JP2010114020A - Manufacturing method of polyelectrolyte membrane, the polyelectrolyte membrane, and solid polymer fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyelectrolyte membrane in which metal oxide particulates are uniformly dispersed in the polyelectrolyte membrane, and which is superior in chemical durability, and to provide the polyelectrolyte membrane manufactured by the method. <P>SOLUTION: This manufacturing method of the polyelectrolyte membrane includes a first process of dissolving metal salt of perfluorosulfonic acid and/or metal salt of perfluorocarboxylic acid, in a polymer dispersion liquid containing a polyelectrolyte precursor, to exhibit proton conductivity by alkaline hydrolysis and acid treatment; a second process of film-forming a polyelectrolyte precursor membrane obtained by the first process; a third process of preparing the polyelectrolyte precursor membrane by alkaline hydrolysis and acid treatment of the polyelectrolyte membrane obtained by the second process; and a fourth process of precipitating the metal oxide to the polyelectrolyte membrane by heating/drying the polyelectrolyte membrane obtained by the third process. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a polymer electrolyte membrane in which metal oxide fine particles are uniformly dispersed in the polymer electrolyte membrane and excellent in chemical durability, and a polymer electrolyte membrane produced by the method. The present invention also relates to a polymer electrolyte fuel cell having the polymer electrolyte membrane.

  A solid polymer electrolyte fuel cell has a structure in which a solid polymer electrolyte membrane is used as an electrolyte and a catalyst electrode layer is bonded to both surfaces of the membrane. The solid electrolyte membrane and the catalyst electrode layer constituting such a solid polymer electrolyte fuel cell are generally formed using a polymer electrolyte material having proton conductivity. As such an electrolyte material, perfluorosulfonic acid resins such as Nafion (registered trademark: Nafion, manufactured by DuPont) have been widely used.

Fluorine-based and hydrocarbon-based electrolyte membranes used in polymer electrolyte fuel cells are deteriorated due to deterioration of the electrolyte polymer by OH radicals generated during power generation. As a means for suppressing deterioration, the radical resistance of MEA is improved by adding a metal oxide typified by CeO ₂ as a radical scavenger to the catalyst layer or diffusion layer of the membrane electrode assembly (MEA). In this case, the radical scavenger added to the catalyst layer or the diffusion layer moves into the membrane with time.

  For example, Patent Document 1 below preferably discloses that a diffusion layer contains a hydrogen peroxide decomposing agent, a radical scavenger, or an antioxidant for the purpose of improving the durability of the polymer electrolyte membrane.

Apart from this, there is also a method of adding a radical scavenger directly to the electrolyte membrane. The method of adding the radical scavenger directly to the electrolyte membrane is roughly classified into a method of adding by ion exchange after film formation, a method of mixing a radical scavenger in the electrolyte polymer before film formation, The latter is desirable when such solids are added. Furthermore, when forming a film by casting, a radical scavenger is added and mixed in advance in the casting solution, and casting is performed. When forming a film by melt molding, radical scavenging is performed on the -SO ₂ F type polymer that is the precursor structure of the electrolyte. The agent is mixed, melted to form a film, and then subjected to hydrolysis treatment to convert it into —SO ₃ H type polymer that can conduct protons.

  As described above, it is known to add a metal oxide to the polymer electrolyte membrane for the purpose of enhancing the functionality of the fuel cell. However, in order to increase the effect of addition, uniform dispersion and a large surface area are effective. Conceivable. The inventors of the present invention have attempted to increase dispersibility and surface area by adding a metal oxide or atomizing an added metal oxide in the process of manufacturing a melt-impregnated film. It was difficult to achieve both uniform dispersion of the metal oxide and an increase in surface area.

  As a cause of difficulty in achieving both uniform dispersion of metal oxide and an increase in surface area, a method for producing a polymer electrolyte membrane is involved. FIG. 1 shows the conventional metal oxide addition time in the polymer electrolyte membrane production scheme. FIG. 2 shows a list of conventional metal oxide addition methods and their outlines.

  As shown in FIGS. 1 and 2, as a conventional method of adding a metal oxide, a method of physically mixing a metal oxide with a polymer before film formation ((1 method), (2 method)), It can be broadly divided into the method of introducing into the membrane by ion exchange after film formation (3 methods). In the former case (1 method), since the metal oxide of the dry powder is added, it is already reduced to a micron size before the addition. Agglomeration was not possible. As for dispersibility, solid polymer powder and metal oxide powder are coarsely mixed, and it is difficult to obtain fine dispersibility. Addition of metal oxide to the polymer solution (2 methods) improves the dispersibility somewhat, but it does not disperse more than the aggregated particles, and it is also poor in the affinity of the fluorinated solvent and oxide as the dispersion medium. I can't hope for dispersion. On the other hand, in the latter case (method 3), since it is introduced into the electrolyte in an ionic state, fine particles are deposited in the electrolyte when the salt is subsequently precipitated. Since the exchange was concentrated and the addition state could be biased, uniform dispersion was difficult. Further, in the case of only cation exchange, there is also a problem of a decrease in conductivity due to a decrease in sulfonic acid groups.

