JP2006278172A - Separator material for fuel sell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator material for a fuel cell reconciling sufficient corrosion resistance with conductivity by using a base material excellent in corrosion resistance and by forming a thinner film of noble metal. <P>SOLUTION: The separator material for the fuel cell, composed of one or not less than two kinds of components selected from Pt, Pd, Rh, and Ru, has a thickness of not less than 10 nm, and formed on a base material made of titanium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a material used for a metal separator for a solid polymer electrolyte fuel cell.

  A solid polymer electrolyte fuel cell separator is a member that constitutes a fuel cell stack in which a plurality of single cells are stacked, and requires sufficient gas impermeability and electrical conductivity for electrical connection between cells. It is. Furthermore, high corrosion resistance is also required for the acid atmosphere. Conventionally, carbon materials or metal materials have been used for such fuel cell gas separators. Since the carbon material has a lower strength than the metal material, it is difficult to reduce the thickness, and the processing cost is high, so in recent years, the metal material has been widely studied.

  There are various characteristics required for materials used as gas separators for fuel cells, but the problem particularly when using metal materials is compatibility between corrosion resistance and conductivity.

  Focusing on the provision of corrosion resistance, a technique for coating a nitride protective layer on a base material (Patent Document 1) is another technique for achieving both conductivity and corrosion resistance. (Patent Documents 2 and 3) are disclosed.

  Furthermore, a technique (Patent Document 4) is disclosed in which a multilayer structure composed of two or more layers of a low electrical resistance layer, a corrosion resistance layer, and a peel resistance layer is formed on a metal substrate to achieve a required characteristic by forming a thickness of 120 nm or more. ing.

JP 2000-353531 A JP 1998-228914 A JP 2001-6713 A JP 2000-164228 A

However, when forming a nitride on a substrate, corrosion resistance is obtained but sufficient conductivity is not obtained. In addition, when Au plating is performed on a base material such as stainless steel, although conductivity is obtained, the occurrence of minute defects is unavoidable in thin film formation of about 0.01 μm, so the corrosion resistance is poor. Although a method of forming a thick Au plating is also conceivable, it is not industrially practical from the viewpoint of cost.
On the other hand, in the case of a multilayer film structure having various functions in order to achieve both corrosion resistance and conductivity, it is difficult to achieve industrial practical use from the viewpoint of workability and cost of the material.
The present invention has been made to solve such problems, and is a fuel cell separator that achieves both sufficient corrosion resistance and conductivity by forming a thin noble metal film using a substrate having excellent corrosion resistance. The purpose is to provide materials.

As a result of earnestly examining the technology for achieving both the corrosion resistance and the conductivity, the present inventors have found that the corrosion resistance of the separator base material is insufficient at the stainless steel level, and uses titanium that is more excellent in corrosion resistance. In order to obtain the above, it has been found that it is effective to thinly form one or more of Pt, Pd, Rh, and Ru on the substrate. In this case, Pt, Pd, Rh, and Ru, which are film forming elements, exhibit excellent corrosion resistance by themselves, but forming a stronger corrosion-resistant layer by alloying with titanium makes it extremely effective in imparting corrosion resistance. It is valid. Also, the surface roughness of the base material is set within a certain range, and one or more of Pt, Pd, Rh, and Ru are formed on the base material, or the base material is formed by rolling or heat treatment after the film formation. It has been found that strengthening the adhesion of the film material is more effective for achieving both corrosion resistance and electrical conductivity.
Here, as for the titanium base material, it is only necessary that the outermost layer portion of the base material has a corrosion resistance equal to or higher than that of pure titanium, and it is also possible to use a titanium alloy or a clad material of pure titanium or titanium alloy. .

