JP2013243113A - Metal plate for separator of polymer electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal plate suitable as a separator of a polymer electrolyte fuel cell, which not only has low contact resistance, but also has excellent corrosion resistance even when exposed to a high-potential environment such as a separator use environment for a long time.SOLUTION: A surface of a metal base is coated with an Sn alloy layer film, and further a surface of the Sn alloy layer film is coated with an oxide film. Conductive particles are contained in the Sn alloy layer film, and the oxide film is of a constituent element of the Sn alloy layer film.

Description

  The present invention relates to a metal plate for a separator of a polymer electrolyte fuel cell having a low contact resistance value and excellent corrosion resistance.

In recent years, from the viewpoint of global environmental conservation, development of fuel cells that are excellent in power generation efficiency and do not emit CO ₂ has been underway. This fuel cell generates electricity by electrochemical reaction from H ₂ and O ₂ , and its basic structure has a sandwich-like structure, an electrolyte membrane (ie, an ion exchange membrane), and two electrodes (ie, A fuel electrode and an air electrode), a diffusion layer of O ₂ (ie air) and H ₂ , and two separators.
Depending on the type of electrolyte membrane used, phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, alkaline fuel cells and polymer electrolyte fuel cells (PEFCs) Membrane fuel cells or polymer electrolyte fuel cells) have been developed.

Among these fuel cells, the polymer electrolyte fuel cell is compared with other fuel cells.
(a) The power generation temperature is about 80 ° C, and power generation is possible at a significantly lower temperature.
(b) The fuel cell body can be reduced in weight and size.
(c) It can be started up in a short time, and has advantages such as high fuel efficiency and high power density.
For this reason, the polymer electrolyte fuel cell is a fuel cell that is attracting the most attention today as a power source for mounting an electric vehicle, a stationary generator for home use or business use, and a small portable generator.

The polymer electrolyte fuel cell takes out electricity from H ₂ and O ₂ through a polymer membrane. As shown in FIG. 1, the membrane-electrode assembly 1 is connected to gas diffusion layers 2 and 3 (for example, Carbon paper or the like) and the separators 4 and 5 are used as a single component (a so-called single cell), and an electromotive force is generated between the separator 4 and the separator 5.
The membrane-electrode assembly 1 is called MEA (that is, Membrance-Electrode Assembly), and an electrode material such as carbon black carrying a platinum-based catalyst on the front and back surfaces of the polymer membrane is integrated. The thickness is several tens of μm to several hundreds of μm. Further, the gas diffusion layers 2 and 3 are often integrated with the membrane-electrode assembly 1.

When the polymer electrolyte fuel cell is applied to the above-described application, a fuel cell stack is configured by using several tens to several hundreds of single cells as described above in series.
Here, the separators 4 and 5 include
(a) In addition to serving as a partition wall that separates single cells,
(b) a conductor carrying the generated electrons,
(c) an air passage 6 through which O ₂ (ie air) and H ₂ flow, a hydrogen passage 7,
(d) Discharge path for discharging generated water and gas (air flow path 6 and hydrogen flow path 7 are combined)
Function is required.

Furthermore, in order to put the polymer electrolyte fuel cell into practical use, it is necessary to use a separator having excellent durability and electrical conductivity.
In terms of durability, when used as a power source for mounting on an electric vehicle, it is assumed to be about 5000 hours. Also, when used as a home-use generator, etc., it is assumed that it is about 40,000 hours. Therefore, the separator is required to have corrosion resistance that can withstand long-time power generation. The reason is that when metal ions are eluted by corrosion, proton conductivity of the polymer membrane (electrolyte membrane) decreases.

  Regarding electrical conductivity, it is desired that the contact resistance between the separator and the gas diffusion layer is as low as possible. The reason is that when the contact resistance between the separator and the gas diffusion layer increases, the power generation efficiency of the polymer electrolyte fuel cell decreases. That is, it can be said that the smaller the contact resistance between the separator and the gas diffusion layer, the better the power generation characteristics.

  To date, polymer electrolyte fuel cells using graphite as a separator have been put into practical use. This separator made of graphite has the advantages of relatively low contact resistance and no corrosion. However, graphite separators are easily damaged by impact, so that they are not only difficult to downsize, but also have the disadvantage of high processing costs for forming air and hydrogen channels. These disadvantages of a graphite separator are factors that hinder the spread of polymer electrolyte fuel cells.

  Therefore, an attempt has been made to apply a metal material instead of graphite as a material for the separator. In particular, from the viewpoint of improving durability, various studies have been made toward the practical application of separators made of stainless steel, titanium, titanium alloys, or the like.

  For example, Patent Document 1 discloses a technique in which a metal that easily forms a passive film such as stainless steel or a titanium alloy is used as a separator. However, the formation of a passive film leads to an increase in contact resistance, leading to a decrease in power generation efficiency. For this reason, it has been pointed out that these metal materials have problems to be improved such as a contact resistance larger than that of a graphite material and inferior in corrosion resistance.

  Patent Document 2 discloses a technique for reducing contact resistance and ensuring high output by performing gold plating on the surface of a metal separator such as austenitic steel plate (SUS304). However, it is difficult to prevent the occurrence of pinholes with thin gold plating, and conversely, the problem of cost remains with thick gold plating.

  Patent Document 3 discloses a method of obtaining a separator having improved electrical conductivity (that is, reduced contact resistance) by dispersing carbon powder in a ferritic stainless steel substrate. However, even when carbon powder is used, a cost problem still remains because the surface treatment of the separator requires a corresponding cost. Further, it has been pointed out that the separator subjected to the surface treatment has a problem that the corrosion resistance is remarkably lowered when scratches or the like are generated during assembly.

  In order to advantageously solve the above-mentioned problem, the inventors previously described in Patent Document 4 that “a film having a Sn alloy layer is provided on the surface of a metal base, and conductive particles are provided in the film. A metal plate for a separator of a polymer electrolyte fuel cell was proposed.

Japanese Patent Laid-Open No. 8-180883 Japanese Patent Laid-Open No. 10-228914 JP 2000-277133 A Japanese Patent Application No. 2011-95031 Specification

  The development of the metal plate for the separator of the polymer electrolyte fuel cell described in Patent Document 4 described above has improved the corrosion resistance in the usage environment of the separator of the polymer electrolyte fuel cell.

  However, it has been found that when a film made of an Sn alloy layer (hereinafter referred to as an Sn alloy layer film) is exposed to a high potential environment for a long time, a small amount of metal ions are eluted and the corrosion resistance deteriorates. When the eluted metal ions are taken into the polymer membrane, the polymer membrane is deteriorated and the fuel cell characteristics are deteriorated.

  The present invention advantageously solves the above problem, and it is needless to say that the contact resistance is low, and even if it is exposed to a high potential environment such as a separator use environment for a long time, the corrosion resistance is deteriorated. An object of the present invention is to provide a metal plate for a separator of a polymer electrolyte fuel cell capable of preventing the above.

As a result of intensive studies to solve the above problems, the present inventors further coat the surface of the Sn alloy layer film containing conductive particles with an oxide film of the constituent elements of the Sn alloy layer film. Thus, it was found that the corrosion resistance when exposed to a high potential environment for a long time can be greatly improved while keeping the contact resistance low.
The present invention is based on the above findings.

That is, the gist configuration of the present invention is as follows.
1. It consists of a metal substrate, a Sn alloy layer film coated on the surface of the substrate, and an oxide film coated on the surface of the Sn alloy layer film.
A metal plate for a separator of a polymer electrolyte fuel cell, wherein the Sn alloy layer film has conductive particles, and the oxide film is composed of an oxide film of a constituent element of the Sn alloy layer film.

2. 2. The metal plate for a separator of a polymer electrolyte fuel cell as described in 1 above, wherein the Sn alloy layer coating contains at least one element selected from Ni and Fe.

