JP4660161B2 - Manufacturing method of separator for fuel cell - Google Patents

Description

The present invention relates to a method of manufacturing a fuel cell separator used in a fuel cell stack formed by laminating a plurality of unit cells each having electrodes arranged on both sides of a solid polymer electrolyte membrane. .

A fuel cell is simply a device that continuously supplies fuel (reducing agent) and oxygen or air (oxidant) from the outside, and reacts electrochemically to extract electrical energy. Recently, depending on the type of electrolyte used, it is largely divided into solid oxide fuel cells, molten carbonate fuel cells, phosphoric acid fuel cells, and solid polymer electrolytes. Generally, the fuel cell is classified into five types: a fuel cell and an alkaline aqueous fuel cell.
In particular, a solid polymer electrolyte fuel cell having a structure in which a solid polymer membrane is sandwiched between two types of electrodes and these members are sandwiched between separators can be operated at a low temperature of 100 ° C. or less, and is easily miniaturized. Since it has the advantage of starting in a short time, it has been attracting attention and is being developed as a fuel cell for automobiles, households and portable devices.

Hereinafter, a known solid polymer electrolyte fuel cell will be described with reference to the drawings.
FIG. 1 is a partial cross-sectional view schematically showing a basic structure of a unit cell of a solid polymer electrolyte fuel cell conventionally used. In FIG. 1, 1 is a solid polymer electrolyte membrane, 2 is a fuel electrode, 3 is an oxidizer electrode, 4 is a separator, 5 is a reaction gas flow path, 6 is a catalyst layer, 7 is a porous gas diffusion layer, 8 Is a unit cell, and 10 is a single cell.
As shown in FIG. 1, a unit cell of a solid polymer electrolyte fuel cell is a unit in which a fuel electrode 2 and an oxidant electrode 3 serving as electrodes are closely arranged on both main surfaces of a solid polymer electrolyte membrane 1. A cell 8 is formed, and further separators 4 are arranged on both outer surfaces thereof to form a unit cell 10.
The separator 4 includes a reaction gas channel 5 that supplies a fuel gas to the fuel electrode 2 and a reaction gas channel 5 that supplies an oxidant gas to the oxidant electrode 3. Or it arrange | positions so that the oxidizing agent electrode 3 may be faced.
Both the fuel electrode 2 and the oxidant electrode 3 are composed of a catalyst layer 6 made of platinum or the like and a porous gas diffusion layer 7 that supports the catalyst layer 6. The catalyst layer 6 is in close contact with the solid polymer electrolyte membrane 1. It is arranged.
As the solid polymer electrolyte membrane 1, a thin film having a perfluorocarbon sulfonic acid structure having a sulfonic acid group as an ion exchange group is used, and a proton (hydrogen ion) exchange group is provided in the molecule. Function.

Next, the operation will be described. When hydrogen as a fuel gas is supplied to the fuel electrode 2 and oxygen or air as an oxidant gas is supplied to the oxidant electrode 3, a three-phase interface is formed at the interface between each catalyst layer 6 and the solid polymer electrolyte membrane 1. The following electrochemical reaction takes place.
Fuel electrode: H ₂ → 2H ⁺ + 2e− (1)
Oxidant electrode: 2H ⁺ + (1/2) O ₂ + 2e− → H ₂ O (2)
That is, the hydrogen supplied from the separator is oxidized at the fuel electrode 2 to generate protons and electrons, and the protons are moved through the solid polymer electrolyte membrane 1 to be supplied to the oxidant electrode 3 and the electrons are Is taken out to an external circuit through the separator 4. On the other hand, the oxidant electrode 3 reacts protons that have moved through the solid polymer electrolyte membrane 1, electrons supplied from an external circuit via the separator 4, and oxygen or air supplied from the separator 4. Electrons taken out to the external circuit at the fuel electrode 2 work as current.

