JPH09245817A - Solid electrolyte type fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a desiring electric power generating performance for a long duration and prolong the life by making a fuel electrode up of a spray deposit membrane of a surface reforming powder with uneven structure as a whole. SOLUTION: At first, a composite powder 60 is produced by sticking nickel oxide particles 62 to the circumference of a titanium powder 61. Then, the composite powder 60 annealed in an inert gas atmosphere. Consequently, oxidation reaction and reduction reaction are caused in the titanium powder 61 and the nickel oxide particles, respectively, and as a result, metal nickel exists as a main body in the surface layer part 72 and titanium oxide exists as nuclei 71 with irregular shape in the inside and a surface reforming powder 70 with uneven structure as a whole is thus obtained. Film formation for a fuel electrode can be carried out by a method as same as a conventional way using the surface reforming powder 70. Since the behavior of nickel in the surface layer part is restricted by the nuclei 71 with irregular shape of titanium oxide in the case of a fuel electrode with such a structure, the proceeding of mutual sintering of nickel particles is inhibited and as a result deterioration of the fuel electrode is retarded as compared with a conventional one.

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 power generation performance which is caused by a change with time of a fuel electrode (progress of sintering of nickel in the fuel electrode). Prevent deterioration,
The present invention relates to a method for improving battery life.

[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 and reach the fuel electrode, reacting with hydrogen and releasing 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 general structure of a cylindrical solid oxide fuel cell.

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

Explaining the outline of each electrode here, first, the air electrode is stable in a high temperature oxidizing atmosphere at about 1000 ° C., has high electron conductivity, is porous and allows good air circulation, and air. It is required that the solid electrolyte formed on the electrode has close thermal conductivity and good adhesion. Therefore, complex oxides such as lanthanum manganate and lanthanum calcium manganate are generally used.

Solid electrolytes have excellent oxygen ion permeability, are chemically stable at high temperatures, and operate batteries.
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 that meets these requirements, but it is stabilized by dissolving an oxide of an alkaline earth metal (Sr, Mg, Ca, etc.) or a rare earth element oxide in order to prevent damage due to its volume change at high temperatures. Zirconia, especially yttria-stabilized zirconia (YSZ), is often used.

The fuel electrode is required to have high electron conductivity, a coefficient of thermal expansion close to that of the solid electrolyte, and good adhesion to the solid electrolyte. Therefore, cermets whose thermal expansion coefficient is adjusted by adding stabilized zirconia to nickel, especially Ni-
YSZ cermet is often used.

Further, since the above-mentioned electrochemical reaction in the 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 to generate power. In order to improve the performance, the fuel electrode must be made porous. So conventionally,
The fuel electrode was 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, and the spraying or firing conditions.

An example of the cross-sectional shape of the solid electrolyte and the fuel electrode formed thereon in such a fuel cell is schematically shown in FIG. When a fuel electrode is formed by spraying a mixed powder of nickel powder and YSZ powder, as shown in FIG.
Nickel particles 41 and YSZ particles 42 are stacked on each other on the solid electrolyte membrane 30 made of and are bonded to each other to form a porous fuel electrode (40).

[0009]

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. The progress of such sintering of nickel particles between nickel and Y
Poor wettability with SZ is also considered to be a factor in promoting the progress.

[0011]

The essence of the present invention is to use a surface-modified powder having an internal structure described below as a raw material for film formation of a fuel electrode. An example of a method of producing powder having such a structure will be described. First, as shown on the left side of FIG. 2, a composite powder 60 in which nickel oxide particles 62 are attached around a titanium powder 61 is prepared. Next, this composite powder is annealed in an inert atmosphere. In this case, it may be pure nickel oxide, or may be a composite powder in which at least one kind of particles of YSZ, cerium oxide (ceria) and samarium-doped ceria is added and adhered thereto.

By this treatment, the titanium powder 61 undergoes an oxidation reaction and the nickel oxide particles 62 undergo a reduction reaction.
As a result, as shown in the right side of FIG.
2 is mainly metallic nickel, and titanium oxide is present in the inside as irregularly shaped nuclei 71, so that a surface-modified powder 70 having a heterogeneous structure as a whole is obtained.

The film formation of the fuel electrode using the surface-modified powder 70 can be performed in the same manner as in the conventional case. That is, a desired fuel electrode can be obtained by using the surface-modified powder alone or by adding and spraying YSZ powder for matching the thermal expansion coefficient with the solid electrolyte. At this time, cerium oxides may be added in place of or in addition to the YSZ powder, and the mixed powder may be granulated prior to calcination, or the surface-modified powder may be mixed in place of the above-mentioned modified powder. Appropriate known means can be applied, such as coating with an oxide powder or gradually changing the ratio of the mixed powder to perform thermal spraying to make the fuel electrode functionally graded.

