JPH06150943A - Oxygen ion conductive material and solid fuel cell - Google Patents

Abstract

PURPOSE:To heighten ion conductivity, eliminate a structural modification between room temperature and operation temperature, and enable oxygen ion conductive material to be practically used as the solid electrolyte of a fuel cell by using an oxygen ion conductive material with fixed composition as the solid electrolyte CONSTITUTION:Oxygen ion conductive material having composition expressed by a formula (1-x-y)ZrO2-xSc2O3-yM2O3 (M is one kind selected out of In, Ga, Ti, V, Cr, Fe, Co, Mg, Ca, Zn, Sr, Ba; 0<x+y<0.16 and x>0, y>0) is used as solid electrolyte 2. LaMnO3 doped with Sr is used as an oxygen electrode 1, Ni-ZrO2 as a fuel electrode 3, and LaCrO3 as an interconnector 4. Thereby, conductivity becomes about four times comparing with that of Y2O3 stabilized ZrO3 (YSZ). Further, by stabilizing cubic crystal to room temperature structurally, mechanical strength against a heat cycle is strengthened, and it is possible to obtain material having small conductivity change with the lapse of time at high temperature.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an oxygen ion conductor and a solid electrolyte fuel cell.

[0002]

2. Description of the Related Art In recent years, interest in solid electrolyte fuel cells using oxygen ion conductors is increasing. Particularly, from the viewpoint of effective use of energy, solid fuel cells have essentially high energy conversion efficiency because they are not restricted by Carnot efficiency, and also have excellent features such as good environmental protection is expected. .

Y ₂ O ₃ -stabilized ZrO ₂ (YSZ), which is the most promising oxygen ion conductor as a solid electrolyte fuel cell electrolyte, has been operated at a high temperature of 1000 ° C. to obtain sufficient ionic conductivity. is necessary.

However, at such a high temperature, the life of parts is greatly deteriorated due to the reaction with the electrode interface, and the solid fuel cell is currently put into practical use. From this point of view, it is desired to lower the operating temperature, and therefore, the emergence of an ion conductive material higher than YSZ is desired.

Generally, in a zirconia-based oxygen ion conductor, the ionic conductivity tends to increase as the ionic radius of the dopant decreases. This is because as the ionic radius of the dopant approaches the ionic radius of Zr ⁴⁺ , the activation energy of oxygen ions that can move becomes smaller. Fact Z
It is known that the rO ₂ —Sc ₂ O ₃ system has the highest ionic conductivity in the zirconia system. However, as the dopant increases, the crystal structure changes from monoclinic to rhombohedral-cubic, and in the region where the ionic conductivity has the maximum value, the rhombohedron becomes stable at room temperature and the cubic crystal is not stabilized. Further, at 650 ° C. or higher, the structural phase transitions to cubic, causing destruction due to thermal cycles, and there are many problems in using it as a solid electrolyte material.

[0006]

The present invention has a higher ionic conductivity than YSZ, no structural transformation between room temperature and operating temperature, and can be used practically as a solid electrolyte for fuel cells. The present invention aims to provide a new oxygen ion conductor and a solid fuel cell.

[0007]

Means for Solving the Problems] Oxygen ions Shirubedentai of the present invention is (1-x-y) ZrO 2 -xSc 2 O 3 -yM 2 O
₃ (M is In, Ga, Ti, V, Cr, Fe, Co, M
one selected from g, Ca, Zn, Sr, and Ba; 0
<X + y <0.16 and x> 0, y> 0).

The solid fuel cell of the present invention is (1-x-
y) ZrO₂-XSc₂O₃-YM₂O ₃(M is In, G
a, Ti, V, Cr, Fe, Co, Mg, Ca, Zn,
One selected from Sr and Ba; 0 <x + y <0.1
6 and x> 0, y> 0) oxygen ion conductor
Is used as a solid electrolyte.

The oxygen ion conductor as described above can be obtained by an ordinary sintering method by a solid phase reaction.

[0010]

The function of the present invention will be described below together with the findings obtained in the present invention.

The inventor of the present invention firstly clarified the reason why the separation between the ZrO ₂ —Sc ₂ O ₃ type ion conductor and the electrode occurs when the ion conductor is used as a solid electrolyte in a fuel cell. I went. As a result, it was found that the peeling might be caused by the following reasons.

