JP2007080548A - Method of manufacturing electrolyte membrane-electrode assembly and direct methanol fuel cell using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrolyte membrane-electrode assembly capable of effectively using a catalyst with little crossover of methanol, and to provide a direct methanol fuel cell using it and having high power generation characteristics. <P>SOLUTION: A catalyst layer is formed on a substrate sheet by using catalyst paste comprising catalyst particles, ion conductive resin, and a solvent, at least two times of transfer of the catalyst layer from the substrate sheet to the electrolyte membrane and/or the electrode are repeated, and the electrolyte membrane is joined to the electrode to interpose the catalyst layer between the electrolyte membrane and the electrode. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing an electrolyte membrane / electrode assembly of a polymer electrolyte fuel cell, and a direct methanol fuel cell using the same.

  A fuel cell using an electrolyte membrane for a polymer electrolyte fuel cell has a low operating temperature of 100 ° C. or lower, and its energy density is high. Therefore, it is expected to be widely put into practical use as a power source for electric vehicles and a simple auxiliary power source. . In this polymer electrolyte fuel cell, there are important elemental technologies related to electrolyte membranes, platinum-based catalysts, gas diffusion electrodes, and electrolyte membrane-electrode assemblies. Among these, electrolyte membrane-electrode assemblies include It is one of the most important technologies involved in fuel cell characteristics.

Conventionally, the following three methods are generally known as a method for producing an electrolyte membrane / electrode assembly of a polymer electrolyte fuel cell.
(1) A method of directly depositing an electrode catalyst on an electrolyte membrane (for example, see Patent Document 1: Japanese Patent Publication No. 58-47471).
(2) A method of producing an electrode sheet having catalytic ability and bonding it to an electrolyte membrane by hot pressing (hereinafter referred to as hot pressing method. For example, Patent Document 2: US Pat. No. 3,134,697, Patent Document 3: US Patent No. 3297484 and Patent Document 4: Japanese Patent Publication No. 2-7398).
(3) A method of forming a catalyst layer on each of an electrolyte membrane and an electrode and joining them (for example, Patent Document 5: Japanese Patent Laid-Open No. 2001-345110)

  However, in any method for producing the electrolyte membrane / electrode assembly of the above polymer electrolyte fuel cell, although it can be effectively used when the amount of catalyst is small, the reaction polarization is large, such as for direct methanol fuel cells, and the amount of catalyst However, when the catalyst layer is thick, cracks occur in the catalyst layer, which not only prevents the catalyst from being used effectively, but also increases the crossover of methanol.

Japanese Patent Publication No.58-47471 US Pat. No. 3,134,697 US Pat. No. 3,297,484 Japanese Patent Publication No.2-7398 JP 2001-345110 A

  The present invention has been made in view of the above circumstances, and in an electrolyte membrane / electrode assembly for a polymer electrolyte fuel cell, solves the above-mentioned problems, allows the catalyst to be used effectively, and electrolyte membrane with less methanol crossover. An object of the present invention is to provide a method for producing an electrode assembly and a direct methanol fuel cell having excellent power generation characteristics using the electrode assembly.

  As a result of intensive studies to achieve the above object, the present inventors formed a catalyst layer without cracks on the base sheet using the catalyst paste, and the catalyst layer was formed on the electrolyte membrane and / or electrode. Electrolyte membranes / electrodes useful for direct methanol fuel cells by transferring at least twice and pasting together so that the catalyst layer is interposed between the electrolyte membranes and the electrodes. It has been found that a joined body can be obtained, and has led to the present invention.

Therefore, this invention provides the manufacturing method of the electrolyte membrane electrode assembly shown below, and the fuel cell for direct methanol using the same.
Claim 1:
Forming a catalyst layer on the substrate sheet using a catalyst paste comprising catalyst particles, an ion conductive resin and a solvent, and transferring the catalyst layer from the substrate sheet to an electrolyte membrane and / or an electrode at least twice. A process for producing an electrolyte membrane / electrode assembly, wherein the electrolyte membrane and the electrode are joined such that the catalyst layer is intermediate between the electrolyte membrane and the electrode after the repetition.
Claim 2:
2. The method for producing an electrolyte membrane / electrode assembly according to claim 1, wherein the catalyst particles are a platinum group metal or a platinum-containing alloy and are previously supported on a conductive material.
Claim 3:
The method according to claim 1 or 2 membrane electrode assembly according platinum group metal or platinum-containing alloy weight, characterized in that at least 2 mg / cm ^2.
Claim 4:
A direct methanol fuel cell comprising the electrolyte membrane / electrode assembly produced by the method according to claim 1.

