JP2002151091A - Air electrode material for alkaline earth-added nickel- iron perovskite type low-temperature operating solid fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air electrode material for alkaline earth-added nickel- iron perovskite type low-temperature operating solid fuel cell, which simultaneously satisfies 2 requirements of electric properties and the matching ability of a coefficient of thermal expansion with an electrolyte that are required of an air electrode for a solid fuel cell operating at a temperature of from 700 deg.C down to 600 deg.C. SOLUTION: For the air electrode material represented by the formula, Ln1-YAYNi1-XFeXO3, (wherein, Ln is an element selected from among La, Pr, Nd and Sm, and A is an element selected from among Sr, Ba and Ca), the compositional range thereof falls within X-0.2<=Y<=X-0.4, and 0.55<=X<=0.90. The material has good electrode activity at about 650 deg.C and is excellent in electron conductivity compared with a conventional material, La0.8Sr0.2MnO3 and has almost the same coefficient of thermal expansion as the conventional material.

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 low-temperature solid-state fuel cell operated with an alkaline earth-added nickel-iron system perovskite.

[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 the Carnot efficiency, and have excellent features such as better environmental protection. .

FIG. 3 schematically shows a cross section of a single cell (tube type) of a solid fuel cell which has been studied most recently in recent years.
Such a tube battery forms a solid electrolyte 2 on the outer wall of a hollow cylindrical porous air electrode substrate 1 and
It has a structure in which a fuel electrode 3 is formed on the outside. Then, power is generated by passing oxygen through the hollow portion of the cylindrical air electrode substrate 1 and passing hydrogen outside the single cell. Reference numeral 4 denotes an interconnector for connecting single cells.

YSZ (yttrium-stabilized zirconia) is regarded as the most promising solid electrolyte for fuel cells as described above. As the electrode material, La _0.8 Sr _0.2 MnO ₃ , which is a perovskite-type manganese-based oxide, has been studied most frequently.

[0005] This tube type cell uses an air electrode as a porous substrate, on which an electrolyte, a fuel electrode and an interconnector are arranged. This method has the advantage that it is easy to build a durable cell and that gas sealing is easy.On the other hand, the main parts are lanthanum-based oxides, so the material cost is high, and the ceramics have complicated shapes, so the manufacturing cost is high. It is also difficult to reduce.

The above cells are designed on the assumption that they operate at around 1000.degree. If the operating temperature can be reduced to about 650 ° C., corrosion of heat-resistant alloys and the like does not occur, and thus these metals can be used for interconnectors, manifolds for accommodating cells, and the like. In this case, a flat cell having a large interconnector portion is suitable.

FIG. 4A and FIG. 4B are schematic diagrams of this. This is a fuel electrode supporting flat plate type cell using Ni-YSZ as a fuel electrode as a support (substrate). That is, the single cell has a structure in which the solid electrolyte 2 is stacked on the fuel electrode substrate 3 and the air electrode 1 is further stacked on the solid electrolyte 2 (see FIG. 4A). By supplying hydrogen and oxygen from both sides of the fuel electrode 3 and the air electrode 1, respectively,
Generate electricity. For interconnecting the single cells C, a metal interconnector 4 having a fuel supply passage 41 and / or an oxygen supply passage 42 is laminated and used (see FIG. 4B). In the figure, 5 is a current collecting mesh, and 6 is a gas seal.

[0008] In such a structure, it is relatively easy to make the solid electrolyte into a thin and dense film, and the conductivity is high.
The main structure is a low-cost fuel electrode. Therefore, it is easy to reduce the cost and the operating temperature.

[0009] However, when the operating temperature is reduced, the conductivity of the electrolyte constituting the cell and the activity of the electrodes are reduced, so that the output voltage of the cell is reduced. Therefore, it is necessary to solve these problems to reduce the operating temperature.

As for the electrolyte, a zirconia-based Sc-added material having high conductivity even at a low temperature (for example, SASZ (0.89ZrO ₂ -0.104Sc ₂ O)
₃ -0.006Al ₂ O _3)), or (La-Sr)
(Ga-Mg) can be accommodated by the use of O ₃ system. Regarding the electrode, it is possible to improve the electrode performance by using a fine powder for the electrode.

