JP4337162B2 - Method for producing electrolyte membrane for polymer electrolyte fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrolyte membrane for a polymer electrolyte fuel cell and a method for producing the same.
[0002]
[Prior art]
Conventionally, as an electrolyte membrane for this type of polymer electrolyte fuel cell, a membrane obtained by subjecting the surface of the electrolyte membrane to surface roughening has been proposed (Japanese Patent Laid-Open No. 5-258756, etc.). In this electrolyte membrane, the reaction field of the electrochemical reaction occurring at the three-phase interface between the electrolyte membrane, the catalyst and the gas is deposited by depositing a metal as a catalyst in the concave and convex portions formed by surface roughening treatment applied to the surface. It is said that it is possible to improve the battery characteristics by increasing the utilization ratio of the catalyst and the battery characteristics.
[0003]
[Problems to be solved by the invention]
However, such an electrolyte membrane has a problem in that catalyst particles near the surface of the catalyst deposited in the recess only contribute to the electrochemical reaction, and many catalyst particles deposited in the recess do not contribute to the reaction. . Such a problem is accompanied by the problem of increasing the cost of a fuel cell using an electrolyte membrane when a noble metal is used as a catalyst.
[0004]
In addition, depending on the treatment method, the electrolyte membrane whose surface is roughened may be chemically altered or physically destroyed, and does not function effectively as an electrolyte membrane. There was also the problem of producing parts. Usually, an ion exchange membrane is used as the electrolyte membrane, but functional groups that contribute to ion exchange may be destroyed by chemical surface treatment or physical surface treatment. In this case, the function of ion exchange is lost, and the electrolyte The performance as a film is reduced.
[0005]
In order to solve some of these problems, the applicant applied plasma sputter etching to the electrolyte membrane surface to form irregularities on the film surface, and the catalyst layer has a substantially uniform thickness along the irregularities. Has been proposed (Japanese Patent Application No. 6-315502).
[0006]
An object of the electrolyte membrane for a polymer electrolyte fuel cell of the present invention is to increase the contact area with the catalyst without increasing the performance as an electrolyte membrane, thereby increasing the reactivity. An object of the method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention is to provide a method for producing an electrolyte membrane that can take a large contact area with a catalyst without deteriorating the performance as an electrolyte membrane.
[0007]
[Means for solving the problems and their functions and effects]
The electrolyte membrane for a polymer electrolyte fuel cell and the method for producing the same according to the present invention employs the following means in order to achieve at least a part of the above object.
[0008]
The method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to the present invention includes:
A method for producing an electrolyte membrane used in a polymer electrolyte fuel cell,
A heavy metal substitution step of substituting protons of the cation exchange membrane with heavy metals;
A surface treatment step of performing surface treatment to irradiate at least one surface of the substituted cation exchange membrane to form a plurality of depressions having a predetermined shape on the surface;
And a proton substitution step for substituting the heavy metal of the surface-treated cation exchange membrane with protons.
[0009]
In the method for producing an electrolyte membrane for a polymer electrolyte fuel cell according to the present invention, the protons of the cation exchange membrane are replaced with heavy metals to prevent functional groups that contribute to ion exchange from being altered or destroyed during surface treatment. can do. As a result, the performance of the electrolyte membrane is not deteriorated by the surface treatment. Moreover, since a plurality of depressions having a predetermined shape are formed on the surface of the film by the surface treatment, the contact area with the catalyst can be increased. Here, “radiation” includes plasma, electron beam, X-ray, γ-ray and the like. Further, “heavy metal” includes lead, zinc, aluminum, iron, platinum and the like.
[0010]
In such a method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention, a strongly acidic cation exchange membrane may be used as the cation exchange membrane. In the method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention, the heavy metal substitution step may be a step of substitution using a weak acid salt aqueous solution of the heavy metal. Here, the “heavy salt aqueous solution of heavy metal” includes an aqueous solution of a heavy metal salt with acetic acid (for example, an aqueous solution of lead acetate, zinc acetate, or the like).
[0011]
In the method for producing an electrolyte membrane for a polymer electrolyte fuel cell of the present invention, the surface treatment step may be a step performed using an electron beam as the radiation. Since the electron beam is easy to control, a depression having a predetermined shape can be easily formed on the surface of the film. In addition, since the electron beam is obtained at a lower cost than plasma, X-rays, and γ rays, the manufacturing cost of the electrolyte membrane can be reduced.
