JPH09106821A - Solid electrolyte fuel cell and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the proceeding of sintering of Ni particles which compose a fuel electrode during operation of a cell and make a solid electrolyte film dense by filling and covering the space between the surface of fuel electrode composing particles and a joining face of a solid electrolyte with a fixing agent by impregnation with the agent. SOLUTION: From the surface side to a solid electrolyte 3 side, a fuel electrode is impregnated with a slurry fixing agent containing a fine power of at least one oxide of Zr, Y, Mg, and C, which is a composing element of an electrolyte. Consequently, the fixing agent is stuck to and cover the gaps between the surface of Ni particles 41 and of yttria-stabilized zirconia(YSZ) particles 42, which are a fuel electrode composing elements, and the joining face of the electrolyte film 3, and at the same time air-through holes 31 of the film 3 are filled with the agent and after that, the resultant body is dried and sintered. By this method, sintering among Ni particles composing the fuel electrode during operation of a cell can be suppressed and the solid electrolyte film becomes dense, so that a fuel cell in which deterioration of the electricity generating function with the lapse of time can be prevented and initial efficiency can last for a long period.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid oxide fuel cell using an oxide ion conductor, and more particularly to a method for preventing deterioration of power generation performance due to aging of a fuel electrode. .

[0002]

2. Description of the Related Art The body of a solid oxide fuel cell has a solid electrolyte membrane sandwiched between an air electrode on one side and a fuel electrode on the other side. )
Is configured to supply a fuel gas containing hydrogen to the fuel electrode side. When an oxide ion conductor is used as the electrolyte, oxygen ions ionized on the air electrode side move through the electrolyte to reach the fuel electrode, react with hydrogen, and emit electrons. Thus, at the same time as the formation of a cell having the air electrode as the anode and the fuel electrode as the cathode, water is produced as a by-product at the fuel electrode.

FIG. 3 shows a solid oxide fuel cell (cylindrical system).
In the figure, reference numeral 1 is a porous base tube for supporting a fuel cell element, and its material is ceramics such as calcia-stabilized zirconia (CSZ) or alumina.

Reference numeral 2 denotes an electrode (air electrode) formed on the outer circumference of the substrate tube 1, which is stable in a high temperature oxidizing atmosphere at about 1000 ° C., has high electron conductivity, and is porous and allows good air circulation. , Thermal conductivity is close to that of the solid electrolyte 3 formed on the air electrode 2, and good adhesion is required. Therefore, composite oxides such as lanthanum manganate and lanthanum calcium manganate are generally used.

The solid electrolyte 3 has excellent oxygen ion permeability, is chemically stable at high temperatures, and operates the battery.
It is required to be resistant to thermal shock due to repeated pauses, dense, and impermeable to air and fuel gas. The reason for this is that if air and fuel gas are mixed together through this membrane, the efficiency of the electrochemical reaction will be reduced and the fuel costs will be disadvantageous.

Zirconia is a material which satisfies these various conditions, but in order to prevent the damage due to the volume change at high temperature, an oxide of an alkaline earth metal (Sr, Mg, Ca, etc.) or a rare earth element oxide is solid-dissolved. Stabilized zirconia, especially yttria-stabilized zirconia (YSZ) is often used.

Numeral 4 is an electrode (fuel electrode), which has a high electron conductivity, a thermal expansion coefficient close to that of the solid electrolyte 3 inside thereof, and good adhesion. Therefore, cermets in which a coefficient of thermal expansion is adjusted by adding stabilized zirconia to nickel, especially Ni-YSZ cermets are often used. Further, since the above-described electrochemical reaction in this fuel cell proceeds at the interface (three-phase interface) where the reaction gas such as oxygen and hydrogen, the solid electrolyte and the electrode are in contact with each other, the number of three-phase interfaces is increased as much as possible to improve the power generation performance. In order to enhance it, the anode must be made porous. Therefore, conventionally, the fuel electrode has been formed into a porous film by adjusting the particle size of the Ni-YSZ cermet powder or the powder of each of Ni and YSZ, the spraying or firing conditions, and the like.

Reference numeral 5 is a conductor (interconnector) for connecting a plurality of cells in series, which is directly connected to the air electrode 2,
Moreover, it is provided so as to be insulated from the fuel electrode 4. In addition to high conductivity, it is required at present to be stable in both oxidizing and reducing atmospheres at a high temperature of about 1000 ° C, and to be highly airtight so that fuel and air do not mix, so that it is currently Lanthanum chromite oxide is mainly used.

In addition to the illustrated cylindrical system, there is also a flat plate system, and there is also a cylindrical system in which the strength of the air electrode is increased and the substrate tube is omitted. The present invention relates to the modification of a film and can be applied to any method regardless of the overall structure.

1 and 2 are cross-sectional views of the solid electrolyte 3 and the fuel electrode 4 formed on the solid electrolyte 3 in such a fuel cell.
Is schematically shown in. When the fuel electrode is formed by the mixed powder spraying of the nickel powder and the YSZ powder as in Examples 1 and 2 which will be described later, as shown on the left side of FIGS.
On the solid electrolyte membrane 3 made of nickel particles 41 and Y
The SZ particles 42 are stacked and bonded to each other to form a porous fuel electrode.

