JPH06111829A - Mixed body suitable for electrode material for solid electrolyte type fuel cell, and electrode for solid electrolyte type fuel cell - Google Patents

Abstract

PURPOSE:To improve electric performance of an electrode for a solid electrolyte type fuel cell (SOFC), by mixing a specific oxide solid solution with zirconium at a fixed ratio. CONSTITUTION:In the mixed body of an oxide solid solution and cubic and/or solution has main components of magnesium oxide and nickel oxide, the magnesium oxide is made to have 5mol or more and 25mol% or less to total mol quantity of the magnesium oxide and the nickel oxide, and the remainder is the nickel oxide. In cubic and/or tetragonal zirconium, its mixed quantity is made 35mol% or less to the total mol quantity of the mixed body. An SOFC electrode is manufactured by a usual method with the mixed body as material. At that time, it is required to reduce the oxide solid solvent to deposit Ni. Consequently electronic conductivity by Ni is given, and concurrently thermal expansion coefficient approaches that of the cubic oxide zirconium, usually used as solid electrolyte material, in the zirconium oxide, and ion conductivity is given.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mixture suitable for an electrode material for a solid oxide fuel cell and a solid oxide fuel cell electrode produced by using this mixture as a main material.

[0002]

2. Description of the Related Art Conventionally, solid oxide fuel cells (hereinafter referred to as S
Nickel (Ni) or cermet of nickel and zirconium oxide (ZrO ₂ ) has been used as a material for a fuel side cell (hereinafter referred to as a fuel electrode) of OFC.

[0003]

[Problems to be Solved by the Invention] However, the conventional SOF
The electrode obtained from the electrode material for C has insufficient electric performance, and an electrode material capable of providing an SOFC electrode having higher electric performance has been desired. Therefore, an object of the present invention is to provide an electrode for SOFC whose electric performance is improved as compared with the conventional one.
An object of the present invention is to provide an electrode material for OFC and an electrode for SOFC with improved electric performance.

[0004]

[Means for Solving the Problems] In order to solve the above problems,
The mixture suitable for the electrode material for solid oxide fuel cells according to claim 1 is a mixture mainly composed of an oxide solid solution and cubic and / or tetragonal zirconium oxide, and the oxide solid solution is magnesium oxide. And 25% by mole or less of magnesium oxide with respect to the total molar amount thereof, and the balance being nickel oxide, while the cubic and / or tetragonal zirconium oxide is in a mixed amount thereof. Is 35 mol% or less based on the total molar amount of the mixture. The electrode for a solid oxide fuel cell according to claim 2 for solving the above-mentioned problems is an electrode for a solid oxide fuel cell which uses the mixture according to claim 1 as a main material, and is mainly composed of fine nickel. It has a part and a part mainly made of zirconium oxide, and the two parts have a network structure.

The oxide solid solution is a nickel atom (N
i), a magnesium atom (Mg) and an oxygen atom (O) are uniformly mixed in atomic order.
As a method for producing this oxide solid solution, Ni and M are used.
wet processes such as thermal decomposition of an aqueous solution of acetic acid salt of g or thermal decomposition of an aqueous solution of nitrate of Ni and Mg.
s) or a dry process such as a method of mixing NiO powder and MgO powder and calcining, or a method of mixing Ni salt powder and Mg salt powder and calcining, etc. can be used.

The cubic and / or tetragonal zirconium oxide means zirconium oxide (ZrO ₂ ) whose crystal system is stabilized in the cubic system or the tetragonal system, respectively. As a method for stabilizing the crystal system, for example, yttria (Y
₂ O ₃ ) or calcium oxide (C
Various methods can be used, such as stabilization with aO).
As described above, it is necessary to stabilize ZrO ₂ to a cubic system or a tetragonal system because when the crystal system of ZrO ₂ changes due to a temperature change, the volume of the ZrO ₂ changes greatly, which is why the electrode is made during electrode preparation. This is because peeling between the electrolyte and the electrolyte occurs. And either one of cubic crystal and tetragonal zirconium oxide may be used, or both of them may be used.

Next, the mixture means the powder of the oxide solid solution and cubic and / or tetragonal zirconium oxide (hereinafter,
Zirconium oxide) is simply mixed in a substantially uniform manner.

