KR102298876B1 - Separator for fuel cell and coating method of separator for fuel cell - Google Patents

Abstract

An embodiment of the present invention provides a separator for a fuel cell and a method for coating a separator for a fuel cell with improved water discharge characteristics while maintaining electrical conductivity and corrosion resistance.
The separator for a fuel cell according to an embodiment of the present invention includes a metal base material and a carbon coating layer formed on the surface of the metal base material, and the surface roughness (Ra) of the carbon coating layer may be 50 nm or less.
A method for coating a separator for a fuel cell according to an embodiment of the present invention includes preparing a metal base material; converting the carbon precursor gas into a plasma state to form a carbon coating layer on the surface of the metal base material; and cooling the carbon coating layer at a cooling rate of 3° C./min or less.

Description

Separator for fuel cell and coating method for separator for fuel cell {SEPARATOR FOR FUEL CELL AND COATING METHOD OF SEPARATOR FOR FUEL CELL}

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

The fuel cell stack consists of a fastening mechanism required to connect the stack module with repeatedly stacked components such as electrode membranes, separators, gas diffusion layers, and gaskets, an enclosure protecting the stack, components necessary for interfacing with the vehicle, and high voltage connectors. It can be divided into non-repeating parts such as A fuel cell stack is a device that emits electricity, water, and heat by reacting hydrogen with oxygen in the air. A fuel cell stack has many dangers because high-voltage electricity, water, and hydrogen coexist in the same place.

In particular, in the case of a fuel cell separator, corrosion resistance is more required due to the direct contact of hydrogen cations generated during fuel cell operation. It acts as an electrical insulator and lowers electrical conductivity. At this time, the dissociated and eluted metal cations contaminate the Membrane Electrode Assembly (MEA), thereby reducing the performance of the fuel cell.

The fuel cell separator, the most important component of the fuel cell stack, requires low contact resistance and corrosion current. Although the metal separator currently in use has excellent electrical conductivity, it has a problem of durability deterioration due to its high corrosion properties, so many researchers are trying to solve the property through coating.

Among the coating materials, carbon has high electrical conductivity and low corrosion properties. A technique for increasing the efficiency of fuel cells by improving the water discharge characteristics of carbon coatings has been proposed. As an example, a technique for improving water discharge characteristics through chemical hydrophilicity and hydrophobic treatment on a carbon coating layer has been proposed. However, in this case, the water discharge characteristics of the surface are improved, but there is a problem that conductivity and corrosion properties are deteriorated at the same time. As another example, a technique for reducing the dynamic contact history through a change in surface roughness by adding a texturing process has been proposed. However, there is a problem in terms of process efficiency because an additional texturing process is required.

One embodiment of the present invention is to provide a method for coating a separator for a fuel cell with improved water discharge characteristics while maintaining electrical conductivity and corrosion resistance.

Another embodiment of the present invention is to provide a separator for a fuel cell with improved water discharge characteristics while maintaining electrical conductivity and corrosion resistance.

The separator for a fuel cell according to an embodiment of the present invention includes a metal base material and a carbon coating layer formed on the surface of the metal base material, and the surface roughness (Ra) of the carbon coating layer may be 50 nm or less.

A contact angle of the carbon coating layer with respect to water may be 70 to 90°.

The contact angle history of the carbon coating layer with respect to water may be 1 to 10°.

The thickness of the carbon coating layer may be 1 μm or less.

The metal base material is formed from the surface of the metal base material in the inner direction of the metal base material, and may include an ion permeation layer containing carbon diffusion hindering ions.

A method for coating a separator for a fuel cell according to an embodiment of the present invention includes preparing a metal base material; converting the carbon precursor gas into a plasma state to form a carbon coating layer on the surface of the metal base material; and cooling the carbon coating layer at a cooling rate of 3° C./min or less.

After the step of preparing the metal base material, the method may further include removing the oxide film formed on the surface of the metal base material.

After the step of removing the oxide film, the method may further include forming an ion permeation layer from the surface of the metal base material to the inner direction of the metal base material.

Forming the carbon coating layer may be performed at 200 to 500 °C.

In the cooling step, the starting temperature may be 200 to 500 °C, and the ending temperature may be 10 to 150 °C.

