JP2018006300A - Metal separator for fuel cell and fuel cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal separator for a fuel cell which can maintain low contact resistance in a corrosive environment.SOLUTION: A metal separator 20 for a fuel cell includes: a metal substrate 21; a chromium oxycarbide layer 23 formed on the surface of the metal substrate 21; and a conductive layer 25 formed on the chromium oxycarbide layer 23. The metal separator 20 for a fuel cell is so configured that the conductive layer 25 is a diamond-like carbon (DLC) layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell metal separator and a fuel cell using the same.

  A polymer electrolyte fuel cell (PEFC) has a structure in which a plurality of single cells that exhibit a power generation function are stacked. Each of the single cells includes a polymer electrolyte membrane, a pair of (anode and cathode) catalyst layers sandwiching the polymer electrolyte membrane, and a pair of (anode and cathode) gas diffusion layers sandwiching them and dispersing the supply gas, The membrane electrode assembly (MEA) containing this is included. And MEA which each single cell has is electrically connected with MEA of an adjacent single cell through a separator. In this way, a fuel cell stack is configured by stacking and connecting single cells. The fuel cell stack can function as power generation means that can be used for various applications. In the fuel cell stack, the separator exhibits a function of electrically connecting adjacent single cells as described above. In addition to this, a gas flow path is usually provided on the surface of the separator facing the MEA. The gas flow path functions as gas supply means for supplying fuel gas and oxidant gas to the anode and the cathode, respectively.

  Briefly explaining the power generation mechanism of the PEFC, during operation of the PEFC, fuel gas (for example, hydrogen gas) is supplied to the anode side of the single cell, and oxidant gas (for example, atmospheric air, oxygen) is supplied to the cathode side. . As a result, in each of the anode and the cathode, an electrochemical reaction represented by the following reaction formula proceeds to generate electricity.

  As separators for fuel cells that require electrical conductivity, replacement of conventional carbon separators and conductive resin separators with metal separators such as SUS (stainless steel) is progressing. This is because the size of the stack can be reduced because the metal separator has excellent strength and conductivity. In recent years, metal separators in which a layer having corrosion resistance is laminated on a metal substrate have been developed in order to prevent the decrease in conductivity due to corrosion, which is a problem of metal separators, and the decrease in stack output associated therewith. .

For example, Patent Document 1 is characterized in that a diamond-like carbon layer (DLC layer) and a chromium oxycarbide layer (Cr _x C _y O _z layer) are laminated in this order on at least one main surface of a metal substrate. A fuel cell metal separator has been proposed. Thereby, dissolution of the DLC layer can be suppressed by covering and protecting the DLC layer with the chromium oxycarbide layer.

JP 2012-146616 A

  However, in the metal separator described in Patent Document 1, the outermost chromium oxycarbide layer, which has been known to have high corrosion resistance and electrical conductivity required for a fuel cell metal separator, is altered in a corrosive environment, There was a problem that low contact resistance could not be maintained.

  Therefore, an object of the present invention is to provide a metal separator for a fuel cell that can maintain a low contact resistance in a corrosive environment, and a fuel cell using the same.

  The object is to provide a metal separator having a metal substrate, a chromium oxycarbide layer formed on the metal substrate, and a conductive layer formed on the chromium oxycarbide layer, and the metal separator. It is solved by a fuel cell using

  In the metal separator of the present invention, by covering and protecting the chromium oxycarbide layer with a conductive layer, the chromium oxycarbide layer can be prevented from being altered in a corrosive environment, low contact resistance can be maintained, and sufficient corrosion resistance is exhibited. it can. Accordingly, it is possible to provide a metal separator for a fuel cell that has corrosion resistance and can realize a low contact resistance, and a fuel cell using the same.

It is a cross-sectional schematic diagram which shows the basic composition of the laminated structure of the metal separator for fuel cells by one Embodiment. It is an upper surface schematic diagram for demonstrating an example of the film-forming apparatus used with the direct current magnetron sputtering method (DCMS method) for forming the electroconductive carbon layer (DLC layer) of the metal separator for fuel cells. FIG. 3 is a partial cross-sectional view schematically showing the potential relationship (power supply system in the vacuum chamber) of each member, omitting the wall of the vacuum chamber (container) of FIG. It is the schematic which shows an example of the film-forming apparatus used with the high power pulse sputtering method (HiPIMS method) for forming the electroconductive carbon layer (DLC layer) of the metal separator for fuel cells. It is a schematic diagram which shows the waveform of the negative pulse voltage applied to a carbon raw material electrode in HiPIMS method. 1 is a schematic cross-sectional view showing a basic configuration of a polymer electrolyte fuel cell. It is the schematic which shows the measuring apparatus for measuring contact resistance. It is a graph which shows the relationship between the measurement surface pressure and contact resistance in the contact resistance measurement performed using the metal separator before a corrosion test. It is a graph which shows the relationship between the measurement surface pressure and contact resistance in the contact resistance measurement performed using the metal separator after a corrosion test. Auger electron spectroscopic analysis (AES analysis) was performed using the metal substrate after the chromium oxycarbide layer of Example 1 was formed, and the depth direction (depth from the surface to 1000 nm) of the metal substrate sample surface (chromium oxycarbide layer) It is drawing which shows the analysis result of).

  Hereinafter, preferred embodiments will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

[Metal separator for fuel cells]
The metal separator for a fuel cell according to this embodiment has a base material, a chromium oxycarbide layer formed on the base material, and a conductive layer formed on the chromium oxycarbide layer. To do. By having such a configuration, the above-described effects of the invention can be effectively expressed.

  FIG. 1 is a schematic cross-sectional view showing one embodiment of a laminated structure of a metal separator for a fuel cell (hereinafter also simply referred to as a metal separator) according to this embodiment. A metal separator 20 shown in FIG. 1 is formed (deposited) on a metal substrate 21, a chromium oxycarbide layer 23 (deposited) formed on both surfaces of the metal substrate 21, and a chromium oxycarbide layer 23. And a conductive layer 25. In FIG. 1, the conductive layer 25 has a two-layer (laminated film) structure in which a conductive intermediate layer 25a and a conductive carbon layer (DLC layer) 25b are formed (film formation) in this order on the chromium oxycarbide layer 23. An example is shown. However, in this embodiment, it is not particularly limited to such a two-layer (laminated coating) structure, and the conductive layer 25 is a one-layer (single-layer coating) structure composed of a conductive carbon layer (DLC layer) 25b ( (Not shown).

  The details of the reason why the above effect is obtained by the metal separator of the present embodiment are not clear, but are considered as follows.

  The present inventors have a problem that the chromium oxycarbide layer is altered in a corrosive environment by covering and protecting the chromium oxycarbide layer on the surface of the metal substrate with a conductive layer (DLC layer), and low contact resistance cannot be maintained. I found out that it could be solved. As a result, it is possible to effectively develop the performance inherent in the chromium oxycarbide layer, such as corrosion resistance, low contact resistance, electrical conductivity, workability, strength, and lightness required for a metal separator for fuel cells. I understood.

  Furthermore, in the configuration in which the DLC layer is formed on the metal substrate, when the outermost DLC layer has a natural potential of +1 V in a corrosive environment, there is a problem that the metal ions of the SUS substrate are eluted by being completely dissolved within one hour. (See the example of Patent Document 1). In order to solve the problem that the outermost conductive layer (DLC layer) is dissolved, it has been considered that a configuration of covering and protecting with a chromium oxycarbide layer as in Patent Document 1 is necessary and effective. However, by providing a chromium oxycarbide layer between the metal substrate and the conductive layer (DLC layer), it is surprisingly possible to suppress dissolution of the outermost DLC layer that is exposed to the harshest environment in a corrosive environment (DLC It has been found that an unexpected effect of having a dissolution inhibiting effect is obtained. (The details of this mechanism of action are unknown). As a result, the outermost conductive layer (DLC layer) functions (acts) as a stable protective layer even in a corrosive environment, thereby preventing an increase in contact resistance due to alteration of the chromium oxycarbide layer (sufficiently). Corrosion resistance can be expressed). Furthermore, it has been found that the elution of metal ions from the metal substrate can be effectively prevented (sufficient corrosion resistance can also be exhibited in this respect).

  As described above, the metal separator according to this embodiment includes a metal base, a chromium oxycarbide layer formed on the metal base, and a conductive layer formed on the chromium oxycarbide layer. With sufficient corrosion resistance, low contact resistance can be realized. In addition, the said mechanism is based on estimation and the metal separator of this embodiment is not restrict | limited to this.

  Hereafter, the component of the metal separator of this embodiment is demonstrated.

[Conductive layer 25]
As the conductive layer 25 constituting the metal separator 20 of the present embodiment, it is preferable to have a conductive carbon layer 25b. Further, if necessary, the conductive intermediate layer 25a may be included, or another conductive layer may be included. Hereinafter, the conductive carbon layer 25b which is a suitable conductive layer 25 and the conductive intermediate layer 25a which can be used in combination with the conductive carbon layer 25b will be described, but it goes without saying that the conductive carbon layer 25b may be used in combination with other conventionally known conductive layers. . The conductive carbon layer 25b may have a single layer (single layer coating) structure or a two or more layer (laminated coating) structure. In the present embodiment, the configuration including the conductive layer 25 (conductive carbon layer 25b, optional conductive intermediate layer 25a), and further the metal substrate and the chromium oxycarbide layer needs to have conductivity. Therefore, the metal separator including the conductive layer has conductivity when the contact resistance of the metal separator (refer to the example for the measurement method) is exposed to the corrosive environment (before the corrosion test of the example) It may be 10 mΩ · cm ² or less, preferably 5 mΩ · cm ² or less at a measurement surface pressure of 1 MPa (see FIG. 8A). In a state exposed to corrosive environments (after the corrosion test of Example), measured surface pressure 1MPa 50mΩ · cm ² or less, as long preferably 30 m [Omega] · cm ² or less (see FIG. 8B).

[Conductive carbon layer 25b]
The conductive carbon layer 25b is a layer containing conductive carbon. The conductive carbon layer 25b can improve adhesion to the chromium oxycarbide layer 23 and the conductive intermediate layer 25a. Furthermore, by covering and protecting the chromium oxycarbide layer 23, the chromium oxycarbide layer 23 can be prevented from being altered in a corrosive environment, low contact resistance can be maintained, and sufficient corrosion resistance can be exhibited. As a result, it is possible to effectively express the performance inherent in the chromium oxycarbide layer, such as corrosion resistance, low contact resistance, electrical conductivity, workability, strength, and lightness required for the metal separator for fuel cells. . In the metal separator of this embodiment, the outermost conductive layer (DLC layer) functions (acts) as a stable protective layer even in a corrosive environment, thereby preventing an increase in contact resistance due to alteration of the chromium oxycarbide layer. (Can exhibit sufficient corrosion resistance). Furthermore, elution of metal ions from the metal substrate can be effectively prevented (sufficient corrosion resistance can also be exhibited in this respect). An example of conductive carbon is polycrystalline graphite. Here, “polycrystalline graphite” has an anisotropic graphite crystal structure (graphite cluster) in which a graphene surface (hexagonal network surface) is laminated microscopically. Aggregated isotropic crystal. Therefore, it can also be said that polycrystalline graphite is a kind of diamond-like carbon (DLC). A conductive diamond-like carbon layer (DLC layer) can be used as the conductive carbon layer 25b. Specifically, in the case of a DLC layer having conductivity of 10 Ω · cm or less, when a layer having a thickness of 1 μm is formed, the resistance value per square centimeter is 1 mΩ or less, and can be used without any problem in practice. . In order to obtain a lower contact resistance (for example, 10 mΩ · cm ² or less), it is desirable that the resistivity of the DLC layer be 0.1 Ω · cm or less.

