KR102783564B1 - Metal separator for fuel cell - Google Patents

Abstract

The present invention relates to a metal separator for a fuel cell, and more specifically, to a metal substrate, a metal layer formed on the metal substrate, and a carbon layer formed on the metal layer, wherein the carbon layer is doped with graphite having crystallinity within a matrix of amorphous carbon. The fuel cell separator according to the present invention has excellent corrosion resistance and electrical conductivity, and maintains excellent fuel cell performance even after long-term use.

Description

METAL SEPARATOR FOR FUEL CELL

The present invention relates to a metal separator for a fuel cell, and more specifically, to a metal separator for a fuel cell with excellent corrosion resistance and conductivity utilizing a carbon-based material.

A fuel cell is a cell that converts chemical energy generated by the oxidation/reduction reaction of fuel, i.e. hydrogen and oxygen, into electrical energy. Typically, an anode and a cathode are arranged with an electrolyte in between, and a gas diffusion layer (GDL) and a separator are sequentially laminated on each of the anode and cathode to form a unit cell. Hydrogen is ionized at the cathode and separated into hydrogen ions and electrons, and the hydrogen ions move to the anode through the electrolyte. The electrons move to the anode through the circuit, and a reduction reaction occurs at the anode where hydrogen ions, electrons, and oxygen react to produce water.

Since the unit cell of a fuel cell has low voltage and thus low commerciality, hundreds of unit cells are stacked and used. When stacking unit cells, the separator serves to ensure electrical connection between each unit cell and to separate the reaction gases.

Fuel cell separators are classified into graphite separators and metal separators depending on the material. Initially, graphite separators were widely used, but because they are thick and heavy, weight reduction is limited, so the use of metal separators is increasing.

However, the metal separator uses stainless steel or titanium as its base material, and the fuel cell power generation environment is high in temperature and humidity, and the surface of the metal separator forms a path through which water can flow, so it can easily corrode. This corrosion increases the contact resistance of the metal separator, which reduces the power generation efficiency of the fuel cell, and the problem occurs that the fuel cell efficiency decreases because an oxide film grows on the surface and increases the electrical resistance.

In order to improve the corrosion resistance and conductivity of a metal separator, Korean Patent No. 10-1165542 discloses a technology for coating the surface of a metal separator with gold, Korean Patent No. 10-1127197 discloses a technology for coating a carbon-based material on the surface of a metal separator, a technology for coating nitride (TiN, CrN), and a technology for coating resin.

The method of coating a metal separator with gold has the problem of increasing the production cost, and the resin coating has the limitation of reducing the electrical conductivity. As a technology for coating a carbon-based material, Korean Patent No. 10-1127197 deposits a carbon layer in the form of graphite (40) partially exposed (protruding) on the surface of an amorphous carbon layer (30) as shown in Fig. 1, on a metal base material (10, 20), thereby improving the corrosion resistance and electrical conductivity of the metal separator by utilizing the complementary properties of amorphous carbon (30) and crystalline graphite (40).

However, in the Korean Patent Registration No. 10-1127197, as hundreds of unit cells as shown in Fig. 1 are stacked on top, stress is applied to the surfaces of the metal separators facing each other in the process of applying a load and a fastening pressure to fasten them into a single pile. Due to this stress, the exposed graphite (40) may fall off from the amorphous carbon layer (30), causing pinholes to occur or cracks to occur on the surface of the carbon layer. These pinholes and cracks weaken the internal properties of the metal separator, significantly reducing the performance and stability of the fuel cell.

Korean Patent No. 10-1165542, Metal separator for fuel cell with coating film formed on the surface and its manufacturing method Korean Patent No. 10-1127197, Separator for fuel cell, method for manufacturing separator for fuel cell, and fuel cell

The inventors of the present invention have developed a structure in which crystalline graphite is not peeled off from a carbon layer due to stress when the metal separator is fastened while utilizing a metal separator to overcome the limitation of reducing the weight of a conventional graphite separator, and thus the corrosion resistance and electrical conductivity of the metal separator can be improved simultaneously, leading to the present invention.