3. _{3. The} metal plate for a separator of a polymer electrolyte fuel cell as described in 1 or 2 above, wherein the Sn alloy layer coating contains Ni ₃ Sn ₂ .

4). 4. The solid according to any one of 1 to 3, wherein the conductive particles have an electric conductivity of 1 × 10 ² Ω ⁻¹ · m ⁻¹ or more and an average particle size of 0.1 to 6 μm. Metal plate for polymer fuel cell separator.

5. 5. The metal plate for a separator of a polymer electrolyte fuel cell according to any one of 1 to 4, wherein the content of the conductive particles in the Sn alloy layer coating is 0.1 to 30% by mass.

6). The conductive particles may be one or more selected from carbon black, TiC, VC, TiN, TiB ₂ , VB ₂ , CrB ₂ , TiSi ₂ , ZrSi ₂ and NbSi ₂ . A metal plate for a separator of a polymer electrolyte fuel cell according to any one of 1 to 5.

7). The oxide film comprises one or more selected from SnO ₂ , Sn (OH) ₂ , Sn (OH) ₄ , Ni (OH) ₂ , NiO ₂ , Ni ₂ O _3, and Ni ₃ O _4. 7. The metal plate for a separator of a polymer electrolyte fuel cell as described in any one of 1 to 6 above.

8). 8. The metal for a separator of a polymer electrolyte fuel cell according to any one of 1 to 7 above, wherein at least one Sn alloy layer is provided as an intermediate layer between the Sn alloy layer coating and the substrate. Board.

9. 9. The metal plate for a separator of a polymer electrolyte fuel cell as described in 8 above, wherein the intermediate layer contains at least one element selected from Ni and Fe.

10. 10. The metal plate for a separator of a polymer electrolyte fuel cell according to 8 or 9, wherein the intermediate layer includes a Ni ₃ Sn ₂ layer.

11. Any one of 1 to 10 above, wherein a pure metal layer or an alloy layer is provided as a base treatment layer between the Sn alloy layer film and the substrate, or between the intermediate layer and the substrate. A metal plate for a separator of the polymer electrolyte fuel cell as described.

12 12. The metal plate for a separator of a polymer electrolyte fuel cell as described in 11 above, wherein the base treatment layer contains at least one element selected from Ni, Cu, Ag and Au.

  ADVANTAGE OF THE INVENTION According to this invention, the metal plate for separators of a polymer electrolyte fuel cell with low contact resistance and excellent corrosion resistance at the time of using it for a long time in the use environment of a separator can be obtained at low cost.

It is a schematic diagram which shows the basic structure of a fuel cell. It is the figure which showed the measuring point of contact resistance. It is a thin film X-ray-diffraction pattern before and behind oxide film formation. It is the spectrum of Sn 3d orbit obtained by X-ray photoelectron spectroscopy. It is a spectrum of Ni 2p orbit obtained by X-ray photoelectron spectroscopy. It is a schematic diagram which shows the test piece for an adhesive test.

Hereinafter, the present invention will be specifically described.
(1) Metal plate used as a substrate In the present invention, the metal plate used as a substrate is not particularly limited, but a stainless steel plate (ferritic stainless steel plate, austenitic stainless steel plate, duplex stainless steel plate) or titanium plate having excellent corrosion resistance, A titanium alloy plate or the like is particularly advantageous.

(2) Sn alloy layer coating The Sn alloy layer coating on the surface of the substrate is corrosion resistant in the use environment (pH: 3 (sulfuric acid environment), use temperature: 80 ° C) of the separator for polymer electrolyte fuel cells. An Sn alloy containing at least one element selected from Ni and Fe, which are excellent in resistance, is preferable. Particularly preferred is Ni ₃ Sn ₂ which is an intermetallic compound.

The reason why the Sn alloy as described above is excellent in corrosion resistance in the use environment of the separator for the polymer electrolyte fuel cell is not necessarily clear, but the inventors consider as follows.
It is considered that the bond in the Sn alloy, for example, the Sn—Ni or Sn—Fe bond is superior to the Sn—Sn bond in the simple substance of metal Sn in order to obtain a more stable bonding state, and thus has better corrosion resistance. In particular, Ni ₃ Sn ₂ has excellent corrosion resistance because the formation temperature is 790 ° C or higher and the Sn-Ni bond is very stable according to the Ni-Sn binary alloy phase diagram. It is thought that it has.

The Sn alloy layer coating contains conductive particles in order to reduce contact resistance. In addition to conductivity, the conductive particles used in the present invention are required to have excellent stability under the environment where the separator is used. Examples of the conductive particles that satisfy these requirements include carbon black, TiC, VC, TiN, TiB ₂ , VB ₂ , CrB ₂ , TiSi ₂ , ZrSi _2, and NbSi ₂ .

Electrical conductivity of the conductive particles: 1 × 10 ² Ω ^-1 · m ^-1 or more From the viewpoint of reducing contact resistance, the electrical conductivity of the conductive particles is 1 × 10 ² Ω ^-1 · m ^-1 or more. It is desirable to do. This is because, if the electric conductivity is less than 1 × 10 ² Ω ⁻¹ · m ⁻¹ , it is difficult to reduce the contact resistance to the target level expected in the present invention. Here, the target contact resistance value in the present invention is less than 10 mΩ · cm ² .
In addition, the electrical conductivity of the conductive particles referred to here is, for example, the reciprocal of the electrical resistivity ρ of the conductive particles obtained by the following measurement method. Here, the electrical resistivity ρ of the conductive particles is the current when a sample is filled between two parallel plate electrodes (area S) (thickness d of the conductive particle layer) and a DC voltage V is applied. By measuring I, it is calculated from the following formula (1).
Record
ρ = (S / d) × (V / I) (1)

Average particle diameter of conductive particles: 0.1-6 μm
The average particle diameter of the conductive particles is preferably 0.1 to 6 μm. This is because if the average particle diameter of the conductive particles is less than 0.1 μm, the effect of reducing the contact resistance is insufficient, while if it exceeds 6 μm, the film becomes brittle and the film is easily peeled off.
The average particle diameter of the conductive particles referred to here is, for example, the porosity is determined from the height of the sample filled in the sample tube, the specific surface area is determined from the flow velocity and the pressure drop through the constant pressure air, and the average particle This is a value obtained by the Fisher method, which is a kind of transmission method, for calculating the diameter.

Content of conductive particles: 0.1-30% by mass
The content of the conductive particles in the Sn alloy layer film is preferably 0.1 to 30% by mass. When the content of the conductive particles is less than 0.1% by mass, the effect of reducing the contact resistance is poor. On the other hand, when the content exceeds 30% by mass, the film becomes brittle and the film is easily peeled off.

  The thickness of the Sn alloy layer coating containing the conductive particles is preferably set to the minimum particle size of the conductive particles to 15 μm. If the thickness of the film is less than the particle size of the conductive particles, the conductive particles are liable to fall off, which is not preferable. On the other hand, if the thickness exceeds 15 μm, the effect of improving the corrosion resistance is saturated and rather uneconomical.

(3) Oxide film Next, the oxide film to be coated on the surface of the Sn alloy layer film is not a natural oxide film formed in an atmospheric environment, but a post-treatment such as immersion in an acidic solution. A film formed automatically is meant to include not only oxide films but also hydroxide films.
The natural oxide film refers to a film having a thickness of about several nm that is not detected as a peak by thin film X-ray diffraction.

As the components of the oxide film, SnO ₂ , Sn (OH) ₂ , Sn (OH) ₄ , Ni (OH) ₂ , NiO ₂ , Ni ₂ O ₃ and Ni ₃ O ₄ are preferable, and selected from these One kind or two or more kinds can be included. The thickness is desirably 100 nm or less. This is because it is difficult to obtain desired electrical conductivity when the oxide film is thick. On the other hand, if the oxide film is too thin, it is difficult to obtain sufficient durability in the usage environment of the separator, and metal ions are eluted. Here, it is desirable that the thickness of the oxide film is so thick that a binding energy peak derived from a metal bond such as Sn, which is a main component of the composite film, is not recognized in X-ray photoelectron spectroscopy (XPS). The above is preferable.

