KR20100119230A - Bipolar plate with nano and micro structures - Google Patents

Abstract

PURPOSE: A bipolar plate for a fuel cell is provided to prevent the flooding phenomenon by controlling the hydrophilic property and the hydrophobic property of the surface of a flow channel, and to enlarge the contact area of a separator and a gas diffusion layer. CONSTITUTION: A bipolar plate(10) for a fuel cell comprises the following: a flow channel(11) formed on one side of the bipolar plate; and a nanostructure on the bottom of the flow channel, the side of a barrier of the flow channel, and the upper surface of the bipolar plate. A microstructure is capable of replacing the nanostructure. The microstructure forms grooves along to the flow channel.

Description

Bipolar plate for fuel cell with nanostructures and microstructures {BIPOLAR PLATE WITH NANO AND MICRO STRUCTURES}

The present invention relates to a bipolar plate for a fuel cell in which nanostructures and microstructures are formed. More specifically, the present invention is a bipolar plate for a fuel cell having a flow path formed on one surface, the microstructure and the nanostructure on the bottom surface of the fuel cell bipolar plate, characterized in that the nanostructure is formed on the bottom surface of the flow path. A bipolar plate for a fuel cell, characterized in that the structure is formed.

A fuel cell is a cell that directly converts chemical energy generated by the oxidation of a fuel into electrical energy. The fuel cell must continuously supply reactants from the outside while continuously removing reaction products caused by the oxidation reaction to the outside of the system.

Molten Carbonate Fuel Cells (MCFCs) use the same basic principle, but operate at a high temperature of 600 ℃ or higher depending on the electrolyte and operating temperature delivered in the unit cell. Solid Oxide Fuel Cells (SOFC) using ceramic oxides as electrolytes, Phosphoric Acid Fuel Cells (PAFC) operating at relatively low temperatures below 200 ° C. and using phosphate electrolytes, It is classified into a polymer electrolyte fuel cell (PEFC) using a polymer membrane electrolyte and an alkaline fuel cell (AFC) using an alkaline electrolyte.

In a fuel cell, an electrochemical reaction consists of two reactions: an oxidation reaction at an anode and a reduction reaction at a cathode. At this time, the two electrodes are formed of a catalyst layer using platinum or platinum and ruthenium metal to promote oxidation and reduction reactions, and use fine carbon particles as catalyst supports to reduce the amount of platinum catalyst used and to increase utilization.

As a result of the reaction, the final by-products are electricity, heat and water, which may require a cooling process to remove heat, in particular the water produced at the reducing electrode is in the form of water and water vapor and the reducing gas (oxygen) Or air).

In the case of a polymer electrolyte fuel cell (PEFC), as shown in FIG. 2, a unit cell is a membrane electrode assembly formed by hot pressing an oxide electrode and a reduction electrode on both sides of a polymer electrolyte membrane. (Membrane Electrolyte Assembly), and 2) a flow path for supplying fuel and reducing gas (such as hydrogen or methanol) to the membrane electrode assembly and discharging water generated by a redox reaction. And it consists of a separator that serves to support the membrane electrode assembly. The unit cell consisting of such a membrane electrode assembly (MEA) and a separator is stacked in series to form a stack to obtain the required output.

As shown in FIG. 1, the separator plate allows the fuel gas (hydrogen, methanol) and the reducing gas (oxygen, air) to flow uniformly to the electrode through the flow path formed on the surface, without mixing, and through proper moisture management. Not only does the membrane not dry, but also performs an important function in the fuel cell, such as performing a mechanical support function of the stacked unit cells.

In operation of a polymer electrolyte fuel cell, the polymer electrolyte membrane must be hydrated with appropriate moisture in order for hydrogen ions generated through a redox reaction to move through the polymer electrolyte membrane. Ions move through the hydrated polymer electrolyte membrane, and the flow of electrons through an external circuit is used as power.

The ionic conductivity of the polymer electrolyte membrane is proportional to the water content up to a certain range. When the water is insufficient, the ionic conductivity of the membrane is reduced, thereby reducing the performance of the fuel cell. However, when too much water is supplied, it blocks the small pores that form the reaction three-phase interface, thereby reducing the electrode reaction area, thereby providing a fuel cell degradation cause.

Looking at the water transport mechanism inside the fuel cell using the polymer electrolyte membrane, an electroosmotic drag phenomenon occurs in which hydrogen ions move together with several water molecules while passing through the polymer electrolyte membrane from the oxidation electrode to the reduction electrode. At this time, back diffusion is also generated in which water generated in the reduction electrode moves to the anode by the concentration gradient across the electrolyte membrane. The movement of water by electroosmosis increases with increasing current density, and the back diffusion at the reduction electrode is inversely proportional to the thickness of the membrane regardless of the current density.

