JP2005078981A - Separator for fuel cell and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell and a method of manufacturing the same in which assemblability of the fuel cell by reducing warpage and power generation efficiency of the fuel cell is improved by reducing scattering of gas distribution flow after the assembling of the fuel cell. <P>SOLUTION: In a separator of a gold fuel cell which is formed of group thin plate and includes a projection or recession-shaped flow channel for oxidant gas or fuel gas at the center, the flow channel is constructed so that a cross section in the direction perpendicular to the flow channel is corrugated shape, has a plurality rib mounds and channels alternately formed, an angle made by a flat portion of the rib mound 7 and an inclined surface portion of the rib mound 8 is an obtuse angle, and the flat portion of the rib mound 7 and a channel bottom portion 9 are arranged substantially in parallel. In a case that the length of the flat portion of the rib mound 7, the length of the inclined surface portion of the rib mound in the surface direction, the length of the channel bottom portion 9 and depth of the channel are represented by L1, L2, L3 and d, the board thickness t of the separator is 0.05-0.10 mm, and the following relations are satisfied;2t≤L2≤6t, 8t≤L1≤20t, and 5t≤d≤15t. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a fuel cell separator applied to a solid polymer electrolyte fuel cell and the like, and a method for producing the same.

  A fuel cell is a device that directly converts a fuel's chemical energy into electric energy by electrochemically reacting a fuel gas such as a hydrogen-containing gas, which is a reaction gas, and an oxidant gas such as air. Since chemical energy can be directly converted into electric energy, the power generation efficiency of fuel cells is higher than other power generation systems such as thermal power generation. In addition, since no fossil fuel is used, depletion of resources does not pose a problem, and since there is an advantage that no exhaust gas is generated with power generation, fuel cells are attracting attention from the viewpoint of protecting the global environment.

  Fuel cells include a solid polymer electrolyte type, a phosphoric acid type, a molten carbonate type, and a solid oxide type, depending on the type of electrolyte used. One of them, a polymer electrolyte fuel cell (PEFC), uses a polymer resin membrane having a proton exchange group in the molecule as an electrolyte, and saturates the polymer resin membrane with water. In other words, the battery functions as a proton conductive electrolyte. Solid polymer electrolyte fuel cells operate at a relatively low temperature and have high power generation efficiency, and therefore are expected to be used in various applications including those for electric vehicles. The solid polymer electrolyte fuel cell exhibits, for example, the following electrode reaction.

[Chemical 1]
Fuel electrode: H ₂ → 2H ⁺ + 2e ⁻ Expression (1)
Oxidant electrode: (1/2) O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2)
Fuel gas is supplied to the fuel electrode, and the reaction of Formula (1) proceeds to generate protons. Protons move through the solid polymer electrolyte in a hydrated state to reach the oxidant electrode. At the oxidant electrode, the reaction of the formula (2) proceeds by this proton and oxygen in the supplied oxidant gas. The reaction of Formula (1) and Formula (2) proceeds at each pole, and the fuel cell generates an electromotive force.

  Such a configuration of the solid polymer electrolyte fuel cell includes a fuel cell stack in which a plurality of single cells as basic units are stacked. Each single cell has an oxidant electrode side separator and a fuel electrode side separator disposed on both sides of a membrane electrode assembly in which a solid polymer electrolyte membrane is sandwiched between an oxidant electrode and a fuel electrode. It connects the current between the cells and isolates the fuel and oxygen.

  Since the separator has a function of electrically connecting each cell, the separator is required to have good electrical conductivity and low contact resistance with a constituent material. For example, a separator in which carbon, which is a raw material, is formed into a plate shape and reaction gas channels are formed on both sides thereof is used (see Non-Patent Document 1). When the separator was made of carbon, the contact resistance between the separator and the constituent material was low, but the strength was low compared to a metal separator. For this reason, the thickness of the carbon separator cannot be reduced, and a thickness of at least about 1 [mm] to 5 [mm] is required, so that the fuel cell cannot be reduced in size.

Therefore, in recent years, in order to realize miniaturization and cost reduction of the fuel cell, an attempt has been made to use a metal sheet as a separator, press the metal sheet, and use a separator having a corrugated shape with a continuous cross section. (See Patent Document 2 and Patent Document 3).
"Development and commercialization of polymer electrolyte fuel cells", published by Technical Information Association, 1999 (page 92) JP 2000-323149 A (page 4, FIG. 1) JP 2002-190305 A (page 3, FIG. 1)

  However, when a metallic separator is press-molded into a corrugated shape, a load is applied to the thin metal plate, and the separator is deformed unevenly, resulting in plastic strain and residual stress in the separator. In addition, when a section having a corrugated cross section was formed into a separator having a concavo-convex shape, the residual stress generated on both surfaces of the separator was different due to the concavo-convex shape of the separator, and the separator after press molding was warped.

