JP2001068130A - Solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolyte fuel cell in which power generating characteristics can be enhanced, adhesion strength of a fuel electrode can be improved with respect to a solid electrolyte and excellent power generation can be maintained for a long period. SOLUTION: In a solid electrolyte fuel cell in which an air electrode 32 is formed at one surface of a ceramics solid electrolyte 31 and a fuel electrode 33 made of mainly metal is formed at the other surface, metal particles 43 are made to exist on a two-plane grain boundary of ceramic grains 41 at the obverse on the fuel electrode 33 side in the solid electrolyte 31, so that the metal particles 43 are connected to the fuel electrode 33 via a boundary metal 45 on the two-plane boundary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid electrolyte fuel cell in which an air electrode is formed on one surface of a solid electrolyte made of ceramics, and a fuel electrode mainly composed of metal is formed on the other surface.

[0002]

2. Description of the Related Art Conventionally, since a solid oxide fuel cell has a high operating temperature of 900 to 1050 ° C., it has a high power generation efficiency and is expected as a third generation power generation system.

[0003] In general, a cylindrical type and a flat type are known as solid oxide fuel cells. Flat fuel cells are
Although it has the feature of high power density per unit volume of power generation, there are problems such as incomplete gas sealing and non-uniformity of temperature distribution in the cell for practical use. On the other hand,
Cylindrical fuel cells are characterized by low mechanical strength of the cells, while maintaining a uniform temperature within the cells, although the output density is low. Both types of solid oxide fuel cells are being actively researched and developed utilizing their respective characteristics.

As shown in FIG. 4, a cylindrical solid oxide fuel cell has a LaMnO having an open porosity of about 30 to 40%.
_A porous air electrode support tube 2 made of a ternary material is formed, and a solid electrolyte 3 made of Y ₂ O ₃ stabilized ZrO ₂ is formed on the surface thereof.
, And a porous Ni-zirconia fuel electrode 4 is provided on the surface.

In a fuel cell module, each cell is La
It is connected via a CrO ₃ -based current collector (interconnector) 5. Power is generated by air (oxygen) inside the cathode support tube 2.
6 and a fuel (hydrogen) 7 flowing outside,
It is performed at a temperature of 0 ° C.

As a method of manufacturing the above-described fuel cell, for example, an insulating powder is formed into a cylindrical shape by an extrusion method or the like, and then fired to form a cylindrical support tube. A slurry of an air electrode, a solid electrolyte, a fuel electrode, and a current collector is applied to the surface and sequentially fired and laminated, or the surface of a cylindrical support tube is subjected to electrochemical deposition (EVD) or plasma spraying. An air electrode, a solid electrolyte, a fuel electrode, and a current collector are sequentially formed by a method or the like.

In recent years, a so-called co-sintering method has been proposed in which at least two of the constituent materials are simultaneously fired in order to simplify the manufacturing process of the cell and reduce the manufacturing cost. In this co-sintering method, for example, a solid electrolyte molded body and a current collector molded body are wound in a roll shape around a molded body of a cylindrical air electrode support tube, and simultaneously fired, and then the fuel electrode is formed on the solid electrolyte surface. It is a method of forming. This co-sintering method is a very simple process with a small number of manufacturing steps, and is advantageous for improving the yield and cost reduction in manufacturing cells.

In order to form a fuel electrode on the surface of a solid electrolyte, generally, a mixture of Ni powder and ZrO ₂ (containing Y ₂ O ₃ ) powder or NiO powder and ZrO ₂ (containing Y ₂ O ₃ ) powder is used. A paste containing the powder was applied to the surface of the solid electrolyte by a screen printing method, or immersed in a solution containing the mixed powder, and then dried to form a fuel electrode. The latter NiO / ZrO ₂ (Y ₂
In the case of the mixed powder (containing O ₃ ), it was formed by heat treatment in a reducing atmosphere at 1000 to 1400 ° C. for 1 to 5 hours.

