JP2000223133A - Gas channel plate-cum-separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-cost material of a gas channel plate-cum-separator for a fuel cell, made of an expanded graphite sheet and allowing enlargement of a strength. SOLUTION: This gas channel plate-cum-separator made of expanded graphite for a fuel cell having plural ribs forming a gas channel on one side or both sides has a bulk density of 1.4-1.7. The gas channel plate-cum-separator is manufactured by pulverizing an expanded graphite sheet of 0.6-1.0 bulk density, and regulating to particle size of 500 μm maximum particle diameter and 150-300 μm mean particle diameter, adding and mixing a granular resin or a liquid resin with the ground graphite sheet, then forming it by molding, vacuum hot pressing, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ribbed separator for a fuel cell, which is made of an expanded graphite composite material having a bulk density of 1.4 to 1.7 obtained by a specific process. The present invention relates to a ribbed separator for a fuel cell having excellent corrosion resistance and the like.

[0002]

2. Description of the Related Art In a fuel cell, hydrogen, methanol or the like is electrochemically reacted with air (oxygen) to directly generate electricity.

At this time, since the voltage and current that can be taken out of the unit cell (one battery) are low, several tens to several hundreds of the unit cells are stacked and connected in series or in parallel.

At this time, each unit cell is provided with conductivity,
A partition plate (hereinafter referred to as a separator) serves as a separation boundary film between fuel and air supplied to the unit cell.

[0005] For this reason, the separator is required to have electrical conductivity and impermeability to gas and liquid, and also to have corrosion resistance to fuel, air, electrolytes (phosphoric acid, sulfuric acid, etc.) and ions.

Various carbon materials and metal materials have been used as materials for such fuel cell separators, but have the following problems.

First, as a carbon material, there is a glassy carbon or a carbon material subjected to gas impermeability treatment.
All of these are expensive material costs, processing costs,
Since the processing cost is expensive, it is a great harm to the practical use of the fuel cell.

[0008] Corrosion-resistant metals such as stainless steel and titanium-based metals are used as the metal material. However, there are problems such as difficulty in ionization and processing by the electrolyte and increase in weight. Thus, attempts have been made to use expanded graphite materials as fuel cell separators.

For example, Japanese Patent Application Laid-Open No. 61-7570 discloses that a plurality of expanded graphite sheets (density: 0.3 g / cm 3, thickness: 1 mm) are laminated and pressure-formed to a thickness of 1.8 mm and a density of 1.
A 7 g / cm @ 3 partition plate for a fuel cell is described.

Japanese Unexamined Patent Publication (Kokai) No. 61-7571 discloses that a sheet having a thickness of 5 mm and a density of 1.4 g / cm 3 is obtained by stacking and forming an expanded graphite sheet obtained by pressing and forming expanded graphites having different expansion ratios. Discloses a grooved separator for a fuel cell.

Japanese Patent Application Laid-Open No. Sho 61-10872 discloses a laminate in which a 1 mm-thick expanded graphite sheet impregnated with water or an organic solvent and a 1 mm-thick expanded graphite sheet not impregnated with water or an organic solvent are combined. , After preforming,
A method for producing a grooved fuel cell partition plate having a total thickness of 5 mm, which is dried and pressure-formed, is described.

[0012] However, since these are all laminates, there is a problem that it is difficult to sufficiently increase the bulk density and the impermeability to phosphoric acid or the like becomes insufficient. Further, since the thickness is large, there are still points to be reduced in size and cost.

[0013] International Publication No. W097 / 02612
No. 1 is composed of expanded graphite powder having an average particle size of 5 μm to 12 μm, and 80% or more of all powder particles having a particle size of 0.1 μm to 20 μm, a thermoplastic resin, a thermosetting resin or a fired product thereof. Alternatively, a separator having gas supply grooves formed on both surfaces is disclosed.

However, the expanded graphite used in this method is natural graphite expanded to 80 to 300 times, and has an extremely small bulk density, and it is difficult for equipment to adjust the particle size by pulverizing the expanded graphite. . The technique of mixing with the resin is not easy, and the amount of the resin tends to increase, so that the electric conductivity is lowered.

Further, Japanese Patent Application Laid-Open No. H10-125 by the present applicant
No. 337 pre-forms expanded graphite powder into an expanded graphite sheet having a bulk density of 0.6 to 1.0, and then uses a mold or a design roll capable of obtaining a final shape to obtain a bulk density of 1.0 to 1..
No. 7 discloses a fuel cell separator press-formed into the final molded product.

JP-A-10-125337 by the present applicant
In (2), if the tightening torque during cell stacking is large due to compression deformation, the cross-sectional area of the gas flow path may decrease, and the rib width and the width around the gas inlet need to be as small as possible to make the battery body compact. However, if the strength of this part is not sufficient, gas permeation cannot be sufficiently suppressed. There has been a demand for a separator that has increased rigidity and has solved this problem.

[0017]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the conventional materials, the present invention has a sufficient bulk density, is excellent in gas-liquid impermeability, electrical conductivity and corrosion resistance, is small, and has a low production cost. A fuel cell separator is provided to contribute to the practical use of a fuel cell.

[0018]

In order to solve the above-mentioned problems, the present inventor proposes that an expanded graphite sheet having a bulk density of 0.6 to 1.0 is pulverized to a maximum particle diameter of 500 μm and an average particle diameter of 150 μm. Adjust to a particle size of ~ 300 μm, add a granular resin or liquid resin to this, mix, mold molding, vacuum hot press molding, etc. to obtain a plurality of ribs that become gas flow paths on one or both sides obtained by molding. Has a bulk density of 1.4 to
1.7 is a gas flow path plate and separator for an expanded graphite fuel cell.

