Manufacturing method for separator for fuel cell

Abstract

To provide a manufacturing method for a separator for a fuel cell capable of reducing electrical resistance at the contact portion of a pair of separators.SOLUTION: The manufacturing method for a separator for a fuel cell includes a pressing step for press-molding a metal separator base material having a first surface and a second surface into a corrugated shape so as to form a gas flow channel for a reactive gas on the first surface and a cooling flow channel for a cooling medium on the second surface, a roughening step for roughening the second surface to increase the surface roughness of the second surface, and a film-forming step for forming a corrosion-resistant coating on the first surface and the second surface after the roughening step.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] In recent years, technological development has been conducted on fuel cells that contribute to energy efficiency in order to ensure that more people have access to affordable, reliable, sustainable, and advanced energy. One known technology related to this type of fuel cell is a separator manufacturing method in which a corrosion-resistant metal coating is formed on the surface of a metal separator substrate formed into a cross-sectional uneven shape by press molding (see, for example, Patent Document 1). In the method described in Patent Document 1, after protrusions are formed on the separator by press molding, a metal coating and a conductive coating are formed on the surface of the separator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-71352 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when forming the protrusions by press molding, it is difficult to form the top surfaces of the protrusions into a flat shape with high precision. Therefore, when the top surfaces of the protrusions of a pair of separators are abutted against each other and assembled into a fuel cell, the electrical resistance (contact resistance) at the contact points between the pair of separators tends to increase, resulting in a decrease in power generation efficiency. [Means for solving the problem]

[0005] One aspect of the present invention is a method for manufacturing a fuel cell separator, which includes a pressing step in which a metal separator substrate having a first surface and a second surface is pressed into an uneven shape so as to form a gas flow path through which a reactant gas flows on the first surface and a cooling flow path through which a cooling medium flows on the second surface; a roughening step in which the second surface is roughened to increase the surface roughness of the second surface; and a film formation step in which a corrosion-resistant coating is formed on the first surface and on the second surface after the roughening step. [Effects of the Invention]

[0006] According to the present invention, it is possible to reduce the electrical resistance at the contact portion between the pair of separators, thereby enabling efficient power generation. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a perspective view schematically showing the overall configuration of a fuel cell stack including a separator to which a manufacturing method for a fuel cell separator according to an embodiment of the present invention is applied; [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 2 is a perspective view showing a schematic configuration of an electrode assembly included in the fuel cell stack of FIG. [Figure 4] 3 is a rear view of a separator to which a manufacturing method of a fuel cell separator according to an embodiment of the present invention is applied. FIG. [Figure 5] FIG. 4 is a diagram schematically illustrating an example of a cross-sectional shape at a contact portion between a pair of plates that constitute a separator. [Figure 6] 3 is a diagram showing a cross-sectional shape of a contact portion between a pair of plates constituting a separator according to an embodiment of the present invention; FIG. [Figure 7] 3 is a flowchart showing the steps of a method for manufacturing a fuel cell separator according to an embodiment of the present invention. [Figure 8] 8 is a diagram specifically showing a manufacturing method corresponding to the flowchart in FIG. 7. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described with reference to Figs. 1 to 8. A separator manufactured by a manufacturing method for a fuel cell separator according to an embodiment of the present invention is incorporated into a fuel cell stack to form a fuel cell. The fuel cell is mounted, for example, in a vehicle and generates electric power for driving the vehicle. First, the configuration of the fuel cell stack will be described.

[0009] FIG. 1 is a perspective view showing a schematic overall configuration of a fuel cell stack 100 having separators manufactured by a manufacturing method for a fuel cell separator according to an embodiment of the present invention. For convenience, the three mutually orthogonal axial directions shown in the figure are defined as the front-rear direction, the left-right direction, and the up-down direction, and the configuration of each part will be described in accordance with these definitions. The front-rear direction corresponds to the stacking direction of the fuel cell stack 100. The front-rear direction, the left-right direction, and the up-down direction are not necessarily the same as the front-rear direction, the left-right direction, and the up-down direction of a vehicle.