  In the present embodiment, the conductive carbon layer 25b may be composed of only polycrystalline graphite, but the conductive carbon layer 25b may include materials other than polycrystalline graphite. Examples of carbon materials other than polycrystalline graphite that can be included in the conductive carbon layer 25b include carbon black, fullerene, carbon nanotubes, carbon nanofibers, carbon nanohorns, and carbon fibrils. Specific examples of carbon black include, but are not limited to, ketjen black, acetylene black, channel black, lamp black, oil furnace black, or thermal black. Carbon black may be subjected to a graphitization treatment. Examples of materials other than the carbon material that can be included in the conductive carbon layer 25b include gold (Au), silver (Ag), platinum (Pt), ruthenium (Ru), palladium (Pd), rhodium (Rh), and indium. Examples thereof include noble metals such as (In); water-repellent substances such as polytetrafluoroethylene (PTFE); and conductive oxides. As for materials other than polycrystalline graphite, only 1 type may be used and 2 or more types may be used together.

The formation (film formation) method of the conductive carbon layer (DLC layer) 25b is not particularly limited, and a conventionally known production method can be used. Either a wet film formation method or a dry film formation method can be used. Can also be used. For example, as a wet film forming method, a method of applying carbon paste (carbon material powder (powder) + resin binder + solvent) such as graphite (coating method) can be used. The average particle size of the powder (powder) of the carbon material such as graphite is not particularly limited as long as it does not impair the effects of the present embodiment, but a range of 50 to 130 nm is preferable. In addition, the resin binder is not particularly limited as long as it does not impair the effects of the present embodiment, and examples thereof include polyvinylidene fluoride (PVdF, polytetrafluoroethylene (PTFE), The solvent is not limited to these, and examples of the solvent include N-methyl-2-pyrrolidone (NMP) and water, but are not limited to these. The blending ratio (mass ratio) of the material powder (powder) and the resin binder is not particularly limited as long as the effects of the present embodiment are not impaired. The amount of the powder) is preferably in the range of 30 to 70% by mass of the solid component, and the amount of the resin binder is also 30 to 70% by mass of the solid component. As a method suitably used for forming (depositing) the conductive carbon layer (DLC layer) 25b, a dry deposition method is preferable. For example, a layer containing conductive carbon is formed on the chromium oxycarbide layer 23 (or conductive intermediate layer 25a) using the constituent material (for example, graphite) of the conductive carbon layer 25b as a target. By laminating (depositing) at the atomic level, a conductive carbon layer can be formed, whereby the directly adhered conductive carbon layer 25b and chromium oxycarbide layer 23 (or conductive intermediate layer 25a) are formed. The interfacial force and the vicinity thereof can be maintained for a long period of time by intermolecular forces and slight carbon atom intrusion. And physical vapor deposition (PVD) methods such as sputtering and ion plating; and chemical vapor deposition (CVD) methods such as thermal CVD (chemical vapor deposition), plasma CVD, and photo-CVD. Examples of the ion beam deposition method include a filtered cathodic vacuum arc (FCVA) method, etc. Examples of the sputtering method include a magnetron sputtering method, an unbalanced magnetron sputtering (UBMS) method, a dual magnetron sputtering method, and an ECR sputtering method. In addition, examples of the ion plating method include an arc ion plating method, etc. Among them, it is preferable to use a sputtering method and an ion plating method. It is particularly preferred to use a ring method. According to such a technique, a carbon layer with a low hydrogen content (particularly a graphite structure with a turbulent layer structure) can be formed as the surface layer portion. As a result, the ratio of bonds between carbon atoms (sp ² hybrid carbon) can be increased, and excellent conductivity can be achieved. In addition to this, the film can be formed at a relatively low temperature, and there is an advantage that damage to the metal substrate, the chromium oxycarbide layer, and the conductive intermediate layer can be minimized. Furthermore, according to the sputtering method, by controlling the bias voltage and the like, there are advantages that the crystal structure of the chromium oxycarbide layer and the conductive intermediate layer can be controlled, and the film quality of each layer to be formed can be controlled. .

  Here, when the conductive carbon layer 25b is formed by sputtering, which is a dry film formation method, a negative bias voltage may be applied to the metal substrate 21 during sputtering as described above. According to such an embodiment, the ion structure can control the crystal structure like the above-described chromium oxycarbide layer 23 and the conductive intermediate layer 25a, and the structure of the conductive carbon layer 25b can be changed from the boundary layer to the surface layer portion. Can be changed. As a result, a conductive carbon layer (DLC) that can achieve both high adhesion and low contact resistance, such as the formation of a chromium oxycarbide layer and a conductive intermediate layer that contributes to improved corrosion resistance and the conductive carbon layer in this embodiment. Layer).

  Furthermore, a conductive carbon layer (DLC layer) having a structure in which graphite clusters are densely assembled can be formed by the ion irradiation effect. Such a conductive carbon layer 25b has high adhesion to the chromium oxycarbide layer 23 and the conductive intermediate layer 25a, and the surface layer portion can exhibit excellent corrosion resistance and conductivity. A conductive member (metal separator) having a low contact resistance with another member (such as MEA) can be provided. In this embodiment, the magnitude (absolute value) of the negative bias voltage to be applied is not particularly limited, and a voltage capable of forming a conductive carbon layer can be adopted. As an example, the magnitude of the applied voltage is preferably 50 to 500V, more preferably 100 to 300V. In addition, specific forms, such as other conditions at the time of film-forming, are not restrict | limited, A conventionally well-known knowledge can be referred suitably. Further, for the conductive carbon layer 25b, a method of changing the (negative) bias voltage from the low value to the high value when forming the conductive carbon layer 25b may be used. Specifically, at the initial stage of forming the conductive carbon layer 25b, a low bias voltage (higher than 0 V is sufficient so as not to cause a gap or a defect between the chromium oxycarbide layer 23 and the conductive intermediate layer 25a. The film formation starts at 0V to 50V). Thereafter, the bias voltage may be shifted to a high value (usually 200 to 500 V, preferably 200 to 300 V) to change to a DLC layer having high conductivity. Alternatively, a method of setting a constant bias voltage (usually 50 to 500 V, preferably 100 to 300 V) may be used. Also in this case, since the chromium oxycarbide layer 23 and the conductive intermediate layer 25a are interposed between the metal base material 21 and the conductive carbon layer (DLC layer) having high conductivity that hardly causes gaps and defects. can do.

  In addition, a magnetron sputtering method can be suitably used as a method for forming (depositing) the conductive carbon layer (DLC layer) 25b. FIG. 2 is a schematic top view for explaining an example of a film forming apparatus used in a direct current magnetron sputtering method (DCMS method), which is a kind of magnetron sputtering method. FIG. 3 is a partial cross-sectional view schematically showing the potential relationship (power supply system in the vacuum chamber) of each member with the wall of the vacuum chamber (container) of FIG. 2 omitted.

As shown in FIG. 2, a film forming apparatus used in a direct current magnetron sputtering method (DCMS method) has a plurality of targets (cathodes) 6101 to 6104 installed in one vacuum chamber 601. The inside of the vacuum chamber 601 is maintained at a 10 ⁻¹ to 10 ⁻² Torr level, and a gas such as N ₂ or Ar (not shown) may be introduced from an air supply port (not shown) as necessary. I can do it. Unnecessary atmospheric gas and excess gas source are appropriately exhausted from an exhaust port (not shown) in order to control a predetermined pressure (vacuum pressure or the like) in the vacuum chamber 601. Thereby, a multilayer film can be continuously formed. By using such a film forming apparatus capable of continuously forming a multilayer film, the inside of the vacuum chamber 601 is once made into a high vacuum, and then the substrate 501 on which the chromium oxycarbide layer is formed without releasing the vacuum. For example, a conductive intermediate layer (Cr layer) (not shown) and a conductive carbon layer (DLC layer) (not shown) can be continuously formed. Therefore, the time required for forming the conductive intermediate layer (Cr layer) and the conductive carbon layer (DLC layer) on the base material 501 on which the chromium oxycarbide layer is formed can be shortened.

  Independent magnetic circuits 6201 to 6204 are arranged on the back surfaces of the targets 6101 to 6104, respectively.

  A rotary stage 650 is provided in the vacuum chamber 601 for fixing a plurality of base materials 501 and realizing uniform film formation. By rotating the rotary stage 650, film formation by sputtering from each of the targets 6101 to 6104 is performed.

  Further, as shown in FIG. 3, the substrate 501 (rotation stage 650) and the targets 6101 to 6104 are connected to independent power sources 656 and 655, respectively. A bias is applied to the substrate 501 from the rotary stage 650. Thereby, the bias of the base material 501 with respect to each target 6101 to 6104 can be freely controlled. 3 shows the case of the target 6101, the other targets 6102 to 6104 are also connected to independent power sources in the same manner. Further, the DC power source 655 and each target 6101 (˜6104) and the vacuum chamber 601 are electrically insulated (blocked) by an insulator 670, and the vacuum chamber 601 is grounded.

  In the direct current magnetron sputtering method (DCMS method), a conductive carbon layer (DLC layer) film formation target (for example, a graphite target) is formed at the position of the target 6101 and the conductive film is formed at the position of the target 6103 using the film formation apparatus described above. A conductive intermediate layer (Cr layer) deposition target (for example, a Cr target) is disposed, and after first forming a conductive intermediate layer (Cr layer), a conductive carbon layer (DLC layer) is formed thereon. Films can be continuously formed. Of the sputtering conditions (film formation conditions) at the time of each film formation, the magnitude (absolute value) of the negative bias voltage to be applied is not particularly limited, and a voltage capable of forming each layer can be adopted. As an example, the magnitude of the applied voltage is preferably 50 to 500V, more preferably 100 to 300V. In addition, specific forms, such as other conditions at the time of film-forming, are not restrict | limited, A conventionally well-known knowledge can be referred suitably. When only the conductive carbon layer (DLC layer) is formed by DC magnetron sputtering (DCMS), the conductive carbon layer (DLC layer) deposition target (for example, graphite) is also formed at the position of the target 6103. Target) may be provided.

  Note that such a film forming apparatus is merely an example of a film forming apparatus used in a DC magnetron sputtering method (DCMS method), and the present embodiment is not limited to using such a film forming apparatus. Absent. Of course, when the direct current magnetron sputtering method (DCM method S) is performed, an apparatus for sputtering a single layer film is used, and a conductive intermediate layer (Cr layer) and a conductive carbon layer (DLC layer) are separately formed. Also good. Alternatively, only the conductive carbon layer (DLC layer) may be formed without providing any conductive intermediate layer (Cr layer).

  In addition to this, as a method for forming (depositing) the conductive carbon layer (DLC layer) 25b, for example, the use of the manufacturing method described in JP 2010-024476 A is also one preferred embodiment. This is because the conductive carbon layer 25b (DLC layer) having a resistivity of 10 mΩ · cm or less, preferably 0.1 Ω · cm or less can be obtained by this manufacturing method. In addition, for example, a high power pulse sputtering method (hereinafter referred to as HiPIMS method) can be used. By adopting the HiPIMS method, this is one of the preferable aspects in that the conductive carbon layer (DLC layer) 25b having a low contact resistance can be formed at a high film formation rate. Furthermore, it is one of the preferred embodiments in that the inhibition of adhesion with the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a) due to the formation of the graphite structure can be sufficiently suppressed. In addition to this, for example, an arc ion plating method and the like can be mentioned. When the chromium oxycarbide layer 23 (or conductive intermediate layer 25a) is formed so as to be in contact with the conductive carbon layer (DLC layer) 25b, the conductive carbon layer (DLC layer) 25b and the chromium oxycarbide layer 23 (or conductive) From the viewpoint of the adhesion of the intermediate layer 25a), the HiPIMS method is preferred. Below, this HiPIMS method is demonstrated.