[0012]
The electrolyte membrane for the first polymer electrolyte fuel cell of the present invention is:
An electrolyte membrane used in a polymer electrolyte fuel cell,
Replacing protons of the cation exchange membrane with heavy metal, irradiating at least one surface of the substituted cation exchange membrane with a plurality of dents of a predetermined shape on the surface, the dent of the predetermined shape The gist of the present invention is that the heavy metal in a plurality of formed cation exchange membranes is replaced with protons.
[0013]
In the electrolyte membrane for the first polymer electrolyte fuel cell of the present invention, the proton of the cation exchange membrane is subjected to a surface treatment by replacing the heavy metal with a heavy metal, and a functional group contributing to ion exchange is provided on the surface of the surface-treated membrane. Since it is provided, the performance as the electrolyte membrane can be sufficiently exhibited. Further, since a plurality of depressions having a predetermined shape are formed on the surface of the film by the surface treatment, the contact area with the catalyst can be increased.
[0014]
The electrolyte membrane for the second polymer electrolyte fuel cell of the present invention is:
An electrolyte membrane used in a polymer electrolyte fuel cell,
Formed by a strongly acidic cation exchange membrane,
The gist is that a plurality of depressions having a predetermined shape of the order of 10 ⁻⁶ m are provided on at least one surface of the strongly acidic cation exchange membrane.
[0015]
In the electrolyte membrane for the second polymer electrolyte fuel cell of the present invention, a plurality of depressions having a predetermined shape are formed on the surface of the membrane, so that the contact area with the catalyst can be increased.
[0016]
In such an electrolyte membrane for a second polymer electrolyte fuel cell of the present invention, a functional group contributing to ion exchange is disposed on the surface of the strongly acidic cation exchange membrane in the vicinity of which the depression having the predetermined shape is formed. It can also be. In this way, the performance of the electrolyte membrane can be sufficiently exhibited.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described using examples. FIG. 1 is a production process diagram illustrating the production of an electrolyte membrane 30 for a polymer electrolyte fuel cell according to one embodiment of the present invention, and FIG. 2 schematically illustrates the production of the electrolyte membrane 30 of the embodiment. FIG.
[0018]
As shown in the drawing, the production of the electrolyte membrane 30 starts from a step of replacing protons of the strong acid cation exchange membrane 22 with heavy metals (step S10). In the examples, a strongly acidic cation exchange membrane (Nafion 122 manufactured by DuPont) having a sulfone group as an exchange group is used as the ion exchange membrane, and the proton of the sulfone group is obtained by an ion exchange reaction represented by the following formula (1) by an electron staining technique. Was replaced with heavy metal (for example, lead, zinc, aluminum, iron, platinum, etc.) to obtain an ion exchange membrane 24 substituted with heavy metal. This substitution was performed by immersing the strongly acidic cation exchange membrane 22 in an aqueous solution of a weak acid salt (for example, an aqueous solution of lead acetate, zinc acetate or the like).
[0019]
Ion exchange reaction: nRH ⁺ + M ^{n +} ⇔R _n M ^{n +} + nH ⁺ (1)
[0020]
FIG. 3 is an explanatory view showing a cluster estimation structure of zinc and a sulfone group when the strongly acidic cation exchange membrane 22 is immersed in a saturated zinc acetate aqueous solution and protons are substituted with zinc, and FIG. 4 is a strongly acidic cation. It is explanatory drawing which shows the cluster estimation structure of lead and a sulfone group when the exchange membrane 22 is immersed in saturated lead acetate aqueous solution, and the proton is substituted with lead. As shown in the figure, the sulfone group is substituted with zinc or lead as heavy metals in place of protons.
[0021]
Next, the ion exchange membrane 24 substituted with heavy metal is irradiated with radiation to form a pattern of depressions 26 having a predetermined shape on the surface of the membrane (step S12). When an ion exchange membrane is irradiated with radiation, the ion exchange membrane is often crosslinked and cured or decomposed. In strong acidic cation exchange membranes, irradiation promotes decomposition, but if protons are replaced with heavy metals, the intensity of the protons increases and the deterioration (decomposition) of the ion exchange membrane due to radiation is suppressed. However, the structure of the ion exchange membrane does not change. Radiation includes plasma, electron beam, X-ray, γ-ray, etc., and any of them can form a pattern. In the examples, pattern formation was performed by electron beam lithography using an electron beam whose intensity and the like can be easily controlled. If electron beam lithography is used for pattern formation, a depression having a desired shape on the order of 10 ⁻⁶ m can be formed on the surface of the film.
