JP2002343375A - Separator for fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for fuel cell which mainly uses a metal plate with small contact resistance to an electrode, has excellent erosion resistant property, and can be manufactured at relatively low cost. SOLUTION: The separator for fuel cell is formed by burying a conductive filler into a synthetic resin layer of a metal lamination body, which is formed by coating the synthetic resin layer including electricity conducting agent at least on one surface of a metal base plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell separator, and more particularly, to a fuel cell formed by stacking a plurality of single cells, provided between adjacent single cells, and provided with a fuel gas flow path and an electrode. The present invention relates to a fuel cell separator for forming an oxidizing gas flow path and separating a fuel gas and an oxidizing gas, and more particularly to a fuel cell separator excellent in moldability, strength and corrosion resistance.

[0002]

2. Description of the Related Art A separator constituting a fuel cell, especially a polymer electrolyte fuel cell, is disposed in contact with each electrode sandwiching a solid electrolyte membrane from both sides, and a fuel gas, an oxidizing agent and the like are interposed between the electrodes. It is required to form a supply gas passage for gas or the like, and to have excellent current collection performance for contacting an electrode to derive a current.

[0003] Generally, a separator for a fuel cell is made of dense carbon graphite carbon having excellent strength and conductivity, or a metal material such as stainless steel (SUS), titanium, and aluminum.

[0004]

Usually, a large number of projections, grooves and the like for forming a gas flow path are formed on the surface of the separator facing the electrode. Therefore, in the separator composed of the dense carbon graphite, the electric conductivity is high, and the high current collecting performance is maintained even when used for a long period of time. It is not easy to perform machining such as cutting in order to form a large number of projections and grooves, which increases the processing cost and makes mass production difficult.

[0005] On the other hand, the separator made of the above-mentioned metal material has strength and strength as compared with dense carbon graphite.
Due to its excellent ductility, the formation of a large number of projections, grooves, and the like for forming the gas flow path has the advantage that the processing cost is low and the mass production is easy because press working is possible.
However, such a metal material tends to form an oxide film due to corrosion on the surface thereof in a use environment of the separator, and the contact resistance between the generated oxide film and the electrode increases, thereby lowering the current collecting performance of the separator. There is a problem.

[0006] Therefore, a material in which a surface of a metal substrate for a separator made of a metal material having excellent workability is coated with a noble metal material such as gold having excellent corrosion resistance has been studied.
However, there is a problem that such a material is extremely expensive and thus lacks versatility.

Further, a material in which at least one surface of the metal substrate is covered with a resin layer mixed with a conductive agent is being studied. However, there is a problem that the contact resistance between the resin layer and the electrode usually increases when the resin layer mixed with the conductive agent is coated.

The present invention solves the above-mentioned problems, and mainly comprises a metal substrate which has a low contact resistance with an electrode, has excellent corrosion resistance, and can be produced at a relatively low cost even when a resin layer mixed with a conductive agent is coated. A fuel cell separator is provided.

[0009]

SUMMARY OF THE INVENTION The present invention has found a fuel cell separator which can solve the above-mentioned problems, and its gist is to provide a synthetic resin in which a conductive agent is mixed on at least one surface of a metal substrate. A fuel cell separator comprising a synthetic resin layer and a conductive filler immersed under the surface of the synthetic resin layer. Including that the volume resistivity of the conductive filler is 0.5 Ωcm or less, and that the conductive filler is selected from carbon, metal carbide, metal oxide, metal nitride, metal powder and metal fiber. Contains.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
As the metal substrate used in the fuel cell separator of the present invention, a thin plate made of stainless steel, titanium, aluminum, copper, nickel, steel can be suitably used, and the thickness is 0.1.
It is preferably in the range of mm to 1.5 mm.

In the fuel cell separator of the present invention, at least one surface of the metal substrate is coated with a synthetic resin layer containing a conductive agent to form a metal laminate. As a raw material used for the synthetic resin layer, a fluororesin or a fluororubber can be suitably used from the viewpoint of chemical resistance. Specifically, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer),
FEP (tetrafluoroethylene-hexafluoropropylene copolymer), EPE (tetrafluoroethylene-
Hexafluoropropylene-perfluoroalkylvinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PCTFE (polychlorotrifluoroethylene), ECTFE (chlorotrifluoroethylene-ethylene copolymer), PVDF (polyfluoroethylene) Vinylidene fluoride), PVF (polyvinyl fluoride),
THV (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer), VDF-HFP
(Vinylidene fluoride-hexafluoropropylene copolymer), TFE-P (vinylidene fluoride-propylene copolymer),

At least one kind of fluorine resin or fluorine rubber comprising fluorine-containing silicone rubber, fluorine-containing vinyl ether rubber, fluorine-containing phosphazene rubber, or fluorine-containing thermoplastic elastomer can be used. In the resins exemplified above, PVDF, THV, VDF-HFP and TFE-
P is preferred.

