JP3582275B2 - Electrode for molten carbonate fuel cell and method for producing the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to an electrode of a molten carbonate fuel cell used in an energy sector in which chemical energy of a fuel is directly converted into electric energy, and particularly to an anode and a method of manufacturing the same.
[0002]
[Prior art]
Conventionally, as a method for producing an electrode (anode) for a molten carbonate fuel cell, as shown in FIG. 6, for example, an intermetallic compound 1 having an Al-based composition such as Ni-25Cr-25Al is subjected to a pulverizing step I. Finely pulverized by a ball mill to have a final particle size of 1 to 10 μm and an average particle size of 5 μm, and as a reinforcing material, add 1 to 10% to Ni powder 2 in mixing step II, mix and form a slurry, After the slurry 3 is formed into a tape shape in the tape forming step III, it is fired at a high temperature of 1000 ° C. or more in a vacuum or a reducing atmosphere in a firing step IV to form a solid solution, and has a thickness of 0.5 to 1.5 mm. There is one that manufactures a porous electrode having a porosity of 50 to 60% and an average pore diameter of 4 to 7 μm (Japanese Patent Application No. 2-135360).
[0003]
[Problems to be solved by the invention]
In order to improve the performance and extend the life of the molten carbonate fuel cell, it is necessary to increase the porosity of the electrode of the porous body manufactured as described above and to enhance the function of the creep resistance. However, even in the case of the above manufacturing method, the intermetallic compound forms a solid solution in Ni at the time of firing and functions as a reinforcing material, so that creep strength can be secured and the microstructure can be stabilized, and the fuel cell However, there is a limit in increasing the porosity in order to achieve higher performance of the fuel cell.
[0004]
Accordingly, an object of the present invention is to provide an electrode for a molten carbonate fuel cell and a method of manufacturing the same, which can further increase the porosity as compared with the conventional manufacturing method.
[0005]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems by adding and mixing an intermetallic compound having an Al-based composition as a fine powder having an average particle diameter of 1.4 μm to a Ni powder, forming a tape, firing the tape, and forming the fine powder. A molten porous electrode is prepared by oxidizing the porous electrode and then reducing it to reduce only Ni, and the oxide is dispersed in the Ni porous body. The electrode for a carbonate fuel cell and an intermetallic compound having an Al-based composition are pulverized into fine particles, and this is added to Ni powder as a reinforcing material, mixed and slurried, and the slurry is formed into a tape shape. After firing, a porous material electrode is produced, and further, the porous material electrode is oxidized to oxidize the Ni porous material and the additional element diffused therein, and then reduced to reduce only Ni. Oxide is dispersed in Ni porous body A manufacturing method of completing the electrodes.
[0006]
Due to the small particle diameter of the fine powder, a porous electrode having a porosity of 60 to 75% can be made by firing at a high temperature in the firing step. By oxidizing and reducing this, the Ni porous body itself is reduced, and the additional elements dispersed in the Ni porous body remain oxidized, whereby an electrode with oxide dispersion strengthening is obtained.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0008]
FIG. 1 shows the steps for carrying out the production method of the present invention. As in the case of the conventional production method shown in FIG. 6, an intermetallic compound 1 having an Al group composition is finely divided in a pulverization step I. The mixture is crushed and mixed with Ni powder 2 as a reinforcing material in a mixing step II to form a slurry. The slurry 3 is formed into a tape in a tape forming step III, and then fired in a firing step IV to form a porous electrode 4. After the porous electrode 4 is oxidized in the oxidation step V, the electrode 5 in which only Ni is reduced in the reduction step VI is completed.
[0009]
The composition of the intermetallic compound 1 includes Al—Ni (AlNi, Ni ₃ Al, Ni ₂ Al ₃ , Al ₃ Ni), Al—Fe (Al ₂ Fe, Al ₃ Fe, AlFe), and Al—CO system _{(AlCO, Al 5 CO 2,} Al 9 CO 2), AlCr system _{(AlCr 2, Al 4 Cr,} Al 8 Cr 5, Al 9 Cr 4), AlTi system (AlTi, _Al 3 Ti), etc. It is.
