JPH11214018A - Low temperature fabrication of ZrO2 based solid electrolyte membrane by sol-gel method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a ZrO ₂ -based thin film solid electrolyte by a sol-gel method with relatively low production cost, and to obtain a solid electrolyte membrane having good conductivity characteristics while keeping the production process temperature low. Aim. SOLUTION: Main component element Zr and main additive element D
A sol-gel solution containing any one of Y, Yb, and Lu as 1 and any one of Al, Mg, and Si as the second additive element D2 is prepared, and the sol-gel solution is placed on a porous electrode substrate. It is characterized in that it is applied and heat-treated in an electric furnace or the like. [Effect] An electrolyte having excellent ion conductivity can be easily formed into a thin film at a low temperature even at a relatively low temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to ZrO
_{The present} invention relates to a method for producing a low-temperature solid electrolyte membrane.

[0002]

2. Description of the Related Art In recent years, interest has been growing in solid electrolyte 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. .

One of the most studied oxygen ion conductors at present is Y ₂ O ₃ stabilized ZrO ₂ (YSZ). This Z
Since the rO ₂ -based material has an ion transport number of approximately 1.0 in an oxidizing / reducing atmosphere, it has hitherto been regarded as the most promising electrolyte for a solid oxide fuel cell. However, operation at a high temperature of 1000 ° C. is necessary to obtain sufficient ionic conductivity, and at such a high temperature, the life of components due to reaction with the electrode interface is severely degraded, and the practical use of solid fuel cells is delayed. It is the current situation. Therefore, a reduction in operating temperature (from 700 ° C. to about 800 ° C.) is desired. In order to operate at a low temperature, it is necessary to reduce the resistance loss in the electrolyte part, so that it is necessary to make the electrolyte thinner.

[0004] As a method of thinning the film, an EVD (Electrochemical Vacuum) which is a kind of a vapor phase growth method is used.
Although the por deposition method is best studied, there are disadvantages in that the apparatus is complicated, the production cost is high, and precise composition control is difficult. In contrast, in the sol-gel method, a film can be formed relatively easily by applying a sol-gel liquid to a substrate or the like and performing a heat treatment. In the final heat treatment process, the ultrafine particles in the amorphous state are aggregated and crystallized to form a dense film. However, by keeping the heat treatment temperature as low as possible, the production cost can be reduced. Further, in this process, reaction degradation due to mutual diffusion of atoms between the electrolyte membrane and the air electrode, which is a porous substrate in contact with the electrolyte membrane, occurs at the same time. Therefore, it is desired to reduce the heat treatment temperature in this sense.

[0005]

The object of the present invention is to provide a solid electrolyte for use in a low-temperature operation type solid fuel cell by producing a ZrO ₂ -based thin film solid electrolyte by a sol-gel method with a relatively low production cost, and keeping the production process temperature low and good. It is an object to obtain a solid electrolyte membrane having excellent conductivity characteristics.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, the method for producing a ZrO ₂ -based thin film solid electrolyte according to the present invention uses any of Y, Yb and Lu as the main component element Zr and the main additive element D1. And a sol-gel liquid containing any of Al, Mg, and Si as the second additive element D2, and applying the sol-gel liquid on a porous electrode substrate, and applying the sol-gel liquid to an electric furnace or the like. It is characterized in that heat treatment is performed in the inside.

[0007] In the course of the heat treatment, organic substances in the sol-gel liquid are decomposed and evaporated, and the metal salt remaining in a state of being mixed at an atomic level reacts to obtain an electrolyte membrane. Here, the metal ions of the sol-gel liquid are Zr as a main component element and Y, Yb, and Y, Yb, which are main additive elements that develop ionic conductivity.
Lu rare earth element, and second additive elements Al and M
g, Si light elements.

[0008] As in the present invention, the second additive element Al, M
Even at a low sintering temperature, by adding a small amount of g and Si, it is possible to sufficiently promote grain growth and realize a dense and good ionic conductivity. In addition, since the amount of the second additive is suppressed to less than half the amount of the main additive, distortion of the crystal lattice due to the second additive hardly occurs, and the ion conductivity is not impaired.

