Manufacturing method of separator for fuel cell

Abstract

To provide a method for manufacturing a fuel cell separator, depositing a dense metal film on the entire separator base material and thereby capable of suppressing the amount of metal elution from the separator base material.SOLUTION: Provided is a method for manufacturing a fuel cell separator 12 in which a metal film 12b is formed on a separator base material 12a. The method includes steps of: preparing, as the separator base material 12a, a separator base material in which a pair of slanted wall faces 22, 22 slanted so as to widen from a bottom wall face 20 toward a groove opening 26 is formed for each linear groove 28 that serves as a passage of a fluid flowing through a fuel cell 1; and depositing a metal film by evaporating particles P for deposition on a surface of the separator base material 12a, while changing the orientation of the separator base material 12a with respect to a target source T, so as to evaporate from a direction perpendicular to the particles P for deposition, for each of the bottom wall face 20, the slanted wall face 22 and a top wall face 24, in the state where the separator base material 12a is disposed in a position facing the target source T.SELECTED DRAWING: Figure 4B

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a separator for a fuel cell. [Background technology]

[0002] Conventionally, fuel cells constructed by stacking a plurality of unit cells have been known. Each unit cell of the fuel cell has a structure in which a membrane electrode assembly is sandwiched between separators. The membrane electrode assembly is composed of a solid polymer electrolyte membrane (hereinafter also referred to as an "electrolyte membrane"), and an anode side catalyst layer and a cathode side catalyst layer bonded to both sides of the electrolyte membrane. The membrane electrode assembly may have gas diffusion layers on the surfaces of the anode side catalyst layer and the cathode side catalyst layer as necessary. The pair of separators sandwiching the membrane electrode assembly have a flow port and a flow path for supplying hydrogen gas and air to the membrane electrode assembly and discharging the supplied hydrogen gas and air.

[0003] In the fuel cell, each unit cell is exposed to a corrosive environment during power generation. For this reason, a metal separator substrate (hereinafter also referred to as "metal substrate") is generally provided with a corrosion-resistant coating on its surface (see, for example, Patent Document 1). Patent Document 1 describes a method for manufacturing a metal separator for a fuel cell, which is manufactured using a metal substrate having concave gas flow paths formed on at least a part of its surface. This manufacturing method includes a step of forming an acid-resistant metal coating on the metal substrate, and a step of forming a conductive alloy coating on the acid-resistant metal coating. In the step of forming the acid-resistant metal coating and the step of forming the conductive alloy coating, the metal substrate is rotated while a platform on which the metal substrate is fixed is revolved, so that the coating is also formed on both sides and sides of the metal substrate. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-45052 A Summary of the Invention [Problem to be solved by the invention]

[0005] When forming an acid-resistant metal coating on the metal substrate by, for example, a sputtering method, the metal substrate and the target source are positioned so that the concave portion is located in front of the target source, whereby particles sputtered from the target source adhere to the surface of the metal substrate, forming an acid-resistant metal coating on the surface of the metal substrate.

[0006] However, the metal base material may include a surface (hereinafter also referred to as a "slant wall surface") that faces obliquely to the target source when the concave portion is disposed in front of the target source. In this case, the particles coming from the target source are incident on the slant wall surface at an angle (i.e., not from the front), and therefore the particles may not be sufficiently diffused on the slant wall surface. In this way, a columnar coating (porous coating) may be formed in the portion where the particles are not sufficiently diffused. In this case, a dense acid-resistant metal coating is not formed on the slant wall surface of the metal base material, and therefore there is a risk that the metal of the metal base material may be dissolved on the slant wall surface of the metal base material.

[0007] In this regard, Patent Document 1 describes a method of forming a film on both sides and sides of a metal substrate by rotating the metal substrate while revolving a platform on which the metal substrate is fixed. However, in the manufacturing method described in Patent Document 1, depending on the arrangement (posture) of the metal substrate with respect to the deposition target, there were cases where a dense acid-resistant metal coating could not be formed on the entire metal substrate.

[0008] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a method for manufacturing a separator for a fuel cell, which can form a dense metal coating over the entire separator substrate and suppress the amount of metal elution from the separator substrate. [Means for solving the problem]

[0009] In order to achieve the above-mentioned object, the manufacturing method of a separator for fuel cells according to the present invention is a manufacturing method of a separator for a fuel cell in which a metal coating is formed on a surface of a separator substrate, the manufacturing method including the steps of: preparing a separator substrate having a plurality of linear grooves formed at intervals in the groove width direction as the separator substrate, the grooves being a flow path for a fluid flowing through the fuel cell, and a pair of inclined wall surfaces inclined so as to widen from a bottom wall surface toward a groove opening, for each of the grooves; and, with the separator substrate positioned opposite a target source, depositing the film-forming particles generated by the target source on the surface of the separator substrate while changing the attitude of the separator substrate relative to the target source so that the film-forming particles are deposited from a direction perpendicular to the bottom wall surface, the inclined wall surface, and the top wall surface formed between the grooves, thereby forming the metal coating.