[0010] As shown in Fig. 1, the fuel cell stack 100 has a cell stack 101 formed by stacking a plurality of power-generating cells 1 in the front-to-rear direction, and end units 102 arranged at both front and rear ends of the cell stack 101, and has a generally rectangular parallelepiped shape as a whole. Although not shown in the figure, the cell stack 101 is surrounded by a generally rectangular parallelepiped case. The length of the cell stack 101 in the left-to-right direction is longer than the length in the up-to-down direction. For convenience, only a single power-generating cell 1 is shown in Fig. 1.

[0011] The power-generating cell 1 has a unitized electrode assembly 2 (UEA) having a membrane electrode assembly including an electrolyte membrane and electrodes, and separators 3, 3 arranged on both the front and rear sides of the unitized electrode assembly 2 to sandwich the unitized electrode assembly 2. The unitized electrode assemblies 2 and the separators 3 are arranged alternately in the front-to-rear direction. The unitized electrode assembly 2 can also be called a membrane electrode structure or a membrane electrode member.

[0012] FIG. 2 is a cross-sectional view of a main portion of the cell stack 101 at the center in the left-right direction (a cross-sectional view taken along line II-II in FIG. 1). As shown in FIG. 2, the separator 3 has a front plate 3F and a rear plate 3R, which are a pair of front and rear metal thin plates with a corrugated cross section. The front plate 3F extends in the vertical and horizontal directions and has a front surface 3Fa and a rear surface 3Fb. The rear plate 3R extends in the vertical and horizontal directions and has a front surface 3Ra and a rear surface 3Rb. The opposing front plate 3F and rear plate 3R are joined by welding at their outer peripheral edges, thereby joining the two together. The separator 3 is made of a conductive material with excellent corrosion resistance, such as stainless steel, titanium, or a titanium alloy.

[0013] A cooling flow path PAw through which a coolant flows is formed inside the separator 3 surrounded by the front plate 3F and the rear plate 3R, i.e., between the rear surface 3Fb of the front plate 3F and the front surface 3Ra of the rear plate 3R. The flow of the coolant cools the power generation surface of the power generation cell 1. Water, for example, can be used as the coolant. The surface of the separator 3 facing the integrated electrode assembly 2 (the front surface 3Fa and the rear surface 3Rb) is formed unevenly by press molding or the like to form a gas flow path between the separator 3 and the integrated electrode assembly 2. More specifically, the separator 3 has a pair of front and rear protrusions 31 that protrude toward the integrated electrode assembly 2, and a pair of front and rear recesses 32 that are connected to the pair of front and rear protrusions 31 and are formed in a concave shape.

[0014] The pair of front and rear protrusions 31 abut against the front surface 2a and rear surface 2b of the integrated electrode assembly 2. A compressive load F is applied to the cell stack 101 in the front-to-rear direction during assembly of the fuel cell stack 100, and this compressive load F is maintained after assembly of the fuel cell stack 100 is complete. As a result, a predetermined surface pressure due to the compressive load F acts on the integrated electrode assembly 2 in the front-to-rear direction via the protrusions 31.

[0015] An anode flow path PAa through which a fuel gas flows is formed by a recess 32 between the front surface 2a of the integrated electrode assembly 2 and the rear plate 3R of the separator 3 facing this front surface 2a. A cathode flow path PAc through which an oxidizer gas flows is formed by a recess 32 between the rear surface 2b of the integrated electrode assembly 2 and the front plate 3F of the separator 3 facing this rear surface 2b. The fuel gas is a gas containing hydrogen, and hydrogen gas can be used, for example. The oxidizer gas is a gas containing oxygen, and air can be used, for example. The fuel gas and the oxidizer gas are sometimes referred to as reactant gases without being distinguished from each other.

[0016] Fig. 3 is a perspective view showing a schematic configuration of the integrated electrode assembly 2. As shown in Fig. 3, the integrated electrode assembly 2 has a substantially rectangular membrane electrode assembly (MEA) 20 and a frame 21 that supports the membrane electrode assembly 20. As shown in the detailed view of part A in Fig. 2, the membrane electrode assembly 20 has an electrolyte membrane 23, an anode electrode 24 provided on a front surface 23f of the electrolyte membrane 23, and a cathode electrode 25 provided on a rear surface 23r of the electrolyte membrane 23.

