JP2019071196A - Manufacturing method of separator for fuel cell - Google Patents

Abstract

To provide a manufacturing method of separator for a fuel cell, in which adhesive strength to an adhesive agent is improved while improving strength of a mixed layer.SOLUTION: In a manufacturing method of a separator 1 for a fuel cell, a titanium base material 2 is prepared, and the surface 21 of the titanium base material 2 is coated with carbon black 31. The titanium base material 2 is subjected to heating treatment under a low oxygen atmosphere containing oxygen gas having an oxygen partial pressure of 25 Pa or lower. With such an arrangement, titanium atoms of the titanium base material 2 are subjected to out diffusion into the carbon black 31, and titanium oxide 32 is generated by reaction of the out diffused titanium atoms and the oxygen gas. Consequently, a mixed layer 3A composed of the titanium oxide 32 and the carbon black 31 is formed. The titanium base material 2 on which the mixed layer 3A is formed is subjected to heating treatment under vacuum atmosphere. Consequently, a titanium oxide 33 of TiO(in the formula, x is 1.3-1.7) is formed on the surface 35 of a mixed layer 3B.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method of manufacturing a separator for a fuel cell.

  The fuel cell has a solid polymer electrolyte membrane sandwiched between an anode electrode and a cathode electrode as a single cell, and a single cell is formed through a separator in which a gas (hydrogen gas, oxygen gas, etc.) flow path is formed. It is configured as a stack of multiple stacks. Since a separator for a fuel cell plays a role of flowing a current generated in a stack to an adjacent cell, high conductivity and conductive durability are required.

  As a method of manufacturing a separator for a fuel cell, for example, in Patent Document 1, carbon black is applied to the surface of a titanium base having a carbon concentration of 10 atomic% or less at a position 10 nm deep from the surface, and applied. The manufacturing method which heat-processes the base material under the low oxygen partial pressure which is 25 Pa or less in oxygen partial pressure is disclosed.

  In this method, titanium atoms of the base material diffuse outward into carbon black and react with a small amount of oxygen gas in a low oxygen atmosphere to form titanium oxide, and a mixed layer of titanium oxide and carbon black is formed. . By forming such a mixed layer, the separator can be provided with high conductivity and conductivity durability.

JP, 2016-122642, A

However, the separator manufactured by the method described in Patent Document 1 is crystal stable on the surface of the mixed layer by the reaction between the outdiffused titanium atoms and a trace amount of oxygen atoms on the surface of the mixed layer. Some titanium oxide (TiO ₂ ) is formed. Such a separator has high conductivity and durability, but has low adhesion to an adhesive used, for example, in bonding to a fuel cell membrane electrode assembly.

Further, as described above, titanium oxide whose composition formula is TiO ₂ is formed on the surface of the mixed layer, but since it is not in contact with oxygen gas inside the mixed layer, the titanium base is formed from the surface of the mixed layer The oxygen concentration of titanium oxide decreases as it approaches the interface of Such a decrease in oxygen concentration may cause a strength difference in the mixed layer, which may reduce the strength of the separator.

  The present invention has been made in view of the above points, and provides a method of manufacturing a separator for a fuel cell capable of improving the strength of the mixed layer and improving the adhesion between the surface of the mixed layer and the adhesive. Do.

  In order to solve the above problems, as a result of extensive investigations by the inventors, the oxygen atoms of titanium oxide on the surface of the mixed layer are diffused into the inside thereof to achieve (1) homogenization of the mixed layer. (2) It was thought that oxygen deficiency of titanium oxide on the surface of the mixed layer could activate the surface and improve the adhesion to the adhesive.

The present invention has been made based on such a concept, and in the method of producing a separator for a fuel cell according to the present invention, the carbon concentration located at a depth of 10 nm from the surface is 10 atomic% or less A step of preparing a titanium base made of titanium or a titanium alloy, a step of applying carbon black to the surface of the titanium base, and an oxygen partial pressure to the titanium base coated with the carbon black By performing heat treatment in a low oxygen atmosphere containing oxygen gas at 25 Pa or less, the titanium atoms of the titanium base material are diffused outward into the carbon black, and the titanium atoms diffused outward and the oxygen gas To react to form titanium oxide, to form a mixed layer consisting of the titanium oxide and the carbon black, and to form the mixed layer. Relative emission substrate, a heat treatment was performed in a vacuum atmosphere, TiO x _(wherein, x is a 1.3 to 1.7) on the surface of the mixed layer and the step of generating an oxide of titanium , And is characterized.

