JPH0689727A - Solid oxide fuel cell - Google Patents

Abstract

(57) [Summary] [Object] The present invention achieves uniform current density in the surface and suppression of temperature distribution in the cell surface by achieving uniform power generation reaction in a single cell. It provides a highly reliable SOFC without cell damage due to reaction. [Configuration] In a solid oxide fuel cell (SOFC) including a solid electrolyte, an air electrode, and a fuel electrode, at least one of the electrodes has a smaller electrode area on the gas inlet side than on the gas outlet side. And That is, in the present invention, since the electrode area near the gas inlet is reduced, the amount of power generation in this portion is reduced, and as a result, the current density can be reduced. At this time, as a result of the reaction amount being suppressed small near the gas inlet, the difference in gas concentration between the gas inlet side and the outlet side becomes small, and the power generation reaction can be made uniform to the vicinity of the gas outlet. Therefore, the current density can be made uniform in the entire cell surface without changing the total amount of power generation in the surface. As a result,
Uniformization of the temperature within the cell surface is achieved, and the damage of the cell due to thermal stress can be effectively prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell, and more particularly to improvement of a single cell structure.

[0002]

As is well known, a fuel cell is a device for directly converting chemical reaction energy into electric energy,
One of them is a solid oxide fuel cell (hereinafter referred to as SO
FC) is an all-solidified fuel cell that uses ceramic materials for all constituent materials.

As a material used for the above SOFC, specifically, stabilized zirconia (YSZ) in which yttria or the like is added to the electrolyte to stabilize the crystal structure, and nickel zirconia cermet (Ni-) is used for the fuel electrode. YSZ), and lanthanum manganite is used for the air electrode.

A unit cell made of such a material is
By heating to 00 ° C and supplying the respective reaction gases to both electrodes, the power generation reaction proceeds and power can be taken out.

FIG. 5 shows an example of the structure of a single cell of SOFC.
In the figure, 1 is a solid electrolyte, 2 is a fuel electrode, and 3 is an air electrode.

In this figure, all three layers constituting the SOFC have a flat plate shape, which is called a flat plate type.

The output voltage obtained from this SOFC is 0.5 to 1 V per cell (depending on the generated current).
It is necessary to stack such single cells in order to obtain a predetermined voltage.

An example of the structure of a stack in which single cells are laminated is shown in FIG.
It was shown to. In the figure, 5 is an interconnector.

In such a stack, the two gases are introduced into the supply port between the cells, and the method of supplying the gas is such that the flow of each gas is orthogonal or parallel.
There is one.

[0010]

In such a flat plate SOFC, however, the gas concentration is higher near the inlet side of each gas regardless of which of the two gas supply methods is used. It has been pointed out that the power generation reaction proceeds preferentially from this part and the current density becomes high ("Electrochemistry" Hirano Vol 158, p842 (1990)). The power generation reaction in SOFC is a reaction that produces water from hydrogen and oxygen, and this reaction is accompanied by heat generation.

Therefore, there is a problem in that the temperature of the portion where the power generation reaction proceeds rises, resulting in a large temperature distribution in the plane of the cell.

Further, since ceramics have a low thermal conductivity, when heated, only the temperature of that part rises, and a difference in the coefficient of thermal expansion with other parts is likely to appear. If the strength is exceeded, the material will be destroyed.

There are three types of materials constituting a single cell of SOFC. Different materials have different thermal expansion characteristics.
When manufacturing a single cell, the material is designed in consideration of minimizing the difference in coefficient of thermal expansion.

However, the difference in expansion coefficient is not 0 at all, but a difference is larger or smaller (for example, YSZ containing 8 mol% of yttrium oxide; 10 × 10 ⁻⁶ ), Ni.
-YSZ; 12 x ^10-6 , lanthanum manganite; 11-12
× 10 ^-6 ).

As a result, when a temperature difference occurs in the cell and a high temperature portion is partially generated, the internal stress based on the coefficient of thermal expansion is expanded at the interface of the ceramic material in this portion, which increases the mechanical strength of the ceramic plate. When it exceeds, it leads to the destruction of the cell.

Therefore, it was necessary to suppress the non-uniformity of the power generation reaction.

However, in the conventional SOFC, such a design has not been made since the emphasis is placed on how to manufacture a cell having a high output density.

In forming a conventional flat plate type cell, an electrode film is formed by a method of laminating and co-sintering a doctor blade sheet, or by applying slurry and sintering to a sheet-like electrolyte plate prepared by a doctor blade method or the like. Has been done.

