JP5233286B2 - Manufacturing method of membrane electrode assembly - Google Patents

Description

  The present invention relates to a method for manufacturing a membrane electrode assembly constituting a fuel cell.

  A solid polymer fuel cell is known as one form of the fuel cell. Solid polymer fuel cells have lower operating temperatures (about -30 ° C to 100 ° C) compared to other types of fuel cells, are low in cost, and can be made compact. ing.

  As shown in FIG. 4, the polymer electrolyte fuel cell has a membrane electrode assembly (MEA) 4 as a main component, and is sandwiched between separators 6 and 6 each having a gas flow path 5 to provide a single unit. One fuel cell A called a cell is formed. The membrane electrode assembly 4 has a structure in which anode-side and cathode-side catalyst layers 2, 2 are laminated on both surfaces of a solid electrolyte resin membrane 1 that is an ion exchange membrane. The catalyst layer 2 is formed of a catalyst mixture including an electrolyte resin and a catalyst-carrying conductor. Platinum-based metals are mainly used for the catalyst, and carbon powder is mainly used for the conductor supporting the catalyst. Usually, diffusion layers 3 and 3 made of carbon paper, carbon cloth, or the like are formed on the outer surface of the catalyst layer 2, and the catalyst layer 2, the diffusion layer 3, and the electrolyte membrane 1 may be collectively referred to as a membrane electrode assembly.

  For the lamination of the electrolyte membrane 1 and the catalyst layer 2, for example, the catalyst layer 2 and the electrolyte membrane 1 prepared in a sheet shape are laminated and hot-pressed, or the electrolyte membrane 1 is coated with a catalyst ink and dried. This procedure is usually performed.

  In order to obtain a membrane electrode assembly having higher performance and higher durability, it is desired that a high interface bond is obtained on the laminated surface of the electrolyte membrane and the catalyst layer. , Forming irregularities on the surface of the solid polymer electrolyte membrane by appropriate means, pressing the catalyst layer on the irregular surface, causing the surface irregularities of the electrolyte membrane to penetrate into the surface of the catalyst layer, and bringing them into close contact with each other Is described. In Patent Document 2, carbon paper used as a diffusion layer (electrode substrate) is heat-pressed against a laminate of a solid polymer electrolyte membrane and a catalyst layer, and carbon is bonded to the interface between the electrolyte membrane and the catalyst layer. It is described that unevenness due to the unevenness of paper is formed to obtain high adhesion.

JP 2007-26836 A Japanese Patent Laid-Open No. 9-63622

  As described in Patent Documents 1 and 2, by making the bonding interface between the electrolyte membrane and the catalyst layer an uneven surface, the adhesion between the two becomes good and a high interface bond is obtained. A membrane electrode assembly can be expected to be obtained. However, in both cases, the electrolyte membrane and the catalyst layer in a non-fluid state are integrated by pressure bonding directly or via carbon paper as an electrode substrate, and the electrolyte membrane or catalyst layer is forcedly deformed. Deterioration due to mechanical stress accompanying processing is unavoidable. Moreover, the other side cannot follow one uneven | corrugated shape, and a fine clearance gap may remain in the interface of both. Such a gap reduces the interface bond strength and causes a decrease in the power generation function of the membrane electrode assembly.

  The present invention has been made in view of the circumstances as described above, and makes the interface bonding between the electrolyte membrane and the catalyst layer more complete without gaps, thereby providing a high-performance and high-durability membrane. It aims at providing the manufacturing method of a membrane electrode assembly which can obtain an electrode assembly.

  The present invention relates to a method for manufacturing a membrane electrode assembly in which an electrolyte membrane and a catalyst layer are joined to each other, wherein an uneven shape is formed on the joining surface of either the electrolyte membrane or the catalyst layer, and the other is melted. It is bonded to the bonding surface as a state or a solution state, and the capillarity generated on the other side in the molten state or the solution state at the bonding interface is used as one means for bonding, and both are integrated. And

  In the above manufacturing method, the other in a molten state or a solution state enters into the concavo-convex shape formed on one joint surface by utilizing capillary action. As a result, the two are integrated with no gap at the bonding interface. Further, since there is no forced deformation processing, mechanical stress is not applied, and the member on the side where the uneven shape is formed on the joint surface does not deteriorate. Thereby, a membrane electrode assembly with high performance and high durability can be obtained.