As a result, the inventors of the present invention, after many years of research, have discovered that the corrosion resistance and electrical conductivity of a metal separator for a fuel cell including a metal base material, a metal layer formed on the metal base material, and a carbon layer formed on the metal layer can be improved by designing the carbon layer to have a structure in which graphite having crystallinity is doped inside a matrix of amorphous carbon.

Accordingly, an object of the present invention is to provide a metal separator for a fuel cell having improved corrosion resistance and electrical conductivity.

In order to achieve the above object, a metal separator for a fuel cell according to one embodiment of the present invention comprises a metal base material, a metal layer formed on the metal base material, and a carbon layer formed on the metal layer, wherein the carbon layer is doped with graphite having crystallinity within a matrix of amorphous carbon. The surface of the carbon layer is smoothly coated with amorphous carbon so that graphite is not exposed on the surface.

The above carbon layer is formed by a deposition method, and can be manufactured by a first deposition that forms graphite doped inside a matrix of amorphous carbon and graphite at least partially exposed on the surface of the amorphous carbon, and a second deposition that covers the surface where the graphite is exposed with amorphous carbon.

The deposition method includes chemical vapor deposition, physical vapor deposition, and atomic layer deposition, and after the first deposition is completed, the second deposition may be performed to form a carbon layer.

The above first deposition and the above second deposition form a carbon layer by a physical deposition method, wherein the first deposition is performed by arc ion plating, and the second deposition can be performed by sputtering. The arc ion plating can be applied with a current of 40 to 150 A to the target, and a bias voltage of 0 to 200 V can be applied to the metal separator.

The thickness of the carbon layer may be 0.02 to 3 μm, and the average thickness (T) of the carbon layer formed by the second deposition may be 0.01 to 2 μm. The metal layer may be formed by depositing at least one metal selected from titanium, aluminum, zirconium, copper, gold, silver, molybdenum, tungsten, chromium, vanadium, manganese, iron, cobalt, and nickel on the metal base material. The metal base material may be subjected to dry etching surface treatment to remove a natural oxide film and impurities.

The metal separator for a fuel cell according to the present invention has a corrosion current value of 1 μA/cm ² in a potentiostatic polarization test performed in a 0.1 NH ₂ SO ₄ + 2 ppm HF aqueous solution at 80°C, and a contact resistance of 15 mΩ·cm ² at a clamping pressure of 1 MPa.

The fuel cell separator according to the present invention has excellent corrosion resistance and electrical conductivity, and maintains excellent fuel cell performance even after long-term use.

Figure 1 is a drawing for explaining a metal separator for a fuel cell according to the prior art.
FIG. 2 is a configuration diagram of a metal separator for a fuel cell according to one embodiment of the present invention.
Figure 3 is a schematic diagram showing a state in which the two fuel cell separator plates illustrated in Figure 2 are partially in contact with each other and face each other when fastened.
Figure 4 shows the results of a potentiostatic polarization test performed on Example 1 in _{a 0.1NH2SO4} + 2ppm HF aqueous solution at 80°C for 1 hour.
Figure 5 shows the results of measuring contact resistance according to changes in the fastening pressure of Example 1.
Figure 6 is a SEM image of the carbon layer surface of Example 1.
Figure 7 is a SEM image of the carbon layer surface of Comparative Example 2.
Figure 8 is a drawing for explaining a pressurizing device that implements a simulation environment in which a stacking load and a fastening pressure are applied when fastening a metal separator for a fuel cell.
Figure 9 is a drawing for explaining a method for measuring the contact resistance of a metal separator for a fuel cell.
Figure 10 shows the results of long-term durability evaluation of Example 2.

Hereinafter, the features of the present invention will be described by way of examples through drawings. However, the illustrated examples, structures, and shapes may be implemented in other embodiments without departing from the technical spirit and scope of the present invention, and therefore should be accepted as encompassing the elements of the patent claims and their equivalents.

