JP4452489B2 - Method for forming noble metal thin film of polymer electrolyte fuel cell separator - Google Patents

Description

  The present invention relates to surface treatment of a thin metal plate used for a polymer electrolyte fuel cell separator, and more particularly to a method for forming a noble metal thin film on the surface of a thin metal plate.

  In the polymer electrolyte fuel cell, a laminated body in which separators are laminated on both sides of a planar electrode structure (MEA) is a single unit, and a plurality of units are laminated to form a fuel cell stack. The The electrode structure has a three-layer structure in which an electrolyte membrane made of an ion exchange resin or the like is sandwiched between a pair of gas diffusion electrodes constituting a positive electrode (cathode) and a negative electrode (anode). A gas diffusion electrode is comprised from the electrode catalyst layer which contacts an electrolyte membrane, and the gas diffusion layer provided in the outer side. In addition, the separator is laminated so as to be in contact with the gas diffusion electrode of the electrode structure, and a gas flow path for allowing gas to flow between the gas diffusion electrode and a refrigerant flow path is formed between the separators. According to such a fuel cell, for example, hydrogen gas, which is a fuel, is allowed to flow in a gas flow channel facing the negative electrode side gas diffusion electrode, and oxygen or air is oxidized in the gas flow channel facing the positive electrode side gas diffusion electrode. When a sex gas is flowed, an electrochemical reaction occurs and electricity is generated.

  The separator needs to have a current collector function of supplying electrons generated by the catalytic reaction of the hydrogen gas on the negative electrode side to the external circuit, and supplying electrons from the external circuit to the positive electrode side. Therefore, conductive materials such as graphite and metal materials are used for the separator. Especially metal materials are excellent in mechanical strength, and can be made lighter and more compact by making them thinner. It is said that it is advantageous at this point. Examples of the metal separator include those formed by pressing a thin plate made of a metal material having corrosion resistance such as stainless steel and titanium alloy so as to have a cross-sectional uneven shape. FIG. 1 shows an example of such a separator.

  Conventionally, separator materials that require corrosion resistance as described above use materials with excellent corrosion resistance such as stainless steel, nickel-base alloys, titanium, titanium alloys, or are plated with copper, nickel, chromium, etc. When higher corrosion resistance is required, it is common to use a precious metal such as gold, silver or platinum after plating.

  When manufacturing such a plated product, since the plated film is easily peeled off from the metal base material when the product is processed after plating, generally, after performing plastic working to give the shape of the product to the metal base material I was plating. However, in this case, the plating film is difficult to be attached to the edge portion such as the groove of the metal base material, and there is a problem in the corrosion resistance of the portion. In addition, since the plating film has a porous structure having fine voids, there is also a problem that the adhesion with the metal substrate is weak. Further, since pinholes due to the porous structure are easily formed in the plated film, the corrosion resistance is lowered when the plated film is thin. For this reason, in order to improve corrosion resistance, it is necessary to form a thick plating film. In the case of noble metal plating, there is a problem that the cost is increased. On the other hand, a process of sealing the pinholes of the plating film with an organic substance is known, but there is a problem that a desired corrosion resistance cannot be obtained because there is no sufficient effect in the operating environment of the fuel cell.

  In response to such a requirement, a noble metal layer such as gold, silver, platinum, palladium, or an alloy thereof is formed on the surface of a metal base material such as an iron base alloy, a nickel base alloy, titanium, or a titanium base alloy, A method has been proposed in which these are rolled at a rolling rate of 5% or more to be clad (see, for example, Patent Document 1). According to this method, the noble metal thin film coated on the surface of a metal base material such as an iron-based alloy is clad by rolling with a metal material, so that the same adhesion force as that of a pressure-bonding material can be obtained. Since the porous structure of the noble metal layer is densified and the pinhole is closed, the corrosion resistance is improved. Therefore, the noble metal layer can be thinned and the cost is improved. Further, since the noble metal layer is formed, the contact electric resistance can be reduced.

  However, when a metal material is rolled by this method, work hardening occurs in the metal base material. Therefore, when this method is applied to a metal material for a fuel cell separator, a flow path for fuel gas and oxidizing gas is formed. The plastic workability required for the process is impaired. On the other hand, Patent Document 1 proposes a heat treatment method for removing work hardening of the noble metal layer caused by rolling in order to solve this problem.

