JP2003282078A - Catalyst particle and manufacturing method of the same, gaseous-diffusion property electrode body, and electrochemical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide catalyst particles by which a reaction in an electrode is raised certainly, a manufacturing method of the same, a gas diffusion electrode, and an electrochemical device. <P>SOLUTION: A platinum nano-particle 1 consists of a platinum particle 2 as a catalyst particle, a conductive polymer layer 18 which consists of polyaniline formed by a polymerization reaction in a water type medium on the surface of the platinum particle 2, and further a water soluble polymer protective layer 19 which consists of polyvinylpyrrolidone, and the gas permeable catalyst electrode 10 is constituted by arranging the platinum nano-particles 1 between a collector body 11 and an ionic-conduction section 5. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to, for example, catalyst particles suitable for manufacturing a fuel cell, a method for manufacturing the same, a gas diffusing electrode body, and an electrochemical device.

[0002]

2. Description of the Related Art In recent years, the need for an alternative clean energy source that can replace fossil fuels such as petroleum has been emphasized, and, for example, hydrogen (gas) fuel is drawing attention.

Hydrogen has a large amount of chemical energy contained per unit mass, and because it does not emit harmful substances or global warming gas when used, it is ideal for being clean and almost inexhaustible. It can be said to be an energy source.

In recent years, in particular, fuel cells capable of extracting electric energy from hydrogen energy have been actively developed, and large-scale power generation to on-site private power generation, and further, a power source for electric vehicles. It is expected that it will be applied as such.

In this fuel cell, a fuel electrode (for example, a hydrogen electrode) and an oxygen electrode are arranged with a proton conductor membrane interposed, and fuel (hydrogen) and oxygen are supplied to these electrodes, respectively. In this process, a proton conductor membrane, a fuel electrode (for example, hydrogen electrode), an oxygen electrode, etc. are molded separately, and they are bonded together. is doing.

Conventionally, in order to obtain good characteristics of a hydrogen electrode or an oxygen electrode including a composite electrode of a solid polymer electrolyte and a catalyst in a water electrolysis cell and a fuel cell, it is necessary to have a wide electrode and an electrolyte interface. And that the supply of the active material to the electrolyte interface and the discharge of the product are smooth, the ionic conductivity to the electrode and the electrolyte interface, especially the proton conductivity is good, and the electron conductivity to the electrode and the electrolyte interface is It is required to be good.

In particular, good ionic conductivity to the electrode / electrolyte interface, particularly good proton conductivity, and good electron conductivity to the electrode / electrolyte interface are
This is a very important item that greatly contributes to increase and decrease in internal resistance in the electrolytic cell and the fuel cell. That is, if the proton conductivity, the electron conductivity, and the like are poor, for example, in a fuel cell, the energy conversion efficiency is lowered, such as the output is lowered.

[0008]

The formation of continuous solid electrolyte channels (electrolyte channels) in the electrode is essential for good proton conductivity, and the continuous catalyst in the electrode is necessary for good electron conductivity. The formation of particle passages (electron conduction channels) is an essential condition.

On the other hand, as shown in FIG. 11, in the case of the electrode type consisting only of the solid polymer electrolyte 61 and the catalyst particles 52, high proton conductivity is actually obtained,
Electronic conductivity is low. This is because formation of continuous catalyst particle passages (electron conduction channels) is hindered.

On the other hand, as shown in FIG. 12, in the case of an electrode type in which Teflon (registered trademark) (PTFE manufactured by DuPont) particles 63 are added to a solid polymer electrolyte 61 and catalyst particles 53, a binder is used. The diameter of the functional Teflon (registered trademark) (PTFE) particles 63 is often larger than the diameter of the catalyst particles 53, and the Teflon particles 63 occupy a large volume in the electrode. It becomes unfilled and the absolute number of electron conduction channels is insufficient.

