JP2021093298A - Separator for fuel cell and manufacturing method for the separator for fuel cell - Google Patents

Abstract

To provide a separator for fuel cell using a metal base with an excellent corrosion resistance.SOLUTION: A separator for fuel cell includes a lamination gas barrier layer formed by a titanium metal layer 13 in a front layer part of a metal base 11, a gas barrier layer 14 containing titanium carbide or titanium nitride on the front surface, and a conductive carbon coating 15 laminated on the front surface of the gas barrier layer. A mixing layer 12 is provided between the metal base and the titanium metal layer, and a corrosion resistance coating 17 is provided in a penetration defect part D2 existed in the lamination gas barrier layer.SELECTED DRAWING: Figure 2

Description

The present invention relates to an inexpensive solid polymer electrolyte fuel cell separator having excellent corrosion resistance and low contact resistance with a gas diffusion layer member.

In recent years, fuel cells have been attracting attention as an energy source for solving global environmental problems and energy problems. In particular, polymer electrolyte electrolyte fuel cells (hereinafter, also simply referred to as fuel cells) can be operated at low temperatures and can be made smaller and lighter, so they can be applied to household power sources and fuel cell vehicles. It is being considered.

A separator is one of the important components that make up a fuel cell. The characteristics required for this separator are that it has excellent corrosion resistance in an acidic solution (fuel cell operating environment), that it has high mechanical strength against vibrations, and that it has a gas diffusion member that serves as an anode and cathode electrode (for example, carbon). It has low contact resistance with paper), has excellent workability such as grooving, is lightweight, and is inexpensive.

Recently, as a base material for a separator satisfying the above characteristics, a metal base material such as stainless steel plate or titanium has been mainly studied. 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 the surface, but this is not always sufficient. Further, it is known that this passivation film increases the contact resistance between the anode and the gas diffusion member serving as the cathode electrode (hereinafter, also referred to as GDL), thereby inhibiting the conductivity and lowering the power generation efficiency of the fuel cell. ing.

On the other hand, steel materials, aluminum, magnesium alloys, etc. are being studied as lightweight and inexpensive separator base materials, but an insulating oxide film is likely to be formed on the base material surface, corrosion resistance is not sufficient, and eluted metal ions are catalysts. It is known that the characteristics are deteriorated and the ionic conductivity of the solid polymer electrolyte membrane is lowered, resulting in deterioration of the power generation characteristics.

It should be noted that the above-mentioned problem can occur similarly with respect to the current collector member for a fuel cell.

Patent Document 1 discloses a fuel cell separator technology in which a titanium base material considered to have the best corrosion resistance as a fuel cell separator is adopted, and a titanium carbide layer and a conductive carbon film are laminated on the surface thereof. There is. It has been shown that the separator has excellent corrosion resistance in the operating environment of a fuel cell by using an expensive titanium base material.

JP-A-2019-106345

The fuel cell separator disclosed in Patent Document 1 is excellent in corrosion resistance, but the contact resistance at the interface between the conductive carbon film and GDL in contact with the surface thereof and the change with time of the contact resistance are specified. Not. Although the conductive carbon film is said to have excellent corrosion resistance, it is difficult to completely suppress the occurrence of penetration defects such as pinholes that cause deterioration of corrosion resistance, which is a major problem in manufacturing. In addition, titanium is a rare metal and expensive, which leaves a big problem for future mass production.

The problem to be solved by the present invention is excellent corrosion resistance using an inexpensive metal base material, for example, a stainless steel base material (hereinafter, also referred to as SUS base material) or an aluminum base material (hereinafter, also referred to as aluminum base material). The present invention is to provide a separator for a fuel cell having a small contact resistance (hereinafter, also simply referred to as a separator). Another object of the present invention is to provide a separator according to the present invention and a fuel cell using the separator at low cost. 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).

The present invention has been made to solve the above problems, and provides the following fuel cell separator and a method for manufacturing the separator.

The separator according to the present invention has a titanium metal layer on the surface layer of a metal base material, for example, a stainless steel base material, and a laminated gas barrier layer composed of a gas barrier layer and a conductive carbon film on the surface of the titanium metal layer, and the metal base. It is characterized by having a mixing layer (inclined composition layer) made of both metals at the bonding interface between the material and the titanium metal layer.

According to the present invention, a titanium metal layer is formed on the surface layer portion of the metal separator base material by sandwiching a mixing layer that gradually changes from the base metal to the titanium metal layer. Thereby, the bonding force between the metal base material and the titanium metal layer can be remarkably increased. The thickness of the mixing layer is 20 to 200 nm. The thickness of the titanium metal layer is 50 nm to 5 μm.