  According to the present invention, since the catalyst layer having a platinum group metal necessary for methanol oxidation can be provided without cracking the catalyst layer, the catalyst works effectively and has excellent power generation characteristics with less methanol crossover. An electrolyte membrane / electrode assembly can be obtained, and is particularly useful as an electrolyte membrane / electrode assembly for a direct methanol fuel cell.

  The catalyst paste used in the present invention is not particularly limited as long as it contains catalyst particles, an ion conductive resin, and a solvent, and known ones can be used. The catalyst particles are not limited as long as they have a catalytic action for methanol oxidation reaction or oxygen reduction reaction. In addition to platinum and other noble metals, iron, chromium, nickel, and alloys thereof may be used. A platinum group metal such as platinum or an alloy of platinum and ruthenium containing 25% by mass or more of platinum is desirable. Among them, platinum having a high oxygen reduction activity is preferable as the cathode catalyst, and platinum / ruthenium alloy having excellent methanol oxidizing property is preferable as the anode catalyst. The particle diameter is preferably 1 to 10 nm in view of a large specific surface area and rich catalytic activity. The catalyst particles are preferably supported on a conductive material, and the conductive material is preferably used in an amount of 0.1 to 10 parts by weight, and more preferably 0.2 to 1 part by weight with respect to 1 part by weight of the catalyst particles.

As the conductive material, carbon-based particles such as carbon black, activated carbon, graphite and the like are suitable, and fine powder particles having an average particle diameter of 10 to 1,000 nm are particularly preferably used. The material may be carbon paper, carbon woven fabric, carbon non-woven fabric, or the like. Typically, carbon black particles having a specific surface area of 20 m ² / g or more are supported with noble metal particles, particularly platinum or an alloy of platinum and ruthenium. The amount of catalyst particles supported on the conductive material is preferably catalyst particles / conductive material = 10/90 to 80/20 parts by mass.

  The ion conductive resin in the catalyst paste is a material that supports the catalyst and serves as a binder for forming the catalyst layer, and also has a role of forming a passage for ions and the like generated by the catalyst to move. As such an ion conductive resin, the same resin that can be used as the solid polymer electrolyte membrane can be used. The ion conductive resin is not particularly limited as long as it has ion conductivity and is difficult to dissolve in water and methanol, and a known one can be used. Typically, a fluorine-containing polymer is used. Examples of the resin include a skeleton and a group such as a sulfonic acid group, a carboxyl group, a phosphoric acid group, or a phosphonic group. As such an ion conductive resin, for example, commercially available products such as Nafion (manufactured by DuPont) can be used. In general, the ion conductive resin is preferably used in an amount of 0.01 to 10 parts by mass, more preferably 0.05 to 1 part by mass with respect to 1 part by mass of the catalyst particles.

  The solvent in the catalyst paste may be any solvent that dissolves or disperses the ion conductive resin and can be efficiently mixed with the catalyst particles, such as water, methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol. Alcohols, polyhydric alcohols such as ethylene glycol and glycerin, methyl ethyl ketone, dibutyl ether, dimethylformamide and the like are used. The amount of the solvent used in the catalyst paste is not particularly limited, but is preferably 1 to 100 parts by weight, more preferably 5 to 30 parts by weight with respect to 1 part by weight of the catalyst particles. The viscosity of the catalyst paste at 25 ° C. is preferably adjusted to 10 to 10,000 mPa · s from the viewpoint of coatability.

  The base sheet on which the catalyst layer is formed by applying the catalyst paste is made of polytetrafluoroethylene (PTFE), ethylene / tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), ethylene fluoride / polypropylene Fluorine films such as polymer (FEP) and polytetrafluoroethylene / perfluoroalkoxy vinyl ether (PFA), and films such as polyimide, polyester, and polyethylene can be used, and the thickness is preferably 25 to 250 μm.