The cooling step may be performed in an inert gas atmosphere.

According to an embodiment of the present invention, it is possible to obtain a fuel cell separator having improved water discharge characteristics while maintaining electrical conductivity and corrosion resistance.

1 is a schematic diagram of a cross-section of a separator for a fuel cell according to an embodiment of the present invention.
2 is a scanning electron microscope (SEM) photograph of the surface of the carbon coating layer of the separator for fuel cell prepared in Example 1. Referring to FIG.
3 is a scanning electron microscope (SEM) photograph of the surface of the carbon coating layer of the separator for a fuel cell prepared in Example 2.
4 is a scanning electron microscope (SEM) photograph of the surface of the carbon coating layer of the separator for fuel cell prepared in Comparative Example 1. Referring to FIG.
5 is a scanning electron microscope (SEM) photograph of the surface of the carbon coating layer of the separator for fuel cell prepared in Comparative Example 2.
6 is a scanning electron microscope (SEM) photograph of the surface of the carbon coating layer of the separator for a fuel cell prepared in Comparative Example 3.
7 is a result of evaluating the performance of a fuel cell using the fuel cell separators prepared in Examples 1 and 2 and Comparative Examples 1 to 3;

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and are common in the art to which the present invention pertains. It is provided to fully inform those with knowledge of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part refers to being "directly above" another part, the other part is not interposed therebetween.

Accordingly, in some embodiments, well-known techniques have not been specifically described in order to avoid obscuring the present invention. Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in the meaning commonly understood by those of ordinary skill in the art to which the present invention pertains. When a part "includes" a certain element throughout the specification, this means that other elements may be further included, rather than excluding other elements, unless otherwise stated. The singular also includes the plural, unless the phrase specifically states otherwise.

1 is a schematic diagram of a cross-section of a separator for a fuel cell according to an embodiment of the present invention.

Referring to FIG. 1 , the fuel cell separator 100 includes a metal base material 10 ; and a carbon coating layer 30 formed on the surface of the metal base material 10 . The cross-section of the separator plate 100 for a fuel cell of FIG. 1 is only for illustrating the present invention, and the present invention is not limited thereto.

Hereinafter, each configuration of the fuel cell separator 100 will be described in detail.

As the metal base material 10 , the metal base material 10 used in the fuel cell separator 100 may be used without limitation. Specifically, a stainless steel plate may be used. More specifically, a SUS 300 series steel sheet may be used.

A carbon coating layer 30 is formed on the surface of the metal base material 10 . In one embodiment of the present invention, by appropriately controlling the surface roughness (Ra) of the carbon coating layer 30, the low contact resistance and low corrosion potential characteristics of the fuel cell separator 100 can be obtained, and the water discharge characteristics can be improved. have. Accordingly, the performance of the fuel cell including the separator 100 for the fuel cell is ultimately improved. Specifically, the surface roughness Ra of the carbon coating layer 30 may be 50 nm or less. When the surface roughness Ra of the carbon coating layer 30 exceeds 50 nm, water discharge characteristics are weakened, which ultimately adversely affects fuel cell performance. Specifically, the surface roughness (Ra) of the carbon coating layer 30 may be 1 to 50 nm. More specifically, the surface roughness (Ra) of the carbon coating layer 30 may be 10 to 40 nm.

Since the carbon coating layer 30 includes carbon as a main material, a contact angle with respect to water may be 70 to 90°. Here, the contact angle means an angle between the solid-liquid interface and the liquid-gas interface when the droplet is positioned on the solid substrate.

In addition, as described above, by controlling the surface roughness (Ra) of the carbon coating layer 30 according to an embodiment of the present invention, a carbon coating layer 30 having a contact angle hysteresis of 1 to 10° to water is obtained. can In this case, the contact angle hysteresis means the advancing angle, which is the contact angle when the solid-liquid contact area increases (that is, the droplet size increases) when the contact angle is measured when the solid-liquid-gas contact line moves and the solid - Means the arithmetic difference of receding wetting angle, which is the contact angle when the contact area of the liquid decreases (ie, the droplet size decreases). When the contact angle hysteresis exceeds 10°, the water discharge characteristic is weakened, which ultimately adversely affects the fuel cell performance. More specifically, the contact angle history of the carbon coating layer 30 with respect to water may be 5 to 10°.

