KR101372645B1 - Metal separator for fuel cell and method of manufacturing the same - Google Patents

Abstract

Disclosed are a metal separator for a fuel cell having excellent physical properties such as adhesion, corrosion resistance, conductivity, and durability through plasma carburization, and a method of manufacturing the same.
Method for manufacturing a metal separator plate for a fuel cell according to the present invention comprises: (a) a pretreatment step of activating a metal base material surface; (b) forming a metal coating layer on the pretreated metal base material; And (c) forming a carburized layer on the surface of the metal coating layer by using a hydrocarbon gas in a plasma state.

Description

METAL SEPARATOR FOR FUEL CELL AND METHOD OF MANUFACTURING THE SAME

The present invention relates to a metal separator plate for fuel cells, and more particularly, by performing a plasma carburizing treatment on a metal base material molded into a separator plate shape to improve physical properties such as corrosion resistance, conductivity, and durability of the metal separator plate for fuel cell. The present invention relates to a metal separator for fuel cells, and a method of manufacturing the same.

Fuel cell is a cell that converts the chemical energy generated by the oxidation of fuel directly into electric energy. In order to overcome problems such as depletion of fossil fuel, greenhouse effect by carbon dioxide generation, and global warming, A lot of research has been done together.

Fuel cells generally convert chemical energy into electrical energy using oxidation and reduction reactions of hydrogen and oxygen. Hydrogen is oxidized at the anode and separated into hydrogen ions and electrons, and the hydrogen ions move through the electrolyte to the cathode. At this time, the electrons move to the anode through the circuit. At the anode, a reduction reaction occurs in which hydrogen ions, electrons, and oxygen react to form water.

Since a unit cell of a fuel cell has low voltage and low practicality, generally, several to hundreds of unit cells are stacked and used. A separator is a separator that performs electrical connection between each unit cell and separates the reaction gas when the unit cells are stacked.

Fuel cell separators are classified into graphite separators and metal separators according to their materials.

The graphite separator is widely used in conventional separators for fuel cells, and is manufactured by milling graphite according to the flow path. In this case, the fraction occupied by the separator of the graphite material occupied 50% of the entire stack and 80% of the weight. Therefore, the separator plate made of graphite has problems such as high cost and large volume.

In order to overcome the problems of the graphite separator plate, a metal separator plate has been developed. The metal separator plate is easy to process and can reduce the overall volume and weight of the fuel cell by reducing the thickness of the separator plate. There are several advantages, such as the ease of mass production.

However, metal corrosion caused by fuel cell use may cause contamination of the membrane electrode assembly, thereby degrading fuel cell stack performance, and thick oxide film growth on the metal surface may increase fuel cell internal resistance after prolonged use. It can act as a factor.

Accordingly, a metal separator for fuel cells having high corrosion resistance and electrical conductivity is required to improve the performance of the metal separator by suppressing corrosion of the metal in the metal separator and increase in internal resistance of the fuel cell.

SUMMARY OF THE INVENTION An object of the present invention is to provide a metal separator plate for a fuel cell and a method of manufacturing the same, by forming a plasma carburized layer having a thin thickness on a metal separator plate coated metal surface, thereby ensuring high corrosion resistance and conductivity.

Method for producing a metal separator plate for a fuel cell according to the present invention for achieving the above object (a) a pretreatment step of activating the surface of the metal base material molded into the shape of the separator; (b) forming a metal coating layer on the pretreated metal base material; And (c) forming a carburized layer on the surface of the metal coating layer by using a hydrocarbon gas in a plasma state.

In this case, the step (a) may include the step of wet treating the surface of the metal base material using a cleaning liquid, and the step of dry treatment of the wet treated metal base material surface using an atmospheric pressure plasma.

In addition, the metal separator for a fuel cell according to the present invention for achieving the above object is formed in the shape of a separator plate, the metal base material surface oxide removed; A metal coating layer formed on a surface of the metal base material; And a plasma carburized layer formed on the surface of the metal coating layer.

In this case, the metal coating layer may be formed of chromium (Cr) or titanium (Ti), in which case the plasma carburized layer is formed with chromium carbide (Cr _x C _Y ) or titanium carbide (Ti _x C _Y ). desirable.