Therefore, as shown in FIG. 13 and FIG. 14 which is a partial detailed sectional view of FIG. 13, a composite electrode generally composed of a solid polymer electrolyte 61 and catalyst particles 53 is provided with an ion exchange membrane (proton conductor) 55 and When it is used as a catalyst electrode assembly and used in a water electrolysis tank or a fuel cell, a dense and porous conductive fiber 62 such as sintered titanium or baked carbon is used as a power supply (current collector).

Now, in this catalyst electrode assembly, a high electron-conductivity is exhibited, and a macroscopic electron conduction channel can be formed by the penetration of the conductive fiber 62 into the electrode.

However, it is preferable that the ion exchange membrane (proton conductor) 55 and the ion exchange membrane (proton conductor) 55 constituting the catalyst electrode assembly are as thin as possible. When the body (current collector) is used, the conductive fiber 62 penetrates the electrode and further the ion exchange membrane (proton conductor membrane) 55 and penetrates to the counter electrode, often causing pinholes. When the resistance value in the electrode was measured, the specific resistance was 4.5 × 10 ⁴ Ω · cm, and the electron conductivity was insufficient.

Next, as shown in FIG. 15, instead of these, a platinum-based P having hydrogen storage capacity and a slight electron conductivity is formed on the ion conduction part (proton conductor film) 55.
An electrode matrix (pores 6) containing a d (palladium) network 65, catalyst particles 53, and a solid polymer electrolyte 61.
(Including 0) is subjected to electroless plating to support platinum, which is an electron conductive substance, on the electrode base material to form the platinum layer 6
Although there is a method of providing No. 4, it was very difficult to sufficiently deposit platinum even inside the electrode having a complicated structure to secure conductivity (formation of electron conduction channel).

The present invention has been made in view of the above-mentioned conventional circumstances, and its object is to provide catalyst particles capable of surely improving the reaction in the electrode, a method for producing the same, and a catalyst therefor. The object is to provide a gas diffusion electrode using particles and an electrochemical device.

[0016]

That is, the present invention relates to catalyst particles composed of a granular catalyst material and a conductive polymer material formed on the surface of the granular catalyst material.

The present invention also provides a step of preparing a first dispersion liquid of a compound which becomes a granular catalyst material, a step of carrying out a reaction for decomposing the compound, a granular catalyst material produced thereby, and a conductive polymer. It has a step of preparing a second dispersion liquid containing a constituent monomer of the substance, and a step of producing the conductive polymer substance covering the granular catalyst substance by a polymerization reaction in the dispersion liquid. The present invention relates to a method for producing catalyst particles.

The present invention also relates to a gas diffusible electrode body comprising catalyst particles comprising a granular catalyst substance and a conductive polymer substance formed on the surface of the granular catalyst substance.

The present invention also comprises a first electrode, a second electrode, and an ionic conductor sandwiched between the two electrodes, and a granular catalyst material and a conductive material formed on the surface of the granular material. A catalyst particle composed of a polymer substance relates to an electrochemical device constituting at least the first pole of the first pole and the second pole.

According to the present invention, since the granular catalyst substance is the catalyst particles coated with the conductive polymer substance, the effective surface area of contact between the catalyst substance and the reaction gas is increased to improve the catalytic reaction, and The electron conductivity of the catalyst particles themselves becomes good, and the electrode reaction can be improved. In addition, since the conductive polymer substance is formed on the surface of the granular catalyst substance, the polymer substance improves the shape retention of the catalyst particles, and the catalyst particles aggregate to form a chain structure. This facilitates the maintenance of the catalyst layer, the catalytic reaction and the electron conductivity within the electrode.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, it is preferable that the conductive polymer substance is also provided with proton conductivity.

For this proton conductivity, it is preferable that the conductive polymer substance is provided with proton conductivity by introducing a proton dissociative group or substance. In this case, the proton dissociative group or substance is -OH,-.
OSO ₃ H, -SO ₃ H, -COOH, -OPO (OH)
_It is preferably selected from the group consisting of Brensted acids such as ₂ , HCl and H ₂ SO ₄ .

