Manufacturing method for fuel cell separators

Abstract

To provide a manufacturing method of a fuel cell separator that can impart electrical conductivity to a stainless steel substrate at low cost and that has high electrical conductivity in the early stages of fuel cell operation.SOLUTION: A manufacturing method of a fuel cell separator according to the present invention includes immersing a stainless steel substrate formed into the shape of a separator in an acidic solution of pH 1±0.2 with a fluorine ion concentration of 0.1 ppm or more at 80°C±5°C for 60 minutes or more to modify the surface of the stainless steel substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a fuel cell separator and to a fuel cell separator. [Background technology]

[0002] Solid polymer fuel cells (hereinafter referred to as fuel cells), which use electrolyte membranes, can operate at low temperatures and can be made small and lightweight, so their application to automobiles and other vehicles is being considered.

[0003] In such fuel cells, multiple cells (single cells), which are the basic units, are stacked together. Each cell comprises a membrane electrode assembly with a pair of gas diffusion layers (GDLs) on both sides, and a pair of separators that sandwich them. The membrane electrode assembly has a structure in which an anode electrode and a cathode electrode are positioned on both sides of an electrolyte membrane, which is an ion exchange membrane.

[0004] Stainless steel separators, which offer excellent corrosion resistance and are inexpensive, are widely used as separators for fuel cells. Stainless steel separators achieve corrosion resistance through a passive film of chromium oxide (generally Cr2O3), but they have low electrical conductivity. Therefore, when using stainless steel substrates for fuel cell separators, it is necessary to improve their electrical conductivity.

[0005] As a method to improve the conductivity of stainless steel substrates, techniques such as applying surface treatments to the stainless steel substrate using highly conductive materials like carbon or gold plating are known. However, since these surface treatments increase costs, they are usually applied only to the minimum necessary areas. For example, surface treatment may be applied to only one side of the power generation section (flow channel forming section) on the gas surface of the anode and cathode separators, or to both sides of the power generation section (flow channel forming section) on the gas and cooling surfaces. However, in the former case, because stainless steel has low conductivity, the contact resistance on the cooling surface side increases, significantly reducing the power generation performance of the fuel cell. In the latter case, the power generation performance of the fuel cell is sufficient, but cost increases are unavoidable. Thus, when using stainless steel substrates for fuel cell separators, complex processing is required to give them the sufficient conductivity required for fuel cell components, and cost increases have been a problem.

[0006] To address these problems, methods other than surface treatment have been considered. For example, Patent Document 1 discloses a technique for restoring the conductivity of a separator by injecting an acidic aqueous solution containing fluoride ions during the use of a fuel cell. Specifically, Patent Document 1 discloses a method for restoring the conductivity of a stainless steel separator that has deteriorated due to the use of a solid polymer fuel cell equipped with a stainless steel separator, characterized by injecting an acidic aqueous solution with a pH of 1 to 5 containing 0.001% by mass or more of fluoride ions into the fuel cell so as to pass through the stainless steel separator.

[0007] While the method disclosed in Patent Document 1 can restore the conductivity of the separator during the use of the fuel cell, there was also a need to improve the conductivity of the stainless steel substrate before using the fuel cell. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2008-27742 [Overview of the project] [Problems that the invention aims to solve]

[0009] As described above, the conventional manufacturing of stainless steel fuel cell separators has been plagued by cost increases, and there has been a need for separators with high conductivity during the initial stages of fuel cell operation. Therefore, the present invention aims to provide a method for manufacturing fuel cell separators that can impart conductivity to a stainless steel substrate at low cost and have high conductivity during the initial stages of fuel cell operation. [Means for solving the problem]

[0010] The inventors have discovered that by treating a stainless steel substrate molded into the shape of a separator with an acidic solution under predetermined conditions, it is possible to impart conductivity to the stainless steel substrate at low cost, and that the resulting separator has high conductivity during the initial stages of operation of a fuel cell, thus completing the present invention.

