JPH0989836A - Electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an electrochemical device having anode and cathode formed on a solid electrolyte layer of barium cerium based oxide in which the service life is prolonged by eliminating deterioration on the interface between an electrode and an electrolyte. SOLUTION: The electrochemical device comprises a barium cerium based oxide layer, a cathode 2 formed on one side thereof, and an anode 4 formed on the other side thereof. At least one of anode and cathode has two layer structure of a first thin film electrode 3 formed on the surface of oxide layer and a second electrode formed thereon. The barium cerium based oxide is represented by a formula BaCe1-x Mx O3-a (M is at least one kind of element selected from Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho and Er. O<x<1, 0<a<1). The first thin film electrode of anode or cathode is preferably composed of Pt, Pd, Au or Ag.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrochemical device using an oxygen ion conductive solid electrolyte, and more particularly to a limiting current type oxygen sensor using a barium cerium oxide solid electrolyte.

[0002]

2. Description of the Related Art Typical electrochemical devices utilizing an oxygen ion conductive solid electrolyte include a fuel cell, an oxygen pump, an oxygen sensor and the like. Among them, an oxygen sensor, particularly a limiting current type oxygen sensor will be described. Conventionally, a stabilized zirconia solid electrolyte is generally used as a limiting current type oxygen sensor. A conventional limiting current type oxygen sensor is shown in FIG. A cathode 7 and an anode 8 are formed on both sides of the oxygen ion conductive solid electrolyte 1, and on the cathode 7 side,
An oxygen diffusion resistance member 5 having a diffusion hole 6 that limits oxygen diffusion is provided.

In the above structure, when a voltage is applied between the cathode 7 and the anode 8, oxygen molecules in the cathode 7 receive electrons and become oxygen ions, and these oxygen ions move in the solid electrolyte 1, A series of operations in which electrons are emitted into oxygen molecules at the anode 8 part occur, and a current flows in the closed circuit. At this time, if there are no diffusion holes that limit the diffusion of oxygen molecules, oxygen molecules are supplied in response to the voltage application and the amount of output current increases. However, in this limiting current type oxygen sensor, the diffusion of oxygen molecules is restricted by the presence of the diffusion holes 6 in the cathode 7, so that when a certain applied voltage value is exceeded, the supply amount of oxygen molecules is saturated, and as shown in FIG. As shown, a constant limiting current value is exhibited. The value is almost proportional to the oxygen concentration in the test gas. That is, if a constant voltage that only indicates the limiting current value is applied to this limiting current type oxygen sensor, a current proportional to the oxygen concentration will flow,
The oxygen concentration can be easily known by reading the current value.

With such a system, the limiting current type oxygen sensor can easily detect oxygen from a low oxygen concentration to a high oxygen concentration. However, when the stabilized zirconia is used as the oxygen ion conductive solid electrolyte, it is necessary to raise the temperature to about 500 ° C. to 800 ° C. for operation because the solid electrolyte has a large internal resistance. For this reason, there are problems such as a heater, a heat insulating structure, and promotion of characteristic deterioration, and an oxygen ion conductive solid electrolyte that operates at a lower temperature has been desired. Under these circumstances, a limiting current type oxygen sensor using a barium-cerium-based oxide has attracted attention. This material has a higher ionic conductivity and a lower activation energy for ion transfer as compared to stabilized zirconia, and therefore has a lower temperature (300 ° C to 350 ° C).
(° C) also shows the limiting current value, and the oxygen concentration can be detected.

[0005]

However, barium-cerium-based oxides capable of operating at a low temperature include:
Although oxygen can be sufficiently detected as an initial characteristic, there is a problem that the current value eventually becomes low when continuous operation is performed, a limit current is not shown, and the life is short. One of the causes is that the interfacial resistance increases due to the progress of the chemical reaction on the surface of the solid electrolyte and the electrode interface. That is, the electrode is usually formed by printing, but a reaction product of a barium-cerium oxide and a substance such as an organic binder contained in the metal-containing ink paste for enhancing the sinterability and adhesion, glass frit, or the like. Are generated, and these substances increase the interfacial resistance.