It is preferred that the conductive polymeric material, eg polyaniline, is further coated with a polymeric protective layer, eg polyvinylpyrrolidone.

In order to increase the contact area with the working gas, the size of the catalyst particles is preferably 0.1 to 1000 nm, and the granular catalyst material is platinum powder or granules. desirable.

It is preferable that the polymer protective layer is made of polyvinylpyrrolidone because the coating property of the conductive polymer substance on the granular catalyst substance is improved and at the same time the catalyst particles are aggregated to form a chain structure.

In the production method of the present invention, it is preferable to use an aqueous dispersion as the first and second dispersions.

It is preferable to add a substance for imparting proton conductivity to the second dispersion liquid containing the constituent monomer of the conductive polymer substance.

It is preferable to introduce a proton dissociative group into the constituent monomer of the conductive polymer substance in order to impart proton conductivity.

It is preferable to add a polymer substance for forming a protective layer of the conductive polymer substance to the first dispersion liquid of the catalyst substance.

In order to ensure and facilitate the formation of catalyst particles, in the second dispersion containing the catalyst material, after forming the particulate catalyst material covered with a protective layer of the polymer material. It is preferable to carry out the polymerization reaction to produce the catalyst particles in which the particulate catalytic material is covered with the conductive polymeric material and the conductive polymeric material is covered with a protective layer of the polymeric material.

In the electrochemical device of the present invention, at least one of the first electrode and the second electrode is preferably a gas electrode, and is preferably constructed as a fuel cell.

Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

The platinum nanoparticles 1 according to the present embodiment are, as shown in FIG. 1, platinum particles (catalyst) 2 serving as cores.
And a conductive polymer layer 18 that covers the platinum particles (catalyst) 2, and a water-soluble polymer protective layer 19 that covers the conductive polymer layer 18.

Polyaniline (PANI) may be used for the conductive polymer layer 18, and polyvinylpyrrolidone (PVP) may be used for the polymer protective layer 19.

The size of the platinum nanoparticles 1 is 0.1 to 1000 nm, for example 4 nm on average. If it is smaller than this, it is difficult to prepare it and it becomes difficult to disperse it. If it is too large, the total surface area of the catalyst becomes small.

The platinum particles (catalyst) 2 include particles of various shapes such as granular, spherical and fibrous shapes, and the same applies hereinafter.

Next, by introducing a proton dissociative group or substance, the conductive polymer layer (PANI) 18 is provided with proton conductivity to promote proton conductivity. Is -OH, -OSO
_{3 H, -SO 3 H, -COOH} , -OPO (OH) 2, H
It is selected from the group consisting of Bronsted's acid such as Cl and H ₂ SO ₄ .

Ponialinin (PANI) when -SO ₃ H is used as the proton-dissociative group or substance
The molecular structure of is shown in (1) of FIG. 4, the molecular structure of polyaniline (PANI) when using HCl is shown in (2) of FIG. 4, and the molecular structure of polyvinylpyrrolidone (PVP) is shown in FIG. 3).

The term "proton dissociative group" means --O.
_{H, -OSO 3 H, -SO 3} H, -COOH, -OPO
(OH) ₂ etc. means a functional group capable of releasing a proton by ionization, and “proton (H ⁺ ) dissociation” means
This means that a proton is separated from a functional group by ionization. Then, in this proton conductor, protons (H ⁺ ) move through the proton dissociative group, and thereby ion conductivity is exhibited.

By the way, as shown in FIG. 2, the platinum nanoparticles 1 aggregate in the gas diffusible electrode 10 to form a chain structure. Here, the gas diffusible electrode is
This refers to an electrode having continuous pores 20 capable of diffusing a working gas, which further has electronic conductivity (hereinafter the same).

