JPH0769720A - Solid electrolytic material reinforced by dispersed composite material - Google Patents

Abstract

PURPOSE:To obtain a solid electrolytic material reinforced by a dispersed composite material, having high electrical conductivity as a solid electrolytic material and excellent in mechanical properties. CONSTITUTION:This solid electrolytic material mainly contains a zirconia electrolytic material stabilized with scandia and is mixed with 0.5-20wt.% of alumina as a high-strength composite material. When applied to a solid-electrolytic fuel cell, the solid electric material exhibits high generating efficiency and can be permanently used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite material dispersion strengthened solid electrolyte material suitable as a solid electrolyte material used in a solid oxide fuel cell (SOFC).

[0002]

2. Description of the Related Art In recent years, so-called solid electrolyte materials have been researched and developed in various technical fields and applications. Among them, for example, the solid oxide fuel cell (SOFC) has higher power generation efficiency and higher exhaust heat temperature than other fuel cells such as phosphoric acid type and molten carbonate type that have been developed so far. In recent years, it has attracted particular attention because it is possible to construct a power generation system that can be used effectively.

By the way, this solid oxide fuel cell (SO
The form of FC) is generally roughly classified into a flat type shown in FIG. 6 and a cylindrical type (not shown). The flat type shown in FIG. 6 is also typified by the external manifold type shown in FIG. 7A and the internal manifold type shown in FIG. 7B. To be

The structure of the solid oxide fuel cell (SOFC) shown in FIGS. 6 and 7A and 7B will be briefly described. Between the fuel electrode 10 in contact with the fuel gas and the oxygen electrode 20 in contact with the air. The solid electrolyte plate 30 is sandwiched between the fuel electrode 10 and
On the outside of the separator and on the outside of the oxygen electrode 20, respectively.
A single cell having a structure in which 0a and 40b are provided is provided in a laminated form over a large number of layers.

In the solid oxide fuel cell (SOFC) thus constructed, the fuel electrode is contacted with the fuel gas (hydrogen, carbon monoxide) and the oxygen electrode is contacted with the oxidizing gas (air or oxygen). Contact. Then, oxygen ions (O ²⁻ ) generated in the oxygen electrode move in the electrolyte to reach the fuel electrode, and in the fuel electrode, O ²⁻ reacts with hydrogen (H ₂ ) to release an electron. This produces electricity, which causes a flow of electricity.

In this solid oxide fuel cell (SOFC), the electrical characteristics of the solid electrolyte material, particularly the electrical conductivity, greatly affect the performance of the battery. Conventionally, stabilized zirconia has been used for this solid electrolyte material. This stabilized zirconia contains zirconia (ZrO ₂ ) at a high temperature (about 11
At around 50 ° C), a volume change occurs as the crystal structure changes from a monoclinic form to a tetragonal form. Therefore, as a means to prevent this volume change, oxides such as calcium (Ca) and yttrium (Y) are solidified. It is intended to stabilize the crystal structure by melting. At present, yttria-stabilized zirconia (Y ₂ O ₃ Stabilized ZrO ₂ ) is most often used. In addition, tetragonal zirconia polycrystalline TZP (Tetragonal Zr), which is a high-strength material with inferior electrical characteristics, is also used.
In some cases, O ₂ Policrystalline) is used.

[0007]

However, in a solid oxide fuel cell (SOFC) using yttria-stabilized zirconia (YSZ) as a solid electrolyte material, the YS
Although the Z solid electrolyte material itself has excellent conductivity characteristics, if a solid electrolyte plate having a large flat area is used to provide a fuel cell having a large power generation capacity, the solid electrolyte plate has a thickness of 0.2 to 0.2. It is necessary to make it as thick as 3 mm. Therefore, there is a problem that the internal resistance of the YSZ solid electrolyte plate increases and only a low power density of about 0.5 W / cm ² can be obtained.

