KR101266096B1 - Fuel cell separator and method for producing same - Google Patents

Abstract

The fuel cell separator 20 of the present invention is formed in the stainless steel substrate 12a, the gold plating layer 22 formed on the stainless steel substrate 12a and having the pinhole 22a, and formed in the pinhole 22a. It has the passivation layer 16 of stainless steel, and has the area | region which the gold plating layer 22 and the stainless steel base material 12a contact without passing through the passivation layer of stainless steel. In the fuel cell separator 20 of the present invention, after forming the strike gold plated layer on the surface of the stainless steel substrate 12 using an acidic gold strike plating solution, the gold plated layer 22 is formed, and then the passivation treatment is performed. It can manufacture by performing. According to this invention, the separator for fuel cells which can be manufactured excellent in corrosion resistance and low cost, and its manufacturing method are provided.

Description

Fuel cell separator and its manufacturing method {FUEL CELL SEPARATOR AND METHOD FOR PRODUCING SAME}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator, and more particularly, to a separator suitable for a solid polymer fuel cell used for an automotive power supply, a portable device power supply, a distributed power supply, and the like.

In view of high power generation efficiency and low environmental burden, research on fuel cells as a next generation energy source is being actively conducted.

A fuel cell is a power generation device that obtains electrical energy by electrochemically reacting hydrogen and oxygen as fuels. The fuel cell is a solid oxide fuel cell (SOFC), a molten carbonate fuel cell (MCFC), a phosphate fuel cell (PAFC), a solid polymer fuel cell (PEFC), or a direct methanol fuel, depending on the type of electrolyte used. It is classified as a battery (DMFC). Among them, PEFCs and DMFCs have a low operating temperature of about 70 to 90 ° C. compared with other types of fuel cells, and are capable of generating high efficiency even at about 1 kW in PEFCs and in hundreds of Ws in DMFCs. Application to the back is expected. In particular, the DMFC is compact and its application to portable devices is being actively studied.

The separator is required to have low gas permeability, excellent conductivity, low contact resistance, excellent corrosion resistance, and the like. In particular, requests for corrosion resistance and conductivity have become stronger in recent years. As a criterion for evaluation of corrosion resistance, it has been suggested that rust (or corrosion) does not occur even if the separator is immersed in a sulfuric acid solution having a pH of about 1000 hours. . In particular, it is required that the DMFC be compact and have excellent surface conductivity.

Carbon materials are widely used as separator materials having such characteristics. However, the carbon material has a problem that it is difficult to process because of lack of toughness and softness, and the processing cost is high. Therefore, in recent years, the use of stainless steel which is easy to process and low in processing cost as a separator material is considered instead of a carbon material.

On the surface of the stainless steel, an oxide film (floating film) in which Cr contained in the steel is combined with oxygen in the atmosphere is produced. Therefore, the corrosion resistance is excellent, but the contact resistance is large, and it cannot be used as a separator material as it is. For this reason, although the surface of stainless steel is coat | covered with the noble metal which is excellent in corrosion resistance and electroconductivity, since the adhesiveness of a passivation film and a metal film is very bad, it is very difficult to form a metal film directly on the surface of stainless steel. Therefore, until now, the passivation film was completely removed by etching or the like, and then a base plating layer containing a metal such as Ni was formed, and then a method of plating precious metals was employed. However, when the separator obtained by the said method is used for a long time, there exists a problem that corrosion resistance falls and the performance as a fuel cell falls. It is thought that this is because the corrosion liquid enters through the pinhole formed in the noble metal film, and dissimilar metal contact corrosion (galvanic corrosion) proceeds. Therefore, this method cannot satisfy the above-mentioned evaluation criteria of corrosion resistance (the occurrence of rust is not recognized even if the separator is immersed in the strong acid solution for 1000 hours or more).

On the other hand, Patent Literatures 1 and 2 disclose separators in which a noble metal layer is directly formed thereon without removing the passivation layer formed on the surface of stainless steel.

According to Patent Document 1, when the coverage of the gold layer formed directly on the passivation layer is 2.3% to 94%, not only the corrosion resistance of the separator can be improved but also the contact resistance can be sufficiently reduced.

