JP2022030734A - Fuel cell separator and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for a fuel cell having improved corrosion resistance by suppressing contact of generated water generated by a fuel cell reaction with a metal base material (metal substrate) of the separator. SOLUTION: A separator for a fuel cell having a metal oxide / conductive polymer composite film having a metal oxide content of 8 to 25 vol% on the surface of a metal substrate. [Selection diagram] Fig. 1

Description

The present application relates to a fuel cell separator and a method for manufacturing a fuel cell separator.

A fuel cell of a solid polymer fuel cell is a membrane electrode assembly composed of an ion-permeable electrolyte membrane, an anode-side catalyst layer (electrode layer) and a cathode-side catalyst layer (electrode layer) sandwiching the electrolyte membrane. (MEA: Membrane Electrode Assembly) is provided. Gas diffusion layers (GDL: Gas Diffusion Layer) are usually formed on both sides of the MEA to provide a fuel gas or an oxidant gas and to collect electricity generated by an electrochemical reaction. The membrane electrode assembly in which the GDL is arranged on both sides is called MEGA (Membrane Electrode & Gas Diffusion Layer Assembly), and the MEGA is sandwiched by a pair of separators.

The separator of a polymer electrolyte fuel cell is required to have a high degree of gas impermeableness in order to supply the fuel gas and the oxidant gas to the electrodes in a completely separated state, and in order to increase the power generation efficiency. It is necessary to have high conductivity. Further, it is required to have excellent corrosion resistance.

As an example of a conventional separator, Patent Document 1 discloses a separator for a fuel cell provided with a metal base material, a tin oxide film provided on the surface of the metal base material, and a conductive polymer film.

Japanese Unexamined Patent Publication No. 2019-114339

In the above-mentioned conventional technique, water generated by the fuel cell reaction (generated water) may permeate the conductive polymer membrane, in which case the metal base material is oxidized, the contact resistance of the separator is increased, and the cell output is increased. Could decrease.

Therefore, the purpose of the present application is to prevent the generated water generated by the fuel cell reaction from coming into contact with the metal substrate (metal substrate) of the separator in view of the above circumstances, so that the corrosion resistance is improved for the fuel cell. The subject is to provide a separator.

As a result of diligent studies by the present inventor in order to solve the above problems, a film obtained by mixing a predetermined amount of metal oxide in a conductive polymer is formed on the surface of a metal base material (metal substrate). As a result, it has been found that the generated water generated by the fuel cell reaction can be suppressed from coming into contact with the metal base material (metal substrate) of the separator, and the corrosion resistance of the fuel cell separator can be improved.

Based on the above, the present application is a fuel having a metal oxide / conductive polymer composite film having a metal oxide content of 8 to 25 vol% on the surface of a metal substrate as one means for solving the above problems. Disclose the separator for a battery.

Further, in the present application, as another means for solving the above-mentioned problems, SiO ₂ / using a Si (silicon) / PEDOT (polystyrene dioxythiophene) / PSS (polystyrene sulfonic acid) sulfuric acid solution having a pH of 2 to 4 is used. Disclosed is a method for manufacturing a separator for a fuel cell, comprising a step of preparing a PEDOT / PSS mixed solution, a step of applying the mixed solution to a metal substrate, and a step of drying the applied mixed solution.

According to the fuel cell separator of the present disclosure, the corrosion resistance of the fuel cell separator can be improved by suppressing the generated water generated by the fuel cell reaction from coming into contact with the metal substrate (metal substrate) of the separator. ..

It is a schematic diagram which shows the layer structure of the separator for a fuel cell of this disclosure. It is a figure which shows the relationship between the SiO ₂ content in a metal oxide / conductive polymer composite film, and the contact resistance ratio of a separator. It is a figure which shows the relationship between the pH of a Si / PEDOT / PSS sulfuric acid solution, and the contact resistance ratio of a separator.

<Fuel cell separator 100>
Hereinafter, the fuel cell separator according to the embodiment of the present invention will be described in detail. FIG. 1 shows the layer structure of the fuel cell separator 100 of the present disclosure. The fuel cell separator 100 is provided with a metal oxide / conductive polymer composite film 20 on the surface of the metal substrate 10.

The fuel cell separator 100 is a plate-shaped member having excellent conductivity, gas impermeableness, and the like. For example, the fuel cell separator 100 is formed in a corrugated shape. It comes into contact with the gas diffusion layer of MEGA, and a reaction gas flow path for fuel gas or oxidant gas is formed between the fuel cell separator 100 and the gas diffusion layer. Further, the other surface side of the fuel cell separator 100 comes into contact with the other surface side of another adjacent separator. Here, the metal oxide / conductive polymer composite membrane 20 may be provided only on one side of the metal substrate 10 on which the reaction gas flow path is formed, or may be provided on both sides of the metal substrate 10. You may be. At least, it is preferable to provide it on one side where the reaction gas flow path is formed.

