JP2022035419A - Fuel cell separator - Google Patents

Abstract

To provide a method which can manufacture a fuel cell separator having high conductivity and excellent corrosion resistance.SOLUTION: There is provided a manufacturing method of a fuel cell separator comprising at least: a metal base; and a carbon nanotube (CNT)-containing layer which is formed on the metal base and contains CNT. The manufacturing method includes steps of: preparing the metal base; providing, on the metal base, slurry which contains at least silicon alkoxide, the CNT, a dispersant, and a solvent; and forming the CNT-containing layer by heating and curing, in a non-oxidizing atmosphere, the metal base provided with the slurry.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a fuel cell separator.

Fuel cells obtain electromotive force by electrochemically reacting hydrogen and oxygen. In principle, water is the only product produced by the power generation of fuel cells. Therefore, it is attracting attention as a clean power generation system with almost no load on the global environment.

The fuel cell is configured with a membrane electrode assembly (hereinafter, also referred to as "MEA") in which electrode catalyst layers are arranged on both sides of the electrolyte membrane as a basic unit. During operation of the fuel cell, a fuel gas containing hydrogen is supplied to the electrode catalyst layer on the anode (fuel electrode) side, and an oxidation gas containing oxygen is supplied to the electrode catalyst layer on the cathode (air electrode) side. To get. An oxidation reaction proceeds at the anode and a reduction reaction proceeds at the cathode, supplying electromotive force to an external circuit.

In a fuel cell, usually, a gas diffusion layer is arranged outside each electrode catalyst layer of the MEA, and a separator is further arranged outside the gas diffusion layer to form a fuel cell. The fuel cell is usually used as a combination of a plurality of required fuel cell cells (hereinafter, also referred to as "fuel cell stack") based on a desired electric power.

The separator not only shuts off the fuel gas and air supplied to each fuel cell, but also functions as a current transmission unit to the outside. Therefore, the separator is required to have not only airtightness but also conductivity, corrosion resistance and thermal conductivity. Conventionally, a carbon base material has been used for the separator, but in recent years, a material in which a conductive film is arranged on the surface of a metal base material is also used in order to secure high conductivity.

As the fuel cell separator, for example, Patent Document 1 is a fuel cell separator provided with a metal base material and a surface layer provided on the surface of the metal base material, and the surface layer includes a carbon-based conductive material and Si. A fuel cell separator containing a system binder and having a surface coverage of the carbon-based conductive material of 90% or more and a Si-based binder ratio of 40% or more in the surface layer. It is disclosed. Patent Document 1 describes that high conductivity can be ensured by a carbon-based conductive material.

Japanese Unexamined Patent Publication No. 2019-133838

As described above, the fuel cell separator is required to have high conductivity in order to enhance the power generation performance of the fuel cell. Specifically, it is important for the fuel cell separator to reduce the contact resistance between the separator and the adjacent electrode or the contact resistance between the separator and the adjacent gas diffusion layer. In addition, high conductivity means that the contact resistance is low. Further, the fuel cell separator is required to have excellent corrosion resistance in addition to high conductivity. That is, since the fuel cell separator is in contact with low pH generated water (corrosive liquid) containing chloride ions and fluoride ions during use, the fuel cell separator is durable even in such a corrosive environment. It is required to have. As described above, Patent Document 1 discloses a fuel cell separator in which a surface layer containing a carbon-based conductive material and a Si-based binder is formed on a metal base material, but further improvement is made from the viewpoint of corrosion resistance. There was room.

Therefore, an object of the present disclosure is to provide a method capable of producing a fuel cell separator having high conductivity and excellent corrosion resistance.

The present disclosure includes the following embodiments.

(1) A method for manufacturing a fuel cell separator, comprising at least a metal base material and a CNT-containing layer formed on the metal base material and containing carbon nanotubes (CNTs).
The process of preparing a metal base material,
A step of arranging a slurry containing at least silicon alkoxide, CNT, a dispersant and a solvent on a metal substrate, and heating and curing the metal substrate on which the slurry is arranged in a non-oxidizing atmosphere to form a CNT-containing layer. A method for manufacturing a fuel cell separator, which comprises a step of making a fuel cell separator.
(2) The method for manufacturing a fuel cell separator according to (1), wherein the surface coverage of CNTs in the CNT-containing layer is 90% or more.
(3) The method for manufacturing a fuel cell separator according to (1) or (2), wherein the CNT-containing layer has a film thickness of 1 to 2 μm.
(4) The method for manufacturing a fuel cell separator according to any one of (1) to (3), wherein the non-oxidizing atmosphere is an inert gas atmosphere or a vacuum atmosphere.
(5) The method for manufacturing a fuel cell separator according to (4), wherein the inert gas atmosphere is a nitrogen gas atmosphere or an Ar gas atmosphere.
(6) Furthermore
It includes a step of arranging a titanium-containing layer on a metal substrate and a step of arranging a carbon layer on the titanium-containing layer.
The method for manufacturing a fuel cell separator according to any one of (1) to (5), wherein the slurry is arranged on a carbon layer.
(7) Furthermore
Including the step of arranging the silver-containing layer on the metal substrate,
The method for producing a fuel cell separator according to any one of (1) to (5), wherein the slurry is arranged on the silver-containing layer.

