JP2006107804A - Manufacturing method of membrane-electrode junction for polymer electrolyte fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane-electrode junction for a polymer electrolyte fuel cell restraining dimensional change accompanying temperature change in a plane direction of a polymer electrolyte film, and restraining damage or exfoliation of an electrode layer arranged on such a polymer electrolyte film, when the junction is used for a polymer electrolyte fuel cell. <P>SOLUTION: Following processes are carried out: (A) expanding the polymer electrolyte film within the range satisfying a relation expressed in formula (1), S<SB>w</SB>≤S<SB>x</SB>; (B) pinching the polymer electrolyte film with a pair of support bodies; (C) retaining the polymer electrolyte film in an expanded state; (D) jointing the polymer electrolyte film with the support bodies; and (E) jointing the electrode layer to the polymer electrolyte film exposed to openings of the support bodies. The membrane-electrode junction for the polymer electrolyte fuel cell is thereby obtained. S<SB>x</SB>in the formula denotes an area of the polymer electrolyte film at manufacturing, and S<SB>w</SB>an area at moisture expansion. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell (PEFC), and more specifically, in the film thickness direction of a polymer electrolyte membrane accompanying a change in humidity when PEFC is used. A membrane / electrode assembly for PEFC that suppresses a change in dimensions in a direction perpendicular to the plane (hereinafter abbreviated as a plane direction) and can suppress breakage and peeling of the electrode layer disposed on the polymer electrolyte membrane. It relates to a manufacturing method.

When manufacturing membrane / electrode assemblies for PEFC, it is known that wrinkles occur at the outer periphery of the membrane (the part that contacts the separator). To suppress this, a sheet is adhered to the outer periphery. Have been proposed (see, for example, Patent Document 1).
JP-A-11-45729

  However, since the polymer electrolyte membrane repeats dimensional changes in the planar direction (swelling / shrinking of the membrane) with changes in humidity conditions, the electrode layer joined to the portion of the polymer electrolyte membrane where the sheet is not bonded Has a problem that it cannot follow the dimensional change of the film and breakage or peeling occurs.

  The present invention has been made in view of such problems of the prior art, and the object of the present invention is to change the dimensional change in the planar direction of the polymer electrolyte membrane accompanying a change in humidity when used in PEFC. An object of the present invention is to provide a membrane / electrode assembly for PEFC that can suppress and prevent the electrode layer disposed on the polymer electrolyte membrane from being damaged or peeled off.

  As a result of intensive studies to achieve the above object, the present inventor has found that the above object can be achieved by, for example, expanding and supporting the polymer electrolyte membrane in advance at the time of production, and has completed the present invention. It was.

That is, in the PEFC membrane / electrode assembly production method of the present invention, the polymer electrolyte membrane is sandwiched between a pair of supports having an opening at the center, and the polymer exposed at the opening of the support. A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell comprising an electrode layer bonded to an electrolyte membrane, comprising the following steps (A) to (E).
(A): The polymer electrolyte membrane is expressed by the following formula (1)
S _w ≦ S _x (1)
(S _x is the area at the time of production of the polymer electrolyte membrane wherein, S _w represents the area at the time of moisture expansion.) A step of expanding a range which satisfies the relationship represented by (B): the polymer electrolyte Step (C) for sandwiching the membrane between the pair of supports: Step (D) for holding the polymer electrolyte membrane in an enlarged state: Step (E) for joining the polymer electrolyte membrane and the support (E): The step of bonding the electrode layer to the polymer electrolyte membrane exposed at the opening of the support

  According to the present invention, since the polymer electrolyte membrane is expanded and supported in advance at the time of production, when used in PEFC, the dimensional change in the planar direction of the polymer electrolyte membrane accompanying a change in humidity is suppressed. It is possible to provide a membrane / electrode assembly for PEFC capable of suppressing breakage and peeling of an electrode layer disposed on a polymer electrolyte membrane.

