JP2001093532A - Manufacturing method for electrode of fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a fuel cell electrode by which an electrode with ideal porosity and pore size is manufactured at low cost without using expensive ultrafine powder. SOLUTION: A blowing agent is added to a slurry containing Ni powder and the slurry including air bubblse is formed into a green tape. The electrode with a porosity of more than 50% and a means pore size of less than 3 μm is obtained by rolling the above green-tape and sintering it thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an electrode for a fuel cell, which produces an electrode having an ideal porosity and pore diameter at low cost without using expensive ultrafine powder.

[0002]

2. Description of the Related Art In a molten carbonate fuel cell, an electrolyte plate containing a molten carbonate is sandwiched between a cathode (oxygen electrode) and an anode (fuel electrode), and an oxidizing gas is supplied to the cathode and a fuel gas is supplied to the anode. The electric power is generated by the potential difference generated during that time. In an actual battery, a cell composed of a cathode, an electrolyte plate (called a tile), and an anode is stacked via a conductive separator plate to form a stacked battery (called a stack), and a desired high voltage is applied. I am getting it.

The operating temperature of a molten carbonate fuel cell (about 65
At 0 ° C.), molten carbonate is distributed in the cathode, tile, and anode by capillary action, and a gas-liquid interface is formed at the anode and cathode, and the following battery reaction occurs. (Anode reaction) H ₂ + CO ₃ ^2- → H ₂ O + CO ₂ +2
e ^- (cathodic _{reaction) CO 2 + 0.5O 2 + 2e} - → CO 3
^2-

In order to carry out these reactions efficiently, it is necessary to optimize the pores of the anode / cathode, in particular. Therefore, especially in the anode, it is required that the porosity is large and the average pore diameter is small. Specifically, for example, in an ideal agglomerate model, the porosity of the anode is desirably about 50% or more in order to extend the battery life by retaining a large amount of electrolyte, and the retention of the electrolyte by surface tension. In order to increase the force, the average pore diameter is desirably about 3 μm or less. In the following, the anode electrode of a molten carbonate fuel cell will be mainly described, but the present invention can be similarly applied to other electrodes.

[0005]

The anode electrode of the conventional molten carbonate fuel cell is prepared by mixing a Ni powder with an organic binder to form a slurry, forming a slurry into a tape, and heating the green tape in an electric furnace. After the binder is removed by heating, the temperature is further raised to 950 to 1100 ° C., and the metal powders are sintered to produce an anode electrode which is a porous metal body. However, the anode electrode obtained by this method is Ni
When nickel powder having an average particle size of about 2 to 4 μm is used as the powder, the porosity can be at least about 50%, but the average pore diameter can be reduced only to about 5 to 6 μm. The Melate model could not be realized.

Further, in order to reduce the average pore diameter of the anode electrode, the present inventors have proposed that the average particle diameter be about 2 to 4 μm.
By mixing about 20 to 30% of ultrafine nickel powder having an average particle diameter of 1 μm or less into a nickel powder having an average particle diameter of about 50% and an average pore diameter of about 4 μm, the anode electrode was successfully manufactured. I have. However, even with this production method, an ideal average pore diameter of about 3 μm or less cannot be achieved at all, and ultrafine nickel powder (average particle diameter of 1 μm or less) is compared with ordinary nickel powder (average particle diameter of about 2 to 4 μm). 3
Since it is more than twice as expensive, there is a problem that the manufacturing cost of the anode electrode is significantly increased.

In general, the porosity and the pore diameter can be adjusted to some extent by the firing conditions (temperature and time) of the electrode. However, if the firing temperature is increased or the firing time is lengthened, sintering proceeds and the voids increase. Both the porosity and the pore diameter become small. Conversely, if the firing temperature is lowered or the firing time is shortened, sintering does not proceed, and both the porosity and the pore diameter increase. That is, since the porosity and the pore diameter tend to contradict each other, it is not possible to manufacture an ideal electrode only by adjusting the firing conditions.

The present invention has been made to solve the above-mentioned problems. That is, the object of the present invention is:
It is an object of the present invention to provide a fuel cell electrode manufacturing method capable of manufacturing an electrode having an ideal porosity and a pore diameter at low cost without using expensive ultrafine powder.

