JP3753013B2 - Fuel cell - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell, and more particularly to a structural improvement of a peripheral portion of a separator constituting a fuel cell stack.
[0002]
[Prior art and problems to be solved]
In a fuel cell that operates at a relatively low operating temperature of 100 ° C. or less, such as a polymer electrolyte fuel cell, water that has not been absorbed by the electrolyte among water supplied for humidification, or produced by a reaction Moisture may exist in a liquid state. This liquid moisture will block the passage part of the gas diffusion layer (or gas reaction layer) in the cell, reducing the diffusibility of the reaction gas, fuel gas or oxidant gas, to the electrode catalyst. , Causing the problem of deteriorating cell performance.
[0003]
On the other hand, Japanese Patent Laid-Open No. 2000-123848 discloses a configuration in which a drainage groove that is continuous from the inlet to the outlet of the gas flow path is provided. However, in this configuration, the drainage grooves provided on the wall surface of the gas flow path are each independently configured from the inlet to the outlet, so that the water generated by the reaction can be efficiently taken into the drainage groove. Can not. In addition, the taken-in water is transported to the outlet by capillary action in a narrow drainage groove, but even if there are multiple narrow grooves near the gas diffusion surface, especially in the vicinity of the gas outlet, due to water vapor condensation in the gas and power generation The capillarity may not function due to the generated water, which is insufficient in terms of the certainty of drainage.
[0004]
Japanese Patent Application Laid-Open No. 10-172586 proposes a high water-absorbing polymer sheet that changes volume in accordance with the amount of water absorption and changes the cross-sectional area of the flow channel in the gas flow channel. However, in such a configuration, since the cross-sectional area of the flow path is reduced due to water absorption, the pressure resistance in the flow path increases, so the pressure near the outlet decreases at the same inlet pressure as before the swelling. In order to compensate for this, further supply is required, which is inefficient.
[0005]
The present invention has been made paying attention to such conventional problems, and has an object to prevent the accumulation of condensed water in the gas flow path and to maintain the fuel cell performance satisfactorily.
[0006]
[Means for Solving the Problems]
According to a first aspect of the present invention, there is provided a membrane electrode assembly (hereinafter referred to as “MEA”) configured by sandwiching an electrolyte membrane between an anode side electrode and a cathode side electrode each having a gas diffusion surface, and a MEA. 1 and a second separator, the first separator supplying a first flow path for supplying fuel gas to the anode side electrode, and the second separator for supplying an oxidant gas to the cathode side electrode. A plurality of drainage grooves, each having two flow paths, on a side wall surface forming the first or second flow path, in a direction intersecting the gas flow direction, and one end thereof facing the gas diffusion surface Formed.
[0007]
In the second invention, the cross-sectional shape of the drainage groove portion of the first invention is formed with a dimension capable of removing water by capillary action.
[0008]
In the third invention, the other end of the drainage groove of the first invention is communicated with a longitudinal groove formed continuously from the inlet to the outlet at the corner of the flow path.
[0009]
In the fourth invention, a porous material is applied to the separator forming the first or second flow path of the first invention.
[0010]
According to a fifth invention, in the first and third inventions, at least one of water repellency treatment on at least a surface of a part of the gas diffusion surface or hydrophilic treatment on each groove portion in the flow path is performed. did.
[0011]
According to a sixth invention, in the first invention, the angle formed by the drainage groove with the bottom surface of the flow path is smaller than 90 degrees when measured from the upstream side of the gas flow.
[0012]
According to a seventh aspect, in the first aspect, the angle formed by the drainage groove with the bottom surface of the flow path is greater than 90 degrees when measured from the upstream side of the gas flow.
[0013]
[Action / Effect]
According to the first invention, when the gas containing moisture passes through the flow path of the separator, the moisture in the gas is captured by the drain groove formed in the direction intersecting the gas flow on the side wall surface of the separator, and the drain groove Since one end of the tube faces the gas diffusion surface, a considerable amount of water vapor condensate in the gas is absorbed by the side wall near the gas inlet. Thereby, the humidity in the flow path can be managed in an appropriate amount even near the entrance where the pressure is high and the reaction is relatively active in the flow path. Therefore, the conventional problem that the vicinity of the inlet has a high flow velocity and it is difficult to maintain an appropriate humidity can be solved, and the amount of humidification near the inlet can be reduced. In addition, when water is generated by the reaction on the gas diffusion surface, the groove end surface is open to the gas diffusion surface, so that it is easy to eliminate excess generated water near the diffusion surface.