In the separator for a fuel cell according to the present invention, a mixed layer of titanium oxide and carbon black is coated on the surface of a titanium base made of titanium or titanium alloy, and the surface of the mixed layer is TiO _x (formula Middle, x is 1.3 to 1.7) titanium oxide is coated.

  In the present invention, the heat treatment is performed in a vacuum atmosphere on the titanium base on which the mixed layer composed of the titanium oxide generated by the outward diffusion and the carbon black is formed. Thereby, the oxygen atom bonded to the titanium atom can be diffused to the inside of the mixed layer while suppressing the oxidation of the titanium atom on the surface of the mixed layer. As a result, since the surface of the mixed layer is in an active state having unpaired electrons due to oxygen deficiency of titanium oxide, the adhesion between the adhesive and the surface of the mixed layer is improved.

  Further, according to the present invention, oxygen atoms are diffused into the mixed layer so that the oxygen concentration (oxygen atomic composition ratio) bonded to titanium oxide is substantially uniform from the surface of the mixed layer to the interface with the titanium base material. Therefore, it is possible to suppress the decrease in strength of the mixed layer caused by the difference in oxygen concentration. As a result of this, it is possible to obtain a separator having improved adhesion to the adhesive while enhancing the strength of the mixed layer.

(A) is a schematic cross-sectional view of the separator after heat treatment in a vacuum atmosphere after the step of forming a mixed layer of titanium oxide and carbon black, and (b) is a cross-sectional view of (a) The electronic state of the mixed layer formed in the separator of. (A) is typical sectional drawing of the separator after heat processing in a vacuum atmosphere, (b) is a figure explaining the electronic state of the mixed layer formed in the separator of (a). It is a figure which shows the spectrum by TEM (Transmission Electron Microscopy) -EELS (Electron Energy Loss Spectroscopy) analysis which concerns on an Example and a comparative example.

  Below, with reference to FIG. 1 and FIG. 2, the separator 1 which concerns on this embodiment of this invention is demonstrated, and the manufacturing method is demonstrated.

  FIG. 1 (a) shows the separator 1 after the step of forming the mixed layer 3A of titanium oxide 32 and carbon black 31 by heat treatment in a low oxygen atmosphere and before heat treatment in a vacuum atmosphere. It is typical sectional drawing of. FIG. 1B is a view for explaining the state of electrons of the mixed layer 3A formed in the separator 1 of FIG. 1A.

  FIG. 2A is a schematic cross-sectional view of the separator 1 after the heat treatment in a vacuum atmosphere. FIG.2 (b) is a figure explaining the state of the electron of the mixed layer 3B of the separator 1 of Fig.2 (a).

As shown in FIG. 2A, the separator 1 according to the present embodiment is used for a cell of a fuel cell, and a mixed layer 3B is formed on the surface 21 of the titanium base material 2. The mixed layer 3B is composed of titanium oxide 32 and carbon black 31. The titanium oxide 33 on the surface 35 of the mixed layer 3B corresponding to the surface of the separator 1 is TiO _x (wherein x is 1.3 to 1.7) and is a titanium oxide having oxygen deficiency.

  Here, when the value of x in the formula is less than 1.3, the amount of oxygen atoms bonded to Ti of the mixed layer 3B is too small, so it can not be said that the strength of the mixed layer 3B is sufficient. On the other hand, when the value of x exceeds 1.7, as described later, the activity of the surface 35 of the mixed layer 3B is not sufficient, and the adhesion between the surface 35 of the mixed layer 3B and the adhesive It will decrease. Below, the manufacturing method of the separator 1 is demonstrated.