Another cause is that the stabilized zirconia and the barium cerium oxide have different thermal expansion coefficients. Therefore, if the electrode that could be used in zirconia is directly applied to the barium cerium oxide, the interface portion will be affected. Distortion may accumulate, causing physical peeling of the electrodes. Countermeasures against deterioration of the electrode-electrolyte interface to overcome these phenomena are major problems in determining the life of oxygen detection in the limiting current type oxygen sensor using the barium cerium oxide. Further, this problem of the electrode-electrolyte interface is the same in other electrochemical devices such as fuel cells and oxygen pumps using barium-cerium oxide as an electrolyte. It is an object of the present invention to solve the above-mentioned problems of the electrode-electrolyte interface and to provide an electrochemical device that can obtain stable operation for a long period of time. Another object of the present invention is to provide a limiting current type oxygen sensor capable of obtaining stable operation for a long period of time.

[0007]

According to the present invention, by inserting a thin film electrode of a pure substance containing no organic binder or glass frit between a cathode and / or an anode and a barium cerium oxide solid electrolyte, The above problems are solved. That is, the present invention comprises a barium-cerium-based oxide layer, a cathode formed on one side of the barium-cerium-based oxide layer, and an anode formed on the other side of the barium-cerium-based oxide layer. In the electrochemical device, a laminate having a two-layer structure of a first thin film electrode having at least one of an anode and a cathode formed on the surface of the barium cerium oxide layer and a second electrode formed on the first thin film electrode. It is structured.

Here, the barium cerium oxide is represented by the formula BaCe _1-x M _x O _3-a (where M is Sc, Y, La,
Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, H
It is at least one element selected from the group consisting of o and Er, and 0 <x <1. Also, the oxygen deficiency a
Is 0 <a <1. ) It is preferable that it is an oxide represented. Further, x is more preferably 0.16 ≦ x ≦ 0.23. As preferable barium-cerium-based oxides, BaCe _1-x Gd _x O _3-a (0 <a <1, 0.
There is 16 ≦ x ≦ 0.23. The first thin film electrode of the anode or the cathode is Pt, Pd, Au, or A.
It is preferably composed of g.

According to the above construction, by separating the organic binder and the glass frit contained in the printing ink paste from the solid electrolyte, it is possible to avoid generation of the resistance increasing substance at the interface. Also, since it is a thin film, it adheres to the barium cerium-based oxide with good adhesion to mitigate the difference in the coefficient of thermal expansion, and then the second electrode is deposited to mitigate the coefficient of thermal expansion in two steps. You can That is, it is possible to obtain a limiting current type oxygen sensor with reduced electrode deterioration and long life. Further, of course, since a solid electrolyte having a high ionic conductivity is used, a sensor having higher sensitivity than a conventional oxygen sensor using stabilized zirconia can be constructed at a low temperature and a small size.
That is, it becomes possible to manufacture an oxygen sensor with higher accuracy, higher reliability, longer life, smaller size, simpler operation, and lower cost than the conventional oxygen sensor of the limiting current type using stabilized zirconia.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an electrochemical device according to the present invention will be described below with reference to the drawings. [Embodiment 1] FIG. 1 is a longitudinal sectional view of an embodiment of the oxygen sensor according to the present invention. A cathode 2 is formed on one surface of the solid electrolyte layer 1. On the other surface of the solid electrolyte layer 1, an anode having a two-layer structure composed of a first thin film electrode 3 and a second electrode 4 is formed. In addition, cathode 2
An oxygen diffusion resistance member 5 having a diffusion hole 6 for controlling the oxygen molecule diffusion rate is provided on the side of. For the solid electrolyte, barium cerium gadolinium oxide BaCe _0.8
Gd _0.2 O _3-a was used. This oxide is a perovskite type oxide and is thermally stable. Usually, many oxides of this kind are unstable in a reducing atmosphere, but they are stable in a reducing atmosphere. The size of this solid electrolyte is 1
The sheet was 0 mm × 10 mm and had a thickness of 0.45 mm.