[0011]

When such a battery is operated, it is placed in a high temperature atmosphere of about 1000 ° C. for a long period of time, so that sintering of nickel particles composing the fuel electrode progresses from the contact portion. As a result of a decrease in the porosity of the fuel electrode and a decrease in the three-phase interface, the power generation performance of the cell deteriorates over time.

When the composite powder in which YSZ powder is coated with nickel is used for the thermal spray coating of the fuel electrode, the surface of the constituent particles is all nickel, and the half surface constituent particles are excellent in the conductivity of the fuel electrode. The demerit due to the progress of sintering is also large. When Ni-YSZ cermet powder is used for the thermal spray coating of the fuel electrode, it is almost the same as the case of the composite powder.

Further, the solid electrolyte 3 needs to be dense as described above and must not have a vent hole, but in reality, it is difficult to form a film with a perfect density. . In particular, in order to improve the adhesion with the fuel electrode and increase the three-phase interface, for example, when the surface is roughly formed by adjusting the particle size of the raw material powder, the spraying conditions, etc. Is hard to avoid. Therefore, some kind of sealing treatment,
A method which can be applied after stacking the fuel electrodes has been desired.

[0014]

Means for Solving the Problems After a solid electrolyte and a fuel electrode are formed into a film, a slurry or a solution containing an immobilizing agent is impregnated from the surface of the fuel electrode, and the surfaces of the constituent particles of the fuel electrode and the joint surface with the solid electrolyte. After being adhered and coated in the gaps, dried and baked. Here, as the immobilizing agent, one that does not adversely affect the characteristics of the electrode is desirable, and in that sense, it is a constituent element of the solid electrolyte and is common to the fuel electrode.
r, Y, Mg, Ca or their oxides are suitable. These immobilizing agents may be used as an aqueous solution of the metal salt, or may be used as a slurry in which fine powder is suspended. In this case, the particle size of the fine powder is 1
It is desirable that it is not more than μm.

These immobilizing agents are N constituting the fuel electrode.
It adheres to the surface of the i particles to prevent direct contact between Ni particles, and suppresses the progress of sintering due to high temperature during operation. Further, when the solid electrolyte membrane has a vent hole, it is impregnated and filled into the vent hole to densify the membrane. As a result of these actions, deterioration of the power generation performance of the battery over time is prevented.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) First, a lanthanum-manganese-based oxide powder was extruded and fired to produce a porous substrate tube 1, and the lanthanum-manganese-based oxide powder was sprayed on the outer peripheral surface of the lanthanum-manganese-based oxide powder in an Ar gas atmosphere by high-frequency plasma spraying. A quality cathode 2 was deposited.

The solid electrolyte 3 is mainly composed of yttria-stabilized zirconia (YSZ) powder having a particle size of 5 to 25 μm, and a mixed powder prepared by adding 10% by weight of Zr-8 mol% Y alloy powder is prepared. The powder was densely formed on the air electrode 2 by plasma spraying under reduced pressure (100 torr). Next, a mixed powder of YSZ powder and nickel oxide powder was sprayed onto the solid electrolyte membrane 3 at atmospheric pressure to form the fuel electrode 4 as a porous film.

The left side of FIG. 1 is a schematic view of a cross section of the solid electrolyte membrane 3 and the fuel electrode 4 thus obtained, in which YSZ particles 42 and nickel oxide particles 41 are formed on the densely formed solid electrolyte membrane 3. It shows a state in which they are connected to each other in a stacked state to form a porous fuel electrode 4. As described above, if it is left as it is, the sintering proceeds from the contact portion between the nickel particles, resulting in an unfavorable result.

Therefore, a slurry containing zirconia powder and zirconia oxide powder having a particle size adjusted to 1 μm or less is impregnated from the fuel electrode side and dried, and then in an oxidizing atmosphere 70
By firing at 0 to 1000 ° C., each particle forming the fuel electrode was coated and fixed, and the gap between the fuel electrode and the solid electrolyte was filled. The right side of FIG. 1 schematically shows a state in which nickel particles are fixed by this fixing treatment.

Next, when an interconnector was formed on each of the samples before and after the immobilization treatment to complete a fuel cell, and the power generation characteristics were compared after 500 hours of operation, the samples before treatment (Fig. In the case of the sample on the left side of (1), the deterioration rate is 13.2% / at 300 mA / cm ^2.
The deterioration rate was 3.1% / in the case of the sample after the immobilization treatment (the sample in the state on the right side of the figure), while it was 1000 h.
It was confirmed that the immobilization treatment according to the present invention was effective, since the result was remarkably reduced to 1000 hours.

(Example 2) The substrate tube 1 and the air electrode were formed in the same manner as in Example 1 described above, and the solid electrolyte 3 was made of yttria-stabilized zirconia (YS) having a particle size of 5 to 25 µm.
Z) Powder was formed on the air electrode 2 by plasma spraying under reduced pressure (100 torr). Then, on the solid electrolyte membrane 3,
A mixed powder of YSZ powder and nickel oxide powder was sprayed at atmospheric pressure to form the fuel electrode 4 in a porous film.

