JPH11273693A - Low temperature fuel cell separator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a metal separator for a low-temperature fuel cell having good acid resistance and conductivity and low contact resistance. SOLUTION: A metal that can be press-formed or the like by coating a surface of stainless steel, which is a good conductor having excellent acid resistance, with conductive titanium oxide having excellent acid resistance and low contact resistance. Provide a separator made of.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a metal separator for a fuel cell, such as a solid polymer electrolyte fuel cell, which operates at a low temperature.

[0002]

2. Description of the Related Art A solid polymer electrolyte fuel cell is a fuel cell using a polymer resin membrane exhibiting proton conductivity as an electrolyte, and is attracting attention as a future clean energy source. This fuel cell is made of a solid material and can be operated at low temperature at room temperature, so it is easy to start and stop, and it not only has excellent maintainability, but also has high current density and high output density. Therefore, development of a compact portable power supply, particularly a power supply for automobiles, taking advantage of these advantages is being promoted.

[0003] A single cell of the fuel cell has a fuel electrode and an air (oxygen) electrode bonded to both surfaces of a polymer electrolyte membrane, and separators are provided on both sides of the cell via gaskets. A graphite (graphite) plate is usually used for the separator, and a fuel or air flow path is formed on the surface on the electrode side, and a cooling water flow path is provided on the opposite surface or inside thereof. I have. These fuel cells and the separator form a single fuel cell unit. However, the fuel cell has a low electromotive force per single cell, and is usually used as a stack of a plurality of units. .

[0004]

In the case of a stacked fuel cell, since electric power is extracted through a large number of separators, a voltage drop due to the separators themselves and the accompanying generation of Joule heat become a serious problem. As for the characteristics, good conductivity and low contact resistance are required. The air electrode side of the solid polymer electrolyte fuel cell is p
H is a strongly acidic atmosphere of 2 to 3, and the separator material is also required to have corrosion resistance. As a material satisfying these characteristics, the above-mentioned graphite has been conventionally used. However, this material has the following problems.

[0005] Graphite separators are not only expensive in material cost but also high in processing cost and low in productivity because the flow path of fuel gas is formed by cutting. Since graphite is brittle in material and weak to mechanical shock, care must be taken when using it as a portable power supply. In order to solve these drawbacks, Japanese Patent Application Laid-Open No. 8-180883 proposes that a metal plate is subjected to press working or punching to form a separator.

Since a metal material is a good conductor, when used for a separator, corrosion resistance and contact resistance in a strongly acidic atmosphere become problems. Precious metals such as Au and Pt are metals that satisfy both of these characteristics. However, these are very expensive materials, and it is difficult to use them as separators in terms of cost. Practical metal materials that exhibit good corrosion resistance in strong acid solutions include various acid-resistant materials such as stainless steel. However, these materials
In an acidic environment, a passive film, which is an insulator, is firmly formed on the surface thereof, which causes a problem of increasing contact resistance.

The present invention has been devised in order to solve such a problem. By coating conductive titanium oxide on the surface of a stainless steel substrate, it is possible to obtain good corrosion resistance in a strongly acidic environment. An object of the present invention is to provide a metal separator exhibiting good conductivity and low contact resistance.

[0008]

In the present invention, in order to solve the above-mentioned problems, stainless steel is used as a base material,
What is claimed is: 1. A low-temperature fuel cell separator having a conductive titanium oxide coating layer mainly made of TiO2 formed on the surface thereof, wherein the coating layer contains impurities for imparting conductivity. A fuel cell separator is provided.

Further, in the present invention, Fe, Cr, Ni, Si, M
A low-temperature fuel cell separator coated with a conductive titanium oxide containing one or more of n, Mo, and Cu is provided. Further, in the present invention, a separator for a low-temperature fuel cell comprising a surface of a stainless steel substrate coated with conductive titanium oxide containing one or more components of stainless steel diffused from the substrate as impurities. Is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The separator for a low-temperature fuel cell according to the present invention has a surface of a stainless steel base material mainly made of T
In this case, a coating layer of a conductive titanium oxide made of iO2 is formed. TiO2 may be either an anatase-type or rutile-type crystalline one or an amorphous one. Further, the coating layer may partially contain TiOx (x <2), which is a non-stoichiometric composition and oxygen-deficient titanium oxide.