The gas diffusible electrode 10 contains platinum nanoparticles 1 in an amount of 1 to 80% by weight, preferably 2%.
It is considered that the content of 0 to 70% by weight is good for active cell reaction.

Next, with reference to FIG. 3, a method for producing platinum nanoparticles as catalyst particles will be described.

This production method comprises the steps of preparing a first dispersion liquid containing a compound (precursor) which becomes platinum particles and a water-soluble polymer substance (polyvinylpyrrolidone), and a step of carrying out a reaction for decomposing this compound. And a step of preparing a second dispersion liquid containing platinum particles produced thereby and aniline which is a constituent monomer of the conductive polymer substance (polyaniline), and a polymerization reaction in the dispersion liquid. A process in which a water-insoluble conductive polymer substance (polyaniline) enters between the platinum particles and the water-soluble polymer protective layer (polyvinylpyrrolidone) to form a conductive polymer substance (polyaniline) that coats the platinum particles. Consists of.

An aqueous dispersion is used as the first dispersion liquid of the compound which becomes the platinum particles, and a water-soluble polymer substance (polyvinylpyrrolidone) which becomes a protective layer of the conductive polymer substance (polyaniline) is added thereto. Added.

In the second dispersion liquid containing the constituent monomer (aniline) of the conductive polymer substance (polyaniline), a substance imparting proton conductivity (eg HCl or H ₂ S) is added.
O ₄ ) is added, or a proton-dissociative group is introduced into polyaniline in advance for imparting proton conductivity.

In summary of the above steps, platinum particles (catalyst) covered with a protective layer of a water-soluble polymeric material (polyvinylpyrrolidone) are produced from the first dispersion and then the platinum particles (catalyst) are contained. Polymerization reaction is performed in the second dispersion liquid, the platinum particles (catalyst) are covered with the conductive polymer substance (polyaniline), and the conductive polymer substance (polyaniline) is converted into the water-soluble polymer substance (polyvinylpyrrolidone). Generates catalyst particles (platinum nanoparticles) covered with a protective layer.

Next, in the negative electrode (fuel cell), positive electrode (oxygen electrode), etc. formed by the gas diffusible electrode containing the platinum nanoparticles, the gas diffusible electrode is formed by spin coating or the like. Since it is formed directly on the current collector (carbon sheet), the mechanical strength required for damage during work is not required,
Therefore, the thickness is 10 μm or less, for example, 2 to 4 μm.
It can be set to be extremely thin, about m.

Next, as the material of the proton conductor used in the fuel cell in the present embodiment, for example, perfluorosulfonic acid resin (for example, manufactured by DuPont, trade name Nafion (R)) is used. Polymer materials with proton (hydrogen ion) conductivity, or polymolybdic acids and oxides with many hydration properties such as H ₃ Mo ₁₂ PO ₄₀ / 29H ₂ O and Sb ₂ O ₅ / 5.4H ₂ O Etc., or various carbonaceous materials including fullerenes, in which a proton dissociative group is introduced, or a compound mainly containing silicon oxide and Bronsted acid, and a polymer having a sulfone group in the side chain. The mixture and the like are preferably used, but these materials are not particularly limited.

Further, in the present embodiment, it can be used in the gas-diffusible electrode or in the ion-conducting portion sandwiched between the first electrode and the second electrode constituting the electrochemical device. Examples of the ionic conductor include fullerene derivatives such as fullerenol (polyhydroxylated fullerene) in addition to general Nafion (perfluorosulfonic acid resin manufactured by DuPont).

In particular, as shown in FIG. 9, fullerene (Fullelenol) having a structure in which a plurality of hydroxyl groups are added to a fullerene molecule is used.
renol) was first reported as a synthetic example by Chiang et al. in 1992 (Chiang, LY; Swirczewski, JW; Hsu, C.
S.; Chowdhury, SK; Cameron, S.; Creegan, K., J.Chem.So
c, Chem. Commun. 1992, 1791).

