JP2000067881A - Separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a fuel cell having excellent electric conductivity, corrosion resistance, high productivity, and inexpensive manufacturing cost. SOLUTION: A separator 2 for a fuel cell forming a gas flow pass 7 in cooperation with a flat plate electrode 6 of a cell 1 consists of a low electric resistance metal plate 9 and an amorphous carbon film 10 constituting a gas flow forming surface (a) by covering the metal plate 9. A hydrogen content CH of the amorphous carbon film 10 is set for 1 atom %<=CH<=20, in order to enhance electric conductivity of the film 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator which forms a gas flow path in cooperation with a flat electrode of a unit cell.

[0002]

2. Description of the Related Art This type of separator is required to have good electrical conductivity and corrosion resistance, and is conventionally made of graphite.

[0003]

However, graphite is poor in machinability due to its high hardness. For example, it takes a lot of time to form a plurality of gas passage grooves, and therefore, the productivity of the separator is low. , High production cost,
There was a problem.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a separator having good electric conductivity and corrosion resistance, high productivity and low production cost.

[0005] To achieve the above object, according to the present invention,
In a fuel cell separator which forms a gas flow path in cooperation with a flat electrode of a unit cell, a low electric resistance metal plate and an amorphous carbon which covers the metal plate to form a gas flow path forming surface A fuel cell separator comprising a membrane, wherein the hydrogen content C _H of the amorphous carbon membrane is 1 at% ≦ C _H ≦ 20 at%.

[0006] In the arrangement, the metal plate is a low electric resistance, also lower the electric resistance of the amorphous carbon film set the hydrogen content C _H as described above. Therefore, the separator has good electric conductivity. In addition, since the amorphous carbon film has excellent corrosion resistance, when the metal plate is coated with the amorphous carbon film to form the gas flow path forming surface, the separator exhibits good corrosion resistance. Further, the metal plate has good machinability, while the amorphous carbon film is efficiently formed by various thin film forming techniques, so that the productivity of the separator can be increased and the production cost can be reduced.

However, if the hydrogen content _CH is _CH <1 atomic%.
In this case, the electrical insulation of the amorphous carbon film is increased, while C _H > 2
At atomic%, the π electrons imparting electric conductivity to the amorphous carbon film are trapped by hydrogen, so that the electric conductivity decreases.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIGS. 1 and 2, flat separators 2 are disposed on the upper and lower sides of a unit cell 1 having a laminated structure, respectively. Stacked fuel cells 3 are configured by stacking. The unit cell 1 includes a flat electrolyte 4 and a pair of flat porous electrodes 6 sandwiching the electrolyte 4 and having a catalyst 5 on a surface facing the electrolyte 4. Each separator 2
Is provided with a plurality of mutually parallel gas flow channel grooves 8 to form a gas flow channel 7 in cooperation with each porous electrode 6 of the unit cell 1.

In this fuel cell 3, a fuel such as hydrogen flows through a gas flow path 7 formed by one of the separators 2 so as to be in contact with one of the porous electrodes 6, and the other separator 2 has
An oxidizing agent such as oxygen is passed through the gas flow path 7 to contact the other porous electrode 6, and electric energy is extracted by utilizing an electrochemical reaction generated by the oxidizing agent.

Each of the separators 2 has the same structure.
As shown in FIG. 9, a low electric resistance metal plate 9 such as an Al alloy plate
And the gas flow channel forming surface a
And an amorphous carbon film 10 having a thickness of 0.5 to 10 μm. In this case, when the metal plate 9 has a plurality of mutually parallel concave ridges 11 and the concave ridge forming surface b is covered with the amorphous carbon film 10 to form the gas flow channel forming surface a, A plurality of gas flow channel grooves 8 corresponding to the plurality of concave stripes 11 can be provided on the flow channel forming surface a. Amorphous carbon film 1
The hydrogen content C _H of 0 is set so that 1 at% ≦ C _H ≦ 20 at%.

[0011] In the arrangement, the metal plate 9 is a low electric resistance, also lower the electric resistance of the amorphous carbon film 10 set the hydrogen content C _H as described above. Therefore, the separator 2 has good electric conductivity. Further, since the amorphous carbon film 10 has excellent corrosion resistance,
By covering the entire surface of the separator 2, the separator 2 exhibits good corrosion resistance. Further, the metal plate 9 has good machinability, while the amorphous carbon film 10 is efficiently formed by various thin film forming techniques, so that the productivity of the separator 2 is high and the production cost is low.

It is not essential that the entire surface of the metal plate 9 is covered with the amorphous carbon film 10, and, for example, only the concave stripe forming surface b may be covered. When each electrode 6 has a gas channel groove, each separator 2
Are formed in a flat plate shape without grooves.

The amorphous carbon film 10 has an SP2 structure and an SP2 structure.
3 thought structure are mixed, in the Raman spectrum shown in FIG. 4, and G band near 1550 cm ^-1 1400
A broad Raman band is observed around the D band near cm ^-1 . The Raman band around 1400 cm ^-1 corresponds to one of the peaks of the density of states of lattice vibration, and is interpreted as being caused by relaxation of the wave vector conservation law due to lattice disorder. The intensity ratio, that is, the G / D ratio changes depending on the existence ratio of the SP2 structure and the SP3 structure. Raman band near 1400cm ^-1 is SP2
A Raman band that increases due to structural disturbances, and a decrease in this band is believed to represent an increase in the SP3 ratio. That is, the G / D ratio shows a large value as the SP3 ratio increases.