Since the voltage generated in this single cell is 1 V or less, a fuel whose electromotive force is increased according to the purpose by stacking a large number of single cells and electrically connecting them in series in order to increase to a practical voltage. Used to form a battery stack. Hereinafter, the fuel cell stack will be described with reference to the drawings. FIG. 2 is a side view schematically showing a configuration of a fuel cell stack formed by stacking unit cells 10 as shown in FIG. In FIG. 2, 11 is an insulating sheet, 12 is an end plate, 13 is a countersunk screw, 14 is a nut, and 20 is a fuel cell stack.
As shown in FIG. 2, the fuel cell stack 20 is formed by laminating a plurality of single cells 10 and arranging an insulating sheet 11 for electrical insulation and thermal insulation on the outside thereof, and then sandwiching them between end plates 12, It is tightened using a countersunk screw 13 and a nut 14 and is held under pressure.

The separator in such a fuel cell stack is interposed between adjacent unit cells of the stacked unit cells, contacts the electrodes of both adjacent unit cells, electrically connects both unit cells, and separates the reaction gas. To act. Hereinafter, the separator in the fuel cell stack will be described with reference to the drawings.
FIG. 3 (a) is a side view schematically showing the configuration of the separator in the fuel cell stack. In FIG. 3 (a), 21 is a reaction gas channel for supplying fuel gas, 22 is a reaction gas channel for supplying oxidant gas, and 30 is a separator. As shown in FIG. 3 (a), the separator 30 has a reaction gas passage 21 for supplying fuel gas to one adjacent unit cell formed on one surface and is adjacent to the other surface. A reaction gas passage 22 for supplying an oxidant gas to the other unit cell is formed, and a fuel gas or an oxidant gas is supplied along the separator surface.
FIG. 3 (b) is a plan view of the separator in the fuel cell stack as seen from one side. In FIG. 3B, 23 is a reaction gas supply port, 24 is a reaction gas discharge port, 25 is a reaction gas supply port communication hole, and 26 is a reaction gas discharge port communication hole. As shown in FIG. 3 (b), the separator 30 is provided with a reaction gas channel 21 at the center thereof. A reaction gas supplied from the outside, that is, a fuel gas such as hydrogen or an oxidant gas such as air is supplied from a reaction gas supply port 23 provided in the upper portion, and flows downward through the reaction gas channel 21. After contributing to the electrochemical reaction, surplus gas is discharged to the outside through a reaction gas outlet 24 provided in the lower part. The reaction gas supply port communication hole 25 and the reaction gas discharge port communication hole 26 are holes that communicate with an inlet and an outlet of a reaction gas that flows to the separator disposed relative to the separator 30. By flowing through, the reaction gas is supplied to each separator of the plurality of stacked unit cells.

 The separator prevents mixing of the fuel gas and the oxidant gas, and takes out electrons generated by the catalytic reaction of hydrogen gas at the fuel electrode to the external circuit, while supplying electrons from the external circuit to the oxidant electrode. There is a role. For this reason, conductive materials made of graphite and metal materials are used for the separator. Especially, metal materials are superior in mechanical strength and can be made lighter and more compact by making them thinner. It is said that it is advantageous at this point. Examples of the metallic separator include a thin plate made of a metal material having corrosion resistance, such as stainless steel and titanium alloy, whose cross section is formed into an uneven shape by etching or pressing. When a stainless steel separator is used, the contact resistance with the gas diffusion layer is larger than when a graphite separator is used, and an increase in contact resistance leads to a decrease in power generation performance. Therefore, in order to reduce the contact resistance, gold is coated on the surface of stainless steel by means such as plating. (Patent Document 1)

In the solid polymer electrolyte fuel cell described above, there is a method of supplying pure hydrogen as fuel as a method of supplying fuel gas to the fuel cell, but for reasons such as safety and infrastructure, methanol, natural gas, A method has been proposed in which gasoline or the like is used as a fuel source, and these are reformed into hydrogen-rich fuel gas by the following reaction using a reformer and then supplied.
Reforming reaction: CH ₃ OH + H ₂ O → 3H ₂ + CO ₂ (3)
However, a small amount of CO is mixed in the fuel gas by the next shift reaction.
Shift reaction: CO ₂ + H ₂ → CO + H ₂ O (4)
When the concentration of CO in the fuel gas supplied to the fuel cell is high, platinum used as a catalyst for the fuel cell is poisoned by CO, and there is a problem that the power generation performance is lowered or in some cases power generation becomes impossible. In particular, since the poisoning due to CO is more remarkable at lower temperatures, it has been studied to reduce the influence of poisoning by CO by dissociating CO adhering to the catalyst by increasing the operating temperature to 150 ° C. or higher.
JP-A-11-162478

