JP2004014272A - Separator for fuel cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator for a fuel cell, in particular, for a solid polymer electrolyte-type fuel cell, satisfying both of power collecting performance and moldability, and strength and corrosion resistance. <P>SOLUTION: This separator for the fuel cell has a conductive layer 12 of a resin prepared by mixing a resin and a conductive filler, on at least one face of a metallic base 11, and the resin conductive layer has (a) the resin, and (b) the first conductive filler of which a content per volume is continuously changed in a state of being high at a metallic base side and low at a surface side. <P>COPYRIGHT: (C)2004,JPO

Description

３．測定方法
図６に示した測定装置により、セパレータ２３を、カーボンペーパー２２を介して両側から真鍮製電極２１で挟み、所定の荷重を加えながら、４端子法にて所定の電流印加時の電圧を測定して接触抵抗を求めた。
【００８９】
測定結果を図７のグラフ中の複合板１〜４で示した。比較のために東海カーボン社製樹脂含浸黒鉛Ｇ３４７Ｂも評価した。
【００９０】
図７のグラフに示す通り、特に複合板２、４は、接触抵抗値が格段に小さく、樹脂含浸黒鉛とほぼ同等の接触抵抗値であった。
【００９１】
【発明の効果】
本発明によれば、集電性能と成形性、強度および耐食性の両方を満足する燃料電池、特に固体高分子電解質型燃料電池用のセパレータを提供することができる。従って、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】燃料電池のセパレータ付近を模式的に示す図である。
【図２】第１の形態のセパレータの層構造の１例を示す図である。
【図３】第２の形態のセパレータの層構造の１例を示す図である。
【図４】第３の形態のセパレータの層構造の１例を示す図である。
【図５】第４の形態のセパレータの層構造の１例を示す図である。
【図６】接触抵抗の測定方法を示す図である。
【図７】接触荷重と接触抵抗値の関係を示すグラフである。
【符号の説明】
１ａ、１ｂ　単電池
２ａ、２ｂ　固体高分子電解質膜
３ａ、３ｂ　電極
４ａ、４ｂ　ガス流路
１０　セパレータ
１１　金属基板
１２　樹脂導電層
１３　低電気抵抗層
１４　樹脂導電層
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 comprising a plurality of unit cells stacked and provided between adjacent unit cells to form a fuel gas flow path and an oxidizing gas flow path with electrodes. Also, the present invention relates to a fuel cell separator for separating a fuel gas and an oxidizing gas, and more particularly to a fuel cell separator excellent in formability, strength and corrosion resistance.
[0002]
[Prior art]
A separator constituting a fuel cell, particularly a polymer electrolyte fuel cell, is disposed in contact with each electrode sandwiching a solid electrolyte membrane from both sides, and a supply gas such as a fuel gas and an oxidizing gas is provided between the electrodes. In order to form a flow path, a large number of protrusions, grooves and the like for forming a gas flow path are formed on the surface of the separator facing the electrode.
[0003]
The electromotive force of a unit cell of a fuel cell is as low as 1 V or less, and is usually formed by stacking a plurality of unit cells via a separator. Therefore, the separator is required to have excellent current collecting performance because it plays a role of deriving a current by contacting the electrode.
[0004]
2. Description of the Related Art Conventionally, a fuel cell separator is generally made of a dense carbon graphite having excellent strength and conductivity as a base material, or a metal material such as stainless steel (SUS), titanium, and aluminum.
[0005]
[Problems to be solved by the invention]
However, a separator composed of dense carbon graphite has high electrical conductivity and maintains a high current collection performance even after long-term use, but since it is a very brittle material, many separators are formed on the surface of the separator. There is a problem that it is not easy to perform machining such as cutting to form the projections and the grooves, and mass production is difficult.
[0006]
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. And mass production is easy. However, even a polymer electrolyte fuel cell that operates at a relatively low temperature is exposed to near-saturated water vapor at a temperature of 70 to 90 ° C. Are easily generated, and as a result, the contact resistance between the generated oxide film and the electrode is increased, and there is a problem that the current collecting performance of the separator is reduced.
[0007]
Therefore, as a constituent material of the separator, a material in which the surface of a metal material excellent in workability is coated with a noble metal material such as gold excellent in corrosion resistance has been studied. However, there is a problem that such materials are extremely expensive and thus lack versatility.
[0008]
In order to solve these problems, the present applicant has disclosed a separator in which a resin layer in which a conductive filler is mixed is provided on the surface of a metal substrate (Japanese Patent Application Laid-Open No. 2002-15750). This separator has high electrical conductivity and excellent current collecting performance, and also has excellent moldability, strength and corrosion resistance.
