JP2005123106A - Membrane for fuel cell and manufacturing method of electrode joint body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for providing a membrane and an electrode joint body each having a smooth joint surface without generating a crease on an electrolyte membrane, in a method for forming a catalyst layer on an electrolyte membrane by using catalyst ink. <P>SOLUTION: This manufacturing method of a membrane for a fuel cell and an electrode joint body for applying catalyst ink containing an electrolyte and catalyst to a surface of an electrolyte membrane is characterized by that the catalyst ink further contains an acid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing an assembly of an ion exchange membrane, which is a solid polymer electrolyte in a fuel cell, and an electrode.

  A fuel cell is a power generation system in which the reaction product is water and has almost no adverse effect on the global environment. Among these, a polymer electrolyte fuel cell (PEFC) has a high output density and an operating temperature range. Due to its low advantages, it is expected to expand the field of use such as on-vehicle use, home use, and portable use.

  A polymer electrolyte fuel cell generally uses an ion-exchange polymer membrane (polymer electrolyte membrane) that permeates hydrogen ions as an electrolyte, and the electrolyte is sandwiched between two diffusion electrodes (cathode and anode).・ Equipped with an electrode assembly, hydrogen gas (methanol solution in the case of DMFC) and an oxidant in a flow path formed between the separator and the diffusion electrode further sandwiching the membrane / electrode assembly The air (oxidizing gas) is supplied to operate in a low temperature range of 100 ° C. or lower.

  As described above, in the polymer electrolyte fuel cell, the layers (catalyst layers) containing the catalyst as the electrodes are arranged in close contact with both surfaces of the ion exchange membrane, which is a solid polymer electrolyte, and if necessary, outside the catalyst layer. It has a gas diffusion layer for efficiently supplying gas to the catalyst layer. In the present specification, a membrane / electrode assembly is referred to as a membrane / electrode assembly in which an electrolyte membrane and a catalyst layer are closely arranged and apparently joined without including a gas diffusion layer.

  As a conventional method for producing a membrane / electrode assembly, a method of directly forming a catalyst layer on an electrolyte membrane, a catalyst layer is formed on a base material to be a gas diffusion layer such as carbon paper, and this is joined to an electrolyte membrane. And a method of forming an electrode on a flat plate and transferring it to an electrolyte membrane. In these methods, a liquid in which a catalyst is dispersed (hereinafter referred to as catalyst ink) is used to form a catalyst layer. The catalyst ink usually contains a catalyst powder in which a platinum group metal is supported on activated carbon or the like, an electrolyte such as an ion exchange resin, and, if necessary, a water repellent, a pore former, and a thickener. Dispersed or dissolved.

In the method of directly applying the catalyst ink to the electrolyte membrane, it is usually applied by an existing method such as a die coater or screen printing. However, application of the catalyst ink causes the electrolyte membrane to swell and wrinkles.
For this reason, the problem that the membrane-electrode assembly with a smooth joining surface cannot be obtained has occurred.

  On the other hand, when the membrane / electrode assembly is prepared by the transfer method, there is a concern that the bonding property between the membrane and the electrode is lower than the method of directly applying the catalyst ink.

  As a technique for preventing the electrolyte membrane from swelling and wrinkling by applying the catalyst ink, after applying the catalyst ink to the electrolyte membrane fixed to the substrate and drying it, the substrate is used as the electrolyte membrane. A method of peeling is disclosed (see Patent Document 1).

  However, according to this method, the electrolyte membrane needs to be sufficiently fixed to the base material, but it must be easily peeled off from the membrane, making it difficult to select the base material and complicated fixing work. Met.

Also disclosed is a method for producing a membrane / electrode assembly by spraying catalyst ink in a state where the electrolyte membrane is held by evacuation on a porous plate held at a constant temperature (see Patent Document 2). .
However, according to this method, a special apparatus is required, and the swelling of the electrolyte membrane due to the catalyst ink cannot be sufficiently suppressed.
JP 2001-160405 A JP 2003-100314 A

  Accordingly, an object of the present invention is to provide a method for producing a membrane / electrode assembly for a fuel cell, which can prevent the electrolyte membrane from swelling and wrinkling by applying a catalyst ink by a simple method. is there.

In view of such a situation, the present inventor has conducted intensive research and found that it is possible to prevent generation of wrinkles due to swelling of the electrolyte membrane only by adding an acid to the catalyst ink solution and applying the solution. Was completed.
That is, the present invention provides the following method.

  <1> A fuel cell membrane / electrode assembly manufacturing method in which a catalyst ink containing an electrolyte and a catalyst is applied onto an electrolyte membrane, wherein the catalyst ink further contains an acid. Manufacturing method of electrode assembly.

  <2> The method for producing a membrane-electrode assembly for a fuel cell according to claim 1, wherein the acid is sulfuric acid.

  According to the present invention, application of the catalyst ink prevents the electrolyte membrane from swelling and wrinkling.

  The present invention relates to a fuel cell membrane / electrode assembly manufacturing method in which a catalyst ink containing an electrolyte and a catalyst is coated on the electrolyte membrane, wherein the catalyst ink further contains an acid. -It is a manufacturing method of an electrode assembly.