However, there is a limit to the size of the miniaturized electrode because sintering is likely to proceed during the cell fabrication stage. Therefore, development of a material having high electrode activity is indispensable. Particularly in the case of an air electrode, since the electrode activity is rapidly reduced by lowering the temperature, development of a material having excellent electrode characteristics is required. Here, the high electrode characteristics means that a large current can flow even with a small decrease in voltage.

In addition, a high electron conductivity is required in order to suppress the current collection loss from the electrode to the interconnector. The coefficient of thermal expansion between the air electrode substrate and the electrolyte must be as close as possible. This is because stress may be applied to the interface between the electrolyte and the air electrode substrate through a temperature cycle between room temperature and operating temperature, and the electrolyte may be cracked.

The present invention provides an alkaline earth which simultaneously satisfies the two requirements of the electrical characteristics and the coexistence with the electrolyte in the coefficient of thermal expansion required for a cathode for a solid fuel cell operating at 700 ° C. to 600 ° C. An object of the present invention is to provide an air electrode material for an added nickel-iron-based perovskite-type low-temperature operating solid fuel cell.

[0014]

In order to solve the above-mentioned problems, an air electrode material for a low-temperature solid-state fuel cell of the present invention, which is a nickel-iron-based perovskite-type perovskite, is provided with a solid electrolyte and an adjoining electrolyte. Fuel cell having a porous air electrode and a fuel electrode, and an interconnector for electrically connecting them, and converting a chemical reaction between a fuel gas and air or oxygen gas into electric energy Air electrode material, Ln _1-Y A _Y Ni
_1-X Fe _X O ₃ (Ln is any one of La, Pr, Nd, Sm or two or more elements selected from La, Pr, Nd, Sm, A is Sr, Ba, Ca, or two or more elements selected from Sr, Ba, and Ca), and the composition range is X-0.2
≦ Y ≦ X−0.4 and 0.55 ≦ X ≦ 0.90.

According to the present invention, Ln _{1-YA Y} Ni _1-x Fe _x
O ₃ (Ln is one or more elements selected from La, Pr, Nd and Sm; A is one or more elements selected from Sr, Ba and Ca; X and Y have a composition range of X-0. 2 ≦ Y ≦ X-
0.4 and 0.55 ≦ X ≦ 0.90. By using the composition range described above in FIG. 1 for the air electrode, it has good electrode activity around 650 ° C. and has excellent electron conductivity as compared with the conventional material La _0.8 Sr _0.2 MnO _3. This has the advantage that the thermal expansion coefficient has substantially the same value as that of the conventional material.

[0016]

The operation of the present invention will be described below.

Table 1 shows the coefficients of thermal expansion of the materials currently most frequently studied as constituent materials of solid fuel cells. The solid electrolyte, which requires complete denseness, and the interconnector material have almost the same thermal expansion coefficient. On the other hand, the fuel electrode Ni-YSZ and the air electrode La _0.8 Sr _0.2 M
nO ₃ has a large coefficient of thermal expansion of about 20-30%,
This degree of mismatch is considered to be acceptable. This is because the fuel electrode and the air electrode are porous, so that the difference in thermal expansion is absorbed to some extent even if the coefficient of thermal expansion is different from that of the electrolyte.

In this case, the air electrode, Ln _1-Y A _Y Ni _1-X F
e _X O ₃ (Ln is 1 selected from La, Pr, Nd and Sm)
One or more elements; A is one or more elements selected from Sr, Ba, Ca; composition range is X-0.2 ≦ Y ≦ X-0.4
And 0.55 ≦ X ≦ 0.90), the electrical conductivity and electrode activity at around 650 ° C. are superior to those of the conventional material La _0.8 Sr _0.2 MnO ₃ , and the thermal expansion coefficient is It turned out to be almost equivalent to the material. When Ln or A is a plurality of elements, X and Y indicate the total amount of the plurality of elements.

