KR20100108101A - Separator and fuel cell stack using thereof - Google Patents

Abstract

PURPOSE: A separator and a fuel cell stack using thereof are provided to improve the flow speed of reactive gas with the low pressure, and to stably generate the electrical energy without degrading the power generation capacity. CONSTITUTION: A fuel cell stack(100) comprises the following: an electricity generation unit(30) including a membrane-electrode assembly(31), and separators(32,33) closely located on both sides of the membrane-electrode assembly; and a reactive gas flow path formed on the separators. The reactive gas flow path includes a first directional path, and a second directional path connected to the first directional path.

Description

Separator and fuel cell stack using same {SEPARATOR AND FUEL CELL STACK USING THEREOF}

The present invention relates to a fuel cell stack and a separator for a fuel cell stack, and more particularly, to a fuel cell stack and a separator for a fuel cell stack having improved structures of a reaction gas flow path.

A fuel cell is a device that produces electricity electrochemically by using fuel (hydrogen or reformed gas) and oxidant (oxygen or air), and converts fuel and oxidant continuously supplied from outside into electric energy directly by electrochemical reaction. Device.

The oxidant of the fuel cell uses pure oxygen or air containing a large amount of oxygen, and the fuel contains a large amount of hydrogen by reforming pure hydrogen, hydrocarbon fuels (LNG, LPG, CH ₃ OH), or hydrocarbon fuels. Use the reformed gas.

These fuel cells are largely divided into polymer electrolyte fuel cells (PEMFC), direct oxidation fuel cells (DMFC), and direct methanol fuel cells (DMFC). Can be.

The polymer electrolyte fuel cell includes a fuel cell body called a stack, which generates electrical energy through an electrochemical reaction of hydrogen gas supplied from the reformer and air supplied by the operation of an air pump or fan. It is made as a structure. Here, the reformer functions as a fuel treatment apparatus for reforming fuel to generate hydrogen gas from the fuel, and supplying the hydrogen gas to the stack.

Unlike the polymer electrolyte type fuel cell, the direct oxidation type fuel cell is directly supplied with alcohol, which is a fuel, without using hydrogen gas. The direct energy fuel cell is supplied by the electrochemical reaction of hydrogen contained in the fuel and separately supplied air. It is made as a structure for generating a. The direct methanol fuel cell refers to a cell using methanol as a fuel in a direct oxidation fuel cell.

Hereinafter, for convenience of description, the polymer electrolyte fuel cell will be described. The membrane-electrode assembly used in a polymer electrolyte fuel cell is formed on both sides of a hydrogen ion conductive polymer electrolyte membrane and includes a catalyst layer mainly composed of a carbon powder carrying a metal catalyst such as a platinum group metal, and an outer surface of the catalyst layer. It consists of a gas diffusion layer having a gas diffusion layer is generally made of carbon paper or carbon nonwoven fabric.

Outside the membrane-electrode assembly, a separator having electrical conductivity for mechanically supporting the membrane-electrode assembly and electrically connecting adjacent membrane-electrode assemblies to each other is provided to form a unit cell. The separator forms a flow path for supplying the reaction gas to the electrode surface and transporting the surplus gas and the reaction product to the portion in contact with the membrane-electrode assembly. The flow path may be provided separately from the separator, but is generally formed in a groove shape on the surface of the separator.

A plurality of unit cells are arranged in a stack and a current collector plate for extracting current and an insulation plate for insulation from the outside are sequentially stacked on the outermost side of the unit cell, and are fixed through the fastening plate and the fastening means.

The fuel and oxidant supplied to the fuel cell are converted to water through an electrochemical reaction in the membrane-electrode assembly, which generates electricity and heat. Unreacted fuel and oxidant are discharged out of the fuel cell stack, and the ratio of the amount of reactant gas to the amount of supply gas used in the electrochemical reaction is called gas utilization.

In order to discharge heat generated in the electrochemical reaction, a cooling unit in which a cooling medium flows is installed every one or several unit cells. The cooling unit includes a fuel separator having a fuel gas flow path on one side and a cooling flow path for the cooling medium on the opposite side, and an oxidant having a cooling flow path for the cooling medium on the opposite side and an oxidant gas flow path on the opposite side. Many methods for attaching the separators to each other are used.