According to the configuration of the present disclosure, it is possible to provide a method capable of producing a fuel cell separator having high conductivity and excellent corrosion resistance.

It is a schematic sectional drawing which shows the structural example of the fuel cell separator manufactured by the manufacturing method of this embodiment. It is a schematic sectional drawing which shows the structural example of the fuel cell separator manufactured by the manufacturing method of this embodiment. It is a schematic sectional drawing which shows the structural example of the fuel cell separator manufactured by the manufacturing method of this embodiment.

The present embodiment is a method for manufacturing a fuel cell separator, which comprises at least a metal base material and a CNT-containing layer formed on the metal base material and containing carbon nanotubes (CNTs), and prepares the metal base material. A step of arranging a slurry containing at least silicon alkoxide, CNT, a dispersant and a solvent on a metal substrate, and a step of arranging the metal substrate on which the slurry is arranged by heating in a non-oxidizing atmosphere to cure the CNT-containing layer. It is a method of manufacturing a fuel cell separator including a step of forming the above.

The present embodiment can provide a method capable of producing a fuel cell separator having high conductivity and excellent corrosion resistance. Specifically, in the present embodiment, the CNT-containing layer is formed by heating and curing the slurry containing silicon alkoxide and CNT in a non-oxidizing atmosphere. By firing the CNT-containing layer in a non-oxidizing atmosphere, decomposition of the binder can be suppressed, and the denseness of the membrane and the liquid permeation barrier property can be improved. As a result, the permeation of the generated water can be suppressed, and the elution of metal ions from the metal substrate can be suppressed. Therefore, according to this embodiment, it is possible to manufacture a fuel cell separator having high conductivity and excellent corrosion resistance.

Hereinafter, a method for manufacturing a fuel cell separator according to the present embodiment will be described.

FIG. 1 is a schematic cross-sectional view for explaining the configuration of the fuel cell separator 100 manufactured by one aspect of the present embodiment. In FIG. 1, the fuel cell separator 100 includes a metal base material 101 and a CNT-containing layer 102 arranged on the metal base material 101. The CNT-containing layer 102 includes a matrix layer 104 composed of carbon nanotubes (CNTs) 103 and silicon alkoxide.

(Base material preparation process)
The manufacturing method according to the present embodiment includes a step of preparing a metal base material.

The metal constituting the metal base material is not particularly limited, and examples thereof include iron, aluminum, and alloys thereof. These materials can be preferably used from the viewpoints of mechanical strength, versatility, cost performance, ease of processing and the like. Iron alloys may include stainless steel. In the present embodiment, the metal base material is preferably a stainless steel base material. The stainless steel base material is excellent in cost performance, and it is easy to sufficiently secure the conductivity of the contact surface with the gas diffusion layer or the like. The stainless steel substrate is not particularly limited, and examples thereof include austenitic stainless steel, ferritic stainless steel, austenitic / ferrite two-phase stainless steel, martensitic stainless steel, and precipitation hardening stainless steel.

The thickness of the metal base material is appropriately selected in consideration of ease of processing, mechanical strength, and improvement of battery energy density by thinning the separator, and is, for example, 0.05 to 0.5 mm. be. When the thickness is within this range, it is easy to satisfy the demands for weight reduction and thinning of the separator, and it has strength and handleability as a separator material. Therefore, it is relatively easy to press the separator material into the shape of the separator. The shape of the metal base material may be a long strip wound in a coil shape or a sheet of paper cut to a predetermined size.

(Applying process)
The production method according to the present embodiment includes a step of arranging a slurry containing at least silicon alkoxide, CNT, a dispersant and a solvent on a metal substrate.

In the present embodiment, the CNT-containing layer is preferably formed by using the sol-gel method. By using the sol-gel method, a CNT-containing layer having excellent durability can be obtained, and CNTs can be well dispersed and fixed in the CNT-containing layer.

