JP2019192570A - Fuel cell separator - Google Patents

Abstract

Provided is a fuel cell separator capable of preventing deterioration of conductivity while ensuring corrosion resistance.
A fuel cell separator 3 is formed on a surface of a separator base 31 made of metal, a metal oxide 32 having a conductivity of 100 S / cm or more, and a surface of the metal oxide 32. And a conductive film 33 having a film thickness of 30 nm or more.
[Selection] Figure 2

Description

  The present invention relates to a fuel cell separator.

  Conventionally, as a technique in such a field, as described in Patent Document 1, for example, a metal separator base material provided with a conductive film is known. In the fuel cell separator having such a structure, by providing a conductive film, penetration of a corrosive liquid such as generated water is prevented and corrosion resistance is ensured.

JP 2017-199535 A

  However, in this type of fuel cell separator, the separator base material is oxidized when the conductive film is formed on the surface of the separator base material, and an oxide film is formed between the separator base material and the conductive film. The As a result, the electric resistance of the fuel cell separator is increased, resulting in a problem that the conductivity is deteriorated.

  The present invention has been made to solve such technical problems, and an object of the present invention is to provide a fuel cell separator capable of preventing deterioration of conductivity while ensuring corrosion resistance.

  The separator for a fuel cell according to the present invention is formed on a metal separator base, a surface of the separator base, a metal oxide having a conductivity of 100 S / cm or more, and a surface of the metal oxide. And a conductive film having a film thickness of 30 nm or more.

  In the fuel cell separator according to the present invention, the conductive film having a film thickness of 30 nm or more is provided. Therefore, the corrosion resistance can be ensured by preventing the penetration of the corrosive liquid by the conductive film. In addition, since a metal oxide having a conductivity of 100 S / cm or more is interposed between the separator substrate and the conductive film, oxidation of the separator substrate when forming the conductive film can be prevented. As a result, it is possible to prevent deterioration of conductivity while ensuring corrosion resistance.

  According to the present invention, deterioration of conductivity can be prevented while ensuring corrosion resistance.

It is a schematic cross section which shows the principal part of the fuel cell provided with the separator for fuel cells which concerns on 1st Embodiment. It is a schematic cross section which shows the structure of the separator for fuel cells which concerns on 1st Embodiment. It is a schematic cross section which shows the structure of the separator for fuel cells which concerns on 2nd Embodiment.

  Hereinafter, embodiments of a fuel cell separator according to the present invention will be described with reference to the drawings. Prior to that, a structure of a fuel cell including a fuel cell separator will be briefly described based on FIG. Further, in the following description, “fuel cell separator” is abbreviated as “separator”.

  FIG. 1 is a schematic cross-sectional view showing a main part of a fuel cell including a fuel cell separator according to the first embodiment. As shown in FIG. 1, a plurality of fuel cells 1 that are basic units are stacked in a fuel cell 10. The fuel cell 1 is a polymer electrolyte fuel cell that generates an electromotive force by an electrochemical reaction between an oxidant gas (for example, air) and a fuel gas (for example, hydrogen gas). The fuel cell 1 includes a MEGA (Membrane Electrode & Gas Diffusion Layer Assembly) 2 and a pair of separators 3 and 3 sandwiching the MEGA 2.

  The MEGA 2 is obtained by integrating an MEA (Membrane Electrode Assembly) 4 and gas diffusion layers 7 and 7 disposed on both sides of the MEA 4. The MEA 4 includes an electrolyte membrane 5 and a pair of electrodes 6 and 6 joined so as to sandwich the electrolyte membrane 5. The electrolyte membrane 5 is made of a proton conductive ion exchange membrane made of a solid polymer material. The electrode 6 is made of, for example, a porous carbon material that supports a catalyst such as platinum. The electrode 6 disposed on one side of the electrolyte membrane 5 serves as an anode electrode, and the electrode 6 on the other side serves as a cathode electrode. The gas diffusion layer 7 is formed of a conductive member having gas permeability, such as a carbon porous body such as carbon paper or carbon cloth, or a metal porous body such as a metal mesh or foam metal.

  The MEGA 2 constitutes a power generation unit of the fuel cell 10, and the separator 3 is disposed so as to be in contact with the gas diffusion layer 7 of the MEGA 2. The separator 3 is formed in a waveform by alternately repeating the concave portions 3a and the convex portions 3b. The bottom of the recess 3 a has a planar shape and is in surface contact with the gas diffusion layer 7 of the MEGA 2. On the other hand, the top part of the convex part 3b is also planar, and is in surface contact with the top part of the convex part 3b in the adjacent separator 3. FIG.

  As shown in FIG. 1, one gas diffusion layer 7 of the pair of gas diffusion layers 7, 7, together with the convex portion 3 b of the separator 3 adjacent to the gas diffusion layer 7, defines a fuel gas passage 21 through which the fuel gas flows. ing. The other gas diffusion layer 7 together with the convex portion 3b of the separator 3 adjacent to the gas diffusion layer 7 defines an oxidant gas flow path 22 through which the oxidant gas flows.

