JP2011249147A - Fuel cell separator material, fuel cell separator using the same, fuel cell stack, and method of manufacturing fuel cell separator material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell separator material in which a layer containing Au can be strongly and uniformly formed on a surface of a stainless steel substrate and adhesiveness and corrosion resistance required to a fuel cell separator can be ensured.SOLUTION: The present invention relates to a fuel cell separator material in which a surface layer 6 containing Au and Cr is formed on a surface of a stainless steel substrate 2, an intermediate layer 2a containing Cr in 20 atom% or more and O in 20 atom% or more to less than 50 atom% is present for 1 nm or more between the surface layer 6 and the stainless steel substrate 2, an area in which the concentration of Au is 65 atom% or more is present for the thickness of 1.5 nm or more, the maximum concentration of Au is 80 atom% or more, and a metal layer containing Cr in 50 atom% or more is not present.

Description

  The present invention relates to a fuel cell separator material having a surface on which Au or an Au alloy (a layer containing Au) is formed, a fuel cell separator using the same, and a fuel cell stack.

The polymer electrolyte fuel cell separator has electrical conductivity, and electrically connects each single cell, collects energy (electricity) generated in each single cell, and supplies fuel to each single cell. Gas (fuel liquid) and air (oxygen) flow paths are formed. This separator is also called an interconnector, a bipolar plate, or a current collector.
Conventionally, a fuel cell separator having a gas flow path formed on a carbon plate has been used, but there is a problem that the material cost and processing cost are high. On the other hand, when a metal plate is used instead of the carbon plate, corrosion and elution become a problem because it is exposed to an oxidizing atmosphere at a high temperature. For this reason, a technique for forming a conductive portion by sputtering a noble metal selected from Au, Ru, Rh, Cr, Os, Ir, Pt, etc. and an alloy of Au on the surface of a stainless steel plate is known. (Patent Document 1).
On the other hand, a fuel cell separator is known in which an Au film is formed on an oxide film of a stainless steel substrate through an intermediate layer made of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, or the like. (Patent Document 2). This intermediate layer has good adhesion to the base oxide film, that is, good bonding with O (oxygen atom), and good adhesion and bonding to the Au film because of the metal or metalloid. .
In addition, a metal separator for fuel cells has been reported in which the surface of a stainless steel plate is subjected to gold plating in an acid bath without applying a base treatment (Patent Document 3).

In addition, in a polymer electrolyte fuel cell, a direct methanol fuel cell (DMFC) that uses methanol that is easy to handle as a fuel gas to be supplied to an anode has been developed. Since DMFC can directly extract energy (electricity) from methanol, a reformer or the like is not necessary, and it can cope with downsizing of the fuel cell, and is also promising as a power source for portable devices.
The following two structures have been proposed as DMFC structures. First, the first structure is a single cell (stacked (active) structure in which a membrane electrode assembly (hereinafter referred to as MEA) in which a solid polymer electrolyte membrane is sandwiched between a fuel electrode and an oxygen electrode) is stacked. This structure is a planar type (passive type) structure in which a plurality of single cells are arranged in the plane direction, each of which is a structure in which a plurality of single cells are connected in series (hereinafter referred to as a stack). Of these, the passive type structure does not require an active fuel transfer means for supplying fuel gas (fuel liquid), air, or the like into the cell, and therefore further reduction in size of the fuel cell is considered promising. Yes.

JP 2001-297777 A JP 2004-185998 A JP 2004-296281 A

However, in the case of the technique described in Patent Document 1 described above, in order to obtain an Au alloy film with good adhesion, it is necessary to remove the oxide film on the surface of the base material. There is a problem that the adhesion of the noble metal film is lowered.
Further, as described in Patent Document 2, simply providing an intermediate layer does not provide sufficient adhesion and corrosion resistance and durability required as a separator for a fuel cell. In particular, when the thickness of Au is reduced in order to reduce the cost, corrosion resistance may not be obtained.
On the other hand, in the case of the technique described in Patent Document 3, since the electrodeposition shape of wet gold plating is granular, if the amount of gold plating is small, a portion that becomes a non-plated portion is generated on a part of the substrate surface. Therefore, in order to uniformly plate the entire surface of the substrate with gold, it is necessary to increase the adhesion amount of Au.