Hereinafter, a method for producing a membrane / electrode assembly (hereinafter abbreviated as a membrane / electrode assembly) for a polymer electrolyte fuel cell (PEFC) of the present invention will be described.
As described above, in the method for producing a membrane / electrode assembly of the present invention, the polymer electrolyte membrane is sandwiched between a pair of supports having an opening at the center and the polymer exposed at the opening of the support. A method for producing a membrane / electrode assembly formed by joining an electrode layer to an electrolyte membrane, wherein the polymer electrolyte membrane is represented by the following formula (1):
S _w ≦ S _x (1)
(S _x is the area at the time of production of the polymer electrolyte membrane wherein, S _w is. Showing the area at the time of moisture expansion) to expand in a range satisfying the relationship represented by (A) step, the polymer electrolyte (B) step of sandwiching the membrane between the pair of supports, (C) step of holding the polymer electrolyte membrane in an expanded state, (D) step of joining the polymer electrolyte membrane and the support, (E) joining the said electrode layer to the said polymer electrolyte membrane exposed to the opening part of a support body.

Here, although slightly different by a polymer electrolyte membrane to be used, the area _{S w} at water expansion, the polymer electrolyte membrane Temperature: 23-85 ° C., at the bottom 10 minutes to 24 hours relative humidity 60-98% conditions It is the area measured after
The polymer electrolyte membrane is not particularly limited as long as it can be applied to PEFC, and conventionally known Nafion, sulfonated polyarylene electrolyte membrane, sulfonated polyimide electrolyte membrane and the like can be mentioned.

In this way, by expanding and holding the polymer electrolyte membrane at the time of production in advance, the portion inside the outer peripheral edge supported by the support in the polymer electrolyte membrane is not only dried but also water-containing Also, the tension is applied in advance in the plane direction.
Therefore, even if the polymer electrolyte swells due to a change in humidity, it is absorbed by the relaxation of the tension, and the dimensional change in the plane direction of the membrane can be suppressed.
Thereby, even when the PEFC is repeatedly operated and stopped, and the polymer electrolyte membrane is repeatedly swelled and contracted, the peeling of the electrode layer from the polymer electrolyte membrane and the damage of the electrode layer itself, that is, the deterioration of the PEFC are suppressed. be able to.
In addition, if the effect of the present invention is exerted, the use conditions of the obtained membrane-electrode assembly are not particularly limited. For example, the membrane-electrode assembly is manufactured at a relative humidity higher than the relative humidity at the time of use of the membrane-electrode assembly. It is preferable.

Further, the support to be used is not particularly limited as long as the generation of wrinkles at the outer edge portion of the membrane / electrode assembly held by the support is suppressed, but it is desirable to perform heat welding. Thereby, the possibility that the polymer electrolyte membrane is contaminated by the solvent is remarkably reduced, and the polymer electrolyte membrane and the support can be bonded by a simple method (so-called hot pressing) such as heating or pressurization.
Furthermore, it is desirable that the support to be used is in the form of a sheet in consideration of the volume and gas sealability when the shape of the support is stacked, and the swelling rate of the support when it contains water exhibits more functions as a support. In particular, it is preferably smaller than the polymer electrolyte membrane, and is preferably larger than the polymer electrolyte membrane in terms of elastic modulus.
For example, a sheet of engineering plastic (such as polyimide or fluorocarbon resin) can be specifically mentioned.
Specific examples of the adhesive that imparts heat weldability to the support include sheets of thermoplastic resins (polyester, polyurethane, polyolefin, etc.).
Furthermore, the electrode layer to be used is not particularly limited, and a conventionally known electrode layer can be applied, but the electrode layer preferably includes a gas diffusion layer.

  In addition, in the step (A) in the method for producing a membrane / electrode assembly of the present invention, when the polymer electrolyte membrane itself is not damaged when the polymer electrolyte membrane is enlarged, the enlargement method is not particularly limited. However, it can be enlarged by, for example, placing the polymer electrolyte membrane to be used in a humidified atmosphere and causing it to swell. In this case, it is preferable from the viewpoint that an appropriate tension reflecting a dimensional change in a humidity condition when actually using PEFC can be given in advance to the polymer electrolyte membrane. Further, it can be expanded by applying an external force (for example, pressure or tension) to the polymer electrolyte membrane to be used. In this case, the polymer electrolyte membrane can be provided in advance with a tension that simulates a dimensional change in humidity conditions when PEFC is used, for example, without requiring a large-scale device that maintains manufacturing environment conditions such as humidity. It is preferable from the viewpoint. In addition, you may combine both expansion methods suitably. In addition, when expanding by applying tension, the direction is not particularly limited as long as the direction can be expanded. For example, when the polymer electrolyte membrane is square, tension may be applied as shown in FIG. Tension may be applied from all sides.

