JP7613340B2 - Manufacturing method of fuel cell separator - Google Patents

Description

This disclosure relates to a method for manufacturing a fuel cell separator.

A fuel cell has a structure in which a solid polymer electrolyte membrane is sandwiched between an anode electrode and a cathode electrode as a single cell. The fuel cell is also configured as a stack in which multiple single cells are stacked via separators (also called bipolar plates) that have grooves that serve as flow paths for gases (hydrogen, oxygen, etc.). The output of a fuel cell can be increased by increasing the number of cells per stack.

The separators for fuel cells also play a role in passing the generated electric current to the adjacent cell through the surface through which the cooling water flows. Therefore, the separator material that constitutes the separator must be electrically conductive.

As an example of a fuel cell separator, Patent Document 1 discloses a method for manufacturing a fuel cell separator in which a titanium film or titanium nitride film is formed on a substrate. Specifically, Patent Document 1 discloses a method for manufacturing a fuel cell separator, which includes a first step of preparing a substrate for a separator, and a second step of forming a Ti film or TiN film by a dry coating method while applying a bias voltage of a predetermined value or less to the surface of the separator substrate.

Patent Document 2 discloses a conductive member having a metal substrate layer and a conductive carbon layer containing conductive carbon located on at least one of the main surfaces of the metal substrate layer, in which the intensity ratio R (I _D /I _G ) of the D band peak intensity (I _D ) to the G band peak intensity (I _G ) measured by Raman scattering spectroscopy of the conductive carbon layer is 1.3 or more. Patent Document 2 also discloses a form in which a columnar structure intermediate layer is interposed between the metal substrate layer and the conductive carbon layer (e.g., claim 3), and titanium is listed as the material of the intermediate layer.

JP 2008-34113 A JP 2010-153353 A

In fuel cell separators, a metal substrate having an uneven flow path shape is used to form grooves that serve as flow paths. Here, the inventors have found that when a titanium layer made of titanium is formed on a metal substrate having an uneven flow path shape by a sputtering method, a difference occurs between the thickness of the titanium layer formed on the convex parts and the thickness of the titanium layer formed on the concave parts. Specifically, they have found that the thickness of the titanium layer formed on the concave parts is smaller than the thickness of the titanium layer formed on the convex parts. From the viewpoint of corrosion resistance, it is desirable to ensure that the thickness of the titanium layer formed on the concave parts is also at least a certain level. However, if the thickness of the titanium layer formed on the concave parts is increased, the thickness of the titanium layer formed on the convex parts will also be larger than necessary, which will lead to increased costs. Therefore, there has been a demand for the development of a titanium layer forming method that can bring the thickness of the titanium layer formed on the concave parts closer to the thickness of the titanium layer formed on the convex parts.

Therefore, the objective of this disclosure is to provide a method for manufacturing a fuel cell separator that can form a titanium layer more uniformly than conventional methods on a metal substrate having an uneven flow path shape.

As described above, the inventors have found that when a titanium layer made of titanium is formed on a metal substrate having an uneven flow path shape by a general sputtering method, the thickness of the titanium layer formed on the concave portion is smaller than the thickness of the titanium layer formed on the convex portion. The sputtering method is usually a method in which a raw material as a target is blown onto the surface of the metal substrate to be coated by impact or the like under reduced pressure to physically form a thin film, but even in a reduced pressure state, sputtering gas is present in the atmosphere. There is a difference in the distance to the target between the convex portion and the concave portion of the metal substrate, and until the raw material molecules reach the concave portion, there are more molecules that become obstacles by that difference compared to the convex portion. Therefore, it is presumed that the number of raw material molecules that reach the concave portion, especially the bottom of the concave portion, is smaller than the raw material molecules that reach the convex portion, and the thickness of the layer formed on the concave portion is smaller than the thickness of the layer formed on the convex portion. Note that this presumption does not limit the present embodiment.

The inventors conducted extensive research and discovered that by forming a titanium layer by sputtering under specified conditions, the thickness of the titanium layer formed on the recessed portions can be made closer to the thickness of the titanium layer formed on the protruding portions.

