JP2001110431A - Fuel cell electrode - Google Patents

Abstract

(57) [Problem] To provide a fuel cell electrode capable of obtaining higher battery output characteristics with a smaller amount of catalyst. SOLUTION: An electric stone having a self-polarizing property is provided on an electrode catalyst layer composed of an ion conductive material such as a perfluorosulfonic acid polymer, an electron conductive material such as carbon black, and a catalytically active material such as a Pt catalyst. Silicate mineral particles such as tourmaline) are compounded as a radical activator. Instead of tourmaline, inorganic ferroelectric particles such as barium titanate, organic ferroelectric materials such as polyvinylidene fluoride, or magnetic materials such as iron oxide can also be blended.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell electrode, and more particularly, to a technique for improving a catalyst layer of an electrode in contact with a solid polymer electrolyte in a fuel cell such as a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art For example, a polymer electrolyte fuel cell has an electrode-electrolyte junction in which a fuel electrode (anode) is provided on one surface of a polymer solid electrolyte and an air electrode (cathode) is provided on the other surface. The body is the basic structure. And the battery electrode is
Usually, it is configured to include a catalyst layer and a gas diffusion layer, and the catalyst layer is in contact with the electrolyte.

In a fuel cell having such a configuration, the reaction mechanism is such that when a fuel gas (such as hydrogen) is supplied to a fuel electrode and an oxidizing gas (such as air) is supplied to an air electrode, the fuel electrode reacts. The generated hydrogen ions move to the air electrode via the electrolyte and are converted into water (H ₂ O) at the air electrode to take out electric energy by utilizing an electrochemical reaction.

In such a case, the electrode reaction of the fuel cell proceeds on the electrode catalyst. For example, in the case of a hydrogen-oxygen fuel cell, the positive electrode) 1/2 O ₂ + 2H ⁺ + 2e ⁻ → H ² O negative electrode) H _As is clear from the formula ₂ → 2H ⁺ + 2e ^−, it is necessary to supply and transfer electrons and ions in addition to reactants such as hydrogen and oxygen.

In such a reaction mechanism, in order to smoothly perform an electrode reaction, a conventionally generally known electrode catalyst layer of a fuel cell includes, for example,
A carbon material such as carbon black is used as an electron conductive catalyst carrier, and a material having a catalytically active material such as Pt supported thereon is mixed with an ion conductive material such as a solid polymer electrolyte. Polytetrafluoroethylene (PTF
In some cases, a binder such as E) is blended.

[0006]

However, according to such an electrode catalyst layer having a generally known structure,
Unless the amount of the catalytically active substance such as t, that is, the amount of the catalyst, is increased, a sufficient battery output cannot be obtained. And since the expensive noble metal such as Pt is generally used as the catalyst metal, there is a problem that the material cost is increased accordingly.

The inventors of the present invention have made various studies and found that the fuel gas supplied to the fuel electrode is activated to form a proton conduction path in cooperation with an ion-conductive substance, They have come to think that it is effective to mix a substance that can form an electron conduction path in cooperation with the substance.

[0008] An object of the present invention is to provide a fuel cell electrode capable of obtaining higher cell output characteristics with a small amount of catalyst. This aims to increase the output of the battery and reduce the cost of the electrode material.

[0009]

In order to solve this problem, a fuel cell electrode according to the present invention has the following features.
The gist is that an electrode catalyst layer composed of an ion conductive substance, an electron conductive substance, and a catalytically active substance is blended with a radical activating substance for promoting radical activation of fuel supplied to the battery.

In this case, as the ion conductive substance,
A suitable polymer is a solid electrolyte material, for example, a perfluorosulfonic acid polymer, or an ion exchange resin such as a styrenedivinylbenzenesulfonic acid polymer.

The electron conductive substance is preferably carbon powder (particles), and the catalytically active substance is selected from noble metals such as Pt, Pd, Ru, Os, Ir, Rh, and Au. One or more mixed catalysts mentioned above are suitable.

[0012] As the "radical activating substance",
4. Particles of a silicate mineral having a self-polarizing property according to claim 3, for example, particles of a substance such as tourmaline (tourmaline) having a particle size of about 0.1 to 10 μm. Are preferred. Tourmaline (tourmaline) is polarized positively and negatively by an external action such as heat and pressure under a battery reaction, and positively ionizes a fuel gas (eg, hydrogen gas) supplied to a fuel electrode.