[0011] In other words, the gist of this invention is as follows: (1) A method for manufacturing a fuel cell separator, comprising immersing a stainless steel substrate molded into the shape of a separator in an acidic solution with a pH of 1±0.2 and a fluoride ion concentration of 0.1 ppm or more at 80°C±5°C for 60 minutes or more to modify the surface of the stainless steel substrate. (2) The method for producing a fuel cell separator according to (1), wherein the acidic solution is sulfuric acid or hydrochloric acid having a fluoride ion concentration of 0.1 ppm to 5 ppm. (3) Passivation film on the surface of the stainless steel substrate of the fuel cell separator, determined by X-ray photoelectron spectroscopy (XPS), The ratio of Cr content (atomic%) to Fe content (atomic%) (Cr / Fe ratio) exceeds 1 when the pre-modification treatment is set to 1. The ratio of Mn content (atomic%) to Fe content (atomic%) (Mn / Fe ratio) is greater than 1 when the pre-modification treatment is set to 1, and The ratio ((Cr + Mn) / Fe ratio) of the total content of Cr and Mn (atomic %) to the Fe content (atomic %) exceeds 1 when the ratio before the reforming treatment is set to 1. The method for manufacturing a fuel cell separator according to the above (1) or (2).

Advantages of the Invention

[0012] According to the present invention, it is possible to impart conductivity to a stainless steel substrate at a low cost, and it becomes possible to provide a method for manufacturing a fuel cell separator having high conductivity at the initial stage of operation of a fuel cell.

Brief Description of the Drawings

[0013] [Figure 1] Figure 1A is a graph showing the contact resistance (against GDL) with respect to the fluorine ion concentration for a treatment time of 30 minutes. Figure 1B is a graph showing the contact resistance (against GDL) with respect to the fluorine ion concentration for a treatment time of 60 minutes. [Figure 2] Figure 2A is a graph showing the contact resistance (against separator) with respect to the fluorine ion concentration for a treatment time of 30 minutes. Figure 2B is a graph showing the contact resistance (against separator) with respect to the fluorine ion concentration for a treatment time of 60 minutes. [Figure 3] Figure 3A is a graph showing the contact resistance (against GDL) with respect to the fluorine ion concentration for hydrochloric acid treatment and nitric acid treatment. Figure 3B is a graph showing the contact resistance (against separator) with respect to the fluorine ion concentration for hydrochloric acid treatment and nitric acid treatment. [Figure 4] Figure 4A is a graph showing the XPS spectrum of Cr oxide. Figure 4B is a graph showing the XPS spectrum of Mn oxide. Figure 4C is a graph showing the XPS spectrum of Fe oxide.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, preferred embodiments of the present invention will be described in detail.

[0015] The present invention relates to a method for manufacturing a stainless steel separator for a fuel cell from a stainless steel substrate. The method for manufacturing a separator for a fuel cell according to the present invention includes immersing a stainless steel substrate formed into the shape of a separator in an acidic solution containing fluoride ions at a predetermined concentration to perform a surface modification treatment on the stainless steel substrate.

[0016] The stainless steel of the stainless steel substrate is not particularly limited, and examples thereof include austenitic stainless steels such as SUS304, SUS316, and SUS430 defined in JIS G 4305:2015, and ferritic stainless steels such as SUS444. From the viewpoints of corrosion resistance and workability, SUS304 is preferred.

[0017] The thickness of the stainless steel substrate is not particularly limited, and is usually 80 μm to 200 μm, preferably 80 μm to 100 μm.

[0018] In the present invention, a stainless steel substrate formed into the shape of a separator is immersed in an acidic solution to perform a surface modification treatment on the surface of the stainless steel substrate. The forming of the stainless steel substrate into the shape of a separator can be performed, for example, by press forming. The shape of the separator may be the shape of a normal separator for a fuel cell. For example, a shape in which a large number of groove portions are formed with irregularities along the longitudinal direction, and flow paths for fuel gas, oxidant gas, and refrigerant are formed. However, if these flow paths can be ensured, the shape is not limited to this.