Magnesium oxide is 5 mol% or more and 25 mol% or less with respect to the total molar amount of the oxide solid solution, and the balance is defined as nickel oxide when magnesium oxide is less than 5 mol% and This is because the electrical performance of the SOFC electrode is not improved when it is more than 10%, and the more preferable amount of magnesium oxide is 10 to 20.
Mol%.

The amount of the zirconium oxide mixed is set to 35 mol% or less with respect to the total molar amount of the mixture because the electrical characteristics of the SOFC electrode are not improved as compared with the conventional case when it is more than 35 mol%. More preferably, the mixing amount of zirconium oxide is 10 to 30 mol%, particularly preferably 20.
Mol%.

The method for producing an SOFC electrode using the mixture of claim 1 as a material includes printing on an electrolyte and firing, dipping on the electrolyte and firing, chemical vapor deposition (CVD) or on electrolyte. Various conventional methods such as thermal spraying can be used. However, it is necessary to reduce the oxide solid solution to precipitate Ni. Further, the mixture according to claim 1 is suitable for use as an electrode material for SOFC, but it has other uses, for example, it can be used as a catalyst.

In the second aspect, the portion mainly composed of fine nickel is a portion having a nickel content of 50 mol% or more, preferably 80 to 90% or more, and this portion has a porous structure of fine nickel particles. is doing. Further, the fine nickel is 0.5 μm or less, more preferably 0.
It means nickel particles of 1 to 0.2 μm.

In the second aspect, the portion mainly composed of zirconium oxide means a portion having a zirconium oxide content of 50 mol% or more, more preferably 80 to 90 mol% or more.

The fact that the two parts have a network-like structure means that the two parts are three-dimensionally connected and form a porous structure as a whole.

[0014]

According to the mixture of the first aspect, the Ni, Mg and O atoms are uniformly mixed in the oxide solid solution in the atomic order, whereby the Ni particles precipitated by the reduction of NiO are miniaturized. Moreover, since the content of Ni and Mg contained in this oxide solid solution is a specific ratio,
It has electronic conductivity due to
Among the zirconium oxides, cubic zirconium oxide (hereinafter referred to as YSZ) which is usually used as a solid electrolyte material.
Say)). Furthermore, since the mixture according to claim 1 contains a specific amount of the zirconium oxide, ionic conductivity is imparted and the coefficient of thermal expansion thereof further approaches YSZ.

According to the SOFC electrode of claim 2, since the mixture of claim 1 is used as a main material, each action of the mixture occurs and at the same time, a portion mainly made of fine nickel has electronic conductivity, while The field mainly composed of zirconium oxide has ionic conductivity, and the network structure of these two parts further expands the field of reaction. And the field of reaction is expanded by the miniaturization of nickel. Moreover, since the sintering of nickel is suppressed by zirconium oxide and MgO, the heat resistance is improved.

[0016]

EXAMPLES Next, a method for manufacturing a solid oxide fuel cell electrode, which is a specific example of the present invention, will be described. First, a specific example of the method for producing an oxide solid solution and a mixture according to claim 1 will be described.

Production Example 1 Production of Oxide Solid Solution Nickel acetate tetrahydrate (Ni (CH ₃ COO) ₂ .4H
₂ O, special grade, Wako Pure Chemical Industries) and magnesium acetate 4
The hydrate (Mg (CH ₃ COO) ₂ .4H ₂ O, special grade, manufactured by Kishida Chemical) has a molar number of 9: 1, 8: 2, 7: 3 or 6:
After weighing 4 and adding pure water, the mixture was stirred with a magnetic stirrer to prepare a 0.5N aqueous solution. These aqueous solutions were dropped into a quartz tube kept at 750 to 850 ° C. at a rate of about 2 cc / min for thermal decomposition. Then, X of powder obtained by heat treatment in air at 1000 ° C. for 24 hours
The line chart was examined using the copper Kα line as the X-ray source. As a result, in all powders, only diffraction peaks of rock salt type crystals were present, and this diffraction peak continuously shifted to the lower angle side as the amount of MgO added increased, and each diffraction peak was separated. It was found that the NiO component and the MgO component were sufficiently solid-dissolved in the powder obtained by the above-mentioned production method, since it was one and the diffraction peak was a sherb.