  In the manufacturing method according to the present invention, preferably, the joining is performed in a state where the viscosity of the member in a molten state or a solution state is 0.01 to 10000 PaS, more preferably 0.1 to 1000 PaS. If the viscosity of the catalyst layer material or the electrolyte material in the molten state or the solution state is in the above range with respect to the membrane-like electrolyte membrane or catalyst layer constituting the conventionally known membrane electrode assembly, the capillary tube Intrusion into the uneven shape due to the phenomenon proceeds reliably. Those having a viscosity of less than 0.01 are not preferable because they penetrate beyond the uneven portion and further into the interior, and those having a viscosity exceeding 10,000 PaS cannot obtain a sufficient capillary effect.

  In the manufacturing method according to the present invention, preferably, the irregularities are irregularities on the order of μm. Due to the unevenness in the size range, the penetration of the member on the side in the molten state or the solution state by capillary action is further ensured.

  In the production method according to the present invention, in a more preferred aspect, the member forming the irregularities is a catalyst layer, and the member in a molten state or a solution state is an electrolyte membrane. In that case, the electrolyte membrane may be a reinforced membrane type electrolyte membrane in which a porous reinforcing membrane is impregnated with an electrolyte resin.

In the production method according to the present invention, the materials for the electrolyte membrane and the catalyst layer constituting the membrane electrode assembly are not limited, and conventionally known materials for forming the electrolyte membrane and the catalyst layer can be appropriately selected and used. The electrolyte resin constituting the electrolyte membrane may be either an H-type electrolyte resin whose polymer chain end is —SO ₃ H or an F-type electrolyte resin whose polymer chain end is —SO ₂ F. When the F-type electrolyte resin is used, the membrane electrode assembly is subjected to a hydrolysis treatment after the joining treatment to impart proton conductivity. As described above, when a reinforced membrane electrolyte membrane is used, for example, a stretched porous PTFE membrane is suitable as the reinforced membrane. As the material of the catalyst layer, a catalyst mixture containing the above-described electrolyte resin and a catalyst-carrying conductor is used. Platinum-based metals are mainly used for the catalyst, and carbon powder is mainly used for the conductor supporting the catalyst.

  The method of forming the uneven shape on the joint surface in either one of the electrolyte membrane and the catalyst layer is arbitrary, for example, a method of applying a material to the uneven surface and drying, an aspect of pressing the uneven shape on the existing film surface, Examples include a method of mechanically cutting an existing film surface. In any case, the irregularities to be formed are irregularities on the order of μm, preferably, irregularities having a depth and pitch of about 1 to 8 μm.

  According to the present invention, it is possible to obtain a membrane electrode assembly having no interfacial gap at the laminated interface between the electrolyte membrane and the catalyst layer and having a high interface bonding force. Therefore, the membrane electrode assembly manufactured by the manufacturing method of the present invention has high power generation performance and high durability.

  Hereinafter, the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a schematic diagram for explaining an example of a method for producing a membrane / electrode assembly according to the present invention. FIGS. 2 (a) and 2 (b) show two modes for producing a membrane / electrode assembly by a conventional method. It is a schematic diagram shown.

  In FIG. 1, reference numeral 10 denotes a catalyst layer, which is obtained by, for example, applying a catalyst mixture containing an ink-like or paste-like electrolyte resin and a catalyst-carrying conductor on a substrate by a spray method or the like and drying it. On the surface to be a joint surface with the electrolyte membrane, a large number of irregularities 11 on the order of μm, preferably having a depth and pitch of about 1 to 8 μm, by means such as pressing an irregularity mold on the film surface. Concavities and convexities 11 are formed. 20 is an electrolyte resin or electrolyte resin precursor for an electrolyte membrane, and is an H-type electrolyte resin that is in a solution state by adjusting the viscosity with a solvent, or an F-type electrolyte resin (electrolyte resin) that has been melted by heating. Precursor).

  When manufacturing a membrane electrode assembly, as shown in FIG. 1 (a), the two are opposed to each other, and as shown in FIG. 1 (b), the F-type electrolyte resin is in the molten state or the solution state. Alternatively, the surface of the catalyst layer 10 on which the irregularities 11 are formed is lightly pressed against the H-type electrolyte resin 20. As a result, as shown in an enlarged view in FIG. 1C, the F-type electrolyte resin or the H-type electrolyte resin 20 in a molten state or a solution state enters into the irregularities 11 by capillary action, Are joined together with no gap at the interface.

  By performing a drying process on the laminate when using an H-type electrolyte resin solution, or by performing a drying process after a hydrolysis process when using a molten F-type electrolyte resin. A membrane electrode assembly is manufactured. In the membrane electrode assembly produced in this way, the bonding interface between the electrolyte membrane and the catalyst layer is a strong bond with no gap.

