JP2011198681A - Membrane electrode assembly for solid polymer fuel cell, method for manufacturing of membrane electrode assembly, and fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane electrode assembly that has no wrinkle at an outer edge of polyelectrolyte membrane, while securing durability and gas sealing property.SOLUTION: The membrane electrode assembly is manufactured so that at the edge of the polyelectrolyte membrane 1, shape of a surface in a perpendicular direction against an edge of electrocatalyst layer 22 produces the maximum peak height of an undulating curve obtained by a contour curve filter with cut-off value of λf 1.25 mm and λc 0.25 mm which becomes ≤20 μm. By this arrangement, the membrane electrode assembly can be obtained in which there is no wrinkle in the polyelectrolyte membrane 1 in the vicinity of the electrocatalyst layer 22, and there is no problem in the initial power generation performance and the long term durability.

Description

  The present invention relates to a membrane electrode assembly for a polymer electrolyte fuel cell, a manufacturing method thereof, and a fuel cell including the membrane electrode assembly.

  A fuel cell is a power generation engine that generates electricity from an electrochemical reaction between hydrogen and oxygen, has high power generation efficiency, and discharges only water during power generation, and is expected as a next-generation power source. A membrane electrode assembly of a polymer electrolyte fuel cell has a structure in which a pair of electrode catalyst layers are bonded to both surfaces of a polymer electrolyte membrane. A fuel cell is used in which a gas diffusion layer is disposed outside the electrode catalyst layer of the membrane electrode assembly and is further sandwiched between separators.

  A transfer method is known as a method for producing a membrane electrode assembly. In the transfer method, a catalyst sheet containing catalyst-carrying carbon, an ionomer, and a solvent is coated on a substrate such as a polymer film and dried to produce a transfer sheet, and the transfer sheet is sized to the size of the electrode. And thermocompression-bonding by heating and pressurizing the polymer electrolyte membrane. When a polymer film or the like is used for the base material, it is necessary to peel the base material after thermocompression bonding, but when the gas diffusion layer is used, it is not necessary to peel the base material.

  In the transfer method, the polymer electrolyte membrane heat shrinks or softens during heating and pressurization, and is easily deformed, so that the polymer electrolyte membrane on the outer edge not in contact with the electrode catalyst layer is wrinkled or scratched. It is easy to happen. When wrinkles and scratches are generated in the polymer electrolyte, there is a problem that air and hydrogen gas leak from the wrinkle portion and gas sealing performance is deteriorated. If the gas sealability is lowered and the reaction gas is not sufficiently supplied, the initial performance of power generation may be lowered.

  As means for eliminating wrinkles at the outer edge of the polymer electrolyte membrane, Patent Document 1 discloses an apparatus in which a groove having a concave cross section is provided at the center of a mold that is in contact with the laminate of the polymer electrolyte membrane and the transfer sheet. Has been. According to the apparatus of Patent Document 1, since the portion of the transfer sheet and the polymer electrolyte membrane at the outer edge portion can be evenly pressurized, the difference in thermal shrinkage between the central portion and the outer edge portion of the polymer electrolyte membrane can be suppressed. Can prevent wrinkling.

Japanese Patent Laid-Open No. 2006-164887

However, the above method has a problem that wrinkles and scratches caused by methods other than heat shrinkage cannot be prevented. The wrinkles of the polymer electrolyte membrane include wrinkles that occur on the entire outer edge of the polymer electrolyte membrane, which are caused by heat shrinkage. In addition, wrinkles and thinning of the shape along the electrode catalyst layer may occur in the polymer electrolyte membrane at the outer edge.
The wrinkles and thinning of the shape along the electrode catalyst layer occur because the end portion of the transfer sheet base material penetrates into the polymer electrolyte membrane. When one of the substrates is bitten, it bends and becomes wrinkled, and when both sides of the substrate bite, it is crushed and thinned. When the polymer electrolyte membrane is thinned, there is a problem that cross leak of the reaction gas is likely to occur. When the cross leak occurs, there is a possibility that a problem occurs in the long-term durability of the power generation. Therefore, when wrinkles and thinning of the shape along the electrode catalyst layer occur, in addition to deterioration of gas sealability due to wrinkles, cross leaks may occur due to thinning, which may cause problems in initial power generation performance and long-term durability. was there.
The present invention relates to a membrane electrode assembly in which there is no wrinkle or thinning of the shape along the electrode catalyst layer in the polymer electrolyte membrane at the outer edge, and there is no problem in the initial performance and long-term durability of power generation, its production method and membrane electrode An object of the present invention is to provide a fuel cell including the joined body.

