JP2014137969A - Metal separators for fuel cell and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide inexpensive metal separators for a fuel cell which are capable of sufficiently suppressing an increase in contact resistance and use a smaller amount of noble metal such as gold than conventional ones.SOLUTION: A first separator 14 and a second separator 16 as the metal separators for a fuel cell are laminated on a membrane electrode structure 12 in which a cathode electrode 122 and an anode electrode 124 are provided on both sides of a solid polymer electrolyte membrane 120. The first separator 14 and the second separator 16 are characterized in that: they are molded in a corrugated plate shape having irregularities; a noble metal thin film 147 having a dot pattern with a flat surface is formed on protrusions 144, 145, 164, and 165 of the separators; and each dot of the noble metal thin film 147 is composed of a base part 148, in which an outer peripheral portion 148b is thicker than a central portion 148a and a recess 148c is formed at the central portion 148a, and a filling part 149 filling the recess 148c and having a flat surface 149a.

Description

  The present invention relates to a metal separator for a fuel cell and a method for producing the same. Specifically, the present invention relates to a fuel cell metal separator having a noble metal thin film formed on its surface and a method for manufacturing the same.

  2. Description of the Related Art In recent years, fuel cells that generate electricity by electrochemical reaction of reaction gases have attracted attention as new power sources for automobiles. A fuel cell is preferred in terms of high power generation efficiency because it directly obtains electricity through an electrochemical reaction. Further, since the fuel cell generates only harmless water during power generation, it is considered preferable from the viewpoint of environmental impact.

  For example, a polymer electrolyte fuel cell has a stack structure in which several tens to several hundreds of cells are stacked. Each cell is configured by sandwiching a membrane electrode structure (MEA) between a pair of separators. The membrane electrode structure is composed of an anode electrode (cathode) and a cathode electrode (anode), and an electrolyte membrane sandwiched between these electrodes. Both electrodes are a catalyst layer in contact with the electrolyte membrane, and a gas in contact with the catalyst layer. A diffusion layer. Further, the separator has a fuel gas channel formed on one surface thereof and an oxidant gas channel formed on the other surface thereof.

  In the polymer electrolyte fuel cell having the above-described configuration, hydrogen as fuel gas is supplied to the anode electrode via the fuel gas flow path. In addition, air as an oxidant gas is supplied to the cathode electrode via the oxidant gas flow path. Then, the hydrogen supplied to the anode electrode is protonated on the catalyst layer, and the generated proton moves to the cathode electrode through the electrolyte membrane. At this time, electrons generated together with protons are taken out to an external circuit and used as electric energy.

  By the way, a metal separator made of stainless steel or the like is usually used as the separator. It is known that the metal separator is subjected to a noble metal plating process for the purpose of suppressing oxidation and suppressing an increase in contact resistance with the membrane electrode structure.

  As the noble metal plating treatment of the metal separator, gold plating treatment is usually used frequently. However, if gold plating is applied to the entire metal separator, the amount of gold used becomes enormous and the manufacturing cost increases. Therefore, a technique is disclosed in which only the convex portions of the fuel cell metal separator in contact with the electrode layer of the membrane electrode structure, which is a power generation site, are subjected to gold plating (see Patent Document 1).

JP 2010-77464 A

  However, in the technique of Patent Document 1, although only the convex portion of the fuel cell metal separator, only the convex portion is subjected to gold plating. Therefore, the amount of gold used is still large, and further reduction in manufacturing cost is desired.

  The present invention has been made in view of the above, and an object of the present invention is to provide a metal separator for a fuel cell that can sufficiently suppress an increase in contact resistance and uses less noble metal such as gold than the conventional metal separator. is there.

  To achieve the above object, the present invention provides a fuel cell metal separator laminated on a membrane electrode structure (for example, a membrane electrode structure 12 described later) provided with a pair of electrodes on both sides of an electrolyte membrane, The metal separator for a fuel cell is formed in a corrugated plate shape having irregularities, and a convex surface (for example, convex portions 144, 145, 164, and 165 described later) is a dot having a flat surface. A noble metal thin film (for example, a noble metal thin film 147 to be described later) having a pattern is formed, and each dot of the noble metal thin film has an outer peripheral portion (for example, an outer peripheral portion to be described later) rather than a central portion (for example, a central portion 148a described later) 148b) is thick and has a base portion (for example, a base portion 148 described later) in which a concave portion (for example, a concave portion 148c described later) is formed in the center portion, and a surface (for example, a surface described later) filled in the concave portion. 149a) is flat packing unit (e.g., to provide a metal separator for a fuel cell, characterized in that it is constituted from a filler portion 149) described later (for example, a first separator 14, the second separator 16 to be described later).