  FIG. 4 is a schematic view schematically showing an example of a film forming apparatus used in the HiPIMS method. The film forming apparatus 100 includes a vacuum chamber 11 and a metal base material 21 that is disposed to face the carbon source electrode 14 disposed in the vacuum chamber 11 with a space therebetween. A chromium oxycarbide layer 23 (and a conductive intermediate layer 25a as necessary) is disposed on the metal substrate 21. The carbon source electrode 14 is connected to a substrate source electrode pulse power source (HiPIMS power source) 17 for applying a pulse voltage (negative voltage). A DC power source 18 is connected to the metal substrate 21. The vacuum chamber 11 is grounded. An argon gas pipe 15 for introducing argon gas, which is a sputtering atmosphere gas, is introduced into the vacuum chamber 11 from the outside via an argon gas introduction port 16.

  In the film forming apparatus 100, argon gas is introduced into the vacuum chamber 11, and a pulse voltage is applied to the carbon source electrode (target) 14 from the sputtering pulse power supply 17. As a result, the argon gas is ionized, and plasma is generated in the vicinity of the carbon source electrode (target) 14. By this plasma, carbon atoms of the carbon raw material are sputtered. In the HiPIMS method, since a high pulse voltage is applied, the plasma density is increased, and sputtered carbon atoms can be ionized. By applying a negative bias voltage to the metal substrate 21, such carbon ions are attracted and deposited as a carbon film. Thereby, a high deposition rate can be realized, and the obtained carbon film is dense and has low contact resistance. Further, when a negative bias voltage is applied to the chromium oxycarbide layer 23 (or conductive intermediate layer 25a), moisture near the chromium oxycarbide layer 23 (or conductive intermediate layer 25a) evaporates and deposits carbon. Moisture is not contained in the coating. This also reduces the contact resistance of the carbon coating.

  As the substrate power source for applying a negative bias voltage to the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a), any of a DC power source, an RF power source, a pulse power source and the like may be used, but the DC power source 18 is preferable. . That is, it is preferable to apply a DC voltage to the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a). This is because by applying a constant negative bias voltage from the DC power source 18, the metal substrate 21 can attract carbon ions constantly, and the film quality including contact resistance can be controlled. When using a pulse power supply, it is preferable to synchronize with the pulse voltage of the pulse power supply 17 for the carbon source electrode in order to attract carbon ions efficiently.

  The negative pulse voltage E1 applied to the carbon raw material electrode 14 is preferably larger than the negative bias voltage of the chromium oxycarbide layer 23 (or conductive intermediate layer 25a). When the negative pulse voltage E1 is higher than the negative bias voltage, a carbon film with good adhesion can be produced.

  The negative pulse voltage E1 applied to the carbon raw material electrode 14 and the negative bias voltage applied to the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a) are both preferably 800V or higher, more preferably 900V or higher. is there. When the pulse voltage E1 is a negative voltage of 800 V or more, the plasma density increases and the sputtered carbon atoms are also ionized. When the negative bias voltage is a negative voltage of 800 V or more, the generated carbon atom ions are attracted, so that the film formation rate is increased, the carbon film is densified, and a carbon film with low contact resistance can be obtained. Further, when the pulse voltage E1 is 800 V or more, there is an effect of preventing film peeling of the deposited carbon film. The difference between the negative pulse voltage E1 and the negative bias voltage is preferably 100 V or more. There is no particular limitation on the upper limits of the negative pulse voltage E1 and the negative bias voltage.

  FIG. 5 is a diagram schematically showing the waveform of the voltage applied to the carbon source electrode 14. In the waveform shown in FIG. 5, the absolute value of the negative voltage A is E1. In FIG. 5, the negative pulse voltage E1 applied to the carbon raw material electrode 14 has a frequency (frequency of the pulse power source) of preferably 500 to 2000 Hz, more preferably 500 to 1500 Hz, and a pulse width C of preferably 50 to 400 μs. Preferably it is 50-200 microseconds. When the frequency is 500 Hz or more, the film formation rate is improved, and the carbon film can be deposited at a sufficient film formation rate. On the other hand, 2000 Hz is the upper limit depending on the power source that is currently available, but there is no particular upper limit on the frequency.

  When the pulse width C is 50 μs or more, the film can be formed at a sufficient speed. On the other hand, 400 μs is the upper limit due to the limitation on the power supply capacity, but the upper limit of the pulse width C is not particularly limited. Further, if the duty (C / B × 100 (%)), which is the ratio between the pulse period B and the pulse width C, is 0 <duty <100%, the film can be formed at a sufficient rate. In addition, specific forms, such as other conditions at the time of film-forming, are not restrict | limited, A conventionally well-known knowledge can be referred suitably.

  The sputtering atmosphere gas introduced into the vacuum chamber 11 is argon, krypton, oxygen, hydrocarbon-based gas, or a mixed gas thereof. Of these, argon gas can be particularly preferably used.

  Moreover, the metal base material 21 is provided with the chromium oxycarbide layer 23 (or conductive intermediate layer 25a), and also functions as a substrate for forming a carbon film. The constituent material of the metal substrate 21 is preferably a metal (alloy) material described later. When the constituent material of the base material 21 is a metal (alloy) as in the present embodiment, the surface of the metal base material 21 is subjected to ion bombarding before the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a) is formed. (Oxide film removal treatment) is particularly preferable. The ion bombardment treatment is a method in which ionized argon gas or the like is struck against a metal surface for cleaning. Thereby, a passive film such as an oxide film or a hydroxide film formed on the surface of the metal substrate can be destroyed. By performing ion bombardment on the surface, the adhesion of the chromium oxycarbide layer 23 to the surface of the metal substrate 21 can be improved, and further, it is possible to effectively prevent an increase in bonding resistance. ing. The oxide film removal process (ion bombardment process, etc.) can be applied to film forming methods other than the HiPIMS method.

The above is one example of film formation conditions (first HiPIMS method) in the case where a conductive carbon layer (DLC layer) is formed (formed) by the HiPIMS method. (DLC layer) can be formed. For example, as another example of film formation conditions (second HiPIMS method) when forming a conductive carbon layer (DLC layer) by the HiPIMS method, the negative bias voltage to be applied is 700 to 1200 V. Is preferred. By applying a negative bias voltage in such a range, Ar ⁺ ions collide with the surface of the carbon coating (conductive carbon layer; DLC layer), and the carbon coating (conductive carbon layer; DLC layer). The surface of the film tends to have dangling bonds. Accordingly, since more electrons can freely move, the formed conductive carbon layer (DLC layer) and other members (especially other constituent members of the fuel cell) come into ohmic contact and contact in the stacking direction. Excellent in reducing resistance. Thus, by reducing the contact resistance in the stacking direction, a conductive carbon layer (DLC layer) in which the conductivity in the stacking direction is sufficiently secured is obtained, and the reduction of the graphite component can be suppressed. Furthermore, the increase in internal stress of the conductive carbon layer (DLC layer) itself can be suppressed, and the adhesion between the entire conductive carbon layer 25b and the chromium oxycarbide layer 23 (or conductive intermediate layer 25a) can be further increased. It is also excellent in that it can be further improved.

  The conductive carbon layer (DLC layer) 25b is a layer closest to the chromium oxycarbide layer 23 (or conductive intermediate layer 25a), and preferably has conductivity with the chromium oxycarbide layer 23 (or conductive intermediate layer 25a). The carbon layer (DLC layer) 25b is in contact with the carbon layer.

  The film thickness of the conductive carbon layer (DLC layer) 25b is not particularly limited, but is preferably 20 to 80 nm. From the viewpoint of preventing the formation of a stable conductive carbon layer (DLC layer) and the deposition time from becoming too long, the thickness is more preferably 20 to 50 nm. If the film thickness of the conductive carbon layer (DLC layer) 25b is in such a range, the above-described effects (effects by the above-described action mechanism) can be sufficiently exhibited.

  In the present embodiment, the conductive carbon layer 25 b may exist only on one main surface of the metal separator 20. However, preferably, as shown in FIG. 1 and the like, it is preferable that the conductive carbon layer 25b exists on the other main surface of the metal separator 20 (that is, on both surfaces of the metal substrate 21). This is because, on both surfaces of the metal substrate 21, the adhesion between the metal substrate 21 and the conductive carbon layer 25b is ensured through the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a), and the corrosive environment. This is because the corrosion resistance (anticorrosion effect) of the metal substrate 21 can be further maintained.

  In the present embodiment, all of the metal substrate 21 is covered with the conductive carbon layer 25b through the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a). In other words, in this embodiment, the ratio (coverage) of the area where the metal base material 21 is covered with the conductive carbon layer 25b is 100%. However, it is not limited only to such a form, and the coverage may be less than 100%. The coverage of the metal substrate 21 by the conductive carbon layer 25b is preferably 50% or more, more preferably 80% or more, still more preferably 90% or more, and most preferably 100%. By setting it as such a structure, the fall of electroconductivity and corrosion resistance accompanying the formation of the oxide film in the exposed part of the metal base material 21 which is not coat | covered with the conductive carbon layer 25b can be suppressed effectively. When the chromium oxycarbide layer 23 (or the conductive intermediate layer 25a) is interposed between the metal substrate 21 and the conductive carbon layer 25b as in the present embodiment, the coverage is determined by the metal separator. When 20 is viewed from the stacking direction, it means the ratio of the area of the metal substrate 21 overlapping the conductive carbon layer 25b.

  Further, the conductive carbon layer 25b shown in FIG. 1 may have a single-layer structure as described above, or may have a two-layer structure in which two layers formed by changing film formation conditions are stacked. . In this case, for example, the conductive carbon layer 25b having a two-layer structure in which the layer formed (formed) by the first HiPIMS method and the layer formed (formed) by the second HiPIMS method are stacked. Etc. can be exemplified. However, the metal separator of this embodiment is not limited to this form, and may have a conductive carbon layer (DLC layer) having a laminated structure of three or more layers. Examples of the conductive carbon layer other than the layer formed (formed) by the first HiPIMS method and the layer formed (formed) by the second HiPIMS method are, for example, the first HiPIMS. Examples thereof include a layer having the same film quality as the layer formed (formed) by the method and a layer having the same film quality as the layer formed (formed) by the second HiPIMS method. The order of the other conductive carbon layers and the number of layers are not particularly limited.

[Conductive intermediate layer 25a]
In the present embodiment, the metal separator 20 forms the conductive layer 25 on the chromium oxycarbide layer 23 (between the chromium oxycarbide layer 23 and the conductive carbon layer (DLC layer) 25b) as necessary. As a layer, you may have the electroconductive intermediate | middle layer 25a. This conductive intermediate layer 25a has a function of improving the adhesion between the chromium oxycarbide layer 23 and the conductive carbon layer 25b on the metal substrate 21, and the ion of the metal substrate 21 and the chromium oxycarbide layer 23. It is excellent in that it has a function of preventing elution. The preferred number of layers of the conductive intermediate layer 25a is 1 to 5 layers.

  The material constituting the conductive intermediate layer 25a is not particularly limited as long as it has a function of imparting adhesion and preventing ion elution. For example, Group 4 metals (Ti, Zr, Nf), Group 5 metals (V, Nb, Ta), Group 6 metals (Cr, Mo, W) in the long-period periodic table, and these Examples thereof include carbides, nitrides, carbonitrides, and the like. Among these, metals with low ion elution such as chromium (Cr), tungsten (W), titanium (Ti), molybdenum (Mo), niobium (Nb) or hafnium (Hf), or their nitrides, carbides or charcoal are preferable. Nitride is used. More preferably, Cr or Ti, or a carbide or nitride thereof is used. In particular, when Cr or Ti, or their carbides or nitrides are used, the role of the conductive intermediate layer 25a is to ensure adhesion to the upper conductive carbon layer 25b, to lower the metal base material 21 and the chromium oxy There is an anticorrosive effect of the carbide layer 23. In particular, Cr and Ti, especially Cr, are particularly useful from the viewpoint that even if an exposed portion is present due to the formation of a passive film, the elution of itself is hardly observed.

