JPH07226209A - Air electrode material for solid fuel cell and solid fuel cell - Google Patents

Abstract

PURPOSE:To provide an air electrode material for a solid fuel cell simultaneously satisfying two requirements of electric performance and consistency of coefficient of thermal expansion with an electrolyte necessary for an air electrode of the solid fuel cell, and provide a solid fuel cell. CONSTITUTION:Material of an air electrode 3 is Pr1-xAxMnO3. Wherein A is an alkali earth metal element or Ce, and 0.05<=x<=0.4. Unconformity of thermal expansion is low compared with La0.8Sr0.2MnO3 conventionally used, but electric performance is almost equal to the conventional material. An electrode simultaneously satisfying the electric performance and consistency of electric characteristics with coefficient of thermal expansion is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air electrode material for a solid fuel cell, a solid fuel cell using the air electrode material, and more particularly to an air electrode material for a praseodymium-based solid fuel cell and a solid fuel cell.

[0002]

2. Description of the Related Art In recent years, solid electrolyte fuel cells using oxygen ion conductors have been gaining interest. In particular, from the viewpoint of effective use of energy, the solid fuel cell has essentially high energy conversion efficiency because it is not restricted by Carnot efficiency, and further has excellent characteristics such as good environmental protection is expected.

FIG. 1 schematically shows a cross section of a single cell (flat plate type) of a solid fuel cell. As a solid electrolyte, YSZ (yttrium-stabilized zirconia) is most promising for operation at 1000 ° C, but for low temperature operation at 800 ° C,
Studies have been conducted on thinning zirconia-scandium, ceria, and YSZ.

Table 2 shows the coefficients of thermal expansion of the substances currently most studied as solid fuel cell component materials. The thermal expansion coefficient of the solid electrolyte and that of the interconnector material, which are required to be completely dense, are almost the same. On the other hand, the fuel electrode Ni-YSZ and the air electrode La _0.8 Sr _0.2
MnO ₃ has a large coefficient of thermal expansion of about 24 to 40%,
The electrolyte is stressed by thermal expansion and contraction.

As the electrode material, La _1-x Sr _x MnO ₃ , which is a perovskite type manganese oxide, (x = 0.1
5-0.4) is the most studied. YSZ and La
_{Since 1-x} Sr _x MnO ₃ has a difference in thermal expansion, YSZ may be cracked through a temperature cycle between room temperature and operating temperature of 1000 to 800 ° C. Especially when assembling a cell using the air electrode as a support, the cross-sectional area of the air electrode becomes large, and the thermal expansion of the air electrode determines the thermal expansion of the cell.Therefore, the thermal expansion coefficients of the air electrode material and the solid electrolyte are the same. There must be. Further, even when a solid electrolyte is used as a support, one side of the cell is proportional to the mismatch between the electrolyte and the electrode due to the difference in thermal expansion.

Therefore, there is a demand for an air electrode whose electric conductivity is similar to that of manganese and whose thermal expansion coefficient is almost the same as that of YSZ which is a solid electrolyte.

Table 2 Thermal expansion coefficient of solid fuel cell material ────────────────────────────────── Material thermal expansion coefficient Part ───────────────────────────────── (ZrO ₂ ) _0.9 (Sc ₂ O ₃ ) _0.09 (Al ₂ O ₃ ) _0.01 10.2 × 10 ^-6 Solid electrolyte ───────────────────────────────── YSZ 10.0 Solid electrolyte ─── ────────────────────────────── La _0.8 Sr _0.2 MnO ₃ 12.4 Air electrode ─────────── ────────────────────── YSZ-Ni cermet (Ni: 60mol%) 13.0 Fuel electrode ─────────────── ────────────────── La _0.8 Sr _0.2 CrO ₃ 10.0 Interconnector ──────────────────────── ────────── Indicates the average value of the coefficient of thermal expansion at 25 to 1000 ° C.

[0008]

An object of the present invention is to provide an air electrode material for a solid fuel cell, which simultaneously satisfies the two requirements of the electric characteristics and the compatibility of the thermal expansion coefficient with the electrolyte required for the air electrode for the solid fuel cell. An object is to provide a solid fuel cell.

[0009]

In order to achieve the above object, an air electrode material for a solid fuel cell according to the present invention is the air electrode material for a solid fuel cell, wherein the air electrode material is Pr.
_1-x A _x air electrode material for a solid fuel cell which is a MnO _3. However, A is an alkaline earth metal element or a Ce element, and 0.05 ≦ x ≦ 0.4.

Further, the solid fuel cell according to the present invention is a solid fuel cell comprising an air electrode, a solid electrolyte and a fuel electrode, wherein the air electrode contains an air electrode material of Pr _1-x A _x MnO _3. It is characterized by However, A is an alkaline earth metal element or Ce element, and z is 0.05 ≦ x ≦ 0.4.

