KR101114298B1 - A Stainless steel Bipolar Plate Adding P On The Surface - Google Patents

Abstract

The present invention relates to a fuel cell separator.

Currently, a lot of research has been reported on the process of replacing the conventional fuel cell separator with stainless steel. On the other hand, the present invention is a technology that can be commercialized while satisfying the price and performance, and to provide a competitive fuel cell separator and a method of manufacturing the same having good corrosion resistance, electrical conductivity, thermal conductivity and gas impermeability and processability.

According to the present invention, P is added to the innermost surface of the fuel cell separator made of stainless steel and the adjacent material by the electrolytic plasma polishing method so that both corrosion resistance and electrical conductivity can be maintained excellent, which is the core technology of the present invention. to be.

According to the present invention, a fuel cell separator plate made of stainless steel is connected to an anode, an electrolyte is introduced into an electrolytic cell, an underwater plasma is generated to polish a stainless fuel cell separator plate, and a P atom is formed on the surface of the fuel cell separator plate. It provides a process for penetrating and thereby commercialization of the fuel cell separator.

Automotive Fuel Cells, Fuel Cell Separator, Electrolytic Plasma Polishing (PEP), P Add Stainless Steel

Description

A stainless steel fuel cell separator with P added to its surface and a method of manufacturing the same {A Stainless steel Bipolar Plate Adding P On The Surface}

The present invention relates to a separator of a stainless steel fuel cell, and more particularly, to a method of manufacturing a separator used for a fuel cell for automobiles using high quality and low cost using an electrolyte plasma.

FIG. 1A is a schematic view showing the structure of a general fuel cell, FIG. 1B is a perspective view schematically showing the structure of a fuel cell employing a fuel cell separator, and FIG. 1C is a front view of the separator showing the structure of the fuel cell separator.

In general, a fuel cell separator plate for a vehicle is a conductive plate separating each cell from a fuel cell stack. In two adjacent cells, a separator plate serves as a fuel electrode plate in one cell and an air electrode plate in another cell. Plays a role. The separation plate secures a flow path of fuel gas and air and transmits current to an external circuit. Accordingly, high electrical and thermal conductivity, corrosion resistance, processability and low gas permeability are required. That is, high corrosion resistance is required for corrosion current at 0.1 V, and electrical conductivity requires 100 S / cm. In addition, it must additionally be stable at heat from -40 to 120 ° C., requiring low gas permeability and, above all, low manufacturing costs.

Fuel cell separators are made of graphite, metal, etc., and are being developed in various ways to simultaneously satisfy corrosion resistance, conductivity, and price competitiveness.

The amount of fuel cell power required by one passenger car is 80 kw to 100 kw. When a single fuel cell separator plate is placed, about 100 watts of power are supplied, so approximately 1000 separator plates are needed for a passenger car. . Therefore, the fuel cell becomes expensive, resulting in an increase in the price of a passenger car, and the price of the current target separator is 5 $ / kw.

Among the materials under study, impregnated graphite plates have the advantages of low surface contact resistance and high corrosion resistance, but they are weak, permeable to gas, high in production cost, and limited to 2 mm even when processed to the minimum thickness. If it is 1,000 pieces, it is very bulky at 2m and is hard to adopt.

In addition, in the case of metal, high mechanical strength, impact and vibration resistance, gas impermeability, excellent fabrication and low production cost compared to graphite, but there is a problem of poor corrosion resistance and poor electrical conductivity due to the formation of oxide on the surface. .

In addition, the metal having good corrosion resistance has the advantage of protecting the bulk metal by the inert oxygen layer, but there is a problem of high surface contact resistance.

In addition, when manufacturing the separator plate with PVD coating to improve the corrosion resistance and conductivity, the quality is somewhat good, but the manufacturing cost is very high.

Therefore, the material suitable for the fuel cell separator is preferably selected to be lightweight, excellent in corrosion resistance, heat resistance, electrical conductivity and processability, and low in processing cost. In such a situation, the current mainstream technology is made of stainless steel S -It is manufacturing a separator plate from stainless steel nitride plate by using phase nitriding technology, and its production has been tried in various ways to secure price competitiveness.

Accordingly, an object of the present invention is to provide a breakthrough manufacturing method of a fuel cell separator having a low cost of production, and a fuel cell separator according to the present invention. Is to provide.

The present invention, in the surface processing of the fuel cell separator plate made of metal,

The P-added fuel cell separator may be provided during the plasma polishing process to continuously provide excellent corrosion resistance and electrical conductivity of the fuel cell separator.

The present invention connects the fuel cell separator plate made of stainless steel to the positive electrode, connects the electrolytic cell to the negative electrode, adds an electrolyte containing P to the electrolytic cell, generates an underwater plasma, and then polishes the fuel cell separator plate. It can provide a method for producing a fuel cell separator, characterized in that to penetrate the P atoms in the fuel cell separator in an electrolyte comprising a.