Further, in the step (D) in the method for producing a membrane / electrode assembly of the present invention, in joining the polymer electrolyte membrane and the support, the relative positions of both in the plane direction are not changed, that is, the membrane / electrode junction. It is desirable to join while maintaining the center alignment as a body. Thereby, a membrane electrode assembly can fully exhibit performance.
In addition, when it is swollen and expanded in a humidified atmosphere, it is easy to maintain center alignment by performing the bonding process in the same humidified atmosphere, but the conditions of the bonding process are limited to this. It is not something.

  Further, in the step (D) in the method for producing a membrane / electrode assembly of the present invention, it is desirable to join the polymer electrolyte membrane and the support by applying one or both of heat and pressure to both. . When the support is heat-weldable, it is particularly desirable for the reasons described above.

Furthermore, in the step (E) in the method for producing a membrane / electrode assembly of the present invention, it is desirable to join the polymer electrolyte membrane and the electrode layer by applying one or both of heat and pressure to both. . By adopting such a joining method, it becomes possible to simultaneously perform the step (D) and the step (E), and the number of steps in the manufacturing method can be reduced, which is preferable.
As described above, the order of the steps in the method for producing a membrane / electrode assembly of the present invention is not limited, for example, before and after the steps (A) and (B). The order of the respective steps can be appropriately changed within a range not impairing the effect obtained by the method.

  Hereinafter, although the manufacturing method of the membrane electrode assembly of this invention is demonstrated in detail by an Example and a comparative example, this invention is not limited to these Examples.

Example 1
First, as a catalyst solution (slurry) for forming a catalyst layer on an electrode layer, carbon black powder (Vulcan XC72) supporting platinum (Pt) fine particles as a catalyst metal and a polymer electrolyte membrane resin solution (Nafion (registered trademark)) ) And an alcohol solution as a solvent and water, the amount of Pt used is 0.3 mg / cm ² , and the mass ratio of the catalyst-supported carbon black powder after drying and the polymer resin is 1: 1. A slurry was prepared.
A catalyst layer was deposited and formed on carbon paper (gas diffusion layer) using this slurry to obtain an electrode layer.

Next, a support sheet (polyimide (Kapton manufactured by Toray DuPont)) was bonded to both surfaces of the polymer electrolyte membrane (Nafion 112) using an adhesive sheet (polyester (3M Thermobond)). Hereinafter, the support sheet and the adhesive are collectively referred to as a heat-weldable sheet.
Here, FIG. 1 (1) and (2) are the top views and sectional drawings in AA which show the outline | summary of the joining method of the polymer electrolyte membrane in this example, and a heat welding sheet | seat.
Describing in detail with reference to the drawings, the polymer electrolyte membrane 2 and a heat-weldable sheet 4 as an example of a support that supports the polymer electrolyte membrane 2 are placed in a humidity control tank (tank) of a humidity controller (not shown). (Internal conditions: temperature 40 ° C., relative humidity 90%) and left to swell for 10 minutes.
Next, the upper and lower surfaces of the polymer electrolyte membrane 2 were sandwiched between the heat-weldable sheets 4 and placed on a press machine placed in a tank. The polymer electrolyte membrane 2 and the heat-weldable sheet 4 were brought into close contact with each other by applying a pressure of 1 MPa in the vertical direction, and the polymer electrolyte membrane 2 and the heat-weldable sheet 4 were joined by heating at 150 ° C. for 5 minutes.

