Separator manufacturing method

Abstract

To provide a method for producing a separator that can suppress the generation of PVD film imperfections.SOLUTION: There is provided a method for producing a separator for fuel cells, and a substrate of the separator comprises a metal material. The method includes: press-forming the substrate into a separator shape; washing the substrate with an acid, and forming an electroconductive film on a surface of the acid-washed substrate by physical vapor deposition. In the acid washing, at least one surface of the substrate is dissolved from the surface to a thickness of 0.49 μm-5.00 μm.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Various studies have been conducted on separators such as those disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-026839 Summary of the Invention [Problem to be solved by the invention]

[0004] In fuel cell separators, which use metal materials such as stainless steel as the base material, surface treatments such as physical vapor deposition (PVD) are usually performed on the base material pressed into the separator shape to achieve the required corrosion resistance and conductivity. However, the surface of the pressed base material can become rough and scratched due to friction between the base material and the mold during pressing, which can cause defects in the physical vapor deposition coating after the physical vapor deposition process. As a result, separators with sufficient corrosion resistance may not be obtained.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a method for manufacturing a separator that can suppress the occurrence of defects in a PVD film. [Means for solving the problem]

[0006] The separator manufacturing method of the present disclosure is a manufacturing method of a separator for a fuel cell, wherein a substrate of the separator includes a metal material, and the manufacturing method includes press-molding the substrate into a separator shape, washing the substrate with acid, and forming a conductive coating on the surface of the acid-washed substrate by physical vapor deposition, wherein the acid washing dissolves at least one surface of the substrate to a thickness of 0.49 μm to 5.00 μm from the surface.

[0007] In the present disclosure, the acid may include at least hydrochloric acid, and the concentration of hydrochloric acid in the acid may be 4% by mass or more and 10% by mass or less.

[0008] The present disclosure may further include washing the substrate with water after washing with the acid and before forming the conductive coating, and drying the substrate after washing with water.

[0009] The present disclosure may further include removing oil from the surface of the base material by cleaning the base material with at least one of alkali cleaning and hydrocarbon cleaning after the press molding and before the cleaning with the acid.

[0010] In the present disclosure, in the acid cleaning, the substrate may be immersed in the acid for 10 minutes or less, the acid may be hydrochloric acid, the concentration of the hydrochloric acid as the acid may be 4 mass% or more, the metal material may be stainless steel, and the conductive coating may be a two-layer film consisting of a titanium coating and a carbon coating. [Effects of the Invention]

[0011] The present disclosure can provide a method for manufacturing a separator that can suppress the occurrence of defects in a PVD film. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a scanning electron microscope (SEM) image of the surface of a pressed substrate. [Figure 2]FIG. 2 is a diagram showing an example of an SEM image of a cross section of a separator in which a PVD film is formed on a pressed substrate without acid treatment. [Figure 3] FIG. 3 is a diagram showing an example of an SEM image of the surface of a substrate that has been pressed and then acid-treated. [Figure 4] FIG. 4 is a graph showing the relationship between the thickness dissolved from the separator surface and the amount of iron eluted from the separator. DETAILED DESCRIPTION OF THE INVENTION

[0013] A method for manufacturing a separator according to the present disclosure is a method for manufacturing a separator for a fuel cell, comprising the steps of: the substrate of the separator includes a metal material, The manufacturing method includes: Press-molding the substrate into the shape of a separator; washing the substrate with an acid; forming a conductive coating on the acid-cleaned surface of the substrate by physical vapor deposition; In the acid washing, at least one surface of the substrate is dissolved to a thickness of 0.49 μm to 5.00 μm from the surface.