The composition range is, in particular, X−0.25 ≦ Y ≦
It is preferable that X−0.35 and 0.55 ≦ X ≦ 0.85. This is because in the case of the above composition range, the thermal expansion coefficient is almost the same as the conventional one, and the electric conductivity and the electrode activity show particularly good values.

From the above, an alkaline-earth-added nickel-iron-based perovskite-type air electrode material for a low-temperature operating solid fuel cell which simultaneously satisfies the two requirements of the compatibility with the electrolyte in the electrical characteristics and the coefficient of thermal expansion. By using the air electrode, a solid oxide fuel cell operating at around 650 ° C. can be realized.

[0021]

[Table 1]

[0022]

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

[0023]

EXAMPLE 1 In order to show the effect of the present invention, a test was performed on a single cell having the structure shown in FIG. 2A using the cell measurement diameter shown in FIG. 2B. 2a and 2b, 1 is an air electrode,
2 is a solid electrolyte, 3 is a fuel electrode, 5 is a current collector mesh made of platinum, 6 is a gas seal, 7 is a platinum terminal, and 8 is an alumina tube. The thickness of the air electrode and the fuel electrode is 0.5 mm, the diameter is 6 mm, the thickness of the solid electrolyte is 0.1 mm, and the size is 22 mm.
mm square.

The solid electrolyte is SASZ (0.89 ZrO
_Two-0.104Sc_TwoO_Three-0.006Al_TwoO_Three), Fuel
Ni-YSZ (Ni: 60 wt%, 0.92Z)
rO _Two-0.08Y_TwoO_Three: 40 wt%) and air
La on the pole_1-YSr_YNi_1-XFe_XO_Three, ｛(X, Y) =
(0.55, 0.15), (0.90, 0.50),
(0.90, 0.70), (0.80, 0.50),
(0.60, 0.30), (0.55, 0.35)}
Using.

The numbers of these cells are associated with FIG. 1 showing the composition range of the present invention, and the cells {1-1 to 1-6 (1 to 6 in FIG. 1-6: the same applies to the following examples). In addition, the cell using the conventional La _0.8 Sr _0.2 MnO ₃ as a comparative example to the air electrode and the cell # 0. In the figure, the range shown on the outside is the range of the present invention, and the range on the inside shows the preferred range in the present invention.

The method of manufacturing the single cell used in the present embodiment will be described below. First, the solid electrolyte 2 was prepared by the doctor blade method.
Green sheet of ceramic thin plate of 1600
Bake at ℃. Then, Ni-YSZ was applied as the fuel electrode 3 and baked at 1300 ° C., and then the air electrode 1 was applied to the opposite surface of the fuel electrode 3 and baked at 750 ° C. Table 2 shows the test results of this single cell at 650 ° C. Here, the terminal voltage is a value at a current density of 200 mA / cm ² , and the higher the terminal voltage, the better the characteristics.

For the measurement of the coefficient of thermal expansion, the material of the air electrode was 12
What was sintered into pellets at 50 ° C was cut into rods,
It measured from room temperature to 700 degreeC in air with a thermal expansion measuring device. Table 2 shows the composition dependence of the coefficient of thermal expansion of the air electrode. Here, the coefficient of thermal expansion is an average value up to 25-700 ° C.

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.

[0029]

[Table 2]

[0030]

Example 2 In the single cell as in Example 1, the material of the air electrode _{La 1-Y Ba Y Ni 1} -X Fe X O 3, {(X, Y)
= (0.55, 0.15), (0.90, 0.50),
(0.90, 0.70), (0.80, 0.50),
The same experiment as in Example 1 was performed in place of (0.60, 0.30), (0.55, 0.35)}. Table 3 shows the results. The numbers of these cells were set as cells # 2-1 to # 2-7 in association with the composition range diagram (FIG. 1). Almost in the same manner as in Example 1, the conventional material La _0.8 Sr _0.2 MnO
_In all cases, better results were obtained.

