JP2002352809A - Guiding method of electrode active oxide into fuel pole for solid electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method wherein, in order to improve the electrode characteristics of a fuel pole, a mixed conductor is guided to the vicinity of an interface with an electrolyte, with no occurrence of degraded material. SOLUTION: A fuel pole and a solid electrolyte are baked. An electrode active oxide containing both electron conduction and oxygen ion conduction is infiltrated, as an organic metal solution or inorganic metal salt solution, into the porous fuel pole. Then by a thermal decomposition oxidative reaction, the electrode active oxide of a desired composition is guided to the vicinity of an interface with the solid electrolyte. Thus, the fuel pole for a solid electrolyte fuel cell of high performance is provided with no strict limit on a baking process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for introducing an electrode active oxide into a fuel electrode for a solid oxide fuel cell.

[0002]

2. Description of the Related Art In recent years, interest has been growing in solid oxide 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 Carnot efficiency, and have excellent features such as better environmental protection. .

However, a solid oxide fuel cell is
Since the main part is made of ceramic, the manufacturing cost is high. This has hindered the spread of solid oxide fuel cells. Here, the operating temperature of this battery is set to the current 1000 ° C.
When the temperature is lowered to 800 ° C. or lower, metal can be used. As a result, the interconnector portion occupying the main volume can be replaced with inexpensive metal, which leads to significant cost reduction.

For the purpose of lowering the temperature, studies have been made on improving the ionic conductivity of the electrolyte, making the electrolyte thinner, and the like. As the solid electrolyte, rare earth-added zirconia ((1-x)
ZrO _2-x A ₂ O ₃ , where A is La, Pr, Ce, Nd, S
m, Eu, Gd, Tb, Dy, Ho, Er, Yb, L
elements such as u, Y, Sc, Al, and Ga, and 0.025 ≦
x ≦ 0.15) to make it thinner, a Sc-added zirconia electrolyte material having a high ionic conductivity, or a lanthanum gallate-based electrolyte Ln _1-x A _x B _1-y Mg _y O ₃ (Ln In elements such as La, Pr, Nd, and Sm, A is Sr, Ca,
X such as Ba is 0.05 ≦ x ≦ 0.2, B is Ga, Al
For example, the total amount y of Mg is mainly considered to be 0.05 ≦ y ≦ 0.3). In addition to these, it is necessary to greatly improve the performance of electrodes such as fuel electrodes. This is because the electrochemical reaction speed sharply decreases due to the low temperature.

A fuel cell is provided with an air electrode and a fuel electrode with an electrolyte interposed therebetween, and these electrodes supply gas and electrons to the electrolyte and generate a field where an electrochemical reaction occurs at an interface with the electrolyte. providing. This reaction field is called a three-phase interface because gas, electrons and ions come into contact with each other.

The fuel electrode is NiO-YSZ, that is, Ni as an electron conductor and YSZ (0.
A mixture of 92ZrO ₂ -0.08Y ₂ O ₃ ) is used, and the three-phase interface can be an interface between Ni and YSZ. It is said that when an electrode active oxide, which is a conductor for both electrons and oxygen ions, is in contact with this interface, a reaction field, that is, a three-phase interface is significantly expanded, and the electrode characteristics are improved.

Examples of electrode active oxides stable in reducing atmosphere
As SDC (Ce_0.8Sm_0.2O _1.9Ceria)
Oxide and (LaSr) (GaMg) O_ThreeLanta such as
Transition of Co, Ni, etc. to the B site of the ngarate oxide
A system to which a metal is added is known.

A fuel electrode can be formed by sintering using a raw material powder obtained by mixing these materials with a conventional material such as NiO-YSZ. However, in the process of fabricating the cell, 1300
When exposed to a high temperature of about ° C, these materials react with the electrolyte or the oxide such as NiO forming the fuel electrode to generate a degraded substance near the interface.

[0009] For example La ₂ Zr ₂ O ₇ zirconia based electrolyte and insulator lanthanum perovskite oxide or SrZrO _3, a very low oxygen ionic conductivity of ceria based material and zirconia electrolyte Ce _0.5 Zr _0.5 O _2, Is generated. In addition, the lanthanum gallate-based mixed conductor and the lanthanum gallate-based solid electrolyte can easily form a solid solution, diffuse deeply into the solid electrolyte, and lower the ionic transport number of the electrolyte. cause.

As described above, the cell electrode and the electrolyte are required to suppress the deterioration reaction even in a considerably high temperature range compared with the operating temperature of 700 ° C. to 1000 ° C. Difficult to use things.