The fuel electrode formed in this manner is attributed to the fact that the nickel particles 41 constituting the fuel electrode 40 in the conventional example of FIG. But both are nickel.

In spite of this, there is a significant difference between the two in terms of the degree of reduction in power generation capacity that occurs when the fuel cell is operated for a long time, as will be shown by the data described later. For this reason, in the case of the fuel electrode according to the present invention, since the behavior of the nickel in the surface layer is restricted by the irregularly shaped nuclei made of titanium oxide, the progress of sintering of the nickel particles is inhibited, As a result, it is considered that the deterioration of the fuel electrode becomes slower than the conventional one.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example) First, a composite powder 60 was prepared in which nickel oxide particles 62 were attached around a titanium powder 61. The particle size of the nickel oxide particles is about 1/10 of the titanium powder.
Next, this composite powder was annealed in an argon gas atmosphere at a temperature of 1000 ° C. for 25 hours. By this treatment, the surface-modified powder 70 having a non-uniform structure as a whole, in which the surface layer portion 72 was metallic nickel, and titanium oxide was present therein as irregular-shaped nuclei 71, was obtained.

Next, YSZ powder was mixed with this surface-modified powder to match the coefficient of thermal expansion with that of the solid electrolyte, and this was granulated and then calcined to obtain raw material powder for thermal spraying. The fuel electrode was formed in the same manner as in the prior art, that is, the above raw material powder was sprayed onto the solid electrolyte at atmospheric pressure to form the fuel electrode in a porous film.

The fuel cell (single cell) thus obtained was connected to a mechanism for supplying and discharging fuel gas and air, and an operation test was carried out to compare with a conventional system by mixed spraying of nickel powder and YSZ powder. As a result, the initial value 0.
After the terminal voltage of 74 V was continuously operated for 1000 hours, the voltage drop rate was 65% in the conventional comparative sample, whereas it was only 0.5% in the sample according to the present invention. From this result, it is estimated that the lifespan before the product is reduced to the same level as that of the conventional product is several times longer.

[0019]

As described above in detail, as a result of the implementation of the present invention, the deterioration of the fuel electrode over time is slowed down, and as a result, a long-life fuel cell in which the desired power generation performance lasts longer than in the past is obtained. be able to.

[Brief description of drawings]

FIG. 1 is a drawing schematically showing a cross section of a fuel electrode and a solid electrolyte in a solid oxide fuel cell.

FIG. 2 is a schematic diagram illustrating an example of a raw material powder used for forming a fuel electrode in the present invention and a manufacturing method thereof.

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 ... Substrate tube 2 ... Air electrode 3,30 ... Solid electrolyte 4,40 ... Fuel electrode 5 ... Interconnector 60 ... Composite powder, 61 ... Titanium powder, 62 ... Nickel oxide powder 70 ... Surface modified powder, 71 ... Core ( Titanium oxide), 72 ... Surface layer (nickel)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Riki Iwasawa 1-5-1, Kiba, Koto-ku, Tokyo Inside Fujikura Ltd.

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 power,
The fuel electrode is characterized by being a thermal spray coating mainly composed of surface-modified powder having a non-uniform structure in which nickel is present in the surface layer and titanium oxide is present in the interior as irregularly shaped nuclei. , Solid oxide fuel cells. 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 power,
As raw material powder for thermal spray coating of the fuel electrode, it is recommended to use surface-modified powder with a generally heterogeneous structure in which nickel is present in the surface layer and titanium oxide is present in the interior as irregularly shaped nuclei. A method for producing a solid oxide fuel cell, which is characterized. 3. 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 membrane. Air is contained in the air electrode side and fuel gas containing hydrogen is contained in the fuel electrode side. In a solid oxide fuel cell configured to supply and generate power,
As a raw material powder for thermal spray film formation of the fuel electrode, nickel is present in the surface layer and titanium oxide is present inside it as irregularly shaped nuclei.
A method for producing a solid oxide fuel cell, which comprises using a mixed powder to which at least one of YSZ powder and cerium oxide powder is added. 4. The solid oxide fuel cell according to claim 3, wherein the mixed powder obtained by adding at least one of YSZ powder and cerium oxide powder to the surface-modified powder is subjected to granulation treatment or calcination treatment. Production method. 5. A composite powder in which nickel oxide particles are adhered around titanium powder is annealed in an inert atmosphere to cause a reduction reaction on nickel oxide in the surface layer and an oxidation reaction on titanium inside. A method for producing a surface-modified powder for film formation of a fuel electrode in a solid oxide fuel cell, comprising: