JP2009152177A - Bipolar metal separator for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bipolar metal separator for a fuel cell, which is made of stainless steel or the like and has adjacent metal separators firmly and surely jointed, and to provide its manufacturing method. <P>SOLUTION: The method for manufacturing a bipolar metal separator P3 of a fuel cell includes: a step S1 of cleaning front and back surfaces 4, 5 of a base board 1 on a steel plate P0 of a thickness of approximately 0.1 mm made of the stainless steel (SUS316L), including degreasing of them; a step S2 of removing a passivated film 2 by applying acid treatment on the degreased and cleaned front and back surfaces 4, 5 of the base board 1; a step S3 of manufacturing a blank plate P1 for a metal separator by coating an Au layer (a thin film layer of noble metal) 3 at a thickness of 0.5-60 nm by electrolytic plating on the front and back surfaces 4, 5 where the passivated film 2 of the base board 1 is removed; a step S4 of obtaining the metal separator P2 by press-forming a passage 6 of a reactant gas on the surface 4 of the blank plate P1; and a step of blazing thin film layers 3, 3 of the back surfaces 5 where a pair of metal separators P2 face each other and are adjacent to each other, via a blazing material such as solder. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a metal bipolar metal separator for a fuel cell in which a pair of adjacent metal separators are joined firmly and reliably, and a method for manufacturing the same.

In general, a unit cell fuel cell includes a membrane electrode assembly comprising a solid polymer membrane and a gas diffusion layer formed on both sides of the unit via a catalyst layer, and a pair of reaction gas channels disposed on both sides thereof. And a separator. As such a separator, a metal separator excellent in press formability has been studied. For example, a stainless steel plate excellent in corrosion resistance is press-formed.
For example, in order to increase the airtightness of the stack type fuel cell, the anode separator and the cathode separator of the unit fuel cells adjacent to each other are previously formed with a nitride layer on the surface of each peripheral portion, and then the gap between the peripheral portions is determined. A fuel cell stack for smoothing the nitride layer by laser welding and a method for manufacturing a fuel cell separator have been proposed (see, for example, Patent Document 1).

JP 2007-73422 A (pages 1 to 28, FIGS. 3 and 4)

However, when metal separators made of stainless steel are laser-welded to each other, a very thin passive film made of Cr oxide (for example, Cr ₂ O ₃ , Cr (OH) _3, etc.) is formed on the surfaces in advance. Therefore, when adjacent metal separators are joined to each other due to precipitation of Cr carbide in the formed welded portion, the corrosion resistance before joining cannot be sufficiently maintained. Further, the corrosion resistance in the vicinity of the welded portion is lowered, and warpage is likely to occur in each metal separator due to high heat during laser welding. In addition, when the welding point and the welding area are increased in order to prevent such warpage, there is a problem that the corrosion resistance is further lowered and the manufacturing cost and time are increased.

  The present invention solves the problems described in the background art, and can be manufactured at low cost by firmly and reliably joining a pair of adjacent metal separators made of stainless steel, Fe-Ni alloy, or Ni-base alloy. An object of the present invention is to provide a metal bipolar metal separator for a fuel cell and a method for producing the same.

Means for Solving the Problems and Effects of the Invention

In order to solve the above-mentioned problems, the present invention was obtained based on earnest studies and experiments by the inventors, and made of the passive state between a pair of adjacent metal separators made of stainless steel or the like. The idea is to braze between surfaces coated with a thin film layer of a noble metal having no coating and an extremely thin thickness.
That is, the bipolar metal separator base plate for a fuel cell according to the present invention (Claim 1) is made of stainless steel, Fe-Ni alloy, or Ni-base alloy, has a front surface and a back surface, and a flow of reaction gas on the surface. In the substrate on which the path is formed, the entire surface or at least a part of the convex portion between the reaction gas flow paths on the surface is covered with the noble metal thin film layer, and the entire back surface or at least the brazed portion on the back surface is formed. A pair of fuel cell metal separators coated with a thin film layer of a noble metal having a thickness of 0.5 to 60 nm, and a brazed part that joins the back surfaces of the pair of fuel cell metal separators facing each other And the brazing part directly below the brazing material is free of the noble metal thin film layer and includes a joining part in which the brazing material and the surface layer of the substrate are joined directly. And which is characterized in that.

According to this, when the flow path of the reactive gas is formed on the surface and the back surfaces of the pair of metal separators provided with the necessary conductivity on the surface side are adjacent to each other and soldering or the like is performed The substrates of the pair of metal separators can be bonded firmly and reliably by making the thin film layers of the noble metal facing each other and brazing with a brazing material between them. Therefore, the bipolar metal separator used for the fuel cell can be provided easily and inexpensively.
If the thickness of the thin film layer coated on the back surface of the metal separator is less than 0.5 nm, a practical surface treatment technique may cause the thickness to vary, and the generation of a passive film cannot be partially suppressed. There is a fear. On the other hand, if the thickness of the thin film layer exceeds 60 nm, the thin film layer of the noble metal cannot be diffused in the entire thickness in the brazing material when brazing described later, and a part of the thin film layer remains on the back surface of the substrate. Variations in bonding strength occur. Therefore, the thickness of the thin film layer of the noble metal on the back side is set to the above range.