CNT means a carbon material having a cylindrical structure on a single-walled surface of graphite. Usually, a CNT having a single-layer tubular structure is a single-walled CNT, a CNT having a two-layer tubular structure is a two-walled CNT, and a CNT having three or more tubular structures is a multi-walled CNT. , Can be classified individually. Normally, in a conductive film containing CNTs, the conductivity can be improved as the number of layers of CNTs increases. The CNT contained in the CNT-containing layer may have any of the above-mentioned structures.

CNTs can contribute to stable contact resistance. Further, the CNTs can be uniformly dispersed over the entire CNT-containing layer by using a dispersant. The length of the CNT is preferably 1 μm to several tens of μm. The length of the CNT is preferably 1 μm to 90 μm. When the length of the CNT is 1 μm or more, the conductive path increases and the contact resistance tends to decrease. When the length of the CNT is 90 μm or less, the aggregation of the CNT can be suppressed, and as a result, the CNT can be easily dispersed uniformly.

The content of the CNTs in the slurry is preferably adjusted so that the surface coverage of the CNTs in the obtained CNT-containing layer is 90% or more. That is, the surface coverage of CNTs in the CNT-containing layer is preferably 90% or more. When the surface coverage of CNTs in the CNT-containing layer is 90% or more, the electron conductive path can be effectively secured and the contact resistance can be lowered. Therefore, the fuel cell separator of this embodiment can have high conductivity by providing the CNT-containing layer containing the CNTs having the surface coverage in the above range.

The surface coverage of CNTs in the CNT-containing layer is not limited, but can be measured by the following procedure. The surface of the fuel cell separator is observed using a laser microscope. The observed image is binarized from the viewpoint of the presence or absence of CNT, and the ratio covered by CNT is calculated as the coverage ratio (area%).

The silicon alkoxide (alkoxysilane) is not particularly limited, but for example, tetraethoxysilane [Si (OC ₂ H ₅ ) ₄ ], tetramethoxysilane [Si (OCH ₃ ) ₄ ], and methyltriethoxysilane. [CH ₃ Si (OC ₂ H ₅ ) ₃ ], Methyltrimethoxysilane [CH ₃ Si (OCH ₃ ) ₃ ], Ethylmethoxysilane [C ₂ H ₅ Si (OCH ₃ ) ₃ ], or Ethyltriethoxysilane [ C ₂ H ₅ Si (OC ₂ H ₅ ) ₃ ] and the like can be mentioned. Preferably, it is tetraethoxysilane or tetramethoxysilane. The silicon alkoxide may be used alone or in combination of two or more.

The dispersant includes a dispersant having a function of dispersing CNTs. Examples of the dispersant include anionic surfactants, cationic surfactants, amphoteric surfactants, nonionic surfactants and the like. As the dispersant, one type may be used alone, or two or more types may be used in combination.

The solvent is not particularly limited as long as it dissolves silicon alkoxide. It is preferable to use alcohol as the solvent. Examples of the alcohol include methanol, ethanol, isopropyl alcohol, n-propyl alcohol, isobutyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, diacetone alcohol and the like. Ethanol is preferred. The solvent may contain water to accelerate the reaction of the silicon alkoxide. By containing water, hydrolysis can proceed and the reaction can be promoted. The solvent is preferably a mixed solvent of alcohol and water.

The slurry may contain other resins in addition to the silicon alkoxide. Examples of other resins include epoxy resins, acrylic resins, phenolic resins, urethane resins, melamine resins, fluororesins and the like. These may be used individually by 1 type and may be used in combination of 2 or more type. Such a resin can also contain a curing agent for accelerating the curing of the CNT-containing layer. The slurry preferably contains an epoxy resin. By containing the epoxy resin, the adhesion between the CNT-containing layer and the base material can be improved.

In one embodiment, a slurry may be prepared using a Si-based binder solution containing silicon alkoxide and a solvent. When a Si-based binder solution is used, a slurry can be easily prepared by adding CNT and a dispersant to the Si-based binder solution and mixing them. The Si-based binder solution preferably contains silicon alkoxide as a main component. The main component means a component present in the highest content in the slurry. In some cases, the Si-based binder solution preferably contains silicon alkoxide as a main component in the components other than the solvent contained in the Si-based binder solution. The Si-based binder may contain other resins in addition to the silicon alkoxide. Examples of other resins include those described above. The content of the Si-based binder solution in the slurry is preferably 40% by mass or more, preferably in the range of 40 to 60% by mass. When the content of the Si-based binder solution is 40% by mass or more, the permeation of the corrosive liquid can be effectively inhibited in the environment where the fuel cell is used. As the permeation of the corrosive liquid progresses, an oxide film may grow on the interface between the metal substrate and the surface treatment film, and the contact resistance between the separator and the GDL may increase. Therefore, by setting the content of the Si-based binder solution to 40% by mass or more, corrosion resistance can be effectively imparted to the fuel cell separator.

