JPH09129252A - Highly durable solid electrlyte fuel cell and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a solid electrolyte fuel cell having high output density as well as good durability by reducing contact resistance between a solid electrolyte layer and an air electrode for a drop in the internal resistance of the battery. SOLUTION: Regarding a solid electrolyte fuel cell made of a cell having an air electrode and a fuel electrode respectively laid on both sides of a solid electrolyte layer, and a separator stacked on top of each other alternately, a layer (CeO2 )1-x (LnO1.5 )x is sandwiched between the solid electrolyte layer and the air electrode (La1-x Ax )y (Mn1-z Bz )O3 +δ. In this case, A stands for one of Sr, Ca, Ba and Y, or a combination of two or more of the elements, and B stands for one of Cr, Ni, Mg, Co, Zr, Ce, Fe and Al, or a combination of two or more of the elements. Furthermore, the value of (x) is between 0 and 0.5, and the value of (z) is between 0 and 0.5. Also, the value of (y) is between 0.7 and 1.2, and δ stands for excess oxygen. Ln stands for one of Sm, La, Nd, Gd, Ho, Dy, Y and Yb, or a combination of two or more of the elements. Also, the value of X is between 0 and 0.5. The fuel cell is manufactured to satisfy each of the above-mentioned conditions.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a highly durable solid electrolyte fuel cell and a method for manufacturing the same.

[0002]

2. Description of the Related Art Recently, fuel cells which directly convert chemical energy inherent in fuel into electric energy by using, for example, air and hydrogen as oxidizing gas and fuel gas, respectively, have attracted attention from the viewpoint of resource saving and environmental protection. Research and development are progressing because solid electrolyte fuel cells have many advantages such as high power generation efficiency and effective use of waste heat.

FIG. 5 is a diagram showing a schematic structure of a solid oxide fuel cell.

In order to supply a fuel gas such as hydrogen and methane and an oxidant gas such as air and oxygen to the solid electrolyte fuel cell, each gas is supplied to and exhausted from the separator and the solid electrolyte layer 1 of the solid electrolyte fuel cell. Is provided, and each gas is supplied to and discharged from each electrode surface of each unit cell through this hole is called an internal manifold type. The flat plate type solid electrolyte fuel cell comprises a flat plate type solid electrolyte layer 1 made of a zirconia sintered body (YSZ) doped with yttria or the like and having (La, Sr) MnO ₃ air electrodes 3 on both sides.
And a plate-shaped unit cell in which a fuel electrode 2 of Ni / YSZ cermet is arranged, and adjacent unit cells are electrically connected in series, and a fuel gas and an oxidant gas are distributed to each unit cell. The separators are alternately laminated, a metal mesh is interposed between the fuel electrode 2 and the fuel gas flow passage side of the separator, and a sealant or a spacer is interposed between the solid electrolyte layer 1 of the unit cell and the separator. It is stacked in a stack. The fuel gas is brought into contact with the electrode surface of the fuel electrode 2 of each unit cell, and the oxidant gas is brought into contact with the air electrode 3, whereby the interface 4 between the solid electrolyte layer 1 and the fuel electrode 2, the solid electrolyte layer 1 and the air. A reaction occurs at the interface 5 with the electrode 3, an electromotive force is generated between the electrodes due to this reaction, and a current flows through the load 6, and the battery performance is greatly influenced by the structure of the electrode.

For the air electrode 3, a perovskite type conductive oxide is usually used. Further, in order to form such an air electrode 3, there is known a method of applying or printing the above-mentioned conductive oxide powder on the surface of the solid electrolyte layer 1 and performing post-baking.

[0006]

The air electrode 3 has a good electrode activity itself and a small reaction polarization, but has a drawback that the ohmic contact resistance with the solid electrolyte layer 1 is large. Further, the LaMnO ₃ based oxide reacts with zirconia of the solid electrolyte layer 1 to form La ₂ Zr on the interface 5 (see FIG. 5).
High resistance reaction layer such as ₂ O ₇ (conductivity is about 2 × 10 ^-4 Sc
m ⁻¹ ), which increases the internal resistance of the battery over time. In order to suppress this reactivity,
There is also a method to make the A site defective, but with long-term power generation, M
n is diffused and solid-dissolved in zirconia, and eventually A site becomes excessive and a reaction layer is formed.

The present invention has been made in view of the above points. The contact resistance between the solid electrolyte layer 1 and the air electrode 3 is reduced and the internal resistance of the battery is lowered, so that the output density is high and the durability is high. An object of the present invention is to provide a solid electrolyte fuel cell having good properties and a method for producing the same at low cost.

