JPS6337569A - Oxygen electrode structure for high-temperature solid electrolyte fuel cell - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the cell characteristic by providing an oxygen electrode made of a specific perovskite compound and a shielding film made of a specific perovskite compound. CONSTITUTION:An La1-yM<3>yM<4>O3-y/2 (M<3> is Sr, Mg, Ca, or Ba; M<4> is Al or In; 0<y<1 perovskite compound film is provided on an oxygen electrode made of a perovskite compound expressed by an equation La1-xM<1>xM<2>O3-x/2(M<1> is Sr, Mg, Ca, or Ba; M<2> is Co, Fe, or Mn; 0<x<1), and stabilized zirconia and the oxygen electrode are cut off. Accordingly, stabilized zirconia and the La1-xM<1>xM<2>O3-x/2 oxygen electrode are cut off by the La1-yM<3>yM<4>O3-y/2 perovskite compound film, thus it is not reacted practically with the perovskite compound, thus a fuel cell whose characteristic is not deteriorated even if it is used for a long time can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an oxygen electrode structure for a fuel cell, and particularly to an oxygen electrode structure for a high-temperature solid electrolyte fuel cell that is used at high temperatures and employs a solid electrolyte. ! 11 Concerning the remains of prime structure.

[Prior Art and Its Disadvantages] A fuel cell is a battery assembled in such a way that the free energy change accompanying the oxidation reaction can be directly extracted as electrical energy by electrochemically carrying out the oxidation reaction of the fuel. Various methods have been proposed and developed since ancient times. The most well-studied type is the hydrogen-oxygen fuel cell, which uses hydrogen as the fuel. Hydrogen-oxygen fuel cells electrochemically react hydrogen and oxygen to directly extract electrical energy, and electrodes often use porous carbon with a catalyst (mainly platinum) added to the surface. . Hydrogen-oxygen electrodes are broadly classified into phosphoric acid fuel cells, molten carbonate fuel cells, and solid electrolyte fuel cells depending on the type of electrolyte.

A phosphoric acid fuel cell is said to be a first generation fuel cell, uses phosphoric acid as an electrolyte, and operates at a temperature of 170 to 220°C. This type of battery has been developed mainly in the United States since the 1960s and is currently in its final development stage, but has the drawbacks of low energy efficiency and short lifespan.

Molten carbonate fuel cells use a molten carbonate, such as a mixture of lithium carbonate and potassium carbonate, as the electrolyte, and are called second-generation fuel cells, but they are generally used as the anode. Since there is a problem with the stability of the nickel oxide used, it has the disadvantage of a short life.

High-temperature solid electrolyte fuel cells use a solid electrolyte, making the battery structure simpler than batteries using electrolyte solutions or molten salts, and also require no precious metal catalyst to operate at high temperatures (around 1000°C). Does it have the advantage of being able to use low-purity, cheap gas such as reformed coal gas as fuel?
Because it is highly difficult to develop, it is positioned as a third-generation fuel cell. As a solid electrolyte, zirconia (z"
Stabilized zirconia in which divalent or trivalent metal oxide is dissolved in solid solution is used. Since the conductivity of stabilized zirconia is low at low temperatures, it is necessary to operate at high temperatures of approximately 1000°C. For this reason, the selection of battery constituent materials, especially the anode material (oxygen electrode material), becomes important. The conditions required for an oxygen electrode for high temperature solid electrolyte fuel cells are (1)
High electrical conductivity, (2) thermal and chemical stability (3) porosity (4)
) Adhesion with solid electrolyte (stabilized zirconia).

Platinum satisfies these conditions relatively well, but it must be excluded from the viewpoint of price and volatility at high temperatures, and there are many metal oxides, Whether multiple oxides have been reported or currently La
l-J”J”03-: (However, Ml is Sr, Ca
or Ba, M” is Co, Fe or Mn, x is a number greater than O and smaller than 0.5), especially LaCoO3, La, Sr, h
It is said that lnO is the best. These perovskite-type compounds are stable in a high-temperature oxygen atmosphere, have high electrical conductivity (~103103S'), and have high catalytic ability for oxygen reduction, and are ideal oxygen electrode materials. However, although these oxide electrodes have good initial characteristics when operated at 1000° C., deterioration of electrode characteristics over time is observed. It was found that the main cause of this deterioration was the formation of non-conductive compounds due to the reaction between the perovskite oxide and the stabilized zirconia.

