JP3414657B2 - Air electrode materials for nickel-iron based perovskite solid fuel cells - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-based perovskite-type solid fuel cell air electrode material, and in particular, an air electrode material capable of improving the reliability and the power generation efficiency of this type of fuel cell. Regarding

[0002]

2. Description of the Related Art A fuel cell is a type of gas cell that uses a fuel such as oxygen or air for the cathode and hydrogen or hydrocarbon for the anode and supplies these reactants from the outside to produce a product (H ₂
It is a battery that can be used continuously for a long time by sequentially removing O or CO ₂ ) to the outside. From the viewpoint of effective use of energy, solid fuel cells have inherently high energy conversion efficiency because they are not restricted by Carnot efficiency, and have excellent characteristics such as good environmental protection. ing.

Among these fuel cells, a solid electrolyte fuel cell using a solid electrolyte, which can be reduced in size and weight, has been particularly studied in recent years, and in particular, a solid electrolyte fuel cell using an oxygen ion conductor is used. Interest is increasing.

A tube type single cell, which is an example of a typical solid oxide fuel cell, has a structure schematically shown in FIG. This tube type single cell has a structure in which an air electrode 1 is a cylindrical porous substrate, and a solid electrolyte 2, a fuel electrode 3, and an interconnector 4 for connecting a large number of cells to each other are arranged thereon. . Using this structure has advantages such as easy assembly of a durable cell and easy gas sealing, but the drawback is that the path of current flowing inside the air electrode is long.

[0005]

As the solid electrolyte 2, YSZ (yttrium-stabilized zirconia) or SAS is used.
Z (scandium aluminum stabilized zirconia) is the most promising. The material of the air electrode 1 is La _0.8 Sr _0.2 MnO which is a perovskite type manganese oxide.
₃ are being considered. Because this material has low electrical conductivity,
The resistance loss in this portion is large, which causes a decrease in the power generation efficiency of the cell. Therefore, an air electrode material having high electron conductivity is required in order to increase power generation efficiency.

Generally, the solid oxide fuel cell has 100
High temperature operation of 0 ° C is required. This is because the characteristics of the air electrode, the fuel electrode, and the solid electrolyte do not have sufficient power generation efficiency at temperatures lower than 1000 ° C. However, at such a high temperature, the power generation efficiency is lowered due to, for example, the sintering of the fuel electrode, etc., and therefore the practical application is delayed.
From this point of view, it is desired to lower the operating temperature to about 800 ^° C.

Various measures are required to lower the operating temperature, but in particular, as the air electrode material, it is required to improve the conductivity, electric activity and the like of the perovskite type oxide material which has been studied so far. ing. Among the perovskite oxides, La (Sr) is used as a material having high electron conductivity.
CoO ₃ is known, but its coefficient of thermal expansion is twice as high as that of YSZ (yttrium-stabilized zirconia), which is an oxide electrolyte, so problems such as peeling occur at the interface with the electrolyte and it operates. There was a problem that the reliability of time was not obtained.

That is, the air electrode material is Y which is an electrolyte.
It is required to have a thermal expansion coefficient as close as possible to that of SZ or SASZ. This is because stress may be applied to the interface between the YSZ and the air electrode substrate due to the temperature cycle between the room temperature and the operating temperature, and the YSZ may be cracked.

As described above, the tube type fuel cell needs to solve the problems of reliability such as peeling due to thermal cycles during operation and stop, and low power generation efficiency due to resistance loss. . Therefore, YSZ which is a solid electrolyte
Alternatively, there is a demand for an air electrode material which has a thermal expansion coefficient close to SASZ and which is excellent in electrical conductivity without resistance loss.

The present invention is an air which simultaneously satisfies the two requirements required for an air electrode for a solid fuel cell, that is, the compatibility of the coefficient of thermal expansion with that of an electrolyte and the excellent electrical conductivity characteristics. The purpose is to provide polar materials.