Figure 2 is a schematic diagram of a metal separator for a fuel cell according to one embodiment of the present invention. Referring to Figure 2, the metal separator (100) for a fuel cell of the present invention includes a metal base material (110), a metal layer (120), and a carbon layer (130).

The metal substrate (110) is not particularly limited as long as it is formed with a plurality of paths so that hydrogen, oxygen, and water can flow using a metal used as a separator for a fuel cell. For example, the material of the metal substrate may be at least one metal selected from aluminum (Al), titanium (Ti), zirconium (Zr), copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), chromium (Cr), titanium (Ti), scandium (Sc), vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni), and a preferred example may be stainless steel (SUS 316, etc.), but is not limited thereto.

The surface of the metal base material (110) may have natural oxides or foreign substances. Natural oxides inhibit electrical conductivity between the metal base material (110) and the metal layer (120), and foreign substances reduce the adhesion between the metal base material and the metal layer, so it is desirable to remove them.

Organic or inorganic substances on the surface of the metal base material can be cleaned with a cleaning agent, and dry etching can be performed to remove natural oxides. Here, dry etching is not particularly limited as long as etching is performed by a reaction using gas plasma or an activated gas, and for example, glow-discharge, hot filament, ion gun etching using argon gas, sputter etching, reactive ion etching, and vapor phase etching using HF can be used.

The metal layer (120) is formed on the metal base material (110). The metal layer (120) is formed between the metal base material (110) and the carbon layer (130) and serves to distribute the load and fastening pressure generated when a plurality of unit cells are laminated and fastened and to improve the adhesion of the carbon layer (130).

The metal layer (120) can use a material having high electrical conductivity together with the metal base material (110), and for example, at least one metal selected from aluminum (Al), titanium (Ti), zirconium (Zr), copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), chromium (Cr), scandinium (Sc), vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni), or a nitride or oxide thereof, but is not limited thereto.

The method of forming a metal layer (120) on a metal substrate (110) can use various deposition methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and atomic layer deposition (ALD). Preferably, when sputtering, which is a physical vapor deposition method, is used, the adhesion to the metal substrate is good, and a metal layer of uniform thickness can be formed.

The thickness of the metal layer (120) may be 0.02 to 5 μm. If the thickness is less than 0.02 μm, the adhesion of the carbon layer is reduced, and if it exceeds 5 μm, the effect of increasing the adhesion of the carbon layer is minimal, but the manufacturing cost increases, which reduces productivity.

The carbon layer (130) has a form in which graphite (132) having crystals is doped inside the matrix of amorphous carbon (131). Graphite (132) has relatively higher crystallinity than amorphous carbon and can complement the corrosion resistance, which is a weak point of a carbon layer composed only of amorphous carbon. Meanwhile, the carbon layer (130) of the present invention has a structure in which graphite (132) is completely impregnated inside the matrix of amorphous carbon (131), that is, when the upper surface of the carbon layer is viewed from above the upper part of the carbon layer (130), a part of the graphite (131) is not observed, and only the smoothly coated amorphous carbon (131) can be observed. This structure of the carbon layer (130) of the present invention enables stability to be maintained even under a load and stress generated when hundreds of unit cells are stacked in a state in which metal separators (100) face each other and are in partial contact with each other.

Specifically, FIG. 3 is a drawing expressing a state in which two metal separators for fuel cells, as shown in FIG. 2, are in contact with each other and face each other when fastened. Referring to FIG. 3, the metal separators for fuel cells face each other and are electrically connected. That is, the metal separators (100) for fuel cells have their carbon layers (130), which are the outermost surface layers, facing each other and making contact and grounding. At this time, when hundreds of unit cells including the metal separators (100) for fuel cells are stacked, stress is generated in the process of fastening hundreds of unit cells by applying a fastening pressure while their heavy load is weighted in the direction of gravity.