In addition, water present in the oxidation or reduction electrode is transferred to the fuel or reducing gas stream by convection and diffusion. The transport of water by fuel or reducing gas is a function of the pressure, temperature, humidification amount, etc. of the fuel or reducing gas supplied.

In particular, the water produced at the reduction electrode side by the redox reaction in the polymer electrolyte membrane exists in the form of water vapor near the channel inlet, and as the reaction proceeds along the longitudinal direction of the channel, the water is gradually accumulated, resulting in a higher than the saturated steam pressure of air. This results in a two-phase flow where water vapor and water coexist.

In the two-phase flow zone, the water droplets block the pores of the gas diffusion layer of the porous carbon material constituting the electrode, preventing the air from flowing smoothly to the electrode, and in the severe case, it blocks the flow of oxygen or air. Phenomenon) The active area of the electrode is reduced.

The pressure of the air is further increased to remove these droplets, but this is undesirable in terms of fuel cell performance because of the additional energy consumed. Therefore, it is important to design a suitable separator to facilitate the diffusion of water vapor in the gas diffusion layer and the mass transfer to the flow channel.

That is, in the case of high current operating conditions exceeding the critical current density, the reduction electrode has an excessive amount of water generated by the electrochemical reaction and water moved from the anode due to the electroosmotic phenomenon. Partial evaporation of the reducing gas (oxygen or air) through the saturation of the reducing gas, wherein the water does not evaporate is present in the gas diffusion layer or the separator channel in the liquid state.

Excessive water present in the gas diffusion layer or the separator channel causes a flooding phenomenon if it is not discharged to the outside by an appropriate engineering mechanism, thereby causing a fatal problem in terms of performance or reliability of the fuel cell.

In order to solve the above problems, US Pat. Nos. 4,88583 and 5441819 use forced convection by gas flow to process water droplets present in a channel by processing a flow path having a single pass or a plurality of passes on a separator plate surface. To discharge to the outside, or to lower the water vapor pressure of the air than the saturated water vapor pressure to vaporize the liquefied water of the reduction electrode with hydrogen or air.

However, this method not only increases the processing cost due to the increase in the length of the channel, but also causes an increase in the pressure loss of the air, and consequently supplies an excessive amount of air to treat the liquefied water. This method has a disadvantage in that the fuel supply device becomes complicated and the fuel cell becomes larger because it requires the increase in the required amount of the reactor gas and the pressure increase necessary for supplying air.

Further, Japanese Patent Laid-Open No. 2003-60669 discloses a method of processing an auxiliary flow path that causes a capillary effect on partition walls between oil passages. However, when pressure is applied to the fuel cell to form a stack, the pressure must be transmitted to the gas diffusion layer in contact with the surface of each flow path. In the case of the gas passage, since the width is wide, a large pressure change does not occur even in the area where the gas diffusion layer and the separator are in contact, but in the case of the inner flow passage, the width is very narrow, so that the gas diffusion layer acts on the gas diffusion layer in the area where the inner flow passage and the gas diffusion layer directly contact each other. The pressure can rise significantly and cause diffusion layer breakage or deformation due to partial hardening and notch effects.

That is, the difference in the contact area between the inner flow path and the fuel flow path may inhibit the uniform contact between the separator and the gas diffusion layer, which may damage the gas diffusion layer, and also reduce the uniformity of the concentration distribution of the supplied reactor. In addition, it has excellent ability of transporting liquefied water through the auxiliary flow channel, but because the flow path is enlarged at the part where the gas flow passage and the internal flow path are connected, the water cannot form the droplets in the internal flow path due to surface tension. Cases may occur.

In addition, when the inner flow path is processed in the partition walls between the gas passages, the strength of the separation plate may be weakened due to the formation of the internal flow path, which increases the spacing of the gas passages more than in the processing of the gas passage alone. There is a problem that causes a reduction in the contact area of the flow rate flowing through the factor to increase the supply pressure of the reactor body.

On the other hand, the registered patents 10-0545992 and 10-0839193, etc. to accelerate the discharge of water or other substances by coating the chemical on the surface of the separator flow path, but may be degraded due to contamination and partial coating damage caused by foreign substances over long periods of use Degradation of electrical conductivity may also occur.

Therefore, the present inventors do not form auxiliary channels or chemical treatments as in the prior art documents, so that they are less contaminated or damaged due to foreign substances, and the flooding phenomenon is prevented by directly adjusting the hydrophilicity and hydrophobicity of the surface to desired levels. The company has developed a bipolar plate for fuel cells that can immediately accelerate the discharge of water from the fuel cell separator.