[0014] When a physical vapor deposition process is performed on a pressed substrate to form a PVD film on the substrate, defects occur in the PVD film in conventional techniques. In conventional technology, the surface roughness of the substrate is adjusted by polishing, but electrolytic polishing, chemical polishing, and physical polishing are all unrealistic as mass production techniques from the standpoint of cost and quality. Electrolytic polishing is not practical for mass production of separators because the area that can be processed in one go is small, making it costly and unrealistic. Chemical polishing requires bath preparation for each process and generates a large amount of waste liquid, making it costly and unrealistic for mass production of separators. Physical polishing reduces the dimensional accuracy of the parts and is unrealistic for mass production when considering the polishing time. Furthermore, the surface roughness of the substrate is not the main cause of the defects. Even if the surface roughness of the substrate is somewhat high, the PVD film will conform to the roughness and will not cause major defects. During the formation of PVD coatings, the severe sliding between the substrate and the mold causes plastic flow of the material on the substrate surface. The main causes of these defects are roughness such as burrs or eaves caused by this plastic flow, deterioration of the mold surface, and scratches and other roughness caused by the roughness of the mold surface. Therefore, even if the surface roughness of the substrate satisfies a predetermined roughness, if these causes remain, the occurrence of defects in the PVD film cannot be sufficiently suppressed.

[0015] FIG. 1 is a diagram showing an example of a scanning electron microscope (SEM) image of the surface of a pressed substrate. FIG. 2 is a diagram showing an example of an SEM image of a cross section of a separator in which a PVD film is formed on a pressed substrate without acid treatment. As shown in Figure 1, the surface of a pressed substrate is rough. As shown in Figure 2, if there are roughnesses 12 on the substrate 10, defects 13 will occur in the PVD film 11. In PVD processing, the film-forming material is sprayed from the evaporation source toward the substrate. If the surface of the substrate is rough as shown in Figure 1, the film-forming material cannot reach the rough areas, and no film is formed, as shown in Figure 2. When a PVD coating is deposited to a thickness of several micrometers or more, it is deposited to cover the entire rough area, which reduces the occurrence of corrosion, but the cost of depositing the PVD coating is high, making it unrealistic from a cost-effectiveness perspective.Even in this case, cracks are likely to occur in the PVD coating when the parts are assembled or when they expand and contract due to heat during use, and these cracks become the starting point for corrosion.

[0016] Figure 3 shows an example of an SEM image of the surface of a substrate that has been pressed and then acid-treated. As shown in Figure 3, the surface of the substrate that has been pressed and then acid-treated has been freed of roughness and other causes of defects in the PVD film. According to the present disclosure, the surface of the pressed substrate is acid-treated to remove the cause of defects, and then physical vapor deposition treatment is performed, thereby improving the corrosion resistance of the separator. Acid treatment dissolves the substrate from the surface to a specified thickness or more, eliminating the cause of defects, eliminating the need to make the PVD film thicker than necessary and preventing deterioration of part dimensions. Acid treatment can be performed on large quantities in compact equipment in a processing time of 1 to 2 minutes or less, so it can be carried out at a lower cost than polishing.

[0017] The manufacturing method of the present disclosure is carried out in the order of a press molding step, an acid washing step, and a physical vapor deposition step. The manufacturing method of the present disclosure may be carried out in the order of a press molding step, an oil removal step, an acid washing step, a water washing step, a drying step, and a physical vapor deposition step.

[0018] The manufacturing method of the present disclosure includes a press molding process. The press molding step is a step of press molding the substrate into the shape of the separator. The substrate of the separator includes a metal material. The metal material may be iron, aluminum, an aluminum alloy, stainless steel (SUS), or the like. The shape of the separator may be rectangular, horizontally elongated hexagonal, horizontally elongated octagonal, circular, oval, or the like. The press molding method may be a method in which the substrate is pressed into a mold having a separator shape.

[0019] The manufacturing method of the present disclosure may include an oil removal step. The oil removal step is a step of removing oil from the surface of the substrate by washing the substrate with at least one of alkali washing and hydrocarbon washing after press molding and before washing with acid. If there is oil on the surface of the substrate after press molding and there is a concern that this may affect the quality of the acid treatment, the oil removal step may be carried out.