[0010] According to the present invention, in the process of forming a metal film, a separator substrate is placed at a position facing a target source, and a film is formed on the surface of the separator substrate while changing the position of the separator substrate with respect to the target source so that the film-forming particles generated by the target source are deposited from a direction perpendicular to the bottom wall surface, the inclined wall surface, and the top wall surface. Therefore, the film-forming particles can be made to enter the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate from the front (i.e., perpendicularly). This makes it possible to suppress the attenuation of the kinetic energy of the film-forming particles after collision with the separator substrate, and to sufficiently diffuse the film-forming particles on the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate. As a result, a dense film can be formed and a sufficient film thickness can be ensured on the entire separator substrate, that is, not only on the bottom wall surface and the top wall surface but also on the inclined wall surface. Therefore, the amount of metal eluted from the separator substrate can be suppressed.

[0011] In a preferred embodiment, in the process of forming the metal coating, the position of the separator substrate is changed by rotating the separator substrate around a rotation axis along the groove. According to this embodiment, by rotating the separator substrate, the film-forming particles coming from the target source can be collided evenly with the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate. As a result, a dense coating can be formed while reducing the difference in film thickness on the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate.

[0012] In a preferred embodiment, in the process of forming a metal coating, the position of the separator substrate is changed by rotating the separator substrate with the direction along the groove as the axis of rotation between a first position of the separator substrate in which the film-forming particles are deposited from a direction perpendicular to one of the inclined wall surfaces, and a second position of the separator substrate in which the film-forming particles are deposited from a direction perpendicular to the other inclined wall surface. According to this embodiment, by rotating the separator substrate between the first position and the second position, the separator substrate can be always directed toward the target source, so that the film-forming particles can be uniformly collided with the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate, and can be continuously collided with them. As a result, a dense coating can be formed while reducing the difference in film thickness on the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate, and efficient film formation can be performed. Effect of the Invention

[0013] According to the present invention, a dense metal coating can be formed over the entire separator substrate, and the amount of metal eluted from the separator substrate can be suppressed. [Brief description of the drawings]

[0014] [Figure 1] 1 is a partial cross-sectional view of a fuel cell including a separator manufactured by a manufacturing method according to an embodiment of the present invention. [Diagram 2] 2 is an exploded perspective view showing a unit cell of the fuel cell shown in FIG. 1. [Diagram 3]FIG. 3 is a partial cross-sectional view of the separator shown in FIGS. 1 and 2. [Figure 4A] 1 is a diagram for explaining a process for forming a metal coating according to a first embodiment of the present invention, showing the attitude of a separator substrate on which film-forming particles are deposited from a direction perpendicular to the bottom wall surface and the top wall surface. [Figure 4B] FIG. 4B is a diagram showing a state in which the separator substrate is rotated clockwise from the state shown in FIG. 4A, and shows the attitude of the separator substrate in which the film-forming particles are deposited from a direction perpendicular to one of the inclined wall surfaces. [Figure 4C] 4C is a diagram showing a state in which the separator substrate is rotated clockwise from the state shown in FIG. 4B. [Figure 4D] FIG. 4D is a diagram showing a state in which the separator substrate is rotated clockwise from the state shown in FIG. 4C, and shows the attitude of the separator substrate in which the film-forming particles are deposited from a direction perpendicular to the other inclined wall surface. [Figure 5A] 11 is a diagram illustrating a process for forming a metal coating according to a second embodiment of the present invention, showing the attitude of a separator substrate on which film-forming particles are deposited from a direction perpendicular to the bottom and top wall surfaces. [Figure 5B] 5B is a diagram showing a state in which the separator substrate has been rotated clockwise from the state shown in FIG. 5A, and shows the attitude of the separator substrate in which film-forming particles are deposited from a direction perpendicular to one of the inclined wall surfaces. [Figure 5C] 5B is a diagram showing a state in which the separator substrate has been rotated counterclockwise from the state shown in FIG. 5A, and shows the attitude of the separator substrate in which the film-forming particles are deposited from a direction perpendicular to the other inclined wall surface. [Figure 6] 4 is a graph showing the results of a durability test of separators manufactured by the manufacturing methods according to the examples of the present invention and the comparative examples, in terms of the amount of eluted Fe. [Figure 7] 1A and 1B are images of cross sections of separators manufactured by the manufacturing methods according to the examples and comparative examples of the present invention, observed with a scanning microscope, showing images of a top wall surface, a sloped wall surface, and a bottom wall surface. [Figure 8]FIG. 1 is a diagram for explaining the collision direction of film-forming particles on an inclined wall surface, where (a) shows the collision direction of film-forming particles on an inclined wall surface in a manufacturing method according to an embodiment, and (b) shows the collision direction of film-forming particles on an inclined wall surface in a manufacturing method according to a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] First, with reference to Figs. 1 to 3, a fuel cell 1 including a separator 12 manufactured by a manufacturing method according to an embodiment of the present invention will be described. Fig. 1 is a partial cross-sectional view of a fuel cell 1 including a separator 12 manufactured by a manufacturing method according to an embodiment of the present invention. Fig. 2 is an exploded perspective view showing a unit cell 10 of the fuel cell 1 shown in Fig. 1. Fig. 3 is a partial cross-sectional view of the separator 12 shown in Figs. 1 and 2. In this specification, the term "separator 12" refers to a separator that is assembled into the unit cell 10 as shown in Figs. 1 and 2. Also, the term "separator substrate 12a" refers to a separator substrate in a state before a titanium film (metal film) 12b and a carbon film (conductive film) 12c are formed by collision of film-forming particles P, as described later.

