JP3342502B2 - Fuel electrode of solid oxide fuel 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 mixture suitable for an electrode material for a solid oxide fuel cell and an electrode for a solid oxide fuel cell prepared 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 cermets of nickel and zirconium oxide (ZrO ₂ ) have been used as materials for fuel cells (hereinafter referred to as fuel electrodes) of OFCs.

[0003]

However, the conventional SOF
The electrode obtained from the electrode material for C has insufficient electric performance, and an electrode material capable of providing a SOFC electrode having higher electric performance has been desired. Therefore, an object of the present invention is to provide a SOFC electrode which can provide an SOFC electrode having improved electric performance as compared with the related art.
An object of the present invention is to provide an electrode material for an OFC and an electrode for a SOFC having improved electric performance.

[0004]

Means for Solving the Problems] To solve the above problems
Further, the present invention provides the following means. That is, the present onset
Akira is a fuel electrode of a solid oxide fuel cell, which is a mixture mainly composed of an oxide solid solution and cubic and / or tetragonal zirconium, wherein the oxide solid solution is mainly composed of magnesium oxide and nickel oxide. , Oxide
Magnesium oxide with respect to the total molar amount of gnesium and nickel oxide
Nesium is not less than 10 mol% and not more than 20 mol%, and the balance
Is nickel oxide, and the cubic and / or tetragonal di
The amount of ruconium is based on the total molar amount of the mixture.
A material having a content of not less than 20 mol% and not more than 30 mol%
The main material and then, a porous portion having the metal Ni particle diameter 0.5μm metal Ni as a main phase, and grain portions that zirconium oxide as a main phase is three-dimensionally bonded to the porous structure of the Providing an anode.

The oxide solid solution is a nickel atom (N
i) means that a magnesium atom (Mg) and an oxygen atom (O) are uniformly mixed in an atomic order.
As a method for producing this oxide solid solution, Ni and M
Wet processes such as thermal decomposition of aqueous acetate solutions of g or nitrates of Ni and Mg.
s) or a conventional method 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.

The cubic and / or tetragonal zirconium oxide means zirconium oxide (ZrO ₂ ) whose crystal system is stabilized to a cubic system or a tetragonal system, respectively. As a method for stabilizing the crystal system, for example, yttria (Y
₂ O ₃ ) or calcium oxide (C
Various methods such as stabilization using aO) can be used.
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 greatly changes. This is because separation between the electrolyte and the electrolyte occurs. Either cubic or tetragonal zirconium oxide may be used, or both may be used.

Next, the above-mentioned mixture is a powder of the above-mentioned oxide solid solution and cubic and / or tetragonal zirconium oxide (hereinafter, referred to as “the mixture”).
(Referred to as zirconium oxide) simply and substantially uniformly mixed.

[0008] Magnesium oxide is 5 mol% to 25 mol% with respect to the total molar amount of the oxide solid solution, and the remainder is nickel oxide when magnesium oxide is less than 5 mol% and 25 mol%. %, The electrical performance of the SOFC electrode is not improved as compared with the conventional one, and the more preferable amount of magnesium oxide is 10 to 20%.
Mol%.

The reason why the mixing amount of the zirconium oxide is 35 mol% or less with respect to the total mol amount of the mixture is that when the mixing amount is more than 35 mol%, the electric characteristics of the SOFC electrode are not improved as compared with the conventional one. More preferably, the mixing amount of zirconium oxide is 10 to 30 mol%, particularly preferably 20 to 30 mol%.
Mol%.

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

[0011] Metal nickel particles having metal Ni as a main phase
The porous portion has a nickel content of 50 mol% or more,
Preferably Ru der least 80-90 mol%. Also said gold
The genus nickel particles mean nickel particles of 0.5 μm or less, more preferably 0.1 to 0.2 μm.

[0012] Further , a grain portion mainly composed of zirconium oxide.
The term "part" refers to 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 portions have a network-like structure means that the two portions are three-dimensionally connected to each other to form a porous structure.

[0014]

According to the fuel electrode of the present invention, the action of each component of the main material of the electrode occurs. In particular, mainly fine metal nickel
The part consisting of metal particles has electronic conductivity, while
The portion made of zirconium fluoride has ionic conductivity,
Furthermore, the network-like structure of these two parts
, The reaction field is diffused. Also fine
The reaction field is also enlarged by the metallic nickel particles. Sa
Luo, the zirconium oxide and MgO, heat resistance is improved since the sintering of the nickel is suppressed. In addition,
In the oxide solid solution contained in the electrode material, Ni, M
Since the g and O atoms are uniformly mixed in the atomic order, metal nickel particles precipitated by reduction of NiO are miniaturized .

[0015] Further, since the content of Ni and Mg contained in the oxide solid solution in the electrode material is a specific ratio, it has the electronic conductivity due to Ni and the thermal expansion coefficient of the zirconium oxide. Cubic zirconium oxide (hereinafter referred to as YSZ)
That. ). Further, the electrode material contains 20 to 30 mol% of the zirconium oxide ,
Fuel electrode of solid oxide fuel cell made from electrode material
Can have favorable electrical properties.

