WO2012053431A1

WO2012053431A1 - Fuel cell separator and method for producing same

Info

Publication number: WO2012053431A1
Application number: PCT/JP2011/073620
Authority: WO
Inventors: 将幸横田
Original assignee: 株式会社Ｎｅｏｍａｘマテリアル
Priority date: 2010-10-20
Filing date: 2011-10-14
Publication date: 2012-04-26
Also published as: KR20130032403A; TW201232892A; TWI489679B; CN103069629B; JP5133466B2; KR101266096B1; CN103069629A; JPWO2012053431A1

Abstract

This fuel cell separator (20) has a region comprising a stainless steel substrate (12a), a gold-plated layer (22) that is formed on the stainless steel substrate (12a) and has pinholes (22a), and a stainless steel passivation layer (16) formed inside the pinholes (22a), wherein the gold-plated layer (22) and the stainless steel substrate (12a) come into contact without involving the stainless steel passivation layer. This fuel cell separator (20) can be produced by forming a strike gold-plated layer on the surface of the stainless steel substrate (12) by using an acidic gold strike plating solution, then forming the gold-plated layer (22), and subsequently performing passivation treatment. The present invention provides: a fuel cell separator that has excellent corrosion resistance and that can be manufactured inexpensively, and a method for producing the fuel cell separator.

Description

Fuel cell separator and method for producing the same

The present invention relates to a separator for a fuel cell, and more particularly to a separator suitable for a polymer electrolyte fuel cell used for a power source for automobiles, a power source for portable devices, a distributed power source and the like.

From the viewpoint of high power generation efficiency and low environmental impact, research on fuel cells is actively conducted as a next-generation energy source.

A fuel cell is a power generation device that extracts electric energy by electrochemically reacting hydrogen, which is a fuel, and oxygen. Depending on the type of electrolyte used, the fuel cell can be a solid oxide fuel cell (SOFC), a molten carbonate fuel cell (MCFC), a phosphoric acid fuel cell (PAFC), or a solid polymer fuel cell (PEFC). ) And direct methanol fuel cell (DMFC). In particular, PEFC and DMFC have an operating temperature as low as about 70 to 90 ° C compared to other types of fuel cells, and PEFC and DMFC can generate high-efficiency power even with PEFC of about 1 kW and DMFC of about several hundred watts. In particular, application to automobiles and portable devices is expected. In particular, the DMFC is small, and its application to portable devices has been energetically studied.

The separator is required to have low gas permeability, excellent conductivity, low contact resistance, and excellent corrosion resistance. In particular, the demand for corrosion resistance and electrical conductivity has recently become stronger, and as an evaluation standard for corrosion resistance, “the rust (or corrosion) does not occur even if the separator is immersed in a sulfuric acid solution having a pH of about 1 for 1000 hours. Is listed. In particular, since DMFC is small, it is required to have excellent surface conductivity.

Carbon materials are widely used as separator materials having such characteristics. However, since carbon materials have poor toughness and are brittle, there is a problem that processing is difficult and processing costs are high. Therefore, in recent years, it has been studied to use stainless steel, which is easy to process and low in processing cost, as the separator material instead of the carbon material.

On the surface of stainless steel, an oxide film (passive film) in which Cr contained in the steel is combined with oxygen in the atmosphere is generated, so it has excellent corrosion resistance, but has high contact resistance. Cannot be used as Therefore, it is conceivable to cover the surface of stainless steel with a noble metal with excellent corrosion resistance and conductivity, but the adhesion between the passive film and the metal film is very poor, so the metal film is formed directly on the surface of the stainless steel. It is very difficult to do. Thus, until now, after completely removing the passive film by etching or the like, a method of plating a noble metal after forming a base plating layer containing a metal such as Ni has been performed. However, when the separator obtained by the above method is used for a long time, there is a problem that the corrosion resistance is lowered and the performance as a fuel cell is lowered. This is presumably because the corrosive liquid enters the inside through the pinholes generated in the noble metal film, and the dissimilar metal contact corrosion (galvanic corrosion) proceeds. Therefore, this method cannot satisfy the above-mentioned evaluation standard of corrosion resistance (the occurrence of rust is not recognized even when the separator is immersed in a strongly acidic solution for 1000 hours or more).

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

According to Patent Document 1, when the coverage of the gold layer formed directly on the passive layer is 2.3% to 94%, the corrosion resistance of the separator can be improved and the contact resistance can be sufficiently reduced.