The composition of the sol-gel solution of the ZrO ₂ -based solid electrolyte membrane by the sol-gel method according to the present invention is preferably in the range shown in FIG. When the main additive element D1 is X and the second additive element is Y (Zr is 1-XY), 0.04
≤X, 0.004≤Y, X≤0.5Y, X + Y≤0.3
04 is better.

Further, according to this method, the final thickness of the sol-gel film can be controlled from 0.1 μm to 100 μm by adjusting the coating thickness of the sol-gel liquid.
Here, the sol-gel solution may be applied by a spin coating method, a screen printing method, a spray method, a dipping method, or the like. Here, in order to form such a thin film on the porous substrate, the surface must be flattened (densified).
For this, a fine electrode material is applied on a porous substrate and baked and hardened, and then the surface is polished, or a mixed conductor layer of Gd ₂ O ₃ added CeO _{2 with} relatively high ion conductivity is formed and sintered. , Can be achieved by densification.

[0011]

[Function] If a ZrO ₂ -based electrolyte can be thinned even in a low-temperature process, and good conductivity characteristics can be realized, a fuel cell suitable for low-temperature operation with high power generation efficiency and high reliability at low manufacturing cost. It is possible to produce a solid electrolyte for use.

By forming a film having the above composition, the film forming temperature can be reduced. This makes it possible to produce an electrolyte that has high power generation efficiency and is suitable for low-temperature operation even in a low-temperature process.

[0013]

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

[0014]

Embodiment 1 FIG. 2a shows a process for forming an electrolyte membrane on an Al ₂ O ₃ plate by the sol-gel method using the material of the present invention. According to this flow, the sol-gel film composition becomes Z
The case of _{r 0. 76 Yb 0.20 Al 0.04 O} 2 will be described below.

As shown in FIG. 2A, aluminum isoproxide (Al
— (OPr ′) ₃ ) 1.14 g and 2,0.8 g of 2,4-pentadione were added, and the mixture was irradiated with ultrasonic waves and then heated and dissolved at 120 ° C. to prepare an about 0.3% aluminum solution. To this, yttrium lithium nitrate tetrahydrate 14.2
g, zirconium normal butoxide (Zr-Obu)
₄ ) Add 22.56 g of (Zr: 19.99%), dissolve again by ultrasonication, and finally add 2-methoxyethanol 22.2 so that the concentration in terms of oxide in the solution becomes 7.2%.
55 g was added to prepare a thin film sol-gel solution. This is the case where the main additive element is Yb, but the main additive element is Lu.
Alternatively, also in the case of Y, lutetium nitrate tetrahydrate or yttrium nitrate tetrahydrate is used in place of ytterbium nitrate tetrahydrate. Also, as a second additive element,
When magnesium or silicon is used instead of aluminum, magnesium isoproxide (Mg- (OP
r ')) or silicon isoproxide (Si-OP
r ') Use ₄ ).

The solution prepared as described above was spin-coated according to the procedure shown in FIG. 2B to apply the solution to an Al ₂ O ₃ substrate.
As shown in the figure, after spin coating,
Dry for 0 minutes. This process was repeated until a desired film thickness was obtained. Finally, heat treatment was performed at 1200 ° C. for 1 hour in an electric furnace to obtain a crystallized sol-gel film. Here, the composition ratio of the metal element is Zr: Yb: Al = 0.76: 0.20:
0.04, but other compositions were also obtained by adjusting the mixing ratio.

The ionic conductivity of these thin film electrolyte materials was measured at 800 ° C. by a DC four-terminal method. Here, the heat treatment temperature was changed from 800 ° C. to 1200 ° C.
Here, the sample was about 4 cm × 2 cm, and a current of 10 ⁻⁷ A was passed in the in-plane direction of the substrate, and the conductivity was determined from the generated voltage. Table 1 shows the measurement results.