  By forming the oxide film on the surface of the Sn alloy layer film, the mechanism of greatly improving the corrosion resistance when used for a long time under the usage environment of the separator is not necessarily clear, the inventors, Since the oxide film is extremely stable even in the usage environment of the separator, it is considered that the elution of metal ions from the Sn alloy layer film can be effectively suppressed.

(4) Method for forming Sn alloy layer coating In order to form the Sn alloy layer coating on the surface of the metal substrate, it is preferable to use a plating method. In this case, the Sn alloy layer coating was adjusted to a predetermined composition. The substrate may be immersed in a plating bath and electroplated.

  In addition, the plating method is also used for blending conductive particles into the Sn alloy layer coating to form a Sn alloy layer coating containing conductive particles (hereinafter referred to as a conductive particle-containing Sn alloy layer coating). It is preferable to do this. When this plating method is used, a predetermined amount of conductive particles may be dispersed in a plating bath adjusted to a predetermined composition, and electroplating may be performed while stirring the plating bath. In addition, as a stirring means, stirring with a propeller, stirring with a pump, etc. are suitable.

  When using the plating method, the density of the conductive particles in the plating bath is preferably about 1 to 50 g / L. If the density of the conductive particles is less than 1 g / L, a sufficient amount of the conductive particles cannot be contained. On the other hand, if the density exceeds 50 g / L, it tends to settle in the plating bath. It becomes difficult to make it contain uniformly.

As mentioned above, although the case where the plating method was utilized was mainly demonstrated, in this invention, a conductive particle containing Sn alloy layer membrane | film | coat can be formed also by the method described below.
(a) Physical vapor deposition (PVD method)
In this method, two or more kinds of metals are used as a target, and the surface of the substrate is Sn alloy layer, preferably Sn alloy layer containing at least one element selected from Ni and Fe, particularly preferably Ni ₃ Sn ₂ layer Is formed. In addition, when the conductive particles are contained, a Sn alloy layer, preferably a Sn alloy layer containing at least one element selected from Ni and Fe, particularly preferably a Ni ₃ Sn ₂ layer is formed in the middle of the formation. After distributing a certain amount of conductive particles on the surface of the substrate, Sn alloy layer containing at least one element selected from Sn alloy layer, Ni and Fe by physical vapor deposition (e.g., vapor deposition etc.) again. Particularly preferably, the conductive particles can be contained by forming a Ni ₃ Sn ₂ layer.

(b) Alloying method After the Sn layer and at least one layer selected from Ni and Fe are formed on the substrate by the above plating method or physical vapor deposition method, alloying treatment (heat treatment) ) To form a Sn alloy layer, preferably a Sn alloy layer containing at least one element selected from Ni and Fe, particularly preferably a Ni ₃ Sn ₂ layer.

Specifically, Ni ₃ Sn ₂ layer is formed by coating metal Ni and metal Sn at an atomic ratio of 3: 2 and then alloying (heat treatment) at a temperature of 790 ° C. or higher. Can do.
In addition, Ni ₃ Sn ₄ layer is formed by coating metal Ni and metal Sn at an atomic ratio of 3: 4 and then alloying (heat treatment) at a temperature of 230 ° C. or higher and lower than 790 ° C. Can do.
Furthermore, after coating metal Fe and metal Sn at an atomic ratio of 1: 1, an FeSn layer can be formed by applying an alloying treatment (heat treatment) at a temperature of 510 ° C. or higher. An FeSn ₂ layer can be formed by coating metal Fe at an atomic ratio of 2: 1 and then performing an alloying treatment (heat treatment) at a temperature of 232 ° C. or higher and lower than 510 ° C.

(5) Forming method of oxide film In order to form the oxide film, there are a method of immersing in an acidic aqueous solution having oxidizing properties such as hydrogen peroxide, sulfuric acid, nitric acid, an electrochemical anodic oxidation method, and the like. Can be mentioned.
For example, in order to form an oxide film by electrochemically performing an anodic oxidation treatment, a potential at which a single metal can form an oxide or hydroxide in an electrolytic solution is obtained from a potential-pH diagram or the like. And a method of holding at this potential. Note that the treatment time can be shortened by holding at a higher potential. However, since the electrolytic solution is decomposed when the potential becomes too high, it is desirable that the treatment be performed within a potential range that does not cause the electrolytic solution to decompose.
In the case of Sn, when an aqueous electrolyte solution having a pH of 1 is used, the potential at which Sn forms SnO ₂ is about -0.2 V to -0.1 V (vs. SHE) from the potential-pH diagram. For this reason, it is preferable to hold at a potential higher than this, but it is more preferable that the potential be up to 1.2 V (vs. SHE) so that water does not decompose.
In addition, physical vapor deposition (PVD), chemical vapor deposition (CVD), coating, and the like can be cited, but these methods are disadvantageous in that the cost is high and a dedicated apparatus is required.

As described above, the case where the conductive particle-containing Sn alloy layer film is directly formed on the surface of the metal base and the oxide film is further formed on the surface of the film has been described. In the present invention, the base and the conductive particle-containing Sn are described. At least one Sn alloy layer can be formed as an intermediate layer between the alloy layer film. The Sn alloy layer as the intermediate layer is also preferably an Sn alloy layer containing at least one element selected from Ni and Fe. Particularly preferred is a Ni ₃ Sn ₂ layer.
In addition, as an intermediate | middle layer, when ensuring adhesiveness with the said electroconductive particle containing Sn alloy layer membrane | film | coat, it is preferable to set it as the Sn alloy layer of the same composition as this membrane | film | coat.

By interposing such an intermediate layer, the durability of the separator in the usage environment can be further improved. Moreover, there is an effect that the thickness of the intermediate layer can be reduced by making the intermediate layer into a plurality of layers.
Here, the thickness of the intermediate layer is preferably in the range of 0.1 to 10 μm. If the thickness of the intermediate layer is less than 0.1 μm, the intermediate layer is not uniformly formed, and the effect of improving durability cannot be obtained. On the other hand, when the thickness of the intermediate layer exceeds 10 μm, the durability improvement effect is saturated.

Further, in the present invention, a base treatment layer can be separately provided between the base and the conductive particle-containing Sn alloy layer film or intermediate layer. By providing this base treatment layer, the base and the Sn alloy layer are provided. Alternatively, the adhesion with the intermediate layer is dramatically improved.
The reason for this is not always clear, but the inventors consider as follows.
That is, when there is no base treatment layer, an inert passive film or the like is easily formed on the surface of the substrate, and high adhesion is not always obtained. In this regard, by providing the base treatment layer, formation of a passive film or the like is suppressed, and the surface of the base body is unlikely to become inactive, so that the adhesion between the base body and the Sn alloy layer or the intermediate layer is improved. In particular, when the base treatment layer has irregularities, the adhesion with the Sn alloy layer or the intermediate layer is further improved by the anchor effect.

  From this, in the manufacturing process of the fuel cell, for example, in the process of processing the separator into a desired shape or the process of assembling the fuel cell, the base and the Sn alloy layer or the intermediate layer are prevented from peeling off from the base. In the case where high adhesion with the layer is required, it is extremely advantageous to form the base treatment layer.

Here, the base treatment layer is preferably a pure metal layer such as Ni, Cu, Ag, or Au, or an alloy layer containing at least one selected from these elements. For example, when the Sn alloy layer or the intermediate layer is a Ni ₃ Sn ₂ layer, it is preferable to provide a Ni layer or a Ni—P layer as a base treatment layer in order to improve adhesion.
Furthermore, it is not always necessary to form the base treatment layer uniformly on the substrate surface, and even when it is formed in an island shape, an effect of improving the film adhesion can be obtained.
In order to form the base treatment layer, a known method such as a plating method, a physical vapor deposition method (PVD method), a chemical vapor deposition method (CVD), or a coating method may be used.

