JP7110961B2 - Manufacturing method of membrane electrode gas diffusion layer assembly for fuel cell - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a membrane electrode gas diffusion layer assembly for a fuel cell.

A fuel cell supplies fuel gas (hydrogen gas) and oxidant gas (oxygen gas) to two electrically connected electrodes to electrochemically oxidize the fuel, converting chemical energy directly into electricity. convert to energy. This fuel cell usually has a membrane electrode assembly in which electrodes (anode and cathode) are joined to both sides of an electrolyte membrane (solid polymer membrane) having proton conductivity, and gas diffusion is performed on both sides of this membrane electrode assembly. A single cell formed by sandwiching a membrane electrode gas diffusion layer assembly formed by joining layers between separators is used as a structural unit, and a plurality of such single cells are laminated. The anode and the cathode each have a catalyst layer for promoting the electrochemical reaction, and the gas diffusion layer diffuses reactant gases (fuel gas and oxidant gas) supplied from the outside of the fuel cell, It is supplied to the catalyst layer.

As a method of manufacturing this membrane electrode assembly, a method of hot-pressing a laminate in which an electrolyte membrane is sandwiched between electrodes is known. For example, in Patent Document 1, a metal press plate/elastic rubber/release agent sheet/electrode/ion exchange membrane/electrode/release agent sheet/elastic rubber/metal press plate are laminated in this order and hot pressed. to produce a membrane electrode assembly. Further, Patent Document 2 discloses laminating an ion-exchange membrane/catalyst layer/base sheet/porous sheet/rubber in this order, performing hot pressing, and transferring the catalyst layer onto the ion-exchange membrane. there is

By the way, when joining a membrane electrode assembly and a gas diffusion layer, if the two are laminated and hot-pressed, there is a risk that the gas diffusion layer will crack. Therefore, in Patent Document 3, a laminate in which a membrane electrode assembly and a gas diffusion layer are laminated is pressurized from the side of the membrane electrode assembly using a fluid while supporting the gas diffusion layer. and a gas diffusion layer.

JP 2003-036862 A JP-A-2002-158014 JP 2012-178231 A

According to the method described in Patent Document 3, since pressure is applied to the gas diffusion layer using a fluid, it is possible to suppress the occurrence of cracks in the gas diffusion layer during bonding. There is a problem of cost.

The present invention has been made in view of the above circumstances, and provides a method for manufacturing a membrane electrode gas diffusion layer assembly in which a gas diffusion layer is joined to an electrode membrane electrode assembly. An object of the present invention is to provide a method for manufacturing a membrane electrode gas diffusion layer assembly by pressing.

The present invention achieves the above objects by the following means.

A method for manufacturing a membrane electrode gas diffusion layer assembly in which a gas diffusion layer is joined to a membrane electrode assembly, comprising:
Preparing a laminate formed by laminating metal press plate/elastic rubber sheet/woven fabric/release sheet/membrane electrode assembly/gas diffusion layer/release sheet/metal press plate in this order; is placed on the press surface of the hot press machine and subjected to hot pressing;
method including.

According to the manufacturing method of the membrane electrode gas diffusion layer assembly of the present invention, by placing the woven fabric between the rubber sheet and the release sheet, gas diffusion is achieved while maintaining the bonding between the membrane electrode assembly and the gas diffusion layer. Cracking of layers can be suppressed.

It is a figure which shows the lamination|stacking structure in the conventional hot press method. FIG. 3 is a view showing a lamination structure in the method for manufacturing the membrane electrode gas diffusion layer assembly of the present invention;

The manufacturing method of the membrane electrode gas diffusion layer assembly of the present invention comprises:
Preparing a laminate formed by laminating metal press plate/elastic rubber sheet/woven fabric/release sheet/membrane electrode assembly/gas diffusion layer/release sheet/metal press plate in this order; is placed on the press surface of the hot press machine and subjected to hot pressing;
including.

This method further comprises hot-pressing the laminate, removing the laminate from the hot-press machine, and exposing the laminate to metal press plate/elastic rubber sheet/woven fabric/releasing sheet from both sides of the laminate. and the release sheet/metal press plate to obtain a membrane electrode gas diffusion layer assembly.

When a membrane electrode assembly and a gas diffusion layer are bonded using a hot press method used in a conventional method for manufacturing a membrane electrode assembly, as shown in FIG. 2 on both sides or one side of the membrane electrode assembly 3, and then a release sheet 5, an elastic rubber sheet 6, and a metal press plate 7 are laminated in this order on both sides. 10 is placed on the press surface of the hot press and hot pressing is performed.

However, it has been found that when hot pressing is performed using a laminate having such a structure, cracks may occur in the gas diffusion layer. Therefore, when hot pressing was performed using a laminate having a structure in which the elastic rubber sheet was removed from the above laminate, cracks did not occur in the gas diffusion layer.

