WO2009034845A1

WO2009034845A1 - Process for producing separator for fuel cell

Info

Publication number: WO2009034845A1
Application number: PCT/JP2008/065345
Authority: WO
Inventors: Kuroudo Maeda; Masahiro Mizuno
Original assignee: Toyota Jidosha Kabushiki Kaisha; Aisin Takaoka Co., Ltd.
Priority date: 2007-09-14
Filing date: 2008-08-20
Publication date: 2009-03-19

Abstract

This invention provides a process for producing a separator for a fuel cell which can separate a gas present between adjacent cells for a fuel cell. In producing a separator for a fuel cell using a metallic material such as titanium, a conductor having a high level of electrical conductivity is generally formed on the surface of the separator to reduce contact resistance between the separator and a gas diffusing layer and the like. However, there has been a possibility that, during power generation in a fuel cell, an oxide is formed on the surface of the separator resulting in lowered electrical conductivity of the separator. The above problem can be solved by a process for producing a separator for a fuel cell, comprising a titanium base forming step of plastically working a titanium material to form a titanium base and a removing step of pickling the titanium base to remove titanium oxide and titanium carbide from the surface of the titanium base.

Description

Manufacturing method of fuel cell separator evening

The present invention relates to a method for manufacturing a fuel cell separator, and more particularly, to a method for manufacturing a fuel cell separator that separates gas between adjacent fuel cell cells. Light

Background art

Thread

In recent years, fuel cells have been in the limelight as batteries with high efficiency and excellent environmental characteristics. Fuel cells generally produce electric energy by electrochemically reacting hydrogen, the fuel gas, with oxygen in the air, the oxidant gas. As a result of the electrochemical reaction between hydrogen and oxygen, water is generated.

Types of fuel cells include phosphoric acid type, molten carbonate type, solid electrolyte type, alkaline type, and solid polymer type. Among these, solid polymer fuel cells that have advantages such as startup at normal temperature and quick startup time are drawing attention. Such a polymer electrolyte fuel cell is used as a power source for a mobile object such as a vehicle.

A polymer electrolyte fuel cell is assembled by stacking a plurality of single cells, current collector plates, end plates, and the like. The fuel cell includes an electrolyte membrane, a catalyst layer, a gas diffusion layer, and a separator.

In Patent Document 1, the use of a fuel cell separator that is surface-treated with a metal made of gold or chromium on a separator base made of stainless steel or titanium prevents corrosion against the corrosive atmosphere of the battery environment. It is described that the performance is improved.

Patent Document 2 describes a high corrosion resistance stainless steel used as a separator for a polymer electrolyte fuel cell and a surface treatment method for reducing contact resistance against carbon to titanium, in which a passive metal is polished with a noble metal attached thereto. It describes that a noble metal is adhered to a passive metal immediately after removing the surface oxide film by polishing with a material.

Patent Document 3 describes a surface treatment method for a passive metal to carbon with a low contact resistance. An appropriate amount of high-hardness particles partially or entirely coated with a precious metal or its alloy are mixed between the surface to be treated of the passive metal and the precious metal or its alloy facing it, and the surface is hardened by ultrasonic waves. It describes that particles are vibrated and flowed, and a noble metal or an alloy thereof is adhered to a part or all of the surface while removing a surface oxide film of a passive metal by collision of a hard particle with a surface to be treated.

Patent Document 1: Japanese Patent Laid-Open No. 2005-158441

Patent Document 2: Japanese Patent Laid-Open No. 2002-134128

Patent Document 3: Japanese Patent Laid-Open No. 2002-134136 Disclosure of Invention

Problems to be solved by the invention

By the way, when manufacturing a separator for a fuel cell with a metal material such as titanium, generally, a conductive material having a high electrical conductivity is formed on the surface to reduce the corrosion resistance between the gas diffusion layer and the like. It is reduced. Here, during power generation of the fuel cell, oxides are generated on the surface of the separator due to oxidation of titanium or the like. Since oxides generally have low electrical conductivity, the conductivity of a separator can be reduced if the oxide is formed thick. Accordingly, an object of the present invention is to provide a method for manufacturing a fuel cell separator capable of suppressing a decrease in conductivity.

