JP2001196083A - Solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte fuel cell preventing deterioration of electric power generation due to chrome poisoning even if alloy containing chromium is used as the structure member thereof. SOLUTION: A single cell is constructed in such a combination of an air electrode and electrolyte of a solid electrolyte fuel cell that electric power generation is not deteriorated at boundary of the air electrode and the electrolyte by the influence of gas containing chromium. For example, the air electrode is formed with La0.6 Sr0.4 Co0.2 Fe0.8 O3 and the electrolyte is formed with samarium doped ceria base oxide. The boundary surface of the air electrode and the electrolyte, therefore, are not affected by chrome vapor and deterioration of electric power generation caused by chromium does not occur even if vapor containing chromium is generated from the inter connector made of heat resistant alloy containing chromium. Accordingly, the solid electrolyte fuel cell can be constructed with using a structure member of alloy containing chromium.

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 a solid oxide fuel cell which uses a heat-resistant alloy containing chromium as a component and generates chromium-containing gas from the component. The present invention relates to a solid oxide fuel cell that does not cause a problem such as a decrease in power generation capacity caused by a chromium-containing gas.

[0002]

2. Description of the Related Art Fuel cells, such as solid oxide fuel cells,
It is attracting attention as a new energy source from the viewpoint of resource saving and environmental impact.

[0003] A solid oxide fuel cell is a unit cell comprising a solid electrolyte layer, a fuel electrode provided on one surface of the solid electrolyte layer, and an air electrode provided on the opposite surface.
It is composed of an interconnector or the like for electrically connecting these cells, and by supplying a fuel gas to the fuel electrode and an oxidizing gas to the air electrode, a power generation action occurs to generate electric power.

Such a solid oxide fuel cell has a relatively high operating temperature of 700 to 1000 ° C. among fuel cells, so that various fuels can be used, power generation efficiency is high, and all fuel cells are made of solid materials. Therefore, there are advantages such as easy handling, and research and development for practical use are in progress.

The solid electrolyte layer is mainly composed of 8YSZ (YSZ:
It is made of stabilized zirconia doped with yttria), 3YSZ, or the like.

As the air electrode, LaSrMnO ₃ (referred to as LSM) is used as a typical material.
A material in which La in M is replaced by another element and a Co-based material in which Mn is replaced by Co have also been proposed. The fuel electrode is Ni
/ YSZ cermet and the like. For the air electrode or the fuel electrode, for example, first, a material to be a fuel electrode is applied to one surface of the solid electrolyte layer, baked at a high temperature of about 1450 ° C., and then the material for the air electrode is applied to the other surface. It is formed by firing at a low temperature of about ° C. Thus, an interface is formed between the air electrode and the solid electrolyte layer, and between the fuel electrode and the solid electrolyte layer.

[0007] Interconnectors are generally doped La
Although ceramics such as CrO ₃ have been used, the use of heat-resistant alloys containing chromium has been studied due to the fact that ceramics are expensive and the operating temperature has been lowered in recent years.

[0008]

However, when a chromium-containing heat-resistant alloy is used for the interconnector, there are the following disadvantages.

That is, when an interconnector made of a heat-resistant alloy containing chromium is used in a solid oxide fuel cell, when a power generation operation is started in the solid oxide fuel cell,
When the interconnector used is exposed to a high temperature in an oxidizing atmosphere, chromium contained in the interconnector is oxidized, and a chromium oxide layer (C
r ₂ O ₃ ) is formed. When a chromium oxide layer (Cr ₂ O ₃ ) is formed on the surface, the chromium oxide in the chromium oxide layer further reacts with oxygen and water to generate gaseous CrO ₂ (OH) ₂ and radiate it. CrO emitted from the interconnector
₂ (OH) ₂ is brought into contact with the air electrode provided opposite to the interconnector, and is reduced at the interface between the air electrode and the electrolyte layer to precipitate chromium oxide at the interface between the air electrode and the electrolyte layer. .

