JP3272980B2 - Fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for forming a plurality of cells each having a polymer electrolyte, an air electrode and a fuel electrode arranged with the polymer electrolyte interposed therebetween, via a separator having a gas supply groove and a manifold portion. The present invention relates to the improvement of individually stacked fuel cells.

[0002]

2. Description of the Related Art A polymer electrolyte fuel cell (hereinafter, referred to as PEFC) has a low operating temperature, a high output density, can be reduced in size and weight, and has a solid electrolyte because of using a polymer membrane as an electrolyte. And features such as excellent durability.
Usually, this fuel cell is used by increasing the output voltage by stacking a plurality of unit cells. FIG. 3 shows a configuration of a unit cell of this type of conventional fuel cell. The cell 1 includes a polymer electrolyte membrane 2,
The air electrode 3 and the fuel electrode 4 sandwiching the air electrode, the gas supply groove 5a for supplying the oxidant gas to the air electrode, and the gas supply manifold 7
a, 8a, a gas supply groove 5b for supplying fuel gas to the fuel electrode 4, and manifolds 7b, 8b.
, And a gas seal material 10. The separator 6b is provided with gas passages 9a and 9b for communicating the gas supply groove 5b with the manifold 7b and the manifold 8b, respectively. Although not shown, a similar gas passage is provided in the separator 6a.

A plurality of such cells are stacked in series to form a stack 20 as shown in FIG. And the stack 20
On both ends of the stack, the header 2 via the insulating plate 21
The fuel cell is constructed by arranging the foot 2 and the footer 23 and tightening them with the tightening bolts 24. The separators at both ends of the stack have gas supply grooves formed only on one side, and a current collecting plate 25 is arranged between the stack and the insulating plate, and a current is taken out therefrom.

Here, the polymer electrolyte membrane 2 functions as an electrolyte membrane by containing water in a saturated state.
During the operation of the fuel cell, the fuel gas and the oxidizing gas are humidified and supplied to prevent evaporation of water from the polymer electrolyte membrane. At the time of battery power generation, water generated on the air electrode side by an electrochemical reaction is also used to keep the electrolyte membrane in a saturated state. When the amount of water generated at the air electrode increases or the amount of water vapor in the reaction gas becomes excessive due to gas consumption, a flooding state occurs, the electrode reaction area decreases, and the battery performance decreases. In addition, in the flooding state, a reverse diffusion phenomenon of water occurs from the air electrode side to the fuel electrode side, and the partial pressure of water vapor also increases on the fuel electrode side. When the water vapor partial pressure increases on the fuel electrode side, flooding occurs on the fuel electrode side as well as on the air electrode side, leading to a decrease in cell performance.
In particular, this flooding is likely to occur at the fuel gas outlet where the fuel gas flow velocity decreases.

[0005]

Conventionally, measures against flooding of the air electrode have been taken, for example, by increasing the width of the flow channel. However, almost no countermeasures have been taken against water flooding on the fuel electrode side due to reverse diffusion. I didn't. In view of the above, development of a separator that does not cause flooding in the fuel-electrode-side flow path is desired for stabilizing and improving the performance of the battery.

[0006]

The fuel cell of the present invention According to an aspect of the polymer electrolyte, the unit cell having the polymer electrolyte disposed across the air electrode and the fuel electrode, a gas supply groove, and the manifold portion Communicates with the gas supply groove and the manifold
And a fuel gas supply groove facing the fuel electrode of the separator, the depth of which is shallower from the gas inlet to the gas outlet. And / or the width thereof is reduced, and the depth and / or width of the gas outlet of the fuel gas supply groove is 0.2 to 0.8 times the gas inlet. and gas of the fuel gas supply groove
The depth of the gas passage that is connected to the scan outlet portion, and wherein the shallower than the gas passage connected to the gas inlet of the fuel gas supply channel.