JP2002260681 (abstract, 0011)

  However, if a high-temperature heat treatment that can remove work hardening is applied, the noble metal layer is dissipated or deteriorated due to thermal diffusion with the metal substrate, and the number of steps for heat treatment increases and the manufacturing cost is expensive. Problems arise. Furthermore, if the rolling reduction is suppressed to maintain plastic workability, there is a problem that sufficient adhesion between the metal substrate and the noble metal layer cannot be obtained.

  The present invention has been made in view of the above circumstances, and the precious metal of the solid polymer fuel cell separator is improved in corrosion resistance, adhesion, contact electric resistance, etc., and is low in cost without almost hardening the metal substrate. It aims at providing the thin film formation method.

A method for forming a noble metal thin film of a polymer electrolyte fuel cell separator of the present invention includes a step of degreasing and cleaning a surface of a corrosion-resistant metal base, a step of coating the surface of the metal base with a noble metal thin film, a step of shot peening I row to close contact with the metal material and the noble metal thin film blowing shots on both sides, the metal material in which the noble metal thin film is formed on the surface, the shape of the solid polymer fuel cell separator And a step of forming a concavo-convex shape by pressing, and a step of performing shot peening on the pressed metal material to bring the metal material and the noble metal thin film into close contact with each other.

In the method for forming a noble metal thin film of the polymer electrolyte fuel cell separator having the above-described configuration, first, one side of the metal base material or both sides as necessary are degreased and washed. This degreasing / cleaning step is performed to improve the adhesion between the metal substrate and the noble metal thin film. Next, a noble metal thin film is formed on one or both sides of the metal substrate by means of plating or sputtering, and then shot peening is performed on the noble metal thin film. Shot peening is a process of spraying a shot onto a metal surface and pressing the surface without significant work hardening inside the metal. Next, a metal material with a noble metal thin film formed on the surface is pressed into the shape of a polymer electrolyte fuel cell separator to form a cross-sectional uneven shape, and shots are shot on both sides of the pressed metal material. Peening is performed to bring the metal material and the noble metal thin film into close contact.

  According to such a method for forming a noble metal thin film of a solid polymer fuel cell separator of the present invention, since the surface of the metal substrate is degreased and washed, foreign matters and the like on the surface of the metal substrate are removed, and the metal substrate Adhesion between the film and the noble metal thin film increases. Further, since shot peening is performed on the noble metal thin film, the noble metal thin film is pressed and enters the concave portion generated by the peening on the surface of the metal base material, and an anchor effect is generated. Thereby, the adhesiveness is further increased without accompanying a large work hardening of the noble metal thin film. Therefore, the work hardening of the noble metal thin film, which has been a problem in the rolling process at a high rolling rate, can be suppressed, and subsequently, the molding process necessary for forming the flow path of the fuel gas and the oxidizing gas is hindered. Can be done without. Furthermore, since it does not involve a large work hardening, a heat treatment step for removing the work hardening is unnecessary, which is effective from the viewpoint of cost reduction. Moreover, corrosion resistance and contact electrical resistance are improved by sufficient adhesion between the metal substrate and the noble metal thin film.

  As described above, according to the present invention, the noble metal of the solid polymer fuel cell separator is improved in corrosion resistance, adhesion, contact electrical resistance, etc. without undergoing a rolling process that causes work hardening, and is low in cost. A thin film forming method can be provided.

  Hereinafter, a method for forming a noble metal thin film of the polymer electrolyte fuel cell separator of the present invention will be described.

1. Step of forming noble metal thin film First, the surface of the corrosion-resistant metal substrate is degreased and washed to remove foreign matters and the like on the surface of the metal substrate. Next, a noble metal thin film is formed on the surface of the metal substrate. The noble metal thin film is preferably thin enough to sufficiently reduce pinholes and reduce costs. As a method for forming the noble metal thin film on the surface of the metal substrate, plating, vapor deposition, sputtering, CVD or the like can be considered.

2. FIG. 2 is a conceptual diagram showing an example of shot peening on a noble metal thin film in the present invention. As shown in FIG. 2, the surface of the noble metal thin film 2 can be blown onto the surface of the noble metal thin film 2 formed on the surface of the metal base 1 so as to be brought into close contact with the metal base 1.

  Examples of such shots include metal particles such as steel, stainless steel, aluminum and zinc, glass particles such as glass beads and glass powder, resin particles such as nylon, polycarbonate and polyplus, ceramic particles such as zirconia and alumina. Carbon-based particles such as carborundum, walnuts, apricot powder, etc. are used, but not limited to these.