  That is, the present invention has been made to solve the above-described problems, and can form a highly corrosion-resistant conductive film containing Au on the surface of a stainless steel substrate with high adhesion, and the fuel cell operating environment. An object of the present invention is to provide a fuel cell separator material having high durability even under, a fuel cell separator and a fuel cell stack using the material, and a method for producing a fuel cell separator material.

As a result of various studies, the present inventors have formed a surface layer containing Au and Cr on the surface of the stainless steel substrate, and formed an intermediate layer containing O and Cr between the stainless steel substrate and the surface layer. It has been found that by forming a region having a relatively high Au concentration to a predetermined thickness, a layer containing Au can be formed firmly and uniformly on stainless steel, and the corrosion resistance and durability required for a fuel cell separator can be secured. It was.
In order to achieve the above object, the fuel cell separator material according to the present invention has a surface layer containing Au and Cr formed on the surface of a stainless steel substrate, and the surface layer is formed between the surface layer and the stainless steel substrate. In addition, an intermediate layer containing Cr of 20 atomic% or more and O containing 20 atomic% or more and less than 50 atomic% exists in an amount of 1 nm or more, the thickness of the region having an Au concentration of 65 atomic% or more is 1.5 nm or more, and the maximum concentration of Au Is 80 atomic% or more, and there is no metal layer containing 50 atomic% or more of Cr.

It is preferable that the adhesion amount of Au is 9000 ng / cm ² or more.

  The separator material for a fuel cell of the present invention is suitably used for a polymer electrolyte fuel cell or a direct methanol type polymer electrolyte fuel cell.

The fuel cell separator of the present invention uses the fuel cell separator material, and after forming a reaction gas flow path and / or a reaction liquid flow path by pressing in advance on the stainless steel substrate, the surface layer is formed. It consists of
Further, the fuel cell separator of the present invention uses the fuel cell separator material, and after forming the surface layer on the stainless steel substrate, forms a reaction gas channel and / or a reaction liquid channel by press working. It consists of

  The fuel cell stack of the present invention uses the fuel cell separator material or the fuel cell separator.

The method for producing a fuel cell separator material according to the present invention is a method for producing the fuel cell separator material, wherein the Cr is dry-formed on the surface of the stainless steel substrate, and then Au is dry-formed. .
(Au thickness / Cr thickness) is preferably 3 or more.
The dry film formation is preferably sputtering.

  According to the present invention, the Au-containing layer can be formed firmly and uniformly on the stainless steel, and the adhesion and corrosion resistance required for the fuel cell separator can be ensured.

It is a schematic diagram which shows the structure of the separator material for fuel cells which concerns on embodiment of this invention. It is a figure which shows the XPS analysis result of the cross section of the separator material for fuel cells of Example 1. FIG.

Hereinafter, a fuel cell separator material according to an embodiment of the present invention will be described. In the present invention,% means atomic (at)% unless otherwise specified.
In the present invention, the “fuel cell separator” has electrical conductivity, electrically connects each single cell, collects energy (electricity) generated in each single cell, and collects each single cell. A fuel gas (fuel liquid) or air (oxygen) flow path is formed. The separator is also referred to as an interconnector, a bipolar plate, or a current collector.
Therefore, as will be described in detail later, as a separator for a fuel cell, in addition to a separator having an uneven flow path on a plate-like substrate surface, a plate-like substrate surface such as the above-described passive DMFC separator is used. It includes a separator with gas and methanol passage holes.

