Separator for fuel cell

Abstract

To improve corrosion resistance of a separator for a fuel cell.SOLUTION: A fuel cell separator 10 includes: a base material 11 made of metal; a first layer 21 laminated on a surface of the base material 11; and a second layer 22 laminated on the first layer 21. The first layer 21 is a self-assembled monolayer formed by bonding organic phosphonic acid to the base material 11. The second layer 22 is a binder containing conductive particles.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a separator for a fuel cell.

Background Art

[0002] Conventionally, a configuration for suppressing corrosion of a separator for a fuel cell has been proposed. For example, Patent Document 1 describes a separator for a fuel cell in which a styrene-butadiene rubber having titanium nitride particles is adhered to the surface of stainless steel.

[0003] For example, Patent Document 2 describes a separator for a fuel cell in which a self-assembled monolayer made of alkanethiol is formed so as to cover the surface of a metal layer.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a demand for further improving the corrosion resistance of a separator for a fuel cell.

Means for Solving the Problems

[0006] A separator for a fuel cell for solving the above problems includes a base material made of metal, a first layer laminated on the surface of the base material, and a second layer laminated on the first layer. The first layer is a self-assembled monolayer formed by bonding an organic phosphonic acid to the base material, and the second layer is a binder containing conductive particles.

[0007] According to the above configuration, elution of metal ions from the base material can be suppressed. Thereby, the corrosion resistance of the separator for fuel cells can be improved.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0009] Hereinafter, an embodiment of a separator for fuel cells will be described with reference to FIGS. 1 to 3. As shown in FIG. 1, the separator 10 for fuel cells includes a base material 11, a first layer 21, and a second layer 22. The base material 11 is made of a metal material. Examples of the base material 11 include stainless steel, titanium alloy, and aluminum alloy.

[0010] In the separator 10 for fuel cells, the first layer 21 is laminated on the surface of the base material 11. In the separator 10 for fuel cells, the second layer 22 is laminated on the first layer 21. The first layer 21 and the second layer 22 are in direct contact with each other.

[0011] <First Layer> The first layer 21 is a self-assembled monolayer. Hereinafter, the self-assembled monolayer may also be referred to as SAM (Self Assembled Monolayer). Hereinafter, the material for forming SAM may also be referred to as SAM forming material.

[0012] The first layer 21 is formed by the bonding of the organic phosphonic acid 30 to the substrate 11. The organic phosphonic acid 30 is a SAM forming material. FIG. 2 shows the substrate 11 and the organic phosphonic acid 30. FIG. 3 shows the substrate 11 on which the first layer 21 is formed.

[0013] As shown in FIGS. 2 and 3, the organic phosphonic acid 30 can be bonded to the substrate 11 by the dehydration condensation of the hydroxy group of the organic phosphonic acid 30 and the hydroxy group on the surface of the substrate 11.

[0014] The first layer 21 is formed by the arrangement of the organic phosphonic acid 30 bonded to the substrate 11. The thickness of the first layer 21, that is, the length from the surface of the substrate 11 to the surface in contact with the second layer 22 in the first layer 21, depends on the structure of the organic phosphonic acid 30.

[0015] 〔SAM Forming Material〕 The organic phosphonic acid 30 as a SAM forming material is not particularly limited, and known organic phosphonic acids can be employed.

[0016] The organic phosphonic acid 30 is preferably a compound represented by the formula (I).

[0017]

Chemical Formula

[0018] L 1 represents a single bond or an alkanediyl group having 1 to 17 carbon atoms which may have a substituent. L 2 represents an alkanediyl group having 1 to 17 carbon atoms which may have a substituent.

[0019] L 1 or L 2The -CH contained in the alkanediyl group in 2 - may be replaced by -O- or -CO-. R A represents an alkylthiol group having 2 to 17 carbon atoms.

[0020] R B represents a hydrocarbon group having 1 to 2 carbon atoms which may have a substituent, a carboxy group, a cyano group or a cyclic hydrocarbon group having 3 to 12 carbon atoms which may have a substituent, and the -CH 2 - contained in the cyclic hydrocarbon group may be replaced by -O-, -S-, -CO- or -SO 2 -.

[0021] R C represents an amino group or a hydroxy group.] R B Examples of the hydrocarbon group in include a methyl group, a vinyl group, an ethynyl group and the like. The hydrocarbon group in B is preferably a methyl group.

[0022] R B Examples of the cyclic hydrocarbon group in include an alicyclic hydrocarbon group, an aromatic hydrocarbon group and a combination of an alicyclic hydrocarbon group and an aromatic hydrocarbon group. R B The cyclic hydrocarbon group in is preferably an aromatic hydrocarbon group. Examples of the aromatic hydrocarbon group include a phenyl group, a naphthyl group, a biphenyl group and the like.