[0009]
The present invention has been made to further improve the performance, and provides a fuel cell, particularly a separator for a solid polymer electrolyte fuel cell, which satisfies both current collecting performance and moldability, strength and corrosion resistance. With the goal.
[0010]
[Means for Solving the Problems]
The present invention relates to the following items.
[0011]
1. A fuel cell separator provided with a resin conductive layer on at least one surface of a metal substrate,
The resin conductive layer comprises: (a) a resin; and (b) a first conductive filler whose content per volume is continuously changed so as to be higher on the metal substrate side and lower on the surface side. A separator for a fuel cell, comprising:
[0012]
2. 2. The method according to the above 1, wherein a low electric resistance layer containing a second conductive filler and having a lower volume lower efficiency than at least the surface of the resin conductive layer is provided on the surface of the resin conductive layer. Fuel cell separator.
[0013]
3. 3. The fuel cell separator according to claim 1, wherein the resin conductive layer further includes a third conductive filler uniformly mixed in the layer.
[0014]
4. The fuel cell separator according to any one of claims 1 to 3, wherein the first conductive filler is selected from the group consisting of a metal carbide, a metal oxide, a metal nitride, and a metal.
[0015]
5. 5. The fuel cell separator according to the above item 4, wherein the first conductive filler is tungsten carbide.
[0016]
6. The fuel cell according to any one of claims 2 to 5, wherein the second conductive filler is selected from the group consisting of a carbon-based material, a metal carbide, a metal oxide, a metal nitride, and a metal. Separator.
[0017]
7. 7. The fuel cell separator according to the above item 6, wherein the second conductive filler is selected from the group consisting of tungsten carbide, carbon nanotubes, and carbon nanofibers.
[0018]
8. The fuel cell separator according to any one of the above items 3 to 7, wherein the third conductive filler is selected from a carbon-based material.
[0019]
9. 9. The fuel cell separator according to the above item 8, wherein the third conductive filler is a carbon nanotube and / or a carbon nanofiber.
[0020]
10. The ratio of the content of the first conductive filler in the vicinity of the interface with the metal substrate to the content in the vicinity of the surface is from 6: 4 to 9: 1. 10. The fuel cell separator according to any one of 1 to 9.
[0021]
11. 11. The fuel cell separator according to any one of the above items 1 to 10, wherein the volume resistivity of the resin conductive layer is 1.0 Ω · cm or less at the largest point in the layer.
[0022]
12. A method for producing a fuel cell separator provided with a resin conductive layer on at least one surface of a metal substrate,
A slurry in which a first conductive filler having a higher density than the resin solution is dispersed in the resin solution is applied to the base material, and it takes time to allow at least a part of the first conductive filler to settle. And drying the solvent in the solution to form the resin conductive layer.
[0023]
13. A method for producing a fuel cell separator provided with a resin conductive layer on at least one surface of a metal substrate,
Dispersed in the resin solution is a first conductive filler having a density higher than that of the resin solution and a third conductive filler having a density that does not substantially cause sedimentation during a subsequent drying and removing operation of the solvent. The slurry is applied to a substrate and the solution in the solution takes a time sufficient for at least a portion of the first conductive filler to settle and a time in which the third conductive filler does not substantially settle. A method for manufacturing a fuel cell separator, comprising a step of forming a resin conductive layer by removing a solvent by drying.
[0024]
14． 14. The method for producing a fuel cell separator according to the above item 12 or 13, wherein the first conductive filler is selected from the group consisting of a metal carbide, a metal oxide, a metal nitride and a metal.
[0025]
15. 15. The method for producing a fuel cell separator according to the above 13 or 14, wherein the third conductive filler is selected from a carbon-based material.
[0026]
16. A low electric resistance layer containing a second conductive filler selected from the group consisting of a carbon-based material, a metal carbide, a metal oxide, a metal nitride and a metal, and having a volume lower efficiency than at least the surface of the resin conductive layer The method for producing a separator for a fuel cell according to any one of the above items 12 to 15, further comprising a step of laminating the resin on the surface of the resin conductive layer.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a schematic diagram in which the vicinity of a separator of a stacked fuel cell in which many unit cells are stacked is enlarged. Each of the unit cells 1a and 1b has solid polymer electrolyte membranes 2a and 2b and electrodes 3a and 3b sandwiching the solid polymer electrolyte membranes 2a and 2b, and the unit cells 1a and 1b are separated by the separator 10 at the same time. The gas passage 4a is formed on the unit cell 1a side in contact with the electrode 3a, and the gas passage 4b is formed on the unit cell 1b side in contact with the electrode 3b. The separator 10 of this embodiment is such that the resin conductive layers 12 are provided on both surfaces of the metal substrate 11 and is in contact with both the electrodes 3a and 3b, so that the unit cells 1a and 1b are connected in series. ing.
