KR100766154B1 - Seperator of a fuel cell - Google Patents

Abstract

A separator of a fuel cell is provided to secure a space that enables reaction fluid to flow without clogging channels in various operation conditions, promote the diffusion of the fluid into a catalytic layer, and discharge excessive water generated from a cathode effectively. A separator(10) of a fuel cell which supports a membrane-electrode assembly has fluid inlets(26) at one end, fluid outlets(27) at the other end, and main channels(20) as extended grooves, which are formed on the surface of the separator. At least one inner channel(30) is formed along the main channel. The inner channel has a width narrower than that of the main channel and gets in contact with the main channel with the surface open.

Description

Separator of fuel cell {SEPERATOR OF A FUEL CELL}

1 is a view showing a fuel cell separator according to an embodiment of the present invention.

2 illustrates a fuel cell separator according to another embodiment of the present invention.

3 illustrates a fuel cell separator according to another embodiment of the present invention.

4 is a view for explaining the operation of the fuel cell separator according to the present invention using the test specimen.

5 is a view showing a fuel cell separator according to the present invention;

6A and 6B are graphs showing fuel cell performance at reference flow rate supply in a fuel cell using the fuel cell separator shown in FIG. 5;

7A and 7B are graphs showing fuel cell performance at 1.5 times the reference flow rate in a fuel cell using the fuel cell separator shown in FIG. 5;

<Explanation of symbols for main parts of the drawings>

10: separator plate 20: gas passage

30,40,50: internal euro

The present invention relates to a fuel cell separation plate, and more particularly, to a fuel cell separation plate in which an internal flow path is formed so that droplets can be quickly moved and discharged along a gas passage.

A fuel cell is a device that continuously supplies external fuel and an oxidant and obtains electrical energy from a change in free energy due to the electrochemical reaction. A molten carbonate fuel cell (MCFC) operating at a high temperature of 600 ° C. or higher depending on the type of electrolyte is used. , Molten Carbonate Fuel Cells (SOFC) and Solid Oxide Fuel Cells (SOFC), Phosphoric Acid Fuel Cells (PAFC) that operate at relatively low temperatures below 200 ° C, and Polymer Electrolyte Fuel Cells ( PEFC, Polymer Electrolyte Fuel Cell).

In a fuel cell, an electrochemical reaction consists of two reactions: an oxidation reaction at an anode and a reduction reaction at a cathode. Both electrodes form a catalyst layer using platinum or platinum and ruthenium metal to promote oxidation and reduction. In order to reduce the amount of platinum catalyst used and increase the utilization rate, fine carbon particles are used as the catalyst support. The final byproducts of the reaction are electricity, heat and water. Cooling process may be required to remove heat, and the water generated from the cathode is in the form of water and steam, and is generally removed by strongly flowing reducing gas (oxygen or air) toward the cathode. .

The unit cell that forms the basis of the stack consists of two electrodes, an anode and a cathode, separated by a polymer electrolyte membrane. The anode and the cathode on the outer surface of the polymer electrolyte membrane are hot pressed. Membrane electrode assembly (MEA), and the membrane electrode assembly supplies hydrogen (fuel, methanol in the case of a direct methanol fuel cell) and oxygen or air, a reducing gas, and is produced by a redox reaction. It is supported by a separator plate formed with a flow path for discharging the water. A gasket is provided to prevent gas or liquid from being supplied or discharged through the flow path of the separation plate. Unit cells composed of such a membrane electrode assembly (MEA), a separator and a gasket are stacked in series to obtain a desired output, and a stack is formed by fixing them with end plates at both ends as a means for fixing them.

The separator serves to prevent the fuel (hydrogen, methanol) and the reducing gas (oxygen, air) from mixing in the cells, and to electrically connect the two electrodes, and serves as a mechanical support for the stacked unit cells. Through the flow path, the fuel gas (hydrogen, methanol) and reducing gas (oxygen, air) flows uniformly to the electrode (uniform) and performs a function to prevent the membrane from drying through proper moisture management. When operating a polymer electrolyte fuel cell, it is important to supply sufficiently humidified fuel and reducing gas (oxygen, air).