Hereinafter, the present invention will be described in detail. First, an expanded graphite sheet having a bulk density of 0.6 to 1.0 is pulverized using a pulverizer such as an impact pulverizer to adjust the particle size to a maximum particle size of 500 μm and an average particle size of 150 to 300 μm. If the maximum particle diameter is larger than 500 μm, the rigidity becomes non-uniform, and the dimensional stability of the gas channel groove is insufficient.

If the average particle size is smaller than 150 μm, the amount of the resin becomes excessively large, resulting in a disadvantage that the electric conductivity is lowered.
If the average particle diameter is larger than 300 μm, the rigidity becomes insufficient.

Next, a powdery resin or a liquid resin whose viscosity has been adjusted with a solvent is added and mixed. Thermosetting resin (phenol resin, urea resin, furan resin, unsaturated polyester resin, alkyd resin, epoxy resin, silicon resin, etc.), thermoplastic resin (polypropylene resin, polyacetal resin, polycarbonate resin, saturated polystyrene resin, Polyamide resin, fluorine resin, ABS resin, etc.).

If the resin content is 2 wt% or less, which is 6 to 3 wt% added to the pulverized powder of the expanded graphite sheet, the strength and rigidity are insufficient, and if it is 7 wt% or more, the electric conductivity is deteriorated. Causes malfunction.

The addition and mixing of the resin is carried out by a usual mixer or the like. If the resin is a powder, a mixer such as a Henschel mixer or a V-type mixer is suitable. If the resin is a resin, a mixer such as a Nauta mixer is used. Use of a twice-diluted resin solution uniformly disperses and impregnates the resin, thereby improving workability.

The mixture is weighed to a predetermined weight and has a surface pressure of 100 to 500 kg / c using a mold capable of obtaining a final shape such as ribs and grooves.
It is pressed at m2. Although hot-press molding is possible, it is preferable to perform cold-forming and then heat-treat and cure from the viewpoint of efficiency.

In the heat treatment, the molded body is placed in a heating and curing oven,
For example, the temperature is raised from room temperature to 150 ° C. over about one hour, and is maintained at that temperature for 30 minutes, and then cooled to 50 ° C. or less over one hour or more.

The product of the present invention obtained as described above has a thickness of 2.3 mm and a bulk density of 1.40 to 1.70 g / c.
[m @ 2] gas permeability is 10 @ -6 (cm @ 2 / sec) or less and excellent in impermeability to gas and liquid.

The electrical resistivity is 30,000 to 10,000 μΩ-cm in the forming direction (plate thickness direction), and 1,000 to 1,100 μm in the direction perpendicular to the forming direction (plate surface direction).
Excellent electrical conductivity at Ω-cm.

In order to further reduce the gas permeability, impregnation can be carried out by reducing the pressure of the liquid resin or the powdered resin after the molding and diluting the resin with a solvent under reduced pressure and pressure. After the impregnation, the resin is cured by a heat treatment or the like.

The fuel cell separator of the present invention is excellent in gas-liquid impermeability, electric conductivity, corrosion resistance, and dimensional stability, and has low processing cost and material cost. INDUSTRIAL APPLICABILITY The present invention greatly contributes to practical use of a fuel cell and is industrially useful.

[0030]

【Example】

EXAMPLE 1 An expanded graphite sheet (bulk density: 1.0) is pulverized by a free pulverizer (Model M-5) manufactured by Nara Seisakusho to obtain a powder having a maximum particle diameter of 500 μm and an average particle diameter of 200 μm. A phenol resin was added to the powder and granules at 4 wt%, mixed and formed at a molding pressure of 150 kg / cm 2, cured by heating to 150 ° C., and had a bulk density of 1.50 and an electrical resistivity in the plate surface direction of 1,
A product having a 050 μΩ-cm and a tensile strength of 125 kg / cm 2 was obtained.

[0031]

EXAMPLE 2 Instead of the phenolic resin of Example 1, 4 wt% of a polyamide resin (nylon 6) was added and molded. Heat treatment was performed at 120 ° C. The bulk density of the obtained product is 1.49 g / cm2, and the electrical resistivity in the plate surface direction is 1,10.
A product having 0 μΩ-cm and a tensile strength of 123 kg / cm 2 was obtained.

[0032]

Example 3 Instead of the phenolic resin of Example 1, a solution obtained by dissolving and diluting 4 wt% of phenolic resin with 7 times methanol was added and mixed and molded. It was cured by heating at 150 ° C. The bulk density of the obtained product is 1.57 g / cm 2, the electrical resistivity in the plate surface direction is 970 μΩ-cm, and the tensile strength is 13
A product of 0 kg / cm2 was obtained.

[0033]

[Comparative Example 1] Using the powdery granules of the expanded graphite sheet used in Example 1, without adding a resin, a molding pressure of 150 kg /
When molded in cm 2, the bulk density was 1.51, the electrical resistivity in the plate surface direction was 1,000 μΩ-cm, and the tensile strength was 75 k.
g / cm @ 2 of product.

In each of the examples, the electrical resistivity in the plate surface direction is equal to that of the comparative example, and the tensile strength is 1.6 times or more. Therefore, the rigidity is increased, and it can withstand the tightening pressure during assembly. The deformation amount is small and contributes to the practical use of the fuel cell as a separator material.

[0035]

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Claims (1)

[Claims] An expanded graphite sheet having a bulk density of 0.6 to 1.0 is pulverized to have a maximum particle size of 500 μm and an average particle size of 150 to 3.
A plurality of ribs serving as gas flow paths on one or both sides obtained by molding to a particle size of 00 μm, adding a granular resin or a liquid resin thereto, mixing and molding by a method such as molding, vacuum hot press molding or the like. Having a bulk density of 1.4 to 1.7
Gas flow plate and separator for expanded graphite fuel cells.