That is, the crystal structure changes as monoclinic-rhombohedral-cubic with the increase of the dopant, and the rhombohedron becomes stable at room temperature and the cubic crystal is not stabilized in the region where the ionic conductivity has the maximum value. . Further, at 650 ° C. or higher, the structure changes to a cubic crystal, and it is considered that the destruction (peeling) due to the thermal cycle is caused based on the difference in the coefficient of thermal expansion.

Therefore, the inventor of the present invention has repeatedly conducted many experiments and sought to find a means for preventing such phase transformation. However, the point that requires attention is that it is not enough to prevent the phase transformation, and it is possible to prevent the phase transformation and
This means that the ionic conductivity must be maintained higher than that of SZ.

In the course of conducting many experiments, the present inventor has found that when a subdopant is added in addition to Sc, a stable phase structure can be obtained and high ionic conductivity may be exhibited.

Then, after further experiments, Sc
It was found that a cubic crystal structure can be stably obtained by substituting a part of the element with a divalent or trivalent stable element.

However, even with such a sub-dopant, high conductivity may not be obtained in some cases, and when the reason for this is further sought, the total content of the main dopant Sc and the sub-dopant is one factor. Therefore, it was clarified that it was necessary to set the addition amount within a certain limited range, and the present invention was completed.

The present invention relates to (1-x-y) ZrO ₂ -xS.
_{c 2 O 3 -yM 2 O 3} (M is In, Ga, Ti, V, Cr,
One selected from Fe, Co, Mg, Ca, Zn, Sr, and Ba; 0 <x + y <0.16 and x> 0, y>
The material having the composition 0) is used.

That is, the ion conductor obtained by the present invention contains Sc as a main dopant. Since the ion radius of Sc is close to Zr, oxygen ions move more easily than YSZ. For this reason, it is possible to realize a remarkably large ionic conductivity at a low temperature as compared with YSZ.

In the present invention, a bi- or tri-valent stable subdopant is added. Due to such a subdopant, the ionic conductivity maintains the characteristic of almost Sc, and the crystal structure is stabilized to cubic crystal, and the crystal transformation does not appear at high temperature.

Further, in the present invention, 0 <x + y <0.16
And An ionic conductor having no phase transformation and high ionic conductivity can be obtained only by the addition amount within the limited range. That is, x + y> 0.16
If so, high ionic conductivity cannot be obtained. With the above-mentioned structure, a material having high ionic conductivity and strong mechanical strength against heat cycle (for example, peeling from the electrode does not occur) can be realized.

[0021]

EXAMPLES Examples of the present invention will be described below. Of course, the present invention is not limited to the following examples.

(Example 1) (1-x-y) ZrO ₂ -x
_{Sc 2 O 3 -yM 2 O 3} (M is In, Ga, Ti, V, C
One selected from r, Fe, Co, Mg, Ca, Zn, Sr, and Ba; 0 <x + y <0.16 and x> 0, y
> 0) with the chemical composition shown in Table 1, mixed well, and molded into a pellet having a diameter of 20 mm and a thickness of 2 mm, and baking the pellet at a temperature of 1620 ° C. for 60 hours in the air to prepare an ion conductor. did. After identifying the production phase of the sample by powder X-ray diffraction, the ionic conductivity was measured by an impedance meter.
After sweeping at a frequency of 10 Hz-1 MHz, impedance plotting was performed and measured.

In FIG. 1, 0.88ZrO ₂ -0.10Sc ₂ O
₃ shows the X-ray diffraction pattern at room temperature in the case of -0.02InO ₃ (Figure 1 (a)). The case of 0.88ZrO ₂ -0.12Sc ₂ O ₃ containing no subdopant is also shown (FIG. 1 (b)). Without a dopant, the rhombohedral phase is obtained as a single phase at room temperature. However, when the temperature is raised, the crystal transitions to cubic at around 650 ° C. However, it can be seen that the cubic crystal is stabilized by the addition of the subdopant.

FIG. 2 shows the temperature dependence of ionic conductivity.
0.88ZrO ₂ -0.12 without addition of In ₂ O ₃
In Sc ₂ O ₃ , the ionic conductivity changes discontinuously near the transition temperature along with the phase transition of the crystal structure (FIG. 2 (b)).
0.88ZrO ₂ -0.10Sc ₂ O with the addition of In ₂ O _3
In 3-0.02In ₂ O ₃ , the ionic conductivity almost satisfies the linear linear Allerius relation (FIG. 2A). In
6.1 × 10 ⁻² o at 800 ° C. even when doped with ₂ O ₃
It exhibits excellent ionic conductivity of hm ^-1 cm ^-1 .