[0008]

DISCLOSURE OF THE INVENTION The present invention relates to a unit cell in which an air electrode and a fuel electrode are arranged on both sides of a solid electrolyte layer, and adjacent unit cells are electrically connected in series and In a solid electrolyte fuel cell in which fuel cells and separators that distribute an oxidant gas are alternately stacked in a cell, the solid electrolyte layer and the air electrode (La _1-x A _x ) _y (Mn
_1-z B _z ) O _{3 +} δ and the layer (CeO ₂ ) _1-X (Ln
O _1.5 ) _X is sandwiched, where A is Sr, Ca, Ba, Y
Any one of them or a combination of two or more thereof, B
Is any one of Cr, Ni, Mg, Co, Zr, Ce, Fe and Al, or a combination of two or more, 0 ≦ x
≦ 0.5, 0 ≦ z ≦ 0.5, 0.7 ≦ y ≦ 1.2, δ is excess oxygen, Ln is Sm, La, Nd, Gd, Ho, D
Any one of y, Y, and Yb, or a combination of two or more thereof, is characterized in that 0 ≦ X ≦ 0.5.

Preferably, (CeO ₂ ) _1-X (Ln
O _1.5 ) _X is (CeO ₂ ) _0.8 (SmO _1.5 ) _0.2 ,
And y <1, A is Sr.

In addition, the present invention provides (C) on the surface of the solid electrolyte layer.
After eO ₂ ) _1-X (LnO _1.5 ) _X was screen-printed and fired, an air electrode (La _1-x A _x ) _y (Mn
_1-z B _z ) O _{3 +} δ is printed and baked, or the solid electrolyte layer and the air electrode (La _1-x A _x ) _y (Cr _1-z B
_z ) O _{3 +} δ and the layer (CeO ₂ ) _1-X (LnO
_1.5 ) Air electrode (La _1-x A _x ) _{y with X} interposed
(Mn _1-z B _z ) O _{3 +} δ and layer (CeO ₂ ) _1-X
It is obtained by simultaneously firing (LnO _1.5 ) _X on the surface of the solid electrolyte layer by a co-sintering technique.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a schematic structure of a solid oxide fuel cell according to the present invention.

The solid electrolyte fuel cell according to the present invention has a YS
(La _1-x A _x ) _{y on} one surface of the solid electrolyte layer 1 made of Z
(Mn _1-z B _z ) O _{3 +} δ air electrode 3 and Ni / YSZ
A separator (not shown) for electrically connecting a unit cell including the cermet fuel electrode 2 and adjacent cell units in series and distributing a fuel gas and an oxidant gas to each unit cell. And are alternately stacked to form a stack.
Here, A is any one or a combination of two or more of Sr, Ca, Ba and Y, and B is Cr, Ni and M.
Any one of g, Co, Zr, Ce, Fe and Al, or a combination of two or more thereof, 0 ≦ x ≦ 0.5, 0 ≦ z
≦ 0.5, 0.7 ≦ y ≦ 1.2, and δ are excess oxygen.

As a typical solid electrolyte layer, a yttria-stabilized zirconia plate formed by tape casting, or a Ni / YSZ substrate is formed by CVD / EVD, ion plating or co-firing. 1
There is a film of yttria-stabilized zirconia below 00 μm.

According to the present invention, the solid electrolyte layer 1 of YSZ and (La _1-x A _x ) _y (Mn _1-z B _z ) O _{3 +} δ are formed.
(CeO ₂ ) _1-X (LnO _1.5 ) between the air electrode 3 and
_A layer 7 made of _X is sandwiched. (CeO ₂ ) _1-X (Ln
O _1.5 ) _X is abbreviated as SDC. Where Ln
Is any one of Sm, La, Nd, Gd, Ho, Dy, Y, and Yb, or a combination of two or more, 0 ≦ X ≦
It is 0.5. The thickness of the SDC layer 7 is about 10 μm. SDC has a conductivity of 0.35 Scm ^-1 ,
It has a conductivity that is 2 to 6 times that of YSZ. The raw material of the SDC layer 7 is a mixture of the powder of this composition and the metal organic compound.

There are various methods for coating the SDC layer 7 on the solid electrolyte layer 1, but in the present invention, the coating is carried out at a low cost by the combination of the screen printing method and the thermal decomposition method of the metal organic compound. In addition, the SDC layer 7 is replaced by the solid electrolyte layer 1
On the SDC layer 7 and then the air electrode 3
However, it is also possible to use a co-firing technology in which the SDC layer 7 and the air electrode 3 are simultaneously fired on the solid electrolyte layer 1. It is a figure showing a result.