  In order to solve the above-mentioned problems, a method for producing a membrane electrode assembly according to the present invention is such that a transfer sheet having an electrode catalyst layer formed on a substrate is disposed on both sides of a polymer electrolyte membrane, and is bonded by heating and pressing. A method for producing a membrane electrode assembly, comprising the polymer electrolyte membrane, the transfer sheet having a smaller area than the polymer electrolyte membrane and covering a central portion of the polymer electrolyte membrane, and the polymer electrolyte membrane, A laminate including a protective member disposed on an outer edge portion not covered by the transfer sheet is formed, and the laminate is heated and pressed to be bonded. By this production method, a polymer electrode membrane in the vicinity of the electrode catalyst layer is free from wrinkles, and a membrane / electrode assembly having no problem in initial power generation performance and long-term durability can be obtained.

In the laminate, the thickness of the outer edge portion including the protective member is larger than the thickness of the central portion including the transfer sheet, and the difference is preferably 30 μm or less. Thereby, a pressure is appropriately applied to the electrode catalyst layer in the thermocompression bonding step, and bonding can be reliably performed.
In the laminate, the distance between the protective member and the transfer sheet is preferably 0.2 mm or less. Thereby, possibility that a base material will contact a polymer electrolyte membrane can be kept low.
When bonding the laminated body by heating and pressing, a buffer material may be disposed between the laminated body and the thermocompression bonding apparatus. The pressure can be dispersed by the buffer material, and the pressure is appropriately applied to the electrode catalyst layer in the thermocompression bonding step, so that the bonding can be reliably performed.

The membrane / electrode assembly according to the present invention is a membrane / electrode assembly having a structure in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, and the polymer electrolyte membrane is exposed at the outer edge of the electrode catalyst layer. The surface shape of the polymer electrolyte membrane exposed at the outer edge portion along the direction perpendicular to the side of the electrode catalyst layer is obtained by a contour curve filter having cutoff values λf 1.25 mm and λc 0.25 mm. The maximum peak height of the undulation curve is 20 μm or less. According to such a configuration, it is possible to obtain a membrane / electrode assembly free from wrinkles in the polymer electrolyte membrane in the vicinity of the electrode catalyst layer and having no problem in the initial performance and long-term durability of power generation.
A membrane / electrode assembly for solving the above problems is produced by the method for producing a membrane / electrode assembly and used in a fuel cell. Thereby, a fuel cell having appropriate characteristics can be obtained.

  According to the present invention, it is possible to obtain a membrane / electrode assembly free from wrinkles in the polymer electrolyte membrane in the vicinity of the electrode catalyst layer and having no problem in the initial performance and long-term durability of power generation.

(A) is a cross-sectional schematic diagram of a membrane electrode assembly without wrinkles in the vicinity of the electrode catalyst layer, and (b) is a schematic cross-sectional diagram of a membrane electrode assembly with wrinkles in the vicinity of the electrode catalyst layer. It is a cross-sectional schematic diagram which shows an example of the thermocompression bonding process of the manufacturing method of the membrane electrode assembly by this invention. It is a perspective view which shows the lamination | stacking state of the laminated body in FIG. It is a cross-sectional schematic diagram which shows the other example of the thermocompression-bonding process of the manufacturing method of the membrane electrode assembly by this invention. It is a decomposition | disassembly schematic diagram of a polymer electrolyte fuel cell.

Embodiments of the present invention will be described below with reference to the drawings. In the drawings referred to in the following description, the same parts as those in the other drawings are denoted by the same reference numerals.
(Membrane electrode assembly)
FIG. 1A is a schematic sectional view of the membrane electrode assembly 12 according to the present embodiment. In the figure, the membrane electrode assembly 12 has a structure in which the electrode catalyst layer 22 is disposed on both sides of the polymer electrolyte membrane 1 and the polymer electrolyte membrane 1 is exposed at the outer edge of the electrode catalyst layer 22. The outer edge A of the polymer electrolyte membrane 1 is flat without wrinkles and has a constant thickness.

On the other hand, in the outer edge portion A of the polymer electrolyte membrane 1, wrinkles or uneven thickness portions may occur in the region B near the electrode catalyst layer 22.
FIG. 1B is a schematic cross-sectional view of the membrane electrode assembly 12 in which the region B in the vicinity of the electrode catalyst layer 22 of the polymer electrolyte membrane 1 is damaged. There are wrinkles and thin portions in the vicinity of the electrode catalyst layer 22. If wrinkles are present, the gas sealing property is lowered, and if the thickness of the polymer electrolyte membrane 1 is thin, the durability may be lowered.