(Metal substrate 10)
The metal substrate 10 can be appropriately selected and used from various metal substrates that can be used for the fuel cell separator. It is preferable that it has properties such as strength resistance and corrosion resistance. Examples of the material constituting the metal substrate 10 include stainless steel (SUS), copper and copper alloys, titanium and titanium alloys, nickel-based base materials, aluminum and aluminum alloys, magnesium alloys, iron and the like. Further, as the above-mentioned stainless steel, all of austenite-based stainless steel (iron-chromium-nickel alloy), ferrite-based stainless steel (iron-chromium alloy), martensite-based stainless steel (iron-chromium alloy), etc. can be applied. be. The above-mentioned reaction gas flow path, cooling water flow path, and the like can be formed on the metal substrate 10 by press molding or the like.

(Metal oxide / conductive polymer composite film 20)
The metal oxide / conductive polymer composite film 20 formed on the surface of the metal substrate 10 contains the metal oxide in the conductive polymer at a ratio of 8 to 25 vol%. Examples of the metal of the metal oxide contained in the metal oxide / conductive polymer composite film 20 include Si, Al, Ti, Sn, and In, and among them, inexpensive Si is preferable. By compounding the metal oxide with the conductive polymer film, the metal oxide suppresses the permeation of water, so that the water (generated water) generated in the fuel cell reaction causes corrosion (oxidation) of the metal substrate 10. Less. As a result, even when the fuel cell is operated for a predetermined period, the contact resistance of the separator does not increase, and the decrease in cell output is suppressed.

The content of the metal oxide in the metal oxide / conductive polymer composite film 20 is 8 to 25 vol%, more preferably 11 to 17 vol%, based on the metal oxide / conductive polymer composite film 20. .. If the content of the metal oxide is too small outside the above range, the effect of suppressing the permeation of water becomes difficult to be exhibited. Further, if the content of the metal oxide is out of the above range and is too large, the contact resistance of the separator becomes high.

The conductive polymer in the metal oxide / conductive polymer composite film 20 is a material that has relatively high conductivity and can cover the surface of the metal substrate 10 to reduce elution of Fe and the like. Applicable. Specifically, polythiophenes and derivatives thereof such as polyethylenedioxythiophene (PEDOT) and polyethylenedioxythiophene / polystyrene sulfonic acid (PEDOT / PSS, a mixture of PEDOT and PSS), doped polyaniline, polyphenylene vinylene, polypyrrole, etc. Examples thereof include polyparaphenylene, polyacetylene, triphenyldiamine (TPD) and the like. Of these, polyethylene dioxythiophene (PEDOT) and polyethylene dioxythiophene / polystyrene sulfonic acid (PEDOT / PSS) are preferably used.

If the thickness of the metal oxide / conductive polymer composite film 20 is too thin, the effect of suppressing the permeation of water cannot be exhibited, the effect of preventing the elution of Fe and the like cannot be obtained, and conversely, the thickness is too thick. Since the volume resistance may increase, it is set appropriately in consideration of these. Specifically, it is in the range of 0.3 nm to 10 μm, preferably in the range of 100 nm to 5 μm, although it depends on the type of the material of the metal oxide / conductive polymer composite film 20.

Further, the metal oxide / conductive polymer composite film 20 has a surface sulfur concentration of 2 atm. % Or more, and particularly preferably 5 atm. % Or more. When the surface sulfur concentration is within the above range, a sufficient coating effect by the metal oxide / conductive polymer composite film 20 can be obtained, and the effect of suppressing the permeation of water is exhibited. The surface sulfur concentration of the metal oxide / conductive polymer composite film 20 can be measured by means such as X-ray photoelectron spectroscopy (XPS).

The metal oxide / conductive polymer composite film 20 may contain various components such as an oxidizing agent such as iodine and paratoluenesulfonic acid and a cross-linking agent, depending on the case. The content of these components other than the conductive polymer should be such an amount that does not hinder the corrosion suppressing effect of the metal oxide / conductive polymer composite film 20, specifically, the metal oxide / conductive polymer composite. It is preferable that the total amount of the film 20 is less than 1% by weight.

