JPS5925338B2 - Fuel cell - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of a fuel cell, and more particularly to a gaseous fuel cell using a novel lightweight diaphragm.

The function of the diaphragm in a gas fuel cell is to hold the active gas involved in the electrochemical reaction by having grooves carved on both sides, and also to sandwich the gas diffusion electrode and electrolyte to form the basic unit of the battery. Another objective is to electrically connect these single cells.

Due to these roles, the following performance is required of the diaphragm and its material.

In other words, first of all, in order to reduce power loss in electrical coupling between cells, they must have high conductivity, and the standard for this is approximately 0.5Ω in terms of resistivity per area.
C! It is desirable that it be less than n''.Secondly, it is used in places that come into contact with liquids or vapors such as phosphoric acid and concentrated aqueous alkaline solutions, and is exposed to temperatures of up to 150°C, so a high degree of corrosion resistance is required. Ru.

Third, since narrow grooves for gas vehicles are carved on both sides, it must be easy to process.

In fact, in manufacturing battery parts, the labor required to process this part is usually much greater than that of other parts. Furthermore, it facilitates the passage of a considerable amount of gas through the gas chamber,
In order to keep the energy required for gas movement as low as possible relative to the battery output, the depth of the groove must be kept above a certain value, and the gas flow path leading to the gas chamber must also be built into the separator. Therefore, it is difficult to reduce the thickness of the separator unnecessarily. From this, it can be said that the separator plate determines the volume and weight of the entire battery. Therefore, in order to reduce the weight of the entire battery, it is desirable that the material for the diaphragm has a low specific gravity. Previously, materials such as stainless steel and aluminum have been experimentally used as materials for separators, but they corrode easily and cannot withstand even relatively short-term use.

These metal materials are processed and then plated with gold.
Alternatively, there are many cases in which tantalum or niobium materials are used, but mass consumption of precious or rare metals itself is not desirable in view of the current resource situation, and it also significantly increases the cost of equipment for military ponds. Although fuel ionization has attracted attention as a clean energy conversion system,4 it has been difficult to put it into practical use for civilian use, which is said to be due to the fact that its economic prospects are still unclear. Therefore, it can be said that reducing equipment costs is an urgent need. So-called sintered graphite satisfies many of the properties required for a separating plate material, but because it is a brittle material, it is difficult to create complex tensioning, and when complex machining is required, the thickness of the separating plate must be adjusted to avoid stress concentration. must be large enough.

As a result, combined with the relatively high specific gravity, it becomes difficult to reduce the weight of the entire battery. Furthermore, since this material is generally cut and processed from a product with standard dimensions, the material yield9 is extremely poor, and although it is relatively easy to cut, the cutting edge of the hard steel tool is subject to significant wear. This includes drawbacks in terms of processing efficiency. Because of the above-mentioned drawbacks, the conventional materials are not ideal as materials for separators, and the emergence of new materials has been desired.

The purpose of the present invention is to meet the above-mentioned needs by using a new carbon-based composite material that is lightweight, low cost, has high conductivity, and has excellent workability as a diaphragm that electrically connects battery units. An object of the present invention is to provide a fuel cell system using the present invention.

Still another object is to provide a high performance, compact, lightweight, and low cost fuel cell system by combining a large number of cell units using such a diaphragm. Such an object of the present invention is to have a composite particle as a basic unit in which carbonaceous particles are attached to the surface of fine fibrillar particles made of a polyolefin polymer, and each particle is partially fused to maintain its shape. This is effectively achieved by a fuel cell in which a large number of gas passage grooves are cut on both sides of a conductive composite material and the plates are provided as bipolar separators.

That is, the present invention takes advantage of the fact that carbon fine particles are efficiently attached to the surface of polymer fifurl particles, and heats the resulting fine fifurl-like composite particles to a temperature higher than the melting point of the polymer and simultaneously applies pressure. A lightweight battery with excellent discharge characteristics that uses a conductive composite material as a battery diaphragm.
This provides an inexpensive fuel cell. The term "fifryl" here refers to a fine fibrous material with an irregular shape.It has a much larger surface area (v) per weight than ordinary fine particles, and because of its irregular shape, It has the property of easily intertwining with each other to form aggregates.