[0011]

The object of the present invention is to improve the electrode characteristics of a fuel electrode, which is required for a method for manufacturing a cell for a solid electrolyte.
It is an object of the present invention to provide a method for manufacturing a fuel electrode in which a mixed conductor is introduced near an interface with an electrolyte and does not cause deterioration.

[0012]

Means for Solving the Problems In order to solve the above problems, the method for introducing an electrode active oxide into a fuel electrode for a solid oxide fuel cell according to the present invention is provided by providing a dense solid electrolyte and both surfaces thereof. A method for introducing an electrode active oxide into a solid oxide fuel cell air electrode of a fuel cell having a fuel cell composed of a porous fuel electrode and an air electrode, wherein the fuel electrode and the solid electrolyte are sintered. After formation, a porous fuel electrode is impregnated with a material of an electrode active oxide having both electron conduction and oxygen ion conduction in the form of an organic metal solution or an inorganic metal salt solution, and then subjected to a thermal decomposition oxidation reaction. Is introduced into the vicinity of the interface with the electrolyte.

That is, according to the present invention, after firing of the fuel electrode and the solid electrolyte which is the highest temperature firing process, the electrode active oxide is formed in the fuel electrode in the form of an organic metal solution or an inorganic metal salt solution. Impregnate the solution to be formed. Thereafter, at an appropriate temperature at which no deterioration reaction occurs, a thermal decomposition oxidation reaction of the liquid in the fuel electrode is caused to introduce a desired mixed conductor, that is, an electrode active oxide, near the solid electrolyte interface.

Here, as a method for producing a cell, when a fuel electrode is first formed and an electrolyte and an air electrode are formed thereon, the solution is impregnated immediately after the electrolyte is produced or after the air electrode is produced. . When the fuel electrode is formed last, impregnation is performed after forming the fuel electrode. When firing all of the interconnectors and the like, they are impregnated after firing.

[0015]

The operation of the present invention will be described below.

In the fuel electrode, in order to suppress deterioration at the interface,
A zirconia-based solid electrolyte and a zirconia-based fuel electrode, or a lanthanum gallate-based solid electrolyte and a lanthanum gallate-based fuel electrode are used. Thereby, the sintering of the fuel electrode and the solid electrolyte can be performed at a sufficiently high temperature, and the fuel electrode and the dense solid electrolyte having sufficiently high mechanical strength can be obtained.

After the firing, the fuel electrode is impregnated with an organic metal solution or an inorganic metal salt solution. Since the fuel electrode is a porous material but has fine pores, it is difficult for a slurry in which ordinary powder is developed into a solution to sufficiently penetrate into the electrolyte interface.

However, since the solution used here does not contain solid matter, it penetrates the fuel electrode and reaches near the interface between the electrolyte and the fuel electrode. This solution generates an electrode active oxide such as SDC by a thermal decomposition oxidation reaction.

Here, the composition of the electrode active oxide can be easily controlled by previously controlling the amount of the metal element contained in the solution for forming the electrode active oxide. Since this electrode active oxide can conduct both electrons and oxygen ions, the three-phase interface contributing to the electrode reaction spreads throughout the electrode active oxide. For this reason, the electrode characteristics of the fuel electrode are greatly improved.

According to the above-mentioned method, the electrode active oxide can be introduced into the fuel electrode without much restriction of the sintering temperature in the cell manufacturing process. Fuel electrode can be realized.

[0021]

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

[0022]

Embodiment 1 FIGS. 1 and 2 show a fuel cell used in the embodiment and a fuel cell assembled using the same.
As is clear from FIGS. 1 and 2, the dense solid electrolyte 1 has an air electrode 2 formed on one surface and a fuel electrode 3 formed on the other surface, and the air electrode 2 and the fuel electrode 3 are formed of platinum. The current collecting mesh 4 is provided. In the figure, 5 is a platinum terminal, and 6 is a gas seal.

First, 0.2 was fired by a doctor blade method.
mm thick with _{Sc 2 O 3, Al 2 O} 3 doped zirconia (SASZ
Or 0.895 ZrO ₂ -0.10 Sc ₂ O ₃ -0.
005Al ₂ O ₃ ) NiO—S on one surface of the solid electrolyte substrate 1
ASZ slurry (10 mol% Sc ₂ O ₃ , 0.5 mol
% Al ₂ O ₃ -added zirconia, NiO is 60 wt%), and a platinum current collecting mesh 4 is placed thereon, and 1300
The fuel electrode 3 was provided by firing at 1 ° C. for 1 hour.