In the present application, the corrosion resistance of the fuel cell separator 100 can be evaluated by subjecting the prepared test piece (fuel cell separator) to a corrosion test and measuring the contact resistance of the test piece after the corrosion test.
As the corrosion test, for example, a corrosion resistance test (constant potential corrosion test) according to the electrochemical high temperature corrosion test method (JIS Z2294) of a metal material of Japanese Industrial Standards can be adopted. In the test, the test piece was immersed in a sulfuric acid aqueous solution (300 ml, pH3) whose temperature was adjusted to 80 ° C. by controlling the temperature in an air release system device, and in this state, a counter electrode made of a platinum plate and a test piece (sample electrode). ) Is electrically connected to generate a potential difference of 0.9V between the counter electrode and the sample electrode, which corrodes the test piece.

As for the contact resistance, for example, a method can be adopted in which carbon paper (thickness 0.5 mm) corresponding to the diffusion layer of the fuel cell is placed on the test piece and a constant load (1 MPa) is applied by a measuring jig to measure the contact resistance. In this state, adjust the current from the power supply so that the current flowing through the test piece is 1A with an ammeter, measure the voltage applied to the test piece with a voltmeter, and connect the test piece and carbon paper. Calculate the contact resistance.

<Manufacturing method of separator for fuel cell>
Hereinafter, a method for manufacturing a fuel cell separator according to an embodiment of the present invention will be described in detail. In the method for producing a separator for a fuel cell of the present invention, a SiO ₂ / PEDOT / PSS mixed solution using a Si (silicon) / PEDOT (polyethylene dioxythiophene) / PSS (polystyrene sulfonic acid) sulfuric acid solution having a pH of 2 to 4 is used. The step of preparing the above, the step of applying the mixed solution to the metal substrate, and the step of drying the applied mixed solution are provided.

(Step of preparing SiO ₂ / PEDOT / PSS mixed solution)
In the step of preparing the SiO ₂ / PEDOT / PSS mixed solution, a Si (silicon) / PEDOT (polystyrene dioxythiophene) / PSS (polystyrene sulfonic acid) sulfuric acid solution having a pH of 2 to 4 is used for SiO ₂ / PEDOT. / Prepare the PSS mixture. That is, if SiO ₂ in the SiO ₂ / PEDOT / PSS mixed solution is not mixed with PEDOT / PSS at the molecular level, the SiO ₂ / PEDOT / PSS film after coating and drying is divided into SiO ₂ and PEDOT / PSS. And the contact resistance becomes high. Therefore, as a method for producing a SiO ₂ / PEDOT / PSS mixed solution, it is preferable to synthesize SiO ₂ in a PEDOT / PSS aqueous solution, and a method for mixing SiO ₂ particles with a PEDOT / PSS solution has the above-mentioned points. It is not preferable.

As a reaction for synthesizing SiO ₂ in a PEDOT / PSS aqueous solution, an inexpensive silane compound hydrolysis or dehydration condensation reaction is preferable. As the hydrolysis catalyst, an acid catalyst is suitable, and a base catalyst is unsuitable because acidic PSS aggregates. As the acid catalyst, sulfuric acid having a chemical structure similar to that of the sulfo group of PSS is suitable, and an acid having a structure different from that of the sulfo group is unsuitable because the sulfo group of PSS dissociates into an acidic aqueous solution. Examples of the acid catalyst include sulfuric acid. Moreover, as a silane compound, tetraethoxysilane can be mentioned.

Increasing the sulfuric acid concentration of the Si / PEDOT / PSS sulfuric acid solution lowers the pH, but if the pH is less than 2, the dehydration condensation reaction of silanol becomes difficult to proceed, which is unsuitable. The higher the pH, the easier the dehydration condensation reaction to proceed, but when the pH is higher than 4, it becomes difficult for the dehydration condensation reaction to proceed uniformly in the liquid, and SiO ₂ in the obtained SiO ₂ / PEDOT / PSS mixed liquid is a molecule. It is not suitable because it tends to be in a state where it does not mix with PEDOT / PSS at the level.

In the above, the method of synthesizing SiO ₂ in a PEDOT / PSS aqueous solution has been exemplified, but the solvent can be appropriately selected depending on the type of the conductive polymer and the like, and for example, water, methanol, ethanol, 1 -Propanol, 2-propanol, 1-butanol, 2-butanol, t-butanol, ethylene glycol, propylene glycol, acetone, methyl ethyl ketone, acetonitrile, tetrahydrofuran, dioxane and the like can be mentioned. These solvents may be used alone or in combination of two or more. Above all, it is preferable to use water, alcohol, or a mixed solvent of water and ethanol.