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

JP 2004-296281 A JP 2007-323988 A

However, according to the study of the present inventor, the fuel cell separator described in Patent Document 1 does not have sufficient corrosion resistance. Moreover, since the separator described in Patent Document 2 requires heat treatment for improving the adhesion of the noble metal layer to the stainless steel, there is a problem that the throughput is low and the cost is high.

An object of the present invention is to provide a fuel cell separator that is excellent in corrosion resistance and can be manufactured at low cost, and a method for manufacturing the same.

The separator for a fuel cell of the present invention includes a stainless steel substrate, a gold plating layer having a pinhole formed on the stainless steel substrate, and a passive layer of stainless steel formed in the pinhole. And the gold plating layer and the stainless steel base material are in contact with each other without a stainless steel passivation layer. Preferably, there is no stainless steel passivation layer between the gold plating layer and the stainless steel substrate. The thickness of the gold plating layer is preferably at least more than 0.01 μm, and more preferably 0.05 μm or more.

In one embodiment, the gold plating layer and the stainless steel base material have a region in contact with each other via an iron oxide layer substantially not containing chromium. An iron oxide layer substantially free from chromium exists between the gold plating layer and the stainless steel substrate.

In one embodiment, the passive layer has a thickness of 4 nm or more.

In one embodiment, the gold plating layer has a thickness of 0.3 μm or less.

In one embodiment, the contact resistance of the gold plating layer is 10 mΩ · cm ² or less.

The method for producing a separator for a fuel cell according to the present invention includes a step a in which a stainless steel substrate is prepared, and a strike gold plating using an acidic gold strike plating solution on the surface of the stainless steel substrate after the step a. Step b for forming a layer, Step c for forming the gold plating layer on the strike gold plating layer after the step b, and the gold plating layer having a pinhole after the step c And a step d of performing a passivation treatment under conditions that allow a stainless steel passivation layer to be formed in the pinhole.

In an embodiment, the passivation treatment preferably uses nitric acid having a concentration of 30% or more.

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 plating layer formed in step c has a pinhole, and in step d, a stainless steel passivation layer is formed in the pinhole.

The fuel cell separator of the present invention may have substantially the same structure as the fuel cell separator manufactured by any one of the above-described fuel cell separator manufacturing methods. That is, at least a part of the passive layer between the gold plating layer and the stainless steel substrate is removed, so that the adhesion between the gold plating layer and the stainless steel substrate is improved, and the pin of the gold plating layer is further improved. It is only necessary to have a structure in which corrosion resistance is improved by forming a passive layer of stainless steel in the hole.

According to the present invention, a fuel cell separator having excellent corrosion resistance and high adhesion of a gold plating layer and a method for producing the same are provided.

(A)-(e) is typical sectional drawing for demonstrating the manufacturing method of the separator 20 for fuel cells of embodiment by this invention. It is a graph which shows the density | concentration profile of a stainless steel base material, (a) is a graph which shows the density | concentration profile of the stainless steel (SUS304) base material currently marketed, (b) is after etching and washing the surface. It is a graph which shows a density | concentration profile. (A) is a graph showing a concentration profile after etching and washing with a 10% nitric acid aqueous solution after washing, and (b) after etching and washing with a 10% nitric acid aqueous solution. It is a graph which shows a density | concentration profile. (A) is a graph which shows the density | concentration profile of the sample corresponding to the sample 4, and (b) is the sample 8, respectively.

Hereinafter, a fuel cell separator according to an embodiment of the present invention and a method for manufacturing the same will be described with reference to the drawings. Note that the present invention is not limited to the illustrated embodiment.

1A to 1E are schematic cross-sectional views for explaining a method for manufacturing a fuel cell separator 20 according to an embodiment of the present invention.

In the method for manufacturing a fuel cell separator according to an embodiment of the present invention, first, a stainless steel substrate 12 is prepared as shown in FIG. The stainless steel base 12 has a main body 12a made of stainless steel and a passive layer (passive film) 14 formed on the surface of the main body 12a. As is well known, the passive layer 14 is naturally formed when the stainless steel is left in the atmosphere, and contains a chromium oxide and chromium and iron hydroxides, and has excellent corrosion resistance. It is considered that a chromium oxide layer is formed on the main body 12a side, and a chromium and iron hydroxide layer is formed on the surface side. The thickness of the passive layer 14 is about several nm although it varies depending on conditions. As the stainless steel, for example, austenitic stainless steel (for example, SUS304, SUS316) or austenitic-ferritic stainless steel (for example, SUS329J1) can be preferably used. Prior to the next step, the surface of the passive layer 14 may be cleaned and / or degreased, if necessary.