The thickness of the carbon coating layer 30 may be 1 μm or less. When the thickness of the carbon coating layer 30 is too thick, it may be separated from the metal base material 10 by itself due to a high residual stress. Specifically, the thickness of the carbon coating layer 30 may be 10 nm to 1 μm.

In the separator plate 100 for a fuel cell according to an embodiment of the present invention, the metal base material 10 is formed from the surface of the metal base material 10 to the inner direction of the metal base material, and an ion permeation layer containing carbon diffusion hindering ions ( 20) may be included. By improving the bonding strength and density of the carbon coating layer 30 including the ion permeation layer 20 formed from the surface of the metal base material 10 in the inner direction of the metal base material 10 and containing carbon diffusion hindering ions, the ultimate As a result, low contact resistance and corrosion potential characteristics of the fuel cell separator 100 are achieved.

When the ion permeation layer 20 containing carbon diffusion hindering ions is formed, carbon diffusion hindering ions are interposed between metal atoms. Thereafter, even if carbon atoms are implanted to form the carbon coating layer 30 , diffusion of carbon atoms into the metal base material 10 is prevented by carbon diffusion hindering ions. For this reason, carbon atoms hardly diffuse inside the metal base material 10 , and relatively large amounts of carbon atoms are present on the outermost surface (ie, the ion permeation layer 20 ) of the metal base material 10 . The carbon atoms present on the outermost surface of the metal base material 10 are carbon-carbon bonds with the carbon atoms in the carbon coating layer 30 , thereby improving the bonding force between the carbon coating layer 30 and the metal base material 10 . In addition, the amount of carbon atoms diffused into the metal base material 10 is reduced, even if the same carbon atoms are supplied, the amount of carbon atoms in the carbon coating layer 30 is relatively increased, and the density of the carbon coating layer 30 is is improved As such, since the bonding strength and density of the carbon coating layer 30 are improved, it is possible to achieve low contact resistance and corrosion potential characteristics of the separator 100 for a fuel cell.

As such, in one embodiment of the present invention, the low contact resistance and corrosion potential characteristics of the fuel cell separator 100 are obtained through the formation of the ion permeation layer 20 interposed between the metal atoms of the metal base material 10 with carbon diffusion hindering ions. be able to achieve In this case, the metal atom may be a metal atom present in the aforementioned stainless steel sheet, for example, an iron (Fe), chromium (Cr), nickel (Ni) or molybdenum (Mo) atom. The intercalation of carbon diffusion hindering ions between metal atoms means that the carbon diffusion hindering ions are permeated or dissolved in the austenite face-centered cubic structure (FCC) lattice.

The ion permeation layer 20 may include 5 to 30% by weight of carbon diffusion hindering ions. When too few carbon diffusion hindering ions are included, the carbon diffusion hindering effect may not be sufficient. When too many carbon diffusion-interfering ions are included, exfoliation may occur due to surface hardening due to external impact, thereby reducing durability. Accordingly, carbon diffusion-interfering ions may be included in the above-described range.

In addition, when the carbon coating layer 30 is formed, carbon atoms are partially diffused into the ion permeation layer 20 , and 5 to 85 wt % of carbon atoms may be included in the ion permeation layer 20 . When too few carbon atoms are included in the ion penetrating layer 20 , carbon-carbon bonding with carbon atoms in the carbon coating layer 30 decreases, so that the bonding strength of the carbon coating layer 30 may be a problem. When too many carbon atoms are included in the ion penetrating layer 20 , the density of the carbon coating layer 30 may be lowered. Accordingly, carbon atoms may be included in the above-described range.

The carbon diffusion-interfering ion may be used without limitation as long as it is an ion that is interposed between metal atoms and may interfere with the diffusion of carbon atoms. Specifically, ions having an atomic number of 20 or less can be used. More specifically, the carbon diffusion hindering ion may include nitrogen or boron ions.

The thickness of the ion penetrating layer 20 may be 30 to 300 nm. If the thickness of the ion permeation layer 20 is too thin, the carbon diffusion hindering effect may not be sufficient. If the thickness of the ion permeation layer 20 is too thick, the hardness increases when too many nitrogen atoms permeate, so that it is easily broken by an external impact.