The table shows that the solid phase reaction method is used at 1600 ° C.
(Sample No. 1-0, the sample was 0.2 cm square and 3 cm long) prepared in the above. 1100 ° C by adding a small amount of the second additive
In the heat treatment, the ionic conductivity almost equivalent to that of the bulk material was obtained. For other compositions, the heat treatment temperature was set to 11
The temperature was fixed at 00 ° C., and the conductivity of the sample was similarly measured at 800 ° C. These results are shown in Table 2-1 and Table 2-2.
It is shown in Table 2-3. Trace amounts of Yb, Lu, Y as the main additive elements and Al, Mg, Si as the second additive elements were added.

In each case, when the same amount of the main additive element was added, the conductivity was improved by the second addition.

Next, this thin film was formed on a porous electrode substrate in the following manner to produce a single cell. First, the particle size is 20μ
m of La _0.8 Sr _0.2 MnO ₃ cathode material was dissolved in an aqueous PVA (polyvinyl alcohol) solution, formed into a sheet by a doctor blade method, and fired at 1400 ° C. to obtain a relatively dense surface layer having a thickness of about 100 μm. The surface was polished to obtain a porous air electrode substrate 1 (cathode electrode) having good surface flatness.

A sol-gel solution was applied thereon several times by spin coating, and heat-treated at 1100 ° C. for 2 hours to obtain a solid electrolyte layer having a thickness of about 5 μm. By this process, recrystallization progressed and the solid electrolyte thin film 2 was formed on the porous air electrode substrate 1. Finally, a platinum paste was applied on the electrolyte membrane, and calcined at 1000 ° C. for 1 hour to obtain a fuel electrode 3.
Further, a current collecting mesh 4 of platinum was provided on the fuel electrode 3 and the air electrode substrate 1. FIG. 3A is a schematic diagram of this single cell.
As shown in FIG.

A fuel cell as shown in FIG. 4 was constructed using this cell, and a test was conducted at 800 ° C. In the figure,
Reference numeral 5 denotes a platinum terminal, and 6 denotes a gas seal. Here, oxygen was supplied to the air electrode side and hydrogen was supplied to the fuel electrode side. Table 3 shows the output voltage at this time. Here, “cell number 0” is Ce _0.8
This is the result of a cell prepared by applying Sm _0.2 O ₂ on the above-described porous air electrode substrate by screen printing and using it as an electrolyte.

In any case of the electrolyte thin film, 1.
An open-circuit voltage value close to 10 V was obtained. These values are calculated according to the Nernst equation [V = (RT / nF) · ln (Po ₂ ca
Tode / Po ₂ anode), T: absolute temperature, R:
Gas constant, n: 4.0, F: Faraday constant, Po ₂ c
anode: partial pressure of oxygen at the cathode, Po ₂ anode:
The theoretical electromotive force value determined from the oxygen partial pressure of the fuel electrode] (1.
(15 eV at 800 ° C.), which indicates that the electrolyte thin film formed on the porous cathode substrate by the sol-gel method has an ion transport number of approximately 1.0 and is excellent in gas sealing properties.

Table 1 In Example 1, the ionic conductivity composition ratio of the sol-gel film at 800 ° C. is shown by the molar ratio of each metal ion. Sample No. 1-0 is a bulk sample prepared at 1600 ° C. by a solid-state reaction method.

(The composition ratio of the film used here is “Zr: Yb: Al = 0.80: 0.20: 0.0 when“ Al is not added ”).
In the case of “Al addition”, Zr: Yb: Al = 0.7
6: 0.20: 0.04. )

Table 2-1 At 800 ° C. in Example 1
The ionic conductivity composition of the sol-gel film depends on the model of each metal ion.
It is shown as a ratio.(When Al is used as the second additive) No. Zr (mol) Yb (mol) Al (mol) σ (S / cm) 1-1-1 0.960 0.040 0.000 0.0030 1-1-2 0.956 0.040 0.004 0.0074 1-1-3 0.940 0.040 0.020 0.0120 1-1-4 0.800 0.200 0.000 0.0100 1-1-5 0.796 0.200 0.004 0.0248 1-1-6 0.750 0.200 0.050 0.0500 1-1-7 0.696 0.200 0.104 0.0300 1-1-8 0.700 0.300 0.000 0.0080 1-1-9 0.696 0.300 0.004 0.0198 No. Zr (mol) Lu (mol) Al (mol) σ (S / cm) 1-2-1 0.960 0.040 0.000 0.0029 1-2-2 0.956 0.040 0.004 0.0071 1-2-3 0.940 0.040 0.020 0.0114 1-2-4 0.800 0.200 0.000 0.0095 1-2-5 0.796 0.200 0.004 0.0236 1-2-6 0.750 0.200 0.050 0.0475 1-2-7 0.696 0.200 0.104 0.0285 1-2-8 0.700 0.300 0.000 0.0076 1-2-9 0.696 0.300 0.004 0.0188

