JPH01189868A - Fuel cell - Google Patents

Abstract

PURPOSE:To improve the application efficiency of an electrode by forming the periphery seal face and center current collecting face of a separator on the same plane and making the end sections of portions in contact with the oxidizer gas and fuel gas of a fuel electrode and an oxidizer electrode airtight. CONSTITUTION:A corrugated plate 9 is provided in a stepped section 8A formed on the separator base material 8 of a separator 4, the projected face of the corrugated plate 9 serves as a current collecting face 10, this current collecting face 10 and a wet seal face 11 are formed on the same plane. On the other hand, end sections 12 and 13 of faces of a fuel electrode 2 and an oxidizer electrode 3 in contact with the oxidizer gas and fuel gas and mating faces are filled with a heat-resistant oxide such as alumina and sintered to obtain gas-tightness. The leakage of reaction gas to the outside of a cell and the occurrence of the gas crossover phenomenon are prevented when the electrode with any thickness is used, the application efficiency if the electrode is improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a molten carbonate fuel cell, and in particular, it is possible to prevent leakage of reactant gas to the outside of the cell and gas crossover phenomenon without restricting the electrode thickness. The present invention relates to a fuel cell suitable for preventing such occurrence.

[Conventional technology]

In a fuel cell, a pair of porous electrodes, a fuel electrode and an oxidizer electrode, are arranged on both sides of an electrolyte plate containing an electrolyte, and flow paths for fuel gas and oxidizer gas are formed outside each electrode. It consists of a unit battery provided with a separator.

In order to increase the capacity of a fuel cell for electric power, it is possible to increase the required scale by increasing the electrode area and configuring a large stacked battery with a large number of unit cells stacked together as a standard stack, and by integrating multiple units. A power generation plant is being built.

One of the biggest problems in the operation of this fuel cell is the so-called gas crossover phenomenon, in which the fuel gas and oxidant gas, which should be separated, mix, and each gas flows outside the cell. leakage, etc. These phenomena significantly reduce battery performance,
This also causes problems such as local overheating of the battery.

As a method for preventing such leakage of reactant gas to the outside of the battery, a method has been proposed in which a sealing material such as an oxide is filled around the electrodes and electrolyte plates. Known proposals of this type include those described in Japanese Patent Laid-Open Nos. 58-129766 and 61-279070.

[Problem to be solved by the invention]

However, in both of the above proposals, the fuel electrode and the oxidizer electrode are installed in a step part of the same area formed at a certain depth to the wet seal surface of the separator, and this step part becomes the current collecting surface. ing. In this case, the step portion of the separator has a constant depth, but the fuel electrode and oxidizer electrode have various thicknesses. Therefore, when the fuel electrode and oxidizer electrode are installed on the stepped portion of the separator, the surface of each electrode may be lower than the wet seal surface of the separator.
Conversely, it may be higher than the wet seal surface. When the surface of the electrode is lower than the wet sealing surface of the separator, the electrode and the electrolyte plate are no longer in contact with each other, so there is no exchange of ions between them, and the battery reaction stops progressing, so no battery electromotive force is generated.

In addition, if the electrode surface is higher than the wet sealing surface of the separator, the larger the gap, the more difficult it becomes to contact the wet sealing surface of the separator and the electrolyte plate. A liquid film is no longer formed by the electrolyte on the surface, the wet sealing effect is lost, and the reaction gas tends to leak to the outside of the battery.

Therefore, there is an optimum range for the gap between the wet sealing surface of the separator and the electrode surface. If we try to reduce this gap to within this range, it is necessary to select an electrode with an appropriate thickness from among electrodes of various thicknesses, resulting in a problem that the applicable range of the electrode becomes extremely narrow. .

The present invention has been made in view of the above circumstances.