The chromium oxide deposited at the interface between the air electrode and the electrolyte layer inhibits the reaction between the oxidant gas and the air electrode, and increases the overvoltage between the air electrode and the electrolyte layer within 2 to 300 minutes from the start of power generation. Thus, the power generation performance of the fuel cell has been significantly reduced. As described above, there is a problem when a chromium-containing heat-resistant alloy is used for an interconnector. Such a problem caused by chromium is called chromium poisoning.

As a method for solving such a problem, a surface of an interconnector made of a heat-resistant alloy is coated with a coating agent to prevent chromium-containing gas from evaporating.
Alternatively, there is known a method of providing a trapping layer for trapping the emitted chromium-containing gas inside the fuel cell, but there is a limitation in a method of coating the interconnector,
On the other hand, the cost is high, and the method of providing the trapping layer cannot trap the chromium-containing gas when the trapping capacity of the trapping layer is exceeded, and the effect does not last for a long time.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and even when a chromium-containing heat-resistant alloy is used for a component such as an interconnector, the problem caused by the chromium-containing gas is eliminated by the air electrode and the electrolyte. It is an object of the present invention to provide a solid oxide fuel cell that does not occur between layers.

[0013]

Therefore, in the present invention, in order to solve the above-mentioned problems, a solid oxide fuel cell is constituted as follows. That is, the material of the air electrode and the electrolyte of the unit cell constituting the solid oxide fuel cell was made a combination that was not affected by the chromium-containing gas at the interface between the air electrode and the electrolyte. For example, when the air electrode is La _0.6 Sr
_0.4 Co _0. A ceria-based oxide composed of ₂ Fe _0.8 O ₃ (LSCF) and doped with an samarium-doped electrolyte;
For example, it was composed of Ce _0.8 Sm _0.2 O _1.9 . According to such a configuration of the air electrode and the electrolyte, even under the atmosphere of the chromium-containing gas, at the interface between the air electrode and the electrolyte, the influence of chromium poisoning, that is, the reduction of the power generation capacity due to the precipitation of chromium oxide may be caused. In addition, problems such as performance degradation do not occur in the solid oxide fuel cell.

Not being affected by chromium poisoning is that when power generation is performed using an interconnector formed of a heat-resistant alloy containing chromium, the conduction resistance generated between the air electrode and the electrolyte is large. It can be seen from no increase. The reason is that when chromium-containing gas is generated from the interconnector and comes into contact with the air electrode, chromium oxide is not formed at the interface between the air electrode and the electrolyte layer, or electricity is supplied even if chromium oxide is formed at the interface. It is considered that this does not cause a problem such as an increase in resistance.

Further, the present invention is not limited to the combination of the above examples, and the electrolyte may be at least a ceria-based oxygen ion conductive fluorite type, and the air electrode may be a perovskite type oxide. In addition, the same material as the conventionally used material can be used for the fuel electrode.

Further, the electrolyte may be composed of a plurality of layers, and at least the electrolyte on the side where the air electrode is provided may be made of a component which is not affected by the chromium-containing gas at the interface with the air electrode. In that case, the other side of the electrolyte may be a commonly used electrolyte such as a ZrO ₂ -based or La-based electrolyte.
GaO ₃ can be used.

By constructing the solid oxide fuel cell in this way, no problem due to chromium oxide occurs at the interface between the air electrode and the electrolyte, and various constituent members such as interconnectors are made of a heat-resistant alloy containing chromium. A solid oxide fuel cell that does not cause a decrease in power generation performance even when manufactured can be provided.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a solid oxide fuel cell (flat solid oxide fuel cell) according to the present invention will be described.

The solid oxide fuel cell is constituted by stacking a plurality of fuel cells 20 each including a separator 10 as an interconnector and a unit cell 12.

