JP2010059462A - Plating treatment method for separator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a plating device which can efficiently form a plating film partially at a desired part in the surface of the material to be treated. <P>SOLUTION: Regarding the plating treatment method for a separator in which gold is electroplated to the surface 10a to be treated in a metallic separator 10 for a fuel cell, the separator 10 is dipped into a gold ion-containing plating liquid in such a manner that the surface 10a to be treated is confronted with the electrode 30, and gold is precipitated on the surface 10a to be treated so as to be a granular shape while flowing an electric current in a pulse waveform to a space between the surface 10a to be treated and the electrode 30. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for plating a metal separator for a fuel cell, and more particularly, to a method for plating a separator suitable for electroplating a noble metal.

  A polymer electrolyte fuel cell using an electrolyte membrane can be operated at a low temperature, and can be reduced in size and weight. Therefore, application to a moving body such as an automobile is being studied. In particular, fuel cell vehicles equipped with polymer electrolyte fuel cells are gaining social interest as ecological cars.

  As shown in FIG. 5, such a polymer electrolyte fuel cell includes a membrane electrode assembly (MEA) 95 as a main component, and includes a fuel (hydrogen) gas passage and an air gas passage. One fuel cell 90 called a single cell is formed by being sandwiched between separators 96 and 96. The membrane electrode assembly 95 has a structure in which an anode side electrode (anode catalyst layer) 93a is laminated on one side of an electrolyte membrane 91 which is an ion exchange membrane, and a cathode side electrode (cathode catalyst layer) 93b is laminated on the other side. The anode catalyst layer 93a and the cathode catalyst layer 93b are provided with diffusion layers 94a and 94b, respectively.

  By the way, titanium-based material, stainless steel, or the like is used as a material for a fuel cell separator. Such a material has a passive oxide film on the surface layer, and since this oxide film has corrosion resistance under a general environment, it is suitable as a material for the separator. However, although the separator of the fuel cell is energized when the fuel cell generates power, the presence of this oxide film increases the contact resistance value, which may impair the conductivity to the separator.

  Therefore, the conductivity of the separator is ensured by performing conductive noble metal plating such as gold plating on the surface of the separator. When plating noble metals, it is desirable to reduce the plating film thickness as much as possible from the viewpoints of reducing manufacturing costs and reducing environmental burden.

  From such a point, as a noble metal plating method, a method is proposed in which a noble metal is deposited in the form of particles on the surface of a titanium material by flowing a constant current (for example, patent literature). 1).

JP 2007-146250 A

  However, as shown in FIG. 6A, when the plating film 90 is coated on the substrate 80 by the method described in Patent Document 1, there is an exposed portion 81a where the oxide film 81 is exposed. In particular, when the amount of noble metal to be deposited is limited in order to reduce the cost of the plating process, the ratio of the exposed portion 81a increases.

  By the way, in the power generation environment of the fuel cell, the generated water is acidic and is in a corrosive environment containing halogen. Furthermore, a portion where the potential becomes higher is generated by the power generation of the fuel cell, and it becomes a more severe corrosive environment with respect to the metal of the separator.

  In such a corrosive environment, when the above-described plating material is used for a fuel cell separator, as shown in FIG. 6B, corrosion or oxidation of the base material 82 proceeds from the exposed portion 81a. In some cases, the oxide film 81 grows in the thickness direction (the thickness Ta of the oxide film is increased to Tb). As the oxide film 81 grows, oxidation may reach the vicinity where the noble metal plating is deposited, and these phenomena are considered to cause the above-described increase in contact resistance. However, when the noble metal plating process is performed so as to reduce the exposed portion 81a shown in FIG. 6A, the thickness of the plating film increases and the manufacturing cost increases.

  The present invention has been made in view of such problems, and the object of the present invention is to reduce the thickness of the noble metal plating film, improve the plating coverage, and reduce the exposed portion of the surface to be processed. Accordingly, an object of the present invention is to provide a separator plating method that can suppress an increase in resistance when a fuel cell is used.

  As a result of intensive studies, the inventors considered that it is important to deposit more fine particles on the surface to be processed in order to coat the surface to be processed with a thin film thickness and a high plating coverage. Further, by using a pulse waveform as a waveform of current to be energized at the time of electroplating treatment, a new finding has been obtained that it is possible to perform the plating treatment in such a deposited form.