[0017] As shown in Fig. 1, in the fuel cell 1 according to this embodiment, a plurality of unit cells 10, which are basic units, are stacked. The unit cells 10 are solid polymer fuel cells that generate electromotive force by an electrochemical reaction between oxygen gas contained in air and hydrogen gas, which is a fuel gas. The air refers to atmospheric air, and air compressed by a compressor (not shown), for example, is supplied to the fuel cell 1. In addition, hydrogen gas filled in a high-pressure tank (not shown) is supplied to the fuel cell 1.

[0018] 2, a single cell 10 constituting the fuel cell 1 includes a power generation assembly 17 and a pair of separators 12, 12 that sandwich the power generation assembly 17. The power generation assembly 17 includes an electrode-gas diffusion layer assembly (MEGA) 11 and a resin frame 14 that surrounds the outer periphery of the MEGA 11.

[0019] 1, the MEGA 11 includes a polymer electrolyte membrane 11a, catalyst layers 11b and 11c bonded to both sides of the polymer electrolyte membrane 11a, and gas diffusion layers 11d and 11d bonded to the catalyst layers 11b and 11c. The portion where the MEGA 11 is disposed is the power generation region of the unit cell 10.

[0020] The polymer electrolyte membrane 11a is a proton-conductive ion exchange membrane made of a solid polymer material, and the catalyst layers 11b and 11c are made of, for example, a porous carbon material carrying a catalyst such as platinum. The catalyst layer 11b arranged on one side of the polymer electrolyte membrane 11a serves as the anode of the fuel cell 1, and the catalyst layer 11c on the other side serves as the cathode of the fuel cell 1. The gas diffusion layer 11d is made of a gas-permeable conductive member such as a carbon porous material such as carbon paper or carbon cloth, or a metal porous material such as a metal mesh or metal foam.

[0021] As shown in FIG. 2, six circulation ports are formed on both sides of the longitudinal direction L of the resin frame 14 to supply hydrogen gas, air, and cooling water to the MEGA11 or its vicinity individually, and to discharge the supplied hydrogen gas, air, and cooling water from the MEGA11 or its vicinity. Specifically, a hydrogen circulation port 14a through which hydrogen gas flows, a cooling water circulation port 14b through which cooling water flows, and an air circulation port 14c through which air flows are provided in this order on one side of the resin frame 14. In addition, an air circulation port 14d through which air flows, a cooling water circulation port 14e through which cooling water flows, and a hydrogen circulation port 14f through which hydrogen gas flows are provided in this order on the other side of the resin frame 14. One of the pair of circulation ports through which each fluid flows is a circulation port for supplying to the MEGA11 or its vicinity, and the other is a circulation port for discharging from the MEGA11 or its vicinity. For example, one hydrogen flow port 14a serves as a flow port for supplying hydrogen to MEGA 11, and the other hydrogen flow port 14f serves as a flow port for discharging hydrogen from MEGA 11. Hydrogen flow port 14a and hydrogen flow port 14f are disposed at diagonal corners of resin frame 14, so that hydrogen gas can be circulated between diagonal corners of the power generation region.

[0022] As shown in FIG. 2, the separator 12 is formed in the same rectangular shape as the MEGA 11 in a plan view. In the portion of the separator 12 that abuts against the MEGA 11, for example, a number of grooves 15 are formed along the longitudinal direction L, and thus, as shown in FIG. 1, flow paths 15a to 15c through which the fuel gas, air, and cooling water flow are formed. The grooves 15 are formed along the long sides of the separator 12. Specifically, the flow path defined between the gas diffusion layer 11d on one catalyst layer 11b side and the separator 12 is the flow path 15a through which hydrogen gas flows. The flow path defined between the gas diffusion layer 11d on the other catalyst layer 11c side and the separator 12 is the flow path 15b through which air flows. The flow path formed between the separators 12 is the flow path 15c through which cooling water flows. In this embodiment, when hydrogen gas is supplied to one flow path 15a and air is supplied to the other flow path 15b, an electrochemical reaction occurs in the single cell 10, generating an electromotive force.