[0009]

Means for Solving the Problems The inventors of the present invention have:
Various tests were carried out to produce an electrode having a porosity of about 50% or more and an average pore diameter of about 3 μm or less, which is ideal as an anode electrode. Successfully balanced.

That is, according to the present invention, a foaming agent is added to a slurry containing Ni powder, and the slurry is formed into a tape shape to produce a green tape containing air bubbles. A method for producing an electrode for a fuel cell, comprising firing to produce an electrode having a porosity of about 50% or more and an average pore diameter of about 3 μm or less.

According to the method of the present invention, by using the slurry to which the foaming agent is added, the green tape has a skeleton containing air bubbles and has a higher porosity than the conventional green tape. Also, by rolling this green tape having a high porosity. The number of contact points between the Ni powders in the skeleton increases, and densification proceeds. Therefore, it has been confirmed by a test that by firing this, it is possible to produce an electrode having a porosity of about 50% or more, which is about the same as the conventional one, and having an average pore diameter of about 3 μm or less, which is smaller than the conventional one. .

That is, by adding a foaming agent, a green tape having large pores (bubbles) can be manufactured. Even if the green tape is subjected to a rolling treatment and then fired, a bubble portion remains and a high void is formed. The portion other than the bubbles is sintered while maintaining the ratio, so that the average pore diameter can be reduced. Therefore, the actual pore distribution is an electrode having a mixture of small pores in the skeleton portion and large pores formed by the foaming agent, and the portion of the skeleton having a small pore size functions as a portion for retaining carbonate, so that the entire electrode has a carbonic acid. The retention of salt is improved, and the battery life is improved. Further, the cost can be reduced because a large amount of expensive ultrafine powder need not be used.
Further, the thickness distribution of the tape is also improved by the rolling treatment of the green tape.

According to a preferred embodiment of the present invention, the foaming agent is a foam stabilizer for increasing the surface tension of the slurry,
This is added and a stirring process is performed to mix bubbles in the slurry. By this method, bubbles can be formed to a desired size in the slurry, and the porosity after firing can be adjusted.

The foaming agent is an ammonium stearate-based foam stabilizer. Further, the foaming agent is added in an amount of about 3 to 7% by weight based on the slurry. As a result of the test, it was found that the ammonium stearate-based foam stabilizer was most effective. Also, about 3% by weight of the slurry
It was confirmed that an electrode having a porosity of about 50% or more and an average pore diameter of about 3 μm or less can be produced in the range of addition of about 7% by weight. If the addition amount is too small, the proportion of large pores (bubbles) becomes small, and a high porosity cannot be obtained. On the other hand, if the addition amount is too large, the ratio of the skeleton portion becomes small, and the creep strength may be reduced.

[0015] About 10% or more of the green tape, about 6%
Rolling is performed at a rolling reduction of 0% or less to adjust the average pore diameter after firing to about 3 μm or less. As a result of the test, in the green tape containing air bubbles, since the porosity is not significantly reduced by the rolling process, the green tape is rolled at a rolling reduction of about 10% or more and about 60% or less, and the average pore diameter after firing is reduced. About 3μ
m or less. When the rolling reduction is too low, the average porosity cannot be sufficiently reduced, and when the rolling reduction is too high, the deformation due to the rolling process is large and the productivity is reduced.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart showing an electrode manufacturing method of the present invention. As shown in this figure, the electrode manufacturing method of the present invention includes a slurry manufacturing step 1, a foaming agent adding step 2, a stirring treatment step 3, a tape forming step 4, a rolling step 5, and a firing step 6. Among them, the foaming agent addition step 2, the stirring treatment step 3 and the rolling step 5 are new steps particularly added in the present invention, but the application conditions are optimized in other steps.

In the slurry production step 1, an aqueous slurry containing Ni powder is produced. Ni powder has an average particle size of 2 to 4
Use μm carbonyl nickel powder. This carbonyl nickel powder includes INCO Type 255 or 2
A commercially available 87 can be used.
Further, a filamentous ultrafine powder (average particle size of 1 μm or less) commercially available as INCO Type 210 is, for example, 2 to 5%
May be added in a very small amount to promote sintering of the Ni powder during firing to improve the strength of the electrode skeleton.

