Manufacturing method of fuel cell separator

Abstract

To provide a method for efficiently manufacturing a separator that can improve the output characteristics of a fuel cell.SOLUTION: The method for manufacturing a separator for a fuel cell having a carbon film in the surface according to the present disclosure includes: a preparation step of preparing an SUS-based base material with a titanium oxide formed; and a carbon ion radiation step of radiating carbon ions to the SUS-based base material to reduce the titanium oxide and forming the carbon film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing a separator for a fuel cell. [Background technology]

[0002] A fuel cell is a battery that generates electrical energy through a chemical reaction between an oxidant gas containing oxygen and a fuel gas containing hydrogen. The basic unit of a fuel cell, called a single cell, generally comprises a membrane electrode assembly (MEA) in which electrode catalyst layers are formed on both sides of a solid polymer electrolyte membrane, a gas diffusion layer (GDL) on the outside of which is arranged a separator with a gas flow path on the outside of that.

[0003] It is known that a carbon film is provided on the surface of the separator to reduce the electrical resistance (contact resistance) between the separator and the fuel cell and obtain good output characteristics of the fuel cell. It is also known that titanium is used as the substrate to improve the corrosion resistance of the separator. For example, Patent Document 1 discloses a method for manufacturing a fuel cell separator in which a carbon film is formed by CVD on a titanium substrate having a titanium oxide layer on its surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-062837 Summary of the Invention [Problem to be solved by the invention]

[0005] Here, a titanium oxide film (a passive oxide film) is formed on the surface of the titanium substrate as a result of the reaction between oxygen in the atmosphere and the titanium. Titanium oxide is a non-conductive substance (a substance that has no electrical conductivity), so if carbon coating is performed in the presence of a titanium oxide film, the titanium oxide film (non-conductive film) may remain, potentially increasing contact resistance. As a result, the output characteristics of the fuel cell may be reduced. For this reason, a step of removing the titanium oxide film before carbon coating or a step of removing the titanium oxide film after carbon coating may be performed. On the other hand, from the perspective of manufacturing costs, it is preferable to reduce the number of steps and efficiently manufacture the separator.

[0006] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a separator manufacturing method that can efficiently manufacture a separator that can improve the output characteristics of a fuel cell. [Means for solving the problem]

[0007] In order to solve the above problems, the present disclosure provides a method for manufacturing a fuel cell separator having a carbon film on its surface, the method comprising: a preparation step of preparing a SUS substrate having a titanium oxide film formed thereon; and a carbon ion irradiation step of irradiating the SUS substrate with carbon ions to reduce the titanium oxide and form the carbon film.

[0008] According to the present disclosure, by irradiating a SUS substrate on which a titanium oxide film has been formed with carbon ions, the titanium oxide is reduced and a carbon film is formed, thereby enabling the efficient production of a separator that can improve the output characteristics of a fuel cell. [Effects of the Invention]

[0009] The present disclosure has an effect of providing a separator manufacturing method that can efficiently manufacture a separator that can improve the output characteristics of a fuel cell. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a flow diagram illustrating a method for producing a separator according to the present disclosure. [Figure 2] FIG. 1 is a schematic cross-sectional view illustrating a separator in Patent Document 1. [Figure 3] 1A to 1C are schematic cross-sectional views illustrating a method for producing a separator according to the present disclosure. [Figure 4] 1 is a graph showing the contact resistivity of the separators produced in Examples 1 to 7. [Figure 5] 1 is a graph showing the contact resistivity of the separators produced in Comparative Examples 1 to 6 and a Reference Example. [Figure 6] 1 shows the results of TEM-EELS analysis of the separator produced in Example 4. [Figure 7] 1 shows the results of TEM-EELS analysis of the separator produced in Example 7. DETAILED DESCRIPTION OF THE INVENTION

[0011] The method for manufacturing a separator according to the present disclosure will be described in detail below. Fig. 1 is a schematic cross-sectional view illustrating the method for manufacturing a separator according to the present disclosure. First, a SUS substrate having a titanium oxide film formed thereon is prepared (preparation step). Then, the prepared SUS substrate is irradiated with carbon ions to reduce the titanium oxide and form a carbon film (carbon ion irradiation step). This allows the manufacture of a separator having a carbon film on its surface.

[0012] According to the present disclosure, by irradiating a SUS substrate on which a titanium oxide film has been formed with carbon ions, the titanium oxide is reduced and a carbon film is formed, thereby enabling the efficient production of a separator that can improve the output characteristics of a fuel cell.