The metal separator plate for fuel cells according to the present invention can improve corrosion resistance, conductivity and durability by forming a carburized layer on the surface side.

In addition, the metal separator plate for fuel cells according to the present invention can form a high density carburized layer even at a low process cost, thereby reducing the overall manufacturing cost of the fuel cell metal separator plate, and reducing the thickness of the fuel cell metal separator plate. Can be reduced.

In addition, the method for manufacturing a metal separator plate for fuel cells according to the present invention may improve the adhesion of the metal coating layer by removing oxides on the surface of the metal base material through a dry treatment using an atmospheric pressure plasma.

1 schematically shows a metal separator for a fuel cell according to an embodiment of the present invention.
2 is a schematic cross-sectional view of a method of manufacturing a fuel cell metal separator according to an exemplary embodiment of the present invention.
Figure 3 schematically shows an apparatus used for measuring the contact resistance of a metal separator specimen in an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and how to accomplish them, will become apparent with reference to the embodiments and drawings described in detail below.

However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

Hereinafter, a metal separator for a fuel cell using plasma carburization and a method of manufacturing the same will be described in detail.

1 is a cross-sectional view schematically showing a metal separator for a fuel cell according to an embodiment of the present invention.

Referring to FIG. 1, the illustrated metal separator includes a metal base material 110, a metal coating layer 120, and a plasma carburizing layer 130.

The metal base material 110 may be used without limitation as long as it is used in a metal separator plate for fuel cells. For example, the metal base material 110 may be formed of a material including stainless steel, aluminum, titanium, nickel, and the like. Among them, the metal base material of stainless steel, which is light and excellent in corrosion resistance, may be regarded as the most preferable.

On the other hand, the material constituting the metal base material 110 does not show a satisfactory level of corrosion resistance and electrical conductivity properties under high temperature and high humidity environment of the fuel cell, in the present invention, the surface of the metal base material 110 to compensate for this point The metal coating layer 120 is formed on the plasma carburizing layer 130 on the surface of the metal coating layer 120.

The metal coating layer 120 is formed to improve the electrical conductivity of the metal separator. In consideration of this point, the metal coating layer 120 may be formed of chromium (Cr) or titanium (Ti) having excellent electrical conductivity and corrosion resistance.

The metal coating layer 120 may be formed to a thickness of about 0.01 to 5.0 ㎛ in consideration of the electrical conductivity improvement effect and manufacturing cost.

Through the metal coating layer 120, it is possible to secure the electrical conductivity, corrosion resistance and the like of the metal separator.

On the other hand, an oxide layer is present on the surface of the metal base material 110. The oxide layer on the surface of the metal base material 110 serves as an element that inhibits the adhesion of the metal coating layer 120. Therefore, the oxide present on the surface of the metal base material 110 may be removed so that the adhesion of the metal coating layer 120 to the metal base material 110 may be improved. This can be done by dry treatment using atmospheric pressure plasma.

On the other hand, when the metal separator plate for fuel cells is exposed to a high temperature and humidity harsh fuel cell use environment for a long time, the metal coating layer 120 may also lower the corrosion resistance and durability.

Therefore, in the present invention, the plasma carburizing layer 130 is formed on the surface of the metal coating layer 120 so as to ensure long-term durability of the metal separation plate.

Of course, carbon coating may be considered to ensure corrosion resistance and durability of the metal separator. In this case, however, the carbon coating layer must be separately formed, and thus adhesion between the carbon coating layer and the heterogeneous metal coating layer may be degraded, and complicated process conditions are required to improve the carbon coating layer. However, in the case of the plasma carburizing layer 130, the adhesion is not a problem because the layer is formed by carburizing rather than a separate coating layer.

The plasma carburizing layer 130 is preferably formed of chromium carbide (Cr _x C _Y ) or titanium carbide (Ti _x C _Y ) having corrosion resistance and electrical conductivity depending on the material of the metal coating layer 120. In this case, it is possible to suppress the formation of metal carbide, which is formed on the surface at high temperature and for a long time of exposure, thereby lowering the corrosion resistance and contact resistance. In the case of the present invention, these compounds were formed by the plasma carburization process described later, and the results of the experiment were excellent in corrosion resistance and contact resistance.

