JP5733182B2 - Manufacturing method of membrane electrode assembly - Google Patents

Description

  The present invention relates to a method for producing a membrane electrode assembly, a membrane electrode assembly, and a fuel cell.

  As a fuel cell that generates electricity by electrochemical reaction between fuel gas and oxidant gas, a membrane electrode joint in which a catalyst layer containing conductive particles carrying a catalyst and an electrolyte resin is joined to both sides of an electrolyte membrane having proton conductivity A body having a body (hereinafter also referred to as MEA (Membrane Electrode Assembly)) is known. In a fuel cell, if the strength of the catalyst layer provided in the MEA is not sufficient, cracks may occur in the catalyst layer during long-time operation, and power generation performance may be reduced. Therefore, in the technique described in Patent Document 1, the strength of the catalyst layer is improved by heat treatment.

  However, in the technique described in Patent Document 1, since the catalyst layer is bonded to the electrolyte membrane after the heat treatment, the resistance at the interface between the catalyst layer and the electrolyte membrane is increased, and the proton conductivity may be decreased.

JP 2007-95582 A JP 2005-276599 A

  In view of the above-described problems, the problem to be solved by the present invention is to provide a technique capable of achieving both improvement in the strength of the catalyst layer and improvement in proton conduction characteristics in the membrane electrode assembly.

SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.
A first aspect of the present invention is a method of manufacturing a membrane electrode assembly,
Forming a membrane electrode assembly by forming a catalyst layer containing a first electrolyte resin on an electrolyte membrane containing a second electrolyte resin ;
In an atmosphere containing water or an organic solvent, the fabricated membrane electrode assembly wherein the catalyst layer of said electrolyte membrane, in the first electrolyte resin and the second temperature higher than the glass transition point of the electrolyte resin, A step of heat-treating the catalyst layer and the electrolyte membrane by applying a pressure of 0.1 MPa or more and 0.5 MPa or less ;
It is a manufacturing method of a membrane electrode assembly provided with this.

[Application Example 1] A method for producing an electrode assembly, comprising: preparing a catalyst layer containing a first electrolyte resin; and an electrolyte membrane; and in an atmosphere containing water or an organic solvent, Joining the electrolyte membrane at a joining temperature equal to or higher than the glass transition point of the first electrolyte resin. According to this method, since the catalyst layer and the electrolyte membrane are bonded at the glass transition point or higher, the bonding strength at the interface is improved. Moreover, since it joins in the atmosphere containing water or an organic solvent, the volatilization of the water | moisture content by heat processing is suppressed, and, thereby, proton conductivity improves. Therefore, in the membrane electrode assembly, it is possible to achieve both improvement in the strength of the catalyst layer and improvement in proton conduction characteristics.

Application Example 2 In the manufacturing method according to Application Example 1, the electrolyte membrane includes a second electrolyte resin, and the bonding temperature is a glass transition point of the first electrolyte resin and the second electrolyte resin. This is the manufacturing method. According to this method, since the entanglement and crystallization at the interface between the catalyst layer and the electrolyte membrane are promoted, the bonding strength between the catalyst layer and the electrolyte membrane can be improved.

[Application Example 3] The manufacturing method according to Application Example 1 or Application Example 2, wherein the glass transition point is not less than 110 degrees and not more than 140 degrees, and the bonding temperature is not more than 200 degrees. According to this method, the strength of the catalyst layer including an electrolyte resin having a glass transition point of 110 degrees or more and 140 degrees or less can be improved, and decomposition of the electrolyte resin can be suppressed.

[Application Example 4] The manufacturing method according to any one of Application Examples 1 to 3, wherein the catalyst layer and the electrolyte membrane are joined at a pressure of 0.1 MPa to 0.5 MPa. A manufacturing method. According to this method, since the catalyst layer and the electrolyte membrane are joined at a relatively low pressure, deformation of the catalyst layer and the electrolyte membrane can be suppressed.

  In addition to the above-described structure as a method for manufacturing a membrane electrode assembly, the present invention provides a membrane electrode assembly, a fuel cell including the membrane electrode assembly, a stationary vehicle installed in a mobile vehicle, a building, or the like including the fuel cell. It can also be configured as a power generator.

It is a fragmentary sectional view showing a schematic structure of a fuel cell provided with MEA manufactured by a manufacturing method as one embodiment of the present invention. It is a flowchart of the manufacturing method of MEA. It is a figure explaining the example which heat-processes in steps. It is a figure explaining the effect by this embodiment. It is a figure which shows the measurement result of a cell voltage.

A. Fuel cell configuration:
FIG. 1 is a partial cross-sectional view showing a schematic configuration of a fuel cell 100 including an MEA 10 manufactured by a manufacturing method according to an embodiment of the present invention. The fuel cell 100 is a solid polymer fuel cell that generates electric power by receiving supply of a fuel gas (for example, hydrogen) and an oxidant gas (for example, oxygen) as reaction gases. The fuel cell 100 has a stack structure in which a plurality of single cells 30 are stacked.

