JP3216150B2 - Method for producing cathode electrode for molten carbonate 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 an electrode for a molten carbonate fuel cell used in the energy sector which directly converts chemical energy of a fuel into electric energy, in particular, a molten carbonate fuel cell for producing a cathode electrode. The present invention relates to a method for manufacturing a cathode electrode.

[0002]

2. Description of the Related Art Among the fuel cells proposed so far, a molten carbonate fuel cell uses an electrolyte plate (tile) formed by impregnating a molten porous material with a porous material as an electrolyte as a cathode (oxygen electrode). The anode and the anode (fuel electrode) are sandwiched from both sides, and an oxidizing gas is supplied to the cathode side and a fuel gas is supplied to the anode side, so that electric power is generated by a potential difference generated between the cathode and the anode. Each cell is a single cell, and each cell is laminated in multiple layers via a separator.

[0003] As a method for forming an electrode of the above-mentioned molten carbonate fuel cell, in recent years, it has been used as a method for manufacturing an electrolyte plate because of its excellent molding accuracy and surface smoothness, and mass production and size increase. It has been manufactured by a tape forming method using a doctor blade method.
As shown in an example in FIG. 3, a conventional method for manufacturing a cathode electrode using a tape forming method by such a doctor blade method is as follows. First, a simple substance of carbonyl Ni powder a as a raw material powder, a dispersant b, and an organic solvent c are used. After pulverizing with a ball mill or the like (pulverizing step d) to disperse the Ni powder a into the primary particles, an organic binder f and a plasticizer g are added and mixed (mixing step e) to form a slurry h, This is formed into a tape shape (sheet shape) by a doctor blade device (tape forming step i), and finally fired at a temperature of 800 to 900 ° C. in an electric furnace, a reducing atmosphere furnace, a vacuum furnace, or the like (a firing step). j)
Thus, a porous (porosity: 70 ± 5%) cathode electrode is obtained.

[0004]

However, the cathode electrode, which is a Ni porous body manufactured by the above manufacturing method, is required to have a high porosity in terms of battery performance, and the Ni powders a are as shown in FIG. 4 (A). Since the Ni powders are bonded in a simple structure, the degree of bonding between the Ni powders is weak. In addition, the above-mentioned conventional cathode electrode is oxidized by an oxidizing gas at an oxidizing temperature of 500 to 600 ° C. to form a NiO porous body during operation as a battery, but the oxidized NiO electrode. As shown in FIG. 4 (B), the bonding force between the NiO (a ′) particles is weak, and the powder is easily compressed and deformed by the tightening stress during the operation of the battery. (Pore distribution, porosity) is changed, and there is a problem that battery performance is deteriorated. In addition, since Ni itself before being oxidized also has a low creep strength, it has a disadvantage that it is easily deformed.

[0005] Therefore, the present invention is intended to increase the bonding force between Ni powders and to obtain a cathode electrode which is hardly deformed and has high creep resistance.

[0006]

According to the present invention, in order to solve the above-mentioned problems, 3 to 5 μm Ni powder is preliminarily pulverized to 3 to 5 μm.
0.1-5% of a fine powder of Al intermetallic compound finely ground to have a particle size of 8μ is mixed as a reinforcing material, and then a sintering inhibitor is added to the mixture at a maximum of 20% to form a slurry. ,
After the slurry is formed into a tape, the slurry is sintered at a high temperature of 950 to 1050 ° C. in a vacuum or a reducing atmosphere, and the sintering inhibitor is thermally decomposed at the time of sintering, such as Al ₂ O ₃ or MgO. The method for producing a cathode electrode for a molten carbonate fuel cell is characterized in that a porous cathode electrode is produced by using a material which is then pulverized.

[0007]

Since the Al intermetallic compound used as a reinforcing material is hard and brittle, it can be easily pulverized (3 to 8 µm). The fine powder of this Al intermetallic compound is mixed with 2 to 5 µm Ni powder by 0.1 to 5%. When sintering at a high temperature of 950 to 1050 ° C. in a vacuum or a reducing atmosphere, sintering of the Al intermetallic compound and the Ni powder can be promoted, and the Al intermetallic compound is easily dissolved in the Ni powder, and It can form a solid solution to function as a reinforcing material, strengthening the bonding force between Ni powders and improving the high-temperature strength of Ni itself. In addition, since a sintering inhibitor using a material which thermally decomposes and becomes finer during the sintering process, such as Al ₂ O ₃ or MgO, is added to the above mixture, the porosity as an electrode is lowered even by high-temperature sintering. Never do.