The slurry can be prepared by uniformly dispersing the predetermined material by means commonly used in the art such as a dissolver or a bead mill.

Examples of the slurry coating method include a dipping coating method, a spin coating method, a bar coater coating method, a spray coating method, and the like.

The coating film of the slurry is usually subjected to a drying treatment for removing volatile substances such as a solvent prior to the subsequent firing step.

(Baking process)
The production method according to the present embodiment includes a step of heating and curing the metal substrate on which the slurry is arranged in a non-oxidizing atmosphere to form a CNT-containing layer.

In this embodiment, firing is performed in a non-oxidizing atmosphere. By firing in a non-oxidizing atmosphere, decomposition of the membrane constituents can be suppressed, the denseness of the membrane can be improved, and as a result, the barrier property against liquid permeation can be improved. Therefore, the CNT-containing layer obtained in the present embodiment suppresses the permeation of the generated water, and as a result, the elution of metal ions from the metal substrate can be suppressed.

The non-oxidizing atmosphere is, for example, an inert gas atmosphere or a vacuum atmosphere. Examples of the inert gas atmosphere include a nitrogen gas atmosphere and an Ar gas atmosphere.

The heating temperature is not particularly limited, but is, for example, 250 ° C. or higher and 450 ° C. or lower. The heating temperature is preferably 310 ° C. or higher and 400 ° C. or lower, and preferably 320 ° C. or higher. In the present embodiment, since the film is heated in a non-oxidizing atmosphere, decomposition of film constituents such as resin can be suppressed even if the heating temperature is raised. When the heating temperature is 310 ° C. or higher, the dispersant can be efficiently volatilized or decomposed, and the residue of the dispersant in the CNT-containing layer can be suppressed. As a result, the conductive network of CNTs is not disturbed, and low contact resistance can be obtained. Further, when the heating temperature is 400 ° C. or lower, thermal deterioration of the resin can be suppressed. As a result, the water resistance and corrosion resistance of the CNT-containing layer can be improved.

The heating time is not particularly limited, but is, for example, in the range of 5 to 30 minutes. When the heating time is 5 minutes or more, the silicon alkoxide can be sufficiently cured. Further, when the heating time is 30 minutes or less, deterioration of the silicone alkoxide resin can be prevented.

The firing can be performed using, for example, a firing furnace.

The film thickness of the obtained CNT-containing layer is preferably 1 to 2 μm. By setting the film thickness of the CNT-containing layer within this range, it is possible to suppress the production cost while ensuring high conductivity and excellent corrosion resistance.

Through the above steps, a fuel cell separator having high conductivity and excellent corrosion resistance can be obtained.

The obtained fuel cell separator has a contact resistance to GDL of preferably 10 mΩcm ² or less, and 5 mΩ cm ² or less. The contact resistance of the fuel cell separator to the GDL is not limited, but can be measured, for example, by the following procedure. The film-forming surface of the fuel cell separator and GDL are overlapped with each other, and a predetermined load (for example, 1 MPa) is applied. In that state, a predetermined current (for example, 1 A) is passed and the voltage between the separator and the GDL is measured. The measured voltage value is converted into a resistance value, and the evaluation area is further multiplied to calculate the contact resistance. Corrosion resistance evaluation can be performed assuming the environment in which the fuel cell is used. First, the fuel cell separator is immersed in a strongly acidic corrosive liquid. With the separator immersed, a potential of a predetermined (for example, 0.9V) constant voltage is applied between the separator and the electrode. After a lapse of a certain period of time, the contact resistance measured by the same procedure as described above is taken as the contact resistance value after the corrosion resistance test. The strong acid corrosive liquid used is, for example, a strong acid solution containing fluorine (F) and chlorine (Cl) at pH 3.