[0009]

However, the fuel electrode manufactured by these methods has a low initial power generation performance, and in a long period of power generation, Ni (NiO is reduced during the power generation to become Ni) aggregates and the like. Due to the grain growth, the fuel electrode is separated from the solid electrolyte, and the resistance at the interface increases, which causes a problem that the power generation performance is reduced when a heat cycle is applied.

The present invention can improve the initial power generation performance and the adhesion strength of the fuel electrode to the solid electrolyte, thereby maintaining a good power generation performance for a long period of time. The purpose is to provide.

[0011]

According to the present invention, there is provided a solid electrolyte fuel cell comprising a solid electrolyte made of ceramics having an air electrode formed on one surface and a fuel electrode mainly composed of a metal formed on the other surface. In the fuel cell of the type, the metal particles are present at the grain boundary between the two surfaces of the ceramic particles in the fuel electrode side surface layer portion of the solid electrolyte, and the metal particles are passed through the grain boundary metal at the grain boundary between the two surfaces. It is connected to.

By adopting such a configuration, the contact area between the solid electrolyte and the fuel electrode is increased by the amount of the metal particles and grain boundary metal penetrating into the solid electrolyte, and the number of electrochemical reaction sites is increased. Therefore, the polarization resistance generated at the fuel electrode / solid electrolyte interface is reduced, so that the power generation performance can be improved.

Further, metal particles are present at the grain boundary between the two surfaces of the ceramic particles of the solid electrolyte, and the metal particles are connected to the fuel electrode via the grain boundary metal at the grain boundary between the two surfaces. By the anchor effect of the metal particles connected to the, it is possible to improve the adhesion strength of the fuel electrode to the solid electrolyte,
In a thermal cycle such as starting and stopping, the separation of the fuel electrode from the solid electrolyte can be effectively prevented, and good power generation performance can be maintained without deterioration for a long time.

A plurality of metal particles are present at the grain boundary between the two surfaces of the ceramic particles, and are desirably connected to each other by a grain boundary metal at the grain boundary between the two surfaces. By adopting such a configuration, the metal particles are electrically connected,
More electrical reactions occur between the metal particles and the solid electrolyte, and the power generation characteristics can be further improved, and the adhesion strength of the fuel electrode to the solid electrolyte can be further improved.

Further, the metal particles are desirably present at a depth of 1 to 50 μm from the fuel electrode side surface of the solid electrolyte. By adopting such a configuration, the conductivity of oxygen ions in the solid electrolyte is not hindered, and the contact area between the fuel electrode and the solid electrolyte interface is increased, so that the overall polarization resistance at the interface is reduced. The size can be reduced, and the power generation performance can be further improved.

The average particle size of the metal particles is 10 to 100.
nm is desirable. By employing such a configuration, the metal particles and the grain boundary metal function as a fuel electrode, so that the power generation characteristics can be improved, and the durability and the heat cycle characteristics can be improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a solid oxide fuel cell according to the present invention comprises a cylindrical solid electrolyte 31 having an air electrode 32 formed on the inner surface and a fuel electrode 33 formed on the outer surface. The current collector 35 electrically connected to the air electrode 32 is formed on the outer surface of the cell body 34.

That is, the notch 36 is formed in a part of the solid electrolyte 31.
Is formed, and a part of the air electrode 32 formed on the inner surface of the solid electrolyte 31 is exposed, and both ends of the solid electrolyte 31 near the exposed surface 37 and the notch 36 are covered with the current collector 35. The current collector 35 is joined to the surfaces of both ends of the solid electrolyte 31 and the surface of the air electrode 32 exposed from the notch 36 of the solid electrolyte 31.

Current collector 35 electrically connected to air electrode 32
Is formed on the outer surface of the cell body 34 so as to cover the continuous same surface 39 having almost no level difference, and is not electrically connected to the fuel electrode 33. When connecting the cells, the current collector 35 is electrically connected to the fuel electrode of another cell via Ni felt, thereby forming a fuel cell module. The continuous same surface 39 is formed by polishing between both ends of the solid electrolyte molded body until both end portions of the solid electrolyte molded body and a part of the air electrode molded body become substantially the same continuous surface.