In addition, the present inventors have developed a bipolar plate that can be applied to all kinds of fuel cells by increasing the contact area between the separator and the gas diffusion layer (GDL) and improving the electrical conductivity at the contact surface, in addition to simply preventing flooding. It was.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bipolar plate capable of accelerating water discharge from a fuel cell separator by preventing the flooding phenomenon by adjusting the hydrophilicity and hydrophobicity of the flow path surface to a desired level.

In addition, it is an object of the present invention to provide a bipolar plate that can improve the electrical conductivity by increasing the contact area between the separator and the gas diffusion layer (GDL) and reducing the electrical resistance at the contact surface.

In addition, an object of the present invention is to provide a bipolar plate that can be applied to not only PEM (Polymer Electrolyte Membrane) fuel cells but also all other types of fuel cells.

In addition, it is an object of the present invention to provide a bipolar plate that does not use a chemical and is less contaminated or damaged by foreign matters, thereby increasing durability.

An object of the present invention is achieved by providing a fuel cell bipolar plate, characterized in that in a fuel cell bipolar plate having a flow path formed on one surface thereof, a nanostructure is formed on the bottom surface of the flow path.

The object of the present invention is achieved by providing a bipolar plate for fuel cell bipolar plate having a flow path formed on one surface, characterized in that the microstructure and nanostructures are formed on the bottom surface of the flow path. .

The object of the present invention is achieved by providing a bipolar plate for a fuel cell, characterized in that the nanostructure is further formed on the side of the partition wall portion of the flow path or the upper surface of the bipolar plate.

The object of the present invention is achieved by providing a bipolar plate for a fuel cell, characterized in that the nanostructures are in the form of nanowires or nanotubes.

The object of the present invention is achieved by providing a bipolar plate for a fuel cell, characterized in that the nanostructure is a carbon material or a metal material.

The object of the present invention is achieved by providing a bipolar plate for a fuel cell, wherein the microstructures form grooves along the flow path.

The bipolar plate for fuel cell in which the nanostructures and microstructures of the present invention are formed prevents flooding by accelerating the hydrophilicity and hydrophobicity of the flow path surface to accelerate water discharge from the fuel cell separator. In addition, by forming the nanostructure further up the upper surface of the plate, it is possible to increase the contact surface area between the separator and the gas diffusion layer (GDL) and to reduce the electrical resistance at the contact surface, thereby improving the electrical conductivity. have.

As described above, since the present invention changes the surface properties of the flow path and increases the reaction area and the electrical conductivity through the mechanical structure in the flow path, not the chemical substance, not only PEM fuel cell but also all other types of fuel cells. Applicable to In addition, since there is little contamination or damage caused by foreign substances, chemicals are not used, and thus durability can be increased compared to plates using coating techniques.

Hereinafter, a bipolar plate for a fuel cell in which nanostructures and microstructures of the present invention are formed will be described in detail with reference to the accompanying drawings.

FIG. 1 is a plan view of a bipolar plate in which a flow path is formed on one surface that is generally used, and FIG. 2 is an enlarged view showing a part of a cross section of a unit cell composed of the bipolar plate and the membrane electrode assembly of FIG.

3 to 5 show a bipolar plate for a fuel cell in which a nanostructure is formed, which is a first embodiment of the present invention, and FIG. 3 is an enlarged view showing a portion of a cross section of the bipolar plate on which a nanostructure is formed, which is an embodiment of the present invention. 4 is a partially enlarged view of the nanostructure of FIG. 3, and FIG. 5 is a cross-sectional view of a bipolar plate flow path in which the nanostructure of FIG. 3 is formed.

In the bipolar plate 10 in which the nanostructures are formed according to the first embodiment of the present invention, a flow path 11 is formed on one surface, and the nano structure 12 is formed on the bottom surface of the flow path 11. By adjusting the shape, material, and spacing of the nanostructure 12, the surface of the flow path in which the nanostructure is formed may be adjusted to have hydrophilic or hydrophobic properties.

As shown in FIG. 3, when the surface of the flow path 11 becomes hydrophobic by the nanostructure 12, water does not adhere to the flow path surface, and droplets 20 form along the flow path and thus water flows. It is possible to prevent the flooding (blocking) phenomenon to block the flow path. On the contrary, although not shown in the drawing, when the surface of the flow path 11 becomes hydrophilic by the nanostructure 12, water does not stay in the flow path but flows down the flow path along the flow path as in the case of hydrophobicity as in the case of hydrophobicity. Can be prevented.