(Process of applying mixed liquid to metal substrate)
The method of applying the mixed solution to the metal substrate 10 is not particularly limited as long as it can uniformly form the metal oxide / conductive polymer composite film 20 with a predetermined film thickness. For example, a method of applying by immersing a metal substrate 10 in a solution (dip coating method), a die coating method, a spin coating method, a roll coating method, a spray coating method, a bar coating method, a gravure coating method, an inkjet method, and a screen. Examples include a printing method and an offset printing method.

(Step to dry the applied mixed liquid)
The applied mixed solution is dried and subjected to curing treatment (heat treatment, ultraviolet treatment, etc.) as necessary to form a metal oxide / conductive polymer composite film 20 to obtain a fuel cell separator 100. be able to. The drying method is not particularly limited, and a normal method can be adopted. When drying, it may be heated or blown with hot air.
In the conductive polymer monomer solution, SiO ₂ particles are synthesized, the mixed solution is applied to the metal substrate 10, and the monomer is polymerized on the metal substrate 10 by heating to a predetermined temperature. It is also possible to synthesize a conductive polymer to form a metal oxide / conductive polymer composite film 20.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

A titanium plate with a metal oxide / conductive polymer composite film (SiO ₂ / PEDOT / PSS film) was prepared as follows, and the contact resistance after the corrosion test was measured.

(Method of manufacturing a titanium plate with SiO ₂ / PEDOT / PSS film)
A titanium thin plate (thickness 0.1 mm) was prepared as a metal plate for film formation.
Ethanol was added to tetraethoxysilane (TEOS) and stirred to prepare a TEOS ethanol solution.
Sodium hydroxide was added to PEDOT / PSS-containing water (SIGMA-ALDORICH, 655201) to adjust the pH to 5, and then the TEOS ethanol solution prepared above was added and stirred. Then, sulfuric acid was added and stirred to prepare a SiO ₂ / PEDOT / PSS mixture.

The above SiO ₂ / PEDOT / PSS mixed solution was applied to a titanium thin plate and dried to prepare a titanium plate (test piece) with a SiO ₂ / PEDOT / PSS film (thickness: 1 μm). A plurality of test specimens were prepared by changing the vol% of SiO ₂ in the SiO ₂ / PEDOT / PSS film and the pH of the Si / PEDOT / PSS solution.

(Corrosion test method)
A corrosion resistance test (constant potential corrosion test) was performed according to the electrochemical high temperature corrosion test method (JIS Z2294) of Japanese Industrial Standards for metal materials. In the air release system device, the test piece was immersed in a sulfuric acid aqueous solution (300 ml, pH 3) whose temperature was adjusted to 80 ° C. by temperature control water. In this state, by electrically connecting the counter electrode made of the platinum plate and the test body (sample electrode), a potential difference of 0.9 V was generated between the counter electrode and the sample electrode, and the test body was corroded. The potential of the test piece was kept constant by the reference electrode. The test time was about 50 hours.

(Measurement method of contact resistance)
A carbon paper (thickness 0.5 mm) corresponding to the diffusion layer of the fuel cell was placed on the test piece subjected to the corrosion test, and the measurement was performed while applying a constant load (1 MPa) with a measuring jig. In this state, adjust the current from the power supply so that the current flowing through the test piece is 1A with an ammeter, measure the voltage applied to the test piece with a voltmeter, and connect the test piece and carbon paper. The contact resistance was calculated. Specifically, each contact resistance ratio was calculated with the contact resistance value of Example (SiO ₂ = 11 vol%, pH = 3) as 1.

The contact resistance ratio after the corrosion test to the SiO ₂ content in the SiO ₂ / PEDOT / PSS film is shown in FIG. 2, and the contact resistance ratio after the corrosion test to the pH of the Si / PEDOT / PSS sulfuric acid solution is shown in FIG. Indicated.

(Evaluation results)
From the results of FIG. 2, it was found that the ratio of contact resistance was 3 or less, which is the target, when the SiO ₂ content was in the range of 8 to 25 vol%.
From the results of FIG. 3, it was found that the ratio of contact resistance was 3 or less, which was the target, when the pH was in the range of 2 to 4.

100 Separator for fuel cell 10 Metal substrate 20 Metal oxide / conductive polymer composite film

Claims (2)

A separator for a fuel cell having a metal oxide / conductive polymer composite film having a metal oxide content of 8 to 25 vol% on the surface of a metal substrate. A step of preparing a SiO ₂ / PEDOT / PSS mixture using a Si (silicon) / PEDOT (polystyrene dioxythiophene) / PSS (polystyrene sulfonic acid) sulfuric acid solution having a pH of 2 to 4, and the mixed solution being made of metal. A method for manufacturing a separator for a fuel cell, comprising a step of applying to a substrate and a step of drying the applied mixed solution.

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