It is an object of the present invention to provide a fuel cell that can prevent reaction gas from crossover or leaking to the outside of the cell, no matter what thickness of electrodes are used.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a unit cell in which a fuel electrode and an oxidizer electrode are respectively provided on both sides of an electrolyte plate.
In a fuel cell in which a plurality of fuel cells are stacked with separators in between, the peripheral sealing surfaces on both sides of the separator and the central current collecting surface are formed on the same plane, and the fuel electrode is placed on one of these surfaces and the fuel electrode is placed on the other side. The oxidizer electrode is disposed, and means for providing airtightness to at least the ends of the portion of the fuel electrode that contacts the oxidizer gas and the portion of the oxidizer electrode that contacts the fuel gas is provided. This is what I did.

(Function) According to the above configuration, the sealing surface around the separator and the current collecting surface in the center are formed on the same plane, so there is no need to select an electrode that corresponds to the depth of the step as in the conventional case. Therefore, electrodes of any thickness can be attached without causing cross-over phenomenon or leakage of reactant gas to the outside.Also, the end of the part of the fuel electrode that comes into contact with the oxidant gas and the part of the oxidizer electrode Each end of the part that comes into contact with the fuel gas is gas-tight, which prevents the reaction gas from leaking to the outside of the cell, and prevents the reaction gas from entering through the pores at the end of each electrode and causing a crossover phenomenon. It can also be prevented from occurring.

〔Example〕

Hereinafter, one embodiment of a fuel cell according to the present invention will be described with reference to the drawings.

A first embodiment of the present invention is shown in FIGS. 1 and 2.
The figure shows an external manifold type cell among molten carbonate fuel cells, and in reality, manifolds (not shown) are attached to each of the four sides. In the figure,
A fuel electrode 2 and an oxidizer electrode 3 having the same area are provided on both sides of a substantially square electrolyte plate 1 containing an electrolyte, and a separator 4 is provided on the outside of each of these fuel electrodes 2 and oxidizer electrode 3. is provided. These separators 4
On the surface facing each of the electrodes 2 and 3, a stepped portion is formed penetrating the opposing sides in mutually orthogonal directions. And separator 4 on one side. Oxidizer electrode 3. Electrolyte plate 1. A unit cell 5 is constituted by the fuel electrode 2, and the fuel cell is made up of a plurality of layers, for example, five layers of the unit cells 5. Further, the separators 4 at the upper and lower ends of this fuel cell serve as an upper end plate 6 and a lower end plate 7, respectively. Fuel gas is supplied from the left side in the figure as shown by arrow A-A, passes through the fuel electrode 2 and is discharged from the opposite side, and oxidant gas is supplied from the right side in the figure as shown by arrow B-B. This is a so-called cross-flow system in which the oxidizing agent is supplied from the oxidizer electrode 3 and discharged from the opposing surface.

The separator 4 has a separator base material 8 as shown in FIG.
It has a structure in which a corrugated plate 9 is provided in a stepped portion 8A formed in the corrugated plate 9, and the surface of the convex portion of the corrugated plate 9 serves as a current collecting surface 10. This current collecting surface and the wet seal surface 11 are on the same plane.

On the other hand, the surface of the fuel electrode 2 in FIG. 1 that comes into contact with the oxidant gas, that is, the right surface in the figure and the end portion 12 of the surface opposite thereto, is filled with a heat-resistant oxide such as alumina and sintered. , gas-tight.

Similarly, the surface of the oxidizer electrode 3 that comes into contact with the fuel gas, that is, the left side surface in the figure and the end portion 13 of the surface opposite thereto, are also made gas-tight in the same manner.

Next, the operation of this embodiment will be explained. Since the electrodes 2, 3 and the separator 4 have the same area, the electrodes 2.3 also cover the wet sealing surface 11 of the separator 4. Therefore, since the porous electrodes 2 and 3 are interposed between the electrolyte plate 1 and the wet seal surface 11 of the separator 4, no liquid film is formed by the electrolyte in these parts, and the wet seal effect is no longer expressed. Therefore, the reaction gas may leak to the outside of the battery. In addition, since the structure is such that the porous end 13 of the oxidizer electrode 3 contacts the space through which the fuel gas flows, the fuel gas flows into the oxidizer electrode 3 from the pores of the end 13 of the oxidizer electrode 3. There is a possibility that the mixture may cause a gas crossover phenomenon. Even in the space where the oxidant gas is flowing, the end portion 12 of the porous fuel electrode 2 comes into contact with this space, so there is a possibility that a gas crossover phenomenon may occur as well.