3. Step of forming into a polymer electrolyte fuel cell separator A metal substrate in which the noble metal thin film obtained as described above is integrated on the surface is subjected to press molding or the like, and a flow passage through which fuel gas or oxidizing gas passes And can be used for a metal separator for a polymer electrolyte fuel cell. An example of such a separator is shown in FIG.

  The metal substrate used in the present invention is not particularly limited and can include all kinds of metals, but considering the performance such as corrosion resistance and contact electric resistance required as a solid polymer fuel cell separator, Aluminum-based alloys, iron-based alloys, nickel-based alloys, titanium-based alloys and the like are particularly preferable because they themselves have high corrosion resistance and low contact electric resistance.

  As the noble metal thin film used in the present invention, gold, silver, platinum, palladium, or an alloy of these metals is used from the viewpoint of improving the performance such as corrosion resistance and contact electric resistance by coating the surface of the metal substrate. Particularly preferred.

  The shot used in the shot peening process of the present invention preferably has an average particle diameter of 3 μm to 0.5 mm, and is preferably sprayed with compressed air having a spraying pressure of 0.01 to 0.5 MPa. Particularly, 5 to 20 μm and 0.05 to 0.2 MPa are more preferable. When the particle size is smaller than 3 μm or the spraying pressure is lower than 0.01 MPa, the pressure applied to the noble metal thin film by the shot is insufficient, so that the adhesion of the noble metal thin film to the metal substrate cannot be sufficiently obtained, In addition, when the particle size is larger than 0.5 mm or the spraying pressure is higher than 0.5 MPa, the noble metal thin film may be damaged and the noble metal thin film may be peeled off.

  By applying shot peening at a particle size and spraying pressure in the above ranges, the noble metal thin film can be brought into close contact with the surface of the metal substrate without causing work hardening on the noble metal thin film. Therefore, the plastic workability performed to form the flow path through which the fuel gas or the oxidizing gas passes is not hindered in the subsequent process. In addition, since no heat treatment is required to remove work hardening, it solves the problem that the noble metal thin film is dissipated and deteriorated due to thermal diffusion with the metal substrate, and the processing cost required for the heat treatment is high. This is preferable.

In the shot peening process of the present invention, Ru spraying shots from both sides of the metal substrate. In general, a polymer electrolyte fuel cell separator is very thin, and when a shot peening is performed from one side, the metal substrate is warped. For this reason, by performing shot peening from both surfaces of the metal base material, the spreading effect of the noble metal thin film by shot peening can be offset on the front and back sides, and warpage can be suppressed.

  Furthermore, the shot peening of the present invention can be performed after a metal base material having a noble metal thin film formed on the surface thereof is molded into the shape of a polymer electrolyte fuel cell separator. According to such an embodiment, even if there is a concern about the decrease in adhesion between the metal substrate and the noble metal thin film due to the molding into the separator shape, the metal of the noble metal thin film is again obtained by performing shot peening. The adhesiveness to the substrate can be improved, which is preferable.

  In the method for forming a noble metal thin film of a polymer electrolyte fuel cell separator according to the present invention, shot peening is performed to remove foreign substances and segregated substances firmly attached to the surface of the metal substrate before the degreasing and cleaning steps of the metal substrate. It can be carried out. FIG. 3 is a conceptual diagram showing a process by such shot peening. As shown in FIG. 3, according to such an aspect, these can be removed by spraying and colliding with the foreign material and the segregated material 3 which exist in the metal base material 1 surface, and making it collide. On the surface of the metal substrate 1 from which the foreign matters and segregated substances have been removed, a recess that is a drop mark is formed. By coating the surface of the metal base 1 with the noble metal thin film 2 and performing shot peening according to the present invention, the noble metal thin film 2 enters the recess, and an anchor effect is produced. Thereby, the adhesive force of the metal base material 1 and the noble metal thin film 2 increases more, and a contact electrical resistance can be suppressed.