According to the present invention, it is difficult to eliminate penetrating defects such as pinholes generated in the titanium metal layer. Corrosion resistance is further improved by forming a laminated gas barrier layer in which a gas barrier layer and a conductive carbon film are laminated on the surface of the titanium metal layer. The conductive carbon film has a role of sealing the defective portion to improve corrosion resistance and reducing the contact resistance of the contact interface with the GDL electrode. The thickness of the conductive carbon film is 20 to 500 nm, preferably 30 to 200 nm. The smaller the resistivity of the conductive carbon film is, the more preferable it is, but the preferable range is 0.01 to 10 Ω · cm.

Further, the separator according to the present invention is characterized by having a corrosion-resistant film in a penetrating defect portion that is not sealed by laminating a conductive carbon film. The corrosion-resistant film is for improving the corrosion resistance and at the same time suppressing the elution of metal ions. Suitable corrosion resistant coatings include metal oxide coatings and / and conductive carbon coatings. According to the present invention, the separator base material temperature is maintained at 400 ° C. or lower in a gas containing ozone or in a plasma containing oxygen gas and hydrocarbon gas, and a metal oxide film is formed on the surface of the SUS base material of the penetration defect portion. Or / and form a conductive carbon film. The treatment temperature is preferably high, but room temperature to 300 ° C. is preferable in consideration of the influence on the laminated gas barrier layer.

According to the present invention, a titanium metal layer having a strong adhesive force can be formed by forming the titanium metal layer on the metal base material and its surface via a mixing layer. As a result, a titanium metal layer having excellent corrosion resistance is formed on the surface of a relatively inexpensive metal base material such as a stainless steel plate, and a gas barrier layer and a conductive carbon film are laminated on the surface thereof, thereby having excellent corrosion resistance and the GDL. It is possible to provide a separator for a fuel cell having a small contact resistance. Further, by covering the penetration defects remaining in the laminated gas barrier layer with the corrosion-resistant film, the elution of metal ions can be reduced to an allowable value or less.

It is the schematic which shows the structure of the solid polymer electrolyte type fuel cell which concerns on this invention. It is sectional drawing of the surface layer part of the fuel cell separator which concerns on this invention.

First, the outline of the fuel cell X of the present embodiment will be described. The fuel cell X is used in, for example, a fuel cell vehicle, and as shown in FIG. 1, a gas diffusion member 1 serving as a fuel electrode, a gas diffusion member 2 serving as an air electrode, and an electrolyte sandwiched between them. The cells 4 made of the film 3 are stacked. Further, a current collecting member 5 is provided in the upper portion and the lower portion, and a separator 110 is provided between the cell 4 and the cell 4. Gas flow paths 6 and 7 for supplying fuel gas and oxidant gas are formed in the separator 110, respectively.
Although the current collecting member 5 is formed thicker than the separator 110, it has substantially the same structure as the separator 110 and is manufactured in the same manner as the separator 110.

The embodiment of the separator 110 according to the present invention is roughly divided into an embodiment 1 in which a titanium metal layer 13 and the laminated gas barrier layer 16 are formed on the surface of a sheet-shaped metal base material 11, and the metal base material is used. The process comprises an implementation step 2 of forming into a separator 110 having uneven grooves 6 and 7 serving as a gas flow path, and an implementation step 3 of forming a corrosion-resistant film on a penetration defect portion existing in the laminated gas barrier layer 16. In this specification, implementation steps 1 and 3 will be mainly described.

Hereinafter, embodiments of the fuel cell separator 110 will be described with reference to the drawings. FIG. 2 shows a schematic cross-sectional view of the surface layer portion of the fuel cell separator 110. The separator 110 is formed on the metal base material 11, for example, a titanium metal layer 13 formed on at least one main surface of a stainless steel base material, a gas barrier layer 14 formed on the surface of the titanium metal layer 13, and the gas barrier layer. It is characterized by having a laminated gas barrier layer 16 composed of a conductive carbon film 15 laminated on the surface of the steel. Further, the joint surface between the metal base material 11 and the titanium metal layer 13 is characterized by having a mixing layer 12 (also referred to as an inclined composition layer) that gradually changes from the base metal to the titanium metal layer.

The mixing layer 12 is a region in which both metals gradually changing from a base metal to a titanium metal coexist, and is a joint surface in which both metals are integrated. Therefore, it is characterized in that the adhesion between the two metal layers is extremely strong.