Therefore, examples of this embodiment are as follows:

(1) A method for manufacturing a fuel cell separator having a titanium layer made of titanium on a metal substrate having an uneven flow channel shape, comprising the steps of:
The method includes the step of depositing a titanium layer on a metal substrate by a sputtering method in which a negative bias voltage is applied to the metal substrate;
The sputtering gas pressure is 0.5 Pa or less,
The manufacturing method, wherein the negative bias voltage is 150V or more.
(2) The manufacturing method according to (1), wherein the negative bias voltage is 150 V or more and 1280 V or less.
(3) The manufacturing method according to (1) or (2), wherein the negative bias voltage is 150 V or more and 500 V or less.
(4) The manufacturing method according to any one of (1) to (3), in which sputtering is carried out using a sputtering target containing titanium as a main component.
(5) The manufacturing method according to any one of (1) to (4), wherein argon is used as the sputtering gas.
(6) The method according to any one of (1) to (5), wherein the formed titanium layer has a flat structure and has no boundary or gap extending from the surface of the titanium layer to the surface of the metal substrate.
(7) The method according to any one of (1) to (6), wherein the ratio (B/A) of the thickness A of the titanium layer formed on the protruding portions of the metal substrate to the thickness B of the titanium layer formed on the recessed portions is 0.8 or more.
(8) The method according to any one of (1) to (7), wherein the metal substrate is a stainless steel substrate.
(9) The manufacturing method according to any one of (1) to (8), further comprising the step of depositing a carbon layer made of carbon on the deposited titanium layer.

This disclosure provides a method for manufacturing a fuel cell separator that can form a titanium layer more uniformly than conventional methods on a metal substrate with an uneven flow path shape.

2 is a schematic cross-sectional view illustrating an example of a layer structure of a fuel cell separator according to the present embodiment. FIG. 2 is a schematic cross-sectional view illustrating an example of a layer structure of a fuel cell separator according to the present embodiment. FIG. 3A to 3C are schematic cross-sectional views illustrating examples of the shape of a fuel cell separator according to the present embodiment. 3A to 3C are schematic cross-sectional views illustrating examples of the shape of a fuel cell separator according to the present embodiment. 1 is a schematic cross-sectional view for explaining a configuration example of a fuel cell according to an embodiment of the present invention. 1 is a SEM photograph of a cross section of separator E1 according to Example 1. 1 is a SEM photograph of a cross section of a separator C1 according to Comparative Example 1.

This embodiment is a method for manufacturing a fuel cell separator having a titanium layer made of titanium on a metal substrate having an uneven flow path shape, and includes a process for forming a titanium layer on the metal substrate by a sputtering method in which a negative bias voltage is applied to the metal substrate, in which the sputtering gas pressure is 0.5 Pa or less and the negative bias voltage is 150 V or more.

According to this embodiment, a titanium layer can be formed more uniformly on a metal substrate having an uneven flow path shape than in the past. In addition, according to this embodiment, a titanium layer with excellent corrosion resistance can be formed. The reason why the thickness of the titanium layer formed on the recessed portion can be made closer to the thickness of the titanium layer formed on the protruding portion is presumed to be as follows. The condition that the sputtering gas pressure is 0.5 Pa or less reduces the sputtering gas that hinders the material molecules from reaching the metal substrate, making it easier for the material molecules to reach the recessed portion, and the condition that the negative bias voltage is 150 V or more is thought to be because the particles emitted from the sputtering target have high energy and can easily reach the recessed portion without changing their course direction even if they collide with the sputtering gas. Note that this presumption does not limit this embodiment.

