JP2003272670A - Metal separator for fuel cell and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal separator for a fuel cell and its manufacturing method which prevents fall of a conductive intercalated matter protruded from a base body surface and thereby attains improvement of power-generating performance through decrease of contact resistance. <P>SOLUTION: With the metal separator for the fuel cell having a conductive intercalated matter in its metal tissues, the conductive intercalated matter is made protruded from the surface of the base body by 1 to 3 μm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a metal separator provided in a polymer electrolyte fuel cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a polymer electrolyte fuel cell, a laminated body in which separators are laminated on both sides of a flat plate-like electrode structure (MEA: Membrane Electrode Assembly) constitutes one unit.
A plurality of units are stacked to form a fuel cell stack. The electrode structure has a three-layer structure in which an electrolyte membrane made of an ion exchange resin or the like is sandwiched between a pair of gas diffusion electrodes forming a positive electrode (cathode) and a negative electrode (anode). The gas diffusion electrode has a gas diffusion layer formed outside the electrode catalyst layer that is in contact with the electrolyte membrane. Further, the separator is laminated so as to be in contact with the gas diffusion electrode of the electrode structure, and a gas flow path or a refrigerant flow path for allowing gas to flow is formed between the separator and the gas diffusion electrode. According to such a fuel cell, for example, hydrogen gas, which is a fuel, is caused to flow in the gas flow passage facing the gas diffusion electrode on the negative electrode side, and oxygen or air is oxidized in the gas flow passage facing the gas diffusion electrode on the positive electrode side. When a volatile gas is flowed, an electrochemical reaction occurs and electricity is generated.

The separator supplies electrons generated by the catalytic reaction of hydrogen gas on the negative electrode side to an external circuit,
It is necessary to have a function of sending electrons from the external circuit to the positive electrode side. Therefore, a conductive material made of graphite-based material or metal-based material is used for the separator. Particularly, the metal-based material has excellent mechanical strength and can be made lighter and more compact by thinning it. Is advantageous in that As a metal separator, a press-formed stainless steel plate in which non-metallic conductive inclusions forming a conductive path are dispersed in a metal structure is promising from an economical point of view. However, since the stainless steel sheet has a natural oxide film on the entire surface of the base material, there is a problem that the contact resistance with respect to the electrode structure is high and the power generation performance is deteriorated as it is. Therefore, it is attempted to reduce the contact resistance by subjecting the conductive inclusions to a protrusion on the surface after press molding. As the treatment for causing the conductive inclusions to project, a means for removing the base material on the surface by, for example, electrolytic etching is adopted.

[0004]

However, simply,
Only by protruding the conductive inclusions from the surface of the base material, some of the conductive inclusions may drop off from the surface, and it is difficult to obtain a large effect of reducing the contact resistance.

Therefore, according to the present invention, a conductive separator protruding from the surface of a base material is prevented from falling off, thereby reducing contact resistance and improving power generation performance, and a method for manufacturing the same. Is intended to provide.

[0006]

A metallic separator for a fuel cell of the present invention is a metallic separator for a fuel cell having a conductive inclusion in a metal structure, wherein the conductive inclusion is formed from a surface of a base material. It is characterized by protruding from 1 to 3 μm.

The greatest feature of the present invention is that the conductive inclusions protrude from the surface of the base material by 1 to 3 μm,
When the protruding amount (height) of the conductive inclusions is less than 1 μm,
It is not possible to obtain a sufficient reduction in contact resistance, while the protrusion amount is 3μ.
If it exceeds m, conductive inclusions may fall off the surface of the base material.

Further, the protrusion of the conductive inclusions from the surface of the base material is such that only the conductive inclusions 2 protrude from the surface of the flat base material 1 as shown in FIG. 1 (a). Alternatively, as shown in FIG. 1B, the conductive inclusions 2 may be protruded from the peaks of the base material 1 that rises in a mountain shape. These protruding forms can be controlled by appropriately changing the conditions of the protruding step of the conductive inclusions in the manufacturing method described later.

The material of the separator according to the present invention includes:
An example is an austenitic stainless steel plate having conductive inclusions. Specifically, each component shown in Table 1 and the balance containing Fe, B and unavoidable impurities, Cr and B satisfy the following formula (1), and B is , M ₂ B and MB type boride, M ₂₃ (C,
B) _6- type boride is deposited on the surface, and these boride are austenitic stainless steel plates which are conductive inclusions forming a conductive path on the surface of the separator. Cr (wt%) + 3 × Mo (wt%) − 2.5 × B (wt%) ≧ 17 (1)

[0010]

[Table 1]

In the above-mentioned stainless steel plate having boride deposited on the surface, two phases, that is, stainless as a matrix phase and boride as a conductive inclusion, are present on the surface. This conductive inclusion generally has a higher hardness than the parent phase, but has a lower solubility in acid than the parent phase. By utilizing this characteristic, it becomes possible to control the protruding form of the conductive inclusions.

Next, a method for producing a metallic separator for a fuel cell according to the present invention is a method for suitably producing the above-mentioned separator according to the present invention.
It is characterized by including a step of projecting 3 μm.

Examples of the step of projecting the conductive inclusions in the manufacturing method of the present invention include physical methods such as sand blasting and wet blasting, and chemical methods such as etching. The physical method is a method that utilizes the difference in hardness between the base material and the conductive inclusions. Specifically, by hitting particles from the surface, only the soft matrix phase is scraped off, and the hard conductive inclusions are removed. The conductive inclusions are projected on the surface without being cut. In addition, the chemical method is a method that uses the solubility of the base material and the conductive foreign substance in acid, and specifically, high solubility is obtained by dipping in a nitric hydrofluoric acid bath or showering iron chloride. The base material is selectively melted, and conductive inclusions are projected on the surface.