In the formation of the mixing layer 12, a thin titanium layer having a thickness of about 20 to 100 nm is formed on the surface of the metal base material, and argon ions accelerated to high energy, for example, 5 to 20 keV, or mixed ions of argon and titanium are formed therein. Is formed by injecting titanium atoms into the surface layer portion of the metal base material. Alternatively, the mixing layer can be formed by directly injecting high-energy titanium ions directly into the surface of the base material. The thickness of the mixing layer is preferably thicker, but it is about 20 to 100 nm because high-energy ion irradiation is required.

By joining through the mixing layer 12, the adhesion between the metal base material 11 and the titanium metal layer 13 can be remarkably improved. For example, in a sample in which a titanium metal layer 13 having a thickness of about 1 μm is formed on the surface of a SUS316L foil having a thickness of 100 μm via a mixing layer, the titanium metal layer does not peel off or crack even in 2000 90-degree bending tests. It was.

A fine penetration defect D1 caused by dust or pinholes having a diameter of less than 1 μm generated in the process of forming the laminated gas barrier layer 16 on the surface of the metal base material 11, or a penetration defect portion D2 due to a crack or peeling of 1 μm or more. It is difficult and impractical to eliminate it. Practical use can be achieved by sealing these defective portions or coating them with a corrosion-resistant film 17. Details will be described below.

According to the present invention, the metal base material 11 includes stainless steel, an inexpensive metal base material such as aluminum, zinc, or magnesium alloy, an alloy base material containing these metals as a main component, or these metals. A laminated base material can be used. Needless to say, an expensive metal base material such as titanium or nickel can also be used.

More specifically, as the metal base material 11, a stainless steel base material having a high chromium content and excellent corrosion resistance can be adopted. For example, SUS430 made of ferritic SUS material, SUS304, SUS305, SUS316L of austenitic SUS material can be used. These metal substrates have a chromium content of 18%, and a corrosion-resistant coating such as chromium oxide and / or chromium carbide is applied to the surface of the SUS substrate of the penetration defect portion D2 existing in the titanium metal layer 13 and the laminated gas barrier layer 16. 17 can be formed.

As the aluminum base material, high-purity aluminum having a purity of 99% by weight or more, for example, a JIS-defined 1000 series alloy (pure industrial aluminum) can be used. High-purity aluminum has a high thermal conductivity (about 200 W / m · K) and is suitable as a separator 110. Considering corrosion resistance, workability, mechanical strength, etc., aluminum alloys, for example, 3000 series alloys (Al-Mn series alloys), 5000 series alloys (Al-Mg series alloys), 6000 series alloys (Al-Mg-Si series alloys) ), Or an 8000 series alloy (Al—Fe—Si based alloy) or the like can be used. The aluminum-based base material is not only lightweight but also has high conductivity and thermal conductivity, and is a desirable material as a separator base material.

In the separator 110 of the present invention, a titanium metal layer is formed via the mixing layer, and a gas barrier layer 14 is formed on the surface layer portion thereof. Titanium metal is known to be excellent in corrosion resistance because it is in a passivation state in the entire region of 0 to 1 V potential region, which is a normal fuel cell usage environment. By forming a titanium metal layer on the surface of a metal base material, for example, a SUS base material, the titanium metal base material is substantially replaced. The thickness of the titanium metal layer 13 is preferably as thick as possible, but there is a limit in consideration of processing costs. The thickness of the titanium metal layer is 50 nm to 5 μm, and a more preferable thickness is 100 nm to 2 μm. The method for forming the titanium metal layer 13 is not specified, but for example, a titanium metal layer having an arbitrary thickness can be formed by a titanium arc vapor deposition method.

The role of the gas barrier layer 14 is to prevent the surface of the titanium metal layer from being oxidized and passivated in a fuel cell usage environment, and the contact resistance at the interface with the GDL, which is a gas diffusion layer, is prevented from increasing. is there. Therefore, it is required to have a conductive film that is chemically stable in the operating environment of the fuel cell and can prevent the permeation of water and oxygen. Specific examples include titanium carbide and titanium nitride. It is known that the titanium nitride or titanium carbide is oxidized when exposed to an electrolytic solution in the operating environment of a fuel cell and the contact resistance is remarkably increased. Since the gas barrier layer 14 is coated with the conductive carbon film 15, it has been confirmed that it is not oxidized and the contact resistance does not increase.