Next, as shown in FIG. 1B, the surface of the stainless steel substrate 12 is etched. If, for example, hydrochloric acid or a mixed acid of hydrochloric acid and nitric acid is used as the etching solution, the passive layer 14 can be removed. Further, the passive layer 14 can be removed by cathodic electrolysis using an aqueous sulfuric acid solution as the electrolytic solution instead of etching. Thus, prior to the step of forming the strike gold plating layer 22s using the next acidic gold strike plating solution, the passivation layer 14 is removed once, thereby achieving the final gold plating uniformity. Can be increased. The uniformity of the gold plating finish can be easily confirmed visually.

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

In addition, in the process of forming a strike gold plating layer using an acidic gold strike plating solution, the passive layer 14 on the surface of the stainless steel substrate 12 is at least partially removed, so that prior to the strike gold plating step. Even if the passive layer 14 is not removed in advance, a gold plating layer having excellent corrosion resistance and adhesion can be obtained. By performing the etching process described with reference to FIG. 1B, the final uniformity of the gold plating can be improved. A naturally formed oxide layer has a non-uniform degree of oxidation, oxide layer thickness and oxide layer composition due to history (rolling conditions, storage environment, processing conditions before processing, etc.), and non-uniformity in the etching process. It is considered that the uniformity of the surface can be improved by removing the oxide layer.

Next, as shown in FIG. 1C, an acidic gold strike plating solution (for example, K-manufactured by Kojima Chemical Co., Ltd.) is formed on the surface of the main body 12a exposed as a result of removing the passive layer. 770) is used to form the strike gold plating layer 22s. As the acidic gold strike plating solution, known ones can be widely used. For example, one having a pH of 0.4 or more and 1.0 or less (liquid temperature of 20 ° C. or more and 40 ° C. or less) is preferable. 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. The thickness of the strike gold plating layer 22s is preferably, for example, 0.005 μm or more and 0.05 μm or less. Since the strike gold plating layer 22s is very thin, it has a pinhole 22sa. 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 step. The structure shown in (c) can be obtained.

Next, as shown in FIG. 1D, the gold plating layer 22m is formed on the strike gold plating layer 22s. The gold plating layer 22m is formed using, for example, a gold cyanide plating solution. A well-known thing can be widely used as a gold plating solution containing a cyanide compound (for example, Nippon High Purity Chemical Co., Ltd. Tempe resist BL). For example, those having a pH of 6.0 or more and 6.5 or less (liquid temperature of 60 ° C. or more and 70 ° C. or less) are preferable. 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.

The gold plating layer 22m does not need to be thick, and the gold plating layer 22 including the strike gold plating layer 22s and the gold plating layer 22m may have a pinhole 22a. According to the study of the present inventor, in order to form the gold plating layer 22 having no pinhole, the total thickness of the gold plating layer 22 is required to be approximately 1.2 μm or more. As will be shown later in the experimental example, the total thickness of the gold plating layer 22 is sufficient if the contact resistance can be sufficiently lowered, is preferably at least over 0.01 μm, and more preferably at least 0.05 μm. Further, the thickness of the gold plating layer 22 does not need to be more than 0.3 μm, and the contact resistance can be sufficiently reduced with a thickness of 0.3 μm or less. The contact resistance of the gold plating layer 22 is preferably 10 mΩ · cm ² or less.

Next, as shown in FIG. 1 (e), the fuel cell separator 20 is obtained by performing a passivation treatment on the main body 12a of the stainless steel base material on which the gold plating layer 22 is formed. The passivation treatment is performed under conditions that allow a stainless steel passivation layer to be formed in the pinhole when the gold plating layer has a pinhole. For example, as shown in an experimental example, it can be performed by immersing in a 30% by mass nitric acid aqueous solution at 30 ° C. for 5 minutes. Of course, it is not restricted to this condition, For example, you may immerse for about 10 second in 30 mass% nitric acid aqueous solution of 50 degreeC. The concentration of the nitric acid aqueous solution is preferably 30% by mass or more. By performing the passivation treatment, the main body 12a of the stainless steel substrate exposed in the pinhole 22a is passivated, and the stainless steel passivation layer 16 is formed in the pinhole 22a. The thickness of the passivation layer 16 may be several nm (for example, 4 nm) or more, like the thickness of a general passivation layer.

