JPH0546666B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method of manufacturing a tape-shaped electrode for a molten carbonate fuel cell.

(Prior art) In general, the electrode reaction in fuel cells is slow, and when current is extracted at a high current density, the voltage drops. Therefore, in order to speed up the electrode reaction, for example, the surface area of the electrode is increased by making it porous, or the electrode surface is Add a catalyst. In addition, it is effective to raise the temperature, so using molten salt or solid electrolyte, it is possible to
The development of high-temperature fuel cells that can be used at 1000°C is also being studied, and in this case it is necessary to increase the creep strength of the electrodes to maintain the initial cell performance.

As an example of electrodes for these fuel cells, the electrode for a molten carbonate fuel cell according to the present invention will be explained. This electrode is a porous body made by sintering fine nickel powder, and is lined with nickel or stainless steel wire mesh,
Alternatively, a wire mesh was inserted in the center of the thickness of the tape-shaped electrode.

(Problems to be Solved by the Invention) However, those lined with wire mesh as a reinforcing material have the disadvantage that the contact between the current collector plate and the wire mesh is a point contact, which increases the resistance. It is difficult to insert the wire mesh exactly in the center, and if there is a difference in the amount of nickel powder on one side of the wire mesh and the other side, distortion may occur during sintering, or the tape may be distorted during sintering due to distortion of the wire mesh itself. The shaped electrode becomes uneven.

In order to prevent the occurrence of such unevenness, it is possible to place a holding plate on the tape-shaped electrode and sinter it, but since sintering is performed while being pressed by the holding plate, the void ratio or vacancy may increase. The pore diameter becomes smaller and the desired value cannot be obtained.

In addition, in order to increase the size of the electrode and mass-produce it, it is desirable to use a doctor blade on a moving film to form it into a tape shape using a doctor blade, as described later. It is difficult to attach it properly.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide a method for manufacturing a tape-shaped electrode with high creep strength without using a wire mesh.

(Means for Solving the Problems) The present invention is a method for manufacturing a tape-shaped electrode for a fuel cell, in which metal fibers are loosened and separated in a solvent containing a dispersant, and nickel, which is used as an electrode base material, is separated. 3~100 parts by weight of powder or nickel alloy powder with metal fibers
15 parts by weight, 5 to 20 parts by weight of metal oxide powder or alloy powder to improve creep strength, and 3 to 3 parts of binder.
5 parts by weight are mixed and kneaded to form a slurry, the solvent of the slurry is evaporated and removed to adjust the viscosity to a tape moldable level, and the tape is spread onto a moving carrier film to the required thickness to form a raw tape. The present invention relates to a method of manufacturing a tape-shaped electrode for a fuel cell. The blending ratios of materials below are expressed in parts by weight unless otherwise specified.

In the present invention, the metal fibers preferably have high corrosion resistance against carbonates; for example, nickel, nickel alloy, or stainless steel fibers are used.
The thicker the diameter, the more difficult it becomes to form the tape, and the smaller the diameter, the better to create a large number of small holes, so a diameter of 2 to 100 μm and a length of about 1 mm or less is suitable.

Using these commercially available metal fibers, the fibers are loosened in a dispersant such as a surfactant using a defibrator and separated into individual fibers.

As the base material of the electrode, nickel or nickel alloy powder with a particle size of 2 to 7 μm is used. If the diameter of the powder is too small, the pores in the product electrode will be too small and the porosity will be small, which is undesirable.If the diameter is too large, the pores will become large, which is undesirable.
It is better to set it to 7μm.

Stable at high temperatures to improve creep strength
Oxide powders such as Al ₂ O ₃ , Cr ₃ O ₃ or LiAlO ₂ or Ni-Cr alloy powders are used. The amount is 5~
If the amount is too small, no improvement in creep strength can be expected, and since 20 parts is sufficient, it is uneconomical to add more than this.

As a binder, a commonly used polymeric resin binder such as polyvinyl butyral (PVB) or polyvinyl alcohol (PVA) is used.
The slurry is partially mixed to increase the viscosity of the slurry during tape molding to make it easier to mold, and also to make it easier to remove the molded raw film from the carrier film. If this is less than 3 times, the binding is insufficient,
On the other hand, if it exceeds 5 parts, it becomes difficult to remove the binder in the sintering process after molding, so it is preferably 3 to 5 parts.

If the amount of metal fibers relative to the electrode base material is less than 3 parts, fiber reinforcement cannot be expected, and if it is more than 15 parts, the metal fibers tend to become entangled with each other in the slurry, making it difficult to disperse them uniformly, which is not preferable.