 As described above, the metal separators conventionally used are plated with gold after forming stainless steel into the shape of the separator, but exceed 150 ° C. in order to reduce the influence of poisoning by CO. When heat is applied, nickel, chromium, etc., mainly iron, which is a component of stainless steel, are deposited on the gold plating film, forming an oxide film on the surface of the metal separator, and contact between the separator and the gas diffusion layer in close contact with it. Resistance increases. Therefore, there is a problem that the internal resistance of the solid polymer electrolyte fuel cell increases and the power generation efficiency decreases. In addition, since iron or the like deposited on the gold plating film is eluted into the solid polymer electrolyte membrane, the ion exchange amount of the electrolyte membrane is reduced and the proton conductivity is inhibited, leading to a decrease in battery performance.

The present invention has been made under such circumstances of the prior art. A separator for a fuel cell in which metal components do not precipitate from the metal material constituting the separator even when the operating temperature of the fuel cell is high. it is to attempt to provide a manufacturing method.

The method for producing a separator for a fuel cell according to the present invention is a method for producing a separator for a fuel cell in which a groove is formed on the surface of a metal plate and the entire surface is plated with a noble metal. Prepare a metal plate for production, and form a resist pattern on the surface of the metal plate according to the processing shape, and etch the metal plate using the resist pattern as an anti-etching mask to form a desired groove A step of performing etching, removing the resist pattern with a predetermined stripping solution, etching the entire surface portion until the surface-processed deteriorated layer is removed, and performing a precious metal plating on the entire surface portion. It is characterized by this.
The method of manufacturing a separator for a fuel cell of the above, as the material of the metal plate material, stainless steel, titanium, aluminum, copper, nickel, iron, 42 nickel - iron alloy, one of the cold-rolled steel sheet one It is characterized by being one.
Further, in any of the above fuel cell separator manufacturing methods, the step of removing the surface-processed deteriorated layer is an etching step using an etchant selected from ferric chloride, sulfuric acid, hydrochloric acid, and hydrofluoric acid. It is characterized by being.
Moreover, it is a manufacturing method of the separator for fuel cells of any one of the said, Comprising: The process of giving the said noble metal plating forms the metal film which consists of any one of gold | metal | money, platinum, and ruthenium. It is characterized by this.

  In the present invention, since the uppermost layer of the metal material constituting the separator is removed by etching, the metal component does not precipitate from the metal material even when the operating temperature of the fuel cell is high. Further, the process of removing the uppermost layer of the metal material is performed without using a complicated process with an etchant used for forming the metal material into a separator shape or an etchant used for pretreatment when plating the separator. Therefore, it can be manufactured at low cost.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Reference embodiment)
FIG. 4 (f) is a partial cross-sectional view showing a reference form 1 of a separator for a solid polymer electrolyte fuel cell according to the present invention, and FIGS. 4 (a) to 4 (f) are cross-sectional views of the manufacturing process. FIG.
In FIG. 4, 31 is a metal plate, 31A is a metal substrate for a separator, 34 is a groove, 32 is a resist pattern, 33 is a resist opening, and 35 is noble metal plating.
The separator for a polymer electrolyte fuel cell in this Reference Embodiment 1, as shown in FIG. 4 (f), the entire surface of the metal substrate 31A having a groove 34 on both sides thereof, noble metal means such as plating Is covered.
In addition, about the shape of the groove part 34, the shape shown in FIG.4 (f) is an example, and is not restricted to this. In the case of a planar fuel cell separator as disclosed in Japanese Patent Application Laid-Open No. 2004-47397, a through hole is formed instead of the groove.
Hereinafter, an example of the manufacturing process of the separator shown in FIG. 4 (f) will be briefly described with reference to FIGS. 4 (a) to 4 (f).
First, a metal plate 31 for preparing a separator is prepared (FIG. 4 (a)).
Examples of the material of the metal plate material 31 include stainless steel, titanium, aluminum, copper, nickel, 42 nickel-iron alloy, cold rolled steel plate, and the like, which are appropriately selected depending on mechanical strength, workability, weight, and the like.
Next, the entire surface portion of the metal plate 31 is etched until the surface-processed deteriorated layer is removed (FIG. 4 (b)).
The thickness of the surface-processed deteriorated layer is considered to be about 1 μm to several tens of μm in the case of a stainless rolled steel plate.
Examples of the etching solution used in this step include ferric chloride, sulfuric acid, hydrochloric acid, hydrofluoric acid (hydrofluoric acid-overwater added with hydrogen peroxide, buffered hydrofluoric acid added with ammonia), and the like. Select according to the selected material.
Next, a resist pattern 32 is formed in accordance with the processed shape (FIG. 4 (c)).
The resist is not particularly limited as long as it has a desired resolution and good processability.
Next, the metal plate 31 is etched using the resist pattern 32 as an etching resistant mask to form a desired groove 34 (FIG. 4D).
Examples of the etching solution used in this step include ferric chloride, sulfuric acid, hydrochloric acid, hydrofluoric acid (hydrofluoric acid-overwater added with hydrogen peroxide, buffered hydrofluoric acid added with ammonia), and the like. Select according to the selected material.
Next, the resist pattern 32 is removed with a predetermined stripping solution to obtain a metal substrate 31A for a separator (FIG. 4 (e)).
Next, after performing a cleaning process, a pre-plating process, and the like as necessary, a precious metal plating 35 is applied to the entire surface portion of the metal base 31A (FIG. 4 (f)).
Examples of the noble metal plating include plating of gold, platinum, ruthenium and the like.