In general, a polymer electrolyte fuel cell is humidified to a predetermined level or more when a reaction gas (a fuel and an oxidant) is supplied to improve conductivity of hydrogen ions in an electrolyte membrane. On the other hand, since water is generated by the electrochemical reaction on the cathode side, when the dew point temperature of the reaction gas is higher than the operating temperature of the fuel cell, water droplets due to water vapor condensation are generated in the gas flow path or the electrode.

This is called flooding, which causes a non-uniform flow of reactant gas and a lack of reactant gas at the electrode, causing a decrease in the performance of the fuel cell.

Flooding can occur at the anode electrode as well as at the cathode electrode due to the water transferred through the electrolyte membrane. In particular, when the clogging phenomenon of the gas oil by the condensate occurs on the anode side, it causes a deficiency of fuel gas, which causes irreversible damage of the electrode.

This is because when the load current is forcibly applied due to the lack of fuel gas, the carbon carrying the catalyst of the anode reacts with water to make electrons and protons in the absence of fuel. As a result of this reaction, a loss of the anode side catalyst occurs and a reduction in the effective electrode area leads to a decrease in fuel cell performance.

In order to prevent flooding and to stabilize fuel cell performance, the dew point temperature of the supplying reaction gas may be humidified to be significantly lower than the operating temperature of the fuel cell. In this case, the flooding phenomenon may be suppressed, but the electrolyte membrane near the reaction gas inlet may be sufficiently There is a problem in that the electrochemical reaction does not occur sufficiently due to the humidification and the life of the electrolyte membrane is shortened.

Another method for solving the flooding phenomenon is to discharge the condensed water by increasing the flow rate of the reaction gas in the flow path of the separator. However, in this case, the gas utilization rate is lowered and the parasitic power of the blower or the fan for supplying the reactive gas is greatly increased because the reactive gas needs to be supplied to the fuel cell.

Another way to eliminate the flooding phenomenon is to pass through the electrode surface in serpentine in order to increase the pressure drop in the separator flow path. This greatly increases the pressure drop of the flow path and the reaction gas has a sufficient shear force to discharge the water droplets present in the electrode and the separator flow path to the outside. However, this also has a problem that excessive parasitic power of the blower or fan to supply the reaction gas is required.

Especially in the case of promising stationary fuel cell systems with small power plants, the parasitic power of peripheral devices should be minimized in order to maximize efficiency. Therefore, the utilization rate of the reaction gas supplied to the fuel cell should be maintained high and the pressure drop of the reaction gas should be minimized.

Moreover, due to the problem of hydrogen supply, it is necessary to embed a reformer that produces hydrogen from city gas or liquefied petroleum gas. In stationary fuel cell systems including reformers, it is very difficult to change the flow rate and pressure of fuel gas in a short time. Changes in pressure also create problems with system stability.

Therefore, in addition to the above-described flooding solution in stationary fuel cell systems, there is a need for a method capable of appropriately controlling the reaction gas even at a high reaction gas utilization rate and a low operating pressure to suppress flooding and ensure stable performance.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a fuel cell stack and a separator used therein that can stably suppress flooding even at a low operating pressure.

The fuel cell stack according to an embodiment of the present invention includes an electric generator including a membrane-electrode assembly (MEA) and a separator disposed on both sides of the membrane-electrode assembly, the separator being in close contact with each other. A reaction gas flow path is formed in the reaction gas flow path, and the reaction gas flow path includes a first direction flow path extending in a first direction and a second direction flow path communicating with the first direction flow path and extending in a second direction in a direction crossing the first direction. The cross-sectional area of the entire flow path of the second direction flow path is larger than that of the entire flow path of the first direction flow path.

The flow rate of the reaction gas in the first direction flow path may be formed to have a larger value than the flow rate of the reaction gas in the second direction flow path, and the separator has a long side and a short side having a length smaller than the long side, and a thickness. The second direction flow path may be a long side flow path, and the second direction flow path may be a short side flow path.