Applicants have identified such a fullerenol in FIG.
As shown in 0 (A), the aggregates were macroscopically prepared by causing an interaction between the hydroxyl groups of the fullerenol molecules (in the figure, ○ represent fullerene molecules) in close proximity to each other. It was for the first time able to find out that such an aggregate exhibits high proton conductivity characteristics (in other words, dissociation of H ⁺ from the phenolic hydroxyl group of the fullerenol molecule).

In the present embodiment, the above-mentioned Frarenault is used.
Other than, for example, a plurality of -OSO ₃Fuller with H group
Ren agglomerates can also be used as ion conductors.
It OH group is OSO₃Fig. 10 (B) replacing the H group
Polyhydroxylated fullerene, that is, hydrogen sulfate
Sterilized fullerenol was also reported by Chiang et al.
Reported in 1994 (Chiang.L.Y.; Wang, L.Y.; Swir
czewski, J.W .; Soled, S .; Cameron, S., J.Org.Chem.199
4,59,3960). And fuller sulfated
Ren has OSO in one molecule₃Also contains only H groups
There is also a
It is possible to have a number.

When a large number of the above-mentioned fullerenol and hydrogen sulfate esterified fullerenol are aggregated, the proton conductivity exhibited as a bulk is that the protons derived from a large amount of hydroxyl groups or OSO ₃ H groups originally contained in the molecule. Since it is directly involved in movement, it is not necessary to take in hydrogen and protons originating from water vapor molecules etc. from the atmosphere, and it is not necessary to replenish moisture from the outside, especially to absorb moisture from the outside air. Absent. Therefore, it can be continuously used even in a dry atmosphere.

The fullerene, which is the base material for these molecules, has a particularly electrophilic property, which means that not only the highly acidic OSO ₃ H group but also the hydroxyl group and the like can dissociate hydrogen ions. It is considered that it contributes greatly to the promotion and shows excellent proton conductivity. In addition, since a large number of hydroxyl groups and OSO ₃ H groups can be introduced into one fullerene molecule, the number density of protons involved in conduction per unit volume of the conductor becomes very large. It develops effective conductivity.

Most of the above fullerenol and hydrogen sulfate esterified fullerenol are composed of carbon atoms of fullerenes, so that they are light in weight and difficult to be deteriorated.
It also contains no pollutants. Furthermore, the manufacturing cost of fullerenes is also rapidly decreasing. Therefore,
Environmentally and economically, fullerene is considered to be a carbonaceous material closer to the ideal than any other material.

Further, the fullerene molecule may be, for example, the above-mentioned
OH, -COOH in addition to _{-OSO 3 H, -SO 3 H,} -O
Those having any of PO (OH) ₂ can also be used.

In order to synthesize the above-mentioned fullerenol which can be used in the present embodiment, the fullerene molecule powder is subjected to appropriate combination with known treatments such as acid treatment and hydrolysis. The desired groups can be introduced at the constituent carbon atoms of the molecule.

Here, when the above fullerene derivative is used as the ionic conductor forming the above ionic conduction part,
It is preferable that the ionic conductor substantially consists of the fullerene derivative or is bound by a binder.

The gas diffusive electrode of this embodiment can be suitably used for various electrochemical devices. That is, in a basic structure consisting of a first pole, a second pole, and an ionic conductor sandwiched between these two poles, at least the first pole of the first pole and the second pole, The gas diffusion electrode of the present embodiment described above can be applied.

Specifically, the gas diffusion electrode of the present embodiment can be preferably applied to an electrochemical device in which at least one of the first electrode and the second electrode is a gas electrode.

Hereinafter, the gas diffusion electrode of the present embodiment,
An example in which an ion conductor substantially made of the above fullerene derivative is applied to a fuel cell will be described with reference to FIG.