  The present invention is based on such new knowledge, and the separator plating method according to the present invention is a separator plating method for electroplating a noble metal on a metal surface to be processed for a fuel cell. Then, the separator is immersed in a solution containing ions of the noble metal so that the surface to be processed is opposed to the electrode, and a current having a pulse waveform is passed between the surface to be processed and the electrode. The noble metal is precipitated in the form of particles.

  According to the present invention, a metallic separator is immersed in a plating solution bath containing noble metal ions, and the surface to be treated for plating the separator is disposed so as to face the electrode. Then, a power source is connected to the separator and the electrode, a current having a pulse waveform is passed between the surface to be processed and the electrode, the noble metal is deposited in the form of particles on the surface to be processed, and a plating film of the noble metal is formed on the surface to be processed. Can be coated. In this case, by supplying a current having a pulse waveform between the surface to be processed of the separator and the electrode, it is possible to increase the number of nuclei that generate plating on the surface to be processed as compared with the case of supplying a direct current. Thus, a larger amount of particulate noble metal precipitates on the surface to be treated of the separator than when a direct current flows. In this way, the surface to be treated of the separator can be coated with a thin plating film having a high plating coverage.

  The pulse waveform of the current that flows between the electrode and the surface to be processed is not limited to a rectangular waveform, and examples thereof include a PR waveform, a single-phase full-wave waveform, an AC / DC superimposed waveform, and a triangular waveform. The shape of the pulse waveform is not particularly limited as long as the current density having a larger peak than the current density of the direct current waveform during plating can be set.

  Further, the material of the metallic separator is more preferably a titanium-based material or stainless steel. Titanium-based material or stainless steel forms a passive oxide film on the surface, and this passive oxide film has corrosion resistance, so it is suitable for the usage environment of the separator. Further, as the noble metal used in the plating method of the present invention, it is more preferable that at least one or more kinds of noble metals are selected from Au, Ru, Rh, Pd, Os, Ir and Pt.

  In the separator plating method according to the present invention, it is more preferable to perform electroplating until the plating coverage of the noble metal with respect to the surface area of the surface to be processed is 73% or more. According to the present invention, the average current density, the peak current density, the processing time, etc. of the current of the pulse waveform are adjusted, and the noble metal is in the form of particles until the plating coverage of the noble metal with respect to the surface area of the surface to be processed is 73%. By depositing and electroplating the surface to be treated, not only the corrosion resistance of the plated separator can be improved, but also low contact resistance can be maintained even in a corrosive environment.

  The “plating coverage” as used in the present invention refers to the ratio of the area occupied by the precious metal plating particles deposited on the surface to be treated to the area of the surface to be treated.

Further, in the separator plating method according to the present invention, the average current density of the pulse waveform current is 0.1 to 0.8 A / dm ² , and the peak current density of the pulse waveform current is 0.00. more preferably 5~8A / dm ^2.

According to the present invention, the plating process can be more suitably performed by performing the plating process on the separator at the average current density and the peak current density of the pulse waveform current in the range shown above. That is, when the average current density is less than 0.1 A / dm ² , it is not preferable from the viewpoint of productivity because the plating process speed is slow, and when the average current density exceeds 0.8 A / dm ^2. May cause plating defects such as deposition failure of precious metals, seizure, or peeling of the plating film. Furthermore, when the peak current density is less than 0.5 A / dm ² , plating nuclei are hardly generated, and the plating coverage may be reduced. When the peak current density exceeds 8 A / dm ² In some cases, defects such as seizure or reduction in plating efficiency may occur.

  ADVANTAGE OF THE INVENTION According to this invention, while reducing the thickness of the plating film plated on the to-be-processed surface of a separator, a plating coverage rate can be improved. Thereby, an increase in resistance during power generation can be suppressed.

  Below, with reference to drawings, the plating treatment method of the separator concerning the present invention is explained based on an embodiment.

  FIG. 1 is an overall configuration diagram of a plating apparatus for performing a separator plating method according to the present embodiment, and FIG. 2 performs a plating process on a surface to be processed using the plating apparatus shown in FIG. It is a fragmentary sectional view of a separator.