The stainless steel used as the substrate includes austenitic, austenitic / ferrite, and precipitation hardened stainless steel. Examples of the austenitic stainless steel include SUS316L, SUS304, and SUS321.
On the other hand, the Fe—Ni alloy used as the substrate includes Fe-43 mass% Ni-23 mass% Cr-2.7 mass% Mo (for example, INCOLOY 825). Further, the Ni-based alloy includes 61.6 mass% Ni-21.9 mass% Cr-8.9 mass% Mo-3.8 mass% Fe-3.6 mass% Nb (for example, INCONEL625). included.
The noble metal includes any one of Au, Pt, Pd, and Ru, or an alloy based on any of these.
Further, the thin film layer includes a plated layer by electrolytic plating, a sputtered layer by sputtering, or the like.

Further, a part of the surface of the substrate means an entire area of the top surface of the convex portion between the flow paths of the reaction gas that will be in contact with the electrode later, or a part of the top surface of the convex portion, and an area where conductivity is ensured. The part which has.
Furthermore, a part of the back surface of the substrate refers to a part of the back surface including the brazed joint portion.
In addition to the entire interface (100%) between the brazing material and the substrate after brazing, the joint portion is at least 30% or more in area ratio, preferably 40% or more, of the brazed interface. Desirably, it refers to a portion where the brazing material and the substrate are directly joined at 50% or more.
Further, in the bipolar metal separator, a thin film layer of a noble metal may be coated (residual) on the entire surface or a part of the back surface of the pair of brazed substrates other than the joined portion.
In addition, a space between the pair of metal separators and including the concave portions between the convex portions including the joint portion on the back side thereof is a circulation path such as cooling water in the stack type fuel cell formed later. Be utilized.

The present invention also includes a bipolar metal separator for fuel cells (Claim 2), wherein the noble metal thin film layer coated on the back surface of the substrate has a thickness of 1 to 20 nm.
According to this, it is possible to coat the back surface of the substrate of the metal separator as a thin film layer having a stable thickness, and it is possible to reliably diffuse the thin film layer of the noble metal throughout the thickness in the brazing material at the time of brazing. .

Furthermore, the present invention provides a fuel cell in which the brazed portion where the brazing material of the brazing portion and the surface layer of the substrate are directly joined is at least 30% or more of the area at the interface between the brazing material and the substrate. A bipolar metal separator base plate (claim 3) is also included.
According to this, at the interface between the surface layer on the back surface of the substrate and the brazing material, both are directly joined by brazing at an area ratio of at least 30%, and a thin film layer of noble metal exists in the remainder. . That is, when a pair of metal separators are arranged adjacent to each other and the noble metal thin film layers are brazed with a brazing material sandwiched between them, for example, an ultrathin thin film layer made of an Au plating layer A portion in which the Au atoms are almost diffused in the brazing material is generated, and the brazing material and each substrate can be brazed directly. Therefore, a bipolar metal separator in which a pair of metal separators are firmly brazed can be provided reliably and inexpensively.
Note that the joint portion where the substrate and the brazing material are directly brazed is preferably 40% or more, more preferably 50% or more of the interface between the two.

  On the other hand, according to the first method for producing a bipolar separator for a fuel cell according to the present invention (claim 4), a reaction gas flow path is formed later on a substrate made of stainless steel, an Fe-Ni alloy, or a Ni-based alloy. Cleaning the entire surface or a part thereof, and the entire back surface or a part thereof where the flow path of the reaction gas is not formed, and the cleaned front and back surfaces of the substrate or a part thereof. The substrate is directly coated with a noble metal thin film layer on the whole or a part of the front and back surfaces of the substrate from which the passive film has been removed. A step of pressing a substrate coated with the noble metal thin film layer to form a fuel cell metal separator for forming a reaction gas flow path on the surface of the substrate, and a pair of the fuel cell gold A process of disposing the brazing material between the portions including the noble metal thin film layers adjacent to each other between the back surfaces of the separator, and heating the brazing material to a temperature higher than its melting point; And a step of diffusing and absorbing the noble metal thin film layer in contact with the substrate and directly brazing the brazing material and a pair of adjacent substrates.

According to this, there is no passive film between the surface layer on the back side of the substrate and the noble metal thin film layer, and a portion where the substrate and the thin film layer are in direct contact is included. Therefore, when brazing a pair of press-molded metal separators, extremely thin noble metal thin film layers coated on the back surface where no reaction gas flow path is formed are adjacent to each other, and a brazing material is interposed between them. By sandwiching and brazing at a relatively low temperature, the metal separators can be joined firmly and reliably. Accordingly, it is possible to easily and inexpensively provide a bipolar metal separator that is used in a fuel cell and has less warpage.
The cleaning includes a degreasing process. The passive film is a Cr oxide (for example, Cr ₂ O ₃ , Cr (OH) _3, etc.). Furthermore, the thickness of the thin film layer of the noble metal coated on the back side of the substrate is preferably 0.5 to 60 nm, more preferably 1 to 20 nm, and further preferably 3 to 10 nm. The brazing includes soldering (soldering).
In addition, the washing, acid treatment, and the three steps of coating the noble metal thin film layer and the pressing step may be performed in the order in which the former is performed after the latter is performed first.