In the present invention, a noble metal thin film having a dot-like pattern with a flat surface is formed on the convex portion of the metal separator for a fuel cell. That is, the noble metal thin film is not formed on the entire convex portion, but is formed in a dot shape so that the noble metal thin film is formed on a part thereof and the surface of the dot-like noble metal thin film is flattened. More specifically, each dot of the noble metal thin film is composed of a base portion having a thicker outer peripheral portion than the center portion and a recess portion formed in the center portion and a filling portion filled in the recess portion and having a flat surface. Flatten the surface of the thin film.
Thereby, compared with the case where the noble metal plating process, such as gold | metal | money, is performed to the whole separator and the whole convex part of a separator like the past, the usage-amount of a noble metal can be reduced and manufacturing cost can be reduced.
In the present invention, since the surface of the noble metal thin film is flattened, an increase in contact resistance at the interface between the convex portion of the metal separator and the membrane electrode structure can be sufficiently suppressed, and high power generation performance can be obtained. When the convex portions of the metal separator are in contact with each other to form the cooling medium flow path, an increase in contact resistance at the interface where the convex portions are in contact with each other can be sufficiently suppressed, and higher power generation performance can be obtained.

  A method of manufacturing a fuel cell metal separator laminated on a membrane electrode structure (for example, a membrane electrode structure 12 described later) provided with a pair of electrodes on both sides of an electrolyte membrane, the corrugated plate having irregularities An ink containing a noble metal and an organic solvent (for example, a first ink to be described later) is formed in a dot-like shape on a convex portion (for example, a protrusion 144, 145, 164, or 165 described later) of the metal separator for a fuel cell formed into a shape. A first step (for example, a first step described later) applied to the pattern, and a second step (for example, a second step described later) for volatilizing the organic solvent in the dot-shaped ink applied in the first step. And a noble metal thin film precursor having a dot-like pattern in which the outer peripheral portion (for example, an outer peripheral portion 146b described later) is thicker than the central portion (for example, a central portion 146a described later) formed in the second step ( For example, A third step (for example, a third step described later) for applying an ink containing a noble metal (for example, a second ink described later) to the vicinity of the central portion (for example, a recess 146c described later) of the metal thin film precursor 146); And a fourth step (for example, a fourth step described later) for forming a noble metal thin film (for example, a later-described noble metal thin film 147) having a flat dot-like pattern by heat treatment. A method for producing a metal separator for a fuel cell is provided.

  In this invention, first, an ink containing a noble metal is applied in a dot-like pattern to the convex portions of the fuel cell metal separator. Next, the organic solvent in the applied dot-like ink is volatilized to form a noble metal thin film precursor having a dot-like pattern whose outer peripheral part is thicker than the central part. Next, after applying an ink containing a noble metal in the vicinity of the center, heat treatment is performed. Thereby, the noble metal thin film which has a dot-like pattern with a flat surface is formed, and the effect of the said invention is show | played reliably.

  According to the present invention, an increase in contact resistance can be sufficiently suppressed, and an inexpensive metal separator for a fuel cell can be provided that uses less noble metal such as gold than conventional ones.

It is a perspective view which shows the structure of the fuel cell stack which concerns on one Embodiment of this invention. It is a disassembled perspective view of the power generation cell which concerns on the said embodiment. It is a longitudinal cross-sectional view of the fuel cell stack which concerns on the said embodiment. It is sectional drawing of the metal separator which concerns on the said embodiment. It is a top view of the noble metal thin film formed in the convex part of the metal separator which concerns on the said embodiment. It is a cut end view of the noble metal thin film precursor formed in the convex part of the metal separator which concerns on the said embodiment. It is a figure which shows the relationship between the average thickness of a noble metal thin film, and contact resistance. It is a figure which shows the measuring method of contact resistance. It is a cut end view of the noble metal thin film formed in the convex part of the metal separator which concerns on the said embodiment. It is a figure which shows the noble metal thin film formation by the inkjet printing method.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a perspective view showing a configuration of a fuel cell stack 1 according to an embodiment of the present invention. The fuel cell stack 1 is a fuel cell stack including the fuel cell metal separator according to the present invention. As shown in FIG. 1, the fuel cell stack 1 includes a plurality of power generation cells 10 stacked in the vertical direction with the electrode surfaces horizontal.

  Terminal plates 82 and 82, insulating plates 84 and 84, and end plates 86 and 86 are disposed at the upper and lower ends of the fuel cell stack 1, respectively. Between the end plates 86, 86, both ends of the plurality of connecting bars 90 are fixed via bolts 92 in a state where a predetermined tightening load is applied. Thereby, an increase in contact resistance is suppressed by applying a predetermined surface pressure to the electrode surface of the power generation cell 10.