All of these methods are methods whose main purpose is to form an electrode having a uniform thickness on a plane.

Heretofore, attempts have been made to reduce the thickness of a single cell mainly for the purpose of producing a single cell and improving its performance, but almost no study has been conducted on the suppression of power generation reaction when a stack is formed. .

When a thermal spraying method is adopted as a method for forming electrodes, it has been considered to control the spraying conditions to have a distribution of porosity in the electrodes in order to homogenize the reaction. Kaihei 3-222261), in the thermal spray method,
It was quite difficult in practice to change the porosity partially by changing the thermal spraying conditions.

The porosity can be changed by changing the degree of sintering of the ceramic material. Specifically, when the same material is used, the particle size of the material can be changed even if the sintering temperature is the same. Can handle.

However, it is impossible to take a measure to partially change the degree of sintering by a method in which uniformly prepared sheets are laminated or a method in which a uniform slurry is applied and sintered.

Therefore, the present invention has been made in view of the above points, and an object thereof is SOFC.
In order to make the power generation reaction in the unit cell uniform, the area of the electrode reaction area is made small near the gas inlet, which makes the current density in the plane uniform. An object of the present invention is to provide a highly reliable SOFC that achieves suppression of the temperature distribution in the cell plane and does not damage the cell due to thermal reaction.

[0025]

That is, in order to solve the above-mentioned problems, the present invention provides a solid oxide fuel cell comprising a solid electrolyte, an air electrode, and a fuel electrode, in which at least one electrode has a gas inlet side It is characterized in that the electrode area is reduced as compared with the gas outlet side.

[0026]

As described above, the present invention is characterized in that in the solid oxide fuel cell, the effective electrode area on the gas inlet side is reduced in at least one of the electrodes.
That is, in the present invention, since the electrode area in the vicinity of the gas inlet is reduced, the power generation amount in this portion is reduced,
As a result, the current density can be reduced.

At this time, as a result of the reaction amount being kept small near the gas inlet, the difference in gas concentration between the gas inlet side and the outlet side becomes small, and the power generation reaction can be made uniform up to the vicinity of the gas outlet.

Therefore, the current density can be made uniform in the entire cell surface without changing the total amount of power generation in the surface. As a result, temperature uniformity in the cell plane is achieved,
Cell damage due to thermal stress can be effectively prevented.

The conventional SOFC does not take such a measure, and since the electrodes are formed uniformly on the entire surface, the power generation reaction preferentially proceeds in the vicinity of the gas introduction port, which causes a large in-cell surface. There is a serious drawback in that a temperature distribution is generated and a cell is broken due to a difference in thermal expansion.

[0030]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a single cell showing a first embodiment of the present invention. In the figure, 1 is a solid electrolyte, 2 is a fuel electrode, and 3 is an air electrode formed on the surface side of 1.

The present embodiment is a self-supporting thin unit cell in which a thin plate of the solid electrolyte 1 is used as a support for the cell.

In the present embodiment, the area of the air electrode 3 near the gas inlet side is reduced. This cell is manufactured by (1) a method in which the solid electrolyte sheet is sintered at 1300 to 1400 ° C, and then electrode slurry is applied to each of these surfaces and sintered at 1200 to 1300 ° C, and (2) a solid electrolyte sheet. The fuel electrode sheets were laminated under heating and pressure and co-sintered at 1300 to 1400 ° C, and the air electrode slurry was applied and sintered at 1200 to 1300 ° C.

Therefore, when manufacturing a cell, in any method, when applying the slurry of the air electrode, the coating area of the electrode in the portion corresponding to the inlet side of air (or oxidant gas) is compared with the gas outlet side. Are decreasing.

Therefore, in the manufacturing process of the single cell, the area of the electrode portion can be changed without changing the manufacturing process itself.

In the cell manufacturing method of this embodiment, it is possible to change the area of the electrode portion only for the fuel electrode or for both the fuel electrode and the air electrode.

In this case, in the method (1), it is only necessary to control the application area of the fuel electrode, and in the method (2), the size and shape of the fuel electrode sheets to be stacked and the stacking method should be devised.

FIG. 2 is a plan view of a single cell showing the second embodiment.

In this embodiment, the fuel electrode made of nickel zirconia cermet is used as the support 4 of the cell, the electrolyte membrane 1 and the air electrode 3 are sequentially formed on the upper side, and the fuel electrode (not shown) is formed on the lower side. It is a supporting film type cell having a formed structure.