[0019] In the present invention, a stainless steel substrate formed into the shape of a separator is immersed in an acidic solution containing fluoride ions at a predetermined concentration (hereinafter, also referred to as "pickling treatment") to perform a surface modification treatment on the surface of the stainless steel substrate. By this pickling treatment (modification treatment), the conductivity of the stainless steel substrate can be increased.

[0020] The acidic solution is not particularly limited and can include, for example, sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, acetic acid, and carbonic acid. However, an acidic solution that destroys the initial passive film and reduces the amount of Fe in the film, thereby relatively increasing the amount of Cr, is desirable. From the viewpoint of reducing contact resistance, sulfuric acid and hydrochloric acid are preferred as the acidic solution, and experimental data suggests that sulfuric acid is more preferred.

[0021] In one embodiment, when applying the method of the present invention to the gas side of a fuel cell separator, it is preferable to use sulfuric acid or hydrochloric acid as the acidic solution. When sulfuric acid or hydrochloric acid is used as the acidic solution, the GDL contact resistance of the fuel cell separator is set to a preferred range of 12 mΩ·cm for this embodiment. 2 The following can be done:

[0022] In one embodiment, when applying the method of the present invention to the cooling surface side of a fuel cell separator, it is preferable to use sulfuric acid as the acidic solution. When sulfuric acid is used as the acidic solution, the contact resistance of the fuel cell separator to the separator is set to a preferred range of 2 mΩ·cm for this embodiment. 2 The following can be done:

[0023] Acidic solutions contain 0.1 ppm or more of fluoride ions (fluoride ions, F) -The acidic solution contains fluoride ions, which significantly increases the conductivity of the stainless steel substrate. The upper limit of the fluoride ion concentration in the acidic solution is, for example, 1000 ppm or less, preferably 100 ppm or less, more preferably 30 ppm or less, particularly preferably 5 ppm or less, and most preferably 1 ppm or less, from the viewpoint of cost reduction. The fluoride ion concentration in the acidic solution is preferably 0.1 ppm to 100 ppm, more preferably 0.1 ppm to 30 ppm, particularly preferably 0.1 ppm to 5 ppm, and most preferably 0.1 ppm to 1 ppm, from the viewpoint of achieving both high conductivity and low cost of the separator. In one embodiment, when the method of the present invention is applied to the gas surface side of a fuel cell separator, the conductivity of the stainless steel substrate can be further increased by setting the fluoride ion concentration in the acidic solution to 30 ppm or more. In this invention, ppm means mass ppm.

[0024] An acidic solution containing a predetermined concentration of fluoride ions can be obtained by adding fluoride to the acidic solution to achieve the desired fluoride ion concentration. The amount of fluoride added to the acidic solution can be appropriately adjusted according to the desired fluoride ion concentration. Examples of fluoride are not particularly limited, but include lithium fluoride, sodium fluoride, potassium fluoride, rubidium fluoride, and cesium fluoride, but sodium fluoride (NaF) is preferred because it is inexpensive and generally easy to handle.

[0025] The pH of the acidic solution used in the pickling process is 1 ± 0.2. When the pH of the acidic solution is within this range, the conductivity of the stainless steel substrate can be increased while reducing the amount of fluorine added to the acidic solution, thus enabling low-cost improvement of the stainless steel substrate's conductivity. The pH of the acidic solution can be adjusted to the desired value by adjusting the amount of acidic solution and fluoride (preferably NaF) added.

[0026] In this invention, a stainless steel substrate is immersed in an acidic solution containing fluoride ions at a predetermined concentration at 80°C ± 5°C for 60 minutes or more.

