JPS6137738B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing carbon bipolar plates used in alkaline aqueous electrolyte fuel cells.

In the configuration of a fuel cell consisting of a plurality of single cells, a so-called bipolar plate is used in which a gas separator plate that separates the gas chamber and electrolyte chamber of each single cell also serves as a conductive plate that connects adjacent cell electrodes. This bipolar plate has high conductivity, corrosion resistance, and sufficient mechanical strength.
It is desired that there be no gas leakage through the plates. Bipolar plates are usually made of carbon and are made by mixing graphite powder and a binder, filling a mold, and hot pressing at a temperature above the hardening or melting temperature of the binder. However, such carbon bipolar plates have only been used for acidic electrolyte fuel cells, and have not been used for alkaline aqueous electrolyte fuel cells. Alkali-resistant carbon plates include those that use furan resin or divinylbenzene resin as a binder, but these sheets can be used for alkali-resistant carbon plates that are exposed to an electrolyte of 30% KCH aqueous solution and an oxygen atmosphere at a temperature of 60°C or higher. Under the operating conditions of an aqueous electrolyte fuel cell, it did not have sufficient corrosion resistance and collapsed or cracked after about 1000 hours. In carbon bipolar plates, if the amount of binder is large, the conductive plate will be low, and if the amount of binder is small, the corrosion resistance, mechanical strength and gas leakage will be poor. Therefore, it has heretofore been impossible to obtain a carbon bipolar plate for use in alkaline aqueous electrolyte fuel cells that satisfies these characteristics.

An object of the present invention is to provide a method for manufacturing a carbon bipolar plate for an alkaline aqueous electrolyte fuel cell, which satisfies all of the above-mentioned characteristics required therefor.

This object is achieved by thermoforming a composite powder obtained by adhering graphite powder whose surface affinity with the resin has been increased by affinity treatment to the surface of an alkali-resistant resin.

Examples of alkali-resistant resins include polysulfone resin, polyphenylene oxide resin, polyallyl ether resin, polybutadiene resin, epoxy resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polytetrafluoroethylene resin,
Polytetrafluoroethylene-hexafluoropropylene resin or the like can be used. Further, as the affinity treatment, stearic acid treatment, phenol resin treatment, polyester treatment, process oil treatment, naphthenic oil treatment, fatty acid treatment, water glass treatment, etc. are applied. A composite powder of resin and graphite produced using such affinity treatment is commercially available, for example, under the trade name "Guracompo" (Nippon Graphite Industries Co., Ltd.).

The present invention will be described below with reference to test examples and figures.

Test Example 1: Graphite powder with a particle size of 180μm or less was subjected to affinity treatment, and "Guracompo" composite powder was attached to polyphenylene oxide resin with a particle size of 230 or less, filled in a mold and pressed at 330℃. A carbon plate sample was obtained. Figure 1 shows the change in characteristics when the resin content is changed using graphite powder containing approximately 60% of powder with a particle size of 60 μm or less, and the graphite curve 11 shows the specific resistance.
The amount of gas leakage is shown by line 12, and the bending strength is shown by line 13. Gas leakage amount is pressure 2
This is the amount of permeation of hydrogen of Kgf/cm ² in the thickness direction of a 5 mm thick sample. From this, it was found that a resin content of less than 10% causes gas leakage, and a resin content of 20% or more causes an increase in specific resistance, so a resin content in the range of 10 to 20% is appropriate. Figure 2 shows a resin content of 15% and a thickness of 60 μm.
Line 21 shows the change in specific resistance and line 22 shows the change in flexural modulus when the content of graphite powder with the following particle size is changed. From this, the content of graphite below 60μm is
If it is less than 30%, the bending elastic modulus increases rapidly and becomes brittle, making it unusable. If it exceeds 80%, the specific resistance increases, so it was found that 30 to 80% is appropriate.