In the solid oxide fuel cell unit according to the present invention, as shown in FIGS.
Of the ceramic particles 41 in the surface layer of the fuel electrode 33 side
A plurality of metal particles 43 are present at the intergranular grain boundaries, and these metal particles 43 are interconnected by the grain boundary metal 45 of the two intergranular boundaries, are formed in a rosary shape, and one end thereof is a fuel. Connected to pole 33. Although the fuel electrode 33 has the metal particles 43, it is omitted in FIGS. 2 and 3, and the ceramic particles 41 are entirely present in the solid electrolyte 31, but in FIG. Described.

As shown in FIG. 3, the metal particles 43 have a depth d of 1 to 50 μm from the side of the fuel electrode 33 of the solid electrolyte 31.
It is desirable that the metal particles 43 have an average particle diameter of 10 to 100 nm.

Here, the distribution range of the metal particles 43 in the grain boundary between the two surfaces is set to a depth d of 1 to 50 μm from the side of the fuel electrode 33 of the solid electrolyte 31 (fuel electrode / solid electrolyte interface) to the solid electrolyte side. This is because in this range, the polarization resistance at the interface between the fuel electrode and the solid electrolyte is small, so that the power generation performance can be improved and the adhesion strength of the fuel electrode to the solid electrolyte can be increased.

On the other hand, if the depth d is less than 1 μm, the contact area between the fuel electrode and the solid electrolyte interface is small, the overall polarization resistance at the interface is large, the power generation performance is liable to decrease, and the fuel for the solid electrolyte This is because the adhesion strength of the electrode is easily reduced, and the durability and the heat cycle characteristics are easily deteriorated.

Further, if the depth d is larger than 50 μm, the conductivity of oxygen ions in the solid electrolyte is hindered, and the power generation performance tends to be reduced. In particular, from the viewpoint of improving power generation performance, durability, and heat cycle characteristics, the depth d is 5 to 30.
The range of μm is desirable.

The average particle size of the metal particles 43 is 10 to 100 n.
m is within this range, the metal particles 43 and the grain boundary metal 4
This is because 5 functions as a fuel electrode, and can improve power generation characteristics, as well as durability and heat cycle characteristics.

On the other hand, the average particle diameter of the metal particles 43 is 10 nm.
If the diameter is smaller, there is no electron path and it is difficult to function as a fuel electrode. If the diameter is larger than 100 nm, a crack is generated in the solid electrolyte due to a difference in thermal expansion, and durability and heat cycle characteristics are liable to deteriorate. In particular, from the viewpoint of satisfying all the power generation performance, durability, and heat cycle characteristics, the metal particles 4
The average particle size of No. 3 is preferably in the range of 10 to 50 nm.

The fuel electrode comprises a metal component and an inorganic component. The inorganic component may be ZrO ₂ or CeO ₂ alone, (Zr, Ce) O ₂ solid solution, or Y, Yb, Sc, Er, Nd, Gd, Dy,
ZrO ₂ , Ce containing 3 to 30 mol% of Sm and Pr
O ₂ can be used.

As the metal component, Ni, Co, Ti, F
e and Ru can be used, but depending on the fuel gas used, Ni metal and ZrO
₂ (containing Y ₂ O ₃ ) or CeO ₂ (containing Y ₂ O ₃ )
Is preferable from the viewpoints of versatility and economy for fuel gas.

The proportion of the inorganic component to the metal component is preferably 10 to 50% by weight of the inorganic component and 50 to 90% by weight of the metal component. When the content of the inorganic component is less than 10% by weight, that is, when the metal component is more than 90% by weight,
The effect of suppressing the grain growth of Ni is reduced. When the content of the inorganic component exceeds 50% by weight, that is, when the metal component is 5% by weight.
If the amount is less than 0% by weight, the electric conductivity of the fuel electrode is impaired.

