JP2006097088A - Gold-plated structure, and separator made of the gold-plated structure for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gold-plated structure which is superior in electroconductivity, corrosion resistance, mechanical properties, and the like, is lightweight, has superior workability, and is inexpensively mass-produced, and to provide a separator for a fuel cell. <P>SOLUTION: The gold-plated structure has gold-plated parts and non-plated parts on the surface of a titanium substrate, wherein each of the gold-plated parts has an insular shape with a diameter of 100 nm to 1 nm, and are interspersed on the surface of the titanium substrate. The separator for the fuel cell is formed of the gold-plated structure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a gold plating structure. More specifically, the present invention relates to a gold-plated structure that is excellent in electrical conductivity, corrosion resistance, mechanical properties, etc., is lightweight, excellent in workability, and can be mass-produced at low cost.

  Such a gold-plated structure according to the present invention can be used in a wide range of applications by taking advantage of the above characteristics, and is particularly suitable as a separator for a fuel cell.

In general, a fuel cell is composed of a plurality of cells, and a separator is disposed on the outermost side of each cell structure. A conceptual diagram of a unit cell structure of a fuel cell is shown in FIG.
Here, the separator is a structure that requires various characteristics as follows.
The first is the mechanical strength for maintaining the cell structural unit.
The second is workability that can form a groove for sending fuel hydrogen gas into the cell at low cost.
The third is a low contact resistance that allows electrons generated inside the cell to be collected by contacting the diffusion layer.
The fourth is sufficient corrosion resistance against sulfuric acid generated in the proton permeable membrane inside the cell.

As a metal separator for a fuel cell and a method for producing the same, there is a technology described in Japanese Patent Application Laid-Open No. 2003-234109, and as a separator for a polymer electrolyte fuel cell and a method for producing the same, described in Japanese Patent Application Laid-Open No. 10-334927. There is a technology.
JP 2003-234109 A JP-A-10-334927

  At present, as a separator, a graphite plate or a stainless steel plate is generally processed, but as far as the present inventors know, a structure satisfying all the above conditions has not yet been obtained.

  The graphite plate utilizes the original conductivity and corrosion resistance of graphite. However, since graphite has insufficient mechanical strength, it is necessary to use a thick graphite plate, and in order to form a groove for sending hydrogen gas to this graphite surface, the surface of the graphite plate is mechanically Therefore, it is necessary to select a method of cutting, which has a disadvantage of disadvantage in terms of manufacturing cost.

  The stainless plate utilizes the mechanical strength and workability of the stainless plate. The lack of electrical conductivity of the stainless steel plate is compensated by applying a precious metal plating such as gold plating on the stainless steel surface. However, if the gold plating film is thin and there is a pinhole, corrosion of the stainless steel tends to occur. On the other hand, if the gold plating is thickened to eliminate pinholes, the manufacturing cost increases.

  The inventors focused on the excellent mechanical strength, corrosion resistance, and workability of titanium, and searched for a structure satisfying the above characteristics by forming various gold plating films on the titanium base material. .

  Conventionally, gold plating on titanium has often been used for decorative items such as glasses and watches. In such a decorative product application, a glossy gold color is required, and a gold plating film having a level of several hundred nanometers is required. A gold film of several hundred nanometers has few pinholes and a uniform film structure is formed on titanium, which is suitable in terms of strength and corrosion resistance. The cost associated with the thickness of the gold film has not been a significant problem for decorative applications.

  On the other hand, when gold plating is applied to the separator structure material, an extremely thin thickness is required from the viewpoint of cost. In addition, such an extremely thin thickness is required to have sufficient contact resistance and satisfy the adhesion and corrosion resistance of the plating film.

  The inventors have found that this goal is met by forming a specially shaped gold-plated thin film on pure titanium material.

  Therefore, the gold-plated structure according to the present invention has a gold-plated portion and a non-plated portion on the surface of the titanium substrate, and the gold-plated portion is an island shape having a diameter of 100 nm or less and 1 nm or more. It is characterized by being scattered on the surface.

  Such a gold-plated structure according to the present invention includes, as a preferred embodiment, one having an average gold-plated thickness of 30 nm or less and 1 nm or more on the surface of the titanium substrate.

  Such a gold-plated structure according to the present invention includes, as a preferred embodiment, one in which the gold-plated portion is island-shaped with a diameter of 50 nm or less and 1 nm or more and is scattered on the surface of the titanium substrate.