In addition, since fuel cell separators come into contact with low-pH generated water (corrosive liquid) containing chloride ions and fluoride ions during use, fuel cell separators are required to have excellent corrosion resistance. Therefore, the quality of the titanium layer formed on the metal substrate has been desired to be improved from the viewpoint of corrosion resistance. For example, in the case of a titanium layer having a columnar structure as described in Patent Document 2, there is a boundary or gap between the columns that leads to the metal substrate surface, and the corrosive liquid may penetrate through the boundary or gap and corrode the metal substrate. Surprisingly, it has been found that the titanium layer obtained by the manufacturing method according to this embodiment has a flat structure in which there is no boundary or gap from the titanium layer surface to the metal substrate surface as seen in the columnar structure, and therefore has excellent corrosion resistance. It is believed that by forming a titanium layer by the sputtering method under the conditions of this embodiment, the titanium particles move in the left and right directions after reaching the substrate and combine with nearby titanium particles to form a dense film. That is, the lower the sputtering gas pressure and the higher the negative bias voltage, the easier it is for the particles emitted from the sputtering target to reach the metal substrate while retaining their high energy, and they meet and bond with nearby titanium particles on the surface of the metal substrate to form a dense film, which is thought to be why the titanium layer has a flat structure that is denser than the columnar structure. Note that this embodiment is not limited by this assumption. The titanium layer produced by the above method has a flat structure and has excellent corrosion resistance because there are no boundaries or gaps that connect the titanium layer surface to the metal substrate surface, as seen in the columnar structure. Therefore, the manufacturing method according to this embodiment can form a titanium layer with excellent corrosion resistance.

The details of this embodiment are explained below.

This embodiment relates to a method for manufacturing a fuel cell separator having a titanium layer on a metal substrate having an uneven flow path shape.

First, the configuration of the fuel cell separator and fuel cell according to the manufacturing method of this embodiment will be described with reference to the appropriate drawings.

1A is a schematic cross-sectional view for explaining an example of the layer structure of a fuel cell separator according to this embodiment. As shown in FIG. 1A, a fuel cell separator 1001 has a titanium layer 102 formed on a metal substrate 101. The titanium layer 102 may constitute the surface of the fuel cell separator itself, or may exist as an intermediate layer, and other layers may be formed on the titanium layer 102. FIG. 1B is a schematic cross-sectional view for explaining an example of the layer structure of a fuel cell separator according to this embodiment, and shows a fuel cell separator 1002 having a configuration in which a carbon layer 103 is formed as a conductive layer on the titanium layer 102. The titanium layer 102 is formed on at least one surface of the metal substrate 101, and may be formed on both surfaces.

2A and 2B are schematic cross-sectional views showing examples of the shape of the metal substrate of a fuel cell separator. The shape of the metal substrate determines the shape of the fuel cell separator. Metal substrate 101a shown in FIG. 2A and metal substrate 101b shown in FIG. 2B are each formed in a corrugated shape and have a repeated structure of concave and convex portions. Both metal substrates have almost the same shape when viewed from the front side and the back side. As described later, the spaces in the concave and convex portions can function as flow paths for gas and cooling water. In this embodiment, when the separator is placed on a horizontal surface with the surface on which the titanium layer is formed facing up, the portions that are concave downward can be understood as concave portions, and the portions that protrude upward can be understood as convex portions.

The shape of the metal substrate 101a in FIG. 2A is not angular, and both the concave and convex portions have continuous round waves. The shape of the metal substrate 101b in FIG. 2B is an approximately isosceles trapezoid, with flat crests and angular ends at equal angles. There are no particular limitations on the metal substrate, so long as it has a flow path shape consisting of a repeating structure of concaves and convex portions, that is, an uneven flow path shape.

The fuel cell comprises a stack of unit cells, each of which is made up of a power generating body and fuel cell separators arranged on both sides of the power generating body. A plurality of unit cells are stacked in the stacking direction, and each unit cell is electrically connected in series. FIG. 3 is a schematic cross-sectional view for explaining an example of the configuration of a fuel cell according to this embodiment, and is a cross-sectional view of a main part of an exemplary fuel cell 10. As shown in FIG. 3, the fuel cell 10 has a plurality of unit cells 1, which are basic units, stacked. Each unit cell 1 is a solid polymer fuel cell that generates an electromotive force by an electrochemical reaction between an oxidant gas (e.g., air) and a fuel gas (e.g., hydrogen). The single cell 1 includes a membrane electrode & gas diffusion layer assembly (MEGA) 2 with gas diffusion layers (GDL: Gas Diffusion Layer) 7 arranged on both sides, and a separator 3 that contacts the MEGA 2 to separate the MEGA 2. In this embodiment, the MEGA 2 is sandwiched between a pair of separators 3, 3.

