JPH059057A - Perovskite type compound oxide for electrode - Google Patents

Abstract

PURPOSE:To facilitate the control of the coefft. of linear expansion and to improve resistance to high temp. and to a high-vacuum reducing atmosphere and performance as a catalyst for decomposition of gas by mixing and firing specified compds. CONSTITUTION:Compds. such as La oxide, Sr carbonate, Co oxide and Mn oxide are mixed in a desired ratio, this mixture is calcined to form perovskite structure and pulverization is carried out. The resulting powder is pressed and fired to produce a perovskite type compd. oxide for an electrode represented by the formula (where A is a rare earth element such as La, Ce or Nb, A' is an alkaline earth metal such as Ca, Sr or Ba, B is a transition metal such as Al or Ni, 0<x<=0.5, 0<y<=0.3, 0.8<=z<=1.0 and 0.5<=a<=1.0).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perovskite type complex oxide used as an electrode material of an element for ionizing gas molecules such as a gas sensor, a fuel cell or an oxygen pump.

[0002]

2. Description of the Related Art As an electrode material for gas sensors and the like, JP-A-62-223054 or JP-A-63-158452.
The perovskite-type composite oxide disclosed in Japanese Patent Publication No. 2003-242242 is known. The perovskite complex oxide disclosed in these prior arts is represented by the following (Chemical Formula 4).

[0003]

[Chemical 4]

[0004]

In the above-mentioned conventional perovskite-type composite oxide, although the conductivity required in the electrode can be satisfied, the conventional perovskite-type composite oxide is used as a solid electrolyte. As Zr
When formed on an O ₂ -based material (stabilized zirconia), there are the following problems.

That is, when used at a high temperature of 600 ° C. or higher,
The electrode and the ZrO ₂ -based material react with each other to deteriorate the electrode performance, and the linear expansion coefficient of the electrode and the ZrO ₂ -based material are greatly different from each other, resulting in peeling. Further, the electrode is weak in a reducing atmosphere and inferior in durability.
When used as an oxygen gas sensor, it is not possible to measure a dilute oxygen concentration.

[0006]

In order to solve the above problems, the perovskite complex oxide for electrodes according to the present invention is specified by the following (Chemical formula 1), (Chemical formula 2) and (Chemical formula 3). .

[0007]

[Chemical 1]

[0008]

[Chemical 2]

[0009]

[Chemical 3]

[0010]

[Function] By forming electrodes on both surfaces of a solid electrolyte such as a stabilized zirconia membrane and measuring the electromotive force, it functions as an oxygen gas sensor, and by applying a voltage between the electrodes, it functions as a gas separation element. Oxygen gas permeates one electrode of the electrodes formed on both sides of the solid electrolyte and hydrogen gas permeates the other electrode to cause a chemical reaction at each electrode,
By extracting this as electric energy, it functions as a fuel cell.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a cross-sectional view of an oxygen gas sensor in which an electrode is formed using the perovskite type complex oxide according to the present invention.

In the oxygen gas sensor 1, the case 2 is divided into chambers S1 and S2 by a gas-tight separation membrane 3, and each chamber S is divided into two chambers.
1, the electrodes 4, 4 are formed on the surface of the separation membrane 3 facing S2,
These electrodes 4 and 4 are connected to a potentiometer 5. Here, as the separation membrane 3, 18 mol% was used for 92 mol% ZrO ₂ .
A solid electrolyte or the like containing mol% Y ₂ O ₃ is used.

Thus, the oxygen partial pressure in the chamber S1 is P1, the chamber S is
When the oxygen partial pressure in 2 is P2 (P1> P2), the separation membrane 3 is gas-tight, so that O ₂ gas flows from the chamber S1 to the chamber S2.
However, the O ²⁻ ions move from the chamber S1 to the chamber S2. As a result, plus occurs on the room S1 side and minus occurs on the room S2 side, and electromotive force is generated. By the way, electromotive force (E)
Is expressed by the following equation.

[0014] However, R is a gas constant, T is an absolute temperature, F is a Faraday constant, and ln is a natural logarithm.

Further, the electrode 4 is formed by forming a perovskite-type composite oxide on the surface of the separation film 3 by means such as thermal spraying. This perovskite-type composite oxide is represented by the following (Chemical formula 1).
Be specified by.