[0023] Furthermore, on both sides of the longitudinal direction L of the separator 12, six circulation ports are formed for individually supplying hydrogen gas, air, and cooling water to the MEGA 11 or its vicinity, and discharging the supplied hydrogen gas, air, and cooling water from the MEGA 11 or its vicinity. These circulation ports are formed at positions corresponding to the circulation ports of the resin frame 14 and have the same size as the corresponding circulation ports. In FIG. 2, the circulation ports of the separator 12 corresponding to the circulation ports of the resin frame 14 are given the same reference numerals as the circulation ports of the resin frame 14. Specifically, on one side of the separator 12, a hydrogen circulation port 14a through which hydrogen gas flows, a cooling water circulation port 14b through which cooling water flows, and an air circulation port 14c through which air flows are formed in this order. On the other side of the separator 12, an air circulation port 14d through which air flows, a cooling water circulation port 14e through which cooling water flows, and a hydrogen circulation port 14f through which hydrogen gas flows are formed in this order. One of the flow ports through which each fluid flows is a flow port for supplying the fluid to MEGA11 or its vicinity, and the other is a flow port for discharging the fluid from MEGA11 or its vicinity. For example, hydrogen flow port 14a is a flow port for supplying the fluid to MEGA11, and the other hydrogen flow port 14f is a flow port for discharging the fluid from MEGA11. Hydrogen flow port 14a and hydrogen flow port 14f are disposed at diagonal corners of separator 12, so that hydrogen gas can be circulated between diagonal corners of MEGA11.

[0024] As shown in FIG. 3, separator 12 includes a metallic separator substrate 12a, a titanium coating (metal coating) 12b formed on the surface of separator substrate 12a, and a carbon coating 12c formed on the surface of titanium coating 12b.

[0025] The separator substrate 12a is a thin plate or foil material that serves as the base of the separator 12, and is formed by press molding or the like from a thin plate or foil material made of, for example, SUS. The separator substrate 12a may be formed from, for example, Ti, Al, or Fe. The thickness of the separator substrate 12a is, for example, 10 μm to 200 μm. The separator substrate 12a is formed into, for example, a corrugated shape by press molding (see, for example, FIG. 4A). The shape of the separator substrate 12a according to this embodiment will be described later.

[0026] The titanium coating 12b as a metal coating suppresses the amount of metal eluted from the separator substrate 12a (i.e., the amount of stainless steel eluted) and improves the corrosion resistance of the separator 12. The material of the metal coating formed on the surface of the separator substrate 12a may be, for example, Ag, Au, Cr, Mo, Rh, Pd, Pt, Pb, Ru, Al, Ni, Co, V, Zr, Sn, Ta, W, or a Ti compound containing these elements. The thickness of the titanium coating 12b is, for example, 30 nm to 300 nm.

[0027] The carbon coating 12c is a conductive coating that improves the conductivity of the separator 12. The material of the conductive coating formed on the surface of the titanium coating 12b may be, for example, Au, Ag, Cu, TiN, or TiC. The thickness of the carbon coating 12c is, for example, 3 nm to 200 nm.

[0028] Next, the manufacturing method according to this embodiment will be described.

[0029] First Embodiment FIG. 4A is a diagram for explaining the process of forming a metal coating according to the first embodiment of the present invention, and shows the attitude of the separator substrate 12a on which the film-forming particles P are deposited from a direction perpendicular to the bottom wall surface 20 and the top wall surface 24. FIG. 4B is a diagram showing a state in which the separator substrate 12a is rotated clockwise from the state shown in FIG. 4A, and shows the attitude of the separator substrate 12a on which the film-forming particles P are deposited from a direction perpendicular to one of the inclined wall surfaces 22. FIG. 4C is a diagram showing a state in which the separator substrate 12a is rotated clockwise from the state shown in FIG. 4B. FIG. 4D is a diagram showing a state in which the separator substrate 12a is rotated clockwise from the state shown in FIG. 4C, and shows the attitude of the separator substrate 12a on which the film-forming particles P are deposited from a direction perpendicular to the other inclined wall surface 22.

[0030] The manufacturing method according to this embodiment includes the steps of preparing a separator substrate 12a, forming a titanium coating (metal coating) 12b on the surface of the separator substrate 12a, and forming a carbon coating 12c on the surface of the titanium coating 12b.

[0031] In the process of preparing the separator substrate 12a, for example, a flat thin plate material of stainless steel is press-formed into the shape of the separator 12 (for example, corrugated), to prepare the separator substrate 12a. Specifically, in this process, the separator substrate 12a is prepared in which a plurality of linear substrate grooves (grooves) 28 are formed at intervals in the groove width direction W to become the flow paths 15a-15c of the fluids (gas, air, coolant) flowing in the fuel cell 1. The substrate grooves 28 of the separator substrate 12a become the grooves 15 of the separator 12 by forming a titanium coating 12b and a carbon coating 12c on the separator substrate 12a. In the separator substrate 12a, a pair of inclined wall surfaces 22, 22 inclined so as to widen from the bottom wall surface 20 toward the groove opening 26 are formed for each substrate groove 28. As shown in Fig. 4A, each of the substrate grooves 28 is a groove having a bottom wall surface 20 on the groove bottom wall 20a and a pair of inclined wall surfaces 22, 22 on the groove side walls 22a, 22a. The groove side walls 22a, 22a are connected to the groove bottom wall 20a at one end. The bottom wall surface 20 and the pair of inclined wall surfaces 22, 22 are formed facing the inside of the groove in the substrate groove 28. Each of the substrate grooves 28 has a groove opening 26 at a position opposite the bottom wall surface 20. The substrate grooves 28 extend in a direction perpendicular to the paper surface as shown in Fig. 4A.