The separator is formed of a rectangular plate having a horizontal direction and a vertical direction, and the second direction flow path may be a vertical flow path or a horizontal flow path.

The gravity direction vector component of the second direction may be configured to have a larger value than the gravity direction vector component of the first direction, wherein the second direction is a direction parallel to the gravity direction and the first direction is a gravity direction It may be in a direction perpendicular to.

The second direction flow path may be formed to have a greater depth than the first direction flow path, and the second direction flow path may be formed to have a greater width than the first direction flow path.

Split ribs for dividing the second directional flow path may be provided in the second directional flow path, and the plurality of first directional flow paths and the second directional flow paths may be formed, and a cross-sectional area of each flow path of the first directional flow path may be formed. The cross-sectional area of each flow path of the two-way flow path is the same, and the number of the second direction flow paths is larger than the number of the first direction flow paths.

The reaction gas flow path may be formed to have a branch portion divided into two flow paths, and the reaction gas flow path may be formed to have a confluence portion in which two flow paths are integrated.

The reaction gas flow path may be formed to have a smaller cross-sectional area of the exit side flow path than the inlet side flow path, and the reaction gas flow path may be an oxidant flow path or a fuel flow path.

In the separator for a fuel cell system according to an embodiment of the present invention, a reaction gas flow path is formed in the separator, and the reaction gas flow path communicates with a first direction flow path and a first direction flow path extending in a first direction, and the first direction. And a second direction flow path extending in the second direction in a direction intersecting with the second flow path, wherein the total flow path cross-sectional area of the second direction flow path is larger than the total flow path cross-sectional area of the first direction flow path.

The second direction may be formed to have a greater gravity direction vector component than the first direction, the second direction may be a direction parallel to the gravity direction, and the first direction may be a direction perpendicular to the gravity direction. . In addition, the flow rate of the reaction gas in the first direction flow path may be formed to be larger than the flow rate of the reaction gas in the second direction flow path.

As described above, according to the present invention, the flow rate of the reaction gas can be increased even at a low pressure, thereby suppressing flooding and stably producing electrical energy without deteriorating power generation performance.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

1 is an exploded perspective view illustrating a fuel cell stack according to a first embodiment of the present invention.

Referring to FIG. 1, the fuel cell stack 100 according to the first exemplary embodiment includes an electricity generation unit 30 in a cell unit that generates electrical energy by electrochemically reacting fuel and an oxidant. It is configured by.

Each of the electricity generating units 30 refers to a unit cell that generates electricity, and includes a membrane electrode assembly (MEA) 31 for oxidizing / reducing oxygen in the fuel and the oxidant, and a fuel that is a reactive gas. Separators (also known in the art as bipolar plates) for supplying oxidant to the membrane-electrode assembly 31.

By providing a plurality of such electricity generating units 30 and arranging these electricity generating units 30 continuously, the fuel cell stack 100 having a laminated structure of the electricity generating units 30 can be formed.

The fuel cell stack 100 according to the present invention may use hydrogen cracked from liquid or gaseous fuel as a fuel through conventional reformers. In this case, the fuel cell stack 100 may be configured as a polymer electrolyte fuel cell system that generates electrical energy by reaction of hydrogen and oxygen by the electricity generating unit 30.

Alternatively, the fuel used in the fuel cell stack 100 may include a liquid or gaseous fuel containing hydrogen, such as methanol, ethanol, LPG, LNG, gasoline, butane gas, and the like. In this case, the fuel cell stack 100 according to the present invention is a direct oxidation fuel cell method for generating electrical energy through the direct reaction of liquid or gaseous fuel and oxygen by the electricity generating unit 30. Can be configured.

The fuel cell stack 100 may use pure oxygen stored in a separate storage means as an oxidant reacting with the fuel, or may use air containing oxygen as it is.

The membrane-electrode assembly 31 includes a polymer electrolyte membrane formed of a solid polymer electrolyte and an anode electrode and a cathode electrode disposed on both sides of the high molecular electrolyte membrane.