 Here, the surface-processed deteriorated layer is a surface layer having a composition different from that of the dough, in which the surface of the material is changed by rolling, heat treatment, or machining. In the work-affected layer, disorder of lattice defects, deformation of crystal grains, refinement, surface flow, etc. occur. Due to these changes, the process-affected layer is in a state where the energy level is higher than that of the fabric, and chemical changes are likely to occur.

In the example of this reference embodiment , in the step shown in FIG. 4 (b), the entire surface portion of the metal plate 31 is etched, and then the precious metal plating is performed in the step shown in FIG. 4 (f). The surface-processed deteriorated layer of the metal plate material is removed.
This has the effect of improving the stability of the metal plate material by removing the work-affected layer in a chemically unstable state.
In addition, when precious metal plating is performed on a work-affected layer in which crystal grains are miniaturized, the crystal grains of the plating become fine and have many crystal grain boundaries.
Within the temperature range in which the separator is used, metal thermal diffusion mainly occurs through the grain boundaries, so the components of the metal plate are likely to diffuse during precious metal plating with many grain boundaries, and corrosion resistance at high temperatures. Inferior.
By removing the work-affected layer, noble metal plating with a large number of crystal grains with few crystal grain boundaries can be applied, and diffusion of the base metal can be suppressed.

(Embodiment)
Figure 5 (f) is a partial sectional view showing a reference embodiment 2 of separators for solid polymer electrolyte fuel cell according to the present invention, FIG. 5 (a) ~ FIG. 5 (f) is a manufacturing step sectional FIG.
In FIG. 5, 41 is a metal plate material, 41A is a metal substrate A for a separator, 41B is a metal substrate B for a separator, 44 is a groove, 42 is a resist pattern, 43 is a resist opening, and 45 is a noble metal plating.
The configuration of the separator for the solid polymer electrolyte fuel cell in Reference Embodiment 2 is the same as that shown in FIG. 4 (f), and as shown in FIG. 5 (f), a metal substrate having grooves 44 on both sides thereof. Noble metal is coated on the entire surface of 41A by means such as plating, and the shape of the groove 44 is not limited to the shape shown in FIG. 5 (f).
Hereinafter, an example of the manufacturing process of the separator shown in FIG. 5 (f) will be briefly described with reference to FIGS. 5 (a) to 5 (f). First, a metal plate 41 for preparing a separator is prepared (FIG. 5 (a)).
Examples of the material of the metal plate 41 include stainless steel, titanium, aluminum, copper, nickel, iron, 42 nickel-iron alloy, cold rolled steel plate, and the like, which are appropriately selected depending on mechanical strength, workability, weight, and the like.
Next, a resist pattern 42 is formed in accordance with the processed shape (FIG. 5 (b)).
The resist is not particularly limited as long as it has a desired resolution and good processability.
Next, the metal plate 41 is etched using the resist pattern 42 as an etching resistant mask to form a desired groove 44 (FIG. 5 (c)).
Examples of the etching solution used in this step include ferric chloride, sulfuric acid, hydrochloric acid, hydrofluoric acid (hydrofluoric acid-overwater added with hydrogen peroxide, buffered hydrofluoric acid added with ammonia), and the like. Select according to the selected material.