FIG. 2 is an exploded perspective view of the power generation cell 10 according to the present embodiment. FIG. 3 is a longitudinal sectional view (Z direction sectional view) of the fuel cell stack 1 according to the present embodiment.
As shown in FIGS. 2 and 3, the power generation cell 10 includes a membrane electrode structure 12, a first separator 14 and a second separator 16 as a pair of fuel cell metal separators sandwiching the membrane electrode structure 12, Is provided.

  At one end of the power generation cell 10 in the longitudinal direction (Y direction in FIG. 2), an oxidant gas inlet communication hole 22a and a cooling medium inlet communicate with each other in the thickness direction of the power generation cell 10 (X direction in FIG. 2). A communication hole 24a and a fuel gas outlet communication hole 26b are provided. Further, the other end side of the power generation cell 10 in the Y direction is provided with a fuel gas inlet communication hole 26a, a cooling medium outlet communication hole 24b, and an oxidant gas outlet communication hole 22b that communicate with each other in the X direction of the power generation cell 10. ing.

The 1st separator 14 and the 2nd separator 16 are comprised by metal plates, such as a steel plate, a stainless steel plate (SUS316), an aluminum plate, for example. These separators are manufactured by forming a thin plate made of the above various metals into a corrugated plate by press molding.
Further, as shown in FIG. 2, a seal member that circulates around the outer peripheral edge of the first separator 14 is integrally formed on the surfaces 140 a and 140 b of the first separator 14. Similarly, on the surfaces 160 a and 160 b of the second separator 16, a seal member that goes around the outer peripheral edge of the second separator 16 is integrally formed. Examples of the sealing member include EPDM (ethylene propylene diene rubber), NBR (nitrile butadiene rubber), fluorine rubber, silicone rubber, fluorosilicone rubber, butyl rubber, natural rubber, styrene rubber, chloroprene rubber, or acrylic rubber. A sealing material having elasticity such as a sealing material, a cushioning material, and a packing material is used.

  The membrane electrode structure 12 includes, for example, a solid polymer electrolyte membrane 120 in which a perfluorosulfonic acid thin film is impregnated with water, and a cathode electrode 122 and an anode electrode 124 that sandwich the solid polymer electrolyte membrane 120.

  Each of the cathode electrode 122 and the anode electrode 124 is a catalyst formed by applying a gas diffusion layer made of carbon paper containing carbon fibers and porous carbon particles having a platinum alloy supported on the surface onto the gas diffusion layer. A layer. These two electrodes are laminated on the solid polymer electrolyte membrane 120 with the gas diffusion layer facing outward so that the catalyst layer is in contact with the solid polymer electrolyte membrane 120.

  As shown in FIGS. 2 and 3, the oxidant gas flow communicating with the oxidant gas inlet communication hole 22 a and the oxidant gas outlet communication hole 22 b is formed on the surface 140 a of the first separator 14 facing the membrane electrode structure 12. A path 142 is formed. A plurality of the oxidant gas flow paths 142 are extended along the Y direction.

  A fuel gas flow path 162 that connects the fuel gas inlet communication hole 26a and the fuel gas outlet communication hole 26b is formed on the surface 160a of the second separator 16 that faces the membrane electrode structure 12. A plurality of the fuel gas flow paths 162 are extended along the Y direction.

  In addition, the second separator 16 and the first separator 14 are overlapped and in contact with each other, so that the surface 140b opposite to the surface 140a of the first separator 14 and the surface opposite to the surface 160a of the second separator 16 are obtained. A cooling medium flow path 240 surrounded by 160b is formed. A plurality of cooling medium flow paths 240 are extended along the Y direction.

As shown in FIG. 3, the first separator 14 and the second separator 16 are corrugated metal separators for fuel cells having a plurality of convex portions whose top surfaces are planar. Here, the convex part of the metal separator for a fuel cell in the present invention means a part protruding in the stacking direction (X direction) of the power generation cell 10, and adjacent to the convex part on the side in contact with the membrane electrode structure 12. And a convex portion on the side in contact with the convex portion of the other metal separator.
The first separator 14 and the second separator 16 both have a surface roughness Ra of 0.1 μm to 0.8 μm.

FIG. 4 is a cross-sectional view of the metal separator according to the present embodiment. Specifically, it is a Z-direction sectional view of the first separator 14 and the second separator 16 that are adjacent to each other.
As shown in FIG. 4, the convex portion of the first separator 14 is formed from the convex portion 145 on the side in contact with the membrane electrode structure 12 (more specifically, the gas diffusion layer 122a of the cathode electrode 122) and the gas diffusion layer 122a. It protrudes in the direction to separate, and is comprised from the convex part 144 of the side which contacts the convex part 164 of the adjacent 2nd separator 16 mentioned later. A plurality of these convex portions 144 and 145 are arranged at predetermined intervals in the Z direction.
Further, the convex portion of the second separator 16 protrudes in a direction away from the convex portion 165 on the side in contact with the membrane electrode structure 12 (more specifically, the gas diffusion layer 124a of the anode electrode 124) and the gas diffusion layer 124a. , And a convex portion 164 on the side in contact with the convex portion 144 of the adjacent first separator 14. A plurality of these convex portions 164 and 165 are arranged at predetermined intervals in the Z direction.