Further, according to Patent Document 2, by forming a noble metal layer directly on the passivation layer, and then heat treatment in a vacuum or inert gas for 5 minutes or less at a temperature of 100 ° C or more and 600 ° C or less, the metal component of the base material is a noble metal layer As a result of the diffusion, the adhesion between the base material (for example, stainless steel) and the noble metal layer is improved.

Patent Document 1: Japanese Patent Application Laid-Open No. 2004-296381 Patent Document 2: Japanese Patent Application Laid-Open No. 2007-323988

However, according to the inventor's examination, the separator for fuel cells described in patent document 1 does not have enough corrosion resistance. In addition, the separator described in Patent Document 2 requires a heat treatment for improving the adhesion of the precious metal layer to stainless steel, and thus has a problem of poor throughput and high cost.

An object of the present invention is to provide a separator for fuel cells and a method for producing the same which are excellent in corrosion resistance and can be manufactured at low cost.

The fuel cell separator of the present invention has a stainless steel substrate, a gold plating layer formed on the stainless steel substrate and having a pinhole, and a passivation layer of stainless steel formed in the pinhole, wherein the gold plating layer and the stainless steel substrate are It has an area | region which contacts without passing through the passivation layer of stainless steel. It is preferable that the passivation layer of stainless steel does not exist between the said gold plating layer and the said stainless steel base material. It is preferable that the thickness of the said gold plating layer exceeds at least 0.01 micrometer, and it is more preferable that it is 0.05 micrometer or more.

In one embodiment, the said gold plating layer and the said stainless steel base material have the area | region which contacts through the iron oxide layer which does not contain chromium substantially. An iron oxide layer substantially free of chromium exists between the gold plated layer and the stainless steel substrate.

In one embodiment, the passivation layer is at least 4 nm thick.

In one embodiment, the thickness of the said gold plating layer is 0.3 micrometer or less.

In one embodiment, the contact resistance of the said gold plating layer is 10 m (ohm) * cm <2> or less.

The manufacturing method of the fuel cell separator of this invention includes the process a of preparing a stainless steel base material, and the process b of forming a strike gold plating layer after the said process a using the acidic gold strike plating liquid on the surface of the said stainless steel base material; After the step b, the step c of forming a pure gold plating layer on the strike gold plated layer, and after the step c, when the gold plated layer has a pin hole, it is possible to form a passivation layer of stainless steel in the pin hole The process d which performs a passivation process on condition is included.

In one embodiment, the passivation treatment preferably utilizes nitric acid at a concentration of at least 30%.

In one embodiment, the method further includes a step of etching the surface of the stainless steel substrate after the step a and before the step b.

In one embodiment, the gold plated layer formed in step c has a pinhole, and in step d, a passivation layer of stainless steel is formed in the pinhole.

The fuel cell separator of this invention should just have a structure substantially the same as the fuel cell separator manufactured by the manufacturing method of any one of said fuel cell separators. That is, the passivation layer between the gold plated layer and the stainless steel substrate is at least partially removed, thereby improving the adhesion between the gold plated layer and the stainless steel substrate, and further improving the corrosion resistance by forming the passivation layer of the stainless steel in the pin hole of the gold plated layer. You just need to have a structure.

According to this invention, the separator for fuel cells which is excellent in corrosion resistance and high adhesiveness of a gold plating layer, and its manufacturing method are provided.

1: (a)-(e) are typical sectional drawing for demonstrating the manufacturing method of the separator 20 for fuel cells of embodiment which concerns on this invention.
2 is a graph showing a concentration profile of a stainless steel substrate, (a) is a graph showing a concentration profile of a commercially available stainless steel (SUS304) substrate, and (b) is a graph showing a concentration profile after etching and washing the surface thereof. to be.
FIG. 3A is a graph showing a concentration profile after passivation with a 10% nitric acid solution after etching and washing with water, and (b) shows a concentration profile after passivation with a 10% nitric acid solution after etching with washing with water It is a graph.
(A) of FIG. 4 is a graph which shows the density profile of the sample corresponding to sample 4, (b) respectively.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to drawings, the separator for fuel cells and embodiment of the manufacturing method of this embodiment by this invention are demonstrated. In addition, this invention is not limited to embodiment to illustrate.

A schematic cross section for demonstrating the manufacturing method of the separator 20 for fuel cells of embodiment which concerns on this invention to FIG.1 (a)-(e) is shown.