By the way, conventionally, the bondability between each layer constituting a fuel cell, for example, the bondability between an electrolyte membrane and an electrode layer, and the bondability between an electrode layer and a gas diffusion layer, affects the power generation performance and durability of a fuel cell. known to do. In order to improve the bondability between layers, an elastic rubber sheet has conventionally been used when using the hot press method. This elastic rubber sheet is used to evenly transmit the pressure in the pressing process. Without the elastic rubber sheet, the surface contact is poor in the pressing process, and the resulting membrane electrode gas diffusion layer assembly may have partial bonding failure. can occur.

Thus, when the membrane electrode gas diffusion layer assembly is manufactured by the hot pressing method, if an elastic rubber sheet is used, cracks will occur in the gas diffusion layer. There was a problem.

Therefore, in the present invention, as shown in FIG. Hot pressing is performed using a laminate formed by laminating the press plates 7 in this order.

When hot pressing is performed using a laminate having a conventional configuration as shown in FIG. It is considered that the gas diffusion layer 4 is cracked because it cannot withstand this shearing force.

On the other hand, in the present invention, in the laminate to be hot-pressed, by not arranging the elastic rubber sheet on the side of the membrane electrode assembly 3 on which the gas diffusion layer 4 is arranged, a It suppresses the occurrence of shear force in A woven cloth 8 is arranged between the elastic rubber sheet 6 and the release sheet 5 on the side of the membrane electrode assembly 3 on which the gas diffusion layer 4 is not arranged. Since the woven fabric 8 is a woven fabric, it can move freely in the in-plane direction to some extent. It is possible to suppress the occurrence of shear force between them, and as a result, it is possible to suppress the occurrence of cracks in the gas diffusion layer 4 .

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail. It should be noted that the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.

The manufacturing method of the membrane electrode gas diffusion layer assembly of the present invention comprises, for example, as shown in FIG.
A laminate obtained by laminating metal press plate 7/elastic rubber sheet 6/woven fabric 8/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5'/metal press plate 7 in this order. preparing (laminate preparation step), and placing the laminate on the press surface of a hot press machine and hot pressing (hot pressing step),
are executed in sequence. Each step of the manufacturing method of the membrane electrode gas diffusion layer assembly of the present invention will be described below.

<Laminate manufacturing process>
In the laminate manufacturing process, metal press plate 7/elastic rubber sheet 6/woven fabric 8/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5'/metal press plate 7 are arranged in this order. Laminated.

Although the metal press plate 7 is not particularly limited, a material such as stainless steel or iron can be used, and in order to improve the hardness of the surface, for example, the surface may be treated with chromium or the like. . The thickness of the metal press plate is on the order of 5 mm to 2 cm in consideration of its rigidity and thermal conductivity.

The elastic rubber sheet 6 is used to evenly transmit pressure to each layer of the laminate during hot pressing, and may be made of silicon rubber, polybutadiene rubber, or the like. be.

The woven fabric 8 is used to relieve strain due to shear force in the plane direction caused by expansion and contraction of each layer constituting the laminate during hot pressing. As the woven fabric, one having excellent heat resistance and thermal conductivity is preferable, and for example, carbon cloth can be used.

The release sheets 5 and 5' are used to prevent sticking between the woven fabric and the membrane electrode assembly, or between the gas diffusion layer and the metal press plate, and are not particularly limited as long as they have flatness and heat resistance. . For example, polytetrafluoroethylene (PTFE) film, ethylene-tetrafluoroethylene copolymer (ETFE) film, polyethylene terephthalate (PET) film, polyimide film and the like can be used.

Here, the PTFE film has a characteristic of being excellent in releasability, although it expands and contracts greatly due to heat. On the other hand, a polyimide film has a characteristic of being inferior in releasability, although it expands and shrinks little due to heat. Therefore, in the present invention, it is preferable to use a PTFE film having excellent releasability as the release sheet 5 that is in direct contact with the membrane electrode assembly. Since the woven fabric is arranged on the side where the release sheet 5 is arranged, the problem of thermal expansion and contraction can be suppressed. On the other hand, as the release sheet 5' placed between the gas diffusion layer and the metal press plate, it is preferable to use a polyimide film that expands and contracts less due to heat. This is because the gas diffusion layer has low adhesion.