  As shown in FIG. 1, the separator material for a fuel cell according to the embodiment of the present invention has an intermediate layer 2a formed on the surface of a stainless steel substrate 2 and a surface layer 6 formed on the surface of the intermediate layer 2a. .

<Stainless steel substrate>
The fuel cell separator material is required to have corrosion resistance and conductivity, and the base material is required to have corrosion resistance. For this reason, stainless steel having good corrosion resistance is used for the base material.
The material of the stainless steel material 2 is not particularly limited as long as it is stainless steel, but high corrosion resistance stainless steel is desirable, and many of the high corrosion resistance stainless steels have a high Cr or Ni concentration (for example, SUS316). Further, the shape of the stainless steel substrate 2 is not particularly limited as long as it can be sputtered with Cr and Au. However, considering the press forming into a separator shape, the shape of the stainless steel substrate is a plate material. It is preferable that the thickness of the entire stainless steel substrate is 50 μm or more.
O (oxygen) contained in the intermediate layer 2a is naturally formed by leaving the stainless steel substrate 2 in the air or leaving it in a vacuum when forming a coating on the surface of the stainless steel substrate 2 by sputtering. However, O may be positively formed on the surface of the stainless steel substrate 2 in an oxidizing atmosphere.

<Surface layer>
A surface layer 6 containing Cr and Au is formed on the stainless steel substrate 2. This surface layer is for imparting Au characteristics (corrosion resistance, conductivity, etc.) and hydrogen embrittlement resistance to the stainless steel substrate.
Cr has the properties that a) easily binds to oxygen, b) constitutes an alloy with Au, and c) hardly absorbs hydrogen. Form and improve the adhesion between the surface layer and the stainless steel substrate.
In addition, Cr is more oxidizable than Au from the potential-pH diagram, and makes use of the characteristic that it is difficult to absorb hydrogen, so Cr is used as a constituent element of the following intermediate layer.

The surface layer can be confirmed by XPS analysis, which will be described later, and is a portion containing Au and Cr from the outermost surface to the lower layer by XPS analysis, and is located in the upper layer below the intermediate layer and the portion of Au 20% or more. The surface layer. The total thickness of the surface layer and the intermediate layer described later is preferably 5 to 20 nm. If the total thickness of the surface layer and the intermediate layer is less than 5 nm, the corrosion resistance required for the fuel cell separator on the stainless steel substrate may not be ensured. The total thickness of the surface layer and the intermediate layer is more preferably 7 nm or more, and further preferably 10 nm or more.
Further, heat treatment may be performed after forming the Cr and Au films. When heat treatment is performed, oxidation and diffusion progress, and the Au concentration in the surface layer may decrease. However, if the thickness of the region having an Au concentration of 65% or more is 1.5 nm or more, Fe which is the main component of the stainless steel base material does not diffuse into the surface layer and functions as a surface layer.

If the thickness of the surface layer exceeds 100 nm, money saving may not be achieved and the cost may increase.
Further, when the thickness of the region having an Au concentration of 65% or more in the surface layer is less than 1.5 nm, the corrosion resistance required for the fuel cell separator cannot be secured.

  Further, the maximum concentration of Au in the surface layer 6 needs to be 80% or more. When the maximum concentration of Au is less than 80%, the characteristics of Au (corrosion resistance, conductivity, etc.) and hydrogen embrittlement resistance are not sufficiently imparted to the stainless steel substrate.

  Note that an Au single layer may be formed on the outermost surface portion of the surface layer 6. The Au single layer is a portion where the concentration of Au is almost 100% by XPS analysis.

