JPS6324558A - Manufacture of electrode for molten carbonate type fuel cell - Google Patents

Abstract

PURPOSE:To improve the electrode property, by forming an inside porous layer of a high porosity on one side of a metal net, over which an outside porous layer of a large surface area respectively to compose a porous plate, and applying the porous plate as an electrode for a fuel cell. CONSTITUTION:A slurry loading device consists of a metal net drawing device to move a metal net 1 together with a carrier tape 2 arranged under the metal net 1 to the right direction along the upper surface of a base board 3 by a drawing motor 4, and a spreading device to spread two kinds of slurries S1 and S2 over the moving metal net 1. The said spreading device consists of hoppers 5 and 6 arranged in the metal net moving direction, and the hoppers 5 and 6 have variable walls 7 and 8 to regulate the spreading thickness. By setting the heights of the movable walls 7 and 8, the outlet slits 9 and 10 of the hoppers 5 and 6 can be controlled to set so that the width of the slit 9 determines the thickness of the inside porous layer while that of the slit 10 determines the thickness of the outside layer. The porous plate composed in such a way is used for the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the production of molten F′ using molten carbonate as an electrolyte.
A. This invention relates to an acid-acid fuel cell, and more specifically to a method for manufacturing a pair of positive and negative porous electrodes arranged on both sides of an electrolyte plate in the same cell.

Background of the Invention and Prior Art A molten carbonate fuel cell has a structure in which porous electrodes mainly made of a nickel-based alloy are arranged on both sides of an electrolyte plate. The electrolyte plate is made by adsorbing a molten mixed carbonate of lithium carbonate and potassium carbonate onto a holding material such as microstructured lithium aluminate by capillary fill phenomenon.

On the other hand, electrodes in molten carbonate fuel cells are generally made of plate-shaped porous bodies manufactured by sintering nickel-based alloy powder in order to improve gas permeability. The performance of an electrode is greatly influenced by the shape of its pores. That is, in order to promote the electrode reaction, it is necessary that the surface area of the electrode, which is the reaction site, be large. Therefore, it is desirable to use metal powder with a small particle size. However, when metal powder with a small particle size is used, the effective bridge area increases, but the carbonate held in the electrolyte holding material is absorbed into the pores of the electrode by capillary action.

The reaction in a molten carbonate fuel cell proceeds at the three-phase interface of carbonate, electrode surface, and reactant gas, so the electrode surface must be covered with carbonate, but carbonate permeates throughout the electrode. If this is done, the three-phase interface will be reduced, which will reduce the performance of the electrode.Also, if the electrode is made only of a nickel-based alloy porous material, the strength will not be sufficient. Although reinforcement is provided and the cell casing is also made of stainless steel, if more carbonate is absorbed into the electrode than necessary, it will come into contact with the stainless steel and eat it, causing the molten carbonate fuel cell to This will cause the lifespan to be significantly shortened.

On the other hand, when an electrode is made of metal powder with a large particle size, the pore size becomes large, so that the electrolyte does not penetrate into the pores more than necessary. However, in this case, since the surface area of the electrode is small, no improvement in performance as an electrode can be expected.

In this way, in the conventional porous plate with a simple structure,
It was not possible to fully demonstrate the function required as an electrode for a fuel cell. Further, nickel, which is an electrode material, is an expensive metal, and using a large amount of nickel as an electrode material increases the cost of the fuel cell.

The present invention provides a method for manufacturing a porous plate comprising a porous layer with a high porosity and a porous layer with a large surface area formed on one side of a wire mesh, and the porous plate thus obtained. By using the quality plate as an electrode for molten carbonate fuel cells, the aim is to improve the performance of the electrode and reduce the cost of the electrode.

Structure of the invention
In order to achieve the above purpose, two types of slurry are prepared: one containing metal powder, an organic pore-forming material, and an organic binder, and the other containing metal powder and a binder. The slurry is deposited in 10 layers on the top surface of a reinforcing wire mesh, and then the latter slurry is deposited in a layer on the top surface of 11 layers made of the former slurry, and the resulting two upper and lower slurry carrier layers are fired, An inner porous layer with a high porosity is formed from the lower slurry carrying layer, and an outer porous layer with a large surface area is formed from the upper slurry carrying layer.