(Electrolyte membrane)

  The electrolyte membrane used in the present invention is not particularly limited as long as it is a solid electrolyte membrane used in a normal fuel cell, but an electrolyte membrane exhibiting proton conductivity is preferable for expressing the effects of the present invention. Used. Examples of the proton exchange group of the proton exchange membrane include, but are not limited to, a sulfonic acid group, a carboxylic acid group, and a phosphoric acid group.

  As a more specific electrolyte membrane, a perfluorosulfonic acid resin typified by Nafion manufactured by DuPont and a reinforcing layer made of poly (tetrafluoroethylene) may be introduced. Also, hydrocarbon electrolyte membranes such as sulfonated polyether ketone resin, sulfonated polyether sulfone resin, sulfonated polyphenylene sulfide resin, sulfonated polyimide resin, sulfonated polyamide resin, sulfonated epoxy resin, and sulfonated polyolefin resin. But you can. Further, it may be a polymer / strong acid complex represented by a poly (benzimidazole) / phosphate complex.

(Catalyst ink)
The catalyst ink used in the present invention is characterized by containing an acid in addition to the catalyst, the electrolyte, and other optional components.

  Examples of acids used in the present invention include inorganic acids such as sulfuric acid and phosphoric acid, organic acids such as acetic acid, and solid acids typified by zirconium phosphate. Of these, sulfuric acid is preferred.

  The acid concentration is preferably in the range of 3.9 to 11.6 mol / L in order to make the dimensional change within 1%, and further in the range of 4.4 to 9 in order to make the dimensional change within 0.5%. A range of .4 mol / L is particularly preferred.

  The catalyst in the catalyst ink used in the present invention is not particularly limited, and examples thereof include those that can be used in ordinary fuel cells. Examples thereof include platinum group metals such as platinum and platinum alloys. These catalysts may be used as metal fine particles as they are, but a supported catalyst in which a metal is supported on a support such as activated carbon or carbon black may be used.

  Examples of the electrolyte in the catalyst ink used in the present invention include the resin of the electrolyte membrane described above. In the present invention, it is preferable that the solvent contained in the catalyst ink contains a solvent capable of dissolving the electrolyte membrane because the catalyst layer and the electrolyte membrane can be strongly bonded. Further, the catalyst ink may contain a water repellent, a thickener for adjusting the viscosity, a diluent, or the like as necessary.

  The method for applying the catalyst ink on the electrolyte membrane is not particularly limited, and can be carried out by a conventional method such as a doctor blade method, a filtration transfer method, a spray spray method, a screen printing method, or the like.

  The membrane / electrode assembly obtained by the method of the present invention preferably has a gas diffusion layer made of carbon paper, carbon cloth, or the like on the outside, and further functions as a current collector by supplying gas to the outside. If a separator is disposed, a solid polymer fuel cell can be obtained.

Comparative Example 1
10 g of a perfluorosulfonic acid resin solution (Nafion solution, manufactured by Aldrich Chemical Co.) was added to 1.4 g of 40% by weight platinum catalyst-supporting carbon (manufactured by E-TEK, USA), and the mixture was stirred using an ultrasonic homogenizer. The catalyst ink thus prepared was directly applied onto a Nafion 112 membrane (5 × 5 cm; manufactured by DuPont) using a doctor blade. As a result, the obtained membrane / electrode assembly exhibited a swelling of 4 mm, and many wrinkles were observed on the membrane. Thereafter, the membrane / electrode assembly was vacuum dried at 80 ° C. for 48 hours. Then, the same operation was performed on the opposite side.

Example 1
10 g of a perfluorosulfonic acid resin solution (Nafion solution, manufactured by Aldrich Chemical Co.) is added to 1.4 g of 40% by weight platinum catalyst-supporting carbon (manufactured by E-TEK, USA), and further 7.8 g of sulfuric acid (Wako Pure Chemical Industries, Ltd.) The product was stirred using an ultrasonic homogenizer. The catalyst ink thus prepared was directly applied onto a Nafion 112 membrane (5 × 5 cm; manufactured by DuPont) using a doctor blade. As a result, the obtained membrane / electrode assembly did not swell and no wrinkles were observed on the membrane. Thereafter, the membrane / electrode assembly was vacuum dried at 80 ° C. for 48 hours. Then, the same operation was performed on the opposite side.

Example 2
The amount of sulfuric acid added in Example 1 was variously changed, and the dimensional change of the obtained membrane / electrode assembly was examined. The results are shown in FIG.

  According to the present invention, since the electrolyte membrane does not swell and wrinkles do not occur by applying the catalyst ink, a membrane / electrode assembly having a smooth joining surface can be obtained. The method of the present invention is a very simple method and can contribute to cost reduction.

It is a figure which shows a sulfuric acid concentration and a dimensional change of a film | membrane.

Claims (2)

  A fuel cell membrane / electrode assembly in which a catalyst ink containing an electrolyte and a catalyst is applied onto an electrolyte membrane, wherein the catalyst ink further contains an acid. Manufacturing method.   The method for producing a membrane-electrode assembly for a fuel cell according to claim 1, wherein the acid is sulfuric acid.

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