It is necessary to mix a conductive agent in the synthetic resin layer made of the above fluororesin or fluororubber. As the conductive agent, carbon, metal carbide, metal oxide, metal nitride, metal powder and metal fiber are used. It can be suitably used.

Carbon is graphite, carbon black, expanded graphite, carbon fiber, and metal carbide is tungsten carbide, silicon carbide, calcium carbide, zirconium carbide, tantalum carbide, titanium carbide, niobium carbide, molybdenum carbide, vanadium carbide, chromium carbide. , Hafnium carbide, metal oxides: titanium oxide, ruthenium oxide, indium oxide, tin oxide, zinc oxide; metal nitrides: chromium nitride, aluminum nitride, molybdenum nitride, zirconium nitride, tantalum nitride, titanium nitride, gallium nitride , Niobium nitride, vanadium nitride, boron nitride, metal powders such as titanium powder, nickel powder, tin powder,
Copper powder, aluminum powder, zinc powder, silver powder tantalum powder, niobium powder,
Examples of the metal fiber include iron fiber, copper fiber, and stainless steel fiber. Among the above conductive agents, metal carbides can be suitably used because they are particularly excellent in conductivity and acid resistance.

The mixing ratio of the conductive agent in the synthetic resin may be appropriately determined so that the volume resistivity of the resin layer is 1 Ω · cm or less (according to JIS K 7194), and is usually 40% by weight to 95% by weight in the synthetic resin. % Is preferable. When the mixing ratio is less than 40% by weight, the volume resistivity exceeds 1 Ω · cm, resulting in poor conductivity. When the mixing ratio exceeds 95% by weight, molding tends to be difficult.

The thickness of the synthetic resin layer is preferably in the range of 10 to 300 μm, and if it is less than 10 μm, the effect of corrosion resistance on the metal substrate is small, and if it exceeds 300 μm, there is a problem that the separator becomes thick and the stacked fuel cell becomes large. easy.

It is necessary to further immerse a conductive filler having a volume resistance of 0.5 Ωcm or less into the synthetic resin layer of the metal laminate having at least one surface of the metal substrate covered with a synthetic resin layer by a hot press or the like. There is. The conductive filler has a volume resistance of 0.5 Ωcm or less (JIS K7
194), preferably 0.00001-0.1Ω
cm, and metal carbide can be suitably used. Examples of the metal carbide include silicon carbide, tungsten carbide, titanium carbide, and the like.

The average particle size of the conductive filler is from 0.1 to 20.
The range of μm, preferably 0.3 to 15 μm is good. If the average particle size of the conductive filler is less than 0.1 μm,
There is a problem that the particles are fine and difficult to handle, resulting in poor productivity. On the other hand, if the average particle size exceeds 20 μm, there is a problem that pinholes are generated at the time of immersion in the synthetic resin layer, and the acid resistance of the separator is poor.

The conductive filler may be used as it is, but may be used in the form of a slurry using a solvent or the like, or may be used after preparing a coating by surface treatment with a surfactant or a silane coupling agent.

The method for producing the separator of the present invention is particularly limited.
Although the film is not formed, the film having the above-mentioned composition formed in advance is formed.
Place the resin sheet on one or both sides of the metal substrate,
After laminating and unifying with the conductive method, place the conductive filler on
The conductive filler is again heated by a hot press
The method of immersion in the sheet surface is preferable from the point of productivity etc.
No. Fluororesin sheet film forming methods include ordinary extrusion molding,
It is sufficient to use the hot pressing method under ordinary press forming conditions.
Conditions, heating temperature 120 ° C to 300 ° C, pressure 2.9 × 1
0⁶Pa ~ 9.8 × 10⁶Pa (30 kgf / cm²~
100kgf / cm ²). Less than,
Examples will be described, but the present invention is not limited to these.
Not something.

[0021]