  As a method of coating the catalyst paste on the substrate, a known coating method such as spray coating, wire bar coating, roll coating, gravure printing, or screen printing can be used.

  The thickness of the catalyst layer obtained by one coating is desirably 50 μm or less, and more desirably 25 μm or less. If the thickness of the catalyst layer is greater than 50 μm, cracking tends to occur. The lower limit of the thickness of the catalyst layer is desirably 1 μm or more, and particularly desirably 5 μm or more.

The amount of catalyst supported is desirably ² mg / cm ² or more in total for both the anode and the cathode, and more desirably 3 mg / cm ² or more. When the amount of catalyst supported is less than 2 mg / cm ² , the output density of direct methanol is lowered. The catalyst amount of the anode and the cathode may be equal, but it is desirable to use the anode catalyst amount more than the cathode catalyst amount. The upper limit of the catalyst loading is appropriately selected, but is preferably 20 mg / cm ² or less, particularly preferably 10 mg / cm ² or less.

  In the present invention, at least two base sheets having the catalyst layer are prepared on the anode side and the cathode side, respectively, and the catalyst layer is provided on the electrolyte membrane and / or electrode in order to obtain a desired amount of catalyst for the anode or cathode. Is transferred from the substrate sheet at least twice, and then the electrolyte membrane and the electrode are joined so that the catalyst layer is intermediate between the electrolyte membrane and the electrode to form an anode or cathode catalyst layer. In order to obtain a desired amount of catalyst with one transfer, it is necessary to make the catalyst layer thicker. In this case, however, the catalyst layer is likely to crack. For this reason, by forming a thin catalyst layer and transferring it in two or more steps, a catalyst layer free from cracks can be formed.

In order to transfer the catalyst layer formed on the substrate to the electrolyte membrane or the electrode, a heat and pressure treatment such as hot pressing is usually performed. The conditions for the heat and pressure treatment are preferably a temperature of about 25 to 150 ° C. and a pressure of 10 to 100 kg / cm ² . The electrolyte membrane and / or electrode to which the catalyst layer has been transferred may be bonded by simply bonding the electrolyte membrane and the electrode so that the catalyst layer is intermediate between the electrolyte membrane and the electrode. By combining them, an electrolyte membrane / electrode assembly can be obtained.

  In this case, the thickness of each of the anode and cathode catalyst layers is desirably 1 to 200 μm, and particularly desirably 3 to 50 μm. If the thickness is less than 1 μm, it may be difficult to form a catalyst layer having a catalyst carrying amount capable of exhibiting sufficient power generation performance. If the thickness is more than 200 μm, there is a risk that the diffusibility of the fuel decreases and the electrical resistance increases. is there.

  In addition, a well-known thing can be used as said electrolyte membrane and an electrode, For example, a polystyrene sulfonic acid, a sulfonated polybenzimidazole, a sulfonated polyetheretherketone, a perfluorocarbon type | system | group ion exchange polymer is mentioned as an electrolyte membrane. Examples of the electrode include carbon paper and carbon cloth.

  Here, FIG. 1 shows an example of an electrolyte membrane / electrode assembly obtained according to the present invention, where 1 is an electrolyte membrane / electrode assembly, 2 is an electrolyte membrane, and 3a is formed by the first transfer. The first anode catalyst layer, 3b is the second anode catalyst layer formed by the second transfer, 4a is the first cathode catalyst layer formed by the first transfer, and 4b is formed by the second transfer. The second cathode catalyst layer 5 is an anode, and 6 is a cathode.

