JP2019169296A - Fuel cell separator - Google Patents

Abstract

To provide a fuel cell separator that can suppress the decrease in conductivity.SOLUTION: A fuel cell separator 1 according to the present invention includes a substrate 10 made of Ti, a TiOx (1≤x≤2) layer 11 formed on the surface of the substrate 10, a carbon film 12 formed on the surface of the TiOx layer 11, and the thickness of the TiOx layer 11 is 0 to 30 nm, and the thickness of the carbon film 12 is 10 to 35 nm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a fuel cell separator.

  A separator used in a fuel cell is required to have high conductivity in order to flow a generated current. As a separator having high conductivity, a separator in which a carbon film is formed on the surface of a titanium substrate having high corrosion resistance is used. In Patent Document 1, a TiOx (1 <x <2) layer is formed on the surface of a titanium substrate, a bonding layer containing Ti, O, and C is formed on the surface of the TiOx layer, and a carbon film is formed on the bonding layer. A fuel cell separator in which is formed is disclosed.

JP 2006-201300 A

In general, a titanium oxide (TiO ₂ ) layer is formed on the surface of titanium by natural oxidation. Usually, since the TiO ₂ layer inhibits the formation of the carbon film, it must be removed by etching or the like before the carbon film is formed. The inventor has a problem that when the etching process before the carbon film formation is omitted, the carbon film is peeled off from the titanium base material when the corrosion liquid used in the corrosion test penetrates the carbon film, so that the conductivity of the separator is lowered. I found it.

  The present invention has been made in view of the above problems, and provides a fuel cell separator capable of suppressing a decrease in conductivity.

  A separator for a fuel cell according to the present invention includes a base material made of Ti, a TiOx (1 ≦ x ≦ 2) layer formed on the surface of the base material, a carbon film formed on the surface of the TiOx layer, The thickness of the TiOx layer is 0 to 30 nm, and the thickness of the carbon film is 10 to 35 nm.

  In the fuel cell separator according to the present invention, the TiOx layer has a thickness of 0 to 30 nm, and the carbon film has a thickness of 10 to 35 nm. With such a configuration, it is possible to suppress a decrease in the conductivity of the fuel cell separator.

  By this invention, the separator for fuel cells which can suppress the fall of electrical conductivity can be provided.

It is a schematic sectional drawing of the separator for fuel cells concerning an embodiment. It is the flowchart which showed a series of flows which form the carbon film of the separator for fuel cells concerning embodiment. It is typical sectional drawing shown about the relationship between thickness and peeling of the carbon film concerning embodiment and a comparative example. It is a graph which shows the measurement result of the contact resistance of the separator for fuel cells concerning an example. It is a graph which shows the temperature profile in the carbon film formation process of the separator for fuel cells concerning an Example and a comparative example.

Embodiments of the present invention will be described below with reference to the drawings.
As a matter of course, the right-handed xyz orthogonal coordinates shown in FIGS. 1 and 3 are convenient for explaining the positional relationship of the constituent elements. Usually, the z-axis positive direction is vertically upward, and the xy plane is a horizontal plane, which is common between the drawings.

(Embodiment)
<Configuration of separator>
FIG. 1 is a schematic cross-sectional view of a fuel cell separator according to an embodiment. As shown in FIG. 1, the fuel cell separator 1 according to the present embodiment includes a titanium base material 10, a TiOx layer 11, and a carbon film 12.

  The titanium substrate 10 is a substrate made of titanium. The thickness of the titanium substrate 10 is, for example, 100 μm.

  As shown in FIG. 1, a TiOx (1 ≦ x ≦ 2) layer 11 is formed on the surface of the titanium substrate 10. The thickness of the TiOx layer 11 is preferably 0 to 30 nm, and more preferably 0 to 10 nm.

  As shown in FIG. 1, the carbon film 12 is formed on the surface of the TiOx layer 11. The thickness of the carbon film 12 is preferably 8 to 35 nm, more preferably 10 to 35 nm, and still more preferably 10 to 25 nm. The carbon film 12 is formed by, for example, direct current plasma CVD (chemical vapor deposition). The carbon film 12 may have an amorphous structure or a crystal structure.

