Fuel cell separator and manufacturing method for the same

Abstract

To provide a fuel cell separator with excellent corrosion resistance.SOLUTION: A fuel cell separator including a passivated metal layer and a conductive carbon membrane stacked on a surface of an aluminum metal substrate has an alloy layer composed of both metals present at the bonding interface between the aluminum metal substrate and a titanium metal layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a separator for a solid polymer electrolyte fuel cell that has excellent corrosion resistance, low volume resistance, and is inexpensive. [Background technology]

[0002] In recent years, fuel cells have been attracting attention as an energy source that can solve global environmental and energy problems. In particular, solid polymer electrolyte fuel cells (hereinafter simply referred to as fuel cells) are being considered for use in household power sources and fuel cell vehicles because they can operate at low temperatures and can be made smaller and lighter.

[0003] The separator is one of the important components of a fuel cell. The separator must have the following characteristics: excellent corrosion resistance in acidic solutions (the fuel cell operating environment), high mechanical strength against vibrations, low contact resistance with the gas diffusion materials (such as carbon paper, also referred to as GDL) that serve as the anode and cathode electrodes, easy processability (e.g., groove processing), and lightweight and inexpensive.

[0004] Recently, metal substrates such as stainless steel plates and titanium have been primarily studied as separator substrates that satisfy the above-mentioned characteristics. Separators made of metals such as stainless steel, titanium, and their alloys are said to have corrosion resistance due to the formation of a passivation film on their surfaces, but this is not necessarily sufficient. Furthermore, it is known that this passivation film increases contact resistance with the gas diffusion members that serve as the anode and cathode electrodes, thereby impairing conductivity and reducing the power generation efficiency of fuel cells.

[0005] On the other hand, aluminum and magnesium alloys have been considered as lightweight, inexpensive separator substrates, but they are prone to forming insulating oxide films on the substrate surface and do not have sufficient corrosion resistance.

[0006] The above problem may also occur in the case of a current collecting member for a fuel cell.

[0007] Patent Document 1 discloses fuel cell separator technology that employs a titanium substrate, which is considered to have the best corrosion resistance for fuel cell separators, and laminates a titanium carbide layer and a conductive carbon film on its surface. It is shown that the separator has excellent corrosion resistance in the operating environment of a fuel cell due to the use of an expensive titanium substrate.

[0008] Patent Document 2 discloses a fuel cell separator having a mixing layer made of base metal and titanium metal at the bonding interface between the metal substrate and the titanium metal layer, which significantly increases the bonding strength between the metal substrate and the titanium metal layer. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2019-106345 [Patent Document 2] Patent Publication No. 2021-093298 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-178914 Summary of the Invention [Problem to be solved by the invention]

[0010] The fuel cell separator disclosed in Patent Document 1 has excellent corrosion resistance, but does not specify the contact resistance at the interface between the conductive carbon film and the GDL that contacts its surface, or the change in contact resistance over time. Although the conductive carbon film is said to have excellent corrosion resistance, when the surface temperature of the substrate increases, existing pinholes become defects, reducing corrosion resistance. Furthermore, titanium is a rare metal and is expensive, posing significant challenges for future mass production.

[0011] In the mixing layer disclosed in Patent Document 2, the metal substrate and titanium metal are simply mixed together, and the crystalline structure of the metal substrate and the crystalline structure of the titanium metal are separately mixed together. Although the mixing layer contributes to improving the adhesion between the metal substrate and the titanium metal layer, it does not significantly contribute to improving corrosion resistance.

[0012] The problem to be solved by the present invention is to provide a fuel cell separator (hereinafter simply referred to as a separator) that uses an inexpensive, lightweight metal substrate, such as an aluminum metal substrate (hereinafter also referred to as an aluminum substrate), has excellent corrosion resistance, and low contact resistance. The present invention also aims to provide an inexpensive separator and a fuel cell using the separator. The present invention can also be applied to a current collecting member for a fuel cell (hereinafter also simply referred to as a current collecting member). [Means for solving the problem]

[0013] The present invention has been made to solve the above problems, and provides the following fuel cell separator and method for producing the same.