In this invention, the organic pore-forming material is polyethylene,
Plastic powder and synthetic fiber pieces such as polystyrene and bouylon are used, or natural stone powder and natural fiber pieces such as wheat flour and wood are used.

Medillulose, polyvinyl butyrate, etc. are used as the organic binder.

Also, carrier tape is usually placed on the underside of the wire mesh. As the carrier tape, filter paper or a synthetic resin film with good liquid absorption properties is used.

Calcining is preferably carried out in a reducing atmosphere, such as in a stream of hydrogen.

In the production of electrodes according to the present invention, the slurry carrying device used directly in the slurry 4Q holding process includes a wire mesh pulling means that moves the wire mesh in a desired direction along the base, and two types of slurry on the top surface of the moving wire mesh. and a slurry coating means for applying the slurry in a layered manner. The slurry application means preferably comprises two hoppers arranged in the moving direction of the wire mesh and each having a slurry outlet slit with an adjustable width between the hopper and the upper surface of the wire mesh. Note that the slurry application means may consist of one hopper having the above structure. in this case,
First, a first slurry is charged into the same hopper for coating, and then a second slurry is charged and coating is carried out.

The significance of an electrode in which an outer porous layer with a large surface area is arranged on the surface of an inner porous layer with a high working porosity will be explained.

In the electrode manufactured by the method of this invention, the outer porous layer t in contact with the electrolyte has a small pore diameter, so it easily absorbs the molten carbonate electrolyte through capillary action, and the
The electrode reaction is facilitated by the sufficient contact of the electrode with the electrode and the large surface area of the electrode. On the other hand, the inner porous layer has two types of pores: pores the size of the organic pore-forming material and pores formed between the metal particles, and has a high porosity. , and the pore size is large, so the absorption capacity for carbonate by capillary action is small. This layer therefore prevents the electrolyte from penetrating into the electrode more than necessary.

In addition, the pores of the inner porous layer are not completely filled with the electrolyte and have a high porosity, so that gas can be supplied and discharged from the back side of the electrode, that is, from the wire mesh side, and has good diffusivity.

Generally, in the case of molten carbonate fuel cells, a nickel-based alloy is used as the material for the electrodes, but since nickel is an expensive metal, it is important to reduce the amount of nickel used. According to the method of this invention,
When producing electrodes of the same thickness, the cost of electrodes can be reduced because the use of nickel, which corresponds to the volume of the artificial flower material on the right, can be omitted.

Effects of the Invention The method of this invention combines two characteristics that could not be achieved with conventional electrodes, namely, a large electrode surface area and good gas diffusivity. An electrode that does not absorb more electrolyte than necessary can be easily obtained.Furthermore, according to the method of the present invention, it is possible to significantly reduce the amount of expensive electrode material used, and the cost of the electrode is reduced. can be significantly reduced.

EXAMPLES Next, examples of the present invention will be given to demonstrate the above effects.

In FIG. 1, the slurry carrying device is made of stainless steel (
A 50-mesh SUS316)%J wire mesh (1) is moved along the top surface of the base (3) along the top surface of the base (3) at a constant speed to the right with a traction motor (4). Two types of slurry (S-+) (S
2> in a layered manner. Filter paper is used as the rear tape (2).

The slurry application means consists of first and second hoppers (5) (6) arranged in the direction of movement of the wire mesh, and these hoppers (5) (6) each have a movable wall (7) (7) for adjusting the slurry application thickness. 8). and a movable wall (708
) The width of the slurry outlet loss slits (9) and (10) of the hopper (506) can be adjusted by setting the height of the hopper (506).
The width of the slit (9) of the first hopper (5) is equal to the thickness of the inner porous layer of the electrode green sheet 1-, and
Hopper = width of slit (10) in (6) is ff1l-4
j to the thickness of the outer porous layer of the green sheet,
Each is set.

