JP3180988B2 - Solid oxide fuel cell - Google Patents

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 an improvement in a porous support tube having an air electrode.

[0002]

2. Description of the Related Art Conventionally, two types of solid electrolyte fuel cells have been known: cylindrical and flat. The flat-type fuel cell has the feature that the power density per unit volume of power generation is high, but when put into practical use, there are problems such as incomplete gas seals and non-uniform temperature distribution in the cell. On the other hand, in a cylindrical fuel cell,
Although the power density is low, the mechanical strength of the cell is high, and the uniformity of the temperature distribution in the cell can be maintained.
Both types of solid electrolyte fuel cells are being actively researched and developed utilizing their respective features.

Generally, a single cell of a cylindrical fuel cell is shown in FIG.
As shown in the figure, a CaO-stabilized Z having an open porosity of about 40%
For example, a porous air electrode 12 made of a LaMnO ₃ -based material is formed on the surface of a support tube 11 made of rO ₂ by a slurry-dip method, and a vapor phase synthesis method (EVD) is formed on the surface.
For example, a stabilized ZrO ₂ solid electrolyte 13 containing Y ₂ O ₃ is formed by a method such as thermal spraying, and a fuel electrode 14 made of porous Ni-zirconia or the like is formed on the surface of the solid electrolyte 13. . The fuel cell module is
The plurality of single cells having the above configuration are connected via an interconnector 15 made of LaCrO ₃ -based material or the like.
Power generation is performed at a temperature of 1000 to 1050 ° C. by flowing air (oxygen) inside the support tube 11 and fuel (hydrogen) outside.

In recent years, in producing the above-mentioned fuel cell,
In order to simplify the process, the air electrode LaMnO ₃
Attempts have been made to use the system material directly as a porous support tube. As a support tube material having a function as an air electrode, for example, 20 mol% of CaO, or 10 to 15%
A LaMnO ₃ solid solution material in which mol% of SrO is dissolved is used.

[0005]

However, when the above-mentioned LaMnO ₃ material containing CaO or SrO as a solid solution is used as a support tube, a gas phase synthesis method (EV
When coating the solid electrolyte membrane or the interconnector by D) or thermal spraying, the support tube is kept at a high temperature of 1000 ° C. or higher, particularly 1200 to 1400 ° C. in the case of vapor phase synthesis. For this reason, there has been a problem that the support tube is crimped during the formation of the solid electrolyte film or the interconnector film and connection between cells cannot be made. Also, in power generation, since the cells are maintained at a high temperature of 1000 ° C. for a long time, the support tube is similarly deformed, the connection between the cells is deteriorated, and there is a problem that the output is reduced.

An object of the present invention is to improve the creep resistance of the support tube having the air electrode function, solve the problem of deformation of the support tube during the cell manufacturing process or power generation, and improve the yield of cells. It is another object of the present invention to provide a cell that has long-term stability even when maintained at a high temperature.

[0007]

As a result of repeated studies to solve the above problems, the present inventor has formed a LaMnO ₃ -based material as a support tube and used a part of La in the LaMnO ₃ -based material. At the same time as the composition comprising a specific trivalent metal substituted with a predetermined alkaline earth element and optionally a part of Mn substituted with another transition metal element,
It has been found that the above object is achieved by controlling the amount of metal impurities to a predetermined amount or less.

That is, the solid oxide fuel cell according to the present invention is a solid oxide fuel cell comprising a solid electrolyte and a fuel electrode sequentially laminated on a porous support tube having an air electrode function. The pipe is

[0009]

Embedded image

Where A is Y, Yb, Sc,
At least one member selected from the group of Er, B is Ca, B
a, at least one selected from the group consisting of Sr, C is Co,
At least one selected from the group consisting of Ni, Zr, Ce, and Fe
X, y, z and p are 0.05
≦ x ≦ 0.3, 0.25 ≦ y ≦ 0.5, 0.9 ≦ z ≦
It is composed of a complex perovskite oxide satisfying 1.0 and 0 ≦ p ≦ 0.3, and the total amount of metal impurities other than the above-mentioned constituent elements is 0.2% by weight or less of Al and Si. Is 0.8% by weight or less.