Since a current having a high current density flows through the gas barrier layer, it is desirable that the resistance be as low as possible. The resistivity of titanium carbide and titanium nitride is several tens of mΩ · cm, although it depends on the manufacturing method. For example, in the case of a gas barrier layer having a resistivity of 1 Ω · cm and a thickness of 100 nm, the resistance value per unit area in the thickness direction is 0.1 mΩ, which is within an allowable range.

The titanium carbide layer can be formed, for example, by a plasma carburizing method or the like in a plasma containing a hydrocarbon gas. Further, the titanium nitride layer can form a titanium nitride layer on the surface of the titanium metal layer in plasma containing nitrogen gas in the same manner as in the plasma carburizing method. Alternatively, it can be formed by heating in a nitrogen atmosphere. The thickness of the gas barrier layer 14 is 10 to 500 nm. It is preferably 30 to 300 nm.

As described above, titanium carbide and titanium nitride are known to be oxidized to titanium oxide in the operating environment of the fuel cell, but the oxidation of the gas barrier layer is suppressed by coating with a conductive carbon film. be able to. That is, the gas barrier layer is prevented from being directly exposed to the electrolytic solution by laminating the conductive carbon film. According to the implementation results of the inventors, even if oxygen gas or water vapor diffuses the conductive carbon film and reaches the gas barrier layer, the gas barrier layer is not oxidized and passivated. It has been confirmed that the contact resistance with GDL does not increase either.

It is difficult to eliminate, for example, fine through holes D1 having a diameter of less than 1 μm or through defects D2 having a diameter of 1 μm or more due to pinholes or the like generated in the gas barrier layer, but a conductive carbon coating is formed on the surface of the gas barrier layer 14. By laminating 15 to form the laminated gas barrier layer 16, the fine defect portion D1 can be sealed and the corrosion resistance can be further improved. The thickness of the conductive carbon film 15 is 20 nm or more in consideration of its effect, and 500 nm or less in consideration of productivity. It is preferably 30 to 200 nm. If the thickness is 10 nm or less, the effect of the gas barrier layer cannot be sufficiently obtained, and if it is 300 nm or more, the film forming time becomes long, which is disadvantageous in terms of productivity.

Further, the conductive carbon film 15 plays a role of improving corrosion resistance and reducing the contact resistance of the contact interface with the GDL electrodes 1 and 2. The resistivity of the conductive carbon film, for example, DLC (diamond-like carbon), varies depending on the manufacturing method. The DLC film formed at room temperature has an amorphous structure and becomes a high resistance film close to an insulator, but the DLC film formed at a substrate temperature of 300 ° C. or higher contains a large number of microcrystals having sp2 hybrid orbitals. DLC film is obtained. Since the GDL electrodes 1 and 2 are also graphite having sp2 hybrid orbitals, the contact resistance between the two can be reduced by using a low resistance DLC film. The current generated in the cell 4 flows through the separator 110. Therefore, it is desirable that the material has a sufficiently small electrical resistance of the conductive carbon film itself and the contact resistance at the contact interface between the two. For example, it is desirable that the resistance value per unit area in the thickness direction of the conductive carbon film is 1 mΩ or less, and the contact resistance at the interface is 5 mΩ · cm ^{2 or less.}

The smaller the resistivity of the conductive carbon film 15, the more preferable it is, but the minimum value of the resistivity of the conductive carbon film is about 1 mΩ · cm. The preferred range of the resistivity of the conductive carbon film is 1 mΩ · cm to 10 Ω · cm, and the more preferable range is 1 mΩ · cm to 1 Ω · cm. This is because if the resistivity of the conductive carbon film is too large, the internal resistance of the fuel cell becomes large and the power loss becomes large, which is not practical.

In the present specification, it is assumed that the resistivity of the conductive carbon film is 10 Ω · cm or less. Further, not only a high-purity carbon film but also a carbon film containing a required amount of impurity elements such as nitrogen and boron may be used. The conductive carbon film can be formed by a direct current discharge of a working gas containing a hydrocarbon gas or a plasma CVD method using a high frequency discharge. The resistivity of the conductive carbon film depends on the substrate temperature at the time of film formation, and a suitable substrate temperature is 150 to 400 ° C.

In the step of carrying out the metal separator 110 according to the present invention, after forming the laminated gas barrier layer 16 on the surface of the sheet-shaped metal base material 11, the uneven groove shape 6 serving as a gas flow path using this metal base material, Molding press processing is performed on the separator 110 having 7 and the like. When the press working is performed, the titanium metal layer 13 is also stretched along with the stretching of the metal base material 11, so that the titanium metal layer is not peeled or cracked. D2 may occur. The corrosion-resistant film 17 seals these penetrating defects and suppresses corrosion of the surface of the metal base material and elution of metal ions.