(6) Stainless steel used as a substrate Next, stainless steel used as a substrate in the present invention will be described. The stainless steel used as the substrate has no particular restrictions on the steel type as long as it has the corrosion resistance required under the operating environment of the fuel cell, whether it is ferritic stainless steel or austenitic stainless steel, Further, any of duplex stainless steels can be used. However, in order to ensure the minimum corrosion resistance, it is preferable to contain 16% by mass or more of Cr. More preferably, it is 18 mass% or more.

  Hereinafter, particularly preferred component compositions of the ferritic stainless steel, austenitic stainless steel, and duplex stainless steel are as follows. In addition, unless otherwise indicated, "%" display regarding a component shall mean the mass%.

(a) Preferred component composition of ferritic stainless steel C: 0.03% or less C is desirable to have a lower C content because it combines with Cr in the steel to lower the corrosion resistance. Is not significantly reduced. For this reason, the C content is preferably 0.03% or less, and more preferably 0.015% or less.

Si: 1.0% or less
Si is an element used for deoxidation, but if contained excessively, ductility is lowered, so 1.0% or less is preferable. More preferably, it is 0.5% or less.

Mn: 1.0% or less
Mn combines with S to form MnS and lowers the corrosion resistance, so 1.0% or less is preferable. More preferably, it is 0.8% or less.

S: 0.01% or less As described above, since S combines with Mn to form MnS and lowers the corrosion resistance, 0.01% or less is preferable. More preferably, it is 0.008% or less.

P: 0.05% or less P is preferable to be low because it causes a decrease in ductility. However, if it is 0.05% or less, the ductility is not significantly decreased. For this reason, 0.05% or less is preferable, More preferably, it is 0.04% or less.

Al: 0.20% or less
Al is an element used for deoxidation, but if contained excessively, ductility is reduced, so 0.20% or less is preferable. More preferably, it is 0.15% or less.

N: 0.03% or less N is combined with Cr in the steel and causes a decrease in corrosion resistance. Therefore, a lower content is desirable, but if it is 0.03% or less, the corrosion resistance is not significantly reduced. For this reason, 0.03% or less is preferable. More preferably, it is 0.015% or less.

Cr: 16% or more
Since Cr is an essential element for maintaining the corrosion resistance of stainless steel, Cr is preferably contained in an amount of 16% or more in order to obtain the effect. When the Cr content is less than 16%, it is difficult to use the separator for a long time. In particular, when a change in environment during use becomes a problem, it is preferably 18% or more, and more preferably 20% or more. On the other hand, if Cr is contained in excess of 40%, the workability is remarkably lowered. Therefore, when workability is important, the content is preferably 40% or less. More preferably, it is 35% or less.

At least one selected from Nb, Ti and Zr: 1.0% or less
Nb, Ti, and Zr are all elements useful for improving the corrosion resistance by fixing C and N in the steel as carbides, nitrides, or carbonitrides. However, when the total content exceeds 1.0%, the ductility is significantly lowered. Therefore, these elements are limited to a total of 1.0% or less in the case of either a single content or a composite content. In addition, in order to fully exhibit the effect of containing these elements, it is preferable to contain 0.02% or more in total.

The basic components have been described above, but in the present invention, the following elements can be appropriately contained as needed.
Mo: 0.02-4.0%
Mo is an element effective for improving the corrosion resistance of stainless steel, particularly local corrosion. To obtain this effect, it is preferable to contain 0.02% or more. On the other hand, when the content exceeds 4.0%, the ductility is remarkably lowered, so the upper limit is preferably 4.0%. More preferably, it is 2.0% or less.

In addition, Ni, Cu, V, and W can each be contained at 1.0% or less for the purpose of improving the corrosion resistance. Furthermore, for the purpose of improving hot workability, Ca, Mg, rare earth elements (also referred to as REM), and B may be contained in amounts of 0.1% or less.
The balance is Fe and inevitable impurities. Of unavoidable impurities, O (oxygen) is preferably 0.02% or less.

(b) Suitable component composition of austenitic stainless steel C: 0.08% or less C reacts with Cr in the austenitic stainless steel for separator to form a compound, and precipitates as Cr carbide at the grain boundary. Bring about a decline. Therefore, the smaller the C content, the better. If it is 0.08% or less, the corrosion resistance will not be significantly reduced. Therefore, C is preferably 0.08% or less. More preferably, it is 0.03% or less.

Cr: 16% or more
Cr is an element necessary for ensuring basic corrosion resistance as an austenitic stainless steel sheet. If the Cr content is less than 16%, it is difficult to use as a separator for a long time. Therefore, 16% or more is preferable. On the other hand, if the Cr content exceeds 30%, it is difficult to obtain an austenite structure. Therefore, 30% or less is preferable. More preferably, it is 18 to 26% of range.

Mo: 0.1-10.0%
Mo is an element effective for suppressing local corrosion such as crevice corrosion of austenitic stainless steel for separator. In order to acquire this effect, it is necessary to make it contain 0.1% or more. On the other hand, if it exceeds 10.0%, the stainless steel for the separator is remarkably embrittled and productivity is lowered. Therefore, the range of 0.1 to 10.0% is preferable. More preferably, it is 0.5 to 7.0% of range.

Ni: 7-40%
Ni is an element that stabilizes the austenite phase. If the Ni content is less than 7%, the effect of stabilizing the austenite phase cannot be obtained. On the other hand, if the Ni content exceeds 40%, excessive consumption of Ni causes an increase in cost. Therefore, the range of 7-40% is preferable.

In the austenitic stainless steel for separator of the present invention, in addition to the above elements, the following elements can be appropriately contained as required.
N: 2.0% or less N has an effect of suppressing local corrosion of the austenitic stainless steel for separator. However, it is industrially difficult to contain N exceeding 2.0%, so 2.0% or less is preferable. Furthermore, in the normal melting method, if it exceeds 0.4%, it takes a long time to contain N in the melting stage of the stainless steel for the separator, resulting in a decrease in productivity. Therefore, 0.4% or less is more preferable in terms of cost. More preferably, it is 0.01 to 0.3% of range.

Cu: 0.01-3.0%
Cu is an element having an action of improving the corrosion resistance of the austenitic stainless steel for separator. In order to acquire such an effect, 0.01% or more is preferable. However, if the Cu content exceeds 3.0%, the hot workability is lowered and the productivity is lowered. Therefore, when it contains Cu, 3.0% or less is preferable. More preferably, it is 0.01 to 2.5% of range.

Si: 0.01-1.5%
Si is an element effective for deoxidation, and is added at the melting stage of the austenitic stainless steel for the separator. In order to obtain such an effect, the Si content is preferably 0.01% or more. However, if excessively contained, the stainless steel for the separator becomes hard and ductility is lowered. Therefore, when Si is contained, 1.5% or less is preferable. More preferably, it is 0.01 to 1.0% of range.

Mn: 0.001 to 2.5%
Mn combines with unavoidably mixed S and has the effect of reducing S dissolved in the austenitic stainless steel for the separator, so it suppresses grain boundary segregation of S and prevents cracking during hot rolling. It is an effective element. Such an effect is exhibited when the Mn content is in the range of 0.001 to 2.5%. Therefore, when it contains Mn, the range of 0.001 to 2.5% is preferable. More preferably, it is 0.001 to 2.0% of range.

At least one selected from Ti, Nb, V and Zr in total: 0.01 to 0.5%
Ti, Nb, V and Zr all react with C in the austenitic stainless steel to form carbides. Ti, Nb, V, and Zr fix C in this manner, and are effective elements for improving the intergranular corrosion resistance of the austenitic stainless steel for separators. In particular, when the C content is 0.08% or less, the effect of improving the corrosion resistance is exhibited when the total content is 0.01% or more in the case of containing Ti, Nb, V and Zr alone or in combination.
On the other hand, even if Ti, Nb, V and Zr are contained alone or in a composite content exceeding 0.5% in total, the effect of improving the corrosion resistance is saturated. Therefore, when Ti, Nb, V, or Zr is contained, it is preferable that at least one selected from these elements is in a range of 0.01 to 0.5% in total.