The separators 32 and 33 are closely arranged with the membrane-electrode assembly 31 interposed therebetween to form a fuel flow passage and an oxidant flow passage on both sides of the membrane-electrode assembly 31, respectively. At this time, the separator 32 in which the fuel flow path is formed is disposed on the anode electrode side of the membrane-electrode assembly 31, and the separator 33 in which the oxidant flow path is formed is disposed on the cathode electrode side of the membrane-electrode assembly 31. The electrolyte membrane then transfers the hydrogen ions generated at the anode to the cathode, thereby enabling ion exchange to combine with oxygen at the cathode to produce water.

The plurality of electricity generating units 30 as described above are continuously arranged to constitute the fuel cell stack 100. Here, the outermost end of the fuel cell stack 100 is provided with an end plate 60 which integrally fixes the fuel cell stack 100.

An oxidant inlet 62 for supplying an oxidant to the fuel cell stack 100, a fuel inlet 64 for supplying fuel to the fuel cell stack 100, and a cooling medium are injected into an upper portion of the one end plate 60. Cooling medium inlet (63) is formed. On the other hand, the lower portion of the one end plate 60 discharges the water and the unreacted air generated by the combined reaction of hydrogen and oxygen at the fuel outlet 67 and the cathode electrode for discharging the remaining unreacted fuel from the anode electrode An oxidant outlet 69 for cooling, and a cooling medium outlet 68 through which the cooling medium is discharged.

The separators 32 and 33 have channel-like reaction gas flow paths formed on one surface thereof, and the reaction gas flows through the reaction gas flow paths. Here, the reactive gas flow path is a concept including an oxidant flow path and a fuel flow path.

The separators 32 and 33 may be divided into an anode separator 32 and a cathode separator 33. In the cathode separator 33, an oxidant flow path 50 is formed on one surface facing the membrane-electrode assembly 31, and an oxidant gas containing oxygen flows into the oxidant flow path. The anode separator 32 has a fuel flow path formed on one surface facing the membrane-electrode assembly 31, and a fuel gas containing hydrogen flows into the fuel flow path.

The separators 32 and 33 may have a cooling channel formed on a rear surface corresponding to the opposite side of the one surface, thereby removing the reaction heat generated together with the electrical energy.

Below, the structure of the separators 32 and 33 is demonstrated in more detail. However, since the anode separator 32 and the cathode separator 33 have the structure of substantially the same shape among the separators 32 and 33, the cathode separator 33 is demonstrated as an example.

FIG. 2 is a partial perspective view of the cathode separator shown in FIG. 1.

As shown in FIGS. 1 and 2, the oxidant flow path 50 is formed on one surface of the cathode separator 33 facing the membrane-electrode assembly 31. The oxidant flow path 50 is divided into a plurality of channels.

The cathode separator 33 is formed with an oxidant inlet manifold 41 in communication with the oxidant inlet 62 at one corner. The oxidant inlet manifold 41 is connected to the oxidant flow path 50. In the cathode separator 33, an oxidant outlet manifold 46 communicating with the oxidant outlet 69 is formed at the other corner facing the one side corner diagonally, and the oxidant outlet manifold 46 is also an oxidant flow path ( 50).

 Due to this structure, the oxidant gas supplied through the oxidant inlet manifold 41 flows into the oxidant flow path 50 and is discharged from the oxidant flow path 50 to the oxidant outlet manifold 46.

The oxidant flow path is connected to the first direction flow path 52 extending in the first direction (y-axis direction) and the second direction extending in the second direction (z-axis direction) communicating with and intersecting the first direction. The flow path 54 is included. Here, the first direction is a direction perpendicular to the gravity direction in which gravity acts, and the second direction is a direction parallel to the gravity direction.

When the cathode separator 33 is formed of a rectangular square plate and has a short side having a length smaller than the long side and the long side, and the thickness as in the present embodiment, when the long side of the cathode separator 33 is erected with respect to the ground, the short side direction This first direction becomes, and the long side direction becomes the second direction. In addition, when the short side of the cathode separator 33 stands with respect to the ground, the long side direction becomes the first direction, and the short side direction becomes the second direction. Here, the long side direction means a direction parallel to the long side and the short side direction means a direction parallel to the short side.