[0016]

Next, a method for manufacturing an electrode for a solid oxide fuel cell, 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.

[0017] Production Example 1 oxide solid solution of the prepared nickel acetate tetrahydrate _{(Ni (CH 3 COO) 2} · 4H
₂ O, special grade, manufactured by Wako Pure Chemical Industries) and magnesium acetate 4
A hydrate (Mg (CH ₃ COO) ₂ .4H ₂ O, special grade, manufactured by Kishida Chemical Co.) was used in a molar ratio of 9: 1, 8: 2, 7: 3 or 6:
4 and pure water was added thereto, followed by stirring with a magnetic stirrer to prepare a 0.5 N aqueous solution. These aqueous solutions were dropped at a rate of about 2 cc / min into a quartz tube maintained at 750 to 850 ° C. to perform thermal decomposition. Thereafter, X of the powder obtained by performing a heat treatment in air at 1000 ° C. for 24 hours.
The line chart was examined using a copper Kα line as the X-ray source. As a result, in all the powders, only the diffraction peak of the rock salt type crystal was present, and this diffraction peak was continuously shifted to the lower angle side as the addition amount of MgO increased, and each diffraction peak was separated. No. 1 and the diffraction peak was a shear peak, indicating that the powder obtained by the above production method had a sufficient solid solution of the NiO component and the MgO component.

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 solution having a value of 4 is referred to as a 10% solid solution of MgO, a 20% solid solution of MgO, a 30% solid solution of MgO, and a 40% solid solution of MgO, respectively. And, for example, MgO2
In a 0% solid solution, the solid solution amount of MgO is 20 mol%, and the solid solution amount of NiO is 80 mol%. Other oxide solid solutions will be similarly described.

Production Example 2 Production of Mixtures The various solid oxide solutions obtained in Production Example 1 were mixed with 0, 10, and 10 mols based on the total moles of the mixture to obtain submicron YSZ.
20, 30, 40, or 60 mol% of each was added and mixed in a mortar until uniform to prepare various mixtures.

Example Preparation of Electrode for SOFC To the various mixtures prepared in Production Example 2, polyethylene glycol was added as a binder to form a paste, which was then made into YSZ pellets (diameter 13
mm (thickness: 1 mm) on a screen (# (mesh) 20
0) Printed. This was baked at 1400 ° C. for 2 hours.
The fuel electrode thickness in this case was 15 μm. The rate of temperature rise and fall during baking was 200 ° C./hour. The electrodes were heated to 1000 ° C. in 3 hours before measuring the electric performance in Test Examples 1 to 4 described later, and then the electrodes were reduced by flowing hydrogen at a flow rate of 50 cc / min for 30 minutes.

Production Example 3 Preparation of Fuel Cell Next, in order to evaluate the performance of the SOFC electrode obtained in the example, a fuel cell was prepared 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 cell. The elevating temperature rate during baking was all 200 ° C./hour.

Next, the following tests 1 to 4 were performed to examine the electric performance of the fuel 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 anode cells 1 prepared as in the embodiment
4, the polarization value η (200 A
/ Cm ² ). For comparison, Ni-YSZ cermet (31% by mole of YSZ with respect to the mole% of the whole electrode material) which is a conventional electrode prepared by the coating sintering method was prepared as in Production Example 3. The polarization value η was measured under the same conditions also for the fuel cell (hereinafter, referred to as a conventional example).

[0023]

[Table 1]

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

As shown in FIG. 5, when a mixture comprising a 20% solid solution of MgO and a YSZ content of 35 mol% or less is used as an electrode material, its polarization value is smaller than that of the conventional example, and a more preferable YSZ content is 10%. ~ 30 mol%, particularly preferably 20 mol%. In particular, when the YSZ content was 20 mol%, the polarization value was 19 mV, while that of 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 that of the Ni-YSZ cermet currently used as the SOFC electrode.
Has been greatly improved.

Test Example 2 Measurement of Polarization Component AC impedance was measured at the AC frequency of 0.1 Hz to 65000 Hz for the fuel cell 1 to 4 and the conventional example, and a Cole-Cole plot was prepared. The unit Ω · cm ² ) was determined. In the examples, the printing temperature of 1400 ° C. after screen printing was set to 13
When the temperature is set to 00 ° C., the same measurement is performed, and the polarization component R
I asked. FIG. 6 shows the result.

In FIG. 6, the horizontal axis represents YSZ for the whole mixture.
Content (numerical unit mol%), and the vertical axis indicates the polarization component R (numerical unit Ω · cm ² ). The white circles have a baking temperature of 140
The results at 0 ° C. are shown, and the white triangle indicates the baking temperature 1
The results at 300 ° C. are shown, and the black circles show the results for the conventional example (baking temperature 1400 ° C.). FIG. 6 shows that the electrical performance is better at 1400 ° C. than at 1300 ° C. As in the case of the test example 1, when a mixture of 20% MgO solid solution and a 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%, particularly preferably 20 to 30 mol%.
Mole%.

