JPH06243872A - Fuel electrode for solid electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To provide fuel electrodes for a solid electrolyte type fuel cell which can be prevented from being damaged when the laminated body of each electrode with electrolyte is manufactured. CONSTITUTION:Each fuel electrode is mainly composed of a mixture which comprises both jirconium and additives mixed together where stabilizing agent is added to nickel oxide or cobolt oxide in zirconium, and the heat-wire expansion coefficient of the additives is smaller than zirconium. By this constitution, the mixing of the additives smaller in a heat-wire expansion coefficient than zirconium to which stabilizing agent is added, enables the heat-wire expansion coefficient of each fuel electrode compact to be approximated to that of an electrolyte compact, so that a composite compact consisting of the fuel electrode compact, and of the electrolyte compact can thereby be prevented from being damaged at the time of sintering.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel electrode for a solid oxide fuel cell, and more specifically, a solid electrolyte fuel having a high conductivity and capable of preventing breakage during the production of a laminate with an electrolyte. The present invention relates to a fuel electrode for a battery.

[0002]

2. Description of the Related Art Since solid oxide fuel cells have an operating temperature of about 1000 ° C., they have been vigorously researched and developed because they can use high temperature exhaust heat and have high energy conversion efficiency. It is being advanced.

As a structure of such a solid oxide fuel cell, a cylindrical single element type or a monolithic type is known, but almost the same materials are used for the air electrode, the electrolyte and the fuel electrode constituting the cell. It is used.

That is, a complex oxide such as LaMnO ₃ added with calcium oxide or strontium oxide is used as an air electrode, and zirconia (hereinafter referred to as YSZ) added with yttria as a stabilizer is used as an electrolyte.
A mixture of nickel oxide and YSZ is used as the fuel electrode.

When hydrogen or carbon monoxide as a fuel heated to an operating temperature of about 1000 ° C. is supplied to the fuel electrode of a solid oxide fuel cell made of the above-mentioned materials, nickel oxide is reduced and Ni− having a small resistance is supplied. The YSZ cermet acts as a negative electrode, and when oxygen or air heated to the same temperature is supplied to the air electrode, the air electrode acts as a positive electrode and operates as a battery.

As a method of forming the fuel electrode of such a solid oxide fuel cell, nickel as described in JP-A-61-225778 is sintered on an electrolyte made of YSZ, and then the resultant is formed. A method of coating the YSZ by the EVD method (electrochemical vapor deposition method), "JA.
m. Ceram. , 69 (8) 628-33 (198
A method in which a slurry obtained by mixing nickel oxide and YSZ as described in 6) is used as a fuel electrode molded body tape by a tape casting method, and both surfaces of the electrolyte molded body tape are fired together with the air electrode molded body tape prepared in the same manner. , "Electrochemistry" 59 (4) 320-324,
A method is known in which a slurry in which nickel oxide and YSZ are mixed is applied onto an electrolyte made of YSZ and sintered, and both are fired in air at 1000 ° C to 1500 ° C.

The laminated body of the electrolyte and the fuel electrode obtained as described above has a coefficient of linear thermal expansion of nickel oxide of 15 × 10 ⁻⁶ K.
^{−1 to} 16 × 10 ⁻⁶ K ⁻¹ , whereas YSZ has a linear thermal expansion coefficient of 10 × 10 ⁻⁶ K ^{−1 to} 11 × 10 ⁻⁶ K ⁻¹ , and therefore oxidation in the fuel electrode It is designed so that the linear thermal expansion coefficient of the fuel electrode is approximated to the linear thermal expansion coefficient of the electrolyte by adjusting the weight ratio of nickel and YSZ so that the laminate is not damaged by the stress during firing.

That is, it is sufficient to reduce the content of nickel oxide in the fuel electrode.

On the other hand, the fuel electrode used in such a solid oxide fuel cell is designed so as to maintain a conductivity of a certain value or more under its operating temperature.

That is, in order to increase the conductivity of the fuel electrode, the content of nickel oxide in the fuel electrode should be increased.

[0011]

In the above-mentioned conventional fuel electrode for a solid oxide fuel cell, the linear thermal expansion coefficient of the fuel electrode when the molded body is laminated on the electrolytic molded body and fired is determined by Since it is necessary to solve the problem of approximating the coefficient of thermal expansion and the problem of increasing the conductivity of the fuel electrode obtained by firing to a certain value or more by contradictory means, there is a problem that the design becomes complicated. there were.

[0012]

In order to solve the above problems, a fuel electrode for a solid oxide fuel cell according to the present invention comprises a zirconia containing a stabilizer added to nickel oxide or cobalt oxide, and a coefficient of linear thermal expansion from the zirconia. It is characterized in that it is mainly composed of a mixture obtained by mixing an additive having a small value.