In the manufacturing method of the fuel cell separator of embodiment which concerns on this invention, first, as shown to FIG. 1 (a), the stainless steel base material 12 is prepared. The stainless steel base material 12 has a main body part 12a made of stainless steel and a passivation layer (floating film) 14 formed on the surface of the main body part 12a. As is well known, the passivation layer 14 is naturally formed when the stainless steel is left in the air, and contains an oxide of chromium and a hydroxide of chromium and iron, and is excellent in corrosion resistance. It is thought that the oxide layer of chromium is formed in the main body part 12a side, and the hydroxide layer of chromium and iron is formed in the surface side. Although the thickness of the passivation layer 14 changes with conditions, it is about several nm. As stainless steel, an austenitic stainless steel (for example, SUS 304, SUS 316) or an austenitic-ferritic stainless steel (for example, SUS 329 J1) can be used preferably. Prior to the next step, the surface of the passivation layer 14 may be cleaned and / or degreased as necessary.

Next, as shown in FIG.1 (b), the surface of the stainless steel base material 12 is etched. As the etching solution, for example, hydrochloric acid or a mixture of hydrochloric acid and nitric acid can be used to remove the passivation layer 14. Instead of etching, the passivation layer 14 can also be removed by a cathodic electrolytic method using an aqueous sulfuric acid solution as the electrolyte. As described above, the passivation layer 14 is once removed prior to the subsequent step of forming the strike gold plated layer 22s using the acidic gold strike plating solution, thereby improving the uniformity of the final gold plating finish. The uniformity of the finish of the gold plating can be easily confirmed with the naked eye.

On the other hand, after removing the passivation layer 14, before forming the strike gold plating layer, it is preferable to remove the etching liquid adhering to the surface of the stainless steel base material 12 (main part 12a), for example by washing with water. . At this time, the passivation layer may be formed again. In addition, depending on the storage environment after removing the passivation layer 14, the passivation layer may be formed again. Once the passivation layer 14 is removed by the above method, the uniformity of the surface of the stainless steel substrate can be improved, so that even after the passivation layer is formed, the uniformity of the final gold plating finish can be improved.

On the other hand, in the process of forming the strike gold plating layer using the acidic gold strike plating solution, the passivation layer 14 on the surface of the stainless steel substrate 12 is at least partially removed, so that the passivation layer 14 is removed before the strike gold plating process. Even if it is not removed, the gold plating layer excellent in corrosion resistance and adhesiveness can be obtained. By performing the etching process described with reference to FIG. 1B, the uniformity of the final gold plating finish can be improved. The naturally formed oxide layer is uneven in the degree of oxidation, the thickness of the oxide layer, or the composition of the oxide layer due to hysteresis (rolling conditions, storage environment, processing conditions before processing, etc.), and the uniformity of the surface is removed by removing the non-uniform oxide layer by etching. I think it can be increased.

Next, as shown in FIG. 1C, an acidic gold strike plating liquid (for example, Kojima Chemical Co., Ltd.) is applied to the surface of the main body portion 12a exposed as a result of the passivation layer 14 is removed. Strike gold plating layer 22s is formed using K-770 by the Corporation. As the acidic gold strike plating solution, known ones can be widely used. For example, it is preferable that pH is 0.4 or more and 1.0 or less (liquid temperature 20 degreeC or more and 40 degrees C or less). The current density is, for example, 0.5 A / dm ² or more and 8.0 A / dm ² or less, and the plating time is, for example, 30 seconds or more and 90 seconds or less. It is preferable that the thickness of the strike gold plating layer 22s is 0.005 micrometer or more and 0.05 micrometer or less, for example. The strike gold plated layer 22s is very thin and has a pinhole 22sa. On the other hand, as described above, even if the step of removing the passivation layer 14 described with reference to FIG. 1B is omitted, the removal of the passivation layer 14 also occurs in the gold strike plating process. The structure shown in c) can be obtained.

Next, as shown to Fig.1 (d), the pure gold plating layer 22m is formed on the strike gold plating layer 22s. The pure gold plating layer 22m is formed using a gold cyanide plating solution, for example. As the gold plating solution containing a cyan compound (for example, Tenper Resist BL manufactured by Japan High Purity Chemical Co., Ltd.), a known one can be widely used. For example, it is preferable that pH is 6.0 or more and 6.5 or less (liquid temperature 60 degreeC or more and 70 degrees C or less). The current density is, for example, 0.02 A / dm ² or more and 0.3 A / dm ² or less, and the plating time is, for example, 100 seconds or more and 300 seconds or less.