  Such a gold-plated structure according to the present invention includes, as a preferred embodiment, one having a gold plating thickness of 15 nm or less and 1 nm or more.

  Such a gold-plated structure according to the present invention includes, as a preferred embodiment, one in which the titanium base material conforms to JIS standard type 1 and has a thickness of 0.4 mm or less and 0.1 mm or more.

  Such a gold-plated structure according to the present invention includes, as a preferred embodiment, one in which the gold-plated portion is formed of an electrolytic gold plating solution containing a trivalent gold compound as an essential component.

  Such a gold-plated structure according to the present invention includes, as a preferred embodiment, one in which the proportion of the gold-plated portion on the surface of the titanium substrate is 10% or more and 90% or less.

  And the separator for fuel cells by this invention consists of said gold plating structure.

  According to the present invention, it is possible to obtain a gold-plated structure that has a gold-plated portion and a non-plated portion on a titanium substrate and has a very thin gold-plated thickness. This gold-plated structure is preferable in terms of manufacturing cost because it requires a small amount of gold material, and at the same time has good contact resistance, plating adhesion, corrosion resistance, and workability. Therefore, according to the present invention, it is possible to obtain a fuel cell separator that is low in cost and excellent in strength and corrosion resistance.

  In order to prevent pinholes, a gold-plated structure having sufficient strength and corrosion resistance can be obtained simply by partially forming a very thin gold-plated layer of 30 nanometers or less as in the present invention. In addition, it is unexpected that a gold plating layer of about several hundred nanometers was uniformly formed.

  On the other hand, the titanium material was not satisfactory in terms of contact resistance due to the oxide film existing on the surface thereof, but in the present invention, a predetermined gold plating part is formed on the surface of the titanium base material from which the oxide film has been removed. Therefore, the function as a current collector of the fuel cell can be sufficiently exhibited.

  The gold plating structure according to the present invention is completely different from the gold plating for decoration in the thickness and shape of the gold plating. That is, the gold plating thickness is usually several hundred nanometers (nm) for decoration, whereas the gold plating thickness in the gold plating structure according to the present invention is several tens of nanometers or less, specifically 30 nm. Below. As for the coating film shape, the gold coating film is uniformly applied to the entire titanium surface for decoration, whereas in the gold plating structure of the present invention, the titanium substrate surface has a gold plating part and non-plating, Preferably, the gold plating is formed in an island shape.

  The titanium base material that is the object of gold plating is generally made of titanium alloy or pure titanium JIS type 2 for decoration, whereas the separator structure of the present invention preferably uses pure titanium JIS type 1. By using pure titanium JIS type 1 as a base material, it becomes easy to form a groove serving as a fuel gas passage on the titanium surface by press working before or after gold plating.

  When satisfying such coating conditions, the gold-plated structure has low contact resistance, good corrosion resistance to sulfuric acid, and the island-shaped gold plating is firmly adhered to the titanium base material. It satisfies the required characteristics as a separator.

  In order to explain the present invention in more detail, an electron micrograph of 50,000 times the surface of the gold-plated structure of the present invention is shown in FIG. In FIG. 2, gold-plated islands are dispersed in white dots. As shown in FIG. 2, in the gold-plated portion, granular islands having a diameter of 30 to 50 nm (nanometers) are scattered on the titanium base material independently or continuously.

  FIG. 3 is a photograph of a cross section of the same gold-plated structure observed from the side using a FIB (Focused Ion Beam) apparatus. FIG. 3 shows that the gold-plated coating portions dispersed in an island shape are arranged in a dotted line on the titanium surface.

  When this gold-plated structure is measured with a fluorescent X-ray film thickness meter, the gold-plated film thickness is 20 nm. This is a gold fluorescent X-ray emitted from a 0.1 mm (100,000 nm) opening diameter on the titanium surface. The film thickness was measured from the strength of the film. Since the plating film thickness measuring device measures the measurement location (opening diameter) much larger than the size of the gold plating island (several tens of nm diameter) on the titanium substrate of the present invention, the gold plating coating film Is dispersed in islands, the film thickness of 20 nm is the average film thickness of the coated and uncoated areas.

  If the area ratio of the gold island on the titanium surface is 66%, when the film thickness of 20 nm is obtained by fluorescent X-ray analysis, the local thickness of the island (gold coated portion) is more than 20 nm. It is large and becomes 30 nm, which is higher than the measured value of the film thickness meter.

