JPH0287469A - Manufacture of porous sintered material for fuel cell - Google Patents

Abstract

PURPOSE:To control two kinds of a large and small pore size distribution as required by mixing two kinds of powder which are different in particle size distribution at a specified mixing rate, temporarily sintering them at comparatively low temperatures so as to be reduced into powder while being classified, regulating temporarily sintered powder with comparatively large size, having it formed into a sheet, and thereby permanently sintering it thereafter. CONSTITUTION:Powder of a single kind, or raw powder of at least two kinds which are different in the peak of particle size distribution is knealed using binder aqeous solution, or is sufficiently mixed by a rocking mixer and the like as it has been powder. Then, the mixture is temporarily sintered at comparatively low temperatures so that primary pores are formed. Following which, they are reduced into powder by a mixer so as to be sifted while being classified so that secondary powder with a definite particle size containing the primary pores inside, is obtained. Then, binder aqeous solution is added to it so as to be mixed as uniformly as possible. In the second place, the aforesaid temporarily sintered secondary powder mixed with one kind or more than two kinds of powder in a paste condition, is formed into a sheet, and is dried while being sintered at high temperatures so that secondary pores are newly formed among secondary powder particles. By this constitution, a porous material can be formed wherein two kinds of pores; large and small ones together with small pores (primary pores) are formed in the porous material for a fuel cell.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is for producing a porous fired body for fuel cells that has two types of pore size distribution, large and small, and in which the pore size distribution is arbitrarily adjusted. Regarding the method.

(Prior art and its problems) In molten carbonate fuel cells, a porous material made by sintering fine nickel powder is used for the anode, and a porous nickel oxide material doped with lithium and oxidized is used for the cathode. A matrix layer made of lithium aluminate fine powder impregnated with a mixed molten salt of lithium carbonate and potassium carbonate having a eutectic composition is sandwiched between the two electrodes, and air, which is a fuel and an oxidizing agent, is introduced from the outer surfaces of the anode and cathode. A battery is constructed by supplying it. Molten salt is supplied to the anode and cathode from the IJx layer, an electrolyte network is formed in the electrode porous body, and the pores in the remaining porous body form a gas supply network. .

In order to improve the performance of a battery, it is important to form the maximum amount of a meniscus region, a so-called three-phase zone, in which the liquid and gas in the porous body and the solid of the electrode structure coexist. For this purpose, it is necessary to control the electrolyte absorption power (P) of the electrode porous body. There is a relationship between this P and the average pore diameter (D) of the porous body as shown in FIG. 1, and if this D can be controlled arbitrarily, the electrolyte absorption capacity can also be controlled. As a result, it becomes possible to control the three-phase band region, making it possible to improve the performance of the battery.

Incidentally, the pore diameter of the porous body is approximately determined by the average particle diameter of the raw material fine powder before sintering. For example, in porous bodies obtained by sintering commercially available single fine powders I NCO255 and I NC0123, the pore diameter peaks appear at 13 μm and 6 μm, respectively. In order to obtain a pore distribution in the intermediate region between 13 μm and 6 μm, it is necessary to prepare a fine powder having a particle size intermediate between the two lNC0 fine powders.

However, it is difficult to obtain such a raw material having a fine powder having an arbitrary particle size in a commercially available product, and it is extremely expensive, making it virtually impossible.

In addition, if a porous body having an arbitrary particle size distribution peak can be produced, and if the porous body has two types of pore size distribution, large and small, as schematically shown in FIG. The small-diameter pore portion 2a of the gas diffusion layer 2 in contact with the layer 1 exhibits a strong electrolyte absorption power and becomes an electrolyte network, while the large-diameter pore portion 2b exhibits a weak absorption power and becomes a gas supply network. The amount of electrolyte retained can be easily adjusted.

(Objective of the Invention) The present invention provides a method for manufacturing a porous body having two types of pore size distributions, large and small, and in which each pore size distribution is arbitrarily controlled, from powder, which can be done manually. With the goal.

(Means for Solving the Problems) The present invention provides one type of powder or at least two or more types of powders having different particle size distribution peaks (these are referred to as -order powders).
are mixed in a predetermined ratio, and then calcined at a relatively low temperature to form relatively small pores with an arbitrary pore size distribution (this is called a secondary pore).
A pre-calcined powder is prepared, and this is crushed and classified to produce a powder (referred to as a secondary powder) that is at least larger in particle size than the primary powder. This is then fired at a higher temperature to produce two sizes of
This is a method for manufacturing a porous fired body for fuel cells having different pore size distributions.

The present invention will be explained in detail below.

In the production method of the present invention, first, in order to prepare a powder with small diameter pores, one type of powder or a mixture of at least two types of commercially available raw material powders having different particle size distribution peaks (secondary powder) are used.
is prefired at a relatively low temperature. The particle size distribution peak is
Although it means the maximum value of the particle size distribution of the powder, it is a convenient value indicating the size of the particle size of the powder, and the size of the particle size of the powder can also be expressed by the average particle size or the like.

Although three or more kinds of the above-mentioned mixed powders used in the present invention may be used, it is most preferable to use two kinds of powders. The larger the difference between the particle size distribution peaks of these powders, the better. You can get a solid body.

As the powder, any materials used as powders in conventional fuel cells, such as metals and metal oxides, can be used. Different types of metals or metal oxides may be used as the two or more types of powder. The particle size distribution peak and average particle size of the powder are preferably in the range of 0.1 μm to 100 μm.