  The first separator 14 and the second separator 16 basically have the same configuration, and the convex portion 145 of the first separator 14 corresponds to the convex portion 165 of the second separator 16, and the convex portion 144 of the first separator 14. Corresponds to the convex portion 164 of the second separator 16. Therefore, in the following, the configuration of the first separator 14 will be described in detail, and the description of the configuration of the second separator 16 will be omitted as appropriate.

  The first separator 14 is characterized in that a noble metal thin film is formed only on the convex portions 144 and 145. More specifically, the noble metal thin film is formed only on the top surface portions 144a and 145a formed of flat top surfaces among the convex portions 144 and 145. The noble metal thin film formed on the top surface portion 144a of the convex portion 144 and the noble metal thin film formed on the top surface portion 145a of the convex portion 145 have the same configuration.

By the way, as described above, since the unevenness of the first separator 14 is formed by press molding, the convex portion 145 has a top surface portion 145a and an R portion in which the corner portions at both ends in the Z direction of the top surface portion 145a are R-shaped. 145b, 145b. Similarly, the convex portion 144 is configured to include a top surface portion 144a and R portions 144b and 144b in which corners at both ends in the Z direction of the top surface portion 144a are R-shaped.
Here, as will be described later, the noble metal thin film according to the present embodiment is coated with an ink containing a noble metal in the vicinity of the center of the noble metal thin film precursor having a dot-like pattern whose outer peripheral part is thicker than the center. It is formed by filling and heating. In addition, the filled ink flows, so that the surface is flattened. Therefore, the noble metal thin film according to the present embodiment is formed only on the top surface portions 145a and 144a made of flat top surfaces.

FIG. 5 is a plan view of the noble metal thin film formed on the convex portion of the metal separator according to the present embodiment. Specifically, it is a plan view of the noble metal thin film 147 formed on the top surface portion 145 a of the convex portion 145 of the first separator 14. A similar noble metal thin film 147 is also formed on the top surface portion 144a of the convex portion 144.
As shown in FIG. 5, the noble metal thin film 147 is formed in a dot shape, and substantially circular dots are formed with a lattice pattern. That is, the dot-like noble metal thin films 147 are regularly arranged in the Z direction and the Y direction, respectively. The interval and diameter of the dot-like noble metal thin film 147 are set to appropriate values when adjusting the area ratio of the noble metal thin film 147 described later.
However, the shape of each dot is not limited to a perfect circle, and may be, for example, a distorted circular shape, a polygonal shape, or the shape of each dot may be different. Further, the arrangement of the dots is not limited, and the dots may be arranged shifted in the Z direction and / or the Y direction.
In the present embodiment, the dot shape means a dot shape (dot shape).

As the noble metal constituting the noble metal thin film 147, for example, gold, silver, rhodium, platinum, an alloy containing these as a main component, or the like can be used. In this embodiment, gold is preferably used as the noble metal.
In addition, since the noble metal thin film 147 hardly generates an oxide and has water repellency, by forming the noble metal thin film 147 on the convex portion of each metal separator, each metal separator and the membrane electrode structure 12 An increase in contact resistance at the interface and an increase in contact resistance at the contact interface between the protrusions of each metal separator are suppressed, and a decrease in terminal voltage is suppressed.

The noble metal thin film 147 of this embodiment is characterized in that the surface is formed flat. More specifically, by constituting each dot of the noble metal thin film 147 from a base part in which the outer peripheral part is thicker than the central part and a concave part is formed in the central part, and a filled part filled in the concave part and having a flat surface, The noble metal thin film 147 is characterized in that the surface is flattened.
The noble metal thin film 147 of the present embodiment is manufactured according to a manufacturing method described later. Specifically, first, a noble metal thin film precursor having a dot-like pattern whose outer peripheral part is thicker than the central part is formed by applying ink to the dot-like pattern and volatilizing the organic solvent in the ink. To do. Next, the noble metal thin film 147 whose surface is flattened is formed by applying the ink again in the vicinity of the central portion.