The ion permeation layer 20 may be formed through plasma or ion implantation. A specific method of forming the ion permeation layer 20 will be described in detail in relation to a method of coating a separator for a fuel cell to be described later.

The coating method of the separator plate 100 for a fuel cell according to an embodiment of the present invention comprises the steps of preparing a metal base material 10; converting the carbon precursor gas into a plasma state to form a carbon coating layer 30 on the surface of the metal base material 10; and cooling the carbon coating layer 30 at a cooling rate of 3° C./min or less.

Hereinafter, each step will be described in detail.

First, the metal base material 10 is prepared. As the metal base material 10 , the metal base material 10 used in the fuel cell separator 100 may be used without limitation. Specifically, a stainless steel plate may be used. More specifically, a SUS 300 series steel sheet may be used.

An oxide film may be present on the surface of the metal base material 10 due to contact with air or the like. Since this causes an increase in contact resistance, the method may further include removing an oxide film on the surface of the metal base material 10 . As the removal method, a method of increasing the temperature of the metal base material 10 and applying argon plasma may be used.

Next, carbon diffusion hindering ions are permeated into the surface of the metal base material 10 to form the ion permeation layer 20 in the inner direction of the metal base material 10 from the surface of the metal base material 10 . Since the reason for the formation of the ion permeation layer 20 has been described above, the overlapping description will be omitted.

The step of forming the ion permeation layer 20 may be to permeate carbon diffusion hindering ions through plasma or ion implantation.

The method of using plasma is a method of infiltrating carbon diffusion hindering ions into the metal base material 10 by using plasma in an ion-forming gas atmosphere that forms carbon diffusion hindering ions. Ion implantation is a method of accelerating ions using high energy to collide with a substrate to penetrate into the inside of the base material.

In the case of a method using plasma, the ion-forming gas means a gas containing carbon diffusion-interfering ions. For example, nitrogen gas (N ₂ ), borane gas (B ₂ H ₆ ), and the like may be used. It may be carried out in an atmosphere containing 10% by volume or more of such an ion-forming gas. If the ion-forming gas is not sufficient, the carbon diffusion hindering ions may not penetrate properly. The remainder of the atmospheric gas may be hydrogen gas.

Forming the ion permeation layer 20 may be performed at 300 to 550 °C. If the temperature of the step of forming the ion permeation layer 20 is too low, it may become difficult to properly permeate carbon diffusion hindering ions. If the temperature in the step of forming the ion permeation layer 20 is too high, the metal in the metal base material 10 and carbon diffusion-interfering ions may react to decrease corrosion properties and increase contact resistance. For example, when nitrogen reacts with chromium as a carbon diffusion-interfering ion in the metal base material 10 _{to form chromium nitride (CrN, Cr 2} N), corrosion properties may be deteriorated and contact resistance may be increased. In one embodiment of the present invention, since the ion permeation layer 20 is formed at a low temperature, it is different from the nitrification process in which nitrogen is added at a high temperature. Therefore, the temperature can be adjusted in the above-described range.

Forming the ion permeation layer 20 may be performed for 10 to 120 minutes. If the time is too short, it may become difficult for carbon diffusion hindering ions to penetrate properly. Even if the time is further increased, there is a limit to the amount of penetration of carbon diffusion hindering ions. Accordingly, the time may be adjusted within the above-described range.

Next, a carbon coating layer 30 is formed on the surface of the metal base material 10 by converting the carbon precursor gas into a plasma state. That is, the carbon coating layer 30 is formed using a plasma enhanced chemical vapor deposition (PECVD) method. Specifically, the carbon coating layer 30 is formed by excitation of carbon atoms in the carbon precursor gas with plasma.

It may be carried out in an atmosphere containing 3 to 30% by volume of the carbon precursor gas. If the content of the carbon precursor gas is too small, the carbon coating layer 30 may not be properly formed. When the content of the carbon precursor gas is too large, the compressive residual stress of the carbon coating layer 30 is increased, and the carbon coating layer 30 may be peeled off. More specifically, it may be carried out in an atmosphere containing 10 to 20% by volume of the carbon precursor gas. In this case, the carbon precursor gas refers to a gas capable of excitation of carbon atoms by applying plasma. Specifically, it may be a hydrocarbon gas. More specifically, it may include _{C 2} H ₂ , CH ₄ , or C ₂ H _{6 .} In addition to the carbon precursor gas, the balance may be argon or hydrogen gas. Specifically, C ₂ H ₂ gas may be supplied at 1 to 30 sccm, and argon gas at 1 to 100 sccm. At this time, the degree of vacuum may be 1 mbar or less.