[0017] The electrolyte membrane 23 is, for example, a solid polymer electrolyte membrane, and a thin film of a perfluorosulfonic acid polymer containing water can be used. The electrolyte membrane 23 is not limited to a fluorine-based electrolyte membrane, and a hydrocarbon-based electrolyte membrane can also be used.

[0018] The anode 24 is formed on the front surface 23f of the electrolyte membrane 23 and includes an electrode catalyst layer 241 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 242 that is provided in front of the electrode catalyst layer 241 and diffuses and supplies a fuel gas. An intermediate layer (base layer) may be provided between the electrode catalyst layer 241 and the gas diffusion layer 242. Only the electrode catalyst layer 241 may be referred to as the anode 24.

[0019] The cathode electrode 25 is formed on the rear surface 23r of the electrolyte membrane 23 and includes an electrode catalyst layer 251 that serves as a reaction field for an electrode reaction, and a gas diffusion layer 252 that is provided on the rear surface of the electrode catalyst layer 251 and diffuses and supplies an oxidant gas. An intermediate layer (base layer) may be provided between the electrode catalyst layer 251 and the gas diffusion layer 252. Only the electrode catalyst layer 251 may be referred to as the cathode electrode 25.

[0020] At the anode electrode 24, the fuel gas (hydrogen) supplied via the anode flow path PAa is ionized by the action of a catalyst and moves toward the cathode electrode side through the electrolyte membrane 23. The electrons generated at this time pass through an external circuit and are extracted as electrical energy. At the cathode electrode 25, the oxidant gas (oxygen) supplied via the cathode flow path PAc reacts with the hydrogen ions introduced from the anode electrode 24 and the electrons moved from the anode electrode 24, producing water. The produced water (referred to as "produced water") provides an appropriate humidity to the electrolyte membrane 23, and excess water is discharged to the outside of the integrated electrode assembly 2 along the gas flow. The produced water on the cathode side also flows toward the anode side by reverse diffusion through the electrolyte membrane 23. Therefore, produced water exists in both the anode flow path PAa and the cathode flow path PAc.

[0021] 3, the frame 21 is a thin plate having a substantially rectangular shape and is made of insulating resin, rubber, or the like. A substantially rectangular opening 21a is provided in the center of the frame 21. The membrane electrode assembly 20 is provided so as to cover the entire opening 21a, and the peripheral edge of the membrane electrode assembly 20 is supported by the frame 21.

[0022] Three through holes 201-203 are aligned vertically and penetrate the frame 21 in the front-to-rear direction on the left side of the opening 21a of the frame 21. Three through holes 204-206 are aligned vertically and penetrate the frame 21 in the front-to-rear direction on the right side of the opening 21a.

[0023] As shown in FIG. 1, the front and rear separators 3 of the integrated electrode assembly 2 are provided with through holes 301 to 306 that penetrate the separators 3 in the front-rear direction at positions corresponding to the through holes 201 to 206 of the frame 21. The through holes 301 to 306 are connected to the through holes 201 to 206 of the frame 21, respectively. A collection of these mutually communicating through holes 201 to 206 and 301 to 306 form flow paths PA1 to PA6 (indicated by arrows for convenience) that penetrate the cell stack 101 and extend in the front-rear direction. The flow paths PA1 to PA6 are sometimes called manifolds. The flow paths PA1 to PA6 are connected to a manifold external to the fuel cell stack 100.

[0024] In the rear end unit 102, a plurality of through holes 102a to 102f are formed at positions corresponding to the through holes 201 to 206, 301 to 306 of the cell stack 101, passing through the end unit 102 in the front-rear direction.

[0025] Fuel gas is supplied to the fuel cell stack 100 via the through-hole 102a along the solid-line flow path PA1. This fuel gas is guided to the anode flow path PAa between the integrated electrode assembly 2 and the rear plate 3R of the separator 3 via the through-holes 201 and 301. After passing through the anode flow path PAa, the fuel gas (fuel exhaust gas) is discharged from the through-hole 102f via the through-holes 206 and 306 and along the solid-line flow path PA6.