  As a method for forming the conductive intermediate layer 25a, a dry film forming method is preferable. Specific examples of such a dry film forming method include, for example, a physical vapor deposition (PVD) method such as a sputtering method and an ion plating method; a thermal CVD (Chemical Vapor Deposition) method, a plasma CVD method, a photo CVD method, and a plasma CVD method. Examples thereof include chemical vapor deposition (CVD) methods. Moreover, ion beam vapor deposition methods, such as a filtered cathodic vacuum arc (FCVA) method, are also mentioned. Examples of the sputtering method include a direct current magnetron sputtering (DCMS) method, an unbalanced magnetron sputtering method, a dual magnetron sputtering method, and an electron cyclotron resonance sputtering (ECR sputtering) method. Examples of the ion plating method include an arc ion plating method. Among these, it is preferable to use a sputtering method or an ion plating method. With such a method, film formation is possible at a relatively low temperature, and damage to the metal substrate 21 and the chromium oxycarbide layer 23 can be minimized. Further, the sputtering method has an advantage that the crystal structure of the conductive intermediate layer 25a can be controlled and the film quality can be controlled by controlling the bias voltage and the like.

  As described above, the conductive intermediate layer 25a can enhance the anticorrosion effect of the metal base material 21 and the chromium oxycarbide layer 23. Even in the case of a corrosive metal such as aluminum, the conductive intermediate layer 25a is used as the metal base material 21 of the metal separator. Applicable. In this embodiment, the magnitude (absolute value) of the negative bias voltage to be applied is not particularly limited, and a voltage capable of forming the conductive intermediate layer 25a can be adopted. As an example, the magnitude of the applied voltage is preferably 50 to 500V, more preferably 100 to 300V.

  Note that specific forms such as other conditions at the time of forming the conductive intermediate layer 25a and the conductive carbon layer 25b are not particularly limited, and conventionally known knowledge can be referred to as appropriate. Further, when the conductive carbon layer 25b is formed by the UBMS method, it is preferable to form the conductive intermediate layer 25a in advance by the same apparatus and manufacturing method, and form the conductive carbon layer 25b thereon. . As a result, the conductive intermediate layer 25a and the conductive carbon layer 25b having excellent adhesion to the base layer can be formed. However, the conductive intermediate layer 25a may be formed by other methods, and the conductive carbon layer 25b may be formed by a different apparatus or manufacturing method. Even in this case, the conductive intermediate layer 25a having excellent adhesion to the chromium oxycarbide layer 23 and the conductive carbon layer 25b can be formed.

  The number of conductive intermediate layers 25a used as necessary is not particularly limited as long as it is one or more. Further, the thickness of the conductive intermediate layer 25a used as necessary is not particularly limited. However, from the viewpoint of making the fuel cell stack as small as possible by making the metal separator 20 thinner, the thickness of the conductive intermediate layer 25a (the total thickness in the case of two or more layers) is preferably The thickness is 10 nm to 10 μm, and more preferably 15 nm to 5 μm. Further, it is more preferably 20 nm to 5 μm, and particularly preferably 100 nm to 2 μm. The thickness is most preferably 100 to 200 nm from the viewpoint of stable formation of the conductive intermediate layer and preventing the film formation time from becoming too long. If the film thickness of the conductive intermediate layer 25a is 10 nm or more, a uniform layer is formed, and the corrosion resistance of the metal substrate 21 and the chromium oxycarbide layer 23 can be effectively improved. On the other hand, if the film thickness of the conductive intermediate layer 25a is 10 μm or less, the increase in the film stress of the conductive intermediate layer 25a is suppressed, and the film follows the metal substrate 21, the chromium oxycarbide layer 23, and the conductive carbon layer 25b. Deterioration and the occurrence of peeling and cracking associated therewith can be prevented.

  The conductive layer 25 shown in FIG. 1 has a two-layer structure in which one conductive intermediate layer 25a and one conductive carbon layer 25b are stacked, but the metal separator of this embodiment is limited to this form. Alternatively, the conductive layer 25 having a laminated structure of three or more layers may be included. Examples of other conductive layers other than the conductive intermediate layer 25a and the conductive carbon layer 25b include a layer having the same film quality as the conductive intermediate layer 25a and a layer having the same film quality as the conductive carbon layer 25b. It is done. The order of the other conductive layers and the number of layers are not particularly limited.

[Chromium oxycarbide (Cr _x C _y O _z ) layer 23]
In the present embodiment, the metal separator 20 has a chromium oxycarbide layer 23 on the metal substrate 21 (between the metal substrate 21 and the conductive layer 25). The chromium oxycarbide layer 23 is excellent in that it has a function of improving the adhesion between the metal substrate 21 and the conductive layer 25 and a function of preventing elution of ions from the metal substrate 21. In the present embodiment, as described above, before the chromium oxycarbide layer 23 is formed, a passive film such as an oxide film or a hydroxide film formed on the surface of the metal substrate 21 by performing ion bombardment in advance. It is preferable to destroy.

  The resistivity of the chromium oxycarbide layer 23 is about 0.2 mΩ · cm. The thickness of the chromium oxycarbide layer 23 is not specified. The thicker the chromium oxycarbide layer is, the more the metal ions can be eluted from the metal substrate. Further, if the chromium oxycarbide layer is thick, the strength as a metal separator increases. Moreover, if it is more than predetermined thickness, since it can express effectively, without impairing the said effect, it is preferable. From such a viewpoint, the film thickness of chromium oxycarbide is preferably 0.5 nm or more, more preferably 2 nm or more, further preferably 3 nm or more, particularly preferably 5 nm or more, particularly preferably 10 nm or more, and most preferably 30 nm. 5 μm or less, preferably 2 μm or less, more preferably 1 μm or less, further preferably 500 nm or less, particularly preferably 200 nm or less, particularly preferably 100 nm or less, particularly preferably 50 nm or less, most preferably 20 nm or less. It is. The thickness is preferably in the range of 0.5 nm to 200 nm, more preferably 0.5 nm to 100 nm, still more preferably 0.5 nm to 50 nm, and still more preferably 0.5 nm to 20 nm. Used in thickness. However, the thickness is not particularly limited to the above range as long as the thickness can be effectively expressed without impairing the above-described effects.

Chromium oxycarbide (which constitutes layer 23 or is the main component) is a cubic crystal similar to a sodium chloride (NaCl) type crystal composed of two face-centered cubic sublattices composed of chromium, carbon and oxygen. is there. Here, the cubic crystal similar to the NaCl type crystal is composed of two face centered cubic sublattices like the NaCl type crystal, but one face centered cubic sublattice is not necessarily occupied by a single element. A cubic crystal. The lattice constant of chromium oxycarbide prepared by the plasma CVD method is 0.410 nm and the composition ratio (x, y, z) of Cr, C, O written as Cr _x C _y O _z is X-ray photoelectron spectroscopy (XPS). : X-ray Photoelectron Spectroscopy) (0.5, 0.25, 0.25) by composition analysis. (See Japan Journal of Applied Physics, Vol. 28, pp. 1450-1454 (1989) (referred to as non-patent document 1).). In general, the lattice constant and chemical composition vary due to differences in manufacturing method and film forming conditions. For example, three chromium oxycarbide films having a lattice constant of 0.42 nm prepared by changing the film formation conditions by reactive sputtering are disclosed. (See Journal of the American Ceramic Society, Vol. 84, pp. 1763-1766 (2001) (referred to as non-patent document 2)). The composition ratios (x, y, and z) of Cr, C, and O of these three samples are (0.368, 0.215, 0) in the composition analysis by an electron probe microanalyzer (EPMA: Electron Probe Micro-Analyzer) method. .417), (0.298, 0.045, 0.666), (0.38, 0.20, 0.421). The lattice constant created by the plasma CVD method and the reactive sputtering method is preferably not less than 0.40 nm and not more than 0.43 nm, more preferably not less than 0.41 nm and not more than 0, considering the fluctuation range due to the manufacturing method of about 0.01 nm. .42 nm or less. In addition, the chromium composition ratio x is preferably 0.298 or more and 0.50 or less in consideration of variation due to a film forming apparatus, a manufacturing method, and the like. In general, the error of quantitative analysis by surface analysis is large, which is said to be about 10% by X-ray photoelectron spectroscopy (for example, see JP-A-8-110313) and about 1% by electron beam microanalyzer method. (For example, Hirofumi Kasada “EPMA Structure and Sample Analysis by KASADA”, [online], October 2002, Tottori University Engineering Department, [searched January 29, 2014], Internet <URL: http: // /Www.eng.tottori-u.ac.jp/~www_tec/epma/epma.html>). Considering such a measurement error, the chromium composition ratio x is not less than 0.28 and not more than 0.60.

  Chromium oxycarbide is a cubic crystal similar to the NaCl type and consists of two face-centered cubic sublattices. One of the sublattices is occupied by Cr as confirmed from the X-ray diffraction data. It can be said that other sublattices are occupied by C and O (see Non-Patent Document 1 above). Therefore, in consideration of the effect of expanding the composition range due to the difference in film formation method and film formation conditions, the chromium composition ratio x in chromium oxycarbide is 0.28 or more and 0.60 or less, and the remaining carbon and oxygen remain together. It can be said that it occupies. In addition, it can be said that the range of the lattice constant is 0.40 or more and 0.43 nm or less in consideration of the difference in the film formation method. Further, if the chromium composition ratio x is less than 0.28, the electrical conductivity can be prevented from being lowered. Moreover, if the chromium composition ratio x is 0.60 or less, sufficient corrosion resistance can be maintained.

Further, regarding the carbon composition ratio y and the oxygen composition ratio z, when the chromium composition ratio x is 1, the carbon composition ratio y is 1/6 to 16/6, preferably 1/6 to 8 / 6, and the oxygen composition ratio z is preferably 1/6 to 16/6, and more preferably 1/6 to 8/6. That is, CrC _{1/6 to 16/6} O _{1/6 to 16/6} is preferable. In particular, y + z = 3/2 is more preferable. However, it is not limited to such a range.

  Chromium oxycarbide exhibits very high corrosion resistance in sulfuric acid and hydrochloric acid, and has an electric conductivity of 2 MS / m, which is equivalent to that of stainless steel (SUS304). In general, a film is obtained in the form of a layer (film) by incomplete decomposition of hexacarbonylchromium or by synthesis in a plasma atmosphere using metallic chromium and hydrocarbons such as carbon dioxide and methane as raw materials. be able to. The former incomplete decomposition of hexacarbonylchromium is performed by a thermal CVD (Chemical Vapor Deposition) method, a plasma CVD method, or a photo CVD method, and a plasma CVD method is generally used. The latter plasma synthesis is performed by a reactive sputtering method or a reactive ion plating method.

  The size of the crystallites of chromium oxycarbide varies depending on the film forming method and the film forming conditions. It is known from X-ray diffraction that the size of crystallites is 8 nm or more and 80 nm or less in a chromium oxycarbide film produced by incomplete decomposition of hexacarbonyl chromium under various film formation conditions by plasma CVD. (See Non-Patent Document 1 above.) There is a correlation between the size of the crystallite and the film hardness, that is, the residual stress inside the film, and the larger the crystallite, the higher the hardness. When the crystallite size is 80 nm, the m hardness is about 20 GPa in terms of Vickers hardness. Therefore, if the size of the crystallite is 80 nm or less, the residual stress does not increase, and adhesion reduction and peeling can be effectively prevented, which is preferable for coating. On the other hand, if the crystallite is 8 nm or more, an amorphous part is not included, which is preferable in that the excellent properties of the original chromium oxycarbide can be exhibited. Therefore, the size of the crystallite is considered to be 5 nm to 100 nm, which is wider than 8 nm to 80 nm in consideration of the difference in film forming method and film forming conditions, but more preferably 10 nm to 80 nm. More preferably, it is 20 nm or more and 60 nm or less.