Since tourmaline has a positive pole and a negative pole due to self-polarization, it has ionic (proton) conductivity and electron conductivity, and H ⁺ ( (Proton) cooperates with an ion conductive material such as a perfluorosulfonic acid polymer to facilitate movement to the air electrode, and converts electrons (e ⁻ ) generated in the electrode catalyst layer into an electron conductive material such as carbon particles. In cooperation with this also makes it easier to move to the air electrode via the electric circuit. Therefore, the battery reaction is promoted even with a small amount of the catalyst, and a high battery output is obtained.

[0014] In addition, as a "radical activating substance"
Is an inorganic ferroelectric substance (for example,
For example, barium titanate TiBa₂O₃) Particles or
Is an organic ferroelectric polymer material according to claim 5.
(For example, polyvinylidene fluoride) in the electrode catalyst layer
It is also effective to do so. Attraction like barium titanate
Dielectric substances generate electricity by heat and pressure during battery reaction.
Promotes ionization of fuel gas
It has the same electron conductivity as carbon particles as a substance
To form an electron conduction path, and the electrode catalyst layer
Generated electrons (e ⁻) To enhance mobility.

Further, since a ferroelectric polymer material such as polyvinylidene fluoride also has ferroelectricity, electricity is generated by heat and pressure during a battery reaction, and ionization of a fuel gas is promoted. Since it also has ion conductivity like a perfluorosulfonic acid polymer, it forms an ion conduction path and generates protons (H
⁺ ) Works to increase the mobility.

In addition, it is also effective to incorporate particles of a magnetic substance (for example, iron ferrite FeO.Fe ₂ O ₃ ) into the electrode catalyst layer. This magnetic substance generates magnetic force due to heat during battery reaction, etc.
Functions such as easy ionization of the fuel gas occur.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. First, FIG. 1 shows a configuration of a polymer electrolyte fuel cell according to one embodiment of the present invention. The polymer electrolyte fuel cell 10 has a fuel electrode 14 provided on one surface with a polymer electrolyte 12 interposed therebetween, and an air electrode 16 provided on the other surface. Current collectors (separators) 18a and 18b are disposed on the fuel electrode 14 side and the air electrode 16 side, respectively.
A fuel gas flow path 20 through which a fuel gas such as hydrogen gas flows is formed on the fuel electrode 14 side, and an oxidizing gas flow path 22 through which an oxidizing gas such as air flows through is formed on the air electrode 16 side. ing. The fuel cells 10 are assembled in a stacked configuration and used as a stacked fuel cell.

In this case, the polymer electrolyte 12 may be an ion exchange resin of a perfluorosulfonic acid polymer known under the trade name of Nafion (registered trademark, manufactured by DuPont) or a styrenedivinylbenzenesulfonic acid polymer. Is used. The thickness of the film is preferably in the range of 100 to 200 μm.

As shown in the enlarged view of FIG. 2, the fuel electrode 14 and the air electrode 16 are provided with catalyst layers 14a, 16a on the contact surface side with the electrolyte 12, and have the spacers 18a, 1a.
Gas diffusion layers 14b and 16b are provided on the contact surface side with 8b. The catalyst layers 14a and 14b are both made of platinum (P
This is a layer in which an electrode catalyst such as t) is supported on carbon particles, and the gas diffusion layers 16a and 16b are made of a porous material. For example, a material that can achieve both the diffusivity of a substance such as a reaction gas, a generated gas, and water and the conductivity of electrons, specifically, carbon paper, carbon cloth, or carbon powder is made of polytetrafluoroethylene. For example, a porous carbon-based material having air permeability and a uniform pore distribution, such as a sheet-shaped material formed together with a polymer binder such as this, is used. Further, as the current collector (separator), dense graphite having high current collecting performance and stable even in an oxidized steam atmosphere is generally used.

An embodiment of the present invention will be specifically described below. <Example 1> 20 mg of a Pt-supported carbon powder in which Pt was supported on a well-dried carbon black fine powder at a weight ratio of 20%, and Nafion, a perfluorosulfonic acid polymer ion-exchange resin (trade name, DuPont alcohol solution (polymer content 10%) with polymer content 40
mg, tourmaline powder 20 mg each was weighed out and mixed well to form a paste. The particle size of tourmaline (tourmaline) powder is about 0.1 to 10 μm. Then, the paste was uniformly applied to the surface of a gas diffusion layer made of carbon cloth having a size of 10 cm × 10 cm and air-dried. Two electrodes were produced by this method, and were bonded to the front and back surfaces of 112 film (dry thickness: 50 μm) of Nafion (same as above) by hot pressing. A fuel cell was formed using the electrode-electrolyte assembly produced in this manner.
And using the fuel cell manufactured in this way,
Air was supplied to the positive electrode and pure hydrogen was supplied to the negative electrode at 2 ata, respectively, and the relationship between discharge current and voltage was examined.