2 is a schematic cross-sectional view of a method of manufacturing a fuel cell metal separator according to an exemplary embodiment of the present invention.

Referring to FIG. 2, the illustrated method for manufacturing a metal separator plate for a fuel cell includes a metal base material pretreatment step S210, a metal coating step S220, and a plasma carburizing step S230.

First, in the metal base material pretreatment step S210, impurities on the surface of the metal base material are removed, and the metal base material surface is activated by removing oxides on the surface of the metal base material.

The metal base material pretreatment step S210 may more specifically include a wet treatment step S212 and a dry treatment step S214.

In the wet treatment step S212, organic or inorganic substances on the surface of the metal base material including stainless steel, aluminum (Al), titanium (Ti), nickel (Ni), and the like are removed through a wet treatment using a cleaning solution.

As the cleaning liquid for wet treatment, a cleaning liquid containing at least one of acetone and ethanol may be used. The wet treatment may be carried out at least once using a cleaning solution, preferably 5-10 minutes each time. If the wet treatment time per time is less than 5 minutes, the cleaning effect may be insufficient. On the other hand, when the wet treatment time per time exceeds 10 minutes, only productivity may be reduced without further cleaning effect.

In the dry treatment step (S214), the surface of the metal base material is activated by removing the fine organic material or the inorganic material on the wet-treated metal base material surface and removing the oxides and the like from the metal base material surface. Through such a dry treatment, the adhesion of the metal coating layer formed on the metal base material may be increased. In the present invention, the atmospheric pressure plasma is used for such a dry treatment. Here, the normal pressure means a state in which no artificial pressure is added or reduced.

In the case of the dry treatment by the atmospheric pressure plasma, it is possible to greatly reduce the cost incurred in the device and the process compared to the dry treatment by the low pressure plasma, there is an advantage that can reduce the stress applied to the metal base material during the dry treatment. In addition, the surface activation energy can be increased to increase the effectiveness of the coating.

The gas to be plasma at normal pressure for the dry treatment may be oxygen (O ₂ ), nitrogen (N ₂ ), hydrogen (H ₂ ), argon (Ar) gas and the like. These gases can be used individually by 1 type of gases, and can mix and use 2 or more types of gases.

The dry treatment can be carried out at a normal pressure to plasma these gases and supply them to the metal substrate surface to etch the metal substrate surface. The etching thickness of the metal base material surface by the atmospheric pressure plasma may be determined by the thickness of the oxide layer or the like, and may be 1 to 10,000 nm.

When the etching thickness of the surface of the metal base material by the atmospheric pressure plasma is less than 1 nm, it is difficult to completely remove the surface oxides, and when the etching thickness of the surface of the metal base material by the atmospheric pressure plasma exceeds 10,000 nm, the productivity decreases due to excessive dry treatment. There is a problem.

Next, in the metal coating step (S220), in order to improve the electrical conductivity of the metal separator, etc., a metal coating layer is formed on the pretreated metal base material.

The metal coating may be applied by sputtering or the like. The metal coating layer may be formed of chromium (Cr) or titanium (Ti).

Next, in the plasma carburization step (S230), a carburized layer is formed on the surface of the metal coating layer by using a hydrocarbon gas in a plasma state.

The hydrocarbon gas to be plasma for plasma carburization may be used a variety of hydrocarbon gas, such as CH ₄ , C ₂ H ₆ , these hydrocarbon gases may be used alone or in combination of two or more.

In addition, these hydrocarbon gases may be mixed and used with gases such as hydrogen (H ₂ ), argon (Ar), and the like. These gases serve to improve the carburizing effect on the surface of the metal coating layer.

Plasma carburization is preferably carried out for 5 minutes to 20 hours under a pressure condition of 1 ~ 10 torr, temperature conditions of 300 ~ 800 ℃. Under these conditions, generation of metal carbide on the surface can be minimized.

