JPH08306361A - Fuel electrode material for solid electrolyte fuel cell and its manufacture - Google Patents

Abstract

PURPOSE: To provide a fuel electrode material which can stably maintain functions equal to or higher than those of a conventional material for a long duration in the case the material is used as a fuel electrode of a solid electrolytic fuel cell. CONSTITUTION: A fuel electrode material for solid electrolytic fuel cell is composed of a mixture of a group of eight YSZ(yttrium-stabilized zirconia) coarse particles 31 with 20-75μm particle size, a group of eight fine particles 33 with 0.1-1μm particle size, and a group of NiO (which becomes metal NI at the time of operation of a fuel cell) particles 32 with 5-20μm particle size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel electrode material for solid electrolyte fuel cells and a method for producing the same. More specifically, the present invention relates to an improvement in the fine structure of a fuel electrode which can prolong the life of a solid oxide fuel cell.

[0002]

2. Description of the Related Art Solid electrolyte fuel cells are roughly classified into two types, that is, a cylindrical type and a flat type. For example, as an example of a cylindrical solid oxide fuel cell, a vertical stripe cylindrical type is shown in FIG.
Shown in In this vertical stripe cylindrical electrolyte fuel cell, an air electrode 21, a solid electrolyte 22 and a fuel electrode 23 are concentrically formed around a cylindrical support 20 to form a solid electrolyte 22 and a fuel electrode 23.
The current on the side of the air electrode 21 is taken out by the interconnector 24 formed on the air electrode 21 so as to divide it. A groove 25 is provided between the interconnector 24 and the fuel electrode 23 for electrically insulating the fuel electrode 23 and the interconnector 24. In this vertical stripe cylindrical solid oxide fuel cell, air is supplied to the air electrode 21 through the inside of the support 20. Further, the fuel gas is supplied to the fuel electrode 23 through the outside of the support 20. Since this vertical-striped cylindrical solid oxide fuel cell has a relatively high mechanical strength, it has been developed before the flat type, and has already succeeded in generating 5 kW class power, and has begun to manufacture 25 kW class. It is in the stage of being.

Further, as a flat plate type solid electrolyte fuel cell, for example, as shown in an exploded perspective view of FIG.
The flat unit cells 1 and the separators 4 are alternately stacked via the spacers 2 and 3, and the fuel gas and the air are fed into the air supply space 5 and the fuel gas supply space 6 formed by the unit cells 1 and the separator 4. The cell 1 is supplied through the cell gas supply pipe 7 and the air supply pipe 8, respectively. Further, the unit cell 1 is formed by forming an air electrode 10 and a fuel electrode 11 on the surface side of the solid electrolyte 9. This flat plate type has succeeded in generating 1 kW class power.

By the way, as a fuel electrode material of these solid electrolyte fuel cells, nickel oxide (NiO, but metallic nickel Ni when the fuel cell is operating) and zirconia (ZrO) are used.
_Since the nickel-zirconia cermet obtained by mixing the fine particles of ₂ ) has high catalytic activity (reduction capacity for hydrogen), and has high conductivity (reciprocal of electric resistance) even at high temperatures from room temperature to 1000 ° C. Was considered suitable.
However, if the content of nickel in the fuel electrode is high,
Thermal stress may occur due to the difference in thermal expansion coefficient, which may lead to cell destruction, and the nickel content cannot be increased so much. On the other hand, when the nickel content is low, the electrode characteristics are not so good and the current flow is reduced. It becomes difficult to take it out,
Further, there is a problem that the sinterability is high and the composition is easily densified. Therefore, conventionally, zirconia whose crystal structure has been stabilized with 8 mol% yttria (hereinafter referred to as 8YS
Write Z. ) Has been adopted.

As described above, the conventional fuel electrode material for a solid electrolyte fuel cell was obtained by mixing fine powders of NiO and 8YSZ. However, although this fuel electrode has excellent initial characteristics, it deteriorates several tens of hours after the start of power generation,
It becomes impossible to generate electricity. As a result of elucidation of the cause, it was found that the cause is the densification and volume contraction of the fuel electrode and the agglomeration of Ni particles under the battery operating conditions (Central Research Institute of Electric Power W93019, May 1994).

[0006] There are other reports on the agglomeration and densification of Ni (Abstracts of the 60th Annual Meeting of the Electrochemical Society of Japan, p. 269, April 1-3, 1993).