[0027] The immersion treatment temperature is 80°C ± 5°C, preferably 80°C ± 2.5°C, and more preferably 80°C. However, from the viewpoints of the temperature rising time and the ease of controlling the temperature inside the furnace, by setting the immersion treatment temperature to 80°C ± 5°C, it is possible to reduce the amount of fluorine added to the acidic solution while increasing the conductivity of the stainless steel substrate. Therefore, the conductivity of the stainless steel substrate can be increased at low cost. Note that the immersion treatment temperature refers to the actual temperature of the stainless steel substrate in the state of being immersed in the acidic solution.

[0028] The immersion treatment time is 60 minutes or more, preferably 60 minutes to 300 minutes, and more preferably 60 minutes to 150 minutes. Particularly preferably, it is 60 minutes to 90 minutes in consideration of the temperature rising and falling times related to productivity and the stable soaking time. In the present invention, by setting the treatment conditions as described above, the conductivity of the stainless steel substrate can be increased by short-time pickling treatment. Therefore, the conductivity of the stainless steel substrate can be increased at low cost. The immersion treatment time can be appropriately adjusted according to the target conductivity.

[0029] In the present invention, by performing surface modification treatment of the stainless steel substrate by pickling treatment, the passive film formed on the surface of the stainless steel substrate before the modification treatment is once broken, and Fe in the film is dissolved and reduced. It is considered that the conductivity of the stainless steel substrate is improved by forming a new high-conductivity film in which the amounts of Cr and Mn relatively increase. Although the mechanism is unknown, according to the literature (written by Katsuhisa Sugimoto, Zairyo-to-Kankyo, Vol. 57, pp. 375 - 384 (2008)), since the change in the film composition makes it have semiconductor properties, for example, Cr x O y (where 0 < x < 2, 0 < y < 3) is presumed to be formed on the surface of the substrate as a semiconductor oxide.

[0030] The manufacturing method for a fuel cell separator of the present invention may include a water washing step after the above-mentioned pickling step, in which the pickled stainless steel substrate is washed with water. The water washing can be carried out by a commonly used method, using water such as tap water or industrial water to remove the acidic solution that adhered to the stainless steel substrate during the pickling process.

[0031] The manufacturing method for a fuel cell separator of the present invention may include a drying step after the water washing step, in which the stainless steel substrate washed with water is dried. The drying step should be carried out under conditions that sufficiently remove moisture from the surface of the stainless steel substrate, and is usually carried out at room temperature to 50°C for 1 minute to 1 hour.

[0032] The method for manufacturing a fuel cell separator of the present invention may include, depending on the desired conductivity, a step of applying a carbon surface treatment to the obtained fuel cell separator by physical vapor deposition (PVD) or chemical vapor deposition (CVD) after the drying process.

[0033] The present invention also relates to a fuel cell separator obtained by the above-described manufacturing method. Accordingly, the fuel cell separator of the present invention is obtained by a method that includes immersing a stainless steel substrate molded into the shape of a separator in an acidic solution with a pH of 1±0.2 and a fluoride ion concentration of 0.1 ppm or more at 80℃±5℃ for 60 minutes or more to modify the surface of the stainless steel substrate.

[0034] The fuel cell separator of the present invention is made of a stainless steel substrate. The stainless steel substrate of the fuel cell separator is as described above in the manufacturing method of the fuel cell separator. The term "stainless steel substrate" used in reference to the fuel cell separator refers to a stainless steel substrate that has undergone the pickling treatment and modification treatment of the present invention.

[0035] The fuel cell separator of the present invention undergoes a modification treatment by pickling, which modifies the passive film on the surface of the stainless steel substrate. Specifically, the pickling treatment changes the passive film on the surface of the stainless steel substrate from an Fe-rich passive film to a Cr and Mn-rich, highly conductive passive film.

[0036] The fuel cell separator of the present invention has high conductivity because the elemental composition on the surface of the stainless steel substrate, as determined by X-ray photoelectron spectroscopy (XPS), is controlled to a specific range of atomic ratios. In this invention, "the surface of the stainless steel substrate" refers to the area from the outermost surface of the stainless steel substrate to a depth of less than 10 nm. Therefore, in this invention, "the surface of the stainless steel substrate" corresponds to the passivation film on the surface of the stainless steel substrate.

