JPH07245107A - Solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To enhance electric conductivity and high temperature peel strength of an electrode in a solid electrolyte fuel cell. CONSTITUTION:In a solid electrolyte fuel cell, an air electrode 4 of a ceramics porous film is formed in one of solid electrolyte 2 composed of stabilizing zirconia, and a fuel electrode 10 of a porous film composed of metal and ceramics is formed in the other one of the solid electrolyte 2, and a cell 1 is composed of a three-layer integrated film. The fuel cell is formed by sandwiching an electrode 10 whose inclined parts 12a and 12b by blending metal 11 and ceramics in an inclined condition are formed on both sides sandwiching an intermediate layer composed of the metal 11 between layers 2 and 6 composed of the ceramics. Since the metal 11 is contained, electric conductivity is improved, and since the so-called same kind joining is applied to the ceramic layers 2 and 6, peel strength at high temperature time is enhanced.

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 (SOFC), and more particularly to the structure of a fuel electrode or an air electrode.

[0002]

2. Description of the Related Art Solid electrolyte fuel cells have been researched and developed for practical use in recent years with the progress of ceramics technology. The basic structure is that stabilized zirconia (YSZ), which is a solid solution of yttria in zirconia, which is a ceramic as a solid ionic conductor, is used as an electrolyte. This stabilized zirconia has high oxygen ion permeability at a high temperature of 1000 ° C., and has almost no electronic conductivity.
Since it has a property of not permeating oxygen or hydrogen gas, this property is used for the electrolyte. In this case, although the ion permeability is high compared with other methods, the solid electrolyte is formed in an extremely thin film. In this way, all of the constituent elements are solid, so that the battery structure is simplified, the electrode reaction is very active and the efficiency is improved because it operates at high temperature, and there is an advantage that a catalyst or the like is unnecessary.

On the other hand, since the solid electrolyte operates at a high temperature of 1000 ° C., the air electrode and the fuel electrode inevitably become the high temperature atmosphere, and are affected by high temperature heating, strong oxidation and reduction reaction, thermal expansion and the like. Therefore, the air electrode is required to be chemically stable in a high temperature atmosphere of oxygen, have high electron conductivity, have good oxygen gas permeability, and have good thermal expansion matching with the electrolyte. For example, a perovskite-type lanthanum-based composite oxide is used as a material satisfying the above conditions to form a thin porous film. The fuel electrode is required to have good electron conductivity and thermal expansion matching with the electrolyte, and to have good combustion reaction with hydrogen and removal of reactants.For this reason, for example, a cermet of nickel metal and zirconia is used. Formed into a thin porous film. Also, as the interconnector for connecting a plurality of cells, ceramics that are stable and have good conductivity in a high temperature atmosphere are used.

Therefore, conventionally, the cell of the above-mentioned solid oxide fuel cell is constructed, for example, as shown in FIG. That is,
Reference numeral 1 denotes a cell, which has a solid electrolyte 2 formed on a thin film of stabilized zirconia ceramics, and a fuel electrode 3 of a cermet porous film of nickel and zirconia is formed on one of the solid electrolytes 2. . Solid electrolyte 2
On the other hand, the air electrode 4 of a porous film of a perovskite-type lanthanum-based complex oxide is formed, and is configured as a three-layer integrated film. An external circuit 5 is connected to the air electrode 4 and the fuel electrode 3.
Are connected.

On the other hand, when a mechanically supporting support is used, it has a porous insulating tube or plate-like support 6 using alumina or zirconia as shown in the figure. The fuel electrode 3, the solid electrolyte 2, and the air electrode 4 of the above-described various films are sequentially laminated on the support 6 by a thermal spraying method or the like.

When the fuel cell is operating, the cell 1
A high temperature atmosphere of 00 ° C. is used to continuously supply hydrogen or the like as a fuel to the fuel electrode 3 side and oxygen in the air to the air electrode 4 side. Then, at the air electrode 4, oxygen obtains an electron flowing through the external circuit 5 and is ionized, and this oxygen ion is converted into the solid electrolyte 2
To reach the fuel electrode 3. Then, at the fuel electrode 3, the oxide ions combine with hydrogen to generate electrons and water, and electricity is generated by such an electrochemical reaction.