Although TiO2 essentially contains unavoidable impurities that are mixed during the production process, its electrical properties are semiconductors. In the case of the present invention, impurity metal ions or nonmetal ions are positively introduced into the titanium oxide coating layer in order to ensure good conductivity. Although the conductivity of the coating layer is increased by the introduction of lattice defects, it is thermally unstable. Therefore, it is preferable to add impurity ions. The titanium oxide coating layer has high acid resistance and hardly dissolves in a strong acid environment. Further, since it maintains low contact resistance, it is suitable for a separator material of a low-temperature fuel cell.

[0012] In order to improve the conductivity of the coating layer itself, various impurity ions are contained in the coating layer. The addition of these impurities lowers the volume resistivity of the coating layer itself,
If the content exceeds 10% by mass, an oxide of the impurity element is formed on the surface of the coating layer and the contact resistance increases. Therefore, the content is preferably 10% by mass or less. As a method of containing impurity ions in the coating layer, the method of simultaneously containing impurities during the formation of the coating layer, or heating after the formation of the coating layer, the constituent elements of the underlying stainless steel base material in the coating layer There is a method of diffusing.

The impurity ions contained in the coating layer may be any as long as they lower the volume resistivity of the coating layer. However, in order to improve the adhesion between the stainless steel substrate and the coating layer, Fe, which is a component of stainless steel,
One or more of Cr, Ni, Si, Mn, Mo and Cu are preferred. When the components of the stainless steel base material are diffused into the coating layer by heating after forming the coating layer to form impurities, Nb, T
a, W, metal ions such as rare earth elements, and non-metal ions such as C and N, etc., which are components of stainless steel and improve their conductivity by being contained in the titanium oxide coating layer. Is included. In the present invention, the conductive titanium oxide coating layer has a volume resistivity of 10 2 Ω · m or less.

In the present invention, the thickness of the coating layer is not particularly limited, but may be 0.005 μm to 5 μm.
Is preferred. If it is less than 0.005 μm, the coating layer tends to be discontinuous and the base material is partially exposed, so that the contact resistance tends to increase. If it exceeds 5 μm, the coating layer is hard, so that high stress is generated in the coating layer during press working or bending, and the coating layer is liable to peel off.

As the substrate of the separator of the present invention, austenitic stainless steel or austenitic / ferritic duplex stainless steel excellent in acid resistance is used. As the required characteristics of the separator material, corrosion resistance to non-oxidizing acids as well as oxidizing acids is required. Therefore, a stainless steel substrate having improved acid resistance by adding Ni in addition to Cr is used. In the case of the separator of the present invention, in order to use a stainless steel excellent in acid resistance as a substrate,
Even if defects such as pinholes and cracks are present in the coating layer, it has sufficient corrosion resistance.

In the present invention, the austenitic stainless steel that can be used as the base material of the separator is Cr: 1.
4 to 35% by mass (hereinafter, all% are mass%), Ni: 5 to
60%. For example, C: 0.008 to 0.2
%, Si: 0.05 to 5.0%, Mn: 0.1 to 5.0
%, Ni: 5.0 to 60%, Cr: 14 to 35%, with the balance being Fe and unavoidable impurities.
The usable austenitic ferritic stainless steel has a Cr content of 17 to 35% and a Ni content of 2 to 60%. For example, C: 0.008 to 0.2%, S
i: 0.05 to 5.0%, Mn: 0.1 to 5.0%, N
i: 2.0 to 60%, Cr: 17 to 35%, the balance consisting of Fe and unavoidable impurities is used.

When the Cr concentration of the base stainless steel is less than the lower limit of each of the above ranges, the corrosion resistance to oxidizing acids is not sufficient. On the other hand, if the Cr concentration exceeds 35%, the deformation resistance of the stainless steel increases, and processing such as press forming becomes difficult. If the Ni concentration is less than the lower limit of each of the above ranges, the corrosion resistance to non-oxidizing acids is not sufficient, and if the Ni concentration exceeds 60%, the effect of improving the acid resistance is saturated. Invite.