  The single cell 30 includes an MEA 10 having an electrolyte membrane 11 and an anode side catalyst layer 12a and a cathode side catalyst layer 12c formed on both surfaces of the electrolyte membrane 11, respectively. An anode-side gas diffusion layer 22a is joined to one surface of the MEA 10, and a cathode-side gas diffusion layer 22c is joined to the other surface. 22c is adjacent to the cathode separator 33c. A fuel gas channel 34a is formed between the anode side gas diffusion layer 22a and the anode side separator 33a, and an oxidant gas channel 34c is formed between the cathode side gas diffusion layer 22c and the cathode side separator 33c. Yes.

  The electrolyte membrane 11 can be constituted by a thin film of a polymer having proton conductivity (hereinafter also referred to as electrolyte resin), for example, a fluorine resin ion exchange membrane. More specifically, Nafion (registered trademark) or the like can be used for the electrolyte membrane 11.

  The anode-side catalyst layer 12 a and the cathode-side catalyst layer 12 c contain conductive particles such as carbon particles carrying a catalyst such as platinum or a platinum alloy and an electrolyte resin, and function as electrodes of the fuel cell 100. Hereinafter, the anode side catalyst layer 12a and the cathode side catalyst layer 12c are also collectively referred to as “catalyst layer 12”.

  The anode side gas diffusion layer 22a and the cathode side gas diffusion layer 22c are formed of a material having gas permeability and conductivity. As a material of the anode side gas diffusion layer 22a and the cathode side gas diffusion layer 22c, for example, a carbon-based porous body such as carbon paper or carbon cloth, or a metal porous body such as a metal mesh or a foam metal can be used. Hereinafter, the anode-side gas diffusion layer 22a and the cathode-side gas diffusion layer 22c are collectively referred to as “diffusion layer 22”.

  The anode side separator 33a and the cathode side separator 33c are formed of members having gas barrier properties and electronic conductivity. In the present embodiment, the anode-side separator 33a and the cathode-side separator 33c are formed of dense carbon that has been made to be gas impermeable by compressing carbon. The anode side separator 33a and the cathode side separator 33c can be formed of a metal member such as press-formed stainless steel in addition to a carbon member such as dense carbon.

The fuel gas flow path 34a is formed between the anode side gas diffusion layer 22a and the anode side separator 33a, and the oxidant gas flow path 34c is formed between the cathode side gas diffusion layer 22c and the cathode side separator 33c. The fuel gas channel 34a is a hydrogen (H ₂ ) gas channel, and the oxidant gas channel 34c is an oxygen (O ₂ ) gas channel.

B. MEA Manufacturing Method FIG. 2 is a flowchart of a method for manufacturing the MEA 10. First, the electrolyte membrane 11 and catalyst ink which are materials of MEA10 are prepared (step S10). In this embodiment, the electrolyte membrane 11 uses a DuPont Nafion membrane NR211. The catalyst ink is prepared by mixing a catalyst carrier 16 in which platinum 13 is supported by carbon particles and an electrolyte solution (DuPont Nafion solution D2020) containing an electrolyte resin 17. In this embodiment, the electrolyte resin (corresponding to the “second electrolyte resin” in the present application) forming the electrolyte membrane 11 and the electrolyte resin (corresponding to the “first electrolyte resin” in the present application) included in the catalyst ink are Both are perfluorosulfonic acid electrolyte resins.

After the electrolyte membrane 11 and the catalyst ink are prepared, the anode side catalyst layer 12a is applied to one surface of the electrolyte membrane 11, and the cathode side catalyst layer 12c is applied to the other surface (step S20). In the present embodiment, the catalyst layer 12 is formed by applying catalyst ink to the electrolyte membrane 11 by a spray method. Basis weight of the platinum 13, anode catalyst layer 12a side is 0.2 mg / cm ^2, a cathode catalyst layer 12c side is 0.4 mg / cm ^2.

  Next, the electrolyte membrane 11 and the catalyst layer 12 are joined at a temperature equal to or higher than the glass transition point of the electrolyte resin 17 in a water vapor atmosphere (step S30). Generally, the glass transition point of the perfluorosulfonic acid electrolyte resin 17 is 110 degrees or more and 140 degrees or less. Hereinafter, the heat treatment for joining the electrolyte membrane 11 and the catalyst layer 12 at a temperature equal to or higher than the glass transition point is also referred to as “joining heat treatment”. In this bonding heat treatment, the relative humidity is 30% to 80%, and the bonding pressure between the catalyst layer 12 and the electrolyte membrane 11 is 0.1 MPa or more and 0.5 MPa or less. This pressure is lower than the joining pressure (approximately 1 MPa or more) at the time of manufacturing a general MEA.