[0011]

The air electrode material for a nickel-iron based solid fuel cell according to the first aspect of the present invention comprises a solid electrolyte and a porous air electrode and fuel electrode provided adjacent to the solid electrolyte. And an interconnector for electrically connecting the cells, wherein the air electrode material of a solid fuel cell converts a chemical reaction of fuel gas and air or oxygen gas into electric energy, wherein the air electrode is LnN
_{i 1-x Fe x O 3} , (Ln: rare earth element) or YNi
_It has a composition represented by _1-x Fe _x O ₃ and x is 0.30.
˜0.60.

The air electrode material for a nickel-based solid fuel cell, which is the second invention of the present invention, has a conventional electron conductivity of La.
_0.8 Sr _0.2 MnO ₃ superior _{to, LnNi 1-x Fe x O} 3 where and thermal expansion coefficient with almost the same value as the solid electrolyte, (L
(n: rare earth element) or YNi _1-x Fex O ₃ and _{x in} the above formula is in the range of 0.4 to 0.55, so that it has improved electrical characteristics and is solid. The two requirements of having a coefficient of thermal expansion that matches that of the electrolyte can be satisfied at the same time.

In the LaNi _1-x Fe _x O ₃ system material used as the air electrode for the nickel-iron system perovskite type solid fuel cell of the third invention of the present invention, the Ln is L
Any one of a, Pr, Nd, Sm, or La,
It is a nickel-iron-based perovskite solid fuel cell air electrode material composed of two or more elements selected from Pr, Nd, Sm, and Ce.

Solid electrolytes and electrolytes required to have sufficient compactness
The thermal expansion coefficients of the connector connectors are almost the same.
On the other hand, the fuel electrode Ni-YSZ and the air electrode
La _0.8Sr_0.2MnO₃Is about 20-80% thermal expansion
Although the coefficient is large, we think that this degree of inconsistency is acceptable.
To be This is because the fuel electrode and air electrode are porous,
Even if the expansion coefficient is different from that of the electrolyte, the difference in thermal expansion is absorbed to some extent.
It depends on being collected.

Further, as an air electrode, LnNi _1-x Fe is used.
_{When x} O ₃ and (Ln: rare earth element) were examined,
x is in the range of 0.3 to 0.6, more preferably 0.4 to
It was found that in the range of 0.55, the electric conductivity was superior to that of the conventional material and the coefficient of thermal expansion was almost the same as that of the conventional material. With the above-described structure, it is possible to realize a nickel-based perovskite solid fuel cell air electrode material that simultaneously satisfies two requirements such as electrical characteristics and thermal expansion coefficient matching with the electrolyte.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. Of course, the present invention is not limited to the following examples.

Generally, in the solid oxide fuel cell, as described above, a large number of tube type single cells having a schematic structure as shown in FIG. 1 are combined. Air or oxygen (represented by O2 in the figure) that is a reaction gas flows inside the electrically conductive air electrode of the tube type single cell, and hydrogen or hydrocarbon that is a reaction gas is present around the fuel electrode on the outermost surface of the single cell. (Displayed as H2 in FIG. 1) flows. The interconnector 4 internally connects the single cells.

The single cell having the above structure is not necessarily suitable for comparing and examining the characteristics as a single cell by changing the material of the air electrode. In the present invention, a simple unit cell having a structure shown in FIGS. 2 and 3 was used for the test, and a practical unit cell for the selected material was also tested.

Various embodiments in which the air electrode material is selected using a simple type single cell will be described below. Table 1 shows the thermal expansion coefficients of various materials used in conventional single cells.

[0020]

[Table 1]

[0021]

[Embodiment] [Embodiment 1] In order to show the effect of the present invention, FIG.
The test was conducted on a simple unit cell having the structure shown in FIG. 2 is a plan view of the single cell, FIG. 3 is a sectional view,
In the figure, 1 is an air electrode, 2 is a solid electrolyte, 3 is a fuel electrode, 5 is a platinum mesh for current collection, 6 is a gold electrode, and 7 is a gas seal.