On the other hand, the inventors of the present invention, as an alternative to the yttria-stabilized zirconia (YSZ) solid electrolyte material, have a scandia-stabilized zirconia (Sc ₂ O ₃ Stabilized ZrO ₂ ) solid electrolyte material which is superior in conductivity characteristics. Was first developed and has already applied.

However, even with this scandia-stabilized zirconia (ScSZ) solid electrolyte material, the electrical conductivity characteristics are further improved, but the mechanical strength is not so different from that of the YSZ solid electrolyte material. Therefore, when trying to make a large-capacity fuel cell using a solid electrolyte plate having a large flat area, the plate thickness of the electrolyte plate must be as thick as 0.2 to 0.3 mm due to handling problems and structural strength problems. There were the following problems. That is,

As the electrolyte plate becomes thicker, the internal resistance increases, so the power density decreases, and high power generation efficiency and power generation performance cannot be obtained. If a thin electrolyte plate is used, it is easily broken by gas pressure or the like. Due to the low material strength of the electrolyte plate, mechanical and thermal fatigue damage is likely to occur, and long-term durability is poor, etc.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a solid electrolyte material having excellent conductivity characteristics and mechanical strength. Especially. Thus, for example, it is intended to improve the power generation efficiency as a solid electrolyte material of a solid oxide fuel cell (SOFC) and achieve permanent use.

[0012]

In order to achieve such an object, the inventors of the present invention have conducted experimental research on various material properties, and as a result, have found that the conventional yttria-zirconia system (Y ₂
O ₃ —ZrO ₂ system) Scandia-zirconia system (Sc ₂ O ₃ —Zr system), which has better conductivity characteristics than solid electrolyte materials.
This is intended to improve the mechanical strength characteristics of the (O ₂ ) solid electrolyte material.

Therefore, the gist of the present invention is that the scandia-stabilized zirconia electrolyte material is the main component and the high-strength composite material is dispersed therein. In that case, as the high-strength composite material, alumina (Al ₂ O ₃ ) or mullite is preferable. When scandia (Sc ₂ O ₃ ) is solid-dissolved in the scandia-stabilized zirconia electrolyte material in an amount of 8 to 15 mol%, and as the high-strength composite material, alumina or the like is mixed in an amount of 0.5 to 20 wt%, the most Excellent electrical conductivity characteristics and high mechanical strength can be obtained.

[0014]

The present invention will be described in detail below. still,
In the examples described below, solid oxide fuel cells (SO
The description is made assuming a solid electrolyte material used for FC). FIG. 1 shows the manufacturing process of the solid electrolyte material. According to this, first, powder particles of zirconia (ZrO ₂ ) which is a main material of the solid electrolyte plate and powder particles of scandia (Sc ₂ O ₃ ) which is a stabilizing material are mixed at an appropriate mixing ratio. Here, they are mechanically mixed by a ball mill or the like. The average particle size of this mixed powder is about 3 μm. If a liquid phase manufacturing process such as a sol-gel method or a coprecipitation method is applied as a method for preparing a mixed powder of zirconia and scandia, it is possible to obtain a uniform mixed powder with few impurities. The mixing ratio of ZrO ₂ and Sc ₂ O ₃ is appropriately selected within the range of ZrO ₂ 92 to 85 mol% and Sc ₂ O ₃ 8 to 15 mol%.

Then, the mixed powder of zirconia (ZrO ₂ ) and scandia (Sc ₂ O ₃ ) is heated at a high temperature (several 100 ° C.).
To obtain scandia-stabilized zirconia (ScSZ) in which Sc ₂ O ₃ is solid-solubilized in ZrO ₂ and then pulverized to obtain an adjusted ScSZ powder. Next, the scandia-stabilized zirconia (ScSZ) powder is mixed with a powder of alumina (Al ₂ O ₃ ) as a high-strength composite material at an appropriate mixing ratio. A suitable blending ratio of Al ₂ O ₃ is 0.5 to 20% by weight based on the ScSZ powder.