According to the present invention, by processing the separator on the fuel electrode side, flooding of water on the fuel electrode side can be prevented, and the cell performance can be stabilized.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. << Embodiment 1 >> FIG. 1 shows the configuration of a unit cell 1 used in the fuel cell of this embodiment. Polymer electrolyte membrane 2, air electrode 3 and fuel electrode 4 sandwiching the polymer electrolyte membrane 2, separator 6 disposed on the side of air electrode 3
a and the sealing material 10 have the same configuration as the conventional example of FIG. The separator 11 disposed on the fuel electrode 4 side includes the manifolds 13 and 14 and the gas supply groove 1 facing the fuel electrode 4.
2, and gas supply groove 12 and manifolds 13 and 1
4 with gas passages 15a and 15b, respectively. The gas supply groove 12 is configured such that its depth decreases from the gas inlet on the gas passage 15a side to the gas outlet on the gas passage 15b side.

In this embodiment, each of the separators 6a and 11 has a size of 160 mm square and a thickness of 5 m.
m. The depth of the oxidizing gas supply groove 5a of the separator 6a is 2 mm, and the width is 2 mm. On the other hand, the separator 11
The fuel gas supply groove 12 has a groove depth of 4 at the fuel gas inlet.
mm and the depth of the groove at the fuel gas outlet is 1 mm. The groove width is 2 mm as in the air electrode side. The fuel gas is supplied to the fuel gas supply manifold 1
3 is introduced into the fuel gas supply groove 12 through the gas passage 15a. Thereafter, the fuel gas is discharged from the fuel gas supply groove 12 to the fuel gas discharge manifold 14 through another gas passage 15b. The polymer electrolyte membrane 2 includes commercially available Nafio
A unit cell was formed using an n-film (DuPont) and Pt-supported carbon as an electrode catalyst.

[0010] The performance of a fuel cell stack in which 30 unit cells thus produced were stacked was examined. The battery operating temperature was set at 60 ° C, and the gas humidification temperature was set at 55 ° C for both the fuel gas and the oxidizing gas. FIG. 4 shows the current-voltage characteristics (average of each cell) at this time in comparison with a conventional fuel gas supply groove having a constant depth. This indicates that the performance is improved as compared with the conventional structure. In particular, the voltage drop in a high current density region where a large amount of generated water is generated is smaller than in the conventional example. Also, Table 1 shows a comparison of the voltage at a current density of 0.7 A / cm ² of the unit cell when the ratio of the groove depth between the inlet part and the outlet part was changed. From this, it is understood that the battery voltage is improved by reducing the ratio of the depth of the outlet groove to the depth of the inlet groove.

[0011]

[Table 1]

As a result, by making the depth of the gas supply groove on the fuel electrode side shallower from the gas inlet to the outlet, it is possible to provide a fuel cell having better performance than before. The groove depth at the gas outlet is 0.2 to
Desirably 0.8 times. The structure is not limited to this embodiment as long as the structure becomes shallow from the entrance to the exit.

Embodiment 2 FIG. 5 shows the structure of a separator used in the fuel cell of this embodiment. Fuel gas supply groove 12a
The groove width at the entrance is 3 mm, and the groove width at the exit is 1 mm. Therefore, the rib 1 formed between the grooves 12a
2b is narrower on the gas inlet side. Groove depth is 2
mm. The groove width and groove depth of the oxidizing gas supply groove are the same as those in the first embodiment. The same electrolyte membrane, electrode catalyst, and the like as in Example 1 were used. The performance of a fuel cell stack in which 30 unit cells produced using this separator were stacked was examined. The operating conditions of the battery were the same as in Example 1. FIG. 6 shows current-voltage characteristics (average of each cell) at this time in comparison with a conventional gas supply groove having a constant width. Thus, according to the present example, it was found that the performance was improved as compared with the conventional structure. In particular, the voltage drop in a high current density region where a large amount of generated water is generated is smaller than in the conventional example. Further, Table 2 shows a comparison of the voltage at a current density of 0.7 A / cm ² of the unit cell when the ratio of the groove width between the inlet and the outlet was changed. It can be seen from this that the battery voltage is improved by reducing the ratio of the outlet groove width to the inlet groove width.