In this simple unit cell, the thickness of the air electrode 1 and the fuel electrode 3 is 0.5 mm, and the thickness of the solid electrolyte 2 is 0.
The diameter was 2 mm and the diameter was 20 mm. The solid electrolyte is SAS
Z (0.89ZrO ₂ -0.105 ScO ₃ -0.005
Al ₂ O ₃ ) and Ni-YSZ (Ni: 60 m) on the fuel electrode.
ol%), and for the cathode x = 0.3, 0.4,
LnNi ranging _{0.5,0.6 1-x Fe x O 3} ( Sample N
o. 1 to 5) were used.

A method of manufacturing the single cell used in this example is shown below. First, the solid electrolyte 2 by the doctor blade method
Was formed into a green sheet of a ceramic thin plate and was fired at 1400 ° C. in air. Ni-YSZ was applied to this as a fuel electrode 3 and fired at 1200 ° C. in air, and then the air electrode 1 was applied to the opposite side of the fuel electrode 3 and baked at 1000 ° C. That is, the air electrode 1 and the fuel electrode 2 are formed on the front and back surfaces of the solid electrolyte 2, the air electrode 1 and the fuel electrode 3 are covered with a platinum mesh 5 for current collection, and the platinum terminal 6 is placed on the self-collecting mesh 5 for current collection. After connecting, oxygen was supplied to the air electrode 1 and hydrogen was supplied to the fuel electrode 3, and the terminal voltage was measured.

Table 2 shows the test results of this single cell at 800 ° C. Here, the terminal voltage has a current density of 1.0 A / cm.
^{At 2} o'clock, the higher this terminal voltage, the better the characteristics as a fuel cell.

In order to measure the characteristics of the air electrode material, in the present embodiment for studying the air electrode material, in order to form a perovskite oxide, powder (LaO, NiO, Fe) is formed.
₂ O ₃ ) is molded and calcined, then 1250 ° C. to 14 ° C.
The pellet was used after firing at 00 ° C.

The coefficient of thermal expansion was measured by cutting out a pellet-shaped sintered body into a rod and measuring the coefficient of thermal expansion in the air from room temperature to 800 ° C. Table 2 shows the compositional dependence of the thermal expansion coefficient of the air electrode. Here, the coefficient of thermal expansion is 25
Average value up to 800 ° C.

The LaNi _1-x Fe x O ₃ based material of the present invention were all compared with conventional La _0.8 Sr _{0. 2} MnO ₃ material showed good thermal expansion characteristics close to that of the solid electrolyte . That is, the YSZ used as a solid electrolyte whereas a _{^{10x10 -6 / K, La 0.8 Sr}} 0.2 MnO 3 of the conventional air electrode material is 12x10 ^-6 / K,
There is a difference of 20% in expansion, and this difference in expansion is a cause of deterioration in reliability such as damage.

On the contrary, in Table 2, No. In the composition formula shown in _{1~4 LaNi 1-x Fe x O} 3, x = 0.3~0.
When materials in the range of 6 were used, the difference in expansion was 10% or less. It was confirmed that when a practical single cell was assembled from this material, the damage due to the difference in thermal expansion did not occur unlike the conventional material, and the reliability of the fuel cell was improved. In particular, when viewed from thermal _{expansion, LaNi 1-x Fe x O} 3 of wherein x
= 0.4 to 0.55 for materials (Sample No. 3,
4) It was found to be particularly preferable.

On the other hand, for measuring the electronic conductivity, a platinum terminal was baked on the sample used for measuring the coefficient of thermal expansion, and the measurement was carried out by the direct current 4-terminal method. As an example, the conventional material and the material of the present application, LaNi _0.6 Fe, measured by the four-terminal method.
The temperature dependence of the electronic conductivity of _0.4 O ₃ is shown in FIG.

In this fuel cell, the electron conductivity at the target operating temperature of 800 ° C. is 150 Sc of the conventional material.
It can be seen that it is greatly improved to 580 Scm ^-1 with respect to m ^-1 . Due to this good electron conductivity, the terminal voltage of the single cell using the conventional air electrode material was 0.20 V, but it was 0.24 to 0.28 V by using the new air electrode material of the present invention. Can be raised up to.