[0016]

[Chemical 1]

However, in (Formula 1), x, y, z and a
The preferred values of are as follows. 0.2 ≦ x ≦ 0.3, 0.015 ≦ y ≦ 0.15,
0.85 ≦ z ≦ 0.95, 0.75 ≦ a ≦ 1.0

Next, the reason for selecting the above range will be described with reference to FIGS. As raw materials, lanthanum oxide, strontium carbonate, cobalt oxide, and manganese oxide (nitrate or acetate may be used as a starting raw material) were weighed to a predetermined composition ratio, mixed, and then calcined. The perovskite structure was used, and the powder that had been calcined after this was pulverized again and pressed and then fired.

First, FIG. 2 is a graph showing the relationship between the value a and the coefficient of linear expansion in (Chemical formula 5). From this graph, Co and Mn are shown.
The linear expansion coefficient is 10 × 10 ^-6 by changing the compounding ratio of
It can be seen that control can be performed within the range of up to 25 × 10 ^-6 . Further, considering the matching property with the ZrO ₂ system material (stabilized zirconia), it should be 0.5 ≦ a <1.0.

[0020]

[Chemical 5]

FIG. 3 is a graph showing the relationship between the composition and ratio of B'in the following (Chemical Formula 6) and the overvoltage. Specifically, Cr, Fe, Al and Ni are selected as the B'composition, an oxide containing these in appropriate amounts is used as a starting material, raw material powder is prepared in the same manner as described above, and then made into a paste using an organic solvent,
92 mol% ZrO ₂ , 18 mol% mol% Y ₂
It was applied to both side surfaces of O ₃ (φ20 × 1.0 t), and the electrical conductivity and overvoltage (perovskite electrocatalytic performance) of the pellet / electrode sample were measured by the direct current method.

[0022]

[Chemical 6]

From this graph, it can be said that the addition of Al and Ni as B'is superior to Cr and Fe, and the overvoltage is reduced and the catalyst performance is excellent. And the addition ratio is 0 <y
≦ 0.3 is suitable, especially for Al, 0.015
˜0.10, and Ni is preferably 0.03 to 0.15.

FIG. 4 is a graph showing the relationship between the a value in (Chemical formula 7) and the ionic conductivity of the separation membrane. In this experiment, a ZrO ₂ pellet / perovskite electrode was prepared in the same manner as in the above (FIG. 3). The electrical conductivity before and after the heat treatment (1100 ° C. × 100 hours) was measured.

[0025]

[Chemical 7]

From this graph, when the compounding ratio of Mn is increased, the conductivity of the stabilized zirconia after heat treatment does not decrease,
It can be seen that the reaction resistance with zirconia is excellent. Based on this reaction resistance alone, the value a is optimally set to 0.75 to 1.0.

FIG. 5 is a graph showing the relationship between the a value in (Chemical formula 7) and the electron conductivity. In this experiment, a ZrO ₂ pellet / perovskite electrode was prepared in the same manner as described above, and electrons were produced by the 4-terminal method. The conductivity was measured. C from this graph
The electron conductivity is as low as 50 s / cm in the composition that does not contain o, but the electron conductivity is greatly improved by including Co. In particular, when the value of a is 0.87 or less, the conductivity is 4 to 5 times. I see.

FIG. 6 is a graph showing the relationship between the composition of B in (Chemical formula 8), the x value, and the electronic conductivity, which was measured by the four-terminal method as described above.

[0029]

[Chemical 8]

From this graph, when Co is used as the composition of B, the x value is preferably around 0.1, and when Mn is used as the composition of B, the x value is 0.2 to 0.4. It can be said to be preferable.

FIG. 7 is a graph showing the relationship between the Z value in (Chemical Formula 9) and electronic conductivity. In this experiment, a bulk body of perovskite oxide was fired / molded and measured by a four-terminal method. From this, it is understood that when the Z value is less than 0.8, the electronic conductivity sharply decreases. On the other hand, when the Z value is 1.0 or more, a reaction between the ZrO ₂ based separation film and the perovskite electrode occurs, which causes a decrease in oxygen ion conductivity.
Therefore, the Z value is 0.8 ≦ Z <1.0,
Preferably, 0.85 ≦ Z <0.95.

[0032]

[Chemical 9]

FIG. 8 is a sectional view of a fuel cell in which an electrode is formed by using a perovskite type composite oxide according to another embodiment, and FIG. 9 is an enlarged sectional view of a main part of the fuel cell.