When a mixed powder of ScSZ powder and Al ₂ O ₃ powder is obtained in this manner, the mixed powder is then formed into a plate having a plate thickness of 100 to 300 μm (square plate of about 20 cm). As this forming means, in this experimental example, a hydrostatic press (CIP) is used to perform pressure forming at a pressure of 1 t / cm ² . However, it is not limited to this forming means, and a thin plate may be manufactured by a doctor blade method or a calendar roll method which has been generally used conventionally. After that, the molded plate
Baking at a temperature of 1700 ° C. Thereby, scandia-stabilized zirconia (Sc ₂ O ₃ Stabilized) in which scandia (Sc ₂ O ₃ ) is solid-solubilized in zirconia (ZrO ₂ ).
A solid electrolyte plate containing a ZrO ₂ ) material as a main component and alumina (Al ₂ O ₃ ) as a high-strength composite material dispersed therein is obtained.

Next, this scandia-stabilized zirconia (S
In forming a fuel electrode or an oxygen electrode on a cSZ-based solid electrolyte plate, a ceramic powder of these electrode materials is formed into a mud, and the so-called slurry coating method is applied to one side and the opposite side of the ScSZ-based solid electrolyte plate. Each is applied and then baked at a predetermined temperature. In the case of the fuel electrode, for example, nickel (Ni) 40 wt% -zirconia (ZrO ₂ ) 60 wt% Ni-cermet material is used.
This ScSZ-based solid electrolyte plate is coated on one side with a thickness of about 0 μm, and fired at a temperature of 1400 to 1500 ° C. As a result, a thin-film fuel electrode is formed on one surface of the ScSZ-based solid electrolyte plate.

In the case of the oxygen electrode, for example, a lanthanum strontium manganate (La (Sr) MnO ₃ ) material is coated on the surface of the solid electrolyte plate on the opposite side of the fuel electrode to a thickness of about 50 μm, Baking at a temperature around 1150 ° C. As a result, a thin film oxygen electrode is similarly formed on the opposite surface of the ScSZ-based solid electrolyte plate. Incidentally, it is suitable that the compounding ratio of the oxygen electrode material is about 5 to 15 mol% of strontium to 95 to 85 mol% of lanthanum manganate.

Next, various experiments were conducted on the solid electrolyte plate of the solid oxide fuel cell (SOFC) manufactured as described above, which will be described below. First, referring to FIG. 2, scandia-stabilized zirconia (Sc) according to the present invention is used.
Alumina (Al ₂
O ₃ ), a conventional yttria-stabilized zirconia (YSZ) electrolyte, and a solid oxide fuel cell (SOFC) with a ScSZ electrolyte containing no alumina (Al ₂ O ₃ ) for comparison. The power generation characteristics of the above were compared, and the results will be shown and described.

The YSZ solid electrolyte material is 8 mol% Y ₂ O ₃
92 mol% ZrO ₂ and a ScSZ solid electrolyte material of 11 mol% Sc ₂ O ₃ -89 mol% ZrO ₂ were tested, and the amount of alumina (Al ₂ O ₃ ) was 20% by weight. And Regarding the thickness of the solid electrolyte plate, a YSZ electrolyte plate and a ScSZ electrolyte plate (without alumina compounding) of 250 μm were prepared, and a ScSZ electrolyte plate (alumina 20% by weight compounding) was 250 μm.
The one having a diameter of 00 μm was prepared. In the figure, the horizontal axis represents current [mA], and the vertical axis represents voltage [mV] and power density [W].
/ Cm ² ], and voltage characteristics and power characteristics were compared with each other.