The air electrode material expressed by the composition formula of LaNi _1-x Fe x O ₃ of the present invention, adaptation of the thermal expansion coefficient, the electron conductivity, any range of x = 0.3 to 0.6 Although it also has preferable characteristics, a fuel cell having more preferable characteristics can be obtained particularly in the range of x = 0.4 to 0.55.

[0032] In single cell similar to Example 2 Example 1, the material of the air _{electrode, PrNi 1-x Fe x O} 3 (x = 0.
3, 0.4, 0.5, 0.6), and the same experiment as in Example 1 was performed. Table 2, sample No. The results are shown in 5-10. Sample No. The coefficient of thermal expansion of any of 5-8 is smaller than that of La _0.8 Sr _0.2 MnO ₃ which is a conventional material. In addition, the sample No. The terminal voltage for 5-8 (value at current density of 1.0 A / cm ² ) is higher than that of the conventional material La _0.8 Sr _0.2 MnO ₃ .

In almost the same manner as in Example 1, favorable results were obtained in comparison with the conventional materials. In addition, among these samples, the sample No. 7-9, that is, the composition formula PrNi
During _1-x Fe x O _3, it showed better results in the range of x = 0.4 to 0.55.

[Embodiment 3] A single cell similar to that of Embodiment ₁ is prepared by using NdNi _1-x Fe _x O ₃ (x = 0.3,
0.4, 0.5, 0.6) was replaced with the same experiment as in Example 1. Table 2, sample No. As shown in 11-15,
Almost the same as in Example 1, the conventional material La _0.8 Sr _0.2
Good results were obtained in comparison with MnO ₃ . In particular, the sample No. 12-14, namely, composition formula NdNi _1-x Fe x
In O ₃ , materials in the range of x = 0.4 to 0.55 showed more preferable results.

[0035] [Example 4] The unit cells as in Example 1 only material of the air electrode _{SmNi 1-x Fe x O 3} , (x = 0.3,
0.4, 0.5, 0.6) was replaced with the same experiment as in Example 1. Table 2, sample No. 16 to 20, almost the same as in Example 1, the conventional material La _0.8 Sr _0.2 M
Good results were obtained in all cases compared to nO ₃ , especially sample No. 17-19, that is, the composition formula SmNi _1-x
Materials with Fe _x O ₃ in the range of x = 0.4 to 0.55 showed more favorable results.

[0036] [Example 5] Similar single cell of Example 1, only the material of the air electrode was subjected to the same experiment as in Example 1 in place of the _{EuNi 1-x Fe x O 3} . Table 2, No. As shown in 20-25, the conventional material La is almost the same as in the first embodiment.
Good results were obtained in comparison with _0.8 Sr _0.2 MnO ₃ .
Further, in particular, the sample No. 21-24, composition formula Eu
In _{Ni 1-x Fe x O 3} , the material in the range of x = 0.4 to 0.55 showed better results.

[Embodiment 6] A single cell similar to that of Embodiment ₁ is used, except that only the material of the air electrode is changed to YNi _1-x Fe _x O _3.
The same experiment was performed. Table 2, No. 26-30, La _0.8 S which is a conventional material is almost the same as in Example 1.
Good results were obtained in comparison with r _0.2 MnO ₃ . Also,
In particular, the sample No. 27-29 composition formula YNi _1-x F
In e _x O ₃ , materials in the range of X = 0.4 to 0.55 showed good results.

[Embodiment 7] A single cell similar to that of Embodiment 1 was used, in which only the material of the air electrode was La _0.4 using a composite composition of rare earths.
An experiment similar to that of Example 1 was conducted in place of Ce _0.1 Pr _0.3 Nd _0.1 Sm _0.1 Ni _0.6 Fe _0.4 O ₃ (Sample No. 31). Table 2, No. As shown in FIG. 31, almost the same as in Example 1, good results were obtained as compared with the conventional material La _0.8 Sr _0.2 MnO ₃ .

In the above embodiments, the simple type single cell (FIGS. 2 and 3) was used for the characteristic evaluation of the material, but it is sufficient to use the simple type single cell for the characteristic evaluation.
It has been confirmed as a result of tests on some samples that the actual tube type (see FIG. 1) cell characteristics can be predicted from the characteristics.