  In addition, the following patent documents 1 and 2 are illustrated as said prior art regarding addition of a metal oxide. Patent Document 1 discloses that a polymer electrolyte precursor is immersed in an alkaline aqueous solution of a metal salt to precipitate a metal oxide on the polymer electrolyte membrane. Patent Document 2 discloses a metal salt on a cation exchange membrane. It is disclosed to immerse the solution and disperse the insolubilized metal oxide in the electrolyte membrane.

JP 2005-19232 A JP 2001-118591 A

  The present invention was invented in view of the above-mentioned problems of the prior art, and a method for producing a polymer electrolyte membrane having excellent chemical durability in which metal oxide fine particles are uniformly dispersed in the polymer electrolyte membrane. And a polymer electrolyte membrane produced by the method. Another object of the present invention is to improve the durability of the polymer electrolyte fuel cell.

  The present inventor has found a method for uniformly and highly dispersing metal oxide fine particles as a radical scavenger in a polymer electrolyte by specific means, and has reached the present invention.

  That is, first, the present invention is an invention of a method for producing a polymer electrolyte membrane in which metal oxide fine particles are uniformly dispersed in the polymer electrolyte membrane, and exhibits proton conductivity by alkali hydrolysis and acid treatment. A first step of dissolving a metal salt of perfluorosulfonic acid and / or a metal salt of perfluorocarboxylic acid in a polymer dispersion containing a polyelectrolyte precursor, and a polymer from the dispersion obtained in the first step Obtained in a second step of forming an electrolyte precursor film, a third step of alkali hydrolysis and acid treatment of the polymer electrolyte precursor film obtained in the second step to obtain a polymer electrolyte membrane, and a third step A fourth step of heating and drying the obtained polymer electrolyte membrane to deposit a metal oxide in the polymer electrolyte membrane.

  Compared to the case where the metal oxide is simply mixed and dispersed, the polymer electrolyte membrane of the present invention is highly dispersed in the polymer electrolyte membrane without agglomeration of the metal oxide. It will be possible to make the most of it. That is, chemical durability is improved by uniformly adding metal oxide fine particles to the polymer electrolyte membrane.

  The metal salt of perfluorosulfonic acid and / or the metal salt of perfluorocarboxylic acid used in the present invention includes cerium salt, silver salt, titanium salt, silicon salt and zirconium salt of perfluorosulfonic acid and perfluorocarboxylic acid. One or more selected are preferably exemplified.

  Examples of the solvent for the polymer dispersion used in the present invention include a polymer electrolyte precursor that exhibits proton conductivity by alkali hydrolysis and acid treatment, and a metal salt of perfluorosulfonic acid and / or a metal salt of perfluorocarboxylic acid. A fluorine-based solvent that is excellent in compatibility with is preferable.

  Second, the present invention is a polymer electrolyte membrane produced by the above method.

  Thirdly, the present invention is a polymer electrolyte fuel cell having the polymer electrolyte membrane produced as described above.

  In the polymer electrolyte membrane of the present invention, (1) metal oxide fine particles, which are radical scavengers to the polymer electrolyte, can be finely and evenly dispersed than before, so that the moldability is improved, the quality is improved, and the stable resistance (2) Since the metal oxide can be immobilized in the polymer electrolyte, the migration and removal of the metal oxide in the polymer electrolyte is suppressed, and as a result, stable radical resistance can be ensured. It has the effect of being able to extend the service life. Thereby, the power generation performance and durability of the solid polymer electrolyte fuel cell can be improved.

FIG. 3 shows the polymer electrolyte membrane production process of the present invention. A metal salt of perfluorosulfonic acid and / or a metal salt of perfluorocarboxylic acid is added to a polymer dispersion containing a polymer electrolyte precursor (-SO ₂ F type) that exhibits proton conductivity by alkali hydrolysis and acid treatment. Dissolve. After the obtained dispersion is mixed and dried, a polymer electrolyte precursor film is formed. The resulting polymer electrolyte precursor membrane to alkali hydrolysis and acid treatment to the polymer electrolyte membrane (-SO 3 _H type). The obtained polymer electrolyte membrane is heated and dried to uniformly deposit metal oxide fine particles in the polymer electrolyte membrane.

The side chain terminal of the polymer electrolyte is converted from -SO ₂ F type to -SO ₃ H type by alkali hydrolysis treatment, and changes from hydrophobic to hydrophilic. Along with this, the alkaline solution penetrates into the film, hydrolyzes the metal salt scattered in the film, and deposits metal hydroxide fine particles. Furthermore, by performing dehydration by drying and heating, it has a form of metal oxide fine particles.