  As a method for forming the chromium oxycarbide layer 23, it is preferable to use the dry film forming method as described above. Specific examples of the dry film forming method include, for example, physical vapor deposition (PVD) method such as (reactive) sputtering method and (reactive) ion plating method; thermal CVD (chemical vapor deposition) method, plasma CVD. And chemical vapor deposition (CVD) methods such as a photo CVD method and a plasma CVD method. Moreover, ion beam vapor deposition methods, such as a filtered cathodic vacuum arc (FCVA) method, are also mentioned. Examples of the sputtering method include a direct current magnetron sputtering (DCMS) method, an unbalanced magnetron sputtering method, a dual magnetron sputtering method, and an electron cyclotron resonance sputtering (ECR sputtering) method. Examples of the ion plating method include an arc ion plating method. Among these, it is preferable to use a sputtering method or an ion plating method. With such a method, film formation is possible at a relatively low temperature, and damage to the metal substrate 21 can be minimized. Furthermore, according to the sputtering method or the ion plating method, there is an advantage that the composition and crystal structure of the chromium oxycarbide layer 23 and the film quality can be controlled by controlling the bias voltage and the like.

  A sputtering method or an ion plating method suitable as a method for forming the chromium oxycarbide layer 23 is not particularly limited. For example, the formation method described in JP-A-2006-044321 can be appropriately used. it can. That is, the above publication forms (deposits) a chromium oxycarbide layer using an ion plating apparatus (see FIG. 2 of the above publication; reference numerals in the text are omitted). Such an ion plating apparatus includes a furnace for performing a coating treatment inside, a focusing coil provided outside the furnace, a plasma gun for generating a plasma state in the furnace, and a coating material (evaporation source). A crucible for installation and a base material holding part for holding a metal base material that coats the raw material for film that has become plasma are provided. The furnace is provided with an exhaust port connected to an exhaust pump, a reaction gas introduction port, and the like in order to maintain the inside at a predetermined degree of vacuum.

  As a method for forming the chromium oxycarbide layer 23 using the above-described apparatus, first, a solid base material serving as a metal base material and an evaporation source is placed on a base material holding part and a crucible, respectively. And after adjusting the inside of the furnace to an appropriate degree of vacuum (for example, 0.04 to 0.08 Pa) using an exhaust pump, argon gas is introduced into the solid chromium installed in the crucible using a plasma gun. A chromium oxycarbide layer is coated and formed on the surface of the metal substrate by reacting with carbon dioxide, which is a reaction gas introduced into the furnace from the reaction gas inlet, while generating a plasma state by applying a high voltage. (Film formation). According to the present embodiment, by forming the chromium oxycarbide layer by a sputtering method or an ion plating method, excellent adhesion can be obtained, and corrosion resistance and wear resistance can be further improved. Furthermore, it can be continuously laminated easily in a short time by a sputtering method or an ion plating method.

  In addition, as a method for forming the chromium oxycarbide layer 23, a formation method (discharge plasma CVD method) described in JP 2012-146616 A may be used. In the forming method (discharge plasma CVD method) described in the above publication, a metal substrate is placed in a plasma processing container. Next, a first step of heating the metal substrate to 100 ° C. to 450 ° C. in a non-oxidizing gas atmosphere, a second step of plasma treating the surface of the metal substrate, and a chromium oxycarbide layer on the metal substrate surface by discharge plasma CVD It can form into a film by the 3rd process of forming. It has a feature that can be implemented by switching the source gas from the first step to the third step in the same plasma processing apparatus.

  Using a plasma processing apparatus (see FIG. 1 of the above publication), a plurality of metal substrates are arranged substantially in parallel and at equal intervals, and odd-numbered metal substrates are electrically connected to form a first substrate electrode. A metal substrate is electrically connected to form a second substrate electrode, and the first substrate electrode and the second substrate electrode are used as a pair of substrate electrodes to generate a discharge plasma by supplying high frequency power from a high frequency power source through a capacitor. In addition, a negative bias voltage is alternately supplied from the bias power source to both substrate electrodes via a low-pass filter, and the second to third steps are performed.

  In the first step, the metal substrate is heated to a predetermined temperature by heating means installed in the plasma processing apparatus in a high vacuum in which the plasma processing chamber is evacuated or in a non-oxidizing gas atmosphere such as argon gas or nitrogen gas. To do. In this step, the gas is sufficiently discharged by heating to 100 ° C. or higher while suppressing the oxidation reaction on the surface of the metal substrate.

  In the second step, an inert gas, for example, non-oxidizing gas such as argon gas or a mixed gas of argon gas and hydrogen is introduced into the plasma processing vessel, and high frequency power is supplied to a pair of substrate electrodes to generate discharge plasma. At the same time, a negative bias voltage is applied to irradiate both surfaces of the metal substrate with ions to remove the oxide film and deposits on the substrate surface. For example, a high frequency power source having a frequency of 13.56 MHz and an output of 300 W to 3 kW can be used. In addition, it is necessary to alternately apply a negative pulsating voltage or / and a negative pulse voltage having a peak value of 300 V to 5 kV to the pair of substrate electrodes as a bias voltage. For this purpose, the output voltage of the AC voltage generator is fed to the primary side of the transformer, the output voltage on the secondary side is rectified in both waves by a diode to generate a negative pulsating voltage, and the pair of voltages is passed through a low-pass filter. The pulsating voltage can be alternately supplied to the substrate electrodes. The frequency of the AC voltage is not specified, but 50 Hz to 200 kHz is preferable. Furthermore, it is preferably 1 kHz to 100 kHz.

  In the third step, a metal substrate installed in the plasma processing vessel is heated to 250 ° C. to 450 ° C., chromium hexacarbonyl gas is introduced as a source gas, and high frequency power is supplied to a pair of substrate electrodes that are metal substrates. A discharge plasma is generated to form a chromium oxycarbide layer 23 on the surface of the metal substrate. At this time, the metal substrate may be held at a temperature of 250 ° C. to 450 ° C., and the bias voltage of −200 V to −500 V may be applied.

  In addition, as a method for forming the chromium oxycarbide layer 23, a formation method (CVD method) described in JP-A-2006-278040 can also be used. In the formation method of the above publication, a metal separator can be produced by forming a layer (coating) containing chromium oxycarbide or chromium oxycarbide as a main component on a metal substrate by chemical vapor deposition as a hexacarbonylchromium raw material. it can. Alternatively, a metal separator can be produced by forming chromium oxycarbide or a layer (coating) mainly composed of chromium oxycarbide on a metal plate by reactive plasma treatment using chromium and carbon-containing gas as raw materials. The chromium oxycarbide layer 23 of the present embodiment includes a layer mainly composed of chromium oxycarbide or chromium oxycarbide obtained by the above forming method.

  The chemical vapor deposition method refers to thermal CVD, plasma CVD, or laser CVD using hexacarbonyl chromium as a raw material. The reactive plasma treatment refers to reactive sputtering, reactive ion plating, and reactive laser deposition using chromium and carbon dioxide as raw materials. In this case, carbon monoxide may be used as a raw material instead of carbon dioxide, and oxygen, hydrocarbons, or a rare gas may be used as an auxiliary gas.

  As the above-mentioned chromium oxycarbide or a layer (coating) containing chromium oxycarbide as a main component, chromium oxycarbide is the most excellent, but molybdenum oxycarbide or tungsten oxycarbide is contained in the layer (coating) made of chromium oxycarbide. Carbide may be contained in a range of 90% by mass or less.

  That is, in the layer (coating) containing chromium oxycarbide as a main component, it is necessary to contain at least 10% by mass of chromium oxycarbide. The above description that the main component is chromium oxycarbide is used in the sense that it always contains chromium oxycarbide, and does not mean that 50% by mass or more is contained.

  Thus, when molybdenum oxycarbide or tungsten oxycarbide is added, there are effects that the adhesion strength to the metal substrate can be improved and the hardness and corrosion resistance of the layer (coating film) can be controlled depending on the application.

  According to the various methods (formation methods) described above, the chromium oxycarbide layer 23 and further the conductive layer 25 (arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) are formed on both surfaces of the metal substrate 21. The manufactured metal separator 20 can be manufactured. In order to manufacture the metal separator 20 in which the chromium oxycarbide layer 23 and further the conductive layer 25 (arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) are formed on both surfaces of the metal substrate 21, a commercially available product is used. An appropriate film forming apparatus (double-sided simultaneous sputtering film forming apparatus and sputter film forming method using the same) may be used. Alternatively, a sputtering apparatus capable of forming a chromium oxycarbide layer 23 and further a conductive layer 25 (an arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) on both surfaces of the metal substrate 21 is manufactured separately. There is no particular limitation such as film formation. Moreover, although it cannot be said that it is advantageous in terms of cost, the chromium oxycarbide layer 23 and further the conductive layer 25 (an arbitrary conductive intermediate layer 25a and conductive carbon layer 25b are formed on one main surface of the metal substrate 21. ). Next, a chromium oxycarbide layer 23 and further a conductive layer 25 (an arbitrary conductive intermediate layer 25a and a conductive carbon layer 25b) are formed on the other main surface of the metal substrate 21 by the same method as described above. May be formed sequentially. Alternatively, first, a chromium oxycarbide layer 23 and an optional conductive intermediate layer 25a (the source gas is switched) are formed on one main surface of the metal substrate 21 in an apparatus targeting a metal material such as chromium. Film. Subsequently, the chromium oxycarbide layer 23 formed on the main surface different from the main surface facing the chromium oxycarbide layer 23 and the conductive intermediate layer 25a formed by the above-described process, and an optional conductive intermediate layer 25a (raw material gas). Is switched). Subsequently, the target is switched to carbon, and the conductive carbon layer 25b is formed on the chromium oxycarbide layer 23 or the conductive intermediate layer 25a formed on one main surface of the metal substrate 21 in the same apparatus. . Subsequently, the step of forming the conductive carbon layer 25b on the main surface different from the main surface facing the main surface different from the main surface facing the conductive carbon layer 25b formed by the above-described step can be performed. That's fine. As described above, the chromium oxycarbide layer 23 on the both surfaces of the metal substrate 21 and the formation of an arbitrary conductive intermediate layer 25a, and the conductive carbon on the surface of the chromium oxycarbide layer 23 or the conductive intermediate layer 25a. As a method of forming the layer 25b, the chromium oxycarbide layer 23 on the one surface of the metal substrate 21 and further the conductive layer 25 (the optional conductive intermediate layer 25a and conductive carbon layer 25b) are formed. There is no particular limitation such that the same method as described above (however, the man-hour can be halved) can be adopted.

  In the present embodiment, the metal separator 20 in which the chromium oxycarbide layer 23 and further the conductive layer 25 (arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) are formed on both surfaces of the metal base 21 are used as the fuel cell. It is preferable to use for. However, the metal separators at both ends of the fuel cell stack may have a structure in which the chromium oxycarbide layer 23 and further the conductive layer 25 are formed only on one side. This is because the outer surfaces (one side) of the metal separators at both ends of the fuel cell stack are not exposed to a corrosive environment because the plates and the like are in contact with each other. This is because the carbide layer 23 and the conductive layer 25 may not be provided. However, from the standpoint of reducing the number of parts and preventing the confusion with the parts, the fuel cell stack is provided with a common metal separator (a metal separator having a chromium oxycarbide layer 23 and further a conductive layer 25 formed on both sides). It may be used.