As a result, the current value is
The voltage value gradually decreases as it is increased.
Is a YSZ solid electrolyte in the case of ScSZ solid electrolyte material.
The same applies to materials. However, ScSZ solid electrolyte
Material is Al₂O₃11ScSZ not mixed with Al₂
O₃In any case of 11ScSZ20A containing
The rate of voltage drop is smaller than that of YSZ solid electrolyte material.
I understand. Also, the higher the current, the larger the voltage difference.
I understand. However, Al of ScSZ solid electrolyte material ₂O₃
11ScSZ material without Al and Al₂O₃20 weight
% In comparison with 11ScSZ20A material
Is Al for the same plate thickness of 250 μm₂O₃Blending
As a result, the rate of voltage drop was slightly high.
Than this Al₂O₃Electrical characteristics by adding
It turns out that it tends to get worse. However, the plate thickness is thin
On the contrary, in comparison with the one (100 μm), the plate thickness should be thin.
And by Al₂O₃ScSZ electrolyte material (1
1ScSZ), the rate of voltage drop is smaller than that of
The result was excellent.

On the other hand, when looking at the power characteristics, the YSZ solid electrolyte material shows a peak value of the power density at about 400 mA in comparison with the same plate thickness (250 μm), and the power density lowers most at higher current values. large.
On the other hand, ScSZ electrolyte (without Al ₂ O ₃ compound and Al
Each of 20% by weight of ₂ O ₃ shows a peak value of power density at about 500 mA, and the decrease in current density at higher current values is smaller than that of YSZ electrolyte. In comparison of the peak value of the power density, YSZ solid electrolyte material has the lowest value of about 0.8 W / cm ^2, and ScSZ solid electrolyte material without alumina blending (1
1ScSZ material) having a power density of 1.2 W / cm ² , and 20% by weight alumina mixed ScSZ solid electrolyte material (11Sc).
It can be seen that the power density of the SZ20A material) is 1.1 W / cm ² and that both show higher peak values of the power density than the YSZ solid electrolyte material.

However, 11ScSZ20A containing alumina
The electrolyte has a lower peak value of power density than the 11ScSZ electrolyte containing no alumina. However, even if alumina is added, if the plate thickness is reduced (plate thickness 100 μm),
The peak value of the power density is higher (1.4 W / cm ² ) than the thick plate (plate thickness 250 μm), and the high power is obtained by reducing the plate thickness even in comparison with 11ScSZ electrolyte material not containing alumina. It can be seen that the peak value of the density is shown.

From the experimental results shown in FIG. 2, Y
A power density higher than that of the SZ electrolyte material is obtained, and the power density is slightly decreased by mixing alumina into the ScSZ solid electrolyte material, but the decrease in the power density is eliminated by reducing the plate thickness, and conversely, it is high. It turns out that you can also do it. And, as will be described later, by adding alumina (Al ₂ O ₃ ) to the ScSZ electrolyte material, the strength as the electrolyte material becomes high, and therefore the plate thickness can be made thin, and thereby the power density can be increased. It is a thing.

FIG. 3 shows scandia-stabilized zirconia (S
cSZ) By changing the compounding ratio of scandia (Sc ₂ O ₃ ) in the electrolyte, that is, by changing the solid solution amount of Sc ₂ O ₃ ,
The results of examining the temperature dependence of the conductivity characteristics of this ScSZ electrolyte are shown. However, in this experiment, ScS
Al ₂ O ₃ is not incorporated in the Z electrolyte at all. The horizontal axis represents the temperature variable 1000 / T [1 / K] (K: absolute temperature), and the vertical axis represents the conductivity variable log σ [S / cm].

Scandia (Sc) in ScSZ electrolyte
_The composition ratio of ₂ O ₃ ) was variously changed to 8 to 15 mol%, and as a result, it was found that the 8 mol% ScSZ electrolyte was the most excellent in the conductivity characteristics. And temperature variable 1000 /
At a temperature where T [1 / K] is about 1.1 or less (about 650K or less), there is no significant difference in the conductivity characteristics due to the difference in scandia compounding ratio (scandia solid solution amount), but the temperature variable is 1. At a temperature of 1 or higher (about 650 K or higher), the conductivity characteristic tends to be conspicuously deteriorated as the scandia compounding ratio increases, that is, as the scandia solid solution amount increases. This shows that it is necessary to consider the mixing ratio of scandia depending on the operating temperature environment of this solid oxide fuel cell (SOFC).