In order for the hydrogen ions generated through the redox reaction to move through the polymer electrolyte membrane, the polymer electrolyte membrane must be hydrated by appropriate moisture. 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, the small pores that form the reaction three-phase interface can be reduced, reducing the electrode reaction area, providing another cause of fuel cell degradation.

The water transport mechanism inside the fuel cell using the polymer electrolyte membrane is known to be affected by the following. In general, an electroosmotic drag phenomenon occurs in which hydrogen ions move together with several water molecules while passing through a polymer electrolyte membrane from an anode to a cathode. In addition, back diffusion occurs in which water generated from the cathode moves to the anode by the concentration gradient across the electrolyte membrane. In addition, water present in the anode or cathode is transferred to the fuel or reducing gas stream by convection and diffusion. The movement of water by electroosmosis increases with increasing current density, and the back diffusion at the cathode is inversely proportional to the thickness of the film regardless of the current density. 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 the polymer electrolyte membrane, the water generated at the cathode side by the redox reaction exists in the form of water vapor near the channel inlet, and as the reaction proceeds along the length of the channel, water is gradually accumulated, resulting in an excess of 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 generated water droplets block the pores of the gas diffusion layer of the porous carbon material constituting the electrode, preventing air from flowing smoothly to the electrode. flooding phenomenon) to reduce the active area of the electrode.

Under the two-phase flow conditions, the water droplets prevent the air from flowing smoothly to the electrode, which blocks the pores of the gas diffusion layer, reducing the active area of the electrode. This consumes energy, which is undesirable in terms of fuel cell performance.

Therefore, the higher the critical current density at which two-phase flow occurs, the more preferable. For this purpose, it is important to use a thin gas diffusion layer and to design a separator to facilitate the diffusion of water vapor in the gas diffusion layer and the mass transfer to the channel. The relative humidity of the air and the air inlet velocity at the channel inlet should be controlled according to the operating conditions.

As described above, in the case of a high current operating condition exceeding the critical current density, the cathode is formed with an excess of water generated by the electrochemical reaction and water moved from the anode by the electroosmotic phenomenon. This excess water is partially evaporated with the reducing gas (oxygen or air) flowing through the separator channel to saturate the reducing gas, and the non-vaporized water is present in the gas diffusion layer or separator channel in a liquid state.

Excess water present in the gas diffusion layer or the separator channel causes flooding if it is not discharged to the outside by appropriate engineering equipment, which is a fatal problem in terms of fuel cell performance or reliability.

Conventional techniques related to the above problems are U.S. Pat.Nos.4988583 and 5441819, which process a flow path having a single pass or two to three passes on the surface of a separator plate by gas flow. A method of discharging the liquefied water of the cathode by hydrogen or air by using a forced convection to discharge to the outside or lowering the water vapor pressure of the air below the saturated water vapor pressure is used.

However, this method causes an increase in the processing cost and an increase in the pressure loss of the air due to an increase in the length of the channel, 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.

In order to overcome this disadvantage, Korean Patent Laid-Open Publication No. 2003-60669 proposes a method of processing an auxiliary flow path that causes a capillary effect on partition walls between gas passages.

However, when pressure is applied to the fuel cell to form a stack, the pressure must be transferred 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. Significant pressure increases can 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 oil flow path may inhibit the uniform contact between the separator and the gas diffusion layer, which may damage the gas diffusion layer, and reduce the uniformity of the concentration distribution of the supplied reactor.

In addition, it is excellent in the ability to transfer liquefied water through the auxiliary flow path, but because the flow path is enlarged at the part where the fuel flow path and the internal flow path are connected, the water cannot be moved to the fuel flow path due to surface tension, and it is in the form of droplets in the internal flow path. 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 than 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.