  On the other hand, when FIG. 2 is seen, it can be seen that an uneven structure exists on the surface of the titanium base material. This is caused by a titanium stretching process for supplying a titanium base material as a base material, a titanium oxide removing process performed as a pre-process for the gold plating treatment of the titanium base material, and the like. Considering such a concavo-convex structure on the surface of the base material, the actual area of the 0.1 mm diameter titanium surface, which is the opening diameter of the film thickness meter, is not the area of a 0.1 mm diameter circle, but a larger value than this. Become. When the surface area of the concavo-convex structure is 1.2 times that of a flat surface, the actual film thickness of the gold coated portion is smaller than 20 nm output from the fluorescent X-ray apparatus and is calculated to be 17 nm.

  Thus, the local film thickness display of the gold-plated part in consideration of the island structure and the unevenness of the titanium base material becomes complicated. Therefore, the film thickness display of the gold plating in the present invention uses a measurement value (average film thickness at an opening diameter of 0.1 mm) of a fluorescent X-ray film thickness meter that is ordinarily widely used in the plating industry. That is, the average gold plating thickness on the surface of the titanium substrate in the present invention means a measured value (average film thickness at an opening diameter of 0.1 mm) of a fluorescent X-ray film thickness meter.

  In the gold plating structure of the present invention, the thickness of the gold plating is preferably 30 nm or less in the fluorescent X-ray film thickness display. More desirable is 15 nm or less. If it exceeds 30 nm, the adhesion of the gold-plated coating film decreases. The lower limit of the plating film thickness is 1 nm, and if it is less than this, the contact resistance increases, and the function as a current collector decreases. In addition, under the gold plating film thickness condition of 30 nm or less, the lemon yellow gold color required for decorative gold plating is not observed. Moreover, a uniform coating film is not formed, and a gold application part having an island shape with a diameter of several tens of nm appears. It is completely unexpected from the conventional knowledge that such an island-like structure in which gold-plated portions are dispersed in the form of dots satisfies various physical properties required as a separator.

  The proportion of the gold-plated portion on the surface of the titanium substrate is preferably 10% or more and 90% or less, particularly preferably 20% or more and 80% or less. Here, the ratio which a gold plating part accounts is calculated | required by the area measurement of an electron micrograph.

  FIG. 4 shows the structure of the measurement terminal portion of the contact resistance measuring device for the gold plating surface used in the present invention. Here, a measurement method based on a four-terminal method, which is widely used for connectors of electronic components, is employed. The contact resistance of one kind of pure titanium base material to which no gold plating is applied becomes 200 mΩ or more, and the function as a current collector is lost. This is because the surface of the titanium base material without the gold plating part is all covered with titanium oxide, and even if it comes into contact with the carbon paper, it cannot receive electrons.

  On the other hand, when the thickness of the gold plating on the titanium substrate is in the range of 1 nm to 30 nm, the contact resistance of the titanium substrate is around 10 mΩ, and by contacting with the carbon paper of the adjacent gas diffusion layer in the cell, It exhibits sufficient conductivity as a current collector that collects the electrons that are sent. This is because even if the gold plating part is divided into islands, the gold plating part comes into contact with the adjacent carbon paper and accepts electrons, and the electrons are transported via the underlying titanium substrate. is there. At present, the resistance of carbon paper used for the gas diffusion layer of the fuel cell is 50 to 200 mΩ, which is considerably higher than that of the titanium substrate of the present invention. Therefore, the gold-plated structure of the present invention is a current collector. It can satisfy the function as a body.

  Next, although it is the magnitude | size of the application part (island) to which gold plating is given, the diameter of an island is desirable at 100 nm or less. More desirable is 50 nm or less. Gold deposited on the titanium substrate is deposited in the form of particles to form islands. The size of the gold particles correlates with the island diameter, and the larger the particle diameter, the larger the island thickness of the coating portion.

  As a result, even if the same amount of gold is applied on the titanium substrate (even if the film thickness meter shows the same gold film thickness), the larger the gold particles (that is, the larger the island diameter), the more titanium The contact area between gold and titanium per unit unit area of the base material is reduced, and the adhesion of the gold-plated coating film is reduced. On the other hand, when the island diameter is less than 1 nm, the coating film thickness is also less than 1 nm, the contact resistance is increased, and the physical properties of the current collector are lowered. Therefore, the diameter of the gold plating part on the titanium substrate is desirably 1 nm or more and 100 nm.