In the present embodiment, the second direction is illustrated as being parallel to the gravity direction, but the present invention is not limited thereto, and the second direction is sufficient if the gravity direction vector component is larger than the first direction. Therefore, the second direction flow path 54 is formed to continue in a direction more similar to the gravity direction than the first direction flow path.

The first direction flow paths 52 are arranged along the first direction at random intervals, and both ends thereof are alternately connected by the second direction flow paths 54 so that the oxidant flow paths are meandered paths. Is done.

The first direction flow passage 52 and the second direction flow passage 54 are formed of groove-shaped channels in the cathode separator 33, and a plurality of channels are arranged in a group. The channels are divided into a plurality by the ribs 56. The rib 56 serves to determine the zone so that the reaction gas does not mix between the channels, and also serves as an electrical passage in contact with the electrode.

The first directional flow path 52 and the second directional flow path 54 have the same width, and the depth h2 of the second directional flow path 54 is more than the depth h1 of the first directional flow path 52. It is largely formed. Accordingly, the entire flow path cross-sectional area of the second direction flow path 54 is larger than the total flow path cross-sectional area of the first direction flow path 52. Here, the total flow path cross-sectional area refers to the sum of the cross-sectional areas of each flow path. Since the cross-sectional area of each flow path of the second direction flow path 54 is formed larger than the cross-sectional area of each flow path of the first direction flow path 52, the total flow path cross-sectional area is also the second direction. The flow path 54 becomes larger than the first direction flow path 52.

Hereinafter, the operation of this embodiment will be described.

Since the dew point temperature inside the oxidant flow path 50 is lower than the operating temperature at the initial stage of the fuel cell operation, water droplets do not exist in the oxidant flow path 50 and the water generated through the electrochemical reaction is discharged in the form of water vapor, thereby causing flooding. The performance reduction problem does not occur.

As the operation continues, the inside of the oxidant flow path 50 reaches saturation and water droplets start to form on the surface of the gas diffusion layer in contact with the oxidant flow path 50. As time passes, the droplets continue to grow, and when the shear force of the oxidant gas flowing inside the oxidant passage 50 becomes greater than the drag of the droplet, the droplets flow along the passage along with the gas.

When the flow rate of the oxidant flowing inside the oxidant flow path 50 is sufficient, the shear force by the gas velocity is sufficient to push out the water droplets, so that the water inside the oxidant flow path 50 is in the form of small droplets, together with the oxidant outside the fuel cell stack 100. Can be discharged.

However, if the operating current of the fuel cell stack is not large and requires a high reaction gas utilization rate, such as a stationary fuel cell, the rate of the oxidant flowing through the oxidant flow path is not fast enough to transfer moisture in the form of droplets through the shear force of the oxidant. Is not easy. In this case, the water droplets inside the oxidant flow path 50 are further grown to form a water film by adhering to the channel wall of the separator plate having a relatively hydrophilic property than the gas diffusion layer.

When a water film is formed on the channel wall of the oxidant flow path 50, the oxidant mainly flows through the center of the flow path, and water existing in the form of a water film on the channel wall is transported by the interaction of surface tension, gravity and shear force by the reaction gas. If the transport of water is not properly controlled, the thickness of the water film becomes thicker, and eventually, the flow path is blocked by water, causing flooding to occur, making it impossible to supply the oxidant.

In general, in the flow path configuration having a slow flow rate in order to reduce pressure loss, the flow rate is low in the first direction flow path 52, so that the shear force required to move the water droplets is insufficient. Therefore, the water droplets inside the oxidant flow path 50 adhere to the channel wall to form a water film. As time passes, the water is insufficient to be transferred only by shearing force, so that the water film becomes thick and the channel may be blocked by water.

In this case, flooding occurs and the performance of the fuel cell stack is degraded and becomes unstable. On the other hand, in the second directional flow path 54, even if a water film is formed, water is sufficiently flowed downward by gravity in addition to the shear force, so that the channel is more likely to be blocked by water than in the first directional flow path.