[0028]
As the metal substrate used in the separator of the present invention, a thin plate made of stainless steel, titanium, aluminum, copper, nickel, or steel can be preferably used, and the thickness is desirably in the range of 0.03 mm to 1.5 mm.
[0029]
A surface treatment layer such as an etching layer or a polishing layer may be provided on the surface of the metal substrate for the purpose of improving the adhesion to the resin layer, and the thickness of the surface treatment layer is desirably 0.001 μm to 30 μm. Further, the surface of the metal substrate may be subjected to a primer treatment with a silane coupling agent or the like.
[0030]
The resin used for the resin conductive layer is preferably a fluororesin or fluororubber from the viewpoint of chemical resistance. Specifically, PTFE (polytetrafluoroethylene), PFA (tetrafluoroethylene-perfluoroalkylvinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), and EPE (tetrafluoroethylene-hexafluoro Propylene-perfluoroalkylvinyl ether copolymer), ETFE (tetrafluoroethylene-ethylene copolymer), PCTFE (polychlorotrifluoroethylene), ECTFE (chlorotrifluoroethylene-ethylene copolymer), PVDF (polyvinylidene fluoride) ), PVF (polyvinyl fluoride), THV (tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer), VDF-HFP (vinylidene fluoride-hexafluoroprop) Pyrene copolymer), TFE-P (vinylidene fluoride - propylene copolymers), may be mentioned fluorine silicone rubber, fluorine-containing vinyl ether rubbers, fluorine-containing phosphazene-based rubber, and a fluorine-containing thermoplastic elastomer. These fluororesins or fluororubbers can be used alone or as a mixture of two or more.
[0031]
In particular, PVDF, THV, VDF-HFP, TFE-P, PTFE, FEP and the like containing vinylidene fluoride are preferred from the viewpoint of dispersion and solubility in a solvent.
[0032]
The first to third conductive fillers used in the present invention have different functions, and may be of the same type or different types depending on the case. However, it is preferable that the first conductive filler and the third conductive filler are different from each other. Although details will be described later, the first to third conductive fillers are selected from the following conductive fillers. That is, as the conductive filler, those having high conductivity and excellent corrosion resistance are preferably used, for example, powders of conductive materials such as carbon-based materials, metal carbides, metal oxides, metal nitrides and metals, or It can be used according to the use environment from fibers.
[0033]
Examples of the carbon-based material include powdery materials such as graphite (artificial graphite and natural graphite), carbon black, and expanded graphite, and examples of the fibrous material include carbon nanotubes, carbon nanofibers, and carbon fibers. . The carbon nanotube and the carbon nanofiber have a fiber diameter of 0.001 to 0.5 μm, preferably 0.003 to 0.2 μm, and a fiber length of 1 to 100 μm, preferably 1 to 30 μm. Is preferred.
[0034]
Examples of the metal carbide include powders and fibers such as tungsten carbide, silicon carbide, tantalum carbide, titanium carbide, niobium carbide, molybdenum carbide, vanadium carbide, chromium carbide, and hafnium carbide. Among these, powders and fibers of tungsten carbide, titanium carbide, niobium carbide, chromium carbide and the like are preferable.
[0035]
Examples of the metal oxide include powders and fibers such as titanium oxide, ruthenium oxide, indium oxide, tin oxide and zinc oxide. Among these, powders and fibers such as tin oxide and indium oxide are preferable.
[0036]
Examples of the metal nitride include powders and fibers such as chromium nitride, aluminum nitride, molybdenum nitride, zirconium nitride, tantalum nitride, titanium nitride, gallium nitride, niobium nitride, vanadium nitride, and boron nitride. Among them, chromium nitride and molybdenum nitride powders and fibers are preferable.
[0037]
Examples of the metal include powders such as titanium, nickel, tin, copper, aluminum, zinc, silver, tantalum, and niobium as powders, and examples of the fiber include iron fiber, copper fiber, and stainless steel fiber. .
[0038]
The conductive filler may be used alone or in combination of two or more. For example, a mixture of carbon nanotubes and / or carbon nanofibers and other carbon-based materials can be used.
[0039]
Among the above conductive fillers, those having particularly high conductivity, stable even when exposed to near-saturated water vapor at a temperature of 70 to 90 ° C., and having a small change in resistance are preferable, and include carbon-based materials, metal carbides, and the like. Metal nitrides are preferred, and carbon-based materials and metal carbides are particularly preferred. Specifically, one or both of carbon nanotubes and carbon nanofibers, or a mixture thereof, tungsten carbide, and a combination of tungsten carbide with carbon nanotubes and / or carbon nanofibers are particularly preferable.