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

[0029]

[Table 2]

In Table 2, the numerical unit of the exchange current density is A
/ Cm ² ). As shown in FIG.
The fuel cell 1 using only a 20% solid solution as an electrode material is:
Although the exchange current density is larger than the conventional example,
The fuel cell 2 using a mixture of 20 mol% of O 20% solid solution and 20 mol% of YSZ as an electrode material had a higher exchange current density. That is, the exchange current density of the fuel cell 2 (the baking temperature is 1400 ° C.) is greatly improved by about 6.4 times as compared with the conventional example. Also, it was improved about 3.4 times compared with the fuel cell 1.

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

[0032]

[Table 3]

The numerical units in Table 3 are mol%. As shown in Table 3, each of the anode cells 5 to 8 uses a mixture of YSZ and an oxide solid solution as an electrode material and has a YSZ content of 20 mol%, and each of the oxide solid solutions is 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 indicates the amount of MgO solid solution (numerical unit mol%) of the oxide solid solution, and the vertical axis indicates 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 amount of MgO dissolved in the oxide solid solution is 5 to 25 mol%. It is preferable because it is smaller, 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 the present example) of the fuel cell 2 after measurement of the polarization value in Test Example 1 was measured by a scanning electron microscope (hereinafter referred to as SEM) and energy dispersion. Observation was performed using a type X-ray analyzer (hereinafter, referred to as EDX).

As a result of SEM observation, as shown in FIGS. 1 to 4, the electrode of this example has a porous part 1 of fine particles of 0.1 to 0.2 μm and a particle part 2 of about 1 μm. The porous portion 1 and the grain portion 2 had a structure in which they were sintered three-dimensionally and connected in a network, 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 was mainly composed of Ni and the grain portion 2 was mainly composed of YSZ. Further, when the amounts of Ni and Mg in the oxide solid solution after hydrogen reduction were analyzed by EDX, it was found that a porous body in which fine Ni particles were surrounded by MgO was formed. This proved that the fine particles of the porous portion 1 were Ni precipitated.

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 material and YSZ as an ion conductive material were sintered.

From the above observation results of Test Example 1, the electrode of this example is (1) that it is porous, (2) that it has electronic conductivity, and (3) that it has ionic conductivity. (4) Ni
(5) The reaction field is expanded by the precipitation of fine particles, and (5) the reaction is caused by the network structure of the portion where Ni is the main phase and the portion where YSZ is the main phase. (6) that YSZ is dispersed and sintering of the porous portion 1 is suppressed, and that MgO between fine Ni particles suppresses sintering of Ni, (7) By adding YSZ to the oxide solid solution, (7) the oxide solid solution had many preferable properties as an electrode for SOFC, such as a coefficient of thermal expansion approaching YSZ which is usually used as a solid electrolyte. .

[0038]

According to the present invention, a specific oxide solid solution and
Uses an electrode material containing zirconium oxide in a specific ratio
And, since the electrode structure has a specific porous structure,
Provide SOFC fuel electrode with improved electrical performance
Wear.

[Brief description of the drawings]

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

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

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

FIG. 4 is an electron micrograph of a crystal structure of a cross section of the electrode of Example 1 (at a magnification of 7000 times).

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

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

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

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

[Explanation of symbols]

 1 porous part 2 grain part

Continued on the front page (72) Inventor Shinji Kawasaki 2-15-15 Takeda-cho, Mizuho-ku, Nagoya-shi, Aichi (72) Inventor Takehito Bogauchi 2429 Kamitsu, Nagao-cho, Kita-ku, Kobe, Hyogo (72) Inventor Takeuchi Shinji 3-11-20 Wakao-ji Temple, Amagasaki City, Hyogo Prefecture (72) Inventor Taihei Kikuoka 3-11-20 Wakao-ji Temple, Amagasaki City, Hyogo Prefecture (72) Inventor Yoshimi Ezaki 20 -1 (72) Inventor Masatoshi Hattori 20-1 Kitasekiyama, Odaka-cho, Midori-ku, Nagoya-shi, Aichi (56) References JP-A-2-33860 (JP, A) JP-A-4-33266 (JP, A ) Shinji Kawasaki and 5 others, "Application of NiO-MgO solid solution to SOFC fuel electrode", Abstracts of the 57th Annual Meeting of the Electrochemical Society of Japan (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4 / 86

Claims (1)

(57) [Claims] 1. A fuel electrode for a solid oxide fuel cell, comprising a mixture mainly composed of an oxide solid solution and cubic and / or tetragonal zirconium, wherein the oxide solid solution is composed of magnesium oxide and nickel oxide. it mainly,
Acid based on the total molar amount of magnesium oxide and nickel oxide
Magnesium iodide is not less than 10 mol% and not more than 20 mol%.
The remainder is nickel oxide, and the cubic and / or positive
The mixed amount of tetragonal zirconium is the total molar amount of the mixture.
20% by mole or more and 30% by mole or less with respect to
As a primary material of the serial electrodes, a porous portion having the metal Ni particle diameter 0.5μm metal Ni as a main phase, and grain portions that zirconium oxide as a main phase is three-dimensionally bonded to the porous The fuel electrode that forms the quality structure.