JP2002008685A - Separator for fuel battery cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for fuel battery cells having high conductivity, high durability, and excellent productivity. SOLUTION: The separators for fuel battery cells (20) which are used for collecting electricity from electrodes while contacting to a pair of the electrodes (11) sandwiching an electrolyte film (12) respectively, has a gas flow pass (21) for supplying gas in the electrode side. A material of the separator is made of a thermoplastic resin containing a low fusing-point metal, and a conductive polymer is coated at least on the above electrode side surface of the separator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell which is in contact with a pair of electrodes sandwiching an electrolyte membrane, is used for current collection from the electrodes, and has a gas supply gas passage at least on the electrode side. For separators for

[0002]

2. Description of the Related Art The above-mentioned separator for a fuel cell (hereinafter simply referred to as "separator") requires a high degree of conductivity in order to collect current from an electrode. Further, gas impermeability, corrosion resistance, mechanical strength, and the like are required.
Then, a gas flow path and a cooling groove for supplying gas to the electrode are formed in the separator.
It has been formed by cutting a conductive material such as a metal plate or a carbon plate with an end mill, a milling machine, or the like.

[0003]

It is known that a separator material is made of a metal material such as pure copper or stainless steel. However, such a metal material becomes heavy in weight and hydrogen used as a fuel gas is used. Due to prolonged contact with gas, hydrogen embrittlement occurs and material deterioration is caused, cutting and etching processing for groove formation, and precious metal plating to prevent metal corrosion and deterioration are also required. As a result, cost increases in man-hours and materials are inevitable.

Further, there is an example in which a dense carbon plate material is adopted in addition to a metal material, and a gas flow path is formed in this plate material through cutting to form a separator. This separator can solve the problem of weight reduction, but has a problem that it takes a long time to manufacture the plate itself and the productivity is poor. Further, in addition to the processing of the flow path similar to that of the metal plate, slice cutting or the like by a diamond cutter for forming a plate material is required, so that an increase in man-hours and an accompanying cost are inevitable.

An object of the present invention is to solve the problems of the conventional separator by providing a separator excellent in current collection and having high conductivity and metal corrosion resistance and excellent in productivity. And

[0006]

SUMMARY OF THE INVENTION The present invention has found a separator for a fuel cell which can solve the above-mentioned problems. The gist of the present invention is to provide a separator for a pair of electrodes 11 sandwiching an electrolyte membrane 12 therebetween. A fuel cell separator 20 having a gas flow path 21 for gas supply on the electrode side, wherein the material of the separator has a low melting point of 300 ° C. or less. A separator for a fuel cell, comprising a metal and a thermoplastic resin or a thermoplastic elastomer containing a metal powder having a melting point of 300 ° C. or more, and the surface of the separator is covered with a conductive polymer 30. .

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
FIG. 1 is a schematic sectional view showing the structure of a polymer electrolyte fuel cell. As shown in FIG. 1, the fuel cell 1
Reference numeral 0 includes an electrolyte membrane 12, a pair of electrodes 11 having a sandwich structure sandwiching the electrolyte membrane 12 from both sides, and a separator 20 contacting the electrodes while sandwiching the sandwich structure from both sides. The separator 20 has a gas passage 21 for gas supply on the electrode side, and a cooling water passage 22 on the opposite side of the electrode. The cooling water passage 22 can be provided as needed. Further, at least the electrode side surface of the separator 20 which is in contact with the electrode is coated with a conductive polymer 30 in order to prevent corrosion of the separator. The total thickness of the separator 20 is usually 1.0 mm to 3.0 mm.
The range is 0 mm.

The fuel cell separator according to the present invention comprises: (a) a thermoplastic resin or a thermoplastic elastomer and a mixture thereof; (b) a low melting point metal having a melting point of 300 ° C. or less; and (c) a metal powder. Mixture of
(Referred to as "mixed material"). By using a specific combination of a thermoplastic resin or a thermoplastic elastomer and a mixture thereof and a metal component for imparting electrical conductivity, a very high level of electrical conductivity and other properties such as mechanical strength are well-balanced. Have been found to be able to be applied.
It is desirable to contain the thermoplastic resin or the thermoplastic elastomer and a mixture thereof in the range of 20 to 80% by volume, preferably 40 to 60% by volume of the whole composition. If the content of the resin component exceeds 80% by volume, the conductivity tends to be difficult to be exhibited. If the content is less than 20% by volume, the fluidity decreases and molding becomes difficult. Further, in order to strongly develop the adhesive strength between the thermoplastic resin or the thermoplastic elastomer and the mixture thereof and the low melting point metal, the thermoplastic resin or the thermoplastic elastomer has a part of which has 3 to 1 carbon atoms.
It needs to be modified with 0 organic unsaturated carboxylic acids. As the organic unsaturated carboxylic acid, for example, acrylic acid, maleic acid, methacrylic acid, fumaric acid, itaconic acid and the like are suitable. The metal powder of (c) acts as a dispersing aid for the low-melting point metal, and the ratio of the metal powder (c) in the metal component is 10 to
It is preferably in the range of 30% by volume, preferably 15 to 25% by volume. If it is less than 10% by volume, the state of dispersion will be poor, and if it exceeds 30% by volume, the fluidity will decrease and the material will be brittle.