The formation of tape-like electrodes is conveniently carried out using an apparatus such as that shown in FIG. In the figure, the carrier film 2 moves between the carrier film unwinding reel 1a and the take-up reel 1b, and the slurry 4 in the slurry supply chamber 3 passes between the cutting edge of the doctor blade 5 and the carrier film 2 to a constant thickness. Then, it is carried out of the supply chamber by the carrier film 2. Next, it passes through a drying chamber 6 to become a dried raw tape, and is cut into a predetermined length by a cutter 7 at the right end.

(Test example) Dispersant (surfactant) 1 part Binder (PVB) 5 parts Solvent (methanol) 100 parts Ni powder (particle size 2 to 3 μm) A slurry mixed with 100 parts was mixed as above without using a wire mesh. This tape was heated and dried at 400 to 550℃ for 3 hours in an electric furnace in a hydrogen atmosphere, and then heated and sintered at 800℃ for 30 minutes to be used as an electrode for a molten carbonate fuel cell. And so.

When this was used in a power generation experiment (650℃, 200 hours, clamping pressure 2Kgf/cm ² ), the anode type electrode was
Creep deformation of 50% occurred, which was inappropriate. Therefore, it was determined that it was necessary to increase the creep strength.

Therefore, the dispersant, binder, and solvent are the same as above,
Add stainless steel fiber (nominal 100μmφ, 300~
500μm length) 10 parts, _Al2O3 powder ( _particle size 6~
A slurry prepared by mixing 10 parts of Ni powder (particle size: 12.5 μm) and 100 parts of Ni powder (particle size: 2 to 3 μm) was formed into a tape shape to obtain the raw tape of the present invention, which was sintered in the same manner as in the above test, and then subjected to power generation under the same conditions. When experiments were conducted, satisfactory results were obtained with creep deformation of 5%.

Figure 1 is a micrograph (100 copies) showing the metallographic structure of the cross section of an electrode manufactured using this manufacturing method.The base is a sintered body of nickel powder, and the white lumps or elongated shapes are stainless steel fibers. The porosity is approximately 60%.

The power generation experiment was as follows. Mixed salt 60% by weight containing 62 mol% lithium carbonate (LiCO ₃ ) and 38 mol% potassium carbonate (K ₂ CO ₃ ) as electrolyte plate
and lithium aluminate (LiAlO ₂ ) 40% by weight
80% hydrogen and 20% CO ₂ as fuel gas, and 70% air as oxidizing gas.
An experiment was conducted at 650°C using a mixed gas containing 30% _{CO2 and} 150mA/ ^cm2 , and 0.75V, but the contrast material electrode had large creep deformation, so the power generation performance gradually decreased. The thickness of the electrodes used was 0.8 mm for the fuel electrode (anode) and 0.8 mm for the oxidizer electrode (cathode).
It was 0.35mm.

(Effects) As explained above, the method of the present invention does not use a wire mesh, but instead uses metal fibers as an aggregate, and furthermore, oxide powder or alloy powder is mixed to increase the creep strength. In addition to eliminating the difficulty of arranging the wire mesh at the center of its thickness, there is no possibility of non-uniformity on both sides of the wire mesh or deformation due to distortion of the wire mesh itself, making it possible to easily mass-produce tape-shaped electrodes by continuous molding. .

In addition, the accuracy of the thickness of the tape-shaped electrode has been improved,
Alternatively, since the binder acts as a pore-forming agent in the electrode, porous electrodes can be easily produced;
In addition to making it easier to control the porosity and pore diameter, the method of the present invention has extremely great practical effects, such as being applicable to the molding of both anode and cathode electrodes of fuel cells.

[Brief explanation of the drawing]

Fig. 1 is a micrograph (100 copies) showing the metallographic structure of the cross section of the tape-shaped electrode of the present invention, and Fig. 2 shows a device convenient for producing the raw tape-shaped electrode. 2...Carrier film, 3...Slurry supply chamber, 4...Slurry, 5...Doctor blade,
6... Drying room, 7... Cutting machine, 8... Raw tape.

Claims (1)

[Claims] 1. In a method for manufacturing a tape-shaped electrode for a fuel cell, metal fibers are loosened and separated in a solvent containing a dispersant, and 100 weight pieces of nickel powder or nickel alloy powder are prepared as an electrode base material. 3 to 3 parts of the mixed solution with metal fibers
15 parts by weight, 5 to 20 parts by weight of metal oxide powder or alloy powder to improve creep strength, and 3 to 3 parts of binder.
5 parts by weight are mixed and kneaded to form a slurry, the solvent of the slurry is evaporated and removed to adjust the viscosity to a tape moldable level, and the tape is spread onto a moving carrier film to the required thickness to form a raw tape. A method for manufacturing tape-shaped electrodes for fuel cells.