Next, an LSM (La _0.78 Sr _0.2
A slurry of MnO ₃ ) was applied and fired at 1200 ° C. for 1 hour to form an air electrode 2. Both the fuel electrode 3 and the air electrode 2 had a diameter of 6 mm. This fuel cell is referred to as cell # 1-0-1.
And This is a comparative example.

Next, Ce _0.9 Sm was used as the electrode active oxide.
_0.1 O _1.95 , Ce _0.8 Sm _0.2 O _1.9 , Ce _0.6 Sm _0.4 O
_1.8 , Ce _0.8 La _0.2 O _1.9 , Ce _0.8 Gd _0.2 O _1.9 , C
e _0.8 Lu _0.2 O _1.9 , Ce _0.8 Y _0.2 O _1.9 , Ce _0.8 Gd
A toluene solution in which the metal alkoxide of the electrode active oxide material was dissolved was prepared so as to have a composition of _0.1 Sm _0.1 O _1.9 .

The concentration of the metal in this solution was about 4 wt%. This was impregnated into the fuel electrode of a cell manufactured under the same conditions as cell # 1-0-1, and then heat-treated at 1100 ° C. in air to deposit an electrode active oxide having a desired composition. These are referred to as cells # 1-1-1 to # 1-1-8.

A fuel cell shown in FIG. 2 was assembled using these cells and the cells of the comparative example, and a power generation test was performed at 800 ° C. Here, hydrogen was supplied to the fuel electrode, and oxygen was supplied to the air electrode. As the open electromotive force, a value of 1.1 V or more was obtained. The results are shown in Table 1 as # 1-0-1 to # 1-1.
-8. In # 1-1-1 to # 1-1-8, a higher cell output was obtained than in the cell # 1-0-1 of the comparative example.

As described above, the production method of the present invention succeeded in producing a cell having better characteristics than the conventional method.

[0029]

Example 2 In the cell # 1-0-1 of Example 1, the electrolyte was changed to SYbSZ (0.89ZrO ₂ −
0.09 Sc ₂ O ₃ -0.02 Yb ₂ O ₃ ) was replaced with cell # 2-0-1 and Ni instead of NiO in the fuel electrode.
_The cell using _0.8 Fe _0.2 O _1.1 was replaced with cell # 2-0-2, N
A cell using i _0.8 Co _0.2 O _1.1 is referred to as cell # 2-0-3,
The cell using Ni _0.8 Fe _0.1 Co _0.1 O _1.1 was replaced with cell # 2-
0-4.

These cells are referred to as cells of the comparative example. Then, as in Example 1, Ce _0.8 Sm _0.2 O
_The electrode active oxide materials Ce and S are formed so as to have a composition of _1.9.
The alkoxide solutions of m and m were mixed to form a toluene solution, and the fuel electrodes of cells # 2-0-1 to # 2-0-4 were impregnated with each other and heat-treated at 1100 ° C. These cells are referred to as cells # 2-1-1 to # 2-1-4.

Using these cells and the cell of the comparative example,
The same experiment as in Example 1 was performed. The results are shown in cells # 2-1-1 to # 2-1-4 in Table 1. All of the results are better than those of cells # 2-0-1 to # 2-0-4 as comparative examples. Characteristics were obtained.

[0032]

Example 3 The metal alkoxide solution to be impregnated in the cell # 2-0-1 of Example 2 was changed to La _0.90 Sr
_0.10 Ga _0.75 Mg _0.15 Ni _0.10 O ₃ and La _0.90 Sr
_{0.10 Ga 0 .75 Mg 0.15 Co 0.10} O 3, and La _0.90 S
A solution was prepared so as to have a composition of r _0.10 Ga _0.71 Mg _0.15 Ni _0.07 Co _0.07 O ₃ , and was impregnated into the fuel electrode.

Then, heat treatment was performed at 1,000 ° C. in air to precipitate an electrode active oxide having a desired composition. These are referred to as cells # 3-1-1 to # 3-1-3. The same experiment as in Example 2 was performed using these cells. The results are shown in cells # 3-1-1 to # 3-1-3 in Table 1. In each case, better cell output characteristics were obtained as compared with cell # 2-0-1 as a comparative example.

[0034]

Embodiment 4 Here, LSGM (La _0.90 Sr _0.10 G
a _0.85 Mg _0.15 O ₃ ) was used as the solid electrolyte. This is La ₂
O ₃ , SrCO ₃ , Ga ₂ O ₃ , and MgO powder were mixed so as to have a desired composition, and a solid phase reaction was caused in air at 1400 ° C. to synthesize. The synthesized powder was formed into a pellet and fired at 1500 ° C. Polish this pellet,
A solid electrolyte having a thickness of 0.3 mm and a diameter of 24 mm was used.