<Comparative Example> A Pt-supported carbon powder in Example 1 was tripled to 60 mg, and a catalyst layer was prepared without blending tourmaline to form a fuel cell. In this fuel cell, air was supplied to the positive electrode and pure hydrogen was supplied to the negative electrode at 2 ata, and the relationship between discharge current and voltage was examined.

FIG. 3 shows Example 1 (mixed tourmaline powder),
FIG. 9 shows a relationship between a discharge current and a voltage when a charge / discharge test was performed on each fuel cell using an electrode catalyst of a comparative example (no tourmaline, Pt-supported carbon powder three times). The horizontal axis represents current density (A / cm ² ), and the vertical axis represents voltage (V).

As shown in FIG. 3, when the first embodiment is compared with the comparative example, the first embodiment is more effective than the comparative example.
It shows a high voltage value in the entire measured current density range (0 to 1.0 A / cm ² ), which indicates that the use of the electrode of Example 1 can provide a higher battery output than the conventional comparative example, It was revealed that the battery had excellent battery characteristics. From this, it is effective to mix tourmaline in the electrode catalyst layer to improve the battery characteristics.
It has also been found that this contributes to a reduction in the amount of Pt catalyst.

FIG. 4 shows the relationship between the amount of tourmaline and the open circuit voltage. The horizontal axis indicates the amount of tourmaline (wt%), and the vertical axis indicates the open circuit voltage (V).
Has been adopted. As is apparent from FIG. 4, it was also found that the blending amount of tourmaline exhibited the highest open circuit voltage per 25 wt%, and the blending amount of tourmaline was appropriate in the range of 15 to 30 wt%.

Example 2 20 mg of a Pt-supported carbon powder in which Pt was supported on a fine powder of carbon black at a weight ratio of 20%, and Nafion which is an ion exchange resin of perfluorosulfonic acid polymer (trade name, DuPont alcohol solution (polymer content 10%) with polymer content 40
Each of 20 mg of barium titanate powder was weighed out and mixed well to form a paste. Then, the paste was uniformly applied to the surface of a gas diffusion layer made of carbon cloth having a size of 10 cm × 10 cm and air-dried. In this method, two electrodes were prepared, and 11 electrodes of Nafion (same as above) were used.
The two films (dry thickness: 50 μm) were joined to the front and back surfaces by hot pressing. A fuel cell was formed using the electrode-electrolyte assembly produced in this manner. Then, as in the case of Example 1, air was applied to the positive electrode and pure hydrogen was applied to the negative electrode at 2 atm.
a, and examined the relationship between the discharge current and the voltage.

FIG. 5 shows a charge / discharge test for each fuel cell using the electrode catalysts of Example 2 (containing barium titanate powder) and Comparative Example (without barium titanate, 3 times the amount of Pt-supported carbon powder). 3 shows the relationship between the discharge current and the voltage when performing the above.

As shown in FIG. 5, when Example 2 is compared with Comparative Example, Example 2 is more effective than Comparative Example.
It shows a high voltage value in the entire measured current density range (0 to 1.0 A / cm ² ), which indicates that the use of the electrode of Example 2 can provide a higher battery output than the conventional comparative example, It was revealed that the battery had excellent battery characteristics. From this, it is also clear that blending a powder of a ferroelectric substance such as barium titanate in the electrode catalyst layer is effective for improving the battery characteristics, and contributes to reducing the amount of Pt catalyst. Was.

FIG. 6 shows the relationship between the amount of barium titanate and the open circuit voltage. As is clear from FIG. 6, the compounding amount of barium titanate is 25 watts.
The highest open circuit voltage was shown per t%, and it was also found that a suitable amount of barium titanate was in the range of 15 to 30 wt%. BaO, TiO ₂ , PbTiO are used as dielectric substances having the same function as barium titanate.
_{3, Bi 4 Ti 3 O 1} 2, BaMgF 4, PbZr X T
i _1-X O _{3 and the} like.