When the current density of the fuel cell is increased and the output density is increased, the pH of the atmosphere on the cathode side is reduced. Therefore, it is necessary to further improve the acid resistance of a separator material for a high-output low-temperature fuel cell. There is. In this case, one or two of Mo, Cu and N are further added to the stainless steel base material.
It is preferred to add more than one species. Specifically, Mo:
0.2-7%, Cu: 0.1-5%, N: 0.02-
Add one or more of 0.5%. In each case,
If the amount is less than the lower limit of the above range, the effect of addition is not sufficient, and if the amount exceeds the upper limit, the effect of addition is saturated.

The ceramic coating layer of the present invention is formed by a wet method such as a sol-gel method, various physical vapor deposition methods, a method such as thermal CVD or plasma CVD. As the physical vapor deposition method, a sputter vapor deposition method and an ion plating method are preferable.

[0020]

EXAMPLE A titanium oxide coating layer was formed on a stainless steel having the composition shown in Table 1 as a base material by a high frequency sputter deposition method. A titanium oxide target was used as a target. In order to improve the in-plane uniformity of the coating layer, the stainless steel as the substrate was rotated during the vapor deposition. The thickness of the coating layer is 0.01 μm. Ar was used as the discharge gas, but when oxygen in the coating layer was insufficient in composition,
A small amount of oxygen gas was introduced as a reactive gas into the sputtering chamber.

Using the same substrate, a titanium oxide coating layer was formed by a sol-gel method. The sol solution was coated by a dip coating method using Ti isopropoxide as a starting material, and then fired at 450 ° C. to obtain a titanium oxide coating layer. Fe, Cr or N in the sol-gel coating layer
When i was added, alkoxides of these metals were added to the starting solution. When the constituents of the stainless steel as the base material are diffused into the coating layer, N 2 -75% H 2
Heated at 1000 ° C. for 10 seconds.

[0022]

[Table 1]

Table 2 shows the results of investigations on the contact resistance and acid resistance of the obtained various coating materials. The contact resistance was measured by contacting a carbon electrode material with a load of 10 kgf / cm 2 on the surface of each coating material before dipping in an acid solution, and measuring the contact resistance between the two. The acid resistance of various coating materials is
It was evaluated by loss of corrosion in an aqueous sulfuric acid solution at pH 90 at 90 ° C. Table 2 also shows the results of similar measurements performed on the base stainless steel itself and the base steel type B plated with 5 μm of Ni, Cu and Cr as comparative materials.

[0024]

[Table 2]

As is clear from the results shown in Table 2, the stainless steel coated with the conductive titanium oxide has low contact resistance and good acid resistance. In the case of stainless steel as the base material, it is not suitable as a separator material as it is because the contact resistance is high. Ni-plated materials and Cr-plated materials have low contact resistance but poor acid resistance, and Cu-plated materials have poor contact resistance and acid resistance, so neither can be used as a separator material.

[0026]

As described above, the separator of the present invention exhibits good acid resistance, conductivity, and low contact resistance, and can be easily formed by pressing or the like. The manufacturing cost can be reduced, and since it is made of metal, it is excellent in safety when used as a portable power supply.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasumi Ariyoshi 5 Ishizu Nishicho, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd., Surface Treatment Research Laboratory (72) Inventor Minoru Saito 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd.

Claims (3)

[Claims] 1. A low temperature fuel cell separator comprising a stainless steel base material and a conductive titanium oxide coating layer mainly composed of TiO2 formed on the surface thereof, wherein the coating layer imparts conductivity. A separator for a low-temperature fuel cell, comprising: 2. The method according to claim 1, wherein the impurities are Fe, Cr, Ni, Si, Mn,
2. The low-temperature fuel cell separator according to claim 1, wherein the separator is one or more of Mo and Cu. 3. The separator for a low-temperature fuel cell according to claim 1, wherein one or more components of stainless steel in which the impurities are diffused from the base material.