It is not necessary to form the pure gold plating layer 22m thickly, and the gold plating layer 22 which combined the strike gold plating layer 22s and the pure gold plating layer 22m may have the pinhole 22a. According to the examination of the present inventors, in order to form the gold plating layer 22 which does not have a pinhole, the thickness of the whole gold plating layer 22 is generally required 1.2 micrometers or more. As will be described later in the experimental example, the thickness of the entire gold plated layer 22 may be sufficiently low in contact resistance, preferably at least 0.01 μm, and more preferably 0.05 μm or more. In addition, the thickness of the gold plated layer 22 does not need to exceed 0.3 micrometer, and the contact resistance can fully be reduced in thickness of 0.3 micrometer or less. It is preferable that the contact resistance of the gold plating layer 22 is 10 m (ohm) * cm <2> or less.

Next, as shown to Fig.1 (e), the fuel cell separator 20 is obtained by performing the passivation process with respect to the main-body part 12a of the stainless steel base material in which the gold plating layer 22 was formed. The passivation treatment is performed under the condition that a passivation layer of stainless steel can be formed in the pin hole when the gold plated layer has the pin hole. For example, as shown in an experiment example, it can carry out by immersing for 30 minutes in 30 mass% nitric acid aqueous solution at 30 degreeC. Of course, it is not limited to this condition, For example, you may be immersed in 30 mass% nitric acid aqueous solution at 50 degreeC for about 10 second. It is preferable that the density | concentration of nitric acid aqueous solution is 30 mass% or more. By performing the passivation process, the main body part 12a of the stainless steel base material exposed in the pinhole 22a is passivated, and the passivation layer 16 of stainless steel is formed in the pinhole 22a. The thickness of the passivation layer 16 may be several nm (for example, 4 nm) or more, similarly to the thickness of a general passivation layer.

As mentioned above, according to the manufacturing method of the fuel cell separator of embodiment which concerns on this invention, since the strike gold plating layer 22s is formed using an acidic strike gold plating liquid, the gold plating layer 22 and the stainless steel base material 12a are made. There is almost no passivation layer 14 of stainless steel in between, and the adhesion between the gold plated layer 22 and the stainless steel base material 12a can be improved. In addition, since the passivation treatment is performed after the gold plated layer 22 is formed, the stainless steel base material 12a exposed in the pin hole 22a is passivated even when the pin hole 22a is present in the gold plated layer 22. As a result, the passivation layer 16 of stainless steel is formed in the pinhole 22a, and as a result, corrosion resistance is improved. Since the gold plating layer 22 may have a pinhole, it is not necessary to form it thickly, the treatment rate of a gold plating process is high, and material cost is low. In addition, if the passivation layer is removed by etching or cathodicly electrolyzing the surface of the stainless steel substrate prior to the strike gold plating step, the uniformity of the final gold plating finish can be improved.

Hereinafter, the separator for fuel cells and embodiment of the manufacturing method of the embodiment of the present invention will be described in detail with reference to experimental examples.

As the stainless steel base material 12 shown to Fig.1 (a), the base material (80 mm in length x 80 mm in width x 1.0 mm in thickness) formed from the austenitic stainless steel (SUS304) was prepared. An example of the concentration profile obtained as a result of analyzing the surface of the substrate by Glow-discharge emission spectrochemical analysis is shown in FIG. The horizontal axis represents depth from the substrate surface, and the vertical axis represents the concentration of each atom in atomic% (at%). 2, the results of carbon, nickel, copper, silicon, and manganese are omitted. The same applies to the following glow discharge emission spectroscopic analysis results.

As can be seen from Fig. 2A, Fe (iron), Cr (chromium) and O (oxygen) are confirmed on the surface of the base material 12, and it can be seen that an oxide layer is formed. This oxide layer is a passivation layer 14, as is well known. The thickness of the passivation layer 14 was about 4.4 nm when it evaluates in the depth which oxygen atom concentration becomes half of a peak value.