  The direct methanol fuel cell of the present invention can have a known configuration except that the electrolyte membrane / electrode assembly obtained by the above method is used.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Example 1]
A paste prepared by mixing 10.4 g of a 5% isopropyl alcohol solution (manufactured by Aldrich) of Nafion (registered trademark of DuPont), 2 g of TEC10E50E (manufactured by Tanaka Kikinzoku) carrying 50% by mass of platinum, 8 g of water, and 8 g of 1-propanol. After coating the catalyst paste in a shape on a 50 μm-thick PTFE film (manufactured by Nichias) using a wire bar so that the platinum catalyst is 1.5 mg / cm ^2, it is heated at 60 ° C. in a hot air circulation dryer. It was dried for 30 minutes to obtain a cathode catalyst layer C1. Further, a cathode catalyst layer C2 was obtained in the same manner.
Except for using TEC10E50E (produced by Tanaka Kikinzoku Co., Ltd.) carrying 50% by mass of platinum, carbon TEC61E54 (produced by Tanaka Kikinzoku) carrying 54% by mass of platinum / ruthenium alloy was used in the same manner as the cathode catalyst layer. Anode catalyst layers A1 and A2 having a platinum / ruthenium amount of 1.5 g / cm ² were obtained.
None of the catalyst layers were cracked or cracked.

A catalyst layer C1 formed on the PTFE is placed on a Nafion 112 (manufactured by DuPont) having a thickness of 50 μm which is a solid polymer electrolyte membrane so that the catalyst layer surface is in contact with the electrolyte at 120 ° C. and a pressure of 20 kg / cm ² . After pressing for 3 minutes and releasing the pressure, the PTFE film was removed, and the first cathode catalyst layer C1 was formed on the electrolyte membrane. Further, the catalyst layer C2 formed on the PTFE is heat-pressed in the same manner so that the catalyst layer surface is in contact with the catalyst layer C1 on the electrolyte membrane, the second cathode catalyst layer C2 is transferred, and the platinum catalyst is added in total. A cathode catalyst layer loaded with 3 mg / cm ² was formed.
Similarly, the first and second anode catalyst layers A1 and A2 were transferred to the surface of the electrolyte opposite to the surface on which the cathode catalyst layer was formed to form an anode catalyst layer having a total of 3 mg / cm ² of platinum / ruthenium alloy catalyst. . Furthermore, carbon paper TGP-H-090 (manufactured by Toray Industries, Inc.) was brought into contact with both electrodes to obtain an electrolyte membrane / electrode assembly. A fuel cell was produced using this joined body, and when a methanol solution having a concentration of 1 mol / L was used as fuel and power was generated at 30 ° C. using air as an oxidizing gas, a maximum output density of 35 mW / cm ² was obtained.

[Comparative Example 1]
Using the catalyst paste prepared in Example 1, the cathode catalyst layer C3 so that the amount of platinum is 3 mg / cm ² on the PTFE used in the example, and the anode catalyst layer so that the amount of platinum / ruthenium is 3 mg / cm ^2. As a result of forming A3, cracks were remarkable in all cases.
A catalyst layer was formed on the electrolyte membrane using the catalyst layers C3 and A3 formed on the PTFE on Nafion 112 (manufactured by DuPont) having a thickness of 50 μm, which is a solid polymer electrolyte membrane, in the same manner as in the example. Although power was generated in the same manner as in Example 1, the maximum output density was as low as 25 mW / cm ² .

It is sectional drawing explaining an example of the electrolyte membrane electrode assembly produced by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electrolyte membrane * electrode assembly 2 Electrolyte membrane 3a 1st anode catalyst layer A1
3b Second anode catalyst layer A2
4a First cathode catalyst layer C1
4b Second cathode catalyst layer C2
5 Anode 6 Cathode

Claims (4)

  Forming a catalyst layer on the substrate sheet using a catalyst paste comprising catalyst particles, an ion conductive resin and a solvent, and transferring the catalyst layer from the substrate sheet to an electrolyte membrane and / or an electrode at least twice. A process for producing an electrolyte membrane / electrode assembly, wherein the electrolyte membrane and the electrode are joined such that the catalyst layer is intermediate between the electrolyte membrane and the electrode after the repetition.   2. The method for producing an electrolyte membrane / electrode assembly according to claim 1, wherein the catalyst particles are a platinum group metal or a platinum-containing alloy and are previously supported on a conductive material. The method according to claim 1 or 2 membrane electrode assembly according platinum group metal or platinum-containing alloy weight, characterized in that at least 2 mg / cm ^2. A direct methanol fuel cell comprising the electrolyte membrane / electrode assembly produced by the method according to claim 1.

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