The solid electrolyte 31 is, for example, 3 to 20 mol%
Of partially stabilized or stabilized ZrO ₂ containing Y ₂ O ₃ or Yb ₂ O _{3, of} which ₃ to ₂
Partially stabilized or stabilized ZrO ₂ containing 0 mol% of Y ₂ O ₃ is desirable.

The air electrode 32 is mainly composed of, for example, a perovskite-type composite oxide containing La and Mn, and contains 8 to 10% by weight of Ca in terms of oxide and at least one of rare earth elements. 10 to 20 in terms of oxide
% By weight. As rare earth elements, Y,
There are Nd, Dy, Er, Yb, etc., of which Y is desirable.

The current collector 35 is made of, for example, L as a metal element.
The main crystal is a perovskite-type composite oxide containing a, Cr and Mg, and may contain a rare earth element or an alkaline earth metal element. Current collector 3
5 further contains a MgO crystal.
5, the solid electrolyte 31 and the air electrode 3 are increased.
This is desirable because it can match that of 2.

Solid electrolyte 31, air electrode 32, fuel electrode 3
3. The current collector 35 is not limited to the above example, and a known material may be used.

In the solid oxide fuel cell according to the present invention,
For example, Y ₂ O ₃ or CaO having an open porosity of about 40%
Stabilized ZrO ₂ is used as a support tube, and La is used as a porous air electrode by a slurry dipping method.
Applying a LaMnO ₂ -based material substituted with 0 to 20 atomic%,
Its vapor phase synthesis on the surface (EVD) and or a solid electrolyte by thermal spraying Y ₂ O ₃ stabilized ZrO ₂ film or Y ₂ O _3, Yb ₂ O ₃ or CeO ₂ containing CaO
And a porous fuel electrode may be formed on this surface.

The solid oxide fuel cell of the present invention is manufactured, for example, as follows. First, for example, La ₂ O ₃ , Y ₂ O ₃ , CaO, Mn according to a predetermined formulation.
After weighing and mixing the raw materials of O ₂ , they are calcined at a temperature of about 1500 ° C. for 2 to 10 hours, and then pulverized to a particle size of 4 to 8 μm.

A binder is mixed with and kneaded with the prepared powder to form a cylindrical air electrode molded body by an extrusion molding method, further debindered, and calcined at 1200 to 1250 ° C. Prepare a fired body.

As a sheet for the solid electrolyte 31, for example, a powder composed of partially stabilized or stabilized ZrO ₂ containing ₃ to 20 mol% of Y ₂ O ₃ or Yb ₂ O ₃ is used.
A sheet having a thickness of 1 to 5 μm is prepared, a commercially available solvent, dispersant, and binder are added at a predetermined concentration, and a sheet having a thickness of 50 to 100 μm is prepared by a method such as a doctor blade.

As a sheet for the current collector 35, LaCrO
To prepare a sheet having a thickness of 50~100μm by a method such as a doctor blade with a powder consisting of ₃ based material.

Then, on the surface of the cylindrical air electrode calcined body,
Paste the solid electrolyte sheet and the current collector sheet respectively,
This is obtained by firing in air at a temperature of 1200 to 1600 ° C. for 2 to 10 hours.

The fuel electrode may be prepared by forming a slurry containing the fuel electrode material into a sheet and affixing it to the surface of the solid electrolyte, applying the slurry, and baking by heating, or applying the slurry to an unfired solid electrolyte sheet, Alternatively, it is manufactured by laminating sheets and co-sintering with a solid electrolyte sheet.

Specifically, for example, NiO and ZrO ₂ raw material powders each having a predetermined particle diameter are adjusted so as to have a predetermined ratio, and then mixed with a ball mill using water or the like as a solvent. It is applied to the surface of the solid electrolyte by printing, or is applied to the surface of the solid electrolyte by a so-called slurry dipping method in which a mixed powder solution using water or the like as a solvent is impregnated. Then, at 1100-1700 ° C in air,
Heat treatment is performed for 8 hours to burn the fuel electrode to the solid electrolyte surface.

