JP3354655B2 - Method for producing fuel electrode of solid electrolyte type electrolytic cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a fuel electrode of a solid oxide fuel cell or a solid oxide electrolytic cell used for high-temperature steam electrolysis.

[0002]

2. Description of the Related Art In a solid electrolyte fuel cell, Ni is used as an anode. However, since the thermal expansion coefficient of the solid electrolyte is different from that of stabilized zirconia, the solid electrolyte may be destroyed. Therefore, stabilized zirconia (stabilized ZrO _{2) is used.} ) And magnesium aluminum spinel (MgAl ₂ O ₄ ). However, in the prior art, heat treatment is not performed before film formation.

[0003]

In order to prevent the destruction of the solid electrolyte, it is necessary to strictly adjust the coefficient of thermal expansion of the electrode to that of the solid electrolyte.
Adding gAl ₂ O ₄ to the electrode is more effective than adding stabilized ZrO ₂ . However, the electrode material to which MgAl ₂ O ₄ is added tends to have a lower conductivity than a target value when the film is formed.

The present invention has been made in view of the above technical level, and has as its object to provide a method of manufacturing a fuel electrode of a solid electrolyte type electrolysis cell which has good adhesion, high conductivity, and does not damage the electrolysis cell. is there.

[0005]

Means for Solving the Problems The present inventors have studied Ni, Mg
Various studies were conducted to improve the electrical conductivity of the Al ₂ O ₄ -based electrode material in a film-formed state. As a result, it was found that it is effective to perform a heat treatment before the film formation to form a solid solution in advance. Was. Further, it has been found that the addition of a small amount of stabilized ZrO ₂ is effective for improving the film forming strength (adhesion).

The present invention has been completed based on the above findings, and the present invention provides (1) NiO and MgAl ₂ O ₄
The solid solution formed by heat-treating the mixture at a temperature of 1500 ° C. or higher is pulverized, then dispersed in a solvent to form a slurry, and the slurry is applied to one surface of a ZrO ₂ -based solid electrolyte, dried, calcined in air, and reduced. Method for producing fuel electrode of solid electrolyte type electrolytic cell characterized by heat treatment in atmosphere
(1st invention) and (2) A solid solution obtained by heat-treating a mixture of NiO and MgAl ₂ O ₄ at a temperature of 1500 ° C. or more is mixed with stabilized ZrO ₂ , pulverized, and then dispersed in a solvent to form a slurry. A method for producing a fuel electrode of a solid electrolyte type electrolysis cell, wherein the slurry is applied to one side of a ZrO ₂ -based solid electrolyte, dried, fired in air, and then heat-treated in a reducing atmosphere (second invention). It is.

[0007]

The reason why the electrical conductivity of the Ni, MgAl ₂ O ₄ -based electrode material in the formed film is low is that the Ni component exhibiting conductivity is not connected in a state of being continuously contacted in the film. In the present invention, in order to make the Ni component in the film continuous, a solid solution treatment for performing a heat treatment in advance and uniformly dispersing the Ni component in the raw material was performed. Further, the adhesiveness of the electrode depends on the adhesive force at the interface between the solid electrolyte and the electrode. In order to improve the adhesion, it is necessary to improve the seizure.
Therefore, stabilized ZrO having the same components as the solid electrolyte is used for the electrode material.
₂ was added to improve the seizure property.