[0014]
According to the second invention, water is trapped in the drain groove by capillarity, so that the water absorption action in the drain groove is more effectively performed.
[0015]
According to the third aspect of the invention, the water trapped in the drain groove is transported to the outlet of the channel through the longitudinal groove far from the gas diffusion surface, thereby further reducing the possibility that moisture in the channel hinders the reaction. be able to.
[0016]
According to the fourth aspect of the invention, since the porous material is used for the separator that forms the flow path, the capacity to absorb the water in the flow path and the drainage capacity to the extent that the water absorbing action to the separator itself is performed. Can only be larger than the capacity. It is also possible to humidify the gas diffusion surface in contact with the separator wall.
[0017]
According to the fifth aspect of the present invention, at least one of the water repellent treatment on at least the surface of the gas diffusion surface or the hydrophilic treatment on each groove portion in the flow path can enhance the above-described drainage function. it can.
[0018]
According to the sixth aspect of the invention, the water trapped in the drainage channel is urged toward the bottom of the channel by the gas flow in the channel, and according to the seventh invention, the water is captured in the drainage channel, contrary to the above. The water is urged toward the gas reaction surface by the gas flow in the flow path. Therefore, by appropriately setting the angle or number of the drain grooves having any one of the structures according to the tendency of the amount of moisture in the flow path, the humidity in all the flow paths from the inlet to the outlet is more appropriate. It becomes possible to adjust to.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a cell unit which is a unit component of a fuel cell, and a fuel cell stack is configured by stacking a required number of cells. In the figure, 10 is an MEA, and 21 and 22 are first and second separators that sandwich the MEA 10, respectively. The MEA 10 has a structure in which an anode side electrode 12 is joined to one surface of a solid polymer electrolyte membrane 11 and a cathode side electrode 13 is joined to the other surface, and the electrodes 12 and 13 are held by a gasket 14. In this manner, the separators 21 and 22 are joined.
[0020]
A first flow path 31 through which hydrogen gas, which is a fuel, circulates on the joint surface of the first separator 21 with the electrode 12, and air as an oxidant circulates on the joint surface of the second separator 22 with the electrode 13. A second flow path 32 is formed. Although the flow paths 31 and 32 are simply illustrated in FIG. 1 for convenience of explanation, in practice, a plurality of systems are meandering along the electrode surface in order to make gas contact with each electrode efficiently. It is densely formed.
[0021]
Both end portions of the first flow path 31 communicate with fuel gas supply holes 33 and fuel gas discharge holes 34 provided in the first separator 21, respectively. Further, both end portions of the second flow path 32 communicate with an air supply hole 35 and an air discharge hole 36 provided in the second separator 22, respectively. Although not shown in the drawings, each of the separators 21 and 22 is also provided with a cooling water flow path for circulating cooling pure water.
[0022]
FIG. 2 shows details of the configuration of the first flow path 31. The arrow A in the figure indicates the flow direction of the fuel gas, and the arrow B indicates the direction in which the MEA is located. As illustrated, a large number of drain grooves 41 are formed on both side walls of the channel 31 so as to intersect the gas flow direction. Further, longitudinal grooves 42 along the gas flow direction are formed over the entire length of the flow path 31 at the corners between the flow path bottom surface and both side wall portions. One end portion of the drainage groove portion 41 is formed so as to open into the longitudinal groove portion 42, and the other end portion is formed so as to face the gas diffusion surface of the MEA 10.
[0023]
The cross-sectional dimensions of the drainage groove 41 are set to about 1 to 0.5 μm, for example, so that condensed water in the gas can be effectively sucked and held by capillary action. In addition, when the inclination angle of the drain groove 41 measured from the upstream side of the gas flow with respect to the bottom surface of the flow path is θ, in this embodiment, θ = 90 degrees for the upstream area of the left flow path, The downstream portion of the flow path is set to satisfy θ <90 degrees, but can be set to satisfy θ> 90 degrees as necessary.
[0024]
Next, the effect | action by the said structure is demonstrated. Hydrogen gas, which is a fuel gas, is supplied from the fuel gas supply hole 33 of the first separator 21 to the first flow path 31, and air is supplied from the air supply hole 35 of the second separator 22 to the second flow path 32. . The hydrogen gas supplied to the first flow path 31 flows downstream while meandering along the flow path 31 and is discharged from the fuel gas discharge hole 34. Further, the air introduced into the second flow path 32 flows downstream while meandering along the flow path 32, and is discharged from the air discharge hole 36.