  In addition, the separator is usually disposed adjacent to the gas diffusion electrode. However, if the separator is excessively warped, the gas diffusion electrode cannot be fully tracked when the fuel cell is assembled, and the gas diffusion electrode is formed from carbon paper. As a result, the fuel cell was difficult to assemble.

  Furthermore, if the separator is excessively warped, even if the fuel cell is assembled, the surface pressure between the assembled gas diffusion electrode and the rib surface of the separator becomes non-uniform, resulting in increased contact resistance and gas Due to variations in distribution, the power generation efficiency of fuel cells has been reduced.

  The present invention has been made to solve the above problems, and in order to achieve a reduction in the size of the fuel cell stack, an improvement in the output density of the fuel cell, and a reduction in cost, the metal sheet is press-molded to have a corrugated cross section. It solves the occurrence of warping that occurs when it is molded into a shape.

  That is, the fuel cell separator according to the first aspect of the present invention is formed of a thin metal plate, and has a concavo-convex oxidant gas or fuel gas flow path at the center, and a cross section perpendicular to the flow path is corrugated. A plurality of rib crests and grooves alternately, the angle formed by the rib crest flat portion and the rib crest slope portion being an obtuse angle, and the rib crest flat portion and the groove bottom portion being substantially parallel to each other The thickness t1 of the separator at the outer peripheral edge which is the outer periphery of the central portion, the length L1 of the rib crest flat portion, the surface direction length L2 of the rib crest slope portion, the length L3 of the groove bottom and the groove depth. In the case of d, the separator thickness t is 0.05 to 0.10 mm, and 2t ≦ L2 ≦ 6t, 8t ≦ L1 ≦ 20t, and 5t ≦ d ≦ 15t. .

  A method for manufacturing a fuel cell separator according to a second aspect of the present invention is a method for manufacturing a fuel cell separator formed from a thin metal plate and having a central portion with an uneven shape to form a flow path for an oxidant gas or a fuel gas, The clearance between the punch and the die of the press mold for forming the uneven shape forming the flow path is set to 3 to 7 times the plate thickness t at the outer peripheral edge of the separator, so that the rib crest portion is not restrained. The gist is to press-mold.

  According to the separator for a fuel cell of the present invention, it is possible to improve the assemblability of the fuel cell by reducing warpage, and to improve the power generation efficiency of the fuel cell by reducing variations in gas distribution after the assembly of the fuel cell.

  According to the method for manufacturing a fuel cell separator of the present invention, it is possible to obtain a fuel cell separator with reduced warpage by preventing the occurrence of warpage during press molding. It is possible to increase the power generation efficiency by reducing variations in gas distribution after assembly.

  Hereinafter, a fuel cell separator and a manufacturing method thereof according to an embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a top view of a fuel cell separator on the gas flow path side, and FIG. 2 is a diagram schematically showing a cross section of the fuel cell separator.

  As shown in FIG. 1, the fuel cell separator 1 includes alternating convex rib crests 3 for conducting current to a central portion 2 as a power generation section and concave gas flow channel grooves 4 adjacent to the rib crests 3. The gas channel groove 4 is connected to a gas manifold 5 formed at the end of the central portion 2 on the diagonal line. A bead portion 6 is formed on the outer peripheral edge of the separator 1 on the outer periphery of the central portion 2. When the separator 1 is observed from a cross section, it has a continuous corrugated shape as shown in FIG.

  FIG. 3 is a view for explaining a cross section in the central portion 2 of the fuel cell separator 1. As shown in FIG. 3, a groove bottom portion 9 is continuous from the rib crest flat portion 7 through the rib crest slope portion 8 to the central portion 2 of the fuel cell separator 1. 9 are arranged substantially in parallel. The angle formed by the adjacent rib crest flat part 7 and rib crest slope part 8 is an obtuse angle.

  The thickness t of the outer peripheral edge portion of the fuel cell separator 1 is 0.05 [mm] to 0.10 [mm], the length of the rib crest flat portion is L1, and the surface direction of the rib crest slope portion is When the length is L2, the length of the groove bottom is L3, and the groove depth is d, the fuel cell separator 1 has 2t ≦ L2 ≦ 6t, 8t ≦ L1 ≦ 20t, 5t ≦ d ≦ 15t. It has a shape that satisfies the relationship. Furthermore, in order to maintain high power generation efficiency, it is preferable to satisfy the relationship of L1 ≧ 3L2.