[0007] Further, there is a report that Ni (Mg) O-8YSZ is used to achieve high dispersion of Ni particles and long life of the fuel electrode (Abstracts of the 33rd Cell Study Meeting, No. 35). ~ P. 36, September 16-18, 1992;
(Proceedings of the 59th Congress of the Electrochemical Society, p. 197, April 2-4, 1992; Proceedings of the 60th Congress of the Electrochemical Society, p. 270, April 1-3, 1993) .

In addition, Ni having a large grain size has YS having a small grain size.
There is also a report of coating Z to improve the performance (Abstracts of the 59th Conference of the Electrochemical Society of Japan, p. 198,
April 2-4, 1992).

Further, a material obtained by electrochemically depositing YSZ on ruthenium metal (Abstracts of the 18th Solid Ionics Conference, pages 5-8, October 12-13, 1992),
A material in which YSZ is attached to metallic Ni by a vapor phase method (Abstracts of the 59th Annual Meeting of the Electrochemical Society of Japan, p. 199, April 2 to 4, 1992) is also being studied.

However, the various reports described above are mainly intended to improve the power generation performance, and the operation data for a long period of time has been scarce. Furthermore, the production method of chemical vapor deposition or vapor deposition of YSZ is considered to be costly (W Central Research Institute of Electric Power, W92028, March 1993).

[0011]

As described above, the above-mentioned prior art is aimed at improving the performance of the fuel electrode in particular, and the study on deterioration during long-term operation is insufficient, and the manufacturing cost is low. No consideration was given to the manufacturing process that directly affects the manufacturing cost, and the manufacturing cost was high due to the complexity of the manufacturing process.

Therefore, the present invention has developed a manufacturing method capable of mass-producing a fuel electrode material for a solid electrolyte fuel cell having an optimum microstructure at a low cost by using a simple manufacturing technique, and further, a solid electrolyte fuel cell. It is an object of the present invention to provide a fuel electrode material which, when used in the fuel electrode of (1), is capable of maintaining a performance equal to or higher than that of a conventional material stably for a long time.

[0013]

In order to achieve the above object, the present invention provides a zirconia coarse particle group having a relatively large particle size and a relatively small particle size in a nickel-zirconia solid electrolyte fuel cell fuel electrode material. It is composed of a mixture of a zirconia fine particle group having a particle size and nickel oxide or a nickel particle group, and the particle size of each particle group satisfies the relationship of zirconia coarse particles> nickel or nickel oxide particles> zirconia fine particles.

The zirconia is preferably stabilized zirconia, particularly zirconia (8YSZ) stabilized with 8 mol% of yttria.

The specific particle size of each particle is as follows.
It is desirable that the zirconia coarse particles have a particle size of 20 to 75 μm, the zirconia fine particles have a particle size of 0.1 to 1 μm, and the nickel or nickel oxide particles have a particle size of 5 to 20 μm.

In order to achieve the above-mentioned object, the present invention provides a method for producing a fuel electrode material for a solid electrolyte fuel cell, wherein zirconia coarse particles, nickel or nickel oxide particles and zirconia fine particles are used as zirconia coarse particles. >
Nickel particles or nickel oxide particles> A step of controlling the particle diameter in advance in the relationship of zirconia fine particles, and using a ball mill under dry conditions, first, a zirconia coarse particle group and a nickel oxide particle group having a relatively large particle size are mixed. Then, a step of adding a zirconia fine particle group having a relatively small particle diameter to the mixture and further mixing is performed.

[0017]

As described above, in the present invention, the particle size of each raw material used for the fuel electrode material for solid electrolyte fuel cells is changed,
The fine structure is improved.

The conventional nickel-zirconia cermet-based solid electrolyte fuel cell fuel electrode material is composed of fine NiO and 8
Although it was a mixed powder with YSZ, in the present invention, it was a mixture of a zirconia coarse particle group having a relatively large particle size, a zirconia fine particle group having a relatively small particle size, and a nickel oxide particle group. It is a thing.

It is considered that each particle constituting the fuel electrode material has a function according to the particle size as described below. (1) Coarse zirconia particles-Forms the skeleton of the fuel electrode material and eliminates the difference in thermal expansion from the electrolyte.・ Forms pores in the gaps between particles (inter-granular slits),
And maintain this. -Agglomeration of nickel particles during electrode operation is prevented, and an electron conduction path (hereinafter referred to as current path) is maintained. (2) Nickel oxide particles (nickel particles when the electrode is operating) -Coating the surface of the zirconia coarse particles and dispersing them in the gaps between the zirconia coarse particles so that nickel agglomeration can be dealt with. -Form a current path. -Increases the number of interfaces with zirconia particles and increases the electrode reaction field. (3) Fine particles of zirconia-Coarse particles of zirconia and good adhesion to zirconia electrolyte plates.・ Fixes nickel particles to prevent current path interruption.