In other words, in preventing flooding and accelerating water discharge, the surface properties of the flow path can be selected according to the purpose and environment of use of the plate so that the suitable surface property of the channel can be selected between hydrophilicity and hydrophobicity. It is much wider. As an embodiment of controlling hydrophilicity and hydrophobicity according to the purpose of use, the manifold 22 portion of FIG. 1 is adjusted to have hydrophilicity, and the flow passage 11 portion is adjusted to have hydrophobicity to accelerate the discharge of water so as to accelerate the drainage of the entire bipolar plate. The efficiency can be increased.

Meanwhile, nanostructures 12 may be further formed on side surfaces of the partition wall of the flow passage 11 and on the upper surface of the bipolar plate 10 in order to obtain a more efficient water discharge effect.

In particular, when the nanostructure 12 is additionally formed on the upper surface of the bipolar plate 10, the contact area between the plate and the membrane electrode assembly 21, that is, the gas diffusion layer (GDL), is separated. In addition to increasing the resistance, it is possible to obtain an effect of improving the electrical conductivity by reducing the electrical resistance at the contact surface.

In general, since the bonding surface of the separator and the membrane electrode assembly (MEA) in the unit cell forms a rough contact surface, the contact area between the separator and the gas diffusion layer (GDL) is reduced. Reduction increases the electrical resistance of the mating surface and reduces the overall electrical conductivity, which reduces the overall fuel cell efficiency.

However, as shown in FIG. 5, by further forming the nanostructures 12 on the upper surface of the bipolar plate 10, the nanostructures can directly penetrate the gas diffusion layer surface, which is a separator and a membrane electrode. The contact area between the joints is further increased, resulting in an overall fuel cell performance improvement.

In addition, through the nanostructures 12 on the upper surface of the plate 10, it is possible to effectively release the fine droplets discharged from the porous structure of the gas diffusion layer (GDL) to the bonding surface.

The nanostructure 12 may have various shapes as needed, but in order to effectively control the surface properties, it is preferable to have a form of a nano wire or a nano tube, and the height thereof is suitable for use. To a few microns to several tens of microns.

The material of the nanostructure 12 may be any material having electrical conductivity, but in consideration of ease of molding and high electrical conductivity, it is preferable to use a carbon material or a metal material. In addition, the type of the metal is not particularly limited, but is preferably any one selected from the group consisting of iron (Fe), copper (Cu), nickel (Ni), and gold (Au).

6 to 8 illustrate a bipolar plate for a fuel cell in which a microstructure and a nanostructure are formed, which is a second embodiment of the present invention, and FIG. 6 is a cross-sectional view of a bipolar plate that is a second embodiment in which the microstructure and the nanostructure of the present invention are formed. 7 is a partially enlarged view of the microstructure and nanostructure of FIG. 6, and FIG. 8 is a cross-sectional view of a flow path of a bipolar plate on which the microstructure and nanostructure of FIG. 6 are formed.

The bipolar plate 10 in which the microstructures and nanostructures are formed according to the second embodiment of the present invention has a flow passage 11 formed on one surface thereof, and the microstructure 13 and the nanostructure 12 formed on the bottom surface of the flow passage 11. ) Is formed. Similarly to the first embodiment, the bipolar plate on which the microstructures and nanostructures are formed also controls the shape, material, and spacing of the nanostructures 12 so that the surfaces of the flow paths on which the nanostructures are formed are hydrophilic or hydrophobicity. Adjusting to prevent flooding phenomenon.

The microstructure 13 of the second embodiment functions as an auxiliary support of the nanostructure 12, and when it is difficult to obtain a required height in the flow path with the nanostructure 11 alone, such as an etching or a molding press in the flow path. After forming the microstructure 13 through a process or the like, the nanostructure 11 may be formed on the microstructure 13.

At this time, the shape of the microstructure is not limited, and as shown in FIG. 6, the microstructures may be formed to form grooves 15 at regular intervals along the flow path 11. At this time, the spacing of the grooves 15 between the microstructures can be variously modified according to the nanostructures and the fuel cell, but in general, it is preferable that the spacing of the microstructures is 10 μm or less in order to control the properties of the flow path surface and increase the water discharge effect.

In addition, the nanostructure 12 of the second embodiment may be additionally formed on the side surface of the partition wall of the flow path 11 or the upper surface of the bipolar plate 10, similarly to the bipolar plate on which only the nanostructures of the first embodiment are formed.

As described in the first embodiment, through the nanostructure 12 on the upper surface of the bipolar plate 10, the contact area between the separator and the membrane electrode assembly 21 may be increased, and the electrical conductivity may be increased. The effect of effectively releasing the fine droplets discharged from the porous structure of the diffusion layer (GDL) to the bonding surface can be obtained.