[0032] In addition, in the separator substrate 12a, a top wall surface 24 is formed between the adjacent substrate grooves 28. The top wall surface 24 is a part of the top wall 24a, and the top wall 24a connects the other end sides of the groove side walls 22a, 22a of the adjacent substrate grooves 28. The top wall surface 24 is a surface facing the same direction as the bottom wall surface 20. The top wall 24a is positioned offset in the groove width direction W with respect to the groove bottom wall 20a. In this way, the separator substrate 12a in this embodiment has a groove bottom wall 20a, groove side wall 22a, top wall 24a, groove side wall 22a, and groove bottom wall 20a repeatedly provided, and has an isosceles trapezoidal wave shape as shown in FIG. 4A. The separator substrate 12a prepared in this way is attached to a rotating device (stage) M and then transported to a position facing the target source T.

[0033] In this embodiment, a case will be described in which the separator substrate 12a is attached to the rotating device M so that one surface is exposed and the other surface is covered by the rotating device M. However, the separator substrate 12a may be attached to the rotating device M so that both surfaces of the separator substrate 12a are exposed. In this case, the titanium coating 12b can be formed on both surfaces of the separator substrate 12a without removing the separator substrate 12a from the rotating device M.

[0034] Next, the step of forming the titanium film 12b will be described with reference to FIG. 4A to FIG. 4D. In the step of forming the titanium film 12b, the titanium film 12b of the separator substrate 12a is formed on the surface of the prepared separator substrate 12a (i.e., the bottom wall surface 20, the pair of inclined wall surfaces 22, and the top wall surface 24). By forming the titanium film 12b on the surface of the separator substrate 12a, the corrosion resistance of the separator 12 is improved. Therefore, a material having a higher corrosion resistance than the material of the separator substrate 12a is formed as the metal film. Examples of the film forming method include physical vapor deposition (PVD) such as sputtering, vacuum deposition, or ion plating. In this step, as shown in FIG. 4A to FIG. 4D, while changing the position of the separator substrate 12a with respect to a target source T made of titanium, film forming particles P are deposited on the surface of the separator substrate 12a to form the titanium film 12b. Specifically, with the separator substrate 12a disposed at a position facing the target source T, the attitude of the separator substrate 12a with respect to the target source T is changed so that the film-forming particles P generated by the target source T are deposited from a direction perpendicular to the bottom wall surface 20, the inclined wall surface 22, and the top wall surface 24. More specifically, the attitude of the separator substrate 12a with respect to the target source T is changed so as to include each attitude of the separator substrate 12a with respect to the target source T where the film-forming particles P generated by the target source T are deposited from a direction perpendicular to each film-forming surface on the film-forming surfaces of the bottom wall surface 20, the inclined wall surface 22, and the top wall surface 24.

[0035] As shown in FIG. 4A to FIG. 4D, the change in the position of the separator substrate 12a with respect to the target source T is performed by rotating the separator substrate 12a with the direction along the substrate groove portion 28 as the rotation axis X. Specifically, the rotation axis X is set at a position where both sides of the separator substrate 12a can face the target source T. In this embodiment, the rotation axis X is set at a position offset from the separator substrate 12a in the thickness direction. However, the rotation axis X may be an axis passing through the separator substrate 12a. Therefore, the change in the position of the separator substrate 12a with respect to the target source T is performed by rotating (i.e., continuously rotating) the separator substrate 12a around the rotation axis X using a rotary drive device such as an electric motor. More specifically, the change in the position of the separator substrate 12a is performed by rotating the separator substrate 12a around the rotation axis X so as to continuously pass through the positions shown in FIG. 4A to FIG. 4D. 4A to 4D are representative postures of the separator substrate 12a for explaining this embodiment. The posture shown in FIG. 4A is the posture of the separator substrate 12a in which the film-forming particles P are deposited from a direction perpendicular to the bottom wall surface 20 and the top wall surface 24. The posture shown in FIG. 4B is the posture of the separator substrate 12a in which the film-forming particles P are deposited from a direction perpendicular to one of the inclined wall surfaces 22. The posture shown in FIG. 4C is the posture of the separator substrate 12a in which the film-forming particles P do not collide with the separator substrate 12a. The posture shown in FIG. 4D is the posture of the separator substrate 12a in which the film-forming particles P are deposited from a direction perpendicular to the other inclined wall surface 22. When the surface of separator substrate 12a facing rotation device M is exposed to target source T, film-forming particles P can be deposited on the surface of separator substrate 12a even in the position shown in Fig. 4C, and a uniform titanium coating can be formed on both sides of separator substrate 12a. Furthermore, the rotation of separator substrate 12a in the step of forming titanium coating 12b may start from any of the positions shown in Figs. 4A to 4D.