FIG. 4 shows scandia-stabilized zirconia (S
The relationship between the content of alumina (Al ₂ O ₃ ) contained in the cSZ) electrolyte and the conductivity of the electrolyte (at 1273K) is shown. ScSZ electrolyte is 11 mol% Sc
₂ O ₃ -89 mol% ZrO ₂ was used, and Al ₂
O ₃ is contained in the range of 0% by weight to 40% by weight.
The horizontal axis indicates the content of Al ₂ O ₃ , and the vertical axis indicates the conductivity σ [S /
cm].

As a result, the conductivity of this ScSZ electrolyte is the highest when Al ₂ O ₃ is not contained at all.
_It can be seen that the content decreases as the content of ₂ O ₃ increases. And, if the content of Al ₂ O ₃ is up to about 20% by weight, it can be used as a value of conductivity, but if it exceeds 20% by weight, the decrease in conductivity is large and it cannot be used. I understood.

FIG. 5 further shows that 11 mol% scandia (S
Scandia-stabilized zirconia (11Sc) containing c ₂ O ₃ )
SZ) electrolyte material and alumina (Al ₂ O ₃ ) 2
Scandia Stabilized Zirconia (11S
In comparison with the cSZ + 20% Al ₂ O ₃ ) electrolyte material, the data of mechanical properties showing the relationship between the bending strength [MPa] and the fracture probability [%] are shown. This test is J
This is due to the ceramic bending test method of ISR1601.

As a result, 11ScSZ electrolyte material and
Both ScSZ + 20% Al ₂ O ₃ electrolyte materials show a nearly linear proportional relationship between bending strength and fracture probability, but it is apparent that 11ScSZ + 20% containing alumina is mixed.
Al ₂ O ₃ electrolyte material does not contain alumina 11S
It can be seen that the bending strength is higher than that of the cSZ electrolyte material, and the fracture probability is low. Therefore, from this test data, Sc
It was confirmed that the bending strength was improved and the breaking strength was excellent by dispersing and mixing Al ₂ O ₃ in the SZ solid electrolyte material.

Table 1 shows the ScSZ solid electrolyte according to the present invention (containing Al ₂ O ₃ ), the YSZ solid electrolyte conventionally known, and the ScSZ electrolyte containing no Al ₂ O ₃ for comparison. In addition to the above-mentioned electrical conductivity characteristics, numerical comparisons of mechanical characteristics (bending strength, fracture toughness strength, Vickers hardness, coefficient of thermal expansion, crystal structure) between the above are shown numerically.

[0032]

[Table 1]

YSZ electrolytes with yttrium solid solution amounts of 3 mol% and 8 mol% are shown, and ScSZ electrolytes with scandia solid solution amounts of 8 mol% and 11 mol% (neither alumina is blended at all). And those containing 20% by weight of alumina).

As can be seen from this table, regarding the conductivity, the ScSZ electrolyte (which does not contain alumina) is superior to the YSZ electrolyte as already explained in FIGS. 2 to 4, but 20% alumina is added to the ScSZ electrolyte. weight%
It is shown that the compounding ratio also decreases to almost the same level as the YSZ electrolyte. The bending strength and Vickers hardness of the YSZ electrolyte are slightly higher than those of the ScSZ electrolyte (without alumina), but S
On the contrary, the result obtained by adding 20% by weight of alumina to the cSZ electrolyte was far superior to the YSZ electrolyte in bending strength, breaking strength and Vickers hardness. Also, the coefficient of thermal expansion is ScSZ electrolyte (alumina blend)
Has a smaller value than the YSZ electrolyte, which means that the amount of thermal expansion strain in a high temperature environment is small and it is less susceptible to thermal deformation.