Platinum was used for the cathode 2. That is, a thick film of platinum paste (4
.About.5 .mu.m) and baked at 900.degree. C. for 1 hour to form a cathode. Anode first thin film electrode 3
Was formed of a platinum sputtered film (<1 μm). Similarly to the cathode 2, the second electrode 4 of the anode was formed by laminating the platinum paste on the surface of the platinum sputtered film by screen printing and firing. In addition, cathode 2
The oxygen diffusion resistance member 5 was attached to the side of the solid electrolyte layer 1 using a glass paste.

According to the current-voltage characteristics of this oxygen sensor, the current value was slightly higher than that in the case without the thin film electrode 3. Further, even at 300 ° C., a sufficient limiting current characteristic was exhibited, and the oxygen concentration and the limiting current were in a proportional relationship with 1.0 V applied. This oxygen sensor is 300 ℃, 1.0V
When a continuous test was performed in the applied state to examine the change over time in the output current, as shown in FIG. 4, very good stability was maintained for a long time as compared with the conventional example. That is, the solid electrolyte 1
A thin film electrode 3 is interposed between the anode electrode 4 and the anode electrode 4 to obtain a limiting current type oxygen sensor with less deterioration in output current, longer life, and lower temperature operation than the conventional example. You can

[Embodiment 2] FIG. 2 is a longitudinal sectional view of another embodiment of the oxygen sensor according to the present invention. Solid electrolyte layer 10
The anode 11 is formed on one surface. On the other surface of the solid electrolyte layer 10, a cathode composed of a first thin film electrode 12 and a second electrode 13 is formed in a two-layer structure. Further, on the side of the electrode 13, an oxygen diffusion resistance member 14 having a diffusion hole 15 for limiting the oxygen molecule diffusion is provided. In this embodiment, the solid electrolyte is barium cerium yttrium oxide BaCe _0.8 Y _0.2 O.
_3-a was used. The manufacturing method of the oxygen sensor is almost the same as that in Example 1, but in this example, the thin film electrode 12 was formed on the cathode 13 side.

Also in the present embodiment, the limiting current characteristic at 300 ° C. and the limiting current value are proportional to the oxygen concentration. Then, when a life test was conducted in the same manner as in Example 1, as shown in FIG. 4, the value was almost the same as in Example 1, and showed stable continuous output characteristics for a long time as compared with the conventional example. It was Thus, even in the cathode, the thin film electrode 1
The presence of 2 makes it possible to obtain a limiting current type oxygen sensor that has less deterioration in output current, has a long life, and can operate at low temperatures, as compared with the conventional example.

[Embodiment 3] FIG. 3 is a longitudinal sectional view of another embodiment of the oxygen sensor according to the present invention. Solid electrolyte layer 20
An anode composed of a first thin film electrode 21 and a second electrode 22 is formed in a double-layer structure on one surface of the first electrode. The first thin film electrode 23 and the second thin film electrode 23 are formed on the other surface of the solid electrolyte layer 20.
The cathode composed of the electrode 24 is formed in a two-layer structure. Further, on the side of the cathode electrode 24, an oxygen diffusion resistance member 25 having a diffusion hole 26 for limiting the diffusion of oxygen molecules.
Is provided. In this example, a barium cerium gadolinium oxide BaCe _0.84 Gd _0.16 O containing a different amount of gadolinium as the solid electrolyte was used as the solid electrolyte.
_3-a was used. The method for manufacturing the oxygen sensor is almost the same as in the first and second embodiments, but in this embodiment, the thin film electrode 21 is used.
Was formed on the anode side, and the thin film electrode 23 was formed on the cathode side.