[0009] The thermoplastic resin or thermoplastic elastomer (a) and the mixture thereof used in the mixture may be any as long as they can withstand the environment in which the separator is used, and may have heat resistance, water resistance and chemical resistance. From the point of view of P
Polyolefin resin such as P, ABS resin, modified PPE
A resin using a resin, a PPS resin, a polyacetal resin, a liquid crystal polymer resin, or the like as a substrate is preferable.

Various kinds of low melting point metals having a melting point of 300 ° C. or less can be used. The melting point can be measured by the differential scanning calorimetry (DSC).
The measurement may be performed according to C), and there is a problem that a metal having a melting point exceeding 300 ° C. has poor moldability. Specifically, P
b / Sn, Pb / Sn / Bi, Pb / Sn / Ag, Pb
/ Ag, Sn / Ag, Sn / Bi, Sn / Cu, Sn /
A solder alloy selected from Zn-based can be suitably used.
The metal powder of the component (c) serves as a dispersing aid for the low-melting-point metal, and Cu, Ni, Al, Cr and alloy powders thereof can be suitably used, and the average particle size is 1 to 50 μm.
Are preferred. The average particle diameter is a number average particle diameter obtained by photographing a sample with a transmission electron microscope and obtaining the photograph. When the average particle size is less than 1 μm, handling during mixing is difficult, and when the average particle size exceeds 50 μm, the dispersibility tends to decrease.

[0011] The conductive polymer (e) covering the surface of the separator is coated for the purpose of preventing corrosion of low melting point metals in the mixture. Polyaniline, polypyrrole, and polythiophene are preferable in practical aspects such as processability,
Other materials may be applied. Other materials for the conductive polymer include, for example, polyacetylene, poly (1,6-heptadiyne), poly (phenylacetylene), polydiacetylene, polyparaphenylene, polynaphthalene, polyanthracene, polypyrene, polyazulene, polyfuran, polyselenophene , Polyisothianaphthene, poly (3-alkylthiophene), poly (3-thiophene-β-ethanesulfonic acid), poly (paraphenylene sulfide), poly (paraphenylene oxide), polyvirylene sulfide, polyparaphenylene vinylene , Polythiophene vinylene, polyphenylene vinylene, and at least one member selected from the group consisting of copolymers and derivatives of two or more monomer pairs contained in these polymers.

As the fuel cell separator of the present invention, a mixture obtained by kneading a mixture of the components of the above-mentioned mixture at a predetermined temperature using a kneader such as a kneader or a twin-screw extruder and then granulating the mixture is used. The method is preferred. In kneading, the temperature at which the low melting point metal is in a semi-molten state is preferable, and it is necessary to select an appropriate alloy composition of the low melting point metal according to the melting temperature of the resin serving as the matrix. In the case of tin-lead solder, dispersion can be performed under appropriate conditions without a dispersing aid, but for lead-free low melting point alloys, metal powders such as copper powder, nickel powder, etc. Addition is required.

The granulated product of the low-melting point alloy-containing resin obtained by the above method can be shaped by performing injection molding, transfer molding, press molding, etc. using a mold having a separator shape. In view of productivity, injection molding is effective. Although the obtained molded article functions as a separator as it is, it is preferable to coat a conductive polymer on the electrode side surface in consideration of durability on the electrode side. The conductive polymer can prevent electrolytic corrosion of the metal component in the separator.

As described above, the fuel cell separator of the present invention exhibits high conductivity because the resin contains a low melting point metal. In addition, since a molding method similar to that of a normal thermoplastic resin can be used, a cutting process is not required for forming a shape having a flow path. Also,
Since the surface is covered with the conductive polymer, there is no occurrence of electrolytic corrosion of the metal component. Therefore, the fuel cell separator of the present invention has high conductivity and durability required as a separator, and has high productivity.

[0015]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Example (a) An acid-modified polyolefin ("Adtex ER320P" manufactured by Nippon Polyolefin Co., Ltd.) was used as a thermoplastic resin (thermoplastic elastomer), and (b) a lead-free solder (Sn-4Cu-2Ni melting point) as a low melting point metal.
(Solidus line 225 ° C.-liquidus line 480 ° C.), and (c) copper powder having an average particle size of 10 μm was used as the metal powder. The volume ratio of each raw material powder is determined in advance by (a) :( b) :( c) = 40: 4.
After physical mixing at 5:15, a twin screw extruder (“2D2
5-S "(manufactured by Toyo Seiki Co., Ltd.), followed by pelletization to prepare solder-containing resin pellets. Extrusion conditions are as follows.