On the contrary, in the oxidant flow path 50 having a high flow rate, the shear force necessary to move the water droplets to the first direction flow path 52 and the second direction flow path 54 sufficiently acts to quickly discharge the water droplets inside the oxidant flow path 50 to the outside. Can be discharged. However, in this case, the pressure drop of the flow path is unnecessarily large and the parasitic power of the blower or the fan for supplying the oxidant is inevitably increased.

When the depth h1 of the first direction flow path 52 is formed lower than the depth h2 of the second direction flow path 54 as in the present embodiment, the flow rate of the oxidant in the first direction flow path 52 is increased in the second direction. It becomes larger than the flow rate of the oxidant in the flow path 54.

The shear force due to the high flow rate of the oxidant gas makes it possible to transfer the downstream with the oxidant gas at a high speed while preventing the water droplets present in the first directional flow path 52 from adhering to the channel wall to form a water film.

On the other hand, since the gravity acts together with the shear force of the gas as a driving force capable of transporting the droplets in the second direction flow path 54, the droplets can be moved in the downstream direction even at a lower speed than the first direction flow path 52. .

As described above, according to the present embodiment, the flow rate of the oxidant is rapidly limited to the first direction flow path 52 and the second direction flow path 54 may move the water from the top to the bottom with the help of gravity, thereby preventing the water discharge. It is not necessary to quickly configure the flow rates of all channels unnecessarily, and it is possible to reduce the pressure loss for supplying the reactant gas.

In the present embodiment, the cathode separator 33 is described as an example, but the anode separator 32 also includes the first flow path and the second direction flow path in the same way as the cathode separator 33, and is a gravity direction second. The directional flow path is formed deeper.

3 is a front view of a cathode separator according to a second embodiment of the present invention, and FIG. 4 is a perspective view of a cathode separator according to a second embodiment of the present invention.

Referring to FIGS. 3 and 4, the cathode separator 200 according to the present exemplary embodiment has a rectangular plate structure, and has an oxidant inlet manifold 241, a cooling medium inlet manifold 242, and a fuel thereon. An inlet manifold 243 is formed, and a fuel outlet manifold 248, a cooling medium outlet manifold 247, and an oxidant outlet manifold 246 are formed below.

In addition, an oxidant flow path 250 connecting the oxidant inlet manifold 241 and the oxidant outlet manifold 246 is formed on the surface of the cathode separator 200. The oxidant flow path 250 is formed of a channel having a groove shape in the cathode separator 200, and a plurality of channels are arranged in a group. The channels are divided into a plurality by the ribs 257.

The oxidant flow path 250 communicates with the first direction flow path 252 extending in the first direction and the second direction flow path 254 connected in the second direction in a direction intersecting the first direction and intersecting the first direction. Include. The first direction is a direction perpendicular to the gravity direction, and the second direction is a direction parallel to the gravity direction.

Eight oxidant flow path 250 is formed, divided into four groups are arranged to pass through different areas. The oxidant flow path 250 includes a branch part 251 in which one flow path is divided into two flow paths, and the branch part 251 is switched from the first direction flow path 252 to the second direction flow path 254. Disposed adjacent to the part. In this embodiment, one flow path is divided into two flow paths in the branch, but the present invention is not limited thereto, and one flow path may be divided into three or more flow paths in the branch.

In addition, the oxidant flow path 250 has a confluence portion 253 in which two flow paths are merged into one, and the confluence portion 253 is a portion that is converted from the second direction flow path 254 to the first direction flow path 252. Are arranged adjacently.

Split ribs 256 for dividing the second direction flow passages 254 are provided in the second direction flow passages 254. Thus, branching portions 251 are formed on the upper ends of the split ribs 256. The confluence 253 is formed at the lower end of the 256. Accordingly, the number of the second direction flow paths 254 is greater than the number of the first direction flow paths 252. When the first direction flow paths 252 are eight as in the second embodiment, the second direction flow paths 254 are formed. 254 is 16. That is, the second direction flow path 254 is formed twice as much as the first direction flow path 252.