  Further, according to the second method for producing a bipolar metal separator for a fuel cell according to the present invention (Claim 5), a reaction gas flow path is formed later on a substrate made of stainless steel, Fe-Ni alloy, or Ni-based alloy. Cleaning the entire surface or a part thereof, and the entire back surface or a part thereof where the flow path of the reaction gas is not formed, and the cleaned front and back surfaces of the substrate or a part thereof. Irradiating the substrate with an ion beam to remove the immobile skin film, sputtering the noble metal to the whole or a part of the front and back surfaces from which the immobile skin film has been removed, and A step of directly coating a noble metal thin film layer, and a metal separator for a fuel cell, wherein a substrate coated with the noble metal thin film layer is press-molded to form a reaction gas flow path on the surface of the substrate. Forming a brazing material, a step of disposing a brazing material between portions including the noble metal thin film layer adjacent to each other between the back surfaces of the pair of fuel cell metal separators, Heating to a temperature higher than the melting point, diffusing and absorbing the thin film layer of the noble metal in contact with the brazing material, and directly brazing the pair of substrates adjacent to the brazing material. And

According to this, there is no passive film between the surface layer on the back side of the substrate and the noble metal thin film layer, and a portion where the substrate and the thin film layer are in direct contact is included. For this reason, when a pair of metal separators obtained by press molding are placed adjacent to each other and brazed, the noble metal thin films are made to face and approach each other, and a brazing material is sandwiched between them to braze at a relatively low temperature. By doing so, metal separators can be brazed firmly and reliably via the brazing material. In addition, since the dry etching process and the sputtering process for irradiating the ion beam can be performed continuously in the same sputtering apparatus, the bipolar metal separator used in the fuel cell can be formed by substantially fewer processes than the first manufacturing method. It becomes possible to manufacture easily and inexpensively with less warping.
The three steps of cleaning, dry etching, and sputtering and the step of pressing may be performed in the order in which the above three steps are performed after pressing.

In the following, the best mode for carrying out the present invention will be described.
FIG. 1 shows a fuel cell metal separator P2 used in the bipolar metal separator for fuel cells of the present invention, and is a front view along the line of sight orthogonal to the surface 4 thereof. 2 is a cross-sectional view taken along line XX in FIG. 1, and FIG. 3 is a cross-sectional view taken along line YY in FIG.
The fuel cell metal separator (hereinafter simply referred to as a metal separator) P2 is formed by press-molding a thin plate made of, for example, austenitic stainless steel (eg, SUS316L) and having a thickness of about 0.1 mm. As shown in FIG. 3, a substrate 1 having a substantially square shape, a front surface 4 and a back surface 5 are provided. The material of the separator P2 may be an Fe—Ni alloy or a Ni base alloy.
In the substantially central portion of the surface 4 of the metal separator P2, there are a plurality of reaction gas flow paths 6, a plurality of projections 7 partitioning between them, and a pair of recesses that are substantially rectangular and located at both ends of each flow path 6. The header portions 10 and 11 are connected to one end of one header portion 10 and the gas supply portion 12 is provided with a supply hole 13 in the center, and the discharge portion 15 is connected to one end of the other header portion 11 and is provided in the center. The gas discharge unit 14 is provided.
On the other hand, a plurality of concave portions 8 and convex portions 9, which are inverted portions of the respective convex portions 7 and the respective flow paths 6, are located at a substantially central portion on the back surface 5 of the metal separator P <b> 2.

As shown in FIGS. 1 to 3, on the outer peripheral side of the surface 4 of the metal separator P <b> 2, a narrow peripheral edge 18, an adjacent recess 17 along the entire inner periphery thereof, and an entire inner periphery thereof. An adjacent wide convex portion 16 is formed, and surrounded by the convex portion 16, the flow path 6, the convex portion 7, the header portions 10 and 11, the gas supply portion 12, and the gas discharge portion 14 are located. Yes.
On the other hand, on the outer peripheral side of the back surface 5 of the metal separator P2, there are formed the peripheral edge 18, and convex portions and concave portions which are the inverted portions of the concave portion 17 and the convex portion 16, and are surrounded by the concave portion 8 and the convex portion. The part 9 and the like are located.
As shown in FIGS. 1 and 2, each reaction gas flow path 6 has a substantially elongated N shape in a plan view, and convex portions 7 located on both sides thereof have a substantially elongated N shape in opposite directions in the plan view. It has a letter shape. In addition, a pair of U-turn portions u that are substantially U-shaped in plan view are located in the middle of each flow path 6. The reaction gas flowing through the flow path 6 is a fuel gas such as hydrogen or an oxidant gas such as air.