Example 3 20 mg of a Pt-supported carbon powder in which Pt was supported on a fine powder of carbon black at a weight ratio of 20%, and Nafion, a perfluorosulfonic acid polymer ion-exchange resin (trade name, DuPont alcohol solution (polymer content 10%) with polymer content 40
20 mg of polyvinylidene fluoride powder was weighed out and mixed well to form a paste. Then, the paste was uniformly applied to the surface of a gas diffusion layer made of carbon cloth having a size of 10 cm × 10 cm and air-dried.
Two electrodes were produced by this method, and were bonded to the front and back surfaces of 112 film (dry thickness: 50 μm) of Nafion (same as above) by hot pressing. A fuel cell was formed using the electrode-electrolyte assembly produced in this manner. Then, air was supplied to the positive electrode and pure hydrogen was supplied to the negative electrode at 2 ata, respectively, and the relationship between discharge current and voltage was examined.

FIG. 7 shows Example 3 (with polyvinylidene fluoride powder) and Comparative Example (without polyvinylidene fluoride, P
3 shows a relationship between a discharge current and a voltage when a charge / discharge test was performed on each fuel cell using an electrode catalyst of 3 times the amount of t-supported carbon powder).

As shown in FIG. 7, when Example 3 is compared with Comparative Example, Example 3 is more effective than Comparative Example.
It shows a high voltage value in the entire measured current density range (0 to 1.0 A / cm ² ), which indicates that the use of the electrode of Example 3 can provide a higher battery output than the conventional comparative example, It was revealed that the battery had excellent battery characteristics. From this fact, it is also clear that blending a powder of a ferroelectric polymer such as polyvinylidene fluoride in the electrode catalyst layer is effective for improving the battery characteristics and contributes to reducing the amount of Pt catalyst. It became.

FIG. 8 shows the relationship between the blending amount of polyvinylidene fluoride and the open circuit voltage. As is clear from FIG. 8, the blending amount of polyvinylidene fluoride shows the highest open circuit voltage per 25 wt%, and it is also found that the blending amount of polyvinylidene fluoride is within a range of 15 to 30 wt%. .

Example 4 20 mg of a Pt-supported carbon powder in which Pt was supported on a fine powder of carbon black at a weight ratio of 20%, and Nafion, a perfluorosulfonic acid polymer ion-exchange resin (trade name, DuPont alcohol solution (polymer content 10%) with polymer content 40
mg of iron ferrite (FeO.Fe ₂
20 mg of O ₃ ) powder was weighed out and mixed well to form a paste. And this paste is 10cm × 10
The liquid was uniformly applied to the surface of a carbon cloth gas diffusion layer having a size of cm and dried naturally. Two electrodes were prepared by this method, and 112 films of Nafion (same as above) (dry thickness: 50 μm)
m) was joined to the front and back surfaces by hot pressing. A fuel cell was formed using the electrode-electrolyte assembly produced in this manner. Then, air was supplied to the positive electrode and pure hydrogen was supplied to the negative electrode at 2 ata, respectively, and the relationship between discharge current and voltage was examined.

FIG. 9 shows Example 4 (containing iron ferrite powder) and Comparative Example (without iron ferrite, Pt-supported carbon powder 3).
2 shows the relationship between the discharge current and the voltage when a charge / discharge test was performed for each fuel cell using an electrode catalyst of (double amount).

As shown in FIG. 9, when Example 4 is compared with Comparative Example, Example 4 is more effective than Comparative Example.
It shows a high voltage value in the entire measured current density range (0 to 1.0 A / cm ² ), which indicates that the use of the electrode of Example 4 can provide a higher battery output than the conventional comparative example, It was revealed that the battery had excellent battery characteristics. From this fact, it was also clarified that blending a powder of a ferromagnetic substance such as iron ferrite into the electrode catalyst layer was effective for improving the battery characteristics and contributed to reducing the amount of Pt catalyst. .

FIG. 10 shows the relationship between the amount of iron ferrite and the open circuit voltage. As is clear from FIG. 10, the content of iron ferrite was 25 wt%.
The highest open circuit voltage was shown per unit, and it was also found that the proper amount of iron ferrite was in the range of 15 to 30 wt%.