Next, the resist pattern 42 is removed with a predetermined stripping solution to obtain a metal substrate B41B for a separator (FIG. 5 (d)).
Next, etching is performed on the entire surface portion of the metal base B41B for the separator until the surface-processed deteriorated layer is removed to obtain a metal base A41A for the separator (FIG. 5 (e)).
The thickness of the surface-processed deteriorated layer is considered to be about 1 μm to several tens of μm in the case of a stainless rolled steel plate.
Examples of the etching solution used in this step include ferric chloride, sulfuric acid, hydrochloric acid, hydrofluoric acid (hydrofluoric acid-overwater added with hydrogen peroxide, buffered hydrofluoric acid added with ammonia), and the like. Select according to the selected material.
Next, after performing a cleaning process, a pre-plating process, and the like as required, a precious metal plating 45 is applied to the entire surface portion of the metal substrate A41A (FIG. 5 (f)).

In the example of this embodiment , in the step shown in FIG. 5 (e), the entire surface of the separator metal substrate B is etched, so that noble metal plating is performed in the subsequent step shown in FIG. 5 (f). The surface-processed deteriorated layer of the metal substrate for the separator has been removed previously.

Next, the present invention will be described in more detail with reference examples, examples and comparative examples.
(Reference Example 1)
Reference Example 1 is an example in which the separator of Reference Example 1 is manufactured, and before the metal plate material is processed into a separator shape, the entire surface portion of the metal plate material is etched, whereby the surface processed deteriorated layer of the metal substrate for the separator It is an example which removes.
First, a stainless steel plate (SUS304, 0.6 mm thickness) was prepared as a metal plate material for a separator, and degreased and washed with water.
Degreasing was performed by using 10% Pakuna FD-1 (Yuken Industry) at 50 ° C. for 30 seconds.
Next, the entire surface of the stainless steel plate was etched to remove the surface-processed deteriorated layer, and then washed and dried.
The etching conditions at this time were 1 minute using 10% ferric chloride at 30 ° C.
The etching amount at this time was about 2.0 μm.
Next, a photoresist film having a thickness of 20 μm made of a photosensitive material in which casein and ammonium dichromate are mixed is formed on both surfaces of the stainless steel plate, and the shape of a reaction gas flow path as a separator is formed from both surfaces. Using a certain pattern, exposure was performed for 60 seconds with a 5 KW high-pressure mercury lamp, and development was performed by spraying hot water at 40 ° C. to form a resist film resistant to etching performed later.
Thereafter, ferric chloride heated to 70 ° C. from both sides of the metal plate was showered, and the etching process was completed when the etching progressed to a predetermined depth.
This is showered with an aqueous solution of 110% caustic soda at 80 ° C. to remove the resist, then washed and dried, and a stainless steel plate having the desired reaction gas channel shape is used as the metal substrate for the separator. Obtained.
Gold plating was performed on the entire surface of the metal base for the separator thus obtained.
As the plating conditions at this time, plating was performed for 5 minutes at a current density of 0.4 A / dm ² using 60 ° C. Tempe resist K-91S (Japan High Purity Chemical).