Hereinafter, the present invention will be described in detail. FIG. 1 is a diagram for explaining one embodiment of a solid oxide fuel cell unit according to the present invention. In FIG. 1, 1 is a support tube, 2 is a solid electrolyte, and 3 is a fuel electrode.

According to the present invention, the support tube 1 itself has a cylindrical shape made of conductive ceramics. A solid electrolyte 2 is formed on the cylindrical support tube 1, and a fuel electrode 3 is formed thereon. When power is generated by the cell having such a structure, a gas containing oxygen such as air is supplied to the inside of the cylindrical support tube 1 while a fuel gas such as hydrogen gas is supplied to the fuel electrode 3 side. Then, electric power is generated between the support tube 1 and the fuel electrode 3. Therefore, the support tube 1 and the fuel electrode 3 are each made of a porous body having an open porosity of 35 to 40% so that the supplied gas can be supplied to the solid electrolyte. Further, the fuel cell module is configured by connecting a plurality of cells via the interconnector 4.

According to the present invention, the support tube 1 is replaced with

[0014]

Embedded image

Where A is Y, Yb, Sc,
At least one member selected from the group of Er, B is Ca, B
a, at least one selected from the group consisting of Sr, C is Co,
At least one selected from the group consisting of Ni, Zr, Ce, and Fe
At the same time as being composed of an element consisting of a seed,
Let y, z and p be 0.05 ≦ x ≦ 0.3, 0.25 ≦
y ≦ 0.5, 0.9 ≦ z ≦ 1.0 and 0 ≦ p ≦ 0.3
It is a major feature that it is made of a material satisfying the following. Such a material is composed of a composite perovskite oxide.

In the present invention, the reason why the composition of the support tube material is limited to the above range is that La, Y, Yb,
If the x value indicating the replacement amount of Sc, Er, etc. is smaller than 0.05 or larger than 0.3, the creep deformation amount increases, and the replacement amount of La, Ca, Sr, Ba is shown. If the y value is smaller than 0.25, the amount of creep deformation becomes large.
It is necessary to raise the temperature to at least ℃, which is not economical, and firing at a low temperature deteriorates the sinterability and makes it difficult to produce a material having a predetermined open porosity.

The z value indicating the ratio between the A site and the B site is usually 1 in a perovskite type crystal structure, but the same effect can be obtained even when the z value is non-stoichiometric up to 0.9. However, if it is smaller than 0.9, a different phase containing Mn or the like other than the perovskite type precipitates and the amount of creep deformation increases. Conversely, if this value exceeds 1.0, La ₂ O ₃ will precipitate and the material will be weathered in a short time.

Furthermore, based on a LaMnO ₃ -based solid solution, even if Mn is replaced by Co, Ni, Zr, Ce, Fe, etc., the lattice defect structure does not substantially change. However, when the substitution value p value exceeds 0.3 due to these elements, the clearing is made.
The deformation amount increases.

In the present invention, a particularly desirable range in the composition system of the above formula 1 is 0.05 ≦ x ≦ 0.2, 0.2
5 ≦ y ≦ 0.4, 0.95 ≦ z ≦ 1.0, 0 ≦ p ≦ 0.
2.

Further, according to the present invention, the amount of metal impurities contained in the material constituting the support tube is 0.8% by weight or less, and the total amount of Al and Si therein is 0.2% by weight. It is important that: The metal impurities are metal elements other than the elements constituting the support tube.
1, Si, Cr, Ti, Nb and the like. If the amount of these metal impurities exceeds 0.8% by weight or
If the amount of 1, Si exceeds 0.2% by weight, the amount of creep deformation increases. According to the present invention, in particular, the amounts of Al and Si are 0.1
% Or less, and the total amount of metal impurities is preferably controlled to 0.5% by weight or less.

In the fuel cell of the present invention, the solid electrolyte used is a well-known stabilized ZrO ₂ containing a stabilizing material such as Y ₂ O _3, and Ni-zirconia is used as a fuel electrode material. Can be

[0022]

The perovskite crystal is generally represented by ABO ₃ , and the lattice points in the crystal are divided into three sites: A site, B site and oxygen (O) site. LaMnO3, L
From the detailed research results on the lattice defect structure in a material in which CaO or SrO is dissolved in aFeO ₃ or LaCoO ₃ system, the amount of solid solution of CaO or SrO in these materials regardless of the degree of defect of A site Is less than 25 mol%,

[0023]

(Equation 1)

By the above reaction, cationic vacancies of La and Mn are predominantly generated.