[0013] For example, in the case of the method disclosed in Patent Document 1, a separator 100 having a base material (Ti base material) 101, an insulator film 102 made of titanium oxide (TiO2), and a carbon film 104 in this order can be obtained. Here, since the oxide film is an insulator film, in order to impart good electron conductivity to the separator, a step of removing the oxide film is further performed. In Patent Document 1, although ultraviolet irradiation of the oxide film in advance is disclosed, it is presumed to be a pretreatment for facilitating the removal of the titanium oxide film after the formation of the carbon film.

[0014] On the other hand, in the method for manufacturing a separator according to the present disclosure, carbon ions are irradiated onto a SUS base material 1 on which a film (insulator film) 2 of titanium oxide is formed as shown in Fig. 3(a). As a result, titanium oxide (TiO2) is reduced by the carbon ions drawn into the film (insulator film) of titanium oxide, and a semiconductor substance TiOx (0 < X < 2) and TiC are formed. Then, a semiconductor film 3 is formed as shown in Fig. 3(b). Further, together with the formation of the semiconductor film 3, a carbon film 4 is formed on the semiconductor film 3. Thus, in the manufacturing method according to the present disclosure, when the carbon film is formed, all or most of the insulator film is removed, so the need to perform an additional step of removing the insulator film is low. Therefore, a separator capable of improving the output characteristics of a fuel cell can be efficiently manufactured. As shown in Fig. 3(a), the film 2 of titanium oxide is usually formed on a titanium film 5 formed on the surface of the SUS base material 1.

[0015] 1. Preparation step The preparation step in the present disclosure is a step of preparing a SUS base material on which a film of titanium oxide is formed.

[0016] The SUS base material may contain only SUS or may contain a metal other than SUS. In the latter case, the proportion of SUS in the entire SUS base material is preferably, for example, 50% by weight or more.

[0017] The thickness, area, and shape of the SUS substrate are not particularly limited. They are preferably set appropriately depending on the fuel cell to be used. Note that the separator usually has grooves formed therein that serve as flow paths for reactant gases (fuel gas, oxidant gas, etc.). Therefore, it is preferable that the SUS substrate has grooves formed therein. The grooves can be formed, for example, by press working.

[0018] The titanium oxide film may be a natural oxide film that is inevitably formed when a titanium film is formed on the surface of a SUS substrate. Alternatively, the titanium oxide film may be a thermal oxide film that is formed by heat-treating a SUS substrate having a titanium film on its surface. The titanium film can be formed, for example, by a sputtering method. The thickness of the titanium film is not particularly limited, but is, for example, 25 nm or more and 10 μm or less.

[0019] The thickness of the titanium oxide film is preferably thin, particularly 50 nm or less, because a thickness of 50 nm or less allows the titanium oxide to be sufficiently reduced and good contact resistance to be obtained.

[0020] 2. Carbon ion irradiation process The carbon ion irradiation step in the present disclosure is a step of irradiating the SUS substrate with carbon ions to reduce the titanium oxide and form the carbon film.

[0021] One method for irradiating a SUS substrate with carbon ions is to ionize and irradiate a carbon source such as graphite. Specifically, the AIP method (arc ion plating) is used. For example, in the AIP method, a SUS substrate having a titanium oxide film is irradiated with ionized carbon (carbon ions) by arc discharge while a negative bias voltage is applied to the substrate. This causes positively charged carbon ions to be attracted to the negatively charged SUS substrate. As a result, the carbon ions can be attracted to the titanium oxide film.

[0022] The conditions of the AIP method are not particularly limited and can be adjusted as appropriate. The negative bias voltage to be applied is, for example, -100 V or more and -1000 V or less. Also, as the negative bias voltage, a pulse voltage may be applied or a DC voltage may be applied.

[0023] The irradiated carbon ions reduce titanium dioxide (TiO2), forming a semiconductor substance TiOx (0 < X < 2) and TiC. Thus, a semiconductor film can be formed from a film of titanium dioxide (insulator film). Also, a carbon film can be formed by irradiating the semiconductor film with carbon ions.

[0024] The carbon film is a film containing at least carbon. Also, the carbon film may contain only carbon or may contain other compounds. Examples of other compounds include titanium carbide. The thickness of the carbon film is not particularly limited, but is, for example, 0.1 nm or more and 1000 nm or less.