[0022]
Then, the heavy metal is replaced with a proton using the reverse reaction of the ion exchange reaction of the above formula (1) for the ion exchange membrane 24 replaced with the heavy metal (step S14), and the electrolyte membrane 30 is completed. In the example, the heavy metal substituted ion exchange membrane 24 was immersed in dilute sulfuric acid to replace the heavy metal with protons.
[0023]
The completed electrolyte membrane 30 is provided with a depression 32 having a predetermined shape on the order of 10 ⁻⁶ m on the surface, and a sulfone group as an ion exchange group is altered on the surface of the surface where the depression 32 having the predetermined shape is formed. It exists without being destroyed. The recess 32 having a predetermined shape may have any shape such as a rectangle, a triangle, other polygons, a circle, or an ellipse.
[0024]
According to the electrolyte membrane 30 of the embodiment described above, the depression 32 having a predetermined shape on the order of 10 ⁻⁶ m is provided on the surface thereof, so that the contact area with the catalyst can be increased, and the highly reactive electrolyte membrane and can do. Further, according to the electrolyte membrane 30 of the embodiment, since the sulfone group as the ion exchange group is present on the surface of the surface where the recess 32 of the predetermined shape is formed without being altered or destroyed, the recess 32 of the predetermined shape. The membrane surface is not altered by the formation of the film, and the performance of the electrolyte membrane can be fully exhibited.
[0025]
According to the manufacturing method of the electrolyte membrane 30 of the embodiment described above, an electrolyte membrane that has a large contact area with the catalyst and can sufficiently exhibit the ion exchange performance can be manufactured. Further, according to the method of manufacturing the electrolyte membrane 30 of the embodiment, the proton of the strong acid cation exchange membrane 22 is replaced with heavy metal, and then the membrane is irradiated with radiation to form a recess 26 having a predetermined shape on the surface. Irradiation can prevent the ion exchange membrane from being decomposed and ion exchange groups from being altered or destroyed. Furthermore, according to the manufacturing method of the electrolyte membrane 30 of the embodiment, since an electron beam whose intensity is easily controlled is used as the radiation, the depressions 26 having a desired shape can be formed in a pattern on the surface of the membrane.
[0026]
In the electrolyte membrane 30 of the embodiment, the strong acid cation exchange membrane 22 is used as the ion exchange membrane, but a weak acid cation exchange membrane or the like may be used as long as it functions as an electrolyte membrane.
[0027]
The embodiments of the present invention have been described using the embodiments. However, the present invention is not limited to these embodiments, and can be implemented in various forms without departing from the gist of the present invention. Of course you get.
[Brief description of the drawings]
FIG. 1 is a manufacturing process diagram illustrating the production of an electrolyte membrane 30 for a polymer electrolyte fuel cell according to an embodiment of the present invention.
FIG. 2 is a production schematic diagram schematically showing the production of the electrolyte membrane 30 of the example.
FIG. 3 is an explanatory diagram showing a cluster estimation structure of zinc and a sulfone group when a strongly acidic cation exchange membrane 22 is immersed in a saturated zinc acetate aqueous solution and protons are substituted with zinc.
FIG. 4 is an explanatory diagram showing a cluster estimation structure of lead and sulfone groups when a strongly acidic cation exchange membrane 22 is immersed in a saturated aqueous lead acetate solution to replace protons with lead.
[Explanation of symbols]
22 strong acid cation exchange membrane, 24 ion exchange membrane substituted with heavy metal, 26 depression of predetermined shape, 30 electrolyte membrane, 32 depression of predetermined shape.

Claims (4)

A method for producing an electrolyte membrane used in a polymer electrolyte fuel cell,
A heavy metal substitution step of substituting the protons of the cation exchange membrane with lead or zinc ;
A surface treatment step of performing surface treatment to irradiate at least one surface of the substituted cation exchange membrane to form a plurality of depressions having a predetermined shape on the surface;
And a proton substitution step of substituting the lead or zinc of the surface-treated cation exchange membrane with protons.   The method for producing an electrolyte membrane according to claim 1, wherein a strongly acidic cation exchange membrane is used as the cation exchange membrane. The method for producing an electrolyte membrane according to claim 1 or 2 , wherein the heavy metal substitution step is a step of substitution using a weak salt aqueous solution of lead or zinc . The surface treatment step is a manufacturing method of the electrolyte membrane according to any one of claims 1 to 3 is a step performed using an electron beam as the radiation.

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