Metal separator

Abstract

The present application relates to a metal separator and a manufacturing method therefor. According to the present application, the metal separator having excellent electrical conductivity and corrosion resistance and the manufacturing method therefor can be provided.

Description

metal separator

[0001] This application relates to a metal separator and a method for manufacturing the same.

[0002] Fuel cells used in hydrogen electric vehicles serve as a power source, generating electricity through the electrochemical reaction between reactant gases and a catalyst. Among the components used in fuel cells, the metal separator is a key component that collects and transmits the electricity generated by the electrochemical reaction.

[0003] Metal separators are typically made of materials with inherently high electrical conductivity, such as stainless steel or polymer composites. However, when exposed to the high temperature and humidity of a fuel cell for extended periods, these metal separators experience accelerated metal corrosion. Metal oxides formed on their surface act as electrical insulators, reducing electrical conductivity and / or catalyst contamination, which can reduce fuel cell performance.

[0004] In particular, the use of titanium metal separators can secure high potential and long-term corrosion resistance compared to stainless steel, but if proper surface modification treatment is not performed, impurities such as carbides (TiC), nitrides (TiN), and / or non-uniform oxides (TiO2) remain on the surface of the base material. These impurities can have a negative effect on the formation of a thin and dense passive film during the heat treatment process for forming the passive film. In addition, the impurities are easily oxidized during the heat treatment process or the fuel cell operating environment, which causes problems such as a decrease in the electrical conductivity and corrosion resistance of the metal separator and a decrease in the performance of the fuel cell.

[0005] Therefore, to solve these problems, a metal separator having excellent electrical conductivity and corrosion resistance and a method for manufacturing the same are required.

[0006] The object of the present application is to provide a metal separator having excellent electrical conductivity and corrosion resistance and a method for manufacturing the same.

[0007] In order to solve the above problem, the metal separator of the present application comprises a base material; and a passive film formed on the surface of the base material, wherein the passive film includes oxygen and titanium in which the atomic ratio of oxygen to titanium (O / Ti) is 0.2 or more and 0.6 or less.

[0008] The content of oxygen contained in the above passive film may be 10 at% or more and 40 at% or less.

[0009] Additionally, the content of titanium included in the above passive film may be 60 at% or more and 90 at% or less.

[0010] In addition, the metal separator of the present application comprises a base material including a plurality of protrusions formed on a surface; and a passive film formed on the surface of the base material, wherein the surface roughness of the base material is 150 nm or more and 250 nm or less, and the spacing between the plurality of protrusions is 700 nm or more and 900 nm or less.

[0011] In addition, the metal separator of the present application comprises a base material including a plurality of protrusions formed on a surface; and a passive film formed on the surface of the base material, wherein the protrusions have an average angle of 35° or more and 80° or less, and an average width of the protrusions is 0.1 ㎛. 2 Above 0.4 ㎛ 2 Below is the text.

[0012] In addition, the metal separator of the present application comprises a base material; and a passive film formed on the surface of the base material, wherein the passive film has a water contact angle of 1° or more and 10° or less.

[0013] Additionally, the passive film may have a thickness of 5 nm or more and 40 nm or less.

[0014] In addition, the above-mentioned passive film may be a layer formed by immersing the surface of the base material in a surface modification solution containing ammonium fluoride and ammonium difluoride to modify the surface, and then heat-treating the surface of the base material.

[0015] Additionally, the parent material may include titanium or a titanium alloy.

[0016] In addition, the metal separator has a contact resistance of 20 mΩ·cm 2 It could be as follows:

[0017] In addition, the metal separator has a current density of 10 ㎂ / cm 2 It could be as follows:

[0018] In addition, the method for manufacturing a metal separator of the present application includes a surface modification step performed by immersing the surface of a base material in a surface modification solution containing ammonium fluoride and ammonium bifluoride; and a heat treatment step of heat-treating the base material that has undergone the surface modification step to form a passive film on the surface of the base material, wherein the heat treatment step is performed at a temperature of 210°C or higher and 550°C or lower in an air atmosphere for 30 seconds or longer and less than 1800 seconds.

[0019] In addition, the method for manufacturing the metal separator may further include an acetone washing step of immersing the base material in acetone before performing the surface modification step and then washing it by applying ultrasonic waves for 1 minute or more and 10 minutes or less.

[0020] Additionally, the surface modification solution may contain 0.1 wt% or more and 10 wt% or less of ammonium fluoride and 0.1 wt% or more and 10 wt% or less of ammonium bifluoride.

[0021] In addition, the surface modification solution may further include at least one selected from sulfuric acid, hydrochloric acid, nitric acid, ammonium persulfate, and hydrofluoric acid, each in an amount of 0.1 wt% to 10 wt%.

[0022] Additionally, the surface modification step can be performed by immersing the base material in the surface modification solution at a temperature of 20°C or higher and 80°C or lower for 10 seconds or longer and 600 seconds or shorter.

[0023] According to the present application, a metal separator having excellent electrical conductivity and corrosion resistance and a method for manufacturing the same can be provided.

[0024] FIG. 1 is a drawing illustrating a metal separator according to one embodiment of the present application.

[0025] FIG. 2 is a drawing showing an example of a base material of a metal separator according to one embodiment of the present application.

[0026] FIG. 3 is an exemplary drawing illustrating a water contact angle in a state where a passive film of a metal separator according to one embodiment of the present application is arranged parallel to the floor.

[0027] Figures 4 and 5 are atomic force microscope (AFM) images measured on the surface of the base material of the metal separator manufactured in Example 2-3 and Comparative Example 2-1, respectively.

[0028] Figures 6 and 7 are scanning electron microscope (SEM) images measured on the surface of the base material of the metal separator manufactured in Example 2-3 and Comparative Example 2-1, respectively.

[0029] Figures 8 to 10 are transmission electron microscope (TEM) images of cross-sections along the thickness direction of the metal separators manufactured in Examples 3-1, 3-3, and Comparative Example 3-3, respectively.

[0030] Figures 11 to 17 are images showing the results of measuring the water contact angle on the surface of the base material before heat treatment in Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-3, respectively.

[0031] Figures 18 to 24 are images showing the results of measuring the water contact angle on the surface of the passive film after heat treatment in Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-3, respectively.

[0032] Hereinafter, the metal separator of the present application will be described with reference to the attached drawings. The attached drawings are exemplary, and the metal separator of the present application is not limited to the attached drawings.

