JP3509180B2 - Fuel cell - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell, and more particularly to a structure of a gas flow path provided at a boundary between a unit cell and a separator, and further to a fuel gas of the fuel cell.
Concerning the supply method.

[0002]

2. Description of the Related Art Conventionally, a fuel cell is known as a device for directly converting the energy of fuel into electrical energy. In this fuel cell, usually, a pair of electrodes are arranged with an electrolyte in between, and a fuel gas such as hydrogen is brought into contact with the surface of one electrode, and an oxidizing gas containing oxygen is brought into contact with the surface of the other electrode. By utilizing the electrochemical reaction that occurs at this time, electric energy is taken out from between the electrodes. The fuel cell can extract electric energy with high efficiency as long as the fuel gas and the oxidizing gas are supplied.

A fuel cell is constructed by stacking a plurality of unit cells each having the above-mentioned electrolyte and both electrodes with a separator interposed therebetween, and the fuel gas and the oxidizing gas are flow channel grooves formed in the separator. It is possible to make contact with the surface of each electrode by flowing.

By the way, the hydrogen contained in the fuel gas and the oxygen contained in the oxidizing gas are continuously consumed by the electrochemical reaction while passing through the flow channel, so that near the inlet of the flow channel, The partial pressure increased, and the partial pressure decreased as it approached the outlet of the flow channel. Therefore, as a fuel cell that eliminates these problems, a configuration has been proposed in which the flow channel groove is gradually narrowed from the inlet side to the outlet side (for example,
JP-A-61-256568). By narrowing the outlet side of the flow channel groove, it is possible to increase the flow velocity on the outlet side and improve gas diffusivity.As a result, variations in power generation reaction within the electrode surface are reduced, and gas flow The current density was homogenized along the direction.

[0005]

However, in such a conventional fuel cell, when a high load is applied, it is not possible to sufficiently cope with the increase in the load. This is because when a high load is applied, a large amount of hydrogen and oxygen in the gas are consumed at the inlet side of the flow channel, so hydrogen and oxygen do not reach the outlet side sufficiently, and Because the reaction decreases, no matter how high the flow rate on the outlet side is, as in the prior art, hydrogen and oxygen reaching the outlet side are not sufficient, and the current density should be made uniform along the gas flow direction. There was a problem that I could not do it.

The fuel cell of the present invention has been made in view of these problems, and an object thereof is to make the current density distribution uniform along the gas flow direction even under high load.

[0007]

In order to achieve such an object, the following constitution is adopted as a means for solving the above problems.

That is, the fuel cell of the present invention includes a unit cell in which an electrolyte is sandwiched between two electrodes, a separator inserted between a plurality of unit cells and connected in series, and the unit cell and the separator. In a fuel cell provided with a gas flow path that is provided at the boundary of the gas flow path for causing an electrochemical reaction to flow in the surface direction of the unit cell, the gas flow path is a series of
As a groove with a gas inlet and gas outlet for the unit cell
A connection Configurations, to the gas flow path, in a range extending to the intermediate portion from the inlet portion of the gas flow path, the surface of the single cell
A side path separating a predetermined area on the side is formed.

In such a fuel cell, preferably,
The gas flow channel groove may be configured such that a cross section of the gas flow channel is gradually narrowed from an inlet portion to an outlet portion. A fuel gas supply method for a fuel cell according to the present invention comprises a series of grooves extending along the cell on an electrode of a fuel cell having a cell sandwiching an electrolyte between two electrodes .
The fuel gas supply method of a fuel cell for supplying hydrogen fuel gas by the gas flow path connected to the gas inlet and gas outlet, the single electric outlet side before SL gas channel
The supply of the fuel gas to the predetermined region in contact with the pond is configured such that new fuel gas having a high hydrogen partial pressure is sent by the second gas passage independent of the gas passage. To do.