Table 2-1 continued No. Zr (mol) Y (mol) Al (mol) σ (S / cm) 1-3-1 0.960 0.040 0.000 0.0015 1-3-2 0.956 0.040 0.004 0.0037 1-3-3 0.940 0.040 0.020 0.0060 1-3-4 0.800 0.200 0.000 0.0050 1-3-5 0.796 0.200 0.004 0.0124 1-3-6 0.750 0.200 0.050 0.0250 1-3-7 0.696 0.200 0.104 0.0150 1-3-8 0.700 0.300 0.000 0.0040 1-3-9 0.696 0.300 0.004 0.0099

Table 2-2 The ion conductivity composition ratio of the sol-gel film at 800 ° C. in Example 1 is shown by the molar ratio of each metal ion. (When Mg is used as the second additive) No. Zr (mol) Yb (mol) Mg (mol) σ (S / cm) 2-1-1 0.960 0.040 0.000 0.0030 2-1-2 0.956 0.040 0.004 0.0067 2-1-3 0.940 0.040 0.020 0.0108 2-1-4 0.800 0.200 0.000 0.0100 2-1-5 0.796 0.200 0.004 0.0223 2-1-6 0.750 0.200 0.050 0.0450 2-1-7 0.696 0.200 0.104 0.0270 2-1-8 0.700 0.300 0.000 0.0080 2-1-9 0.696 0.300 0.004 0.0179

Table 2-2 continued No. Zr (mol) Lu (mol) Mg (mol) σ (S / cm) 2-2-1 0.960 0.040 0.000 0.0029 2-2-2 0.956 0.040 0.004 0.0064 2-2-3 0.940 0.040 0.020 0.0103 2-2-4 0.800 0.200 0.000 0.0095 2-2-5 0.796 0.200 0.004 0.0212 2-2-6 0.750 0.200 0.050 0.0428 2-2-7 0.696 0.200 0.104 0.0257 2-2-8 0.700 0.300 0.000 0.0086 2-2-9 0.696 0.300 0.004 0.0170 No. Zr (mol) Y (mol) Mg (mol) σ (S / cm) 2-3-1 0.960 0.040 0.000 0.0015 2-3-2 0.956 0.040 0.004 0.0033 2-3-3 0.940 0.040 0.020 0.0054 2-3-4 0.800 0.200 0.000 0.0050 2-3-5 0.796 0.200 0.004 0.0112 2-3-6 0.750 0.200 0.050 0.0225 2-3-7 0.696 0.200 0.104 0.0135 2-3-8 0.700 0.300 0.000 0.0040 2-3-9 0.696 0.300 0.004 0.0089

Table 2-3 Ion of sol-gel film at 800 ° C. in Example 1
The conductivity composition ratio is shown by the molar ratio of each metal ion.(When Si is used as the second additive) No. Zr (mol) Yb (mol) Si (mol) σ (S / cm) 3-1-1 0.960 0.040 0.000 0.0030 3-1-2 0.956 0.040 0.004 0.0063 3-1-3 0.940 0.040 0.020 0.0102 3-1-4 0.800 0.200 0.000 0.0100 3-1-5 0.796 0.200 0.004 0.0211 3-1-6 0.750 0.200 0.050 0.0425 3-1-7 0.696 0.200 0.104 0.0255 3-1-8 0.700 0.300 0.000 0.0080 3-1-9 0.696 0.300 0.004 0.0169 No. Zr (mol) Lu (mol) Si (mol) σ (S / cm) 3-2-1 0.960 0.040 0.000 0.0029 3-2-2 0.956 0.040 0.004 0.0060 3-2-3 0.940 0.040 0.020 0.0097 3-2-4 0.800 0.200 0.000 0.0095 3-2-5 0.796 0.200 0.004 0.0200 3-2-6 0.750 0.200 0.050 0.0404 3-2-7 0.696 0.200 0.104 0.0242 3-2-8 0.700 0.300 0.000 0.0076 3-2-9 0.696 0.300 0.004 0.0160