That is, the electrical conductivity of the conventional material La _{1 -x}
Pr _1-x A _x M, which is equivalent to Sr _x MnO ₃ (x = 0.15-0.4) and has a thermal expansion coefficient almost the same as that of the solid electrolyte.
nO ₃ (A: alkaline earth metal element or Ce element) is used.

The present invention will be described in more detail. The cathode material for a solid fuel cell according to the present invention comprises Pr _1-x A _x MnO ₃
Is. However, in the formula, A is an alkaline earth metal element or Ce, and x is 0.05 ≦ x ≦ 0.4.

In the above formula, A is an alkaline earth metal or C
It is e. In particular, Sr and Ca can be preferably used as the alkaline earth metal element, and Ce can also be preferably used in order to satisfy the lattice matching depending on the size of the ionic radius.

Further, x is from the point of conformity of the coefficient of thermal expansion,
As is clear from the examples described below, 0.05 ≦ x ≦ 0.4
Is.

The present invention also relates to a solid fuel cell, which uses the cathode material for a solid fuel cell as described above.

As the solid electrolyte, one having a coefficient of thermal expansion of about 10.0 × 10 ⁻⁶ can be used as described above. Such solid electrolyte, such as zirconium compound - Sunanjiumu compound - alumina solid electrolyte (e.g. _{(ZrO 2) 0.9 (Sc 2} O 3) 0.09 (A
1 ₂ ) ₃ ) _0.01 etc.), yttrium-scandium-zirconia-based (for example, YSZ) solid electrolyte, and the like.

As the fuel electrode, those conventionally used as fuel cells can be effectively used.

[0018]

The function of the present invention will be described below.

When Pr _1-x A _x MnO ₃ (A: alkaline earth metal element or Ce element) in which lanthanum of the air electrode is replaced by praseodymium was examined, the electric conductivity was almost the same as that of the conventional material, La coefficient of expansion of conventional material
_{It was} found that it is closer to YSZ, which is a solid electrolyte, than _1-x Sr _x MnO ₃ . With the above-described structure, it is possible to realize an air electrode material for a solid fuel cell that simultaneously satisfies two requirements of electrical characteristics and compatibility of thermal expansion coefficient with an electrolyte.

[0020]

EXAMPLES Examples of the present invention will be described below. The present invention is not particularly limited to the examples below.

[0021]

Example 1 In order to show the effect of the present invention, a test was conducted on a single cell having the structure shown in FIG. In FIG. 1, 1 is a fuel electrode, 2 is a solid electrolyte, and 3 is an air electrode. Also the air electrode,
The thickness of the fuel electrode is 0.1 mm, the thickness of the solid electrolyte is 0.3 mm, and the diameter is 20 mm. The solid electrolyte is
YSZ (Yttrium 8 mol%; Zr _0.84 Y
_0.16 O ₂ ) and Ni powder in the fuel electrode were dispersed in YSZ (yttrium 8 mol%) (Ni: 60 mol%;
Ni _0.6- (Zr _0.84 Y _0.16 O ₂ ) _0.4 ) and Pr _1-x Sr _x MnO ₃ were used for the air electrode.

Where x = 0.05, 0.1, 0.2,
Single cells were prepared with 0.3 and 0.4, respectively. The method for producing the single cell used in this example is shown below. First,
A green sheet of a ceramic thin plate of solid electrolyte is formed by the doctor blade method and baked at 1600 ° C.
Ni-YSZ was applied to the fuel electrode by screen printing and baked at 1400 ° C, and then the above air electrode was applied and baked at 1100 ° C.

Table 1-1 shows the test results of these single cells at 800 ° C. Here, the terminal voltage has a current density of 0.
It is a value at 2 A / cm ² . To measure the coefficient of thermal expansion, the cathode material was sintered into pellets at 1300 ° C and cut into rods.
Measurements were performed in air over the temperature range up to. Table 1-1 shows the dependence of the thermal expansion coefficient of the air electrode on the air electrode composition.
Here, the coefficient of thermal expansion is an average value from 25 to 800 ° C.

When the air electrodes of the present invention were used, all exhibited better characteristics than the cells using the conventional La _0.8 Sr _0.2 MnO ₃ as the air electrode. It can be seen that when the substitution amount of praseodymium (ratio of x) is 5 to 40%, the coefficient of thermal expansion is equal to or lower than that of the conventional material, and the compatibility with the electrolyte material is improved.

Table 1-1 Dependence of terminal voltage and coefficient of thermal expansion on air electrode composition in Example 1 ──────────────────────────── ─── Pr _1-x Sr _x MnO ₃ terminal voltage thermal expansion coefficient ────────────────────────────── Pr _0.95 Sr _0.05 MnO ₃ 0.22 (V) 9.3 × 10 ^-6 ────────────────────────────── Pr _0.90 Sr _0.10 MnO ₃ 0.24 9.4 ─ ───────────────────────────── Pr _0.80 Sr _0.20 MnO ₃ 0.28 9.5 ───────────── ───────────────── Pr _0.70 Sr _0.30 MnO ₃ 0.30 11.0 ───────────────────────── ───── Pr _0.60 Sr _0.40 MnO ₃ 0.32 12.0 ────────────────────────────── La _0.8 Sr _0.2 MnO ₃ ( Comparative example) 0.22 12.0 ───────────────────────────────

Terminal voltage: value at current 0.2 A / cm ² coefficient of thermal expansion: average value from room temperature to 800 ° C.