Here, FIG. 6 is a cut end view of the noble metal thin film precursor formed on the convex portion of the metal separator according to the present embodiment. Specifically, it is a cut end view passing through the central portion 146a of the noble metal thin film precursor 146 having a dot-like pattern formed on the top surface portion 145a of the convex portion 145 of the first separator 14.
As shown in FIG. 6, the noble metal thin film precursor 146 having a dot-like pattern is formed in a dot shape in which the outer peripheral part 146b is thicker than the central part 146a. That is, the film thickness T1 of the central portion 146a is smaller than the film thickness T2 of the outer peripheral portion 146b, whereby a concave portion 146c is formed in the central portion 146a of the noble metal thin film precursor 146 having a dot-like pattern. . The noble metal thin film precursor 146 having such a shape is formed by applying ink to a dot-like pattern and volatilizing an organic solvent in the applied ink, as will be described in detail later.
In addition, film thickness T1 of the center part 146a is 10-30 nm, More preferably, it is 20-30 nm. The film thickness T2 of the outer peripheral portion 146b is 30 nm to 100 nm, more preferably 50 to 100 nm.

  By the way, if the film thickness of the noble metal thin film precursor 146 is insufficient, the film thickness of the noble metal thin film obtained by heating the film becomes insufficient, and oxygen passes through the noble metal thin film and an oxide film is formed on the surface of the metal separator. Form. In particular, when the noble metal thin film is formed, the growth of the oxide film is promoted in the heat treatment after applying the ink. When the oxide film is formed, the contact resistance increases and the power generation performance decreases, so it is necessary to avoid the formation of the oxide film.

FIG. 7 is a diagram showing the relationship between the average film thickness of the noble metal thin film and the contact resistance. Specifically, FIG. 7 is a diagram showing the relationship between the average film thickness of the gold thin film and the contact resistance, but the same tendency is recognized for noble metals other than gold. In FIG. 7, the horizontal axis represents the average film thickness (nm) of the noble metal thin film, and the vertical axis represents the contact resistance (mΩ · cm ² ).
Here, a method for measuring the contact resistance shown in FIG. 7 will be described.
FIG. 8 is a diagram illustrating a method for measuring contact resistance. As shown in FIG. 8, the contact resistance measuring device 70 has a pair of terminal plates 71 and 72 that are gold-plated on the entire surface, and a current of a predetermined magnitude between the pair of terminal plates 71 and 72. A power source 73 and a voltmeter 74 for measuring a voltage between the first separator 14 and the second separator 15.

The measurement procedure is as follows. First, the carbon paper 75 is sandwiched between the first separator 14 and the second separator 16 as a pair of metal separators, and is sandwiched between the pair of terminal plates 71 and 72.
Next, a predetermined surface pressure is applied between the pair of terminal plates 71 and 72 with a press machine (not shown). The surface pressure is the conventional power generation state. For example, it is 10 kgf / cm ² .
A current is passed between the pair of terminal plates 71 and 72 while applying a surface pressure, and a voltage drop between the first separator 14 and the second separator 16 is measured by a voltmeter 74. The measurement current density is 1 A / cm ^2, and the area of each separator is calculated in terms of the separator projected contact area.
As described above, the contact resistance between the first separator 14, the carbon paper 75, and the second separator 16 is measured. The contact resistance measured in this way is the contact resistance shown in FIG.

  Returning to FIG. 7, it can be seen that, in the region where the average film thickness of the noble metal thin film is 30 nm or less, the contact resistance increases as the average film thickness of the noble metal thin film decreases. This is because if the average film thickness of the noble metal thin film is too small, the surface of the metal separator cannot be sufficiently covered with the noble metal thin film and pores are formed in the noble metal thin film so that oxygen can permeate the metal separator. This is probably because the oxide film is formed on the surface.

On the other hand, in the region where the average film thickness of the noble metal thin film exceeds 30 nm, the contact resistance reaches saturation, and even if the average film thickness is increased further, no significant change in the contact resistance is observed. This is because when the average film thickness of the noble metal thin film exceeds 30 nm, the surface of the metal separator can be sufficiently covered with the noble metal thin film, so that permeation of oxygen is avoided and formation of an oxide film is avoided.
Therefore, when the noble metal thin film precursor 146 having the dot-like pattern shown in FIG. 6 having the film thickness T1 of the central portion 146a of 10 to 30 nm is heated as it is to form a noble metal thin film, an oxide film is formed. This increases the contact resistance.

  Therefore, in the present embodiment, ink is applied again to the concave portion 146c formed in the vicinity of the central portion 146a of the noble metal thin film precursor 146 having the dot-like pattern shown in FIG. 6, that is, the inner side of the top portion 146d of the outer peripheral portion 146b. By doing so, the film thickness exceeding 30 nm is ensured, and at the same time, the surface is flattened. Thereby, the increase in contact resistance is suppressed and high power generation performance is obtained.

FIG. 9 is a cut end view of the noble metal thin film 147 formed on the convex portion of the metal separator according to the present embodiment. Specifically, it is a cut end view passing through the central portion of the noble metal thin film 147 formed on the top surface portion 145 a of the convex portion 145 of the first separator 14.
As shown in FIG. 9, each dot of the noble metal thin film 147 having a dot-like pattern has a base portion 148 in which outer peripheral portions 148b and 148b are thicker than the central portion 148a and a concave portion 148c is formed in the central portion 148a, and a concave portion 148c and a filling portion 149 having a flat surface 149a. The noble metal thin film 147 is formed by applying ink again to the concave portion 146c formed in the central portion 146a of the noble metal thin film precursor 146 having the dot-like pattern described above.

