JP3128099B2 - Air electrode material for low temperature operation type solid 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 an air electrode for a low temperature operation type solid fuel cell.

[0002]

2. Description of the Related Art In recent years, interest has been growing in solid electrolyte fuel cells using oxygen ion conductors. In particular, from the viewpoint of effective use of energy, solid fuel cells have essentially high energy conversion efficiencies because they are not restricted by Carnot efficiency, and have excellent features such as better environmental protection. I have. As a solid electrolyte, YSZ (yttrium-stabilized zirconia) has conventionally been regarded as the most promising. However, it is necessary to operate at a high temperature of 1000 ° C. in order to obtain sufficient oxygen ion conductivity. Deterioration reactions and the like occur at the interface of the electrolyte, and the life of parts is greatly deteriorated, making it difficult to realize a highly reliable battery.

Therefore, development of a solid fuel cell that operates at a low temperature of about 800 ° C. is required. In order to obtain a sufficient oxygen ion conductivity during low-temperature operation, studies have been made on zirconia-scandium-based, ceria-based, and YSZ thinner layers.

[0004] In addition to the solid electrolyte, the problem of lowering the electrical conductivity of the air electrode arises in operating at a low temperature. As shown in FIG. 1, the air electrode 3 is porous and has a role of contacting the solid electrolyte 2, supplying oxygen gas thereto, and extracting current (reference numeral 1 is a fuel electrode). From the viewpoint of electrical connection, the electrical conductivity of the air electrode 3 needs to be as high as possible. On the other hand, from the viewpoint of gas supply to the solid electrolyte 2, it is as porous as possible, and this porous state needs to be stably maintained at the operating temperature.

Conventionally, La which has been studied as an air electrode is
_{In 0.8} Sr _0.2 MnO ₃ , the fine structure is kept stable even at an operating temperature of 1000 ° C., and the thermal expansion coefficient is 12.4 × 10 ⁻⁶ , which is 10.0 × 10 ^{−6 of} YSZ (yttrium-doped zirconia) as a solid electrolyte. Has almost the same value as
The drawback is that the electrical conductivity is as low as 100 S / cm.
When the operating temperature is lowered from 1000 ° C. to 800 ° C., the electric conductivity is further reduced to 90 S / cm.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to simultaneously satisfy two requirements of electrical characteristics and microstructure stability at operating temperatures required for a cathode for a low-temperature operation type solid fuel cell.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an air electrode material for a low temperature operation type solid fuel cell according to the present invention is an air electrode material forming an air electrode of a low temperature operation type solid fuel cell. Wherein the air electrode is a mixture of one selected from zirconia, alumina, and a lanthanoid pyrochlore and a copper oxide having a K ₂ NiF ₄ structure in a volume mixing ratio of 1: 9 to 7: 3. I do.

The air electrode material for a low-temperature operation type solid fuel cell of the present invention has excellent electrical conductivity and a K ₂ NiF ₄ structure perovskite type copper oxide having a thermal expansion coefficient substantially equal to that of the solid electrolyte. Dispersing a chemically inert oxide into the material prevents sintering at operating temperatures and maintains a porous state suitable for air supply.

[0009]

The operation of the present invention will be described below.

[0010] La _1.86 Sr _0.14 CuO ₄ , a kind of perovskite type copper oxide having a K ₂ NiF ₄ structure, is known as an oxide superconducting material, and is 10000 S / c at room temperature.
m and 1000 S / cm or more even at a high temperature of 800 ° C., and the electric conductivity is very high. However, among the perovskite oxides, the melting point is relatively low at 1300 ° C., and when the operating temperature is set at around 1000 to 800 ° C., each microcrystalline particle is fused, grain growth occurs, and sintering shrinks, so that the porosity increases. Quality structure is lost. Therefore, oxides such as alumina, zirconia, and pyrochlore, which are chemically inert to this oxide, are dispersed to form an oxide composite, which prevents sintering at operating temperatures and is suitable for supplying air. The state can be maintained for a long time.