[0033] FIG. 1 is a drawing exemplarily showing a metal separator according to one embodiment of the present application. As shown in FIG. 1, the metal separator of the present application includes a base material (10) and a passive film (20) formed on the surface of the base material (10). According to the metal separator of the present application, excellent electrical conductivity and corrosion resistance can be achieved. As used herein, the term "surface" means a surface located at the outermost surface. In addition, as used herein, the term "formed on the surface" means formed on the inner side of the surface. In addition, as used herein, the term "formed on the surface" means formed on the outer side of the surface.

[0034] The above-mentioned parent material (10) is a material used for a metal separator for a fuel cell.

[0035] In one example, the base material (10) may include titanium or a titanium alloy. Specifically, Grade 1 or the like may be used as the base material (10). By including the aforementioned components, the base material (10) can secure high potential and long-term corrosion resistance compared to stainless steel.

[0036] In another example, the base material (10) may include a plurality of protrusions (11) formed on the surface. The plurality of protrusions (11) formed on the surface of the base material (10) may be formed through surface modification as described below. By including the plurality of protrusions (11) formed on the surface of the base material (10), the contact area increases, thereby preventing a decrease in electrical conductivity. In the present specification, the term "plurality" means two or more, and the upper limit is not particularly limited unless the upper limit is specifically limited.

[0037] In one example, the base material (10) may have a surface roughness of 150 nm or more and 250 nm or less, and the spacing between the plurality of protrusions (11) may be 700 nm or more and 900 nm or less. Specifically, the base material (10) may have a surface roughness of 151 nm or more and 245 nm or less, 152 nm or more and 240 nm or less, or 153 nm or more and 236 nm or less, and the spacing between the plurality of protrusions (11) may be 700 nm or more and less than 900 nm, 700 nm or more and less than 850 nm, or 700 nm or more and 800 nm or less. Since the base material (10) has a surface roughness and a spacing between the plurality of protrusions that satisfy the above-described ranges, the metal separator may secure excellent electrical conductivity and corrosion resistance. The surface roughness refers to the arithmetic average roughness (Ra) of the protrusions (11). In addition, the spacing between the plurality of protrusions (11) means the average spacing (RSm) between the peaks or valleys of the protrusions (11) in the plurality of protrusions (11).

[0038] Fig. 2 is a drawing showing an example of a base material of a metal separator according to one embodiment of the present application. As shown in Fig. 2, the protrusion (11) has an average angle (θ1) of 35° or more, and an average width (A) of the protrusion is 0.1 ㎛. 2 It may be ideal. Specifically, the above protrusion (11) has an average angle (θ1) of the protrusion of 40° or more or 45° or more, and an average area (A) of the protrusion of 0.14 ㎛. 2 or more than 0.18 ㎛ 2 It may be ideal. In addition, the upper limit of the average angle (θ1) of the protrusion (11) may be 80° or less, and specifically, 75° or less or 70° or less. In addition, the upper limit of the average area (A) of the protrusion (11) may be 0.4 ㎛. 2 May be less than, specifically, 0.35 ㎛ 2It may be as follows. The above protrusion (11) can ensure excellent electrical conductivity and corrosion resistance of the metal separator by satisfying the above-mentioned ranges of the average angle (θ1) of the protrusion and the average area (A) of the protrusion. In this specification, the term “angle (θ1) of the protrusion” means the angle formed by the base (B), which is an imaginary straight line drawn in a direction parallel to the base material (10) (a direction perpendicular to the thickness direction of the base material (10)) at the point where the valley of the protrusion is, and the tangent (C) at the point where the valley of the protrusion is. That is, when the base (B) and the protrusion form an isosceles triangle as in Fig. 2, the angle (θ1) of the protrusion means the base angle. In addition, the term "area of ​​a protrusion (A)" in this specification means the area of ​​a single protrusion, which is the area formed by an imaginary line connecting the point where the protrusion becomes the valley and the point where the other valley is formed in a transmission electron microscope (TEM) image of an arbitrary cross-section of a parent material (10). That is, as in Fig. 2, when the base (B) and the protrusion form an isosceles triangle, the imaginary line connecting the point where the protrusion becomes the valley and the point where the other valley is formed becomes the base (B), and the area (A) means the area of ​​the isosceles triangle.

[0039] The above-mentioned base material (10) may have a thickness of 0.05 mm to 0.5 mm, and specifically, may have a thickness of 0.08 mm to 0.3 mm or 0.1 mm to 0.2 mm. In this case, the thickness of the above-mentioned base material (10) means the maximum length between one surface and the surface facing it.

[0040] The above-mentioned passive film (20) is a film formed on the surface of the above-mentioned base material (10) to improve the corrosion resistance of the above-mentioned metal separator, and is formed on the surface of the above-mentioned base material (10).

[0041] The above-described passive film (20) may include oxygen and titanium in which the atomic ratio of oxygen to titanium (O / Ti) is 0.2 or more and 0.6 or less. Specifically, the oxygen and titanium included in the passive film (20) may have an atomic ratio of oxygen to titanium (O / Ti) of 0.23 or more and 0.48 or less, or 0.25 or more and 0.46 or less. At this time, the atomic ratio of oxygen to titanium may be uniform at any point measured throughout the passive film (20). When the atomic ratio of oxygen to titanium (O / Ti) within the passive film (20) satisfies the above-described range, the metal separator may secure excellent electrical conductivity and corrosion resistance. In contrast, when the atomic ratio of oxygen to titanium (O / Ti) in the passive film (20) is less than the lower limit of the aforementioned range, a dense passive film of an appropriate thickness is not formed, so corrosion resistance cannot be secured. When the atomic ratio of oxygen to titanium (O / Ti) in the passive film (20) exceeds the upper limit of the aforementioned range, a thick passive film is formed, so that the target electrical conductivity cannot be secured. When the impurities on the surface of the base material (10) are not sufficiently removed when the passive film (20) is formed, the impurities may be oxidized during heat treatment, so that the atomic ratio of oxygen to titanium (O / Ti) may exceed the aforementioned range, and in this case, the electrical conductivity of the metal separator may deteriorate. In addition, even when the thickness of the passive film is thick, such as due to harsh heat treatment conditions, the atomic ratio of oxygen to titanium (O / Ti) may exceed the aforementioned range, and in this case, the electrical conductivity of the metal separator may deteriorate. The atomic number of oxygen and titanium in the above-mentioned passive film (20) can be measured using energy dispersive X-ray spectroscopy (EDS) equipment.

[0042] In one example, the content of oxygen included in the passive film (20) may be 10 at% or more and 40 at% or less. Specifically, the content of oxygen included in the passive film (20) may be 15 at% or more and 36 at% or less or 20 at% or more and 32 at% or less. When a dense passive film of an appropriate thickness is formed, the content of oxygen included in the passive film (20) satisfies the above-described range, thereby ensuring corrosion resistance.