The noble metal thin film 147 is manufactured by the method for manufacturing a metal separator for a fuel cell according to this embodiment. Hereinafter, the detail of the manufacturing method of the metal separator for fuel cells which concerns on this embodiment is demonstrated.
The manufacturing method of the fuel cell metal separator according to the present embodiment includes first to fourth steps.

  In the first step, a first ink containing a noble metal and an organic solvent is applied to a dot-like pattern on a convex portion of a metal separator for a fuel cell formed into a corrugated plate having irregularities. At this time, the temperature of the fuel cell metal separator is set to 25 to 70 ° C. That is, in the first step, only the organic solvent is volatilized, and the noble metal fine particles are not sintered.

  In the second step, the organic solvent in the dot-like ink applied in the first step is volatilized. Since the ink amount of each dot applied in the first step is very small, the organic solvent in the ink volatilizes in a short time even when the temperature of the fuel cell metal separator remains at 25 to 70 ° C. That is, in the second step, the organic solvent is only volatilized, and the noble metal fine particles are not sintered. By this step, the noble metal thin film precursor 146 having a dot-like pattern in which the outer peripheral portion 146b is thicker than the central portion 146a is formed.

Next, in the third step, the noble metal is formed in the concave portion 146c formed in the vicinity of the central portion 146a of the noble metal thin film precursor 146 having the dot-like pattern formed in the second step, that is, inside the top portion 146d of the outer peripheral portion 146b. A second ink containing is applied. At this time, as in the first step, the temperature of the fuel cell metal separator is set to 25 to 70 ° C. That is, in the third step, the organic solvent is only volatilized and the noble metal fine particles are not sintered.
Further, as will be described later, the viscosity of the second ink is preferably lower than the viscosity of the first ink. Thereby, the second ink flows in the recess 146c of the noble metal thin film precursor 146 having a dot-like pattern, and the surface can be flattened.
The application position of the second ink only needs to be inside the top portion 146d of the outer peripheral portion 146b, and the application amount may be sufficient to satisfy the concave portion 146c, and may be equal to or larger than the volume of the concave portion 146c.

In the first step and the third step, an ink jet printing method is preferably employed. FIG. 10 is a diagram showing the formation of a noble metal thin film by an ink jet printing method. 10 shows a state where the noble metal thin film 147 is formed on the top surface portion 145a of the convex portion 145 of the first separator 14, the same applies to the other convex portions 144, 164 and 165. FIG.
As shown in FIG. 10, the ink jet device 5 used in the ink jet printing method is supplied by an ink container 52 in which ink 50 is stored, an ink supply line 54 for supplying ink 50, and an ink supply line 54. And an inkjet head 56 having a plurality of ejection nozzles (not shown) for ejecting the ink 50 toward the top surface portion 145a of the convex portion 145 of the first separator 14.
In the inkjet device 5, the ink 50 can be applied to both the first step and the third step by exchanging the ink 50 with the first ink and the second ink.

As the ink 50, an ink in which noble metal fine particles are dispersed in an organic solvent by the action of a dispersant is used for both the first ink and the second ink. As the dispersant, a dispersant having a hydrophilic group and a hydrophobic group is used. The hydrophilic group is coordinated on the surface of the noble metal fine particle and solvated by the hydrophobic group, whereby the noble metal fine particle is stably dispersed in the organic solvent. Is done.
As the noble metal fine particles, for example, gold fine particles, silver fine particles, rhodium fine particles, platinum fine particles and the like can be used. In this embodiment, gold fine particles are preferably used as the noble metal fine particles, and the average particle diameter thereof is 4 to 8 nm. .
As the organic solvent, for example, cyclododecene or the like can be used in the first ink, and cyclohexylbenzene or the like can be used in the second ink.

  The first ink and the second ink are preferably the same except for the organic solvent. They are at least different in viscosity, and the viscosity of the first ink is preferably 10 to 12 mPa · s, for example, and the viscosity of the second ink is preferably 3 to 5 mPa · s. When the viscosity of each ink is within this range, a noble metal thin film precursor 146 having a dot-like pattern in which the outer peripheral portion 146b is thicker than the center portion 146a is obtained, and the inside of the recess 146c of the noble metal thin film precursor 146 is obtained. As the second ink flows, the noble metal thin film 147 whose surface is flattened is more reliably formed.