  The fuel cells 1 are stacked such that the anode electrode 6 of one fuel cell 1 and the cathode electrode 6 of another fuel cell 1 adjacent to the fuel cell 1 face each other. Thereby, a space 23 is formed between the recesses 3 a of the adjacent separators 3. This space 23 becomes a refrigerant flow path through which the refrigerant flows.

  FIG. 2 is a schematic cross-sectional view showing the structure of the fuel cell separator according to the first embodiment. As shown in FIG. 2, the separator 3 includes a metallic separator base 31, a metal oxide 32 formed on the surface of the separator base 31, and a conductive film 33 formed on the surface of the metal oxide 32. And. The separator base material 31 has a flat plate shape and is formed of stainless steel, titanium, aluminum, niobium, antimony, or the like that is excellent in conductivity, gas impermeability, and the like.

  The metal oxide 32 is formed in a thin film shape over the entire surface of the separator substrate 31 and has a thickness of 2 nm or more. Preferably, the thickness of the metal oxide is 5 nm or more. As a component of the metal oxide 32, at least one of titanium, tin, zinc, and indium is included. In the present embodiment, the metal oxide 32 is ATO (Antimony doped Tin Oxide, ie, tin oxide doped with Sb), and its conductivity is 100 S / cm or more.

  The conductive film 33 has, for example, excellent corrosion resistance and penetration barrier properties against an acidic aqueous solution. As a component of the conductive film 33, at least a metal oxide or carbon is included. In consideration of ensuring corrosion resistance and preventing cost increase, the thickness of the conductive film 33 is preferably 30 nm or more and 5000 nm or less. In the present embodiment, the conductive film 33 is formed so as to include, for example, carbon nanotubes (hereinafter referred to as CNT (Carbon nanotube)) and a Si-based binder.

  The separator 3 having the above configuration is produced by, for example, the following manufacturing method. That is, a plate-like separator base material 31 is prepared, and a metal oxide 32 is formed on the surface of the separator base material 31 by a PVD (physical vapor deposition) method in an oxidizing atmosphere or a chlorine atmosphere. Thereafter, a conductive film 33 is formed on the surface of the metal oxide 32 by a spray method, an immersion method, or a CVD (chemical vapor deposition) method.

  In the separator 3 of the present embodiment, since the conductive film 33 having a film thickness of 30 nm or more is provided, the corrosion resistance of the separator 3 is ensured by preventing penetration of a corrosive liquid such as generated water by the conductive film 33. Can do. In addition, since the metal oxide 32 having a conductivity of 100 S / cm or more is interposed between the separator base 31 and the conductive film 33, the separator base 31 is oxidized when the conductive film 33 is formed. Can be prevented. As a result, it is possible to prevent deterioration of conductivity while securing the corrosion resistance of the separator 3.

  In addition, in this embodiment, although the example (refer FIG. 2) in which the metal oxide 32 and the electroconductive film 33 were formed in one side among two main surfaces of the flat separator base material 31 was demonstrated, as needed The metal oxide 32 and the conductive film 33 may be formed on both main surfaces of the separator substrate 31. In the present embodiment, ATO having a conductivity of 100 S / cm or more has been described as the metal oxide 32. However, ITO (Indium doped Tin Oxide, that is, indium oxide doped with Sn) may be used in addition to ATO. good. For example, the metal oxide 32 may be made of ITO having a conductivity of 1000 to 10000 S / cm.

Second Embodiment
FIG. 3 is a schematic cross-sectional view showing the structure of the fuel cell separator according to the second embodiment. The separator 3A of the present embodiment is different from the first embodiment in the formation range of the metal oxide 32A. The other configuration is the same as that of the first embodiment, and a duplicate description thereof is omitted.

  Specifically, as shown in FIG. 3, the metal oxide 32 </ b> A is not formed over the entire surface of the separator substrate 31 but is formed in an island shape. The separator 3A configured as described above can obtain the same effects as those of the first embodiment, and the metal oxide 32A is formed in an island shape on the surface of the separator base 31. Cost reduction can be expected compared to the case where the entire surface is formed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to the range of an Example.

<Examples 1-4>
In Examples 1 to 4, based on the separator 3 of the first embodiment, each sample having various conditions shown in Table 1 was manufactured by the following manufacturing method, and conductivity and corrosion resistance were evaluated on each manufactured sample. did.

  Specifically, a SUS447 plate (thickness 0.1 mm) was prepared as a separator substrate, and a metal oxide made of ATO was formed on the surface of the separator substrate by sputtering. ATO having a conductivity of 100 S / cm was used, and the thickness of ATO was as shown in Table 1.

  Further, as the conductive film, CNT-containing Si-based sol-gel films were used in Examples 1 to 3, and ATO was used in Example 4. As a method of forming a CNT-containing Si-based sol-gel film, first, a raw material in which CNTs are dispersed in a Si-based binder solution is prepared, and then the prepared raw material is dropped on the surface of the metal oxide formed on the separator substrate. Then, coating was performed using a bar coater until the film thickness shown in Table 1 was reached, and then heated at a temperature of 400 ° C. for 30 minutes to cure the coating film.