Table 2-3 continued No. Zr (mol) Y (mol) Si (mol) σ (S / cm) 3-3-1 0.960 0.040 0.000 0.0015 3-3-2 0.956 0.040 0.004 0.0032 3-3-3 0.940 0.040 0.020 0.0051 3-3-4 0.800 0.200 0.000 0.0050 3-3-5 0.796 0.200 0.004 0.0105 3-3-6 0.750 0.200 0.050 0.0213 3-3-7 0.696 0.200 0.104 0.0128 3-3-8 0.700 0.300 0.000 0.0040 3-3-9 0.696 0.300 0.004 0.0084

Table 3 Output Voltage Characteristics of the Fuel Cell of Example 1 The sol-gel film was applied by a spin coating method. Cell number Zr (mol) Yb (mol) Al (mol) * Open circuit voltage (V) ** Output voltage (V) * 0 0.000 0.000 0.000 0.75 0.60 0-1 0.960 Yb = 0.040 Al = 0.000 1.05 0.50 1-1- 2 0.956 Yb = 0.040 Al = 0.004 1.11 0.74 1-1-3 0.940 Yb = 0.040 Al = 0.020 1.12 0.73 1-1-4 0.800 Yb = 0.200 0.000 1.08 0.52 1-1-5 0.796 Yb = 0.200 Al = 0.004 1.10 0.73 1-1-6 0.750 Yb = 0.200 Al = 0.050 1.12 0.75 1-1-7 0.696 Yb = 0.200 Al = 0.104 1.14 0.74 1-1-8 0.750 Yb = 0.200 Mg = 0.050 1.10 0.71 1-1-9 0.750 Yb = 0.200 Si = 0.050 1.11 0.68 0-10 0.700 Yb = 0.300 0.000 1.08 0.48 1-1-11 0.696 Yb = 0.300 Al = 0.004 1.11 0.61 0-10 0.800 Lu = 0.200 0.000 1.07 0.51 1-1-11 0.750 Lu = 0.200 Al = 0.050 1.10 0.73 1-1-12 0.750 Lu = 0.200 Mg = 0.050 1.10 0.68 1-1-13 0.750 Lu = 0.200 Si = 0.050 1.10 0.65 0-14 0.800 Y = 0.200 0.000 1.09 0.42 1-1-15 0.750 Y = 0.200 Al = 0.050 1.15 0.65 1-1-16 0.750 Y = 0.200 Mg = 0.050 1.12 0.60 1-1-17 0.750 Y = 0.200 Si = 0.050 1.12 0.59 * The open-circuit voltage of the cell at 800 ° C. ** Cell output voltage at 800 ° C., current density 0.5 A / cm ² .

[0033]

EXAMPLE 2 A sol-gel solution having the same composition as in Example 1 was applied to a ceria substrate (solid electrolyte substrate) 7 having a thickness of about 0.15 mm.
(Composition: 0.80 CeO ₂ -0.20 Gd ₂ O ₃ ) 1 was applied by a spray method. The application procedure is spraying instead of spin coating in FIG. 2b. Other conditions such as heat treatment are the same. Heat treatment was performed at 1100 ° C. for 2 hours to recrystallize, and a solid electrolyte thin film (sol-gel film) 8 having a thickness of about 1 μm was obtained.

Next, on the side opposite to the solid electrolyte thin film 8, the first embodiment
La _0.8 Sr _0.2 M having the same composition as in the above but having an average particle size of 1.0 μm
nO ₃ was baked at 1100 ° C. to provide an air electrode 10, and the solid electrolyte thin film 8 was baked at 1000 ° C. with a platinum pace to form a fuel electrode 9 to form a single cell. Reference numeral 11 denotes a reference electrode (Pt paste), and reference numeral 4 denotes a current collecting Pt mesh (16 mmφ). FIGS. 5A and 5B are schematic diagrams of this single cell.