Cylinder temperature: 200 ° C. Screw rotation speed: 20 r. p. m. Thereafter, the resin pellet containing the low melting point alloy prepared by the above method was injection-molded in a molding die for injection molding in which the female mold and the male mold were opposed to each other under the following conditions.

Mold temperature: 40 ° C. Cylinder temperature: 200 ° C. Screw rotation speed: 50 r. p. m. Injection rate: 60 cm3 / sec Injection pressure: 80 MPa Back pressure: 2 MPa Holding pressure (cooling) time: 40 seconds After cooling, the mold was removed to obtain a 2 mm-thick separator-shaped molded product of interest.

The conductive polymer polyaniline is converted to N,
It was dissolved in a solvent of N-dimethylpyrrolidone, applied to the molded article obtained above, dried and heated to give a 50 μm conductive polymer coating layer on the surface. Polyaniline was polymerized as follows. Add aniline to hydrochloric acid aqueous solution,
An aqueous solution of ammonium peroxodisulfate is slowly added dropwise thereto while stirring at a temperature of ° C. A few minutes after the start of the dropwise addition, polymerization takes place to obtain polyaniline.

The characteristics of this separator were as follows. Volume resistivity: 8 × 10 ⁻⁴ Ω · cm Gas permeability: 10 ⁻⁶ cc / atm / sec or less (relative to helium gas) Weight change in sulfuric acid solution (pH 1): almost 0% (10%)
(Immerse for 00 hours)

[0020]

Comparative Example The same property evaluation as that of the above-described example was performed on a molded article having no conductive polymer applied to the surface. Volume resistivity: 3 × 10 ⁻⁴ Ω · cm Gas permeability: 10 ⁻⁶ cc / atm / sec or less (relative to helium gas) Weight change in sulfuric acid solution (pH 1): −4% (100
(0 hours immersion)

As is clear from the examples and comparative examples, it is clear that the fuel cell separator of the present invention has excellent performance in all of conductivity, gas permeability and metal corrosion resistance. is there.

[0022]

As described above, the fuel cell separator of the present invention exhibits high conductivity because the resin contains a low melting point metal. In addition, since injection molding and compression molding can be performed in the same manner as a normal thermoplastic resin, cutting processing is not required for forming a shape having a flow path. As a result, the separator has a high degree of conductivity required as a separator and has an advantage of excellent productivity, and is highly applicable to a fuel cell having a large number of stacked cells. Further, the electrode-side surface coated with a conductive polymer is also excellent in chemical resistance.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a fuel cell unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Fuel cell 11 ... Electrode 12 ... Electrolyte membrane 20 ... Separator 21 ... Gas flow path 22 ... Cooling water channel 30 ... Conductive polymer

Claims (6)

[Claims] 1. A gas flow path (2) for contacting a pair of electrodes (11) sandwiching an electrolyte membrane (12) to collect current from the electrodes and for supplying gas to the electrodes.
The fuel cell separator (20) according to 1), wherein the material of the separator is a thermoplastic resin or a thermoplastic elastomer containing a low melting point metal having a melting point of 300 ° C. or lower and a metal powder having a melting point of 300 ° C. or higher. And a separator for a fuel cell, wherein the surface of the separator is covered with a conductive polymer (30). 2. A fuel composition comprising (a) a thermoplastic resin or a thermoplastic elastomer and a mixture thereof comprising 20 to 80% by volume of a fuel cell separator, (b) a low melting point metal and (c) a metal powder. (C) in metal component
2. The fuel cell separator according to claim 1, wherein the proportion of the metal powder is in the range of 10 to 30% by volume. 3. The low melting point metal of component (b) is Pb / S
n, Pb / Sn / Bi, Pb / Sn / Ag, Pb / A
g, Sn / Ag, Sn / Bi, Sn / Cu, Sn / Zn
3. The fuel cell separator according to claim 1, comprising a low melting point alloy selected from the group consisting of: 4. The metal powder of component (d) is Cu, Ni, A
2. The powder of claim 1, wherein said powder is made of l, Cr or an alloy powder thereof, and has an average particle diameter in the range of 1 to 50 μm.
4. The fuel cell separator according to any one of claims 1 to 3. 5. The fuel cell according to claim 1, wherein (a) a part of the thermoplastic resin or the thermoplastic elastomer and a mixture thereof is acid-modified and contains a carboxyl group. For separator. 6. The fuel cell separator according to claim 1, wherein the conductive polymer (e) covering the surface of the separator is selected from polyaniline, polypyrrole, and polythiophene.