The left side of FIG. 2 is a schematic view of the cross section of the solid electrolyte membrane 3 and the fuel electrode thus obtained, and YSZ particles 4
The state in which 2 and the nickel oxide particles 41 are stacked to form a porous fuel electrode is similar to that in the case of Example 1 (left side of FIG. 1), but the solid electrolyte 3 has the vent holes 31, It communicates with the air electrode side (not shown). If this is left as it is, there is a possibility that air and fuel gas may be mixed in addition to the progress of sintering of the nickel particles described above.

Therefore, an aqueous solution of zirconium acetate is impregnated from the fuel electrode side and dried, and then 700 to 700 in an oxidizing atmosphere.
By firing at 1000 ° C., each particle constituting the fuel electrode was covered and fixed, and the gap between the fuel electrode and the solid electrolyte and the vent hole 31 of the solid electrolyte 3 were filled. The right side of FIG. 2 schematically shows a state in which nickel particles are fixed by this fixing treatment and the air holes 31 of the solid electrolyte are sealed.

Next, an interconnector was formed on each of the samples before and after the immobilization treatment to complete a fuel cell, and a comparative test of power generation characteristics was carried out after 500 hours of operation. 300 for the sample
The deterioration rate was 12.9% / 1000 h at mA / cm ² , whereas the deterioration rate was 2.2% / 1000 h for the sample after the immobilization treatment. It was confirmed that the immobilization treatment was also effective in.

[0025]

As described above in detail, according to the present invention, the progress of sintering of Ni particles constituting the fuel electrode during the operation of the fuel cell is suppressed, and the solid electrolyte membrane has a vent hole. In some cases, the film is densified. As a result of these actions, there is an effect of preventing the power generation performance of the fuel cell from deteriorating with time and making the initial efficiency permanent.

[Brief description of the drawings]

FIG. 1 is a schematic view of a cross section of a fuel electrode 4 and a solid electrolyte 3 for explaining an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a fuel electrode 4 and a solid electrolyte 3 for explaining another embodiment of the present invention.

FIG. 3 is a perspective view showing a general structure of a solid oxide fuel cell (cylindrical method).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Base tube 2 Air electrode 3 Solid electrolyte 4 Fuel electrode 5 Interconnector 31 Vent hole 41 Nickel particle 42 YSZ particle 43 Composite particle 44 Immobilizing agent

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoru Yamaoka 5-5-1 Kiba, Koto-ku, Tokyo Inside Fujikura Stock Company

Claims (5)

[Claims] 1. A solid electrolyte membrane is sandwiched between an air electrode on one side and a fuel electrode on the other side, and air is placed on the side of the air electrode and fuel gas containing hydrogen is placed on the side of the fuel electrode. In a solid oxide fuel cell configured to supply and generate electric power, an immobilizing agent is impregnated into the solid electrolyte side from the surface of the fuel electrode, and adheres to and covers the gaps between the surface of the constituent particles of the fuel electrode and the joint surface with the solid electrolyte. A method for producing a solid oxide fuel cell, which comprises performing drying and firing. 2. A solid electrolyte membrane is sandwiched and an air electrode is laminated on one surface of the solid electrolyte membrane, and a fuel electrode is laminated on the other surface of the solid electrolyte membrane. Air is placed on the air electrode side and fuel gas containing hydrogen is placed on the fuel electrode side. In a solid oxide fuel cell configured to supply and generate electric power, an immobilizing agent is impregnated into the solid electrolyte side from the surface of the fuel electrode, and the surface of the constituent particles of the fuel electrode, the gap between the joint surface of the fuel electrode and the solid electrolyte, and the solid A method for producing a solid oxide fuel cell, which comprises drying and firing after depositing and covering the inside of the remaining vent holes of the electrolyte membrane. 3. The immobilizing agent is a slurry containing a fine powder of at least one kind of Zr, Y, Mg, Ca which is a constituent element of the solid electrolyte and an oxide thereof. The method for producing a solid oxide fuel cell according to item 1. 4. The solid according to claim 1, wherein the immobilizing agent is a solution containing at least one metal salt of Zr, Y, Mg, and Ca, which is a constituent element of the solid electrolyte. Method for manufacturing electrolyte fuel cell. 5. A solid electrolyte membrane is sandwiched and an air electrode is laminated on one surface of the solid electrolyte membrane, and a fuel electrode is laminated on the other surface of the solid electrolyte membrane. Air is placed on the air electrode side and fuel gas containing hydrogen is placed on the fuel electrode side. In a solid oxide fuel cell configured to supply and generate power,
At least one of Zr, Y, Mg, Ca, which is a constituent element of the solid electrolyte, and an oxide thereof is present on the surface of the constituent particles of the fuel electrode, the gap between the joint surface of the fuel electrode and the solid electrolyte, and the remaining vent holes of the solid electrolyte membrane. A solid oxide fuel cell characterized in that it is impregnated and fixed with one type of fixing agent.