As shown in FIG. 1, the cell 12 has a fuel electrode 1
4, a solid electrolyte layer 16, and an air electrode 18.
Are formed. As shown in FIG. 1, the solid electrolyte layer 16 is made of a zirconia sintered body (Y
SZ) and a second layer 6 of a samarium-doped ceria-based oxide. The second electrolyte 6 has an appropriate thickness, for example, 0.05 mm. 4 is laminated on the surface.

The air electrode 18 is made of La _0.6 Sr _0.4 Co
_0.2 Fe _0.8 O ₃ , formed on the surface of the second electrolyte 6, and the fuel electrode 14 made of Ni / YSZ cermet is formed on the surface of the first electrolyte 4.

The separator 10 comprises an alloy separator 22 and a ceramic separator 24 as shown in FIG.
At four corners of the separator 10, an oxidizing gas supply hole through which an oxidizing gas such as air flows, an oxidizing gas exhaust hole,
A fuel gas supply hole for supplying fuel gas such as city gas;
Exhaust holes and the like (not shown) for the fuel gas are respectively formed. These holes are continuous when the fuel cells 20 are stacked, and form respective supply passages and exhaust passages.
The formation of each passage is not limited to this.

The alloy separator 22 is made of Inconel 6
It is made of a 00 heat-resistant alloy and contains a predetermined amount of chromium. A groove 15 is formed on the side of the contact surface with the air electrode 18, and the groove 15 forms an oxidant gas passage communicating the oxidant gas supply hole and the oxidant gas exhaust hole.

The ceramic separator 24 is made of ceramic, and has a concave portion 25 for accommodating the unit cell 12 in the center. A groove 17 (fuel passage) communicating with a fuel gas supply hole and a fuel gas exhaust hole is formed at the bottom of the concave portion 25, and has a nickel mesh 32 on the groove 17.

Although the separator 10 is formed from two kinds of materials, an alloy separator 22 and a ceramic separator 24, the present invention is not limited to this.
It may be formed only from a heat-resistant alloy such as nconel600.

Further, the separator 10 may be formed only of a ceramic such as lanthanum chromite doped with strontium. In that case, the fuel cell 20,
Alternatively, when a chromium-containing alloy containing chromium is used in a part of the surrounding components, for example, a gasket of a gas passage, the problem of chromium poisoning caused by such components is sufficiently prevented. be able to.

Next, the operation of the fuel cell 20 will be described.

First, the concave portion 2 of the ceramic separator 24
The fuel cell 20 is constituted by housing the unit cell 12 in 5 and covering the alloy separator 22 from above. Then, the air electrode 18
Is in contact with the alloy separator 22 and
The fuel electrode 14 is electrically connected to a fuel cell (not shown) superimposed on the lower part through a current collecting hole 34 through a nickel mesh 32 provided at the bottom of the recess 25. I do.

When the fuel cells 20 are sequentially stacked to form a solid oxide fuel cell, the temperature is raised to a predetermined temperature, and air is supplied from the oxidizing gas passage and fuel gas such as city gas is supplied from the fuel gas passage. Each gas is brought into contact with the air electrode 18 and the fuel electrode 14 to start power generation. Then, since the alloy separator 22 is made of Inconel 600 as a base material, the alloy cell 22 is exposed to a high-temperature oxidizing atmosphere due to the power generation action of the fuel cell 20, and chromium contained in the alloy is oxidized. A layer is formed.

Further, the formed chromium oxide is converted into oxygen and water.
Reacts with gaseous CrO₂(OH)₂Occurs and diverges
And comes into contact with the air electrode 18. However, the material of the air electrode 18
Is La _0.6Sr_0.4Co_0.2Fe_0.8O₃In
And the second electrolyte 6 in contact with the air electrode 18 is made of Samaria dope.
From the ceria-based oxide
At the interface between the two, chromium generated from the alloy separator 22
Gas (CrO₂(OH)₂)
Absent. For this reason, solid oxide fuel cells have
Power generation is stable for a long time without any decrease
It is.