[0014] The present invention is based on a configuration in which a passivated metal layer, such as a titanium metal layer (hereinafter simply referred to as the titanium metal layer), is laminated on the surface of an inexpensive aluminum substrate, and a conductive carbon coating (hereinafter also referred to as the carbon coating) is laminated on the surface of the titanium metal layer. A chemically extremely stable TiAl alloy layer is provided at the interface between the aluminum substrate and the passivated metal layer. The present invention is also characterized by the presence of a conductive ceramic layer at the interface between the titanium metal layer and the conductive carbon coating. Titanium carbide or titanium nitride is suitable as the conductive ceramic layer. In this specification, the laminated member consisting of the TiAl alloy layer, titanium layer, conductive ceramic layer and conductive carbon film is referred to as a corrosion barrier layer.

[0015] The TiAl alloy layer has excellent chemical corrosion resistance. According to the present invention, the TiAl alloy layer preferably has a thickness of 10 nm to 100 nm. The titanium layer preferably has a thickness of 100 nm to 1 μm. By providing the TiAl alloy layer at the interface between the aluminum substrate and the titanium metal layer, the bonding strength between the aluminum substrate and the titanium metal layer can be significantly increased.

[0016] According to the results of our experiments, it is extremely difficult to completely cover the uneven surface of the substrate that occurs in the corrosion barrier layer made of passivated metal, making it extremely difficult to completely eliminate through-hole defects. However, by forming a corrosion barrier layer in which a conductive carbon film is laminated on the surface of the passivated metal layer, corrosion resistance can be improved. The conductive carbon film seals the defects to improve corrosion resistance and also plays a role in reducing the contact resistance at the contact interface with the GDL electrode that comes into contact with it. The lower the resistivity of the conductive carbon film, the better, with a suitable range being 0.01 Ω·cm to 1 Ω·cm.

[0017] Furthermore, the separator of the present invention has enhanced corrosion resistance by interposing a conductive ceramic layer at the interface between the titanium metal layer and the conductive carbon coating. Suitable conductive ceramic layers include titanium carbide, titanium nitride, and chromium oxide coatings.

[0018] According to the present invention, after forming the corrosion barrier layer on the surface of the metal substrate, or after pressing into the shape of a separator, the metal substrate is immersed in a concentrated nitric acid solution or the like to form a passivation film on the surface of the metal substrate or the titanium metal surface in the through hole defect area, thereby improving and maintaining the corrosion resistance. [Effects of the Invention]

[0019] According to the present invention, a titanium metal layer with strong adhesion can be formed by forming the titanium metal layer or the like on the surface of the aluminum substrate via an alloy layer. This allows a titanium metal layer with excellent corrosion resistance to be formed on the surface of a relatively inexpensive metal substrate such as an aluminum plate, and then a conductive carbon coating is laminated on that surface, thereby providing a fuel cell separator with excellent corrosion resistance and low contact resistance at the interface with the GDL. Furthermore, by covering any through defects remaining in the corrosion barrier layer with the passivation coating, the occurrence of pitting corrosion can be suppressed and metal ion elution can be reduced to below an acceptable level. Furthermore, a lightweight and inexpensive aluminum substrate can be used. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram showing the configuration of a solid polymer electrolyte fuel cell according to the present invention. [Figure 2] 1 is a schematic cross-sectional view of a surface layer portion of a fuel cell separator according to the present invention. [Figure 3] 1 is a diagram showing the corrosion resistance of a separator according to the present invention. [Figure 4] 1 is a diagram showing the power generation characteristics of a fuel cell using a separator according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] First, an outline of the fuel cell X of this embodiment will be described. The fuel cell X is used, for example, in fuel cell vehicles, and as shown in Fig. 1, is configured by stacking cells 4 each consisting of a gas diffusion member 1 serving as a fuel electrode, a gas diffusion member 2 consisting of an air electrode, and an electrolyte membrane 3 sandwiched between them. Current collecting members 5 are provided in the upper and lower sections, and a separator 110 is provided between the cells 4. Gas flow paths 6 and 7 for supplying a fuel gas and an oxidant gas, respectively, are formed in the separator 110. Although the current collecting member 5 is formed to be thicker than the separator 110, it has substantially the same configuration as the separator 110 and is manufactured in the same manner as the separator.