1. Step of Preparing Titanium Substrate 2 (First Step) In the present embodiment, first, a titanium group made of titanium or a titanium alloy having a carbon concentration of 10 nm or less located at a depth of 10 nm from the surface 21 Prepare material 2

  The carbon concentration at a position 10 nm deep from the surface 21 of the titanium base material 2 is subjected to composition analysis in the depth direction using, for example, an X-ray photoelectron spectroscopy (XPS). It can be measured by

  Since a part of carbon atoms contained in the rolling oil at the time of rolling or the lubricating oil at the time of forming may diffuse to the surface layer of the titanium base material 2, the carbon concentration located at a depth of 10 nm from the surface 21 However, it may exceed 10 atomic percent.

  When the carbon concentration exceeds 10 atomic% at a position 10 nm deep from the surface 21 of the titanium substrate 2, a region contaminated with an organic substance or a region where titanium carbide is formed is present on the surface 21 of the titanium substrate 2 Very likely to exist. When such a titanium base material 2 is used, carbon black 31 is less likely to be bonded to the surface of titanium base material 2 in heat treatment under a low oxygen atmosphere described later, and as a result, outward diffusion of titanium atoms is inhibited. .

  Therefore, in the present embodiment, when the carbon concentration exceeds 10 atomic% at a position 10 nm deep from the surface 21 of the titanium base material 2, the surface such that the carbon concentration at that position is 10 atomic% or less Do the processing. As such surface treatment, for example, the titanium base 2 is pickled in an acidic aqueous solution containing hydrofluoric acid. Besides, for example, heat treatment may be performed at a temperature of 650 ° C. or higher in a vacuum atmosphere to diffuse carbon into the titanium base material 2, and a layer having a high carbon concentration is physically obtained by shot blasting or polishing. May be removed.

  As titanium of the titanium base material 2 to prepare, 1-4 types prescribed | regulated to JISH4600 can be mentioned, for example. Moreover, as a titanium alloy, Ti-Al, Ti-Nb, Ti-Ta, Ti-6Al-4V, Ti-Pd can be mentioned, for example. However, in any case, it is not limited to the said illustration. When the base material is made of titanium or titanium alloy, it can be light and excellent in corrosion resistance.

  As a raw material of the titanium base material 2, for example, a plate material cold-rolled to a thickness of 0.05 to 1 mm is preferable. When the thickness is in this range, the requirements for weight reduction and thickness reduction of the separator 1 are satisfied, the strength and the handling property as the separator 1 are provided, and it becomes relatively easy to press into the shape of the separator 1.

2. Step of Applying Carbon Black (Second Step) In this step, carbon black 31 is applied to the surface 21 of the titanium base material 2 prepared in the first step. Specifically, an aqueous or oily liquid (dispersion liquid) in which a powder of carbon black 31 is dispersed is applied, or a powder of carbon black 31 is directly applied. As an aqueous solution, water can be used as a solvent, for example. As an oily liquid, for example, ethanol, toluene, or cyclohexanone can be used.

  The particle size of the carbon black 31 powder is preferably 20 to 200 nm. When the powder of carbon black 31 easily forms an aggregate, for example, it is preferable to use a powder of carbon black 31 in which a functional group such as a carboxyl group is chemically bonded to the surface. By preparing a dispersion liquid with such carbon black 31 powder, the mutual repulsion of the carbon black 31 powder can be strengthened and the dispersibility can be enhanced, so that the formation of aggregates can be suppressed.

The lower limit value of the coating amount of the carbon black 31 powder on the surface 21 of the titanium base material 2 is preferably 1 μg / cm ² or more. By setting such a lower limit value, high conductivity and conductivity durability can be obtained. On the other hand, the upper limit of the coating amount is preferably about 50 μg / cm ² . By setting such an upper limit value, it is possible to suppress an increase in cost.

  As a method of applying the dispersion liquid in which the powder of carbon black 31 is dispersed to titanium substrate 2, for example, brush coating, bar coater, roll coater, gravure coater, die coater, dip coater, or spray coater etc. Although it is mentioned, it is not limited to these. Moreover, when apply | coating by powder form, it can carry out by electrostatic-coating on the titanium base material 2 using the toner produced using carbon black 31. FIG.

