JPS6276158A - Electrode material for fuel cell of molten carbonate type - Google Patents

Abstract

PURPOSE:To provide a fuel cell electrode material which has a greatly enhance strength and long life and does not undergo cracks or the like under the influence of heat, by making a nickel powder with short nickel fibers. CONSTITUTION:A nickel powder 1 and short nickel fibers 2 of 20-30mum in diameter and 2-20 in aspect ratio (L/D) each are mixed with each other and sintered together to constitute a fuel cell electrode material. Although the diameter of each grain of the nickel powder 1 is selected in terms of the properties (pore diameter and porosity ratio) of the electrode material, it is preferable that the diameter is 0.5-50mum. If the diameter of each of the short fibers 2 were less than 2mum, an electrolyte would not sufficiently enter into the material and the reinforcement thereof would not be enough. If the aspect ratio were less than 2, the nickel fibers 2 would become almost powdery to make it difficult to attain a porosity ratio required for the electrode material and would not perform a reinforcing function. If the aspect ratio were more than 20, it would be difficult to uniformly disperse the nickel fibers 2 and it would be likely to make the strength of the electrode material nonuniform.

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a molten carbonate fuel cell that uses molten lithium carbonate or an alkali carbonate such as potassium carbonate as an electrolyte and uses the movement of carbonate ions to carry out a cell reaction. The present invention relates to a molten carbonate fuel cell electrode material which can be used as an electrode material including an anode or a cathode of a fuel cell (hereinafter simply referred to as a fuel cell) and which can improve strength and life.

[Conventional technology]

Molten carbonate fuel cells generally have a molten electrolyte heated to about 500 to 800°C sandwiched between a pair of electrode materials, an anode and a cathode, arranged on both sides, and a fuel gas containing hydrogen is placed at the anode. Electric power is generated by supplying air and carbon dioxide to the cathode. Conventionally, such an electrode material is a sintered porous plate made by sintering a powder material made of nickel or a nickel alloy such as nickel-cobalt into a thin plate with a thickness of 0.5 mm and a thickness of about 300 to 500 mm. I've been exposed to it.

Typical powder materials include: (A) Fine, irregularly shaped powder with an average particle size of 3 μm or less and an apparent density of about 0.6 g/cc, such as INC0TYPE 255 manufactured by International Nickel Co., Ltd. .

(B) Thin metal wires, metal nets, etc. are embedded in the powder sintered material.

etc. are known.

[Problem that the invention seeks to solve]

However, in the electrode material made only of the nickel powder material in item (A) above, it is necessary to avoid oversintering in order to suppress changes in the powder shape due to sintering and increase the porosity. As a result, each powder is joined to each other at a microscopic surface close to a point contact, and the thickness is small, which has the disadvantage of inferior strength and the need for hasty handling. .

In addition, fuel cells are repeatedly heated to 500 to 800°C during power generation and cooled down when stopped. During cooling, the electrolyte solution, which was in a molten state at a high temperature, rapidly crystallizes, and as a result, the electrode material also deteriorates to an extremely high temperature. As a result of shrinkage, such conventional electrode materials may be bent, deformed, and in some cases cracks such as cracks may occur.

In addition, regarding electrode materials using reinforcing materials such as thin metal wires and meshes in item (B), the diameter of the reinforcing material is considerably larger than that of the powder, so sintering defects are likely to occur due to differences in diffusion energy.
In addition, defects such as cracks tend to appear at the boundary due to differences in rigidity, curvature diameter with respect to bending deformation, and shrinkage rate during cooling.

These defects will expand with use, and eventually molten electrolyte will flow out from the defect, making it difficult to use.

[Purpose of the invention]

The present invention was made in order to solve these problems, and in particular, by mixing nickel short fibers with nickel powder, the strength can be dramatically improved, and the strength can be improved evenly by thermal effects. The purpose of this invention is to provide fuel cell electrode materials that have a long life and are free from oxidation.

[Means to solve the problem]

The present invention is an electrode material characterized in that nickel powder 1, nickel short fibers 2 having a fiber diameter of 2 to 30 μm, and an aspect ratio (L/D) of 2 to 20 are mixed and sintered together. .

〔Example〕

The present invention will be further explained below based on Examples.

The nickel powder 1 is, for example, a fine carbonyl powder or atomized powder produced by thermal decomposition of nickel tetracarbonyl N1 (GO), and these are metals that are insoluble in the electrolyte used, such as pure nickel and nickel. Nickel alloys, in which some other elements are mixed in, and nickel plating on the surface of different powder materials are also used.

The powder diameter is selected depending on the characteristics (pore diameter, porosity) of the electrode to be used, but the range is 0.
Approximately 5 to 50 μm is preferable.

The pore diameter t) formed in powders finer than 0.5 μm
The size becomes so small that a good battery reaction does not take place, and on the contrary, the size of 50 μm
In the above case, the pores become a phase and the 7ItM' substance tends to flow out, which is not preferable.

Further, as the nickel short fiber 2, nickel powder 1 of No. 111 is used.
It is a nearly acicular short fiber with a fiber diameter of 2 to 30 μm and a length of 2 to 20 times the fiber diameter, and this relationship is generally defined as the aspect ratio (L/'D). be done.

Such short fibers can be produced, for example, by cutting a plurality of fine fiber materials at their fine grain boundaries, as disclosed in Japanese Patent Application Laid-Open No. 57-21520, or by cutting them into a predetermined length with a tool. Short fibers obtained by this method and various other methods can be used.