Means for solving the problem

A method for manufacturing a fuel cell separator according to the present invention is a method for manufacturing a fuel cell separator that separates gas between adjacent fuel cell cells, wherein a titanium substrate is formed by plastically adding a titanium material. A titanium substrate forming step for forming; and a removal step of pickling the titanium substrate to remove titanium oxide and titanium carbide from the surface of the titanium substrate.

In the method for manufacturing a fuel cell separate according to the present invention, the titanium substrate forming step is characterized by rolling and forming a titanium material.

The method for manufacturing a fuel cell separator according to the present invention is characterized by having a conductive layer forming step of forming a conductive layer on the surface of the titanium substrate after the removing step. The invention's effect As described above, according to the method for manufacturing a fuel cell separator according to the present invention, since the generation of oxides formed in the fuel cell separator is reduced, the conductivity of the fuel cell separator overnight is reduced. Can be suppressed.

Brief Description of Drawings

FIG. 1 is a diagram showing a cross section of a fuel cell in an embodiment of the present invention. FIG. 2 is a flow chart showing a method for manufacturing a separator overnight in an embodiment of the present invention.

FIG. 3 is a schematic diagram showing a method of rolling a titanium material in the embodiment of the present invention.

FIG. 4 is a view showing a cross section of the titanium substrate after rolling in the embodiment of the present invention.

FIG. 5 is a diagram showing a cross section of the separator evening in the embodiment of the present invention. FIG. 6 is a diagram showing a test apparatus used in the electrochemical high temperature corrosion test in the embodiment of the present invention.

FIG. 7 is a diagram showing a corrosion test result in a separate evening specimen in the embodiment of the present invention.

FIG. 8 is a diagram showing a method for measuring contact resistance in the embodiment of the present invention. FIG. 9 is a graph showing the measurement results of contact resistance in a separate evening specimen in the embodiment of the present invention. Explanation of symbols

1 0 Fuel cell, 1 2 Electrolyte membrane, 1 4 Catalyst layer, 1 6 Gas diffusion layer, 1 8 Membrane electrode assembly, 2 0 Expanded molding, 2 2 Separator, 2 4 Titanium substrate, 2 6 Conductive Layer, 30 titanium material, 3 2, 3 6 titanium oxide, 3 4 titanium carbide, 3 8 titanium oxide layer, 40 metal jig, 4 2 gas diffusion layer material, 4 4 specimen. BEST MODE FOR CARRYING OUT THE INVENTION Embodiments according to the present invention will be described below in detail with reference to the drawings. First, the configuration of the fuel cell will be described. FIG. 1 is a cross-sectional view of a fuel cell 10. A fuel cell 10 includes a membrane electrode assembly 18 (Membran e lectrode A sse mb 1) that integrates an electrolyte membrane 12, a catalyst layer 14, and a gas diffusion layer 16 to form a fuel cell electrode. y: ME A), an expanded molded body 20 that is a gas flow path structure that forms a gas flow path, and a separator gas that separates fuel gas or oxidant gas between adjacent cells (not shown). And including.

The electrolyte membrane 12 has a function of moving hydrogen ions generated on the anode electrode side to the force sword electrode side. As the material of the electrolyte membrane 12, a chemically stable fluorine-based resin, for example, an ion exchange membrane of perfluorocarpone sulfonic acid is used.

The catalyst layer 14 has a function of promoting a hydrogen oxidation reaction on the anode electrode side and an oxygen reduction reaction on the force sword electrode side. The catalyst layer 14 includes a catalyst and a catalyst carrier. In order to increase the electrode area to be reacted, the catalyst is generally used in the form of particles and attached to the catalyst carrier. As the catalyst, platinum, which is a platinum group element having a smaller activation overvoltage, is used for the oxidation reaction of hydrogen and the reduction reaction of oxygen. A carbon material such as a car pump rack is used as the catalyst carrier.

The gas diffusion layer 16 has a function of diffusing hydrogen gas, which is a fuel gas, and air, which is an oxidant gas, into the catalyst layer 14 and a function of moving electrons. The gas diffusion layer 16 is made of carbon fiber woven fabric, force-on-paper, or the like, which is a conductive material.