The carbon layer (130) of the present invention utilizes the complementary properties of amorphous carbon (131) and crystalline graphite (132), but since the graphite (132) is completely doped within the matrix of the amorphous carbon (131) and the graphite is not exposed on the surface of the carbon layer, even if stress occurs due to the load and clamping pressure described above, the occurrence of pinholes and cracks on the surface of the carbon layer (130) is significantly reduced.

In order to form the carbon layer (130) of the fuel cell separator of the present invention, at least one of a physical vapor deposition (PVD) method, a chemical vapor deposition (CVD) method, and an atomic layer deposition (ALD) method may be used, but is not limited thereto. Preferably, in order to induce a form in which crystalline graphite is doped in the matrix of amorphous carbon, a physical vapor deposition (PVD) method is used, and it is preferable to sequentially perform the first deposition and the second deposition separated in time. Here, the physical deposition method includes sputtering, arc ion plating, thermal evaporation, E-Beam evaporation, etc.

More preferably, the first deposition and the second deposition may be performed by different physical deposition methods, for example, the first deposition may be performed by arc ion plating, and the second deposition may be performed by sputtering, but is not limited thereto. For example, through the first deposition, doped graphite is formed inside the matrix of amorphous carbon and graphite at least partially exposed on the surface of the amorphous carbon, and then the upper surface of the graphite partially exposed in the first deposition is covered with amorphous carbon through the second deposition. Here, the first deposition may be performed by arc ion plating, and the second deposition may be performed by sputtering.

When the first deposition is performed by arc ion plating, unlike other physical deposition methods, it is easy to manufacture a form in which graphite is partially doped into the amorphous carbon matrix, so that a carbon layer having complementary properties of amorphous carbon and crystalline graphite can be obtained. However, when the first deposition is performed by arc ion plating, a form in which some graphite is exposed on the surface of the amorphous carbon may be obtained. However, as explained above, this form of graphite surface exposure causes pinholes and cracks during the fastening process of the unit cell, which lowers the corrosion resistance and electrical conductivity of the metal separator.

Therefore, it is desirable to cover the surface exposed by the graphite formed by the first deposition with amorphous carbon through the second deposition to ultimately form a carbon layer having a smooth surface. The second deposition is intended to smoothly cover the graphite exposed on the surface by the first deposition, and it is desirable to perform the second deposition after the first deposition is completed.

The second deposition can also be performed by a physical vapor deposition method, but if the first deposition is performed by arc ion plating, it is recommended that the second deposition be performed by another deposition method, sputtering. For example, if the second deposition is performed by arc ion plating in the same manner as the first deposition, the graphite exposed to the amorphous carbon surface is re-deposited, making it difficult to achieve the desired surface smoothness of the carbon layer.

As a specific example, the arc ion plating used for the first deposition may be applied to the target (cathode) at a current of 40 to 150 A (10 to 30 V), and the bias voltage applied to the metal base material may be 0 to 200 V. If the current applied to the target is less than 40 A, the carbon layer contains less crystalline graphite, which increases the contact resistance and lowers the deposition rate, thereby lowering the productivity. On the other hand, if the current applied to the target exceeds 150 A, a large amount of crystalline graphite is formed in the carbon layer, which deteriorates the surface smoothness, and the detachment of the crystalline graphite causes pinholes or cracks to occur.

If the bias voltage applied to the metal base material exceeds 200 V, the coating peeling due to Re-Sputtering may occur at the edge of the metal separator, which may deteriorate both the contact resistance and the corrosion resistance. The bias applied to the metal separator may be preferably 0 to 200 V, and more preferably 0 to 150 V.

The thickness of the carbon layer formed by the first deposition and the second deposition may be 0.02 to 3.0 μm. If the film thickness of the carbon layer is less than 0.02 μm, the amount of crystalline graphite deposited is small, making it difficult to expect improvement in electrical conductivity and corrosion resistance. On the other hand, if the film thickness of the carbon layer exceeds 3.0 μm, a large number of pinholes are generated due to exfoliation of excessively deposited crystalline graphite, which adversely affects corrosion resistance, and the probability of exfoliation of the crystalline graphite and amorphous carbon coating due to internal stress in the coating generated during the process increases, which may lower electrical conductivity and corrosion resistance, and there is a problem of increased manufacturing cost.