[0040]
In the case of powder, the conductive filler usually has a weight average particle size (measured by laser scattering) of 20 μm or less, preferably 15 μm or less, particularly preferably 10 μm or less, and usually 0.01 μm or more, preferably 0.1 μm or less. It is at least 05 μm, particularly preferably at least 0.1 μm. In the case of a fibrous form, carbon nanotubes and carbon nanofibers are as described above, and in the case of fibers of other materials, the fiber diameter is 50 μm or less, preferably 20 μm or less, and usually 1 μm or more, preferably 5 μm or more, and a fiber length of 1 to 10,000 μm, preferably 5 to 1,000 μm is preferable from the viewpoint of conductivity.
[0041]
The thickness of the resin conductive layer is usually 5-300 μm, preferably 10-150 μm.
[0042]
Hereinafter, each embodiment of the present invention will be described with reference to the drawings. In the following first to fourth embodiments, a configuration of a composite plate of a metal substrate and a resin conductive layer, which is a stage before final processing into a separator, will be described. When the separator is used for a terminal cell, the resin conductive layer may be provided only on one side of the metal substrate. Therefore, only the layer structure on one side of the metal substrate is shown in the following examples.
[0043]
<First embodiment>
FIG. 2 shows an example of a layer structure of a composite plate having a metal substrate 11 and a resin conductive layer 12 provided on the surface thereof. The resin conductive layer 12 contains the first conductive filler, and contains the first conductive filler so that the content per volume is large on the interface side of the metal substrate 11 and small on the surface side. The amount has changed.
[0044]
In this embodiment, since the volume resistance of the resin conductive layer is reduced at the interface with the metal substrate, the interface resistance between the metal substrate and the metal substrate is small and the current collecting performance is excellent, and the resin component on the surface side maintains the strength. Therefore, the moldability is good and the resin conductive layer can be thinned.
[0045]
The first conductive filler is preferably selected from the group consisting of metal carbides, metal oxides, metal nitrides, and metals among the conductive fillers described above. Preferred specific examples of each material are as described above. In particular, metal carbides and metal nitrides are preferable.For metal carbides, powders or fibers of tungsten carbide, titanium carbide, niobium carbide, and chromium carbide are preferable.For metal nitrides, powders or fibers of chromium nitride and molybdenum nitride are preferable. preferable.
[0046]
In the case of powder, the first conductive filler usually has a weight average particle size (measured by laser scattering) of 20 μm or less, preferably 15 μm or less, and usually 0.05 μm or more, preferably 0.1 μm or more. is there. In the case of fibers, the fiber diameter is 50 μm or less, preferably 20 μm or less, usually 1 μm or more, preferably 5 μm or more, and the fiber length is 1 to 10,000 μm, preferably 5 to 1,000 μm. Is preferred.
[0047]
The content of the first conductive filler is from 20% by volume to 80% by volume, preferably from 20% by volume to 40% by volume, based on the total amount with the resin. The first conductive filler has a ratio of (content near the interface with the metal substrate) :( content near the surface) in the range of 6: 4 to 9: 1, particularly 7: 4. It is preferable that the distribution be made in the range of 3 to 9: 1. In addition, the distribution of the content from the surface side to the interface with the metal substrate is not particularly limited as long as the volume content monotonically increases, and is about the distribution generated when manufactured by a manufacturing method described later. I just need.
[0048]
As a result, the volume resistivity of the resin conductive layer changes between the metal substrate side and the surface side, but the volume resistivity is 1.0 Ω · cm or less even on the largest surface side in the layer (according to JIS K 7194. The same), and particularly preferably 0.8 Ω · cm or less.
[0049]
The thickness of the resin conductive layer in this mode is usually 5 to 300 μm, preferably 10 to 200 μm.
[0050]
Next, an example of a preferred method of manufacturing the composite plate of this embodiment will be described.
[0051]
The resin and the first conductive filler are added to a suitable solvent capable of dispersing or dissolving the resin to prepare a slurry of the first conductive filler. After this is applied on a metal substrate, the solvent is dried and removed to form a resin conductive layer on the base material. Here, when selecting the first conductive filler, by selecting the one having a density higher than the density of the resin solution, the first conductive filler settles after the slurry is applied, and the base is set by the end of drying. The content of the first conductive filler increases on the interface side with the material, and decreases on the surface side. The gradient of the content on the interface side and the content on the surface side is adjusted by the density of the first conductive filler, the viscosity of the resin solution (for example, adjusted by the amount and type of the solvent), and the drying speed of the solvent (for example, the standing time, etc.). ) Can be controlled so as to fall within the above range.