In order to solve the above problem, in this embodiment, as described above, the end 12 of the part of the fuel electrode 2 that comes into contact with the oxidant gas and the end 13 of the part of the oxidizer electrode 3 that comes into contact with the fuel gas are sealed in a gas-tight manner. I made it into a sex.

In the above embodiment, the end portions 12 and 13 are filled with a heat-resistant oxide such as alumina and sintered as a means to make them gas-tight, but the heat-resistant oxide is titania, magnesia, or zirconia.

Iron oxide, chromium oxide, etc. may also be used. Alternatively, molten metals such as aluminum, zinc, tin, and lead or alloys thereof may be filled and oxidized and fired to form oxides of these metals.

Another way to make the ends 12 and 13 gas-tight is to make the parts that you want to make gas-tight by using gold or silver.

There are methods of coating with heat-resistant thin films such as stainless steel, nickel, and aluminum, methods of sealing the pores by press-working the parts you want to make gas-tight, electric welding, gas welding,
There are also methods of welding, such as electron beam welding and laser welding. Note that the end of the surface of the fuel electrode 2 that comes into contact with the fuel gas and the end of the surface of the oxidizer electrode 3 that comes into contact with the oxidizer gas do not pose any problem even if the gas diffuses, so gas-tightness is ensured. I haven't.

According to this embodiment, the wet seal surface 1 of the separator 4
Since the structure eliminates the step between 1 and the current collecting surface 10 and has both surfaces on the same plane, it is no longer necessary to select an electrode with a thickness that corresponds to the depth of the step as in the past. It can also be used with a small electrode. Furthermore, by making the end 12 of the fuel pi 2 and the end 13 of the oxidizer electrode 3 gas-tight, oxidant gas may get mixed into the fuel electrode 2 or fuel gas may get mixed into the oxidizer electrode 3. It is possible to prevent a crossover phenomenon from occurring. At the same time, the fuel gas supplied to the fuel electrode 2 may leak to the outside of the cell from a fuel end other than the fuel end at the fuel gas outlet, or the oxidant gas supplied to the oxidizer electrode 3 may It is possible to prevent the oxidant from leaking to the outside of the battery from the oxidant extremes other than the oxidant extremes at the outlet. Furthermore, since it is only necessary to make the ends 12 and 13 of the two opposing sides of the fuel electrode 2 and the oxidizer electrode 3 gas-tight, the work time required to make the ends of each electrode 2 and 3 gas-tight is shortened. be able to.

FIG. 3 shows a second embodiment of the invention. In the figure, the first
The same or equivalent parts as in the first embodiment shown in the drawings are denoted by the same reference numerals, and the explanation thereof will be omitted.

In this embodiment, ten unit cells 5 of internal manifold type molten carbonate fuel cells are stacked.

A fuel gas outlet 14 is provided on one side of the same side of the upper and lower end plates 6, 7, and a fuel gas outlet 15 is provided on one side opposite to this side.

Similarly, an oxidizer gas port 17 is provided on one side of the intermediate end plate 16 in a direction perpendicular to the side on which the fuel gas inlets and outlets 14 and 15 are provided, and an oxidizer gas port 17 (not shown) is provided on one side opposite to this side. A gas outlet is provided. Also, fuel electrode 2
．． Electrolyte plate 1. Oxidizer electrode 3. A plurality of fuel gas manifold holes 18 are formed through each peripheral portion of the separator 4 and communicate with the fuel gas inlet/outlet 14,15. Similarly, a plurality of oxidizing gas manifold holes 19 communicating with the oxidizing gas inlet/outlet are also provided through the opening. Wet seal surfaces 11 are formed on all four peripheral portions of the separator 4, and the fuel gas manifold holes 18 and oxidant gas manifold holes 19 are formed perpendicularly to these surfaces. This separator 4
The wet seal surface 11 and the current collecting surface 10 are on the same plane and have no step, similar to the first embodiment described above.