[0022] The embodiment of the separator 110 according to the present invention is roughly divided into three steps: a corrosion barrier layer formation step 1 in which a corrosion barrier layer 16 is formed by laminating a titanium metal layer 13 and a conductive carbon coating 15 on the surface of a sheet-like metal substrate 11; a press-molding step 2 in which this metal substrate is molded into a separator 110 having uneven grooves 6, 7, etc. that serve as gas flow paths; and a passivation treatment step 3 in which a passivation coating is formed on portions of the laminated corrosion barrier layer 16 that have through defects. This specification will mainly describe steps 1 and 3.

[0023] An embodiment of a fuel cell separator 110 will be described below with reference to the drawings. Fig. 2 shows a schematic cross-sectional view of the surface layer of an aluminum fuel cell separator 110. The separator 110 is characterized by having a corrosion-resistant barrier layer 16 consisting of a titanium metal layer 13 formed on at least one main surface of the metal substrate 11, for example, an aluminum alloy substrate, and a conductive carbon coating 15 laminated on the surface of the titanium metal layer 13. A TiAl alloy layer of aluminum substrate metal and titanium metal is formed at the bonding interface between the aluminum substrate 11 and the titanium metal layer 13. Furthermore, a conductive ceramic layer made of titanium metal and a compound of carbon or nitrogen, such as titanium carbide or titanium nitride, is also interposed at the bonding interface between the titanium metal layer 13 and the conductive carbon coating 15.

[0024] The TiAl alloy layer 12 is a bonding interface where both metals are integrated, and is expected to not only significantly strengthen the bonding strength between the two metal layers but also significantly improve electrical conductivity and corrosion resistance. Here, the TiAl alloy refers to a material in which aluminum atoms and titanium atoms exist in the same crystal lattice. The TiAl alloy layer 12 in this embodiment is, for example, a material based on a lamellar structure composed of TiAl (γ phase) and a small amount of Ti3Al (α2 phase).

[0025] This interfacial alloy layer 12 can be formed by forming a TiAl alloy layer on the surface of a metal substrate by titanium arc deposition or the like while maintaining the substrate temperature at 200 to 400°C. Alternatively, a thin titanium layer approximately 20 to 100 nm thick can be formed on the surface of an aluminum substrate, and then irradiating the titanium layer with high-energy argon ions or a mixture of argon and titanium ions accelerated to, for example, 5 to 20 keV to implant titanium atoms into the surface of the metal substrate, thereby forming a TiAl alloy layer. Alternatively, the substrate temperature can be maintained at 200 to 400°C, and high-energy titanium ions can be directly implanted into the substrate surface to form a TiAl alloy layer. While a thicker TiAl alloy layer is preferable, the required high-energy ion irradiation results in a thickness of approximately 20 to 100 nm.

[0026] Bonding via this interfacial alloy layer 12 significantly improves the bonding strength between metal substrate 11 and titanium metal layer 13. For example, in a sample in which a titanium metal layer 13 of approximately 1 μm in thickness was formed on the surface of a 200 μm thick aluminum plate via an interfacial compound layer, no peeling or cracking of the titanium metal layer occurred even after 200 90-degree bending tests.