[0026] The oxidant gas is supplied to the fuel cell stack 100 via the through-hole 102d along the dotted flow path PA4. This oxidant gas is guided via the through-holes 204 and 304 to the cathode flow path PAc between the integrated electrode assembly 2 and the front plate 3F of the separator 3. After passing through the cathode flow path PAc, the oxidant gas (oxidant exhaust gas) is discharged from the through-hole 102c via the through-holes 203 and 303 and along the dotted flow path PA3.

[0027] A cooling medium is supplied to the fuel cell stack 100 via the through-hole 102e along the flow path PA5 shown in dashed dotted line. This cooling medium is guided to the cooling flow path PAw between the front plate 3F and the rear plate 3R of the separator 3 via the through-holes 205 and 305. After passing through the cooling flow path PAw, the cooling medium is discharged from the through-hole 102b via the through-holes 202 and 302 along the flow path PA2 shown in dashed dotted line. The above is a schematic configuration of the fuel cell stack 100.

[0028] The structure of the separator 3 will be described in more detail. Fig. 4 is a rear view (view from behind) of the separator 3. That is, Fig. 4 is a view showing the rear surface 3Rb (Fig. 2) of the rear plate 3R that faces the anode electrode 24 on the front surface 2a of the integrated electrode assembly 2.

[0029] In Figure 4, the region of the integrated electrode assembly 2 facing the membrane electrode assembly 20, i.e., the region AR1 facing the power generation surface, is called the active region of the separator 3, and the region AR2 other than the active region is called the inactive region. The active region AR1 is the region where power generation occurs. As shown in Figure 4, in the active region AR1 on the rear surface 3Rb of the rear plate 3R, a plurality of protrusions 31 (Figure 2) are provided protruding rearward at equal intervals in the vertical direction over almost the entire area, although some are not shown.

[0030] More specifically, as shown in the detailed view of part B in Fig. 4, the multiple protrusions 31 each extend in a meandering manner in the left-right direction, and recesses 32 are provided between adjacent protrusions 31 in the up-down direction. An anode flow path PAa is formed between the multiple recesses 32 and the front surface 2a (Fig. 2) of the membrane electrode assembly 20. Note that in the detailed view of part B, only the outline of the bottom surface of the anode flow path PAa (the bottom surface of the recesses 32) is shown by a solid line.

[0031] A plurality of protrusions 31 (FIG. 2) are also provided protruding forward across almost the entire active area AR1 of the front surface 3Fa of the front plate 3F, at equal intervals in the vertical direction. Each of the plurality of protrusions 31 extends in a meandering manner in the left-right direction, and a recess 32 is provided between adjacent protrusions 31 in the vertical direction. A cathode flow path PAc is formed between the plurality of recesses 32 and the rear surface 2b (FIG. 2) of the membrane electrode assembly 20. In the detailed view of part B, only the outline of the bottom surface of the cathode flow path PAc (the bottom surface of the recess 32) is shown by a dotted line.

[0032] 2, the recesses 32 of the rear plate 3R and the recesses 32 of the front plate 3F form protrusions 320 when viewed from the cooling flow path PAw side. The top surfaces 321 of these protrusions 320, i.e., the front end surfaces of the protrusions 320 of the rear plate 3R and the rear end surfaces of the protrusions 320 of the front plate 3F, abut against each other. Current flows between the pair of plates 3R and 3F, i.e., between the power generating cells 1, 1, via this abutment 320a.

[0033] 4, the recesses 32 (protrusions 320) of the rear plate 3R and the recesses 32 (protrusions 320) of the front plate 3F are formed out of phase with each other in the left-right direction. Therefore, the protrusions 320 of the rear plate 3R and the protrusions 320 of the front plate 3F intersect and come into contact at the contact portions 320a, and the overall contact area is small.

[0034] 5 is a diagram schematically illustrating an example of the cross-sectional shape of the contact portion 320a of the separator 3, showing an ideal state and an actual state. As shown in FIG. 5, in the ideal state, the top surface 321 of the protrusion 320 is flat. Therefore, the flatness of the top surface 321 is small, and the top surface 321 of the protrusion 320 of the rear plate 3R and the top surface 321 of the protrusion 320 of the front plate 3F come into surface contact with each other over a predetermined length L.