Therefore, what can be said from this table is that Sc
It is not necessary to mix 20% by weight of alumina (Al ₂ O ₃ ) into the SZ electrolyte, but with a smaller amount, a conductivity higher than that of the YSZ electrolyte conventionally known can be obtained, and high temperature strength is high. It can be seen that the one having excellent mechanical properties can be obtained.

As a result, according to the alumina-dispersed high-strength ScSZ solid electrolyte of the present invention, higher strength than that of the conventional YSZ electrolyte can be obtained, and the plate thickness of the electrolyte plate can be reduced accordingly. As a result, the internal resistance of the material can be further reduced, and the electrical characteristics can be improved by ensuring high conductivity.

On the contrary, the alumina dispersion type high strength S of the present invention
If the plate thickness of the cSZ solid electrolyte is the same as that of the conventional YSZ electrolyte, the plate area can be increased due to the excellent mechanical strength, and a large capacity solid oxide fuel cell (SOF) can be obtained.
It is also compatible with C). Moreover, since the strength of the electrolyte plate can be secured, the reliability as a fuel cell is improved, and mechanical and thermal fatigue damage is less likely to occur, so that it can withstand long-term use.

In the above example, alumina (Al ₂ O ₃ ) was used as the high-strength composite material to be dispersed and mixed in the ScSZ electrolyte.
However, other materials such as mullite are applicable as the same purpose and material. Further, this high-strength composite material can be applied in various ways such as being dispersed and compounded in a fiber form.

[0039]

As shown in the various experimental examples above, the present invention has not only high electrical conductivity but also high mechanical strength by dispersing high strength composite material such as alumina in scandia-stabilized zirconia solid electrolyte material. It is possible to obtain a high solid electrolyte plate. Therefore, when the solid electrolyte material of the present invention is applied to a solid oxide fuel cell, many effects such as large capacity and large power generation efficiency can be achieved, and the industrial benefit is extremely high.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram in the case of manufacturing a composite material dispersion-strengthened solid electrolyte material according to the present invention as a solid electrolyte plate in a solid oxide fuel cell.

FIG. 2 Scandia-stabilized zirconia (S
It is the figure which showed the electric power generation comparison characteristic data of the cSZ) solid electrolyte material and the yttria-stabilized zirconia (YSZ) solid electrolyte material generally known conventionally.

FIG. 3 is a view showing data on temperature dependence of conductivity characteristics of ScSZ solid electrolyte material.

FIG. 4 is a diagram showing the relationship between the content of alumina (Al ₂ O ₃ ) contained in the ScSZ solid electrolyte material according to the present invention and the electrical conductivity.

FIG. 5 is a diagram showing mechanical property data showing the relationship between bending strength and fracture probability in comparison between the ScSZ solid electrolyte material according to the present invention in which alumina is not mixed and the ScSZ solid electrolyte material which is mixed with alumina.

FIG. 6 is a diagram showing an example of a single cell structure of a conventionally known flat plate type solid oxide fuel cell (SOFC) to which the composite material dispersion strengthened solid electrolyte material according to the present invention is applied.

7A is a diagram showing a schematic configuration of an external manifold type of the flat plate type fuel cell shown in FIG. 6, and FIG. 7B is a diagram showing a schematic configuration of an internal manifold type of the same.

Claims (3)

[Claims] 1. A composite dispersion-strengthened solid electrolyte material comprising a scandia-stabilized zirconia electrolyte material as a main component, and a high-strength composite material dispersed therein. 2. The composite material dispersion-strengthened solid electrolyte material according to claim 1, wherein the high-strength composite material is alumina or mullite. 3. The scandia-stabilized zirconia electrolyte material contains 8 to 15 mol% of scandia as a solid solution, and the high-strength composite material is mixed with 0.5 to 20 wt% of the scandia-stabilized zirconia electrolyte material. The composite material dispersion-strengthened solid electrolyte material according to claim 1, wherein