One embodiment of the present embodiment further comprises a step of arranging the titanium-containing layer on the metal substrate and a step of arranging the carbon layer on the titanium-containing layer, and the slurry is arranged on the carbon layer. To. That is, one embodiment of the present embodiment includes a step of preparing a metal base material, a step of arranging a titanium-containing layer on the metal base material, a step of arranging a carbon layer on the titanium-containing layer, silicon alkoxide, CNT, and the like. It includes a step of arranging a slurry containing at least a dispersant and a solvent on a carbon layer, and a step of heating and curing the metal substrate on which the slurry is arranged in a non-oxidizing atmosphere to form a CNT-containing layer. As in this embodiment, an intermediate layer composed of a titanium-containing layer containing titanium (Ti) and a carbon layer containing carbon (C) is arranged on the surface of a metal base material, and CNTs containing CNTs are further arranged on the surface of the intermediate layer. By arranging the content layer, a fuel cell separator having reduced contact resistance with GDL can be obtained even in a corrosive environment. Therefore, the fuel cell separator having such a configuration can have high conductivity and excellent corrosion resistance.

FIG. 2 is a schematic cross-sectional view for explaining the configuration of the fuel cell separator 200 manufactured according to the embodiment. In FIG. 2, the fuel cell separator 200 includes a metal base material 201, a titanium-containing layer 205 arranged on the metal base material 201, a carbon layer 206 arranged on the titanium-containing layer 205, and a carbon layer 206. Includes the CNT-containing layer 202 disposed above. The CNT-containing layer 202 includes a matrix layer 204 composed of carbon nanotubes (CNT) 203 and silicon alkoxide.

In the fuel cell separator of this embodiment, the titanium-containing layer contains titanium or a titanium alloy, and may optionally contain carbon or nitrogen. Examples of the metal that can be contained in the titanium alloy include aluminum, niobium, tantalum, vanadium, palladium, or a combination thereof, in addition to titanium. Specifically, examples of the titanium alloy include Ti-Al, Ti-Nb, Ti-Ta, Ti-6Al-4V, Ti-Pd and the like. The titanium-containing intermediate layer is preferably formed on the metal substrate directly, that is, in contact with the metal substrate. By providing the titanium-containing layer, in the fuel cell separator of this embodiment, the elution of metal ions derived from the metal substrate can be suppressed, and the fuel cell separator can be bonded to the carbon layer containing carbon (C) with high affinity. can. For example, in the fuel cell separator of this embodiment, when stainless steel is used as the material constituting the metal base material, by providing the titanium-containing layer, the corrosive liquid permeates and the iron ions are eluted in the fuel cell usage environment, and the fuel is fueled. It is possible to suppress the poisoning of the power generation film in the battery cell. Further, since titanium and stainless steel have a high affinity, the distance between the metal base material and the titanium-containing layer is higher than in the case where a carbon-containing carbon layer or a CNT-containing layer is arranged on the surface of the metal base material. It can be joined by affinity. Therefore, by providing the titanium-containing layer having the above-mentioned characteristics, the fuel cell separator of this embodiment can have high conductivity and corrosion resistance.

The film thickness of the titanium-containing layer is preferably in the range of 30 to 500 nm, and more preferably in the range of 100 to 200 nm. When the thickness of the titanium-containing layer is 30 nm or more, the resistance at the interface between the metal substrate and the CNT-containing layer containing CNT can be effectively suppressed. Further, when the film thickness of the titanium-containing layer is 500 nm or less, it is possible to effectively suppress the decrease in the adhesion to the metal substrate due to the increase in the film stress.

In the fuel cell separator of this embodiment, the carbon layer contains carbon (C). Since carbon has high acid resistance, it is possible to suppress an increase in contact resistance in the fuel cell separator of this embodiment by providing a carbon layer containing carbon. For example, by providing the carbon layer in the fuel cell separator of the present embodiment, even if the corrosive liquid permeates to the carbon layer in the fuel cell usage environment, deterioration of the surface of the metal base material and the titanium-containing layer can be suppressed. Therefore, by providing the carbon layer, the fuel cell separator of this embodiment can have high conductivity. The carbon layer is preferably formed on the titanium-containing layer directly, that is, in contact with the titanium-containing layer.

The film thickness of the carbon layer is preferably in the range of 10 to 500 nm, and more preferably in the range of 30 to 50 nm. When the film thickness of the carbon layer is 10 nm or more, an increase in resistance at the interface between the metal substrate and the CNT-containing layer containing CNT can be effectively suppressed. Further, when the film thickness of the carbon layer is 500 nm or less, an increase in film stress can be effectively suppressed.

