realized in various forms such as a conventional fuel cell and a fuel cell system using the fuel cell.

It is explanatory drawing which shows the preparation methods of the membrane electrode assembly as an Example. It is explanatory drawing which shows the preparation methods of the membrane electrode assembly as a comparative example. It is a table | surface which compares and shows the electric power generation performance of the fuel cell using the membrane electrode assembly obtained by the preparation method of an Example and a comparative example.

Embodiments of the present invention will be described in the following order based on examples.
A. Example:
B. Variations:

A. Example:
(1) Example of Manufacturing Method of Membrane / Electrode Assembly FIG. 1 is an explanatory view showing a manufacturing method of a membrane / electrode assembly as an example. The manufacturing method of the membrane electrode assembly of this embodiment consists of three processes described below.

[Step 1]
In step 1, a flexible conductive porous film is used as the deposition target 20s, and platinum (Pt) is deposited as a catalyst on one surface of the deposition target 20s, thereby forming a surface of the deposition target 20s. A catalyst layer forming body 20cts in which a catalyst layer (hereinafter also referred to as “deposition catalyst layer”) 20ct is formed is produced. As a vapor deposition method, a sputtering method, a chemical vapor deposition method, or the like may be used.

  As the conductive porous film, a flexible film made of a conductor such as carbon and a binder resin such as PTFE (polytetrafluoroethylene) or polyimide is used. The flexibility can be defined by Young's modulus, and can be defined, for example, under the condition of 1 MPa or more and 0.1 GPa or less. In general, a material having a Young's modulus of 1 GPa or more is considered to be poor in flexibility. When the gas diffusion layer (GDL) is a vapor-deposited body as in a comparative example described later, the carbon fiber aggregate generally used is used. Since the Young's modulus is about 10 GPa to 50 GPa, it can be said that there is no flexibility.

  As a catalyst for vapor deposition, platinum alloy containing other transition metals (Co, Ni, Fe, etc.) can be used in addition to platinum.

[Step 2]
In step 2, the deposited catalyst layer 20ct of the catalyst layer forming body 20cts produced in step 1 is joined to one surface of the electrolyte membrane 10 to produce a membrane / deposited catalyst layer assembly 10cts. The joining conditions are appropriately selected according to the physical properties of the electrolyte membrane 10 and the catalyst layer forming body 20cts, respectively, within a temperature range of 80 ° C. to 200 ° C. and a pressure of 0.1 MPa to 10 MPa.

[Step 3]
In step 3, the gas diffusion layer 50, the catalyst layer 30ct, the vapor deposition catalyst layer assembly 10cts, and the GDL base material layer 40b are laminated in this order, and are joined together to produce a membrane electrode assembly (MEA). As for the bonding conditions, as in step 2, the temperature and pressure are appropriately selected according to the physical properties of the gas diffusion layer 50, the catalyst layer 30ct, the vapor deposition catalyst layer assembly 10cts, and the GDL base material layer 40b. .

  The gas diffusion layer 50 has a joined body structure in which a conductive GDL base material layer 50b and a porous layer 50s are joined, and the catalyst layer 30ct is laminated and joined on the porous layer 50s. As the GDL base material layer 50b, carbon paper, carbon cloth, or the like is used. As the porous layer 50s, for example, a conductive porous film is used in the same manner as the deposition target 20s.

  The catalyst layer 30ct is a conventional catalyst layer produced without vapor deposition. For example, the catalyst layer 30ct can be produced by applying a catalyst ink on a catalyst layer forming sheet and drying it. As the catalyst ink, for example, a mixture of an electrolyte solution and a carbon (for example, carbon black) carrier carrying platinum (Pt) as a catalyst can be used. As the electrolyte solution, for example, a fluorine resin material made of a perfluorocarbon polymer having a sulfonic acid group (for example, Nafion, manufactured by DuPont) dissolved in water and alcohols as a solvent may be used. it can.

  The deposited catalyst layer assembly 10cts is laminated and joined on the catalyst layer 30ct in a direction in which the electrolyte membrane 10 is in contact.

  Similar to the GDL base layer 50b of the gas diffusion layer 50, the GDL base layer 40b is made of carbon paper or carbon cloth as the GDL base layer 50b.

  The GDL base material layer 40b and the deposition target 20s using the porous film constitute the gas diffusion layer 40 on the anode side, and the gas diffusion layer 40 and the deposition catalyst layer 20ct include the gas diffusion electrode 20 on the anode side. Configure. The gas diffusion layer 50 and the catalyst layer 30ct constitute a cathode-side gas diffusion electrode.

  In the membrane / electrode assembly produced as described above, the pores of the porous film are not impregnated with catalyst particles, electrolyte, conductive material, etc., but on the surface of a flexible porous film (deposited body). Since the vapor deposition catalyst layer is formed, the catalyst layer forming body on which the vapor deposition catalyst layer is formed also has a flexible structure. Therefore, at the time of joining the electrolyte membrane and the catalyst layer forming body, it is considered that the joining property at the interface between the electrolyte membrane and the deposited catalyst layer is high and the power generation performance is good.

(2) Comparative Example of Manufacturing Method of Membrane / Electrode Assembly FIG. 2 is an explanatory view showing a manufacturing method of a membrane / electrode assembly as a comparative example. The manufacturing method of the membrane electrode assembly of the comparative example includes two steps described below.