In the following description, the molar ratio of nickel acetate tetrahydrate and magnesium acetate tetrahydrate used in the production of the oxide solid solution is 9: 1, 8: 2, 7: 3 or 6 :.
The oxide solid solutions in the case of 4 are represented as MgO 10% solid solution, MgO 20% solid solution, MgO 30% solid solution and MgO 40% solid solution, respectively. And, for example, MgO2
In the 0% solid solution, the solid solution amount of MgO is 20 mol%, and the solid solution amount of NiO is 80 mol%. The same applies to other oxide solid solutions.

Production Example 2 Production of Mixture 0 to 10, based on the total moles of the mixture, which can obtain submicron YSZ in the various oxide solid solutions obtained in Production Example 1.
Various mixtures were prepared by adding amounts of 20, 30, 40 or 60 mol% each and mixing until uniform in a mortar.

Example Preparation of SOFC electrode Polyethylene glycol was added as a binder to the various mixtures prepared in Production Example 2 to form a paste, which was made into a YSZ pellet (diameter 13).
mm (thickness: 1 mm) and screen (# (mesh) 20
0) Printed. This was baked at 1400 ° C. for 2 hours.
The fuel electrode wall thickness in this case was 15 μm. The rate of temperature increase / decrease during baking was 200 ° C./hour. The electrode was heated to 1000 ° C. for 3 hours and then hydrogen was flowed at a flow rate of 50 cc / min for 30 minutes to reduce the electrode before measuring electrical performance in Test Examples 1 to 4 described below.

Production Example 3 Production of Fuel Electrode Cell Next, in order to evaluate the performance of the SOFC electrode obtained in the example, a fuel electrode cell was produced by the following method. That is, an air electrode (La _0.8 Sr _0.2 ) _0.9 MnO ₃ ) was screen-printed on the back surface of the YSZ pellet of the electrode obtained in the example, and baked at 1200 ° C. for 4 hours. Next, the reference electrode was baked at 1000 ° C. for 2 hours to obtain a fuel electrode cell. The rate of temperature rise and fall during baking was 200 ° C./hour.

Next, the following tests 1 to 4 were conducted for the electric performance of the fuel electrode cell prepared in Production Example 3. Test Example 1 Measurement of Polarization Value Production Example 1 using various mixtures having the compositions shown in Table 1
3 and various fuel electrode cells prepared as in Examples 1 to 3
4, the polarization value η (200 A
/ Cm ² when energized) was measured. For comparison, as in Production Example 3, a conventional electrode made of Ni-YSZ cermet (the amount of YSZ is 31 mol% based on the total mol% of the electrode material) is prepared by the coating and sintering method. The polarization value η of the fuel electrode cell (hereinafter, referred to as a conventional example) was also measured under the same conditions.

[0023]

[Table 1]

In Table 1, the numerical unit is mol%. As shown in Table 1, each of the anode cells 1 to 4 uses MgO 20% solid solution as an oxide solid solution, and 0, 20, 30, and 40 mol% YSZ with respect to the total moles of the mixture, respectively.
The mixture produced as in Production Examples 1 and 2 is used as the electrode material. The results of the fuel electrode cells 1 to 4 and the conventional example are shown in FIG. In FIG. 5, the horizontal axis represents YSZ for the entire mixture.
(Hereinafter referred to as YSZ content), and the vertical axis represents the polarization value η (numerical unit mV). The white circle is the fuel electrode cell 1.
4 are the results, and the black circles are the results of the conventional example.

As shown in FIG. 5, when a mixture of a solid solution of MgO 20% and a YSZ content of 35 mol% or less was used as an electrode material, its polarization value was smaller than that of the conventional example, and a more preferable YSZ content was 10. ˜30 mol%, particularly preferably 20 mol%. In particular, when the YSZ content was 20 mol%, the polarization value was 19 mV, while that in the conventional example was 75 mV. That is, the SO of the present embodiment
The FC electrode has a polarization value of about 1/4 of that of the Ni-YSZ cermet currently used as the SOFC electrode.
Was greatly improved.

Test Example 2 Measurement of Polarization Component AC impedance measurement was performed on the fuel electrode cells 1 to 4 and the conventional example at an AC frequency of 0.1 Hz to 65000 Hz to prepare a Cole-Cole plot, and the polarization component R (numerical value) of each electrode was measured. The unit Ω · cm ² ) was calculated. In the examples, a baking temperature of 1400 ° C. after screen printing is 13
The polarization component R
I asked. The result is shown in FIG.