Next, the surface of the substrate 12 was etched by immersing the substrate 12 in an etching solution (mixed acid and hydrochloric acid) at 30 ° C. for 5 minutes, and then the etching solution was washed by immersing the substrate 12 twice in a tap water. An example of the result of analyzing the surface of this base material by the glow discharge emission spectroscopy is shown in FIG.2 (b). The oxygen atom concentration near the outermost surface was slightly lower than that in Fig. 2A, and was the same as the concentration profile in Fig. 2A except that the change in the depth direction was gentle. Even if the passivation layer 14 is removed by etching from this, it is thought that the passivation layer 14 was again formed during water washing and / or storage in air | atmosphere after that. In addition, the thickness of the passivation layer 14 calculated | required as mentioned above from the density | concentration profile of FIG. 2 (b) was about 6.1 nm.

In addition, the result of having performed the passivation process using nitric acid to the base material which carried out the etching and water washing, and analyzed the surface of the obtained base material by the glow discharge spectroscopy method is shown to FIG. 3 (a) and (b). FIG. 3A shows the results when 10% nitric acid solution is used, and FIG. 3B shows the results when 30% nitric acid solution is used. The concentration profiles of FIGS. 3A and 3B are almost the same as those of FIG. 2A, and the composition and thickness of the passivation layer on the surface are not changed by the passivation treatment with nitric acid. do. On the other hand, the thickness of the passivation layer 14 calculated | required as mentioned above from the concentration profile of FIG.3 (a) and (b) was about 4.5 nm and about 4.3 nm, respectively. From the result of FIG. 2 and FIG. 3, it is thought that the thickness of the passivation layer 14 formed in the surface of the base material used by this experiment is in the range of about 4 nm-about 6 nm.

Gold plating was performed by strike gold plating using an acidic strike gold plating solution and pure gold plating using a cyanide gold plating solution. Strike gold plating was carried out for 40 seconds at a current density of 1 A / dm ² using a gold strike plating solution (K-770 500 ml / L (2 times dilution) of Kojima Chemical Co., Ltd.) with a pH of 0.8 and a temperature of 35 ° C in cyanide. Plating was performed. The thickness of the strike gold plating layer obtained on this condition was about 0.01 micrometer. The thickness of a plating layer is the thickness measured using the fluorescent X-ray film thickness measuring system unless there is particular notice.

When forming the gold plating layer thicker than about 0.01 micrometer, pure gold plating was performed following strike gold plating. Gold plating has a pH of 6.3, cyanide geumdo amount of the temperature is 65 ℃ (Japan High Purity Chemicals Co., Ltd. tenpe resist BL 200g / L, cyanide gold potassium 8.0 g / L) used, and the current density of the power application time from 0.1 A / dm ² The thickness of the pure gold plating layer was adjusted by adjusting. A pure gold plating layer having a thickness of about 0.1 μm was obtained at a current supply time of 4 minutes.

The above conditions were changed and the sample was produced and corrosion resistance and contact resistance were evaluated. The preparation conditions and evaluation results of each sample are shown in Table 1 below.

Corrosion resistance was evaluated by visually observing the surface after immersion for 1000 hours in aqueous sulfuric acid solution (80 degreeC) of pH 1. The thing which could confirm the corrosion of a gold plated layer x and which does not lead to corrosion, but which showed discoloration was (triangle | delta) and the thing which did not show discoloration was made into (circle). On the other hand, ○ has practical corrosion resistance.

The contact resistance was a current of 1 A using a Milio Ohm meter while sandwiching each sample (separator) with carbon paper interposed therebetween at a surface pressure of 10 kgf / cm 2 with a gold plated copper plate (current collector plate). It evaluated by the resistance value at the time. On the other hand, when used for a fuel cell for PEFC of about 1 W, the contact resistance of the gold plated layer is preferably 10 mΩ · cm 2 or less, and more preferably 5 mΩ · cm 2 or less.

sample
No.

etching

acid
strike
gold plating

Pure gold
Plated

Gold plated layer
thickness
(탆)

Passivation
process

Corrosion
exam

Contact resistance
(mΩ · ㎠) Corrosion
Before the test Corrosion
After the test One - ○ ○ 0.1 - △ 4.64 4.99 2 ○ ○ ○ 0.1 - × 4.49 5.63 3 ○ ○ ○ 0.2 - △ 4.39 4.94 4 ○ ○ ○ 0.1 10% nitric acid * △ 4.97 5.25 5 ○ ○ ○ 0.1 10% nitric acid × 4.46 5.51 6 ○ ○ - 0.01 30% nitric acid × 4.63 5.42 7 ○ ○ ○ 0.05 30% nitric acid ○ 4.53 4.57 8 ○ ○ ○ 0.1 30% nitric acid ○ 4.48 4.51 9 ○ ○ ○ 0.2 30% nitric acid ○ 4.28 4.32