An example of manufacturing this battery partition material is as follows. When fine fifriles made of an olefin polymer are dispersed in water, carbon particles are added thereto, and the mixture is stirred and mixed, a large amount of carbon particles are uniformly attached to the surface of the polymer fifrils, forming fine fifrill-shaped composite particles, which are then submerged in water. dispersed into

The adhesion between the carbon particles and the polymer fibrils is strong and
Almost no carbon particles are observed to fall off even when left alone or when mechanical stimulation is applied. The composite particles can be separated from water using conventional separation methods such as static vacuum drying, heat drying, water filtration, and centrifugation.

In this way, the fine fibrillar composites or their weakly agglomerated cakes are separated. To heat-fuse this powder or cake, it is necessary to heat it above the melting point of the polymer and pressurize it, but in order to obtain a strong molded product suitable for battery diaphragms, it is necessary to apply strong pressure during cooling. is important.

When heating, a so-called hot press, in which heating and pressurization are performed simultaneously, may be used, or only heating may be performed. In order to manufacture a battery diaphragm using the conductive composite material obtained as described above, grooves of various shapes must be created on both sides of the plate-shaped molded material to form gas flow areas. However, this can be produced by conventional groove cutting or drilling.

However, in order to bring out the features of the present invention, it is preferable to use a mold in which a concavo-convex structure has been formed in advance to match the shape of the grooves of the partition plate in the process of heating and pressurizing the basic composite fine fibrils. In other words, according to this method, the desired grooves are formed at the same time as hot pressing, so
The machining process can be significantly shortened, and the bulkhead can be completed with just a few holes drilled. The polyolefin polymer fifuryl used in the present invention may be of any kind as long as it has heat melting properties, but particularly preferred ones include polyethylene, polypropylene, polybutene-1, poly-3-methylbutene, and polymethylbenzene. It will be done.

In addition to these homopolymer compositions, monomer components of these polymers can also be obtained by random copolymerization, block copolymerization, graft copolymerization, etc. with each other or with other types of monomer components. It is also possible to use various polymers. Furthermore, there are various methods for producing such fine fifrilled polymers.

For example, long and short fibrous materials that can be used as raw materials for fifrills by methods such as flash spinning, emulsion flash spinning, solution shearing method: split fiber method, direct fiber application method, melt spinning method, and wet spinning method, or directly Fifurils can be obtained. These fibrous materials are further stretched as necessary, cut into appropriate lengths, and then subjected to a beating machine to form fifrilled materials. Activated carbon, acetylene black, etc. can be used as the carbon particles used in the present invention, but the thickness of the battery diaphragm is approximately 5 to 15 m1z because it is necessary to form a gas flow path.
Therefore, it is desirable that the volume resistivity is 0.5Ω or less, and in this sense, it is advantageous to use acetylene black in that a low resistivity can be achieved.

In the conventional method of mixing powders, that is, mixing fine carbon particles and heat-fusible polymer powder, heating, and pressurizing, it is difficult to mix the powders uniformly, and it is difficult to obtain a strong molded product. If the proportion of polymer powder is increased, the contact between the carbon particles becomes poor and the electrical resistivity increases.On the other hand, if the proportion of carbon particles is increased in an attempt to achieve low resistivity, the cohesion between the polymer particles is broken. However, it is not possible to form a strong molded product, and therefore it is difficult to maintain mechanical strength as well as a low resistivity required for a battery diaphragm. However, since the present invention is based on a fine fifurl composite in which most of the surface of the polyolefin polymer fifril is covered with carbon fine particles, even in the process of pressurizing and heating the basic composite fifryl, the surface of the original polymer fifryl remains unchanged. Since it is covered with carbon fine particles having good conductivity, the contact between the carbonaceous fine particles is maintained even after pressurization and heating, and the conductivity is not impaired.

At the same time, since it is originally in the shape of a fibril, during the pressurization and heating process, the polymer fifrils partially fuse with adjacent fifriles, forming a uniform and fine network.P1 As a result, the shape retention is In good condition. In this way, a new material can be obtained that satisfies the requirements for shape retention, strength, and at the same time exhibits high electrical conductivity. Furthermore, even in the case of large-scale processing, since the carbon fine particles are attached to the polymer fifrils simply by stirring, uniform mixing is naturally achieved, making it easy to carry out large-scale processing without losing uniformity.