In addition, the present invention can provide a method for producing a fuel cell separator, wherein the voltage applied to the positive electrode and the negative electrode is 100 V to 350 V in the method of manufacturing the fuel cell separator.

In addition, the present invention, in the fuel cell separator manufacturing method, the concentration of the electrolyte may provide a method for producing a fuel cell separator, characterized in that 3 to 20% by weight.

In addition, the present invention, in the fuel cell separator manufacturing method, the electrolyte is H ₃ PO ₄ or Na ₃ PO ₄ It is possible to provide a method for producing a fuel cell separator, which is characterized in that.

In addition, the present invention can provide a method for producing a fuel cell separator, wherein the initial temperature of the electrolyte introduced into the electrolytic cell is 60 ° C to 80 ° C.

In addition, the present invention is the manufacturing method of the fuel cell separator, wherein the applied voltage is performed in a pulsed manner, the frequency is 5 kHz to 20 kHz, and plasma polishing is performed for 3 to 6 minutes. It is possible to provide a method for producing a fuel cell separator.

In addition, the present invention, in the method of manufacturing the fuel cell separator, the duty time in the pulse method is D ⁺ / D ^- 50/45% (the ratio of the duty on / duty off duration of the pulse voltage 50:45) can be provided.

In addition, the present invention can provide a fuel cell separation plate having improved corrosion resistance by penetrating P into the surface layer of the fuel cell separation plate made of stainless steel.

According to the present invention, fuel cell separators having excellent corrosion resistance, electrical conductivity, gas impermeability, heat resistance, and processability, and low manufacturing costs can be supplied with a competitive price.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a schematic diagram of a device for fabricating a fuel cell separator using Electrolytic Plasma Electrloytic Polishing (PEP) in accordance with the present invention.

Electrolytic plasma polishing technology (hereinafter referred to as PEP) applies a voltage to the aqueous electrolyte solution, forms a plasma layer through bubbles generated around the anode, oxidizes the surface layer of the sample on the anode, and simultaneously removes the metal. It is a new technique for cleaning or polishing surfaces. Compared to chemical polishing and electropolishing, the process is simpler, and a weak alkali electrolyte is mainly used for environment-friendly technology, but the application of the polishing mechanism is not yet fully known. The principle of plasma polishing is that the iron part of the surface of the uneven material such as electrolytic polishing or chemical polishing first dissolves in the electrolyte to create gas bubbles, and the dissolved ions and electrolyte ions form a vapor gas film (VGE). It is speculated that a thin film oxide layer is formed on the iron portion of the instantaneously heated surface, and the planarization proceeds to polish by the same principle as the previous polishing.

The inventors of the present invention fabricated a fuel cell separator by applying an electrolyte plasma technique to stainless steel, which is widely applied to electropolishing industrially, and also pursued process optimization by investigating the characteristics of each process variable.

The electrolyzer consists of stainless steel material and fills the electrolyte therein, and in this embodiment, fills the electrolyte including P in particular.

Examples of the electrolyte including P include, but are not limited to, H ₃ PO ₄ or Na ₃ PO ₄ .

Usually, when P exists in Fe, including stainless steel, it is known to deteriorate physical properties, such as mechanical strength of steel, and, mostly, effort was made to remove P from steel. However, the inventors attempted to reinforce the corrosion resistance of stainless steel by adding a small amount of P to the stainless steel in reverse conception.

The electrolyte containing P contained in the electrolytic cell is preheated to raise the temperature to 60 ℃ to 80 ℃, preferably 70 ℃.

The negative electrode of the power supply device is connected to the electrolytic cell, and the fuel cell separator base material of stainless steel is connected to the positive electrode. In addition, a stirrer for stirring the electrolyte solution and a thermometer for measuring the temperature of the electrolyte are installed in the electrolytic cell. It is the temperature range chosen for system optimization because of the higher current density in this temperature range.

In addition, voltage application was attempted by dividing into a direct current method and a pulse method. As a result, it was found that the pulse method was effective, and the pulse method was adopted, and the voltage was applied at 100 V to 350 V, preferably 300 V.

The concentration of the electrolyte was also found to be related to the surface roughness of the specimen on the anode, and the optimum condition was sought. Therefore, the concentration of the electrolyte was 3% to 20% by weight, preferably 5% by weight.

In addition, we found that the duty time and frequency influence the quality of the polished surface of the specimen in pulsed voltage application, and also in search of the optimum conditions, the duty time is set to D ⁺ / D ^- to 50/45%. The pulse frequency was set to 5 kHz to 20 kHz, preferably 10 kHz. Here, setting D ⁺ / D ⁻ to 50/45% means that the ratio of the duration of duty on / duty off, which is represented by the high / low state of the pulse waveform of the pulse voltage, is 50:45.