Here, if the membrane electrode assembly 12 has a surface shape in the direction C perpendicular to the side of the electrode catalyst layer 22 and the maximum peak height of the undulation curve is 20 μm or less, there are few problems in gas sealing properties. The maximum peak height of the waviness curve is more desirably 5 μm or less. The waviness curve is a curve obtained by removing the surface roughness component having a short wavelength and the component having a long wavelength from the roughness curve cross-sectional curve, and in this embodiment, is a wavelength of a branch point of each component. Cut-off values were λf 1.25 mm and λc 0.25 mm.
In the case of an electrode catalyst layer having a shape such as a circle or an ellipse that does not have a side, the “direction C” is a direction perpendicular to a tangent line on the contour line of the shape.

(Method for producing membrane electrode assembly)
The manufacturing method of the membrane electrode assembly according to the present embodiment includes a thermocompression bonding in which a transfer sheet having an electrode catalyst layer formed on a substrate and a protective member are disposed on both sides of a polymer electrolyte membrane and bonded by heating and pressing. It has a process. In this thermocompression bonding step, a laminated body in which a protective member is disposed on the outer edge portion of the polymer electrolyte membrane that is not covered by the transfer sheet is formed, and this laminated body is heated and pressurized to be bonded.

(Thermocompression bonding process of membrane electrode assembly)
In FIG. 2, the cross-sectional schematic diagram of the thermocompression bonding process of the said membrane electrode assembly is shown. In the thermocompression bonding process, the transfer sheet 2 in which the electrode catalyst layer 22 is formed on the base material 21 is disposed on both surfaces of the polymer electrolyte membrane 1. The transfer sheet 2 has a smaller area than the polymer electrolyte membrane 1 and covers a part (central portion) of the polymer electrolyte membrane 1. In this example, a protective member 3 is arranged in addition to this. Referring to FIG. 3 which is a perspective view of the laminate 12a, in this example, the protective member 3 is arranged so as to cover the outer edge portion of the polymer electrolyte membrane 1.

In addition, a buffer material or the like may be disposed between the laminated body 12a and the thermocompression bonding device 60 for the purpose of dispersing the pressure. In the configuration example of FIG. 4, the cushioning material 50 is provided between the laminated body 12 a and the thermocompression bonding device 60.
Here, when the laminate is heated and pressurized in the absence of the protective member 3, the end portion of the base material 21 may come into contact with the polymer electrolyte membrane 1 and be deformed by pushing it. For this reason, the protective member 3 is provided in FIG. 2 or FIG. 4, and the protective member 3 prevents the end portion of the base material 21 from getting into the polymer electrolyte membrane 1.

  In this example, in the arrangement as shown in FIG. 2 or FIG. 4, the laminate 12 a is heated and pressurized to adhere the polymer electrolyte membrane 1 and the electrode catalyst layer 22. A film having good peelability is used for the base material 21, and only the base material 21 is peeled after the thermocompression bonding step to form the membrane electrode assembly 12. A gas diffusion layer can also be used for the base material 21. In this case, it is not necessary to peel off the substrate after the thermocompression bonding step.

  In the present embodiment, the laminated body 12a including the polymer electrolyte membrane 1, the transfer sheet 2, and the protective member 3 includes a region D (that is, the central portion) that includes the electrode catalyst layer and a region E that does not include the electrode catalyst layer (that is, The difference in thickness from the outer edge portion is 30 μm or less. If the thickness of the region D is smaller than that of the region E, it is difficult to apply pressure to the electrode catalyst layer depending on the configuration in the thermocompression bonding process and bonding may not be possible.

When the gap between the protective member 3 and the transfer sheet 2 is too wide, the base material 21 comes into contact with the polymer electrolyte membrane, so that the effect of preventing the base material 21 from contacting is reduced. If the thickness of the base material 21 is 50 to 300 μm, the gap (that is, the distance) between the protective member 3 and the transfer sheet 2 is preferably 0.2 mm or less.
The protective member 3 may be any material as long as it is excellent in heat resistance and creep resistance and satisfies the above conditions. If the substrate 21 is a polymer film, the polymer film of the same material is used. May be used.

(Transfer sheet)
The transfer sheet 2 can be produced by applying a catalyst ink containing at least carbon particles carrying a catalyst and a polymer electrolyte to the substrate 21. As the base material 21, a polymer film can be used in addition to the gas diffusion layer. As the polymer film, any material having good transferability may be used. For example, ethylene tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroperfluoroalkyl vinyl ether copolymer Fluorine resins such as coalescence (PFA) and polytetrafluoroethylene (PTFE) can be used. Polymer films such as polyimide, polyethylene terephthalate, polyamide (nylon), polysulfone, polyethersulfone, polyphenylene sulfide, polyether ether ketone, polyetherimide, polyarylate, and polyethylene naphthalate can also be used. You may use what processed the release layer etc. to these base materials.