[0052]
When forming the resin conductive layer by such a solution coating method, a first conductive filler having a higher density than the resin solution is selected, and a metal carbide, a metal oxide, a metal nitride, and a metal are used. Usually, it can be used, but depending on the case, it is preferable to select and use a density. Tungsten carbide, titanium carbide, niobium carbide, chromium carbide, etc., tin oxide, indium oxide, chromium nitride, molybdenum nitride, titanium, nickel, tin, copper, aluminum, zinc, silver, tantalum, niobium, stainless steel can be used .
[0053]
<Second embodiment>
In this embodiment, as shown in FIG. 3, a low electric resistance layer 13 containing a second conductive filler is provided on the surface of a resin conductive layer 12 in the first embodiment.
[0054]
The second conductive filler is preferably selected from the group consisting of carbon-based materials, metal carbides, metal oxides, metal nitrides and metals, among the above-mentioned conductive fillers, and has a volume resistivity of the filler itself. Preferably, the ratio is 0.5 Ω · cm or less (according to JIS K 7194), particularly preferably 0.1 Ω · cm or less. Usually, it is 0.00001Ω · cm or more. Preferred specific examples of each material are as described above. Among these, carbon-based materials, metal carbides, and metal nitrides are preferred, and carbon-based materials and metal carbides are particularly preferred. As the carbon-based material, graphite (artificial graphite, natural graphite), carbon black, expanded graphite, and fibrous carbon nanotubes, carbon nanofibers, and carbon fibers are preferable. As the metal carbide, powders and fibers of tungsten carbide, titanium carbide, niobium carbide, chromium carbide and the like are preferable. Among these, carbon nanotubes, carbon nanofibers and tungsten carbide are most preferred.
[0055]
In the case of powder, the second conductive filler usually has a weight average particle size (measured by laser scattering) of 20 μm or less, preferably 15 μm or less, and usually 0.05 μm or more, preferably 0.1 μm or more. is there.
[0056]
In the case of fibers, in the case of carbon nanotubes and carbon nanofibers, the fiber diameter and fiber length are as described above, and in the case of other fibers, the fiber diameter is 50 μm or less, preferably 20 μm or less, and is usually The fiber length is 1 μm or more, preferably 5 μm or more, and the fiber length is preferably 1 to 10,000 μm, and more preferably 5 to 1,000 μm from the viewpoint of conductivity.
[0057]
Regarding the volume resistivity of the low electric resistance layer, the volume resistivity is smaller than at least the surface of the resin conductive layer, preferably 0.5 Ω · cm or less, more preferably 0.1 Ω · cm or less. The content of the second conductive filler in the low electric resistance layer is preferably 45 to 90% by volume, and more preferably 60 to 90% by volume. Further, the thickness of the low electric resistance layer is preferably 0.1 to 20 μm, and more preferably 1 to 15 μm.
[0058]
According to the separator of the second embodiment, after obtaining a laminated structure in which a resin conductive layer is formed on a metal substrate in accordance with the first embodiment, a low-level material containing a second conductive filler on the surface of the resin conductive layer is obtained. The electric resistance layer can be manufactured by laminating, for example, by a transfer method. The method of transferring the layer containing the second conductive filler is not particularly limited. For example, a coating obtained by dispersing the second conductive filler in a liquid in which a resin is dissolved is applied to a suitable base film by a bar coater or the like. It is preferable to apply and dry the solvent to obtain a transfer sheet, transfer the transfer sheet to the surface of the resin conductive layer having the laminated structure of the first embodiment, and remove the base film.
[0059]
Further, an embedding method may be used as a method for forming the low electric resistance layer. In this method, the second conductive filler is sprayed (for example, slurry is applied and dried) on the surface of the resin conductive layer formed according to the first embodiment, and hot pressed to form a second conductive filler on the surface of the resin conductive layer. Two conductive fillers can be embedded.
[0060]
In the laminated structure of the second embodiment, since the contact resistance with the electrode of the fuel cell can be greatly reduced, there is an effect that the current collecting performance is significantly improved.
[0061]
<Third embodiment>
This embodiment has a structure in which a resin conductive layer 14 containing a first conductive filler and a third conductive filler is provided on the surface of a metal substrate 11 as shown in FIG. The content of the first conductive filler changes such that the content per volume is large on the interface side of the metal substrate 11 and is small on the surface side. On the other hand, the third conductive filler is almost uniformly dispersed and mixed in the resin conductive layer.
[0062]
The first conductive filler can be selected and configured in the same manner as in the first embodiment.