On the other hand, a mist CVD method was used as the ATO film formation method. Specifically, as raw materials for the tin oxide film, SnCl ₂ (Sn concentration is 0.01 mol / L), SbCl ₃ (Sb concentration is 0.0005 mol / L), hydrochloric acid 1 vol. % And nitric acid 1 vol. % Aqueous solution was prepared. Next, the separator base material on which the metal oxide was formed was placed on a hot plate, and when the film formation temperature was reached, the raw material for the mist-like tin oxide film atomized on the surface of the metal oxide was supplied ( Atomized with a 2.4 MHz ultrasonic transducer). Next, mist was vaporized on the surface of the metal oxide and chemically reacted to form an ATO film. At that time, the raw materials were supplied so that the ATO film thickness was as shown in Table 1.

  And contact resistance was measured in electroconductivity evaluation. Specifically, a copper plate subjected to gold plating is stacked on the film-forming surface of the separator substrate, and carbon paper (TGP-H-120 manufactured by Toray Industries, Inc.) is sandwiched between the two, and a pressure of 0.98 MPa per unit area In the state which added, the voltage value when a constant current was applied between the separator base material and the copper plate was measured.

  In the evaluation of corrosion resistance, a constant potential corrosion test was performed in accordance with the electrochemical high temperature corrosion test method (JIS Z2294) of Japanese Industrial Standard metal materials. Specifically, the electric potential of 0.9 V vs SHE is kept constant in a state where each sample of Examples 1 to 4 prepared by the above method is immersed in an aqueous sulfuric acid solution adjusted to a temperature of 80 ° C. I let you. In addition, what dissolved NaF so that the fluoride ion density | concentration might be 3000 ppm was used for sulfuric acid aqueous solution. The time of the constant potential corrosion test was 100 hours. And after the constant potential corrosion test, the elution amount of Fe as a separator base material was measured and evaluated.

<Comparative Examples 1-7>
For comparison, samples (Comparative Examples 1 to 7) having various conditions as shown in Table 1 were prepared, and conductivity and corrosion resistance were evaluated in the same manner as in the above-described Examples. In all the comparative examples, the SUS447 board (thickness 0.1 mm) was used as a separator base material similarly to the Example.

  As shown in Table 1, Comparative Example 1, Comparative Example 2 and Comparative Example 7 are separators composed only of a separator base material and a conductive film (that is, a separator having no metal oxide). A CNT-containing Si-based sol-gel film (Comparative Example 1 and Comparative Example 2) or ATO (Comparative Example 7) was directly formed on the surface.

  In Comparative Example 3, a tin oxide film was formed on the surface of the separator substrate by sputtering, and then a CNT-containing Si-based sol-gel film was further formed on the surface of the tin oxide film. The conductivity of the tin oxide film was 10 S / cm.

  As shown in Table 1, Comparative Example 4 was formed by forming ATO on the surface of the separator substrate in the same manner as Example 3, and further forming a CNT-containing Si-based sol-gel film on the surface of ATO. The film thickness of the Si-based sol-gel film was 20 nm.

  In Comparative Example 5 and Comparative Example 6, strike Ni plating or strike Ag plating was formed on the surface of the separator substrate, and a CNT-containing Si-based sol-gel film was further formed on the surface of strike Ni plating or strike Ag plating. .

  The evaluation results of each example and comparative example are shown in Table 1. As can be seen from Table 1, in Examples 1 to 4, the contact resistance was low and the corrosion resistance could be ensured. On the other hand, in Comparative Examples 2, 3, 6 and 7, the corrosion resistance could be ensured, but the contact resistance was increased. In Comparative Examples 4 and 5, the contact resistance was low but the corrosion resistance was poor. On the other hand, in the case of Comparative Example 1, the contact resistance was high and the corrosion resistance was poor.

  From these results, a metal separator base material, a metal oxide formed on the surface of the separator base material with a conductivity of 100 S / cm or more, and a metal oxide formed on the surface of the metal oxide with a film thickness of 30 nm or more. In the case of a separator provided with a conductive film, it has been revealed that deterioration of conductivity can be prevented while ensuring corrosion resistance.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various designs can be made without departing from the spirit of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 1 Fuel cell 2 MEGA (membrane electrode gas diffusion layer assembly)
3, 3A Separator 4 MEA (membrane electrode assembly)
6 Electrode 7 Gas diffusion layer 31 Separator base material 32, 32A Metal oxide 33 Conductive film

Claims (1)

A fuel cell separator,
A metal separator substrate;
A metal oxide formed on the surface of the separator substrate and having an electrical conductivity of 100 S / cm or more;
A conductive film formed on the surface of the metal oxide and having a thickness of 30 nm or more;
A fuel cell separator, comprising:

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