JP2020087618A - Method for manufacturing fuel cell separator - Google Patents

Abstract

To provide a method for manufacturing a separator having high corrosion resistance, which suppresses an increase in contact resistance when used in a fuel cell.SOLUTION: In a method for manufacturing a fuel cell separator, antimony-doped tin oxide particles are arranged on the surface of a substrate containing titanium or titanium alloy (S1), and the substrate on which the antimony-doped tin oxide particles are arranged is heat-treated under a low oxygen partial pressure (S2).SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for manufacturing a separator for a fuel cell.

In a fuel cell, a solid polymer electrolyte membrane sandwiched between an anode electrode and a cathode electrode is used as a single cell, and the single cell is formed through a separator in which a gas (hydrogen gas, oxygen gas, etc.) flow path is formed. It is configured as a stack of a plurality of layers. Since a separator for a fuel cell is used by applying a voltage in a heated acidic solution, it is required to have high corrosion resistance against an acid.

Patent Document 1 includes a step of applying carbon black to the surface of a base material made of pure titanium or a titanium alloy, and a step of thereafter heat-treating the base material under a low oxygen partial pressure where the oxygen partial pressure is 25 Pa or less. A method for producing a fuel cell separator is described, and by heat treatment under a low oxygen partial pressure, titanium atoms in the base material diffuse into the carbon black layer, and the diffused titanium atoms react with oxygen in the atmosphere to oxidize. It is described to be titanium.

JP, 2016-122642, A

The inventors of the present invention have earnestly studied and found that when the separator obtained by the manufacturing method described in Patent Document 1 is used in a fuel cell, the contact resistance of the separator may increase. This is because titanium carbide with low corrosion resistance is generated at the interface between the base material and carbon black during the heat treatment under a low oxygen partial pressure, and this titanium carbide is oxidized by the water generated in the acidic cells of the fuel cell and insulated. The present inventor believes that it is caused.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method of manufacturing a separator having high corrosion resistance, in which an increase in contact resistance when used in a fuel cell is suppressed.

A method for producing a fuel cell separator according to the present invention comprises arranging antimony-doped tin oxide (ATO) particles on the surface of a base material containing titanium or a titanium alloy, and a base material on which the antimony-doped tin oxide particles are arranged. Heat treatment under a low oxygen partial pressure.

In the production method of the present invention, a substance having low corrosion resistance such as titanium carbide is not formed during heat treatment, so that a separator having high corrosion resistance can be obtained. This separator has a small increase in contact resistance even when used in a fuel cell.

FIG. 3 is a schematic cross-sectional view of a fuel cell separator. It is a flowchart of the manufacturing method of the separator for fuel cells. It is a typical conceptual diagram explaining an ATO particle arrangement process. It is a typical conceptual diagram explaining the heat processing process under low oxygen partial pressure. It is a typical conceptual diagram explaining a surplus ATO particle removal process. It is a graph which shows the contact resistance value of the test piece of an Example and a comparative example before and behind a corrosion resistance test.

First, the separator 1 according to the embodiment will be described with reference to FIG. The separator 1 is used for a cell of a fuel cell, and has a base material 2 and a mixed layer 3 formed on a surface 21 of the base material 2. In the mixed layer 3, antimony-doped tin oxide (ATO) particles 31 and titanium oxide 32 are mixed.

The base material 2 contains titanium or a titanium alloy. Examples of titanium include 1 to 4 types defined in JIS H 4600. Examples of titanium alloys include Ti-Al, Ti-Nb, Ti-Ta, Ti-6Al-4V, and Ti-Pd. However, in any case, it is not limited to the above example. A base material containing titanium or a titanium alloy is light and has excellent corrosion resistance. The material of the base material 2 may be, for example, a plate material cold-rolled to a thickness of 0.05 to 1 mm. When the thickness is within this range, the separator 1 satisfies the requirements for weight reduction and thickness reduction, has strength and handleability, and can be relatively easily pressed into the shape of the separator 1.