Likewise, the nanostructure 12 may have various shapes as needed, and in order to effectively control the surface properties, the nanostructure 12 may have a form of a nano wire or a nano tube.

The material of the nanostructure 12 may be any material having electrical conductivity, but in consideration of ease of molding and high electrical conductivity, it is preferable to use a carbon material or a metal material. The kind is not particularly limited but is preferably any one selected from the group consisting of iron (Fe), copper (Cu), nickel (Ni), and gold (Au).

The bipolar plate for a fuel cell in which the nanostructure is formed as the first embodiment of the present invention described above, or the bipolar plate for the fuel cell in which both the nanostructure and the microstructure are formed as the second embodiment is the surface property of the flow path through the mechanical structure in the flow path rather than the chemical. By changing (hydrophilicity or hydrophobicity) and increasing reaction surface area and electrical conductivity, it is applicable to all kinds of fuel cells as well as PEM fuel cells.

In addition, since there is little contamination or damage caused by foreign substances, chemicals are not used, and thus durability can be increased compared to plates using coating techniques.

The present invention is not limited to the above-described specific embodiments and descriptions, and various modifications can be made to those skilled in the art without departing from the gist of the present invention claimed in the claims. And such modifications are within the scope of protection of the present invention.

1 is a plan view of a bipolar plate in which a flow path is formed on a general surface.

FIG. 2 is an enlarged view illustrating a part of a cross section of a unit cell formed of the bipolar plate and the membrane electrode assembly of FIG. 1.

Figure 3 is an enlarged view showing a portion of the cross-section of the bipolar plate formed nanostructures of an embodiment of the present invention.

4 is a partially enlarged view of the nanostructure of FIG. 3.

5 is a cross-sectional view of a flow path formed with a nanostructure of a bipolar plate according to an embodiment of the present invention.

Figure 6 is an enlarged view showing a portion of a bipolar plate cross section which is another embodiment in which the microstructures and nanostructures of the present invention are formed.

FIG. 7 is a partially enlarged view of the microstructure and nanostructure of FIG. 6.

8 is a cross-sectional view of a flow path in which the microstructures and nanostructures of the bipolar plate of one embodiment of the present invention are formed.

Explanation of symbols on the main parts of the drawings

10 bipolar plate 11: euro

12 nanostructure 13 microstructure

14: Home 20: Drops

21: membrane electrode assembly (MEA) 22: manifold

Claims (18)

A fuel cell bipolar plate (10) having a flow path (11) formed on one surface thereof, wherein the nanostructure (12) is formed on the bottom surface of the flow path (11). The bipolar plate according to claim 1, wherein the nanostructure (12) is further formed on a side surface of the partition wall of the flow path (11). The bipolar plate according to claim 1, wherein the nanostructure (12) is further formed on an upper surface of the bipolar plate (10). The bipolar plate of claim 1, wherein the nanostructures are in the form of nanowires. The bipolar plate of claim 1, wherein the nanostructures are in the form of nanotubes. 2. The bipolar plate of claim 1, wherein the nanostructures are made of carbon. The bipolar plate according to claim 1, wherein the nanostructure (12) is made of metal. The bipolar plate according to claim 7, wherein the metal is any one selected from the group consisting of iron (Fe), copper (Cu), nickel (Ni), and gold (Au). In the fuel cell bipolar plate 10 (bipolar plate) having a flow path 11 formed on one surface, the fuel characterized in that the microstructure 13 and the nanostructure 12 is formed on the bottom surface of the flow path (11) Battery bipolar plate. 10. A bipolar plate according to claim 9, wherein said microstructures (13) form grooves (15) along said flow path (11). 11. The bipolar plate for fuel cell according to claim 10, wherein an interval of the grooves (15) is 10 mu m or less. 10. The bipolar plate according to claim 9, wherein the nanostructure (12) is further formed on the side surface of the partition wall of the flow path (11). 10. The bipolar plate according to claim 9, wherein the nanostructure (12) is further formed on an upper surface of the bipolar plate (10). 10. The bipolar plate for fuel cell according to claim 9, wherein the nanostructure (12) is in the form of a nano wire. 10. The bipolar plate according to claim 9, wherein the nanostructures (12) are in the form of nanotubes. 10. The bipolar plate according to claim 9, wherein the nanostructure (12) is made of carbon. 10. The bipolar plate for fuel cell according to claim 9, wherein the nanostructure (12) is made of metal. 18. The bipolar plate according to claim 17, wherein the metal is any one selected from the group consisting of iron (Fe), copper (Cu), nickel (Ni), and gold (Au).

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