[0027] The TiAl binary alloy layer is known to have excellent oxidation resistance and not oxidize at temperatures below 800°C. It has also been reported that TiAl alloys containing Nb and Si exhibit the oxidation resistance characteristics of Alloy 713C, a nickel casting alloy. According to the present invention, the corrosion-resistant barrier layer 16 containing the TiAl alloy layer significantly suppresses the initiation and growth of pitting corrosion.

[0028] It is difficult and impractical to completely eliminate microscopic defects D1 caused by dust, pinholes, etc., that occur during the process of forming the corrosion-resistant barrier layer 16 on the surface of the aluminum base material 11, or through defects D2 caused by cracks or peeling that occur during the press working process. Practical application can be achieved by sealing these defects or covering them with a passivation film 17. Details will be described below.

[0029] According to the present invention, inexpensive metal substrates such as aluminum, stainless steel, and zinc, alloy substrates containing these metals as main components, or laminated substrates of these metals can be used as the metal substrate 11. Needless to say, expensive metal substrates such as titanium and nickel can also be used.

[0030] A feature of the present invention is the practical application of fuel cell separators using inexpensive, lightweight aluminum substrates. While the aluminum substrate is not particularly limited, high-purity aluminum with a purity of 99% by weight or higher, such as JIS-specified 1000-series alloys (industrially pure aluminum), can be used. High-purity aluminum has a high thermal conductivity (approximately 200 W / m·K), making it suitable for use as separator 110. Considering corrosion resistance, processability, mechanical strength, and other factors, aluminum alloys, such as 3000-series alloys (Al-Mn-based alloys), 5000-series alloys (Al-Mg-based alloys), 6000-series alloys (Al-Mg-Si-based alloys), or 8000-series alloys (Al-Fe-Si-based alloys), can be used. Aluminum substrates are not only lightweight but also have high electrical and thermal conductivities, making them the most desirable material for separator substrates.

[0031] The separator 110 of the present invention has a titanium metal layer 13 formed on the TiAl alloy layer 12, and a conductive carbon film laminated on the surface of the titanium metal layer 13 via a conductive ceramic layer 14 to form a corrosion-resistant barrier layer 16. The titanium metal layer surface is known to have excellent corrosion resistance because it remains passivated over the entire potential range of 0 to 1 V, which is the typical environment for fuel cells. Forming a titanium metal layer on the surface of a metal substrate, such as an aluminum substrate, results in a metal substrate with corrosion resistance substantially equivalent to that of a titanium metal substrate. While the thickness of the titanium metal layer 13 is preferably as thick as possible, there are limitations due to factors such as processing costs. The thickness of the titanium metal layer is 50 nm to 5 μm, and more preferably 100 nm to 2 μm. The method for forming the titanium metal layer 13 is not limited, but a titanium metal layer of any desired thickness can be formed, for example, by titanium arc deposition.

[0032] The conductive carbon coating 15 may be laminated directly on the surface of the titanium metal layer 13, or a conductive ceramic layer 14 may be interposed at the bonding interface between the titanium metal layer 13 and the conductive carbon coating 15. The role of the conductive ceramic layer 14 is to prevent the surface of the titanium metal layer from being oxidized and passivated in the fuel cell usage environment, thereby preventing an increase in contact resistance at the interface with the GDL, which serves as a gas diffusion layer. Therefore, a conductive coating that is chemically stable in the fuel cell operating environment and can prevent the permeation of moisture and oxygen is preferred.

[0033] Specifically, the conductive ceramic layer 14 can be made of titanium carbide or titanium nitride. These conductive ceramic layers 14 can be easily formed by surface treatment in a plasma atmosphere containing hydrocarbon gas or nitrogen gas. It is believed that titanium nitride, titanium carbide, etc., oxidize when exposed to the electrolyte in the operating environment of a fuel cell, causing a significant increase in contact resistance. However, it has been confirmed that the corrosion-resistant barrier layer 16 containing titanium nitride or titanium carbide of the present invention is not oxidized and does not increase contact resistance because it is coated with the conductive carbon coating 15.