  Moreover, in this invention, shot peening can also be given after the removal of the foreign material and the segregated material 3 on the surface of the metal substrate. FIG. 4 is a conceptual diagram showing shot peening with respect to a recess which is a drop mark of the foreign matter and segregated matter. When the recess formed on the surface of the metal base 1 has a size that cannot be ignored compared to the thickness of the noble metal thin film 2, the noble metal thin film 2 enters the recess by subsequent shot peening, and the recess is formed on the surface of the noble metal thin film 2. Will be. This concave portion of the noble metal thin film is not preferable because it causes the contact electrical resistance to increase when the MEA (electrode structure) and the separator are brought into contact with each other after the separator is formed. Therefore, it is preferable to arrange the concave portion, which is a drop mark of foreign matter and segregated matter, into a suitable surface property by shot peening.

Hereinafter, the present invention will be described in detail by way of examples.
[Example 1]
SUS316L having a thickness of 0.1 mm was used as a metal substrate, and the surface was degreased and washed to remove foreign matter, segregated material, oxide film and the like. Next, a gold thin film having a thickness of 100 nm was formed on the surface of the metal substrate by a plating method. Glass powder having an average particle size of 10 μm was used as a shot, and sprayed on the gold thin film at a spraying pressure of 0.1 MPa for 10 seconds.

[Example 2]
A gold thin film was formed on a metal substrate in the same manner as in Example 1 except that the spraying time was set to 30 seconds.

[Example 3]
A gold thin film was formed on a metal substrate in the same manner as in Example 1 except that the spraying time was set to 60 seconds.

[Example 4]
A gold thin film was formed on a metal substrate in the same manner as in Example 1 except that the spraying time was set to 120 seconds.

[Comparative Example 1]
A gold thin film was formed on a metal substrate in the same manner as in Example 1 except that no shot was sprayed, and Comparative Example 1 was obtained.

[Comparative Example 2]
A gold thin film was formed on a metal substrate in the same manner as in Example 1 except that a sealing treatment with a resin was performed instead of shot spraying, and Comparative Example 2 was obtained.

[Comparative Example 3]
A gold thin film was formed on a metal substrate in the same manner as in Example 1 except that a passive treatment was performed after plating instead of shot spraying, and Comparative Example 3 was obtained.

  Table 1 shows implementation conditions and performance evaluation results of Examples and Comparative Examples.

  A separator was produced by pressing the metal substrate / gold thin film assembly obtained in the above Examples and Comparative Examples, and the separator was assembled into a fuel cell and subjected to a power generation durability test. Among these, the result of Example 2 and a comparative example is shown in the graph of FIG. As is apparent from this graph, the contact resistance increased with time in the comparative example, but in Example 2, the increase in contact resistance was gradual.

  As described above, according to the method for forming a noble metal thin film of the polymer electrolyte fuel cell separator of the present invention, the corrosion resistance, adhesion, and contact electric resistance are improved, and the polymer polymer fuel cell separator is reduced in cost. Can be produced.

It is a photograph which shows an example of the polymer electrolyte fuel cell separator of this invention. It is a conceptual diagram which shows the shot peening process with respect to the metal base material and noble metal thin film in this invention. It is a conceptual diagram which shows the removal process of the foreign material on the surface of a metal base material by a shot peening in this invention, and a segregated material. It is a conceptual diagram which shows the shot peening with respect to the fallen trace of the foreign material and segregated material which arose in this invention. It is a graph which shows the elapsed time and contact resistance increase of the Example and comparative example in the electric power generation durability test of this invention.

Explanation of symbols

1 Metal substrate 2 Precious metal thin film 3 Foreign material, segregated material

Claims (3)

Degreasing and cleaning the surface of the corrosion-resistant metal substrate ;
The surface of the metal substrate and the step of coating with a noble metal thin film,
A step of adhering the above metal material and the noble metal thin film both shot peening to blow shots to the plane of the I line of the noble metal thin film,
A step of pressing the metal material having the noble metal thin film formed on the surface thereof into a shape of a solid polymer type fuel cell separator to form a concavo-convex shape;
Performing shot peening on the pressed metal material to bring the metal material and the noble metal thin film into close contact with each other;
Noble metal thin film forming method of a polymer electrolyte fuel cell separator comprising the. The foreign matter and segregated matter on the surface are removed by performing shot peening on the surface of the metal base before the step of degreasing and cleaning the surface of the metal base. A method for forming a noble metal thin film of a solid polymer fuel cell separator. After removing the foreign matter and segregated material on the surface of the metal base material, before coating the surface of the metal base material with a noble metal thin film, the surface properties of the foreign matter and segregated material drop mark are shot peened on the surface. The method for forming a noble metal thin film for a polymer electrolyte fuel cell separator according to claim 1 or 2, wherein

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