[0013]

[Operation] Therefore, according to the present invention, since zirconia in which a stabilizer is added to nickel oxide or cobalt oxide and an additive having a smaller linear thermal expansion coefficient than this zirconia are mixed, It is possible to approximate the linear thermal expansion coefficient of the fuel electrode to the linear thermal expansion coefficient of the electrolyte when the fuel electrode molded body is laminated and fired on the electrolyte molded body without reducing the content.

[0014]

EXAMPLES Prior to the description of the examples, the specific surface area was 0.23.
60% by volume of nickel oxide of m ² / g and 3 mol% of yttria as a stabilizer were added to give a specific surface area of 14.3 m ^2.
/ G YSZ 10% by volume, alumina 30 as additive
A slurry obtained by mixing a mixture prepared by mixing volume% with a predetermined amount of water together with a dispersant, a defoaming agent, and a binder is poured into a plaster mold to form a fuel electrode compact with a diameter of 4 mm and a length of 15 mm. Then, the fuel electrode A obtained by firing at a temperature of 1450 ° C. for 3 hours, the nickel oxide 50% by volume, the YSZ
A mixture of 12% by volume and 38% by volume of the above-mentioned alumina was made into the same slurry and poured into a gypsum mold to obtain the same fuel electrode compact, and similarly fired to obtain the fuel electrode B and the fuel electrode A. All without YSZ
The electric conductivity of the fuel electrode C and the fuel electrode D of YSZ which did not contain alumina in the fuel electrode B were measured and the results are shown in Table 1.

[0015]

[Table 1]

From Table 1, it can be seen that the fuel electrode A and the fuel electrode C have almost the same electric conductivity, and the fuel electrode B and the fuel electrode D have almost the same electric conductivity.

Further, the coefficient of linear thermal expansion in air at 200 ° C. to 900 ° C. was measured for the above fuel electrodes A, B, C and D, and the results are shown in Table 2.

[0018]

[Table 2]

From Table 2, the fuel electrode A is
The fuel electrode B has a linear thermal expansion coefficient of 0.
It can be seen that it can be reduced by about 5 × 10 ^-6 K ^-1 . Also,
It can also be seen that the difference in the coefficient of linear thermal expansion increases when the amount of alumina as an additive in the fuel electrodes A and C increases, and decreases when the amount of alumina decreases.

Next, a slurry obtained by mixing YSZ having a specific surface area of 18.8 m ² / g containing 8 mol% of yttria as a stabilizer together with a dispersant, a defoaming agent and a binder in a predetermined amount of water. And the slurry prepared from the above fuel electrodes A, B, C and D are continuously poured into a gypsum mold to form an electrolyte-fuel electrode composite molded body having an inner diameter of 12 mm and a length of 40 mm.
The damage state of composites A, B, C, and D obtained by producing each of them and firing at a temperature of 1450 ° C. for 3 hours was investigated, and the results are shown in Table 3.

[0021]

[Table 3]

From Table 3, complex A is
It can be seen that the composite B has a smaller number of damages than the composite D. This means that the linear thermal expansion coefficient of the fuel electrode could be approximated to the linear thermal expansion coefficient of the electrolyte by adding alumina as an additive to the composites A and B.

Although alumina as an additive is 30% by volume and 38% by volume in the above-mentioned examples, it can be adjusted within a range of 3 to 50% by volume depending on the content of nickel oxide and the content of YSZ. it can.

Besides the alumina, mullite, spinel, silicon carbide, titanium carbide, boron carbide, zirconium silicate, calcium aluminate or calcium zirconate can be used as the additive.

Further, cobalt oxide may be used in the fuel electrode instead of nickel oxide, but it is necessary to contain at least about 50% by volume from the viewpoint of conductivity.

[0026]

As described above, the fuel electrode for a solid oxide fuel cell of the present invention can prevent damage during firing of a composite molded body of a fuel electrode molded body and an electrolyte molded body without lowering the conductivity. Can be prevented.

Claims (3)

[Claims] 1. A solid electrolyte mainly composed of a mixture of zirconia containing a stabilizer added to nickel oxide or cobalt oxide, and an additive having a linear thermal expansion coefficient smaller than that of zirconia. Type fuel cell fuel electrode. 2. The additive having a smaller linear thermal expansion coefficient than zirconia to which a stabilizer is added is alumina, mullite, spinel, silicon carbide, titanium carbide, boron carbide, zirconium silicate, calcium aluminate or calcium zirconate. The fuel electrode for a solid oxide fuel cell according to claim 1, wherein 3. The solid oxide fuel cell according to claim 1, wherein the amount of the additive having a linear thermal expansion coefficient smaller than that of zirconia to which the stabilizer is added is 3 to 50% by volume. Fuel electrode.