  FIG. 2A shows a case where the catalyst layer 10 manufactured as described above and the electrolyte membrane 20a manufactured in advance are stacked and stacked and integrated by pressing. In this manufacturing method, when the concavo-convex shape 11 is a fine pitch on the order of μm, the electrolyte membrane 20a is not fully adapted to the concavo-convex, and the gap 12 is generated at the interface. Moreover, it is inevitable that the pressing causes damage to both the catalyst layer 10 and the electrolyte membrane 20a.

  In FIG. 2B, the catalyst layer ink described with reference to FIG. 1A is applied to the uneven surface side of the electrolyte membrane 20b that has a large number of unevenness 21 on the surface and is manufactured in advance, and the catalyst layer 10 The case of stacking the layers is shown. In this case as well, when the uneven shape 21 has a fine pitch on the order of μm, the catalyst layer ink does not become familiar with the unevenness, and a gap 12 is also generated at the interface.

  As described above, in the manufacturing method according to the conventional method shown in FIGS. 2A and 2B, high interfacial strength is not obtained on the laminated surface of the electrolyte membrane and the catalyst layer, and the life of the membrane electrode assembly is extended. In contrast, in the method of the present invention shown in FIG. 1, a membrane electrode assembly having a high performance and a long life having a strong interface bond can be obtained.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
[Example 1]
1) A PTFE tape with a thickness of 18 mm and 50 mm x 50 mm produced by bead extrusion from PTFE fine powder and rolled by the usual method is set in a multiaxial stretching machine, heated to 30 times, and stretched. A 0.020 mm porous membrane was obtained.
2) On both surfaces of the porous membrane obtained in 1), an electrolyte resin precursor polymer (F-type electrolyte resin) (polymer chain terminal is —SO ₂ F, polymer NE111F manufactured by DuPont) is extruded using an extrusion molding machine. A thin film prepared to a thickness of 12 μm was attached.
3) The membrane was impregnated at a pressure of 5 kg / cm ^{2 in} a 230 ° C. vacuum environment to obtain a membrane.
4) Each of the cathode catalyst layer and the anode catalyst layer coated on the PTFE sheet by the doctor blade method is pressed with a Ni mold having irregularities formed on the surface at a depth of 5 μm at a pitch of 5 μm. Unevenness was formed on the surface.
5) The cathode catalyst layer and the anode catalyst layer whose surfaces are roughened are bonded to both surfaces of the film obtained in 3) and heated by a low pressure hot press (0.1 kg / cm ² or less, 250 ° C.). The membrane electrolyte resin precursor polymer was dissolved (heat melted), and the membrane and the catalyst layer were fixed to produce a membrane electrode assembly. The dissolved (heat-melted) electrolyte resin precursor polymer has a viscosity of about 800 PaS.
6) After the membrane electrode assembly was hydrolyzed with a mixed solution of 1 mol / L sodium hydroxide aqueous solution and alcohol, the end of the polymer chain was converted to acid form (-SO ₃ H) with 1 mol / L sulfuric acid aqueous solution.
7) Washed with ion-exchanged pure water and dried to obtain a membrane electrode assembly.

[Example 2]
1) The same porous membrane as in Example 1, and a cathode catalyst layer and an anode catalyst layer having a rough surface were prepared.
2) An electrolyte resin solution in which the porous membrane is bonded to the uneven surface of the cathode catalyst layer or the anode catalyst layer and the viscosity is adjusted to 0.5 PaS (the polymer chain end is —SO ₃ H, solution DE2020 manufactured by DuPont). ) Is cast from the porous membrane, and the anode catalyst layer or the cathode catalyst layer is immediately superimposed on the porous membrane side to impregnate the electrolyte resin into the porous membrane and fill the irregular surface. Went.
3) The laminated body obtained in 2) was dried at 80 ° C. for 30 minutes to obtain a membrane electrode Tsuyoshi rigid body.

[Comparative Example 1]
1) A PTFE tape with a thickness of 18 mm and 50 mm x 50 mm produced by bead extrusion from PTFE fine powder and rolled by the usual method is set in a multiaxial stretching machine, heated to 30 times, and stretched. A 0.020 mm porous membrane was obtained.
2) On both surfaces of the porous membrane obtained in 1), an electrolyte resin precursor polymer (F-type electrolyte resin) (polymer chain terminal is —SO ₂ F, polymer NE111F manufactured by DuPont) is extruded using an extrusion molding machine. A thin film prepared to a thickness of 12 μm was attached.
3) The membrane was impregnated at a pressure of 5 kg / cm ^{2 in} a 230 ° C. vacuum environment to obtain a membrane.
4) After the membrane was hydrolyzed with a mixed solution of 1 mol / L sodium hydroxide aqueous solution and alcohol, the end of the polymer chain was converted to acid form (—SO ₃ H) with 1 mol / L sulfuric acid aqueous solution.
5) Washed with ion-exchanged pure water and dried to obtain an electrolyte membrane.
6) A cathode catalyst layer and an anode catalyst layer having a rough surface similar to those of Examples 1 and 2 were prepared.
7) The cathode catalyst layer and the anode catalyst layer having an uneven surface are bonded to both surfaces of the electrolyte membrane obtained in 5), and hot pressing (5 kg / cm ² , 150 ° C.) is performed to obtain a membrane electrode assembly. Produced.