[0043] In addition, the content of titanium included in the passive film (20) may be 60 at% or more and 90 at% or less. Specifically, the content of titanium included in the passive film (20) may be 64 at% or more and 85 at% or less or 68 at% or more and 80 at% or less.

[0044] Additionally, the passive film (20) may not contain carbon. If the passive film (20) contains carbon, the carbon may be oxidized in the operating environment of the fuel cell, thereby reducing conductivity.

[0045] For example, the passive film (20) may have a thickness of 5 nm or more and 40 nm or less. When the thickness of the passive film (20) satisfies the above-mentioned range, the electrical conductivity and corrosion resistance of the metal separator can be improved. In contrast, when the thickness of the passive film (20) is less than the lower limit of the above-mentioned range, the electrical conductivity of the metal separator can be improved, but the corrosion resistance of the metal separator can be reduced. In addition, when the thickness of the passive film (20) exceeds the upper limit of the above-mentioned range, the corrosion resistance of the metal separator can be improved, but the contact resistance increases excessively, making it impossible to secure the target electrical conductivity of the metal separator.

[0046] FIG. 3 is an exemplary drawing illustrating a water contact angle in a state where a passive film of a metal separator according to an embodiment of the present application is arranged parallel to the floor. As shown in FIG. 3, the passive film (20) may have a water contact angle (θ3) of 1° to 10°. Specifically, the passive film (20) may have a water contact angle (θ3) of 1.5° to 9.9° or 1.9° to 9.8°. Since the water contact angle (θ3) of the passive film (20) satisfies the above-described range, not only can the metal separator secure excellent hydrophilicity, but also can secure excellent electrical conductivity and corrosion resistance.

[0047] The above-mentioned passive film (20) may be a layer formed by immersing the surface of the base material (10) in a surface modification solution containing ammonium fluoride and ammonium bifluoride to modify the surface, and then heat-treating the surface of the base material (10). A specific description of the method for manufacturing the above-mentioned passive film (20) is the same as that described in the method for manufacturing a metal separator below, and therefore will be omitted.

[0048] The above metal separator has a contact resistance of 20 mΩ·cm 2 It may be as follows. Specifically, the contact resistance of the metal separator is 19 mΩ·cm. 2 Less than or equal to 18 mΩ·cm 2 It may be below. The metal separator may have excellent electrical conductivity as the contact resistance satisfies the above-mentioned range. In addition, the lower the contact resistance of the metal separator, the better the electrical conductivity, and therefore, the lower limit is not particularly limited, but, for example, 3 mΩ·cm. 2 It can be more than, specifically, 5 mΩ·cm 2 or more than 10 mΩ·cm 2 It could be strange.

[0049] In addition, the metal separator has a current density of 10 ㎂ / cm 2It may be less than or equal to. Specifically, the current density of the metal separator is 5 ㎂ / cm 2 Below, 3 ㎂ / cm 2 Less than or equal to 1 ㎂ / cm 2 It may be below. The metal separator may have excellent corrosion resistance as the current density satisfies the above-mentioned range. In addition, the lower the current density of the metal separator, the better the corrosion resistance, and therefore, the lower limit is not particularly limited, but, for example, 0.1 ㎂ / cm 2 It could be strange.

[0050] The present application also relates to a method for manufacturing a metal separator. The method for manufacturing the metal separator relates to a method for manufacturing the aforementioned metal separator. Since the specific details of the metal separator described below are equally applicable to the metal separator described above, they will be omitted.

[0051] The method for manufacturing a metal separator of the present application comprises a surface modification step and a heat treatment step. According to the method for manufacturing a metal separator of the present application, a metal separator having excellent electrical conductivity and corrosion resistance can be manufactured.

[0052] The above surface modification step is a step for removing impurities from the surface of the base material, and is performed by immersing the surface of the base material in a surface modification solution containing ammonium fluoride and ammonium difluoride. Through this step, a plurality of protrusions can be formed on the surface of the base material.

[0053] Since the above-mentioned base material can be used as the base material described in the above-mentioned metal separator, a detailed description of the above-mentioned base material will be omitted.

[0054] The surface modification solution may contain 0.1 wt% or more and 10 wt% or less of ammonium fluoride and 0.1 wt% or more and 10 wt% or less of ammonium bifluoride. Specifically, the surface modification solution may contain 0.3 wt% or more and 5 wt% or less of ammonium fluoride, or 0.5 wt% or more and 3 wt% or less of ammonium bifluoride, and 0.1 wt% or more and 5 wt% or less, 0.1 wt% or more and 3 wt% or less, 0.1 wt% or more and 1 wt% or less, or 0.1 wt% or more and 0.5 wt% or less of ammonium bifluoride. The surface modification solution contains ammonium fluoride and ammonium bifluoride satisfying the above-described content ranges, thereby removing impurities through surface modification, thereby preventing a decrease in electrical conductivity due to oxidation of impurities during heat treatment, and furthermore, forming a plurality of protrusions on the surface of the base material to obtain an effect of improving electrical conductivity by increasing the contact area.

[0055] In one example, the surface modification solution may further include at least one selected from sulfuric acid, hydrochloric acid, nitric acid, ammonium persulfate, and hydrofluoric acid, each in an amount of 0.1 wt% to 10 wt%. Specifically, the surface modification solution may further include at least one selected from sulfuric acid, hydrochloric acid, nitric acid, ammonium persulfate, and hydrofluoric acid, each in an amount of 0.3 wt% to 5 wt% or 0.5 wt% to 3 wt%. By including the above-described components in the above-described amounts, the impurity removal efficiency may be improved during surface modification.

[0056] In another example, the surface modification solution may further include a surfactant and / or an oxidizing agent as needed.

[0057] The above surface modification step can be performed by immersing the base material in the surface modification solution at a temperature of 20°C or more and 80°C or less for a period of 10 seconds or more and 600 seconds or less. Specifically, the surface modification step can be performed by immersing the base material in the surface modification solution at a temperature of 40°C or more and 80°C or less or at 60°C or more and 80°C or less for a period of 10 seconds or more and 600 seconds or less. The surface modification step is performed under the above-described temperature and time conditions, thereby removing impurities through surface modification, and thereby preventing a decrease in electrical conductivity due to oxidation of impurities during heat treatment, and further, forming a plurality of protrusions on the surface of the base material can obtain an effect of improving electrical conductivity by increasing the contact area.