  Moreover, as a gas diffusion layer, what is used for the normal fuel cell can be used. Specifically, porous carbon materials such as carbon cloth, carbon paper, and non-woven fabric can be used as the gas diffusion layer. The gas diffusion layer can also be used as a substrate. A material layer may be formed between the gas diffusion layer and the electrode catalyst layer. The mesh layer is a layer that prevents the catalyst ink from penetrating into the gas diffusion layer, and deposits on the mesh layer to form a three-phase interface even when the coating amount is small. Such a filler layer can be formed, for example, by kneading carbon particles and a fluororesin and sintering them at a temperature equal to or higher than the melting point of the fluororesin. As the fluororesin, polytetrafluoroethylene (PTFE) or the like can be used.

As a method for applying the catalyst ink, a die coating method, a screen printing method, a roll coating method, a spray method, or the like can be used.
The polymer electrolyte is not particularly limited as long as it has proton conductivity, and a fluorine-based polymer electrolyte and a hydrocarbon-based polymer electrolyte can be used. Examples of the fluoropolymer electrolyte include Nafion (registered trademark) manufactured by DuPont, Flemion (registered trademark) manufactured by Asahi Glass Co., Ltd., Aciplex (registered trademark) manufactured by Asahi Kasei Co., Ltd., and Gore Select (registered trademark) manufactured by Gore. Etc. can be used. As the hydrocarbon polymer electrolyte membrane, electrolyte membranes such as sulfonated polyetherketone, sulfonated polyethersulfone, sulfonated polyetherethersulfone, sulfonated polysulfide, and sulfonated polyphenylene can be used. Among these, a Nafion (registered trademark) material manufactured by DuPont can be suitably used as the polymer electrolyte membrane.

(Configuration example of polymer electrolyte fuel cell)
FIG. 5 shows an exploded schematic view of a polymer electrolyte fuel cell using the membrane electrode assembly according to the present embodiment. In the polymer electrolyte fuel cell of this example, the membrane electrode assembly 12 is provided with the electrode catalyst layers 22 on both sides of the solid polymer electrolyte membrane 1 and faces the electrode catalyst layers 22 on both sides. Thus, the air electrode side gas diffusion layer 4 and the fuel electrode side gas diffusion layer 5 are arranged. Thereby, the air electrode 6 and the fuel electrode 7 are comprised, respectively. A set of separators 10 made of a conductive and impermeable material is provided, which includes a gas flow path 8 for gas flow and a cooling water flow path 9 for cooling water flow on the opposing main surface. For example, hydrogen gas is supplied as a fuel gas from the gas flow path 8 of the separator 10 on the fuel electrode 7 side. On the other hand, a gas containing oxygen, for example, is supplied as an oxidant gas from the gas flow path 8 of the separator 10 on the air electrode 6 side. An electromotive force can be generated between the fuel electrode and the air electrode by causing an electrode reaction between hydrogen and oxygen gas of the fuel gas in the presence of the catalyst.
The solid polymer fuel cell shown in FIG. 5 is a so-called single cell solid polymer type in which a solid polymer electrolyte membrane 1, an electrode catalyst layer 22, and gas diffusion layers 4 and 5 are sandwiched between a pair of separators. Although it is a fuel cell, in this example, a plurality of cells can be stacked via the separator 10 to form a fuel cell.

(Examples and Comparative Examples)
<Preparation of transfer sheet>
A platinum-supported carbon catalyst (trade name: TEC10E50E, manufactured by Tanaka Kikinzoku Kogyo Co., Ltd.) and a 20% by mass polymer electrolyte solution (Nafion: registered trademark, manufactured by Dupont) are mixed with a mixed solvent of water and ethanol. Dispersion treatment was performed to prepare a catalyst ink. A transfer sheet was produced by applying the catalyst ink to the substrate using a die coater, setting the oven at 80 ° C., and drying for 10 minutes.

<Thermocompression bonding process>
Place the transfer sheet and various protective members on the outside of the polymer electrolyte membrane (Nafion 211: registered trademark, manufactured by Dupont), perform hot pressing at 130 ° C. for 10 minutes, and then peel off the PTFE film of the base material Thus, a membrane electrode assembly was obtained.
<Measure wrinkles>
Using a microscope laser displacement meter (manufactured by Oplens), the surface shape of the outer edge portion of the polymer electrolyte membrane of the membrane electrode assembly of the example and the comparative example was observed. The maximum peak height of the undulation curve obtained using the contour curve filter having the cutoff values λf 1.25 mm and λc 0.25 mm was calculated.