[Metal base material 21]
In the metal separator 20 of this embodiment, the material which comprises the metal base material 21 is not restrict | limited in particular, The metal etc. which were conventionally used as a constituent material of a metal separator are employ | adopted suitably. Specific examples include iron, titanium, and aluminum, and alloys thereof. These materials can be preferably used from the viewpoint of mechanical strength, versatility, cost performance, or processability. Here, the iron alloy includes stainless steel. Especially, it is preferable that the metal base material 21 is comprised from stainless steel (SUS), aluminum, or an aluminum alloy. In particular, when stainless steel (SUS) is used as the metal substrate 21, when the metal separator 20 is applied to a fuel cell, the conductivity of the contact surface with the gas diffusion substrate that is a constituent material of the gas diffusion layer (GDL). Can be secured sufficiently.

  Examples of the stainless steel include austenite, martensite, ferrite, austenite / ferrite, and precipitation hardening. Examples of austenite include SUS201, SUS202, SUS301, SUS302, SUS303, SUS304, SUS305, SUS316 (L), and SUS317. Examples of the austenite-ferrite type include SUS329J1. Examples of the martensite system include SUS403 and SUS420. Examples of the ferrite type include SUS405, SUS430, and SUS430LX. Examples of the precipitation hardening system include SUS630. Among these, it is more preferable to use austenitic stainless steel such as SUS304 and SUS316. Moreover, the content rate of iron (Fe) in stainless steel becomes like this. Preferably it is 60-84 mass%, More preferably, it is 65-72 mass%. Further, the content of chromium (Cr) in the stainless steel is preferably 16 to 20% by mass, and more preferably 16 to 18% by mass.

  On the other hand, examples of the aluminum alloy include pure aluminum, aluminum / manganese, and aluminum / magnesium. The elements other than aluminum in the aluminum alloy are not particularly limited as long as they are generally usable as an aluminum alloy. For example, copper, manganese, silicon, magnesium, zinc and nickel can be included in the aluminum alloy. Specific examples of the aluminum alloy include A1050P as the pure aluminum system, A3003P and A3004P as the aluminum / manganese system, and A5052P and A5083P as the aluminum / magnesium system. When the surface-treated member is applied to a separator, mechanical strength and formability are also required. Therefore, in addition to the above alloy types, the tempering of the alloy can be appropriately selected. In addition, when the base material 21 is comprised from the simple substance of titanium or aluminum, the purity of the said titanium or aluminum becomes like this. Preferably it is 95 mass% or more, More preferably, it is 97 mass% or more, More preferably, it is 99 mass% That's it.

  The thickness of the metal substrate 21 is not particularly limited. From the viewpoint of ease of processing, mechanical strength, and improvement of battery energy density when the metal separator 20 is applied to a fuel cell, it is preferably 50 to 500 μm, more preferably 80 to 300 μm, and still more preferably Is 80-200 μm. In particular, the thickness of the metal substrate 21 when stainless steel (SUS) is used as the constituent material is preferably 80 to 150 μm. On the other hand, the thickness of the metal base material 21 when aluminum is used as a constituent material is preferably 100 to 300 μm. In the case of the above-mentioned range, it is excellent in processability and has a suitable thickness while having a sufficient strength.

  When using the metal base material 21, it is preferable to degrease and clean the surface of the material. Specifically, these materials having a desired thickness are prepared, and the surface of the material is degreased and cleaned using an appropriate solvent (for example, ethanol, ether, acetone, isopropyl alcohol, trichlorethylene, and caustic agent). Process. Examples of the cleaning treatment include ultrasonic cleaning. The ultrasonic cleaning conditions are a processing time of about 1 to 10 minutes, a frequency of about 30 to 50 kHz, and a power of about 30 to 50 W. Subsequently, it is preferable to remove the oxide film formed on the surface (both sides) of the constituent material of the metal substrate 21. Examples of the method for removing the oxide film include an acid cleaning treatment, a dissolution treatment by applying a potential, or the above-described ion bombardment treatment.

[Production method of metal separator]
Examples of the method for producing the metal separator include a method in which a chromium oxycarbide layer 23 and a conductive layer 25 (any conductive intermediate layer 25a and conductive carbon layer 25b) are sequentially formed on the surface of the metal substrate 21. . Since the method for forming each layer is as described above, detailed description thereof is omitted here.

  According to the above-described method, a metal separator in which the chromium oxycarbide layer 23 and the conductive layer 25 (arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) are formed on both surfaces of the metal base 21 can be manufactured. . Although not advantageous in terms of cost, a chromium oxycarbide layer 23 and a conductive layer 25 (arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) are formed on one main surface of the metal substrate 21. Film. Next, the chromium oxycarbide layer 23 and the conductive layer 25 (the arbitrary conductive intermediate layer 25a and the conductive carbon layer 25b) are sequentially formed on the other main surface of the metal base 21 by the same method. Good.

  Further, in the present embodiment, the chromium oxycarbide layer 23 and the conductive layer 25 (arbitrary conductive intermediate layer 25a and conductive carbon layer 25b) may exist only on one main surface of the metal substrate 21. . Preferably, as shown in FIG. 1 and the like, the chromium oxycarbide layer 23 and the conductive layer 25 (an optional conductive intermediate layer) are also formed on the other main surface of the metal substrate 21 (that is, on both surfaces of the metal substrate 21). 25a and conductive carbon layer 25b) are preferably present. This ensures adhesion between the metal substrate 21 and the conductive layer 25 (arbitrary conductive intermediate layer 25a, conductive carbon layer 25b) via the chromium oxycarbide layer 23 on both surfaces of the metal separator 20. However, the corrosion resistance and low contact resistance of the metal substrate 21 can be further maintained.

[Polymer fuel cell]
The metal separator described above has low contact resistance in the laminating direction and has a characteristic that it is not easily corroded even under a condition where a potential is applied (especially a corrosive environment). It is suitably used as a metal separator for a fuel cell. That is, according to another embodiment, there is provided a metal separator for a fuel cell, particularly a polymer electrolyte fuel cell, comprising the metal separator. According to yet another embodiment, there is provided a polymer electrolyte fuel cell having a membrane electrode assembly and a pair of anode separator and cathode separator that sandwich the membrane electrode assembly. Here, the fuel cell separator is applied to at least one of the anode separator and the cathode separator. The membrane electrode assembly includes a polymer electrolyte membrane, a pair of anode catalyst layers and a cathode catalyst layer sandwiching the polymer electrolyte membrane, and a pair of anode gas diffusion layers and a cathode gas diffusion layer sandwiching them. Further, the fuel cell separator is formed in a concavo-convex shape, the convex portion comes into contact with the membrane electrode assembly, and the concave portion serves as a gas flow path for circulating fuel gas or oxidant gas. In the fuel cell separator and the polymer electrolyte fuel cell according to the present embodiment, by using the above-described metal separator as a separator material, corrosion hardly occurs even with an electric potential during operation, and contact resistance can be kept low. Therefore, it is possible to exhibit excellent battery performance over a long period of time.

  FIG. 6 is a cross-sectional view schematically showing a basic configuration of a polymer electrolyte fuel cell (PEFC) 1 according to an embodiment. The PEFC 1 first includes a solid polymer electrolyte membrane 2 and a pair of catalyst layers (an anode catalyst layer 3a and a cathode catalyst layer 3c) that sandwich the membrane. The laminate of the solid polymer electrolyte membrane 2 and the catalyst layers (3a, 3c) is further sandwiched between a pair of gas diffusion layers (GDL) (the anode gas diffusion layer 4a and the cathode gas diffusion layer 4c). Thus, the polymer electrolyte membrane 2, the pair of catalyst layers (3a, 3c), and the pair of gas diffusion layers (4a, 4c) constitute an electrolyte membrane-electrode assembly (MEA) 10 in a stacked state. To do.

  In PEFC1, the MEA 10 is further sandwiched between a pair of separators (anode separator 5a and cathode separator 5c). In FIG. 6, the separators (5a, 5c) are illustrated so as to be located at both ends of the illustrated MEA. However, in a fuel cell stack in which a plurality of MEAs are stacked, the separator is generally used as a separator for an adjacent PEFC (not shown). In other words, in the fuel cell stack, the MEAs are sequentially stacked via the separator to form a stack. In an actual fuel cell stack, a gas seal portion is disposed between the separator (5a, 5c) and the solid polymer electrolyte membrane 2, or between the PEFC 1 and another adjacent PEFC. These descriptions are omitted in FIG.

  The separators (5a, 5c) are obtained by molding the above metal separator into a concavo-convex shape as shown in FIG. Alternatively, after pressing the metal substrate to form a concavo-convex shape, a chromium oxycarbide layer 23 and a conductive layer 25 (an arbitrary conductive intermediate layer 25a, conductive carbon layer 25b are formed on both surfaces of the metal substrate. ) To form metal separators (5a, 5c). In the former case, the adhesion between the layers of the metal substrate 21, the chromium oxycarbide layer 23, and the conductive layer 25 (arbitrary conductive intermediate layer 25a, conductive carbon layer 25b) is high, and even if press treatment is performed. It can be formed into a concavo-convex shape without affecting the chromium oxycarbide layer 23 and the conductive layer 25 (arbitrary conductive intermediate layer 25a, conductive carbon layer 25b). Further, in the latter case, the chrome oxycarbide layer 23 and the conductive layer 25 (arbitrary conductivity) are uniformly (homogeneously) uniform on both surfaces (particularly, any surface of the concavo-convex shape) of the concavo-convex shape metal substrate. The conductive intermediate layer 25a and the conductive carbon layer 25b) can be formed and formed.

  The convex part seen from the MEA side of the separator 5 (5a, 5c) is in contact with the MEA 10. Thereby, the electrical connection with MEA10 is ensured. Further, a recess (space between the separator and the MEA generated due to the concavo-convex shape of the separator) viewed from the MEA side of the separator (5a, 5c) is a gas for circulating gas during operation of the PEFC 1 Functions as a flow path. Specifically, a fuel gas (for example, hydrogen) is circulated through the gas flow path 6a of the anode separator 5a, and an oxidant gas (for example, air) is circulated through the gas flow path 6c of the cathode separator 5c.

  On the other hand, the recess viewed from the side opposite to the MEA side of the separator (5a, 5c) serves as a refrigerant flow path 7 for circulating a refrigerant (for example, water) for cooling the PEFC 1 during operation of the PEFC 1. . Further, the separator is usually provided with a manifold (not shown). This manifold functions as a connection means for connecting cells when a stack is formed. With such a configuration, the mechanical strength of the fuel cell stack can be ensured.

  When the above-described metal separator is used as a separator for a fuel cell (particularly for a polymer electrolyte fuel cell) as shown in FIG. 6, the conductive layer 25, particularly the conductive carbon layer 25b is in contact with the gas diffusion layer. It is preferable that they are arranged.

  In addition, in embodiment shown in FIG. 6, the separator (5a, 5c) is shape | molded by the uneven | corrugated shape. However, the separator is not limited to such a concavo-convex shape, and may be any form such as a flat plate shape and a partially concavo-convex shape as long as the functions of the gas flow path and the refrigerant flow path 7 can be exhibited. May be. Hereinafter, each member constituting the solid polymer fuel cell will be described.

<Electrolyte layer>
The electrolyte membrane is composed of a solid polymer electrolyte membrane 2. The solid polymer electrolyte membrane 2 has a function of selectively permeating protons generated in the anode catalyst layer 3a during operation of the PEFC 1 to the cathode catalyst layer 3c along the film thickness direction. The solid polymer electrolyte membrane 2 also has a function as a partition wall for preventing the fuel gas supplied to the anode side and the oxidant gas supplied to the cathode side from being mixed.

  The solid polymer electrolyte membrane 2 is roughly classified into a fluorine-based polymer electrolyte membrane and a hydrocarbon-based polymer electrolyte membrane depending on the type of ion exchange resin that is a constituent material. Examples of ion exchange resins constituting the fluorine-based polymer electrolyte membrane include Nafion (registered trademark, manufactured by DuPont), Aciplex (registered trademark, manufactured by Asahi Kasei Co., Ltd.), Flemion (registered trademark, manufactured by Asahi Glass Co., Ltd.), and the like. Perfluorocarbon sulfonic acid polymer, perfluorocarbon phosphonic acid polymer, trifluorostyrene sulfonic acid polymer, ethylene tetrafluoroethylene-g-styrene sulfonic acid polymer, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride- Examples include perfluorocarbon sulfonic acid polymers. From the viewpoint of improving power generation performance such as heat resistance and chemical stability, these fluorine-based polymer electrolyte membranes are preferably used, and particularly preferably fluorine-based polymer electrolytes composed of perfluorocarbon sulfonic acid polymers. A membrane is used.