The method for forming the titanium-containing layer and the carbon layer is not particularly limited, but is, for example, a physical vapor deposition (PVD) method such as a sputtering method or an ion plating method, or a filtered cascade vacuum arc (filtered cascade vacuum arc). Examples thereof include an ion beam vapor deposition method such as the FCVA) method. Examples of the sputtering method include a magnetron sputtering method, an unbalanced magnetron sputtering (UBMS) method, a dual magnetron sputtering method, an ECR sputtering method and the like. Moreover, as an ion plating method, an arc ion plating method and the like can be mentioned. Above all, it is preferable to use the sputtering method or the ion plating method. According to these methods, a carbon layer having a low hydrogen content can be formed. As a result, the ratio of bonds between carbon atoms (sp2 hybrid carbon) can be increased, and excellent conductivity can be achieved.

Further, in the sputtering method, it is also possible to control the film quality obtained by controlling the bias voltage and the like. When the titanium-containing layer and the carbon layer are formed by a sputtering method, a negative bias voltage may be applied to the metal substrate during sputtering. Thereby, the titanium-containing layer or the carbon layer can be formed densely, and the corrosion resistance can be enhanced. The magnitude of the negative bias voltage applied during the formation of the carbon layer is not particularly limited, but is, for example, 5 to 50 V or 10 to 40 V.

By carrying out each step described above, a fuel cell separator having high conductivity and excellent corrosion resistance can be obtained.

One embodiment of the present embodiment further comprises the step of arranging the silver-containing layer on the metal substrate, and the slurry is arranged on the silver-containing layer. That is, one aspect of the present embodiment is a step of preparing a metal base material, a step of arranging a silver-containing layer on the metal base material, and a slurry containing at least silicon alkoxide, CNT, a dispersant and a solvent in the silver-containing layer. It includes a step of arranging on the top and a step of heating and curing the metal substrate on which the slurry is placed in a non-oxidizing atmosphere to form a CNT-containing layer. Since the silver-containing layer has excellent conductivity, an intermediate layer made of a silver-containing layer is arranged on the surface of the metal base material as in this embodiment, and a CNT-containing layer containing CNT is further provided on the surface of the intermediate layer. By arranging the fuel cell separator, a fuel cell separator having reduced contact resistance with the GDL can be obtained even in a corrosive environment. Therefore, the fuel cell separator having such a configuration can have high conductivity and excellent corrosion resistance.

FIG. 3 is a schematic cross-sectional view for explaining the configuration of the fuel cell separator 300 manufactured according to the embodiment. In FIG. 3, the fuel cell separator 300 includes a metal base material 301, a silver-containing layer 307 arranged on the metal base material 301, and a CNT-containing layer 302 arranged on the silver-containing layer 307. The CNT-containing layer 302 includes a matrix layer 304 composed of carbon nanotubes (CNT) 303 and silicon alkoxide.

The silver-containing layer contains silver or a silver alloy, and preferably contains carbon or nitrogen. When the silver-containing layer contains a silver alloy, examples of the metal forming the alloy include gold, copper, tin, and the like.

The film thickness of the silver-containing layer is preferably 10 nm to 500 nm, preferably 20 to 200 nm. When the film thickness of the silver-containing layer is 10 nm or more, an increase in resistance at the interface between the metal substrate and the CNT-containing layer can be effectively suppressed. Further, when the film thickness of the silver-containing layer is 500 nm or less, an increase in film stress can be effectively suppressed.

The silver-containing layer can be formed by, for example, a physical vapor deposition (PVD) method such as a plating method, a sputtering method or an ion plating method. Among them, the plating method is preferable, and in this case, the silver-containing layer includes silver plating or silver alloy plating. Contact resistance can be reduced by providing a silver-containing layer containing silver or a silver alloy. For example, when stainless steel is used as a material constituting a metal base material, the contact resistance can be suppressed as compared with the interface with the stainless steel inactive film by providing a silver-containing layer containing silver or a silver alloy. Therefore, by forming the silver-containing layer having the above-mentioned characteristics, it is possible to provide a fuel cell separator having high conductivity and excellent corrosion resistance.

By carrying out each step described above, a fuel cell separator having high conductivity and excellent corrosion resistance can be obtained.

Hereinafter, this embodiment will be described with reference to examples. However, the technical scope of the present disclosure is not limited to these examples.

