JP2004192855A - Separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell with excellent conductivity, and especially, small contact resistance with an electrode, excellent in corrosion resistance and heat resistance. <P>SOLUTION: The separator for the fuel cell is made of a mixture of a conductive carbon material and a polymer material, and is provided with a low-resistance layer at an outermost layer of at least one side of a conductive base material layer, with a sheet resistivity value of the low-resistance layer at a load of 1 MPa of 1/5 or less of that of the conductive base material layer at a load of 1 MPa. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２９】
表１に示す通り、本発明の低電気抵抗層を有した実施例１作製のセパレータは、低電気抵抗層が無い比較例１作製のセパレータに比べ、１ＭＰａ荷重時の面積抵抗値が格段に小さくなることが分かる。
【００３０】
【発明の効果】
上述したように、本発明の燃料電池用セパレータは、導電性が高く、耐熱性と耐蝕性を兼ね備えた高分子材料である。特に、電極との接触抵抗が小さく、耐蝕性に優れ、比較的低コストで生産可能なことから、長時間の運転が可能な燃料電池用としての利用性が大きい。
【図面の簡単な説明】
【図１】面積抵抗値の測定方法を示す装置の概略図。
【符号の説明】
２１：真鍮製電極
２２：カーボンペーパー
２３：セパレータ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell separator, and more particularly to a fuel cell separator excellent in moldability, strength, and corrosion resistance.
[0002]
[Prior art]
A fuel cell configured by stacking a plurality of single cells (stack), particularly a fuel cell separator used in a polymer electrolyte fuel cell, is disposed in contact with each electrode sandwiching a solid electrolyte membrane from both sides. It is required to form a supply gas passage for a fuel gas, an oxidizing gas, or the like between the electrode and the electrode, and to have an excellent current collection performance for contacting the electrode and extracting a current.
[0003]
Generally, a fuel cell separator is made of dense carbon graphite having excellent strength and conductivity as a base material, a mixture of a conductive carbon material and a corrosion-resistant resin, or a metal material such as stainless steel (SUS), titanium, and aluminum. I have.
[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 electrical conductivity is high, and the high current collection performance is maintained even after long-term use, but since the separator is a very brittle material, the separator surface is 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, in the separator made of the above metal material, the strength and ductility are superior to that of the dense carbon graphite, so that a large number of projections, grooves, and the like for forming the gas flow path are formed by press working. It is advantageous in that processing cost is low and mass production is easy.
However, in the use environment of a metal material, an oxide film due to corrosion is easily formed on the surface of the separator, and the contact resistance between the generated oxide film and the electrode increases, thereby deteriorating the current collecting performance of the separator. is there.
[0006]
In view of this, a large number of separators made by mixing a conductive carbon material such as graphite powder and a corrosion-resistant resin have been proposed (for example, Patent Documents 1 and 2). Such a mixture of a conductive carbon material and a corrosion-resistant resin is excellent in acid resistance, and by mixing a large amount of the conductive carbon material with the corrosion-resistant resin, the volume resistance of the separator itself can be reduced. Can be.
[0007]
However, since such a material contains a large amount of a conductive carbon material, there is a problem that the separator becomes brittle, cannot be reduced in thickness, and cannot be reduced in weight.
Further, as a fuel cell separator having sufficient strength and conductivity, an injection moldable separator having a larger amount of a conductive agent on the outer surface than in the separator has been proposed (Patent Document 3). ).
However, since such a separator has a small amount of the conductive agent in the core material portion of less than 10% by weight, the sheet resistance under load generated when stacking as a fuel cell is high, and sufficient conductivity as a fuel cell separator is obtained. There was a problem that can not be.
[0008]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-40517 [Patent Document 2]
JP 2000-348740 A [Patent Document 3]
JP 2000-323150 A
[Problems to be solved by the invention]
An object of the present invention is to provide a fuel cell separator having excellent conductivity, heat resistance, and corrosion resistance, and further having excellent moldability and mass productivity.
[0010]
[Means for Solving the Problems]
The present invention has found a fuel cell separator that can solve the above-mentioned problems, and the gist of the invention is to
A fuel cell separator comprising a mixture of a conductive carbon material and a polymer material, wherein a low electric resistance layer is provided on at least one outermost layer of a conductive base material layer. It is in.