Further, by mixing a small amount of Al and Cr with Ni powder, these elements are oxidized in the battery and dispersed as oxides in the skeleton, thereby improving the creep strength of the electrode. As the metal oxide to be contained, iron oxide, cobalt oxide, magnesium oxide, or alumina is added alone or in combination. By the addition of these oxides, the oxides form a solid solution on the Ni surface, and the elution of NiO can be suppressed by these oxide films.

To produce a slurry, water, a binder, a plasticizer, and a dispersant are added to the metal powder described above. Methyl cellulose or polyvinyl alcohol can be used as a binder. Further, phthalic acid is used as a plasticizer. Further, by adding an ammonium salt type dispersant, dispersion of the Ni powder can be promoted.

Furthermore, it is preferable to mix an antifoaming agent into the slurry before the stirring treatment, if necessary. By adding an antifoaming agent to the slurry before the stirring treatment, it is possible to reduce the small bubbles in the slurry that will be the skeleton portion of the fired Ni, without impairing the function of the foaming agent.

In the foaming agent addition step 2 shown in FIG. 1, a small amount of a foam stabilizer is added to increase the surface tension of the slurry. As the foaming agent, an ammonium stearate-based foam stabilizer is preferable. Also, from the examples described below, the foaming agent is preferably added in the range of about 3% by weight to 7% by weight based on the slurry.

By using a slurry to which a foaming agent is added, the green tape has a skeleton containing air bubbles and has a higher porosity than a conventional green tape. As the proportion of the foaming agent is increased, the proportion of the pores of 10 μm or more in the electrode can be increased.
It was confirmed that an electrode having a porosity of about 50% or more and an average pore diameter of about 3 μm or less can be produced in the range of addition of about 7% by weight. If the addition amount is too small, the proportion of large pores (bubbles) becomes small, and a high porosity cannot be obtained. On the other hand, if the addition amount is too large, the ratio of the skeleton portion becomes small, and the creep strength may be reduced.

Further, in the stirring step 3 in FIG. 1, bubbles are mixed into the slurry by stirring. By this step, bubbles can be formed to a desired size in the slurry, and the porosity after firing can be adjusted. The size of the bubble diameter can also be controlled by adjusting the amount of the binder.

Next, in a tape forming step 4, the slurry is formed into a tape shape to produce a green tape. After forming the green tape, the green tape may be dried in a container reduced in pressure to 500 to 600 mmHg.

Next, in the rolling step, the green tape is rolled at a rolling reduction of about 10% or more and about 60% or less. The rolling reduction is adjusted by a test so that the average pore diameter after firing becomes about 3 μm or less. By this rolling treatment, the number of contact points between the Ni powders in the skeleton increases, and densification proceeds.

Further, in the firing step 6, the above-mentioned organic binder is removed by heating in an electric furnace, and then the temperature is further raised to 950 to 1100 ° C. to sinter the metal powders to form a porous metal body. A certain anode electrode is manufactured. Firing step 6
Then, the green tape is fired at a temperature of 950 ° C. or more and 1100 ° C. or less in an atmosphere furnace of, for example, 5% H ₂ —N ₂ .

As described above, according to the method of the present invention,
A foaming agent is added to the slurry containing the Ni powder, the slurry is formed into a tape shape to produce a green tape containing air bubbles, and the green tape is subjected to a rolling treatment and then fired. As will be described later, an electrode having a porosity of about 50% or more and an average pore diameter of about 3 μm or less was able to be stably manufactured by a prototype test performed under these conditions.

[0028]

FIG. 2 is a test result showing the relationship between the average pore diameter (A) and the rolling reduction of the porosity (B) in the conventional method. That is, a case is shown in which a green tape formed by a conventional manufacturing method is rolled and fired as in the present invention.

As shown in FIG. 2A, it can be seen that the average pore diameter can be reduced by increasing the rolling reduction. Therefore, in this example, the average pore diameter can be reduced to about 3 μm or less by reducing the pressure to about 40% or more. However, on the other hand, as shown in FIG. 2B, the porosity decreases as the rolling reduction increases, and when the rolling is reduced to about 40% or more, the porosity decreases to about 45% or less. Therefore, from the results of FIG. 2, it can be seen that even if the green tape is simply rolled and then fired, it is not possible to achieve both the high porosity and the small average pore diameter, which originally tend to contradict each other.