Also in the present embodiment, the limiting current characteristic at 300 ° C. and the limiting current value are proportional to the oxygen concentration. The limiting current value at this time was slightly higher than those in Example 1 and Example 2. Then, a life test was performed in the same manner as in Examples 1 and 2, and as shown in FIG. 4, the current value was slightly higher than that in Examples 1 and 2, and was stable in comparison with the conventional example. And showed continuous output characteristics for a long time. As described above, since the thin film electrode 21 is present on the anode side and the thin film electrode 23 is present on the cathode side, the output current is less deteriorated, the life is long, and the low temperature operation is possible as compared with the conventional example. An electric current type oxygen sensor can be obtained. This embodiment has the effect of increasing the output current value in addition to the effects of Embodiments 1 and 2. Further, since it is possible to deal with both the deterioration at the anode and the deterioration at the cathode, it has the effect of extending the life.

In Examples 1 and 3, barium cerium gadolinium oxide B was used as the solid electrolyte.
aCe _0.8 Gd _0.2 O _3-a and BaCe _0.84 Gd _0.16 O
_{Although 3-a is} used, a solid electrolyte having a composition ratio of cerium and gadolinium other than that can also be used. Further, although BaCe _0.8 Y _0.2 O _3-a was used in Example 2, _a barium cerium-based oxide to which a rare earth element other than Gd and Y is added can also be used. Further, in Examples 1, 2 and 3, platinum was used as the electrode material, but materials such as Ag and Pd can also be used. Furthermore, in Examples 1, 2 and 3, platinum was used as the material for the thin film electrode.
A thin film electrode made of a pure substance such as g or Pd may be used.

Further, in Examples 1, 2 and 3, the sputtering method was used as the method for forming the thin film electrode, but vacuum deposition, C
Other methods may be used as long as the pure substance can be formed in a thin film (1 μm or less) state by using a technique such as VD or printing firing of metallo organic paste. In the examples, the effectiveness of the barium cerium oxide in the electrode part was shown using a limiting current type oxygen sensor as an electrochemical device, but the present invention is applicable to other electrochemical devices such as a fuel cell and an oxygen pump. It is needless to say that the above is similarly effective when applied to.

[0019]

As described above, according to the present invention, it is possible to obtain a long life and high reliability as compared with a conventional electrochemical device using a barium-cerium oxide.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of an oxygen sensor of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the oxygen sensor of the present invention.

FIG. 3 is a sectional view showing another embodiment of the oxygen sensor of the present invention.

FIG. 4 is a graph showing changes over time in the output current value of the oxygen sensor of the present invention.

FIG. 5 is a sectional view of a conventional limiting current type oxygen sensor.

FIG. 6 is a graph showing a limiting current characteristic in a conventional limiting current type oxygen sensor.

[Explanation of symbols]

 1, 10, 20 Solid electrolyte layer 2, 7, 13, 24 Cathode 3, 21 Anode first thin film electrode 4, 8, 11, 22 Anode 5, 14, 25 Oxygen diffusion resistance member 6, 15, 26 Diffusion hole 12, 23 Cathode first thin film electrode

Claims (5)

[Claims] 1. A barium-cerium-based oxide layer, a cathode formed on one side of the barium-cerium-based oxide layer, and an anode formed on the other side of the barium-cerium-based oxide layer. At least one of the anode and the cathode has a laminated structure having a two-layer structure of a first thin film electrode formed on the surface of the barium cerium oxide layer and a second electrode formed on the first thin film electrode. An electrochemical device characterized by the above. 2. The barium-cerium oxide has the formula BaC.
e _1-x M _x O _3-a (where M is Sc, Y, La, Pr,
An oxide represented by 0 <x <1, 0 <a <1), which is at least one element selected from the group consisting of Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, and Er. The electrochemical device according to claim 1, wherein the electrochemical device is an electrochemical device. 3. The electrochemical device according to claim 2, wherein x is 0.16 ≦ x ≦ 0.23. 4. The electrochemical device according to claim 1, 2 or 3, wherein the first thin film electrode of the anode or the cathode is made of Pt, Pd, Au, or Ag. 5. The limiting current type oxygen sensor according to claim 1, which has a mechanism for limiting the amount of diffused oxygen on the cathode side.