[0008]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a process flow of the production method of the present invention, where I is Ni powder 1 as a raw material powder produced by pyrolyzing nickel carbonyl and Al as a reinforcing material.
II is a mixing step in which the intermetallic compound 2, the dispersant 3, and the solvent 4 are added and mixed, and II is a slurry obtained by adding the sintering inhibitor 5 and the binder 6 to the mixture obtained in the mixing step. This is a tape forming process for forming the slurry 7 into a tape.
I is a firing step for firing the tape formed in the tape forming step II to obtain the porous cathode electrode 8.

More specifically, as the Al intermetallic compound 2 for strengthening the Ni powder 1, for example, 50Cr-50Al fine powder (particle diameter 3 to 8 μm) is prepared in advance, and this is mixed with the particle diameter 2 to 5 μm. 0.1 to 5% of Ni powder 1 and further, as a dispersant 3, for example, a nonionic surfactant 0.5
~ 2 parts and a solvent 4 such as water are added and mixed in the mixing step I. Subsequently, a sintering preventive (assistant) agent 5 is added to the mixture at a maximum of 20% by volume, and a binder 6 is added in an amount of 2 to 10 parts with respect to the whole powder to form a slurry 7. Next, the slurry 7 is formed into a tape (sheet) by a doctor blade method in a tape forming step II, and then dried to form a green tape. Thereafter, the green tape is sintered at a high temperature of 950 to 1050 ° C. in a vacuum or in a reducing atmosphere in a firing step III, whereby a porous cathode electrode 8 is obtained.

The Al intermetallic compound 2 includes:
Al-Ni system _{(NiAl, Ni 2 Al, Ni} 2 Al 3,
Al ₃ Ni ₂ ), Al—Fe system (Al ₂ Fe, Al ₃ F)
e, AlFe), Al—Co system (AlCo, Al ₅ Co)
₂ , Al ₉ Co ₂ ), Al—Cr-based (AlCr ₂ , Al
₄ Cr, Al ₉ Cr ₄ ), Al-Ti (AlTi, A
Any material having a composition such as l ₃ Ti ₂ ) can be used. Examples of the sintering inhibitor 5 include oxides and hydroxides of Al, Mg, and Ca that are thermally decomposed and pulverized (about 0.5 to 2 μm) during sintering (at a high temperature). And Mg,
Ca carbonate or the like is used. In this case, for example, Al
(OH) ₃ → Al ₂ O ₃ , MgCO ₃ → MgO, CaC
It is desirable that the material changes like O ₃ → CaO and becomes finely divided and adheres uniformly to the metal surface, and when an aqueous slurry is used, a substance that is insoluble or hardly soluble in water is desirable. Furthermore,
As the binder 6, in the case of an aqueous system, polyvinyl alcohol or methylcellulose, or in the case of an organic solvent system,
Use polyvinyl butyral.

In the present invention, a small amount of Al
Since the mixture to which the intermetallic compound 2 has been added is tape-formed and then sintered at a high temperature, as shown in FIG.
There is no bonding portion between the powders 1 and the Al intermetallic compound 2 forms a solid solution in the Ni powder 1 to exhibit a function as a reinforcing material, whereby the bonding force between the Ni powders 1 can be strengthened. At the same time, the high-temperature strength of Ni itself can be improved. Further, as shown in FIG. 2B, the bonding force between NiO (1 ') is strong even after being oxidized and changed to NiO. (2 ′) indicates an oxidized Al intermetallic compound. Therefore, it is possible to obtain the cathode electrode 8 which is not easily deformed and has high creep resistance. The above Al intermetallic compound 2
Was mixed in the range of 0.1 to 5% with respect to Ni powder 1. However, when the content was 0.1% or less, the creep resistance was low and the
%, The electrical resistance becomes too large. A
l It is preferable that the amount of the intermetallic compound 2 is small, and the amount is small as described above. Although the porosity may decrease, in the present invention, in order to prevent such a point, the sintering inhibitor 5 which thermally decomposes and pulverizes the mixture of the Ni powder 1 and the Al intermetallic compound 2 at a high temperature.
Is added, so that the porosity does not decrease and the microstructure can be stabilized. In the above, the amount of addition of the sintering inhibitor 5 is up to 20%.
This is because if it is 20% or more, sintering of metal powders is hindered. The sintering temperature is 950-1
The temperature was set to 050 ° C., because the porosity is increased when the temperature is 950 ° C. or less, and the porosity is decreased when the temperature is 1050 ° C. or more.

Table 1 shows the test results of the compressive creep strength of the electrode 8 obtained by adding the Al intermetallic compound 2 to the Ni powder 1 for comparison with the conventional Ni simple electrode. Table 2 shows the test results of the conductivity when the oxidation treatment was performed. The creep test conditions are 700 ° C. × 50 hr, a compressive load of 15.4 kgf / cm ² , and in Air (oxidizing atmosphere). The conductivity test condition is 650 ° C. in Air-CO ₂ .