[0040]

[Table 2]

[0041]

As described above, the solid electrolyte fuel cell is
The air electrode material of the pond is LnNi_1-xFe_xO ₃, (Ln: rare earth
Group elements, x = 0.30-0.60)
Heat La which is a conventional material_0.8Sr_0.2MnO₃Compare to
It has excellent electronic conductivity, and its thermal expansion coefficient is
Succeeded in obtaining a closer air electrode. The present invention is solid
Greatly contributes to the improvement of fuel cell reliability and high-efficiency operation
It is an eggplant.

[Brief description of drawings]

FIG. 1 is a schematic view of the structure of a tubular fuel cell.

FIG. 2 is a structural schematic plan view of a single cell of a fuel cell used in one example of the present invention.

FIG. 3 is a structural schematic cross-sectional view of a single cell and a cell measuring system of a fuel cell used in one example of the present invention.

FIG. 4 La _0.8 Sr _0.2 O which is a conventional material for air electrode
₃ is a comparative diagram of the temperature dependence of the electron conductivity of the LaNi _0.6 Fe _0.4 O _3, which is one of the materials of the present invention.

[Explanation of symbols]

1 air pole 2 Solid electrolyte 3 fuel pole

Front page continued (56) References JP-A-4-275923 (JP, A) JP-A-4-51461 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4 / 86 C04B 35/495 H01M 8/12

Claims (6)

(57) [Claims] 1. A single cell comprising a solid electrolyte and a porous air electrode and a fuel electrode which are provided so as to be bonded to the solid electrolyte, and an interconnector for electrically connecting the single cell, and hydrogen or fuel gas is provided. the chemical reaction with air or oxygen gas to a cathode material for a solid fuel cell for converting into electrical energy, the air Kikyoku is _{LnNi 1- x Fe x O 3 (} L
(n: rare earth element) or YNi _1-x Fex O _{3 and} the _{x in} the formula is in the range of 0.30 to 0.60. Air electrode material for perovskite type solid fuel cells. 2. The cathode comprises, in particular, LnNi _1-x Fe11 _x
O _3: having a composition represented by the formula (Ln rare earth element) or _{YNi 1-x Fe x O 3} , x in the formula is from 0.40 to 0.
It is in the range of 55, The air electrode material for Nikkell-based perovskite solid fuel cells according to claim 1. 3. A wherein LnNi _1-x Fe x O ₃ system of the air electrode material, Ln is one of La, Pr, Nd, Sm, Eu, or La, Pr, Nd, Sm, Eu, Ce
The nickel-based perovskite-type solid fuel cell air electrode material according to claim 1, which is composed of a combination of two or more elements selected from the above. 4. A solid electrolyte and a solid electrolyte bonded to the solid electrolyte.
A single cell consisting of a porous air electrode and a fuel electrode, and
Has an interconnector for electrically connecting single cells
Chemistry of hydrogen or fuel gas with air or oxygen gas
A solid fuel cell that converts reactions into electrical energy.
And the air electrode of the solid fuel cell is LnNi _1-xFe_xO
₃(Ln: rare earth element) or YNi_1-xFe_xO₃With the formula
It has a composition represented and x in the above formula is 0.30 to 0.6
Nickel-type Perovska characterized by being in the range of 0
It is characterized by having a porous air electrode of an ITO type material.
Body-electrolyte solid fuel cell. 5. The porous air electrode, LnNi _1-x Fe x O
_3: having a composition represented by the formula (Ln rare earth element) or _{YNi 1-x Fe x O 3} , x in the formula is 0.40 to 0.5
The solid oxide fuel cell according to claim 4, which has a porous air electrode using a material having a composition within the range of 5. 6. The LnNi _1-x Fe _x O ₃ -based air electrode material, wherein Ln is any one of La, Pr, Nd, Sm, and Eu, or La, Pr, Nd, Sm, Eu, C
The solid oxide solid fuel cell according to claim 4, further comprising an air electrode made of a material having a composition composed of a combination of two or more elements selected from e.