Here, the catalyst layer 10 in FIG. 8 is a mixed layer made of a mixture of the above-mentioned platinum nanoparticles, a fullerene derivative as an ionic conductor, and a pore-forming agent (CaCO ₃ ) in some cases, The gas diffusive electrode of the present embodiment is a porous gas diffusive electrode body including the catalyst layer 10 and a carbon sheet 11 as a porous gas permeable current collector. In addition, a first electrode (for example, an oxygen electrode) and a second electrode using the gas diffusion electrode body of the present embodiment
A film-like ion conduction part 5 formed by press-molding a fullerene derivative (or made of Nafion) is sandwiched between (for example, a hydrogen electrode).

As shown in FIG. 8, this fuel cell has a negative electrode (fuel electrode or hydrogen electrode) 16 and a positive electrode, which are opposed to each other and which use the gas diffusion electrode of the present embodiment with terminals 14 and 15. An (oxygen electrode) 17 is provided, and an ion conducting part (proton conductor film) 5 made of the above fullerene derivative or the like is sandwiched between these two electrodes. However, the gas diffusion electrode of the present embodiment does not necessarily have to be used as the negative electrode. During use, hydrogen is passed through the H ₂ flow passage 12 on the side of the negative electrode 16 and hydrogen ions are generated while the fuel (H ₂ ) passes through the flow passage 12, and the hydrogen ions are generated by the negative electrode 1.
The hydrogen ions generated in 6 and the hydrogen ions generated in the ion conduction part (ion exchange membrane) 5 move to the positive electrode 17 side, where they react with oxygen (or air) passing through the O ₂ channel,
As a result, the desired electromotive force is extracted.

In this fuel cell, since the gas diffusion electrode of the present embodiment constitutes the first pole and / or the second pole, it has a good catalytic action, and Since the contact area between the catalyst and the gas (H ₂ etc.) is sufficiently secured, the specific surface area of the catalyst contributing to the reaction is increased, the catalytic ability is improved, and good output characteristics are obtained.

Further, hydrogen ions are dissociated in the negative electrode 16,
Further, since the hydrogen ions dissociate in the ion conducting portion 5 and move to the positive electrode 17 side, the conductivity of the hydrogen ions is high even in a dry state. Therefore, since the humidifier is not necessary, the system can be simplified and the weight can be reduced, and the function as an electrode such as current density and output characteristics can be improved.

A binder is used instead of the ion-conducting portion (sandwiched between the first pole and the second pole) consisting only of the film-form fullerene derivative obtained by pressure-molding the fullerene derivative. The bound fullerene derivative may be used for the ion conducting part 5. In this case, the ion conductive portion having sufficient strength can be formed by binding with the binder.

Here, as the polymer material usable as the above-mentioned binder, one or more known polymers having a film-forming property are used, and the compounding amount thereof in the ion conducting part is usually It is better to keep it to 40% by weight or less. This is because if it exceeds 40% by weight, the conductivity of hydrogen ions may be reduced.

Since the ionic conductor having such a constitution also contains the above-mentioned fullerene derivative as an ionic conductor, it can exhibit hydrogen ion conductivity similar to that of the above-mentioned ionic conductor substantially consisting of a fullerene derivative. it can.

Further, unlike the case of the fullerene derivative alone, the film-forming property derived from the polymer material is imparted, and the strength is high and the gas permeation preventive ability is higher than that of the powder compression molded product of the fullerene derivative. It can be used as a thin ion conductive thin film (thickness is usually 300 μm or less).

The polymer material is not particularly limited as long as it does not hinder the conductivity of hydrogen ions as much as possible (due to the reaction with the fullerene derivative) and has film-forming properties. Usually, those having no electron conductivity and having good stability are used, and specific examples thereof include polyfluoroethylene, polyvinyl alcohol, and the like, and these are also preferable polymers for the reason described below. It is a material.