As another method, a slurry is applied to the solid electrolyte sheet formed on the surface of the air electrode calcined body by the method described above, and the slurry is applied at 1200 to 1600 ° C.
Co-firing may be performed for 8 hours.

Factors that affect the distribution and size of the metal particles 43 include the temperature and time of heat treatment such as firing and fuel electrode baking temperature, the cooling rate from the firing and heat treatment temperature, or the solid electrolyte on which the fuel electrode is formed. Density, heat treatment state, heat treatment condition and composition of the air electrode on the opposite side, addition of diffusion promoting element, and the like.

That is, the diffusion amount (depth d) of the metal component in the fuel electrode to the grain boundary of the solid electrolyte greatly depends on the temperature and the firing time of firing and heat treatment. When baking on the sintered solid electrolyte, a heat treatment at 1100 to 1700 ° C is performed, and when the solid electrolyte is not fired, a heat treatment (firing) at 1200 to 1600 ° C is performed. In both cases, the higher the temperature,
The longer the firing time, the greater the amount of diffusion. That is, the depth d of the solid electrolyte from the side surface of the fuel electrode increases. The co-sintering with the unsintered solid electrolyte sheet has a larger diffusion amount than the case of baking.

As a method of controlling the amount of diffusion under conditions other than the heat treatment, diffusion promoters Ca, Sr,
There is also a method in which Ba, Mg, Mn and the like are excessively added. These surplus elements easily diffuse into the solid electrolyte and are affected by mutual diffusion, so that the metal component in the fuel electrode easily diffuses into the solid electrolyte. Further, the control of the minute amount of diffusion can be controlled by the heat treatment time of 1 to 8 hours.

The size of the metal particles 43 formed by the diffused metal component of the fuel electrode is controlled by a cooling process for 3 to 20 hours after heat treatment or firing. That is, the size of the metal particles 43 greatly depends on the cooling rate, and can be formed by setting the cooling rate to 100 to 300 ° C./hour. Fine control can be performed by changing the cooling rate by 1 to 5 steps.

In the above example, the cylindrical solid oxide fuel cell has been described, but the present invention is also applicable to a flat fuel cell.

[0048]

EXAMPLE A ZrO ₂ (Y ₂ O ₃ containing 3 to 10 mol%) powder having an average particle size of 0.5 to 3 μm was prepared as a raw material powder, and had an outer diameter of 20 mm, a thickness of 0.5 mm, and a thickness of 1000 to 17 μm.
It was fired at 00 ° C. to obtain a solid electrolyte disk.

A commercially available air electrode powder of La _0.9 Sr _0.1 MnO _{3 having} a purity of 99.9% and an average particle diameter of 1 to 10 μm was prepared, and a binder was added thereto to prepare an air electrode paste. Further, NiO having an average particle size of 0.1 to 10 μm
A powder was prepared, and a binder was added thereto to prepare a fuel electrode paste.

An air electrode paste was applied to one surface of the solid electrolyte disk and a fuel electrode paste was applied to the other surface so as to have a thickness of 50 μm after the heat treatment. Bake the electrode and fuel electrode,
The solid electrolyte was also densified and cooled from the heat treatment temperature under the conditions shown in Table 1 to produce a cell.

Thereafter, oxygen is supplied to the air electrode side and hydrogen is supplied to the fuel electrode side to generate power at 1000 ° C., and the initial performance and the reduction rate of the output density after 1000 hours (the output density after 1000 hours with respect to the output density after 100 hours) Output density reduction rate: durability), 10
The reduction rate of the output density after applying 20 thermal cycles between 00 and 600 ° C. (the reduction rate of the output density after 20 cycles with respect to the output density without the thermal cycle: thermal cycle characteristics) was determined.

The samples of the same lot were observed with a transmission electron microscope (TEM) to determine the size of the metal particles at the solid electrolyte grain boundaries, and the results were measured by X-ray microanalysis (EPMA).
Was used to investigate the distribution distance from the fuel electrode / air electrode interface.