[0063]
In this case, the content of the first conductive filler is 5% by volume to 40% by volume, preferably 5% by volume to 20% by volume, based on the total amount with the resin. The first conductive filler has a ratio of (content near the interface with the metal substrate) :( content near the surface) in the range of 6: 4 to 9: 1, particularly 7: 4. It is preferable that the distribution be made in the range of 3 to 9: 1.
[0064]
The third conductive filler is preferably selected from carbon-based materials among the conductive fillers described above. Examples of powdery materials include graphite (artificial graphite, natural graphite), carbon black, and expanded graphite, and examples of fibrous materials include carbon nanotubes, carbon nanofibers, and carbon fibers. Preferred sizes, forms, and the like are as described above.
[0065]
The content of the third conductive filler is 15% to 40% by volume, preferably 15% to 20% by volume.
[0066]
In this embodiment, in addition to the effects described in the first embodiment, the volume resistivity of the entire resin conductive layer can be reduced uniformly, and the overall conductivity can be increased.
[0067]
An example of a preferred manufacturing method of the separator of this embodiment will be described below.
[0068]
A resin, a first conductive filler and a second conductive filler are added to a suitable solvent capable of dissolving the resin to prepare a slurry, and then the slurry is prepared in exactly the same manner as in the first embodiment. To manufacture. Here, by selecting the density of the first conductive filler to be higher than the density of the resin solution and the density of the third conductive filler to be substantially the same as the density of the resin solution, after the slurry application, By the end of the drying, the first conductive filler settles and is fixed in a distribution in which the content changes continuously in the thickness direction of the layer, while the third conductive filler is substantially uniform in the layer. Fixed in distribution.
[0069]
The method of changing the gradient of the content on the interface side and the surface side is the same as that described in the first embodiment.
[0070]
Incidentally, the carbon-based material can be dispersed almost uniformly in the resin solvent, and even if such a solvent coating method is used, the sedimentation after application can be ignored, and the carbon-based material is distributed almost uniformly in the layer. be able to.
[0071]
<Fourth embodiment>
In this embodiment, as shown in FIG. 5, the low electric resistance layer 13 containing the second conductive filler is provided on the surface of the resin conductive layer 14 in the third embodiment. That is, in the resin conductive layer, the first conductive filler has a high content on the metal substrate 11 side and a low content on the surface side, and the third conductive filler is dispersed and mixed almost uniformly in the layer. Further, a low electric resistance layer 13 containing a second conductive filler is provided on the surface of the resin conductive layer 14.
[0072]
Therefore, the configuration before forming the low electric resistance layer 13 is exactly the same as that of the third embodiment, and the structure of the low electric resistance layer 13 is the same as that described in the second embodiment. This embodiment can be manufactured by forming the laminated structure of the third embodiment, and then forming the low electric resistance layer containing the second conductive filler by the method described in the second embodiment.
[0073]
With this configuration, in addition to the effects described in the third embodiment, the contact resistance with the electrode of the fuel cell can be further reduced, and thus the current collection performance is significantly improved.
[0074]
As described above, a method of forming the composite plate described in the first to fourth embodiments, and then forming a protrusion or a groove by press working to form a separator having a predetermined shape is preferable from the viewpoint of productivity and the like.
[0075]
【Example】
Hereinafter, although an Example is described, the present invention is not limited to this.
[0076]
Example 1 <Preparation of First Embodiment Composite Plate>
After dissolving 10% by weight of a fluororesin (THV220G, specific gravity 2 manufactured by “Sumitomo 3M Ltd.”) in 90% by weight of MIBK (methyl isobutyl ketone), tungsten carbide (“Allied Co., Ltd.”) is used as a first conductive filler. Material (WC20, specific gravity 15; average particle size 2.0 μm) was mixed so that the ratio of the conductive filler to the fluororesin was 20% by volume to 80% by volume to obtain a slurry.
[0077]
As the metal substrate, SUS304 (manufactured by Nippon Metal Co., Ltd .: thickness 0.3 mm) having a surface polishing layer of 0.1 μm formed by blast polishing is used, and a silane coupling agent (“GE Toshiba Silicone ( Co., Ltd.) TSL8331) 3% ethanol solution was applied to both surfaces of the above-polished SUS304 with a # 10 bar coater (“Matsuo Sangyo”), and dried at 100 ° C. for 10 minutes.
[0078]
The obtained slurry was applied on one surface of the metal substrate subjected to the primer treatment with a bar coater (# 80 manufactured by Matsuo Sangyo), left for 1 minute, and then dried at 80 ° C. The thickness of the obtained resin conductive layer was 30 μm. Further, a resin conductive layer having a thickness of 20 μm was formed on the other surface of the metal substrate in the same manner. The obtained composite board was used as composite board 1.