[0014]

[Table 1]

[0015]

[Table 2] From Table 1 above, it can be seen that the electrode to which the Al intermetallic compound is added has higher creep resistance than the electrode of Ni alone. Also, from Table 2, it can be seen that although the conductivity is slightly reduced by alloying, the function as an electrode is not impaired.

It should be noted that the present invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the present invention.

[0017]

As described above, according to the method of manufacturing a cathode for a molten carbonate fuel cell of the present invention, 2 to 5 μm
0.1-5% of a fine powder of an Al intermetallic compound, which has been pulverized in advance to a particle size of 3 to 8 μm, with Ni powder of 0.1 to 5% as a reinforcing material, and then sintered to the mixture. A slurry is formed by adding a maximum of 20% of an inhibitor, and the slurry is formed into a tape shape.
A porous cathode electrode is manufactured by using a material which is sintered at a high temperature of 1050 ° C. and which is thermally decomposed and pulverized such as Al ₂ O ₃ or MgO during the sintering process as the sintering inhibitor. Since the Al intermetallic compound is hard and brittle, it can be easily pulverized to have a particle size of 3 to 8 μm, and mixed with Ni powder in a vacuum or a reducing atmosphere to produce 950 to 105 μm.
By sintering at a high temperature of 0 ° C., the Al intermetallic compound can easily form a solid solution in the Ni powder and can function as a reinforcing material by dissolving in the Ni powder. It is possible to obtain a cathode electrode that is difficult to perform and has high creep resistance. Also, since the mixing amount of the Al intermetallic compound is small, sintering of Ni powder proceeds at high temperature sintering, and the porosity as an electrode may decrease. Even if there is, a sintering inhibitor which is thermally decomposed and pulverized like Al ₂ O ₃ or MgO at the time of sintering treatment is added to the mixture, so that sintering at a higher temperature is required. As a result, sintering of the Ni powders and sintering of the Ni and the Al intermetallic compound as the reinforcing material are promoted, and the microstructure can be stabilized without lowering the porosity of the electrode. It can contribute to performance improvement, and A l The mixing ratio of the intermetallic compound is 0.1 to 5%
, The creep resistance is improved, the electric resistance is not excessively increased, and the sintering between metals is inhibited by setting the addition amount of the sintering inhibitor to a maximum of 20%. Without sintering at 950 to 1050 ° C., a porous cathode electrode can be obtained.

[Brief description of the drawings]

FIG. 1 is a process flow showing a method for producing a cathode electrode for a molten carbonate fuel cell of the present invention.

FIGS. 2A and 2B show a crystal structure of a cathode electrode manufactured by the manufacturing method of the present invention, in which FIG. 2A shows a state before oxidation, and FIG. 2B shows a state after oxidation. FIG.

FIG. 3 is a process flow showing an example of a conventional method for manufacturing a cathode electrode.

4A and 4B are schematic diagrams showing a crystal structure of a cathode electrode manufactured by a conventional manufacturing method, wherein FIG. 4A shows a state before oxidation, and FIG. 4B shows a state after oxidation. It is.

[Explanation of symbols]

 Reference Signs List 1 Ni powder 2 Al intermetallic compound 5 Sintering inhibitor 7 Slurry 8 Cathode electrode I Mixing process II Tape forming process III Firing process

Continuation of the front page (72) Inventor Tetsuyuki Morita 3-1-1, Toyosu, Koto-ku, Tokyo Ishikawa Shima-Harima Heavy Industries Co., Ltd. Inside the Toji Technical Center (72) Inventor Minoruichi Ota 3-1-1, Toyosu, Koto-ku, Tokyo No. 15 Ishikawa Shima Harima Heavy Industries, Ltd. Toji Technical Center (56) References JP-A-2-103681 (JP, A) JP-A-2-103860 (JP, A) JP-A-61-271749 (JP, A) JP-A-62-165864 (JP, A) JP-A-2-288069 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/86-4/98

Claims (1)

(57) [Claims] 1. A pulverization method in which 2 to 5 μ Ni powder is pulverized in advance to 3 to 5 μm.
0.1-5% of a fine powder of Al intermetallic compound finely ground to have a particle size of 8μ is mixed as a reinforcing material, and then a sintering inhibitor is added to the mixture at a maximum of 20% to form a slurry. ,
After the slurry is formed into a tape, the slurry is sintered at a high temperature of 950 to 1050 ° C. in a vacuum or a reducing atmosphere, and the sintering inhibitor is thermally decomposed at the time of sintering, such as Al ₂ O ₃ or MgO. A method for producing a cathode electrode for a molten carbonate type fuel cell, comprising producing a porous cathode electrode by using a material that is pulverized.