For the support 4, NiO was mixed with YSZ in a ratio of 30 to 70 wt%, and binder-treated Ni-YSZ powder was press-molded at a pressure of 1 t / cm ² , which was then pressed at 1250-
The electrolyte membrane 1 was produced by sintering at 1300 ° C. and plasma spraying.

Finally, the air electrode slurry was applied and sintered under the same conditions as in Example 1.

Also in this embodiment, when the air electrode slurry is applied, the electrode area involved in the reaction is reduced by adjusting the application area of the portion located on the air (or oxidant gas) inlet side. There is.

In each of the examples, the air electrode was produced by slurry coating and sintering, and the coating area was changed depending on the mold of the screen mask at the time of slurry coating.

FIGS. 3 (a), (b) and (c) show examples of different patterns of the air electrode part.

By making the coating portion sparse near the gas inlet side, the average current density per unit area in this portion is reduced. As the shape of the electrode portion near the gas inlet, it is significant to make it sparse as in the present invention. This is because if the coating portion is simply shifted to the downstream side, the portion having a high current density will move to the downstream side as it is, and the effect of the present invention cannot be expected.

FIG. 4 shows a comparison of the generated current density in the cell surface between the conventional example and this example.

In the present invention, the electrodes at the gas inlet are not connected to each other in the plane, but in the single cell of the present invention, the interconnector is placed in contact with the entire surface of the cell and laminated, so that The current flowed perpendicularly to the cell, and even if the electrodes were not in contact with each other, there was no problem in actual power generation.

As described above, since the electrode area in the vicinity of the gas inlet is reduced in both the first and second embodiments, the power generation amount in this portion is reduced, and as a result, the current density can be reduced. .

At this time, as a result of the reaction amount being suppressed small near the gas inlet, the difference in gas concentration between the gas inlet side and the outlet side becomes small, and the power generation reaction can be made uniform up to the gas outlet.

Therefore, the current density can be made uniform in the entire cell surface without changing the total amount of power generation in the surface. As a result, temperature uniformity in the cell plane is achieved,
Cell damage due to thermal stress can be effectively prevented.

In the embodiment of the present invention, regarding the air electrode,
Although an example of the slurry coating method has been shown, the flat plate type SOFC can also be prepared by a method of laminating three types of sheets and co-sintering.

In this case, the electrode sheet whose area is desired to be reduced can be cut into small pieces, laminated and sintered.

It is also effective when the electrodes are formed by the thermal spraying method. In this case, it can be easily carried out by controlling the scanning position and the number of times of the thermal spraying gun.

In the above embodiment, the case where the electrode area on the gas inlet side of the air electrode 3 is reduced as compared with the gas outlet side is shown, but this should be applied to the fuel electrode 2 side with the same purpose. You can

[0055]

As described above, according to the present invention, only the reaction area of the electrode on the gas inlet side is reduced without taking the difficult process of changing the porosity of the electrode depending on the position of the electrode plate. The same effect of equalizing the current density can be obtained by changing the porosity with.

Further, in the present invention, if the method of applying slurry and sintering is used for forming the electrode, it is sufficient to make the mask pattern of the screen printing machine into the pattern of the electrode in advance when applying, and the ordinary cell is used. There is no need to change the manufacturing process.

Further, the method of laminating the sheet forming bodies and co-sintering can be dealt with only by changing the size of the sheets.

As described above, according to the present invention, a highly reliable SOFC cell can be realized by simply changing the mask pattern by the method based on the conventional cell manufacturing method, which is very industrially significant. The effect can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention,

FIG. 2 is a diagram showing a second embodiment of the present invention,

FIG. 3 is a view showing an example of an electrode pattern embodying the present invention,

FIG. 4 is a diagram showing a current density distribution of a cell embodying the present invention in comparison with a conventional one;

FIG. 5 is a view showing a structural example of a conventional flat plate SOFC single cell;

FIG. 6 is a diagram showing an example of a stack structure of a conventional flat plate SOFC.

[Explanation of symbols]

 1 ... Solid electrolyte, 2 ... Fuel electrode, 3 ... Air electrode, 4 ... Support body.

Claims (1)

[Claims] 1. A solid oxide fuel cell comprising a solid electrolyte, an air electrode, and a fuel electrode, characterized in that at least one of the electrodes has a smaller electrode area on the gas inlet side than on the gas outlet side. Solid oxide fuel cell.