Accordingly, an object of the present invention is to form an internal flow path for droplets to move quickly along the main flow path in forming a channel for inducing the flow of fluid in the separator plate of the fuel cell, so that the reaction fluid without clogging the flow path under various operating conditions It is to provide a separation plate of the fuel cell to secure the space to flow to promote the diffusion of the fluid to the catalyst layer and to smoothly discharge the excess water generated from the cathode (cathode).

In addition, another object of the present invention is advantageous to ensure the uniformity of the humidity and temperature, fuel that can reduce the supply pressure of the reactor through the increase of the contact area between the main passage and the reactor by minimizing the allowable gap between the main passage It is to provide a separator plate of the battery.

In order to achieve the above object, the present invention is a separation plate of a fuel cell for supporting a membrane electrode assembly, the surface of the separation plate has a fluid inlet at one end and a fluid outlet at the other end of the gas passage is an extension And at least one internal flow path extending along the fuel passage, the width of the fuel passage being smaller than the width of the fuel passage and having a cross-sectional area smaller than that of the fuel passage.

According to the present invention, the inner flow passage is formed on the bottom surface of the fuel passage. As the narrower width and smaller cross-sectional internal flow paths are formed along the bottom of the fuel flow path, droplets formed in the fuel flow path rapidly propagate along the internal flow path as they meet the internal flow path and do not obstruct the flow of fluid through the fuel flow path. .

In addition, the inner flow passage is formed of a single pass or a plurality of passes, and has a section located at least partially on one side of the bottom surface of the oil passage to be located below the wall surface of the oil passage. As a result, the droplets formed on the wall of the gas passage are quickly moved to the inner flow path and discharged along the inner flow path.

To this end, the inner flow path of the present invention has a first straight portion formed in parallel along the oil passage to one side of the bottom surface of the oil passage, and a second straight line formed in parallel along the oil passage to the other side of the bottom surface. And a plurality of separate portions formed as meandering channels formed by repetition of intersection portions connecting the first straight portion and the second straight portion in an intersecting direction in the extending direction of the oil passage, or formed as a central portion of the bottom surface of the oil passage. It consists of a channel consisting of a single path and two paths connecting the separated single paths to each other and located below the wall of the gas passage.

On the other hand, in the internal flow path of the pattern consisting of a single path and two paths connecting therebetween, the section formed by the two paths also has the advantage of serving as a storage space of the liquefied water.

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

1 to 3 are views for explaining the configuration of a separator plate of a fuel cell according to an embodiment of the present invention.

In the separator according to the present invention, graphite and a composite carbon-based material having low electrical contact resistance and strong corrosion resistance are used, and a fuel gas supply manifold and a fuel gas discharge manifold are used on the surface of the separator for gas exchange with the outside of the stack. The air supply manifold and the air discharge manifold are formed, respectively, and the oil passage and the internal flow path are formed by a dry etching process.

The oil passage 20 is formed in the central region of the surface of the separator plate having one end of the inlet 26 and the other end 27. According to the present invention, the oil passage 20 is wider than the oil passage 20 along the oil passage 20. Narrow inner flow passages 30, 40, and 50 are formed with the surface open and in contact with the fuel passage.

Referring to FIG. 1, in which an embodiment of the present invention is shown, the separator 10 of the fuel cell according to the present invention includes at least one internal flow path 30 formed in parallel along the oil passage 20. The gas passage 20 is illustrated as a serpentine that meanders a plurality of grooves, but is not limited thereto and may be a parallel passage or a deformation meandering passage.

The inner flow passage 30 is formed on the bottom surface 22 of the oil passage 20. The main flow path may be a rectangular flow path having a vertical wall surface formed on a flat bottom surface, and may be a trapezoidal flow path having an angle of 90 degrees to 130 with respect to the flat bottom surface.

The inner flow path 30 is formed to have a narrower width than the bottom surface of the oil passage, and may have a rectangular shape having a width of several hundred micrometers or less, or another shape that facilitates water discharge, and has one or a plurality of internal flow paths 30. ) May be formed along the oil passage 20. In this case, when one inner flow passage 30 is formed, it is formed along the center portion of the bottom surface 22 of the oil passage 20.