[0008] The reasons for limiting the components and the processing conditions for the first invention are described below. Starting material NiO particle size range: In order to form a solid solution, it is desirable that the powder has high reactivity, that is, the powder has a small particle size, and generally a particle size of 5 μm or less. Starting material MgAl ₂ O ₄ particle size range: As in the case of NiO particle size range, in order to form a solid solution, it is desirable that the powder has high reactivity, that is, the powder has a fine particle size.
Particle sizes below μm are preferred. Mixing ratio of NiO and MgAl ₂ O ₄ : The thermal expansion coefficient of the ZrO ₂ -based solid electrolyte used as the solid electrolyte is about 10 × 10
^-6 / K. The thermal expansion coefficient of NiO is about 14 × 10 ^-6
/ K and MgAl ₂ O _{4 have} a coefficient of thermal expansion of about 8 × 10 ⁻⁶ / K.
It is desirable that the coefficient of thermal expansion be close to the coefficient of thermal expansion of the rO ₂ -based solid electrolyte. However, when the NiO content decreases, the electrical conductivity decreases, and in consideration of this point, the NiO content is set to 40 to 60 vol.
1% is appropriate. At this time, the thermal expansion coefficient of the mixture sintered body is about 10.4 to 11.6 × 10 ⁻⁶ / K. Solid solution heat treatment: To form a solid solution of NiO and MgAl ₂ O ₄ , a somewhat high temperature and time are required, and 1
Appropriately at 500 ° C. or higher for 1 hour or longer. Pulverization of solid solution (including baking conditions after film formation on solid electrolyte): If the particle size of the solid solution is too large, it is thermally stable and does not stick sufficiently when film formation and baking on the solid electrolyte. Strength may be low. The temperature at which the film is formed and fired on the solid electrolyte is 1300 to 1500 ° C. (If this temperature is extremely high, it may react with the electrolyte to form an insulator.)
It is preferable that the particle diameter of the solid solution is 5 μm or less in order to form and bake a film in this temperature range. For this purpose, it is necessary to pulverize the solid solution fired body with a stamp mill and then pulverize it with a ball mill for 50 hours or more. Type of solvent to be slurried: Since the slurry is formed for the purpose of coating on the solid electrolyte, the type of the solvent is not particularly limited. Generally usable solvents include water, alcohols such as ethanol, toluene and the like. However, when an aqueous solvent is used, the addition of a dispersant is necessary for the purpose of improving the stability of the slurry (preventing precipitation), and the addition amount of the dispersant is generally 2% or less. Temperature conditions at the time of reduction: Reduction is performed under operating conditions of the solid oxide fuel cell. Specifically, the temperature is 1000 ° C., and the reducing agent is hydrogen, CO, CH ₄ or the like of the fuel.