  The gold-plated structure according to the present invention can be obtained by treating titanium as a base material through a series of steps of degreasing, etching, and gold plating.

  The degreasing step is mainly a step of removing an organic compound or the like attached on the titanium base material. This degreasing step can be carried out as it is, or if necessary, modified as it is, when a titanium material is plated. For example, it can be carried out by immersing the titanium base material in a degreasing liquid (particularly preferably, a titanium degreasing liquid “DG-1”, manufactured by Nippon Kogyo Chemical Co., Ltd.). In this case, the treatment time is preferably about 30 to 300 seconds, and the treatment temperature is preferably about 25 to 65 ° C.

  The degreased titanium substrate is washed with water and then etched. This etching process is mainly a process of removing the titanium oxide film formed on the surface of the titanium substrate. This degreasing process can also be performed as it is or after modification as necessary. For example, by immersing the substrate in an etching solution (fluorine titanium etching solution “ET-1” or (and) non-fluorine titanium etching solution “ET-2”, both of which are manufactured by Nihon Kojun Chemical Co., Ltd.) Can do. Both of these degreasing and etching processes are steps necessary to remove factors that interfere with the adhesion of the gold-plated coating film to the substrate. In this case, the treatment time is preferably about 1 to 10 minutes, and the treatment temperature is preferably about 25 to 85 ° C.

  The gold plating treatment in the present invention can be performed using an electrolytic gold plating solution. The gold plating solution used here is preferably one containing a trivalent gold compound. Specifically, it is possible to use a plating solution containing a compound such as second gold potassium cyanide, second gold sodium cyanide, second gold chloride, second gold potassium sulfite and second gold sodium sulfite as a gold source. As a preferable example of such a gold plating solution, for example, “Tempe Resist-TX” (manufactured by Nippon High Purity Chemical Co., Ltd.) can be exemplified. The gold plating treatment in the present invention can be performed by immersing the titanium base material in the above electrolytic gold plating solution and energizing it. The thickness of the gold plating can be performed by adjusting the current density, the energization time, the gold compound concentration in the gold plating solution, etc. in the electrolytic plating process.

  Although it is a titanium base material used for this invention, the thing of 1 type of the JIS specification of pure titanium is desirable. Conventionally, two types of decorative objects and insoluble anodes have been used. Comparing 1 type and 2 types of JIS standards, 2 types are superior in strength and 1 type is excellent in workability. In consideration of application to a fuel cell separator, it is preferable to use one kind of titanium substrate. This is because type 1 titanium can be pressed and a fine gas passage for a separator can be formed at low cost by pressing.

  The thickness of the titanium substrate is desirably 0.4 mm or less and 0.1 mm or more. Particularly desirable plate thicknesses for the separator are 0.2 mm or less and 0.15 mm or more.

  The press working can be performed either before or after the gold plating process of the titanium substrate. The press working can be performed according to the specific shape and size of the fuel cell separator. For example, as shown in FIGS. 5A and 5B, a titanium base material is pressed so that triangular convex portions having a height of 2 mm and a width of 1.5 mm are formed in parallel at intervals of 3 mm. Can do.

Hereinafter, specific examples of the present invention will be described by way of examples. The analysis apparatus and evaluation apparatus used here are as follows.
Film thickness meter: SEA5100 Micro fluorescent X-ray analyzer (manufactured by Seiko Instruments Inc.)
Electron microscope: S-4300 High-resolution scanning electron microscope (manufactured by Hitachi, Ltd.)
FIB: FB-2100 Focused ion beam processing observation device (manufactured by Hitachi, Ltd.)
Contact resistance: CRS-113-Au Electrical contact simulator (manufactured by Yamazaki Seiki Laboratory Co., Ltd.)
The area ratio of the gold-plated portion on the titanium surface was determined by printing an electron micrograph on A4 size paper, cutting out the island-shaped gold-plated portion with scissors, and weighing with an electronic balance.

<Example 1>
The press-processed 0.16 mm thick JIS type 1 titanium substrate (FIG. 5) was electrolyzed (cathode) degreased at 5 V for 15 seconds with a titanium degreasing solution (“DG-1”, manufactured by Nippon Kogyo Kagaku Co., Ltd.) and washed with water. Thereafter, the surface oxide layer was removed by immersing in a fluorine-based titanium etching solution (“ET-1”, manufactured by Nippon Kosei Kagaku Co., Ltd.) at room temperature for 2 minutes.