[0035] On the other hand, because the protrusions 320 are formed by press working, in actual use, the protrusions 320 are, for example, approximately arc-shaped and protrude toward the center in the left-right direction, increasing the flatness PL of the protrusions 320. Therefore, the front plate 3F and the rear plate 3R do not make surface contact but make point contact at contact points 321a on the top surfaces 321, reducing the contact area. In particular, because the protrusions 320 abut against each other at an intersection (FIG. 4), a sufficient contact area cannot be obtained. As a result, contact resistance increases, hindering the flow of current between the pair of plates 3R and 3F.

[0036] Therefore, in order to reduce the contact resistance, the present embodiment configures the contact portion 320a of the separator 3 as follows. FIG. 6 is a diagram schematically illustrating the cross-sectional shape of the contact portion 320a of the separator 3 according to the present embodiment. As shown in FIG. 6, the top surfaces 321 of the pair of plates 3R, 3F are roughened to increase the surface roughness Ra, forming the top surfaces 321 in an uneven shape. The roughening is performed by, for example, laser processing using a laser processing machine. That is, the roughening (also called roughening treatment) is performed by irradiating the top surfaces 321 with a laser beam.

[0037] The size (length in the front-to-rear direction) of the uneven portions of top surface 321 is minute. For example, the surface roughness (arithmetic mean roughness) Ra of top surface 321 is 1 μm or more and 20 μm or less, and preferably 1 μm or more and 10 μm or less. The target surface roughness of top surface 321 is set according to the flatness PL of top surface 321. In other words, the target surface roughness is set so that it increases as the flatness PL increases. More specifically, the target surface roughness is set to a value that is the same as or equivalent to the magnitude of the flatness PL, and top surface 321 is laser-processed so that the actual surface roughness Ra becomes the target surface roughness. Note that instead of using the arithmetic mean roughness Ra as the target surface roughness, the maximum height Ry or ten-point mean roughness Rz may be used.

[0038] By roughening the top surfaces 321 by laser processing (increasing the surface roughness), the number of points of contact increases, or contact occurs between the inclined surfaces extending in the front-to-rear direction. This increases the contact area between the top surfaces 321 of the pair of plates 3R, 3F. This reduces contact resistance and promotes the flow of current between the pair of plates 3R, 3F.

[0039] However, if iron ions leach from the gas-side surfaces of the separators 3 (the rear surface 3Rb of the rear plate 3R and the front surface 3Fa of the front plate 3F) into the water in the gas flow paths PAa and PAc, the iron ions may reach the electrolyte membrane 23 and cause deterioration of the electrolyte membrane 23. Therefore, to prevent the leaching of iron ions, it is necessary to apply a corrosion-resistant coating to the gas-side surfaces of the separators 3. On the other hand, even if iron ions leach from the coolant-side surfaces of the separators 3 (the front surface 3Ra of the rear plate 3R and the rear surface 3Fb of the front plate 3F), they do not cause deterioration of the electrolyte membrane 23. Therefore, from the perspective of preventing deterioration of the electrolyte membrane 23, it is not necessary to coat the coolant-side surfaces of the separators 3.

[0040] However, in this embodiment, as described above, the top surface 321 of the separator 3 is processed to increase its surface roughness. Therefore, as the fuel cell is used for a longer period of time, an oxide film is formed on the top surface 321 due to the dissolved oxygen contained in the water used as a coolant. As a result, the contact resistance increases, and there is a risk that the effect of reducing the contact resistance achieved by the laser processing will be lost. Therefore, in this embodiment, in order to prevent the formation of an oxide film on the top surface 321, a coating is applied to the top surface 321 after the laser processing.

[0041] Specifically, a highly corrosion-resistant metal film (titanium film) made of titanium, a titanium alloy, or the like is formed on top surface 321 by physical vapor deposition (PVD) such as sputtering, vacuum deposition, or ion plating. The thickness of the titanium film is thinner than the surface roughness Ra, and is preferably at least 85 nm and on average 90 to 100 nm.

[0042] Furthermore, a highly conductive film (carbon film) made of carbon or the like is formed on the titanium film by physical vapor deposition to increase the conductivity of the separator 3. The thickness of the carbon film is thinner than the surface roughness Ra, and is, for example, at least 65 nm or more, and preferably an average of 70 to 75 nm.