Therefore, the G / D ratio of the amorphous carbon film 10 by Raman spectroscopy is set to 0.1 ≦ G / D ratio ≦ 2.0. This G / D ratio indicates the SP3 property of the amorphous carbon film 10. By setting the G / D ratio as described above, the amorphous carbon film 10 can have good electric conductivity.

However, when the G / D ratio is less than 0.1, the SP2 property of the amorphous carbon film 10 becomes high, and the quality of the film may be deteriorated and peeling may occur. On the other hand, when the G / D ratio is> 2.0, the SP3 property of the amorphous carbon film 10 is increased, and the film 10 becomes an electric insulator.

Hereinafter, specific examples will be described.

First, a plurality of metal plates 9 having seven concave stripes 11 of 30 mm in length, 30 mm in width, 3 mm in thickness, 2 mm in width and 0.5 mm in depth were manufactured from an Al alloy plate according to JIS A5052.

Next, using these metal plates 9,
An amorphous carbon film 10 was formed on the entire surface under the conditions shown in (1) to obtain a plurality of separators 2.

[0019]

[Table 1]

[0020]

[Table 2]

Next, the hydrogen content C _H , G / D ratio, and electric resistance of Examples 1 to 8 of the amorphous carbon film 10 were examined, and the results shown in Table 3 were obtained.

[0022]

[Table 3]

As is clear from Table 3, the amorphous carbon film 1
In order to increase the electrical conductivity of 0, as in Examples 3 to 7,
It is necessary to set the hydrogen content C _{H so} that 1 at% ≦ C _H ≦ 20 at%. On the other hand, in order to improve the peeling resistance of the amorphous carbon film 10, the G / D ratio should be G ≧ D ≧ 0.1.
In consideration of the electrical conductivity of the film 10, it can be said that it is desirable that the G / D ratio ≤ 2.0.

As a thin film forming technique, it has been found that the ion beam evaporation method is superior to the P-CVD method in terms of the concealing property with respect to the metal plate 9 and the uniformity of the film thickness.

Next, the separator 2 having the amorphous carbon film 10 of Example 6 was immersed in concentrated sulfuric acid at pH 3 for 72 hours, and the corrosion loss of the amorphous carbon film 10 was determined to be 0.001 g. And thus Example 6 was found to have excellent corrosion resistance. For comparison, the same tests were performed on the ceramics CrN, TiN, and ZrN to determine the corrosion weight loss of the ceramics, which were 0.173 g, 0.066 g, and 0.023 g, respectively.
g, indicating that these ceramics have significantly lower corrosion resistance than the amorphous carbon film 10.

[0026]

According to the first aspect of the present invention, a fuel cell separator having good electrical conductivity and corrosion resistance, high productivity, and low production cost can be provided by the above-described structure. Can be provided.

According to the second aspect of the present invention, it is possible to provide a fuel cell separator in which the amorphous carbon film has improved peeling resistance in addition to the above effects.

According to the third aspect of the present invention, there is provided a fuel cell separator having an amorphous carbon film having all of the above-mentioned effects, a uniform thickness, and excellent concealing properties. can do.

[Brief description of the drawings]

FIG. 1 is a front view of a main part of a stack type fuel cell.

FIG. 2 is an exploded perspective view of the unit.

FIG. 3 is an enlarged sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a Raman spectrum diagram.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single cell 2 Separator 6 Electrode 7 Gas flow path 9 Metal plate 10 Amorphous carbon film 11 Concave stripe a Gas flow path formation surface b Concave stripe formation surface

Claims (3)

[Claims] 1. Cooperating with a flat electrode (6) of a unit cell (1)
Cell Separator Forming Gas Flow Path (7)
In (2), a low electric resistance metal plate (9) and its gold
Cover the metal plate (9) to form the gas flow path forming surface (a)
An amorphous carbon film (10);
(10) Hydrogen content C_HIs 1 atomic% ≦ C _H≤20 atoms
% Of the fuel cell separator. 2. The fuel cell separator according to claim 1, wherein the G / D ratio of the amorphous carbon film (10) by Raman spectroscopy is 0.1 ≦ G / D ratio ≦ 2.0. 3. A plurality of gas flow channel grooves (8) in a fuel cell separator (2) forming a gas flow channel (7) in cooperation with a flat electrode (6) of a unit cell (1). A low electrical resistance metal plate (9) provided with a plurality of concave stripes (11) for obtaining a gas flow path, and a gas flow passage forming surface (a) covering the concave stripe forming surface (b) of the metal plate (9). ), An amorphous carbon film (10) formed by an ion beam evaporation method, wherein the hydrogen content C _{H of the} amorphous carbon film (10) is 1 atomic% ≦ C _H ≦ 20. Atomic%, and the G / D ratio of the amorphous carbon film (10) by Raman spectroscopy was 0.1 ≦
A fuel cell separator, wherein the G / D ratio satisfies 2.0.