After washing with water, etching was performed at 60 ° C. for 10 minutes with a non-fluorine-based titanium etching solution (“ET-2”, manufactured by Nippon Pure Chemical Co., Ltd.), followed by washing with water. This pre-treated titanium substrate was plated for 30 seconds at room temperature and a current density of 10 A / dm ² using a gold plating solution (“Tempe Resist-TX”, manufactured by Nippon Kogyo Kagaku Co., Ltd.). A plating structure was created. As shown in the electron micrographs of FIGS. 6 and 7, this gold-plated structure is composed of one or more islands having a diameter of 35 to 50 μm, and the proportion of the gold-plated portion is 50 to 58%. It was a thing.

  The adhesion of the obtained gold plating film was measured by a cello tape peeling method. Here, when the fine point of the gold plating was not transferred onto the adhesive surface of the cello tape, it was determined that the adhesiveness was good, whereas when it was transferred, it was determined that the adhesiveness was insufficient. This observation was performed using an optical microscope.

The contact resistance of the gold-plated structure was measured by the 4-terminal method. The contact resistance was measured by changing the load from 0 to 50 gf, and judged by the value at 50 gf.
The corrosion resistance was evaluated by immersing the prepared test piece in a 10% aqueous sulfuric acid solution at room temperature for 1 week, and measuring the contact resistance after immersion as described above.
The results are as shown in Table 1.

<Example 2>
JIS type 1 titanium substrate (25 × 50 × 0.16 mm) was used, electrolytic degreasing with titanium degreasing liquid (“DG-1”) at 5 V for 15 seconds, water washing, and then fluorine-based titanium etching liquid (“ET-1”) )) At room temperature for 1 minute to remove the oxide layer on the surface. After washing with water, etching was performed at 60 ° C. for 10 minutes with a non-fluorinated titanium etching solution (“ET-2”), followed by washing with water. The pretreated titanium substrate was plated with a Tempe resist-TX gold plating solution at room temperature and a current density of 10 A / dm ^{2 for} 15 seconds to prepare a gold-plated structure having a thickness of 10 nm. As shown in FIG. 8, this gold-plated structure was composed of one or more islands having a diameter of 25 to 35 μm, and the proportion of the gold-plated portion was 54%.
The results of adhesion, contact resistance and corrosion resistance of the gold plating film evaluated in the same manner as in Example 1 are shown in Table 1.

<Example 3>
The same titanium substrate as in Example 2 is subjected to the same pre-plating treatment, and then plated for 3 seconds at a gold plating solution (“Tempresist TX”), room temperature, and a current density of 10 A / dm ² , and a gold plating structure with a film thickness of 2 nm. Created the body. In this gold-plated structure, one or a plurality of islands having a diameter of 8 to 12 μm are continuous, and the proportion of the gold-plated portion is 30%. FIG. 9 shows an SEM image.
The results of adhesion, contact resistance and corrosion resistance of the gold plating film evaluated in the same manner as in Example 1 are shown in Table 1.

<Comparative Example 1>
The same titanium base material as that of Example 2 was subjected to the same plating pretreatment, and a gold plating solution in which Tl ₂ SO ₄ (10 ppm as Tl) was added as a crystal modifier to a gold plating solution (“Tempresist-TX”) was used. Then, plating was performed at room temperature and a current density of 10 A / dm ^{2 for} 30 seconds to prepare a gold-plated structure with a film thickness of 30 nm.

FIG. 10 shows an SEM image. Since the gold island diameter was about 150 nm and the contact area between gold and titanium was reduced, the adhesion of the gold plating film was insufficient and a tendency to peel off immediately after plating was observed.
The results of adhesion, contact resistance and corrosion resistance of the gold plating film evaluated in the same manner as in Example 1 are shown in Table 1.

<Comparative example 2>
JIS type 1 titanium substrate (25 × 50 × 0.16 mm) was used, electrolytic degreasing with titanium degreasing liquid (“DG-1”) at 5 V for 15 seconds, water washing, and then fluorine-based titanium etching liquid (“ET-1”) )) At room temperature for 1 minute to remove the oxide layer on the surface. Thereafter, a gold plating solution (Tempresist-TX, room temperature, current density of 1.0 A / dm ² was plated for 5 seconds to prepare a gold plating structure having a film thickness of less than 1 nm.
The results of adhesion, contact resistance and corrosion resistance of the gold plating film evaluated in the same manner as in Example 1 are shown in Table 1. When the film thickness was less than 1 nm, the gold film was not sufficiently formed, and a satisfactory contact resistance value could not be obtained.