  The fuel cell separator 1 is composed of a clad alloy plate in which a coating layer is formed by subjecting both surfaces of a base material to a corrosion-resistant and conductive surface treatment.

  As a base material, it is good to form from the alloy which combined 1 type, or 2 or more types selected from Fe base alloy, Ni base alloy, Ti base alloy, and stainless steel alloy. Among the Fe-based alloys, ferritic stainless steel plates such as SUS430 or austenitic stainless steel plates such as SUS304 and SUS316 are most preferable from the viewpoints of corrosion resistance, workability, and cost.

  The coating layer formed on both surfaces of the base material is composed of a noble metal such as gold (Au), platinum (Pt), or silver (Ag). Among these noble metals, Au is particularly preferable, corrosion resistance and spreadability are good, and high electrical conductivity can be obtained.

  The covering layer is a layer formed by forming a noble metal layer having a thickness of 0.01 to 0.05 μm on a base material and rolling it at a rolling rate of 5% or more. As described above, when a clad alloy plate having a noble metal layer formed on a base material is used, the power generation efficiency of the fuel cell can be maintained because the contact resistance is low, and a fuel cell separator having excellent durability and reliability can be obtained at low cost. be able to.

  Further, by forming the clad alloy plate from the above material, the strength can be ensured even when the fuel cell is downsized, the fuel cell separator can be thinned, and a fuel cell with high output density can be obtained. be able to.

  The fuel cell separator 1 is manufactured by the following manufacturing method.

  First, as a base material, an alloy plate combining one or more selected from an Fe-based alloy, Ni-based alloy, Ti-based alloy and stainless steel alloy is prepared, and gold (Au) is formed on both surfaces of the base material. A noble metal layer having a thickness of 0.01 to 0.05 μm is formed of a noble metal such as. Thereafter, rolling is performed at a rolling rate of 5% or more to produce a clad alloy plate.

  Examples of the method for forming the noble metal layer on the book include PVD processes such as vacuum deposition, sputtering, and ion plating, CVD processes, and plating processes such as electroplating and electroless plating. Rolling improves the adhesion between the base metal and the noble metal layer, densifies the porous structure of the noble metal layer, and closes the pinhole to improve the corrosion resistance. It can be rolled using a roll.

  The produced clad alloy plate is put into a press die and press-molded to obtain a corrugated fuel cell separator.

  FIG. 4 is a cross-sectional view schematically showing a cross section of a press die and a clad alloy plate at the time of press forming. As shown in FIG. 4, the clearance C between the punch 10 and the die 11 that are the upper die and the lower die is 3 to 7 times the plate thickness t of the outer peripheral edge of the separator, and the rib crest slope portion 8 is Then, press molding is performed in a state where the press dies 10 and 11 are not restrained.

  Next, for Example 1 to Example 11 and Comparative Examples 1 to 6, various production conditions were changed to produce fuel cell separators, and the amount of warpage was measured for each produced fuel cell separator. The assembly of the fuel cell was evaluated.

Examples 1 to 11
In each of Examples 1 to 11, all of the SUS316L thin plate material were plated with gold (Au) to form a coating layer having a thickness of 0.03 [μm], and then rolled at a rolling rate of 10%. Thus, a clad thin plate material having a thickness of 0.05 [mm] to 0.20 [mm] was produced. The produced clad thin plate material was cut into 150 [mm] squares in length and width to form a square plate material, and then press molded to obtain the shape shown in FIGS.

  The vertical and horizontal of the uneven central part 2 forming the gas flow path and rib crest of the fuel cell separator 1 obtained after press molding is 100 [mm], and the vertical and horizontal of the outer periphery of the bead part 6 is 120 [mm]. The width is 4 [mm]. Further, in any of the separators of Examples 1 to 11, the thickness t of the outer peripheral edge portion is 0.05 to 0.10 [mm], the length of the rib crest flat portion is L1, and the rib crest When the length in the surface direction of the slope portion is L2, the length of the groove bottom portion is L3, and the groove depth is d, 2t ≦ L2 ≦ 6t, L1 ≧ 3L2, 8t ≦ L1 ≦ 20t, 5t ≦ d ≦ The shape satisfies all the relationships of 15t.