Regarding the second invention, the reasons for limiting the components and the reasons for limiting the processing conditions will be described below. Starting material NiO particle size range: In order to form a solid solution, it is desirable that the powder has high reactivity, that is, the powder has a small particle size, and generally a particle size of 5 μm or less. Starting material MgAl ₂ O ₄ particle size range: As in the case of NiO particle size range, in order to form a solid solution, it is desirable that the powder has high reactivity, that is, the powder has a fine particle size.
Particle sizes below μm are preferred. Starting material ZrO ₂ particle size range: The particle size of ZrO ₂ needs to have good sinterability for the purpose of improving the adhesion to the solid electrolyte. Therefore, it is desirable that the particle size is small.
μm or less is preferred. Further, ZrO ₂ can of course containing stabilized ZrO ₂ and similar stabilizers to be used as a solid electrolyte. Mixing ratio of NiO and MgAl ₂ O ₄ and ratio of ZrO ₂ : The thermal expansion coefficient of the ZrO ₂ -based solid electrolyte used as the solid electrolyte is about 10 × 10 ⁻⁶ / K. NiO has a thermal expansion coefficient of about 14 × 10 ⁻⁶ / K, MgAl ₂ O _{4 has} a thermal expansion coefficient of about 8 × 10 ⁻⁶ / K, and ZrO _{2 has} a thermal expansion coefficient of about 10 × 1.
0 is ^-6 / K, these mixing ratio Write thermal expansion coefficient of the mixture sintered body is close to the coefficient of thermal expansion of the ZrO ₂ based solid electrolyte is desirable. However, when the NiO content decreases, the electrical conductivity decreases.
60 vol% is appropriate. Further, ZrO ₂ is added to improve the adhesion to the solid electrolyte, and if it is too much, the thermal expansion coefficient becomes large, so ZrO ₂ is desirably 15 vol% or less. The thermal expansion coefficient of the mixture sintered body in the case where the ZrO ₂ was added 10 vol% will be 10.6~11.8 × 10 ^-6 / K approximately. Solid solution heat treatment: To form a solid solution of NiO and MgAl ₂ O ₄ , a somewhat high temperature and time are required, and 1
Appropriately at 500 ° C. or higher for 1 hour or longer. Grinding of solid solution and ZrO ₂ (including conditions for firing after film formation on solid electrolyte): If the particle size of solid solution and ZrO ₂ is too large, it is thermally stable, and when film forming and firing on solid electrolyte, sufficient There is a possibility that the film formation strength is lowered without being burned to the surface. The temperature for firing the film on the solid electrolyte is 1300 to 15
00 ° C. (if this temperature is extremely high, there is a possibility that an insulator may be formed by reacting with the electrolyte). In order to form a film in this temperature range, the particle diameter of the solid solution and ZrO ₂ is 5 μm It is desirable to make the following. For this purpose, after the solid solution and the fired body of ZrO ₂ are pulverized by a stamp mill,
It is necessary to grind in a ball mill for 50 hours or more. Type of solvent to be slurried: Since the slurry is formed for the purpose of coating on the solid electrolyte, the type of the solvent is not particularly limited. Generally usable solvents include water, alcohols such as ethanol, toluene, and the like. However, when an aqueous solvent is used, the addition of a dispersant is necessary for the purpose of improving the stability of the slurry (preventing precipitation), and the addition amount of the dispersant is generally 2% or less. Temperature conditions at the time of reduction: Reduction is performed under operating conditions of the solid oxide fuel cell. Specifically, the temperature is 1000 ° C., and the reducing agent is hydrogen, CO, CH ₄ or the like of the fuel.

[0010]

【Example】

 (Example 1) 50 vol of NiO having an average particle size of 0.5 μm
%, MgAl with average particle size of 0.3 μm _TwoO_Four50vol
% In a ball mill for 24 hours using ethanol as a solvent.
And mix wet. After drying, a disc with a diameter of 50 mm
Large load 1000kg / cm^TwoFormed by isostatic pressing
Then, firing was performed at 1600 ° C. for 2 hours using an electric furnace. Next
Then, the fired body is pulverized with a stamp mill,
Milling was performed for 100 hours using a mill. Then, this powder
Dispersed in water, dispersant (ammonium polycarboxylate)
Then, a slurry having a powder concentration of 72 wt% was prepared. The dispersant is
1 wt%, dispersion treatment for 100 hours using a ball mill
did. Next, the slurry is dense and 300 μm thick.
m stabilized ZrO_TwoImmerse the solid electrolyte tube in the
A film was formed. The electrode film is dried at room temperature for 12 hours
And fired in the air. After firing, under a reducing atmosphere (100
Nickel oxide as nickel at 0 ° C in a hydrogen atmosphere)
The conductivity was measured. The measurement was performed using a direct current 4
It was measured by the terminal method.

As Comparative Material 1, an average particle size of 0.5 μm was used.
50 vol% of NiO of m, Mg of 0.3 μm in average particle size
50 vol% of Al ₂ O ₄ was weighed, and this powder was dispersed in water and a dispersant (ammonium polycarboxylate) to prepare a slurry having a powder concentration of 72 wt%. 1 wt% dispersant
And a dispersion treatment was performed for 100 hours using a ball mill. Further, as comparative material 2, 40 NiO having an average particle size of 0.5 μm was used.
vol%, 8 mol% -ZrO _{2 having} an average particle size of 0.2 μm
Is weighed at 60 vol%, and the powder is dispersed in water and a dispersant (ammonium polycarboxylate) to give a powder concentration of 72 w
A t% slurry was made. The dispersant was 1 wt%, and dispersion treatment was performed for 100 hours using a ball mill. The final firing and measurement in air and in a reducing atmosphere are the same as in the case of the present invention. The results are shown below.