The expanded molded body 20 is laminated on both surfaces of the membrane electrode assembly 18 and has a function as a gas channel structure that forms a gas channel. The expanded molded body 20 is laminated in contact with the gas diffusion layer 16 of the membrane electrode assembly 18 and the separator 22, and is electrically connected to the membrane electrode assembly 18 and the separator 22. Since the expanded molded body 20 has a mesh structure composed of a large number of openings, more fuel gas or the like comes into contact with the membrane electrode assembly 18 to cause a chemical reaction, thereby generating power from the fuel cell 10. Efficiency can be increased.

As the expanded molded body 20, for example, an expanded metal shown in JISG 3351, a metal lath or a metal porous body shown in JISA 5505, or the like is used. The expanded molded body 20 is preferably molded from titanium, titanium alloy stainless steel or the like. These metal materials, mechanical strength high degree of stable oxide on the surface (T I_〇, T i ₂ 〇 _3, T I_〇 _2, C R_〇 _2, C R_〇, C r ₂ 〇 ₃ This is because an inert film such as a passive film is formed and thus has excellent corrosion resistance. As the stainless steel, an austenitic stainless steel, a ferritic stainless steel, or the like can be used.

The separate evening 22 is laminated on the expanded molded body 20 and has a function of separating the fuel gas and the oxidant gas in the adjacent cell (not shown). In addition, the separator overnight 22 has a function of electrically connecting adjacent cells (not shown). Separate Night 22 is made of pure titanium or a titanium alloy. As described above, the titanium material has high mechanical strength and has an excellent corrosion resistance because an inert film such as a passive film made of a stable oxide is formed on the surface thereof.

The separate evening 22 includes a titanium substrate 24 formed of a titanium material and a conductive layer 26 formed on the titanium substrate 24. The conductive layer 26 is set to a thickness of 311111 to 2001 m, and has a function of reducing contact resistance between the expanded molded body 20 and the titanium substrate 24. The conductive layer 26 is made of a metal material such as gold (Au), silver (Ag), copper (Cu), platinum (Pt), rhodium (Rh), iridium (Ir), palladium (Pd), etc. It is formed by. Because these metal materials have high electrical conductivity, the contact resistance can be further reduced. Among these metal materials, gold (Au) is preferable as a metal material for forming the conductive layer 26 because it is excellent in corrosion resistance and has high electric conductivity. The conductive layer 26 may be formed of an alloy such as gold (Au) or platinum (Pt).

Next, a method for manufacturing the separate evening 22 will be described.

FIG. 2 is a flowchart showing a method for manufacturing the separate evening 22. The manufacturing method of Separat 22 includes a titanium substrate forming step (S 10), a cleaning step (S 12), a neutralization step (S 14), a removal step (S 16), and a conductive layer forming step (S 18 ) When, It is comprised including.

The titanium substrate forming step (S 10) is a step of forming a titanium substrate 24 by plastic working a titanium material. The titanium substrate 24 is formed by, for example, roll rolling a titanium material. Fig. 3 is a schematic diagram showing a method of rolling a titanium material. As described above, pure titanium or a titanium alloy is used for the titanium material 30. For example, the titanium material is hot-rolled at a temperature of 700 to 900 ° C. As the rolling apparatus for rolling the titanium material 30, a rolling apparatus generally used for rolling titanium material can be used. In rolling the titanium material 30, a lubricant containing fats and oils and carbons is used to prevent seizure and the like. Of course, depending on other conditions, the plastic working of the titanium material 30 is not limited to rolling, but may be press working or the like.

FIG. 4 is a view showing a cross section of the titanium substrate 24 after rolling. On the surface of the titanium substrate 2 4, T I_〇 the titanium material 3 0 is a base material was produced by oxidation, T i ₂ 〇 _3, T I_〇 ₂ titanium oxides such as 3 2 are formed. On the titanium oxide 3 2, T i C, T i C ₂ , T i produced by chemical reaction with carbon produced by carbonization of oils and fats contained in the lubricant during the rolling process. Titanium carbide 3 4 such as C ₃ is formed. Further, on the titanium oxide 3 2, titanium oxide 3 6 such as T i O, T i ₂ 0 ₃ , T i 0 _2, etc. formed by oxidizing the titanium carbide 3 4 is also formed.