If the internal pressure of the equipment during plasma carburization is less than 1 torr, the plasma carburization cost may increase significantly. If the internal pressure of the equipment exceeds 10 torr, the carburizing layer may not be properly formed.

In addition, if the internal temperature of the equipment is less than 300 ° C during plasma carburization, the formation of a carburized layer may not be performed properly. If the internal temperature of the device exceeds 800 ° C, a large amount of metal carbide is formed in the plasma carburized layer to reduce corrosion resistance and contact resistance. can do. In addition, when the carburizing time of the plasma is less than 5 minutes, the carburizing layer formation is insufficient, and when the carburizing time of the plasma exceeds 20 hours, productivity is a problem.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

1. Preparation of Metal Separator Specimen for Fuel Cell

Example 1

Stainless steel (SUS 316L, 0.1 mm thick) was used as the metal base material, and wet treatment was performed for 5 minutes with acetone and 5 minutes with ethanol. Dry treatment was performed. Thereafter, a chromium coating layer having a thickness of 2 μm was formed by sputtering. Thereafter, CH ₄ and argon gas were plasmalated at ₅ torr and 300 ° C. for 30 minutes to carburize the surface, thereby preparing a metal separator specimen.

Example 2

A metal separator was prepared in the same manner as in Example 1 except that the titanium coating layer was formed instead of the chromium coating layer.

Comparative Example 1

A metal separator specimen was prepared in the same manner as in Example 1 except that the wet treatment and the dry treatment were not performed.

Comparative Example 2

A metal separator plate specimen was prepared in the same manner as in Example 1 except that the dry treatment was not performed.

Comparative Example 3

A metal separator plate specimen was prepared in the same manner as in Example 1 except that the temperature condition of the plasma carburizing was 1000 ° C.

2. Property evaluation

(1) Contact resistance measurement

Figure 3 schematically shows an apparatus used for measuring the contact resistance of a metal separator specimen in an embodiment of the present invention.

Referring to Figure 3, the modified David method (Davies method) to measure the contact resistance between the metal separator and the carbon paper in order to obtain an optimized constant for fastening the cell for measuring the contact resistance of the metal separator specimen 300 It was used to.

Contact resistance was measured with Zahner's IM6D instrument using a four-wire current-voltage measurement principle.

In the constant current mode, the contact resistances were measured in the range of 10 kHz to 10 mHz with DC 5A and AC 0.5A in the measurement range. Carbon paper used 10BB of SGL Corporation.

The contact resistance measuring device 30 is provided with carbon paper 320, gold plated copper plate 310 up and down with the specimen 300 between, and the copper plate 310 is a current supply device ( 330 and the voltage measuring device 340.

The voltage was measured by applying a current of DC 5A / AC 0.5A to a current supply device (330, IM6 manufactured by Zahner) capable of supplying current to the specimen 300.

In addition, an instron capable of providing pressure to the specimen 300, the carbon paper 320, and the copper plate 310 to have a stacked structure above and below the copper plate 310 of the contact resistance measuring device 30. (Model 5566, compression test) is prepared. The pressure gauge provides a pressure of 100 N / cm ² to the contact resistance measuring device 30.

The contact resistance of the specimen 300 manufactured according to Examples 1 to 2 and Comparative Examples 1 to 3 was measured by the contact resistance measuring apparatus 30 prepared as described above.

 (2) Measurement of corrosion current

EG & G 273A was used as a measuring device for measuring the corrosion current of the metal separator according to Examples 1 to 2 and Comparative Examples 1 to 3. Corrosion endurance experiments were conducted under a similar environment to the driving atmosphere of the PEFC (Polymer Electrolyte Fuel Cell).

As a test solution for corrosion of the metal separator, 0.1NH ₂ SO ₄ + 5ppm HF solution at 80 ° C was used, and after N ₂ bubbling for 1 hour, OCP (Open Circuit Potential) was measured in the range of 0.25V to 1.2V vs SCE. .

In addition, physical properties were measured at -0.24V vs SCE for PEFC anode environment and 0.6V vs SCE for Saturated Calomel Electrode (SCE).