In FIG. 6, the horizontal axis represents YSZ for the entire mixture.
The content (numerical unit: mol%), and the vertical axis is the polarization component R (numerical unit: Ω · cm ² ). The white circles are the baking temperature 140.
The results for 0 ° C are shown, the open triangles indicate the baking temperature 1
The results for 300 ° C. are shown, and the black circles are the results for the conventional example (baking temperature 1400 ° C.). From FIG. 6, it can be seen that the electrical performance is better when the baking temperature is 1400 ° C. than when the baking temperature is 1300 ° C. When the mixture of MgO 20% solid solution and YSZ content of 35 mol% or less was used as the electrode material, the polarization component R was smaller than that of the conventional example, and more preferable YS was obtained.
The Z content is 10 to 30 mol%, and particularly preferably 20.
It was mol%.

Test Example 3 Next, the relationship between the current density and the polarization value of the fuel electrode cells 1 and 2 and the conventional example was measured by the current interruption method to prepare a Tafel plot. The result is shown in FIG. 7. Figure 7
In the figure, the horizontal axis represents the polarization value η (numerical unit mV), and the vertical axis represents the current density I (numerical unit A / cm ² ). The white circles are the results for the fuel electrode cell 2 (baking temperature 1400 ° C), and the open triangles are the fuel electrode cell 2 (baking temperature 1300 ° C).
C.), the black circles are the results for the fuel electrode cell 1, and the open squares are the results for the conventional example. The exchange current density was calculated for each cell from the Tafel plot shown in FIG. The results are shown in Table 2.

[0029]

[Table 2]

In Table 2, the numerical unit of the exchange current density is A.
/ Cm ² ). As shown in FIG. 7 and Table 2, MgO
The fuel electrode cell 1 using only a 20% solid solution as an electrode material,
Its exchange current density is higher than that of the conventional example, but Mg
The exchange current density was further higher in the fuel electrode cell 2 in which the electrode material was a mixture of O 20% solid solution content 80 mol% and YSZ content 20 mol%. That is, the exchange current density of the fuel electrode cell 2 (baking temperature 1400 ° C.) was greatly improved to about 6.4 times that of the conventional example. Also, it was improved about 3.4 times compared to the fuel electrode cell 1.

Test Example 4 Next, various fuel electrode cells 5 to 8 prepared as in Production Examples 1 to 3 and Examples using various mixtures having the compositions shown in Table 3 were the same as in Test Example 3. The polarization component R (numerical unit: Ω · cm ² ) was measured by the method described in 1. The result is shown in Fig. 8.
Shown in.

[0032]

[Table 3]

The numerical unit in Table 3 is mol%. As shown in Table 3, in the fuel electrode cells 5 to 8, a mixture of YSZ and an oxide solid solution was used as an electrode material, the YSZ content was 20 mol%, and each of the oxide solid solutions was MgO.
This corresponds to the case where a solid solution of 10, 20, 30 or 40 mol% is used. In FIG. 8, the horizontal axis represents the MgO solid solution amount (numerical unit: mol%) of the oxide solid solution, and the vertical axis represents the polarization component R (numerical unit: Ω · cm ² ). As shown in FIG. 8, when the YSZ content of the electrode material is constant at 20 mol%, the MgO solid solution amount of the oxide solid solution is set to 5 to 25 mol%. Since it is smaller, it is preferable, and the more preferable MgO solid solution amount is 10 to 20 mol%.

Test Example 5 The microstructure of the fuel electrode (hereinafter, referred to as the electrode of this example) of the fuel electrode cell 2 after the polarization value was measured in Test Example 1 was examined with a scanning electron microscope (hereinafter referred to as SEM) and energy dispersion. It observed using the type | mold X-ray analyzer (henceforth EDX).