  As shown in FIG. 1, the plating apparatus 100 includes an electrode 30 for plating, a power supply unit 40 for energization, and a plating solution storage tank 50. An electrode 30 in which titanium is covered with platinum is disposed in the plating solution storage tank 50 and is connected to the positive electrode of the power supply unit 40. A metal separator 10 is disposed in the plating solution storage tank 50 and is connected to the negative electrode of the power supply unit 40. The power supply unit 40 is a current supply source for supplying a current between the electrode 30 and the separator 10 that is a material to be processed, and a current adjusting unit that adjusts the current so that a current having a desired pulse waveform can be supplied. (Not shown).

  Using such a plating apparatus 100, electroplating is performed on the surface 10a to be processed of the separator 10 as described below. First, the plating solution L containing gold ions is put into the plating solution storage tank 50. Next, a separator 10 that has been subjected to alkaline degreasing on at least the surface to be treated 10a is prepared.

  The material of the separator 10 is preferably a titanium-based material (for example, a JIS standard type 1 equivalent titanium plate) or stainless steel (for example, JIS standard: 430). As shown in FIG. 2, such a material is suitable for a member used in a corrosive environment such as a separator because a passive oxide film 11 is formed on a base material 12.

  Next, it arrange | positions in the plating solution storage tank 50 so that the to-be-processed surface 10a of the separator 10 may be immersed in the plating solution L. FIG. At this time, the treated surface 10 a of the separator 10 is disposed so as to face the electrode 30. This posture is maintained, and the positive electrode of the power supply unit 40 is connected to the electrode 30 and the negative electrode of the power supply unit 40 is connected to the separator 10.

  Then, a current is passed between the surface to be treated 10 a of the separator 10 and the electrode 30 using the power supply unit 40. At this time, a current adjusted to a desired pulse waveform is applied by the power supply unit 40 to deposit gold in the form of particles on the surface to be processed 10a. As a result, as shown in FIG. 2, the plating film 20 having the gold particulates attached thereto can be coated on the surface 10 a of the passive oxide film 11 of the separator 10.

  The plating film 20 obtained in this way has a peak current density compared to the case where a direct current is passed by passing a current having a pulse waveform between the surface to be treated 10 a of the separator 10 and the electrode 30. Since an intermittent current (or voltage) flows to the surface to be processed 10a, the number of nuclei that generate plating on the surface to be processed 10a can be increased. As a result, in comparison with the case where the plating process is performed by energizing a direct current, the fine gold particles 20a are deposited innumerably on the surface 10a to be processed, so that the plating film thickness T is reduced and the plating coating is performed. The rate can be increased. As a result, a separator having high corrosion resistance, low contact resistance, and high reliability can be manufactured at a lower cost.

The present invention will be described below based on examples.
Example 1
A plate material corresponding to a titanium separator for a fuel cell was prepared, and the surface to be treated was alkali degreased. Next, the plate material was immersed in a non-cyanide plating bath containing gold ions, and the surface to be processed for plating the plate material was disposed so as to face the platinum electrode. Then, a power source is connected to the plate material and the electrode, and a current having a pulse waveform with an average current density of 0.2 A / dm ² and a peak current density of 0.8 A / dm ² is passed between the surface to be processed and the electrode for 30 seconds. Then, gold was deposited in the form of particles on the surface to be treated, and the surface to be treated was coated with a gold plating film.

<Plating thickness measurement test>
The plating thickness of the plating film of the separator treated in Example 1 was measured using a fluorescent X-ray analyzer (XRF). The results are shown in Table 1.

<Plating coverage measurement test>
The plating coverage of the plated separator of Example 1 was measured. Specifically, the plated surface was observed with a scanning electron microscope (FE-SEM), and the plating coverage was determined by image processing. The results are shown in Table 1 and FIG. 4A and 4B are photographic views observed with a scanning electron microscope of Comparative Example 2 and Example 3 described later.