The membrane electrode assembly 3 is composed of a laminate in which the electrolyte membrane 1 is sandwiched between the electrodes 2 . Here, as the electrolyte membrane 1, an electrolyte membrane generally used for electrolyte membranes of fuel cells can be used. The electrolyte membrane is a proton (H ⁺ )-conducting polymer, such as a cation exchanger polymer with proton-conducting groups (such as sulfonic acid groups (SO ₃ ⁻ ), etc.), especially polybenzoxazole (PBO). , polybenzothiazole (PBT), polybenzimidazole (PBI), polysulfone (PSU), polyethersulfone (PES), polyetherethersulfone (PEES), polyphenylene oxide (PPO), polyphenylene sulfoxide (PPSO), polyphenylene sulfide ( PPS), polyphenylene sulfide sulfone (PPS/SO2), polyparaphenylene ₍ PPP), polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyimide (PI), etc. Ion exchangers obtained by sulfonating a part of the molecule, polyvinylsulfonic acid, polyallylsulfonic acid, polystyrenesulfonic acid, polyallyloxybenzenesulfonic acid and the like can be mentioned. Copolymers or mixtures of multiple species can be used.

The thickness of the electrolyte layer 1 is preferably 1 to 100 μm, more preferably about 10 μm.

As the electrode 2, an electrode generally used as an electrode of a fuel cell can be used. The electrode generally consists of a catalyst and a proton-conducting polymer, such as an ionomer.

The catalyst may be a catalyst metal supported on conductive carbon particles. Examples of conductive carbon particles that can be used include carbon black such as furnace black, channel black, and acetylene black, activated carbon, and graphite. The particle size of the conductive carbon particles may be 1 nm or more, 5 nm or more, or 10 nm, and may be 10 μm or less, 1 μm or less, or 500 nm or less.

The catalytic metal is a metal that promotes hydrogen oxidation reaction and oxygen reduction reaction. and alloys thereof can be used, with platinum being preferred. Although the particle size of the catalyst metal is not particularly limited, it may be, for example, 1 nm or more, or 1.5 nm or more, or 100 nm or less, 50 nm or less, or 10 nm or less.

The amount of catalyst metal supported is preferably 1 to 99% by weight, more preferably 10 to 90% by weight, and most preferably 30 to 70% by weight, based on the conductive carbon particles.

The proton-conducting polymer is not particularly limited as long as it is a polymer having hydrogen ion conductivity, and various ionomers commonly used in electrode catalyst layers of fuel cells can be used. As an example of this ionomer, a perfluorosulfonic acid polymer containing acidic functional groups and cyclic groups, specifically the commercial product Nafion®, can be used. In addition, recently developed highly oxygen-permeable ionomers can also be used.

Electrodes 2 are laminated on both surfaces of the electrolyte membrane 1 as described above to produce a membrane electrode assembly 3. In this lamination process, the electrodes 2 are attached to the electrolyte membranes 1 which are independently produced or prepared. Alternatively, the electrode 2 may be laminated on the release base sheet by coating the release base sheet with the catalyst ink, and then the electrolyte membrane 1 may be laminated on the electrode 2 .

The catalyst ink contains the above catalyst, proton-conducting polymer, water and/or organic solvent. As the organic solvent, protic organic solvents such as methanol, ethanol, n-propanol and butanol, and aprotic solvents such as N,N-dimethylformamide, N,N-dimethylacetamide and N-methylpyrrolidone can be used. can be done.

The content of the catalyst in the catalyst ink is preferably 1-3% by weight relative to the proton-conducting polymer. Also, the content of the proton-conducting polymer in the catalyst ink is preferably 5 to 30% by weight of the catalyst ink.

Coating of such a catalyst ink on a release substrate sheet is generally performed by a knife coater, bar coater, blade coater, spray coater, dip coater, spin coater, roll coater, die coater, curtain coater, clean printing, and the like. method. The coating amount of the catalyst ink on the release substrate sheet is not particularly limited, but may be about 5 to 100 g/m ² , preferably about 10 to 50 g/m ² in terms of solid content.

After applying the catalyst ink to the release substrate sheet, the electrode catalyst layer can be laminated on the substrate sheet by drying, for example, at 50 to 150° C. in the air.

The gas diffusion layer 4 is a layer that diffuses the reaction gas used for the electrode reaction in the surface direction of the electrolyte membrane, and is made of a porous material such as a carbon porous body such as carbon paper or carbon cloth, a metal mesh or a foam metal. etc. can be used. A water-repellent layer may be formed on the gas diffusion layer in order to obtain water repellency.

<Hot press process>
In the hot pressing process, the laminated body 20 produced in the laminated body producing process is placed on the pressing surface of the hot press machine and hot pressed by applying pressure while applying heat. Specifically, the laminate 20 is placed in a commonly used press, heated to 80 ° C. or higher, or 135 ° C. or higher, 200 ° C. or lower, or 150 ° C. or lower, and heated to 0.5 MPa or higher, or 1 MPa or higher, or 10 MPa. Press at the following pressure levels:

<Peeling process>
In the present invention, after the hot pressing step, the laminated body 20 pressed in the hot pressing step is taken out from the hot pressing machine, and from both sides of the taken out laminated body 20, a metal press plate/elastic rubber sheet/woven fabric/separate. It can include peeling off the constituent material consisting of the mold sheet and the constituent material consisting of the release sheet/metal press plate to obtain a membrane electrode gas diffusion layer assembly (peeling step).