As shown in the schematic partial enlarged sectional view of the alternate long and short dash line portion in FIG. 1 and the alternate long and short dash line portion Z1 in FIG. 2, the entire surface 4 and the entire back surface 5 of the metal separator P2 are made of stainless steel or Fe—Ni. An Au layer (a noble metal thin film layer) 3 is coated with a thickness of 0.5 to 60 nm on both surfaces of the substrate 1 made of an alloy. As shown in FIG. 2, there is usually no passive film made of Cr oxide formed on the surface of a stainless steel material or the like between the substrate 1 and each Au layer 3, and the substrate 1 and each Au layer 3 And are in direct contact.
As shown in the schematic partial enlarged cross-sectional view of the alternate long and short dash line portion Z2 in FIG. 2, the Au layer 3 is at least a convex portion that divides the reaction gas flow path 6 on the surface 4 of the metal separator P2. 7 has a form in which only the whole top surface (a part of the surface) or only a part of the top surface (a part of the surface) is covered, and the convex part 9 located on the opposite side of each flow path 6 in the back surface 5. It is good also as a form which covered only the whole top surface (a part of back surface), or only a part (a part of back surface) including the brazing part mentioned later which is the top surface concerned. In the case of such a form covering a part, the Au layer 3 and the substrate 1 are in direct contact with each other on the surface coated with the Au layer 3. A passive film is produced.

Here, the 1st and 2nd manufacturing method for obtaining the bipolar metal separator P3 for fuel cells of this invention is demonstrated along FIGS. The metal separator P2 in FIGS. 4 and 5 is shown slightly simplified.
FIG. 4 relates to the previous stage of the first manufacturing method. As schematically shown in each frame of the left and right alternate long and short dash lines at the uppermost end in FIG. 4, the thickness made of stainless steel (for example, SUS316L) or Fe—Ni alloy (for example, INCOLOY 825) is about 0.1 mm. The base steel plate P0 is a substrate 1 containing a predetermined amount of Cr, Ni, and the like, and the entire front / back surfaces 4 and 5 have Cr oxides (for example, Cr ₂ O ₃ , Cr (OH) having a thickness of about several nanometers. ) ₃ etc.) is formed.
First, the steel sheet P0 is washed with cleaning water or pure water containing a surfactant to remove dust adhering to the front and back surfaces, and further in an aqueous solution of sodium hydroxide or an organic solution such as acetone. A degreasing cleaning step (S1) is performed to remove the fats and oils attached to the front and back surfaces 4 and 5 by dipping.

Next, a step (S2) of performing an acid treatment of immersing the cleaned raw steel sheet P0 in mixed acid (mainly a mixed solution of sulfuric acid, nitric acid, and hydrochloric acid), hydrochloric acid, or sulfuric acid is performed. As a result, as shown in the left frame in FIG. 4, only the substrate 1 from which the passive film 2 has been removed from the entire front and back surfaces 4 and 5 is obtained. In addition, as shown in the right side frame in FIG. 4, it is good also as the board | substrate 1 from which the passive film 2 was removed from a part of front and back, 4 and 5 by performing the pickling process by masking.
Next, electrolytic Au plating is applied to the entire front / back surfaces 4 and 5 of the substrate 1 or a part of the substrate 1 to coat the Au plating layer (noble metal thin film layer) 3 (S3). As a result, as shown in each frame of the alternate long and short dash line in FIG. 4 and the alternate long and short dash line portions U1 and U2, the thickness is 0.5 to 0.5 on the entire front and back surfaces 4 and 5 of the substrate 1, or a part thereof. The metal separator base plate P1 coated with the 60 nm Au plating layer 3 is obtained.

The operations from the acid treatment step (S2) to the step (S3) for coating the Au plating layer 3 are performed in a non-oxidizing atmosphere such as argon or nitrogen. Further, when the Au plating layer 3 is covered only on a part of the front surface 4 and the back surface 5 of the substrate 1, the electrolytic Au plating is performed in a state where the other surfaces of the front surface 4 and the back surface 5 are masked.
Further, a step (S4) is performed in which the metal separator base plate P1 whose front / back surfaces 4 and 5 are coated with the Au plating layer 3 is inserted between a pair of press dies (not shown) and press-molded. As a result, as shown at the lowermost end in FIG. 4, the reaction gas flow path 6, the convex portion 7, the U-turn portion u and the like are formed in the substantially central portion of the surface 4, and the concave portion is formed in the substantially central portion of the back surface 5. The metal separator P2 similar to the above in which the 8 and the convex portion 9 are formed is formed.

FIG. 5 relates to the previous stage in the second manufacturing method for obtaining the bipolar metal separator P3 for fuel cells of the present invention.
As shown in the uppermost row in FIG. 5, the base steel plate P0 is brought into contact with a cleaning solution containing a surfactant, and further immersed in an aqueous sodium hydroxide solution or acetone to degrease and clean the front and back surfaces 4 and 5. Then, a cleaning step (S1) for removing dirt and oils and the like adhering to the surface layer is performed.
Next, the steel sheet P0 whose front and back surfaces 4 and 5 have been cleaned is carried into a high vacuum sputtering apparatus, and irradiated with an ion beam of an ion gas such as Ar. As shown in each frame, a dry etching step (S5) is performed to remove the passive film 2 formed on all or part of the front and back surfaces 4 and 5 with a required thickness (for example, about 20 nm). .