Other examples include a melting method in which droplets of molten material fall onto the surface of a disk that rotates at high speed and has a plurality of protrusions around it, or a method in which droplets of molten material are dropped directly onto the surface of a disk that rotates at high speed and has a plurality of protrusions formed around it, or a method in which droplets of the molten material are dropped directly onto the surface of a disk that rotates at high speed to form a desired short distance while inducing chatter vibrations in the tool. For example, cutting into fibers.

It is preferable that the short fibers 2 have no hooks at their ends because they can be easily dispersed uniformly.

The fiber diameter of the short fibers 2 is selected depending on the characteristics required for the electrode material, and when the fiber diameter is smaller than 2 μm, the pore diameter is made fine as in the case of the powder, Along with insufficient electrolyte penetration,? ili
It cannot be said that it is sufficient in terms of strength.

Moreover, if it exceeds 30 μm, the pore diameter and porosity become too large, which causes electrolyte leakage, which is not preferable.

If the aspect ratio is less than 2, the material becomes substantially powder-like, making it difficult to obtain the porosity required for fuel cell electrode materials, and failing to function as a reinforcing material.

Moreover, if it is 30 or more, it becomes difficult to uniformly disperse it, and there is a problem that it is easy to generate unevenly distributed parts.

Note that the electrode material referred to in the present invention refers to one or both of an anode and a cathode.

Nickel powder and short nickel fibers 1.2 are uniformly mixed in a desired ratio, then filled in a mold and sintered to form, for example, a plate-shaped body. The sintering conditions include, for example, a temperature of 900 to 1200°C and a pressure of 100 to 3.
000kg/cd, time of about 10 minutes to 5 hours,
It is better to avoid oversintering.

Further, the mixing ratio of the image material, the pore diameter, and the porosity are determined depending on the electrode characteristics. - For example, for an anode electrode, pore diameter is 0.5 to 10 μm, porosity is 50 to 90%
, about 0.8 nm in thickness and containing 5 to 50-t% of short fibers, and for the cathode, 30-t% of the above-mentioned short fibers were used.
~90-t% and a pore diameter of approximately 5 to 15 μm.

In the present invention, by dispersing short nickel fibers 2 having a size similar to that of the nickel powder in the nickel powder 1 at a desired ratio, the diffusion bonding between the two is strengthened, and it is also resistant to thermal effects and bending. It can be easily tracked and has flexibility. In particular, the short fiber 2 which is a reinforcing material is i
As shown in Figure i, the short fibers 2 are oriented in a three-dimensional direction inside the electrode material 4, so that the short fibers 2 further subdivide the pores P constituted by the nickel powder 1, etc., and form fine and high-porosity particles. The electrode material 4
It adapts well to deformation, etc.

In this way, the electrode material of the present invention may be made of a sintered web using metal fibers on one side, or a metal mesh. The strength can be further increased by using scales made of 'fi reinforced material.
At this time, it is also possible to have a composite structure in which both are further sintered.
Particularly in the case of a sintered web, it has excellent flexibility and can also prevent peeling at the interface. To introduce this into the device, gas is supplied to the reinforcing material side, and the powder layer side is installed adjacent to the electrolyte.

[Example-1] Nickel powder with a powder diameter of 30 μm and an apparent density of 3.6 g/cc obtained by the melt atomization method and 45 wt% of short nickel fibers with a fiber diameter of 20 μm and an average aspect ratio of 8.8 were mixed in a container. After uniformly mixing, a sintering process was performed to obtain a sintered body 4 having a thickness of 0.8 B. The sintering conditions at this time were a temperature of 1000° C. and a pressure of 100 kg/eta, and the porosity of the obtained sintered body 4 was 72%.

This sample was cut into 25mm diameter pieces and subjected to a tensile test and a repeated bending test as shown in FIG. 2 to determine the number of times it took to break. The results are shown in Table 1.

[Example-2] The same material as in Example 1 was used, and the fiber diameter was 12 μm and the thickness Q
, 5+U was uniformly filled onto a web sintered body to form a composite sintered body with a total thickness of 0.8 mm, and a tensile test piece with a width of 25 mm and a repeated bending test piece were obtained, and the test was performed. I did it.

The results are shown in Table 1.

[Comparative example]

Melted atomized powder, nickel powder with a powder diameter of 30 μm,
Thickness: 0.8 fl, porosity: 50%, sintered body, width: 25 mm
A test similar to that of the example was conducted using a sample piece of 2.0 m in diameter. Ratio 2~
At 20! Since the arranged nickel short fibers are uniformly dispersed, the short fibers are uniformly distributed in the three-dimensional direction, which greatly improves the strength of the short fibers, and also reduces the pore size. Porosity can be adjusted easily and accurately.

Moreover, the pores can be made uniform, and the strength and life can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is an enlarged perspective view showing one embodiment of the present invention, and FIG. 2 is a schematic diagram showing a method for testing electrode materials. 1- Nickel powder, 2- Nickel short fiber, 4- Electrode material.

Claims (1)

[Claims] (1) A molten carbonate fuel cell electrode characterized by being formed by integrally sintering a mixed powder of nickel powder and short nickel fibers with a fiber diameter of 2 to 30 μm and an aspect ratio (L/D) of 2 to 20. Material.