Therefore, the fuel electrode material according to the present invention, which is a composite of these raw materials having different particle sizes, has a higher porosity under a high temperature / reducing atmosphere (an atmosphere close to the operating condition of the cell) than the conventional materials. And the contraction of the volume are extremely small, and the current path is not interrupted. As a result, even in long-term power generation, deterioration of the fuel electrode is unlikely to occur, and the performance of the fuel cell is not degraded. Further, the performance of the fuel electrode itself can be improved by the effect of increasing the electrode reaction field.

On the other hand, in the second invention as a method for producing such a fuel electrode material, dry mixing and stirring is performed by a ball mill to maintain the desired particle size of each raw material as described above, and the desired particle size as described above is maintained. Since the fuel electrode material having high performance is produced and a general and simple apparatus called a ball mill is used, it is excellent in productivity and manufacturing cost.

Hereinafter, the present invention will be described in more detail based on embodiments.

The fuel electrode material of the present invention comprises a mixture of coarse zirconia particles having a relatively large particle diameter, zirconia fine particles having a relatively small particle diameter, and nickel oxide or nickel particles. FIG. 1 is a conceptual diagram showing the fine structure of a fuel electrode formed by using the fuel electrode material according to the present invention. In the figure, reference numeral 31 is zirconia coarse particles, reference numeral 32 is nickel oxide particles, and reference numeral 33. Indicates fine zirconia particles.

As shown in FIG. 1, zirconia coarse particles 31
Form a skeleton in the fuel electrode and form pores 34 by the gaps (intergranular gaps) formed between the particles. By these, thermal compatibility with the electrolyte (stabilized zirconia) is achieved, and contraction of the fuel electrode and clogging of pores due to progress of sintering are prevented. Further, zirconia fine particles 33
For more firmly adhering the zirconia coarse particles 31 having a large particle size to each other or improving the adhesion between the electrolyte and the fuel electrode. The large and small zirconia particles 31 and 33 control the sinterability of the entire electrode to prevent nickel agglomeration and increase the electrode reaction field. Further, the nickel oxide particles 32 are dispersed around the zirconia coarse particles having a large particle size, and change into nickel when the battery operates. by this,
A current path of the fuel electrode is formed, and the zirconia particles 31,
Electrode reaction occurs at the interface between 33 and the pores.

In order to impart such functionality, in the present invention, the particle size of each particle group is set to satisfy the relationship of coarse zirconia particles> nickel or nickel oxide particles> zirconia fine particles. More specifically, for example, the zirconia coarse particles have a particle size of 20 to 75 μm, more preferably 45 to 75 μm, and the zirconia fine particles have a particle size of 0.1 to 0.1 μm.
1 μm, more preferably 0.1 to 0.5 μm, the particle size of nickel or nickel oxide particles is 5 to 20 μm, and more preferably 1/10 or less of the particle size of coarse zirconia particles.

As the zirconia, stabilized zirconia, particularly 8YSZ is preferable. The reason for this is that, as described above, if the content of nickel in the fuel electrode is large, thermal stress is generated due to the difference in the thermal expansion coefficient, which may lead to cell destruction, and it is possible to increase the nickel content too much. This is because when the amount of nickel is small, on the other hand, when the amount of nickel is small, the electrode characteristics are not so good and the sinterability is high. Therefore, the optimum nickel content can be obtained by using stabilized zirconia or 8YSZ.

The fuel electrode material of the present invention can be suitably used for producing a fuel electrode of a solid electrolyte fuel cell of various forms as exemplified in FIGS. 12 and 13 described above, and can be used for a fuel cell or a fuel electrode. The shape and the like are not limited at all, and in any case, excellent performance as described below can be exhibited.

The method for producing the fuel electrode material of the present invention includes:
Although it is not particularly limited, while maintaining a predetermined particle diameter of each particle as described above, particularly the particle diameter of the zirconia coarse particles, it is possible to stably mix, using a ball mill, dry conditions It is desirable to mix with stirring. As the ball mill, it is desirable to use a device having a relatively soft surface such as a combination of a poly soft bottle and nylon balls.

Stir mixing is performed by first mixing 8YSZ coarse particles and Ni.
For example, the O particles are mixed for about 48 to 60 hours, and then the 8YSZ fine particle group is added to this mixture, and the mixture is further mixed for about 48 hours.

[0030]

EXAMPLES The present invention will be described more specifically below based on examples.