[0034] The conductive carbon coating 15 not only improves corrosion resistance but also reduces the contact resistance at the interface with the GDL electrodes 1 and 2. The resistivity of the conductive carbon coating, e.g., diamond-like carbon (DLC), varies depending on the manufacturing method. DLC coatings formed at room temperature have an amorphous structure and are high-resistance coatings similar to insulators, but DLC coatings formed at substrate temperatures of 200°C or higher contain many microcrystals with sp2 hybrid orbitals, resulting in low-resistance DLC coatings. Since the GDL electrodes 1 and 2 are also made of graphite with sp2 hybrid orbitals, using a low-resistance DLC coating can reduce the contact resistance between them. The current generated by the cell 4 flows through the separator 110. Therefore, it is desirable for the conductive carbon coating to be made of a material with sufficiently low electrical resistance and low contact resistance at the interface between them. For example, the resistance per unit area in the thickness direction of the conductive carbon coating is 1 mΩ or less, and the contact resistance at the interface is 5 mΩ·cm. 2 It is desirable that the following:

[0035] The lower the resistivity of the conductive carbon coating 15, the better, but the minimum resistivity of a conductive carbon coating is about 1 mΩ·cm. The preferred range for the resistivity of the conductive carbon coating is 1 mΩ·cm to 10 Ω·cm, and a more preferred range is 1 mΩ·cm to 1 Ω·cm. This is because if the resistivity of the conductive carbon coating is too high, the internal resistance of the fuel cell increases, resulting in increased power loss and making it impractical.

[0036] In this specification, the conductive carbon coating is assumed to have a resistivity of 1 Ω·cm or less. It may be not only a high-purity carbon coating, but also a carbon coating containing a required amount of impurity elements such as nitrogen or boron. The conductive carbon coating can be produced by a plasma CVD method using direct current discharge of a working gas containing a hydrocarbon gas or high-frequency discharge. The resistivity of the conductive carbon coating depends on the substrate temperature during film production, with a suitable substrate temperature being 150 to 400°C.

[0037] The thickness of the conductive carbon coating 15 is 20 nm or more in consideration of its effectiveness, and 500 nm or less in consideration of productivity. It is preferably 30 to 200 nm. A thickness of 10 nm or less does not provide a sufficient corrosion barrier layer effect, and a thickness of 300 nm or more prolongs the coating formation time, which is disadvantageous in terms of productivity. The passivation coating 17 seals these through defects and inhibits corrosion of the metal substrate surface and the elution of metal ions.

[0038] Because a high-density current flows through the corrosion barrier layer, it is desirable for the resistance to be as low as possible. The resistivity of titanium nitride or titanium carbide is several tens of mΩ·cm, depending on the manufacturing method. For example, if the corrosion barrier layer has a resistivity of 1 Ω·cm and a thickness of 100 nm, the resistance per unit area in the thickness direction is 0.1 mΩ, which is within the acceptable range.

[0039] In the process for producing metal separator 110 according to the present invention, corrosion-resistant barrier layer 16 is formed on the surface of sheet-like aluminum substrate 11, and then this metal substrate is press-formed into separator 110 having uneven grooves 6, 7, etc., which serve as gas flow paths. When press-forming is performed, titanium metal layer 13 expands and contracts in accordance with the expansion and contraction of aluminum substrate 11, so peeling or cracking does not occur in the titanium metal layer. However, penetration defects D2 such as cracks or peeling may occur in corrosion-resistant barrier layer 16 including conductive carbon coating 15.

[0040] When the corrosion barrier layer is formed or after it is formed, pressing into the required separator shape cannot completely avoid the occurrence of minute defects D1 caused by pinholes, dust, etc., and through-hole defects D2 caused by cracks or peeling. These minute defects must be sealed or passivated.