[0014]

[Table 2]

As a result, by narrowing the width of the gas supply groove on the fuel electrode side from the gas inlet to the outlet, it is possible to provide a fuel cell having better performance than before. The groove width at the gas outlet is 0.2 to
Desirably 0.8 times. The groove width is not limited to this embodiment as long as the groove width decreases from the entrance to the exit.

<< Embodiment 3 >> The fuel gas supply groove of the separator used in the fuel cell of this embodiment is configured such that the groove width is narrower and the depth is shallower from the gas inlet to the gas outlet. ing. That is, the groove width at the inlet portion of the fuel gas supply groove is 3 mm, the groove width at the outlet portion is 2 mm, the groove depth at the fuel gas inlet portion is 4 mm, and the groove depth at the fuel gas outlet portion is 2 m.
m. The groove width and groove depth of the oxidizing gas supply groove are the same as those in the first embodiment. The same electrolyte membrane, electrode catalyst, and the like as in Example 1 were used. The performance of a fuel cell stack in which 30 unit cells produced using this separator were stacked was examined. The operating conditions of the battery were the same as in Example 1. At this time, the current-voltage characteristics (average of each cell) were found to be 0.68 V at a current density of 0.7 A / cm 2, which is almost the same as those of Examples 1 and 2. As a result, the width of the gas supply groove on the fuel electrode side is reduced from the inlet to the outlet, and the depth of the groove is reduced from the gas inlet to the outlet. Can be provided. The shape of the groove depth and the groove width is not limited to this embodiment.

[0017]

As described above, according to the present invention, a decrease in performance due to flooding of water on the fuel electrode side can be suppressed, and a fuel cell with stable performance can be provided.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a unit cell of a polymer electrolyte fuel cell according to an embodiment of the present invention.

FIG. 2 is a front view showing the appearance of a fuel cell stack using the same cell.

FIG. 3 is a longitudinal sectional view of a unit cell of a conventional polymer electrolyte fuel cell.

FIG. 4 is a diagram showing current-voltage characteristics of a fuel cell stack of an example and a conventional example.

FIG. 5 is a plan view of a separator of a polymer electrolyte fuel cell according to another embodiment of the present invention.

FIG. 6 is a diagram showing current-voltage characteristics of the fuel cell stack.

[Explanation of symbols]

 1 unit cell 2 polymer electrolyte membrane 3 air electrode 4 fuel electrode 5a, 5b, 12 gas supply groove 6a, 6b, 11 separator 7a, 7b, 13 gas supply manifold 8a, 8b, 14 gas exhaust manifold 9a, 9b, 15a, 15b Gas passage 10 Gas seal material 20 Stack 21 Insulating plate 22 Header 23 Footer 24 Tightening bolt 25 Current collector plate

Continuation of front page (72) Inventor Koji Gamo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-267564 (JP, A) JP-A-9-161819 (JP) , A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 8/02 H01M 8/10

Claims (1)

(57) [Claims] 1. A cell comprising a polymer electrolyte, an air electrode and a fuel electrode disposed with the polymer electrolyte interposed therebetween, is provided with a gas supply groove, a manifold portion, the gas supply groove and the manifold .
A plurality of fuel cells stacked via a separator having a gas passage communicating with a manifold portion , wherein a fuel gas supply groove facing a fuel electrode of the separator extends from a gas inlet to a gas outlet. The fuel gas supply groove is configured such that the depth and / or width of the fuel gas supply groove is 0.2 to 0. A fuel cell, wherein the depth of a gas passage connected to a gas outlet of the fuel gas supply groove is shallower than that of a gas passage connected to a gas inlet of the fuel gas supply groove.