  Thereafter, the electrode layer is placed on the polymer electrolyte membrane exposed from the opening of the heat-weldable sheet, and a pressure of 1 MPa is applied and heated at 150 ° C. for 5 minutes to join the polymer electrolyte membrane and the electrode layer. As a result, a membrane / electrode assembly was obtained.

(Example 2)
When joining the heat-weldable sheet to the upper and lower surfaces of the polymer electrolyte membrane, the same operation as in Example 1 was repeated except that the joining was performed by the joining method described below without using a humidity controller. An electrode assembly was obtained.
Here, FIGS. 2 (1) and (2) are a plan view and a cross-sectional view taken along line BB showing an outline of a method for joining the polymer electrolyte membrane and the heat-weldable sheet in this example.
Describing in detail based on the drawings, both ends of the polymer electrolyte membrane 2 were supported by blocks, and expanded by applying a tension of 2 MPa in the direction of the arrow.
Next, the upper and lower surfaces of the polymer electrolyte membrane 2 were sandwiched between the heat-weldable sheets 4 and placed on a press machine. The polymer electrolyte membrane 2 and the heat-weldable sheet 4 were brought into close contact with each other by applying a pressure of 1 MPa in the vertical direction, and the polymer electrolyte membrane 2 and the heat-weldable sheet 4 were joined by heating at 150 ° C. for 5 minutes.

(Example 3)
In Example 1, the step of bonding the heat-weldable sheet to both surfaces of the polymer electrolyte membrane and the step of bonding the polymer electrolyte membrane and the electrode layer are performed at the same time.
Here, FIGS. 3A and 3B are a plan view and a cross-sectional view taken along the line C-C showing an outline of a method for joining the polymer electrolyte membrane, the heat-weldable sheet, and the electrode layer in this example.
Describing in detail with reference to the drawings, the polymer electrolyte membrane 2 and the heat-weldable sheet 4 that supports the polymer electrolyte membrane 2 are placed in a humidity control tank of a humidity controller (not shown) (in-machine conditions: temperature 40 ° C., Relative humidity 90%) and allowed to swell for 10 minutes.
Next, the upper and lower surfaces of the polymer electrolyte membrane 2 were sandwiched between the heat-weldable sheet 4 and the electrode layer 6 and placed on a press machine placed in a humidity controller. By applying a pressure of 1 MPa in the vertical direction, the polymer electrolyte membrane 2 and the heat-weldable sheet 4 are further brought into close contact with each other, and the polymer electrolyte membrane 2 and the electrode layer 6 are closely adhered and heated at 150 ° C. for 5 minutes. The molecular electrolyte membrane 2, the heat-weldable sheet 4, and the electrode layer 6 were joined to obtain the membrane / electrode assembly 1.

(Comparative Example 1)
Without carrying out the method for producing a membrane-electrode assembly of the present invention, the upper and lower surfaces of the polymer electrolyte membrane are sandwiched between the heat-weldable sheets, placed on a press machine, and a pressure of 1 MPa is applied in the vertical direction. In addition, the polymer electrolyte membrane 2 and the heat-weldable sheet 4 were brought into close contact with each other and heated at 150 ° C. for 5 minutes to join the polymer electrolyte membrane 2 and the heat-weldable sheet 4.
Next, the electrode layer is placed on the polymer electrolyte membrane exposed from the opening of the heat-weldable sheet, and a pressure of 1 MPa is applied and heated at 150 ° C. for 5 minutes to join the polymer electrolyte membrane and the electrode layer. A membrane / electrode assembly was obtained.

[Performance evaluation]
The membrane / electrode assembly of each of the above examples is sandwiched between a gas flow path forming member and a current collector, a single cell of PEFC is produced, a long-term power generation operation is performed under the following conditions, and an electrochemically effective catalytic surface area ( ECA) was measured.
The obtained results are shown in FIG. FIG. 4 is a graph showing the relationship between the operation time and the ECA remaining rate. The present invention shows the result of the single cell of the PEFC of Example 1, and the conventional technology shows the result of the single cell of the PEFC of Comparative Example 1.