[Problem to be solved by the invention] An object of the present invention is to provide an oxygen electrode structure for a high-temperature solid electrolyte fuel cell using stabilized zirconia as a solid electrolyte, which eliminates oxygen even when operated at high temperatures for a long time. An object of the present invention is to provide an oxygen electrode structure for a high-temperature solid electrolyte fuel cell in which the electrode and electrolyte do not substantially react with each other, so that cell characteristics do not deteriorate.

[Means for Solving the Problems] In this invention, the general formula La+-J'J20i-' (where Ml is Sr, Mg, Ca or Ba, M" is Co, Fe or Mn, and X is greater than 0) Lal-, M'yM'0.4 (where P is Sr, Mg, Ca or Ba, M' is AI or In
, y is a number greater than 0 and less than l) y! The above-mentioned problem was solved by forming a perovskite-type alloy film and blocking the stabilized zirconia from the oxygen electrode.

[Effects of the Invention] When the oxygen electrode structure of the present invention is applied to a high-temperature solid electrolyte fuel cell using stabilized zirconia as a solid electrolyte, stabilized zirconia and Lal-J', M”O
, -5 oxygen electrodes are blocked, so no reaction occurs between them. Also, the La, -, Mco VM'03-y-type perovskite compound does not react with stabilized zirconia or Lal- even at high temperatures. , M'J"03-x type perovskite compounds. Therefore, when the oxygen electrode structure of the present invention is used, a fuel cell whose characteristics do not deteriorate even after long-term use can be obtained. yM'yM'o
Although the oxygen ion conductivity of s-Z is generally about an order of magnitude lower than that of stabilized zirconia.

If the thickness is too small, it will not significantly increase the internal resistance of the battery.

[Detailed Description of the Invention] The operating principle of a fuel cell using the oxygen electrode structure of the present invention is exactly the same as that of a conventional high temperature solid electrolyte fuel cell. Figure 1 schematically shows the operating principle.
As shown in the figure, at the oxygen electrode (anode), oxygen molecules accept and take electrons and become oxygen ions, and at the hydrogen electrode (cathode), oxygen ions react with hydrogen molecules to produce water and release electrons. In other words, it can be expressed as follows.

Oxygen electrode: -0□+2e-0"- Hydrogen electrode: 02- ◆11□ -H20◆2e whole:
−0□◆H2←H,0 The solid electrolyte employed in the high temperature solid electrolyte fuel cell in which the oxygen electrode structure of the present invention is used is stabilized zirconia, as in the conventional high temperature solid electrolyte fuel cell. Stabilized zirconia is obtained by adding preferably 3 to 15 mol % of a divalent or trivalent metal oxide such as yttrium oxide, yttribium oxide, scandium oxide, calcium oxide, acid, or magnesium oxide to zirconia.

The oxygen electrode employed in the oxygen electrode structure of the present invention has the general formula La+-+tM'J"03-%- (where - is S"
, Mg, Ca or Ba, M” is Co, Fe or M
It is a perovskite type compound represented by a), where n and x are larger than O and smaller than l. Among the compounds represented by this general formula, particularly preferred are LaCo0. It is.

In the oxygen electrode structure of the present invention, the general formula L
a1-. M3. M'O, I-Z (However, Myanmar 3 is Sr
, klg, Ca or Ba, M' is AI or In,
A barrier film made of a perovskite compound represented by y is a number greater than O and smaller than 1 is provided,
This results in stable ividirconium and La+-HM'xM.
``01-4 are separated and do not come into contact with each other.

The thickness of the La+-J"yM'03-z barrier film is preferably tog■ or less in order to keep the internal resistance of the battery small, and is particularly preferably about le-.
Among the perovskite compounds represented by the general formula La, -, M'yM'03-%, particularly preferred are La.
o, 5Bao, +Alt, ss and a. , 9
srO, (lnJ, ss.

What is essential for the oxygen electrode structure of the present invention is that the barrier film is formed on the oxygen electrode, and there are no particular restrictions on the shape or size of the oxygen electrode.
For example, it is made of porous (ZrOt) like the conventionally used oxygen electrode. The oxygen electrode may have a structure in which it is laminated on a substrate made of as(CaO)o, ts, and the thickness of the oxygen electrode is, for example, about 200 mm as in the conventional case.