[0020] The manufacturing method of the present disclosure includes an acid washing step. The acid washing step is a step of washing the substrate with an acid. In the acid washing, at least one surface of the substrate is dissolved to a thickness of 0.49 μm to 5.00 μm from the surface. The upper limit of this thickness may be 2.55 μm or less. In the acid washing, it is sufficient to wash at least one surface of the substrate with acid, or both surfaces may be washed with acid. The thickness of the surface roughness of the substrate caused by pressing is less than 0.49 μm, and in order to remove the surface roughness, it is necessary to dissolve and remove 0.49 μm or more of the substrate. The thickness of the substrate before acid washing is, for example, 0.02 mm to 0.4 mm, and may be 0.1 mm or less. If 5.00 μm or more is dissolved and removed from one side, or 10.00 μm or more is dissolved and removed from both sides, the strength of the separator will decrease if the plate thickness is reduced. In the acid cleaning, the substrate may be immersed in the acid for 10 minutes or less, or for 0.5 minutes or more. In washing with acid, the temperature of the acid may be 25°C to 35°C. The acid may be, for example, hydrochloric acid, nitric acid, sulfuric acid, hydrofluoric acid, etc. The acid may contain at least hydrochloric acid, or may be hydrochloric acid. Hydrochloric acid can be handled more safely than nitric acid, sulfuric acid, and hydrofluoric acid. The concentration of hydrochloric acid in the acid may be 4% by mass or more and 10% by mass or less. The concentration of hydrochloric acid as an acid may be 4% by mass or more, 10% by mass or less, or 8% by mass or less. If the hydrochloric acid concentration is less than 4% by mass, the dissolving power is weak and the immersion time becomes long. If the hydrochloric acid concentration is 10% by mass or less, handling is easy.

[0021] The manufacturing method of the present disclosure may include a water washing step. The water washing step is a step of washing the substrate with water after washing with acid and before forming the conductive coating.

[0022] The manufacturing method of the present disclosure may include a drying step. The drying step is a step of drying the substrate after washing with water.

[0023] The manufacturing method of the present disclosure includes a physical vapor deposition process. The physical vapor deposition step is a step of forming a conductive coating by physical vapor deposition on the surface of the base material that has been washed with the acid. Examples of physical vapor deposition include sputtering and ion plating. The conductive coating may be a titanium coating, a carbon coating, or the like. The formed titanium coating improves the corrosion resistance of the separator. The carbon coating improves the conductivity of the separator. The thickness of the conductive coating may be 0.01 μm or more and 1 μm or less. The conductive coating may be a two-layer film made up of a titanium coating and a carbon coating. The conductive coating may have a titanium coating and a carbon coating formed in this order from the substrate side. The material of the titanium coating can be pure titanium or a titanium alloy. The thickness of the titanium coating may be, for example, 10 nm to 1000 nm. The carbon coating may be formed, for example, by the physical vapor deposition method described above using carbon as a target. Examples of the material for the carbon coating include carbon black. The thickness of the carbon coating may be, for example, 10 nm to 1000 nm.

[0024] The separator of the present disclosure is for use in a fuel cell. The fuel cell may have only one unit cell of the fuel cell, or may be a fuel cell stack in which a plurality of unit cells are stacked. In this disclosure, both a single fuel cell and a fuel cell stack may be referred to as a fuel cell. The number of stacked unit cells of the fuel cell is not particularly limited, and may be, for example, from 2 to several hundred.

[0025] A single cell of the fuel cell may include a membrane electrode gas diffusion layer assembly and two separators that sandwich the membrane electrode gas diffusion layer assembly. The membrane electrode gas diffusion layer assembly has, in this order, an anode gas diffusion layer, an anode catalyst layer, an electrolyte membrane, a cathode catalyst layer, and a cathode gas diffusion layer. The cathode (oxidant electrode) includes a cathode catalyst layer and a cathode-side gas diffusion layer. The anode (fuel electrode) includes an anode catalyst layer and an anode-side gas diffusion layer. In the present disclosure, the reactant gas supplied to the anode is a fuel gas (anode gas), and the reactant gas supplied to the cathode is an oxidant gas (cathode gas). The fuel gas is a gas that mainly contains hydrogen and may be hydrogen. The oxidant gas is a gas that contains oxygen and may be air or the like. One of the two separators is an anode-side separator and the other is a cathode-side separator, and in the present disclosure, the anode-side separator and the cathode-side separator are collectively referred to as separators. The separator of the present disclosure may be used as an anode-side separator or a cathode-side separator. [Example]

[0026] Example 1 (1) A 0.1 mm thick SUS304 plate was used as the base material and press-molded to form the base material into a separator shape. (2) Hydrocarbon cleaning was performed to remove surface oils from the substrate. (3) Acid treatment was carried out under the conditions shown in Table 1. (4) Using a PVD device, a two-layer PVD film consisting of a titanium film (150 nm thick) and a carbon film (30 nm thick) was formed on the surface of the substrate, in that order from the substrate side. This produced a separator. (5) A corrosion test (measurement of iron elution amount) was carried out using a constant potential test. Potential test conditions A 4cm x 5cm sample was cut from the separator in the power generation area and immersed in the electrolyte. While the sample was immersed in the electrolyte, a counter electrode made of a platinum plate was electrically connected to the sample (sample electrode), creating a potential difference of 0.9V between the counter electrode and the sample electrode, causing the sample to corrode. During the test, the potential of the sample was kept constant using a reference electrode. Electrolyte: sulfuric acid (pH 3), chlorine 10 ppm, fluorine 3 ppm Test temperature: 80℃ ·Applied potential: 0.9V vs SHE (standard hydrogen electrode) Test duration: 60 hours (6) After the test, the electrolyte was recovered and the iron component dissolved in the electrolyte was measured using an inductively coupled plasma (ICP) emission spectrometer. Based on the obtained measurement values, the iron content of 1 cm of the evaluation area of ​​the sample after 1 hour of testing was calculated. 2 The amount of iron (Fe) dissolved per unit was calculated. The results are shown in Table 1.

[0027] (Comparative Example 1) A separator was obtained under the same conditions as in Example 1 except that the acid treatment was not carried out, and a constant potential test was carried out.

[0028] (Comparative Example 2, Examples 2 to 9) Separators were obtained under the same conditions as in Example 1, except that the acid treatment was carried out under the conditions shown in Table 1, and a constant potential test was carried out.

[0029] [Table 1]

[0030] [Evaluation results] FIG. 4 is a graph showing the relationship between the thickness dissolved from the separator surface and the amount of iron eluted from the separator. As shown in Table 1 and Figure 4, by dissolving the separator to a depth of 0.49 μm or more from the surface of the separator, the occurrence of defects in the PVD film can be suppressed, and the amount of iron elution is 0.48 × 10 -10 mol / cm 2 / hr or less, extremely excellent corrosion resistance was obtained. [Explanation of symbols]

[0031] 10 Base material 11 PVD membrane 12 Rough 13 Defects

Claims

1. A method for manufacturing a separator for a fuel cell, comprising: the substrate of the separator includes a metal material, The manufacturing method includes: Press-molding the substrate into the shape of a separator; washing the substrate with an acid; forming a conductive coating on the acid-cleaned surface of the substrate by physical vapor deposition; the acid comprises at least hydrochloric acid; The concentration of hydrochloric acid in the acid is 4% by mass or more and 10% by mass or less, In the acid washing, the substrate is immersed in the acid for 10 minutes or less, and at least one surface of the substrate is dissolved to a thickness of 0.49 μm to 5.00 μm from the surface.

2. 2. The method for producing a separator according to claim 1, further comprising: washing the substrate with water after washing with the acid and before forming the conductive coating; and drying the substrate after washing with water.

3. 2. The method for producing a separator according to claim 1, further comprising, after the press-molding and before the washing with the acid, cleaning the substrate with at least one of alkali cleaning and hydrocarbon cleaning to remove oil from the surface of the substrate.

4. In the acid cleaning, the substrate is immersed in the acid for 0.5 minutes or more and 10 minutes or less; the acid is hydrochloric acid, the metal material is stainless steel, 2. The method for producing a separator according to claim 1, wherein the conductive coating is a two-layer film consisting of a titanium coating and a carbon coating.

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