As described above, according to the fuel cell separator manufacturing method of the embodiment of the present invention, the strike gold plating layer 22s is formed using the acidic strike gold plating solution, so that the gold plating layer 22 and the stainless steel substrate 12a are formed. Between them, the stainless steel passive layer 14 is hardly present, and the adhesion between the gold plating layer 22 and the stainless steel substrate 12a can be improved. Further, since the passivation treatment is performed after the gold plating layer 22 is formed, the stainless steel substrate 12a exposed in the pin hole 22a is passivated even if the pin hole 22a exists in the gold plating layer 22. As a result of the formation of the passive layer 16 made of stainless steel in the pinhole 22a, the corrosion resistance is improved. Since the gold plating layer 22 may have pinholes, the gold plating layer 22 does not need to be formed thick, and the gold plating process has high throughput and low material costs. Moreover, if the passivation layer is removed by etching or cathodic electrolysis of the surface of the stainless steel substrate prior to the strike gold plating step, the final gold plating finish can be improved. .

Hereinafter, an experimental example will be shown to describe in detail a fuel cell separator and a method for manufacturing the same according to an embodiment of the present invention.

As the stainless steel substrate 12 shown in FIG. 1 (a), a substrate (length 80 mm × width 80 mm × thickness 1.0 mm) formed from austenitic stainless steel (SUS304) was prepared. FIG. 2A shows an example of a concentration profile obtained as a result of analyzing the surface of this substrate by glow discharge emission spectrometry. The horizontal axis represents the depth from the substrate surface, and the vertical axis represents the concentration of each atom in atomic% (at%). In FIG. 2, results for 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 substrate 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 passive layer 14 was about 4.4 nm when evaluated at a depth at which the oxygen atom concentration was half the peak value.

Next, the surface of the base material 12 is etched by immersing the base material 12 in an etching solution (mixed acid of hydrochloric acid and nitric acid) at 30 ° C. for 5 minutes, and then immersed twice in tap water stored in a container. As a result, the etching solution was washed away. FIG. 2B shows an example of the result of analyzing the surface of this substrate by glow discharge emission spectrometry. The oxygen atom concentration in the vicinity of the outermost surface was a little 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. From this, even if the passive layer 14 is removed by etching, it is considered that the passive layer 14 was formed again during washing with water and / or subsequent storage in air. The thickness of the passive layer 14 obtained in the same manner as described above from the concentration profile in FIG. 2B was about 6.1 nm.

Further, the substrate subjected to etching and washing with water was subjected to passivation treatment using nitric acid, and the results of analyzing the surface of the obtained substrate by glow discharge emission spectrometry were shown in FIGS. 3 (a) and 3 (b). Shown in FIG. 3A shows the results when a 10% nitric acid aqueous solution is used, and FIG. 3B shows the results when a 30% nitric acid aqueous solution is used. The concentration profiles in FIGS. 3 (a) and 3 (b) are almost the same as the concentration profile in FIG. 2 (a), and the composition and thickness of the surface passivation layer are changed by the passivation treatment with nitric acid. It is thought that it is not. In addition, the thickness of the passive layer 14 calculated | required similarly to the above from the density | concentration profile of Fig.3 (a) and (b) was about 4.5 nm and about 4.3 nm, respectively. From the results of FIGS. 2 to 3, the thickness of the passive layer 14 formed on the surface of the substrate used in this experiment is considered to be in the range of about 4 nm to about 6 nm.

Gold plating was performed by strike gold plating using an acidic strike gold plating solution and main gold plating using a gold cyanide plating solution. Strike gold plating uses a gold-based strike plating solution (K-770 500 ml / L (2 times dilution) manufactured by Kojima Chemical Co., Ltd.), which is cyan, has a pH of 0.8, and a temperature of 35 ° C. Electroplating was performed at dm ² for 40 seconds. The thickness of the strike gold plating layer obtained under these conditions was about 0.01 μm. The thickness of the plating layer is a thickness measured using a fluorescent X-ray film thickness meter unless otherwise specified.

When a gold plating layer thicker than about 0.01 μm was formed, the gold plating was performed following the strike gold plating. For this gold plating, a gold cyanide plating solution having a pH of 6.3 and a temperature of 65 ° C. (Tempresist BL 200 g / L, potassium gold cyanide 8.0 g / L, manufactured by Japan High Purity Chemical Co., Ltd.) The thickness of the gold plating layer was adjusted by adjusting the energization time at a current density of 0.1 A / dm ² . The energized time was 4 minutes, and a gold plating layer having a thickness of about 0.1 μm could be obtained.