Example 1
A transfer sheet prepared using a PTFE film having a thickness of 100 μm as a base material was punched into a square. A transfer sheet was disposed on both surfaces of the polymer electrolyte membrane, and a PTFE film having a thickness of 100 μm was disposed as a protective member on the exposed portion of the polymer electrolyte membrane. The difference in thickness between the center portion and the outer edge portion of the laminate was 10 μm, and the gap between the transfer sheet and the protective member was 0.2 mm. After hot pressing, the base PTFE film was peeled off to obtain a membrane electrode assembly.

(Example 2)
A transfer sheet prepared using a PTFE film having a thickness of 100 μm as a base material was punched into a square. A transfer sheet was disposed on both surfaces of the polymer electrolyte membrane, and a PTFE film having a thickness of 100 μm was disposed as a protective member on the exposed portion of the polymer electrolyte membrane. The difference in thickness between the center portion and the outer edge portion of the laminate was 10 μm, and the gap between the transfer sheet and the protective member was 1.0 mm. After hot pressing, the base PTFE film was peeled off to obtain a membrane electrode assembly.

(Comparative Example 1)
A transfer sheet prepared using a PTFE film having a thickness of 100 μm as a base material was punched into a square. Transfer sheets were placed on both sides of the polymer electrolyte membrane. Other protective members were not arranged. The difference in thickness of the laminate was 110 μm. After hot pressing, the base PTFE sheet was peeled off to obtain a membrane electrode assembly.
(result)
Table 1 summarizes the results of this example and the comparative example. Referring to Table 1, the maximum peak height was 20 μm or less in Examples 1 and 2, whereas it was 30 μm or more in Comparative Example 1.

  When the membrane / electrode assembly of the present invention is used in a polymer electrolyte fuel cell, there are few problems in the initial performance and long-term durability of power generation. Therefore, the present invention can be suitably used for a fuel cell using a polymer electrolyte membrane, particularly a stationary cogeneration system and an electric vehicle.

DESCRIPTION OF SYMBOLS 1 Polymer electrolyte membrane 2 Transfer sheet 3 Protection member 4 Air electrode side gas diffusion layer 5 Fuel electrode side gas diffusion layer 6 Air electrode 7 Fuel electrode 8 Gas flow path 9 Cooling water flow path 10 Separator 12 Membrane electrode assembly 12a Laminate 21 Base material 22 Electrode catalyst layer 50 Buffer material 60 Thermocompression bonding device

Claims (7)

A method for producing a membrane electrode assembly in which a transfer sheet having an electrode catalyst layer formed on a base material is disposed on both sides of a polymer electrolyte membrane, and is bonded by heating and pressing,
The polymer electrolyte membrane, the transfer sheet having a smaller area than the polymer electrolyte membrane and covering the central portion of the polymer electrolyte membrane, and the outer periphery of the polymer electrolyte membrane not covered by the transfer sheet A method of manufacturing a membrane electrode assembly, comprising: forming a laminate including the protective member, and heating and pressurizing the laminate.   2. The film according to claim 1, wherein the laminated body has a thickness of an outer edge portion including a protective member larger than a thickness of a central portion including the transfer sheet, and a difference thereof is 30 μm or less. Manufacturing method of electrode assembly.   The method for producing a membrane electrode assembly according to claim 1 or 2, wherein in the laminate, a distance between the protective member and the transfer sheet is 0.2 mm or less.   4. The shock absorber according to claim 1, wherein a buffer material is disposed between the laminate and the thermocompression bonding device when the laminate is bonded by heating and pressing. 5. Manufacturing method of membrane electrode assembly.   The membrane electrode assembly manufactured by the manufacturing method of any one of Claim 1- Claim 4. A membrane electrode assembly comprising a structure in which a polymer electrolyte membrane is sandwiched between a pair of electrode catalyst layers, wherein the polymer electrolyte membrane is exposed at the outer edge of the electrode catalyst layer,
The surface shape of the polymer electrolyte membrane exposed at the outer edge portion along the direction perpendicular to the side of the electrode catalyst layer is a swell obtained by a contour curve filter having cutoff values λf 1.25 mm and λc 0.25 mm. A membrane electrode assembly, wherein the maximum peak height of the curve is 20 μm or less.   A fuel cell comprising the membrane electrode assembly according to claim 5.

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