FIG. 2 is a diagram showing the results of durability performance tests of the solid electrolyte fuel cell of the present invention and the conventional solid electrolyte fuel cell.

FIG. 2 shows the electrodes of the respective anodes 2 of the solid electrolyte fuel cell of the present invention having an SDC layer (shown by curve A) and the conventional solid electrolyte fuel cell having no SDC layer (shown by curve B). The fuel gas is brought into contact with the surface and the air electrode 3
Is contacted with an oxidizer gas to generate an electromotive force between both electrodes, and the generated voltage (unit: V) when a current of 0.3 amps flows through the load 6 is plotted on the vertical axis, and the operating time (unit: hr) The horizontal axis represents the result of the durability performance test. From FIG. 2, it can be seen that the voltage of the curve B gradually decreases as the operating time elapses, but the voltage of the curve A does not decrease and remains substantially horizontal. In other words, the durability performance of the solid oxide fuel cell of the present invention is clearly improved as compared with the conventional one. This is probably due to the action of the SDC layer.

[0019]

Example: 3YSZ ((ZrO ₂ ) having a thickness of 100 μm
_0.97 (Y ₂ O ₃ ) _0.03 ) 30μ thickness on one side of the electrolyte plate
After forming m NiO / YSZ fuel electrode, SDC was screen-printed on the opposite surface of the electrolyte plate and fired at 1450 ° C. The slurry used for screen printing is (CeO ₂ )
It was a mixture of powder of _0.8 (SmO _1.5 ) _0.2 composition and octylate salt of Ce. After that, (La _0.85 Sr _0.15 )
An air electrode having a composition of _0.98 MnO _{3 +} δ was printed and fired at 1150 ° C. The partial cross-sectional structure of the unit cell thus produced is shown in the following electron micrograph photograph.

FIG. 3 is a graph showing the performance test results of the solid electrolyte fuel cell manufactured by the method of the embodiment of the present invention and the conventional solid electrolyte fuel cell.

FIG. 3 shows the electrodes of the anode 2 of the solid electrolyte fuel cell of the present invention having an SDC layer (shown by curve C) and the conventional solid electrolyte fuel cell having no SDC layer (shown by curve D). The fuel gas is brought into contact with the surface and the air electrode 3
Voltage generated when the oxidant gas is brought into contact with the electrodes to generate an electromotive force between both electrodes and a current flows through the load 6 (unit: V)
The vertical axis represents the current density (unit: A / cm ² ) and the horizontal axis represents the result of the performance test. In both the curves C and D, the generated voltage decreases as the current density increases, but the curve C decreases less. That is, it is shown that the solid electrolyte fuel cell of the present invention having the SDC layer has lower internal resistance and excellent performance as compared with the conventional solid electrolyte fuel cell having no SDC layer.

FIG. 4 is an electron micrograph of a partial cross section of a unit cell used in the solid oxide fuel cell of the present invention.

In the electron micrograph of FIG. 4, the uppermost layer A is the air electrode, the lower layer B is the SDC layer, and the lowermost layer C.
Is a solid electrolyte layer. From this photograph, it can be seen that the SDC layer having a dense and uniform structure is coated between the solid electrolyte layer and the air electrode.

[0024]

As described above, according to the present invention, a single cell in which an air electrode and a fuel electrode are arranged on both sides of a solid electrolyte layer and adjacent cells are electrically connected in series and In a solid electrolyte fuel cell in which fuel cells and separators that distribute an oxidant gas are alternately stacked in each cell, the solid electrolyte layer and the air electrode (La _1-x A _x ) _y
A layer (CeO ₂ ) _1-X between (Mn _1-z B _z ) O _{3 +} δ
(LnO _1.5 ) _X is sandwiched, where A is Sr, Ca, B
Any one of a and Y or a combination of two or more, B is Cr, Ni, Mg, Co, Zr, Ce, F
e, one or a combination of two or more of Al, 0 ≦ x ≦ 0.5, 0 ≦ z ≦ 0.5, 0.7 ≦ y ≦
1.2, δ is excess oxygen, Ln is Sm, La, Nd, G
Since any one or a combination of two or more of d, Ho, Dy, Y, and Yb is set to 0 ≦ X ≦ 0.5, the following excellent effects can be obtained. (1) The internal resistance of the solid electrolyte fuel cell is reduced by the reduction of the contact resistance in the unit cell, and the output density thereof is improved. (2) La ₂ Zr ₂ O is formed at the interface between the solid electrolyte layer and the air electrode.
_Since a high resistance reaction layer such as _{7 is} not formed, the durability performance of the solid electrolyte fuel cell is improved. (3) By combining the screen printing method and the thermal decomposition method of a metal organic compound, SDC coating can be inexpensively performed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of a solid oxide fuel cell according to the present invention.