Specimens were prepared by changing the above conditions, and corrosion resistance and contact resistance were evaluated. The production conditions for each sample and the evaluation results are shown in Table 1 below.

Corrosion resistance was evaluated by visually observing the surface after being immersed in a sulfuric acid aqueous solution (80 ° C.) having a pH of 1 for 1000 hours. The case where the corrosion of the gold plating layer was confirmed was rated as “X”, the case where corrosion was not reached but a discoloration was observed was indicated as “Δ”, and the case where no discoloration was observed was indicated as “◯”. In addition, (circle) has the corrosion resistance which can be used practically.

The contact resistance is 1A using a milliohm meter in a state where each sample (separator) is sandwiched between a carbon plate and a copper plate (current collector plate) plated with gold at a surface pressure of 10 kgf / cm ^2. It was evaluated by the resistance value when a current of. In the case of using the PEFC for a fuel cell of about 1W, it is preferable that the contact resistance of the gold plating layer is 10 m [Omega · cm ² or less, and more preferably 5 m [Omega · cm ² or less.

Looking at the resistance values before the corrosion resistance test, the contact resistance of all the samples was 5 mΩ · cm ² or less, which was good. That is, it can be seen that the contact resistance can be sufficiently reduced if the thickness of the gold plating layer is at least 0.01 μm.

Regarding the corrosion resistance, the corrosion resistance of Sample 2 plated with gold after etching is inferior to that of Sample 1 plated with gold without etching. The reason why the corrosion resistance of Sample 1 is not sufficient is that the adhesion between the passive layer and the gold plating layer is low. The corrosion resistance of the sample 2 is lower than that of the sample 1 because the passive layer (FIG. 2 (b)) regenerated after removing the passive layer by etching is a passive layer that has been previously formed on the surface of the substrate. This is probably because the corrosion resistance is lower than that of the layer (FIG. 2A). That is, as described with reference to FIGS. 2A and 2B, even if the passive layer is removed by etching, the passive layer is formed again during washing and storage. The chemical stability of this is inferior to the passive layer formed on the surface of the original substrate (the surface of a general stainless steel substrate is passivated), and the corrosion resistance of this passive layer This difference is considered to have appeared as a difference in resistance to corrosion from pinholes in the gold plating layer.

Compare sample 4 and sample 2. The manufacturing process of sample 4 includes a passivation treatment with 10% nitric acid after the etching process in the manufacturing process of sample 2 and before the strike gold plating. That is, the passivation process is performed on the surface to which gold plating is applied. As a result, although the corrosion resistance of the sample 4 is superior to that of the sample 2, it is equivalent to the sample 1 and is not at a sufficient level. The manufacturing process of the sample 4 is a simulation of the manufacturing process described in Patent Document 2.

Further, as can be seen from a comparison between Sample 3 and Sample 2, when the thickness of the gold plating layer is 0.2 μm, the corrosion resistance is improved as compared with Sample 2 (thickness of the gold plating layer is 0.1 μm). Can not get good corrosion resistance.

On the other hand, Samples 7 to 9 (Examples) have sufficient corrosion resistance, and as can be seen from the results of Sample 7, it is sufficient that the thickness of the gold plating layer is 0.05 μm. It can be seen that the contact resistance of these samples hardly increased even after the corrosion resistance test, and has very excellent corrosion resistance.

In addition, it can be seen from the results of Sample 6 that when the thickness of the gold plating layer is 0.01 μm or less, the corrosion resistance is low, and the thickness of the gold plating layer is preferably more than 0.01 μm. In addition, as can be seen from the results of Sample 5, a 10% by mass nitric acid aqueous solution cannot form a passive layer of stainless steel in the pinhole, and the nitric acid aqueous solution is used to form a passive layer in the pinhole. It is understood that it is preferable to use a 30% by mass or more nitric acid aqueous solution. Although it is difficult to measure the surface profile of the composition in the pinhole and no direct analysis results have been obtained, if the conditions of the passivation treatment are adjusted from the above experimental results, the gold plating layer It can be seen that a sufficiently stable passive layer of stainless steel can be formed in the pinhole.