In the present invention, in addition to the above elements, in order to improve the hot workability of the austenitic stainless steel for separator, each of Ca, Mg, B, and rare earth element (REM) may be contained in an amount of 0.1% or less. Al may be included in the range of 0.2% or less for the purpose of deoxidation in the molten steel stage.
The balance is Fe and inevitable impurities. Of inevitable impurities, O (oxygen) is preferably 0.02% or less.

(c) Preferred component composition C of duplex stainless steel: 0.08% or less C reacts with Cr to form a compound and precipitates as Cr carbide at the grain boundary, resulting in a decrease in corrosion resistance. Accordingly, the smaller the C content, the better. If it is 0.08% or less, the corrosion resistance will not be significantly reduced. Therefore, C is preferably 0.08% or less. More preferably, it is 0.03% or less.

Cr: 16% or more
Cr is an element necessary for ensuring basic corrosion resistance as a duplex stainless steel sheet. If the Cr content is less than 16%, it is difficult to use as a separator for a long time. Therefore, 16% or more is preferable. On the other hand, if the Cr content exceeds 30%, it is difficult to obtain a two-phase structure (hereinafter, unless otherwise specified, means a two-phase structure of a ferrite phase and an austenite phase). Therefore, 30% or less is preferable. More preferably, it is 20 to 28% of range.

Mo: 0.1-10.0%
Mo is an element effective for suppressing local corrosion such as crevice corrosion. In order to obtain this effect, it is necessary to contain 0.1% or more. On the other hand, if it exceeds 10.0%, the stainless steel becomes extremely brittle and the productivity is lowered. Therefore, the range of 0.1 to 10.0% is preferable. More preferably, it is 0.5 to 7.0% of range.

Ni: 1-10%
Ni is an element that stabilizes the austenite phase. If the Ni content is less than 1%, an austenite phase is difficult to form and a two-phase structure is difficult to obtain. On the other hand, if the Ni content exceeds 10%, it becomes difficult to form a ferrite phase and it becomes difficult to obtain a two-phase structure. Therefore, the range of 1 to 10% is preferable.

In addition to the above elements, the duplex stainless steel for separator according to the present invention may appropriately contain the following elements as necessary.
N: 2.0% or less N is an element having an action of suppressing local corrosion of the duplex stainless steel for separator. However, since it is difficult industrially to contain N exceeding 2.0%, it is preferable to make this the upper limit. Furthermore, in the normal melting method, if it exceeds 0.4%, it takes a long time to contain N in the melting stage of the stainless steel for the separator, resulting in a decrease in productivity. Therefore, in terms of cost, 0.4% or less is more preferable. More preferably, it is 0.01 to 0.3% of range.

Cu: 3.0% or less
Cu is an element having an action of improving the corrosion resistance of the duplex stainless steel for separator. In order to acquire such an effect, 0.01% or more is preferable. However, if the Cu content exceeds 3.0%, the hot workability is lowered and the productivity is lowered. Therefore, when it contains Cu, 3.0% or less is preferable. More preferably, it is 0.01 to 2.5% of range.

Si: 1.5% or less
Si is an element effective for deoxidation, and is added at the melting stage of the duplex stainless steel for the separator. In order to acquire such an effect, 0.01% or more is preferable. However, if excessively contained, the stainless steel for the separator becomes hard and ductility is lowered. Therefore, when Si is contained, 1.5% or less is preferable. More preferably, it is 0.01 to 1.0% of range.

Mn: 0.001 to 2.5%
Mn combines with the unavoidably mixed S and has the effect of reducing the S dissolved in the duplex stainless steel for the separator, so it suppresses S grain boundary segregation and prevents cracking during hot rolling. It is an effective element to do. Such an effect is exhibited when the Mn content is in the range of 0.001 to 2.5%. Therefore, when it contains Mn, the range of 0.001 to 2.5% is preferable. More preferably, it is 0.001 to 2.0% of range.

At least one selected from Ti, Nb, V or Zr in total: 0.01 to 0.5%
Ti, Nb, V and Zr all react with C in the duplex stainless steel to form a carbide. Ti, Nb, V, and Zr fix C in this way, and are effective elements for improving the intergranular corrosion resistance of the duplex stainless steel for separator. In particular, when the C content is 0.08% or less, the effect of improving corrosion resistance is exhibited when the total content is 0.01% or more in the case of containing Ti, Nb, V and Zr alone or in combination.
On the other hand, even if Ti, Nb, V, and Zr are contained alone or in combination in a combined content exceeding 0.5% in total, the effect of improving corrosion resistance is saturated. Therefore, when Ti, Nb, V, or Zr is contained, it is preferable that at least one selected from these elements is in a range of 0.01 to 0.5% in total.

In the present invention, in addition to the above elements, in order to improve the hot workability of the duplex stainless steel for separators, Ca, Mg, B, and rare earth elements (REM) are each 0.1% or less and are removed at the molten steel stage. Al may be contained in an amount of 0.2% or less for the purpose of acid.
The balance is Fe and inevitable impurities. Of the inevitable impurities, O (oxygen) is preferably 0.02% or less.

(7) Suitable manufacturing method of stainless steel Next, in the present invention, there are no particular restrictions on the manufacturing conditions for the manufacturing method of ferritic stainless steel, austenitic stainless steel or duplex stainless steel as the base material. A conventionally known method may be followed, but suitable manufacturing conditions are described as follows.
A steel slab adjusted to a suitable component composition is heated to a temperature of 1100 ° C or higher, hot-rolled, then annealed at a temperature of 800-1100 ° C, and then cold rolled and annealed repeatedly to obtain a stainless steel plate. . The thickness of the obtained stainless steel plate is preferably about 0.02 to 0.8 mm. Here, it is efficient that the finish annealing and pickling are performed continuously online, but on the other hand, some or all of the processes are performed independently offline, and between these processes. May be washed.

(8) Titanium and titanium alloy used as a substrate Next, titanium and a titanium alloy used as a substrate in the present invention will be described.
The structure and chemical composition of titanium (industrial pure titanium, hereinafter referred to as titanium) and titanium alloy according to the present invention are not particularly limited, but in order to obtain a passive film mainly composed of titanium oxide having excellent corrosion resistance, 70% It is desirable to contain the above Ti. Furthermore, various elements may be included for the purpose of improving corrosion resistance, strength, and moldability.

Next, specific structures of titanium and titanium alloy will be described.
The structure of titanium and titanium alloy according to the present invention is not particularly limited. The structure of titanium is α phase (close-packed hexagonal structure (hcp)) at 882 ° C. or lower, and β phase (body-centered cubic structure (bcc)) at higher temperatures. Although the number of sliding systems when plastically deformed is small, the work hardenability is small, and among hexagonal metals, it is a material rich in plastic workability, and is generally cheaper than titanium alloys. It is a preferable material for processing into one separator.

  On the other hand, the structure of the titanium alloy is classified into three types: α type mainly composed of α phase, β type mainly composed of β phase, and (α + β) type composed of two phases of α phase and β phase. The structure of these titanium alloys is determined by the type and content of alloy elements contained in pure titanium, the processing method and heat treatment, and the properties differ greatly depending on the type of alloy because the properties differ between the α phase and the β phase. One of the objects of the present invention is that the (α + β) type alloy is superplastic because it exhibits superplasticity, and the β type alloy is excellent in cold plastic workability. It can be processed into a separator, which is preferable.

Next, regarding titanium, particularly preferred component compositions are as follows.
As titanium, it is advantageous to use industrial pure titanium, and therefore elements other than Ti are impurities. Impurities include Fe, O, C, N, and H. Among these elements, O and Fe may be contained in titanium in order to increase the strength. The higher the amount, the higher the strength, but the effect is saturated when the total amount exceeds 1%. Therefore, the total of O and Fe is preferably 1% or less, and the balance is Ti.