[0010]

According to the fuel cell of the present invention constructed as described above, the reaction gas is allowed to flow from the inlet portion of the gas passage to the midway portion due to the side passage formed in the gas passage formed of the series of grooves. Up to a plurality of flows, and the reaction gas on the branched side does not touch the surface portion apart from a predetermined region on the surface side of the unit cell. Therefore, even when a large amount of the effective component in the reaction gas is consumed at the inlet side of the gas flow path at the time of high load, a new reaction gas is sent to the outlet side by the side passage. The side can also receive a sufficient amount of the active ingredient, and variation in the power generation reaction within the electrode surface is reduced.

Further, since the cross section of the gas flow passage is constructed to be gradually narrowed from the inlet portion to the outlet portion, the flow velocity on the outlet side can be increased and the supply efficiency of the reaction gas can be further improved. It is possible. According to the fuel gas supply method of the fuel cell of the present invention, even in a predetermined region in contact with the unit cell on the outlet side of the gas flow path formed of a series of grooves ,
Fuel gas having a high hydrogen partial pressure can be supplied, variation in power generation reaction on the surface of the electrode can be reduced, and the current density distribution can be made uniform along the gas flow direction. Therefore, even under a high load, the current density distribution can be made uniform along the gas flow direction.

[0012]

Preferred embodiments of the present invention will be described below in order to further clarify the structure and operation of the present invention described above.

FIG. 1 is a schematic view of a cell structure of a solid polymer fuel cell 1 to which an embodiment of the present invention is applied. As shown in this figure, the fuel cell 1 has, as its cell structure,
An electrolyte membrane 10 and an anode 2 as a gas diffusion electrode having a sandwich structure in which the electrolyte membrane 10 is sandwiched from both sides.
0 and the cathode 30, and a separator 60 that forms a fuel gas flow channel 40 and an oxidizing gas (oxygen-containing gas) flow channel 50 while sandwiching the sandwich structure from both sides. In FIG. 1, the electrolyte membrane 10 and the anode 2 are shown.
Although only one unit cell including 0 and the cathode 30 is shown, actually, a plurality of unit cells are stacked in the order of the separator 60, the anode 20, the electrolyte membrane 10, the cathode 30, and the separator 60 to form a polymer electrolyte fuel cell. Constitute.

The electrolyte membrane 10 is an ion exchange membrane made of a polymer material such as a fluorine resin, and exhibits good electric conductivity in a wet state. The anode 20 and the cathode 30 are formed of a carbon cloth woven with a yarn made of carbon fiber.
Carbon powder carrying platinum or an alloy of platinum and another metal as a catalyst is kneaded into the gap of the cloth.

The separator 60 is formed of gas-impermeable carbon which is made impermeable by compressing carbon.
A rib 62 is formed on one side of the separator 60, and the rib 62 and the surface of the anode 20 form the flow channel 40 of the fuel gas. A rib 64 is formed on the other surface of the separator 60.
4 and the surface of the cathode 30 flow path groove 50 for the oxidizing gas
Is formed. The fuel gas flow channel groove 40 and the oxidizing gas flow channel groove 50 are formed in directions orthogonal to each other.

The structure of the separator 60 will be described in more detail with reference to FIGS. As shown in these drawings, the separator 60 includes the fuel gas flow channel 40 and the oxidizing gas flow channel 50 described above on both surfaces thereof. The fuel gas passage groove 40 is formed such that the depth of the groove gradually decreases from the inlet portion 40i to the outlet portion 40e, and the current plate 42 is provided in the groove. Baffle plate 4
Reference numeral 2 denotes a resin plate having a trough shape with a U-shaped cross section, the depth D of which is the inlet portion 40i of the fuel gas passage groove 40.
Is about half the depth d of the groove, and its longitudinal length L
Is approximately one half of the length l of the fuel gas flow channel 40.
In the current plate 42, the U-shaped opening is directed toward the depth direction of the fuel gas passage groove 40, and the end portion 42 a is formed in the fuel gas passage groove 4.
Fuel gas flow channel groove 40 so that it is located at the inlet 40i of 0.
It is fixed inside and divides the inside of the fuel gas passage groove 40 into two gas passages 40a and 40b. In addition,
The rectifying plate 42 is made of a material having corrosion resistance instead of the resin,
For example, it may be formed of carbon, ceramic, or the like.