The first direction flow path 252 and the second direction flow path 254 are formed to have the same width, so that the sum of the total widths of the second direction flow paths 254 is twice the sum of the total widths of the first direction flow paths 252. do. Accordingly, although each flow path has the same cross-sectional area, the total flow path cross section of the second direction flow path 254 is larger than the total flow path cross-sectional area of the first direction flow path 252 in the total flow path cross-sectional area which is the sum of the cross-sectional areas of each flow path. do. The flow rate of the oxidant in the first direction flow path 252 is twice the flow rate of the oxidant in the second direction flow path 254.

As shown in the second embodiment, when the flow velocity in the first direction flow path 252 is larger, water droplets that cannot move due to gravity can be easily discharged. In the second direction flow path 254, even at a small flow rate, sufficient moisture is sufficient. Emissions can be minimized to reduce pressure losses for the supply of oxidant.

In addition, the sum of the total widths of the second direction flow paths 254 is larger than that of the first direction flow paths 252, but the individual flow paths are formed to have the same width as the first direction flow paths 252, thereby minimizing the pressure drop. A uniform amount of oxidant may be supplied to the second direction flow path 254 to induce a uniform reaction in all regions.

Since the oxidant gas moves at a low flow rate in the second direction flow path 254, the gas utilization rate can be improved by sufficiently reacting the oxidant gas in the second direction flow path 254 formed with a relatively large area.

In addition, the oxidant flow path 250 is divided into two and disposed in different regions, and the flow path is formed by alternately repeating the first direction flow path 252 and the second direction flow path 254. As a result, the sum of the lengths occupied by the first direction flow path 252 in the total flow path becomes smaller than the sum of the lengths occupied by the second direction flow path 254, and the second direction flow paths 254 with less pressure loss are increased. The pressure drop in the flow path is further reduced.

5 is a front view illustrating a cathode separator according to a third embodiment of the present invention.

Referring to FIG. 5, the cathode separator 300 according to the third embodiment has a rectangular plate structure, and has an oxidant inlet manifold 341, a cooling medium inlet manifold 342, and a fuel inlet at an upper end thereof. A manifold 343 is formed, and at the bottom, a fuel outlet manifold 348, a cooling medium outlet manifold 347, and an oxidant outlet manifold 346 are formed.

Also formed on the surface is an oxidant flow path 350 connecting oxidant inlet manifold 341 and oxidant outlet manifold 346. The oxidant flow path 350 is formed of a groove-shaped channel in the cathode separator 300, and a plurality of channels are arranged in a group. The channels are divided into a plurality of ribs 353.

The oxidant flow path 350 communicates with the first direction flow path 352 extending in the first direction and the second direction flow path 356 connected in the second direction in a direction crossing the first direction and intersecting the first direction. Include. Here, the first direction is a direction perpendicular to the gravity direction which is a direction in which gravity acts, and the second direction is a direction parallel to the gravity direction.

The width W1 of the first direction flow path 352 is smaller than the width W2 of the second direction flow path 356. Accordingly, the first direction flow path 352 has a smaller flow path cross-sectional area than the second direction flow path 356, and the flow rate of the oxidant in the first direction flow path 352 is the flow rate of the oxidant in the second direction flow path 356. It is larger than that.

Also, in the second half region of the oxidant flow path 350 (the point closer to the oxidant outlet manifold 346 than the oxidant inlet manifold 341), the second direction flow path 254 is switched to the first direction flow path 352. In the process, a confluence 358 in which two oxidant flow paths 250 are integrated into one is formed. Accordingly, six flow paths are changed to three flow paths, and the sum of the widths of the entire oxidant flow path 350 is reduced due to the confluence. In the present exemplary embodiment, two flow paths are merged into one in the confluence unit 358, but the present invention is not limited thereto, and three or more flow paths may be combined into one in the confluence unit 358.

Accordingly, the oxidant flow path 350 has a smaller cross-sectional area at the outlet side than the entire cross-sectional area at the inlet side.

The joined first direction flow passage 352 may be formed to have the same width and depth as the first direction flow passage 352 before joining, and may be formed to have a smaller width or a lower depth to speed up the flow rate of the oxidant. have.