* Passivation treatment before gold plating

When looking at the resistance value before a corrosion test, the contact resistance of all the samples was favorable in 5 m (ohm) * cm <2> or less. That is, it turns out that a contact resistance can fully be reduced if the thickness of a gold plating layer is at least 0.01 micrometer.

In terms of corrosion resistance, the corrosion resistance of Sample 2 which was plated with gold after etching was lower than that of Sample 1 which was plated without etching. The corrosion resistance of Sample 1 is not sufficient because the adhesion between the passivation layer and the gold plating layer is low. The corrosion resistance of the sample 2 is lower than that of the sample 1, the passivation layer (FIG. 2 (b)) produced again after removing the passivation layer by etching is the passivation layer previously formed on the surface of a base material (FIG. 2 (a). It seems to be because corrosion resistance is lower than)). That is, as described with reference to Figs. 2A and 2B, even if the passivation layer is removed by etching, the passivation layer is formed again during washing and preservation. The chemical stability of the passivation layer is based on the surface of the original substrate. It is thought that the difference in the corrosion resistance of this passivation layer was shown as the difference in the resistance to corrosion from the pinhole of a gold-plated layer apart from the passivation layer formed in the surface (the surface of a general stainless steel base material is passivated).

Compare Sample 4 and Sample 2. The manufacturing process of sample 4 includes the passivation process by 10% nitric acid after the etching process in the manufacturing process of sample 2, and before strike gold plating. That is, the passivation process is given to the surface in which gold plating is performed. As a result, although the corrosion resistance of the sample 4 is superior to the sample 2, it is equivalent to the sample 1 and is not a sufficient level. In addition, the manufacturing process of the sample 4 simulates the manufacturing process of patent document 2. As shown in FIG.

In addition, as can be seen by comparing Sample 3 with Sample 2, when the thickness of the gold plated layer is 0.2 µm, the corrosion resistance is improved compared to Sample 2 (0.1 µm thickness of the gold plated layer), but sufficient corrosion resistance cannot be obtained.

In contrast, Samples 7 to 9 (Examples) have sufficient corrosion resistance, and as can be seen from the results of Sample 7, the thickness of the gold plated layer is only 0.05 µm. The contact resistance of these samples hardly increases even after a corrosion test, and it turns out that it has very excellent corrosion resistance.

On the other hand, it is understood from the results of Sample 6 that corrosion resistance is low when the thickness of the gold plated layer is 0.01 μm or less, and that the thickness of the gold plated layer exceeds 0.01 μm. In addition, as can be seen from the results of Sample 5, in the 10 mass% nitric acid solution, a passivation layer of stainless steel in the pinholes cannot be formed, and in order to form a passivation layer in the pinhole using the nitric acid solution, a 30 mass% or more nitric acid solution is used. It is understood that it is preferable to use. Although it is difficult to measure the surface profile of the composition in the pinhole, a direct analysis result was not obtained, but from the above experimental results, if the conditions of the passivation treatment were adjusted, the passivation layer of stainless steel sufficiently stable in the pinhole of the gold plated layer was obtained. It can be seen that it can form.

Here, Fig. 4A and Fig. 4B show the results of analyzing the surfaces of Samples 4 and 8 by glow discharge emission spectroscopy, respectively.

In the concentration profiles of Fe and Cr in Figs. 4A and 4B, after the Fe concentration begins to increase, Cr begins to increase. That is, it turns out that the iron oxide layer which does not contain chromium substantially is formed near the surface. This is in contrast to the presence of an oxide layer containing iron and chromium on the outermost surface in the passivation layer formed on the surface of the substrate shown in FIGS. 2 and 3. That is, in Sample 4 and Sample 8, there exists a region where the gold plated layer and the stainless steel base material contact without passing through the passivation layer of stainless steel. From the viewpoint of adhesiveness, it is considered preferable that no passivation layer of stainless steel exists between the gold plating layer and the stainless steel base material, but if the gold plating layer and the stainless steel base material are in contact without at least partially passing through the passivation layer, I think it will improve.