The MEGA2 includes a membrane electrode assembly (MEA) 4 and gas diffusion layers 7, 7 arranged on both sides of the MEA. The membrane electrode assembly 4 is composed of an electrolyte membrane 5 and a pair of electrodes 6, 6 joined to sandwich the electrolyte membrane 5. The electrolyte membrane 5 is, for example, a proton-conductive ion exchange membrane formed of a solid polymer material. The electrodes 6 are formed of, for example, a porous carbon material carrying a catalyst such as platinum. The electrode 6 arranged on one side of the electrolyte membrane 5 functions as an anode, and the electrode 6 on the other side functions as a cathode. The gas diffusion layer 7 is formed of a conductive material having gas permeability. Examples of the conductive material having gas permeability include carbon porous bodies such as carbon paper or carbon cloth, or metal porous bodies such as metal mesh or foam metal.

The MEGA2 is the power generation part of the fuel cell 10, and the separator 3 is in contact with the gas diffusion layer 7 of the MEGA2. If the gas diffusion layer 7 is not present, the membrane electrode assembly 4 is the power generation part, and in this case, the separator 3 is in contact with the membrane electrode assembly 4. Therefore, the power generation part of the fuel cell 10 includes the membrane electrode assembly 4, and is in contact with the separator 3.

The separator 3 is a plate-shaped member having a metal substrate (e.g., a stainless steel substrate). The metal substrate has excellent electrical conductivity and gas impermeability. In FIG. 3, the surface of the separator 3 on the power generation side is in contact with the gas diffusion layer 7 of the MEGA 2, and the other surface is in contact with another adjacent separator 3.

In FIG. 3, each separator 3 is formed in a wave shape, and has an uneven flow path shape. The shape of the separator 3 in FIG. 3 is an isosceles trapezoid, the crest of the wave is flat, and both ends of the crest are angular at equal angles. Each separator 3 has approximately the same shape whether viewed from the front or back. The top of the separator 3 is in surface contact with one gas diffusion layer 7 of MEGA2, and the top of the separator 3 is in surface contact with the other gas diffusion layer 7 of MEGA2.

The gas flow path 21 defined between the gas diffusion layer 7 on one electrode (i.e., anode) 6 side and the separator 3 is a flow path through which fuel gas flows, and the gas flow path 22 defined between the gas diffusion layer 7 on the other electrode (i.e., cathode) 6 side and the separator 3 is a flow path through which oxidizer gas flows. When fuel gas is supplied to one of the gas flow paths 21 facing each other via the cell 1 and oxidizer gas is supplied to the gas flow path 22, an electrochemical reaction occurs in the cell 1, generating an electromotive force.

Furthermore, a certain cell 1 and another adjacent cell 1 are arranged with the anode electrode 6 and the cathode electrode 6 facing each other. Also, the top of the rear side of the separator 3 arranged along the anode electrode 6 of a certain cell 1 is in surface contact with the top of the rear side of the separator 3 arranged along the cathode electrode 6 of the other cell 1. A refrigerant (e.g., water) that cools the cell 1 flows through the space (coolant flow path) 23 defined between the separators 3, 3 that are in surface contact between two adjacent cells 1.

In this embodiment, it is preferable that a titanium layer is formed on the surface of the separator facing the power generation section. As described above, when the fuel cell separator is in use, it comes into contact with low-pH generated water (corrosive liquid) that contains chloride ions and fluoride ions, so the fuel cell separator is required to have excellent corrosion resistance. Therefore, it is preferable that a titanium layer is formed on the surface of the separator facing the power generation section.

As described above, in this embodiment, another layer may be formed on the titanium layer. The other layer can be appropriately selected from the viewpoint of improving the electrical conductivity and/or corrosion resistance. As the other layer, a carbon layer made of carbon is preferably formed. The carbon layer made of carbon has excellent durability due to its high film strength, and can reduce the contact resistance of the separator due to its excellent electrical conductivity. In addition, since the adhesion between the titanium layer and the metal substrate such as a stainless steel substrate and the adhesion between the titanium layer and the carbon layer are both good, the titanium layer can bond the carbon layer more firmly to the metal substrate, which leads to a further improvement in the film strength of the carbon layer and can contribute to a reduction in the contact resistance of the separator. In addition, the corrosion resistance of the separator can be significantly improved by adding the corrosion resistance of the titanium layer having a flat structure obtained by this embodiment.