[0027]

Example 2 The same single cell as in Example 1 was used as a solid electrolyte instead of YSZ with (ZrO ₂ ) _0.9 (Sc ₂ O ₃ ).
An oxide having a composition of _0.09 (Al ₂ O ₃ ) _0.01 and an air electrode material of Pr _1-x Ca _x MnO ₃ (0.05 ≦ x ≦
0.3), the same experiment as in Example 1 was performed. The results are shown in Table 1-2. Here, the terminal voltage is a value when the current density is 1.0 A / cm ² . Almost the same results as in Example 1 were obtained as compared with the conventional material La _0.8 Sr _0.2 MnO ₃ .

Table 1-2 Dependence of Terminal Voltage and Coefficient of Thermal Expansion on Air Electrode Composition in Example 2 ──────────────────────────── ─── Pr _1-x Ca _x MnO ₃ terminal voltage coefficient of thermal expansion ────────────────────────────── Pr _0.95 Ca _0.05 MnO ₃ 0.20 (V) 9.3 × 10 ^-6 ────────────────────────────── Pr _0.90 Ca _0.10 MnO ₃ 0.22 9.3 ─ ───────────────────────────── Pr _0.80 Ca _0.20 MnO ₃ 0.24 9.4 ───────────── ───────────────── Pr _0.70 Ca _0.30 MnO ₃ 0.26 10.0 ───────────────────────── ───── Pr _0.60 Ca _0.40 MnO ₃ 0.26 11.0 ────────────────────────────── La _0.8 Sr _0.2 MnO ₃ ( Comparative example) 0.20 12.0 ───────────────────────────────

Terminal voltage: value at current 1.0 A / cm ² coefficient of thermal expansion: average value from room temperature to 800 ° C.

[0030]

[Embodiment 3] In the same single cell as in Embodiment 2, only the material of the air electrode is Pr _{1 -x} Ce _x MnO ₃ (0.05 ≦ x ≦ 0.
As 4), the same experiment as in Example 1 was performed. As shown in Table 1-3, the results were almost the same as in Example 1 and were good as compared with the conventional material La _0.8 Sr _0.2 MnO ₃ .

Table 1-3 Dependence of terminal voltage and thermal expansion coefficient on air electrode composition in Example 3 ──────────────────────────── ─── Pr _1-x Ce _x MnO ₃ terminal voltage thermal expansion coefficient ────────────────────────────── Pr _0.95 Ce _0.05 MnO ₃ 0.21 (V) 9.3 × 10 ^-6 ────────────────────────────── Pr _0.90 Ce _0.10 MnO ₃ 0.22 9.8 ─ ───────────────────────────── Pr _0.80 Ce _0.20 MnO ₃ 0.26 10.6 ───────────── ───────────────── Pr _0.70 Ce _0.30 MnO ₃ 0.28 11.4 ────────────────────────── ───── Pr _0.60 Ce _0.40 MnO ₃ 0.30 11.8 ──────────────────────────────

Terminal voltage: value at current 1.0 A / cm ² coefficient of thermal expansion: average value from room temperature to 800 ° C.

[0033]

As described above, by using Pr _1-x A _x MnO ₃ (A: alkaline earth metal element or Ce element) as the air electrode material of the solid electrolyte fuel cell, the thermal expansion coefficient The mismatch is lower than that of the conventional material, La _0.8 Sr _0.2 MnO ₃ , and the electric characteristics are almost the same as the conventional one, that is, the air electrode having the characteristics satisfying the matching of the electric characteristics and the thermal expansion coefficient at the same time is obtained. Was successful. The present invention makes a great contribution to high efficiency operation of a solid fuel cell.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Fuel electrode 2 Solid electrolyte 3 Air electrode

Claims (5)

[Claims] 1. An air electrode material for a solid fuel cell, wherein the air electrode material is Pr _1-x A _x MnO ₃ . However, A is an alkaline earth metal element or Ce element, and 0.05 ≦ x
≦ 0.4. 2. The alkaline earth metal element is Sr or C
The air material for a solid fuel cell according to claim 1, wherein the air material is a. 3. A solid fuel cell comprising an air electrode, a solid electrolyte and a fuel electrode, wherein the air electrode contains an air electrode material of Pr _1-x A _x MnO _3. . However, A is an alkaline earth metal element or C
e element and x is 0.05 ≦ x ≦ 0.4
Is. 4. The alkaline earth metal element is Sr or C.
The air material for a solid fuel cell according to claim 1, wherein the air material is a. 5. The solid fuel cell according to claim 3, wherein the solid electrolyte is a yttrium-scandium-zirconia system or a zirconium compound-scandium compound-alumina solid electrolyte.