(Power generation operation conditions)
・ Temperature: 70 ℃
・ Relative humidity: 60%
・ Fuel: anode side; hydrogen, cathode side; air ・ current density: 0 A / cm ² (1 hour) • 1 A / cm ² (1 hour) repetitive cycle

As shown in FIG. 4, although the ECA decreases with the lapse of the operation time, the PEFC single cell of Example 1 using the membrane-electrode assembly produced by the production method of the present invention has a membrane / electrode produced by the conventional production method. It turns out that the fall of ECA is suppressed rather than the single cell of the PEFC of the comparative example 1 using an electrode assembly.
From this, it can be seen that the dimensional change in the planar direction of the polymer electrolyte membrane accompanying the change in humidity is suppressed, and the breakage or peeling of the electrode layer disposed on the polymer electrolyte membrane is suppressed. The PEFC single cells of Examples 2 and 3 exhibited the same performance as the PEFC single cell of Example 1.

(1) And (2) is the top view which shows the outline | summary of the joining method of the polymer electrolyte membrane and heat-weldable sheet in Example 1, and sectional drawing in AA. (1) And (2) is the top view which shows the outline | summary of the joining method of the polymer electrolyte membrane and heat-weldable sheet in Example 2, and sectional drawing in BB. (1) And (2) is the top view which shows the outline | summary of the joining method of the polymer electrolyte membrane in Example 3, a heat-weldable sheet | seat, and an electrode layer, and sectional drawing in CC. It is a graph which shows the relationship between driving | running time and ECA residual rate.

Explanation of symbols

1 Membrane / Electrode Assembly 2 Polymer Electrolyte Membrane 4 Thermal Weldable Sheet 6 Electrode Layer

Claims (10)

For a polymer electrolyte fuel cell, in which a polymer electrolyte membrane is sandwiched between a pair of supports having an opening at the center, and an electrode layer is joined to the polymer electrolyte membrane exposed at the opening of the support A method for producing a membrane / electrode assembly, comprising the following steps (A) to (E)
(A): The polymer electrolyte membrane is expressed by the following formula (1)
S _w ≦ S _x (1)
Step (the S _x in formula area during production of the polymer electrolyte membrane, the S _w to. Showing the area at the time of moisture expansion) to expand in a range satisfying the relationship represented by,
(B): a step of sandwiching the polymer electrolyte membrane between a pair of the supports,
(C): a step of holding the polymer electrolyte membrane in an expanded state,
(D): a step of joining the polymer electrolyte membrane and the support;
(E): a step of bonding the electrode layer to the polymer electrolyte membrane exposed in the opening of the support;
A method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell, comprising:   2. The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to claim 1, wherein the support is heat-weldable.   The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to claim 1 or 2, wherein the support is further in the form of a sheet.   4. The polymer electrolyte fuel cell according to any one of claims 1 to 3, wherein the swelling rate of the support when it contains water is smaller than the swelling rate when the polymer electrolyte membrane contains water. Manufacturing method of membrane / electrode assembly.   The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein the electrode layer includes a gas diffusion layer.   In the step (A), the polymer electrolyte membrane is left to swell in a humidified atmosphere and / or is expanded by applying an external force to the polymer electrolyte membrane. The manufacturing method of the membrane electrode assembly for polymer electrolyte fuel cells as described in one term.   In the step (D), the relative position between the polymer electrolyte membrane and the support in a direction perpendicular to the film thickness direction is not changed. The manufacturing method of the membrane electrode assembly for polymer electrolyte fuel cells as described in one term.   In said (D) process, heat and / or pressure are applied to both said polymer electrolyte membrane and said support body, The polymer electrolyte form as described in any one of Claims 1-7 characterized by the above-mentioned. Manufacturing method of membrane-electrode assembly for fuel cell.   The polymer electrolyte form according to any one of claims 1 to 8, wherein in the step (E), heat and / or pressure are applied to both the polymer electrolyte membrane and the electrode layer. Manufacturing method of membrane-electrode assembly for fuel cell.   The method for producing a membrane / electrode assembly for a polymer electrolyte fuel cell according to any one of claims 1 to 9, wherein the step (D) and the step (E) are performed simultaneously.

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