The following operations were performed in the slurry supporting device having the above configuration. First, 8°09 of methyl cellulose was dissolved in a mixed solvent consisting of 807 g of water and 70 g of methanol, and the resulting binder solution and 200 g of nickel powder (particle size 2 to 7) were dissolved.
g and 60 g of polyethylene powder as an organic pore-forming material,
The mixture was stirred and mixed under reduced pressure for 24 hours to form a slurry, and the resulting slurry (Sl) was charged into the first hopper (5). In addition, 1.5 g of methyl cellulose was dissolved in a mixed solvent consisting of 15 g of water and 139 methanol, and the resulting binder solution and 100 g of nickel powder (particle size 2 to 7 p) were stirred and mixed under reduced pressure for 24 hours to form a slurry. (The slurry (S2) was poured into the second hopper (6).

Next, place the wire mesh (1) and carrier tape (2) on the base (3).
The slurry (
Sl) and slurry (S2) were applied thereon in a layered manner.

The wire mesh (1), that is, the green sheet carrying the layered slurry in this way is removed from the slurry carrying device, the slurry is dried, the carrier tape (2) is peeled off from the green sheet, and then the green sheet is placed in an electric furnace. After replacing the air in the furnace with hydrogen, the green sheet was held in a hydrogen stream at a temperature of 400° C. for 12 hours and at 900° C. for 1 hour, respectively, and the layered slurry was fired to obtain a porous sintered plate.

The porous plate thus obtained has a thickness of Q, 5 mm, and a porosity of 7.
8%, and as is clear from the micrograph shown in Figure 2, it was formed from a wire mesh as a reinforcing material and a slurry (S) containing an organic pore-forming material, and the organic pore-forming material was evaporated. an inner porous layer with large porosity pores left behind;
It was a porous plate consisting of an outer porous layer with a large surface area formed by densely sintering metal powder. Therefore, this two-layer porous plate had a suitable structure as an electrode for a molten carbonate fuel cell.

Also, the amount of nickel powder used to manufacture this electrode with a thickness Q of 5 mm was 9.9 mm per 100 cui of surface area of the electrode.
It was 9g. On the other hand, the amount of nickel powder used in the electrode manufactured without using the modified hole material is 18.1z
Met. Therefore, according to the method of the present invention, the amount of nickel used (m) was reduced by 45%, and it can be seen that it has a remarkable effect on reducing the cost of the electrode.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing a slurry supporting device according to the present invention, and FIG. 2 is a microscopic photograph showing the grain structure of a porous plate prepared by the present invention. (1)...wire mesh, (2)...carrier tape, (3
)... Base, (4)... Traction motor, (5)...
・First hopper, (6)...Second small hopper -1 (7) (
8)...Movable wall, (9)(10)...Slurry 1-1
(S+) (32)...Slurry. that's all

Claims (8)

[Claims] (1) Two types of slurry are prepared: one containing metal powder, an organic pore-forming material, and an organic binder, and the other containing metal powder and an organic binder, and the former slurry is first supported in a layer on the top surface of a reinforcing wire mesh. Then, the latter slurry is supported in a layered manner on the upper surface of the support layer made of the former slurry, and the obtained upper and lower slurry support layers are fired to form inner pores with high porosity from the lower slurry support layer. 1. A method for producing an electrode for a molten carbonate fuel cell, comprising forming a porous layer and forming an outer porous layer having a large surface area from an upper slurry supporting layer. (2) A lower slurry support layer is formed from a slurry containing an organic pore-forming material and is fired at a high temperature to scatter the organic pore-forming material and form an inner porous layer obtained from the lower slurry support layer. 2. A method according to claim 1, wherein the porosity is increased. (3) Production of an inner porous layer obtained from the lower slurry support layer by forming a lower slurry support layer from a slurry containing an organic pore former and firing it at a high temperature to scatter the organic pore former. reducing the amount of metal powder required for
A method according to claim 1. (4) Polyethylene, polystyrene, as an organic pore-forming material
2. The method according to claim 1, wherein a plastic powder such as nylon or a piece of synthetic fiber is used, or a powder of a natural organic material such as wheat flour or wood flour or a piece of natural fiber is used. (5) The method according to claim 1, wherein methylcellulose, polyvinyl butyrate, or the like is used as the organic binder. (6) The method according to claim 1, wherein a carrier tape is placed on the lower surface of the wire mesh. (7) The method according to claim 6, wherein filter paper or a synthetic resin film with good liquid absorption properties is used as the carrier tape. (8) Claim 1, in which the firing is performed in a reducing atmosphere.
The method described in section.