[Example] Fluororesin (manufactured by Sumitomo 3M Limited)
THV220G) 15 parts by weight and conductive filler (tungsten carbide WC2 manufactured by Allied Materials Co., Ltd.)
0) 85 parts by weight were mixed with a twin-screw extruder (extruder temperature: 250 ° C.). The above mixture is roll-formed (roll temperature 24
(0 ° C.) to prepare a conductive fluororesin sheet having a thickness of 200 μm. The volume resistivity of the obtained sheet is 0.1 Ωcm
Met. The metal substrate is an aluminum 5052 plate (0.5 m thick)
m) using a 20 μm etching layer formed by electrolytic etching, placed in the order of conductive fluororesin sheet / etched aluminum 5052 plate / conductive fluororesin sheet, and laminated by heat press did. The hot pressing conditions were as follows: temperature 200 ° C., 10 minutes, pressure 3.5 × 10 ⁶ Pa
(36 kgf / cm ² ). A conductive filler previously slurried with ethanol was applied to one surface of the obtained resin / metal laminate using a bar coater, and was formed by hot press working. In the same manner, a conductive filler slurried with ethanol was applied on the other surface with a bar coater, and was formed by hot pressing. The hot press conditions were as follows: temperature 200 ° C., 5 minutes, pressure 3.5 × 10 ⁶ Pa (36
kgf / cm ² ). Conductive fillers
Titanium carbide (average particle size 1.2 μm, volume resistance value 1 × 10 ⁻⁴ Ωcm) obtained from Allied Material was used. The total thickness of the obtained composite board was 0.86 mm.
Using the above laminate, press processing was again performed to form a gas flow path, and a fuel cell separator was obtained. Press conditions are room temperature,
One minute, pressure 1.8 × 10 ⁷ Pa (180 kgf / c
m ² ).

The resulting fuel cell separator had good adhesion between the fluororesin layer containing the conductive filler and the conductive agent and the fluororesin layer containing the conductive agent and the aluminum plate, and did not peel off.

The contact resistance was measured using the obtained separator. The evaluation of the contact resistance was performed as follows.
The measurement results are shown in FIG. One sample was shown. 1. Measuring device Resistance meter: Model YMR-3 (manufactured by Yamazaki Seiki Laboratories Co., Ltd.) Load device: Model YSR-8 (manufactured by Yamazaki Seiki Laboratories Co., Ltd.) Electrodes: Two flat plates made of brass (1 square inch area) , Mirror finish) 2. Measurement conditions Method: 4-terminal method Applied current: 10 mA (AC, 287 Hz) Open terminal voltage: 20 mV peak or less Contact load: 0.90 × 10 ⁵ Pa 1.8 × 10 ⁵ Pa 4.5 × 10 ⁵ Pa 9.0 ^{× 10 5 Pa 18 × 10 5} Pa carbon paper: manufactured by Toray Industries, Inc. TGP-H-090 (thickness 0.28 mm) 3. Measuring method It was measured by the measuring device shown in FIG.

The contact resistance value of the separator evaluated by the above method is shown in the graph of FIG. For comparison, No. A separator (No. 2) in which a channel was press-formed with one sample of a conductive fluorine sheet having the same composition / etched aluminum 5052 plate / conductive fluorine sheet was obtained. As a comparative sample, resin-impregnated graphite G347B (N
o. 3) was also evaluated.

As shown in the graph of FIG. 2, Sample No. 1 was obtained by coating a metal plate with a resin layer containing a conductive agent and further immersing a conductive filler under the surface of the resin layer. Sample No. 1 in which a resin layer containing a conductive agent was coated on a metal plate. Compared to 2,
The contact resistance value with the carbon paper used as the electrode material of the fuel cell was significantly reduced. The contact resistance value was almost the same as that of the resin-impregnated graphite of No. 3.

[0026]

As described above, the fuel cell separator of the present invention has a low contact resistance with the electrode, is excellent in corrosion resistance,
Since it can be produced at a relatively low cost, it has great utility as a fuel cell that can be operated for a long time.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of an apparatus showing a method for measuring contact resistance.

FIG. 2 is a graph showing a relationship between a contact load and a contact resistance value.

[Explanation of symbols]

 1: Brass electrode 2: Carbon paper 3: Separator

Claims (7)

[Claims] 1. A fuel cell separator comprising a metal substrate coated on at least one surface with a synthetic resin layer mixed with a conductive agent, and a conductive filler immersed below the surface of the synthetic resin layer. 2. The conductive filler according to claim 1, wherein said conductive filler has a volume resistance of 0.5.
The fuel cell separator according to claim 1, wherein the thickness is 5 Ωcm or less. 3. The fuel cell separator according to claim 1, wherein the conductive filler is selected from carbon, metal carbide, metal oxide, metal nitride, metal powder, and metal fiber. . 4. The method according to claim 1, wherein the metal substrate is made of stainless steel, titanium,
The fuel cell separator according to any one of claims 1 to 3, wherein the separator is selected from aluminum, copper, nickel, and steel. 5. The method according to claim 1, wherein the conductive agent is carbon, metal carbide,
The fuel cell separator according to any one of claims 1 to 4, wherein the separator is selected from a metal oxide, a metal nitride, a metal powder, and a metal fiber. 6. The fuel cell separator according to claim 1, wherein the synthetic resin layer is made of a fluororesin or a fluororubber. 7. A synthetic resin sheet mixed with a conductive agent is placed on at least one surface of a metal substrate, the metal substrate and the synthetic resin sheet are laminated and integrated by a hot press method, and a conductive filler is further placed thereon. Then, the conductive filler is immersed again by the hot press method.