[0058] For example, the above-mentioned base material may have a surface roughness of 150 nm or more and 250 nm or less, and the spacing between the plurality of protrusions may be 700 nm or more and 900 nm or less. Since a specific description of the surface roughness of the above-mentioned base material and the spacing between the plurality of protrusions are the same as those described in the metal separator, they will be omitted.

[0059] In addition, the average angle of the protrusions is 35° or more, and the average width of the protrusions is 0.1 ㎛. 2 It may be ideal. Since the specific description of the angle and width of the above protrusion is the same as that described in the above metal separator, it will be omitted.

[0060] In addition, the base material before heat treatment may have a water contact angle of 20° to 30°. Specifically, the base material before heat treatment may have a water contact angle of 22° to 29.8°, 24° to 29.6°, or 25° to 29.4°. By satisfying the water contact angle range described above, the base material before heat treatment can not only secure excellent hydrophilicity, but also enable the metal separator to be manufactured to have excellent electrical conductivity and corrosion resistance.

[0061] In one example, the method for manufacturing the metal separator may further include a distilled water washing step after performing the surface modification step. The distilled water washing step is a step for removing residual organic substances remaining on the surface of the base material that has undergone the surface modification step, and the washing may be performed by immersing the base material in distilled water and then applying ultrasonic waves for 1 minute or more and 10 minutes or less. The method for manufacturing the metal separator may further include a distilled water washing step under the conditions described above, thereby removing residual impurities and organic substances on the surface of the base material and forming a thin and dense passive film through the heat treatment step, thereby preventing a decrease in electrical conductivity and ensuring corrosion resistance.

[0062] The above heat treatment step is a step for improving the corrosion resistance of the metal separator by forming a passive film on the surface of the base material, and is performed by heat treating the base material that has undergone the surface modification step.

[0063] In one example, the heat treatment step may be performed in an air atmosphere at a temperature of 210°C or more and less than 550°C for 30 seconds or more and less than 1800 seconds. Specifically, the heat treatment step may be performed in an air atmosphere at a temperature of 230°C or more and less than 530°C or 250°C or more and less than 500°C for 30 seconds or more and less than 1500 seconds or 30 seconds or more and less than 1200 seconds. By performing the heat treatment step under the above-described temperature and time conditions, a thin passive film may be formed on a base material having a plurality of protrusions formed on the surface, thereby ensuring electrical conductivity of the metal separator manufactured, and improving corrosion resistance.

[0064] The above-mentioned passive film may include oxygen and titanium in which the atomic ratio of oxygen to titanium (O / Ti) is 0.2 or more and 0.6 or less. A specific description of the atomic ratio of oxygen to titanium (O / Ti) in the above-mentioned passive film is the same as that described in the above-mentioned metal separator, and therefore will be omitted.

[0065] For example, the above-mentioned passive film may have a thickness of 5 nm or more and 40 nm or less.

[0066] In addition, the passive film may have a water contact angle of 1° or more and 10° or less. A detailed description of the water contact angle of the passive film is the same as that described in the metal separator, and thus will be omitted.

[0067]

[0068] Hereinafter, the present application will be described in more detail through examples according to the present application and comparative examples not according to the present application, but the scope of the present application is not limited by the examples presented below.

[0069]

[0070] Experimental Example 1. Experimental evaluation of physical properties according to the atomic ratio of oxygen to titanium (O / Ti) in the passive film.

[0071] Example 1-1

[0072] Manufacturing of metal separators

[0073] A 0.1 mm thick titanium substrate (Grade 1) was prepared. At this time, impurities such as carbide (TiC), nitride (TiN), and oxide (TiO2) remained on the surface of the substrate.

[0074] Thereafter, the surface of the above-mentioned base material was immersed in a surface modification solution shown in Table 1 below at 60°C for 300 seconds to remove impurities on the surface of the base material and form a plurality of protrusions. Thereafter, the surface-modified base material was immersed in distilled water and then washed by applying ultrasonic waves for 5 minutes to remove any residual organic matter remaining on the surface of the base material.

[0075] Thereafter, the surface-modified base material was heat-treated in an air atmosphere at the temperature and time shown in Table 1 below to form a passive film on the surface of the base material, thereby manufacturing a metal separator.

[0076]

[0077] Examples 1-2 to 1-5 and Comparative Examples 1-2 to 1-8

[0078] Manufacturing of metal separators

[0079] A metal separator was manufactured in the same manner as in Example 1-1, except that the surface modification solution and the temperature and time for performing the heat treatment were changed as shown in Table 1 below.

[0080]

[0081] Comparative Example 1-1

[0082] Manufacturing of metal separators

[0083] A metal separator was manufactured in the same manner as Example 1-1, except that the surface of the base material was heat-treated at the temperature and time shown in Table 1 below, without performing surface modification and distilled water washing.

[0084] Surface modification solution heat treatment passivation film thickness (nm) Ammonium fluoride (wt%) Ammonium difluoride (wt%) Temperature (℃) Time (min) Example 1-10.500.103001010~15 Example 1-21.000.205001025~30 Example 1-31.250.253501015~25 Example 1-41.250.255001030~35 Example 1-51.500.302501010~15 Comparative example 1-1--50010115~150 Comparative example 1-20.100.025001040~55 Comparative example 1-30.250.055001035~50 Comparative example 1-41.250.255501075~100Comparative example 1-51.250.2560010165~200Comparative example 1-61.2505001040~50Comparative example 1-700.255001045~65Comparative example 1-80.100.02150105~10

[0085]

[0086] Evaluation Example 1. Analysis and evaluation of the surface components of the passive film

[0087] Using energy dispersive X-ray spectroscopy (EDS) equipment, the elements contained in the surface of the passive film in the metal separators manufactured in each of the examples and comparative examples were analyzed, and the results are shown in Table 2 below.

[0088]

[0089] Evaluation Example 2. Contact Resistance Evaluation

[0090] After applying a contact pressure of 1.0 MPa to the metal separator manufactured in each of the examples and comparative examples, the contact resistance was measured using a Hioki ammeter, and the results are shown in Table 2 below.

[0091]

[0092] Evaluation Example 3. Current Density Evaluation

[0093] The current density for the metal separators manufactured in each of the examples and comparative examples was measured by performing a potentiodynamic polarization test in the range of -0.25 V vs. OCP (Open circuit potential) to 1.6 V under a simulated environment of a PEMFC (Polymer Electrolyte Membrane Fuel Cell), and the results are shown in Table 2 below. Specifically, the current density was measured by loading the metal separators manufactured in each of the examples and comparative examples into a solution of 0.1 N H2SO4 + 2 ppm HF + 3000 ppm H2O2 at 80°C, and then applying a current density of 0.6 V. SCE was measured in .