Comparative Examples 1 to 6
In this comparative example, the clad thin plate material made of the same material as that of the above-described Example 1 to Example 11 is used. In Comparative Example 1 and Comparative Example 2, 0.05 [mm] to 0.20 [mm]. A clad thin plate material having a thickness was used, and in Comparative Examples 3 to 6, a clad thin plate material having a thickness outside the range of 0.05 [mm] to 0.20 [mm] was used. In Comparative Examples 1 to 6, using a clad thin plate material having a predetermined thickness, the width of the clearance C is changed, and the clearance C is 3 to 7 times the plate thickness t of the outer peripheral edge of the separator. Press molding was performed as a condition outside the range, and the shapes shown in FIGS. 1 and 2 were obtained. The separator after press molding does not have a shape that satisfies all the relationships of 2t ≦ L2 ≦ 6t, 8t ≦ L1 ≦ 20t, and 5t ≦ d ≦ 15t, and any of the conditions falls outside the above range.

Evaluation is made on the cross-sectional shape of the fuel cell separator produced in Examples 1 to 11 and Comparative Examples 1 to 3, the difference in clearance between the press die and the clad plate at the time of press molding, and the quality of the product. As an index, the amount of warpage was measured and the assembly property of the fuel cell was evaluated. The amount of warpage is, for example, by placing the separator on a horizontal surface plate, gradually lowering the pressing plate parallel to the horizontal surface plate from the top of the separator, and starting from the height at which the pressing plate starts to contact the separator. The descent distance until it touches the horizontal surface plate was measured, and the descent distance was taken as the amount of warpage. Moreover, the assembly property of the fuel cell is calculated by calculating the average of the assembly time (the number of assembly steps) of the fuel cell using each separator of Examples 1 to 11, and is, for example, 70% with respect to the calculated average assembly time. Those with less assembly time were evaluated as “good” and those with assembly time longer than 30% were evaluated as “bad”. Each evaluation result is shown in Table 1.

  As is apparent from the measurement results of the warpage amount shown in Table 1, in Comparative Examples 1 to 6, the warpage amount shows a high value of 10 [mm], whereas Examples 1 to Examples In No. 11, the amount of warpage was 3.0 [mm] or less, and it was found that the amount of warpage could be greatly reduced. In particular, when a clad thin plate material having a plate thickness of 0.05 [mm] was used, the value of the warp amount was extremely low, and the assembly of the fuel cell was good.

  As described above, in Example 1 to Example 11, when one rib crest and groove bottom are seen with respect to the channel portion in which the unevenness is formed in the central portion 2, the groove depth d, the length L3 of the groove bottom, and the ribs are observed. The length L1 of the mountain flat portion is sufficiently larger than the plate thickness t of the separator. And when the separator is viewed as a molded product, the rib rigidity due to flow path formation is improved compared to the bending rigidity of the separator, so the warpage of the separator can be greatly reduced and the gas diffusion electrode can be damaged. Therefore, it becomes easy to assemble the fuel cell.

  Further, in the portion where the plastic working is performed by press molding, the clearance C, which is the distance in the surface direction between the punch and the die, is larger than the plate thickness of the outer peripheral edge of the separator, that is, the plate thickness before plastic working, and the slope portion is restrained. It was press-molded as an unfinished state. For this reason, when it sees about one rib crest and a groove bottom part, a nonuniform plastic strain and a residual stress become difficult to enter, and the separator for fuel cells which reduced curvature can be obtained.

  Further, since the rib crest slope portion 8 is press-molded so as not to be constrained, the rib crest slope portion 8 does not substantially generate frictional force during press molding, and remains in the direction of the thin metal plate in the shear, compression, and tension. Stress can be reduced. Moreover, since the press mold punch and die have been press-molded with the clearance C larger than the thickness t of the metal thin plate, the rib crest slope portion 8 is not crushed by the punch and the die, and the rib crest slope portion 8 When forming, it is possible to eliminate the difference in residual stress generated between the front and back of the applied thin metal plate. By reducing the residual stress in this way, it is possible to reduce the difference in non-uniform residual stress between the front and back sides of the separator, and to significantly reduce the warpage of the separator.

  In addition, according to Example 1- Example 11, the separator without a sliding trace can be obtained at the time of press molding in the rib crest slope part 8. FIG. For this reason, when forming a gas channel part by press molding, while preventing the direct contact between the metal thin plate used as the rib crest slope part 8 and a press die, it is provided when forming the rib crest slope part 8. It can be confirmed in the component state that there is almost no difference in residual stress between the front and back of the thin metal plate.