(1) The fuel electrode material used in the experiment was a powder having a mixing ratio shown in Table 1, and each powder will be denoted by a sample number in Table 1 hereinafter. The material was manufactured based on the flow shown in FIG. That is, first, as the first step, the particle size of the powder used is adjusted. 8YSZ coarse particles are 1
It was obtained by firing at 400 ° C. for 20 hours and then classifying with a sieve. On the other hand, 8YSZ fine particles and Ni
The O particles were obtained by crushing under appropriate conditions in a wet ball mill consisting of a special nylon resin container and partially stabilized zirconia balls. Next, as a second step, the respective powders are dry-mixed by a ball mill consisting of a poly ointment bottle and nylon balls. Incidentally, 8YSZ coarse particles and NiO particles were first mixed, and then 8YSZ fine particle group was added to this mixture and further mixed. The conventional material has a particle size of several μm so that the Ni content after reduction is 40% by volume.
It was obtained by mixing NiO of m and 8YSZ.

(2) An electron microscope (EPMA) is used to examine the microstructure of the fuel electrode material thus obtained before and after power generation.
Observed by. The conventional material (FEM000) is composed of Ni and 8YSZ having a small particle size (Fig. 3).
It was observed that the FEM 461 according to the present invention has a microstructure as shown in the conceptual diagram as shown in FIG.

(3) For use in the experiment, each material powder was fired in air at 1400 ° C. for 10 hours, and the shrinkage ratio was examined. The results are shown in Table 2. From this result, it can be seen that the material according to the present invention has a smaller shrinkage than the conventional material.

(4) The sintered body of each material obtained in the above (3) was placed in an electric furnace for reduction test as shown in FIG.
Change in volumetric shrinkage after holding in hydrogen atmosphere at 00 ° C,
The change in porosity was investigated. The obtained results of changes in volume contraction are shown in FIG. 7, and the results of changes in porosity are shown in FIG.
As is clear from the results shown in FIG. 7, NiO (sample FE
The shrinkage of M010 is extremely large, and the conventional material (Sample F)
EM000) also shrinks 17% after 300 hours.
In contrast, the fuel electrode material according to the present invention has a small shrinkage.
Further, as shown in FIG. 8, the change in porosity was also small in the fuel electrode material according to the present invention. Further, in the fuel electrode material according to the present invention, 8YSZ
As the amount of 8YSZ fine particles mixed with coarse particles increases, the shrinkage when fired in air tends to increase, and the volume shrinkage and the change in porosity when held at 1000 ° C in hydrogen tend to decrease. From this, it can be seen that large and small 8YSZ controls the densification of the material. That is, the 8YSZ fine particles have the effect of strengthening the skeleton structure in the material, and when fired in air to obtain a sintered body, densification occurs and the volume of the material slightly shrinks.
However, since the skeleton of the material is formed at this point, the densification of 8YSZ does not proceed in hydrogen, so that the volume of the material hardly changes and the porosity does not change either.

(5) Of the above-mentioned materials, a solid electrolyte fuel cell was prepared using FEM461, which showed the smallest change, and a power generation test and performance evaluation of the fuel electrode were performed. For the evaluation, the current interpolation method was used by using a measuring device having a configuration as shown in FIG. Further, the evaluation unit cell was prepared by applying a slurry of the fuel electrode material to the electrolyte plate, baking it at 1400 ° C. for 10 hours, and applying a slurry of lanthanum manganite with strontium added to the air electrode. After that, it was baked at 1150 ° C. for 4 hours, and a platinum paste was baked as a reference electrode.

(6) From the results shown in FIG. 10 obtained in the power generation test for FEM461, it was possible to generate power for 3000 hours. Note that 250 in FIG.
The decrease in the cell voltage after 0 hours was due to the separation of the air electrode and the cell destruction due to the earthquake that occurred during the experiment, and the performance of the fuel electrode did not decrease. On the other hand, the life of a single cell using a conventional fuel electrode material is at most a dozen hours (see Central Research Institute of Electric Power W93019, May 1994), which shows remarkable stabilization of performance. It was

(7) The results of the performance evaluation of the fuel electrode by the current interpolation method are shown in FIG. 11 (a). The overvoltage after 500 hours is remarkably large with respect to the initial performance, but this is because an overcurrent has flowed, and no major deterioration has occurred after 500 hours. When continuous power generation was performed for 2500 hours without changing the current in order to obtain reproducibility, no large change was observed in the overvoltage (FIG. 11 (b)).