[0094] Surface element of passive film (at%) Contact resistance (mΩ·cm) 2 )Current density (㎂ / cm 2)CarbonOxygenTitaniumO / TiExample 1-1021.8678.140.2814.50.63Example 1-2024.2175.790.3117.20.66Example 1-3020.3979.610.2516.10.45Example 1-4031.7468.260.4615.40.47Example 1-5027.6672.340.3817.90.78Comparative Example 1-11.9740.0857.950.698625.014.2Comparative Example 1-23.7542.9353.320.80954.30.17Comparative Example 1-32.9552.7944.261.1948.80.25Comparative example 1-4048.9951.010.96154.50.49Comparative example 1-5058.9141.091.431019.10.37Comparative example 1-62.2549.3548.401.01264.52.60Comparative example 1-72.6248.7348.651.00311.61.85Comparative example 1-82.1511.9685.760.1415.538.1

[0095] As shown in Table 2 above, the metal separators manufactured in each of Examples 1-1 to 1-5, unlike the metal separators manufactured in each of Comparative Examples 1-1 to 1-8, were confirmed to have low current density and contact resistance at the same time because the oxygen and titanium included in the surface of the passive film satisfied a specific atomic ratio of oxygen to titanium (O / Ti) range, and thus, it was confirmed that excellent electrical conductivity and corrosion resistance could be secured at the same time.

[0096]

[0097] Experimental Example 2. Experiment to evaluate physical properties according to the surface roughness of the base material and the spacing between multiple protrusions.

[0098] Example 2-1

[0099] Manufacturing of metal separators

[0100] A 0.1 mm thick titanium substrate (Grade 1) was prepared. At this time, impurities such as carbide (TiC), nitride (TiN), and oxide (TiO2) remained on the surface of the substrate.

[0101] Thereafter, the surface of the above-mentioned base material was immersed in a surface modification solution shown in Table 3 below at 60°C for 300 seconds to remove impurities on the surface of the base material and form multiple protrusions. Thereafter, the surface-modified base material was immersed in distilled water and then washed by applying ultrasonic waves for 5 minutes, thereby removing any residual organic matter remaining on the surface of the base material.

[0102] Afterwards, the surface-modified base material was heat-treated in an air atmosphere at the temperature and time shown in Table 3 below to form a passive film on the surface of the base material, thereby manufacturing a metal separator.

[0103]

[0104] Examples 2-2 to 2-4 and Comparative Examples 2-3 to 2-6

[0105] Manufacturing of metal separators

[0106] A metal separator was manufactured in the same manner as in Example 2-1, except that the surface modification solution and the temperature and time for performing the heat treatment were changed as shown in Table 3 below.

[0107]

[0108] Comparative Example 2-1

[0109] Manufacturing of metal separators

[0110] A metal separator was manufactured in the same manner as in Example 2-1, except that surface modification, distilled water washing, and heat treatment were not performed.

[0111]

[0112] Comparative Example 2-2

[0113] Manufacturing of metal separators

[0114] A metal separator was manufactured in the same manner as in Example 2-1, except that the surface of the base material was heat-treated at the temperature and time shown in Table 3 below, without performing surface modification and distilled water washing.

[0115] Surface modification solution heat treatment passivation film thickness (nm) Ammonium fluoride (wt%) Ammonium difluoride (wt%) Temperature (℃) Time (min) Example 2-10.850.175001025~30 Example 2-21.000.205001025~30 Example 2-31.250.253501015~25 Example 2-41.250.255001030~35 Comparative example 2-1----2~4 Comparative example 2-2--50010115~150 Comparative example 2-30.100.025001040~55 Comparative example 2-40.400.085001035~45 Comparative example 2-51.2505001040~50Comparative example 2-600.255001045~65

[0116]

[0117] Evaluation Example 1. Evaluation of surface roughness of the parent material and spacing between multiple protrusions

[0118] Using a 3D shape measuring device (VR-6000, Keyence) with a resolution of 0.1 ㎛, the surface roughness of the base material of the metal separator manufactured in each of the examples and comparative examples and the spacing between multiple protrusions were measured, and the average results were calculated, and are shown in Table 4 below. In particular, for comparison, the surfaces of the base materials of the metal separators manufactured in each of the examples 2-3 and comparative examples 2-1 were photographed using an atomic force microscope (AFM) and a scanning electron microscope (SEM), and the results are shown in FIGS. 4 to 7, respectively.

[0119]

[0120] Evaluation Example 2. Contact Resistance Evaluation

[0121] After applying a contact pressure of 1.0 MPa to the metal separator manufactured in each of the examples and comparative examples, the contact resistance was measured using a Hioki ammeter, and the results are shown in Table 4 below.

[0122]

[0123] Evaluation Example 3. Current Density Evaluation

[0124] The current density for the metal separators manufactured in each of the examples and comparative examples was measured by performing a potentiodynamic polarization test in the range of -0.25 V vs. OCP (Open circuit potential) to 1.6 V under a simulated environment of a PEMFC (Polymer Electrolyte Membrane Fuel Cell), and the results are shown in Table 4 below. Specifically, the current density was measured by loading the metal separators manufactured in each of the examples and comparative examples into a solution of 0.1 N H2SO4 + 2 ppm HF + 3000 ppm H2O2 at 80°C, and then applying a current density of 0.6 V. SCE was measured in .

[0125] Surface roughness (nm) Spacing between multiple protrusions (nm) Contact resistance (mΩ·cm) 2 )Current density (㎂ / cm 2 ) Example 2-115380016.30.22 Example 2-217775015.80.28 Example 2-320870015.40.47 Example 2-423670014.60.20 Comparative Example 2-113 No protrusion 1447.86 Comparative Example 2-213 No protrusion 862514.2 Comparative Example 2-333 No protrusion 954.30.17 Comparative Example 2-498150035.30.17 Comparative Example 2-594900264.52.6 Comparative Example 2-686850311.61.85

[0126] As shown in Table 4 above, the metal separators manufactured in each of Examples 2-1 to 2-4, unlike the metal separators manufactured in each of Comparative Examples 2-1 to 2-6, had surface roughness of the base material and spacing between multiple protrusions that satisfied specific ranges, thereby confirming that they simultaneously had low current density and contact resistance, and thus, it was confirmed that excellent electrical conductivity and corrosion resistance could be secured simultaneously.

[0127]

[0128] Experimental Example 3. Experiment to evaluate physical properties according to the average angle of the protrusion and the average area of ​​the protrusion.