[0036] The change in the position of the separator substrate 12a does not necessarily have to be performed by continuously rotating the separator substrate 12a around the rotation axis X. For example, the change in the position of the separator substrate 12a may be performed by rotating the separator substrate 12a around the rotation axis X intermittently. For example, the change in the position of the separator substrate 12a may be performed by rotating the separator substrate 12a while temporarily stopping the position of the separator substrate 12a in the state shown in FIG. 4A, FIG. 4B, and FIG. 4D (i.e., rotating the separator substrate 12a intermittently). In other words, the titanium film 12b may be formed on the separator substrate 12a while repeating such intermittent rotation. The position of the separator substrate 12a with respect to the target source T may include at least the states shown in FIG. 4A, FIG. 4B, and FIG. 4D, and may include more detailed positions. In this way, when titanium coating 12b is formed on separator substrate 12a while repeating intermittent rotation, even if a coarse titanium film is formed on inclined wall surface 22 when separator substrate 12a is in the position shown in FIG. 4A, a dense titanium film can be formed on inclined wall surface 22 when separator substrate 12a is in the position shown in FIG. 4B and FIG. 4D.

[0037] In addition, the titanium coating 12b is not limited to being formed on the separator substrate 12a while repeating intermittent rotation, but may be formed, for example, by completing the formation of the bottom wall surface 20 and the top wall surface 24 of the separator substrate 12a in the position shown in Fig. 4A, then completing the formation of one of the inclined wall surfaces 22 with the separator substrate 12a in the position shown in Fig. 4B, and finally completing the formation of the other inclined wall surface 22 with the separator substrate 12a in the position shown in Fig. 4D. Note that, although the present specification has described the formation of a film on one surface of the separator substrate 12a, the formation of a film on the other surface of the separator substrate 12a facing away from the one surface may also be performed in the same manner.

[0038] The rotation axis X may be an axis that does not pass through the separator substrate 12a. In this case, the position of the separator substrate 12a relative to the target source T may be changed by continuously or intermittently revolving the separator substrate 12a around the rotation axis X.

[0039] Furthermore, in this embodiment, a step of forming the carbon coating 12c is performed. In this step, the carbon coating 12c is formed on the titanium coating 12b in order to increase the electrical conductivity of the separator 12. The carbon coating 12c is formed by the above-mentioned physical vapor deposition (PVD) method using carbon as a target, for example. In this step, the separator substrate 12a may be rotated as in the step of forming the titanium coating 12b, or the separator substrate 12a may be fixed (i.e., not rotated) during the deposition.

[0040] Next, the operation and effects of the method for manufacturing the fuel cell separator 12 according to the first embodiment will be described.

[0041] As described above, according to the manufacturing method of this embodiment, in the step of forming the titanium film 12b, the separator substrate 12a is placed at a position facing the target source T. In this arrangement, the attitude of the separator substrate 12a is changed with respect to the target source T so that the film-forming particles P generated by the target source T are deposited from the orthogonal direction on each of the bottom wall surface 20, the inclined wall surface 22, and the top wall surface 24. While changing the attitude in this way, a film is formed on the surface of the separator substrate 12a (i.e., the bottom wall surface 20, the inclined wall surface 22, and the top wall surface 24). Therefore, the film-forming particles P can be made to enter the surface of the separator substrate 12a from the front (i.e., perpendicularly). This makes it possible to suppress the attenuation of the kinetic energy of the film-forming particles P after collision with the separator substrate 12a, and to sufficiently diffuse the film-forming particles P on the surface of the separator substrate 12a. As a result, a dense coating can be formed and a sufficient thickness can be ensured over the entire separator substrate 12a, that is, not only on the bottom wall surface 20 and the top wall surface 24 but also on the inclined wall surface 22. This makes it possible to suppress the amount of metal eluted from the separator substrate 12a.

[0042] Furthermore, according to the manufacturing method of this embodiment, in the step of forming the titanium coating 12b, the attitude of the separator substrate 12a is changed by rotating the separator substrate 12a about the rotation axis X in the direction along the substrate groove portion 28. According to this embodiment, by rotating the separator substrate 12a, the film-forming particles P flying from the target source T can be caused to collide evenly with the surface of the separator substrate 12a. As a result, a dense coating can be formed while reducing the difference in film thickness on the bottom wall surface 20, the inclined wall surface 22, and the top wall surface 24 of the separator substrate 12a.

[0043] <Second embodiment> Next, a second embodiment of the present invention will be described. The manufacturing method according to the second embodiment is different from the manufacturing method according to the first embodiment in the posture of the separator substrate 12a in the process of forming the titanium film 12b. Specifically, in the manufacturing method according to the first embodiment, the separator substrate 12a is rotated (i.e., rotated 360° around the rotation axis X) to change the posture of the separator substrate 12a, whereas in the manufacturing method according to the second embodiment, the separator substrate 12a is rotated within a predetermined range to change the posture of the separator substrate 12a. Hereinafter, the same reference numerals are used to designate components having the same or similar functions as those in the manufacturing method according to the first embodiment, and the description thereof is omitted, and only the different parts are described.

[0044] Fig. 5A is a diagram illustrating a process for forming a titanium coating 12b according to a second embodiment of the present invention, and shows the position of the separator substrate 12a on which the film-forming particles P are deposited from a direction perpendicular to the bottom wall surface 20 and the top wall surface 24. Fig. 5B is a diagram illustrating a state in which the separator substrate 12a has been rotated clockwise from the state shown in Fig. 5A, and shows the position of the separator substrate 12a on which the film-forming particles P are deposited from a direction perpendicular to one of the inclined wall surfaces 22. Fig. 5C is a diagram illustrating a state in which the separator substrate 12a has been rotated counterclockwise from the state shown in Fig. 5A, and shows the position of the separator substrate 12a on which the film-forming particles P are deposited from a direction perpendicular to the other inclined wall surface 22.