Meanwhile, the average thickness (T) of the amorphous carbon formed by the second deposition may be 0.01 to 2 μm. If the thickness of the amorphous carbon formed by the second deposition is less than 0.01 μm, graphite may be exposed on the surface of the carbon layer, and if it exceeds 2 μm, the manufacturing cost increases unnecessarily.

The metal separator for a fuel cell of the present invention has a corrosion current value of 1 μA/cm ² or less in a potentiostatic polarization test performed in a 0.1 NH ₂ SO ₄ + 2 ppm HF aqueous solution at 80°C, and a contact resistance of 15 mΩ·cm ² or less at a clamping pressure of 1 MPa. Therefore, it not only has sufficient corrosion resistance and contact resistance as a separator for fuel cells, but is also stable for long-term use.

Hereinafter, preferred examples are presented to help understand the present invention. However, the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

<Example>

Using stainless steel (SUS 316L) as a metal base material, metal separators for fuel cells were manufactured according to examples and comparative examples as shown in Table 1.

division Middle layer Carbon layer thickness (um) Carbon layer structure Adhesion
(N) Corrosion current
(μA/ ^cm2 @0.6VSCE) Contact resistance
(mΩ cm ² @1MPa) First deposition Second deposition Example 1 Ti 0.04~0.05 0.02~0.03 Graphite doping inside the carbon layer 25N or more 0.5~0.7 9.5 Example 2 Ti 0.19~0.20 0.02~0.03 25N or more 0.3~0.6 11.2 Example 3 Ti 0.48~0.50 0.02~0.03 25N or more 0.1~0.5 12.3 Example 4 Ti 1.8~2.0 0.13~0.15 20.1N 0.1~0.5 13.0 Example 5 TiN 0.48~0.50 0.02~0.03 25N or more 0.1~0.5 13.2 Example 6 Cr 0.19~0.20 0.02~0.03 25N or more 0.5~0.8 12.7 Example 7 CrN 0.19~0.20 0.02~0.03 25N or more 0.4~0.6 13.7 Comparative Example 1 Ti 3.3~3.5 0.28~0.30 15.6N 0.1~3.0 17.0 Comparative Example 2 Ti 0.04~0.05 - From the carbon layer surface
Graphite extrusion (exposure) 25N or more 2.5~3.5 9.2 Comparative Example 3 Ti 0.48~0.50 - 25N or more 1.7~2.7 11.9

Metal separators for fuel cells of specific examples and comparative examples were manufactured as follows.

<Example 1>

A dry etching method was used to remove the natural oxide film and foreign substances on the surface of the metal base material. The metal base material was placed in the chamber, and Ar gas was injected into the chamber. The injected Ar gas was ionized into Ar ⁺ and electrons due to the impact of electrons. At this time, a bias (-) voltage was applied to the separator, and the natural oxide film and foreign substances of the metal base material were removed by an etching method in which Ar ⁺ strikes the separator. Subsequently, a 0.06 μm metal layer (Ti) was formed on the metal base material by sputtering. In order to form a carbon layer on the metal layer, a current of 60 A was applied to the carbon material target by arc ion plating, and a bias voltage of 20 V was applied to the metal base material. As a result, a carbon layer in the form of doped graphite inside the amorphous carbon and some graphite derived from the surface of the amorphous carbon was obtained (first deposition). Thereafter, amorphous carbon was deposited on the surface of the carbon layer on which the first deposition was completed using a carbon material target by sputtering (second deposition). As a result of SEM image analysis of the surface of the carbon layer on which the second deposition was completed, no graphite protruding from the surface of the carbon layer was observed.