3. Step of Forming Mixed Layer 3A (Third Step) In this step, as shown in FIG. 1A, the oxygen partial pressure is applied to the titanium base material 2 to which the carbon black 31 is applied in the second step. Heat treatment is performed in a low oxygen atmosphere containing oxygen gas at 25 Pa or less. As a result, the titanium atoms of the titanium base material 2 are diffused outward into the carbon black 31, and the titanium atoms diffused outward are reacted with oxygen gas to form titanium oxide 32, thereby forming the titanium oxide 32 and the carbon black. A mixed layer 3A of 31 is formed.

  Here, if the oxygen partial pressure exceeds 25 Pa, the carbon of the carbon black 31 and the oxygen gas may react with each other to become carbon dioxide (burn). For this reason, it is difficult to form the mixed layer 3A made of the titanium oxide 32 and the carbon black 31 which are produced by reacting the outdiffused titanium atoms with the oxygen gas.

In addition, it is preferable that oxygen partial pressure exists in the range of 1.3 * 10 < ^-3 > -21Pa, for example. Moreover, it is preferable that the temperature of heat processing exists in the temperature range of 300-800 degreeC, for example. When the oxygen partial pressure and the temperature of the heat treatment are in the above-mentioned ranges, some or all of the titanium atoms diffused outward from the titanium base material 2 react with a trace amount of oxygen in the atmosphere to form titanium oxide, titanium oxide The mixed layer 3A in which the carbon black 32 and the carbon black 31 are mixed can be reliably formed.

On the surface 35 of the mixed layer 3A corresponding to the surface of the separator 1 obtained in this step, as shown in FIG. 1 (b), a crystallographic structure having a rutile type crystal structure represented by the composition formula TiO ₂ There is a stable titanium oxide. From the surface 35 of the mixed layer 3A to the interface 34 with the titanium base 2 (ie, from the surface 35 of the mixed layer 3A to the thickness direction of the mixed layer 3A), the concentration of oxygen bonded to titanium atoms decreases Do. And, at the interface 34, TiO _x with low oxygen concentration (wherein x is about 1) may be present.

Since titanium oxide (TiO ₂ ) has a stable crystal structure when titanium oxide (TiO ₂ ) is present on the surface 35 of such a separator 1 (mixed layer 3A), an element of which titanium atoms constitute an adhesive The bonding energy between the titanium atom and the oxygen atom is larger than the energy bonding with. For this reason, the adhesion between the surface 35 of the mixed layer 3A and the adhesive is low.

In addition, although titanium oxide represented by the composition formula TiO ₂ is formed on the surface 35 of the mixed layer 3A, since it is not in contact with oxygen gas inside the mixed layer 3A, as described above, As the surface 35 progresses to the interface 34 with the titanium base material 2, the oxygen concentration contained in titanium oxide decreases. As a result, the strength of the mixed layer 3A may decrease due to the difference in the oxygen concentration of titanium oxide.

  So, in this embodiment, in order to diffuse the oxygen atom of the surface 35 of the mixed layer 3A into the inside of the mixed layer 3A while suppressing the oxidation of the surface 35 of the mixed layer 3A, after performing heat treatment under a low oxygen atmosphere Further, heat treatment is further performed in a vacuum atmosphere. Below, the detail of each process of the manufacturing method of this embodiment is demonstrated.

4. Step of Producing TiO _x (x: 1.3 to 1.7) (Step 4) In this step, as shown in FIG. 2A, with respect to the titanium base material 2 obtained in the step 3, By performing heat treatment in a vacuum atmosphere, titanium oxide 33 of TiO _x (wherein x is 1.3 to 1.7) is formed on the surface 35 of the mixed layer 3B. As a result, the fuel cell separator 1 according to the present embodiment can be obtained. That is, in the separator 1 for a fuel cell, the mixed layer 3B of titanium oxide 32 and carbon black is coated (formed) on the surface of the titanium base 2 of titanium or titanium alloy, , TiO _x (wherein x is 1.3 to 1.7) is coated (formed).

In this embodiment, since the heat treatment is performed in a vacuum atmosphere, the oxygen atoms bonded to the titanium atoms can be diffused inside while suppressing the oxidation of the titanium atoms on the surface 35 side of the mixed layer 3B. As a result, titanium oxide 33 which becomes TiO _x (wherein x is 1.3 to 1.7) can be generated on the surface 35 of the mixed layer 3B, and titanium oxide contained in the mixed layer 3B. The difference in the oxygen concentration of 32 can be suppressed.