  Specific examples of the hydrocarbon electrolyte include sulfonated polyethersulfone (S-PES), sulfonated polyaryletherketone, sulfonated polybenzimidazole alkyl, phosphonated polybenzimidazole alkyl, sulfonated polystyrene, and sulfonated poly. Examples include ether ether ketone (S-PEEK) and sulfonated polyphenylene (S-PPP). These hydrocarbon polymer electrolyte membranes are preferably used from the viewpoint of production such that the raw material is inexpensive, the production process is simple, and the material selectivity is high. In addition, as for the ion exchange resin mentioned above, only 1 type may be used independently and 2 or more types may be used together. Moreover, it is not restricted only to the material mentioned above, Other materials may be used.

  The thickness of the electrolyte layer may be appropriately determined in consideration of the characteristics of the obtained fuel cell, and is not particularly limited. The thickness of the electrolyte layer is usually about 5 to 300 μm. When the thickness of the electrolyte layer is within such a range, the balance between the strength during film formation, durability during use, and output characteristics during use can be appropriately controlled.

<Catalyst layer>
The catalyst layers (the anode catalyst layer 3a and the cathode catalyst layer 3c) are layers in which the cell reaction actually proceeds. Specifically, the oxidation reaction of hydrogen proceeds in the anode catalyst layer 3a, and the reduction reaction of oxygen proceeds in the cathode catalyst layer 3c.

  The catalyst layer includes a catalyst component, a conductive catalyst carrier that supports the catalyst component, and an electrolyte. Hereinafter, a composite in which a catalyst component is supported on a catalyst carrier is also referred to as an “electrode catalyst”.

  The catalyst component used in the anode catalyst layer 3a is not particularly limited as long as it has a catalytic action in the hydrogen oxidation reaction, and a known catalyst can be used in the same manner. The catalyst component used for the cathode catalyst layer 3c is not particularly limited as long as it has a catalytic action for the oxygen reduction reaction, and a known catalyst can be used in the same manner. Specifically, it may be selected from metals such as platinum, ruthenium, iridium, rhodium, palladium, osmium, tungsten, lead, iron, chromium, cobalt, nickel, manganese, vanadium, molybdenum, gallium, aluminum, and alloys thereof. .

  Among these, those containing at least platinum are preferably used in order to improve catalyst activity, poisoning resistance to carbon monoxide and the like, heat resistance, and the like. Although the composition of the alloy depends on the type of metal to be alloyed, the content of platinum is preferably 30 to 90 atomic%, and the content of the metal to be alloyed with platinum is preferably 10 to 70 atomic%. In general, an alloy is a generic term for a metal element having one or more metal elements or non-metal elements added and having metallic properties. The alloy structure consists of a eutectic alloy, which is a mixture of the component elements as separate crystals, a component element completely melted into a solid solution, and a component element composed of an intermetallic compound or a compound of a metal and a nonmetal. There is what is formed, and any may be used in the present application. At this time, the catalyst component used for the anode catalyst layer 3a and the catalyst component used for the cathode catalyst layer 3c can be appropriately selected from the above. In the present specification, unless otherwise specified, descriptions of the catalyst components for the anode catalyst layer and the cathode catalyst layer have the same definition for both. Therefore, they are collectively referred to as “catalyst components”. However, the catalyst components of the anode catalyst layer 3a and the cathode catalyst layer 3c do not have to be the same, and can be appropriately selected so as to exhibit the desired action as described above.

  The shape and size of the catalyst component are not particularly limited, and the same shape and size as known catalyst components can be adopted. However, the shape of the catalyst component is preferably granular. At this time, the average particle diameter of the catalyst particles is preferably 1 to 30 nm. When the average particle diameter of the catalyst particles is within such a range, the balance between the catalyst utilization rate related to the effective electrode area where the electrochemical reaction proceeds and the ease of loading can be appropriately controlled. The “average particle diameter of the catalyst particles” in the present specification is the crystallite diameter determined from the half-value width of the diffraction peak of the catalyst component in X-ray diffraction or the particle diameter of the catalyst component determined from a transmission electron microscope image. It can be measured as an average value.

  The catalyst carrier functions as a carrier for supporting the above-described catalyst component and an electron conduction path involved in the transfer of electrons between the catalyst component and another member.

  Any catalyst carrier may be used as long as it has a specific surface area for supporting the catalyst component in a desired dispersion state and sufficient electron conductivity, and the main component is preferably carbon. Specific examples include carbon particles made of carbon black, activated carbon, coke, natural graphite, artificial graphite and the like. “The main component is carbon” means that the main component contains carbon atoms, and is a concept that includes both carbon atoms and substantially carbon atoms. In some cases, elements other than carbon atoms may be included in order to improve the characteristics of the fuel cell. Note that “substantially consisting of carbon atoms” means that contamination of about 2 to 3 mass% or less of impurities can be allowed.

The BET specific surface area of the catalyst carrier may be a specific surface area sufficient to carry the catalyst component in a highly dispersed state, but is preferably 20 to 1600 m ² / g, more preferably 80 to 1200 m ² / g. When the specific surface area of the catalyst carrier is in such a range, the balance between the dispersibility of the catalyst component on the catalyst carrier and the effective utilization rate of the catalyst component can be appropriately controlled.

  The size of the catalyst carrier is not particularly limited, but from the viewpoints of easy loading, catalyst utilization, and catalyst layer thickness control within an appropriate range, the average particle size is preferably about 5 to 200 nm, more preferably. Is preferably about 10 to 100 nm.

  In the electrode catalyst in which the catalyst component is supported on the catalyst carrier, the supported amount of the catalyst component is preferably 10 to 80% by mass, more preferably 30 to 70% by mass with respect to the total amount of the electrode catalyst. When the supported amount of the catalyst component is within such a range, the balance between the degree of dispersion of the catalyst component on the catalyst support and the catalyst performance can be appropriately controlled. The amount of the catalyst component supported on the electrode catalyst can be measured by inductively coupled plasma emission spectroscopy (ICP).

  The catalyst layer includes an ion conductive polymer electrolyte in addition to the electrode catalyst. The polymer electrolyte is not particularly limited, and conventionally known knowledge can be referred to as appropriate. For example, the above-described ion exchange resin constituting the electrolyte layer 2 can be added to the catalyst layer as a polymer electrolyte.

<Gas diffusion layer (GDL)>
The gas diffusion layer has a function of accelerating diffusion of gas (fuel gas or oxidant gas) supplied through the gas flow path of the separator to the catalyst layer and a function as an electron conduction path.

  The material which comprises the base material of a gas diffusion layer (Anode gas diffusion layer 4a, cathode gas diffusion layer 4c) is not specifically limited, A conventionally well-known knowledge can be referred suitably. For example, a sheet-like material having conductivity and porosity such as a carbon woven fabric, a paper-like paper body, a felt, and a non-woven fabric can be used. Although the thickness of the base material of a gas diffusion layer should just be determined suitably in consideration of the characteristic of the gas diffusion layer obtained, what is necessary is just to be about 30-500 micrometers. If the thickness of the base material of the gas diffusion layer is within such a range, the balance between mechanical strength and diffusibility such as gas and water can be appropriately controlled.

  The gas diffusion layer preferably contains a water repellent for the purpose of further improving water repellency and preventing a flooding phenomenon or the like. Although it does not specifically limit as a water repellent, Fluorine-type high things, such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyhexafluoropropylene, and tetrafluoroethylene-hexafluoropropylene copolymer (FEP), are included. Examples thereof include molecular materials, polypropylene, and polyethylene.

  In order to further improve the water repellency, the gas diffusion layer has a carbon particle layer (microporous layer; MLP, not shown) made of an aggregate of carbon particles containing a water repellent agent on the catalyst layer side of the substrate. You may have.

  The carbon particles contained in the carbon particle layer are not particularly limited, and conventionally known materials such as carbon black, graphite, and expanded graphite can be appropriately employed. Among them, carbon black such as oil furnace black, channel black, lamp black, thermal black, acetylene black and the like can be preferably used because of excellent electron conductivity and a large specific surface area. The average particle diameter of the carbon particles is preferably about 10 to 100 nm. Thereby, while being able to obtain the high drainage property by capillary force, it becomes possible to improve contact property with a catalyst layer.

  Examples of the water repellent used in the carbon particle layer include the same water repellent as described above. Among these, fluorine-based polymer materials can be preferably used because of excellent water repellency, corrosion resistance during electrode reaction, and the like.

  The mixing ratio of the carbon particles to the water repellent in the carbon particle layer is about 90:10 to 40:60 (carbon particles: water repellent) in terms of mass ratio in consideration of the balance between water repellency and electron conductivity. It is good. The thickness of the carbon particle layer is not particularly limited and may be appropriately determined in consideration of the water repellency of the obtained gas diffusion layer, but is preferably 10 to 1000 μm, more preferably 50 to 500 μm. Good.

<Separator>
The separators (anode separator 5a and cathode separator 5c) have a function of electrically connecting each cell in series when a plurality of single polymer electrolyte fuel cells are connected in series to form a fuel cell stack. Have. The separator also functions as a partition that separates the fuel gas, the oxidant gas, and the coolant from each other. In order to secure these flow paths, as described above, each of the metal separators is preferably provided with a gas flow path and a cooling flow path.

  The separator of this embodiment is composed of the metal separator 20 described above. The thickness and size of the metal separator and the shape and size of each flow path provided are not particularly limited, and can be appropriately determined in consideration of the desired output characteristics of the obtained fuel cell.

  The method for producing the solid polymer fuel cell of this embodiment is not particularly limited, and can be produced by appropriately referring to conventionally known knowledge in this technical field.

  The fuel used when operating the polymer electrolyte fuel cell is not particularly limited. For example, hydrogen, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, secondary butanol, tertiary butanol, dimethyl ether, diethyl ether, ethylene glycol, diethylene glycol and the like can be used. Of these, hydrogen and methanol are preferably used in that high output is possible.

  In addition, since the metal separator for fuel cells of this embodiment has excellent corrosion resistance and conductivity, it can be applied to fuel cells other than the above-described polymer electrolyte fuel cells. Examples of other types of fuel cells include phosphoric acid fuel cells (PAFC), molten carbonate fuel cells (MCFC), solid electrolyte fuel cells (SOFC), and alkaline fuel cells (AFC). Among them, a polymer electrolyte fuel cell (PEFC) is preferable because it is small and can achieve high density and high output. The fuel cell is useful as a stationary power source in addition to a power source for a moving body such as a vehicle in which a mounting space is limited. Among them, it is particularly preferable to use as a power source for a mobile body such as an automobile that requires a high output voltage after a relatively long time of operation stop.

  Hereinafter, although the metal separator for fuel cells of this embodiment is demonstrated concretely further through an Example, this embodiment is not limited to the following Examples.

Example 1
A metal plate (test piece) made of SUS304BA and having a thickness of 0.1 mm was used as a metal substrate. This metal plate was subjected to ultrasonic cleaning in ethanol solution for 3 minutes as a pretreatment. After that, a metal plate was installed in the vacuum chamber, and ion bombardment treatment with argon gas was performed (argon plasma was generated and a bias voltage of 300 to 450 V was applied to the substrate to strike the substrate) to remove the oxide film on the surface. . Both the pretreatment and the ion bombardment treatment were performed on both surfaces of the metal plate.