Under such conditions, underwater plasma is generated to surround the fuel cell separator connected to the anode to form an underwater plasma envelope. With the action of the underwater plasma envelope, the fuel contained in the electrolyte penetrates the surface of the fuel cell separator plate made of stainless steel together with the polishing of the fuel cell separator plate, thereby maintaining the excellent corrosion resistance and electrical conductivity. Battery separators can be manufactured through low cost manufacturing processes.

The P-added stainless steel fuel cell separator prepared as described above is washed with water and then hot air dried.

The production, the stainless steel fuel cell separator containing a small amount of P was confirmed by the salt spray test excellent corrosion resistance.

The following provides test data demonstrating the optimum conditions of temperature and concentration, duty time and frequency of the electrolyte in the process.

3A and 3B are graphs of current density variation with electrolyte temperature, showing results from various applied voltages (FIG. 3A) and various duty times (applied voltage is constant at 300 V). .

As can be seen in FIGS. 3A and 3B, the current density becomes maximum at an initial temperature of 70 ° C., the initial current density is relatively low at an applied voltage of 300 V, and the duty time is rapidly lowered at 45% at D ^+. It can be seen. Therefore, it can be seen that the plasma can be generated quickly at an applied voltage of 300 V and a duty time D ⁺ of about 45%.

Next, FIGS. 4A to 4D are micrographs of the surface state of the specimen according to the electrolyte concentration. 4A is the surface of the specimen taken at the initial stage of the process, ie 45 seconds after polishing, and the specimen surface photographs for 2 wt%, 3.5 wt% and 5 wt% electrolyte concentrations are FIGS. 4 b, 4c and 4d, respectively. From this, it can be seen that the electrolyte concentration showing the smoothest surface with the lowest surface roughness of the specimen is 3.5% by weight.

Next, FIGS. 5A to 5D are micrographs of the specimen surface while varying the duty time at an applied voltage of 300 V and a frequency of 10 kHz.

The cleanest polished surface can be seen that D ⁺ / D ^- is 50/45 (%).

6A to 6D show the results of observing the energy loss and the surface of the specimen at different frequencies. At an applied voltage of 300 V, electrolyte concentration of 3.5% by weight, and duty time D ⁺ / D ^- of 50/45 (%), the frequency was able to reduce the surface roughness while minimizing energy loss at 10 kHz.

By adjusting the conditions of the manufacturing process as described above, it is possible to proceed quickly to improve the productivity, and to reduce the surface roughness, thereby reducing the origin of corrosion can further improve the corrosion resistance.

As described above, a fuel cell separator having excellent physical properties such as corrosion resistance can be manufactured through a simple process using a simple manufacturing facility.

The rights of the present invention are not limited to the embodiments described above, but are defined by the claims, and a person skilled in the art can make various modifications and adaptations within the scope of the claims. It is self-evident.

1A is a schematic diagram showing the configuration of a typical fuel cell.

1B is a perspective view schematically showing a fuel cell configuration in which a fuel cell separator is employed.

1C is a front view of the separator showing the structure of the fuel cell separator;

2 is a schematic diagram of an apparatus for fabricating a fuel cell separator using electrolyte plasma polishing (PEP) in accordance with the present invention.

3A and 3B are graphs of current density change with electrolyte temperature.

4a to 4d are micrographs observing the surface state of the specimen according to the electrolyte concentration.

5a to 5d are micrographs of the specimen surface with varying duty time.

6a to 6d are photomicrographs of the energy loss rate and the specimen surface with varying frequencies.

Claims (8)

Connect the fuel cell separator plate made of stainless steel to the positive electrode, connect the electrolytic cell to the negative electrode, inject an electrolyte containing P into the electrolytic cell, generate an underwater plasma to polish the fuel cell separator plate, and then A method of manufacturing a fuel cell separator, characterized by infiltrating P atoms into the fuel cell separator. The method of manufacturing a fuel cell separator according to claim 1, wherein the voltage applied to the positive electrode and the negative electrode is 100 V to 350 V. The method of claim 2, wherein the concentration of the electrolyte is 3 wt% to 20 wt%. The method of claim 3, wherein the electrolyte is H ₃ PO ₄ or Na ₃ PO ₄ A method for producing a fuel cell separator, characterized in that. The method of claim 4, wherein the initial temperature of the electrolyte introduced into the electrolytic cell is 60 ° C. to 80 ° C. 6. The method of manufacturing a fuel cell separator according to claim 5, wherein the applied voltage is performed in a pulsed manner, the frequency is 5 kHz to 20 kHz, and plasma polishing is performed for 3 to 6 minutes. 7. The fuel according to claim 6, wherein the duty time in the pulse method is D ⁺ / D ^- 50/45% (the ratio of the duty on / duty off duration of the pulse voltage is 50:45). Method for producing a battery separator.  A fuel cell separator with improved corrosion resistance by penetrating P into the surface of the stainless steel fuel cell separator.

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