FIG. 2 is a diagram showing results of durability performance tests of the solid electrolyte fuel cell of the present invention and the conventional solid electrolyte fuel cell.

FIG. 3 is a diagram showing performance test results of a solid oxide fuel cell manufactured by a method of an example of the present invention and a conventional solid oxide fuel cell.

FIG. 4 is an electron micrograph showing a particle structure of a partial cross section of a unit cell used in the solid oxide fuel cell of the present invention.

FIG. 5 is a diagram showing a schematic configuration of a solid oxide fuel cell.

[Explanation of symbols]

 1 Solid Electrolyte Layer 2 Fuel Electrode 3 Air Electrode 4 Interface 5 Interface 6 Load 7 SDC Layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01M 8/12 H01M 8/12

Claims (9)

[Claims] 1. A unit cell in which an air electrode and a fuel electrode are arranged on both sides of a solid electrolyte layer, and adjacent unit cells are electrically connected in series, and a fuel and an oxidant gas are connected to each unit cell. In a solid electrolyte fuel cell in which separators that distribute and are alternately stacked, the solid electrolyte layer and the air electrode (La _1-x A _x ) _y (Mn _1-z B _z ) O _{3 +} δ A highly durable solid electrolyte fuel cell, comprising a layer (CeO ₂ ) _1-X (LnO _1.5 ) _X sandwiched therebetween. Here, A is any one or a combination of two or more of Sr, Ca, Ba and Y, and B is Cr, Ni, Mg, Co and Z.
any one of r, Ce, Fe and Al or a combination of two or more thereof, 0 ≦ x ≦ 0.5, 0 ≦ z ≦ 0.5,
0.7 ≦ y ≦ 1.2, δ is excess oxygen, Ln is Sm, L
Any one or a combination of two or more of a, Nd, Gd, Ho, Dy, Y, and Yb is 0 ≦ X ≦ 0.5. 2. The (CeO ₂ ) _1-X (LnO _1.5 ) _X
Is (CeO ₂ ) _0.8 (SmO _1.5 ) _0.2 . The highly durable solid electrolyte fuel cell according to claim 1, wherein 3. The (La _1-x A _x ) _y (Mn _1-z B
_z ) O _{3 +} δ, y <1, A is Sr, The highly durable solid electrolyte fuel cell according to claim 1. 4. The method for producing a highly durable solid electrolyte fuel cell according to claim 1, wherein (CeO ₂ ) _1-X (LnO _1.5 ) _X is screen-printed and baked on the surface of the solid electrolyte layer. , On which the air electrode (La _1-x A _x ) _y
A method for producing a highly durable solid electrolyte fuel cell, which comprises printing (Mn _1-z B _z ) O _{3 +} δ and firing. 5. The method for producing a highly durable solid electrolyte fuel cell according to claim 1, wherein the solid electrolyte layer and the air electrode (La _1-x A _x ) _y (Mn _1-z B _z ) O _{3 are included. The} air electrode (La _1-x A _x ) _y (Mn _1-z B _z ), so that the layer (CeO ₂ ) _1-x (LnO _1.5 ) _x is interposed between the positive electrode and ₊ δ.
A method for producing a highly durable solid electrolyte fuel cell, which comprises simultaneously sintering O _{3 +} δ and a layer (CeO ₂ ) _1-X (LnO _1.5 ) _X on the surface of the solid electrolyte layer by a co-sintering technique. 6. The highly durable solid electrolyte fuel cell according to claim 1, wherein the solid electrolyte layer is a yttria-stabilized zirconia plate prepared by tape casting. 7. The solid electrolyte layer is a CVD / EVD method,
Ni / Y by ion plating method or co-firing method
The highly durable solid electrolyte fuel cell according to claim 1, which is a film of yttria-stabilized zirconia having a thickness of 100 μm or less formed on an SZ substrate. 8. The (CeO ₂ ) _1-X (LnO _1.5 ) _X
The high-durability solid electrolyte fuel cell according to claim 1, wherein the raw material is a mixture of powder having this composition and a metal organic compound. 9. The metal organic compound is Ce octylate, and the powder is (CeO ₂ ) _0.8 (SmO _1.5 ).
The highly durable solid electrolyte fuel cell according to claim 1, wherein the composition is _0.2 and the mixture of the powder and the metal organic compound is screen-printed on the electrolyte.