Next, regarding the titanium alloy, particularly preferred component compositions are as follows.
Ti: 70% or more In order to obtain a passive film mainly composed of titanium oxide having excellent corrosion resistance, it is desirable to contain 70% or more of titanium.

Al: 0.5-9%
Al is contained as an α-phase stabilizing element in the titanium alloy, and contributes to an increase in strength without impairing corrosion resistance. In order to obtain the effect, the Al content is preferably 0.5% or more. On the other hand, when Al exceeds 9%, an embrittled phase is precipitated, hot deformation resistance is increased, crack sensitivity is remarkably increased, and productivity is deteriorated. Therefore, the Al content is preferably 9% or less. More preferably, it is 0.5 to 7% of range.

Furthermore, the titanium alloy for separators of the present invention can contain the following elements as needed in addition to the above elements.
Fe, Ni, Co and Cr: 0.2-3% each
Fe, Ni, Co and Cr are eutectoid β-phase stabilizing elements, which are mainly dissolved in the β-phase to increase the strength. Moreover, the superplasticity expression temperature can be lowered by lowering the β transformation point. Furthermore, these elements have a high diffusion rate in titanium, and by increasing the volume fraction of the β phase with good hot workability, the deformation resistance during hot working, particularly during superplastic forming, is reduced. There is an effect of suppressing the occurrence of defects such as cracks. In order to obtain these effects, Fe, Ni, Co and Cr are each preferably 0.2% or more. On the other hand, if the contents of Fe, Ni, Co and Cr each exceed 3%, an intermetallic compound which is an embrittled phase is formed between these elements and Ti, and β-flex and A segregation phase called is formed, which results in a deterioration of the mechanical properties of the alloy, in particular the ductility. Therefore, the content of Fe, Ni, Co and Cr is preferably in the range of 0.2 to 3%.

One or two types selected from Mo and V: 1-25%
Both Mo and V are all solid solution type β-phase stabilizing elements, and are mainly dissolved in the β phase to increase the strength. In order to obtain the effect, the total content is preferably 1% or more, but when the total exceeds 25%, the effect is saturated. Moreover, since Mo and V are heavy elements and expensive elements, it is not preferable to contain more than 25% in total. Furthermore, since Mo has a low diffusion rate in titanium, deformation stress increases during hot working, particularly during superplastic forming. Therefore, it is preferable to make it into the range of 1 to 25% by the total of 1 type selected from Mo and V, or 2 types.

O: 0.05-0.5%
O dissolves in the α phase to increase the strength. In order to obtain the effect, 0.05% or more is preferable. On the other hand, when the content of O exceeds 0.5%, cold workability and ductility are deteriorated. Therefore, the range of 0.05 to 0.5% is preferable.

One or two selected from Zr and Sn: 0.2-6%
Zr and Sn are contained as neutral elements in the titanium alloy, increase the strength without reducing ductility, and do not impair the corrosion resistance. Also, the corrosion resistance is improved. In order to obtain the effect, the total content is preferably 0.2% or more. On the other hand, if the total content of Zr and Sn exceeds 6%, the intended effect cannot be obtained. Therefore, it is preferable that the content is in the range of 0.2 to 6% in one or a total of two selected from Zr and Sn.

Si: 0.5% or less
Si is an element effective for improving the corrosion wear resistance, and is added at the stage of melting the titanium alloy. However, if it is excessively contained, an intermetallic compound is formed between Ti and ductility is lowered. Therefore, when Si is contained, 0.5% or less is preferable. More preferably, it is 0.05 to 0.5% of range.

One or two types selected from Mn and Cu: 5% or less
Mn and Cu are eutectoid β-phase stabilizing elements, respectively, and mainly dissolve in the β-phase to increase the strength. Moreover, the superplasticity expression temperature can be lowered by lowering the β transformation point. In order to obtain these effects, it is preferable that the total amount of one or two selected from Mn and Cu is 0.2% or more. On the other hand, when the total amount of Mn and Cu exceeds 5%, an intermetallic compound that is an embrittlement phase is formed between these elements and Ti, and a segregation phase called β-flex is formed during dissolution and solidification. As a result, the mechanical properties of the alloy, in particular the ductility, deteriorate. Therefore, it is preferable to contain 5% or less of one or two kinds selected from Mn and Cu.

Further, the titanium alloy of the present invention may contain 0.5% or less of Pd or Ru in addition to the above composition. These elements improve the corrosion resistance of the titanium alloy. In order to acquire the effect, 0.01% or more is preferable respectively. However, these elements are very expensive, and excessive addition causes cost increase, so the upper limit is made 0.5%.
Other elements are inevitable impurities.

(9) Suitable manufacturing method of titanium or titanium alloy Next, in the present invention, a manufacturing method of titanium or titanium alloy as a base material will be described.
After breaking the cast structure of the titanium or titanium alloy ingot having the above-mentioned composition by partial forging or partial rolling to make it structurally nearly homogeneous, heat such as hot forging, hot rolling, hot extrusion, etc. Manufactured into a predetermined shape by inter-processing. At this time, from the viewpoint of workability, there is a temperature range suitable for hot working and hot rolling, so when rolling from a large cross-section ingot or rough piece, or rolling to a thin material (hereinafter referred to as thin materials) In the case of rolling), it is difficult to produce a desired product in the process of heating the ingot or coarse piece once and then rolling it into a product. Therefore, multi-heat rolling in which reheating and rolling are preferred. The hot-rolled sheet is annealed and descaled, and then cold-rolled with a large steel or stainless steel cold rolling mill, Sendzimir rolling mill, or the like. The cold-rolled cold-rolled sheet is annealed in a vacuum furnace or an inert gas atmosphere furnace to uniformize the mechanical properties and crystal grain size of the entire sheet. In particular, cold rolling of α-type titanium alloys and α + β-type titanium alloys is often more difficult to roll than pure titanium, and at least two upper and lower surfaces are covered with carbon steel and hot rolled. (Pack rolling) may be used to reduce the thickness. Although the β-type alloy has good cold workability, the number of cold rolling intermediate annealings may be increased in order to prevent ear cracks and to prevent the occurrence of internal cracks accompanying excessive cold rolling.

  The titanium plate or titanium alloy plate thus obtained is preferably used as a separator after forming a gas flow path by press working, superplastic working or the like. Alternatively, a gas flow path may be formed by cutting using a hot-rolled sheet that has been hot-rolled or a hot-rolled sheet that has been annealed after hot-rolling to form a separator.

  A separator of a polymer electrolyte fuel cell is required to have a low contact resistance in order to suppress a decrease in power generation efficiency. In addition, since the polymer electrolyte fuel cell is used in a severe environment where the electric potential fluctuates and the temperature is 80 ° C. and the pH is about 3 when starting and stopping, it is also required to have excellent corrosion resistance. Therefore, in view of these required characteristics, the following two tests were performed on the samples described later.