[0010]
More specifically, in the pulverizing step I, instead of pulverizing by a conventional ball mill, a pulverized material 9 is caught in a groove of the table 7 by a grooved table 7 and a spherical roller 8 as shown in FIG. 8 Using a super hybrid mill 6 that forms a uniform biting layer over the entire width and enables efficient pulverization by ultra-pulverization, finely pulverizes the intermetallic compound 1 to 0.3 to 4 μm and an average particle diameter of 1.4 μm. Then, as shown in the electron micrograph of × 3000 in FIG. 3A, the ultrafinely pulverized fine powder of the intermetallic compound 1 has a small particle diameter and a large number of irregularities on the surface to increase the surface area (contact point is increased). ) And is observed as almost 1 μm or less. On the other hand, in the case of a fine powder pulverized by a conventional ball mill showing the same 3000 × electron micrograph shown in (b), the surface is round, the particle size is large, and the average particle size is 5 μm, so that it is about 10 μm. Many particles are observed.
[0011]
Next, in the above-mentioned pulverizing step I, 0.5 to 1.0% of fine powder, which has been superfinely pulverized by the super hybrid mill 6 and has an increased surface area, is added to the Ni powder 2 as a reinforcing material and mixed. Mix and slurry in Step II. Next, the slurry 3 is formed into a tape shape in a tape forming step III and then dried to form a green tape, and the green tape is fired in a firing step IV at a high temperature of 1000 ° C. or higher in a vacuum or a reducing atmosphere. In this case, by finely pulverizing in the above-mentioned pulverizing step I so as to have an average particle size of 1.4 μm and granulating so as to increase the surface area, the powder can be sufficiently diffused into the porous body having Ni powder as a matrix. Thus, the number of contact points can be increased, and in the firing at 1000 to 1200 ° C. in the firing step IV, the fine powder of the intermetallic compound as an additional element is so fine that sintering shrinkage is less likely to occur. The porous body electrode 4 having a volume ratio of 55 to 75% can be produced, but the porosity is set to 60% or more, which is higher than the conventional one, depending on the amount of the fine powder of the intermetallic compound 1 and the firing temperature in the firing step IV. can do. Eventually, the porous electrode 4 having a thickness of 0.5 mm to 1.5 mm, a porosity of 60 to 75%, and an average pore diameter of 4 to 7 μm can be formed through the above-described firing step IV.
[0012]
Subsequently, in order to maintain the porosity, the porous material electrode 4 is oxidized by an oxidizing operation in an oxidizing step V to oxidize the additional element diffused into the porous body having Ni powder as a mother phase. Then, in the reduction step VI, hydrogen is added to the porous material electrode 4 to perform a reduction operation to reduce only Ni, thereby completing the electrode 5 in a state where the oxide is dispersed in the Ni porous material. That is, since the additive element diffused into the Ni porous body has a stronger affinity for oxygen than Ni in the Ni porous body and the additive element is not reduced, the electrode with the oxide dispersion strengthened during operation of the battery ( Anode) 5.
[0013]
The oxidation step V and the reduction step VI may be performed by incorporating the electrode 4 in the fuel cell FC, or may be performed outside the fuel cell FC and then incorporated in the fuel cell FC.
[0014]
When performed in the fuel cell FC, when the temperature of the fuel cell is initially raised, the temperature is raised to 400 to 450 ° C. and air having an oxygen concentration of 1 to 50% is flowed, and the air is added to the Ni powder and the Ni powder. The diffused additive is oxidized, and nitrogen is flowed at 450 ° C. or higher. Thereafter, when reducing, hydrogen is flowed to reduce only Ni, so that the parent phase is made of Ni metal and the added element remains as an oxide.
[0015]
On the other hand, when the operation is performed outside the fuel cell FC, before assembling the fuel cell, the porous electrode 4 is oxidized in air at 600 to 800 ° C., and the additive added together with Ni and diffused into Ni is oxidized. . Thereafter, when the reduction is performed, hydrogen is flowed to reduce only Ni, and the electrode 5 is made of only the additive element as an oxide. After the electrode 5 is incorporated in a battery, the temperature is increased and the operation is performed. To do.
[0016]
In the present invention, since the intermetallic compound 1 is finely pulverized to 0.3 μm to 4 μm and the average particle diameter to 1.4 μm in the pulverization step I, when the same addition amount as the conventional case shown in FIG. As the number of particles increases, the particles diffuse accordingly, and the effect of mixing with Ni can be expected when mixing with Ni powder. Further, since the particles are small, the number of contact points with the Ni powder increases, and diffusion during firing can be sufficiently expected. Further, since the additive particle size is smaller than the Ni particles and the conventional additive powder, if the addition amount is the same, solid solution strengthening during firing can be sufficiently achieved, and the addition amount may be reduced to maintain strength. It becomes possible.