[0025] 3. Separator The separator in the present disclosure is used in a fuel cell. A fuel cell (single cell) usually has a membrane electrode assembly (MEA) in which a cathode-side gas diffusion layer, a cathode catalyst layer, an electrolyte membrane, an anode catalyst layer, and an anode-side gas diffusion layer are laminated in this order, and the MEA is sandwiched between two of the above-described separators. The fuel cell may be a single cell or a laminate in which a plurality of single cells are laminated.

[0026] The materials of each layer constituting the MEA can be conventionally known materials. Also, examples of applications of the fuel cell include vehicles such as fuel cell vehicles (FCEVs). Further, the fuel cell may be used in a moving body other than a vehicle (for example, railway, ship, aircraft), or may be used other than a moving body.

[0027] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0028] [Example 1] A titanium film was formed on the surface of a SUS substrate (SUS304) using the sputtering method. The substrate was then annealed in air at 50°C for 2 minutes to intentionally form a titanium oxide film (non-conductive film) on the titanium film. Carbon ions were then irradiated using the AIP method (bias voltage: -250V). This resulted in the production of a separator consisting of a SUS substrate, titanium film, semiconductor film, and carbon film, in that order.

[0029] [Examples 2 to 7] Separators were produced in the same manner as in Example 1, except that the annealing heat treatment temperature was changed as shown in Table 1. Note that the higher the heat treatment temperature, the thicker the non-conductive film.

[0030] [Comparative Example 1] The titanium substrate was annealed in air at 40°C for 2 minutes to intentionally form a titanium oxide film (non-conductive film) on the titanium substrate. Au particles were then sprayed onto the non-conductive film by vapor deposition to form an Au film on the non-conductive film. This resulted in the production of a separator having a titanium substrate, non-conductive film, and Au film in that order.

[0031] [Comparative Examples 2 to 6] Separators were produced in the same manner as in Comparative Example 1, except that the annealing heat treatment temperature was changed as shown in Table 2.

[0032] [Reference example] Au particles were sprayed onto the titanium substrate by vapor deposition without annealing, forming an Au film on the titanium substrate, thereby producing a separator having a titanium substrate and an Au film in that order.

[0033] [Table 1]

[0034] [Table 2]

[0035] [evaluation] (Contact resistance measurement) The contact resistance was measured for the separators obtained in Examples 1 to 7, Comparative Examples 1 to 6, and Reference Example. Specifically, a measurement sample was prepared by stacking the separator / gas diffusion layer (carbon paper) / separator in this order. The separator was stacked so that the carbon film and the carbon paper were in contact with each other. A load of 1 MPa was applied to the measurement sample, and the contact resistance between the separator and the carbon paper was measured using the AC four-terminal method (current 1 A). The results are shown in Figures 4 and 5.

[0036] (TEM-EELS analysis) TEM-EELS analysis was performed on the separators produced in Examples 4 and 7. The results are shown in FIGS.

[0037] As shown in Figures 4 and 5, Examples 1 to 7 had significantly lower contact resistance than Comparative Examples 1 to 6. This is thought to be because, as shown in Figures 6(a) and 6(b) and Figures 7(a) and 7(b), all or most of the titanium oxide, a non-conductive material, was reduced by carbon ion irradiation to form TiC and TiOx, which are semiconductor materials. These results confirmed that the method disclosed herein can produce separators that exhibit good contact resistance without performing a step of removing the titanium oxide film.

[0038] Furthermore, although carbon (C) has a higher electrical resistivity than gold (Au), Examples 1 to 7 exhibited contact resistances equivalent to those of the Reference Example. Therefore, it was confirmed that the method of the present disclosure can produce separators with good contact resistance using less expensive materials. On the other hand, as shown in Figures 7(a) and (b), when the titanium oxide film was too thick, a small amount of titanium oxide film remained even after the carbon film was formed. This suggests that a thinner titanium oxide film is preferable. [Explanation of symbols]

[0039] 1...SUS base material 2...Non-conductive film 3...Semiconductor film 4...Carbon film 5...Titanium film 10...Separator

Claims

1. A method for manufacturing a fuel cell separator having a carbon film on its surface, comprising: A preparation step of preparing a SUS substrate on which a TiO2 film is formed; a carbon ion irradiation step of irradiating the SUS substrate with carbon ions to reduce the TiO 2 film and form the carbon film so that the thickness of the TiO 2 film is 50 nm or less; A method for manufacturing a separator having the above structure.

2. The method for producing a separator according to claim 1, wherein the TiO 2 film is not observed in a TEM-EELS analysis of a cross-sectional image of the separator.

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