In this embodiment, it is preferable that the power generation unit includes a gas diffusion layer, and it is also preferable that the carbon layer of the separator is in contact with the gas diffusion layer of the MEGA serving as the power generation unit.

The metal constituting the metal substrate is not particularly limited, but examples thereof include iron, aluminum, and alloys thereof. These materials are preferably used from the viewpoints of mechanical strength, versatility, cost performance, ease of processing, and the like. The iron alloy may include stainless steel. In this embodiment, the metal substrate is preferably a stainless steel substrate. When the metal substrate is a stainless steel substrate, the electrical conductivity of the contact surface with the gas diffusion layer, etc. can be sufficiently ensured. The stainless steel substrate is not particularly limited, but examples thereof include austenitic, ferritic, austenitic-ferritic two-phase, martensitic, and precipitation hardened substrates.

The thickness of the metal substrate is appropriately selected taking into consideration ease of processing, mechanical strength, and the improvement of battery energy density by thinning the separator, and is, for example, 0.05 to 1 mm. If the thickness is within this range, it is easy to satisfy the requirements for a lightweight and thin separator, and has the strength and handleability required as a separator material.

The manufacturing method according to this embodiment includes a step of forming a titanium layer on a metal substrate by a sputtering method in which a negative bias voltage is applied to the metal substrate, the sputtering gas pressure is 0.5 Pa or less, and the negative bias voltage is 150 V or more.

This process allows the titanium layer to be formed uniformly on a metal substrate having an uneven flow path shape, with the thickness of the titanium layer formed on the recesses being close to the thickness of the titanium layer formed on the protrusions. In addition, the titanium layer formed in this process has a flat structure and has excellent corrosion resistance because there are no boundaries or gaps connecting the titanium layer surface to the metal substrate surface, as is the case with columnar structures.

The titanium layer is preferably formed directly on the metal substrate, i.e., in contact with the metal substrate (e.g., a stainless steel substrate).

The thickness of the titanium layer is not particularly limited, but is, for example, 0.1 to 1000 nm, preferably 10 nm to 500 nm, and more preferably 30 to 300 nm.

The titanium layer is preferably composed of substantially pure titanium. The purity of the titanium is preferably 99% by weight or more, and more preferably 99.9% by weight or more.

The method for forming the titanium layer is not particularly limited as long as it is a sputtering method. Examples of sputtering methods include DC sputtering, RF sputtering, AC sputtering, DC magnetron sputtering, RF magnetron sputtering, ion beam sputtering, unbalanced magnetron sputtering (UBMS), dual magnetron sputtering, and ECR sputtering. Of these, it is preferable to use DC sputtering and unbalanced magnetron sputtering.

In this process, when forming the titanium layer by sputtering, the sputtering gas pressure is set to 0.5 Pa or less, and the negative bias voltage is set to 150 V or more. By forming the titanium layer under these conditions, it is possible to form the titanium layer on the metal substrate having an uneven flow path shape, reducing the difference in thickness between the titanium layer formed in the recesses and the titanium layer formed in the protrusions. It is also possible to form a titanium layer having a flat structure with excellent corrosion resistance.

The negative bias voltage applied to the metal substrate is 150V or more. By setting the negative bias voltage to 150V or more, the difference between the thickness of the titanium layer formed on the concave portion and the thickness of the titanium layer formed on the convex portion can be effectively reduced, and a titanium layer having a flat structure can be formed. The negative bias voltage applied to the metal substrate is preferably 200V or more, preferably 250V or more, and preferably 300V or more. The negative bias voltage applied to the metal substrate is preferably 1280V or less, preferably 1200V or less, preferably 1100V or less, preferably 1000V or less, preferably 900V or less, preferably 800V or less, preferably 700V or less, preferably 600V or less, and preferably 500V or less. By setting the negative bias voltage to 1280V or less, excessive reduction in film thickness can be avoided.