[0011]
The sheet resistance of the low electric resistance layer at a load of 1 MPa is 1/5 or less of the sheet resistance of the conductive base material layer at a load of 1 MPa, and the polymer material is a thermoplastic resin. The thickness of the low electric resistance layer is preferably in the range of 5 to 100 μm, and further, as the conductive carbon material, use of a material selected from graphite powder, expanded graphite, carbon black, carbon fiber, and carbon nanofiber Is preferred.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The polymer material used for the fuel cell separator of the present invention is preferably a thermoplastic resin, and a polyolefin (PO) -based resin or elastomer such as a homopolymer or a copolymer such as ethylene, propylene or butene, or a cyclic polyolefin. Amorphous polyolefin resin (APO), polystyrene (PS), polystyrene resin such as ABS, SBS or hydrogenated styrene elastomer, polyvinyl chloride (PVC) resin, polyvinylidene chloride (PVDC) resin, polymethyl Acrylic resins such as methacrylate (PMMA) and copolymerized acrylic; polyurethane (PU) resins; epoxy resins; polyester resins such as polyethylene terephthalate (PET) and polyethylene-2,6-naphthalate (PEN);
[0013]
Polyamide (PA) resin such as nylon 6, nylon 12, copolymer nylon, polyvinyl alcohol (PVA) resin, polyvinyl alcohol resin such as ethylene-vinyl alcohol copolymer (EVOH), polyimide (PI) resin, polyether Imide (PEI) resin, polysulfone (PS) resin, polyethersulfone (PES) resin, polyamide imide (PAI) resin, polyetheretherketone (PEEK) resin, polycarbonate (PC) resin, polyvinyl butyral (PVB) resin, Polyarylate (PAR) resin, ethylene-tetrafluoroethylene copolymer (ETFE), ethylene trifluoride ethylene chloride (PCTFE), ethylene tetrafluoride-propylene hexafluoride copolymer (FEP), ethylene tetrafluoride Perfluoroalkoxy ethylene Fluorinated resins such as unified (PFA), vinylidene fluoride (PVDF), vinyl fluoride (PVF), perfluoroethylene-perfluoropropylene-perfluorovinylether terpolymer (EPE), and (meth) acrylate-based resins And the like.
[0014]
Among the above thermoplastic resins, polyolefin (PO) resins or elastomers from the viewpoint of acid resistance, styrene elastomers obtained by hydrogenating polystyrene resins such as SBS, polyimide (PI) resins, polyetherimide (PEI) resins, polysulfone At least one kind of thermoplastic resin composed of (PS) resin, polyethersulfone (PES) resin, polyamideimide (PAI) resin, polyetheretherketone (PEEK) resin, and fluorine resin is preferable.
[0015]
Examples of the conductive carbon material to be mixed with the polymer material include graphite powder such as natural graphite, pyrolytic graphite, and quiche graphite; expanded graphite obtained by immersing the above-described graphite in an acidic solution and then expanding by heating; Examples include carbon black produced by black, acetylene black, furnace method, etc., carbon fiber such as PAN type and pitch type, and carbon nanofiber produced by arc discharge method, laser vapor deposition method, vapor phase growth method and the like.
[0016]
The separator of the present invention has a low electric resistance layer on at least one outermost layer of the conductive base material layer, and makes the area resistance under a constant load in the low electric resistance layer smaller than that of the conductive base material layer. This can significantly reduce the contact resistance with the electrode material. Furthermore, since the contact resistance with the electrode material is reduced by providing the low electric resistance layer, the amount of the conductive agent in the conductive base material layer can be made relatively small, and the separator is less likely to crack.
The sheet resistance of the low electric resistance layer at a load of 1 MPa is preferably ５ or less, more preferably １ ／ or less of the sheet resistance of the conductive base material layer at a load of 1 MPa. If the area resistance of the layer at 1 MPa exceeds 1/5 of the area resistance of the conductive base material layer, the contact resistance between the separator material and the electrode material is likely to increase, and the separator strength is also reduced. There is a problem that it becomes easier.
[0017]
The volume ratio of the conductive carbon material to the polymer material in the conductive base material layer is not particularly limited, but is 80/20 to 40/60 when the conductive carbon material is graphite powder, expanded graphite, or carbon fiber. When the conductive carbon material is carbon black or carbon nanofiber, the range is preferably 40/60 to 5/95. When the volume ratio of the conductive carbon material to the polymer material is 80/20 (when the conductive carbon material is graphite powder, expanded graphite, or carbon fiber) or 40/60 (when the conductive carbon material is carbon black or carbon nanofiber) When the ratio exceeds ()), the volume ratio of the conductive carbon material becomes large, and there is a problem that the separator is easily brittle and cannot be thin. Further, the volume ratio of the conductive carbon material to the polymer material is 40/60 (when the conductive carbon material is graphite powder, expanded graphite, or carbon fiber) or 5/95 (when the conductive carbon material is carbon black or carbon nanofiber). In the case of less than (2), since the volume ratio of the conductive carbon material is small, the internal resistance of the separator becomes large, and the problem that the performance of the fuel cell deteriorates easily occurs.