Subsequently, a step of performing sputtering for depositing Au (noble metal) disposed as a target in the sputtering apparatus on the entire front / back surfaces 4 and 5 of the steel plate P0 immediately after dry etching, or a part thereof (S6). )I do. As a result, as shown in each frame on the left and right of the third stage in FIG. 5, Au having a thickness of 0.5 to 60 nm is formed on the entire front / back surfaces 4 and 5 of the substrate 1 or a part thereof. A metal separator base plate P1 directly coated with the sputter layer (a noble metal thin film layer) 3 is obtained.
Then, the same pressing step (S4) as described above is performed on the metal separator base plate P1 in which the Au sputter layer 3 is coated on the entire front / back surfaces 4 and 5 of the substrate 1 or a part thereof. As a result, as shown in the lowermost stage in FIG. 5, the same metal separator P2 as described above is obtained.

6 to 8 relate to the latter stage of the manufacturing method of the bipolar metal separator P3 common to the first and second manufacturing methods of the present invention.
First, as shown in FIG. 6, the pair of metal separators P <b> 2 are brought close to each other so that the back surfaces 5 and 5 where the flow paths 6 are not formed face each other. A solder paste (a brazing material) R is applied in advance in a linear, dotted or planar shape on the top surface of the convex portion 9 on the back surface 5 of one metal separator P2 or the back surface of the header portion 10. Yes.
The solder (brazing material) R is located on the thin film layer 3 of Au (noble metal). Further, the brazing material R used in the present invention is replaced with the solder (Pb-Sn) described above, Sn-Ag series, Sn-Cu series, Sn-Ag-Cu series, Sn-Ag-Bi series, Sn-Bi series. Alternatively, a paste material or a preform material made of a low melting point alloy such as a Sn-Zn-Bi-based alloy may be used.

As shown in the partial enlarged cross-sectional view on the left side of FIG. 7 in which the one-dot chain line portion V in FIG. 6 is enlarged, the paste-like solder R is coated with Au on the entire back surface 5 of the pair of metal separators P2. It arrange | positions so that it may pinch | interpose between thin film layers (Au plating layer or Au sputter layer) 3,3. In this state, the pair of metal separators P2 was restrained and heated at about 200 ° C. for several seconds.
As a result, as shown on the right side of the white arrow in FIG. 7, the solder R is once melted and then solidified and compressed. At the same time, Au atoms in the Au thin film layer 3 are diffused into the adjacent solder R by the above heating, so that the solidified solder R is brazed (bonded) directly to each substrate 1 of the pair of metal separators P2. It was done.
On the other hand, as shown in the partial enlarged cross-sectional view on the left side of FIG. 8, the paste-like solder R is placed between the Au thin film layers 3 and 3 covered with a part of each back surface 5 of the pair of metal separators P2. You may arrange | position between. In this state, the pair of metal separators P2 was restrained and heated at about 200 ° C. for several seconds.
As a result, as shown on the right side of the white arrow in FIG. 8, the solder R is once melted and then solidified and compressed. At the same time, the Au atoms in the thin film layer 3 of Au are In order to diffuse into the adjacent solder R, the solidified solder R was brazed (joined) directly to each substrate 1 of the pair of metal separators P2.

The directly brazed joint portion may be at least 30% or more, desirably 40% or more, and more desirably 50% or more at the interface between the substrate 1 and the solder (brazing material) R. Further, the direct brazing between the substrate 1 and the solder R is an extremely thin thin film having a thickness of the Au plating layer 3 of 0.5 to 60 nm, and preferably 1 to 20 nm, so that the above-described diffusion is possible. This is due to the fact that Moreover, the pair of metal separators P2 can be brazed firmly and reliably in a relatively low heating temperature zone.
Then, by the soldering (brazing), as shown in the cross-sectional view of FIG. 9, the pair of metal separators P2 are placed between the back surfaces 5 and 5 facing and approaching each other so that the flow paths 6 are orthogonal to each other. Then, by brazing via the low melting point solder R, a bipolar metal separator P3 was obtained in which the reaction gas flow paths 6 and the like on the surface 4, 4 side of each metal separator P2 were arranged orthogonally.

  According to the bipolar metal separator P3 and the manufacturing method thereof of the present invention as described above, when the pair of metal separators P2 formed by press-molding the metal separator base plate P1 are adjacent to each other and soldering or the like is extremely performed, The thin Au (noble metal) thin film layers 3 and 3 are opposed to each other, and solder (brazing material) R is sandwiched between the thin film layers 3 and 3, so that the relatively thin film does not pass through the passive film 2. The substrates 1 and 1 of the metal separators P2 and 2 can be joined firmly and reliably only through the solder R soldered at a low temperature. Therefore, a bipolar metal separator P3 in which a pair of metal separators P2 with little warpage and corrosion resistance are firmly joined can be provided easily and inexpensively.