The sputtering gas pressure in the film formation process is 0.5 Pa or less. By setting the sputtering gas pressure to 0.5 Pa or less, the difference in thickness between the titanium layer formed on the recessed portion and the titanium layer formed on the protruding portion can be effectively reduced, and a titanium layer having a flat structure rather than a columnar structure can be formed. As described above, the flat structure has excellent corrosion resistance because there is no boundary or gap from the titanium layer surface to the metal substrate surface as seen in the columnar structure. The sputtering gas pressure is preferably 0.4 Pa or less, preferably 0.3 Pa or less, preferably 0.2 Pa or less, preferably 0.1 Pa or less, and preferably 0.08 Pa or less.

In the film-forming process, the ratio (B/A) of the thickness A of the titanium layer formed on the convex parts of the metal substrate to the thickness B of the titanium layer formed on the concave parts is preferably 0.8 or more, more preferably 0.85 or more, and even more preferably 0.9 or more. The thickness A of the titanium layer formed on the convex parts of the metal substrate can be obtained by measuring the thickness of the titanium layer at the top, which is the highest part of the convex parts. The thickness B of the titanium layer formed on the concave parts can be obtained by measuring the thickness of the titanium layer at the bottom, which is the lowest part of the concave parts. The thickness of the titanium layer can be obtained by observing the cross section of the separator using a SEM or the like, and averaging the thicknesses of at least 10 points on the convex parts (or concave parts) in the cross section.

The sputtering target used is preferably made of titanium. It is also preferable that the purity is high, and the content of metal impurities is preferably less than 1% by weight, preferably less than 0.1% by weight, and preferably less than 0.01% by weight.

The degree of vacuum in the film formation apparatus before film formation is preferably 3×10 ⁻⁵ Pa or less, and more preferably 1×10 ⁻⁵ Pa or less. By setting the degree of vacuum at a lower pressure, residual gas is less likely to be mixed in as an impurity during film formation, improving the quality of the thin film.

The metal substrate may be pretreated before the deposition of the titanium layer. By carrying out the pretreatment of the metal substrate, it is possible to remove any impurities that may impede adhesion to the surface of the metal substrate. Examples of pretreatment methods include reverse sputtering, acid treatment, and UV treatment, but reverse sputtering is preferred from the viewpoint of preventing re-adhesion of impurities after treatment. Reverse sputtering is a method of cleaning the surface by colliding plasma atoms with the metal substrate, rather than the sputtering target. By utilizing this mechanism, the substrate surface is cleaned and sent to the deposition chamber without exposure to the outside air, making it possible to deposit a film while maintaining the cleanliness of the substrate surface. When performing reverse sputtering, it is preferable to perform the treatment separately from the deposition chamber in order to prevent reverse sputtered impurities from adhering to the deposition chamber. For example, argon, nitrogen, oxygen, etc. can be used as the gas species for reverse sputtering.

The sputtering gas is not particularly limited, but for example, argon can be used. A mixed gas containing argon can also be used.

The power density during discharge is preferably 0.5 W/cm ² or more and 20 W/cm ² or less, and more preferably 1 W/cm ² or more and 10 W/cm ² or less. The power density is calculated by dividing the power applied during discharge by the area of the sputtering target.

The distance from the sputtering target to the metal substrate is not particularly limited, but is, for example, 100 to 250 mm, and preferably 180 to 220 mm.

As described above, another layer may be formed on the titanium layer. The other layer may be appropriately selected from the viewpoint of improving electrical conductivity and/or corrosion resistance, and a preferred example of the other layer is a carbon layer made of carbon.

The carbon layer is made of carbon and is composed of a crystalline structure and/or an amorphous structure, and may include a polycrystalline graphite structure. The carbon layer is preferably formed directly on, i.e., in contact with, the titanium layer. The carbon layer is preferably the top layer of the separator. The carbon layer is substantially free of other materials such as resin.

The thickness of the carbon layer is not particularly limited, but is, for example, 0.1 to 1000 nm, preferably 10 nm to 500 nm, and more preferably 15 to 200 nm.