Furthermore, the grooves for gas passage necessary to function as a battery diaphragm can be easily formed by mold pressing, and the graphite block, which has been commonly used for this type of battery diaphragm, can be easily formed. How about cutting a groove? The process can be made much easier by doing so.

Examples will be described below.

EXAMPLE A polypropylene fibrous material was prepared according to the method disclosed in Japanese Patent Publication No. 47-32133.

That is, polypropylene, trichlorethylene, and water were mixed at weight ratios of 4%, 33%, and 63%, respectively, and the mixture was sealed in a steel autoclave with an inner diameter of 181LW and a depth of 1001Jm, and heated at 150°C in silicone oil.
After heating for 30 minutes, the autoclave was vented and a nozzle (diameter 2.0 m, length 201 mm valve) was opened, and the stock solution was jetted out from inside the autoclave under its own pressure to obtain a polypropylene fibrous material. Furthermore, after cutting this into an appropriate length, fine fifrills of polypropylene were obtained by subjecting it to a beating machine.Such fine fifrills are commonly called synthetic pulp. Acetylene black was added to the pulp-aqueous dispersion system so that the pulp content was 30%, and after stirring and mixing with a mixer for about 5 minutes, water was filtered off and dried at 100° C. for 1 hour in a hot air dryer.

400 m9/d of composite fine fifrills obtained in this way
Fill the mold so that it becomes 170℃, 60kg/Cf
After heating and pressurizing in L2 for 15 minutes, transfer to a cooling press and press 2.
The mixture was cooled to room temperature in 15 minutes while being pressurized to 50 kg/d. FIG. 1 is a diametrical cross-sectional view of the mold used here. 1 is an upper mold, and 2 is a lower mold, each having a diameter of 6 cm.

Each concentric convex part is 1 m in height, 111 m in width and 4 m in width, and the diameter of the largest one is 3 CT.
It is I1. FIG. 2 shows a diametrical cross-sectional view of the disc-shaped molded product produced as described above, provided with a reactive gas inlet and a reactive gas outlet. Note that another set of gas inlets and outlets that pass through the other surface of this partition plate is omitted from the drawing. 3 is a battery diaphragm, 4 is a gas passage formed by mold press, 5 is a reaction gas inlet, and 6
is the reaction gas outlet.

The volume resistivity of this battery partition plate is 0.35Ω and the specific gravity is 1.
It was 1. A stacked battery consisting of three single cells stacked together was fabricated using this diaphragm, and its discharge characteristics were investigated, as shown in Figure 3.

FIG. 4 is a side view of this stacked battery. 7 is a fuel electrode, 8 is an oxidation electrode, 9 is a matrix impregnated with electrolyte, and 10 is a battery diaphragm.

Gas piping is omitted from the diagram. Concentrated phosphoric acid was used as the electrolyte, air was sent to the fuel electrode and the hydrogen gas oxidizing electrode, and the operating temperature was 130°C. As described above, the conductive composite material produced according to the present invention has many advantages such as chemical resistance, light weight, workability, process simplification, and low resistivity, and is particularly preferable as a battery diaphragm.

[Brief explanation of drawings]

FIG. 1 is a sectional view of the mold. FIG. 2 is a cross-sectional view of the battery diaphragm. FIG. 3 shows the discharge characteristics of the stacked battery. FIG. 4 is a model diagram of a stacked battery. DESCRIPTION OF SYMBOLS 1... Upper mold, 2... Lower mold, 3... Battery partition, 4... Groove for gas passage, 5... Reactant gas inlet, 6... Reactant gas outlet , 7... Fuel electrode, 8...
- Oxidation electrode, 9... Matrix, 10... Battery partition plate.

Claims (1)

[Claims] 1 Both sides of a conductive composite material that has as its basic unit a composite particle in which carbonaceous particles are attached to the surface of fine fibrillar particles made of a polyolefin polymer, and each particle is partially fused to maintain its shape. A fuel cell characterized in that a number of grooves for gas passages are cut in the plate and the plate is provided as a bipolar separator.