Here, the vacuum atmosphere is a pressure atmosphere of at least 1.3 × 10 ⁻⁴ Pa and is in a non-oxygen atmosphere. Moreover, the conditions of heat processing performed under a vacuum atmosphere are a heating temperature of 300-840 degreeC, and processing time is 10 to 60 second. The composition ratio (value of x) of oxygen atoms of titanium oxide TiO _x formed on the surface 35 of the mixed layer 3B is set to 1 by performing processing under a vacuum atmosphere at such heating temperature and processing time range. It can be in the range of .3 to 1.7.

  Since the surface 35 of the mixed layer 3B of the separator 1 obtained in this step has titanium unpaired electrons as shown in FIG. The adhesion between the surface 35 of the mixed layer 3B and the adhesive is improved.

  Here, examples of the adhesive include thermoplastic adhesives such as polypropylene (PP), polyethylene (PE) and polyethylene terephthalate (PET), thermosetting adhesives such as silicone and epoxy, and acrylic two-pack type Adhesives and rubber-elastomers such as epilene propylene diene rubber (EPDM), nitrile rubber (NBR), and fluorine-type rubbers can be mentioned.

  According to the present embodiment, as described above, the titanium base 2 (see FIG. 1A) on which the mixed layer 3A made of the titanium oxide 32 and the carbon black 31 formed by the outward diffusion is formed. In contrast, heat treatment was performed in a vacuum atmosphere. Thereby, the oxygen atom bonded to the titanium atom is internally diffused while suppressing the oxidation of the titanium atom on the surface 35 of the mixed layer 3A. Therefore, the difference in concentration of oxygen atoms bonded to titanium atoms in the mixed layer 3B is reduced, and as a result, the strength of the mixed layer 3B of the separator 1 is improved.

Furthermore, since the titanium oxide on the surface 35 of the mixed layer 3B is in an active state (see FIG. 2B) having titanium unpaired electrons due to oxygen deficiency, the surface of the mixed layer 3B, which is the surface of the separator 1. The adhesion between 35 and the adhesive applied to this surface 35 is improved.

  The invention will now be described by way of example.

<Example>
The test body according to Example 1 was produced as a test body corresponding to the separator of the present invention along the first to fourth steps described above.

[First step]
First, a titanium base having a carbon concentration of 10 atomic% or less located at a depth of 10 nm from the surface was prepared. The prepared titanium substrate is a cold-rolled material of pure titanium (a type 1 specified in JIS H 4600), the size of the titanium substrate is 50 × 150 mm, and the thickness is 0.1 mm. The The carbon concentration at a depth of 10 nm from the surface of the substrate was measured by XPS analysis to be 5 atomic% or less.

[Second step]
Next, the surface of the titanium base was coated with carbon black. A commercially available paint (Aqua Black-162, manufactured by Tokai Carbon Co., Ltd.) was used as a paint in which carbon black was dispersed. The paint was appropriately diluted with distilled water and ethanol and applied onto the substrate by brushing. The application amount was 30 μg / cm ² .

[Third step]
Next, a 20 × 50 mm test body was cut out of the titanium substrate coated with carbon black obtained in the second step. By subjecting this test body to a heat treatment (temperature 700 ° C., treatment time 30 seconds) under a low oxygen atmosphere containing oxygen gas at an oxygen partial pressure of 10 Pa, the titanium atoms of the titanium base material in the carbon black Outward diffusion was performed, and the outward diffused titanium atoms were reacted with oxygen gas to form titanium oxide, thereby forming a mixed layer of titanium oxide and carbon black.

[Step 4]
Next, heat treatment (temperature 750 ° C., treatment time 15 seconds) was performed on the test sample obtained in the third step under a vacuum atmosphere. This heat treatment was performed using the vacuum heat treatment furnace used in the third step. The obtained test body was made into the Example.

Comparative Example
The test body produced similarly to the example except that the 4th process mentioned above was not performed was made into the comparative example.

<TEM-EELS analysis>
The valence number of titanium oxide was measured by analyzing the composition state of the surface of the mixed layer of the example and the comparative example by TEM-EELS.