<Outline of manufacturing process of fuel cell separator>
Here, the outline of the manufacturing method of the separator 1 for fuel cells is demonstrated. First, titanium is processed into a titanium substrate 10. For example, titanium is formed into a plate shape by rolling or the like, and processed into a titanium base material 10 having a desired shape using a press or the like.

  Next, the TiOx layer 11 is formed on the surface of the titanium substrate 10. The formation method of the TiOx layer 11 differs depending on the thickness. The thin TiOx layer 11 having a thickness of about 10 nm is formed by natural oxidation when the titanium substrate 10 is placed in the atmosphere. The thick TiOx layer 11 having a thickness of about 30 nm is formed by heating and cooling the titanium substrate 10 to about 200 to 300 ° C. in the atmosphere.

Next, the carbon film 12 is formed on the surface of the TiOx layer 11 by using, for example, direct current plasma CVD. Details of the formation of the carbon film 12 will be described later.
The above is the outline of the manufacturing process of the fuel cell separator 1.

<Method for forming carbon film>
Hereinafter, a method of forming the carbon film 12 for forming the carbon film 12 on the fuel cell separator 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a flowchart showing a series of flows for forming the carbon film 12 of the fuel cell separator 1 according to the embodiment.

  First, the titanium substrate 10 having the TiOx layer 11 formed on the surface is placed in a vacuum chamber, and a vacuum pump is operated to perform evacuation (step S1).

Next, a small amount of film forming gas is introduced into the vacuum chamber, and nucleation as a film forming nucleus is performed on the surface of the TiOX layer 11 using DC plasma CVD (step S2). The film forming gas decomposed by the plasma collides with the base material, and the base material is heated. Further, the deposition gas that collides with the base material becomes a nucleus for forming the carbon film 12 in the next step. In this embodiment, for example, a deposition gas containing acetylene (C ₂ H ₂ ) as a carbon source of the carbon film 12 and argon (Ar) for plasma formation can be used as the deposition gas.

  Next, the carbon film 12 is formed (step S3). A film forming gas is introduced into the vacuum chamber, and the carbon film 12 is formed using DC plasma CVD. Specifically, the film forming gas introduced into the vacuum chamber is decomposed by plasma to form the carbon film 12 on the surface of the TiOx layer 11. In this embodiment, DC plasma CVD is used for generating plasma, but high-frequency plasma CVD, microwave plasma CVD, or the like can also be used.

  Next, nitrogen plasma treatment is performed on the surface of the carbon film 12 (step S4). After the carbon film 12 is formed, nitrogen (N) gas is introduced into the vacuum chamber, and the surface of the carbon film 12 is treated with nitrogen plasma to terminate the surface functional groups of the carbon film with nitrogen.

Finally, the atmosphere is released (step S5).
The above is a series of flows of the method for forming the carbon film 12.

Hereinafter, the relationship between the thickness of the carbon film 12 and peeling will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view showing the relationship between the thickness and peeling of the carbon film 12 according to the present embodiment and the comparative example. FIG. 3 shows a case where the corrosion test is performed after the carbon film 12 is formed. The white double arrow indicates the internal stress remaining during the formation of the carbon film, and the wavy black arrow indicates the corrosive liquid used in the corrosion test. Shows a state where the water penetrates into the carbon film 12. An example of the corrosive liquid used in the corrosion test is sulfuric acid (H ₂ SO ₄ ).

  3A to 3D for the relationship between the thickness of the carbon film 12 according to the present embodiment and peeling, and the relationship between the thickness of the carbon film 102 according to the comparative example and peeling is shown in FIG. 3 (e) to FIG. 3 (h) will be described. In FIG. 3, the TiOx layer is omitted, but it may be formed.