Example 1
Example 1 is an example in which the separator of Reference Embodiment 2 is manufactured. After obtaining a metal substrate by processing a metal plate material into a separator shape, the entire surface portion of the metal substrate is etched to obtain a metal substrate for a separator. It is an example which removes a surface processing deterioration layer.
In this example, the reference example 1 does not perform the etching process for the entire surface portion of the metal plate material before being processed into the separator shape, but is a reference except for the process for etching the entire surface portion of the metal substrate processed into the separator shape. A separator was produced in the same manner as in Example 1.
The separator thus manufactured was evaluated for heat resistance, and the result is shown in FIG.
This heat resistance is evaluated by measuring the amount of elements deposited on the plating surface when the separator is heated at 125 ° C. to 250 ° C. for 4 hours in the atmosphere under XPS (photoelectron spectroscopy) under the following conditions. did.
Measuring device: Quantum 2000 manufactured by ULVAC-PHI
X-ray source: AlKα monochromatic light X-ray beam system: 200 μm
X-ray output: 30W
Photoelectron capture angle: 45 °
From the results shown in FIG. 6A, no precipitation of iron, which is a component of the metal plate material, was observed even when the separator was at a high temperature of 225 ° C.

[Comparative example]
In the example, a conventional separator that does not etch the entire surface of the metal plate or metal substrate was subjected to the same heat resistance evaluation as in the example, and the result is shown in FIG. From this result, precipitation of iron which is a component of the metal plate was observed in the separator of the comparative example when heat of 175 ° C. or higher was applied.

Examples of the present invention, in the reference embodiment has been described with the separators method for producing a solid polymer electrolyte fuel cell, if also used at high temperatures in the other fuel cell has the same advantages.

 The present invention can be applied to the production of fuel cells for automobiles, households and portable devices.

It is a fragmentary sectional view which shows the basic composition of the unit cell of the conventional solid polymer electrolyte fuel cell. It is a side view which shows the structure of a fuel cell stack. It is the side view and top view which show the structure of the separator in a fuel cell stack. The reference embodiment 1 of the separator for solid polymer electrolyte fuel cell according to the present invention is a cross-sectional view and a manufacturing step sectional view showing. It is sectional drawing which shows the reference form 2 of the separator for solid polymer electrolyte fuel cells in connection with this invention , and its manufacturing process sectional drawing. It is a figure which shows the result of the heat resistance evaluation of the separator for solid polymer electrolyte fuel cells by this invention, and the conventional separator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Solid polymer electrolyte membrane 2 ... Fuel electrode 3 ... Oxidant electrode 4, 30 ... Separator 5 ... Reaction gas flow path 6 ... Catalyst layer 7 ... Gas diffusion layer 8 unit cell 10 unit cell 11 insulation sheet 12 end plate 13 flat head screw 14 nut 20 fuel cell stack 21 fuel gas supply Reaction gas channel 22 for supplying the reaction gas channel 23 for supplying the oxidant gas ... reaction gas supply port 24 ... reaction gas discharge port 25 ... reaction gas supply port communication hole 26 ... Reactive gas discharge port communication holes 31, 41 ... Metal plate material 31A ... Metal substrate for separator 32,42 ... Regist pattern 33,43 ... Resist openings 34,44 ... Groove 35, 45 ... Precious metal plating 41A ... Metal for separator Body A
41B ... Metal base B for separator

Claims (4)

  A method of manufacturing a separator for a fuel cell in which a groove is formed on the surface of a metal plate and the entire surface is plated with a noble metal, and in order, a metal plate for preparing a separator is prepared, and the metal plate A step of forming a resist pattern on the surface in accordance with a processing shape, a step of etching the metal plate material using the resist pattern as an etching resistant mask to form a desired groove, and the resist pattern with a predetermined stripping solution And a step of etching the entire surface portion until the surface-processed deteriorated layer is removed, and a step of applying noble metal plating to the entire surface portion. . It is a manufacturing method of the separator for fuel cells of Claim 1, Comprising: As a material of the said metal plate material, any of stainless steel, titanium, aluminum, copper, nickel, iron, 42 nickel-iron alloy, and a cold-rolled steel plate A method for producing a separator for a fuel cell, characterized by comprising: 3. The method for manufacturing a separator for a fuel cell according to claim 1, wherein the step of removing the surface-processed deteriorated layer is selected from ferric chloride, sulfuric acid, hydrochloric acid, and hydrofluoric acid . A method for producing a separator for a fuel cell, which is an etching step using an etchant. 4. The method for manufacturing a separator for a fuel cell according to claim 1, wherein the precious metal plating step forms a metal film made of any one of gold, platinum, and ruthenium. 5. A method for producing a separator for a fuel cell, characterized in that :

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