  A plurality of ejection nozzles provided in the inkjet head 56 are provided at intervals equivalent to the intervals between the adjacent convex portions 145. A plurality of discharge nozzles are provided in the inkjet head 56, and by arranging the discharge nozzles in a predetermined arrangement, a dot-like lattice pattern can be simultaneously formed on the top surface portions 145a of the plurality of convex portions 145. That is, by changing the arrangement of these discharge nozzles, it is possible to draw a desired dot-like pattern with the ink 50 on the top surface portion 145 a of the convex portion 145. The ink ejection speed is set to 6 to 10 m / min, for example.

  When ink jet printing is performed, first, the first separator 14 is scanned by a transport mechanism (not shown) while the ink jet head 56 is scanned by a scan mechanism (not shown) as necessary depending on the relationship between the width of the ink jet head 56 and the drawing width. Transport. Thereby, a dot-like lattice pattern by the first ink is drawn on the entire top surface portion 145 a of the convex portion 145 of the first separator 14.

  At this time, since the amount of each dot of the dot-shaped first ink is very small, the organic solvent in the dot-shaped first ink volatilizes in a short time. Thereby, the noble metal thin film precursor 146 having a dot-like lattice pattern in which the outer peripheral portion 146b is thicker than the central portion 146a is already formed at this time.

  Next, after sufficiently volatilizing the organic solvent in the ink applied in the second step, the first ink is replaced with the second ink, and the vicinity of the central portion 146a of the noble metal thin film precursor 146 having a dot-like lattice pattern That is, while the inkjet head 56 is again scanned by the scanning mechanism (not shown) so that the second ink is applied to the recess 146c formed inside the top portion 146d of the outer peripheral portion 146b, the first separator is scanned by the transport mechanism (not shown). 14 is conveyed. Thereby, the second ink flows in the recess 146c of the noble metal thin film precursor 146, and the surface is flattened.

  Next, in the fourth step, heat treatment is performed. As a result, a noble metal thin film 147 having a dot-like lattice pattern with a flat surface is formed. Since the temperature of each separator in the first step and the third step is set to 25 to 70 ° C., at least the heating temperature needs to be a temperature exceeding 70 ° C. From the viewpoint of sintering the noble metal fine particles, the heating conditions Is preferably heated at 250 to 350 ° C. for 30 minutes.

  When heated in the fourth step, the dispersant in the ink 50 is oxidized and decomposed and removed, and the remaining noble metal fine particles are sintered and integrated, whereby a noble metal thin film 147 is formed. At this time, the dot-like lattice pattern is maintained, and the noble metal thin film 147 having the dot-like lattice pattern is formed.

  As described above, in the method for manufacturing a fuel cell metal separator according to the present embodiment, heating is performed so that the precious metal fine particles are sintered in the second step after the first step, and the precious metal fine particles are sintered after the third step. Only one heat treatment is performed. As described above, the formation of the oxide film is promoted by heat treatment. However, in the manufacturing method of this embodiment, the number of times of heat treatment is limited to one even though the number of times of application is two. That is, since the number of heat treatments is reduced, the formation of an oxide film is suppressed, and an increase in contact resistance and thus a decrease in power generation performance are suppressed.

  In the method of manufacturing a fuel cell metal separator according to the present embodiment, a conventionally known cleaning process is performed before the noble metal thin film 147 is formed by the ink jet printing method. For example, after a metal thin plate after the forming process is subjected to alkali cleaning as a degreasing process, plasma cleaning or UV ozone cleaning is performed, and then a noble metal thin film is formed. Thereby, it becomes possible to form the noble metal thin film 147 having good adhesion to each metal separator.

The fuel cell stack 1 according to the present embodiment operates as follows.
Returning to FIG. 2, first, an oxidant gas is supplied to the fuel cell stack 1 by an oxidant gas supply device (not shown). Then, the supplied oxidant gas flows from the oxidant gas inlet communication hole 22 a and flows through the oxidant gas flow path 142 formed between the solid polymer electrolyte membrane 120 and the first separator 14. As a result, the oxidant gas is supplied to the cathode electrode 122.

  At this time, fuel gas is supplied to the fuel cell stack 1 by a fuel gas supply device (not shown). Then, the supplied fuel gas flows from the fuel gas inlet communication hole 26 a and flows through the fuel gas channel 162 formed between the solid polymer electrolyte membrane 120 and the second separator 16. As a result, the fuel gas is supplied to the anode electrode 124.

  At this time, a cooling medium is supplied to the fuel cell stack 1 by a cooling medium supply device (not shown). Then, the supplied cooling medium flows in from the cooling medium inlet communication hole 24 a and flows through the cooling medium flow path 240 formed between the first separator 14 and the second separator 16.

  In the membrane electrode structure 12, power generation is performed by an electrochemical reaction between the oxidant gas supplied to the cathode electrode 122 and the fuel gas supplied to the anode electrode 124. The membrane electrode structure 12 heated by the heat generated by the power generation is cooled by the cooling medium flowing through the cooling medium flow path 240.