<Constant potential corrosion test>
The constant potential corrosion test is an environmental evaluation test that simulates the power generation of a fuel cell. Specifically, first, the plated separator of Example 1 was immersed in a sulfuric acid solution (300 ml, pH 4, 80 ° C.). . In this state, a counter electrode made of a platinum plate and the separator were electrically connected to generate a potential difference between the counter electrode and the separator, and a corrosion test of the separator was performed. During the test, the potential of the separator is kept constant (immersion potential to 1 V) by a reference electrode made of a platinum wire. Further, the evaluation area of the separator in the constant potential corrosion test is 16 cm ² (4 cm × 4 cm), and the test time is about 50 hours.

<Contact resistance test>
Carbon paper was placed on the plating film of the separator subjected to the plating treatment of Example 1, and the separator and carbon paper were sandwiched between the electrodes at a constant load (1 MPa). In this state, the contact resistance of the plated surface was examined by measuring the voltage applied to each fuel cell separator while flowing a current of 1 A between the electrodes. The contact resistance test was performed once before and after the constant potential corrosion test. The evaluation area of each sample in the contact resistance test is 4 cm ² (2 cm × 2 cm). In addition, the rate of increase in contact resistance before and after the potentiostatic corrosion test was also calculated. The results are shown in Table 1 and FIG. In addition, the contact resistance ratio shown in Table 1 and FIG. 3 is normalized by the value of the contact resistance before the test of Comparative Example 1 described later.

(Examples 2 and 3)
In the same manner as in Example 1, the surface of the separator to be processed was subjected to gold plating. The difference from Example 1 is that the respective peak current densities were set to 2.0 A / dm ² and 3.0 A / dm ² . And it carried out similarly to Example 1, and calculated | required the plating thickness of the plating film, the plating coverage, the contact resistance, and the resistance increase magnification. The results are shown in Table 1 and FIG. In addition, the photograph figure observed with the scanning electron microscope of Example 3 was shown in FIG.4 (b).

(Comparative Examples 1-3)
In the same manner as in Example 1, the surface of the separator to be processed was subjected to gold plating. The difference from Example 1 is that a power source is connected to the plate material and the electrode, a direct current is passed between the surface to be treated and the electrode for 30 seconds to 10 minutes, and gold is particulated on the surface to be treated. It is the point which deposited and coat | covered the gold plating film | membrane on the to-be-processed surface. Incidentally, each of the average current density of Comparative Example ^{1~3, 0.05A / dm 2, 0.2A} / dm 2, was 0.1 A / dm ^2. And it carried out similarly to Example 1, and calculated | required the plating thickness of the plating film, the plating coverage, the contact resistance, and the resistance increase magnification. The results are shown in Table 1 and FIG. In addition, the photograph figure observed with the scanning electron microscope of the comparative example 2 was shown to Fig.4 (a).

(Result 1 and Discussion 1)
The separators of Examples 1 to 3 and Comparative Examples 1 to 3 were all coated with a good plating film. Further, as is clear from FIGS. 4A and 4B, the gold particulate precipitates constituting the plating films of Examples 1 to 3 are finer than those of Comparative Examples 1 to 3. there were. The plating thicknesses of the plating films of Examples 1 to 3 are considered to be thinner than those of Comparative Example 3, and the coverage with respect to the plating thickness is also high.

  This is because the separators of Examples 1 to 3 have a peak compared to the case where the direct current of Comparative Examples 1 to 3 is passed by passing a pulse waveform current between the treated surface of the separator and the electrode. This is probably because the current density is increased and intermittent current (or voltage) flows to the surface to be processed, so that the number of nuclei that generate plating increases. As a result, it is considered that a larger amount of particulate noble metal was deposited on the surface to be treated of the separator than when a direct current was passed. As a result, it is considered that the surface of the separators of Examples 1 to 3 could be coated with a particulate gold plating film having a high coverage and a thin film thickness (20 nm or less).

(Result 2 and discussion 2)
Furthermore, the plating coverage of Examples 2 and 3 was 73% or more, and the resistance increase magnification was also about 1 time. This is because the separators of Examples 2 and 3 have a small ratio of exposed portions of the surface to be treated, so that not only the corrosion resistance of the plated separator is improved, but also low contact resistance is maintained even in a corrosive environment. It is thought that it was because it was able to do. Therefore, it can be said that the plating coverage of the surface to be treated of the fuel cell separator is more preferably 73% or more.