Forming the carbon coating layer 30 may be performed at 200 to 500 °C. If the temperature is too low, a problem that the carbon coating layer 30 is not properly formed may occur. When the temperature is too high, chromium carbide (Cr ₇ C ₃ ) is formed, and a problem in which corrosion properties are deteriorated may occur. Therefore, the temperature can be adjusted in the above-described range.

Next, the carbon coating layer may be cooled at a cooling rate of 3° C./min or less. In an embodiment of the present invention, by precisely controlling the cooling rate in the cooling step, water discharge characteristics can be improved without changing the electrical characteristics of the carbon coating layer 30 . When the cooling rate is too fast, the surface roughness (Ra) value of the carbon coating layer 30 increases, and the water discharge characteristic becomes poor. More specifically, the carbon coating layer may be cooled at a cooling rate of 1 to 3° C./min.

The cooling step may start at the temperature in the step of forming the carbon coating layer 30 . That is, the starting temperature may be 200 to 500 ℃. The termination temperature may be 10 to 150°C.

The cooling step may be performed in an inert gas atmosphere. When carried out in an inert gas atmosphere, it is possible to prevent oxidation of carbon during cooling, thereby improving the electrical conductivity and corrosion resistance of the fuel cell separator. Specifically, the inert gas atmosphere may be a nitrogen (N ₂ ) or argon (Ar) atmosphere. The cooling rate can be controlled by adjusting the supply flow rate of the inert gas. Specifically, the cooling rate can be controlled by supplying an inert gas of 10 to 30° C. at a rate of 100 to 1000 sccm.

Since other descriptions of the metal substrate 10 , the ion permeation layer 20 , and the carbon coating layer 30 have been described in detail with respect to the above-described separator 100 for a fuel cell, overlapping descriptions will be omitted.

The separator for a fuel cell according to an embodiment of the present invention has improved water discharge characteristics while maintaining electrical conductivity and corrosion resistance, and can ultimately improve the performance of the fuel cell.

Hereinafter, preferred examples and comparative examples of the present invention will be described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited thereto.

Example 1

As a metal base material, SUS 316L, which is an austenitic stainless steel, was prepared. After heating the metal base material to 300° C. in an argon atmosphere, plasma was applied to remove the oxide film formed on the metal base material surface. Afterwards, the metal base material was heated to 400 °C again. The atmospheric gas was replaced with 15% by volume of nitrogen and 85% by volume of hydrogen, and plasma was applied to permeate nitrogen ions for 10 minutes.

The atmospheric gas was replaced with acetylene (C ₂ H ₂ ) 20% by volume and hydrogen 80% by volume, and plasma was applied for 30 minutes. Thereafter, the atmospheric gas _{was changed to nitrogen (N 2} ) gas and cooled to 25° C. at a cooling rate of 1° C./min.

A carbon coating layer was formed to a thickness of 10.3 nm.

2 shows a photograph observing the surface of the carbon coating layer. As shown in FIG. 2 , it can be confirmed that a carbon coating layer having a small surface roughness is formed.

Example 2

The same procedure as in Example 1 was performed, but the cooling rate was 3° C./min.

3 shows a photograph observing the surface of the carbon coating layer. As shown in FIG. 3 , it can be confirmed that a carbon coating layer having a small surface roughness is formed.

Comparative Example 1

The same procedure as in Example 1 was performed, but the cooling rate was 5° C./min.

4 shows a photograph observing the surface of the carbon coating layer. As shown in FIG. 4 , it can be confirmed that a carbon coating layer having a relatively large surface roughness is formed.

Comparative Example 2

The same procedure as in Example 1 was performed, but the cooling rate was 7° C./min.

5 shows a photograph of observing the surface of the carbon coating layer. As shown in FIG. 5 , it can be confirmed that a carbon coating layer having a relatively large surface roughness is formed.