By laminating the gas diffusion layer on the surface of the membrane electrode gas diffusion layer assembly obtained in this way, in which the gas diffusion layer is bonded to the membrane electrode assembly, on the surface where the gas diffusion layer of the membrane electrode assembly is not arranged, A membrane electrode assembly with gas diffusion layers can be produced in which gas diffusion layers are arranged on both sides of the membrane electrode assembly.

<Example 1>
As shown in FIG. 2, metal press plate 7/elastic rubber sheet 6/woven fabric 8/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5'/metal press plate 7 are arranged in this order. to produce a laminate. The following materials were used for each layer.

Metal press plate 7: SUS304
Elastic rubber sheet 6: Silicon rubber sheet fabric 8: Carbon cloth (manufactured by Toray, C6644B)
Release sheet 5: Teflon (registered trademark) sheet Gas diffusion layer 4: Carbon fiber (manufactured by Toray, TGPH-030)
Release sheet 5': polyimide film

Moreover, the membrane electrode assembly was produced by the following procedures.

32 mL of pure water was added to 5.0 g of a catalyst in which 30% by weight of platinum was supported on an acetylene black-based carbon black carrier and stirred. Ethanol was added thereto so that the volume ratio of water:ethanol was 6:4, and the mixture was stirred. DE2020 (manufactured by DuPont) as an ionomer was added thereto and stirred so that the ratio of the weight of the ionomer to the weight of the carbon support of the catalyst was 6:4. Then, it was dispersed using an ultrasonic homogenizer to prepare a catalyst ink.

This catalyst ink was applied onto a release substrate sheet made of Teflon (registered trademark) using a die coater so that the coating amount of platinum was 0.2 mg/cm ² . The coated release base sheet was placed in a hot air dryer at 80° C. and dried for 3 minutes to prepare an electrode catalyst layer.

The electrode catalyst layer was laminated on the electrolyte membrane (trade name Nafion (manufactured by DuPont) so that it was in contact with the electrode catalyst layer, and pressed at 140° C. and 4 MPa for 3 minutes to crimp the electrode catalyst layer to the electrolyte membrane. The electrode catalyst layer was transferred. Then, the release substrate sheet was peeled off from the electrode catalyst layer. The electrode catalyst layer was similarly transferred to the other surface of the electrolyte membrane to obtain a membrane electrode assembly.

<Comparative example 1>
Metal press plate 7/elastic rubber sheet 6/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5/elastic rubber sheet 6/metal press plate 7 are laminated in this order to form a laminate. made.

<Comparative example 2>
Metal press plate 7/elastic rubber sheet 6/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5/metal press plate 7 were laminated in this order to prepare a laminate.

<Comparative example 3>
Metal press plate 7/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5/elastic rubber sheet 6/metal press plate 7 were laminated in this order to prepare a laminate.

<Comparative Example 4>
Metal press plate 7/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5/metal press plate 7 were laminated in this order to prepare a laminate.

<Comparative Example 5>
Metal press plate 7/woven fabric 8/release sheet 5/membrane electrode assembly 3/gas diffusion layer 4/release sheet 5/metal press plate 7 were laminated in this order to prepare a laminate.

The laminates obtained in Example 1 and Comparative Examples 1 to 5 were placed on the press surface of a hot press and hot pressed under conditions of a temperature of 100° C., a pressure of 3 MPa, and a time of 3 minutes. The obtained membrane electrode gas diffusion layer assembly was observed for the presence or absence of delamination (bonding property) between layers and the presence or absence of cracks in the gas diffusion layer. Results are shown in the table below. In the table, with respect to bondability, ◯ means that there was no peeling, and × means that peeling was present. Regarding cracks, ◯ means no cracks, and × means that cracks occurred.

REFERENCE SIGNS LIST 1 electrolyte membrane 2 electrode 3 membrane electrode assembly 4 gas diffusion layer 5, 5' release sheet 6 elastic rubber sheet 7 metal press plate 8 woven fabric

Claims (1)

A method for manufacturing a membrane electrode gas diffusion layer assembly in which a gas diffusion layer is joined to a membrane electrode assembly, comprising:
Preparing a laminate formed by laminating metal press plate/elastic rubber sheet/woven fabric/release sheet/membrane electrode assembly/gas diffusion layer/release sheet/metal press plate in this order; is placed on the press surface of the hot press machine and subjected to hot pressing;
method including.

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