That is, the present invention
(1) A material for a fuel cell separator, wherein the composition is one or more of Pt, Pd, Rh, and Ru, the thickness is 10 nm or more, and a film is formed on a titanium substrate.
(2) A fuel cell comprising a titanium substrate having a composition of one or more of Pt, Pd, Rh, and Ru, a thickness of 10 nm or more, and a thickness of 90 μm or less. Separator material,
(3) The composition is one or more of Pt, Pd, Rh, and Ru, the thickness is 10 nm or more, the surface roughness Ra is 0.2 to 2.0 μm, and the composition is formed on a titanium substrate. A fuel cell separator material, characterized by being formed into a film.
(4) The fuel cell separator material as described in (1) to (3) above, which is formed by a dry process such as vapor deposition or sputtering.
(5) A material for a fuel cell separator, wherein the composite material according to (1) to (4) is rolled at a rolling degree of 0.1 to 40%.
(6) A fuel cell separator material, wherein the composite material according to (1) to (5) is heat-treated at a temperature of 800 to 1000 ° C. and a heat treatment time of 5 minutes or more.
(7) The film-forming layer on the titanium substrate is an alloy layer of one or more of Pt, Pd, Rh, and Ru and the titanium substrate, and the thickness thereof is 10 nm or more. Fuel cell separator material,
It is.

  A material for a fuel cell separator having both corrosion resistance and conductivity by using titanium as a base material and forming a thin film of one or more of Pt, Pd, Rh, and Ru in the composition. Can be provided.

The reason for limitation will be described below.
(1) Substrate and film-forming element In the present invention, a film having excellent conductivity and corrosion resistance is formed on the substrate and used as a separator for a fuel cell. However, the film-forming material is expensive, and the cost is low. From the viewpoint, it is necessary to reduce the film thickness. When the film formation layer becomes thin, fine defects such as pits are likely to be generated, and the base material is directly exposed to a corrosive environment through the defective portion. Therefore, the base material needs to have sufficient corrosion resistance. In the above corrosive environment, the corrosion resistance of stainless steel as a separator substrate is insufficient, and a material with more excellent corrosion resistance is essential.
When titanium is used for the substrate and Pt, Pd, Rh, Ru is used for the film formation layer, titanium has corrosion resistance, Pt, Pd, Rh, Ru has both corrosion resistance and conductivity, and titanium and Pt, Pd, Rh, When Ru is alloyed, stronger corrosion resistance that can cope with the above-described corrosive environment is provided.
Therefore, titanium was used for the base material, and Pt, Pd, Rh, and Ru were used for the film formation layer.

(2) Thickness of base material Considering the amount of power generation per volume of the battery from the viewpoint of practicality, it is essential to reduce the size of the fuel cell, and a separator that contributes to this requires a thin base material. Considering a separator that is currently in practical use, the thickness is required to be 90 μm or less, so the upper limit was set to 90 μm.

(3) Thickness of film forming layer In order for the separator to obtain sufficient conductivity, the film forming layer needs to have high conductivity, and the lower limit of the thickness is 10 nm. On the other hand, there is no technical limitation on the upper limit of the thickness. However, Pt, Pd, Rh, and Ru, which are film forming components, are expensive noble metals and are preferably set to 100 nm or less in consideration of cost.

(4) Surface roughness of base material The surface roughness of the titanium base material greatly affects the adhesion with the film-forming layer on the base material. When the surface roughness Ra of the substrate is less than 0.2 μm, the adhesion of the fuel cell separator in a corrosive environment is insufficient, so the lower limit is set to 0.2 μm. Further, if the surface roughness Ra exceeds 2.0 μm, it is difficult to form a film with a uniform thickness in a thin film-forming layer, so the upper limit was set to 2.0 μm.

(5) Rolling degree of composite material The rolling process carried out after depositing one or more of Pt, Pd, Rh, and Ru on the titanium base material is carried out between the base material and the film forming material. The purpose is to improve adhesion. The adhesiveness is improved even at a low pressure reduction rate (low processing degree), and the lower limit is 0.1%. Further, if the degree of processing becomes too high, the film formation layer becomes too thin and the conductivity is impaired, so the upper limit was made 40%.