The method for forming the carbon layer is not particularly limited, but examples thereof include physical vapor deposition (PVD) methods such as sputtering or ion plating, or ion beam deposition methods such as filtered cathodic vacuum arc (FCVA). Among them, it is preferable to use the sputtering method or ion plating method. Examples of the sputtering method include ion beam sputtering, DC sputtering, RC sputtering, magnetron sputtering, unbalanced magnetron sputtering (UBMS), dual magnetron sputtering, and ECR sputtering. Examples of the ion plating method include the arc ion plating method. In particular, it is preferable to use the ion plating method for forming the carbon layer, and it is preferable to use the arc ion plating method. According to these methods, it is possible to form a carbon layer with a low hydrogen content. As a result, it is possible to increase the proportion of bonds between carbon atoms (sp2 hybrid carbon), and excellent conductivity can be achieved.

In addition, in the sputtering method, the quality of the film obtained can be controlled by controlling the bias voltage, etc. When forming a layer by the sputtering method, a negative bias voltage may be applied to the substrate during sputtering. This allows the layer to be formed densely and improves corrosion resistance. The magnitude of the negative bias voltage applied when forming the carbon layer is not particularly limited, but is, for example, 5 to 50 V, or 10 to 40 V.

In fuel cells, fluoride ions are easily generated from fluorine-based electrolyte resins such as perfluorosulfonic acid polymers. Therefore, when a fuel cell uses a solid electrolyte membrane containing a fluorine-based electrolyte resin, the fuel cell separator of this embodiment is particularly useful. Examples of fluorine-based electrolyte resins include perfluorosulfonic acid polymers, and specific examples include Nafion (trade name, manufactured by DuPont), Flemion (trade name, manufactured by Asahi Glass Co., Ltd.), and Aciplex (trade name, manufactured by Asahi Kasei Co., Ltd.). Among these, Nafion (trade name, manufactured by DuPont) is preferably used because of its excellent proton conductivity.

By using this embodiment, it is possible to form a titanium layer on a metal substrate having an uneven flow path shape more uniformly than in the past, and also to form a titanium layer with excellent corrosion resistance.

The following describes this embodiment using examples.

[Example 1]
A stainless steel substrate (SUS304) on which a concave-convex flow path shape was formed was prepared as the metal substrate. The stainless steel substrate had a corrugated shape as shown in FIG. 2A, and was composed of a repeated structure of concaves and convexities. The distance between the tops of two adjacent convexities was 1.3 mm, and the vertical distance (depth) between the bottom of the concave and the top of the convex was 0.5 mm.

Then, a titanium layer was formed on the stainless steel substrate using a sputtering device (product name: FC1500, manufactured by IHI Hauser Techno Coatings Co., Ltd.). Specifically, the stainless steel substrate was first placed in the reaction vessel of the device, and then the reaction vessel was evacuated and heated by an internal heater. Next, the pure Ti cathode target used for sputtering was etched (cleaned) with plasma Ar gas. In addition, in order to remove the passivation present on the surface of the stainless steel substrate, the stainless steel substrate was etched with plasma Ar gas. Next, using the above-mentioned pure Ti cathode target, a titanium layer was formed by unbalanced magnetron sputtering under the following conditions. Next, a carbon layer was formed on the titanium layer by arc ion plating (AIP) under the following conditions to produce separator E1.

(Titanium layer deposition conditions)
Target film thickness: 150 nm
Treatment temperature: 140°C
Sputtering gas: Ar
Sputtering gas flow rate: 380 sccm
Sputtering gas pressure: 0.5 Pa
Bias voltage: -150V
Frequency: 40kHz
Ti cathode output: 35 kW
Revolution speed: 0.5 rpm
Distance between substrate and target: 190 mm

(Carbon layer formation conditions)
Target film thickness: 150 nm
Treatment temperature: 140°C
Sputtering gas pressure: 0.5 Pa
Sputtering gas (input gas): Ar
Sputtering gas flow rate: 380 sccm
Voltage value: -250V
Frequency: 40kHz
C cathode output: 80A
Revolution speed: 4.0 rpm

[Example 2]
A separator E2 was produced in the same manner as in Example 1, except that the bias voltage was set to −200V.

[Example 3]
A separator E3 was produced in the same manner as in Example 1, except that the bias voltage was set to −300V.

[Comparative Example 1]
A separator C1 was produced in the same manner as in Example 1, except that the bias voltage was set to 0V.