Referring to FIG. 2, which shows another embodiment of the present invention, the inner passage 40 is formed along a central portion of the bottom surface 22 of the filling passage 20 and includes a plurality of single passes 42 separated from each other. It consists of two paths 44 and 45 that connect between the single paths 42. That is, a single pass 42 proceeds and branches into two paths 44 and 45 and then repeats a pattern in which the ends of the two paths 44 and 45 are connected to the single path 42 again. In this case, the cross-sectional area of each of the two paths 44 and 45 is the same as that of the single path 42 between the two paths 44 and 45.

The pattern of the internal flow path 40 is a pattern in which one flow path and two flow paths are repeated for each section, and two paths 44 and 45 formed between a single path 42 have a storage space for liquefied moisture. The droplets propagate along the inner passage 40 more quickly.

Furthermore, according to the present invention, the two paths 44 and 45 are each formed at one side and the other side of the bottom surface 22 of the oil passage, each of which is disposed at the lower side of both side wall surfaces 24 of the oil passage 20. Located. Accordingly, the liquefied water formed on the wall surface 44 of the oil passage 20 is formed by the two paths 44 and 45 of the inner flow passage 40 positioned below the wall surface 24 of the oil passage 20. It can be flowed into the inner flow path 40 more quickly.

3 shows another embodiment of the present invention.

Referring to FIG. 3, an inner flow path 50 is formed in a meander on the bottom surface 22 of the oil passage 20. The first straight portion 52 formed in parallel along the oil passage 20 to one side of the bottom surface 22 of the oil passage 20 and the oil passage 20 to the other side of the bottom surface 22. A second straight portion 54 is formed in parallel, and the first straight portion 52 and the second straight portion 54 are connected by the connecting portion 55 formed to cross the extending direction of the oil passage 20. It is connected by one continuous pass.

The internal flow path 50 of the meandering shape may have a rectangular shape and a trapezoidal cross section of several hundred micrometers or less, and each of the first linear part 52 and the second linear part 54 may have a gas path 20. Since it is located below the wall surface 24, the liquefied water formed in the wall (24) of the gas passage 20 can be more quickly introduced into the inner flow path 50 to be propagated and discharged along the inner flow path (50).

Hereinafter, with reference to the drawings of the operation of the fuel cell separator according to the present invention.

The fuel cell in the separator plate is formed as a fine flow path using a dry etching process such as a mask pattern process. Generally, the width of the flow path is in the range of 100 to 3000 μm and the depth is 80 to 1000. It is formed in the range of 탆. The inner flow passage is formed along the bottom surface of the fuel passage, and the width of the passage is several hundred micrometers or less, preferably smaller than the width of the fuel passage, for example, 4: 1 or less.

The cross-sectional shape of the inner flow path is rectangular, but a trapezoidal shape having a side of 90 degrees or more and 135 degrees or less may be used. In the case of the Saradoid shape flow path, the propagation of the droplets can be faster by increasing the contact area with the droplet. have.

According to the present invention, the internal flow paths 30, 40, and 50 formed along the fuel path 20 may include droplets 1 (liquefied water) formed on the fuel cell separator 10 along the path of the fuel path 20. By fast propagation ensures a smooth electrochemical reaction of the fuel cell separator 10, it is possible to maintain a uniform humidity throughout the electrode reaction area.

FIG. 4 is a view showing droplet propagation when an internal flow path is formed along a fuel flow path using test specimens. A specimen is shown forming an internal flow path 30 of mm ² .

Referring to FIG. 4A, the droplet 1 is formed on the oil passage 20 to block the oil passage 20, thereby preventing the flow of air. However, referring to FIG. 4B, the droplet 1 proceeds from a portion where the inner passage 30 is not formed to a portion where the inner passage 30 is formed. When the droplet 1 meets the inner passage 30, the droplet 1 is inside. It can be seen that the liquid droplets spread rapidly along the flow path 30 and the oil flow path 20 has no droplets that hinder the air flow as shown in FIG. 4A. This phenomenon is the same even when the cross-sectional area of the internal flow path is changed to 0.6 × 0.6 mm ² and 0.4 × 0.4 mm ² . This phenomenon is seen as a kind of capillary phenomenon, it can be seen that the droplet is quickly moved along the inner flow path when the inner flow path 30 of the narrower cross-sectional area than the main flow path (20).