Comparative Example 3

The same procedure as in Example 1 was performed, but the cooling rate was 10° C./min.

6 shows a photograph observing the surface of the carbon coating layer. As shown in FIG. 6 , it can be confirmed that a carbon coating layer having a relatively large surface roughness is formed.

Experimental example 1: surface roughness and contact angle measurement

The surface roughness and contact angle with respect to water of the separators for fuel cells prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were measured and summarized in Table 1 below.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Cooling rate (°C/min) One 3 5 7 10 Surface roughness (Ra, nm) 21 38 78 104 198 Advance angle (°) 81.9 82.3 84.0 83.7 84.9 Reverse angle (°) 75.6 72.3 65.3 55.2 53.6 Contact angle history (°) 6.3 10.0 18.7 28.5 31.3

As shown in Table 1, in Examples 1 and 2, in which the cooling rate in the cooling step was precisely controlled, the surface roughness was low, and the contact angle history was small, so it could be confirmed that the water discharge performance was excellent. On the other hand, in Comparative Examples 1 to 3, it can be confirmed that the cooling rate is too fast, the surface roughness is large, and the contact angle history is large, so that the water discharge performance is excellent.

Experimental example 2: Evaluation of contact resistance and corrosion current density

The contact resistance and corrosion current density of the separators for fuel cells prepared in Examples 1 and 2 and Comparative Examples 1 to 3 were measured, and the results are summarized in Table 2.

Contact resistance was measured with a contact resistance meter after placing a separator and a gas diffusion layer between two copper plates and ^{applying a pressure of 10 kgf/cm 2 .}

For corrosion current density measurement, 0.1NH ₂ SO ₄ + 2ppm HF solution was used, and after heating the solution to 65° C., air bubbling for 1 hour was measured in the range of -0.25 to 1V vs SCE, and the anode environment ( 0.6V vs SCE) data were used to compare and evaluate physical properties.

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Cooling rate (°C/min) One 3 5 7 10 Surface roughness (Ra, nm) 21 38 78 104 198 Contact resistance (mΩ˙cm ² ) 81.9 82.3 84.0 83.7 84.9 Corrosion Current Density (μA/cm ² ) 75.6 72.3 65.3 55.2 53.6

As shown in Table 2, it was confirmed that there was no significant change in the contact resistance or corrosion current density characteristics according to the cooling rate or surface roughness. That is, it was confirmed that the control of the cooling rate did not change the structure of the carbon in the carbon coating layer, but only affected the surface roughness.

Experimental example 3: Fuel cell performance evaluation

A 5-cell unit stack was manufactured using the separators for fuel cells prepared in Examples 1 and 2 and Comparative Examples 1 to 3, and the stack was humidified by 50% of both hydrogen and air at a coolant inlet temperature of 65°C. IV performance evaluation was performed. The results are shown in FIG. 7 .

As shown in FIG. 7 , it can be confirmed that the fuel cells using the separator plates for fuel cells prepared in Examples 1 and 2 have excellent performance. This is because the water discharge characteristics are improved while maintaining the electrical conductivity and corrosion resistance characteristics of the fuel cell separator.

The present invention is not limited to the above embodiments, but can be manufactured in a variety of different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

100: fuel cell separator 10: metal base material
20: ion permeation layer 30: carbon coating layer

Claims (11)

delete delete delete delete delete preparing a metal base material;
removing the oxide film formed on the surface of the metal base material;
forming an ion permeation layer in an inner direction of the metal base material from the surface of the metal base material;
converting the carbon precursor gas into a plasma state to form a carbon coating layer on the surface of the metal base material; and
A method for coating a separator for a fuel cell, comprising the step of cooling the carbon coating layer at a cooling rate of 1°C/min to 3°C/min. delete delete 7. The method of claim 6,
The step of forming the carbon coating layer is a coating method of a separator for a fuel cell performed at 200 to 500 ℃. 7. The method of claim 6,
In the cooling step, the starting temperature is 200 to 500 ℃, and the ending temperature is 10 to 150 ℃ coating method of a separator for a fuel cell. 7. The method of claim 6,
The cooling step is a method of coating a separator for a fuel cell performed in an inert gas atmosphere.

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