[Comparative Example 2]
A separator C2 was produced in the same manner as in Example 1, except that the sputtering gas pressure was set to 2.5 Pa by adjusting the flow rate of the sputtering gas.

[Comparative Example 3]
Separator C3 was produced in the same manner as in Example 1, except that the sputtering gas pressure was set to 5.0 Pa by adjusting the flow rate of the sputtering gas.

[evaluation]
(Film thickness ratio of convex and concave parts)
For the obtained separators E1 to E3 and C1 to C3, the thickness of the titanium layer at the convex and concave portions was measured, and the thickness ratio was calculated. The thickness of the titanium layer was measured at least 10 points on the tops of the convex portions and the bottoms of the concave portions in an SEM photograph of the separator cross section, and the thickness was calculated as the average value. The results are shown in Table 1 below.

(Structure of titanium layer)
For the obtained separators E1 to E3 and C1 to C3, the cross section of the titanium layer was observed by SEM to confirm the structure. The results are shown in Table 1 below. Also, Fig. 4 shows an SEM photograph of the cross section of separator E1 according to Example 1. Also, Fig. 5 shows an SEM photograph of the cross section of separator C1 according to Comparative Example 1.

From the above results, it was confirmed that the manufacturing method according to this embodiment can increase the film thickness ratio of the convex portion to the concave portion, and in particular can increase the film thickness ratio to 0.80 or more. It was also confirmed that the manufacturing method according to this embodiment can obtain a titanium layer having a flat structure. Specifically, as shown in FIG. 4, the titanium layer formed in the example had a flat structure in which there were no boundaries or gaps from the titanium layer surface to the metal substrate surface, as seen in a columnar structure. This flat structure has excellent corrosion resistance because there are no boundaries or gaps leading to the metal substrate surface. On the other hand, as shown in FIG. 5, the titanium layer formed in the comparative example had a columnar structure, and there were boundaries or gaps leading from the titanium layer surface to the metal substrate surface.

The upper and/or lower limit values of the numerical ranges described in this specification can be arbitrarily combined to define a preferred range. For example, the upper and lower limit values of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limit values of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limit values of the numerical ranges can be arbitrarily combined to define a preferred range.

Although this embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and any design changes that do not deviate from the gist of this disclosure are included in this disclosure.

1: Cell 2: MEGA
3: Separator 4: Membrane electrode assembly (MEA)
5: Electrolyte membrane 6: Electrode 7: Gas diffusion layer 10: Fuel cell 21: Gas flow path 22: Gas flow path 23: Coolant flow path 101: Metal substrate 101a: Metal substrate 101b: Metal substrate 102: Titanium layer 103: Carbon layer 1001: Fuel cell separator 1002: Fuel cell separator

Claims (9)

A method for manufacturing a fuel cell separator having a titanium layer made of titanium on a metal substrate having an uneven flow channel shape, comprising the steps of:
The method includes the step of depositing a titanium layer on a metal substrate by a sputtering method in which a negative bias voltage is applied to the metal substrate;
The sputtering gas pressure is 0.5 Pa or less,
The manufacturing method, wherein the negative bias voltage is 150V or more. The manufacturing method according to claim 1, wherein the negative bias voltage is 150 V or more and 1280 V or less. The manufacturing method according to claim 1 or 2, wherein the negative bias voltage is 150 V or more and 500 V or less. The manufacturing method according to any one of claims 1 to 3, in which sputtering is performed using a sputtering target whose main component is titanium. The manufacturing method according to any one of claims 1 to 4, in which argon is used as the sputtering gas. The manufacturing method according to any one of claims 1 to 5, in which the formed titanium layer has a flat structure and there is no boundary or gap between the titanium layer surface and the metal substrate surface. The method of any one of claims 1 to 6, wherein the ratio (B/A) of the thickness A of the titanium layer formed on the protruding parts of the metal substrate to the thickness B of the titanium layer formed on the recessed parts is 0.8 or more. The manufacturing method according to any one of claims 1 to 7, wherein the metal substrate is a stainless steel substrate. The method according to any one of claims 1 to 8, further comprising the step of depositing a carbon layer made of carbon on the deposited titanium layer.

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