[0018]
The volume ratio between the conductive carbon material and the polymer material in the low electric resistance layer may be appropriately determined so as to be 1/5 or less of the sheet resistance value of the conductive base material layer under a load of 1 MPa. When the proportion of the material is small, the problem that the conductive carbon material cannot be fixed tends to occur. Conversely, when the proportion of the polymer material is large, the contact resistance with the electrode increases, and the performance of the fuel cell deteriorates. Easy to occur.
[0019]
The thickness of the low electric resistance layer is preferably in the range of 5 to 100 μm, and more preferably 10 to 80 μm. When the thickness is less than 5 μm, a pinhole is formed in the low electric resistance layer because the thickness is small. Is likely to be formed in a region where the size becomes larger. On the other hand, if the thickness of the low electric resistance layer exceeds 100 μm, a problem that the separator is easily broken is likely to occur.
[0020]
The method for producing the fuel cell separator of the present invention is not particularly limited, but the polymer material and the conductive carbon material can be mixed and dispersed by a usual industrial mixing method such as a kneader, a mixer, or an extrusion kneader.
It is necessary to provide an oxidizing gas or fuel gas supply groove in the fuel cell separator. For example, a gas supply groove to be provided in at least one of an upper mold and a lower mold (or a male mold or a female mold) to be used is used. May be formed by using an injection molding method, a transfer molding method, a hot press molding method, or the like.
[0021]
For example, in the case of the hot press molding method, after a polymer material and a conductive agent are mixed in advance by a twin screw extruder or the like, a polymer resin sheet is formed by extrusion molding and roll molding. If it is difficult to form a low electric resistance layer, dissolve the polymer material in a solvent, mix a conductive agent to make a paint, apply it on a peelable substrate, and dry it to form a film. May be.
Next, a sheet is placed in the order of the low electric resistance layer, the conductive base material layer, and the low electric resistance layer between the male mold and the female mold of the stamping-shaped engraved press mold, and the protrusion is formed by a hot press method. What is necessary is just to form a part and a groove part.
Conditions of thermal press method may be performed at a pressure ^{2.9 × 10 6 Pa~14.7 × 10 6} Pa (30kgf / cm 2 ~150kgf / cm 2) approximately.
[0022]
Hereinafter, although an Example is described, the present invention is not limited to this.
【Example】
<Preparation of conductive base material layer>
35 volume% of polyolefin elastomer ("T310E", specific gravity 0.88, manufactured by Idemitsu Kosan Co., Ltd.) and 65 volume% of conductive carbon material ("UFG-30", specific gravity 2.2, manufactured by Showa Denko KK) are used. The mixture was mixed by a screw extruder (extruder temperature: 230 ° C.).
The prepared mixture was extruded from a die with a single screw extruder (extruder temperature: 230 ° C.) to form a conductive sheet (conductive base material layer).
The thickness of the obtained conductive sheet was 380 μm, and the sheet resistance under a load of 1 MPa was 77 mΩcm ² .
[0023]
<Preparation of low electric resistance layer>
SEBS (Asahi Kasei Corporation's “Toughtec H1041” specific gravity 0.91) and fine carbon fiber (Showa Denko Corporation's vapor-phase carbon fiber “VGCF” specific gravity 2) at a volume ratio of 60/40, Each was dispersed in THF (tetrahydrofuran) so as to have a solid concentration of 20% by weight to prepare a dispersion.
The fine carbon fibers used had a fiber diameter of 150 nm, a fiber length of 10 to 20 μm, a bulk specific gravity of 0.035 g / ml, and a true specific gravity of 2.0 g / ml.
This dispersion was applied on a base film (polyethylene terephthalate, manufactured by Mitsubishi Chemical Polyester, Ltd .: thickness 50 μm) using a bar coater (# 70 manufactured by Matsuo Sangyo), dried at 80 ° C., and dried at 80 ° C. A layer composite was obtained.
After drying, the thickness of the low electric resistance layer was 30 μm.
[0024]
Next, the two pairs of the base film and the low electric resistance layer composite are overlapped so that the low electric resistance layers face each other, and the two pairs of the base film and the low electric resistance layer composite are bonded by a hot press method. Then, both base films were peeled off to obtain a low electric resistance layer sheet.