The present invention is not limited to the above-described embodiment at all, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, Nafion (registered trademark, DuPont) is used as the solid polymer electrolyte.
The same material was used for the ion conductive material of the electrode catalyst layer, but the material is not limited to this material, and a polystyrene-based polymer solid electrolyte may be used or the ion conductive material of the electrode catalyst layer may be used. The conductive substance may be changed as appropriate, such as using a polystyrene-based conductive substance.
Further, the catalytically active substance is not limited to Pt in each of the above-described embodiments, and the use of other noble metals such as Pd, Ru, Os, Ir, Ru, and Au can reduce the amount of the catalyst. It can be inferred.

As the "radical activating substance" applied to the present invention, tourmaline (the tourmaline), barium titanate, polyvinylidene fluoride,
Not only iron ferrite but also various kinds of inorganic ferroelectric substances or organic ferroelectric polymer substances are applicable as long as they are polar substances having a positive pole and a negative pole due to self-polarization. In addition, various magnetic substances such as cobalt-based and nickel-based materials can be similarly applied.

[0039]

According to the fuel cell electrode of the present invention, a polar activating substance such as tourmaline or a ferroelectric substance or a radical activating substance such as a magnetic substance is blended in the electrode catalyst layer. Radicalization of fuel (hydrogen gas, etc.) supplied to the battery is promoted, so high battery output can be obtained, and the amount of catalyst can be reduced accordingly, contributing to lower material costs. It is.

Therefore, if the present invention is applied to a fuel cell mounted on a vehicle, not only can high electric output be continuously exhibited, but also the cost of the battery can be reduced by reducing the amount of expensive catalyst. Economic benefits are great.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a polymer electrolyte fuel cell according to one embodiment of the present invention.

FIG. 2 is a sectional structural view of an electrode (fuel electrode, air electrode) of the fuel cell shown in FIG.

FIG. 3 is a diagram showing a difference in discharge current-voltage characteristics of a fuel cell in comparison between the electrode catalyst of Example 1 and an electrode catalyst of a comparative example.

FIG. 4 is a diagram showing the relationship between the amount of tourmaline in the electrode catalyst of Example 1 and the open circuit voltage.

FIG. 5 is a diagram showing a difference in discharge current-voltage characteristics of a fuel cell in comparison between the electrode catalyst of Example 2 and the electrode catalyst of Comparative Example.

FIG. 6 is a diagram showing the relationship between the blending amount of barium titanate and the open circuit voltage in the electrode catalyst of Example 2.

FIG. 7 is a diagram showing a difference in discharge current-voltage characteristics of a fuel cell in comparison between an electrode catalyst of Example 3 and an electrode catalyst of a comparative example.

FIG. 8 is a diagram showing the relationship between the blending amount of polyvinylidene fluoride and the open circuit voltage in the electrode catalyst of Example 3.

FIG. 9 is a diagram showing a difference in discharge current-voltage characteristics of a fuel cell in a comparison between the electrode catalyst of Example 4 and the electrode catalyst of Comparative Example.

FIG. 10 is a diagram showing the relationship between the compounding amount of iron ferrite and the open circuit voltage in the electrode catalyst of Example 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Fuel cell 12 Polymer electrolyte 14 Fuel electrode 14a Catalyst layer 16 Air electrode 16a Catalyst layer

Continued on the front page F term (reference) 5H018 AA06 AS01 BB01 BB03 BB06 BB08 BB12 DD06 DD08 EE03 EE08 EE13 EE18 5H026 AA06 CC03 CX05 EE02 EE05 EE18

Claims (6)

[Claims] 1. A radical activating substance for promoting radical activation of fuel supplied to a battery is blended in an electrode catalyst layer comprising an ion conductive substance, an electron conductive substance and a catalytically active substance. Fuel cell electrode. 2. The method according to claim 1, wherein the ion conductive substance is a solid polymer electrolyte material, the electron conductive substance is carbon powder, and the catalytically active substance is fine particles containing at least one kind of noble metal. 2. The fuel cell electrode according to item 1. 3. The fuel cell electrode according to claim 1, wherein the radical activating substance is particles of a silicate mineral having a self-polarizing property. 4. The fuel cell electrode according to claim 1, wherein the radical activating substance is a particle of a ferroelectric substance. 5. The fuel cell electrode according to claim 1, wherein the radical activating substance is a ferroelectric polymer substance. 6. The fuel cell electrode according to claim 1, wherein the radical activating substance is a particle of a magnetic substance.