<Intermediate layer>
Between the surface layer (or Au single layer) 6 and the stainless steel substrate 2, an intermediate layer 2a containing 20 atomic% or more of Cr and containing 20 atomic% or more and less than 50 atomic% of O is 1 nm or more.
Even if it is going to form Au on a stainless steel base material in order to give conductivity to separator material for fuel cells, since a stainless steel base material has an oxidation layer on the surface, it is difficult to oxidize Au (containing) It is difficult to form the layer directly on the stainless steel surface. Therefore, it is conceivable to remove the surface oxide film of the stainless steel substrate appropriately and perform reverse sputtering (ion etching) for the purpose of cleaning the surface of the substrate. Particularly, stainless steel with a high Cr concentration has a surface oxide layer. Therefore, it may take time to remove the oxide film or the oxide film may not be sufficiently removed.
Further, as described in Patent Document 2, even if Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, etc. are simply formed as an intermediate layer, sufficient adhesion as a fuel cell separator is achieved. , Conductivity and corrosion resistance cannot be obtained.
Here, when the intermediate layer contains Cr, the corrosion resistance may be lowered. In other words, when the thickness of Cr is larger than necessary with respect to the thickness of Au, Cr is exposed on the surface of the surface layer, the contact resistance after the test increases in the corrosion resistance test with a chlorine-containing corrosive liquid, and Cr is also eluted. Relatively many. On the other hand, if the thickness of Au is increased, the exposure of Cr to the surface of the surface layer can be suppressed. However, since Au is an expensive metal, a method of increasing the thickness of Au is not practical. Further, when the thickness of Cr is extremely reduced, there is a problem that a surface layer with good adhesion cannot be obtained.

For this reason, in the present invention, the intermediate layer 2a containing 20 atomic% or more of Cr and containing 20 atomic% or more and less than 50 atomic% of O is formed. Cr has the properties that a) easily bonds with oxygen, b) constitutes an alloy with Au, and c) hardly absorbs hydrogen, and is suitable as a constituent element of the intermediate layer. In addition, Cr is more easily oxidized than Au, and it is considered that O atoms and oxides are formed on the surface of the stainless steel substrate and are firmly bonded to the surface of the stainless steel substrate. And the separator material with favorable electroconductivity and durability can be provided by prescribing | regulating the density | concentration of Cr and O of an intermediate | middle layer.
When the Cr of the intermediate layer 2a is less than 20 atomic%, the above-described properties of Cr are not exhibited. When the O of the intermediate layer 2a is less than 20 atomic%, the corrosion resistance is inferior, Cr is eluted from the intermediate layer 2a, and the contact resistance is also increased. On the other hand, when O of the intermediate layer 2a exceeds 50 atomic%, the adhesion of Au is lowered and the conductivity is deteriorated.

  Further, it is necessary that the intermediate layer 2a has a thickness of 1 nm or more. When the intermediate layer is less than 1 nm, Cr is thin and the portion where the stainless steel substrate and Au are in contact with each other increases, so that the adhesion of the surface layer deteriorates.

As a method of controlling the Cr of the intermediate layer to 20 atomic% or more and controlling O to 20 atomic% or more and less than 50 atomic%, dry plating (sputtering) using a Cr-containing target is performed, and O present on the stainless steel surface. The amount of Cr sputtering (adhesion amount) and the sputtering conditions may be adjusted in accordance with the concentration of each. For example, in sputtering, the energy of sputtered particles is large, and even if the oxide film on the surface of the stainless steel is not removed, a film having good adhesion can be formed as long as it is a metal that bonds with O. Then, O originally present on the surface of the base material or O present in the sputter film forming chamber after evacuation is combined with Cr formed by sputtering to improve the adhesion, conductivity and corrosion resistance of the surface layer.
If there is a thickness portion where Cr is 50 atomic% or more (this portion is appropriately referred to as a “metal layer”), the amount of Cr eluted after the corrosion resistance test under Condition 2 described later increases, and the corrosion resistance of the coating film. Is inferior. Therefore, it is preferable that there is no metal layer (thickness portion) in which Cr is 50 atomic% or more. The thickness of the metal layer can be measured by XPS (X-ray photoelectron spectroscopy) analysis. Further, as a method for preventing the formation of a metal layer containing 50 atomic% or more of Cr, the proportion of Au formed on the stainless steel substrate may be made larger than that of Cr.