Among these methods, in order to form only the conductive inclusions protruding from the flat surface of the base material, a method having a high base material removal ability such as dipping in a nitric hydrofluoric acid bath or sand blasting. On the other hand, in order to form the conductive inclusions protruding from the peaks of the base material, a method such as iron chloride showering or wet blasting, which has a relatively weak base material removing ability, is preferable.

[0015]

EXAMPLES Next, the effects of the present invention will be described in detail with reference to examples of the present invention. A. Production of Separator <Example 1> A 0.2 mm-thick austenitic stainless steel sheet containing the components shown in Table 2 and the balance Fe and unavoidable impurities was cut into a square shape of 100 mm x 100 mm to form a separator. I got a blank board. Next, this material plate was press-molded with a press load of 50 ton. Next, this press-formed material plate was immersed in a nitric-hydrofluoric acid bath in a jet-stirred state of nitric acid: 20% and hydrofluoric acid: 8% held at 30 ° C. for 30 minutes to perform etching. To obtain a separator. The protruding amount of the conductive inclusions in the separator of Example 1 was 2 μm.

[0016]

[Table 2]

<Comparative Example 1> A separator of Comparative Example 1 was obtained in the same manner as in Example 1 except that etching was not performed. The protruding amount of the conductive inclusions in the separator of Comparative Example 1 was 0 μm.

Comparative Example 2 A separator of Comparative Example 2 was obtained in the same manner as in Example 1, except that the immersion time in the nitric hydrofluoric acid bath was changed to 7 minutes. The protrusion amount of the conductive inclusions in the separator of Comparative Example 2 was 0.5 μm.
It was m.

Comparative Example 3 A separator of Comparative Example 3 was obtained in the same manner as in Example 1 except that the immersion time in the nitric hydrofluoric acid bath was changed to 60 minutes. Comparative Example 3
Of the conductive inclusions in the separator of 4 μm
Met.

B. Observation of surface layer cross section The surfaces of the separators of Example 1 and Comparative Example 1 obtained as described above were observed with a microscope. 2 is a micrograph of the separator of Example 1, and FIG. 3 is a micrograph of the separator of Comparative Example 1. It can be clearly seen that the separator of Example 1 has conductive inclusions protruding from the surface of the base material. On the other hand, Comparative Example 1 in which the protruding step was not performed
It can be seen that in the separator (1), the surface of the base material and the conductive inclusions are substantially flat.

C. Measurement of Contact Resistance Next, using the separators of Example 1 and Comparative Examples 1 to 3, one fuel cell unit in which separators were laminated on both sides of an electrode structure (MEA) was constructed, and this unit was caused to generate electricity. The initial value of the contact resistance of the separator to the electrode structure was measured. The result is shown in FIG. As is clear from FIG. 4, the contact resistance of the separator of Example 1 is significantly lower than that of Comparative Example 1, demonstrating the effect of protrusion of the conductive inclusions from the surface of the base material in the present invention.
Further, in Comparative Example 2 in which the protruding amount of the conductive inclusions from the base material was smaller than the range of the present invention, sufficient reduction in contact resistance could not be obtained. On the other hand, in Comparative Example 3 in which the protruding amount of the conductive inclusions from the base material was larger than the range of the present invention, the conductive inclusions fell off the surface of the base material, and Comparative Example 1 in which the protruding step was not performed. It was almost the same.

[0022]

As described above, according to the present invention,
In a metal separator for a fuel cell having a conductive inclusion in the metal structure, the protrusion of the conductive inclusion from the surface of the base material is set to 1 to 3 μm to prevent the conductive inclusion from falling off. This has the effect of reducing the contact resistance and improving the power generation performance.

[Brief description of drawings]

FIG. 1 is a schematic view showing a mode of projection of conductive inclusions from a base material in a separator of the present invention.

FIG. 2 is a micrograph showing the surface of the separator of Example 1 of the present invention.

FIG. 3 is a micrograph showing the surface of the separator of Comparative Example 1 of the present invention.

FIG. 4 is a graph showing an initial value of contact resistance measured in a fuel cell unit using the separators of Examples and Comparative Examples.

[Explanation of symbols]

1 ... Base material, 2 ... Conductive inclusion.

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[Procedure amendment]

[Submission date] October 30, 2002 (2002.10.
30)

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Continued front page    (72) Inventor Kouji Kotani             1-4-1 Chuo 1-4-1 Wako City, Saitama Prefecture             Inside Honda Research Laboratory (72) Inventor Masao Utsunomiya             1-4-1 Chuo 1-4-1 Wako City, Saitama Prefecture             Inside Honda Research Laboratory F-term (reference) 5H026 AA06 BB00 BB03 EE02 EE08                       HH03

Claims (2)

[Claims] 1. A metal separator for a fuel cell having a conductive inclusion in a metal structure, wherein the conductive inclusion is projected from the surface of the base material by 1 to 3 μm. Made separator. 2. A method for producing a metallic separator for a fuel cell having a conductive inclusion in a metal structure, comprising a step of projecting the conductive inclusion from the surface of a base material by 1 to 3 μm. And a method for producing a metal separator for a fuel cell.