[0011] Table 4 shows alumina, zirconia, pyrochlore and LaCuO as examples of copper oxide used in this embodiment.
₄ shows the average values of the thermal expansion coefficients of La _1.86 Sr _0.14 CuO ₄ at 25 to 1000 ° C. When these fine particles are mixed to form an oxide composite, the coefficient of thermal expansion is between the two values, and the value is substantially a proportional distribution value from the mixing volume ratio.
Therefore, it can be seen that the difference in thermal expansion from YSZ depends on the mixing ratio, but is almost the same as that of La _0.8 Sr _0.2 MnO ₃ which is a conventional air electrode material.

Here, since these inactive oxides are insulators, the mixing ratio with copper oxide, which is a good conductor, needs to be within a certain range. That is, the volume mixing ratio of copper oxide and one kind of oxide selected from alumina, zirconia, and pyrochlore is 1: 9 to 7: 3, as is clear from Table 1-2 in Example 1 described later. In this range, the copper oxide grain growth is suppressed, and the copper oxide fine particles are in contact with each other, so that they have high electric conductivity.

The above-mentioned copper oxide is represented by the general formula (Ln _2-x A _x ) _1-d Cu _{1 + d} O ₄ (where Ln is a lanthanoid element or yttrium, and A is divalent A metal element, 0.05 ≦ x ≦ 0.44 and −0.0
5 ≦ d ≦ 0.10). This is because it has good conductivity as described above. This is because if x and d deviate from the above ranges, conductivity may be reduced.

With the above configuration, it is possible to realize an air electrode material for a low-temperature operation type solid fuel cell which simultaneously satisfies the electrical characteristics and the stability of the microstructure at the operating temperature.

[0015]

Embodiments of the present invention will be described below. Note that, needless to say, the present invention is not limited to the following embodiments.

[0016]

EXAMPLE 1 In order to show the effect of the present invention, a test was conducted with a single cell having the structure shown in FIG. In the present invention, 1 is a fuel electrode, 2 is a solid electrolyte, and 3 is an air electrode. As a solid electrolyte, (ZrO ₂ ) _0.9 (Sc ₂ O ₃ ) _0.09 (Al ₂ O ₃ )
_An oxide having a composition of _0.01 and a fuel electrode of Ni-YS
Z and La _2-x Sr _x CuO ₄ + YSZ for the air electrode
Was used. Here, YSZ is stabilized zirconia and the composition is Y
_0.16 Zr _0.84 O ₂ . 30 vol. % ≦ ｛La
_1.86 Sr _0.14 CuO ₄ / (La _1.86 Sr _0.14 CuO ₄ + Y
SZ)｝ ≦ 90 vol. % Range, and 0.05 ≦ x
When ≦ 0.44, ΔLa _2-x Sr _x CuO ₄ / (La _2-x Sr _x
CuO ₄ + YSZ)｝ = 60 vol. Two types of experiments were performed under the condition of%.

A method for manufacturing a single cell used in this embodiment will be described below. First, a green sheet of a ceramic thin plate of a solid electrolyte is formed by a doctor blade method, and 1600 ° C.
Bake with. This is screen printed with N on the fuel electrode.
i-YSZ was applied and baked at 1400 ° C., after which the air electrode was applied and baked at 1000 ° C.

The thickness of the air electrode and fuel electrode in FIG. 1 is 0.1 m.
m, the thickness of the solid electrolyte was 3 mm, and a single cell of 20 mmφ was formed. In FIG. 2, the air electrode is La _1.86 Sr _0.14 CuO
₄ and the mixture ratio of YSZ is 40 vol. 5 shows current density-voltage characteristics of a single cell in a hydrogen-oxygen atmosphere at 800 ° C. under the condition of%. For comparison, only the air electrode of the above single cell is L
The characteristics of the cell with a _0.8 Sr _0.2 MnO ₃ are also shown.
Tables 1-1 and 1-2 show the relationship between the terminal voltage and the terminal voltage and the copper oxide composition at the air electrode, and the mixing ratio of the copper oxide and YSZ and the terminal voltage. Here, the terminal voltage is such that the current density is 1 A / cm ²
The hour value. When these air electrodes of the present invention were used, all exhibited better characteristics than the conventional cell using La _0.8 Sr _0.2 MnO ₃ as the air electrode.