The oxidizing gas passage groove 50 is also formed so that the depth of the groove becomes gradually shallower from the inlet portion 50i to the outlet portion (not shown) like the fuel gas passage groove 40. The same rectifying plate 52 as the rectifying plate 42 is provided in the groove, and the rectifying plate 52 divides the oxidizing gas passage groove 50 into two gas passages 50a and 50b.

The flow of gas in the fuel cell 1 will be described below. When the fuel gas is sent from the fuel gas source (not shown) to the fuel gas passage groove 40 on the anode 20 side,
This fuel gas, as shown in FIG.
It is branched by the straightening vane 42 at the inlet 40i of 0 and flows through the two gas flow paths 40a and 40b. In FIG. 4, the anode 2
Although the surface S of No. 0 is shown by a one-dot chain line, as shown in this figure, the fuel gas G1 flowing through the gas flow passage 40a closer to the anode 20 is in the surface S of the anode 20 inside the fuel gas flow passage groove The fuel gas G2 that is sent toward the region S1 located on the inlet side when divided into two regions S1 and S2 in the direction of and flows through the gas passage 40b on the other side to the region S2 located on the outlet side. Sent to you.

On the other hand, when the oxidizing gas is sent from the oxidizing gas source (not shown) to the oxidizing gas passage groove 50 on the cathode 30 side,
This fuel gas flows through the two gas flow paths 5 in the oxidizing gas flow path groove 50 similarly to the flow of the fuel gas in the fuel gas flow path groove 40.
0a and 50b are branched and sent to two regions in the surface of the cathode 30 which are arranged in parallel in the oxidizing gas flow channel groove 50 direction.

According to the fuel cell 1 of this embodiment described in detail above, when the load is high, a large amount of hydrogen in the fuel gas is generated in the region S1 on the anode 20 located on the inlet side of the fuel gas passage groove 40. Even if consumed, new fuel gas G2 is sent to the region S2 located on the outlet side of the fuel gas flow channel groove 40 from the gas flow channel 40b that is independent of the gas flow channel 40a that sends the fuel gas G1 to the region S1. Therefore, it is possible to supply the fuel gas in which the partial pressure of the hydrogen component is high and hydrogen is not yet consumed to the region S2. Therefore, it is possible to reduce variations in the power generation reaction on the surface S of the anode 20, and as a result, it is possible to make the current density distribution uniform along the gas flow direction. Further, for the same reason, it is possible to reduce variations in the power generation reaction on the surface of the cathode 30, and to make the current density distribution uniform on the cathode side along the gas flow direction. As a result, since the temperature distribution in the gas flow direction can be made uniform, the fuel cell 1
The local deterioration of the fuel cell 1 can be suppressed, and the life of the fuel cell 1 can be extended. Further, since the stable output characteristic can be maintained even in the high current density region, the battery performance can be improved.

An experiment conducted to confirm the performance of the fuel cell 1 will be described below. The specifications of the fuel cell 1 used in this experiment will be described first. There is one unit cell stacked as the fuel cell 1, and the dimensions of each part are as follows. Each of the anode 20 and the cathode 30 has a side length of 100 mm and an area of 100 cm ² , and platinum is supported on both surfaces at 0.5 mg / cm ^{2 as a} catalyst. The fuel gas passage groove 40 formed in the anode 20 has a groove width of 1 mm, a groove-to-groove spacing of 1 mm, a groove inlet 40i depth of 3 mm, and an outlet 40e depth of 1 mm. The oxidizing gas passage groove 50 formed in the cathode 30 has a depth of 2 mm at the outlet portion 50e of the groove, and other widths, groove intervals, and depths at the inlet portion 50i of the groove are the fuel gas passage grooves. 40
It has the same dimensions as.