Here, a depth profile by XPS (X-ray photoelectron spectroscopy) analysis is measured, and concentration analysis of Au, O, Cr, Fe, and Ni is performed to determine the layer structure of the sputtered layer. In the concentration detection by XPS, the concentration of each element is analyzed with the total of designated elements (Au, O, Cr, Fe, Ni) being 100%. In the XPS analysis, the distance of 1 nm in the thickness direction is the distance on the horizontal axis of the chart by XPS analysis (distance in terms of SiO ₂ ).

In the fuel cell separator material of the present invention, the amount of Au deposited needs to be 9000 ng / cm ² or more.
When the adhesion amount of Au is less than 9000 ng / cm ² , the corrosion resistance required for the fuel cell separator cannot be secured.
On the other hand, it is preferable that the adhesion amount of Au is less than 40000 ng / cm ² from the viewpoint of saving money.

<Manufacture of fuel cell separator materials>
As a method for forming the intermediate layer of the separator material for the fuel cell, the surface oxide film of the stainless steel base material is not removed, but sputtering is performed on this base material using Cr as a target, so that the O in the surface oxide film is formed. Cr can be bonded to form an intermediate layer. Also, after removing the surface oxide film of the stainless steel base material 2, sputter deposition is performed using Cr oxide as a target, or after removing the surface oxide film of the stainless steel base material 2, sputtering is performed using Cr as a target in an oxidizing atmosphere. The intermediate layer can also be formed by forming a film.
In addition, reverse sputtering (ion etching) may be performed for the purpose of cleaning the surface of the substrate by appropriately removing the surface oxide film of the stainless steel substrate during sputtering. Reverse sputtering can be performed, for example, by irradiating the substrate with argon gas at an output of about RF 100 W and an argon pressure of about 0.2 Pa.
The Au in the intermediate layer is included in the intermediate layer by Au atoms entering the intermediate layer by Au sputtering for forming the following surface layer. Alternatively, sputtering may be performed on the surface of the stainless steel substrate using an alloy target containing Cr and Au.

As a method for forming the surface layer, for example, after Cr is formed on a stainless steel substrate by sputtering as described above, Au can be formed by sputtering on the Cr film. In this case, since the sputtered particles have high energy, even if only the Cr film is formed on the surface of the stainless steel substrate, by sputtering Au there, Au enters the Cr film and becomes a surface layer. When forming the surface layer, it is preferable to adjust the film forming conditions so that (Au thickness / Cr thickness) is 3 or more. In this way, a film having good corrosion resistance can be formed with a thickness of Au with respect to a thickness of Cr.
First, sputter film formation may be performed on a stainless steel substrate surface using an alloy target having a low Au concentration of Cr and Au, and then using an alloy target having a high Au concentration of Cr and Au. .

  According to the separator material for a fuel cell according to the embodiment of the present invention, a layer containing Au can be formed firmly and uniformly on a stainless steel substrate, and this layer has conductivity, corrosion resistance and durability. Therefore, it is suitable as a fuel cell separator material. Further, according to the embodiment of the present invention, if a layer containing Au is sputter-deposited, this layer becomes a uniform layer. Therefore, the surface becomes smoother than wet gold plating, and Au is not wasted. There is an advantage that it can be done.

In the fuel cell separator of the present invention, it is preferable that a reaction gas flow path and / or a reaction liquid flow path by press working is formed in advance on the substrate. In this case, it is not necessary to form a reaction gas channel (reaction liquid channel) in a subsequent process, and the reaction gas flow can be easily performed by pressing the base material before forming the intermediate layer, the surface layer, or the like. Since a channel (reaction liquid channel) can be formed, productivity is improved.
In the fuel cell separator of the present invention, a reaction gas channel and / or a reaction liquid channel is formed later by press working on the fuel cell separator material having a surface layer or a single Au layer formed on the surface of the substrate. May be. In the fuel cell separator material of the present invention, the surface layer or the Au single layer is firmly adhered to the surface of the base material. ) To improve productivity.