The ATO particles 31 in the mixed layer 3 are conductive particles. Also, the ATO particles 31 may have a granular form. The titanium oxide 32 in the mixed layer 3 is titanium oxide (TiO _x ) having oxygen deficiency. The ATO particles 31 are embedded in a matrix of titanium oxide 32. One or more ATO particles 31 are connected in the mixed layer 3 so that the ATO particles 31 are present between the interface 34 between the mixed layer 3 and the base material 2 and the surface 35 of the mixed layer 3 corresponding to the surface of the separator 1. Acts as a conductive path. Therefore, the separator 1 has high conductivity. Further, since the base material 2 containing titanium or titanium alloy and the titanium oxide 32 have high affinity, the adhesion between the base material 2 and the mixed layer 3 is high. As the conductive particles, there are particles containing a noble metal, tin-doped indium oxide (ITO), LaNiO ₃ , SrMoO ₃ , (La,Sr)CoO ₃ , LaTiO ₃ , MgZnO, Ta ₂ O, ZnMgAlO, SrSnO _3. , ATO particles have the advantage of being less expensive than these particles. Further, although carbon black is also a conductive particle, ATO particles have an advantage that they have higher electrolytic corrosion resistance (hard to be oxidized even at a high potential) as compared with carbon black.

Next, a method for manufacturing the fuel cell separator will be described. As shown in FIG. 2, the method for manufacturing a fuel cell separator comprises arranging ATO particles on the surface of a base material (S1) and heat treating the base material on which the ATO particles are arranged under a low oxygen partial pressure (S2). ) And removing excess ATO particles (S3). Note that removing excess ATO particles (S3) is an optional step and is not essential. Hereinafter, each step will be described in order.

(1) Arrangement of ATO particles (S1)
As shown in FIG. 3, ATO particles 31 are arranged on the surface 21 of the base material 2 containing titanium or a titanium alloy to form an ATO particle layer 30. The method for disposing the ATO particles 31 on the base material 2 is not particularly limited, but for example, a dispersion liquid in which the ATO particles 31 are dispersed in a dispersion medium such as water or ethanol is applied on the base material 2 and dried. As a result, the ATO particles 31 can be arranged on the base material 2. Examples of the coating method include a roll coating method. Further, the thickness of the ATO particle layer 30 may be larger than the thickness of the mixed layer 3 formed in the heat treatment step (S2) described later. In this case, the surplus ATO particles 31 not included in the mixed layer 3 can be removed in a surplus ATO particle removing step (S3) described below.

(2) Heat treatment under low oxygen partial pressure (S2)
The base material 2 on which the ATO particles 31 are arranged is heat-treated under a low oxygen partial pressure. As a result, as shown in FIG. 4, the titanium atoms of the base material 2 are outwardly diffused into the ATO particle layer 30 (see FIG. 3), and the outwardly diffused titanium atoms are reacted with oxygen gas to form the titanium oxide 32. Is generated. As a result, the mixed layer 3 including the titanium oxide 32 and the ATO particles 31 held by the titanium oxide 32 is formed.

Here, the low oxygen partial pressure means that the oxygen partial pressure is 13 Pa or less. In particular, the oxygen partial pressure during the heat treatment may be 0.001-13 Pa. If the oxygen partial pressure is less than 0.001 Pa, titanium may be insufficiently oxidized. When the oxygen partial pressure exceeds 13 Pa, inward diffusion of oxygen becomes more dominant than outward diffusion of titanium, so that titanium oxide is not generated.

The ambient temperature of the heat treatment may be 300 to 800°C. The heat treatment time may be 1 to 30 minutes. By setting the temperature and time of the heat treatment within the above range, the mixed layer 3 having a thickness capable of sufficiently holding the ATO particles 31 can be formed.