On the other hand, when the amount of solid solution exceeds 25 mol%,

[0026]

(Equation 2)

It has been clarified that the oxygen ion vacancy becomes dominant by the above reaction.

These results show that the above solid solution is CaO,
Alternatively, when the solid solution amount of SrO is less than 25 mol%, it means that the diffusion rate of the cation through the cation vacancy increases.

Concerning the creep deformation, if the deformation occurs by diffusion and intraparticle (volume) diffusion is dominant, then the creep deformation
The deformation speed is as follows:

[0030]

(Equation 3)

## EQU1 ##

When the grain boundary diffusion is dominant, the following equation 4

[0033]

(Equation 4)

It is expressed as follows.

In general, DV and Db are the diffusion coefficients of the slower of the anions and cations in the crystal.
In the perovskite type crystal, the diffusion coefficient in Equations 1 and 2 is that of a cation. According to these formulas, it can be easily determined that the creep resistance is superior as the diffusion coefficient is smaller and as the particles are larger.

Solid solution amount of CaO, BaO and SrO (y value)
The reason why the amount of deformation due to the creep is large when is less than 25 mol% is that the concentration of the cation vacancy generated by the equation (1) is high in consideration of the lattice defect structure described above, so that the amount of It is considered that the diffusion speed of the grain boundary was high, and as a result, the creep deformation speed was increased. Also,
Regarding the effect of the addition of rare earth elements such as Y and Yb, the addition amount (x value) of the rare earth element is less than 5 mol% and 30 mol%.
Is exceeded, a large crystal lattice distortion occurs in the material in this range due to the difference in ionic radius between the rare earth ion and the La ion, the activation energy of cation diffusion decreases, and the diffusion coefficient increases. It is considered that as a result, the creep deformation speed was increased. The same result is obtained in the non-stoichiometric system in which the A site is lost, because there is no essential change in the lattice defect structure as compared with the stoichiometric system.

With respect to the amount of impurities in the material, a very small amount is dissolved in the crystal, but if it is more than this, the material segregates at the grain boundaries or forms a glass phase at the grain boundaries. In such a case, slip between the grain boundaries occurs, and the creep speed increases. It is presumed that the increase in the amount of creep deformation when the amount of metal impurities exceeds 0.8% by weight is caused by such slip between the grain boundaries. In particular, A
Since l and Si easily form a glass phase, their amounts need to be controlled to a particularly small range.

Further, even if the Mn at the B site is replaced with Ni, Co or the like, it has the same lattice defect structure as LaMnO ₃ , so the mechanism of the creep deformation is the same as that of the LaMnO ₃ system. However, LaNiO ₃ , LaCoO ₃
The sintering rate of the solid solution system is faster than that of LaMnO ₃ . This result means that the cation diffusion coefficient in the LaNiO ₃ or LaCoO ₃ solid solution system is larger than that of LaMnO ₃ . Therefore, the Mn at the B site
Is replaced with Ni, Co, or the like, the replacement amount (p value) is 0.
It is judged that the reason why the creep speed increases when the value exceeds 3 is that the cation diffusion speed increases due to the addition of Ni or Co.

As is apparent from the above description, according to the constitution of the present invention, by limiting the x, y, z and p values in the composition system shown in Chemical formula 1 to the above specific ranges, It has excellent creep resistance even when held at a high temperature, and when a solid electrolyte and a fuel electrode are formed on a support tube, peeling of the solid electrolyte and the fuel electrode membrane due to creep is suppressed, and the fuel cell As a result, excellent durability can be imparted during operation at a high temperature.

According to the present invention, even when the air electrode is used as a gas diffuser in a flat fuel cell, the deformation at high temperature is small, so that the connection with the electrolyte is excellent, and as a result, power generation due to poor connection is achieved. Output reduction can be suppressed.