The hot pressing was performed at a temperature of 150 ° C. and a pressure of 2.9 × 10 ⁶ Pa. Further, two low electric resistance layer sheets were produced in the same manner as described above.
The thickness of each of the obtained two sheets of the low electric resistance layer was 50 μm, and the sheet resistance under a load of 1 MPa was 1.2 mΩcm ² .
[0025]
<Preparation of fuel cell separator>
The two conductive sheets (thickness: 380 μm each) and the two low electrical resistance layer sheets (thickness: 50 μm each) obtained by the above method were converted into one low electrical resistance layer sheet / two conductive sheets / one low electrical resistance layer sheet. Was placed between a male mold and a female mold of a press mold in which the shape of the separator was engraved, and a fuel cell separator was prepared by a hot press method.
The conditions of the hot press method were a heating temperature of 180 ° C. and a pressure of 9.7 × 10 ⁶ Pa (100 kgf / cm ² ).
The maximum thickness of the obtained fuel cell separator was 850 μm, the minimum thickness was 250 μm, and the sheet resistance under a load of 1 MPa was shown in Table 1.
[0026]
The sheet resistance of the conductive sheet, the low electric resistance layer sheet, and the separator obtained by hot pressing these sheets prepared in Example 1 were as follows.
1. Measuring device Resistance meter: YMR-3 type (Yamazaki Seiki Laboratory Co., Ltd.)
Load device: YSR-8 type (manufactured by Yamazaki Seiki Laboratory Co., Ltd.)
Electrode: 2 brass flat plates (1 square inch area, mirror finish)
2. Measurement condition method: 4-terminal method Applied current: 10 mA (AC, 287 Hz)
Open terminal voltage: 20 mV peak or less Load: 1.0 MPa
Carbon paper: “TGP-H-090” manufactured by Toray Industries, Inc. (0.28 mm thick)
3. Measuring method It was measured by the measuring device shown in FIG.
[0027]
[Comparative Example 1]
30% by volume of a polyolefin elastomer ("T310E", specific gravity 0.88, manufactured by Idemitsu Kosan Co., Ltd.) and 70% by volume of conductive carbon material ("UFG-30", specific gravity 2.2, manufactured by Showa Denko KK) The mixture was mixed by a screw extruder (extruder temperature: 230 ° C.).
The prepared mixture was extruded from a die with a single screw extruder (extruder temperature: 230 ° C.) to produce a conductive resin sheet.
The thickness of the obtained conductive resin sheet was 430 μm.
Two conductive resin sheets (430 μm in thickness) were placed between a male die and a female die of a press die engraved with a separator shape, and a separator for a fuel cell was prepared by a hot press method.
The conditions of the hot press method were a heating temperature of 180 ° C. and a pressure of 9.7 × 10 ⁶ Pa (100 kgf / cm ² ).
The maximum thickness of the obtained fuel cell separator was 850 μm, the minimum thickness was 250 μm, and the sheet resistance under a load of 1 MPa was shown in Table 1.
[0028]
[Table 1]

[0029]
As shown in Table 1, the separator of Example 1 having the low electric resistance layer of the present invention has a much smaller sheet resistance under a 1 MPa load than the separator of Comparative Example 1 without the low electric resistance layer. It turns out that it becomes.
[0030]
【The invention's effect】
As described above, the fuel cell separator of the present invention is a polymer material having high conductivity and having both heat resistance and corrosion resistance. In particular, since it has low contact resistance with electrodes, has excellent corrosion resistance, and can be produced at 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 view of an apparatus showing a method of measuring a sheet resistance value.
[Explanation of symbols]
21: Brass electrode 22: Carbon paper 23: Separator

Claims (5)

A fuel cell separator comprising a mixture of a conductive carbon material and a polymer material, wherein a low electric resistance layer is provided on at least one outermost layer of a conductive base material layer. . 2. The fuel cell separator according to claim 1, wherein an area resistance value of the low electric resistance layer at a load of 1 MPa is 1/5 or less of an area resistance value of the conductive base layer under a load of 1 MPa. 3. . 3. The fuel cell separator according to claim 1, wherein the polymer material is a thermoplastic resin. 4. The fuel cell separator according to claim 1, wherein the low electric resistance layer has a thickness in a range of 5 to 100 μm. 5. The fuel cell separator according to any one of claims 1 to 4, wherein the conductive carbon material is selected from graphite powder, expanded graphite, carbon black, carbon fiber, and carbon nanofiber.

Images