JP2007258031A - Manufacturing method for polymer electrolyte membrane-electrode assembly - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method which allows a porous electrode layer (catalyst support) for a fuel cell to be formed on an industrial scale as a manufacturing method for a polymer electrolyte membrane-electrode assembly. <P>SOLUTION: The polymer electrolyte membrane-electrode assembly is manufactured in such a method that a carbon material is dispersed in a hydrocarbon-based solvent with added basic high-molecular dispersant, a voltage is applied using a polymer electrolyte membrane as a positive electrode in this solvent, and a carbon material thin film is attached on a surface of a positive electrode material. On applying a voltage using a coating material as a positive electrode to attach the carbon material on the surface of the positive electrode material, the carbon material is dispersed in a hydrocarbon-based solvent with added basic high-molecular dispersant to improve the dispersibility of the carbon material in the solvent. This can lead to formation of the carbon material thin film with superior absorption performance, that is, increased amount of absorption. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer electrolyte membrane-electrode assembly (MEA). More specifically, the present invention relates to a method for producing a polymer electrolyte membrane-electrode composite formed with a carbon material thin film electrode that is effectively used as an electrode catalyst layer of a fuel cell.

The electrode catalyst layer of the fuel cell is the main part where the reaction of the fuel cell occurs, and is formed from a catalyst held on a carbon material, a solution of a polymer electrolyte membrane, and a binder. A method of directly applying an electrode catalyst layer to an electrolyte membrane is known. More specifically, a thin film is formed using a paste in which the catalyst-supporting carbon that forms the electrode catalyst layer is dispersed in a polymer resin solution that is the same as the solid polymer electrolyte membrane, and selectively transmits hydrogen ions. A method for forming an electrode catalyst layer in close contact with a solid polymer electrolyte membrane has been proposed. In this method, a polymer resin solution having the same quality as the solid polymer electrolyte membrane is used for preparing the paste dispersion, and the basic functional group in which the catalyst-carrying carbon is bonded to the aromatic ring on the surface of the polymer resin solution is positive in the polymer resin solution. It is necessary to disperse in a state of transition to ions.
Japanese Patent No. 3736545

  Further, a cell for a fuel cell is generally manufactured as a membrane / electrode assembly (MEA) by thermally compressing a fuel electrode and an air electrode on both sides of a polymer electrolyte membrane. In practice, a method of forming an electrode catalyst layer into a sheet and simultaneously hot pressing it onto a polymer electrolyte membrane is generally performed, but at the time of forming the electrode catalyst layer by hot pressing or heat roll, It is unavoidable that plastic deformation occurs in the polymer electrolyte membrane due to the applied heating and pressurization.

On the other hand, as a method of forming a catalyst layer without performing hot pressing, there is a method using an electrophoresis method, but this method is not suitable for mass production because cells are placed between electrodes to perform electrophoresis. is there.
J. of Electrochem. Soc. 151 (10) A 1733-7 (2004)

  An object of the present invention is to provide a method for producing a polymer electrolyte membrane-electrode assembly (MEA), which can form a porous electrode layer (catalyst support) for a fuel cell on an industrial scale. .

  An object of the present invention is to disperse a carbon material in a hydrocarbon solvent to which a basic polymer type dispersant is added, and in this solvent, a voltage is applied using the polymer electrolyte membrane as an anode, on the surface of the anode material. This is achieved by a method of producing a polymer electrolyte membrane-electrode composite by forming a carbon material thin film on the substrate.

  When a voltage is applied using the material to be coated as an anode and the carbon material is deposited on the surface of the anode material, the carbon material is dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added. It is possible to improve the dispersibility in the solvent and form a carbon material thin film with good adsorbability, in other words, with an increased amount of adsorption. In this way, carbon materials, particularly carbon nanotubes, are dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added, and an electric field is applied to the dispersion liquid to adsorb the carbon nanotubes on the surface of the polymer electrolyte. be able to.