[Example 1]
First, CNT and a dispersant were added to the Si-based binder solution and mixed to prepare a slurry. Regarding the composition of the slurry, the content of the Si-based binder solution was 60% by mass, the content of CNT was 20% by mass, and the content of the dispersant was 20% by mass. Next, a titanium-containing layer was formed on the surface of the metal substrate (stainless steel substrate) by the PVD method. Next, a carbon layer was formed on the surface of the titanium-containing layer by the PVD method. Next, the slurry was applied to the surface of the carbon layer and heated at 370 ° C. for 30 minutes in a nitrogen gas atmosphere to cure the coating film. Through the above steps, the fuel cell separator E1 was obtained. The thickness of the titanium-containing layer was 170 nm, and the film thickness of the carbon layer was 30 nm. The film thickness of the CNT-containing layer was 2 μm.

[Example 2]
The fuel cell separator E2 was produced in the same manner as in Example 1 except that the amount of the slurry applied was reduced. The film thickness of the CNT-containing layer was 1 μm.

[Comparative Example 1]
A fuel cell separator C1 was produced in the same manner as in Example 1 except that the fuel cell was heated at 300 ° C. in an atmospheric atmosphere.

[Comparative Example 2]
The fuel cell separator C2 was produced in the same manner as in Comparative Example 1 except that the amount of the slurry applied was reduced. The film thickness of the CNT-containing layer was 1 μm.

[analysis]
(Measurement of CNT surface coverage)
The surface of the separator of each sample was observed using a laser microscope. The observed image was binarized from the viewpoint of the presence or absence of CNT, and the ratio covered by CNT was calculated as the coverage ratio (area%).

[evaluation]
(Contact resistance)
The film-forming surface of the separator of each sample and GDL (manufactured by Toray Industries, Inc., TGP-H-060) were overlapped and a load of 1 MPa was applied. In that state, a current of 1 A was applied and the voltage between the separator and the GDL was measured. The measured voltage value was converted into a resistance value, and the evaluation area was further multiplied to calculate the initial contact resistance.

(Corrosion resistance)
The corrosion resistance test was conducted assuming a fuel cell usage environment. First, the separator of each prepared sample was immersed in a strong acid corrosive solution. With the separator immersed, a constant voltage of 0.9 V was applied between the separator and the electrode. After 60 hours, the separator was removed from the corrosive liquid. The strong acid corrosive liquid used was a strong acid solution containing fluorine (F) and chlorine (Cl) at pH 3.

Regarding the contact resistance after the corrosion resistance test, the contact resistance of the separator after the corrosion resistance test was measured by the same procedure as described above.

Regarding the elution amount of metal ions, iron ions were targeted in this test example. The elution amount (μg) of metal ions per unit volume (L) in the corrosive liquid after the corrosion resistance test was measured by ICP-MS (inductively coupled plasma mass spectrometry) and converted into mol amount. The elution amount of the metal ion (mol) was gradually increased by the evaluation area (cm ² ) and the time (hr), and multiplied by the amount of the corrosive liquid (L) to calculate the elution amount of the metal ion.

[Results and discussion]
Production conditions (firing atmosphere, firing temperature) when preparing the separator for each sample, film thickness of the CNT-containing layer of the obtained separator, surface coverage, initial contact resistance, contact resistance after corrosion resistance test, metal ion elution amount. The results are shown in Table 1.

As shown in Table 1, good initial contact resistance and contact resistance after the corrosion resistance test were obtained in all the examples, but in Comparative Examples 1 and 2 in which the CNT-containing layer was formed by firing in an air atmosphere, the metal was obtained. While the amount of ion elution was relatively large, the amount of metal ion elution was small in Examples 1 and 2 in which the CNT-containing layer was formed by firing in a nitrogen gas atmosphere. Further, even when compared in Example 1 and Comparative Example 1 having the same CNT-containing layer thickness (2 μm), the amount of metal ion elution of Example 1 in which the CNT-containing layer was formed by firing in a nitrogen gas atmosphere. It was smaller than the amount of metal ion elution of Comparative Example 1 in which the CNT-containing layer was formed by firing in an air atmosphere. Similarly, when compared with Example 2 and Comparative Example 2 having the same CNT-containing layer thickness (1 μm), the metal ions of Example 2 formed by firing in a nitrogen gas atmosphere to form a CNT-containing layer. The elution amount was smaller than the metal ion elution amount of Comparative Example 2 in which the CNT-containing layer was formed by firing in an air atmosphere. From this, it can be seen that by heating in a non-oxidizing atmosphere such as nitrogen gas to form a CNT-containing layer, not only high conductivity but also excellent corrosion resistance can be imparted.