Figure 4 shows the results of a potentiostatic polarization test (corrosion current) for 1 hour in a _0.1NH2SO4 + 2ppm _HF aqueous solution at 80℃ in Example 1, and Figure 5 shows the results of changes in contact resistance according to pressure changes in Example 1. Specific methods for measuring corrosion current and contact resistance of the examples and comparative examples of the present invention will be described later.

Figure 6 is a SEM image of the carbon layer surface of Example 1 after the first and second depositions were completed.

<Example 2>

In the same manner as in Example 1, a metal layer and a first deposition were performed on a metal base material, and a carbon layer having graphite doped inside the amorphous carbon in the lower layer and some graphite exposed on the surface of the amorphous carbon in the upper layer was deposited. Thereafter, amorphous carbon was deposited on the surface of the carbon layer on which the first deposition was completed using a carbon material target by sputtering. (Second deposition) The thicknesses of the carbon layers of the first deposition and the second deposition are 0.19 to 0.20 um/0.02 to 0.03 um (first deposition thickness/second deposition thickness), respectively.

<Example 3>

A carbon layer (performing the first and second depositions) is formed in the same manner as in Example 1, but the thickness of the carbon layer is 0.48 to 0.50 μm/0.02 to 0.03 μm. As the thickness of the carbon layer increases, the corrosion current is more excellent than in Example 1, and has a contact resistance value of less than 15 mΩ·cm ² .

<Example 4>

A carbon layer (performing the first and second depositions) is formed in the same manner as in Example 1, but the thickness of the carbon layer is 1.8 to 2.0 μm/0.13 to 0.15 μm.

<Example 5>

In order to remove the natural oxide film and foreign substances on the surface of the metal base material in the same manner as Example 1, a dry etching method was used. Then, a 0.06 μm metal layer (TiN) was formed on the metal base material by sputtering. Thereafter, a carbon layer (first and second depositions) was formed, and the thickness of the carbon layer was 0.48 to 0.50 μm/0.02 to 0.03 μm. When the metal layer was deposited with TiN, the corrosion current was at the same level as in Example 3, and had a contact resistance value of less than 15 mΩ·cm ² .

<Example 6>

In order to remove the natural oxide film and foreign substances on the surface of the metal base material in the same manner as Example 1, a dry etching method was used. Then, a 0.06 μm metal layer (Cr) was formed on the metal base material by sputtering. Thereafter, a carbon layer (first and second depositions) was formed, and the thickness of the carbon layer was 0.19 to 0.20 μm/0.02 to 0.03 μm. When the metal layer was deposited with Cr, the corrosion current was at the same level as in Example 2, and had a contact resistance value of less than 15 mΩ·cm ² .

<Example 7>

In order to remove the natural oxide film and foreign substances on the surface of the metal base material, a dry etching method was used in the same manner as Example 1. Then, a 0.06 μm metal layer (CrN) was formed on the metal base material by sputtering. Thereafter, a carbon layer (first and second depositions) was formed, and the thickness of the carbon layer was 0.19 to 0.20 μm/0.02 to 0.03 μm. At this time, in a static potential polarization test, it had a corrosion current value of less than 1 μA/cm ² and a contact resistance of less than 15 mΩ·cm ² .

<Comparative Example 1>

In order to remove the natural oxide film and foreign substances on the surface of the metal base material, a dry etching method was used in the same manner as in Example 1. Then, a 0.06 μm metal layer (Ti) was formed on the metal base material by sputtering. Thereafter, a carbon layer (first and second depositions were performed) was formed, and the thickness of the carbon layer was 3.3 to 3.5 μm/0.28 to 0.30 μm. Comparative Example 1 showed that the contact resistance exceeded 15 mΩ·cm ² .

<Comparative Example 2>

In the same manner as in Example 1, a metal layer and a first deposition were performed on a metal base material, and a carbon layer with doped graphite inside the amorphous carbon in the lower layer and some graphite exposed on the surface of the amorphous carbon in the upper layer was deposited to a thickness of 0.04 to 0.05 μm. That is, Comparative Example 2 did not perform the second deposition, unlike Example 1. As a result of analyzing the SEM image of the surface of the fuel cell separator of Comparative Example 2, many graphite parts exposed from the surface of the carbon layer were observed. Fig. 7 is an SEM image of the surface of the carbon layer of Comparative Example 2. Comparative Example 2 was found to have a corrosion current exceeding 1 μA/cm ² .