[0045] As shown in Figures 5A to 5C, in this embodiment, the attitude of the separator substrate 12a is changed by rotating the separator substrate 12a between a first attitude (Figure 5B) and a second attitude (Figure 5C) with the direction along the substrate groove portion 28 as the rotation axis X. Here, the first attitude is the attitude of the separator substrate 12a in which the film-forming particles P are deposited from a direction perpendicular to one of the pair of inclined wall surfaces 22 (Figure 5B). The second attitude is the attitude of the separator substrate 12a in which the film-forming particles P are deposited from a direction perpendicular to the other of the pair of inclined wall surfaces 22 (Figure 5C). Specifically, the change in the position of the separator substrate 12a may be performed by swinging the separator substrate 12a between a first position and a second position while passing through a position (FIG. 5A) of the separator substrate 12a in which the bottom wall surface 20 and the top wall surface 24 face the target source T. That is, the titanium coating 12b is formed on the separator substrate 12a while repeating such swinging, so that a uniform titanium coating 12b can be formed on the separator substrate 12a. Note that the change in the position of the separator substrate 12a is not limited to repeating the swinging of the separator substrate 12a as described above. For example, the formation of one of the inclined wall surfaces 22 may be completed in the position shown in FIG. 5B, then the formation of the bottom wall surface 20 and the top wall surface 24 may be completed in the position shown in FIG. 5A, and finally the formation of the other inclined wall surface 22 may be completed in the position shown in FIG. 5C.

[0046] Thus, in the process of forming the titanium film 12b according to the second embodiment, the position of the separator substrate 12a is changed by rotating the separator substrate between the first position (FIG. 5B) and the second position (FIG. 5C). According to this embodiment, the separator substrate 12a can be always directed toward the target source T by rotating the separator substrate 12a between the first position and the second position. This allows the film-forming particles P to collide evenly with the surface of the separator substrate 12a and to continue to collide continuously. As a result, a dense film can be formed while reducing the difference in film thickness on the bottom wall surface 20, the inclined wall surface 22, and the top wall surface 24 of the separator substrate 12a, and efficient film formation can be performed. EXAMPLES

[0047] The invention is illustrated by the following examples.

[0048] [Example] As the separator substrate, a flat plate made of austenitic stainless steel (JIS standard: SUS304) having a thickness of 100 μm was press-formed into the groove shape shown in FIG. 1. Next, the separator substrate was etched with Ar to remove the passivation film from the surface of the separator substrate. Then, a target source of pure titanium was prepared, and a titanium film was formed on the surface of the separator substrate using a sputtering device while rotating the separator substrate relative to the target source as shown in FIG. 4A to FIG. 4D. Finally, in order to form a carbon film on the titanium film formed on the separator substrate, ion plating was performed using carbon as a target source. The carbon film was formed without rotating the separator substrate. The separator product obtained in this manner was used as a test piece corresponding to a fuel cell separator.

[0049] [Comparative Example] Comparative example test pieces were prepared in the same manner as in the examples, except that the titanium coating was formed on the surface of the separator substrate without rotating the separator substrate relative to the pure titanium target source (i.e., in a fixed state).

[0050] [Durability test (potential corrosion test)] The durability test was performed on the test pieces according to the examples and the comparative examples to simulate a fuel cell environment. Specifically, test samples were cut out to a predetermined size (10 cm x 5 cm) from the test pieces according to the examples and the comparative examples, and the test samples were immersed in a solution (pH 3, fluorine 3 ppm, 80°C). In this state, a counter electrode made of a platinum plate and the test sample (working electrode) were electrically connected to generate a potential difference of 0.9 V between the counter electrode and the working electrode, and this state was continued for 60 hours to corrode the test sample. During the test, the potential of the test sample was kept constant by a reference electrode.

[0051] [Iron (Fe) elution amount measurement, film thickness measurement] During the durability test, the iron components dissolved in the immersion liquid in which the test sample was immersed were measured using an inductively coupled plasma (ICP) emission spectrometer. Based on the measured values, the evaluation area of ​​the test sample after one hour of durability test was 2 The amount of eluted iron per unit time was calculated. Fig. 6 is a graph showing the results of durability tests of the separators manufactured by the methods according to the embodiment of the present invention (with rotation) and the comparative example (without rotation) in terms of the amount of eluted Fe. Table 1 shows the results of measuring the film thickness (unit: nm) of the titanium layer in the separators manufactured by the methods according to the embodiment of the present invention (with rotation) and the comparative example (without rotation).

[0052] [Table 1]

[0053] [Cross-section observation] FIG. 7 shows images of the cross sections of separators produced by methods according to an embodiment of the present invention (with rotation) and a comparative example (without rotation) observed with a scanning microscope, showing images of the top wall surface, inclined wall surface, and bottom wall surface.