[0129] Example 3-1

[0130] Manufacturing of metal separators

[0131] A 0.1 mm thick titanium substrate (Grade 1) was prepared. At this time, impurities such as carbide (TiC), nitride (TiN), and oxide (TiO2) remained on the surface of the substrate.

[0132] Thereafter, the surface of the above-mentioned base material was immersed in a surface modification solution shown in Table 5 below at 60°C for 300 seconds to remove impurities on the surface of the base material and form multiple protrusions. Thereafter, the surface-modified base material was immersed in distilled water and then washed by applying ultrasonic waves for 5 minutes to remove any residual organic matter remaining on the surface of the base material.

[0133] Afterwards, the surface-modified base material was heat-treated in an air atmosphere at the temperature and time shown in Table 5 below to form a passive film on the surface of the base material, thereby manufacturing a metal separator.

[0134]

[0135] Examples 3-2 to 3-3 and Comparative Examples 3-3 to 3-9

[0136] Manufacturing of metal separators

[0137] A metal separator was manufactured in the same manner as in Example 3-1, except that the surface modification solution and the temperature and time for performing the heat treatment were changed as shown in Table 5 below.

[0138]

[0139] Comparative Example 3-1

[0140] Manufacturing of metal separators

[0141] A metal separator was manufactured in the same manner as in Example 3-1, except that surface modification, distilled water washing, and heat treatment were not performed.

[0142]

[0143] Comparative Example 3-2

[0144] Manufacturing of metal separators

[0145] A metal separator was manufactured in the same manner as in Example 3-1, except that the surface of the base material was heat-treated at the temperature and time shown in Table 5 below without performing surface modification and distilled water washing.

[0146] Surface modification solution heat treatment passivation film thickness (nm) Ammonium fluoride (wt%) Ammonium difluoride (wt%) Temperature (℃) Time (min) Example 3-10.850.175001025~30 Example 3-21.000.205001025~30 Example 3-31.250.255001030~35 Comparative example 3-1----2~5 Comparative example 3-2--50010115~150 Comparative example 3-30.100.025001040~55 Comparative example 3-40.250.055001035~50 Comparative example 3-50.050.255001045~55 Comparative example 3-612.52.55001020~30Comparative example 3-72.512.55001015~25Comparative example 3-81.0005001050~60Comparative example 3-900.205001050~65

[0147]

[0148] Evaluation Example 1. Evaluation of the average angle and average area of ​​the protrusions

[0149] Using a transmission electron microscope (TEM), cross sections along the thickness direction of the metal separators manufactured in each of the examples and comparative examples were photographed, and then, as shown in Fig. 3, the angle (θ1), the vertex angle (θ2), and the area (A) of the protrusions were measured, and the average results calculated are shown in Table 6 below. In particular, for comparison, cross sections along the thickness direction of the metal separators manufactured in each of Examples 3-1, 3-3, and Comparative Example 3-3 were photographed using a transmission electron microscope (TEM), and the results are shown in Figs. 8 to 10, respectively.

[0150]

[0151] Evaluation Example 2. Contact Resistance Evaluation

[0152] After applying a contact pressure of 1.0 MPa to the metal separator manufactured in each of the examples and comparative examples, the contact resistance was measured using a Hioki ammeter, and the results are shown in Table 6 below.

[0153]

[0154] Evaluation Example 3. Current Density Evaluation

[0155] The current density for the metal separators manufactured in each of the examples and comparative examples was measured by performing a potentiodynamic polarization test in the range of -0.25 V vs. OCP (Open circuit potential) to 1.6 V under a simulated environment of a PEMFC (Polymer Electrolyte Membrane Fuel Cell), and the results are shown in Table 6 below. Specifically, the current density was measured by loading the metal separators manufactured in each of the examples and comparative examples into a solution of 0.1 N H2SO4 + 2 ppm HF + 3000 ppm H2O2 at 80°C, and then applying a current density of 0.6 V. SCE was measured in .

[0156] Average angle of protrusion (θ1) (°) Average apex angle of protrusion (θ2) (°) Average width of one protrusion (㎛) 2 )Contact resistance (mΩ·cm) 2 )Current density (㎂ / cm 2 ) Example 3-145.12900.19616.30.22 Example 3-262.5752.580.25815.80.28 Example 3-368.4838.550.33215.40.47 Comparative Example 3-10001447.86 Comparative Example 3-20008625.014.2 Comparative Example 3-3000954.30.17 Comparative Example 3-400048.80.47 Comparative Example 3-531.598.180.29430.20.67 Comparative Example 3-642.6394.220.03173.53.37 Comparative Example 3-7000124.58.6 Comparative Example 3-854.5670.800.05264.52.6Comparative example 3-958.4263.100.067311.61.85

[0157] As shown in Table 6 above, it was confirmed that the metal separators manufactured in each of Comparative Examples 3-1 to 3-4 and 3-7 did not form protrusions, and thus, like the metal separators manufactured in each of Examples 3-1 to 3-3, it was impossible to have both low current density and contact resistance at the same time. In addition, it was confirmed that the metal separators manufactured in each of Comparative Examples 3-5, 3-6, 3-8 and 3-9 did not have both the average angle of the protrusions and the average width of one protrusion within a specific range, and thus, like the metal separators manufactured in each of Examples 3-1 to 3-3, it was impossible to have both low current density and contact resistance at the same time. That is, it was confirmed that the metal separator manufactured in each of the above Examples 3-1 to 3-3 had both a low current density and a low contact resistance because the average angle of the protrusions and the average width of each protrusion both satisfied a specific range, and thus it was confirmed that excellent electrical conductivity and corrosion resistance could be secured simultaneously.

[0158]

[0159] Experimental Example 4. Experimental Evaluation of Physical Properties of Passive Films According to Water Contact Angle

[0160] Example 4-1

[0161] Manufacturing of metal separators

[0162] A 0.1 mm thick titanium substrate (Grade 1) was prepared. At this time, impurities such as carbide (TiC), nitride (TiN), and oxide (TiO2) remained on the surface of the substrate.

[0163] Thereafter, the surface of the above-mentioned base material was immersed in a surface modification solution shown in Table 7 below at 60°C for 300 seconds to remove impurities on the surface of the base material and form a plurality of protrusions. Thereafter, the surface-modified base material was immersed in distilled water and then washed by applying ultrasonic waves for 5 minutes, thereby removing any residual organic matter remaining on the surface of the base material.

[0164] Afterwards, the surface-modified base material was heat-treated in an air atmosphere at the temperature and time shown in Table 7 below to form a passive film on the surface of the base material, thereby manufacturing a metal separator.