[0041] According to the present invention, it has been found that this problem can be solved by using an aluminum substrate coated with a passivated metal layer 13, such as a titanium metal layer, on the surface of the aluminum substrate. That is, even if a through-hole defect D2 such as a crack or peeling occurs in the corrosion-resistant barrier layer 16, if the surface exposed to the through-hole defect is a passivated metal, the hole can be substantially sealed by passivation treatment.

[0042] As the passivation metal, an alloy containing titanium, chromium, aluminum or zirconium as a main component can be used.

[0043] Various passivation treatment methods have been studied, and it has been found that immersion in concentrated nitric acid solutions with a concentration of 30% or more or hydrogen peroxide solutions with strong oxidizing power is effective. Hydrogen peroxide solutions containing ozone are just as effective or more effective than the passivation treatment method using concentrated nitric acid solutions that has been used traditionally, and provide high corrosion resistance. In addition, passivation treatment methods using hydrogen peroxide solutions are environmentally friendly and inexpensive. However, this method is not limited to passivation treatment using hydrogen peroxide solutions.

[0044] Furthermore, according to the present invention, after the formation of the corrosion barrier layer or after press molding, the metal substrate surface at defective portions of the corrosion barrier layer can be passivated by exposing it to an ozone atmosphere or an oxygen plasma atmosphere. In this passivation treatment method, the substrate temperature is preferably 70°C or higher to 450°C. It has been found that passivation treatment in an ozone atmosphere or an oxygen plasma atmosphere can significantly reduce the contact resistance with the GDL.

[0045] According to the present invention, the conductive carbon coating may be a conductive resin coating, or a laminated coating of a conductive carbon coating and a conductive resin coating. According to Patent Document 3, the conductive resin coating uses a phenolic resin, an epoxy resin, or the like as a resin matrix, and contains needle-like or flattened graphite particles with a major axis of 1 μm to 30 μm as a conductive filler. The contact resistance depends on the volume fraction of the graphite particles, and a volume fraction of 30% to 70% is generally considered suitable. If the volume fraction of graphite particles in the conductive resin coating is 70% or more, cracks will occur on the surface, and if the volume fraction is 30% or less, the contact resistance will be 50 mΩ·cm. 2 Furthermore, the thickness of the conductive resin coating is preferably 5 μm to 30 μm, and if the thickness is less than 5 μm, sufficient corrosion resistance cannot be obtained, while if it exceeds 30 μm, the time required for formation becomes unnecessarily long, resulting in poor productivity.

[0046] According to the present invention, the corrosion resistance is improved by sandwiching a conductive carbon coating between the metal separator substrate and the conductive resin coating. It is also possible to use graphite particles with a particle size of 0.1 μm to 5 μm as the conductive filler. Therefore, the thickness of the conductive resin coating can be reduced to 5 μm or less, and the contact resistance can be reduced to 5 mΩ·cm. 2 It has become possible to make the thickness of the conductive resin coating film as follows: The thickness of the conductive resin coating film is preferably 0.3 μm to 10 μm, and more preferably 0.5 μm to 5 μm.

[0047] Example 1 An aluminum alloy plate (Al3003) measuring 6 cm wide and 18 cm long was used as the aluminum substrate. After chemical polishing and plasma cleaning of its surface, a 150 nm thick titanium metal layer was formed on the surface by titanium arc deposition while maintaining the substrate temperature at 300°C. A 100 nm thick DLC film was then laminated on the surface by plasma CVD while maintaining the substrate temperature at 300°C to form a corrosion-resistant barrier layer. The results of corrosion resistance evaluation using electrochemical methods are shown in Figure 3. The characteristic potential (pitting corrosion potential) was 1.4 V or higher, exceeding the US DOE standard value of 0.8 V, and the leakage current was 1 μA / cm. 2 The following have been fully cleared:

[0048] <Example 2> A single fuel cell was constructed using an aluminum alloy separator with the above properties. The solid polymer electrolyte membrane was DuPont NR211 (25 μm thick), and the anode / cathode catalyst layers were TEC10E50E (0.35 / 0.35 mg cm) manufactured by TKK. 2 ) was used to construct a single cell fuel cell.