Test Example 2: "Guracompo", in which graphite powder containing about 60% of particles with a particle size of 180 μm or less and 60 μm or less was attached to polyphenylene oxide resin and polysulfone resin, each with a particle size of 230 μm or less, at 15% by weight based on the total amount.
The powder was filled into a mold and pressed at 330°C to create a carbon plate sample. These and a carbon sample using 15% by weight of each of conventional furan resin and divinylbenzene resin as binders were immersed for a long time in a 30% KOH aqueous solution bubbled with oxygen at 80°C, and the changes in bending strength were measured. The measurement results are shown in Figure 3. In the figure, line 31 is a sample made by the method based on the present invention using polyphenylene oxide as a resin, line 32 is a sample made using a method based on the present invention using polysulfone as a resin, line 33 is a sample made using furan resin, and line 34 is a sample using divinylbenzene resin. This is a sample of a conventional alkali-resistant carbon plate. That is, conventional carbon plates are good initially, but cracks occur after 500 to 1000 hours and the bending strength becomes zero. On the other hand, the carbon plate according to the present invention does not deteriorate even after 2000 hours.

In conventional alkali-resistant carbon plates, the resin itself does not have sufficient alkali resistance under the conditions in which fuel cells are operated, and since graphite and resin are simply mixed mechanically, the mixture is uneven. It is thought that if the immersion time in the alkaline solution becomes longer, the parts with relatively less resin will swell, leading to the occurrence of cracks. On the other hand, in the carbon plate according to the present invention, the resin and graphite powder are mixed very uniformly, so there is no local unevenness in quality, and therefore the mechanical strength is improved even with a small amount of resin. It is believed that a product with satisfactory strength and no gas leakage can be obtained.

As described above, the present invention uses a composite powder with graphite powder attached to the surface of an alkali-resistant resin as a raw material, so that it has good corrosion resistance, mechanical strength, and gas leakage resistance despite having a high conductive plate. This makes it possible to manufacture a carbon bipolar plate with a high degree of stability, and it can be extremely effectively applied to bipolar plates for alkaline aqueous electrolyte fuel cells.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the relationship between the resin content in the bipolar plate material used in the method of the present invention and the characteristics of the carbon plate, and Fig. 2 is a diagram showing the relationship between the content of graphite powder with a particle size of 60 μm or less and the carbon plate. FIG. 3 is a diagram showing changes in bending strength of carbon plates according to two embodiments of the present invention and a conventional corrosion-resistant carbon plate due to immersion in a KOH aqueous solution. 31...Sample using polyphenylene oxide resin, 32...Sample using polysulfo resin.

Claims (1)

[Scope of Claims] 1. An alkaline aqueous electrolyte fuel cell characterized by thermoforming a composite powder obtained by adhering graphite powder whose surface affinity with the resin is increased by affinity treatment to the surface of an alkali-resistant resin. Method of manufacturing bipolar plates for use. 2. In the method according to claim 1, the alkali-resistant resin includes polysulfone resin, polyphenylene oxide resin, polyallyl ether resin, polybutadiene resin, epoxy resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polytetrafluoroethylene resin,
A method for producing a bipolar plate for an alkaline aqueous electrolyte fuel cell, characterized by using either polytetrafluoroethylene or hexafluoropropylene resin. 3. In the method according to claim 1 or 2, the affinity treatment includes stearic acid treatment, phenol resin treatment, polyester treatment,
A method for producing a bipolar plate for an alkaline aqueous electrolyte fuel cell, which comprises performing any one of process oil treatment, naphthenic oil treatment, fatty acid treatment, and water glass treatment. 4. In the method according to any one of claims 1 to 3, particles with a particle size of 180 μm or less
Graphite powder with a particle size of 30 to 80% below μm
Alkali-resistant resin with a diameter of 230 μm or less with a total resin content of 10
A method for producing a bipolar plate for an alkaline aqueous electrolyte fuel cell, characterized by using a composite powder attached so as to have a concentration of ~20%.