  As shown in FIG. 3A, when the carbon film 12 is formed thin as in the present embodiment, the internal stress (white arrow) remaining when the carbon film 12 is formed is small. Next, as shown in FIG. 3B, when the corrosive liquid penetrates the carbon film 12, the internal stress remaining inside the carbon film 12 increases. Next, as shown in FIG. 3C, although the internal stress increases, the remaining internal stress is small because the carbon film 12 is thin as described above. That is, since the internal stress which causes destruction such as cracks does not remain in the carbon film 12, it is possible to prevent the carbon film 12 from peeling off from the titanium base material 10 as shown in FIG. Further, even when the corrosive liquid penetrates into the carbon film 12, the thickness of the carbon film 12 is thin, and the destruction and peeling of the carbon film 12 are suppressed, so that the corrosion resistance can be maintained.

  On the other hand, as shown in FIG. 3E, when the carbon film 102 is formed thick as in the comparative example, the internal stress (white arrow) remaining when the carbon film 102 is formed is Bigger than that. In other words, as the film thickness of the carbon film 102 increases, the internal stress remaining inside the carbon film 102 increases. Next, as shown in FIG. 3F, when the corrosive liquid is permeated into the carbon film 102, the internal stress remaining inside the carbon film 102 increases. Next, as shown in FIG. 3G, a fracture such as a crack occurs in the portion of the carbon film 102 that cannot withstand the increased internal stress, and the carbon film 102 is peeled off from the titanium substrate 100. Therefore, as shown in FIG. 3 (h), the titanium base material 100 in the portion where the carbon film 102 is broken and peeled is exposed. When further corrosive liquid penetrates into the carbon film 102, a corroded portion cr is formed in the exposed titanium substrate 100.

  The inventor of the present application has found that there is a correlation between the thickness of the TiOx layer 11 and the carbon film 12 and the electrical conductivity of the fuel cell separator 1. Specifically, the thickness of the TiOx layer 11 formed on the surface of the titanium substrate 10 is 0 to 30 nm, more preferably 0 to 10 nm, and the thickness of the carbon film 12 formed on the surface of the TiOx layer 11 is 8 to 8 nm. The thickness is set to 35 nm, more preferably 10 to 35 nm, and still more preferably 10 to 25 nm. That is, by reducing the thickness of the TiOx layer 11 and the carbon film 12 to a predetermined thickness, the peeling of the carbon film 12 due to the increase in internal stress due to the penetration of the corrosion liquid used in the corrosion test is as described above. It is suppressed. Accordingly, it is possible to suppress a decrease in the conductivity of the fuel cell separator 1.

  Furthermore, when the TiOx layer 11 is about 10 nm, the TiOx layer 11 is formed by natural oxidation when the titanium substrate 10 is placed in the atmosphere, and therefore the step of forming the TiOx layer 11 is substantially omitted. be able to. Further, by reducing the thickness of the carbon film 12 formed on the surface of the TiOx layer 11 to a predetermined thickness, the TiOx layer 11 formed by natural oxidation on the titanium base material 10 is not corroded, and corrosion is not caused. The peeling of the carbon film 12 due to the increase in internal stress due to the penetration of the corrosive liquid used in the test is suppressed as described above, and the decrease in conductivity can be suppressed. That is, the step of removing the TiOx layer 11 by etching or the like can be omitted. Therefore, the formation time of the carbon film 12 can be shortened, and productivity can be improved.

Next, examples of the present invention will be described.
EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited only to these Examples.

<Example>
In Examples, a plurality of samples having different thicknesses of the TiOx layer and the carbon film were prepared, and the value of contact resistance (mΩ · cm ² ) at each film thickness was measured. Specifically, first, 8 samples each were prepared so that the TiOx layer was 10 nm, 30 nm, and 50 nm on the titanium substrate. Next, samples formed so that the thickness of the carbon film was 5 nm, 8 nm, 10 nm, 15 nm, 25 nm, 35 nm, 45 nm, and 60 nm on the surface of the TiOx layer of each sample were prepared.