Specifically, regarding the measurement of the distribution state of the metal particles, the sample after the heat treatment was polished in the cross-sectional direction, and the fuel electrode / solid electrolyte interface was analyzed using EPMA. The vicinity of the fuel electrode / solid electrolyte interface was captured in a square of about 100 μm, and the count of metal components was made into a color map. The average count of the metal component in the fuel electrode was set to 100 in a map shape, and the portion of the solid electrolyte farthest from the fuel electrode was set to 0 count. At that time, the part where the count became 50 counts or less was defined as the interface. The distribution range was a range from the interface to 10 counts or less in the vertical direction.

The average particle size of the metal particles 41 was measured by using a TEM after slicing and polishing the interface between the fuel electrode and the solid electrolyte in the sectional direction. It was confirmed from the difference and composition of the structure of the grain boundary in the solid electrolyte that it was a metal component in the fuel electrode, and the average of the particle size was defined as the average particle size of the metal particles. The results are shown in Table 1.

[0055]

[Table 1]

According to Table 1, in the sample No. 1 of the comparative example,
According to the TEM observation, although the grain boundary metal exists at the grain boundary between the two surfaces of the ceramic particles on the fuel electrode side surface layer of the solid electrolyte,
No metal particles were present, which resulted in poor power generation performance and heat cycle characteristics.

On the other hand, in the sample of the present invention, the initial power generation performance was good, and the durability and the heat cycle characteristics were good. In particular, the average particle size of the metal particles is 10 to 50 nm.
When the diffusion depth d is 5 to 30 μm, the initial power generation performance is 0.30 W / cm ² or more, the durability is 3% or less, and the thermal cycle characteristics are 3% or less. Was.

[0058]

The solid oxide fuel cell according to the present invention has the following features.
Metal particles were present at the grain boundary between the two surfaces of the ceramic particles on the fuel electrode side surface of the solid electrolyte, and the metal particles were connected to the fuel electrode via the grain boundary metal at the two surface grain boundary. The contact area of the fuel electrode increases, the polarization resistance generated at the fuel electrode / solid electrolyte interface decreases, the power generation performance can be improved, and the fuel electrode adheres firmly to the solid electrolyte. Peeling is eliminated, and a high state can be maintained without deteriorating the initial power generation performance.

[Brief description of the drawings]

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

FIG. 2 is an enlarged sectional view showing the vicinity of an interface between a fuel electrode and a solid electrolyte in FIG. 1;

3A is a view showing a state in which metal particles are present at a grain boundary between two surfaces of ceramic particles of the solid electrolyte of FIG. 2;
(B) is a diagram showing a state in which metal particles are connected by a grain boundary metal and one end is connected to a fuel electrode.

FIG. 4 is a perspective view showing a conventional cylindrical solid oxide fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 31 ... Solid electrolyte 32 ... Air electrode 33 ... Fuel electrode 35 ... Current collector 41 ... Ceramic particle 43 ... Metal particle 45 ... Grain boundary metal

Claims (4)

[Claims] 1. A solid electrolyte fuel cell comprising a ceramic solid electrolyte having an air electrode on one surface and a fuel electrode mainly composed of metal on the other surface, wherein a fuel electrode side surface layer of the solid electrolyte is provided. Solid electrolyte fuel cell characterized in that metal particles are present in a grain boundary between two surfaces of ceramic particles in the above, and the metal particles are connected to the fuel electrode via a grain boundary metal of the grain boundary between the two surfaces. cell. 2. The solid according to claim 1, wherein a plurality of metal particles are present at a grain boundary between the two surfaces of the ceramic particles and are connected to each other by a grain boundary metal of the grain boundary between the two surfaces. Electrolyte fuel cell. 3. The method according to claim 1, wherein the metal particles are separated from the fuel electrode side of the solid electrolyte.
2. The method according to claim 1, wherein said metal is present at a depth of about 50 .mu.m.
Or a solid oxide fuel cell according to 2. 4. The solid oxide fuel cell according to claim 1, wherein the average particle size of the metal particles is 10 to 100 nm.