[0079]
[Example 2] <Preparation of second form composite plate>
Fluororesin (THV220G, specific gravity 2 manufactured by Sumitomo 3M Limited) and carbon nanotubes (manufactured by Showa Denko KK) as a second conductive agent so that MEK (methyl ethyl ketone) has a solid content of 10% by weight. Phase method carbon fiber <VGCF> Specific gravity 2) was mixed at a volume ratio of 30/70 to prepare a coating material.
[0080]
The above coating material is applied on a base film (polyethylene terephthalate, manufactured by Mitsubishi Chemical Polyester Co., Ltd .: thickness 25 μm) with a bar coater (# 24 manufactured by Matsuo Sangyo), and the solvent is dried at 80 ° C. to dry the transfer layer. Thus, a transfer sheet having a thickness of 10 μm was obtained.
[0081]
Using two transfer sheets obtained, the resin surface was superimposed on the resin conductive layer of the resin conductive layer / metal substrate / resin conductive layer composite board obtained in the same manner as in [Example 1], and the temperature was changed. 200 ° C, 10 minutes, pressure 3.5 × 10 ⁶ Pa (36 kgf / cm ² ), The base film was peeled off to form a low electric resistance layer. The obtained composite plate was designated as composite plate 2.
[0082]
Example 3 <Preparation of Third Embodiment Composite Plate>
After dissolving 10% by weight of a fluororesin (THV220G, specific gravity 2 manufactured by “Sumitomo 3M Ltd.”) in 90% by weight of MIBK (methyl isobutyl ketone), tungsten carbide (“Allied Co., Ltd.”) is used as a first conductive filler. Material WC20, specific gravity 15; average particle size 2.0 μm); and carbon short fiber (HTA-0040, manufactured by Toho Tenax Co., Ltd.) having a diameter of 4 to 7 μm and a length of 40 to 1,000 μm as a third conductive filler. , Specific gravity 1.77) are mixed such that the ratio of the first conductive filler, the third conductive filler, and the fluororesin is 10% by volume to 20% by volume to 70% by volume, and the slurry is obtained. Got.
[0083]
The obtained slurry was applied on one surface of a metal substrate (SUS304: thickness 0.3 mm) that had been subjected to a primer treatment in the same manner as in [Example 1] using a bar coater (# 80 manufactured by Matsuo Sangyo) and allowed to stand for 1 minute After that, the solvent was dried at 80 ° C. The thickness of the obtained resin conductive layer was 30 μm. Furthermore, a resin conductive layer having a thickness of 30 μm was formed on the other surface of the metal substrate in the same manner. The obtained composite plate was designated as composite plate 3.
[0084]
Example 4 <Production of Fourth Embodiment Composite Plate>
Using two transfer sheets obtained by the same method as in [Example 2], the resin conductive layer (including the first and third conductive fillers) obtained by the same method as in [Example 3] / The resin surface of the transfer sheet was superimposed on the resin conductive layer of the metal substrate / resin conductive layer (including the first and third conductive fillers). Next, at a temperature of 200 ° C. for 10 minutes and a pressure of 3.5 × 10 ⁶ Pa (36 kgf / cm ² ), The base film was peeled off, and low electric resistance layers were formed on both sides.
[0085]
The obtained composite plate was designated as composite plate 4.
[0086]
<Result of press working>
The composite plate 14 obtained in each of Examples 1 to 4 can be formed into a gas channel having a corrugated shape after pressing, a gas channel pitch of 3 mm, and a difference between a corrugated convex portion and a concave portion of 0.5 mm. Using a mold, press molding was performed at room temperature with a torque pack press (press speed: 45 spm, manufactured by Amada Co., Ltd.) using a press molding machine.
[0087]
The resulting fuel cell separator had good adhesion between the fluorocarbon resin layer containing tungsten carbide or carbon nanotubes and the metal plate, and did not peel off.
[0088]
<Measurement of contact resistance>
The contact resistance of the composite plates 1 to 4 obtained in Examples 1 to 4 was measured. The evaluation of the contact resistance was performed as follows.
1. measuring device
Resistance meter: YMR-3 type (manufactured by 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)

3. Measuring method
With the measuring device shown in FIG. 6, the separator 23 is sandwiched between the brass electrodes 21 from both sides via the carbon paper 22, and the voltage at the time of applying a predetermined current is measured by a four-terminal method while applying a predetermined load. To determine the contact resistance.
[0089]
The measurement results are shown by composite plates 1 to 4 in the graph of FIG. For comparison, resin-impregnated graphite G347B manufactured by Tokai Carbon Co., Ltd. was also evaluated.