[0025]
Here, the hydrogen gas supplied to the first flow path 31 contains water vapor for humidification in advance, and a part of this water vapor is condensed without being absorbed by the MEA 10 side and flows in the water state. 31 may stay in the tank. When the water stays, as described above, the flow of hydrogen gas is hindered and the performance of the fuel cell is deteriorated. On the other hand, according to the configuration of the present embodiment, the condensed water in the gas is absorbed by the drainage grooves 41 formed on both side walls of the flow path 31 and is captured by the capillary phenomenon. Further, the trapped water flows out from the drainage groove portion 41 to the longitudinal groove portion 42 by the dynamic pressure of the gas flow, and is conveyed along the longitudinal groove portion 42 to the fuel gas discharge hole 34.
[0026]
In this way, water present in the gas is reliably captured in the drain groove 41 near the gas inlet that is the upstream area of the flow path, and further, by the inclined drain groove 41 near the gas outlet that is the downstream area of the flow path, The water produced by the reaction can be smoothly discharged to the fuel gas discharge hole 35 while being kept away from the gas diffusion surface of the MEA 10. Therefore, the flow path 31 is not blocked or blocked by water, and the uniform gas distribution is stably continued along the flow path 31, so that all the fuel cells are stably generated. Therefore, the performance of the entire fuel cell can be improved.
[0027]
In the above-described configuration, the surface of the gas diffusion surface (MEA 10) on the fuel gas outlet side is subjected to water repellency treatment and the groove portions 41 and 42 are subjected to hydrophilic treatment, whereby water on the gas diffusion surface surface is supplied to the groove portions 41 to 42. The water generated in the flow path 31 can be discharged more effectively while making it easier to guide.
[0028]
In addition, as shown in FIG. 3, by configuring the first separator 21 with a porous material, the capacity of the trapped water in the flow path 31 can be increased to the limit that the porous material can absorb. Further, it is possible to humidify the gas diffusion surface in contact with the separator wall.
[0029]
The above embodiment is an example in which the drainage groove 41 and the longitudinal groove 42 are provided in the first flow path 31 through which the fuel gas passes, but also in the second flow path 32 through which the air passes, condensation of water vapor contained in the air In addition, there is a possibility that the air flow and reaction may be hindered by the reaction product water. Therefore, the performance of the fuel cell can be improved by applying the same configuration to the second flow path 32.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of an embodiment of the present invention.
FIG. 2 is a perspective view of a main part of a separator for illustrating the flow channel structure of the embodiment.
FIG. 3 is a cross-sectional view of main parts of another embodiment of the present invention relating to a separator configuration.
[Explanation of symbols]
10 MEA (membrane electrode assembly)
DESCRIPTION OF SYMBOLS 11 Solid electrolyte membrane 12 Anode side electrode 13 Cathode side electrode 14 Gasket 21 1st separator 22 2nd separator 31 1st flow path 32 2nd flow path 41 Drain groove part 42 Longitudinal groove part

Claims (7)

A membrane electrode assembly configured by sandwiching an electrolyte membrane between an anode side electrode and a cathode side electrode each having a gas diffusion surface; and first and second separators sandwiching the membrane electrode assembly,
The first separator has a first flow path for supplying fuel gas to the anode side electrode, and the second separator has a second flow path for supplying oxidant gas to the cathode side electrode. ,
A fuel characterized in that a plurality of drainage grooves are formed on a side wall surface forming the first or second flow path in a direction intersecting a gas flow direction and one end thereof facing a gas diffusion surface. battery. In claim 1,
The drainage groove part is a fuel cell in which a cross-sectional shape thereof is formed to have a dimension capable of removing water by capillary action. In claim 1,
The other end of the drainage groove is a fuel cell that communicates with a longitudinal groove formed continuously from the inlet to the outlet at the corner of the channel. In claim 1,
The fuel cell which applied the porous material to the separator which forms the said gas flow path. In claims 1 and 3,
A fuel cell that has been subjected to at least one of a water repellency treatment on at least a surface of a part of the gas diffusion surface and a hydrophilic treatment on each groove in the flow path. In claim 1,
A fuel cell in which the angle formed by the drainage groove with the bottom surface of the flow path is smaller than 90 degrees when measured from the upstream side of the gas flow. In claim 1,
A fuel cell in which the angle formed by the drainage groove portion with the bottom surface of the flow path is greater than 90 degrees when measured from the upstream side of the gas flow.

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