Therefore, it is desirable that the corrosion-resistant film 17 has a corrosion-resistant function equivalent to that of the laminated gas barrier layer 16. Specifically, the oxide film of the metal base material or the conductive carbon film can be mentioned. A metal substrate, for example, by exposing the surface of the mixing layer of the fine through holes or through defects shown in FIG. 2 or the exposed surface of the metal substrate in a high-concentration ozone atmosphere at room temperature or in a plasma containing oxygen, for example. A dense oxidative passivation film can be formed on the surface of the SUS substrate or the surface of the titanium metal, and the elution of metal ions can be reduced. It is considered that this is because the activation energy of the passivation film increases, and as a result, the electrochemical oxygen-consuming moisturizing reaction is suppressed.
According to the implementation results of the inventors, the elution of metal ions can be reduced to an allowable value or less, and the contact resistance at the interface between the conductive carbon film and the GDL is reduced to 1 ^{to 5 mΩ · cm 2.} I was able to.

Further, the corrosion resistant film is not specified as a metal oxide or a conductive carbon film, and may be a metal carbide such as chromium or titanium, or a metal nitride. These corrosion-resistant films can be formed by a plasma carburizing method, an ion implantation method, or the like while maintaining the substrate temperature at 200 to 400 ° C. in a plasma containing a hydrocarbon gas or a nitrogen compound gas.

Although the typical embodiments have been described above, the present invention is not limited to the above embodiments unless the gist thereof is changed. Further, the technique disclosed in the present invention can also be applied to a metal separator molded as a separator. That is, the order of the implementation step 1 and the implementation step 2 is reversed, and the sheet-shaped metal base material 11 is preformed into a separator 110 having uneven grooves 6, 7 and the like serving as a gas flow path, and the surface thereof is formed. The titanium metal layer 13 and the laminated gas barrier layer 16 are formed. Further, if necessary, a corrosion-resistant film 17 can be formed on the penetration defect portion existing in the laminated gas barrier layer 16 to put into practical use a metal separator having excellent corrosion resistance.

1, 2 Gas diffusion member 11 Metal base material 12 Mixing layer 13 Titanium metal layer 14 Gas barrier layer 15 Conductive carbon film 16 Laminated barrier layer 17 Corrosion resistant film 110 Separator D1 Fine defect part D2 Penetration defect part

Claims (8)

It has a laminated gas barrier layer composed of a titanium metal layer on the surface layer of the metal base material, a gas barrier layer containing titanium carbide or titanium nitride on the surface of the titanium metal layer, and a conductive carbon film laminated on the surface of the gas barrier layer. A separator for fuel cells
A fuel cell separator characterized by having a mixing layer composed of a base metal and the titanium metal at a bonding interface between the metal base material and the titanium metal layer. The fuel cell separator according to claim 1, wherein the mixing layer has a thickness of 20 to 200 nm. The separator for a fuel cell according to claim 1 or 2, wherein the titanium metal layer has a thickness of 50 nm to 5 μm. The separator for a fuel cell according to any one of claims 1 to 3, wherein the conductive carbon film has a thickness of 20 to 500 nm and a resistivity of 0.01 to 10 Ω · cm. The invention according to any one of claims 1 to 4, wherein a corrosion-resistant film made of a metal oxide and / and a conductive carbon film is provided on the surface of the metal base material of the penetration defect portion remaining in the gas barrier layer. Separator for fuel cells. The method for producing a fuel cell separator according to claims 1 to 5, which is obtained in steps 1 and 1 of forming the titanium metal layer and the laminated gas barrier layer on the surface of the sheet-shaped metal base material. Manufacture of a fuel cell separator, which comprises a step 2 of molding a metal base material into a fuel cell separator and a step 3 of forming a corrosion-resistant film on a penetration defect portion existing in the laminated gas barrier layer. Method. A titanium metal thin layer is formed on the surface of the metal base material, and the metal thin layer is irradiated with argon ions accelerated to 3 to 20 keV or a mixed ion of argon and titanium to form the mixing layer, and the mixing layer is formed. The method for manufacturing a fuel cell separator according to claim 6, wherein a titanium metal layer is formed on the surface. In the step of forming the corrosion-resistant film, the separator base material temperature is maintained at room temperature to 400 ° C. in a gas containing ozone or in a plasma containing any one of oxygen, hydrocarbon gas, nitrogen and nitrogen compound gas. The method for producing a separator for a fuel cell according to claim 6 or 7, wherein the surface is modified.

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