The contents of this experiment are as follows. The temperature of the unit cell was adjusted to 75 ° C., and the fuel gas flow channel groove 40
Is H ₂ : C moistened with a bubbler at a water temperature of 80 ° C.
A reformed gas of methanol having an O ₂ ratio of 3: 1 is supplied, and air humidified by a bubbler at a water temperature of 60 ° C. is supplied to the oxidizing gas channel groove 50. Then, a discharge test was conducted on this fuel cell 1. The gas pressure at this time is 3 at absolute pressure (3 × 9.80665 × 10 ⁴⁾ on both electrodes.
Pa) and the flow rate was set so that the reaction gas became 1.5 times the theoretical consumption amount for each current density. The results of this experiment are shown in the table below.

[0023]

[Table 1]

In the above table, as a comparative example, the straightening plates 42,
Experimental results are also shown in the case where 52 is not provided and the other conditions are the same. The values in the table are the inter-terminal voltage detected by discharge, with a rectifying plate, and a current density of 0.5.
It is shown as a relative value when the terminal voltage at A / cm ² is 1.

From the above table, the fuel cell 1 is
By providing 52, it can be seen that a stable inter-terminal voltage can be obtained even when the current density is changed, and battery performance is excellent, as compared with the case where the rectifying plates 42 and 52 are not provided.

Further, in the fuel cell 1 of the above-mentioned embodiment, the reaction gas is usually humidified in order to maintain the wet state of the electrolyte as in the experiment. The partial pressure of water vapor in the reaction gas varied from the side to the side of the outlet, and the water content in the electrode surface varied. On the other hand, in this fuel cell 1, it is possible to reduce the variation in the water content in the electrode surface, make the conductivity of the electrolyte membrane 10 uniform, and prevent local dry-up. .

In the fuel cell 1 of the above-described embodiment, one flow straightening plate 42 was provided in the fuel gas flow channel groove 40. Instead of this, as shown in FIG. 5, two flow straightening plates are provided . 101,
The configuration may be such that 102 is provided. Baffle plate 101, 10
Similar to the flow straightening plate 42 of the above-mentioned embodiment, 2 is a resin plate having a trough shape with a U-shaped cross section, and both are laminated in the fuel gas flow channel groove 40. With this configuration, the inside of the fuel gas flow channel groove 40 has three gas flow channels 111, 112,
It branches to 113. Therefore, independent new fuel gas can be supplied toward the three regions in the surface of the anode 20 that are arranged in parallel in the direction of the fuel gas flow channel 40.
Therefore, the fuel gas having a high hydrogen partial pressure can be supplied to the surface of the anode 20 irrespective of the position in the direction of the fuel gas passage groove 40, and variation in the power generation reaction on the surface of the anode 20 can be reduced. The current density distribution can be made uniform along the gas flow direction. The oxidizing gas flow channel groove 50 on the cathode 30 side may also be configured to have three gas flow channels by using two flow straightening plates.

Further, if three or more rectifying plates are used and the insides of the fuel gas passage groove 40 and the oxidizing gas passage groove 50 are divided into a larger number of gas passages, the current density distribution becomes a gas flow. More uniform along the direction.

Further, the fuel cell of the above-mentioned embodiment is a so-called ribbed separator type in which ribs 62 and 64 are provided in the separator 60 to form the flow channels 40 and 50 of the fuel gas and the oxidizing gas. Instead, the anode 2
0 and cathode 30 may be provided with ribs to form passage grooves for fuel gas and oxidizing gas, so-called electrode type with ribs. In this configuration as well, by similarly using the flow straightening plate to branch the flow path groove into a plurality of pieces, it is possible to obtain the same effect as that of the above-described embodiment.