Next, NiO and La _0.90 Sr _0.10 Ga _0.85 M
A slurry of a mixture of g _0.15 O ₃ fine particles was applied on the solid electrolyte, and calcined at 1300 ° C. to obtain a fuel electrode. Then, an LSM air electrode was provided on the opposite surface of the fuel electrode in the same manner as in Example 1.

This cell is referred to as cell # 4-0-1. Cell # 4-0-1 in composition _{Ce 0.8 Sm 0 .2 O 1.9,} Ce 0.8 G
d _0.2 O _{1.9 A} metal alkoxide solution was prepared and impregnated into the fuel electrode.
Thermal decomposition reaction, and the electrode active oxide Ce _0.8 S
Fine particles of m _0.2 O _1.9 and Ce _0.8 Gd _0.2 O _1.9 were deposited in the fuel electrode.

This cell is referred to as cell # 4-1-1, cell # 4-
1-2, and the same experiment as in Example 1 was performed. The results are shown in cell # 4-1-1 and cell # 4-1-2 in Table 1. As a result, better cell output characteristics were obtained compared to cell # 4-0-1 of the comparative example.

[0038]

Fifth Embodiment The same type as the cell # 4-0-1 of the fourth embodiment is used.
La is used as an electrode active oxide in the cell. _0.90Sr_0.10Ga
_0.75Mg_0.15Ni_0.10O_ThreeAnd La_0.90Sr_0.10Ga
_0.75Mg_{0 .15}Co_0.10O_Three, La_0.90Sr_0.10Ga_0.71
Mg_0.15Ni_0.07Co_0.07O_Three, Pr_0.90Sr_0.10Ga
_0.75Mg_0.15Ni_0.10O_Three, Sm_0.90Sr_0.10Ga_0.75
Mg_{0 .15}Ni_0.10O_Three, Gd_0.90Sr_0.10Ga_0.75Mg
_0.15Ni_0.10O_Three, La_0.90Ca _0.10Ga_0.75Mg_0.15
Ni_0.10O_Three, La_0.90Ba_0.10Ga_0.75Mg_0.15Ni
_{0.1 0}O_ThreePrepare a metal alkoxide solution to obtain the composition of
And the same experiment as in Example 4 was performed.
Was.

The results are shown in Table 1 in cells # 5-1-1 to # 5.
It shows in -1-8. Cell # 4-0- is a comparative example.
As a result, good cell output characteristics were obtained.

[0040]

Example 6 The electrolyte of Example 1 was replaced with YSZ (0.9
A ₂ mm ZrO ₂ -0.08 Y ₂ O ₃ ) sheet is prepared, a slurry containing a NiO-YSZ mixture (60 wt% of NiO) is applied thereto, and the resultant is calcined at 1300 ° C. to form a fuel electrode. did.

Next, 0.92 (Zr _0.93 Ti _0.07 ) O ₂ −
A metal alkoxide solution was prepared so as to have a composition of 0.08 Y ₂ O ₃ , and this fuel electrode was impregnated and heat-treated at 1100 ° C. to precipitate an electrode active oxide.

Next, an LSM air electrode was provided thereon in the same manner as in Example 1. This cell is referred to as a cell # 6-1-1. Here, a cell in which the fuel electrode was not impregnated with the above solution was produced as a comparative example. This is called cell # 6-0-1.

An experiment similar to that of the first embodiment was performed using these cells. The results are shown in Table 1 in cells # 6-0-1, # 6.
It shows in -1-1. Cell # 6-1-1 had better output characteristics than cell # 6-0-1 as a comparative example.

[0044]

Seventh Embodiment Cell # 1-0-1 which is a comparative example of the first embodiment
Is again used as a comparative example. Then, Ce _0.9 Sm _0.1 O _1.95 , Ce _{0.8
Sm 0 .2 O 1.9, Ce 0.6} Sm 0.4 O 1.8, Ce 0.8 La 0.2
O, _1.9 , Ce _0.8 Y _0.2 O _1.9
A nitrate aqueous solution having a molar ratio of m, La, and Y was prepared, and this was impregnated into the fuel electrode of a cell of the same type as cell # 6-0-1.

Then, heat treatment was performed in air at 1100 ° C. to precipitate an electrode active oxide having a desired composition. These were designated as cells # 7-1-1 to # 7-1-5, and the same experiment as in Example 5 was performed. The result is shown in cell # 7-1- in Table 1.
1 to cell # 7-1-5. In these, a higher cell output was obtained as compared with cell # 1-0-1 of the comparative example.