  In addition, in order to perform the press work for forming the reaction gas flow path (reaction liquid flow path), it is preferable that the thickness of the base material is 10 μm or more as the fuel cell separator material. The upper limit of the thickness of the base material is not limited, but is preferably 200 μm or less from the viewpoint of cost.

<Fuel cell stack>
The fuel cell stack of the present invention comprises the fuel cell separator material of the present invention or the fuel cell separator of the present invention.
The fuel cell stack is formed by connecting a plurality of cells in which an electrolyte is sandwiched between a pair of electrodes, and a fuel cell separator is interposed between the cells to block fuel gas and air. The electrode in contact with the fuel gas (H ₂ ) is the fuel electrode (anode), and the electrode in contact with the air (O ₂ ) is the air electrode (cathode).

<Preparation of sample>
As the stainless steel substrate, a stainless steel material (SUS316) having a thickness of 100 μm was used.
Next, Cr was deposited on the surface of the stainless steel substrate so as to have a predetermined target thickness by sputtering. Pure Cr was used for the target. Next, Au was deposited using a sputtering method so as to have a predetermined target thickness. Pure Au was used for the target.
The target thickness was determined as follows. First, an object (Cr, Au) is formed in advance on a stainless steel substrate by sputtering, and the actual thickness is measured with a fluorescent X-ray film thickness meter (SEA Instruments 100A, collimator 0.1 mmΦ) manufactured by Seiko Instruments. The sputter rate (nm / min) was ascertained. Based on the sputtering rate, the sputtering time for a thickness of 1 nm was calculated, and sputtering was performed under these conditions.
Sputtering of Cr and Au was performed using a sputtering apparatus manufactured by ULVAC, Inc. under the conditions of an output DC of 50 W and an argon pressure of 0.2 Pa.

<Measurement of layer structure>
About the obtained sample, the depth (Depth) profile by XPS (X-ray photoelectron spectroscopy) analysis was measured, the density | concentration analysis of Au, Cr, O, Ni, and Fe was performed, and the layer structure of the sputter | spatter layer was determined. As an XPS device, ULVAC-PHI Co., Ltd. 5600MC was used, ultimate vacuum: 6.5 × 10 ⁻⁸ Pa, excitation source: monochromatic AlK, output: 300 W, detection area: 800 μmΦ, incident angle: 45 degrees, The take-off angle was 45 degrees, no neutralization gun was used, and the measurement was performed under the following sputtering conditions.
Ion species: Ar +
Acceleration voltage: 3 kV
Sweep area: 3mm x 3mm
Rate: 2 nm / min. (SiO ₂ equivalent)
For concentration detection by XPS, the total of specified elements (Au, Cr, O, Ni, Fe) was taken as 100%, and the concentration (at%) of each element was analyzed. Further, the distance in the thickness direction from the outermost surface in XPS analysis is the distance on the horizontal axis of the chart (distance in terms of SiO ₂ ) by XPS analysis.

FIG. 2 shows an actual XPS image of the cross section of the sample of Example 1.
A surface layer 6 containing Cr and Au is formed on the surface of the stainless steel substrate 2. Further, it can be seen that an intermediate layer 2a containing 20 atomic% or more of Cr and containing 20 atomic% or more and less than 50 atomic% of O is present at 1 nm or more between the stainless steel substrate 2 and the surface layer 6.
In the present invention, the concentration of Cr, O, etc. is defined in order to define the intermediate layer. Therefore, since the boundary of the intermediate layer is determined by the Cr and O concentration for convenience, a layer different from the intermediate layer and the stainless steel substrate is interposed between the intermediate layer and the upper and lower layers (for example, the stainless steel substrate 2). In some cases.