FIG. 3 is a test result showing the relationship between the porosity and the rolling reduction in the method of the present invention, and FIG. 4 is a test result showing the relationship between the average pore diameter and the rolling reduction in the method of the present invention. is there. 3 and 4, black circles are obtained by rolling and firing the conventional green tape shown in FIG. 2, and open circles (（) and triangles (△) are obtained by rolling and firing the green tape according to the present invention. is there. The amount of the foaming agent added to each green tape is as shown in Table 1.

[0031]

[Table 1]

FIG. 3 shows that even in the case of the green tape (に よ る, Δ) according to the present invention, as in the conventional example, the average pore diameter can be reduced by increasing the rolling reduction. That is, in the case where the amount of the foaming agent added is about 3% by weight, the average pore diameter before rolling is about 5.5 μm, which is larger than the conventional one, but by reducing this by about 60% or more, the average pore diameter becomes about 3 μm.
It can be seen that the following can be achieved. Similarly, in the case where the addition amount is about 7% by weight, the average pore diameter before rolling is about 5.0 μm, which is equivalent to the conventional one, and by reducing this by about 40% or more, the average pore diameter becomes about 3 μm. It can be seen that the following can be achieved.

Further, it can be seen from FIG. 4 that, in the case of the green tape (○, Δ) according to the present invention, unlike the conventional example, the porosity does not decrease much even if the rolling reduction is increased. That is, in the example where the amount of the foaming agent added is about 3% by weight,
The porosity is maintained at about 50% even when the pressure is reduced by%.
Similarly, in the case of the addition amount of about 7% by weight, the porosity is maintained at about 50% when the pressure is reduced by about 40%.

FIG. 5 is a photomicrograph of an electrode fired after the rolling process in the prior art and the present invention. In this figure,
(A) shows a conventional green tape fired after rolling, and (B) shows a green tape according to the present invention fired after rolling. In FIG. 5A, there are almost no fine holes (black portions) between the metal particles (white portions).
The large holes are also smaller than those in FIG. On the other hand, in FIG. 5B, it can be seen that there are many fine holes between the metal particles and the large holes are relatively large.

As described above, according to the method of the present invention, by using a slurry to which a foaming agent has been added, the green tape has a skeleton containing air bubbles and has a higher porosity than a conventional green tape. Also, by rolling this green tape having a high porosity. N of skeleton
The number of contact points between i powders increases, and densification proceeds. Therefore, by firing this, it has a porosity of about 50% or more, which is about the same as the conventional one, and has an average pore diameter of about 3 μm smaller than the conventional one.
Tests confirmed that the following electrodes could be manufactured.

That is, by adding a foaming agent, a green tape having large pores (bubbles) can be produced. Even if the green tape is subjected to a rolling treatment and then fired, a bubble portion remains and high voids remain. The portion other than the bubbles is sintered while maintaining the ratio, so that the average pore diameter can be reduced. Therefore, the actual pore distribution is an electrode having a mixture of small pores in the skeleton portion and large pores formed by the foaming agent, and the portion of the skeleton having a small pore size functions as a portion for retaining carbonate, so that the entire electrode has a carbonic acid. The retention of salt is improved, and the battery life is improved. Further, the cost can be reduced because a large amount of expensive ultrafine powder need not be used.
Further, the thickness distribution of the tape is also improved by the rolling treatment of the green tape.

It should be noted that the present invention is not limited to the above-described embodiments and examples, and it is needless to say that various changes can be made without departing from the gist of the present invention. For example, in the above description, the method for producing an anode electrode of a molten carbonate fuel cell was mainly described, but the present invention can also be applied to a cathode electrode. It can also be applied to the manufacture of substrates and metal filters.

[0038]

As described above, the method for producing an electrode according to the present invention can produce an electrode having an ideal porosity and pore diameter at low cost without using expensive ultrafine powder. And so on.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an electrode manufacturing method of the present invention.