[0041]

Next, the present invention will be described based on embodiments. Example 1 Commercially available 99.9% pure Y ₂ O ₃ , La ₂ O ₃ , Yb ₂
O ₃ , Sc ₂ O ₃ , Er ₂ O ₃ , CaCO ₃ , SrCO
₃ , BaCO ₃ , Mn ₂ O ₃ , NiO, CoO, ZrO
₂ , CeO ₂ , and FeO were used as starting materials, mixed to obtain the compositions shown in Tables 1 and 2, mixed with zirconia balls for 10 hours, and then subjected to a solid-phase reaction at 1300 ° C. for 10 hours. . In some cases, Al ₂ O ₃ , SiO _2
2 , Cr ₂ O ₃ , TiO ₂ , and MgO were added in an amount of up to 2% by weight, and this powder was further ground and mixed using zirconia balls for 24 hours. After this,
It was formed into a cylindrical shape having an outer diameter of 15 mm, an inner diameter of 11 mm, and a length of 200 mm, and was fired at 1450 to 1500 ° C. to obtain a cylindrical sintered body having an open porosity of 38 to 41%. The impurities in the obtained sintered body were measured by fluorescent X-ray analysis, and the amount was measured by ICP emission spectroscopy.

For the above sintered body, the distance between the fulcrums was 15
It was supported by a zirconia block so as to be 0 mm, kept at 1400 ° C. in the atmosphere for 10 hours, and the ratio of the maximum deformation before and after heating divided by the distance between the fulcrums was defined as the creep deformation. The measurement results are shown in Tables 1 and 2.

[0043]

[Table 1]

[0044]

[Table 2]

As is apparent from the results of Tables 1 and 2, when the substitution amount (y value) of the divalent metal is smaller than 0.25, the deformation amount is large. On the other hand, when the y value exceeds 0.5, the sinterability deteriorates and a cylindrical support tube having a predetermined open porosity cannot be produced. The amount of deformation was similarly large for those having a trivalent metal substitution amount (x value) smaller than 0.05 or larger than 0.3. When the z value was less than 0.9, a hetero phase other than the perovskite type containing Mn was precipitated, and the deformation amount became large. Deformation was observed in all the samples deviating from the range of the present invention with respect to other x, y, z, and p values.

Also, those having an impurity amount exceeding 0.8% by weight or Al and Si amounts exceeding 0.2% by weight also showed a large deformation amount.

Example 2 In Tables 1 and 2 of Example 1, samples No. 1, 2, 3, 4, 1
1, 12, 19, 31, 33, 42, 45, 51, 5
Length 50c consisting of the composition of 8, 65, 74, 76, 78
m, and a support tube having a thickness of 11 m is formed on the surface thereof by a gas phase synthesis method.
A solid electrolyte made of ZrO ₂ containing 10 mol% of Y ₂ O ₃ was formed at 00 ° C., and ten solid electrolytes were produced.
For 2, 3, 12, 19, 31, and 45, creep deformation occurred, and partial exfoliation of the solid electrolyte membrane was observed. However, the other samples of the present invention showed no deformation even when the solid electrolyte was formed. Did not occur.

[0048]

As described above, according to the present invention, the creep resistance of the support tube itself at high temperatures is improved, and the yield of cells in the cell manufacturing process is improved,
It is possible to provide a highly durable fuel cell that does not cause connection failure between cells due to deformation even during long-time power generation during high-temperature operation.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the structure of a fuel cell unit according to the present invention.

FIG. 2 is a view for explaining the structure of a conventional fuel cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support pipe 2 Solid electrolyte 3 Fuel electrode 4 Interconnector

Claims (1)

(57) [Claims] 1. A solid oxide fuel cell comprising a solid electrolyte and a fuel electrode sequentially laminated on a porous support tube having an air electrode function, wherein the support tube is represented by the following chemical formula 1. Wherein A is at least one member selected from the group consisting of Y, Yb, Sc, and Er; B is at least one member selected from the group consisting of Ca, Ba, and Sr; and C is Co, Ni, Zr. ,
It is composed of at least one member selected from the group consisting of Ce and Fe, and x, y, z and p are 0.05 ≦ x ≦ 0.
3, composed of a composite perovskite oxide satisfying 0.25 ≦ y ≦ 0.5, 0.9 ≦ z ≦ 1.0 and 0 ≦ p ≦ 0.3, among metal impurities other than the constituent elements, A
A solid oxide fuel cell unit characterized in that the total amount of l and Si is 0.2% by weight or less and the total amount of metal impurities is 0.8% by weight or less.