FIG. 10 relates to a process of manufacturing a unit cell fuel cell B1 using the bipolar metal separator P3.
First, as shown by a black arrow on the right side in FIG. 10, a central polymer film body 20 and a pair of electrodes 26 disposed on both sides thereof are sandwiched between a pair of bipolar metal separators P3. The polymer film body 20 is a film material having the same size as that of the metal separator P2 as a whole, and includes a solid polymer film 22 at the center and a frame-shaped reinforcing seal part 24 surrounding the periphery. One of the pair of electrodes 26 is an anode electrode, and the other is a cathode electrode. The electrode 26 is made of, for example, a sheet-like carbon fiber and is coated with a carbon catalyst mainly supporting Pt fine particles on the side in contact with the film body 20, or Pt fine particles are in contact with the film body 20. A carbon catalyst is applied on a carbon catalyst.

Electrodes 26 are respectively attached to both surfaces of the polymer film body 20, a pair of bipolar metal separators P3 are brought into contact with the outside thereof, a sealing material is sandwiched between peripheral portions thereof, a bolt (not shown) is penetrated, and the bolt Fasten the nut to the male screw part.
As a result, as shown on the left side of the white arrow in FIG. 10, a unit cell fuel cell B1 in which the electrode 26 and the bipolar metal separator P3 are symmetrically fixed on both surfaces of the polymer film body 20 is obtained.
Furthermore, as shown in FIG. 11, a stack type fuel cell B2 can be obtained by laminating and fixing a plurality of the fuel cells B1 of the unit cell along the thickness direction. In such a fuel cell B2, one bipolar metal separator P3 is shared in each fuel cell B1 of unit cells adjacent to each other.

According to the fuel cells B1 and B2, hydrogen (fuel gas: reactive gas) flowing through the flow path 6 of the metal separator P3 on one side with the solid polymer film 22 in contact with the adjacent anode electrode 26 is hydrogen ion. The electrons are used for power generation when passing through an external circuit (not shown), and then sent to the cathode electrode 26 on the other side. On the other hand, when the air (oxidant gas: reaction gas) flowing through the flow path 6 of the metal separator P3 on the other side sandwiching the solid polymer film 22 comes into contact with the adjacent cathode electrode 26, oxygen in the air is ionized. At the same time, the hydrogen ions that have passed through the solid polymer film 22 react with the electrons to generate water, which is discharged to the outside.
By repeating the above operation, it is possible to perform power generation continuously and stably using hydrogen and air.

Here, specific examples of the present invention will be described below.
In advance, 90 test base plates made of stainless steel (SUS316L) and having a thickness of 0.1 mm and a length and width of 100 × 100 mm were prepared. Of these, the cleaning process, the acid treatment process, and the electrolytic Au plating (S1 to S3) process are the same for the entire front / back surfaces 4 and 5 or a part of the front / back surfaces 4 and 5 of the 76 base plates. As shown in Tables 1 to 3, an Au plating layer (a noble metal thin film layer) 3 having a thickness of 3 nm, 5 nm, 8 nm, 10 nm, 15 nm, 20 nm, or 30 nm was coated. The remaining 14 base plates were left as they were. Note that “part of both surfaces” in Tables 1 to 3 indicates that the Au plating layer 3 is coated at least on the top surface of the convex portion 9 formed on the back surface of the base plate.

Next, using the same press die for the 90 test base plates, a plurality of the flow paths 6, convex portions 7, header portions 10 and 11 having the same dimensions on the front surface 4 are formed on the back surface 5. The concave portions 8 and the convex portions 9 were formed to form 90 metal separators.
Further, as shown in Tables 1 to 3, a pair of separators A and B were combined from the 90 metal separators, and a set of Examples 1 to 18, 22 to 35 and Comparative Examples 1 to 13 was made. . For each set of examples, a plurality of convex portions 9 facing each other on the back surfaces 5 of the pair of separators A and B are brought close to each other, and 0.9 × between the Au plating layers 3 and 3 covered on these top surfaces. A 0.9 mm solder paste was applied at 1.8 mm intervals and in a range of 40 × 40 mm in length and width, and further soldered by passing through a reflow oven at about 200 ° C.

And it pulled with both hands so that a pair of metal separators A and B in the bipolar metal separator for each example obtained by soldering might be separated along the plane direction. As a result, examples where the pair of separators were separated easily or with a slight force were shown as “X”, and examples where they were not separated even when pulled strongly were shown as “◯” in Tables 1-3.
As shown in Tables 1 to 3, Examples 1 to 18 and 22 to 35 were not separated even when the pair of metal separators A and B were pulled strongly. As a result, since both the metal separators A and B were previously coated on the surface to be soldered with the Au plating layer 3 having a thickness of 3 to 30 nm, the solder R and the substrates 1 of the metal separators A and B were directly joined. It is presumed that it was due to having the portion that was made.
On the other hand, as shown in Tables 1 to 3, in Comparative Examples 1 to 13, the pair of metal separators A and B separated easily or with a slight force. As a result, since the Au plating layer 3 was not coated on the soldered surfaces of the separators A and B and the passive film 2 containing Cr oxide was generated, the substrates of the solder R and the separators A and B It is estimated that 1 was not directly joined.