[0037] XPS analysis is performed using an XPS instrument (e.g., ULVAC PHI5000 VersaProbeII) under the following conditions: X-ray source; AlKα monochromatic light, output 25W, voltage 15kV, irradiation area; φ100μm, analysis area; 1000×200μm, neutralization gun; ON state, pulse energy (wide; 187.85eV, narrow; 46.95-117.40eV), step size (wide; 0.4eV, narrow; 0.1eV), shift correction is performed with C1s; CC, CH, 284.8eV. Depth analysis can be performed while etching with Ar monomer at a voltage of 3kV, irradiation area of ​​2×2mm, and etching speed of 9.3nm / min. From the obtained data, the atomic ratios are determined using the data (atomic%) for Cr2p3, Mn2p3, and Fe2p3.

[0038] In the fuel cell separator of the present invention, the ratio of Cr content (atomic%) to Fe content (atomic%) in the passive film on the surface of the stainless steel substrate (Cr / Fe ratio), as determined by XPS analysis, exceeds 1 when the value before the modification treatment is set to 1. In other words, the Cr content is relatively higher than the Fe content before the modification treatment.

[0039] In the fuel cell separator of the present invention, the ratio of Mn content (atomic%) to Fe content (atomic%) in the passive film on the surface of the stainless steel substrate (Mn / Fe ratio), as determined by XPS analysis, exceeds 1 when the value before the reforming treatment is set to 1. In other words, the Mn content is relatively higher than the Fe content before the reforming treatment.

[0040] In the fuel cell separator of the present invention, the ratio of the total content of Cr and Mn (atomic%) in the passivation film on the surface of the stainless steel substrate to the Fe content (atomic%) ((Cr+Mn) / Fe ratio), as determined by XPS analysis, exceeds 1 when the value before the reforming treatment is set to 1. In other words, the total content of Cr and Mn is relatively higher than the Fe content before the reforming treatment.

[0041] The fuel cell separator of the present invention has a Cr content in the passivation film on the surface of the stainless steel substrate, as determined by XPS analysis, which is greater than 1 when the content before modification treatment is set to 1.

[0042] The fuel cell separator of the present invention has a Mn content in the passivation film on the surface of the stainless steel substrate, as determined by XPS analysis, which is greater than 1 when the content before modification treatment is set to 1.

[0043] The fuel cell separator of the present invention has an Fe content in the passivation film on the surface of the stainless steel substrate, as determined by XPS analysis, which is less than 1 when the content before modification treatment is set to 1.

[0044] Preferably, in the fuel cell separator of the present invention, the count numbers (intensity) of Cr oxide and Mn oxide are higher and the Fe oxide is lower in the profile (vertical axis) of XPS analysis (narrow analysis) compared to before the reforming treatment, meaning that Fe has decreased and Cr and Mn have increased compared to before the reforming treatment.

[0045] The fuel cell separator of the present invention has high conductivity. Preferably, the fuel cell separator of the present invention has a conductivity of 12 mΩ·cm. 2The following contact resistance to GDL (contact resistance to GDL) is present. Furthermore, the fuel cell separator of the present invention preferably has a contact resistance of 2 mΩ·cm. 2 The following contact resistance to the separator (contact resistance to the separator) is observed. [Examples]

[0046] The present invention will be described in more detail below using examples. However, the technical scope of the present invention is not limited to these examples.

[0047] <Examination of pickling treatment conditions> NaF was added to a sulfuric acid solution to achieve a predetermined fluoride ion concentration, thereby preparing a pH 1 sulfuric acid solution containing the predetermined concentration of fluoride ions. A SUS304 separator molded into the shape of a fuel cell separator was immersed in this fluoride-containing sulfuric acid solution at 80°C for 30 or 60 minutes. After immersion, the SUS304 separator was removed from the sulfuric acid solution, washed with water, air-dried, and then its contact resistance was measured.