In the fuel cell 11, the porous first electrode layer 13 made of the perovskite type complex oxide according to the present invention is formed on the surface of a porous support 12 made of zirconia or the like through which a gas can pass, by a dipping method or a CVD method. And the like, and a gas-tight solid electrolyte layer 14 made of stabilized zirconia or the like is formed on the surface of the first electrode layer 13.
Similarly, the second electrode layer 15 made of the perovskite type complex oxide according to the present invention is formed on the surface of No. 4.

A conduit 16 is inserted in the cylindrical porous support 12 having one end closed. The tip of this conduit 16 faces the closed bottom of the porous support 12, and air containing oxygen is ejected to the inside of the porous support 12 through a hole 16a formed at the tip.

In the above, when oxygen gas (air) is flown inside the porous support 12 and hydrogen gas is flown outside the second electrode layer 15, the oxygen gas permeates into the first electrode layer 13. , Hydrogen gas permeates into the second electrode layer 15, and the following reactions occur in the first and second electrode layers.

The first _{electrode; H 2 O + 1 / 2O} 2 + 2e → 2OH - a second ^{_{electrode; H 2 + 2OH - → 2H}} 2 O + 2e becomes, 2e is supplied to the load. OH ⁻ moves in the solid electrolyte layer 12.

The composition of the perovskite type complex oxide forming the first and second electrode layers 13 and 15 is as shown in Chemical formula 2.
Or, it shall be as described in (Chemical Formula 3). Then, the reason why the ranges of x, y ₁ , y ₂ , z and a in (Chemical Formula 2) or (Chemical Formula 3) are specified will be described below.

First, an electrode containing (Chemical Formula 2) containing cobalt was prepared and its performance was evaluated. As a production method, various nitrates and acetates were weighed so as to have a predetermined composition ratio, sufficiently mixed as an aqueous solution, dried, and calcined at 850 ° C. to obtain a perovskite structure.

In order to evaluate the electronic conductivity of the above-mentioned perovskite structure electrode material, it was molded into 4 × 4 × 30 mm,
After firing at 1300 ° C., evaluation was made by the 4-terminal method. The result is shown in FIG. It can be seen from FIG. 10 that the higher the cobalt content, the higher the electron conductivity.

In order to evaluate the effect of adding Al and Ni on the electrocatalytic property of the above-mentioned perovskite structure electrode material, an overvoltage of 8 by the current interrupter method was used.
It was measured at 00 ° C. The results are shown in (Table 1).

[0042]

[Table 1]

From Table 1, for Al, 0.01
≤y ₁ ≤0.20, preferably around 0.015, and for Ni 0.03 ≤y ₂ ≤0.20, preferably 0.0
It turns out that it should be around 9.

FIG. 12 is a graph showing the relationship between the value a and the coefficient of linear expansion in (Chemical formula 2). From this graph, the coefficient of linear expansion is 10 × 1 by changing the compounding ratio of Co and Mn.
It turns out that it can be controlled in the range of 0 ^{-6 to} 20 x 10 ^-6 ,
Considering the matching property with the ZrO ₂ +8 mol% Y ₂ O ₃ material (stabilized zirconia), it should be 0.6 ≦ a <1.0, preferably 0.75 ≦ a <1.0.

FIG. 13 is a graph showing the relationship between the Z value and the electron conductivity in (Chemical formula 2). From this, it is understood that the electron conductivity sharply decreases when the Z value is less than 0.8. Also,
When the Z value exceeds 1.0, a reaction between the ZrO ₂ -based separation film and the perovskite electrode occurs, which causes a decrease in oxygen ion conductivity. Therefore, the Z value is 0.8
≦ Z ≦ 1.0.

The above-mentioned electrode material having a perovskite structure containing cobalt exhibited high durability particularly when used at 400 to 800 ° C.

Next, an electrode according to (Chemical Formula 3) containing no cobalt was prepared and its performance was evaluated. As a method of preparation, various nitrates and acetates are weighed so as to have a predetermined composition ratio, sufficiently mixed as an aqueous solution, and then dried, and 900 ° C.
It was calcined to obtain a perovskite structure.

In order to evaluate the electronic conductivity of the above-mentioned perovskite structure electrode material, it was molded into 4 × 4 × 30 mm,
After firing at 1300 ° C., evaluation was made by the 4-terminal method. The result is shown in FIG. It can be seen from FIG. 14 that 0 <x ≦ 0.5, particularly 0.2 ≦ x ≦ 0.3 is preferable. Also, Al
Regarding the effect of addition of Ni and Ni and the z value, the same results as in (Chemical Formula 2) were obtained.