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

As described above, the fuel electrode material of the present invention hardly causes densification such as volume shrinkage and reduction of porosity even in the air and in the operation atmosphere of the cell, and
Compared with the fuel electrode manufactured using the conventional material, the fuel electrode manufactured using the material of the present invention has excellent power generation performance, and stable power generation is possible over a long period of time. Therefore, by using the fuel electrode material of the present invention, it is possible to improve the performance and extend the life of the solid electrolyte fuel cell. In addition, the production method of the present invention can produce a fuel electrode material exhibiting the above-described excellent characteristics using a conventional simple device,
It is also advantageous in terms of productivity and manufacturing cost.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a fine structure of a fuel electrode when the fuel electrode material of the present invention is used as a fuel electrode of a solid oxide fuel cell.

FIG. 2 is a diagram showing measurement results of a particle size distribution of each particle used in Examples of the present invention, (a) is 8YSZ coarse particles, (b) is NiO particles, and (c) is 8YSZ fine particles. Is.

FIG. 3 is an electron micrograph showing a fine structure of a conventional fuel electrode before and after power generation, where (a) is a secondary electron image before power generation, (b) is a Ni distribution image before power generation, and (c). ) Is a secondary electron image after power generation, and (d) is a Ni distribution image after power generation.

FIG. 4 is an electron micrograph showing a fine structure of a fuel electrode according to an embodiment of the present invention after power generation, where (a) is a secondary electron image, (b) is a Ni distribution image, and (c) is Zr. Distribution image of
(D) is a Zr distribution image (enlarged area A in (a)).

FIG. 5 is a diagram showing a manufacturing process in a manufacturing method according to the present invention.

FIG. 6 is a conceptual diagram of an apparatus used for holding in a hydrogen reducing atmosphere in an example of the present invention.

FIG. 7 is a graph showing changes over time in volumetric shrinkage in a reducing atmosphere of each material produced in the examples of the present invention.

FIG. 8 is a graph showing changes with time in porosity of each material produced in Examples of the present invention in a reducing atmosphere.

FIG. 9 is a conceptual diagram of an apparatus used for power generation / electrode evaluation in an example of the present invention, in which (a) shows a measuring apparatus configuration,
(B) shows a measurement circuit, respectively.

FIG. 10 is a graph showing a power generation state of a unit cell using the fuel electrode material according to one example of the present invention.

FIG. 11 is a graph showing changes in the performance of the fuel electrode material of one example of the present invention with time, where (a) shows a case where an overcurrent is passed and (b) shows a case where a constant current is passed.

FIG. 12 is a perspective view showing the structure of an example of a vertical stripe cylindrical solid oxide fuel cell.

FIG. 13 is an exploded perspective view of a flat plate-resistant solid electrolyte fuel cell.

[Explanation of symbols]

 1 Single Cell 11,23 Fuel Electrode 31 Coarse Zirconia Particles 32 Nickel Oxide Particles 33 Zirconia Fine Particles

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H01M 8/02 H01M 8/12 8/12 C04B 35/48 B (72) Inventor Yu Yamamoto Yu Kanagawa 2-6-1 Nagasaka, Yokosuka City Yokosuka Research Center

Claims (5)

[Claims] 1. A fuel electrode material for a nickel-zirconia solid electrolyte fuel cell, comprising zirconia coarse particles having a relatively large particle diameter, zirconia particles having a relatively small particle diameter, and nickel or nickel oxide. A fuel electrode material for a solid electrolyte fuel cell, comprising a mixture with particle groups, wherein the particle size of each particle group satisfies the relationship of zirconia coarse particles> nickel or nickel oxide particles> zirconia fine particles. 2. The fuel electrode material according to claim 1, wherein the zirconia is stabilized zirconia. 3. The fuel electrode material according to claim 1, wherein the zirconia is zirconia stabilized with 8 mol% of yttria. 4. The zirconia coarse particles have a particle size of 20 to 75 μm.
4. The fuel electrode material according to claim 1, wherein the zirconia fine particles have a particle size of 0.1 to 1 μm, and the nickel or nickel oxide particles have a particle size of 5 to 20 μm. 5. The method for producing a fuel electrode material according to claim 1, wherein each of the zirconia coarse particles and nickel or nickel oxide particles and zirconia fine particles is replaced with zirconia coarse particles> nickel particles or Nickel oxide particles> A step of controlling the particle size in advance in the relation of fine particles of zirconia, and using a ball mill, in a dry condition, first, a zirconia coarse particle group having a relatively large particle diameter and a nickel or nickel oxide particle group are mixed, Next, a step of adding a zirconia fine particle group having a relatively small particle size to the mixture and further mixing the mixture, the method for producing a fuel electrode material for a solid electrolyte fuel cell.