(6) Heat treatment In the heat treatment performed after depositing one or more of Pt, Pd, Rh, and Ru on a titanium substrate, an intermetallic compound of the substrate and the film-forming material is generated. The purpose is to improve adhesion. When the temperature is low, the diffusion rate of metal atoms is slow, and it takes time to generate an intermetallic compound, so the lower limit of the temperature was set to 800 ° C. Further, when the temperature is increased, an extremely thin film-forming layer generates an intermetallic compound in a short time, so that it becomes difficult to control the thickness of the intermetallic compound layer. Therefore, the upper limit temperature was set to 1000 ° C. The heating time varies depending on the temperature, but the object can be achieved in 5 minutes or more.

(1) Example 1
Titanium or SUS316 having a thickness of 60 μm was ultrasonically cleaned with acetone and pretreated with oxygen gas plasma irradiation, and a film having a thickness of 5 to 1000 nm was formed by sputtering on Pt, Pd, Rh, and Ru. The surface roughness of the base material was adjusted to 0.8 to 1.2 μm by adjusting the roll roughness of the final rolling.
The contact resistance after the sulfuric acid immersion of the titanium foil formed into a film with each noble metal thus prepared and the amount of titanium elution were investigated under the following conditions.

Contact resistance <br/> Made by Yamazaki Tester: Electric contact simulator CRS-1
Probe: Gold contact pressure: 10 gf
Side constant: 400 points

Sulfuric acid immersion test Solution: Sulfuric acid 5%
Temperature: 80 ° C
Liquid volume: 5cc
Specimen: 10 × 50 mm Immersion immersion time: ˜30 days Measurement method: Ti base material is Ti and SUS316 base material is Fe ion determined by ICP analysis

Invention Example No. Nos. 1 to 7 use Ti as the base material of the separator, the thickness of the Pt, Pd, Rh, and Ru film formation layer on the base material is 10 nm or more, and the contact resistance is 20 mΩ or less and the conductivity is high. Further, the Ti concentration eluted in 30 days after immersion in sulfuric acid is less than 1 mg / L, and the corrosion resistance is also good.
On the other hand, Comparative Example No. No. 8 uses Ti as a base material and has good corrosion resistance. However, since the thickness of the Pt film-forming layer is as small as 5 nm, the contact resistance exceeds 100 mΩ and the conductivity is poor.
Comparative Example No. 9, 10 and 11 have good contact resistance of 20 mΩ or less because the thickness of the Pt film-forming layer is 10 nm or more, but SUS316 is used for the base material, and the amount of Fe elution after immersion for 30 days is Since both exceed 1000 mg / L, corrosion resistance is bad.
Comparative Example No. No. 12 is good with a contact resistance of 20 mΩ or less, and even though SUS316 is used as the base material, the Fe elution amount after immersion for 30 days is as good as 12 mg / L. Since the thickness of the film layer is 1000 nm and the cost is industrially high, practical application is difficult.

(2) Example 2
The rolling roll roughness of final rolling was adjusted to produce a titanium foil having a thickness of 60 μm and different surface roughness. A Pt film having a thickness of 10 nm was formed in the same manner as in Example 1, and the same sulfuric acid immersion test as in Example 1 was carried out for 30 days, followed by washing with pure water and drying to measure contact resistance.

Invention Example No. 1-4, the surface roughness of titanium as a base material: Ra is in the range of claims from 0.2 μm to 2.0 μm, and there is almost no change in contact resistance before and after sulfuric acid immersion for 30 days. No peeling is seen.
On the other hand, Comparative Example No. In 5 and 6, the surface roughness Ra of titanium as a base material is less than 0.2 μm, and the contact resistance before sulfuric acid immersion is good, but the contact resistance after 30 days sulfuric acid immersion is large. Pt peeling is observed.

Comparative Example No. 7 and 8, the surface roughness Ra of titanium as a base material exceeds 2.0 μm, and the contact resistance before immersion in sulfuric acid exceeds 20 mΩ. This is because the surface roughness of the base material is too large, the thickness of the film formation layer is partially uneven, and the film formation layer is partially thinned. This has a stronger effect as the surface roughness of the base material increases. Comparative example no. In the case of 8, contact resistance further increased.