Separately, 32 test base plates made of an Fe—Ni alloy (INCOLOY 825) and having a thickness of 0.1 mm and a length and width of 100 × 100 mm were prepared. Among these, the cleaning step, the acid treatment step, and the electrolytic Au plating (S1 to S3) step are performed under the same conditions on both surfaces or a central portion (part) of 24 base plates. As shown, an Au plating layer (a noble metal thin film) 3 having a thickness of 3 nm, 10 nm, or 30 nm was coated. The remaining 8 base plates were left as they were.
Next, with respect to the 32 test base plates, the same flow path 6, the convex portion 7, the header portions 10 and 11, the concave portion 8, the convex portion 9 and the like are used by using the same press die as described above. Molded to form 32 metal separators.

Next, as shown in Table 4, a pair of separators A and B was combined from the 32 metal separators described above, and pairs of Examples 36 to 44 and Comparative Examples 14 to 20 were made. For each set of examples, a plurality of convex portions 9 facing each other on the back surfaces 5 of the pair of separators A and B are adjacent to each other, and 0.9 × between the Au plating layers 3 and 3 covered on the top surfaces thereof. 0.9mm Pb-free solder (Sn-Ag-Cu alloy) paste is applied at 1.8mm intervals and in the range of 40x40mm in length and width, and then passed through a reflow oven at about 240 ° C for soldering did.
Pull the pair of metal separators A and B of the bipolar metal separator obtained for each example in the same manner as described above, and the pair of base plates can be separated easily or with a slight force as “X” and pulled strongly. Table 4 shows an example in which the distance was not left as “◯”.

As shown in Table 4, Examples 36 to 44 were not separated even when the pair of metal separators A and B were pulled strongly. As a result, since both the metal separators A and B were previously coated on the surface to be brazed with the Au plating layer 3 having a thickness of 3 to 30 nm, the solder R and the substrates 1 of the metal separators A and B were directly joined. It is presumed that it was due to having the portion that was made.
On the other hand, as shown in Table 4, in Comparative Examples 14 to 20, the pair of metal separators A and B separated easily or with a slight force. As a result, since the Au plating layer 3 was not coated on the brazed surfaces of the separators A and B, and a passive film containing Cr oxide was generated, the solder R and the substrates of the separators A and B It is presumed that 1 was not joined directly.

Furthermore, 30 test base plates made of stainless steel (SUS316L) and having a thickness of 0.1 mm and a length and width of 100 × 100 mm are prepared. The cleaning process, the dry etching process, and the Au sputtering (S1, S5, S6) process are performed on the front and back surfaces 4 and 5 under the same conditions. As shown in Table 5, the thickness is 10 nm, 30 nm, Alternatively, a 100 nm Au sputter layer (a noble metal thin film layer) 3 was coated. The remaining 6 base plates were left as they were.
Next, the same metal separator as described above was formed on the 30 test base plates using the same press die as described above.
Next, as shown in Table 5, a pair of separators A and B was combined from the 30 metal separators described above, and a set of Examples 45 to 50 and Comparative Examples 21 to 29 was formed. For each set of examples, a plurality of convex portions 9 facing each other on the back surfaces 5 of the pair of separators A and B are adjacent to each other, and between the Au sputtered layers 3 and 3 covered on the top surfaces, the same solder as described above. After applying the paste, it was passed through a reflow oven at about 200 ° C. and soldered.
Example of the pair of metal separators A and B of the bipolar metal separator obtained for each example was pulled in the same manner as described above, and was easily separated or separated by a slight force as “X”, and even when pulled strongly, the example was not separated Is shown in Table 5.

As shown in Table 5, in Examples 45 to 50, none of them separated from each other even when the pair of metal separators A and B were pulled strongly. As a result, since both the metal separators A and B were previously coated on the surface to be brazed with the Au sputter layer 3 having a thickness of 10 to 30 nm, the solder R and the substrates 1 of the metal separators A and B were directly bonded. It is presumed that it was due to having the portion that was made.
On the other hand, as shown in Table 5, in Comparative Examples 21 to 29, the pair of metal separators A and B separated easily or with a slight force. Among these, since Comparative Examples 21-24, 28, and 29 were not coated with the Au sputter layer 3 on the brazed surfaces of the separators A and B, and a passive film containing Cr oxide was generated, It is presumed that the solder R and the substrates 1 of the separators A and B were not directly joined. Furthermore, Comparative Examples 25 to 27 marked with * were brazed but were easily separated when the metal separators A and B were pulled strongly. As a result of observing the peeled interface, it was presumed that the solder R did not reach the substrate 1 and was soldered (brazed) through the remaining Au sputter layer 3.
The effects of the bipolar metal separator P3 of the present invention were supported by Examples 1 to 18 and 22 to 50 as described above.