<Comparative Example 3>
The same plating pretreatment as in Example 2 was performed, and an acid strike (manufactured by Nihon Kojun Kagaku) gold plating solution composed of a monovalent gold compound was used for plating for 15 seconds at a current density of 4.0 A / dm ² and room temperature. A gold-plated structure having a thickness of 10 nm was prepared.

The results of adhesion, contact resistance and corrosion resistance of the gold plating film evaluated in the same manner as in Example 1 are shown in Table 1, and the SEM image is shown in FIG.
Thus, when a monovalent gold compound is used, the gold particles are dispersed and scattered, and the island diameter is 100 nm or more. Therefore, the adhesion is insufficient, and a tendency to peel off immediately after plating was observed. .

As is apparent from Table 1 above, the gold plating structures prepared in Examples 1 to 3 had a gold island diameter in the range of 20 to 50 nm and good adhesion. The contact resistance value was also a level sufficient to be used as a separator for a fuel cell, and the change in the value before and after immersion in sulfuric acid was small and the corrosion resistance was also good.
On the other hand, in Comparative Examples 1 and 3, the gold island diameter was 100 nm or more, and the adhesion was insufficient. In Comparative Example 2, a satisfactory contact resistance was not obtained due to insufficient gold film formation.

<Effect of the invention>
As described above, according to the gold-plated structure for a separator of the present invention, since it is a structure in which gold is dispersed and plated on a titanium base material excellent in corrosion resistance, it is lower than conventional separators for fuel cells. It can be used as a separator having excellent cost, strength and corrosion resistance. In particular, by adjusting the island diameter of the gold plating, it is effective in forming a thin gold plating structure having low contact resistance and excellent adhesion. In addition, by using pure titanium JIS type 1 as a base material, it becomes easy to form a groove serving as a fuel gas passage on the titanium surface by press working before or after gold plating. improves.

Conceptual diagram showing the structure of a typical fuel cell Electron micrograph showing the surface of the gold-plated structure according to the present invention (magnification: 50,000 times) The photograph by the FIB (Focused Ion Beam) apparatus which shows the cross section of the gold plating structure by this invention The figure which shows the outline | summary of the contact electrical resistance measurement by the 4 terminal method implemented about the gold plating structure Fig.5 (a) is sectional drawing of the press-processed titanium base material, FIG.5 (b) is a top view of the titanium base material. Electron micrograph showing the front surface of the gold-plated structure according to the present invention obtained in Example 1 (magnification: 50,000 times) Electron micrograph showing the back side surface of the gold-plated structure according to the present invention obtained in Example 1 (magnification: 50,000 times) Electron micrograph showing the front surface of the gold-plated structure according to the present invention obtained in Example 2 (magnification: 50,000 times) Electron micrograph showing the front surface of the gold-plated structure according to the present invention obtained in Example 3 (magnification: 50,000 times) Electron micrograph showing the front surface of the gold-plated body obtained in Comparative Example 1 (magnification: 50,000 times) Electron micrograph showing the front surface of the gold-plated body obtained in Comparative Example 3 (magnification: 50,000 times)

Claims (8)

  It has a gold-plated part and a non-plated part on the surface of the titanium base material, and the gold-plated part is scattered on the surface of the titanium base material in an island shape having a diameter of 100 nm or less and 1 nm or more. A gold-plated structure.   The gold plating structure according to claim 1, wherein an average gold plating thickness on the surface of the titanium substrate is 30 nm or less and 1 nm or more.   The gold-plated structure according to claim 1, wherein the gold-plated portions are island-shaped with a diameter of 50 nm or less and 1 nm or more and are scattered on the surface of the titanium substrate.   The gold plating structure according to any one of claims 1 to 3, wherein the gold plating thickness is 15 nm or less and 1 nm or more.   The gold-plated structure according to any one of claims 1 to 4, wherein the titanium base material conforms to JIS standard type 1 and has a thickness of 0.4 mm or less and 0.1 mm or more.   The gold plating structure according to any one of claims 1 to 5, wherein the gold plating part is formed by an electrolytic gold plating solution containing a trivalent gold compound as an essential component.   The gold plating structure according to any one of claims 1 to 6, wherein a proportion of the gold plating portion on the surface of the titanium base material is 10% or more and 90% or less.   The separator for fuel cells which consists of a gold plating structure of any one of Claims 1-7.