[Step 1]
In step 1, as in the gas diffusion layer 50 of the example, the gas diffusion layer 40B having a joined structure in which the conductive GDL base material layer 40b and the porous layer 40s are joined is used as a deposition target, and the porous layer By depositing platinum (Pt) as a catalyst on the surface on the 40s side, a catalyst layer forming body 40ct in which a catalyst layer (deposition catalyst layer) 20ct is formed on the surface of the gas diffusion layer 40B is produced. Hereinafter, the gas diffusion layer 40B may be referred to as “deposition target body 40B”. Note that the Young's modulus of the gas diffusion layer 40B is about 10 GPa to 50 GPa and is not flexible.

[Step 2]
In step 2, the gas diffusion layer 50, the catalyst layer 30ct, the electrolyte membrane 10, and the catalyst layer forming body 40ct are laminated in this order, and are joined together to produce a membrane electrode assembly (MEA). As for the joining conditions, similarly to the embodiment, the temperature and pressure are appropriately selected according to the physical properties of the gas diffusion layer 50, the catalyst layer 30ct, the electrolyte membrane 10, and the catalyst layer forming body 40ct. The catalyst layer 30ct is laminated and joined on the porous layer 50s of the gas diffusion layer 50, and the catalyst layer forming body 40ct is laminated and joined on the electrolyte membrane 10 in the direction in which the deposited catalyst layer 20ct is in contact. .

  The gas diffusion layer 40B and the vapor deposition catalyst layer 20ct constitute an anode side gas diffusion electrode 20B, and the gas diffusion layer 50 and the catalyst layer 30ct constitute a cathode side gas diffusion electrode.

  In the membrane / electrode assembly produced as described above, the deposited catalyst layer is formed on the surface of the gas diffusion layer as the deposition target, and the catalyst layer formed body on which the deposited catalyst layer is formed is poor in flexibility. . For this reason, it is considered that a gap is generated at the time of joining the electrolyte membrane and the catalyst layer forming body, and the joining property at the interface between the electrolyte membrane and the deposited catalyst layer is poor.

(3) Performance of Membrane / Electrode Assembly of Example FIG. 3 is a table showing comparison of power generation performance of fuel cells using membrane / electrode assemblies obtained by the production methods of Examples and Comparative Examples. The voltage [V] at a load of 0.5 [A / cm ² ] and a load of 1.5 [A / cm ² ] was measured at 80 ° C. and 100% RH. As shown in FIG. 3, it can be seen that the membrane electrode assembly of the example has better power generation performance than the membrane electrode assembly of the comparative example.

  As can be seen from the above results, the membrane / electrode assembly produced according to the example can improve the bondability at the interface between the electrolyte membrane and the vapor deposition catalyst layer, and can improve the power generation performance.

B. Variations:
In addition, elements other than the elements claimed in the independent claims among the constituent elements in the above embodiment are additional elements and can be omitted as appropriate. The present invention is not limited to the above-described examples and embodiments, and can be implemented in various modes without departing from the scope of the invention.

  In the above embodiment, the catalyst used for the vapor deposition catalyst layer on the anode side has been described as being platinum or a platinum alloy, but any catalyst having hydrogen oxidizing power may be used.

  In the above embodiment, the case where a gas diffusion layer (GDL) having a structure of a porous layer and a GDL base material layer is used has been shown. There may be.

In the said Example, although the Young's modulus is prescribed | regulated as a flexible porous film as 1 Mpa or more and 0.1 GPa or less, it is not limited to this and any one of the following should just be materialized.
1) 1 MPa or more and 0.1 GPa or less 2) Young's modulus of gas diffusion layer, preferably 1/10 of Young's modulus of vapor-deposited body
3) Range of 1/10 to 10 times the Young's modulus of the electrolyte membrane

  In the above embodiment, a structure in which a catalyst layer on the anode side is formed by bonding a catalyst layer forming body, in which a catalyst layer is formed by vapor-depositing a catalyst on a porous film, to the electrolyte membrane only on the anode side. However, the catalyst layer on the cathode side may have the same structure. However, if at least the catalyst layer on the anode side has the structure of the embodiment, it is possible to exhibit the same or better performance as before while reducing the amount of the catalyst used for forming the catalyst layer on the anode side.

DESCRIPTION OF SYMBOLS 10 ... Electrolyte membrane 10cts ... Deposition catalyst layer assembly 20cts ... Catalyst layer formation body 20 ... Gas diffusion electrode 20B ... Gas diffusion electrode 20s ... Deposited body (porous film)
20 ct ... deposition catalyst layer 30 ct ... catalyst layer 40 ... gas diffusion layer 40B ... gas diffusion layer (deposition body)
40 s ... porous layer 40 b ... GDL substrate layer 40 ct ... catalyst layer forming body 50 ... gas diffusion layer 50 s ... porous layer 50 b ... GDL substrate layer

Claims (1)

A method for producing a membrane electrode assembly,
i) producing a catalyst layer forming body in which a catalyst layer is formed by depositing a catalyst on the surface of the porous film;
ii) joining the electrolyte membrane and the catalyst layer of the catalyst layer forming body;
A method for producing a membrane electrode assembly, comprising:

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