In addition, this invention is not limited to the form and Example which were mentioned above.
For example, the stainless steel used as the substrate may be austenitic stainless steel (for example, SUS316L, SUS304, SUS321, etc.), austenitic / ferritic, or precipitation hardening stainless steel.
The thin film layer of the noble metal is not limited to Au, and may be a plating layer made of Pt, Pd, or Ru, or an alloy based on these.
Furthermore, the flow path of the reaction gas formed on the metal separator may be arranged in a plurality of linear shapes parallel to each other between a pair of opposing header portions.
In addition, the brazing material for brazing the pair of metal separators is not limited to the solder, and may be a paste made of various low melting point alloys or a preform material.

The front view which shows the metal separator of one form used for this invention. Sectional drawing along the arrow of the XX in FIG. Sectional drawing along the arrow of the YY line in FIG. The flowchart which shows the 1st manufacturing method of the bipolar metal separator of this invention. The flowchart which shows the 2nd manufacturing method of the bipolar metal separator of this invention. The schematic sectional drawing which shows the manufacturing process of the bipolar metal separator of this invention. The partial expanded sectional view which shows typically one form of the dashed-dotted line part V in FIG. The partial expanded sectional view which shows typically the different form of the dashed-dotted line part V in FIG. Sectional drawing which shows the bipolar metal separator for fuel cells of this invention. Schematic which shows the process of manufacturing the fuel cell of a unit cell using the said bipolar metal separator. Schematic which shows the process of manufacturing a stack type fuel cell using the said bipolar metal separator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Board | substrate 2 ... Passive film 3 ... Au plating layer / Au sputter layer (thin film layer of a noble metal)
4 ... Front surface 5 ... Back surface 6 ... Reactive gas flow path P2 ... Metal separator P3 ... Bipolar metal separator R ... Solder (brazing material)
S1 ... Cleaning step S2 ... Acid treatment step S3 ... Au plating step S4 ... Pressing step S5 ... Dry etching step S6 ... Au sputtering step

Claims (5)

In a substrate made of stainless steel, Fe-Ni alloy, or Ni-based alloy, having a front surface and a back surface, and having a reaction gas flow path formed on the surface, the entire surface or at least the flow of the reaction gas on the surface A part of the convex part between the roads is covered with a noble metal thin film layer, and the whole of the back surface or at least a part including the brazing part on the back surface is covered with a noble metal thin film layer having a thickness of 0.5 to 60 nm. A pair of metal separators for fuel cells,
A brazing part that joins the back surfaces of the pair of fuel cell metal separators facing each other, and
Immediately below the brazing material in the brazing portion, there is no thin film layer of the noble metal, and a joining portion in which the brazing material and the surface layer of the substrate are directly joined is included.
A bipolar metal separator for a fuel cell. The thickness of the noble metal thin film layer coated on the back surface of the substrate is 1 to 20 nm.
The bipolar metal separator for fuel cells according to claim 1. The joint portion where the brazing material of the brazing portion and the surface layer of the substrate are directly joined is at least 30% or more of the area at the interface between the brazing material and the substrate.
The bipolar metal separator for fuel cells according to claim 1 or 2. In the substrate made of stainless steel, Fe-Ni alloy, or Ni-based alloy, the whole or part of the surface where the reaction gas flow path is formed later, and the whole back surface where the reaction gas flow path is not formed later. Or a step of cleaning a part thereof,
A step of removing the passive film by acid-treating all or a part of the cleaned front and back surfaces of the substrate;
Directly coating the substrate with a thin film layer of noble metal on the whole or a part of the front and back surfaces from which the passive film of the substrate has been removed,
A step of press-molding a substrate coated with the noble metal thin film layer to form a fuel cell metal separator that forms a reaction gas flow path on the surface of the substrate;
Arranging the brazing material between the portions including the noble metal thin film layer adjacent to each other between the back surfaces of the pair of fuel cell metal separators;
Heating the brazing material to a temperature higher than its melting point, diffusing and absorbing the thin film layer of the noble metal in contact with the brazing material, and directly brazing the pair of substrates adjacent to the brazing material; Including,
A method for producing a bipolar metal separator for a fuel cell. In the substrate made of stainless steel, Fe-Ni alloy, or Ni-based alloy, the whole or part of the surface where the reaction gas flow path is formed later, and the whole back surface where the reaction gas flow path is not formed later. Or a step of cleaning a part thereof,
Irradiating the whole or a part of the cleaned front and back surfaces of the substrate with an ion beam to remove the passive film;
Sputtering a noble metal to the whole or a part of the front and back surfaces from which the passive film of the substrate has been removed, and directly coating the noble metal thin film layer on the substrate;
A step of press-molding a substrate coated with the noble metal thin film layer to form a fuel cell metal separator that forms a reaction gas flow path on the surface of the substrate;
Arranging the brazing material between the portions including the noble metal thin film layer adjacent to each other between the back surfaces of the pair of fuel cell metal separators;
Heating the brazing material to a temperature higher than its melting point, diffusing and absorbing the thin film layer of the noble metal in contact with the brazing material, and directly brazing the pair of substrates adjacent to the brazing material; Including,
A method for producing a bipolar metal separator for a fuel cell.

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