Further, in place of the above embodiment, the fuel gas passage groove 40 has a shape in which the cross section does not change from the inlet portion to the outlet portion, and the depth of the groove is in the range from the inlet portion to the midway portion. You may comprise so that the partition plate which divides a direction into two may be provided. According to this configuration, it is possible to make the current density distribution uniform along the gas flow direction, even though it is the simplest configuration.

The embodiment of the present invention has been described above.
The present invention is not limited to these examples, for example, instead of the polymer electrolyte fuel cell, a phosphoric acid type, or a molten carbonate type, etc.,
Needless to say, the present invention can be implemented in various modes without departing from the scope of the present invention.

[0032]

As described above, in the fuel cell of the present invention, the current density can be made uniform along the flow direction of the reaction gas even when the load is high, as in the case where the load is low. As a result, since the temperature distribution in the flow direction of the reaction gas can be made uniform, the local deterioration of the battery can be suppressed, and the life of the battery can be extended. Further, since the stable output characteristic can be maintained even in the high current density region, the battery performance can be improved.

Further, in a fuel cell, the reaction gas is usually humidified in order to keep the electrolyte wet, but in such a case, conventionally, the partial pressure of water vapor in the reaction gas is changed from the inlet side to the outlet side of the gas passage. Difference occurred, and the water content in the electrode surface varied. On the other hand, in the fuel cell of the present invention,
It is possible to reduce the variation of the water content in the electrode surface and make the conductivity of the electrolyte uniform.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a cell structure of a fuel cell 1 to which an embodiment of the present invention is applied.

FIG. 2 is an exploded perspective view of a separator 60 of the fuel cell 1.

3 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 4 is a fuel gas G branched at a fuel gas flow channel groove 40.
It is explanatory drawing which shows the surface S of the anode 20 which contacts 1 and G2.

FIG. 5 is a sectional view of a separator showing a modified example of the embodiment.

[Explanation of symbols]

1 ... Fuel cell 10 ... Electrolyte membrane 20 ... Anode 30 ... Cathode 40 ... Fuel gas passage groove 40a, 40b ... Gas flow path 40e ... Exit 40i ... Entrance 42 ... Current plate 50 ... Oxidizing gas flow channel groove 50a, 50b ... Gas flow path 50e ... Exit 50i ... Entrance 52 ... Rectifier plate 60 ... Separator 62 ... rib 64 ... rib 101, 102 ... Rectifier plate 111, 112, 113 ... Gas flow path

Claims (3)

(57) [Claims] 1. A unit cell that holds an electrolyte between two electrodes, a separator that is inserted between a plurality of unit cells and that connects the unit cells in series, and a separator that is provided at the boundary between the unit cell and the separator. In a fuel cell provided with a gas flow path for causing a reaction gas that causes a chemical reaction to flow in a plane direction of the unit cell, the gas flow path is a series of grooves for introducing gas into the unit cell.
Is configured to be connected to the mouth portion and a gas outlet, the gas flow path, in a range extending to the intermediate portion from the inlet portion of the gas flow path, the bypass separating the predetermined region of the surface side of the single cell A fuel cell characterized by being formed. 2. The fuel cell according to claim 1, wherein the gas flow passage is configured such that a cross section of the gas flow passage is gradually narrowed from an inlet portion to an outlet portion. 3. A series of grooves extending along a unit cell on an electrode of a fuel cell including a unit cell in which an electrolyte is sandwiched between two electrodes.
A gas inlet and a gas outlet for the unit cell.
The fuel gas supply method of a fuel cell for supplying hydrogen fuel gas by the gas flow path which is connected to the mouth, where contact with the unit cell at the outlet side before SL gas channel
The fuel cell is characterized in that the supply of the fuel gas to the constant region is configured such that a new fuel gas having a high hydrogen partial pressure is sent by a second gas passage independent of the gas passage. Fuel gas supply method.