It is desirable that the width of the particle size distribution of the two or more types of powders is narrow, and the powders are thoroughly kneaded with an aqueous binder solution, which will be described later, or are thoroughly mixed in the powder state using a Rotsu mixer, a King mixer, or the like. This mixture is pre-sintered at a relatively low temperature to first form primary pores. This is pulverized with a mixer and then classified with a sieve to obtain a secondary powder with a constant particle size and internal holes. Add the binder aqueous solution to this and mix as uniformly as possible. It is desirable that the binder can be decomposed and removed at the firing temperature described below.

Next, a paste of the pre-sintered secondary powder of the one or more mixed powders is formed into a sheet, dried, and then fired at a high temperature to create new secondary pores between the secondary powder particles. . Thus, together with the aforementioned small pores (-secondary pores), there are two large and small pores.
It is possible to produce a porous body for fuel cells in which seed pores are formed in the porous body. In addition, there is a secondary hole! The size of fleas can be increased by using a secondary powder with a large particle size. The firing temperature is not particularly limited, and may be any temperature at which the powders are firmly bonded to each other. When a metal oxide is used as the raw material powder, and even when an elemental metal is used, the powder becomes a metal oxide by the calcination. Therefore, the metal oxide is reduced to an elemental metal using a reducing agent such as ammonia decomposition gas.

Examples of the present invention are described below, but the examples are not intended to limit the present invention.

(Example) 0.03 g of an antifoaming agent and 0.5 g of Metrose as a binder are dispersed and mixed in 50 ml of distilled water, and nickel powder, which will be described later as an electrode material, is added alone or in combination of two types and is stirred. did. The paste thus prepared was dried at room temperature and 120°C for half a day and 3 hours, respectively, and then dried for about 6 hours.
The binder was oxidatively decomposed at 00° C. to form a primary powder aggregate having pores.

The nickel raw material powder is composed of lNCO255, which has a large particle size in which the particles are connected in a chain shape, and INC255, which has a relatively small particle size in which each particle is individually separated.
OL 23 was used. As mentioned above, the particle size peaks of lNCO255 and lNC0123 are 13 μm and 6 μm, respectively, and in each experiment, the electrodes were prepared by changing the single mixing ratio of both lNC0 fine powders having different particle sizes, and The peak value of the pore size distribution was measured using a porosimeter. The results are shown in FIG.

I NCO255 whose particle size distribution peak is about 13 μm
50.5 μm, respectively, with a particle size distribution peak of about 6 μm.
By adding 75.85% and 95% by weight of lNC0123 and sintering to produce an electrode, the particle size distribution peak of the sintered body in the electrode gradually shifts to the smaller diameter side, and the peak of the particle size distribution of lNC0123 alone shifts to approximately It approached 6 μm. The effect on the particle size distribution peak was similarly investigated by changing the sintering temperature from 850°C to 750°C, 800°C, and 950°C, but the same distribution peak was observed at each temperature, and the distribution due to temperature change was Almost no effect on the peak was observed. The pore diameter of the obtained fine powder sintered body and the above lNCO255 and l
The relationship with the mixing ratio of NC0123 is shown in FIG.

Among these, both lN with a mixing ratio of 50:50
After calcining the C0 mixture at 580°C, it was pulverized and classified to prepare a relatively large secondary powder having an average particle size of about 58 μm. When this powder was main fired at 850° C., a porous body having a particle size distribution as shown in FIG. 5 was obtained. As can be seen from FIG. 5, the porous body has a diameter of about 6 μm and about 6 μm.
Size 2f with pore size distribution peak at 0μm! ! It had a similar pore size distribution.

(Effects of the Invention) The present invention mixes one type of powder or at least two types of powder with different particle size distribution peaks in a predetermined ratio, then pre-calcinates the powder at a relatively low temperature, crushes and classifies the powder, and then creates a powder with a small diameter inside. Prepare a relatively large diameter pre-fired powder (secondary powder) with primary pores,
By forming this into a sheet using a doctor blade method using a binder and then performing main firing, large-diameter pores (secondary pores) corresponding to the powder diameter can be created in the sintered part of the secondary powder. . In this way, a porous fired body having two types of pore size distribution, large and small, can be provided.

This makes it possible to control the meniscus region, the so-called tertiary body region, where liquid and gas and the solid of the electrode structure coexist within the electrode porous body, thereby making it possible to improve the performance of the battery.

Moreover, in the present invention, a porous fired body having two types of pore size distribution, large and small, is manufactured, and the small pores exhibit a strong electrolyte absorption ability, and the large pores exhibit a weak electrolyte absorption ability. The amount retained can be easily adjusted.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the electrolyte absorption capacity (P) of a porous body and the average pore diameter (D) of the porous body. FIG. 3 is a graph showing the influence on the pore size distribution peak of the porous sintered body produced when the mixing ratio of rNC0123 and rNcO255 is changed, and FIG. Graph showing the relationship between the pore diameter of the porous sintered body obtained in the example and the mixing ratio of lNCO255 and lNC0l23, No. 5
The figure is a graph showing the pore size distribution of a porous body having two types of pore size distributions, large and small, obtained in Examples.

Claims (1)

[Claims] (1) One type of powder or at least two or more types of powder with different particle size distribution peaks are mixed in a predetermined ratio, and then calcined at a relatively low temperature to produce a calcined powder having relatively large pore sizes. After preparing one type of powder or at least two or more types of powders having different particle size distribution peaks at a predetermined ratio, firing at a relatively high temperature to prepare a fired powder, and after mixing both of the fired powders, A method of producing a porous fired body for fuel cells having two types of large and small pore size distribution through main firing.