  Next, the metal plate (metal substrate) after the ion bombarding treatment is obtained by an ion plating apparatus (FIG. 2 of the above publication) by an ion plating method (the apparatus and forming method described in JP-A-2006-044321 described above). Was used to form a chromium oxycarbide layer having a thickness of 5 μm. That is, first, the metal base material and solid chromium serving as an evaporation source were placed on the base material holding part and the crucible, respectively. Then, after adjusting the inside of the furnace to an appropriate degree of vacuum (0.04 to 0.08 Pa) using an exhaust pump, the solid chromium placed in the crucible is introduced into the argon gas using a plasma gun to increase the pressure. A chromium oxycarbide layer is coated and formed on the surface of a metal substrate by reacting with carbon dioxide, which is a reactive gas introduced into the furnace from the reactive gas inlet, while generating a plasma state by applying a voltage ( Film formation). The film forming conditions are as follows: plasma current 180A, bias voltage −150 V, vacuum degree 0.04 to 0.08 Pa, introduced argon gas flow rate about 20 sccm, introduced carbon dioxide flow rate about 100 sccm, furnace The inner temperature was about 400 ° C., and the film formation (coating) time was set to the above film thickness (approximately 60 minutes). The chromium oxycarbide layer was also formed on both sides of the metal plate (metal substrate).

  Next, a solid graphite is used as a target while applying a (negative) bias voltage to the metal substrate by an unbalanced magnetron sputtering (UBMS) method on the chromium oxycarbide layer. A diamond-like carbon layer (DLC layer) having a film thickness of 0.05 μm (50 nm) was formed on both surfaces of the metal base material on which the metal separator 1 was formed, and the metal separator 1 was produced. The applied voltage and time during the formation of the diamond-like carbon layer (DLC layer) were held at a bias voltage of 300 V until the film thickness was reached (approximately 5 minutes). At this time, the input power was 4 kW, and the argon gas (carrier gas) was 150 sccm.

(Example 2)
In Example 1, a metal separator 2 was produced in the same manner as in Example 1 except that the ion bombardment treatment was not performed.

(Comparative Example 1)
In Example 2, a metal separator 3 was produced in the same manner as in Example 1 except that a diamond-like carbon layer (DLC layer) was not formed or formed.

<Measurement of contact resistance>
For the metal separators before and after the corrosion test shown below, the contact resistance was measured by the following method. Specifically, as shown in FIG. 7, both sides of the metal separator 5 produced in the above examples and comparative examples are sandwiched between a pair of gas diffusion base materials (gas diffusion layers 4a and 4c), and the obtained laminate is obtained. Both sides of the body were further clamped by a pair of electrodes 26a, 26c. And the power supply was connected to the both ends, the whole laminated body containing an electrode was hold | maintained with the predetermined surface pressure (0.5, 1.0, 1.5, 2.0 MPa load), and the measuring apparatus was comprised. . The contact resistance value of the laminate was calculated from the energization amount and voltage value when a constant current of 1 A was passed through the measuring device and a predetermined surface pressure was applied. The above measurement was repeated three times for each surface pressure. The contact resistance value was judged from the average value when measured three times.

  The graph which shows the relationship between the measurement surface pressure and the contact resistance in the contact resistance measurement performed using the metal separators 1 to 3 before and after the corrosion test is shown in FIGS. 8A and 8B. Even after the corrosion test, the metal separators 1 and 2 of Examples 1 and 2 had almost the same contact resistance value. Therefore, FIG. 8B shows the metal separators 2 and 3 of Example 2 and Comparative Example 1. Only the results obtained are shown.

  As can be seen from FIGS. 8A and 8B, the metal separators 1 and 2 of Examples 1 and 2 have lower contact resistance and excellent corrosion resistance than the metal separator 3 of Comparative Example 1 even in a corrosive environment. I understood. For this reason, in the metal separator of this example, the chromium oxycarbide layer is covered and protected with a conductive layer (DLC layer), thereby suppressing deterioration of the chromium oxycarbide layer in a corrosive environment and low contact resistance. Can be maintained, and sufficient corrosion resistance can be exhibited. In addition, by providing a chromium oxycarbide layer between the metal substrate and the conductive layer (DLC layer), sufficient corrosion resistance can be suppressed to prevent dissolution of the outermost DLC layer exposed to the harshest environment in a corrosive environment. An unexpected effect of being able to express) was obtained. As a result, the outermost conductive layer (DLC layer) functions (acts) as a stable protective layer even in a corrosive environment, resulting in increased contact resistance due to alteration of the chromium oxycarbide layer and elution of metal ions from the metal substrate. It can be effectively prevented (sufficient corrosion resistance can be expressed). Accordingly, it is possible to provide a metal separator having corrosion resistance and capable of realizing a low contact resistance, and a fuel cell using the metal separator.

  Specifically, from FIG. 8A, it was found that the chromium oxycarbide layer can realize a low contact resistance without a DLC layer in a state where it is not exposed to a corrosive environment (before the corrosion test) (Example 1, FIG. 8A). 2 and Comparative Example 1 for comparison).

  In addition, it was found that the chromium oxycarbide layer alone deteriorates when exposed to a corrosive environment (after a corrosion test), low contact resistance cannot be maintained, contact resistance increases, and corrosion resistance is insufficient. (Refer to the comparison between Example 2 and Comparative Example 1 in FIG. 8B).

  From FIG. 8A, in the state where it is not exposed to the corrosive environment (before the corrosion test), even if the oxide film is removed or not, even if it is exposed to the atmosphere with the chromium oxycarbide layer formed, The same contact resistance was found (refer to Examples 1 and 2 in FIG. 8A). Here, exposure to the atmosphere refers to a process in which a chromium oxycarbide layer is formed by an ion plating apparatus and then transferred to a sputtering apparatus for DLC film formation from the apparatus to a room (in the atmosphere) for a short time (4 (Approx. Hours) Exposure to the atmosphere when stored. From this, it was also found that there is no need for re-oxidation after the chromium oxycarbide layer is formed.

<Corrosion test>
After measuring the contact resistance value before the corrosion test according to the above <Measurement of contact resistance>, the metal separators produced in the above examples and comparative examples were subjected to a corrosion test (immersion test) against acidic water. Measurement of contact resistance> The contact resistance value after the corrosion test was measured. In addition, specifically as a corrosion test (immersion test), the metal separator produced by the said Example and comparative example was cut out to 30 mm x 30 mm size, and it was set as the test piece. This test piece is immersed in 1000 ml of a test solution (pH 3 dilute sulfuric acid aqueous solution, liquid temperature 80 ° C.), a constant potential of 1.0 V is applied to the test piece, and the appearance of the test piece is observed for 4 hours. Current characteristics at potential were measured. For the measurement, a potentiostat was used as an electrochemical measurement system.

  The corrosion test conditions are as follows.

1) Solution: 0.5 mM H ₂ SO ₄ (corresponding to pH 3)
2) Liquid temperature: 80 ° C
3) Liquid volume: 1000ml
4) Atmosphere: Atmospheric equilibrium 5) Constant potential holding: 1.0 Vvs. SHE (flat plate) Converted using SCE.

6) Low potential holding time: 4 hours 7) Number of repetitions: n1 (once)
8) Specimen shape: 30 mm square.

(Elution analysis method for corrosion test solutions)
After diluting the sample (solution after the above corrosion test; corrosive solution) to a concentration that allows analysis using the following equipment, 50 ml is taken and quantitative analysis of Cr, Fe, Ni is performed by ICP mass spectrometry. went.

  Device: Perkin Elmer ICP mass spectrometer ELAN DRC II.

  The results of elution analysis are shown in Table 1 below.

  From the results in Table 1 above, it was confirmed that there was almost no difference in the amount of eluted metal with and without the DLC layer. Therefore, by providing a chromium oxycarbide layer between the SUS substrate and the DLC layer, dissolution of the outermost DLC layer exposed to the harshest environment can be suppressed in a corrosive environment (sufficient corrosion resistance can be expressed). It was found that an unexpected effect was obtained. As a result, the outermost DLC layer functions (acts) as a stable protective layer even in a corrosive environment, thereby increasing contact resistance due to alteration of the chromium oxycarbide layer and metal ions (Cr, Fe, Ni, etc.) from the SUS substrate. It was found that elution of) can be effectively prevented. Thereby, sufficient corrosion resistance can be expressed. Although the chromium oxycarbide layer alone can prevent the elution of metal ions from the metal substrate, the DLC layer does not function (act) as a stable protective layer even in a corrosive environment. Alteration occurred, contact resistance increased, and corrosion resistance was insufficient. (Refer to the comparison between Example 2 and Comparative Example 1 in FIG. 8B).

<Auger electron spectroscopy analysis (AES analysis)>
Using the metal substrate after forming the chromium oxycarbide layer of Example 1 (Example 2 and Comparative Example 1 were also used as a common sample because the chromium oxycarbide layer was produced under the same film forming conditions). Electron spectroscopic analysis (AES analysis) was performed.

(Analysis equipment)
A field emission Auger electron spectroscopy (FE-AES) apparatus (SAM-680 manufactured by Physical Electronics, USA) was used.

(Measurement condition)
Electron beam energy: 5 keV
Sputter ion species: Ar ⁺ .

(Depth direction analysis results)
FIG. 9 shows the analysis result in the depth direction (depth from the surface to 1000 nm) of the metal substrate sample surface (chromium oxycarbide layer). The vertical axis represents the atomic percentage calculated using the sensitivity coefficient attached to the device. The depth of the horizontal axis is a SiO ₂ converted value. The etching rate of sputter ions used this time was 4.94 nm / min.

  From FIG. 9, it can be seen that the chromium oxycarbide layer has an elemental composition of 30 to 40% for carbon, 15 to 30% for oxygen, and the balance of chromium for the remainder.

1 Polymer electrolyte fuel cell (PEFC),
2 solid polymer electrolyte membrane,
3 catalyst layer,
3a anode catalyst layer,
3c cathode catalyst layer,
4a Anode gas diffusion layer,
4c cathode gas diffusion layer,
5 separator,
5a anode separator,
5c cathode separator,
6a Anode gas flow path,
6c cathode gas flow path,
7 Refrigerant flow path,
10 Membrane electrode assembly (MEA),
11 vacuum chamber,
14 Carbon raw material electrode,
15 Argon gas tube,
16 Argon gas introduction port,
17 Pulse power supply,
18 DC power supply,
20 metal separator,
21 metal substrate,
23 Chromium oxycarbide layer,
25 conductive layer,
25a conductive intermediate layer,
25b conductive carbon layer,
26a, 26c electrodes,
A film forming apparatus used in the 100 HiPIMS method;
501 substrate,
600 Film forming apparatus used in DCMS method,
601 vacuum chamber;
6101-6104 target (cathode),
6201-6204 magnetic circuit,
650 rotary stage,
655, 656 power supply,
670 Insulator.

Claims (3)

  A metal separator for a fuel cell, comprising: a metal substrate; a chromium oxycarbide layer formed on the surface of the metal substrate; and a conductive layer formed on the chromium oxycarbide layer.   The metal separator for a fuel cell according to claim 1, wherein the conductive layer is a diamond-like carbon (DLC) layer. A polymer electrolyte membrane, a pair of anode catalyst layer and cathode catalyst layer sandwiching the polymer electrolyte membrane, and a membrane electrode assembly including a pair of anode gas diffusion layer and cathode gas diffusion layer sandwiching them;
A polymer electrolyte fuel cell having a pair of anode separator and cathode separator sandwiching the membrane electrode assembly,
At least one of the anode separator or the cathode separator is a metal separator for a fuel cell according to claim 1 or 2,
At this time, the metal separator for a fuel cell is formed in a concavo-convex shape, the convex portion comes into contact with the membrane electrode assembly, and the concave portion serves as a gas flow path for circulating fuel gas or oxidant gas. A polymer electrolyte fuel cell.