First, polytetrafluoroethylene is preferable because a thin film having higher strength can be easily formed with a smaller amount than other polymer materials. In this case, the compounding amount is 3% by weight or less, preferably 0.5 to 1.
Only a small amount of 5% by weight is required, and the thickness of the thin film is usually 100 μm
Can be made as thin as 1 to 1 μm.

Polyvinyl alcohol is preferable because an ion conductive thin film having a better gas permeation preventing ability can be obtained. The compounding amount in this case is 5 to 40
It is preferable to set it in the range of% by weight.

If the compounding amount of polyfluoroethylene or polyvinyl alcohol is less than the lower limit value of each range described above, the film formation may be adversely affected.

In order to obtain a thin film of the ion conductive part formed by binding each fullerene derivative of this embodiment with a binder, a known film forming method such as pressure molding or extrusion molding may be used.

Further, in the electrochemical device of this embodiment, the ion conductor sandwiched between the gas diffusible electrodes of this embodiment is not particularly limited, and it is ion (hydrogen ion) conductive. Any of those having a can be used, and examples thereof include hydroxylated fullerenes, hydrogen sulfate esterified fullerenol, and Nafion. Further, the above binder can be used as a water-repellent resin for the gas diffusion electrode.

Next, in the present embodiment, the following may be taken into consideration.

For example, in the case of platinum particles (catalyst), the particle size, the preparation method, etc. may be arbitrary as long as they have a predetermined effect.
The metal used is not limited to platinum, and other metals such as iridium (Ir), rhodium (Rh), Au (gold) may be used.

Further, a conductive polymer layer (polyaniline: PA
In NI), the thickness of the platinum particles (catalyst) to be coated, the coating method, the type and amount of the substance to be coated, etc. may be arbitrary as long as they have a predetermined effect.

Further, in the case of a proton dissociative group or substance, if there is a predetermined effect, the amount, method, kind, etc. of doping,
The timing of doping in the forming process may be arbitrary.

Further, in the water-soluble polymer protective layer (polyvinylpyrrolidone: PVP), the thickness, coating method, and substance to be coated on the conductive polymer layer (polyaniline: PANI) have a predetermined effect. The type, amount, etc. of the may be arbitrary.

In addition, in the manufacturing process of platinum nanoparticles, if there is a predetermined effect, the order of the process, the manufacturing method,
The type and amount of solvent used and the type of device may be freely changed.

When the gas diffusive electrode is formed, the weight% of the platinum nanoparticles to be mixed, the mixing method, the mixing conditions, etc. may be freely changed as long as there is a predetermined effect.

Further, the gas diffusion electrode (catalyst layer) in the present embodiment is composed of only platinum nanoparticles as described above, or binds the platinum nanoparticles in addition to the platinum nanoparticles. Other components such as a resin may be contained, and in the latter case, the above-mentioned other components include a pore-forming agent (for example, CaCO ₃ ) and an ionic conductor. Furthermore, the platinum nanoparticles are used as a porous gas-permeable current collector (for example, a carbon sheet).
It is preferable to hold it on top.

Since the granular catalyst substance is the catalyst particles coated with the conductive polymer substance, the effective surface area of contact between the catalyst substance and the reaction gas is increased to improve the catalytic reaction, and in the diffusible electrode, The electron conductivity of the catalyst particles themselves becomes good, and the electrode reaction can be improved.

Further, since the conductive polymer substance is formed on the surface of the granular catalyst substance, the polymer substance improves the shape retention of the catalyst particles, and the catalyst particles aggregate to form a chain structure. Is easily formed, and the retention of the catalyst layer in the electrode, the catalytic reaction, and the electron conductivity are sufficient.

Further, by making it porous, the supply of the active material (reaction gas etc.) to the interface with the catalyst particles and the discharge of the product (water etc.) become smooth.

Further, when the solid polymer electrolyte and the like are contained in the gas diffusible electrode together with the platinum nanoparticles, the proton conductivity is improved.