(1) Contact resistance As shown in Fig. 2, two test pieces 8 are alternately sandwiched between three carbon papers 9 (TGP-H-120 manufactured by Toray) of the same size from both sides, and gold plating is applied to the copper plate. Measure the resistance between the two separators by applying the applied electrode 10 and applying a pressure of 0.98 MPa per unit area (= 10 kgf / cm ² ), multiplying the contact area, and the number of contact surfaces (= 2) The value divided by the value was defined as the contact resistance value. Note that the measurement was performed at four locations by changing the position, and the average value was obtained.
○: Contact resistance less than 10mΩ · cm ² ×: Contact resistance of 10mΩ · cm ² or more

(2) Evaluation of stability in the separator environment The sample was immersed in a sulfuric acid aqueous solution at a temperature of 80 ° C and pH: 3, and the reference electrode was swept at 200 mV / min using Ag / AgCl (saturated KCl). Measure cyclic voltammograms of -0.2 to 1.2V (vs.SHE) at a speed of 100 cycles, and evaluate the stability in the separator environment with a current density value of 1.0V (vs.SHE) when the potential rises at the 100th cycle. The smaller the current density, the more stable the separator was used.
That is, the current density value of 1.0 V (vs. SHE) at the time of potential increase at the 100th cycle was evaluated according to the following criteria.
○: Current density less than 2.5 μA / cm ² ×: Current density of 2.5 μA / cm ² or more

Furthermore, in order to evaluate the stability when exposed to a high potential environment, the sample was immersed in a sulfuric acid aqueous solution of temperature: 80 ° C. and pH: 3, and Ag / AgCl (saturated KCl) was used as a reference electrode. Corrosion resistance in the separator environment was evaluated according to the following criteria based on the value of the amount of electricity applied when held at a potential of 1.0 V (vs. SHE) for 24 hours.
○: Amount of energized electricity less than 10 mQ / cm ² ×: Amount of energized electricity 10 mQ / cm ²

Example 1
Plate thickness: 0.1 mm SUS447J1 (C: 0.003%, Si: 0.20%, Mn: 0.10%, Cr: 30.0%, Ni: 0.20%, Mo: 2.0%, Cu: 0.02%, Nb: 0.14%, N: 0.007%, balance Fe), SUS304 (C: 0.05%, Si: 0.55%, Mn: 1.0%, Cr: 18.2%, Ni: 8.5%, Mo: 0.2%, N: 0.03%, balance Fe) and Thickness: 0.2mm titanium plate (JIS Class 1 pure titanium, H: 0.002%, O (oxygen): 0.04%, N: 0.01%, Fe: 0.19%, balance Ti) Using the plating bath composition and conductive particles shown in Fig. 1, electroplating is performed under the conditions of pH: 8.1, temperature: 60 ° C, current density: 5A / dm ² while stirring the bath, and Sn alloy, specifically, A composite coating containing conductive particles in a Sn alloy layer containing Ni was formed on the substrate surface. The addition amount of conductive particles in the plating bath was 25 g / l, and the plating film thickness was 10 μm.
<Plating bath composition>
NiCl ₂ · 2H ₂ O: 0.15 mol / l
SnCl ₂ · 2H ₂ O: 0.15 mol / l
K ₂ P ₂ O ₇ : 0.45 mol / l
Glycine: 0.15mol / l
<Conductive particles>
TiN average particle size: 1.5μm

  A sample having the above-mentioned conductive particle-containing Sn alloy layer film was applied to the surface of the film by applying a potential of 1.0 V (vs. SHE) for 1 hour in a sulfuric acid aqueous solution of temperature: 80 ° C. and pH: 3. An oxide film was formed. Moreover, the sample which does not perform an oxide film formation process was also produced for the comparison. Thin film X-ray diffraction (thin film XRD) and X-ray photoelectron spectroscopy (XPS) were used for characterization of the prepared samples.

FIG. 3 shows thin film X-ray diffraction patterns of the sample with the oxide film formed and the sample with no oxide film formed. As is apparent from the figure, Ni ₃ Sn ₂ and Ni ₃ Sn ₄ that are Ni—Sn intermetallic compounds are formed on the surface, and in addition, a diffraction peak of TiN that is conductive particles is observed. Furthermore, a diffraction peak attributed to SnO ₂ was observed in the sample on which the oxide film was formed.

Next, FIG. 4 and FIG. 5 show the results of analyzing the sample formed with the oxide film and the sample not formed with the oxide film by XPS. As is clear from the figure, the sample formed with the oxide film does not have a binding energy peak derived from the metal bond of Sn and Ni, which are the main components of the Sn alloy layer film containing the conductive particles, and the conductivity It can be seen that an oxide film having a sufficient thickness is formed on the surface of the particle-containing Sn alloy layer film.
3, 4, and 5, in the oxide film forming process, an oxide film mainly composed of SnO ₂ that is Sn oxide is formed sufficiently thick on the surface of the conductive particle-containing Sn alloy layer film. I understand that

  The results of examining the contact resistance of each sample obtained as described above and the stability in the separator environment are summarized in Table 1.

From the table, the following matters are clear.
(a) Samples of Invention Examples Nos. 2 to 4, 6 to 8, and 10 to 12 having an oxide film formed thereon were compared with samples of Comparative Examples No. 1, 5, and 9 having no oxide film formed thereon. The current density during the 100 cycle test and the amount of electricity applied during the 24-hour endurance test are both reduced, and the corrosion resistance is greatly improved even when exposed to a high potential environment such as the separator usage environment for a long time. It has improved.
(b) In any sample, the contact resistance is less than 10 mΩ · cm ² , and a low contact resistance is maintained.

Example 2
The same SUS447J1 as in Example 1 was used as the substrate, and the plating treatment was performed with the following plating bath composition. About other conditions, the sample was produced similarly to Example 1 except having formed the film | membrane and oxide film of Sn-Fe alloy system instead of Sn-Ni alloy system. Moreover, the sample which does not perform an oxide film formation process was also produced for the comparison.
<Plating bath composition>
FeCl ₂ · 4H ₂ O: 0.15 mol / l
SnCl ₂ · 2H ₂ O: 0.36mol / l
K ₂ P ₂ O ₇ : 0.45 mol / l
Glycine: 0.15mol / l

  Table 2 summarizes the results of examining the contact resistance of each sample obtained as described above and the stability in the separator environment.

From the table, the following matters are clear.
(c) In the same way as the results obtained from Table 1, the samples of Invention Examples No. 14, 15, and 16 in which an oxide film was formed were compared with the samples of Comparative Example No. 13 in which no oxide film was formed. Both the current density during the 100-cycle test and the amount of energized electricity during the 24-hour endurance test are both low, and the corrosion resistance is greatly improved even when exposed to a high-potential environment such as the separator usage environment for a long time. Has improved.
(d) In any sample, the contact resistance is less than 10 mΩ · cm ² , and a low contact resistance is maintained.

Example 3
The same SUS447J1 as in Example 1 was used as the substrate, and plating was performed using the following conductive particles. The other conditions were the same as in Example 1, and a sample was prepared. Moreover, the sample which does not perform an oxide film formation process was also produced for the comparison.
<Conductive particles>
TiC average particle size: 1-2μm
VC average particle size: 1.4μm
TiB ₂ average particle size: 2-3 μm
VB ₂ average particle size: 2-5 μm
CrB ₂ average particle diameter: 3-6 μm
TiSi ₂ average particle size: 2-5μm
ZrSi ₂ average particle diameter: 2 to 5 μm
NbSi ₂ average particle diameter: 2 to 5 μm

  The results of examining the contact resistance of each sample obtained as described above and the stability in the separator environment are summarized in Table 3.

From the table, the following matters are clear.
(e) In the same manner as the results obtained from Table 1, Invention Examples No. 18, 19, 21, 22, 24, 25, 27, 28, 30, 31, 33, 34, 36, The samples of 37, 39, and 40 were compared with the samples of Comparative Examples No. 17, 20, 23, 26, 29, 32, 35, and 38 in which an oxide film was not formed. The amount of energized electricity during the 24-hour endurance test has decreased, and the corrosion resistance has been greatly improved even when exposed to a high potential environment such as a separator use environment for a long time.
(f) In any sample, the contact resistance is less than 10 mΩ · cm ² , and a low contact resistance is maintained.