  Since the entanglement and crystallization proceed when the electrolyte resin 17 reaches the glass transition point or higher, the strength of the catalyst layer 12 including the electrolyte resin 17 is improved by forming the MEA 10 by the above-described method. Moreover, in this embodiment, since the upper limit of the temperature of joining heat processing was 200 degree | times, decomposition | disassembly of a sulfonic acid group can be suppressed. Therefore, a proton conduction path can be secured.

  3 and 4 are diagrams for explaining the effect of this embodiment. FIG. 3 shows a case where heat treatment is performed in stages, and FIG. 4 shows a case where bonding heat treatment is performed according to the present embodiment. In the present embodiment, the catalyst layer 12 is formed on the electrolyte membrane 11 (step S20), and then a bonding heat treatment is performed (step S30). As shown in FIG. 3, for example, after the catalyst layer 12 is formed on the diffusion layer 22 and the first heat treatment is performed at a temperature exceeding the glass transition point (FIG. 3A), the diffusion layer including the catalyst layer 12 is provided. The strength of the catalyst layer 12 can also be improved by sandwiching the electrolyte membrane 11 at 22 and performing the second heat treatment (FIG. 3B). However, when heat treatment is performed in such a stepwise manner, the crystallization of the electrolyte resin 17 proceeds in the catalyst layer 12 by the first heat treatment. As a result, the electrolyte membrane 11 and the catalyst layer 12 that has already been crystallized are joined, so that the resistance at the interface between the electrolyte membrane 11 and the catalyst layer 12 is increased as shown in FIG. The power generation performance will be reduced.

  On the other hand, in the present embodiment, the above-described bonding heat treatment is performed after the catalyst layer 12 is formed on the electrolyte membrane 11. Therefore, as shown in FIG. 4, since crystallization proceeds integrally at the interface between the electrolyte membrane 11 and the catalyst layer 12, an increase in the interface resistance between the electrolyte membrane 11 and the catalyst layer 12 can be suppressed. Further, in the present embodiment, since the entanglement and crystallization proceed integrally at the interface between the electrolyte membrane 11 and the catalyst layer 12 by the bonding heat treatment described above, the electrolyte resin 17 included in each of the electrolyte membrane 11 and the catalyst layer 12 is It will be intertwined. Therefore, sufficient bonding strength can be obtained even at a pressure lower than the bonding pressure (approximately 1 MPa or more) at the time of manufacturing a general MEA. Therefore, deformation of the catalyst layer 12 and the electrolyte membrane 11 at the time of pressure bonding can be suppressed. In this embodiment, the above-described bonding heat treatment is performed in a steam atmosphere. Therefore, in the electrolyte membrane 11 and the catalyst layer 12, volatilization of moisture due to the bonding heat treatment is suppressed, and a proton conduction path can be secured. Therefore, it is possible to achieve both improvement in the strength of the catalyst layer 11 and improvement in proton conduction characteristics.

C. Single Cell Power Generation Test In order to investigate the effect of the above-described bonding heat treatment, MEA1 that did not perform the bonding heat treatment in step S30 in the above-described manufacturing method and MEA2 that performed the bonding heat treatment without supplying water vapor and an organic solvent in step S30 And MEA3 produced by step S10 to step S30 was prepared. The joining temperature in step S30 of MEA2 and MEA3 is 160 degrees, and the joining pressure is 0.39 MPa. Next, single cells 1, 2, and 3 were prepared using these MEAs 1, 2, and 3, and a power generation test was performed. In manufacturing the single cells 1, 2, and 3, in step S20, the MEA 1, 2, and 3 are both sandwiched between the catalyst layers 12 by the diffusion layer 22 and pressed at a pressure of 100 degrees and 1.2 MPa for 4 minutes. . Since this pressure bonding is performed below the glass transition point of the electrolyte resin 17, crystallization of the electrolyte resin 17 has not progressed.

FIG. 5 is a diagram showing measurement results of cell voltages when the single cell 1, single cell 2, and single cell 3 are generated at a current density of 0.2 A / cm ² . The measurement was performed at a cell temperature of 80 degrees and in a non-humidified state. Compared with the single cell 1 that was not subjected to the bonding heat treatment in step S30, the cell voltage of the single cell 3 that was subjected to the bonding heat treatment by supplying water vapor above the glass transition point increased by 18 mV. On the other hand, the cell voltage of the single cell 2 that was subjected to the bonding heat treatment without supplying water vapor above the glass transition point was 16 mV lower than the single cell 1 that was not subjected to the bonding heat treatment.