The results of ionic conductivity at 800 ° C. measured in the same manner are shown in Table 1 below. 800 ℃ in either case
Shows high ion conductivity than the value 2xl0 ^-2 ohm ^-1 cm ^-l of YSZ in, also the crystal structure had been cubic stabilized to room temperature.

[0026]

[Table 1] Material Conductivity (ohm ^-1 cm ^-1 ) 0.88ZrO ₂ -0.115Sc ₂ O ₃ -0.005In ₂ O ₃ 5.1xl0 ^-2 0.88ZrO ₂ -0.10Sc ₂ O ₃ -0.02In ₂ O ₃ 6.1 x10 ^-2 0.88ZrO ₂ -0.08Sc ₂ O ₃ -0.04In ₂ O ₃ 5.7x10 ^-2 0.88ZrO ₂ -0.06Sc ₂ O ₃ -0.06In ₂ O ₃ 5.1x10 ^-2 0.88ZrO ₂ -0.04Sc ₂ O ₃ -0.08In ₂ O ₃ 4.8x10 ^-2 0.88ZrO ₂ -0.02Sc ₂ O ₃ -0.10In ₂ O ₃ 2.2x10 ^-2 (Example 2) (1-x-y) ZrO ₂ -xSc ₂ O ₃ -y
M ₂ O ₃ (M is In, Ga, Ti, V, Cr, Fe, C
1 selected from o, Mg, Ca, Zn, Sr, Ba
Species; 0 <x + y <0.16 and x> 0, y> 0)
20mmφ after mixing with the chemical composition shown in
The pellets having a thickness of 2 mm were fired in air at a temperature of 1620 ° C. for 60 hours to prepare an ion conductor. After identifying the produced phase of the sample by powder X-ray diffraction, the ionic conductivity was measured by an impedance meter at 10 Hz-1M.
After sweeping at a frequency of Hz, impedance plots were performed and measured. The rhombohedral phase did not appear in the crystal structure due to the subdopant In ₂ O _3, and the cubic crystal was stabilized up to room temperature. Table 3 shows the results of the ionic conductivity at 800 ° C. measured in the same manner as in Example 1. When x + y <0.16, the value of YSZ at 800 ° C. is ² × 10 ⁻² ohm ^−l cm.
^It showed higher ionic conductivity than ^-l .

[0027]

[Table 2] Material Conductivity (ohm ^-1 cm ^-1 ) 0.96ZrO ₂ -0.02Sc ₂ O ₃ -0.02In ₂ O ₃ 2.4xl0 ^-2 0.94ZrO ₂ -0.04Sc ₂ O ₃ -0.02In ₂ O ₃ 3.1 xl0 ^-2 0.92ZrO ₂ -0.06Sc ₂ O ₃ -0.02In ₂ O ₃ 4.2xl0 ^-2 0.90ZrO ₂ -0.08Sc ₂ O ₃ -0.02In ₂ O ₃ 7.4xl0 ^-2 0.88ZrO ₂ -0.10Sc ₂ O ₃ -0.02In ₂ O ₃ 6.1xl0 ^-2 0.86ZrO ₂ -0.12Sc ₂ O ₃ -0.02In ₂ O ₃ 4.2xl0 ^-2 0.84ZrO ₂ -0.14Sc ₂ O ₃ -0.02In ₂ O ₃ 2.1xl0 ^-2 0.80ZrO ₂ -0.18Sc ₂ O ₃ -0.02In ₂ O ₃ 1.2xl0 ^-2 (Example 3) (1-x-y) ZrO ₂ -xSc ₂ O ₃ -y
M ₂ O ₃ (M is In, Ga, Ti, V, Cr, Fe, C
1 selected from o, Mg, Ca, Zn, Sr, Ba
Species; 0 <x + y <0.16 and x> 0, y> 0)
20mmφ after mixing with the chemical composition shown in
The pellets having a thickness of 2 mm were fired in air at a temperature of 1620 ° C. for 60 hours to prepare an ion conductor. After identifying the produced phase of the sample by powder X-ray diffraction, the ionic conductivity was measured by an impedance meter at 10 Hz-1M.
After sweeping at a frequency of Hz, impedance plots were performed and measured. Subdopant M ₂ O ₃ (M is In,
Ga, Ti, V, Cr, Fe, Co, Mg, Ca, Z
The rhombohedral phase did not appear in the crystal structure, and the cubic crystal was stabilized up to room temperature by one kind selected from n, Sr, and Ba).