Here, FIGS. 4 (a) and 4 (b) show the results of analyzing the surfaces of Sample 4 and Sample 8 by glow discharge optical emission spectrometry, respectively.

4A and 4B, the Fe and Cr concentration profiles show that after the Fe concentration starts to increase, Cr begins to increase. That is, it can be seen that an iron oxide layer substantially free of chromium 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 passive layer formed on the surface of the substrate shown in FIGS. . That is, in Sample 4 and Sample 8, there is a region where the gold plating layer and the stainless steel base material are in contact with each other without passing through the stainless steel passive layer. From the viewpoint of adhesion, it is considered preferable that there is no stainless steel passive layer between the gold plating layer and the stainless steel base material, but at least partially without passing through the passive layer, If the gold plating layer and the stainless steel substrate are in contact, the adhesion is considered to be improved.

In particular, after performing the etching shown in FIG. 4B, the sample 8 plated with gold without performing the passivation treatment performed the etching shown in FIG. 4A. Then, the thickness of the iron oxide layer which does not contain chromium substantially is thicker than the sample 4 which performed the passivation process and performed gold plating after that. This is because the passive layer formed by washing with water and storing in the air after removing the passive layer is removed in the acidic strike gold plating process rather than the passive layer formed by the passivation treatment. It is thought that it is easy to be done. In the acidic strike gold plating step, it is considered that not all of the passive layer is removed but a portion rich in chromium oxide in the passive layer is removed.

From the above, when acidic gold strike plating is performed, the chromium oxide rich portion of the passive layer on the surface of the stainless steel substrate is at least partially removed. Since chromium oxide reduces the adhesion with the gold plating layer, the adhesion between the gold plating layer and the stainless steel substrate is improved by removing the portion rich in chromium oxide. In particular, the chromium oxide can be more effectively removed by performing strike gold plating after removing the previously formed passive layer by etching. As a result of various experiments, it has also been found that by performing etching, the uniformity of the surface of the substrate can be increased, and the uniformity of the final gold plating finish can be improved.

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

The strike gold plating and the gold plating may be electroless plating, but as exemplified here, electrolytic plating is more preferable. In particular, 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 passive layer, and for this purpose, electrolytic plating is preferred.

The present invention is widely used in fuel cell separators and manufacturing methods thereof.

12 Stainless steel substrate 12a Stainless steel substrate body (also called stainless steel substrate)
14 Passive layer (naturally formed)
16 Passive Layer Formed in Pinhole 20 Fuel Cell Separator 22 Gold Plating Layer 22a Pinhole 22s Strike Gold Plating Layer 22sa Strike Gold Plating Pinhole 22m Real Gold Plating Layer

Claims

A stainless steel substrate;
A gold plating layer having a pinhole formed on the stainless steel substrate;
A stainless steel passivation layer formed in the pinhole, and a fuel having a region in which the gold plating layer and the stainless steel substrate are in contact with each other without a stainless steel passivation layer Battery separator.
2. The fuel cell separator according to claim 1, wherein the gold plating layer and the stainless steel substrate have a region in contact with each other through an iron oxide layer substantially not containing chromium.
The fuel cell separator according to claim 1 or 2, wherein the passive layer has a thickness of 4 nm or more.
The fuel cell separator according to any one of claims 1 to 3, wherein the gold plating layer has a thickness of 0.3 µm or less.
The fuel cell separator according to any one of claims 1 to 4, wherein a contact resistance of the gold plating layer is 10 mΩ · cm 2 or less.
Preparing a stainless steel substrate a;
After the step a, a step b of forming a strike gold plating layer on the surface of the stainless steel substrate using an acidic gold strike plating solution;
A step c of forming a gold plating layer on the strike gold plating layer after the step b;
After the step c, when the gold plating layer has a pinhole, a step d for performing a passivation treatment under a condition that a passive layer of stainless steel can be formed in the pinhole. A method for producing a fuel cell separator.
The method for producing a fuel cell separator according to claim 6, wherein the step d is performed using nitric acid having a concentration of 30% or more.
The method for manufacturing a fuel cell separator according to claim 6 or 7, further comprising a step of etching the surface of the stainless steel substrate after the step a and before the step b.
The gold plating layer formed in the step c has a pinhole,
The method for producing a fuel cell separator according to any one of claims 6 to 8, wherein a passivating layer of stainless steel is formed in the pinhole in the step d.
A fuel cell separator manufactured by the method for manufacturing a fuel cell separator according to any one of claims 6 to 9.