[0007]

By the way, in the above-mentioned prior art, the fuel electrode 3 comprises nickel, which is a metal in consideration of conductivity, and zirconia, which is in consideration of thermal compatibility with the solid electrolyte 2. Since it is a cermet mixed at a constant ratio, the electric resistance increases.

Here, when the cermet of the fuel electrode 3 is manufactured by the thermal spraying method or the like, the mixing ratio can be graded so that the solid electrolyte side has a large amount of zirconia and the opposite side has a large amount of nickel. . By imparting the gradient function in this way, the components of nickel and zirconia are separated, and the electrical conductivity and the thermal compatibility with the solid electrolyte 2 can be further improved.

However, when the fuel electrode 3 having the tilting function is formed on the support 6, the support 6 made of zirconia or the like is bonded to the nickel-rich portion of the fuel electrode 3. Therefore, in the above-mentioned high-temperature atmosphere, the support 6 and the fuel electrode 3 are thermally mismatched due to the difference in thermal expansion between the support 6 and the fuel electrode 3, causing peeling and the like, and there is a problem that a large adhesive strength cannot be maintained.

In view of the above, the present invention aims to improve the conductivity and the thermal compatibility with the solid electrolyte and the support, whether the fuel electrode is formed alone or on the support. It is intended.

[0011]

In order to achieve this object, the present invention is to form an air electrode of a ceramic porous film on one of the solid electrolytes made of stabilized zirconia, and to make the metal electrode on the other side of the solid electrolyte. In a solid electrolyte fuel cell in which a fuel electrode having a porous film made of ceramics is formed and the cell is made of a three-layer integrated film, the metal and the ceramic are graded and mixed on both sides with an intermediate layer made of metal sandwiched therebetween. The electrode having the inclined portion is formed so as to be sandwiched between the layers made of the ceramic.

[0012]

In the present invention having the above structure, the fuel electrode or the air electrode is formed by being sandwiched between the layers made of ceramic such as the solid electrolyte or the support, and the electric current generated by the electrochemical reaction sandwiching the solid electrolyte is generated. Shed. And this electrode is
Since it has a three-layer structure of the metal and the inclined portion, the conductivity of the electrode becomes good because the specific resistance of the metal is small. Further, the sloped portion has a higher ceramic mixing ratio toward the outside, that is, toward the side in contact with the ceramic layer, so that the thermal compatibility between the electrode and the ceramic layer sandwiching the electrode in a high temperature atmosphere is improved. There is no problem such as peeling.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, the structure of a cell using a solid electrolyte fuel cell support will be described. Reference numeral 1 is a cell, and the fuel electrode 10 is formed by giving a tilt function from the middle to both sides in the film thickness direction. That is, the fuel electrode 10
Is a porous metal 11 such as nickel having good conductivity.
Is arranged, and inclined portions 12a and 12b are formed on both sides of the metal 11 by inclining the metal and ceramics. These inclined portions 12a and 12b are inclined by controlling the mixing ratio of the mixture of metal and ceramics when they are manufactured by the thermal spraying method, etc. On the outside, however, the ceramics are mixed in a large amount, and the ceramics layers, that is, the solid electrolyte 2 and the support 6, are graded so as to be bonded in the same kind, and the three layers can be thermally matched. In this way, the fuel electrode 10 has the metal 11 having good conductivity in the middle and the inclined portions 12 having good thermal compatibility with the solid electrolyte 2 and the support 6 on both outer sides.
The electrodes a and 12b are provided, and both sides in the film thickness direction are inclined so as to obtain thermal matching of the electrodes themselves.

As the cell 1, the fuel electrode 10 having the above three-layer structure is provided on one side of the solid electrolyte 2 formed on the thin film of ceramics of stabilized zirconia, and the inclined portion 12 on one side.
It is formed by joining a. On the other hand of the solid electrolyte 2, a perovskite-type lanthanum-based composite oxide porous air electrode 4 is formed to form a three-layer integrated film. An external circuit 5 is connected to the metals of the air electrode 4 and the fuel electrode 10.