(3) Removal of surplus ATO particles (S3)
When the thickness of the mixed layer 3 is smaller than the thickness of the ATO particle layer 30 (see FIG. 3 ), as shown in FIG. 4, surplus ATO particles 31 a not retained by the titanium oxide 32 remain on the surface 35 of the mixed layer 3. To do. When the surplus ATO particles 31a thus exist, they may be removed. Thereby, the separator 1 as shown in FIG. 5 is obtained. The method for removing the surplus ATO particles 31a is not particularly limited, and examples thereof include water jet cleaning, blast cleaning, brush cleaning, and ultrasonic cleaning.

Since the ATO particles 31 used as the conductive particles in the present embodiment do not contain carbon, even if the heat treatment (S2) under a low oxygen partial pressure is performed, at the interface between the base material 2 and the conductive particles (ATO particles 31). Titanium carbide with low corrosion resistance is not formed. Therefore, the separator 1 obtained by the manufacturing method according to the embodiment has high durability, and it is possible to suppress an increase in contact resistance when used by incorporating it into a fuel cell.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various design modifications are possible without departing from the spirit of the present invention described in the claims. It can be performed.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example A pure titanium plate having a thickness of 0.1 mm was prepared as a base material. ATO particles (particle size: 10 nm, manufactured by Mitsubishi Materials, T-1) were dispersed in distilled water and ethanol to obtain an ATO dispersion liquid, which was applied to the surface of the base material to form an ATO particle layer. Then, the base material was heat-treated at 700° C. for 2 minutes under an oxygen partial pressure of 0.1 Pa. As a result, titanium of the base material diffused outward into the ATO particle layer, and the outwardly diffused titanium reacted with oxygen to generate titanium oxide (TiO _x ). As a result, a mixed layer composed of titanium oxide and ATO particles held by titanium oxide was formed. Then, brush cleaning and ultrasonic cleaning were performed to remove excess ATO particles on the mixed layer. Thus, a test piece having a mixed layer of titanium oxide and ATO particles held by titanium oxide on the substrate was obtained.

Comparative Example A test piece was prepared in the same manner as in the example except that a carbon black dispersion (Aqua Black, particle size 10 nm, manufactured by Tokai Carbon Co., Ltd.) was applied instead of the ATO dispersion. Thereby, a test piece having a mixed layer of titanium oxide and carbon black retained by titanium oxide on the substrate was obtained.

A corrosion resistance test (constant potential corrosion test) according to the electrochemical high temperature corrosion test method (JIS Z2294) of metal materials of Japanese Industrial Standards was performed as follows. The test was conducted in an open system. The test pieces prepared in Examples and Comparative Examples were immersed in 80° C. sulfuric acid. In this state, the counter electrode made of a platinum plate and each test piece (sample electrode) were electrically connected to generate a potential difference of 0.9 V between the counter electrode and each sample electrode, which was held for 100 hours. The potential of the test piece was kept constant by the reference electrode.

The contact resistance of each test piece before and after the corrosion resistance test was measured as follows. Carbon paper (Toray Industries, Inc., TGP-H120, thickness 0.5 mm) was sandwiched between each test piece and a gold-plated copper plate, and a constant load (0.98 MPa) was applied. Carbon paper corresponds to the diffusion layer of a fuel cell. In this state, a constant current was passed between each test piece and the copper plate to measure the voltage. Based on the measurement results, the contact resistance between the test piece and the carbon paper was calculated. FIG. 6 shows the calculation result. The contact resistance of the test piece of the comparative example increased after the corrosion resistance test, but the contact resistance of the test piece of the example hardly changed before and after the corrosion resistance test.

1: Separator, 2: Base material, 3: Mixed layer, 30: Antimonide tin oxide particle layer, 31: Antimonide tin oxide particle, 32: Titanium oxide

Claims (1)

A method of manufacturing a separator for a fuel cell, comprising:
Disposing antimony-doped tin oxide particles on the surface of a substrate containing titanium or a titanium alloy,
A method of manufacturing a separator for a fuel cell, comprising: heat-treating a base material on which the antimony-doped tin oxide particles are arranged under a low oxygen partial pressure.

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