[0012]

[Table 1] According to the present invention, it is possible to provide an electrode material having good adhesion and high conductivity. Also, the element is not damaged.

Example 2 NiO having an average particle size of 0.5 μm
Is 40 vol%, MgAl having an average particle size of 0.3 μm _TwoO_Four
50 vol%, 8 mol% -Z having an average particle size of 0.2 μm
rO_TwoIs weighed at 10 vol%. First, NiO
And MgAl_TwoO_FourOnly in a ball mill for 24 hours
And wet mixed with the solvent. 50mm diameter after drying
Maximum load 1000kg / cm^TwoHydrostatic press
And baking at 1600 ° C for 2 hours using an electric furnace.
Done. Next, the fired body is pulverized with a stamp mill,
Further, it was pulverized for 100 hours using a ball mill. This and
ZrO_TwoWas added and mixed at the same time. Then,
Powder in water, dispersant (polyammonium polycarboxylate)
And a slurry having a powder concentration of 72 wt% was prepared.
Dispersant is 1 wt%, 100 hours using a ball mill
Distributed processing. Then, in this slurry dense and thick
300 μm stabilized ZrO_TwoAttach the solid electrolyte tube
An extreme film was formed. The electrode film is dried in a room for 12 hours and then dried for 150 hours.
Calcination was performed in air at 0 ° C. After firing, under a reducing atmosphere (1
2,000 ° C, hydrogen atmosphere)
The conductivity was measured. The measurement was made using platinum as the electrode.
The current was measured by a four-terminal method.

As a comparative material, the average particle size is 0.5 μm
MgO with 40 vol% of NiO and average particle diameter of 0.3 μm
50 mol% of l ₂ O ₄ , 8 mo having an average particle size of 0.2 μm
1% -ZrO ₂ is weighed at 10 vol%, and this powder is
Dispersed in a dispersant (ammonium polycarboxylate)
A slurry having a powder concentration of 72 wt% was prepared. 1w dispersant
The dispersion treatment was performed using a ball mill for 100 hours. Further, as comparative material 2, NiO having an average particle size of 0.5 μm was used.
Is 8 mol% -Z with an average particle diameter of 0.2 μm.
60 vol% of rO ₂ was weighed, and this powder was dispersed in water and a dispersant (ammonium polycarboxylate) to prepare a slurry having a powder concentration of 72 wt%. The dispersant was 1 wt%, and dispersion treatment was performed for 100 hours using a ball mill. The final firing and measurement in air and in a reducing atmosphere are the same as in the case of the present invention. The results are shown below.

[0015]

[Table 2] According to the present invention, it is possible to provide an electrode material having good adhesion and high conductivity. Also, the element is not damaged.

[0016]

According to the present invention, it is possible to manufacture a fuel electrode of a solid electrolyte type electrolytic cell having good adhesion, high electric conductivity, and without damaging the electrolytic cell.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-33266 (JP, A) JP-A-5-67472 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/88 C25B 11/04

Claims (2)

(57) [Claims] The method according to claim 1 mixture of NiO and MgAl ₂ O ₄ 1
A solid solution obtained by heat treatment at a temperature of 500 ° C. or more is pulverized and then dispersed in a solvent to form a slurry.
A method for producing a fuel electrode of a solid electrolyte type electrolysis cell, comprising applying and drying one surface of an O ₂ -based solid electrolyte, firing it in air, and then performing heat treatment in a reducing atmosphere. 2. A method a mixture of NiO and MgAl ₂ O ₄ 1
Stabilizes the solid solution formed by heat treatment at a temperature of 500 ° C. or more.
A solid characterized by being mixed with rO ₂ , pulverized, dispersed in a solvent to form a slurry, applied to one surface of a ZrO ₂ -based solid electrolyte, dried, fired in air, and then heat-treated in a reducing atmosphere. A method for manufacturing a fuel electrode of an electrolyte type electrolytic cell.