In particular, after performing etching, as shown in Fig. 4B, after the gold plating without the passivation treatment, the sample 8 is subjected to the passivation treatment after etching shown in Fig. 4A. The thickness of the iron oxide layer which does not substantially contain chromium is thicker than the sample 4 which carried out the gold plating to this. This is considered to be because the passivation layer formed by washing with water or preservation in air is more likely to be removed in an acid strike gold plating process than the passivation layer formed by the passivation treatment. On the other hand, in the acidic strike gold plating process, it is thought that the whole of a passivation layer is not removed but the chromium oxide rich part is removed in a passivation layer.

As mentioned above, when acidic gold strike plating is performed, the chromium oxide rich part of the passivation layer on the surface of a stainless steel base material is removed at least partially. Since chromium oxide reduces adhesiveness with a gold plating layer, the adhesiveness of a gold plating layer and a stainless steel base material is improved by removing the part rich in chromium oxide. In particular, after removing the passivation layer formed in advance by etching, chromium oxide can be removed more effectively by performing strike gold plating. On the other hand, as a result of various experiments, it was also found that the uniformity of the surface of the substrate is increased by etching, thereby improving the uniformity of the final gold plating finish.

In addition, even when the thickness of the gold plated layer is less than 0.3 µm and has a pinhole, the passivation treatment may be performed on the surface of the stainless steel substrate exposed in the pinhole by performing passivation treatment under predetermined conditions after the gold plating. Since it can be, corrosion resistance can be improved. In order to obtain high corrosion resistance, it is preferable to use 30 mass% or more nitric acid aqueous solution.

On the other hand, although strike gold plating and pure gold plating may be electroless plating, electroplating is preferable as illustrated here. In particular, the acidic strike gold plating not only forms a strike gold plating layer but also has an action and effect of removing a chromium-rich portion of the underlying passivation layer, so that electrolytic plating is preferable.

&Lt; Industrial Availability &gt;

The present invention is widely used in a fuel cell separator and a method of manufacturing the same.

12 stainless steel substrate
Body part of 12a stainless steel base (also called stainless steel base)
14 Passive layers, naturally formed
Passive layer formed in 16-pin hole
20 Fuel Cell Separator
22 gold-plated layer
22a pin hole
22s Strike Gold Plated Layer
22sa strike gold plated pinhole
22m pure gold plating layer

Claims (10)

Stainless steel base material,
A gold plated layer formed on the stainless steel substrate and having pin holes;
Having a passivation layer of stainless steel formed in the pin hole,
A fuel cell separator having a region in which the gold plated layer and the stainless steel substrate are in contact with each other without passing through a passivation layer of stainless steel. The method of claim 1,
A fuel cell separator having a region in which the gold plated layer and the stainless steel substrate are in contact with each other via an iron oxide layer substantially free of chromium. The method according to claim 1 or 2,
The thickness of the said passivation layer is 4 nm or more separator for fuel cells. The method according to claim 1 or 2,
The thickness of the said gold plating layer is 0.3 micrometer or less of separators for fuel cells. The method according to claim 1 or 2,
The separator for fuel cells whose contact resistance of the said gold plating layer is 10 m (ohm) * cm <2> or less. Process a for preparing a stainless steel base material,
A step b of forming a strike gold plated layer on the surface of the stainless steel base material using an acidic gold strike plating solution after the step a;
A step c of forming a gold plated layer on the strike gold plated layer after the step b;
And a step d of performing a passivation process on the condition that a passivation layer of stainless steel can be formed in said pinhole when said gold plating layer has a pinhole after said step c. The method according to claim 6,
The said process d is a manufacturing method of the separator for fuel cells performed using nitric acid of 30% or more concentration. 8. The method according to claim 6 or 7,
After the said process a and before the said process b, The manufacturing method of the fuel cell separator further includes the process of etching the surface of the said stainless steel base material. 8. The method according to claim 6 or 7,
The gold plated layer formed in the step c has a pin hole,
In the said process d, the manufacturing method of the separator for fuel cells which forms a passivation layer of stainless steel in the said pinhole. The fuel cell separator manufactured by the manufacturing method of the fuel cell separator of Claim 6 or 7.

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