<Preparation of each sample>
Samples of Examples 1 to 5 were prepared by changing the target thicknesses of the Cr film and Au film at the time of sputtering with respect to the stainless steel substrate.
As Comparative Example 6, a sample was prepared with the same sputtering thickness (10 nm) for the Au film and the Cr film.
As Comparative Example 7, a sample was prepared by increasing the thickness of the Au film to 30 nm.
As Comparative Example 8, a sample was prepared by reducing the sputtering thickness of the Au film to 4 nm.
As Comparative Example 9, a sample was prepared by reducing the sputtering thickness of the Cr film to 0.25 nm.
As Comparative Example 10, a sample was prepared by performing atmospheric heat treatment (120 ° C. × 12 hours) after sputtering.
As Comparative Example 11, the substrate was heated (300 ° C.) during sputtering to prepare a sample.

<Evaluation>
The following evaluation was performed for each sample.
A. Adhesion of coating After marking the grids at 1 mm intervals on the outermost surface (surface layer) of each sample, adhesive tape (Sumitomo 3M, Scotch Mending Tape) is applied, and each test piece is A peel test was performed in which the tape was bent and returned to its original state, and the tape at the bent portion was peeled off rapidly and strongly.
The case where there was no peeling at all was marked as ◯, and the case where some peeling was visually observed was marked as x.

B. Contact resistance The contact resistance was measured by applying a load to the entire surface of the sample. First, carbon papers were laminated on the front and back sides of a 40 × 50 mm plate-like sample, and Cu / Ni / Au plates were further laminated on the outer sides of the front and back carbon papers. The Cu / Ni / Au plate is a material in which a 10 μm thick copper plate is plated with a 1.0 μm thick Ni base, and the Ni layer is plated with a 0.5 μm Au plate. The carbon paper was placed in contact with it.
Further, a Teflon (registered trademark) plate was arranged outside the Cu / Ni / Au plate, and a load of 10 kg / cm ² was applied in the compression direction from the outside of each Teflon (registered trademark) plate with a load cell. In this state, when a constant current with a current density of 100 mA / cm ² was passed between the ^two Cu / Ni / Au plates, the electrical resistance between the Cu / Ni / Au plates was measured by a four-terminal method.

The contact resistance was measured before and after the sample was tested under the following two conditions.
Condition 1: immersion test of sample in sulfuric acid aqueous solution (bath temperature 90 ° C., sulfuric acid concentration 0.5 g / L, immersion time 240 hours, liquid volume 1000 cc)
Condition 2: immersion test of sample in aqueous solution of sulfuric acid (0.5 g / L) + sodium chloride (Cl: 10 ppm) (bath temperature 90 ° C., immersion time 240 hours, liquid volume 1000 cc)

C. Metal Elution Amount The metal elution amount was evaluated by ICP (inductively coupled plasma) emission spectroscopic analysis of all metal concentrations (mg / L) in the test solution after the test under the above conditions 1-2.
Typical characteristics required for fuel cell separators are low contact resistance (10 mΩ · cm ² or less), corrosion resistance in the environment of use (low contact resistance after corrosion test, no leaching of harmful ions) There are two.

D. Amount of adhesion The amount of adhesion was evaluated by acid decomposition / ICP (inductively coupled plasma) emission spectroscopic analysis. Specifically, the entire amount of one 50 mm × 50 mm sample was dissolved in a hydrofluoric acid solution, and the amount of Au deposited was analyzed. The number of samples per condition was five, and the average values of the five measurement results are shown in Table 1, respectively.
The obtained results are shown in Tables 1 and 2.

  As is apparent from Tables 1 and 2, the surface layer and the intermediate layer exist, the thickness of the region where Au is 65 atomic% or more is 1.5 nm or more, and the maximum concentration of Au is 80 atomic% or more. In each of the examples in which there was no metal layer containing 50 atomic% or more, the contact resistance of the sample did not change before and after the corrosion resistance test, and the film adhesion and corrosion resistance were excellent.