In general, the oxidant supplied to the fuel cell stack is gradually consumed by reacting at the electrode as it flows along the flow path, and the closer to the oxidant outlet manifold 346, the lower the flow rate in the channel due to the decrease in flow rate, so that the shear force required to move the droplets may be insufficient. . In order to overcome this, the flow paths are integrated in the latter half of the flow path to reduce the sum of the flow path width to prevent the flow rate from being excessively reduced.

If the flow velocity in the second direction flow path 356 is slower than the breaking speed of the first direction flow path 352 and the pressure loss is small as in the present embodiment, even if the confluence portion 358 is formed as described above, the pressure loss is reduced. It does not increase significantly, allowing operation at high utilization and low operating pressures.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the range of.

1 is an exploded perspective view illustrating a fuel cell stack according to a first embodiment of the present invention.

2 is a partial perspective view illustrating a separator of a fuel cell stack according to a first embodiment of the present invention.

3 is a front view illustrating a separator according to a second embodiment of the present invention.

4 is a perspective view illustrating a separator according to a second embodiment of the present invention.

5 is a front view illustrating a separator according to a third embodiment of the present invention.

-Explanation of symbols for the main parts of the drawing-

100: fuel cell stack 251: branch portion

253: merger 256: split rib

30: electricity generating unit 31: membrane-electrode assembly

32: anode separator 33: cathode separator

50: oxidant flow path 52: first direction flow path

54: second direction flow path 56: rib

60: end plate

Claims (18)

An electric generator including a membrane-electrode assembly (MEA) and a separator disposed on both surfaces of the membrane-electrode assembly, A reaction gas flow path is formed in the separator, and the reaction gas flow path communicates with the first direction flow path extending in the first direction and the second direction flow path extending in the second direction in a direction crossing the first direction flow path. And a total flow path cross-sectional area of the second direction flow path is greater than a total flow path cross-sectional area of the first direction flow path. The method of claim 1, And a flow rate of the reaction gas in the first direction flow path is greater than a flow rate of the reaction gas in the second direction flow path. The method of claim 1, The separator includes a long side, a short side having a length smaller than the long side, and a rectangular plate having a thickness, and the second direction flow path is the long side flow path. The method of claim 1, The separator includes a long side, a short side having a length smaller than the long side, and a rectangular plate having a thickness, and the second direction flow path is the short side direction flow path. The method of claim 1, And the gravity direction vector component in the second direction has a larger value than the gravity direction vector component in the first direction. The method of claim 1, And the second direction is a direction parallel to the gravity direction and the first direction is a direction perpendicular to the gravity direction. The method of claim 1, And the second direction flow passage has a greater depth than the first direction flow passage. The method of claim 1, And the second direction flow passage has a larger width than the first direction flow passage. The method of claim 1, And a split rib that divides the second direction flow path in the second direction flow path. The method of claim 1, The first direction flow path and the second direction flow path are formed in plural, each cross-sectional area of each flow path of the first direction flow path and each flow path cross-sectional area of the second direction flow path are the same, and the number of the second direction flow paths is More fuel cell stacks than the number of first directional flow paths. The method of claim 1, And the reactive gas flow path has a branch portion divided into a plurality of flow paths. The method of claim 1, The reaction gas flow path has a fuel cell stack having a confluence in which a plurality of flow paths are integrated. The method of claim 1, And the reaction gas flow passage has a smaller cross-sectional area at the outlet side than the entire cross-sectional area at the inlet side. The method of claim 1, The reaction gas flow path is an oxidant flow path or a fuel flow path. In separators for fuel cell systems A reaction gas flow path is formed in the separator, and the reaction gas flow path communicates with the first direction flow path extending in the first direction and the second direction flow path extending in the second direction in a direction crossing the first direction flow path. And a total flow path cross-sectional area of the second direction flow path is greater than a total flow path cross-sectional area of the first direction flow path. The method of claim 15, And wherein the second direction has a greater gravity direction vector component than the first direction. The method of claim 15, And the second direction is a direction parallel to the gravity direction and the first direction is a direction perpendicular to the gravity direction. The method of claim 15, The flow rate of the reaction gas in the first direction flow path is larger than the flow rate of the reaction gas in the second direction flow path.

Images