This cell was used as a fuel cell in the same configuration as in Example 1, and its electromotive force was measured at 800 ° C. Table 4 shows the results. Here, the measurement was also performed on a cell having only a ceria substrate without a thin film electrolyte. Although the ceria substrate has high ion conductivity, a theoretical electromotive force cannot be obtained because the ion transport number is 1.0 or less. On the other hand, a cell having a ZrO ₂ -based electrolyte thin film provided by the sol-gel method almost reaches the theoretical electromotive force. This indicates that the electrolyte thin film of the present invention having an ion transport number of 1.0 functions as a solid electrolyte.

Table 4 Output voltage characteristics of the fuel cell unit of Example 2 Sol-gel film coating method * Oxygen ion conductivity ** Release voltage *** Output voltage (S / cm) (V) (V) No sol-gel film-0.75 0.44 Spin coating 0.050 1.12 0.50 Dipping 0.053 1.12 0.52 Spray 0.040 1.10 0.40 Screen printing 0.048 1.09 0.42 * Ionic conductivity at 800 ° C ** Open cell voltage at 800 ° C. *** Output voltage of cell at 800 ° C., current density 0.5 A / cm ² .

[0037]

As described above, the method for producing a thin film according to the present invention is a method for producing an electrolyte having excellent ion conductivity at a relatively low temperature at a low temperature and easily.

[Brief description of the drawings]

FIG. 1 is a diagram showing a composition ratio of an added metal in a sol-gel solution in the claims of the present invention.

FIG. 2a is a flowchart of a sol-gel solution preparation process in the sol-gel method.

FIG. 2B is a flowchart of a coating process in a sol-gel method.

FIG. 3A is a sectional view of a single cell used in Example 1.

FIG. 3B is a plan view of a single cell used in Example 1.

FIG. 4 is a structural diagram of a fuel cell used in Example 1.

FIG. 5A is a sectional view of a single cell used in Example 2.

FIG. 5B is a plan view of a single cell used in Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air electrode board 2 Solid electrolyte thin film 3 Fuel electrode 4 Pt current collecting mesh 5 Platinum terminal 6 Gas seal 7 Solid electrolyte substrate 8 Solid electrolyte thin film 9 Fuel electrode 10 Air electrode 11 Reference electrode

Continuing on the front page (72) Inventor Junichi Yamaki 3-2-19-1 Nishishinjuku, Shinjuku-ku, Tokyo Japan Telegraph and Telephone Corporation (72) Inventor Masaru Yonezawa 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation (72) Inventor Keiko Endo 1-297 Kitabukuro-cho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Research Laboratory

Claims (5)

[Claims] 1. A main component element Zr and a main additive element D1.
A sol-gel solution containing any of Y, Yb, and Lu and containing any of Al, Mg, and Si as the second additive element D2 is prepared, and the sol-gel solution is applied on a porous electrode substrate. Z by the sol-gel method
Low-temperature production method of rO ₂ -based solid electrolyte membrane. 2. ZrO ₂ prepared by the sol-gel method according to claim 1.
In the method for producing a low temperature solid electrolyte membrane, Zr, D1 and D
2 is 1-XY: X: Y (provided that 0.04 ≦
X, 0.004 ≦ Y, X ≦ 0.5Y, X + Y ≦ 0.30
4) ZrO ₂ by a sol-gel method,
Low-temperature production method of solid electrolyte membrane. 3. The method for producing a ZrO ₂ -based solid electrolyte membrane at a low temperature by a sol-gel method according to claim 1, further comprising a step of forming an electrolyte membrane by recrystallization by heat treatment. 4. The sol-gel method according to claim 1, wherein an ion conductor, a mixed conductor, or a porous electron conductor is used as the substrate.
Low-temperature fabrication method for _2- system solid electrolyte membrane. 5. A low-temperature preparation of a ZrO ₂ -based solid electrolyte membrane by a sol-gel method according to any one of claims 1 to 4, wherein a spin coating method, a screen printing method, a spraying method or a dipping method is used as a coating method. Law.