[0049] The cell temperature was set to 80°C, the humidification temperature to 75°C, and the generated current density to 0.2 A / cm 2 A long-term power generation test was conducted using this system. Figure 4 shows the change in IR-free cell voltage over time. The initial evaluation value for the generated voltage was 0.777V, but after 2000 hours of continuous operation, the generated voltage was 0.720V, with a voltage drop rate of 7.3% per 2000 hours. This exceeded the self-target value of 10%.

[0050] While representative embodiments have been described above, the present invention is not limited to these embodiments as long as the gist of the present invention is not altered. Furthermore, the technology disclosed in the present invention can also be applied to metal separators formed into separators. That is, the order of steps 1 and 2 can be reversed to form a separator 110 from a sheet-like metal substrate 11, with concave-convex grooves 6, 7, etc., which serve as gas flow paths, and then form a titanium metal layer 13 and a corrosion-resistant barrier layer 16 on the surface of the separator 110, comprising the DLC coating. Furthermore, if necessary, a corrosion-resistant coating 17 (passivation coating) can be formed on any penetrating defects in the corrosion-resistant barrier layer 16 to produce a practical aluminum separator with excellent corrosion resistance. [Explanation of symbols]

[0051] 1, 2 Gas diffusion member 11...Metal base material 12...Interfacial alloy layer 13··Titanium metal layer 14··Titanium carbide layer 15. Conductive carbon coating 16. Corrosion-resistant barrier layer 17. Corrosion-resistant coating 110··Separator D1: Micro-defect D2: Through-hole defect

Claims

1. A fuel cell separator having a passivated metal layer and a conductive carbon film laminated on the surface of an aluminum metal substrate, A fuel cell separator comprising an alloy layer made of both metals at the bonding interface between the aluminum metal substrate and the passivated metal layer.

2. 2. The fuel cell separator according to claim 1, further comprising a conductive ceramic layer at the interface between the passivated metal layer and the conductive carbon film.

3. 2. The fuel cell separator according to claim 1, wherein the passivation metal is an alloy containing titanium, chromium, zirconium or nickel as a main component.

4. 3. The fuel cell separator according to claim 2, wherein the conductive ceramic layer is made of titanium carbide or titanium nitride.

5. 2. The fuel cell separator according to claim 1, wherein the conductive carbon film is a diamond-like carbon film having a thickness of 20 nm to 500 nm and a resistivity of 0.01 Ω·cm to 1 Ω·cm.

6. 2. The fuel cell separator according to claim 1, wherein the conductive carbon film is a conductive resin film having a thickness of 2 μm to 50 μm and a resistivity of 0.01 Ω·cm to 1 Ω·cm.

7. A method for manufacturing a fuel cell separator having a corrosion barrier layer comprising a passivated metal layer on the surface of the aluminum metal substrate and a conductive carbon coating laminated on the surface of the passivated metal layer, comprising:

2. The method for manufacturing a fuel cell separator according to claim 1, wherein the substrate temperature is maintained at 200°C to 400°C after the formation of the corrosion barrier layer, to form an alloy layer composed of aluminum metal and the passivated metal, and a conductive ceramic layer at the bonding interface between the passivated metal layer and the conductive carbon coating.

8. 8. The method for manufacturing a fuel cell separator according to claim 7, wherein after the formation of the corrosion barrier layer or after the press working, the plate is immersed in concentrated nitric acid or hydrogen peroxide solution.

9. 9. The method for manufacturing a fuel cell separator according to claim 7, wherein after the formation of the corrosion barrier layer or after the press working, the plate is exposed to an ozone atmosphere or an oxygen plasma atmosphere.

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