The results of ionic conductivity at 800 ° C. measured in the same manner as in Example 1 are shown in Table 3. x + y <0.16
Then, the value of YSZ at 800 ° C is 2 × 10 ^-2 ohm ^-1 c
It showed an ionic conductivity higher than m ^-1 .

[0029]

[Table 3] Material Conductivity (ohm^-1cm^-1) 0.90ZrO₂-0.08Sc₂O₃-0.02In₂O₃ 7.4x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Ga₂O₃ 3.1x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Ti₂O₃ 4.2x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02V₂O₃ 5.3x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Cr₂O₃ 6.1x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Fe₂O₃ 2.4x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Co₂O₃ 4.1x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Mg₂O₃ 3.4x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Ca₂O₃ 3.1x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Zn₂O₃ 4.2x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Sr₂O₃ 4.3x10^-2 0.90ZrO₂-0.08Sc₂O₃-0.02Ba₂O₃ 5.1x10^-2 (Embodiment 4) FIG. 3 is a single cell solid using the material of the present invention.
It is a figure which shows the structural example of a fuel cell. Battery configuration of this example
, 1 is an oxygen electrode, 2 is a solid electrolyte, 3 is a fuel cell
Poles 4 are interconnectors. As an oxygen electrode
LaMnO doped with Sr ₃Ni- for the fuel electrode
ZrO₂, The interconnector is LaCrO₃Using
It was The method for producing a single cell is as follows.

First, Sr-doped LaMnO ₃ is baked into a ceramics sintered body by a normal solid-phase reaction method, and a ceramics thin film of a solid electrolyte is formed thereon by a doctor blade method and baked at 1600 ° C.

The fuel electrode and interconnector were formed at 1300 ° C. and 120 ° C., respectively, by the single film sequential lamination forming method.
It is made by baking at 0 ° C. Next, the effect of this embodiment will be shown by a measurement example. In FIG. 3, the oxygen electrode 1 and the fuel electrode 3 have a thickness of 1 mm, the solid electrolyte 2 has a thickness of 0.1 mm, and the interconnector has a thickness of 1 mm.
A single cell of φ was formed. The material of the solid electrolyte 2 is 0.90
FIG. 4 shows the current (current density) -voltage characteristics of a single cell in a H ₂ -air atmosphere of 800 ° C. in the case of ZrO ₂ -0.08Sc ₂ O ₃ -0.02In ₂ O ₃ . The curve on the YSZ side is the characteristic of the conventional example shown for comparison.

In this way, the battery characteristic of this example was better than that of the conventional example, that is, the current-voltage characteristic was obtained. Similarly, when the material of the present invention was used as a solid electrolyte, all the battery characteristics were better than those of the conventional example.

[0033]

As described above, ZrO ₂ --Sc ₂ O
_{The 3} type has the highest ionic conductivity of the zirconia type, but could not be used as a material due to the instability of the crystal structure, but it is about 4 compared with the oxygen ion conductor YSZ which is conventionally used due to the devise of the second dopant. We have succeeded in obtaining a material that has double the conductivity and structurally stabilizes the cubic crystal to room temperature and has a high mechanical strength against thermal cycling and a small change in conductivity with time at high temperatures.

The present invention also makes a great contribution to the low temperature operation of the solid fuel cell.

[Brief description of drawings]

FIG. 1 (a) 0.88ZrO ₂ −0. 10 Sc ₂ O ₃ −
0.02In ₂ O ₃ (b) X-ray diffraction pattern of 0.88ZrO ₂ -0.12Sc ₂ O _3.

FIG. 2 (a) 0.88ZrO ₂ −0.10Sc ₂ O ₃ −
Ion conductivity of _{0.02In 2 O 3 (b) 0.88ZrO} 2 -0.12Sc 2 O 3.

FIG. 3 is a configuration diagram of a single-cell solid fuel cell.

FIG. 4 is a current-voltage characteristic diagram of a single cell.

Claims (2)

[Claims] [Claim 1] (1-x-y) ZrO 2 -xSc 2 O 3 -
yM ₂ O ₃ (M is In, Ga, Ti, V, Cr, Fe, C
1 selected from o, Mg, Ca, Zn, Sr, Ba
Seed; 0 <x + y <0.16 and x> 0, y> 0). Wherein (1-x-y) ZrO 2 -xSc 2 O 3 -
yM ₂ O ₃ (M is In, Ga, Ti, V, Cr, Fe, C
1 selected from o, Mg, Ca, Zn, Sr, Ba
Seed; a solid fuel cell using an oxygen ion conductor having a composition of 0 <x + y <0.16 and x> 0, y> 0) as a solid electrolyte.