In the above example, the solid electrolyte layer 16 is
Although the solid electrolyte layer 16 is formed of two layers of the electrolyte 4 and the second electrolyte 6, the solid electrolyte layer 16 may be formed of only predetermined components equivalent to the second electrolyte 6 instead of the two layers. For example, the solid electrolyte layer 16 may be formed of a ceria-based oxide doped with Samaria, and the air electrode 18 and the fuel electrode 14 may be formed on the front and back surfaces. Also in this case, since the interface between the air electrode 18 and the solid electrolyte layer 16 is maintained under predetermined conditions, it is possible to prevent a decrease in power generation capacity due to the chromium-containing gas.

In the above example, the alloy separator 22 is N
Although formed with Inconel 600 of i-base alloy, the present invention is effective for a separator made of other alloys such as an Fe-base alloy, which also generates a chromium-containing gas.

(Experimental Example) Hereinafter, an experimental example of the solid oxide fuel cell will be described. FIG. 4 shows the experimental apparatus, and FIGS. 2 and 3 show the experimental results.

As shown in FIG. 4, the experimental apparatus includes a ceramic container 52 and a test piece 54 housed inside the container 52.
The lid 56 has a supply port 58 for introducing air, and a discharge port 60 for discharging the introduced air.
Are formed. Reference numeral 78 denotes a platinum electrode, and reference numeral 80 denotes a mesh-shaped platinum electrode.

As the test piece 54, a first test piece according to the present invention and a second test piece of a conventional example are prepared.
An alloy made of console 600 and a ceramic made were used.

The first test piece is provided on the electrolyte 16 and on it.
And the electrolyte 16 is the first electrolyte 4 (8Y
SZ pellets (diameter 20mm, thickness 2mm)
) And the second electrolyte 6 (ceria doped with Samaria (S
DC) film (comprising a thickness of 20 μm).
The air electrode 18 is La_0.6Sr_0.4Co
_0.2Fe_0.8O₃(LSCF) powder into hexylene grease
Dispersed during coal, and the solution was screened for second electrolysis.
Coated on the material 6 and baked at 1100 ° C for 4 hours to form
Was. Then, the electrode 62 is wound around the first electrolyte 4.
Was.

Second test piece as conventional example (not shown)
Means that the electrolyte is formed of 8YSZ and the average particle size is 2μ
m of La _0.6 Sr _0.4 MnO _{3 + δ} (LSM) powder is dispersed in hexylene glycol, the solution is applied by a screen method, and calcined at 1150 ° C. to form an air electrode 18. Was wrapped around the electrolyte.

In the experiment, the test piece 54 was placed in the container 52,
With the lid 56 covering the upper portion of the test piece 54, a current is passed in the vertical direction of the test piece 54, the whole is heated to a predetermined temperature (800 ° C.), and air is flowed from the supply port 58 to the discharge port 60,
Under the same conditions as the conditions for use of the fuel cell, a current was applied vertically at a current density of 0.3 A / cm ² , and the polarization (overvoltage) between the air electrode 18 and the electrolyte 16 (electrode 62) was measured.

FIG. 2 shows the results. As shown in FIG. 2, in the first test piece according to the present invention, the overvoltage hardly changed even after 2500 minutes had elapsed, and was almost the same as when the ceramic lid 56 that does not generate a chromium-containing gas was used. It is clear that the value is not affected by the chromium-containing gas. On the other hand, in the experiment using the second test piece, it can be seen that the overvoltage increased to -2000 mV within 100 minutes and the chromium was poisoned from the lid 56.

FIG. 3 shows the results of another experimental example.