(3) Example 3
A titanium substrate having a thickness of 60 μm was formed into a 20-nm thick Pt film by the same method as in Example 1, and then rolled. This was subjected to the same sulfuric acid immersion test as in Example 1 for 30 days, then washed with pure water and dried to measure contact resistance. Note that the surface roughness Ra of the substrate was less than 0.2 μm.

Invention Example No. 1 to 3, the rolling degree after film formation of Pt on the titanium substrate is in the range of 0.1 to 40%, and there is no change in the contact resistance before and after immersion in sulfuric acid for 30 days. No peeling is observed.
On the other hand, Comparative Example No. In No. 4, Pt was not rolled after forming a film on a titanium substrate, and the contact resistance before sulfuric acid immersion was good, but the contact resistance after 30 days of sulfuric acid immersion was large, and Pt was peeled off. It can be seen.

Comparative Example No. 5, the degree of rolling after forming Pt on the titanium base material is 0.05%, which is less than the lower limit of the claims, and the adhesion between the base material and the film forming layer is insufficient. Therefore, the contact resistance after 30 days of sulfuric acid immersion is increased, and Pt peeling is observed.
Comparative Example No. No. 6, the rolling degree after film formation of Pt on the titanium base material is 42%, which exceeds the upper limit of the claim, and there is no significant difference in contact resistance before and after sulfuric acid immersion for 30 days. The resistance value has already exceeded 20 mΩ, and the contact resistance has increased as a part of the film formation layer has become thinner.

(4) Example 4
A Pt film having a thickness of 20 nm was formed on a titanium substrate having a thickness of 60 μm in the same manner as in Example 1, and then heat-treated in a vacuum annealing furnace. This was subjected to the same sulfuric acid immersion test as in Example 1 for 30 days, then washed with pure water and dried to measure contact resistance. In addition, the surface roughness Ra of the substrate was 0.11 μm.

Invention Example No. 1 to 6, the heat treatment temperature after film formation of Pt on the titanium substrate is 800 to 1000 ° C., and the heat treatment time is 5 minutes or more, and the contact resistance before and after 30 days of sulfuric acid immersion changes. No peeling of Pt is observed.
On the other hand, Comparative Example No. In No. 7, the heat treatment time after depositing Pt on the titanium substrate is within the range of the claims, but the heat treatment temperature is less than the lower limit value of the claims, and the alloying of the substrate and the film formation layer has progressed sufficiently. In addition, the contact resistance after 30 days of sulfuric acid immersion is increased, and Pt peeling is observed.
Comparative Example No. In Nos. 8 and 9, the heat treatment temperature after depositing Pt on the titanium substrate is in the range of the claims, but the heat treatment time is less than the lower limit of the claims, and the alloying of the substrate and the film formation layer is sufficient The contact resistance after immersion in sulfuric acid for 30 days has increased, and Pt has been peeled off.

Claims (7)

A material for a separator for a fuel cell, characterized in that the composition is one or more of Pt, Pd, Rh, and Ru, the thickness is 10 nm or more, and the film is formed on a titanium substrate. A material for a separator of a fuel cell, characterized in that it is formed on a titanium substrate having a composition of one or more of Pt, Pd, Rh, and Ru, a thickness of 10 nm or more, and a thickness of 90 μm or less. . The composition is one or more of Pt, Pd, Rh, and Ru, the thickness is 10 nm or more, the surface roughness Ra is 0.2 to 2.0 μm, and the film is formed on the titanium substrate. A fuel cell separator material. The fuel cell separator material according to claim 1, wherein the film is formed by a dry process such as vapor deposition or sputtering. 5. A fuel cell separator material, wherein the composite material according to claim 1 is rolled at a rolling degree of 0.1 to 40%. A fuel cell separator material, wherein the composite material according to claim 1 is heat-treated at a temperature of 800 to 1000 ° C and a heat treatment time of 5 minutes or more. A fuel cell characterized in that the film-forming layer on the titanium substrate is an alloy layer of one or more of Pt, Pd, Rh, and Ru and the titanium substrate, and the thickness thereof is 10 nm or more. Separator material.