[0048] Measurement of contact resistance against GDL A SUS304 separator was cut into 5cm x 6cm pieces to prepare the measurement sample. Carbon paper was also prepared as a material equivalent to the gas diffusion layer (GDL) and cut into 40cm x 50cm pieces. The carbon paper and measurement sample were stacked together, and this was clamped in the Au-plated conductive jig of the measuring instrument. A load of 1 MPa was applied, and a current of 1 A was passed through, and the reading was measured after 10 seconds.

[0049] Measurement of contact resistance against separator Measurement samples were prepared by cutting SUS304 separators into 5cm x 6cm pieces. Two measurement samples were stacked on top of each other, clamped in the gold-plated conductive jig of the measuring instrument, a load of 1 MPa was applied, and a current of 1 A was passed through them. The readings were measured after 10 seconds.

[0050] Figure 1A shows the contact resistance (vs. GDL) with respect to the fluorine ion concentration for a treatment time of 30 minutes. Figure 1B shows the contact resistance (vs. GDL) with respect to the fluorine ion concentration for a treatment time of 60 minutes. Figure 2A shows the contact resistance (vs. separator) with respect to the fluorine ion concentration for a treatment time of 30 minutes. Figure 2B shows the contact resistance (vs. separator) with respect to the fluorine ion concentration for a treatment time of 60 minutes.

[0051] As shown in FIGS. 1A and 1B, when treated with a sulfuric acid solution or a sulfuric acid solution containing fluorine ions, the contact resistance (vs. GDL) of the SUS304 separator decreased significantly compared to before immersion in the sulfuric acid solution (described as "initial" in the figure). Here, generally, on the gas side of the fuel cell separator, the contact resistance against GDL is 12 mΩ·cm 2 It is preferably as follows. As shown in FIG. 1A, at a treatment time of 30 minutes, this target contact resistance value was achieved at a fluorine ion concentration of 100 ppm or more. On the other hand, as shown in FIG. 1B, at a treatment time of 60 minutes, this target contact resistance value was achieved at a fluorine ion concentration of 0.1 ppm or more. Therefore, under the treatment conditions of pH 1, 80°C, and 60 minutes, it was possible to increase the conductivity of the separator while reducing the amount of fluorine added to the sulfuric acid solution.

[0052] As shown in FIGS. 2A and 2B, when treated with a sulfuric acid solution or a sulfuric acid solution containing fluorine ions, the contact resistance (vs. separator) of the SUS304 separator decreased significantly compared to before immersion in the sulfuric acid solution (described as "initial" in the figure). Here, generally, on the cooling side of the fuel cell separator, the contact resistance against the separator is 2 mΩ·cm 2 It is preferably as follows. As shown in FIG. 2A, at a treatment time of 30 minutes, this target contact resistance value was achieved at a fluorine ion concentration of 30 ppm or more. On the other hand, as shown in FIG. 2B, at a treatment time of 60 minutes, this target contact resistance value was achieved at a fluorine ion concentration of 0.1 ppm or more. Therefore, under the treatment conditions of pH 1, 80°C, and 60 minutes, it was possible to increase the conductivity while reducing the amount of fluorine added to the sulfuric acid solution.

[0053] <Examination of the type of acidic solution> Using sulfuric acid, hydrochloric acid, and nitric acid as acidic solutions, the effect of reducing the contact resistance of the separator was confirmed. The sample treated with sulfuric acid used the sample obtained in the examination of the pickling treatment conditions described above. In addition, the samples treated with hydrochloric acid or nitric acid were obtained in the same manner as the examination of the pickling treatment conditions described above, except that sulfuric acid was changed to hydrochloric acid or nitric acid. The pickling treatment conditions were pH 1, fluoride ion concentration 0 ppm or 5 ppm, 80 °C, and 60 minutes. The contact resistance (against GDL and against the separator) of the SUS304 separator after pickling treatment was measured.