FIG. 2 is a test result showing a relationship between an average pore diameter and a reduction ratio of a porosity in a conventional method.

FIG. 3 is a test result showing the relationship between the porosity and the rolling reduction in the method of the present invention.

FIG. 4 is a test result showing the relationship between the average pore diameter and the rolling reduction in the method of the present invention.

FIG. 5 is a photomicrograph of an electrode fired after rolling in the conventional and the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slurry manufacturing process 2 Foam stabilizer addition process 3 Stirring process 4 Tape forming process 5 Rolling process 6 Baking process

[Procedure amendment]

[Submission date] June 20, 2000 (2006.2.
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

[0009]

Means for Solving the Problems The inventors of the present invention have:
Various tests were conducted to produce an electrode having a porosity of 50% or more and an average pore diameter of 3 μm or less, which is ideal as an anode electrode. Successful.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

That is, according to the present invention, a foaming agent is added to a slurry containing Ni powder, and the slurry is formed into a tape shape to produce a green tape containing air bubbles. A method for producing an electrode for a fuel cell, comprising firing to produce an electrode having a porosity of 50% or more and an average pore diameter of 3 μm or less.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

According to the method of the present invention, by using the slurry to which the foaming agent is added, the green tape has a skeleton containing air bubbles and has a higher porosity than the conventional green tape. Further, by rolling this green tape having a high porosity, the number of contact points between Ni powders in the skeleton increases, and the densification proceeds. Therefore , it was confirmed by a test that by firing this, an electrode having a porosity of about 50% or more , which is almost the same as the conventional one, and having an average pore diameter of 3 μm or less, which is smaller than the conventional one, can be produced.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

The foaming agent is an ammonium stearate-based foam stabilizer. Further, the foaming agent is added in an amount of 3 to 7% by weight based on the slurry. As a result of the test, it was found that an ammonium stearate-based foam stabilizer was most effective. In addition, 3% by weight to 7 %
It was confirmed that an electrode having a porosity of 50% or more and an average pore diameter of 3 μm or less can be manufactured within the range of the addition by weight%. If the amount is too small, large pores (bubbles)
Occupies a small proportion, and a high porosity cannot be obtained. On the other hand, if the addition amount is too large, the ratio of the skeleton portion becomes small, and the creep strength may be reduced.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

10% or more of the green tape, 60%
Rolling treatment at the following reduction ratio, the average pore diameter after firing is 3
Adjust to less than μm . The results of the test, with green tape containing bubbles, since the decrease in the void ratio due to the rolling process less green tape of 10% or more, and rolling treatment at a reduction ratio of 60% or less, the following average pore diameter 3μm after firing Can be adjusted. If the draft is too low,
If the average porosity cannot be made sufficiently small and the rolling reduction is too high, the deformation due to the rolling process is large and the productivity is reduced.

Continued on the front page (72) Inventor Shinichiro Sakai 3-1-1-15 Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries, Ltd. Tokyo Engineering Center (72) Inventor Masami Ichihara 3-1-1-15 Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries, Ltd. Tokyo Engineering Center F term (reference) 5H018 AA05 AS01 BB01 BB03 BB08 BB12 DD01 EE02 EE04 HH04 HH05 5H026 AA05 BB01 BB02 BB04 BB08 CX01 EE02 HH04 HH05

Claims (5)

[Claims] 1. A foaming agent is added to a slurry containing Ni powder, and the slurry is formed into a tape shape to produce a green tape containing air bubbles. 50% or more and average pore diameter about 3μ
A method for manufacturing an electrode for a fuel cell, comprising manufacturing an electrode having a diameter of m or less. 2. The electrode according to claim 1, wherein the foaming agent is a foam stabilizer for increasing the surface tension of the slurry, and is added and stirred to mix bubbles in the slurry. Production method. 3. The method according to claim 1, wherein the foaming agent is an ammonium stearate-based foam stabilizer. 4. The method according to claim 1, wherein the foaming agent is added in an amount of about 3% to 7% by weight based on the slurry. 5. The method according to claim 1, wherein the green tape is rolled at a rolling reduction of about 10% or more and about 60% or less to adjust the average pore diameter after firing to about 3 μm or less. The electrode manufacturing method according to the above.