[0165]

[0166] Examples 4-2 to 4-4 and Comparative Examples 4-2 to 4-8

[0167] Manufacturing of metal separators

[0168] A metal separator was manufactured in the same manner as in Example 4-1, except that the surface modification solution and the temperature and time for performing the heat treatment were changed as shown in Table 7 below.

[0169]

[0170] Comparative Example 4-1

[0171] Manufacturing of metal separators

[0172] A metal separator was manufactured in the same manner as Example 4-1, except that the surface of the base material was heat-treated at the temperature and time shown in Table 7 below, without performing surface modification and distilled water washing.

[0173] Surface modification solution heat treatment passivation film thickness (nm) Ammonium fluoride (wt%) Ammonium difluoride (wt%) Temperature (℃) Time (min) Example 4-10.850.175001025~30 Example 4-21.000.205001025~30 Example 4-31.250.255001030~35 Example 4-41.250.253501015~25 Comparative example 4-1--50010115~150 Comparative example 4-20.100.025001040~55 Comparative example 4-30.250.055001035~50 Comparative example 4-40.050.255001045~55 Comparative example 4-512.52.55001020~35Comparative example 4-62.512.55001015~25Comparative example 4-71.0005001050~60Comparative example 4-800.205001050~65

[0174]

[0175] Evaluation Example 1. Water Contact Angle Evaluation

[0176] When manufacturing metal separators in Examples and Comparative Examples using Phoenix 300, a water droplet was dropped on the surface of the base material before heat treatment and the passive film after heat treatment, and the contact angle generated according to the solid-liquid interfacial energy at that time was measured, and the results are shown in Table 8 below. At this time, since physicochemical reactions such as the solid surface dissolving into the liquid or the liquid seeping into the solid due to gravity may occur after some time after dropping the liquid droplet, the contact angle was measured immediately upon introduction to the surface. In particular, for comparison, the results of measuring the water contact angle on the surface of the base material before heat treatment in Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-3 are shown in FIGS. 11 to 17, respectively, and the results of measuring the water contact angle on the surface of the passive film after heat treatment in Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-3 are shown in FIGS. 18 to 24, respectively.

[0177]

[0178] Evaluation Example 2. Contact Resistance Evaluation

[0179] After applying a contact pressure of 1.0 MPa to the metal separator manufactured in each of the examples and comparative examples, the contact resistance was measured using a Hioki ammeter, and the results are shown in Table 8 below.

[0180]

[0181] Evaluation Example 3. Current Density Evaluation

[0182] The current density for the metal separators manufactured in each of the examples and comparative examples was measured by performing a potentiodynamic polarization test in the range of -0.25 V vs. OCP (Open circuit potential) to 1.6 V under a simulated environment of a PEMFC (Polymer Electrolyte Membrane Fuel Cell), and the results are shown in Table 8 below. Specifically, the current density was measured by loading the metal separators manufactured in each of the examples and comparative examples into a solution of 0.1 N H2SO4 + 2 ppm HF + 3000 ppm H2O2 at 80°C, and then applying a current density of 0.6 V. SCE was measured in .

[0183] Water contact angle (°) on the base material before heat treatment; Water contact angle (°) on the passive film after heat treatment; Contact resistance (mΩ·cm) 2 )Current density (㎂ / cm 2 ) Example 4-129.42.416.30.22 Example 4-225.72.415.80.28 Example 4-325.31.915.40.47 Example 4-425.39.814.60.20 Comparative Example 4-192.230.48625.014.2 Comparative Example 4-253.516.9954.30.17 Comparative Example 4-348.316.348.80.47 Comparative Example 4-439.510.630.20.67 Comparative Example 4-542.113.573.53.37 Comparative Example 4-641.913.8124.58.6 Comparative Example 4-751.216.9264.52.6Comparative example 4-847.315.9311.61.85

[0184] As shown in Table 8 above, the metal separators manufactured in each of Examples 4-1 to 4-4, unlike the metal separators manufactured in each of Comparative Examples 4-1 to 4-8, had water contact angles for the base material before heat treatment and water contact angles for the passive film after heat treatment both satisfying specific ranges, thereby confirming that they simultaneously had low current density and contact resistance, and thus confirmed that excellent electrical conductivity and corrosion resistance could be secured simultaneously.

[0185]

[0186] Experimental Example 5. Experimental Evaluation of Physical Properties According to Manufacturing Method

[0187] Example 5-1

[0188] Manufacturing of metal separators

[0189] A 0.1 mm thick titanium substrate (Grade 1) was prepared, and the prepared substrate was immersed in acetone and then washed by applying ultrasonic waves for 5 minutes to remove any residual organic matter remaining on the surface of the substrate. At this time, impurities such as carbide (TiC), nitride (TiN), and oxide (TiO2) remained on the surface of the substrate.

[0190] Thereafter, the surface of the above-mentioned base material was immersed in a surface modification solution shown in Table 9 below at 60°C for 300 seconds to remove impurities on the surface of the base material and form a plurality of protrusions. Thereafter, the surface-modified base material was immersed in distilled water and then washed by applying ultrasonic waves for 5 minutes, thereby removing any residual organic matter remaining on the surface of the base material.

[0191] Thereafter, the surface-modified base material was heat-treated in an air atmosphere at the temperature and time shown in Table 9 below to form a passive film on the surface of the base material, thereby manufacturing a metal separator.

[0192]

[0193] Examples 5-2 to 5-9 and Comparative Examples 5-2 to 5-7

[0194] Manufacturing of metal separators

[0195] A metal separator was manufactured in the same manner as in Example 5-1, except that the surface modification solution and the temperature and time for performing the heat treatment were changed as shown in Table 9 below.

[0196]

[0197] Comparative Example 5-1

[0198] Manufacturing of metal separators

[0199] A metal separator was manufactured in the same manner as in Example 5-1, except that heat treatment was not performed.

[0200]

[0201] Comparative examples 5-8 to 5-10

[0202] Manufacturing of metal separators

[0203] A metal separator was manufactured in the same manner as in Example 5-1, except that acetone washing was not performed and the surface modification solution and the temperature and time for performing the heat treatment were changed as shown in Table 9 below.