The oxygen electrode structure of the present invention can be produced by depositing and laminating a hydrogen electrode, stabilized zirconia, and an oxygen electrode on a porous substrate by a chemical vapor deposition method or a plasma spray method in accordance with a conventional method, for example, on a porous substrate. It can be manufactured by

Example 1 Stabilized zirconia (containing 8 mol% Y20.) was electrolytically purchased and Lao,
5Bao, +AIQ*, 9% was deposited to a thickness of approximately IJL-. Rf-sputtering method uses argon gas pressure of 2~
5 torr and a power of 100 to 200 w for 1 hour. On top of that, LaCo0 was similarly evaporated to a thickness of about 1 circuit. For comparison, Rf sputtering was performed directly on stabilized zirconia. LaCo0 was deposited by evaporation.These samples were heat-treated in air at 1000°C for 12 hours.

As a result of identifying the surface of the heat-treated sample by X-ray diffraction, the formation of LatZrzOy was observed when Labors were directly deposited on stabilized zirconia. On the other hand, when Lao, 5BaO, +Al0t,s was interposed between the stabilized zirconia and LaC0Q3, no reaction product was observed.

Example 2 Stabilized zirconia (8 mol% Y2O3) as in Example 1
Lao,
*The oxygen reduction polarization characteristics at 800°C were investigated using Bao, +AIO,,,s deposited to a thickness of approximately 1 g, and LaCoOU deposited on top of it to a thickness of approximately 1 μm. , and for comparison, Rf on directly stabilized zirconia
- Oxygen reduction polarization characteristics were similarly investigated using a sample on which LaCoO3 was deposited by sputtering. In either case, measurements were performed after the electrodes were heat-treated at 1000° C. for 12 hours. Oxygen reduction polarization characteristics were determined by examining the relationship between current density and overvoltage. The measurement was carried out by using a platinum paste electrode as a counter electrode, and using a part of the electrode as a reference electrode, the potential difference between the electrode and the measurement electrode was determined by using the interlator method to remove the resistance component. If oxygen is reversibly reduced, the overvoltage will be zero, but since an irreversible reaction generally occurs, an overvoltage will occur. The smaller the overvoltage, the better the battery characteristics.

The results are shown in Figure 2.As can be seen from Figure 2, LaC
o0. Lao, 5B as a barrier film compared to the case alone
When using ao, +AIO□9S, the overvoltage is much smaller and the oxygen reduction property is better.

The high overvoltage in the case of LaCoO3 alone is due to the reaction between the stabilized zirconia and LaCoO3, which is non-conductive.
, Zr, and O, were generated.

Example 3 Stabilized zirconia (8 mol% Y2O3) as in Example 1
Lao,
gSro, l 1noi, lls 1.40gm
LaCo0. about 1.77μ
Oxygen reduction polarization characteristics were investigated in the same manner as in Example 2 using the material deposited to a thickness of (2). The results are shown in FIG. 3. From the comparative examples in FIGS. 3 and 2, LaCo0. Compared to the case alone, Lao, 5srollnoz,
It was found that the overvoltage was smaller and the oxygen reduction properties were better when using LLs, and also Lao, 5
Sro, l1not, and ss were found to have excellent long-term stability and high temperature operability.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the operating principle of a fuel cell in which the oxygen electrode structure of the present invention is used, and FIGS. 2 and 3 are diagrams showing the oxygen electrode structure of the present invention and the oxygen electrode of a conventional fuel cell. It is a graph showing oxygen reduction polarization characteristics. Spear I S ′ Recitation l Ro

Claims (2)

[Claims] (1) An oxygen electrode structure for a high-temperature solid electrolyte fuel cell using stabilized zirconia as a solid electrolyte, which has the general formula La_1_-_xM^1_xM^2O_3_-_x
＿／＿２(However, M^1 is Sr, Mg, Ca or Ba
, M^2 is Co, Fe, or Mn;
1_-_yM^3_yM^4O_3_-_y_/_2(
However, M^3 is Sr, Mg, Ca or Ba, M^4 is Al or In, and y is a number greater than 0 and less than 1. Oxygen electrode structure for batteries. (2) The above film has La_0_. _9Ba_0_. _1Al
O_2_. _9_5 or La_0_. _9Sr_0_.
_1InO_2_. Claim 1 which is _9_5
The oxygen electrode structure described in Section 1.