<Other embodiments>
A fuel cell can be constituted by using a fuel cell stack in which a plurality of single cells are stacked using the fuel cell separators of Examples 1 to 11 manufactured according to the above-described embodiment of the present invention.

  The fuel cell stack has a bipolar plate structure in which a plurality of single cells are stacked and a cooling water flow path is formed inside each single cell. Each single cell forms a membrane electrode assembly (MEA) by forming a gas diffusion layer having an oxidant electrode and a gas diffusion layer having a fuel electrode on both surfaces of the solid polymer electrolyte membrane, respectively. An oxidant electrode side separator is disposed on the oxidant electrode side of the body to form an oxidant gas flow path therein, and a fuel electrode side separator is disposed on the fuel electrode side of the membrane electrode assembly to provide a fuel gas flow path therein. Is forming.

  According to the present embodiment, it is possible to prevent uneven surface pressure between the gas diffusion electrode and the rib surface of the separator in each single cell of the assembled fuel cell stack, and to reduce the total contact resistance and the variation in gas distribution. Thus, power generation efficiency can be increased. In the state where the separator is used, since the polymer material is peeled off at least on the portion of the rib crest in the portion where the unevenness is formed, the adjacent separators, or between the adjacent separator and the gas diffusion electrode The contact resistance can be effectively reduced, and the power generation characteristics can be improved.

It is a top view which shows typically the separator for fuel cells in the Example and comparative example which concern on embodiment of this invention. It is a schematic diagram which shows the cross section of the separator for fuel cells shown in FIG. It is a principal part enlarged view which shows the cross section of the separator for fuel cells explaining the dimension of the gas flow path part of the separator for fuel cells which concerns on embodiment of this invention. It is sectional drawing which expands and shows the principal part of the separator for fuel cells at the time of press-molding the separator for fuel cells which concerns on embodiment of this invention.

Explanation of symbols

1 ... Fuel cell separator,
2 ... Central part,
3 ...
4 ... Gas channel groove,
5 ... Gas manifold,
6 ... Bead part,
7… Rib mountain flat part,
8 ... Rib Mountain slope,
9 ... groove bottom,
10 ... punch,
11 ... Dice,

Claims (6)

A separator for a fuel cell that is formed from a thin metal plate and has a concavo-convex oxidant gas or fuel gas flow path at the center,
The cross section in the direction perpendicular to the flow path is corrugated, and a plurality of rib crests and grooves are alternately formed, and the angle formed by the rib crest flat portion and the rib crest slope is an obtuse angle, The rib crest flat part and the groove bottom part are arranged substantially in parallel,
The thickness t of the separator at the outer peripheral edge which is the outer periphery of the central portion, the length L1 of the rib crest flat portion, the surface direction length L2 of the rib crest slope portion, the length L3 of the groove bottom portion, and the groove depth d. In this case, the thickness t of the separator is 0.05 to 0.10 mm, and 2t ≦ L2 ≦ 6t, 8t ≦ L1 ≦ 20t, and 5t ≦ d ≦ 15t are satisfied. Separator.   2. The fuel cell separator according to claim 1, further satisfying a relationship of L1 ≧ 3L2.   The metal thin plate is made of a base material formed of an alloy selected from an Fe-based alloy, a Ni-based alloy, a Ti-based alloy, and a stainless alloy, or a combination of two or more, and has corrosion resistance on both surfaces of the base material. 3. A fuel cell separator according to claim 1, wherein the separator is a clad alloy plate having a coating layer formed by conducting a conductive surface treatment.   The said coating layer is a layer formed by forming a noble metal layer having a thickness of 0.01 to 0.05 μm on the base material and rolling at a rolling rate of 5% or more. The fuel cell separator as described. A method for producing a separator for a fuel cell, which is formed from a thin metal plate and has a concavo-convex shape at the center portion to constitute a flow path for an oxidant gas or a fuel gas,
The clearance between the punch and the die of the press die for forming the uneven shape forming the flow path is set to 3 to 7 times the plate thickness t at the outer peripheral edge of the separator, so that the rib crest portion is not restrained. A method for producing a separator for a fuel cell, comprising press molding. A method for producing a separator for a fuel cell, which is formed from a thin metal plate and has a concavo-convex shape at the center portion to constitute a flow path for an oxidant gas or a fuel gas,
The clearance between the punch and the die of the press mold for forming the concavo-convex shape forming the flow path is set to be 3 to 7 times the plate thickness t of the outer peripheral edge of the separator, and the rib crest is not restrained. A method for producing a fuel cell separator according to claim 1, wherein the fuel cell separator is molded.

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