[0054] [Results / Discussion] As is clear from the graph in Figure 6, it was found that the separator produced by the method according to the embodiment (with rotation) had a lower amount of Fe elution than the separator produced by the method according to the comparative example (without rotation). The reasons for this result include the improvement in the film quality of the titanium film and the improvement in the film thickness of the titanium film.

[0055] 7, in the comparative example (without rotation), it is observed that a columnar (porous) titanium film is formed (poor film quality) especially on the inclined wall surface. In contrast, in the example (with rotation), it is observed that a flat titanium film (dense titanium film) is formed (good film quality) on the inclined wall surface.

[0056] Here, FIG. 8 is a diagram for explaining the collision direction of the film-forming particles P on the inclined wall surface 22, where (a) shows the collision direction of the film-forming particles P on the inclined wall surface 22 when manufactured by the manufacturing method according to the embodiment (with rotation), and (b) shows the collision direction of the film-forming particles P on the inclined wall surface 22 when manufactured by the manufacturing method according to the comparative example (without rotation). As shown in FIG. 8(a), in the manufacturing method according to the embodiment, it is considered that the film-forming particles P can be made to enter the inclined wall surface 22 of the separator substrate 12a from the front (i.e., perpendicularly). This makes it possible to suppress the attenuation of the kinetic energy of the film-forming particles P after collision with the separator substrate 12a, and it is considered that the film-forming particles P can be sufficiently diffused not only on the bottom wall surface 20 and the top wall surface 24 of the separator substrate 12a but also on the inclined wall surface 22. As a result, it is considered that a dense titanium film can be formed on the entire separator substrate 12a (the quality of the titanium film is improved). Therefore, it is considered that the amount of Fe elution can be suppressed, as shown in FIG.

[0057] In contrast, as shown in Fig. 8(b), in the manufacturing method according to the comparative example, the separator substrate 12a is held with the inclined wall surface 22 facing obliquely to the target source, so that the film-forming particles P flying from the target source are considered to be obliquely incident on the inclined wall surface 22 (i.e., not incident from the front). For this reason, the kinetic energy of the film-forming particles P after colliding with the separator substrate 12a is attenuated (the vertical component is reduced), and the film-forming particles P are considered not to be sufficiently diffused on the inclined wall surface 22. Therefore, it is considered that a columnar coating (porous coating) is formed on the inclined wall surface 22, and as shown in Fig. 6, the amount of eluted Fe is considered to be larger than that in the example.

[0058] Also, as shown in Table 1, it can be seen that the thickness of the titanium film on the inclined wall surface of the separator manufactured by the manufacturing method of the embodiment is thicker than the thickness of the titanium film on the inclined wall surface of the separator manufactured by the manufacturing method of the comparative example. In this way, it is possible to increase the thickness of the titanium film on the inclined wall surface, and therefore it is considered that the amount of Fe elution can be suppressed as shown in Figure 6.

[0059] Also, as shown in Table 1, it can be seen that the thickness of the titanium film of the separator manufactured by the manufacturing method of the embodiment has less variation (smaller difference between the maximum and minimum values) than the thickness of the titanium film of the separator manufactured by the manufacturing method of the comparative example. This is thought to be because the manufacturing method of the embodiment allows the film-forming particles to collide evenly with the bottom wall surface, the inclined wall surface, and the top wall surface of the separator substrate, thereby making it possible to reduce the difference in film thickness over the entire surface of the separator substrate. Therefore, as shown in FIG. 6, it is thought that the amount of Fe elution can be suppressed.

[0060] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the manufacturing method according to the above-mentioned embodiment, and includes all aspects included in the concept of the present invention and the scope of the claims. In addition, each configuration may be appropriately and selectively combined to achieve the above-mentioned problems and effects. For example, the shape, material, arrangement, size, etc. of each component in the above-mentioned embodiment may be appropriately changed depending on the specific embodiment of the present invention. [Explanation of symbols]

[0061] 1: fuel cell, 12: separator, 12a: separator substrate, 12b: titanium coating (metal coating), 20: bottom wall surface, 22: inclined wall surface, 24: top wall surface, 26: groove opening, 28: substrate groove portion (groove portion), P: film-forming particles, T: target source, X: rotation axis

Claims

[Claim 1] A method for manufacturing a separator for a fuel cell, comprising forming a metal coating on a surface of a separator substrate, the method comprising the steps of: preparing a separator substrate having a plurality of linear grooves formed at intervals in a groove width direction as the separator substrate, the linear grooves being channels for fluid flowing through the fuel cell, and a pair of inclined wall surfaces inclined so as to widen from a bottom wall surface toward a groove opening of each of the grooves; and depositing the film-forming particles on a surface of the separator substrate while changing the attitude of the separator substrate with respect to a target source so that the film-forming particles generated by the target source are deposited from a direction perpendicular to each of the bottom wall surface, the inclined wall surface, and the top wall surface formed between the groove portions, with the separator substrate disposed at a position facing a target source, thereby forming the metal coating. a second position of the separator substrate in which the film-forming particles are deposited on the other of the pair of inclined wall surfaces from a direction perpendicular to the first position of the separator substrate, the second position being changed by repeatedly rocking the separator substrate with a direction along the groove portion as a rotation axis, the second position being changed by repeatedly rocking ...

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