  According to the method of the present invention, the catalyst layer can be formed without damaging the polymer electrolyte membrane. A carbon material such as carbon nanotubes coated on the polymer electrolyte membrane has electrical conductivity and has a nano-sized space, and therefore can be suitably used as a support for the catalyst layer. Furthermore, since the polymer electrolyte membrane can be used as the anode, continuous production is possible.

  Examples of the carbon material include carbon nanotube, carbon black, graphite, carbon fiber, fullerene, and the like. Preferably, from the viewpoint of excellent electrical conductivity and thermal conductivity, the carbon nanotube is from the viewpoint of electrical characteristics and bulk density. Carbon black or graphite is used. These can be used without particular limitation as long as they are dispersed in a solution, such as single-walled carbon nanotubes or multi-walled carbon nanotubes as carbon nanotubes, ketjen black, acetylene black, etc. as carbon black, and graphite. As such, either artificial graphite or natural graphite is used.

  As the basic polymer type dispersant, a molecular weight of several thousand to several tens of thousands can be used without particular limitation as long as it has an ester structure, and a fatty acid ester or the like, preferably a polyester acid amide amine salt is used. Used. In practice, commercially available products such as Enomoto Kasei products Disparon DA-703-50, DA-705, DA-725, DA-234 and the like are used. In addition, the company's product Disparon DA-325, which is an amine salt of polyether phosphate, is also used. These are used by being added to a hydrocarbon solvent in a proportion of 1 to 20% by weight, preferably 3 to 10% by weight. If the use ratio is less than this, the object of the present invention is not achieved. On the other hand, if the use ratio is more than this, a large amount of the basic polymer type dispersant is adhered to the formed thin film, which is not preferable.

  The average particle size of carbon material, preferably carbon nanotubes (50% particle size by wet laser scattering method) dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added is preferably 100 to 1000 nm, preferably The thickness is preferably set to 500 to 800 nm. Such adjustment to the average particle diameter is also performed using a ball mill or the like, but is preferably performed using an ultrasonic homogenizer. If an ultrasonic cleaner is used instead of an ultrasonic homogenizer, the average particle diameter of the carbon nanotube aggregates in the dispersion will be 1000 nm or more, and if a pot-type ball mill is used, the carbon nanotubes may break. is there.

  In addition, when the carbon material dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added, particularly when the average particle diameter of the carbon nanotube is set in the range of 100 to 1000 nm, the above carbon sheet is used. Similarly, both the adsorption amount and the weight ratio of carbon nanotubes in the adsorption layer can be increased. This means that the weight ratio of the basic polymer dispersant adsorbed simultaneously during the adsorption decreases, and as a result, the weight ratio of the carbon nanotubes increases, and is required as a function of the carbon nanotube adsorption layer. Conductivity is sufficiently obtained, and the effect of reducing electric resistance is achieved.

  Examples of the hydrocarbon solvent include aromatic hydrocarbon solvents, and preferably xylene or toluene is used. These hydrocarbon solvents are generally used in an amount of about 100 to 1000 times the carbon material.

A polymer electrolyte membrane is used as the anode to be coated. The polymer electrolyte membrane is a polymer membrane having an acidic group such as a sulfonic acid group (-SO ₃ H) or a carboxylic acid group (-COOH) as an ion exchange group for hydrogen ions, and having conductivity in water. Generally, a polymer having a perfluoro main chain substituted with a sulfonic acid group is used. The film thickness is about 25 to 500 μm, preferably about 50 to 300 μm. In practice, commercially available products such as Nafion manufactured by DuPont are used. Further, in order to reinforce the film strength of the thin film, those reinforced with PTFE fibers or a porous PTFE film are also used.