[0090]
As shown in the graph of FIG. 7, the contact resistance of the composite plates 2 and 4 was remarkably small, and was substantially the same as that of the resin-impregnated graphite.
[0091]
【The invention's effect】
According to the present invention, it is possible to provide a separator for a fuel cell, particularly a solid polymer electrolyte fuel cell, which satisfies both the current collecting performance and the moldability, strength and corrosion resistance. Therefore, the fuel cell of the present invention has a great utility as a fuel cell capable of operating for a long time.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing the vicinity of a separator of a fuel cell.
FIG. 2 is a diagram illustrating an example of a layer structure of a separator according to the first embodiment.
FIG. 3 is a diagram illustrating an example of a layer structure of a separator according to a second embodiment.
FIG. 4 is a diagram illustrating an example of a layer structure of a separator according to a third embodiment.
FIG. 5 is a diagram illustrating an example of a layer structure of a separator according to a fourth embodiment.
FIG. 6 is a diagram showing a method for measuring contact resistance.
FIG. 7 is a graph showing a relationship between a contact load and a contact resistance value.
[Explanation of symbols]
1a, 1b cell
2a, 2b solid polymer electrolyte membrane
3a, 3b electrode
4a, 4b gas flow path
10 Separator
11 Metal substrate
12 Resin conductive layer
13 Low electric resistance layer
14 Resin conductive layer
21 Brass electrodes
22 carbon paper
23 Separator

Claims (16)

A fuel cell separator provided with a resin conductive layer on at least one surface of a metal substrate,
The resin conductive layer comprises: (a) a resin; and (b) a first conductive filler whose content per volume is continuously changed so as to be higher on the metal substrate side and lower on the surface side. A separator for a fuel cell, comprising: The low electric resistance layer containing a second conductive filler and having a lower volume efficiency than at least the surface of the resin conductive layer is provided on the surface of the resin conductive layer. Fuel cell separator. 3. The fuel cell separator according to claim 1, wherein the resin conductive layer further includes a third conductive filler uniformly mixed in the layer. 4. 4. The fuel cell separator according to claim 1, wherein the first conductive filler is selected from the group consisting of a metal carbide, a metal oxide, a metal nitride, and a metal. 5. The fuel cell separator according to claim 4, wherein the first conductive filler is tungsten carbide. The fuel cell according to any one of claims 2 to 5, wherein the second conductive filler is selected from the group consisting of a carbon-based material, a metal carbide, a metal oxide, a metal nitride, and a metal. For separator. The fuel cell separator according to claim 6, wherein the second conductive filler is selected from the group consisting of tungsten carbide, carbon nanotubes, and carbon nanofibers. The fuel cell separator according to any one of claims 3 to 7, wherein the third conductive filler is selected from a carbon-based material. The fuel cell separator according to claim 8, wherein the third conductive filler is a carbon nanotube and / or a carbon nanofiber. The ratio of the content of the first conductive filler near the interface with the metal substrate to the content near the surface is from 6: 4 to 9: 1. Item 10. A fuel cell separator according to any one of Items 1 to 9. The fuel cell separator according to any one of claims 1 to 10, wherein the volume resistivity of the resin conductive layer is 1.0 Ω · cm or less at the largest point in the layer. A method for producing a fuel cell separator provided with a resin conductive layer on at least one surface of a metal substrate,
A slurry in which a first conductive filler having a higher density than the resin solution is dispersed in the resin solution is applied to the base material, and it takes time to allow at least a part of the first conductive filler to settle. And drying the solvent in the solution to form the resin conductive layer. A method for producing a fuel cell separator provided with a resin conductive layer on at least one surface of a metal substrate,
Dispersed in the resin solution is a first conductive filler having a density higher than that of the resin solution and a third conductive filler having a density that does not substantially cause sedimentation during a subsequent drying and removing operation of the solvent. The slurry is applied to a substrate and the solution in the solution takes a time sufficient for at least a portion of the first conductive filler to settle and a time in which the third conductive filler does not substantially settle. A method for manufacturing a fuel cell separator, comprising a step of forming a resin conductive layer by removing a solvent by drying. 14. The method for manufacturing a fuel cell separator according to claim 12, wherein the first conductive filler is selected from the group consisting of a metal carbide, a metal oxide, a metal nitride, and a metal. The method according to claim 13, wherein the third conductive filler is selected from a carbon-based material. A low electric resistance layer containing a second conductive filler selected from the group consisting of a carbon-based material, a metal carbide, a metal oxide, a metal nitride and a metal, and having a volume lower efficiency than at least the surface of the resin conductive layer The method for producing a fuel cell separator according to any one of claims 12 to 15, further comprising a step of laminating on a surface of the resin conductive layer.

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