<Results and Discussion>
FIG. 3: is a figure which shows the spectrum by TEM-EELS analysis which concerns on an Example and a comparative example. Spectral lines A and B are spectral lines of the example (after the vacuum heat treatment of the fourth step) and the comparative example (before the vacuum heat treatment of the fourth step). The 図 in the figure indicates the peaks of the spectral lines A and B.

  In the TEM-EELS measurement, the lower the measured loss energy, the more the oxygen deficiency in the titanium oxide is present. Then, as can be seen from FIG. 3, the loss energy at the surface of the mixed layer decreased from 463.0 eV to 462.2 eV before and after heat treatment in a vacuum atmosphere.

From this, TiO ₂ is formed on the titanium oxide on the surface of the mixed layer before the heat treatment in the vacuum atmosphere, and titanium oxide having oxygen deficiency is formed on the surface of the mixed layer after the heat treatment in the vacuum atmosphere It is considered to be formed. And from the measured loss energy, it was found that the titanium oxide on the surface of the mixed layer was about TiO _1.5 .

When the heating temperature in a vacuum atmosphere is in the range of 300 to 840 ° C. and the treatment time is in the range of 10 to 60 seconds, the value of x of TiO _x is in the range of 1.3 to 1.7. Was confirmed.

  Furthermore, with respect to the example, a plurality of test bodies before vacuum heating before the fourth step and a plurality of test bodies after vacuum heating where the fourth step was performed were prepared. Then, after placing an adhesive (adhesive tape) of 30 μm thick modified polypropylene on the surface of these test bodies at 160 ° C. for 3 seconds under the condition of indentation amount of 5 μm, the force to peel it off (initial adhesion Force) was measured. The results are shown in the left column of Table 1. If the adhesive strength is 0.6 N / mm or more, the adhesive state is good.

  In addition, for the example, a plurality of test bodies before vacuum heating before the fourth step and a plurality of test bodies after vacuum heating after the fourth step are prepared. A durability test was conducted by immersing in hot water of 100 ° C. for 100 hours. After that, after attaching an adhesive (an adhesive tape having an adhesive) made of modified polypropylene to the surface of these test bodies under the same conditions as described above, the force to pull it off from the surface of the test bodies (after the endurance test) The adhesion was measured. The results are shown in the right column of Table 1.

  From this result, as in the present invention, by performing the fourth step, the adhesion of the test body after vacuum heating is improved, and the adhesion is 0.6 N / mm or more even after the endurance test (specifically, (0.6 to 0.8 N / mm). On the other hand, the specimen before vacuum heating, which has not been subjected to the fourth step, has an adhesion of 0.6 N / mm or less (specifically, 0.2 to 0.6 N / mm) after the endurance test. The adhesion decreased significantly.

  As mentioned above, although one embodiment of the present invention was explained in full detail, the present invention is not limited to the above-mentioned embodiment, It is a range which does not deviate from the spirit of the present invention indicated in a claim. It is possible to make design changes.

  1: Separator, 2: Titanium base, 3A, 3B: mixed layer, 31: carbon black, 32, 33: titanium oxide

Claims (2)

A method of manufacturing a separator for a fuel cell, comprising:
Preparing a titanium substrate made of titanium or a titanium alloy, wherein the carbon concentration located at a depth of 10 nm from the surface is 10 atomic% or less;
Applying carbon black to the surface of the titanium substrate;
The titanium atom of the titanium base material is contained in the carbon black by performing heat treatment on the titanium base material coated with the carbon black under a low oxygen atmosphere containing oxygen gas at an oxygen partial pressure of 25 Pa or less. Forming a mixed layer of titanium oxide and the carbon black by causing the titanium atoms diffused outward to react with the oxygen gas to form titanium oxide.
The titanium base on which the mixed layer is formed is subjected to heat treatment in a vacuum atmosphere to obtain TiO _{x on} the surface of the mixed layer (in the formula, x is 1.3 to 1.7). And producing a titanium oxide of a fuel cell separator. A mixed layer of titanium oxide and carbon black is coated on the surface of a titanium base made of titanium or a titanium alloy,
A separator for a fuel cell, wherein titanium oxide of TiO _x (wherein x is 1.3 to 1.7) is coated on the surface of the mixed layer.

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