  The unit cell 2 is not supplied with water vapor during the bonding heat treatment in step S30. Therefore, in the single cell 2, the moisture contained in the catalyst layer 12 is volatilized in the heat treatment exceeding the glass transition point, and the proton conduction path is reduced. As a result, the power generation performance is lowered as compared with the single cell 1. it is conceivable that. On the other hand, since the single cell 3 is bonded at a glass transition point or higher in a water vapor atmosphere, a proton conduction path can be secured, and power generation performance is considered to be improved as compared with the single cell 1. From the above power generation test, it was confirmed that the MEA produced in this embodiment has improved proton conduction characteristics.

D. Variation:
As mentioned above, although one Embodiment of this invention was described, this invention is not limited to such Embodiment, A various structure can be taken in the range which does not deviate from the meaning.

D1. Modification 1:
In the above-described embodiment, the electrolyte resin 17 forming the electrolyte membrane 11 and the electrolyte resin 17 included in the catalyst ink are the same, but different electrolyte resins may be used. In this case, if the heat treatment is performed at a temperature exceeding the glass transition point of both the electrolyte resin 17 forming the electrolyte membrane 11 and the electrolyte resin 17 included in the catalyst ink, the electrolyte membrane 11 and the catalyst are the same as in the above embodiment. It is possible to obtain the MEA 10 having a reduced interface resistance at the interface with the layer 12 and a high bonding strength between the electrolyte membrane 11 and the catalyst layer 12.

D2. Modification 2:
In step S20 of the above-described embodiment, the catalyst layer 12 is coated with the catalyst ink on the electrolyte membrane 11 by the spray method, but the catalyst layer 12 is coated on the electrolyte membrane 11 by the doctor blade method, the screen printing method, or the like. May be. Further, the catalyst layer 12 is not directly applied to the electrolyte membrane 11, but the sheet is peeled after the electrolyte membrane 11 is sandwiched with a transfer sheet coated with catalyst ink and heat-treated at a temperature lower than the glass transition point. Thus, it may be formed on both sides of the electrolyte membrane 11. The bonding heat treatment may be performed after the catalyst ink is applied to the diffusion layer 22 and then the electrolyte membrane 11 is held between the diffusion layers 22. Further, the bonding heat treatment may be performed simultaneously with the holding of the electrolyte membrane 11 by the transfer sheet coated with the catalyst ink or the diffusion layer 22.

D3. Modification 3:
In the above-described embodiment, platinum 13 is used as the catalyst. Examples of the catalyst include noble metals such as gold, silver, ruthenium, rhodium, palladium, osmium, iridium, iron, nickel, manganese, cobalt, chromium, and copper. Base metals such as zinc, molybdenum, tungsten, germanium and tin, alloys of these noble metals and base metals, and compounds such as metal oxides and metal complexes can also be employed.

D4. Modification 4:
In the above-described embodiment, carbon particles carry platinum 13 as a catalyst, but instead of carbon particles, for example, carbon materials such as carbon black, carbon nanotubes, carbon nanofibers, and silicon carbide are representative. The carbon compound etc. which are made can be used.

D5. Modification 5:
In the above-described embodiment, Nafion is used as the electrolyte membrane 11. However, as the electrolyte membrane 11, for example, other fluorine-based sulfonic acid membranes such as Aciplex (registered trademark) and Flemion (registered trademark) are used. Also good.

D6. Modification 6:
In the above-described embodiment, the bonding heat treatment between the electrolyte membrane 11 and the catalyst layer 12 is performed in a water vapor atmosphere, but may be performed in an organic solvent atmosphere or an atmosphere containing water and an organic solvent. For example, ethanol or the like can be used as the organic solvent.

DESCRIPTION OF SYMBOLS 11 ... Electrolyte membrane 12 ... Catalyst layer 12a ... Anode side catalyst layer 12c ... Cathode side catalyst layer 13 ... Platinum 16 ... Catalyst support 17 ... Electrolyte resin 22 ... Diffusion layer 22a ... Anode side gas diffusion layer 22c ... Cathode side gas diffusion layer 30 ... Single cell 33a ... Anode side separator 33c ... Cathode side separator 34a ... Fuel gas channel 34c ... Oxidant gas channel 100 ... Fuel cell

Claims (2)

A method for producing a membrane electrode assembly, comprising:
Forming a membrane electrode assembly by forming a catalyst layer containing a first electrolyte resin on an electrolyte membrane containing a second electrolyte resin ;
In an atmosphere containing water or an organic solvent, the fabricated membrane electrode assembly wherein the catalyst layer of said electrolyte membrane, in the first electrolyte resin and the second temperature higher than the glass transition point of the electrolyte resin, A step of heat-treating the catalyst layer and the electrolyte membrane by applying a pressure of 0.1 MPa or more and 0.5 MPa or less ;
The manufacturing method of a membrane electrode assembly provided with this. A method of manufacturing a mounting serial to claim 1,
The glass transition point is 110 degrees or more and 140 degrees or less, and the temperature is 200 degrees or less.

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