  In the present invention, the polymer electrolyte membrane may be used as a single membrane, or may be used as a composite polymer electrolyte membrane in which a porous membrane and a polymer electrolyte membrane are combined from the viewpoint of strength and durability. The method of combining the porous membrane and the polymer electrolyte to form the composite polymer electrolyte membrane is not particularly limited, and various known methods can be employed. By using the composite polymer electrolyte membrane, it is possible to reduce the thickness of the solid polymer electrolyte membrane, and since the polymer film or the polymer sheet substrate is used as a support for the electrolyte membrane, the electrolyte membrane Therefore, the fuel cell provided with the composite polymer electrolyte membrane is highly durable, has a small amount of fuel gas cross-leakage, and can improve current-voltage characteristics.

Examples of the present invention will be described below.
[Example]
Perfluorosulfonic acid (C ₄ H ₉ SO ₃ H) and cerium oxide (CeO ₂ ) were mixed to prepare a cerium salt of perfluorosulfonic acid. This is dissolved in a Nafion precursor solution (—SO ₂ F type ionomer, fluorine-based solvent HFE7300) and stirred, and then the solvent is removed by volatilization to obtain a polymer electrolyte. This was formed into a film, hydrolyzed with a 1N NaOH / DMSO mixed solution, treated with 1N sulfuric acid, and then heated and dehydrated at 100 ° C. to obtain a polymer electrolyte membrane (polymer electrolyte membrane 1).

[Comparative example]
A cerium oxide powder (particle size: about 1 μm) was added to a Nafion precursor solution (—SO ₂ F type ionomer, fluorine-based solvent HFE7300) and stirred, and then the solvent was removed by volatilization to obtain a polymer electrolyte. This was formed into a film, hydrolyzed with a 1N NaOH / DMSO mixed solution, treated with 1N sulfuric acid, and then heated and dehydrated at 100 ° C. to obtain a polymer electrolyte membrane (polymer electrolyte membrane 2).

On the other hand, Nafion precursor solution (-SO ₂ F type ionomer, a fluorine-based solvent HFE7300) and the volatiles removed to obtain a polymer electrolyte. After film formation, hydrolysis with 1N NaOH / DMSO mixed solution, treatment with 1N sulfuric acid, immersion in a predetermined concentration of Ce (NO ₃ ) ₃ solution, immersion in 1N phosphoric acid solution, and heating and dehydration at 100 ° C. The treatment was performed to obtain a polymer electrolyte membrane (polymer electrolyte membrane 3).

[Evaluation 1]
Table 1 below shows the results of observing the cross sections of the polymer electrolyte membranes 1 to 3 with SEM and TEM, and comparing the additive particle diameter with the existing state.

[Evaluation 2]
In FIG. 4, the result of having compared the additive effect in the polymer electrolyte membranes 1-3 by the Fenton test (radical resistance test) is shown. In addition, all addition amounts shall be 1 wt%.
From the results of FIG. 4, it can be seen that the polymer electrolyte membrane of the present invention is excellent in radical resistance.

  According to the present invention, metal oxide fine particles as a radical scavenger can be highly dispersed in the polymer electrolyte membrane, and radical resistance can be ensured. Thereby, the power generation performance and durability of the solid polymer electrolyte fuel cell can be improved.

The conventional metal oxide addition time in the polymer electrolyte membrane production scheme is shown. A list of conventional addition methods and outlines of metal oxides are shown. The polymer electrolyte membrane manufacturing process of this invention is shown. The result of having compared the additive effect in the polymer electrolyte membranes 1-3 by the Fenton test (radical resistance test) is shown.

Claims (5)

  A first step of dissolving a metal salt of perfluorosulfonic acid and / or a metal salt of perfluorocarboxylic acid in a polymer dispersion containing a polymer electrolyte precursor that exhibits proton conductivity by alkaline hydrolysis and acid treatment; A second step of forming a polymer electrolyte precursor membrane from the dispersion obtained in the first step, and a polymer electrolyte membrane obtained by subjecting the polymer electrolyte precursor membrane obtained in the second step to alkali hydrolysis and acid treatment And a fourth step of heating and drying the polymer electrolyte membrane obtained in the third step to deposit a metal oxide in the polymer electrolyte membrane. Manufacturing method.   The metal salt of perfluorosulfonic acid and / or the metal salt of perfluorocarboxylic acid is selected from cerium salt, silver salt, titanium salt, silicon salt and zirconium salt of perfluorosulfonic acid and perfluorocarboxylic acid It is the above, The manufacturing method of the polymer electrolyte membrane of Claim 1 characterized by the above-mentioned.   The method for producing a polymer electrolyte membrane according to claim 1 or 2, wherein the solvent of the polymer dispersion is a fluorine-based solvent.   A polymer electrolyte membrane produced by the method according to claim 1.   A polymer electrolyte fuel cell having a polymer electrolyte membrane produced by the method according to claim 1.

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