[0043] The above-described method for manufacturing a fuel cell separator can be summarized as follows. FIG. 7 is a flowchart showing the main steps of the method for manufacturing a fuel cell separator, and FIG. 8 is an image diagram explaining each step in FIG. 7. Hereinafter, the separator 3 before the carbon coating is formed, i.e., before completion, will be referred to as the separator substrate 3a to distinguish it from the completed separator 3. In FIG. 8, the separator manufacturing method will be described using the rear plate 3R, but the same applies to the front plate 3F.

[0044] 7 and 8, first, in step S1, the separator substrate 3a is pressed using a press (not shown) to form convex portions 31 and concave portions 32 for the gas flow paths PAa and PAc in the separator substrate 3a. As a result, convex portions 320 that protrude forward are formed on the front surface 3Ra of the separator substrate 3a, which is the back side of the concave portions 32 (pressing process). Although not shown, convex portions for sealing and the like are also simultaneously formed in the inactive area AR2 (FIG. 4) of the separator substrate 3a.

[0045] Next, in step S2, a laser beam is irradiated onto the top surfaces 321 of the convex portions 320 using a laser processing machine (not shown) so that the surface roughness Ra of the top surfaces 321 becomes the target surface roughness. As a result, the top surfaces 321 are roughened and the surface roughness increases (roughening step). At this time, the positions of the convex portions 320 are stored in a computer in advance, and the operation of the laser processing machine is controlled by the computer so that the laser beam is irradiated only onto the top surfaces 321. This reduces the processing time.

[0046] Next, in step S3, a titanium film 322 is formed by physical vapor deposition on the laser-processed top surface 321 (metal film formation step). At this time, the film formation area is limited so that the film is formed only on the top surface 321. This makes it possible to save film formation materials.

[0047] Next, in step S4, a carbon coating 323 is formed on the surface of the titanium coating 322 by physical vapor deposition (carbon coating process). At this time, the area of ​​the coating is limited so that the coating is formed only on the top surface 321. This makes it possible to save on the coating material. Note that in FIG. 8, the unevenness of the top surface 321 is exaggerated for convenience.

[0048] This completes the rear plate 3R of the separator 3. Then, the front plate 3F is manufactured in the same way, and the pair of plates 3F, 3R are welded together to form the separator 3. Although not explained further, the manufacturing method of the separator 3 also includes a polishing process and the like.

[0049] According to this embodiment, the following effects can be achieved. (1) A manufacturing method of a fuel cell separator (e.g., a rear plate 3R) includes a pressing process (step S1) in which a metallic separator substrate 3a having a rear surface 3Rb and a front surface 3Ra is pressed into an uneven shape so as to form an anode flow path PAa through which fuel gas flows on the rear surface 3Rb and a cooling flow path PAw through which a coolant flows on the front surface 3Fa; a roughening process (step S2) in which the front surface 3Ra (particularly the top surface 321) is roughened to increase the surface roughness Ra of the front surface 3Ra; and a metal deposition process (step S3) in which a corrosion-resistant titanium coating is formed on the rear surface 3Rb and on the front surface 3Ra (particularly the top surface 321) after the roughening process (FIGS. 7 and 8).

[0050] This configuration reduces the contact resistance at the contact portion 320a where the pair of plates 3R, 3F contact each other across the cooling flow path PAw. This promotes the flow of current between the plates 3R, 3F, thereby reducing the number of stacked power-generating cells 1 required to generate a predetermined amount of power, enabling more efficient power generation. As a result, costs can be reduced and the fuel cell stack 100 can be made smaller.

[0051] (2) The roughening step includes irradiating a laser beam onto the front surface 3Ra of the rear plate 3R, particularly onto the top surface 321. This makes it possible to easily process a predetermined area of ​​the top surface 321 to have a desired surface roughness Ra.

[0052] (3) The pressing step includes forming convex portions (protrusions) 320 that protrude toward the front surface 3Ra on the separator substrate 3a of the rear plate 3R (FIG. 8). The roughening step includes roughening the top surfaces 321 of the convex portions 320 on the front surface 3Ra (FIG. 8). This narrows the range to be laser-processed, allowing the roughening step to be completed in a short time, enabling the separator 3 to be manufactured efficiently.