[0204] Surface modification solution heat treatment passivation film thickness (nm) Ammonium fluoride (wt%) Ammonium difluoride (wt%) Temperature (℃) Time (min) Example 5-11.250.252501010~15 Example 5-21.250.252502010~20 Example 5-31.250.253001015~20 Example 5-41.250.253002020~30 Example 5-51.250.254001025~35 Example 5-61.250.254002030~40 Example 5-71.250.25500110~20 Example 5-81.250.255001030~35 Example 5-91.250.255500.515~25Comparative example 5-11.250.25--2~5Comparative example 5-21.250.25100105~10Comparative example 5-31.250.25200105~15Comparative example 5-41.250.252006030~45Comparative example 5-51.250.254003035~50Comparative example 5-61.250.255006050~80Comparative example 5-71.250.256000.540~80Comparative example 5-81.250.252001015~25Comparative example 5-91.250.252006045~60Comparative example 5-101.250.256000.560~85

[0205]

[0206] Evaluation Example 1. Contact resistance evaluation

[0207] After applying a contact pressure of 1.0 MPa to the metal separator manufactured in each of the examples and comparative examples, the contact resistance was measured using a Hioki ammeter, and the results are shown in Table 10 below.

[0208]

[0209] Evaluation Example 2. Current Density Evaluation

[0210] The current density for the metal separators manufactured in each of the examples and comparative examples was measured by performing a potentiodynamic polarization test in the range of -0.25 V vs. OCP (Open circuit potential) to 1.6 V under a simulated environment of a PEMFC (Polymer Electrolyte Membrane Fuel Cell), and the results are shown in Table 10 below. Specifically, the current density was measured by loading the metal separators manufactured in each of the examples and comparative examples into a solution of 0.1 N H2SO4 + 2 ppm HF + 3000 ppm H2O2 at 80°C, and then applying a current density of 0.6 V. SCE was measured in .

[0211] Contact resistance (mΩ·cm) 2 )Current density (㎂ / cm 2 )Example 5-116.50.79Example 5-219.10.85Example 5-314.60.20Example 5-419.60.44Example 5-516.61.67Example 5-619.51.66Example 5-715.85.4Example 5-816.10.31Example 5-919.30.45Comparative Example 5-19.829.7Comparative Example 5-214.521.5Comparative Example 5-317.314.5Comparative Example 5-424.59.8Comparative Example 5-520.11.87Comparative Example 5-623.70.35Comparative Example 5-7387.70.28Comparative Example 5-819.615.7Comparative Example 5-933.410.1Comparative Example 5-10435.20.36

[0212] As shown in Table 10 above, the metal separators manufactured in each of Examples 5-1 to 5-9 were heat-treated, unlike the metal separator manufactured in Comparative Example 5-1, and, unlike the metal separators manufactured in each of Comparative Examples 5-2 to 5-10, the temperature and time for performing the heat treatment satisfied specific ranges, thereby confirming that they simultaneously had low current density and contact resistance, and thus, it was confirmed that excellent electrical conductivity and corrosion resistance could be secured simultaneously. In addition, it was confirmed that Comparative Examples 5-8 to 5-10 had higher current density and contact resistance than Comparative Examples 5-3, 5-4, and 5-7, respectively, by not further performing acetone washing.

[0213] <Explanation of symbols>

[0214] 10: Mother material

[0215] 11: Protrusion

[0216] 20: Passive film

[0217] A: Width of the protrusion

[0218] B: Base, an imaginary straight line drawn parallel to the parent material at the point where the protrusion's ridge is formed

[0219] C: Tangent at the point where the bone of the protrusion is formed

[0220] θ1: Angle of the protrusion

[0221] θ2: vertex angle of the protrusion

[0222] θ3: Water contact angle

Claims

1. A metal separator including a base material and a passive film formed on the surface of the base material, The above-mentioned passive film is a metal separator containing oxygen and titanium, wherein the atomic ratio of oxygen to titanium (O / Ti) is 0.2 or more and 0.6 or less.

2. In paragraph 1, A metal separator having an oxygen content of 10 at% or more and 40 at% or less in the above-mentioned passive film.

3. In paragraph 1, A metal separator having a titanium content of 60 at% or more and 90 at% or less in the above-mentioned passive film.

4. A metal separator comprising a base material including a plurality of protrusions formed on a surface; and a passive film formed on the surface of the base material, The above-mentioned base material is a metal separator having a surface roughness of 150 nm or more and 250 nm or less and a spacing between multiple protrusions of 700 nm or more and 900 nm or less.

5. A metal separator comprising a base material including a plurality of protrusions formed on a surface; and a passive film formed on the surface of the base material, The above protrusions have an average angle of 35° or more and 80° or less, and an average width of the protrusions is 0.1 ㎛. 2 Above 0.4 ㎛ 2 Below is the metal separator.

6. A metal separator including a base material and a passive film formed on the surface of the base material, The above passive film is a metal separator having a water contact angle of 1° or more and 10° or less.

7. In any one of paragraphs 1 to 6, The above-mentioned passive film is a metal separator having a thickness of 5 nm or more and 40 nm or less.

8. In any one of paragraphs 1 to 6, The above-mentioned passive film is a metal separator layer formed by heat-treating the surface of the base material after surface-modifying it by immersing the surface of the base material in a surface-modifying solution containing ammonium fluoride and ammonium bifluoride.

9. In any one of paragraphs 1 to 6, The above-mentioned parent material is a metal separator comprising titanium or a titanium alloy.

10. In any one of paragraphs 1 to 6, Contact resistance is 20 mΩ·cm 2 Below is the metal separator.

11. In any one of paragraphs 1 to 6, Current density is 10 ㎂ / cm 2 Below is the metal separator.

12. A surface modification step performed by immersing the surface of the parent material in a surface modification solution containing ammonium fluoride and ammonium difluoride; and It includes a heat treatment step of forming a passive film on the surface of the base material by heat treating the base material that has undergone the surface modification step, A method for manufacturing a metal separator, wherein the above heat treatment step is performed at a temperature of 210°C or higher and 550°C or lower in an air atmosphere for 30 seconds or longer and less than 1800 seconds.

13. In paragraph 12, A method for manufacturing a metal separator, further comprising an acetone washing step of immersing a base material in acetone before performing a surface modification step and then washing it by applying ultrasonic waves for at least 1 minute and no more than 10 minutes.

14. In paragraph 12, A method for manufacturing a metal separator, wherein the surface modification solution comprises 0.1 wt% or more and 10 wt% or less of ammonium fluoride and 0.1 wt% or more and 10 wt% or less of ammonium bifluoride.

15. In paragraph 12, A method for manufacturing a metal separator, wherein the surface modification solution further contains at least one selected from sulfuric acid, hydrochloric acid, nitric acid, ammonium persulfate, and hydrofluoric acid, each in an amount of 0.1 wt% to 10 wt%.

16. In paragraph 12, A method for manufacturing a metal separator, wherein the surface modification step is performed by immersing the base material in the surface modification solution at a temperature of 20°C or higher and 80°C or lower for 10 seconds or longer and 600 seconds or shorter.

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