As a result of SEM observation, as shown in FIGS. 1 to 4, the electrode of this example had a porous portion 1 of fine particles of 0.1 to 0.2 μm and a grain portion 2 of about 1 μm. The porous portion 1 and the granular portion 2 had a structure in which they were three-dimensionally sintered and connected in a network form, and were porous as a whole. Further, from the EDX analysis results of the porous portion 1 and the grain portion 2, both portions are made of Ni, MgO and YSZ,
It was found that the porous portion 1 had Ni as the main phase and the grain portion 2 had YSZ as the main phase. Further, line analysis of the amounts of Ni and Mg in the oxide solid solution after hydrogen reduction was found by EDX to reveal that a fine Ni particle was surrounded by MgO to form a porous body. From this, it was found that the fine particles in the porous portion 1 were precipitated Ni.

From the above results, it was found that the microstructure of the electrode of this example had a network structure in which fine Ni particles as an electron conductive substance and YSZ as an ion conductive substance were sintered.

From the above observation result of Test Example 1, the electrode of this example has (1) porous property, (2) electronic conductivity, and (3) ionic conductivity. (4) Ni
Is expanded as fine particles, the field of the reaction is expanded, and (5) the part where Ni is the main phase and the part where YSZ is the main phase forms a network structure. (6) YSZ is dispersed to suppress the sintering of the porous portion 1 and MgO between the fine Ni particles suppresses the sintering of Ni. The heat resistance was improved, and (7) YSZ was added to the oxide solid solution, so that the coefficient of thermal expansion was close to that of YSZ which is usually used as a solid electrolyte. .

[0038]

The mixture according to claim 1 contains a specific oxide solid solution and zirconium oxide in a fixed ratio, so that SOF can be obtained.
When used as an electrode for C, its electrical performance can be improved as compared with conventional ones, and thus it is suitable as an electrode material for SOFC. The SOF of claim 2 obtained by using the mixture of claim 1 as a main material
The C electrode improves the electric performance over the conventional SOFC electrode.

[Brief description of drawings]

FIG. 1 is an electron micrograph of the crystal structure of the electrode surface of Example 1 (magnification: 10,000 times).

2 is an electron micrograph of the crystal structure of the electrode surface of Example 1 (magnification: 2,000 times).

FIG. 3 is an electron micrograph of the crystal structure of the electrode surface of Example 1 (magnification: 7,000 times).

FIG. 4 is an electron micrograph of a crystal structure of a cross section of an electrode of Example 1 (magnification: 7,000 times).

FIG. 5 is a graph showing the relationship between the YSZ content in the SOFC electrode material and the polarization value of the electrode.

FIG. 6 is a graph showing the relationship between the YSZ content in the SOFC electrode material and the polarization component of the electrode.

FIG. 7 is a Tafel plot for fuel electrode cells 1 and 2 and a conventional example.

FIG. 8: MgO of oxide solid solution in electrode material for SOFC
It is a graph showing the relationship between the amount of solid solution and the polarization component of the electrode.

[Explanation of symbols]

 1 porous part 2 grain part

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinji Kawasaki 2-15 Takeda-cho, Mizuho-ku, Nagoya, Aichi (72) Inventor Takehito Bokenai 2429 Uetsu, Nagao-cho, Kita-ku, Kobe-shi, Hyogo (72) Invention Shinji Takeuchi 3-11-20 Wakaoji, Amagasaki City, Hyogo Prefecture (72) Inventor Taihei Kikuoka 3-11-20 Wakaoji Temple, Amagasaki City, Hyogo Prefecture Inventor Yoshimi Ezaki Kita Otakacho, Midori-ku, Aichi Prefecture Aichi Prefecture 20-1 Sekiyama (72) Inventor Masatoshi Hattori 20-1 Kitakousan, Otaka-cho, Midori-ku, Nagoya-shi, Aichi

Claims (2)

[Claims] 1. A mixture mainly composed of an oxide solid solution and cubic and / or tetragonal zirconium oxide, wherein the oxide solid solution is mainly composed of magnesium oxide and nickel oxide, relative to a total molar amount thereof. Magnesium oxide is 5 mol or more and 25 mol% or less, and the balance is nickel oxide, while the cubic and / or tetragonal zirconium oxide has a mixing amount of 35 mol% or less with respect to the total molar amount of the mixture. Which is suitable for an electrode material for a solid oxide fuel cell. 2. An electrode for a solid oxide fuel cell using the mixture of claim 1 as a main material, which has a part mainly made of fine nickel and a part mainly made of zirconium oxide, An electrode for a solid oxide fuel cell, characterized in that the portion has a network-like structure.