The above electrode material having a perovskite structure containing no cobalt exhibited high durability particularly when used at 800 to 1100 ° C.

[0050]

Perovskite-type composite oxide according to the present invention, as described EFFECT above, the linear control expansion coefficient easily performed, thus excellent in matching with the ZrO ₂ based materials such as, ZrO ₂ be used at high temperatures It hardly reacts with system materials, can withstand use in a high-vacuum reducing atmosphere, and also improves gas decomposition catalyst performance.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an oxygen gas sensor in which an electrode is formed using a perovskite type complex oxide according to the present invention.

FIG. 2 is a graph showing the relationship between the a value of La _0.6 Sr _0.4 Co _1-a Mn _a O ₃ and the coefficient of linear expansion.

FIG. 3 is a graph showing the relationship between the overvoltage and the composition and ratio of B ′ in La _0.6 Sr _0.4 Mn _1-y B ′ _y O _3.

FIG. 4 is a graph showing the relationship between the a value of La _0.6 Sr _0.4 Co _1-a Mn _a O ₃ and the ionic conductivity of the separation membrane.

FIG. 5 is a graph showing the relationship between a value and electronic conductivity of La _0.6 Sr _0.4 Co _1-a Mn _a O ₃

FIG. 6 is a graph showing the relationship between the B composition of La _1-x Sr _x BO ₃ and the x value and electronic conductivity.

FIG. 7: Z of (La _0.6 Sr _0.4 ) z · Co _0.94 Al _0.06 0 ₃
Graph showing the relationship between values and electronic conductivity

FIG. 8 is a cross-sectional view of a fuel cell in which electrodes are formed using the perovskite type complex oxide according to the present invention.

FIG. 9 is an enlarged cross-sectional view of the main part of the fuel cell.

Fig. 10 (La _0.75 Sr _0.25 ) _0.9 (Co _1-a Mn _a ) _0.895
Graph showing the relationship between the a value of Al _0.015 Ni _{0.090 3} and electronic conductivity

FIG. 11: (La _0.75 Sr _0.25 ) _0.9 (Co _1-a Mn _a ) _0.895
Graph showing the relationship between the a value of Al _0.015 Ni _{0.090 3} and the electrocatalytic property

Fig. 12 (La _0.75 Sr _0.25 ) _0.9 (Co _1-a Mn _a ) _0.895
Graph showing the relationship between the a value and the coefficient of linear expansion of Al _0.015 Ni _{0.090 3}

FIG. 13: La _1-x Sr _x Mn _0.895 Al _0.015 Ni _0.09 0 ₃ x
Graph showing the relationship between the value and electronic conductivity

FIG. 14: (La _0.75 Sr _0.25 ) zMn _0.895 Al _0.015 Ni
Graph showing the relationship between z value of _{0.090 3} and electronic conductivity

[Explanation of symbols]

1 ... Oxygen gas sensor, 3 ... Separation membrane, 4, 13, 15 ... Electrode, 11 ... Fuel cell, 12 ... Porous support, 14 ... Solid electrolyte layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location H01B 1/08 7244-5G H01M 4/90 X 7308-4K (72) Inventor Hiroyuki Kawashima Kitakyushu, Fukuoka Prefecture 2-1-1, Nakajima, Kokurakita-ku, Tochi, Ltd. (72) Inventor Akira Ueno 2-1-1, Nakajima, Nakajima, Kokura-kita, Kitakyushu, Fukuoka Prefecture (72) Inventor, Kobayashi Chihiro Fukuoka Prefecture Kitakyushu City Nakajima 2-1, 1-1 Totoki Equipment Co., Ltd. (72) Inventor Masahiro Kuroishi Nakajima 2-1, 1-1 Nakajima Kokurakita-ku, Kitakyushu, Fukuoka Prefecture Totoki Equipment Co., Ltd.

Claims (3)

[Claims] 1. A perovskite complex oxide for an electrode specified by the following (Chemical formula 1). [Chemical 1] 2. A perovskite-type composite oxide for an electrode specified by the following (Chemical formula 2). [Chemical 2] 3. A perovskite complex oxide for an electrode specified by the following (Chemical Formula 3). [Chemical 3]