[0031]

[Table 3]

[0032]

Embodiment 3 A single cell similar to that of Embodiment 1 was prepared by changing only the material of the air electrode to La _{1 -Y} Ca _Y Ni _{1 -X} Fe _X O ₃ , ｛(X, Y) =
(0.55, 0.15), (0.90, 0.50),
(0.90, 0.70), (0.80, 0.50),
The same experiment as in Example 1 was performed instead of (0.60, 0.30), (0.55, 0.35)}. The numbers of these cells are associated with the composition range diagram (FIG. 1), and the cells # 3-1
~ Cell # 3-7. As shown in Table 4, 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 .

[0033]

Example 4 The unit cells as in Example 1 only material of the air electrode _{La 0.5 Sr 0.3 Ca 0.1 Ba 0.1} Ni 0.2 Fe 0.8 O 3
An experiment similar to that of Example 1 was performed in place of the above. Cell in Table 4
As shown in 4-1, 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 .

[0034]

[Table 4]

[0035]

Fifth Embodiment In a single cell similar to the first embodiment, the material of the air electrode is Ln _0.5 Sr _0.5 Ni _0.2 Fe _0.8 O ₃ , (Ln =
Pr, Nd, Sm) or La _0.2 pr _0.1 Nd _0.1 S
The same experiment as in Example 1 was performed instead of m _0.1 Sr _0.5 Ni _0.2 Fe _0.8 O ₃ . Table 5 shows the results in cells # 5-1 to # 5-4. In almost 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 .

[0036]

[Table 5]

[0037]

As described above, according to the present invention, the air electrode material of the solid electrolyte fuel cell _{Ln 1-Y A Y Ni 1} -X Fe X O 3 (Ln is one selected La, Pr, Nd, from Sm The above elements;
A is one or more elements selected from Sr, Ba and Ca; composition range; X−0.2 ≦ Y ≦ X−0.4 and 0.55
≦ X ≦ 0.90) With, superior to La _0.8 Sr _0.2 MnO ₃ electric characteristics is a conventional material even at 650 ° C., thermal expansion coefficient to obtain an air electrode is substantially equal to the conventional Successful. The present invention makes a great contribution to reducing the cost of a solid fuel cell.

[Brief description of the drawings]

FIG. 1 is a view showing a composition range of the present invention.

FIG. 2a is a plan view of a single cell of a fuel cell used in an example.

FIG. 2B is a schematic structural diagram of a cell measurement system used in the example.

FIG. 3 is a schematic structural view of a tubular fuel cell.

FIG. 4a is a schematic structural diagram of a single cell of a flat plate type low temperature operation fuel cell.

FIG. 4b is a schematic structural view of a flat plate type low temperature operation fuel cell.

[Explanation of symbols]

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

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yoji Sakurai 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 4G030 AA08 AA09 AA10 AA11 AA13 AA27 AA29 BA01 BA02 CA01 CA09 5H018 AA06 AS03 EE13 HH05 5H026 AA06

Claims (2)

[Claims] A cell comprising a solid electrolyte, a porous air electrode and a fuel electrode provided adjacent to the solid electrolyte, and an interconnector for electrically connecting the cells to each other. the reaction with an air electrode material for solid fuel cell of the solid fuel cell for converting into electric _{energy, Ln 1-Y a Y Ni} 1-X Fe X O 3 (Ln is La, Pr,
Any one of Nd, Sm or La, Pr, Nd, S
m is two or more elements selected from m, A is Sr,
Ba, Ca, or two or more elements selected from Sr, Ba, Ca), and the composition range is X-0.2 ≦ Y ≦ X-0.4. And 0.55
An air electrode material for a low-temperature solid-state fuel cell operating at low temperature, wherein nickel-iron-based perovskite is added, wherein ≦ X ≦ 0.90. 2. The composition range of X−0.25 ≦ Y ≦ X−
3. The alkaline earth-added nickel according to claim 2, wherein 0.35 and 0.55 ≦ X ≦ 0.85.
Air electrode material for iron-based perovskite-type low-temperature operating solid fuel cells.