  Thereafter, the oxidant gas consumed by being supplied to the cathode electrode 122 is discharged from the oxidant gas outlet communication hole 22b, and the fuel gas consumed by being supplied to the anode electrode 124 is discharged from the fuel gas outlet communication hole 26b. Is done. Further, the cooling medium used for cooling the membrane electrode structure 12 is discharged from the cooling medium outlet communication hole 24b.

According to this embodiment, the following effects are produced.
In this embodiment, the noble metal thin film 147 having a dot-like pattern with a flat surface is formed on the convex portions 144 and 145 of the first separator 14 and the convex portions 164 and 165 of the second separator 16. That is, the noble metal thin film 147 is not formed on the whole of each convex portion, but is formed in a dot shape so that the noble metal thin film 147 is formed on a part thereof and the surface of the noble metal thin film 147 having a dot-like pattern is flattened. To do. More specifically, the noble metal thin film is formed from a base portion 148 in which the outer peripheral portions 148b and 148b are thicker than the central portion 148a and a concave portion 148c is formed in the central portion 148a, and a filled portion 149 filled in the concave portion 148c and having a flat surface 149a. By configuring each of the dots 147, the surface of the noble metal thin film 147 is planarized.
Thereby, compared with the case where the noble metal plating process, such as gold | metal | money, is performed to the whole separator and the whole convex part of a separator like the past, the usage-amount of a noble metal can be reduced and manufacturing cost can be reduced.
Moreover, in this embodiment, since the surface of the noble metal thin film 147 is flattened, an increase in contact resistance at the interface between the convex portions 145 and 165 of each metal separator and the membrane electrode structure 12 can be sufficiently suppressed, and high power generation performance is achieved. can get. Further, when the convex portions 144, 164 of each metal separator are in contact with each other to form the cooling medium flow path 240, an increase in contact resistance at the interface where the convex portions 144, 164 are in contact with each other can be sufficiently suppressed, Higher power generation performance can be obtained.

  Moreover, in this embodiment, the manufacturing method of the above-mentioned 1st separator 14 and the 2nd separator 16 is provided. Specifically, first, the convex portions 144 and 145 (more specifically, the top surface portions 144a and 145a) of the first separator 14 and the convex portions 164 and 165 (more specifically, the top surface portions 164a and 165a) of the second separator 16, A first ink containing a noble metal is applied to a dot pattern. Next, the organic solvent in the applied dot-like first ink is volatilized to form a noble metal thin film precursor 146 having a dot-like pattern in which the outer peripheral part 146b is thicker than the central part 146a. Next, after the second ink containing the noble metal is applied to the concave portion 146c formed in the vicinity of the central portion 146a, that is, the inner side of the top portion 146d of the outer peripheral portion 146b, heat treatment is performed. As a result, a noble metal thin film 147 having a dot-like pattern with a flat surface is formed, and the above-described effect is reliably achieved.

  It should be noted that the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within a scope that can achieve the object of the present invention are included in the present invention.

12 ... Membrane electrode structure 14 ... First separator (metal separator for fuel cell)
16 ... 2nd separator (metal separator for fuel cell)
120 ... solid polymer electrolyte membrane (electrolyte membrane)
122 ... Cathode electrode (electrode)
124 .. Anode electrode (electrode)
144, 145, 164, 165 ... convex portion 146 ... noble metal thin film precursor 147 ... noble metal thin film 148 ... base portion 148a ... central portion 148b ... outer peripheral portion 148c ... concave portion 149 ... filled portion 149a ... surface

Claims (2)

A fuel cell metal separator laminated on a membrane electrode structure provided with a pair of electrodes on both sides of an electrolyte membrane,
The metal separator for a fuel cell is formed into a corrugated plate having irregularities,
A noble metal thin film having a dot-like pattern with a flat surface is formed on the convex portion of the fuel cell metal separator,
Each dot of the noble metal thin film is composed of a base part having a thicker outer peripheral part than the central part and a concave part formed in the central part, and a filled part filled in the concave part and having a flat surface. A fuel cell metal separator. A method for producing a fuel cell metal separator laminated on a membrane electrode structure provided with a pair of electrodes on both sides of an electrolyte membrane,
A first step of applying an ink containing a noble metal and an organic solvent in a dot-like pattern on a convex portion of a fuel cell metal separator formed into a corrugated plate having irregularities;
A second step of volatilizing the organic solvent in the dot-like ink applied in the first step;
A third step of applying an ink containing a noble metal to the vicinity of the central portion of the noble metal thin film precursor having a dot-like pattern having a thicker outer peripheral portion than the central portion formed in the second step;
And a fourth step of forming a noble metal thin film having a dot-like pattern with a flat surface by heat treatment, and a method for producing a metal separator for a fuel cell.

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