[0023] R B The aromatic hydrocarbon group in is preferably a phenyl group. L 1 or L 2Examples of the alkanediyl group in [the compound] include linear alkanediyl groups such as methylene, ethylene, propane-1,3-diyl, butane-1,4-diyl, pentane-1,5-diyl, hexane-1,6-diyl, heptane-1,7-diyl, octane-1,8-diyl, nonane-1,9-diyl, decane-1,10-diyl, undecane-1,11-diyl, dodecane-1,12-diyl, tridecane-1,13-diyl, tetradecane-1,14-diyl, pentadecane-1,15-diyl, hexadecane-1,16-diyl, and heptadecane-1,17-diyl. L 1 Or L 2 The alkanediyl group in [the compound] may have a branched chain.

[0024] Examples of the substituent include a halogen atom, a hydroxy group, a cyano group, an alkyl group having 1 to 4 carbon atoms, a haloalkyl group having 1 to 4 carbon atoms, etc. The haloalkyl group is an alkyl group having a halogen. Examples of the halogen atom include a fluorine atom, a chlorine atom, etc. The number of substituents is not particularly limited, and the compound may have a plurality of substituents. The number of carbon atoms of the substituent is not included in the number of carbon atoms of the above group which may have a substituent.

[0025] R is preferably an alkyl group having 1 to 18 carbon atoms, an alkylthiol group having 2 to 17 carbon atoms, or a benzyl group. As the alkyl group having 1 to 18 carbon atoms in R, a linear alkyl group having 1 to 18 carbon atoms is preferred.

[0026] The number of carbon atoms of the alkyl group in R is preferably 4 to 18, more preferably 7 to 18, and even more preferably 10 to 18. As the alkylthiol group having 2 to 17 carbon atoms in R, a linear alkylthiol group having 2 to 17 carbon atoms is preferred.

[0027] The number of carbon atoms of the alkylthiol group in R is preferably 2 to 12, more preferably 5 to 12, and even more preferably 8 to 12. As R, preferably, it is an octadecyl group, a mercaptododecyl group or a benzyl group, more preferably, an octadecyl group or a mercaptododecyl group, still more preferably, a mercaptododecyl group.

[0028] <Second layer> The second layer 22 is a binder containing conductive particles. In the second layer 22, the conductive particles are dispersed in the binder.

[0029] The binder is not particularly limited, and a known binder that can be used for a fuel cell separator can be adopted. Examples of the binder include polymer materials such as styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Preferably, the binder is SBR. The binder may be used alone or as a mixture of two or more kinds.

[0030] The conductive particles are not particularly limited, and known conductive particles that can be used for a fuel cell separator can be adopted. Examples of the conductive particles include particles such as titanium nitride (TiN), titanium carbide (TiC), and carbon (C). Preferably, the conductive particles are TiN particles. The conductive particles may be used alone or in combination of two or more kinds.

[0031] As the second layer 22 provided in the fuel cell separator 10, particularly preferably, a layer combining TiN particles as conductive particles and SBR as a binder, that is, styrene-butadiene rubber (SBR) containing titanium nitride (TiN) particles.

[0032] <Method for manufacturing a fuel cell separator> An example of the method for manufacturing a fuel cell separator will be described. The manufacturing method of the separator for a fuel cell includes, for example, a first layer forming step and a second layer forming step. By performing the first layer forming step and the second layer forming step in order, the separator for a fuel cell can be manufactured. The manufacturing method of the separator for a fuel cell may include a pickling step as a step before performing the first layer forming step.

[0033] 〔Pickling Step〕 The pickling step is a step of pickling the base material 11 with a solution containing an acid. Known methods can be adopted for pickling.

[0034] 〔First Layer Forming Step〕 The first layer forming step is a step of laminating a first layer 21 on the surface of the base material 11 by forming a self-assembled monolayer on the surface of the base material 11. In the first layer forming step, for example, the base material 11 is immersed in a solution containing a SAM forming material. Then, the taken-out base material 11 is dried. The immersion time can be set as appropriate.

[0035] 〔Second Layer Forming Step〕 The second layer forming step is a step of further laminating a second layer 22 on the base material 11 provided with the first layer 21 with a binder containing conductive particles.

[0036] Known methods can be adopted for forming a layer of a binder containing conductive particles. Examples of the method for forming a layer of a binder containing conductive particles include an electrophoretic deposition method, a spray method, and the like.

[0037] <Function and Effect> The function and effect of this embodiment will be described. (1) According to the separator 10 for a fuel cell in which the first layer 21 and the second layer 22 are sequentially laminated on the base material 11, elution of metal ions from the base material 11 can be suppressed. Thereby, the corrosion resistance of the separator 10 for a fuel cell can be improved.

[0038] (2) According to the separator 10 for a fuel cell of this embodiment, the corrosion rate can be reduced. (3) By laminating the second layer 22 that employs SBR as a binder on the first layer 21, the adhesion between the SAM which is the first layer 21 and the second layer 22 can be improved. Due to the high adhesion between the first layer 21 and the second layer 22, the base material 11 can be coated more firmly. As a result, the corrosion resistance of the fuel cell separator 10 can be further improved.