<Comparative Example 3>

In the same manner as Example 1, a metal layer and a first deposition were performed on a metal base material, and a carbon layer having a thickness of 0.48 to 0.50 μm was deposited, with graphite doped inside the amorphous carbon in the lower layer and some graphite exposed on the surface of the amorphous carbon in the upper layer, and the second deposition was not performed separately. Comparative Example 3 showed that the corrosion current exceeded 1 μA/cm ² .

In order to simulate the environment during lamination and fastening of the metal separators for fuel cells of the examples and comparative examples, the following experiment was conducted. Prior to the property evaluation test, in order to provide the same conditions as the environment during lamination and fastening of the separators for fuel cells, a pressure equal to the load and fastening pressure was applied to the separators (two pieces) for fuel cells of the examples and comparative examples using the pressurizing device of Fig. 8.

Specifically, referring to Fig. 8, while two separator plates (100) are facing each other, a pressure plate (200) is placed on the upper and lower surfaces facing each separator plate, and then the pressure plates (200) are simultaneously and slowly moved in the direction of the fuel cell separator plates (100) while pressurizing up to a maximum pressure of 1 MPa. Thereafter, the pressure is released by simultaneously and slowly moving the pressure plates (200) away from each separator plate (100). This is repeated 10 times.

When stacking and fastening metal separators for fuel cells, the load and fastening pressure are simulated in a state where the outermost surfaces of the fuel cell separators, i.e. the carbon layers, are in contact with each other, and stress is applied between the carbon layers that occurs during fastening by repeating the pressing and releasing.

The metal separator plates for fuel cells of the examples and comparative examples were separated from the pressurized plate (200), and the contact resistance, corrosion current, and long-term durability were measured as follows.

Experimental Example 1: Contact Resistance Measurement

Figure 9 is a drawing for explaining a method for measuring the contact resistance of a metal separator for a fuel cell.

Referring to the left drawing of Fig. 9, after laminating three gas diffusion layers (GDL) of SGL, each gas diffusion layer located at both ends was pressurized to 1 MPa, and a current of DC 5 A and AC 0.5 A was applied to a current supply device capable of supplying current to the gas diffusion layers, and the contact resistance value (R ₁ ) was measured.

As shown in the right drawing of Fig. 9, two metal separators (100) to be measured (Anode/Cathode) were laminated between four gas diffusion layers (GDL) of SGL, and each gas diffusion layer located at both ends was pressurized to 1 MPa. Then, a current of DC 5 A and AC 0.5 A was applied to a current supply device capable of supplying current to the metal separator (100) to measure the contact resistance value (R ₂ ).

The results of calculating the contact resistance (R) of the metal separator using the following mathematical formula 1 based on the values of R ₁ and R ₂ are as shown in Table 1.

[Mathematical Formula 1]: (R ₂ - R ₁ ) X Reaction Area = R (Unit: mΩ·㎠)

In the above mathematical expression 1, the reaction area refers to the area of the metal separator facing the membrane electrode assembly (MEA) among the total area of the metal separator and through which the flow of fuel gas occurs in the membrane electrode assembly. Examples 1 to 7 and Comparative Examples 1 to 3 all have the same reaction area of 276 cm ² .

Experimental Example 2: Corrosion Current Measurement

In order to measure the corrosion current of the metal separator for fuel cells according to Examples 1 to 7 and Comparative Examples 1 to 3, GAMRY INTERFACE 1010E was used as the measuring device. The corrosion durability test was conducted in an environment similar to the operating environment of a PEMFC (Polymer Electrolyte Membrane Fuel Cell).