  The 10 nm TiOx layer was formed by natural oxidation. The 30 nm TiOx layer was formed by heating the titanium substrate to 300 ° C. in the atmosphere. The 50 nm TiOx layer was formed by heating the titanium substrate to 400 ° C. in the atmosphere. The carbon film was formed on the surface of the TiOx layer by direct current plasma CVD so as to have the above-described thicknesses. Specifically, the titanium base material on which the TiOx layer was formed was placed in a vacuum chamber evacuated, nucleated using plasma CVD, a carbon film was formed, nitrogen plasma treatment was performed, and the atmosphere was released.

The contact resistance was measured for each sample produced as described above.
The measurement results of the contact resistance of each sample are shown in Table 1 below.

As shown in Table 1, the contact resistance of the sample having a TiOx layer thickness of 10 nm and a carbon film thickness of 8 to 35 nm was 10 mΩ · cm ² or less, respectively. On the other hand, the samples in which the thickness of the TiOx layer was 10 nm and the thickness of the carbon film was 5 nm, 45 nm, and 60 nm showed values of contact resistance larger than 10 mΩ · cm ^2, respectively.

As shown in Table 1, the contact resistance of the sample having a TiOx layer thickness of 30 nm and a carbon film thickness of 10 to 25 nm was 10 mΩ · cm ² or less, respectively. On the other hand, in the samples in which the thickness of the TiOx layer is 30 nm and the thickness of the carbon film is 5 nm, 8 nm, 35 nm, 45 nm, and 60 nm, the contact resistances are larger than 10 mΩ · cm ^2, respectively.

As shown in Table 1, in the samples in which the thickness of the TiOx layer was 50 nm, the contact resistance was larger than 10 mΩ · cm ² in all samples.

  FIG. 4 is a graph showing the measurement results of the contact resistance of the fuel cell separator according to the example. The measurement results of the contact resistance shown in Table 1 are graphed. In FIG. 4, a sample in which the thickness of the TiOx layer is 10 nm is shown by a black rhombus plot. Similarly, a sample with a TiOx layer thickness of 30 nm is shown by a black square plot, and a sample with a TiOx layer thickness of 50 nm is shown by a black triangle plot.

As shown in Table 1 and FIG. 4, the thickness of the TiOx layer is 0 to 30 nm, more preferably 0 to 10 nm, and the thickness of the carbon film is 8 to 35 nm, more preferably 10 to 35 nm, still more preferably 10 to 10 nm. When the thickness was 25 nm, the contact resistance was 10 mΩ · cm ² or less, and it was possible to suppress the decrease in conductivity.
From the above results, it was possible to suppress a decrease in the conductivity of the fuel cell separator by reducing the thickness of the TiOx layer and the carbon film to a predetermined thickness.

  Hereinafter, the results of measuring the time required for forming the carbon film together with the temperature profile in each step of forming the carbon film will be described with reference to FIG. FIG. 5 is a graph showing a temperature profile in the carbon film forming step of the fuel cell separator according to the example and the comparative example. In measuring the temperature profile, a sample in which the thickness of the TiOx layer was 3 nm and the thickness of the carbon film was 20 nm was produced.

  As shown in FIG. 5, in the formation of the carbon film in this example, the step of removing the TiOx layer by etching or the like is omitted. As shown in the results of the embodiment shown in Table 1 and FIG. 4 described above, the thickness of the TiOx layer and the carbon film can be obtained without removing the TiOx layer formed on the titanium base material by omitting the steps such as etching. By reducing the thickness to a predetermined thickness, it was possible to suppress a decrease in the conductivity of the fuel cell separator. In this example, the step of forming the carbon film can be shortened by omitting the etching step, and the productivity compared to the conventional case can be improved by 20%.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention.

1 Fuel Cell Separator 10, 100 Titanium Base 11 TiOx Layer 12, 102 Carbon Membrane

Claims (1)

A substrate made of Ti;
A TiOx (1 ≦ x ≦ 2) layer formed on the surface of the substrate;
A carbon film formed on the surface of the TiOx layer,
The TiOx layer has a thickness of 0 to 30 nm,
The carbon film has a thickness of 10 to 35 nm.
Fuel cell separator.

Images