Example 4
The separator was plated in the same manner as in Example 1. The difference from Example 1 is the combination of the current densities of the pulse waveform currents, where (average current density, peak current density) is (0.2 A / dm ² , 0.8 A / dm ² ), (0.1 A / dm ² , 1.5 A / dm ² ), (0.8 A / dm ² , 6.0 A / dm ² ), (0.1 A / dm ² , 0.5 A / dm ² ), (0.4 A / dm ²⁾ , 8 A / dm ² ), the separator was plated. Under these conditions, a good plating film was formed on the surface of the separator.

(Example 5)
The separator was plated in the same manner as in Example 1. The difference from Example 1 is the combination of the current densities of the pulse waveform currents, where (average current density, peak current density) is (1.2 A / dm ² (value exceeding 0.8 A / dm ² )), 5 .0A ^/ (value of ^{0.5~8A / dm 2) dm 2)} , ( the value of 0.5A / dm 2 (0.1~0.8A / dm 2), 12.0A / dm 2 (8A / The separator was plated under the condition of a value exceeding dm ² )).

(Result 3 and discussion 3)
In the plating treatment of Example 5, when the average current density exceeded 0.8 A / dm ² , plating defects such as precious metal deposition failure, seizure, or peeling of the plating film may occur. Furthermore, when the peak current density exceeds 8 A / dm ² , defects such as seizure or a decrease in plating efficiency may occur. Therefore, when plating the surface to be treated of the separator for a fuel cell, the average current density of the pulse waveform current is 0.8 A / dm ² or less, and the peak current density of the pulse waveform current is More preferably, it is 8 A / dm ² or less. In addition, from other experiments by the inventors, in consideration of the plating treatment efficiency, the average current density is 0.1 A / dm ² or more, and the peak current density of the pulse waveform current is 0.5 A / dm ² or more. It turned out to be more preferable.

  As mentioned above, although embodiment of this invention has been explained in full detail using drawing, a concrete structure is not limited to this embodiment, Even if there is a design change in the range which does not deviate from the gist of the present invention. These are included in the present invention.

  In the present embodiment, the fuel cell separator has been described in detail. However, the separator is not particularly limited as long as it is a member that performs precious metal plating on the assumption that the separator is used in a corrosive environment.

The whole block diagram of the plating processing apparatus for performing the plating processing method of the separator which concerns on this embodiment. The fragmentary sectional view of the separator which plated the to-be-processed surface using the plating processing apparatus shown in FIG. The figure which showed the result of the contact low efficiency before and behind the constant potential corrosion test of Examples 1-3 and Comparative Examples 1 and 2. FIG. It is the photograph figure which observed the surface after plating processing with the scanning electron microscope (FE-SEM), (a) is the photograph figure of the surface which concerns on the comparative example 2, (b) concerns on Example 3. A photograph of the surface. The schematic diagram explaining an example of a polymer electrolyte fuel cell (single cell). It is sectional drawing of the plating processing material which performed the conventional plating processing, (a) is sectional drawing of the plating processing material immediately after plating processing, (b) is the plating processing material after use in a corrosive environment. Sectional drawing.

Explanation of symbols

  10: Separator, 10a: Surface to be treated, 11: Passive oxide film, 12: Base material, 20: Plating film, 20a: Gold particulate, 30: Electrode, 40: Power supply unit, 50: Plating solution storage tank, 100: plating apparatus, L: plating solution

Claims (3)

A separator plating method for electroplating a noble metal on a metal surface to be processed for a fuel cell,
The separator is immersed in a solution containing ions of the noble metal so that the surface to be processed is opposed to the electrode, and a current having a pulse waveform is passed between the surface to be processed and the electrode, and the surface is processed. A method for plating a separator, comprising precipitating a noble metal in a particulate form.   2. The separator plating method according to claim 1, wherein a plating coverage of the noble metal with respect to a surface area of the surface to be processed is set to 73% or more. An average current density of the pulse waveform current is 0.1 to 0.8 A / dm ² , and a peak current density of the pulse waveform current is 0.5 to 8 A / dm ^2. The separator plating method according to claim 1 or 2.

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