As described above, the production method of the present invention succeeded in producing a cell having better characteristics than the conventional method.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

[Table 3]

[0050]

[Table 4]

[0051]

As described above, after firing the fuel electrode and the solid electrolyte, the fuel electrode is impregnated with a solution of an organic metal or inorganic metal salt containing a metal element for forming a mixed conductor oxide. This oxide was formed near the interface with the electrolyte by a thermal decomposition reaction. As a result, a high performance fuel electrode for a solid oxide fuel cell was successfully obtained without much restriction on the firing process. The present invention makes a great contribution to improving the efficiency of a solid fuel cell.

[Brief description of the drawings]

FIG. 1 is a diagram showing the structure of a single cell and a fuel cell in an embodiment.

FIG. 2 is a cross-sectional view illustrating a structure of a fuel cell according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Solid electrolyte 2 Air electrode 3 Fuel electrode 4 Current collection mesh 5 Platinum terminal 6 Gas seal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yoji Sakurai 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term within Nippon Telegraph and Telephone Corporation (reference) 5H018 AA06 AS02 AS03 BB01 BB05 CC06 DD01 EE02 EE04 EE10 EE12 EE13

Claims (7)

[Claims] 1. An electrode active oxidation of a fuel cell having a dense solid electrolyte and a fuel cell composed of a porous fuel electrode and an air electrode provided on both surfaces thereof to a fuel electrode for a solid oxide fuel cell. In the method for introducing a substance, after sintering the fuel electrode and the solid electrolyte, the material of the electrode active oxide having both electron conduction and oxygen ion conduction inside the porous fuel electrode is treated with an organic metal solution or an inorganic metal salt. The electrode active oxide having a desired composition is introduced into the vicinity of the interface with the electrolyte by a thermal decomposition oxidation reaction after impregnation in the form of a solution. How to introduce. 2. The solid electrolyte according to claim 1, wherein the solid electrolyte is made of a zirconia-based oxide to which at least one element selected from the group consisting of rare earth and Al and Ga is added, and the fuel electrode is made of rare earth, Al and G.
A fuel electrode for a solid oxide fuel cell, comprising a zirconia-based oxide and Ni or an alloy of Ni and Co or Fe to which at least one of a is added, or a mixture of these oxides. Of introducing an electrode active oxide into the electrode. 3. The solid electrolyte according to claim 1, wherein the solid electrolyte is made of a lanthanum gallate-based oxide, and the fuel electrode is made of a lanthanum gallate-based oxide and Ni or an alloy of Ni and Co or Fe, or a mixture of these oxides. A method for introducing an electrode active oxide into a fuel electrode for a solid oxide fuel cell, characterized by comprising: 4. The method of claim 2 and claim 3, the electrode composition active _{oxide, Ce 1-x Ln x O} 2-x / 2 (Ln is Y
Or a system in which Ce in Lu is removed from La in the periodic table of elements or a system to which two or more elements are added, and the total amount x is 0.1 ≦ x ≦ 0.4) A method for introducing an electrode active oxide into a fuel electrode for a solid oxide fuel cell, comprising the steps of: 5. The method of claim 2, the composition of the electrode active oxides, (1-y) (Zr 1-x Ti x O 2) -y (Ln
₂ O ₃ ) (Ln is L from Y, Sc or Gd of the periodic table)
u, or two or more of these elements, and the total amount x of Ti is 0.03 ≦ x ≦ 0.2 and Ln ₂
A method for introducing an electrode active oxide into a fuel electrode for a solid oxide fuel cell, wherein the total amount y of O ₃ is 0.03 ≦ y ≦ 0.15). 6. The method according to claim 2, wherein the composition of the electrode active oxide is Ln _1-x C _x Ga _1-y D _y O ₃ (Ln
Is one or more of La, Pr, Nd, Eu, Gd, and Tb; C is one or more of Ca, Sr, and Ba; and D is Mg, Ni, Co, Fe, and Al. One or more elements, 0.05 ≦ x ≦ 0.2, 0.1 ≦ y ≦ 0.
3) A method for introducing an electrode active oxide into a fuel electrode for a solid oxide fuel cell, wherein 7. The porous fuel electrode according to claim 1, wherein the electrode active oxide material forming the electrode active oxide is impregnated in the form of an alkoxide solution or a nitric acid solution. A method for introducing an electrode active oxide into an air electrode for a solid oxide fuel cell.