The cleaning step (S 1 2) is a step of cleaning the titanium substrate 24 formed by rolling the titanium material 30. The titanium substrate 24 is cleaned by, for example, alkaline immersion degreasing. For alkaline immersion degreasing, an alkaline solution such as caustic soda is used. By washing the titanium substrate 24 with alkali dipping degreasing or the like, oil or the like adhering to the surface of the titanium substrate 24 is removed.

The neutralization step (S 14) is a step of neutralizing and removing the alkali remaining on the cleaned titanium substrate 24. The neutralization treatment is performed by immersing the cleaned titanium substrate 24 in a neutralizing solution. For the neutralizing solution, sulfuric acid solution, hydrochloric acid solution, nitric acid solution, etc. are used. Then, the titanium substrate 24 taken out from the neutralized solution is washed with deionized water or the like. In the removal step (S 1 6), the titanium substrate 24 that has been subjected to the neutralization treatment is pickled to remove the titanium oxides 3 2 and 3 6 and the titanium carbide 3 4 from the surface of the titanium substrate 24. It is a process. According to the removal step (S 16) for removal by pickling, the productivity of the fuel cell separator can be improved as compared with the step for removal by polishing or the like. The pickling treatment is performed by immersing the titanium substrate 24 in a solution containing fluoride such as a nitric hydrofluoric acid solution or a hydrofluoric acid solution. When the titanium substrate 24 is immersed in a nitric hydrofluoric acid solution or the like, the titanium oxide 36, titanium carbide 34, and titanium oxide 32 on the surface of the titanium substrate 24 are etched. Thereby, the titanium oxides 3 2 and 3 6 and the titanium carbide 3 4 formed on the titanium substrate 24 are removed. Here, a solution containing a fluoride such as a nitric hydrofluoric acid solution is not used for the pickling solution unless it contains a fluoride. From the surface of the titanium substrate 24, titanium oxide 3 2, 3 6 And titanium carbide 3 4 cannot be removed. The titanium substrate 24 taken out from the nitric hydrofluoric acid solution or the like is washed with deionized water or the like.

The conductive layer forming step (S 1 8) is a step of forming the conductive layer 26 on the titanium substrate 24 that has been pickled. The conductive layer 26 is set to a thickness of 3 nm to 200 nm, and is formed by coating a conductor such as gold (A u). For the coating of gold (A u) or the like, for example, an electrolytic plating method can be used. For the electrolytic plating method, a general alkaline plating method such as gold (A u) is used. This completes the production of Separe Ichiba 22 Note that the separator layer may be manufactured by omitting the conductive layer forming step (S 1 8).

FIG. 5 is a view showing a cross section of the manufactured separator 22. The separator 22 has a titanium substrate 24 and a conductive layer 26. Here, in the titanium substrate 24, the titanium oxides 3 2 and 3 6 and the titanium carbide 3 4 are removed in the removal step (S 16). Therefore, generation of titanium oxide due to oxidation of titanium carbide 34 can be prevented during fuel cell power generation. It should be noted that the separate evening may be configured by omitting the conductive layer 26 from the separate evening 22 shown in FIG.

As described above, according to the above configuration, by removing the titanium oxide and the titanium carbide formed on the titanium substrate, it is possible to prevent the generation of the titanium oxide due to the oxidation of the titanium carbide during power generation of the fuel cell. As a result, an increase in contact resistance between the expanded molded product and the separator is suppressed, and a decrease in conductivity in the separator can be suppressed. (Example)

Two types of separate specimens were manufactured and evaluated for corrosion resistance and conductivity.