[0017]
【Example】
(1) The inventors of the present invention use hydrogen / carbon dioxide gas in the case of using the fine powder as shown in FIG. 3A according to the present invention and the case of using the conventional fine powder as shown in FIG. When the compression creep deformation rate (%) was examined under the conditions of 80/20, a temperature of 650 ° C., a load of 12.5 kgf / cm ² , a load application time of 1000 hours, and the presence of carbonate, the results shown in FIG. 4 were obtained. Was done. FIG. 4 shows the results when the added amount of the improved powder of the present invention and that of the conventional powder were the same and the preparation conditions were the same. In both cases, although the porosity was 60%, the compressive creep change was shown. It can be seen that the amount is small.
(2) The present inventors next examined the compression creep change rate (%) of the improved powder of the present invention subjected to oxidation-reduction treatment and that of the powder not subjected to the oxidation-reduction treatment under the same conditions as in (1) above. The results as shown in FIG. 5 were obtained. FIG. 5 also shows that the oxidation-reduction treatment reduces the amount of compressive creep deformation.
(3) The present inventors examined the cell performance under the conditions of a fuel utilization of 150 mA / cm ^{2 at} a load fuel utilization of 75%, an oxidizing gas utilization of 50%, and an operation temperature of 650 ° C. The voltage of 0.78 to 0.79 V was 0.81 to 0.83 V in the electrode of the present invention, indicating that the performance was improved.
[0018]
【The invention's effect】
As described above, according to the electrode for a molten carbonate fuel cell of the present invention and the method for producing the same, an intermetallic compound having an Al-based composition finely pulverized to 0.3 μm to 4 μm and an average particle diameter of 1.4 μm. After mixing the Ni powder with the Ni powder as a reinforcing material to form a slurry, forming the slurry into a tape, firing it to form a porous electrode, and further oxidizing it, then reducing it to reduce only Ni, Since the electrode in which the oxide is dispersed in the Ni porous body is completed, the porosity can be increased, the battery performance can be improved, and the oxide dispersion is enhanced during the operation of the battery. As a result, it is possible to obtain an excellent effect that creep resistance is generated and a longer life can be achieved.
[Brief description of the drawings]
FIG. 1 is a view showing a production process of a method for producing an electrode for a molten carbonate fuel cell of the present invention.
FIG. 2 is a schematic diagram showing a pulverizing section of a super hybrid mill used in the pulverizing step of the present invention.
FIG. 3 is an enlarged view of the fine powder pulverized in the pulverizing step. (A) shows the particle size of the fine powder used in the present invention, and (B) is an electron micrograph showing the conventional fine powder.
FIG. 4 is a view showing an experimental result showing a difference in a compression creep change amount between a fine powder used in the present invention and a conventional fine powder.
FIG. 5 is a view showing an experimental result showing a difference in the amount of compressive creep deformation between a fine powder used in the present invention and a fine powder not subjected to an oxidation-reduction treatment.
FIG. 6 is a view showing a manufacturing process of a conventional electrode for a molten carbonate fuel cell.
[Explanation of symbols]
I Pulverizing Step II Mixing Step III Tape Forming Step IV Firing Step V Oxidation Step VI Reduction Step 1 Intermetallic Compound 2 Ni Powder 3 Slurry 4 Porous Electrode 5 Electrode

Claims (4)

An intermetallic compound having an Al-based composition was added as a fine powder having an average particle diameter of 1.4 μm to Ni powder, mixed and formed into a tape shape, and fired to produce a porous electrode in which the fine powder was diffused. An electrode for a molten carbonate fuel cell, wherein the body electrode is oxidized and then reduced to reduce only Ni, and the oxide is dispersed in the Ni porous body. The electrode for a molten carbonate fuel cell according to claim 1, wherein the porosity is 60 to 75%. An intermetallic compound having an Al-based composition is pulverized into fine particles, added to Ni powder as a reinforcing material, mixed and slurried, and the slurry is formed into a tape shape, and then fired to form a porous electrode. After the porous electrode is oxidized to oxidize the Ni porous body and the additional element diffused therein, only the Ni is reduced by the reduction treatment, and the oxide is contained in the Ni porous body. A method for producing an electrode for a molten carbonate fuel cell, comprising completing an electrode in which is dispersed. 4. The method for producing an electrode for a molten carbonate fuel cell according to claim 3, wherein a fine powder having a particle size of 0.3 to 4 [mu] m and an average particle size of 1.4 [mu] m is used.

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