[0019] The terminal voltage is a value at a current of 1 A / cm ² La _2-x Sr _x CuO ₄ / (YSZ + La _2-x Sr _x CuO ₄ ) = 60 vol.%

[0020] The terminal voltage is a value at a current of 1 A / cm ² Copper oxide: La _1.86 Sr _0.14 CuO ₄

[0021]

Embodiment 2 A single cell similar to that of Embodiment 1 was prepared by using only the material of the air electrode as alumina and Pr _2-x Ca _x CuO ₄ (0.05 ≦ x ≦
An experiment similar to that of Example 1 was performed in place of the composite of 0.44). As shown in Tables 2-1 and 2-2, almost in the same manner as in Example 1, good results were obtained in comparison with the conventional material La _0.8 Sr _0.2 MnO ₃ .

[0022] The terminal voltage is a value at a current of 1 A / cm ² Pr _2-x Ca _x CuO ₄ / (Al ₂ O ₃ + Pr _2-x Ca _x CuO ₄ ) = 60 vol.%

[0023] The terminal voltage is a value at a current of 1 A / cm ² Copper oxide: Pr _1.86 Ca _0.14 CuO ₄

[0024]

Example 3 A single cell similar to that of Example 1 was prepared by using only pyrochlore material (Nd ₂ Zr ₂ O ₇ ) and Nd _2-x Mg _x C
The same experiment as in Example 1 was performed instead of the composite of uO ₄ (0.05 ≦ x ≦ 0.44). As shown in Tables 3-1 and 3-2, almost in the same manner as in Example 1, the conventional material La
_In each case, good results were obtained as compared with _0.8 Sr _0.2 MnO ₃ .

[0025] The terminal voltage is a value at a current of 1 A / cm ^2. Nd _2-x Mg _x CuO ₄ / (Nd ₂ Zr ₂ O ₇ + Nd _2-x Mg _x CuO ₄ ) = 60 vol.%

[0026] The terminal voltage is a value at a current of 1 A / cm ² Copper oxide: Nd _1.86 Mg _0.14 CuO ₄

[0027] The average value of the coefficient of thermal expansion at 25 to 1000 ° C is shown.

[0028]

As described above, the interconnector of the solid oxide fuel cell is formed by dispersing a chemically inactive oxide in a perovskite type copper oxide having a K ₂ NiF ₄ structure. Thus, it was possible to prevent sintering at the operating temperature, maintain a porous state suitable for air supply, and succeed in obtaining an air electrode capable of suppressing electric resistance to a low level without impairing the efficiency of air supply to the electrolyte. . The present invention greatly contributes to high efficiency operation of a solid fuel cell.

[Brief description of the drawings]

FIG. 1 is a sectional view of a single cell used in an example.

FIG. 2 shows current-voltage characteristics of a single cell performed in Example 1.

[Explanation of symbols]

 1 fuel electrode 2 solid electrolyte 3 air electrode

Continuation of the front page (56) References JP-A-47-2967 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/86

Claims (2)

(57) [Claims] 1. An air electrode material forming an air electrode of a low temperature operation type solid fuel cell, wherein the air electrode is one selected from zirconia, alumina and lanthanoid pyrochlore, and copper oxide having a K ₂ NiF ₄ structure. Volume mixing ratio 1:
An air electrode material for a low-temperature operation type solid fuel cell, which is a mixture of 9 to 7: 3. 2. The method according to claim 1, wherein said copper oxide is (Ln _2-x A _x ) _1-d Cu
_{1 + d} O ₄ cold operation type solid fuel cell air electrode material according to claim 1, wherein the a. Here, Ln is a lanthanoid element or yttrium, A is a divalent metal element, and 0.05 ≦ x ≦ 0.44 and −0.05.
≤ d ≤ 0.10.