A 0.1 N H2SO4 + 2 ppm HF solution at 80°C was used as the experimental solution for corrosion of the metal separator. After air bubbling for 30 minutes, a constant potential of 0.6 V (SCE) was applied and the current density was measured for 1 hour.

The results of measuring the corrosion current of the examples and comparative examples are shown in Table 1.

Experimental Example 3: Long-term durability evaluation

A 20-cell fuel cell stack was fabricated by placing a membrane electrode assembly and a gas diffusion layer between metal separators and then fastening them together.

Hydrogen and air were used as reaction gases, and the flow rate was supplied after humidifying at 50% relative humidity while maintaining the stoichiometric ratio of hydrogen 1.5 and air 2.0 constant depending on the current. The temperature of the stack was maintained at 65℃, and the performance was evaluated under atmospheric pressure conditions.

The deterioration rate calculation formula for evaluation is as shown in Mathematical Formula 2 below.

[Mathematical expression 2] Deterioration rate = (evaluation start voltage - evaluation end voltage) χ (evaluation time)

Figure 10 shows the results of a long-term durability evaluation of Example 2 of the present invention. As a result of the evaluation, the starting voltage was 0.7751 V, the ending voltage was 0.7733 V, and the deterioration rate was calculated as 1.8 μV/h according to mathematical expression 2.

Examples 1 to 7 of the present invention were confirmed to simultaneously satisfy corrosion resistance and electrical conductivity since the corrosion current was within 1 μA/cm ² and the contact resistance was within 15 mΩ·cm ² . However, Comparative Examples 1 to 3 were confirmed to have corrosion currents exceeding 1 μA/cm ² or The contact resistance exceeded 15 mΩ·cm ^2. Therefore, the metal separator according to the embodiment of the present invention can maintain durability even under stress generated during fastening.

100: Metal separator
110: metal base material 120: metal layer
130: Carbon layer 131: Amorphous carbon
132: Graphite
200: Pressurized plate

Claims (9)

metal substrate;
A metal layer formed on the above metal base material; and
A metal separator for a fuel cell including a carbon layer formed on the metal layer, wherein the carbon layer is doped with graphite having crystallinity within a matrix of amorphous carbon, such that when the upper surface of the carbon layer is viewed from above the carbon layer, exposed graphite is not observed and only smooth amorphous carbon is observed. delete In the first paragraph,
The above carbon layer is formed by a deposition method,
A first deposition forming graphite doped within a matrix of amorphous carbon and graphite at least partially exposed on the surface of the amorphous carbon; and
A metal separator for a fuel cell, characterized in that it is manufactured by a second deposition that covers the exposed surface of graphite with amorphous carbon. In the third paragraph,
The above deposition methods include chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD).
A metal separator for a fuel cell, characterized in that after the first deposition is completed, the second deposition is performed to form the carbon layer. In the third paragraph,
The above first deposition and the above second deposition form a carbon layer by a physical deposition method.
A metal separator for a fuel cell, characterized in that the first deposition is performed by arc ion plating and the second deposition is performed by sputtering. In the third paragraph,
The thickness of the above carbon layer is 0.02 to 3.0 μm,
A metal separator for a fuel cell, characterized in that the average thickness (T) of the carbon layer formed by the second deposition is 0.01 to 2 μm. In the first paragraph,
The above metal layer
A metal separator for a fuel cell, characterized in that it is formed by depositing at least one metal selected from titanium (Ti), aluminum (Al), zirconium (Zr), copper (Cu), gold (Au), silver (Ag), molybdenum (Mo), tungsten (W), chromium (Cr), titanium (Ti), scandinium (Sc), vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni) on a metal base material. In the first paragraph,
A metal separator for a fuel cell, characterized in that the above metal base material is surface-treated by dry etching to remove a natural oxide film and impurities. In the first paragraph,
The above metal separator for fuel cell
A metal separator for a fuel cell, characterized in that the corrosion current is 1 μA/cm ² or less and the contact resistance is 15 mΩ·cm ² or less.