As shown in FIG. 4, the fuel electrode 2 has an outer end 20 of the fuel gas manifold hole 18 formed on the left and right sides of the figure that are opposite to each other, and an oxidant gas that is formed on the upper and lower sides of the opposite side of the figure. The periphery of the manifold hole 19 and its outer end 21 are made gas-tight by the same means as in the first embodiment.

Similarly, as shown in FIG. 5, the oxidizer electrodes 3 are formed at the outer ends 22 of the oxidant gas manifold holes 19 formed on the upper and lower sides of the opposing figure, and on the left and right sides of the opposing figure. The periphery of the fuel gas manifold hole 18 and its outer end 23
The structure is made gas-tight by the same means as in the first embodiment.

In this embodiment as well, as in the first embodiment, the wet sealing surface 11 and the current collecting surface 10 of the separator 4 are formed on the same plane without any difference in level, so that electrodes of any thickness can be applied. . In addition, since the periphery of the oxidant gas manifold hole 19 and the fuel gas manifold hole 20 that penetrate the fuel electrode 2 and the oxidizer electrode 3, respectively, are gas-tight, the gas crossover is prevented as in the first embodiment. This can prevent the occurrence of this phenomenon and the leakage of gas to the outside of the battery.

〔Effect of the invention〕

As described above, according to the present invention, the peripheral sealing surface and the central current collecting surface of the separator of a fuel cell are formed on the same plane, and the fuel gas and oxidant gas of the fuel electrode and the oxidizer electrode can flow through each other. Since at least the ends other than the ends where the electrodes It is possible to significantly increase the application efficiency of the battery and maintain stable battery performance safely. Furthermore, since the electrodes, electrolyte plates, and separators each have the same area, there is also the effect that the pressure when tightening the entire battery is equalized.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of a fuel cell according to the present invention, FIG. 2 is a partial side view showing the separator of FIG. 1,
FIG. 3 is a partially exploded perspective view showing a second embodiment of the present invention;
4 and 5 are plan views showing the fuel electrode and oxidizer electrode of FIG. 3, respectively. 1... Electrolyte plate, 2... Fuel electrode, 3... Oxidizer electrode,
4... Separator, S... Unit battery, 10... Current collecting surface, 11... Wet seal surface, 12, 13, 20,
21°22.23...end.

Claims (1)

[Claims] 1. In a fuel cell in which a plurality of unit cells each having a fuel electrode and an oxidizer electrode provided on both sides of an electrolyte plate are stacked with a separator in between, seals around both sides of the separator are provided. A surface and a central current collecting surface are formed on the same plane, and the fuel electrode is disposed on one of these surfaces and the oxidizer electrode is disposed on the other, and a portion of the fuel electrode that contacts the oxidant gas. and a fuel cell, further comprising means for providing airtightness to at least the ends of each of the portions of the oxidizer electrode that come into contact with the fuel gas. 2. The fuel cell according to claim 1, wherein the separator, the fuel electrode, and the oxidizer electrode have approximately the same area. 3. The fuel cell according to claim 1 or 2, wherein the means for imparting airtightness is a heat-resistant material filled in the end portion. 4. The fuel cell according to claim 1 or 2, wherein the means for imparting airtightness is molten metal filled in the end portion. 5. The fuel cell according to claim 1 or 2, wherein the means for imparting airtightness is a heat-resistant thin film covering the end portion. 6. The fuel cell according to claim 1 or 2, wherein the means for imparting airtightness is to press the end portion to form a sealed portion. 7. The fuel cell according to claim 1 or 2, wherein the means for imparting airtightness is a welded portion formed at the end.