The table of FIG. 3 shows the values of the overvoltages when the materials of the air electrode and the second electrolyte were changed and the combination was measured in the same manner as in the above experiment. From the results, when the chromium-containing heat-resistant alloy is used for the separator, the combination that is least susceptible to chromium poisoning uses La _0.6 Sr _0.4 Co _0.2 Fe _0.8 O ₃ for the air electrode. It can be seen that the combination uses Ce _0.8 Sm _0.2 O _1.9 as the second electrolyte.

In the above example, a flat solid electrolyte fuel cell has been described as an example. However, the present invention is not limited to a flat solid fuel cell. It may be a fuel cell.

Further, the chromium-containing alloy may be used not only for an interconnector such as a separator, but also for other components such as a support member for supporting a solid oxide fuel cell, a container, a pipe, and the like. It does not specify the point of use.

[0044]

According to the solid oxide fuel cell of the present invention, the air electrode and the electrolyte of the unit cell are made of a combination of materials that does not cause a decrease in the power generation capacity due to the chromium-containing gas at the interface between the air electrode and the electrolyte. Accordingly, a chromium-containing alloy can be used as a constituent member of the solid oxide fuel cell such as a separator, and a solid oxide fuel cell that is inexpensive and performs stable power generation operation for a long time can be provided.

Further, since the electrolyte has at least two layers and the electrolyte on the air electrode side is a component that does not cause chromium poisoning with the air electrode, the predetermined electrolyte is used only at a portion required to form an interface with the air electrode. Since the base portion of the electrolyte other than the above can be composed of a general electrolyte that is easy to handle, efficiency, price, performance, etc. can be set well.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a unit cell according to the present invention.

FIG. 2 is a graph showing experimental results.

FIG. 3 is a diagram showing a table of experimental results.

FIG. 4 is a view showing an experimental apparatus.

FIG. 5 is a sectional view showing a fuel cell.

[Explanation of symbols]

 Reference Signs List 4 first electrolyte 6 second electrolyte 10 separator (interconnector) 12 unit cell 14 fuel electrode 15, 17 groove 16 solid electrolyte 18 air electrode 20 fuel cell 22 alloy separator 24 ceramic separator 25 concave part 32 nickel mesh 34 current collecting hole 54 test Piece 56 lid 58 supply port 60 discharge port 62 electrode 78 platinum electrode 80 mesh-shaped platinum electrode

Claims (8)

[Claims] 1. A solid electrolyte fuel cell, wherein the air electrode and the electrolyte of the solid oxide fuel cell are made of a combination of materials that are not susceptible to Cr poisoning at the interface between the air electrode and the electrolyte. 2. The solid oxide fuel cell according to claim 1, wherein the air electrode is composed mainly of a perovskite oxide. 3. The air electrode according to claim 1, wherein the air electrode is La _1-X Sr _X Fe.
_{1-Y Co Y O 3 (} X = 0.05~0.6, Y = 0~
2. The solid oxide fuel cell according to claim 1, wherein 1) is constituted as a main component. 4. The solid electrolyte according to claim 1, wherein the electrolyte is composed mainly of an oxygen ion conductive fluorite or perovskite electrolyte. Type fuel cell. 5. The solid electrolyte type according to claim 1, wherein the electrolyte is mainly composed of ceria (CeO ₂ ) -based fluorite type oxide. Fuel cell. 6. The electrolyte according to claim 1, wherein the electrolyte is at least two layers of a first electrolyte and a second electrolyte, and the second electrolyte is
5. The electrolyte according to any one of 5 to 5, wherein the air electrode is the second electrolyte.
A solid oxide fuel cell formed on an electrolyte. 7. The air electrode according to claim 1, wherein the air electrode is La _1-X Sr _X Fe.
_{1-Y Co Y O 3 (} X = 0.05~0.6, Y = 0~
7. The solid oxide fuel cell according to claim 6, wherein 1) is constituted as a main component. 8. The solid oxide fuel cell according to claim 1, wherein a chromium-containing alloy is used for at least a part of the constituent members of the solid oxide fuel cell.