[0054] Fig. 3A shows the contact resistance (against GDL) with respect to the fluoride ion concentration for hydrochloric acid treatment and nitric acid treatment. Fig. 3B shows the contact resistance (against the separator) with respect to the fluoride ion concentration for hydrochloric acid treatment and nitric acid treatment.

[0055] As shown in Fig. 1B and Fig. 3A, in any case of sulfuric acid, hydrochloric acid, and nitric acid as the acidic solution, the contact resistance against GDL decreased compared to before treatment. Here, the effect of reducing the contact resistance was greater for sulfuric acid and hydrochloric acid than for nitric acid. Also, as shown in Fig. 2B and Fig. 3B, in any case of sulfuric acid, hydrochloric acid, and nitric acid as the acidic solution, the contact resistance against the separator decreased compared to before treatment. Here, the effect of reducing the contact resistance was greater for sulfuric acid than for hydrochloric acid and nitric acid.

[0056] <XPS surface elemental analysis> The elemental composition of the passivation film on the surface of a SUS304 separator treated under the pickling conditions of the present invention was measured by X-ray photoelectron spectroscopy (XPS). The pickling treatment was carried out as described above regarding the investigation of pickling conditions. The pickling conditions were pH 1, fluoride ion concentration of 100 ppm, 80°C, and 60 minutes. XPS analysis was performed using an XPS instrument (ULVAC; PHI5000 VersaProbeII) under the following conditions: X-ray source; AlKα monochromatic light, output 25W, voltage 15kV, irradiation area; φ100μm, analysis area; 1000×200μm, neutralization gun; ON state, pulse energy (wide; 187.85eV, narrow; 46.95-117.40eV), step size (wide; 0.4eV, narrow; 0.1eV), shift correction was performed with C1s; CC, CH, 284.8eV. Depth analysis was performed while etching with Ar monomer at a voltage of 3kV, irradiation area of ​​2×2mm, and etching speed of 9.3nm / min.

[0057] Table 1 and Figures 4A to 4C show the results of XPS surface elemental analysis. Figure 4A shows the XPS spectrum of Cr oxide. Figure 4B shows the XPS spectrum of Mn oxide. Figure 4C shows the XPS spectrum of Fe oxide. In Table 1 and Figures 4A to 4C, "pressed product" refers to an unmodified SUS304 separator.

[0058] [Table 1]

[0059] As shown in Table 1 and Figures 4A to 4C, the passivation film on the surface of the unmodified SUS304 separator was an Fe-rich passivation film. On the other hand, the passivation film on the surface of the SUS304 separator treated under the pickling conditions of the present invention was a Cr and Mn-rich passivation film.

Claims

1. A method for manufacturing a fuel cell separator, comprising immersing a stainless steel substrate molded into the shape of a separator in an acidic solution with a pH of 1 ± 0.2 and a fluoride ion concentration of 0.1 ppm or more at 80°C ± 5°C for 60 minutes or more to modify the surface of the stainless steel substrate, wherein the acidic solution is a sulfuric acid solution.

2. The method for manufacturing a fuel cell separator according to claim 1, wherein the acidic solution is a sulfuric acid solution having a fluoride ion concentration of 0.1 ppm to 5 ppm.

3. In the passivation film on the surface of the stainless steel substrate of the fuel cell separator, the following is determined by X-ray photoelectron spectroscopy (XPS): The ratio of Cr content (atomic%) to Fe content (atomic%) (Cr / Fe ratio) exceeds 1 when the pre-modification treatment is set to 1. The ratio of Mn content (atomic%) to Fe content (atomic%) (Mn / Fe ratio) is greater than 1 when the value before modification treatment is set to 1, and The ratio of the total content of Cr and Mn (atomic%) to the Fe content (atomic%) ((Cr+Mn) / Fe ratio) is greater than 1 when the pre-modification treatment is set to 1. A method for manufacturing a fuel cell separator according to claim 1 or 2.

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