[Comparative Example 2]
1) A PTFE tape with a thickness of 18 mm and 50 mm x 50 mm produced by bead extrusion from PTFE fine powder and rolled by the usual method is set in a multiaxial stretching machine, heated to 30 times, and stretched. A 0.020 mm porous membrane was obtained.
2) On both surfaces of the porous membrane obtained in 1), an electrolyte resin precursor polymer (F-type electrolyte resin) (polymer chain terminal is —SO ₂ F, polymer NE111F manufactured by DuPont) is extruded using an extrusion molding machine. A thin film prepared to a thickness of 12 μm was attached.
3) The membrane was impregnated at a pressure of 5 kg / cm ^{2 in} a 230 ° C. vacuum environment to obtain a membrane.
4) The film was pressed with a Ni mold having irregularities formed on the surface at a pitch of 5 μm at a depth of 5 μm to form irregularities on the film surface.
5) The membrane was hydrolyzed with a mixed solution of a 1 mol / L sodium hydroxide aqueous solution and an alcohol, and then the polymer chain end was converted to an acid form (—SO ₃ H) with a 1 mol / L sulfuric acid aqueous solution.
6) Washed with ion-exchanged pure water and dried to obtain an electrolyte membrane.
7) A membrane electrode assembly was obtained by applying and drying the catalyst layer ink on the surface of the electrolyte membrane.

[Evaluation Test 1]
The cross sections of the membrane electrode assemblies of each Example and Comparative Example were cut, and the interface between the electrolyte membrane and the catalyst layer was observed with an electron microscope. As a result, in Comparative Example 1 and Comparative Example 2, it was confirmed that there was a gap partially at the membrane / catalyst layer interface. On the other hand, in Example 1 and Example 2, a similar gap could not be confirmed. This shows that the interfacial bondability between the electrolyte membrane and the catalyst layer is improved by producing a membrane electrode assembly by the method of the present invention.

[Evaluation Test 2]
Next, the battery performance was evaluated in the membrane electrode assemblies of the examples and comparative examples. The results are shown in FIG. As shown in FIG. 3, compared to Examples 1 and 2, both Comparative Examples 1 and 2 have a large voltage drop that seems to be caused by flatting at a portion where the current density is large. In Comparative Examples 1 and 2, this drop is presumed to be caused by the presence of a gap at the interface, where water generated by power generation accumulated therein, thereby inhibiting power generation.

[Evaluation]
From the results of the evaluation tests 1 and 2, the membrane electrode assembly made by the production method of the present invention has improved bondability at the interface between the electrolyte membrane and the catalyst layer than the membrane electrode assembly of the comparative example, and the battery performance It turns out that it improves. By using the membrane electrode assembly according to the present invention, a battery having high performance and excellent durability can be provided.

Schematic diagram illustrating an example of a method for producing a membrane electrode assembly according to the present invention Schematic explaining two aspects when manufacturing a membrane electrode assembly by a conventional method. The graph which shows the electric power generation performance of the fuel cell using the membrane electrode assembly manufactured by this invention, and the fuel cell using the membrane electrode assembly manufactured by the conventional method. The figure for demonstrating a fixed polymer fuel cell.

Explanation of symbols

  10 ... catalyst layer, 11 ... micrometer order irregularities formed on the catalyst layer, 20 ... electrolyte resin for electrolyte membrane (H-type electrolyte resin in a solution state by adjusting the viscosity with a solvent) or electrolyte resin precursor (heating) F-type electrolyte resin in a molten state), 12, 22 ... gaps formed at the interface

Claims (2)

A method for producing a membrane electrode assembly formed by joining an electrolyte membrane and a catalyst layer, wherein a concavo-convex shape is formed on the joint surface on the catalyst layer side, and the joint surface on the electrolyte membrane side is melted or in a solution state in it and so viscosity is joined to the joint surface of the catalyst layer side as the state of 0.1～1000PaS, the capillary phenomenon occurring in the catalyst layer side of the electrolyte membrane side in the state of the molten state or in solution in a bonding interface A method of manufacturing a membrane electrode assembly, wherein the two are integrated as one means for bonding. 2. The method for producing a membrane electrode assembly according to claim 1 , wherein the unevenness of the joint surface on the catalyst layer side is unevenness on the order of μm.

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