[0039] (4) According to the SAM formed by the organic phosphonic acid 30 in which R in the above formula (I) is an alkylthiol group, that is, the organic phosphonic acid 30 having a thiol group at the terminal, the adhesion between the first layer 21 and the second layer 22 is further improved. Also, R C According to the organic phosphonic acid 30 having an amino group or a hydroxy group as R, the adhesion between the first layer 21 and the second layer 22 is further improved in the same manner as when R is an alkylthiol group.

[0040] (5) The organic phosphonic acid 30 is a stable compound and is easy to handle. Also, the SAM can be laminated by a simple method of immersing the base material 11 in a solution containing the organic phosphonic acid 30. Therefore, the fuel cell separator 10 can be manufactured without going through complicated processes when laminating the first layer 21 on the base material 11.

Example

[0041] The fuel cell separator will be described in more detail based on the following examples. Note that the fuel cell separator is not limited to the configuration described in the example column. Samples of fuel cell separators shown in Examples 1 to 3, Comparative Example 1, and Comparative Example 2 were manufactured. Each sample was evaluated according to the following test examples.

[0042] <Example 1> The stainless steel as the base material 11 was pickled. Next, the stainless steel was immersed in a solution containing a SAM forming material to form a SAM on the surface of the stainless steel. Then, by drying, the base material 11 on which the first layer 21 was formed was obtained. As the SAM forming material, a compound (benzylphosphonic acid) represented by the formula (X1) was used. Subsequently, a layer of SBR containing TiN particles was formed by a spraying method on the surface of the stainless steel on which the SAM was formed. In this way, a fuel cell separator in which the first layer 21 and the second layer 22 were laminated in this order on the surface of the base material 11 was obtained.

[0043] [Chemical formula] [Example 2] A fuel cell separator was obtained in the same manner as in Example 1, except that a compound (octadecylphosphonic acid) represented by the formula (X2) was used as the SAM forming material instead of the compound represented by the formula (X1).

[0044] [Example 3] A fuel cell separator was obtained in the same manner as in Example 1, except that a compound (12-mercaptododecylphosphonic acid) represented by the formula (X3) was used as the SAM forming material instead of the compound represented by the formula (X1).

[0045] [Comparative Example 1] The same stainless steel as the base material 11 used in Example 1 was pickled. The single stainless steel without a layer formed on the surface was used as Comparative Example 1.

[0046] [Comparative Example 2] The same stainless steel as the base material 11 used in Example 1 was pickled. A layer of SBR containing TiN particles was formed on the surface of the stainless steel by a spraying method.

[0047] [Test Example] 353K, pH3 H 2 SO 4 +2 ppm F -The sample was immersed in the solution. Using a silver / silver chloride electrode as the reference electrode, the potentiodynamic polarization curve was measured. Measurements were performed on the samples of Examples 1 to 3, Comparative Example 1, and Comparative Example 2, and the obtained polarization curves are shown in FIG. 4.

[0048] <Evaluation> In FIG. 4, the potential at which the current density is the smallest represents the corrosion potential. As shown in FIG. 4, in Examples 1 to 3, ennoblement of the corrosion potential was confirmed as compared with Comparative Examples 1 and 2.

[0049] Furthermore, as shown in FIG. 4, in Examples 1 to 3, a decrease in the current density in the active region and the passive region was confirmed as compared with Comparative Examples 1 and 2. That is, a decrease in the corrosion rate can be expected.

[0050] It was confirmed that Examples 1 to 3 have the same conductivity as Comparative Examples 1 and 2. Moreover, the same effect was confirmed also in a fuel cell separator manufactured using another organic phosphonic acid as a SAM forming material instead of the compounds shown in Formulas (X1) to (X3).

[0051] According to the fuel cell separator 10 including the first layer 21 which is a SAM formed on the surface of the substrate 11 by the organic phosphonic acid 30 and the second layer 22 which is a binder laminated on the first layer 21 and contains conductive particles, it can be seen that the corrosion resistance can be improved.

Explanation of Signs

[0052] 10…Fuel cell separator 11…Substrate 21…First layer 22…Second layer 30…Organic phosphonic acid

Claims

Claim 1 a substrate made of metal, a first layer laminated on the surface of the substrate, a second layer laminated on the first layer, and comprising, the first layer is a self-assembled monolayer formed by the bonding of an organic phosphonic acid to the substrate, the second layer is a binder containing conductive particles a separator for a fuel cell. Claim 2 The separator for a fuel cell according to claim 1, wherein the organic phosphonic acid is a compound represented by the formula (I). 【Chemical 1】 [In the formula (I), R is -R Ａ , -L １ -R Ｂ or -L ２ -R Ｃ represents. L １ represents a single bond or an alkanediyl group having 1 to 17 carbon atoms. L ２ represents an alkanediyl group having 1 to 17 carbon atoms. R Ａ represents an alkylthiol group having 2 to 17 carbon atoms. R Ｂ represents a methyl group or a phenyl group. R Ｃ represents an amino group or a hydroxy group.] Claim 3 The separator for a fuel cell according to claim 1, wherein the organic phosphonic acid is benzylphosphonic acid, octadecylphosphonic acid or 12-mercaptododecylphosphonic acid.

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