In the case of Comparative Example 6 in which a metal layer (Cr having a thickness region of 50 atomic% or more) was present because the Au and Cr sputter thicknesses were the same, the contact resistance after the test increased in the corrosion resistance test of Condition 2, and the condition 2 The amount of Cr elution was large, and the corrosion resistance of the film was poor.
In the case of the comparative example 7 in which the sputtering thickness of Au is made thicker than that of the comparative example 6, the metal layer (thickness region where Cr is 50 atomic% or more) is present in the same manner as the comparative example 6. Contact resistance increased, the amount of Cr eluted under condition 2 was large, and the corrosion resistance of the coating was poor.
In the case of Comparative Example 8 in which the Au adhesion amount is less than 9000 ng / cm ² , since the Au adhesion amount is small, the contact resistance after the test in the corrosion resistance test of Condition 2 is increased, and the Cr elution amount in Condition 2 is also Many of the coatings were inferior in corrosion resistance.
In the case of Comparative Example 9 in which the thickness of the intermediate layer was less than 1 nm, the adhesion of the sputtered film deteriorated and the corrosion resistance could not be evaluated.

In Comparative Example 10 where the maximum concentration of Au was less than 80 atomic% due to the atmospheric heat treatment after sputtering, the contact resistance after the test increased in the corrosion resistance test of Condition 2, and the elution of Cr under Condition 2 The amount was large and the corrosion resistance of the film was poor.
In the case of Comparative Example 11 in which the thickness of the region having an Au concentration of 65% or more is less than 1.5 nm, the contact resistance after the test increased in the corrosion resistance test of Condition 2, the amount of Cr eluted under the condition 2 was large, Corrosion resistance was inferior.

2 Stainless steel substrate 2a Intermediate layer 6 Surface layer

Claims (10)

A surface layer containing Au and Cr is formed on the surface of the stainless steel substrate,
Between the surface layer and the stainless steel substrate, there is an intermediate layer containing 20 nm% or more of Cr, and containing 20 nm% or more and less than 50 atom% of O and 1 nm or more,
A fuel cell separator material having a thickness of 1.5 nm or more in a region having an Au concentration of 65 atomic% or more, a maximum Au concentration of 80 atomic% or more, and no metal layer containing 50 atomic% or more of Cr. The fuel cell separator material according to claim 1, wherein the adhesion amount of Au is 9000 ng / cm ² or more. The separator material for fuel cells according to claim 1 or 2, which is used for a polymer electrolyte fuel cell. The separator material for fuel cells according to any one of claims 1 to 3, which is used for a direct methanol type polymer electrolyte fuel cell. A fuel cell separator using the fuel cell separator material according to any one of claims 1 to 4, wherein a reaction gas flow path and / or a reaction liquid flow path is formed in advance on the stainless steel substrate by pressing. Then, a fuel cell separator formed by forming the surface layer. A fuel cell separator using the fuel cell separator material according to any one of claims 1 to 4, wherein the surface layer is formed on the stainless steel substrate, and then a reaction gas flow path and / or by press working. Alternatively, a fuel cell separator formed by forming a reaction liquid channel. A fuel cell stack using the fuel cell separator material according to claim 1 or the fuel cell separator according to claim 5 or 6. It is a manufacturing method of the separator material for fuel cells in any one of Claims 1-4,
A method for producing a separator material for a fuel cell, wherein a dry deposition of Cr is performed on the surface of the stainless steel substrate, followed by a dry deposition of Au.   The method for producing a fuel cell separator material according to claim 8, wherein (Au thickness / Cr thickness) is 3 or more.   The method for producing a fuel cell separator material according to claim 9, wherein the dry film formation is sputtering.

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