On the other hand, when a mechanically supporting support is used, it has a porous insulating tube or plate-like support 6 using alumina or zirconia as shown in the figure. The fuel electrode 10 having the three-layer structure is formed on the support 6 by joining the other inclined portion 12b in the same manner. The solid electrolyte is formed on the one inclined portion 12a side of the fuel electrode 10 in the same manner as described above. 2 and the air electrode 4 are sequentially laminated.

Next, the operation of this embodiment will be described. First, when the cell 1 is in a high temperature atmosphere of 1000 ° C. during the operation of the fuel cell, the solid electrolyte 2 and the air electrode 4, the metal 11 of the fuel electrode 10 having the three-layer structure and the inclined portions 12a, 1 are formed.
2b is heated to a high temperature. Therefore, in the fuel electrode 10, since the metal 11 arranged in the middle and a part of the inclined portions 12a, 12b arranged on both outer sides are bonded to each other in the same kind, a large adhesion without causing peeling or the like even in the high temperature atmosphere. The strength is secured.

Further, one inclined portion 12a of the fuel electrode 10
However, by jointing the same to the solid electrolyte 2 of the stabilized zirconia ceramics, the fuel electrode 10 and the solid electrolyte 2 are also thermally matched in the above-mentioned high temperature atmosphere, and a large adhesive strength is secured. Further, since the solid electrolyte 2 and the air electrode 4 are ceramics, they are naturally thermally matched. Thus, even if the fuel electrode 10 has a structure having the metal 11 inside, the fuel electrode 10 itself mechanically bonds strongly in a high temperature atmosphere, and the fuel electrode 10, the solid electrolyte 2 and the air electrode 4 also join the ceramics together. It is mechanically tightly bound and retained.

Subsequently, hydrogen or the like of the fuel is continuously supplied to the fuel electrode 10 side, and oxygen in the air is continuously supplied to the air electrode 4 side. Then, in the air electrode 4, oxygen is actively combined with the electrons flowing in the external circuit 5 in the high temperature atmosphere and ionized, and the oxygen ions pass through the solid electrolyte 2 of stabilized zirconia in the high temperature atmosphere due to its characteristics. Then, in the fuel electrode 10, the oxygen ions actively combine with hydrogen to generate electrons and water, and electric power is generated by such an electrochemical reaction. At this time, the entire three-layer fuel electrode 10 undergoes a combustion reaction to generate electrons. However, since the metal 11 having a very low resistance is present inside, the metal 11 can collect current well and have a high loss. It will flow in a very small amount, thus improving power generation efficiency.

When the cell 1 is constructed by using the support 6, the other inclined portion 12b of the fuel electrode 10 with respect to the support 6 made of ceramics such as zirconia has the solid electrolyte 2
The same type of bonding is performed as in the case of. Therefore, in the high temperature atmosphere, the support 6 and the fuel electrode 10 are thermally matched by the ceramics, and a large adhesive strength is secured. Therefore, the support 6, the fuel electrode 10, the solid electrolyte 2, and the air electrode 4 can be mechanically strongly coupled to generate electricity.

The embodiments described above are examples in which the present invention is applied to a so-called cylindrical solid electrolyte fuel cell, but the present invention can also be applied to a flat plate fuel cell. Figure 2
Is a schematic cross-sectional view showing an example thereof, in which a groove 2 having a rectangular cross-section is formed on both front and back surfaces of a metal plate 20 having high heat resistance such as Ni.
1a and 21b are formed vertically and horizontally so as not to intersect with each other. Inclined portions 22a and 22b are formed on both the upper surface side and the lower surface side of the metal plate 20 in the figure. Figure 2
The upper sloped portion 22a in FIG. 2 has a continuous or stepwise characteristic by increasing the metal compounding ratio on the metal plate 20 side and increasing the compounding ratio of stabilized zirconia (YSZ) on the opposite side. It is a layer that changes to
A solid electrolyte layer 23a made of stabilized zirconia is formed on the upper side (a surface side) of a, and the solid electrolyte layer 23 is further formed.
An air electrode layer 24a made of a perovskite-type lanthanum-based composite oxide is formed on the upper side (front side) of a.
That is, on the upper side of the metal plate 20 in FIG.
A cell 25a having 0 and the inclined portion 22a as a fuel electrode is formed.