Here, the physical property comparison was evaluated through the corrosion current data of 0.6 V vs SCE in the cathode environment similar to the fuel cell environment.

The anode environment is an environment in which hydrogen is separated into hydrogen ions and electrons in a membrane electrode assembly (MEA), and the cathode environment is a reaction in which oxygen combines with hydrogen ions and electrons to generate water. It's an environment that happens.

In this case, since the potential of the cathode environment is high and the harsher corrosion conditions are more severe, it is preferable to test the corrosion resistance based on the cathode environment.

3. Results of physical property evaluation

Table 1 shows the results of evaluation of physical properties of the metal separator plate prepared according to Examples 1 to 2 and Comparative Examples 1 to 3.

[Table 1]

Referring to Table 1, in the case of the specimens according to Examples 1 to 2 of the present invention, it can be seen that the corrosion current is 1 mA / cm ² or less, and the contact resistance is 10 mPa · cm ² or less. In addition, as a result of the analysis, in the case of the specimen according to Example 1, chromium carbide (Cr _x C _Y ) was formed in the plasma carburized layer, and in the case of the specimen according to Example 2, titanium carbide (Ti _x C _Y ) in the plasma carburized layer this Formed.

However, in the case of the specimens according to Comparative Examples 1 and 2 not subjected to the dry treatment, the corrosion current and the contact resistance could not be measured due to the peeling of the metal coating layer.

In addition, in the specimen according to Comparative Example 3 subjected to surface carburization at 1000 ° C., the corrosion current and the contact resistance were relatively higher than those in Examples 1 and 2. Cr ₂₃ C ₆ was formed in the plasma carburizing layer in a large amount in the specimen according to Comparative Example 3, and it appears that the corrosion current and the contact resistance were relatively increased due to the Cr ₂₃ C ₆ .

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

110: metal base material
120: metal coating layer
130: plasma carburized layer
S210: Metal Matrix Pretreatment Step
S212: wet processing steps
S214: Dry Processing Step
S220: metal coating step
S230: Plasma Carburization Step
30: contact resistance measuring device
300: metal separator specimen
310: copper plate
320: carbon paper
330: current supply device
340: voltage measuring device

Claims (12)

(a) a pretreatment step of activating a metal matrix surface;
(b) forming a metal coating layer on the pretreated metal base material; And
(c) plasma treatment of at least one hydrocarbon gas under a pressure condition of 1 to 10 torr and a temperature of 300 to 800 ° C. for 5 minutes to 20 hours to form a carburized layer having corrosion resistance and electrical conductivity under the surface of the metal coating layer. Method for producing a metal separator plate for a fuel cell comprising a.
The method of claim 1,
The step (a)
Wet treating the surface of the metal base material using a cleaning liquid,
Method of manufacturing a metal separator plate for a fuel cell comprising the step of dry treating the surface of the wet metal base material using an atmospheric pressure plasma.
3. The method of claim 2,
The wet treatment is
Method for producing a metal separator plate for a fuel cell, characterized in that carried out one or more times using a cleaning solution containing at least one of acetone and ethanol, each 5 to 10 minutes.
3. The method of claim 2,
The dry treatment is
Plasma-forming at least one of oxygen (O ₂ ), nitrogen (N ₂ ), hydrogen (H ₂ ) and argon (Ar) gases at atmospheric pressure so that the etching thickness of the surface of the metal base material is 1 to 10,000 nm. Method for producing a metal separator plate for a fuel cell, characterized in that.
The method of claim 1,
The step (c)
A method for producing a metal separator plate for fuel cells, characterized in that the plasma is formed by at least one gas selected from hydrogen (H ₂ ) and argon (Ar) and at least one hydrocarbon gas.
delete The method of claim 1,
The metal base material is
Method for manufacturing a metal separator plate for a fuel cell, characterized in that formed of a material containing a metal selected from stainless steel, aluminum (Al), titanium (Ti) and nickel (Ni).
The method of claim 1,
The metal coating layer
Method for manufacturing a metal separator plate for a fuel cell, characterized in that formed of chromium (Cr) or titanium (Ti).
delete delete delete delete

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