Example 4
A sample was prepared under the same conditions as in Example 1 except that the same SUS447J1 as in Example 1 was used as the substrate, and 1 to 3 intermediate layers were formed between the substrate and the composite coating containing conductive particles. did. Moreover, the sample which does not perform an oxide film formation process was also produced for the comparison.
In forming the intermediate layer, electroplating was carried out under the conditions of pH: 8.1, temperature: 60 ° C., current density: 5 A / dm ^{2 with} the following plating bath composition, and 1 to 3 intermediate layers were formed on the substrate surface. Formed.
<Plating bath composition>
NiCl ₂ · 2H ₂ O: 0.15 mol / l
SnCl ₂ · 2H ₂ O: 0.15 mol / l
K ₂ P ₂ O ₇ : 0.45 mol / l
Glycine: 0.15mol / l

  The results of examining the contact resistance and the stability in the separator environment of each sample obtained as described above are summarized in Table 4.

From the table, the following matters are clear.
(g) Similar to the results obtained from Table 1, the samples of Invention Examples No. 42 to 44 in which an oxide film was formed were compared with the samples of Comparative Example No. 41 in which an oxide film was not formed. Both the current density during the 100-cycle test and the amount of energized electricity during the 24-hour endurance test have both decreased, greatly improving corrosion resistance even when exposed to a high-potential environment such as a separator environment for a long time. doing.
Further, in the samples of Invention Examples No. 43 and 44 having a plurality of intermediate layers, the total film thickness of the intermediate layer remains the same, and the current density during the 100 cycle test and the energized electricity during the 24-hour endurance test are the same. The corrosion resistance is further improved when exposed to a high potential environment such as a separator use environment for a long time.
(h) In any sample, the contact resistance is less than 10 mΩ · cm ² , and a low contact resistance is maintained.

Example 5
The sample was prepared under the same conditions as in Example 1 or 4 except that the same SUS447J1 as in Example 1 was used as the substrate and a base treatment layer was formed between the substrate and the composite coating or intermediate layer containing conductive particles. Produced. When forming the base treatment layer, electroplating was performed in various commercially available plating baths to form the base treatment layer on the substrate surface.
The results of examining the contact resistance and the stability in the separator environment of each sample obtained as described above are summarized in Table 5.

In addition, the following tests were conducted in order to evaluate the adhesion of the film.
That is, a sample in which a film was formed on the surface of a substrate (thickness: 0.1 mm) as described above was cut into 25 mmW × 80 mmL. Next, the cut sample and a cold-rolled steel sheet of 25 mmW × 80 mmL × 1 mmt were joined so that a part thereof overlapped on the surface on which the film was formed, and a test piece for the adhesion test shown in FIG. 6 was produced. Here, an adhesive (manufactured by Sunrise MSI: E-56) was used to join the sample and the cold-rolled steel sheet, and the adhesive was joined so that the thickness of the adhesive was 2 mm and the adhesion area was 25 mmW × 20 mmL. In addition, since the plate | board thickness of the sample (base | substrate) was thin, another cold-rolled steel plate (25mmWx80mmLx1mmt) was joined and reinforced also to the surface on the opposite side to the surface which bonded said cold-rolled steel plate.
In FIG. 6, reference numeral 11 is a sample, 12 is a substrate, 13 is a base treatment layer, 14 is an intermediate layer, 15 is a composite coating (Sn alloy layer) containing conductive particles, 16 is a cold-rolled steel sheet, and 17 is an adhesive. is there.
The test piece for adhesion evaluation thus obtained was pulled from both sides with a tensile tester to determine the tensile strength (peel strength) when the substrate and the film peeled, and the film adhesion was evaluated according to the following criteria. .
○: Peel strength of 2.0 MPa or more △: Peel strength of 1.5 MPa or more and less than 2.0 MPa ×: Peel strength of less than 1.5 MPa For comparison, a sample without a base treatment layer was adhered in the same manner as described above. Sex was evaluated.
The test results are summarized in Table 5.

From the table, the following matters are clear.
(i) In the same manner as the results obtained from Table 1, the samples of Invention Examples Nos. 45 to 54 all have small current density during the 100-cycle test and energized electricity during the 24-hour endurance test. Even when exposed to a high potential environment such as a separator use environment for a long time, good corrosion resistance is obtained.
(j) In any sample of Invention Examples Nos. 45 to 54, the contact resistance is less than 10 mΩ · cm ² , and a low contact resistance is maintained.
(k) Further, each of the present invention examples Nos. 45 to 54 in which the base treatment layer was formed is necessary for peeling of the film as compared with the present invention examples No. 2 and 42 in which the base treatment layer was not formed. Tensile strength (peel strength) has been greatly increased, and adhesion has improved dramatically.

According to the present invention, the contact resistance is not only as low as that of conventionally used gold-plated stainless steel separators and graphite separators, but also when exposed to a high potential environment such as a separator use environment for a long time. However, a metal plate for a separator having excellent corrosion resistance can be obtained. Furthermore, high adhesion can be secured even when the separator needs to be processed.
In addition, since the separator can be manufactured at low cost from the metal plate according to the present invention, it is not necessary to use an expensive gold-plated stainless steel separator or graphite separator as in the prior art, and the production cost of the polymer electrolyte fuel cell is reduced. Can be reduced.

DESCRIPTION OF SYMBOLS 1 Membrane-electrode assembly 2,3 Gas diffusion layer 4,5 Separator 6 Air flow path 7 Hydrogen flow path 8 Test piece 9 Carbon paper
10 electrodes
11 samples
12 substrate
13 Ground treatment layer
14 Middle layer
15 Composite film containing conductive particles (Sn alloy layer)
16 Cold rolled steel sheet
17 Adhesive

Claims (12)

It consists of a metal substrate, a Sn alloy layer film coated on the surface of the substrate, and an oxide film coated on the surface of the Sn alloy layer film.
A metal plate for a separator of a polymer electrolyte fuel cell, wherein the Sn alloy layer film has conductive particles, and the oxide film is composed of an oxide film of a constituent element of the Sn alloy layer film.   The metal plate for a separator of a polymer electrolyte fuel cell according to claim 1, wherein the Sn alloy layer coating contains at least one element selected from Ni and Fe. The metal plate for a separator of a polymer electrolyte fuel cell according to claim 1 or 2, wherein the Sn alloy layer coating contains Ni ₃ Sn ₂ . 4. The conductive particle according to claim 1, wherein the conductive particles have an electric conductivity of 1 × 10 ² Ω ⁻¹ · m ⁻¹ or more and an average particle diameter of 0.1 to 6 μm. Metal plate for separator of polymer electrolyte fuel cell.   The metal plate for a separator of a polymer electrolyte fuel cell according to any one of claims 1 to 4, wherein the content of the conductive particles in the Sn alloy layer coating is 0.1 to 30% by mass. The conductive particles may be one or more selected from carbon black, TiC, VC, TiN, TiB ₂ , VB ₂ , CrB ₂ , TiSi ₂ , ZrSi ₂ and NbSi ₂ . Item 6. A metal plate for a separator of a polymer electrolyte fuel cell according to any one of Items 1 to 5. The oxide film comprises one or more selected from SnO ₂ , Sn (OH) ₂ , Sn (OH) ₄ , Ni (OH) ₂ , NiO ₂ , Ni ₂ O _3, and Ni ₃ O _4. The metal plate for a separator of a polymer electrolyte fuel cell according to any one of claims 1 to 6.   8. The separator for a polymer electrolyte fuel cell according to claim 1, wherein at least one Sn alloy layer is provided as an intermediate layer between the Sn alloy layer coating and the substrate. Metal plate.   9. The metal plate for a separator of a polymer electrolyte fuel cell according to claim 8, wherein the intermediate layer contains at least one element selected from Ni and Fe. The metal plate for a separator of a polymer electrolyte fuel cell according to claim 8 or 9, wherein the intermediate layer includes a Ni ₃ Sn ₂ layer.   11. A pure metal layer or an alloy layer is provided as a base treatment layer between the Sn alloy layer film and the substrate, or between the intermediate layer and the substrate. A metal plate for a separator of a polymer electrolyte fuel cell according to 1. The metal plate for a separator of a polymer electrolyte fuel cell according to claim 11, wherein the base treatment layer contains at least one element selected from Ni, Cu, Ag and Au.

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