[Example 3]
First, CNT and a dispersant were added to the Si-based binder solution and mixed to prepare a slurry. Regarding the composition of the slurry, the content of the Si-based binder solution was 60% by mass, the content of CNT was 20% by mass, and the content of the dispersant was 20% by mass. Next, a silver-containing layer was formed on the surface of the metal substrate (stainless steel substrate) by a plating method. Next, the slurry was applied to the surface of the silver-containing layer and heated at 370 ° C. for 30 minutes in a nitrogen gas atmosphere to cure the coating film. Through the above steps, a fuel cell separator E3 was obtained. The film thickness of the silver-containing layer was 30 nm. The film thickness of the CNT-containing layer was 2 μm.

[Example 4]
The fuel cell separator E4 was produced in the same manner as in Example 3 except that the amount of the slurry applied was reduced. The film thickness of the CNT-containing layer was 1 μm.

[Comparative Example 3]
A fuel cell separator C3 was produced in the same manner as in Example 3 except that the fuel cell was heated at 300 ° C. in an atmospheric atmosphere. The film thickness of the CNT-containing layer was 3 μm.

[Comparative Example 4]
The fuel cell separator C4 was produced in the same manner as in Comparative Example 3 except that the amount of the slurry applied was reduced. The film thickness of the CNT-containing layer was 1 μm.

[analysis]
The surface coverage of CNTs was measured by the same method as described above.

[evaluation]
The initial contact resistance, the contact resistance after the corrosion resistance test, and the amount of metal ion elution were measured by the same method as described above.

[Results and discussion]
Production conditions (firing atmosphere, firing temperature) when preparing the separator for each sample, film thickness of the CNT-containing layer of the obtained separator, surface coverage, initial contact resistance, contact resistance after corrosion resistance test, metal ion elution amount. The results are shown in Table 2.

As shown in Table 2, similar to the results of Examples 1 and 2 and Comparative Examples 1 and 2 described above, good initial contact resistance and post-corrosion resistance test contact resistance were obtained in each of the examples, but the atmosphere. In Comparative Examples 3 and 4 in which the CNT-containing layer was formed by firing in an atmosphere, the amount of metal ions eluted was relatively large, while in Examples 3 and 4 in which the CNT-containing layer was formed by firing in a nitrogen gas atmosphere. The amount of metal ion elution was small. Further, even when compared in Example 4 and Comparative Example 4 having the same CNT-containing layer thickness (1 μm), the amount of metal ion elution of Example 4 in which the CNT-containing layer was formed by firing in a nitrogen gas atmosphere. It was smaller than the amount of metal ion elution of Comparative Example 4 in which the CNT-containing layer was formed by firing in an air atmosphere. From this, it can be seen that by heating in a non-oxidizing atmosphere such as nitrogen gas to form a CNT-containing layer, not only high conductivity but also excellent corrosion resistance can be imparted.

Although the present embodiment has been described in detail above, the specific configuration of the present disclosure is not limited to this embodiment, and even if there are design changes within the scope of the gist of the present disclosure, they are the present. It is included in the disclosure.

The present disclosure is not limited to the above-described embodiment, but includes various modifications. For example, the above-described embodiment has been described in detail in order to explain the present disclosure in an easy-to-understand manner, and is not necessarily limited to the one including all the configurations described. In addition, it is possible to add, delete, and / or replace a part of the configuration of each embodiment with another configuration.

The upper limit value and / or the lower limit value of the numerical range described in the present specification can be arbitrarily combined to specify a preferable range. For example, an upper limit value and a lower limit value of a numerical range can be arbitrarily combined to specify a preferable range, an upper limit value of a numerical range can be arbitrarily combined to specify a preferable range, and a lower limit of a numerical range can be specified. A preferable range can be defined by arbitrarily combining the values.

100: Fuel cell separator, 101: Metal substrate, 102: CNT-containing layer, 103: CNT, 104: Matrix layer, 200: Fuel cell separator, 201: Metal substrate, 202: CNT-containing layer, 203: CNT, 204 : Matrix layer, 205: Titanium-containing layer, 206: Carbon layer, 300: Fuel cell separator, 301: Metal substrate, 302: CNT-containing layer, 303: CNT, 304: Matrix layer, 307: Silver-containing layer

Claims (1)

A method for manufacturing a fuel cell separator, comprising: a metal substrate and a CNT-containing layer formed on the metal substrate and containing carbon nanotubes (CNTs).
The process of preparing a metal base material,
A step of arranging a slurry containing at least silicon alkoxide, CNT, a dispersant and a solvent on a metal substrate, and heating and curing the metal substrate on which the slurry is arranged in a non-oxidizing atmosphere to form a CNT-containing layer. A method for manufacturing a fuel cell separator, which comprises a step of making a fuel cell separator.

Images