  The carbon material thin film is formed by adhering (adsorbing) the carbon material on the anode material by applying a voltage to the anode in a hydrocarbon solvent to which a basic polymer type dispersant is added. Here, the applied voltage is 1 to 1000 V, preferably 5 to 500 V. When the applied voltage is lower than this, the amount of adhesion of the carbon material decreases, whereas when larger than this, The adhesion film of the carbon material is not uniform, and the power efficiency is deteriorated, which is not preferable. The application time varies depending on the amount of film formation required, but it can be applied, for example, for 1 to 3000 seconds, preferably 30 to 1000 seconds, or periodically. At this time, in order to prevent sedimentation of the carbon material, a film is also formed while stirring the dispersion solution. Further, by performing masking at the time of film formation, the carbon material can be attached only to a portion requiring conductivity.

  The anode material having the carbon material thin film formed on the surface is taken out of the dispersion solution, and then washed and dried so as to remove other than the carbon material formed on the surface.

  By repeating the above steps, the film thickness of the carbon material formed on the anode material surface can be increased. That is, by setting the number of repetitions of the above steps, the film thickness of the carbon material to be formed can be controlled to a desired thickness, for example, about 1 to 50 μm.

  Next, the present invention will be described with reference to examples.

Example: To 90 ml of xylene, 10 ml of a 50% xylene solution of polyester acid amide amine salt (Enomoto Kasei product Disparon DA-703-50) was added. Vapor growth multi-walled carbon nanotubes (Nikkiso product; fiber diameter 10-30 nm) were added to this solution. And fiber length 1 to 100 μm) were added, and irradiation with an output of 300 W was performed with an ultrasonic homogenizer (SONIFIER450 manufactured by BRANSON) for 12 hours to obtain a multi-walled carbon nanotube dispersion. The average particle diameter of the multi-walled carbon nanotubes in this dispersion by wet laser scattering was 600 nm.

Next, a polymer electrolyte membrane (DuPont Nafion 117; film thickness 183 μm) is used as the anode, SUS304 is used as the cathode, and the electrodes are installed so that the distance between the electrodes is 2 cm using a mini clamp, and a voltage of 200 V is applied for 5 minutes. By doing so, the film forming process (film forming area 25cm < ² >) to an anode material was performed. After film formation, the polymer electrolyte membrane was dried at room temperature. Even when this polymer electrolyte membrane is bent, no peeling of the carbon nanotube thin film is observed, and it is considered that the polymer electrolyte membrane is adsorbed by the van der Waals force of the carbon nanotube.

As a result of observation of the produced carbon nanotube thin film with a scanning electron microscope, the film thickness of the adsorption layer was about 20 μm, and the volume resistivity of the carbon nanotube thin film was measured by the 4-terminal method, 3 × 10 ¹ Ω · cm Met.

Claims (9)

  A carbon material is dispersed in a hydrocarbon solvent to which a basic polymer type dispersant is added, and a voltage is applied in this solvent using the polymer electrolyte membrane as an anode to form a carbon material thin film on the surface of the anode material. A method for producing a polymer electrolyte membrane-electrode composite, comprising:   The method for producing a polymer electrolyte membrane-electrode composite according to claim 1, wherein the carbon material is carbon nanotube, carbon black, or graphite.   2. The method for producing a polymer electrolyte membrane-electrode composite according to claim 1, wherein the basic polymer type dispersant is a polyester acid amide amine salt.   The method for producing a polymer electrolyte membrane-electrode composite according to claim 1, wherein the hydrocarbon solvent is an aromatic hydrocarbon solvent.   The high carbon material according to claim 1, wherein the carbon material dispersed in the hydrocarbon solvent to which the chlorinated polymer type dispersant is added has an average particle size of 100 to 1000 nm (50% particle size by wet laser scattering method). A method for producing a molecular electrolyte membrane-electrode composite.   6. The method for producing a polymer electrolyte membrane-electrode composite according to claim 5, wherein the carbon material is a carbon nanotube.   The method for producing a polymer electrolyte membrane-electrode assembly according to claim 5 or 6, wherein the average particle diameter of the carbon material is adjusted to 100 to 1000 nm using an ultrasonic homogenizer.   A polymer electrolyte membrane-carbon material thin film electrode assembly produced by the method according to claim 1. The composite according to claim 8, wherein the carbon material thin film electrode is used as an electrode catalyst layer for a fuel cell.