[0053] (4) The film forming process includes forming a corrosion-resistant titanium film on the rear surface 3Rb of the rear plate 3R and the front surface 3Ra (particularly the top surface 321) after the roughening process, and then forming a conductive carbon film (step S4) (FIGS. 7 and 8). This, together with the reduction in contact resistance, further improves the conductivity between the plates 3R and 3F.

[0054] (5) The roughening step includes roughening the front surface 3Ra (particularly the top surface 321) of the rear plate 3R to a surface roughness of 1 μm or more and 20 μm or less. This effectively increases the contact area of ​​the contact portion 320a, which may otherwise come into point contact due to press working.

[0055] The above embodiment can be modified in various ways. Some modifications will be described below. In the above embodiment, the separator substrate is pressed into an uneven shape so that the gas flow paths PAa and PAc through which the fuel gas and the oxidant gas flow are formed on the rear surface 3Rb (first surface) of the rear plate 3R and the front surface 3Fa (first surface) of the front plate 3F, and the cooling flow paths PAw through which the coolant flows are formed on the front surface 3Ra (second surface) of the rear plate 3F and the rear surface 3Fb (second surface) of the front plate 3F. However, the shapes of the flow paths PAa, PAc, and PAw are not limited to those described above.

[0056] In the above embodiment, the roughening step involves irradiating the laser beam only onto the portion of the front surface 3Ra of the rear plate 3R that comes into contact with the front plate 3F, but the laser beam may be irradiated onto the entire front surface 3Ra. In the above embodiment, the roughening step is performed by laser processing, but the roughening step may be performed by other processing. In the above embodiment, the film-forming step (metal film-forming step, carbon film-forming step) involves forming the corrosion-resistant titanium film 322 and the conductive carbon film 324 only on the top surfaces 321 of the convex portions 320 of the front surface 3Ra of the rear plate 3R, but films may be formed on other portions. In the film-forming step, only the corrosion-resistant film may be formed.

[0057] In the above embodiment, an example of applying the fuel cell stack 100 to a vehicle has been described. However, a fuel cell stack having a separator manufactured by the manufacturing method according to an embodiment of the present invention can also be applied to moving bodies other than vehicles, such as aircraft and ships, robots, and various industrial machines.

[0058] The above description is merely an example, and the present invention is not limited to the above-described embodiment and modifications as long as the features of the present invention are not impaired. One or more of the above-described embodiment and modifications can be arbitrarily combined, and modifications can also be combined with each other.

[0059] 3 Separator, 3F Front plate, 3R Rear plate, 3Fa Front surface, 3Fb Rear surface, 3Ra Front surface, 3Rb Rear surface, 3a Separator substrate, 320 Convex portion, 321 Top surface, 322 Titanium coating, 323 Carbon coating, PAa Anode flow path, PAc Cathode flow path, PAw Cooling flow path

Claims

1. a pressing step of pressing a metallic separator substrate having a first surface and a second surface into an uneven shape so as to form a gas flow path through which a reaction gas flows on the first surface and a cooling flow path through which a cooling medium flows on the second surface; a roughening step of roughening the second surface so as to increase the surface roughness of the second surface; a film-forming step of forming a corrosion-resistant film on the first surface and on the second surface after the roughening step.

2. 2. The method for producing a fuel cell separator according to claim 1, 4. A method for manufacturing a fuel cell separator, wherein the roughening step includes irradiating the second surface with a laser beam.

3. 3. The method for producing a fuel cell separator according to claim 1 or 2, the pressing step includes forming a protruding portion on the separator substrate that protrudes toward the second surface side, The method for manufacturing a fuel cell separator, wherein the roughening step includes roughening the top surfaces of the protrusions on the second surface.

4. 3. The method for producing a fuel cell separator according to claim 1 or 2, a second surface formed on the second surface after the roughening step; a second surface formed on the second surface after the roughening step; a second surface formed on the second surface after the roughening step; a second surface formed on the second surface;

5. 3. The method for producing a fuel cell separator according to claim 1 or 2, The method for manufacturing a fuel cell separator, wherein the roughening step includes roughening the second surface to a surface roughness of 1 μm or more and 20 μm or less.

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