On the other hand, the sloped portion 22b formed on the lower side of the metal plate 20 in the figure has characteristics because the mixing ratio of the perovskite-type lanthanum-based composite oxide increases as the distance from the metal plate 20 increases. A solid electrolyte layer 2 that is a layer that changes continuously or stepwise in the thickness direction and that is made of stabilized zirconia on the lower side (surface side) of the inclined portion 22b.
3b is formed, and a fuel electrode layer 24b made of Ni or Ni / YSZ cermet is further formed on the lower side (surface side) of the solid electrolyte layer 23b. That is, a cell 25b having the metal plate 20 and the inclined portion 22b as an air electrode is formed on the lower side of the metal plate 20 in FIG.

The solid oxide fuel cell shown in FIG. 2 is formed by connecting two flat plate cells 25a and 25b in series. Air is flown to the upper surface side in FIG.
A fuel gas such as hydrogen gas is flown into the groove 21a on the upper surface side of the. Further, while air is allowed to flow in the groove 21b on the lower surface side of the metal plate 20, fuel gas such as hydrogen gas is allowed to flow to the lower side in FIG. As a result, in each of the upper and lower cells 25a and 25b, an electrochemical redox reaction occurs via the solid electrolyte layers 24a and 24b, and electromotive force is generated respectively. In that case, the upper cell 25a in FIG. 2 has a negative pole on the metal plate 20 side, whereas the lower cell 25b in FIG. Cells 25a, 25
b is connected in series. Therefore, electric power can be taken out from the upper air electrode 24a and the lower fuel electrode 24b.

Even in the structure shown in FIG. 2, since the layer connecting the cells 25a and 25b is composed of the metal plate 20 and the inclined portions 22a and 22b, its conductivity is high. Since the electromotive force of the fuel cell as a whole can be improved, and the so-called same-type connection is made to the upper and lower solid electrolytes 23a and 23b, thermal compatibility at high temperature is good and there is no risk of peeling. .

Here, an example of a preferred embodiment of the present invention will be described. According to the present invention, a ceramic layer is disposed on both sides of a metal layer, and a functionally graded layer is formed between the metal layer and each ceramic layer in which the mixing ratio of the metal and the ceramic is continuously changed. The solid electrolyte fuel cell may be characterized in that the electrode is formed between the ceramic support and the solid electrolyte.

[0025]

As described above, according to the present invention, in the solid electrolyte fuel cell, since the electrode having the metal in the middle is used, the resistance as the electrode becomes very small, and the conductivity is improved. The electrodes are heated in a high temperature atmosphere by forming inclined parts on both sides of the intermediate metal, in which the metal and ceramic are inclined and mixed, and integrally forming ceramics on both outsides of these inclined parts to form a three-layer structure. In addition to being mechanically and mechanically strong, when a cell is formed using a solid electrolyte and a support, the thermal and mechanical strength of the support in a high temperature atmosphere is increased.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a solid oxide fuel cell according to the present invention.

FIG. 2 is a sectional view schematically showing another embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a cell of a conventional solid electrolyte fuel cell.

[Explanation of symbols]

1, 25a, 25b ... Cell, 2, 23a, 23b ... Solid electrolyte, 4, 24a ... Air electrode, 10, 24b ...
Fuel electrode, 11, 20 ... Metal, 12a, 12b, 2
2a, 22b ... Inclined portion.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Satoru Yamaoka 1-5-1 Kiba, Koto-ku, Tokyo Fujikura Ltd. (72) Inventor Mikiyuki Ono 1-1-5 Kiba, Koto-ku, Tokyo Shares Inside Fujikura

Claims (1)

[Claims] 1. An air electrode having a porous film of ceramics is formed on one of solid electrolytes made of stabilized zirconia,
On the other side of the solid electrolyte, a fuel electrode of a porous film made of metal and ceramics is formed, and in a solid electrolyte fuel cell in which the cell is composed of a three-layer integrated film, on both sides sandwiching an intermediate layer made of metal, A solid electrolyte fuel cell, characterized in that an electrode having an inclined portion in which the metal and the ceramic are obliquely mixed is formed and sandwiched between layers of the ceramic.