FIG. 5 shows a pannel formed by forming a gas channel 20 having a width of 2.5 mm and an inner channel 30 having a diameter of 0.6 × 0.6 mm ² along a central portion of a bottom surface of the fuel channel 20 in the separator plate 10 of the fuel cell. It is a figure which shows a parallel type separator.

6A and 6B are graphs showing the performance of the fuel cell when the reference flow rate is supplied in the separator shown in FIG. 5, and FIGS. 7A and 7B are 1.5 times the reference flow rates in the separator shown in FIG. 5. It is a performance graph of the city's fuel cell. 6A to 7B, the A curve shows a case of forming only a fuel oil as a non-example, and the B curve shows a case of forming an internal flow path as shown in FIG. 5.

6A to 7B, when the internal flow path is formed along the fuel passage, the voltage and the power in the region where the concentration loss occurs are increased when both the reference flow rate and the flow rate 1.5 times the reference flow rate are supplied. You can check it. In addition, it can be seen that the gap further increases as the supply flow rate increases. This is because the droplets are quickly propagated and discharged along the inner flow path so that the flow of the supplied fuel gas or air is performed smoothly along the oil passage. Through this, the fuel cell using the separator plate when the internal flow path is formed along the fuel passage as in the present invention achieves an effect of about 10-30% performance improvement in comparison with the fuel cell using the separator plate formed only as the fuel passage. You can see that you can.

According to the present invention, it is possible to secure a space for the reaction fluid to flow without clogging the flow path formed in the fuel cell separator under various operating conditions, thereby promoting the diffusion of the fluid into the catalyst layer, The water can be discharged smoothly. In addition, it is advantageous to ensure the uniformity of humidity and temperature of the polymer electrolyte membrane, it is possible to achieve a reduction in the supply pressure of the reactor through the increase of the contact area between the main passage and the reactor by minimizing the allowable gap between the main passage.

Claims (10)

In the separator of a fuel cell for supporting a membrane electrode assembly (MEA), On the surface of the separating plate is formed a flow path which is a groove having a fluid inlet at one end and a fluid outlet at the other end and extending, The fuel cell separating plate of the fuel cell having a width smaller than the width of the oil passage, the at least one inner passage communicating with the oil passage is formed in communication with the oil passage. The method of claim 1, The inner passage has a width of 1/4 or less than the width of the fuel passage separation plate of the fuel cell. The method of claim 1, The inner passage is a separator of a fuel cell, characterized in that formed on the bottom surface of the oil passage. The method of claim 3, The inner flow passage is a separator of a fuel cell, characterized in that formed in parallel along the bottom surface. The method of claim 4, wherein The inner flow passage is a separator of a fuel cell, characterized in that extending along the bottom center portion of the fuel passage. The method of claim 3, The inner flow passage is at least partly positioned to one side of the bottom surface of the fuel passage has a section located below the wall surface of the fuel passage. The method of claim 6, The inner flow passage may include a first straight portion extending along the oil passage to one side of the bottom surface of the oil passage, a second straight portion extending along the oil passage to the other side of the bottom surface, and the first straight portion and the Separation plate of the fuel cell, characterized in that the connecting portion extending in the cross direction in the extending direction of the fuel passage connecting the second straight portion is formed of a meandering channel repeatedly made. The method of claim 3, The inner flow passage is divided into two passes, and then divided into two passes, the separation plate of the fuel cell, characterized in that the pattern is formed repeatedly connected to a single pass at the end of the two passes. The method of claim 8, Each of the two paths is disposed on both sides of the bottom surface of the fuel passage and located below both side walls of the fuel passage. The method according to claim 8 or 9, Wherein each of the two passes has the same cross-sectional area as the single pass.

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