A method for manufacturing the separate overnight specimen in Example 1 will be described. Pure titanium was used for the titanium material. A pure titanium material was roll-rolled to form a titanium sheet. The titanium sheet was degreased by alkali soaking and washed to remove oil adhering to the titanium sheet. The titanium sheet washed with alkali degreasing was neutralized by dipping in a sulfuric acid solution. Next, the titanium sheet was immersed in a nitric hydrofluoric acid solution and pickled, and titanium oxide and titanium carbide formed on the surface of the titanium sheet were etched and removed. In addition, the manufacturing method of the separator evening specimen in the comparative example 1 which uses what does not form a conductive layer for the separator evening specimen used for the evaluation test is explained. In the manufacturing method of the separate evening specimen in Comparative Example 1, it was manufactured by the same manufacturing method as that of the separate evening specimen in Example 1 except that pickling with a nitric hydrofluoric acid solution was not performed. Therefore, the separator oxide specimen of Comparative Example 1 did not remove the titanium oxide and titanium carbide formed on the surface.

Next, the corrosion test method for the separator specimen will be described. The corrosion test was conducted in accordance with the electrochemical high temperature corrosion test method for metallic materials specified in JISZ 2 2 9 4. Figure 6 shows the test equipment used in the electrochemical hot corrosion test. The test was conducted in an open air system. The solution used for the test was a sulfuric acid solution. The temperature of the test solution was 50 ° C. Then, a corrosion test was performed by applying a constant potential for 50 hours. The corrosion resistance was evaluated by observing the appearance of the separate overnight specimen after the corrosion test.

Fig. 7 is a diagram showing the results of a corrosion test on a separate evening specimen. The separate evening specimen of Example 1 was less discolored than the separate evening specimen of Comparative Example 1. The separation overnight specimen of Comparative Example 1 has a lot of discoloration because the titanium oxide and titanium carbide remained on the surface of the separation evening specimen of Comparative Example 1, so that the titanium carbide was oxidized during the corrosion test. This is because the titanium oxide is formed thick.

Next, contact resistance was measured for the separate evening specimen subjected to the above corrosion test. . FIG. 8 is a diagram showing a method for measuring contact resistance. After attaching the gas diffusion layer material 4 2 to the metal jig 40, sandwich the separator sample of Example 1 or Comparative Example 1 as the test piece 4 4 between the two gas diffusion layer materials 4 2, A predetermined surface pressure was applied to bring it into close contact. Then, the contact resistance was determined by measuring the voltage between the test piece 44 and the gas diffusion layer material 42 when a current of 1 A was passed.

Fig. 9 is a graph showing the measurement results of contact resistance of the separate overnight specimen. As shown in Fig. 9, the horizontal axis indicates the type of the specimen to be separated, the vertical axis indicates the relative value of contact resistance (mΩ · cm ² ), and the contact resistance before the corrosion test is indicated by a white square. Corrosion test The contact resistance after 50 hours is indicated by a black square. In the separate evening specimen of Example 1, the contact resistance before the corrosion test and the corrosion resistance after the corrosion test were substantially the same level. On the other hand, the contact resistance after the corrosion test in the separate evening specimen of Comparative Example 1 increased significantly compared to the contact resistance before the corrosion test. The increase in contact resistance of the separator evening specimen of Example 1 was suppressed because the formation of titanium oxide during the corrosion test was suppressed because titanium oxide and titanium carbide were removed. Because. In contrast, in the separator evening specimen of Comparative Example 1, because titanium oxide and titanium carbide remained, the titanium carbide was oxidized during the corrosion test, resulting in a thicker titanium oxide. Because.

In addition, a separate layer specimen was manufactured by forming a conductive layer (gold or palladium having a thickness of 10 nm) on the separator specimen of Example 1, and the same as in Example 1 and Comparative Example 1. As a result, a corrosion test was performed on a separate specimen and contact resistance was obtained. Although not shown here, the present inventors have confirmed that the corrosion test results and the contact resistance measurement results were better than those in Example 1.

Claims

The scope of the claims

1. A method of manufacturing a fuel cell separator that separates gas between adjacent fuel cell cells,

A titanium substrate forming step in which a titanium material is plastically processed to form a titanium substrate;

A method for producing a fuel cell separator.

2. A method for manufacturing a separator for a fuel cell according to claim 1, wherein the titanium substrate forming step includes forming a titanium material by rolling the titanium material. .

3. A method for producing a fuel cell separator according to claim 1 or claim 2, comprising:

A method for manufacturing a separator for a fuel cell, characterized by having a conductive layer forming step of forming a conductive layer on the surface of the titanium substrate after the removing step.