Further, the platinum nanoparticles aggregate to form a chain structure, and electron conduction channels are formed in every corner of the gas diffusible electrode, so that the electron conductivity in the electrode becomes good.

Next, in the process of compounding the conductive polymer substance and the platinum particles, for example, the conductive polymer substance (PANI: polyaniline) and the water-soluble polymer substance (polymer stabilizer: PVP: polyvinylpyrrolidone) are used. ) Is used as a polymer in a ratio of 1: 2 or 2: 1 and is mixed with platinum particles, the platinum particles will precipitate during the step of synthesizing the platinum nanoparticles. .

When platinum nanoparticles and an organic solution of a conductive polymer (PANI: polyaniline) in dimethylformamide (DMF) are mixed, the platinum nanoparticles precipitate immediately after mixing and have a high boiling point. Since dimethylformamide (DMF) causes a problem, and the conductive polymer substance (PANI: polyaniline) is strongly dissolved by dimethylformamide (DMF), pores are hardly formed.

However, as shown in the present embodiment, when aniline is subjected to oxidative polymerization in an aqueous dispersion of platinum nanoparticles coated with PVP in advance to thereby prepare catalyst particles coated with PANI, A composite of platinum particles and a conductive polymer layer can be realized with good reproducibility, and since no organic solvent is used, problems in preparation are reduced and a relatively stable dispersion liquid can be obtained.

That is, in the present embodiment, by using a water-soluble solvent that is easy to dry, and is easy to construct a porous (porous) structure excellent in gas permeability, Low process easiness (Processability) without using an organic solvent (such as dimethylformamide solution) that is difficult to dry and difficult to build a structure that is porous and has excellent gas permeability The conductive polymer substance can be coated on the platinum particles relatively easily by polymerization, and the sparingly soluble conductive polymer substance and the platinum particles can be composited.

Further, in the production of the gas diffusible electrode, the water-soluble polymer protective layer (PVP) covering the conductive polymer layer (PANI) binds the platinum nanoparticles to each other. There is no need to separately mix a binder to serve as a material. Therefore, not only a catalyst layer can be formed relatively easily by applying an aqueous dispersion containing platinum nanoparticles onto a carbon sheet, drying and then pressing, but also the constituent materials in the gas diffusion electrode and the number of mixing steps. Etc. can be relatively simplified.

Further, when the platinum nanoparticles are coated with a crystalline conductive polymer substance, it helps maintain the structure of the platinum nanoparticles and contributes to the porosity.

Further, since the conductivity of the conductive polymer substance is controlled by the proton dissociative group or the doping of the substance, it is possible to suppress the supply of excess electrons and to function as a proton buffer. There is also a nature.

Further, the gas diffusion electrode and the conductive polymer substance function as a proton-doped body by doping or mixing with a proton dissociative group or substance, so that they function as a proton pool and promote the transport of protons. .

When the protons are lost and the conductivity is lost, the excessive oxidation reaction is suppressed and the life of the electrode can be extended.

Further, the electron conductivity can be imparted to the gas diffusible electrode more easily and cheaply than the method using a titanium sintered body or the electroless plating method.

[0099]

EXAMPLES The present invention will be specifically described below based on examples. Example 1 A method for synthesizing platinum nanoparticles will be described with reference to FIG. First, it consists of a balloon, a three-way cock and a reflux tower 1
In a 1-necked two-necked flask, under a nitrogen stream, 666 mg of polyvinylpyrrolidone (PVP: weight average molecular weight 40000), which is a water-soluble polymer, and chloroplatinic acid (H ₂ PtC).
l ₆ ) (molecular weight 310.7 mg: 0.60 mmol, P
t concentration 117.0 mg) and ethanol / water (7/3
(V / v)) After adding 1.0 l of the mixed solution, another 10
Nitrogen was bubbled through the solution for a minute to completely degas.

Next, when this aqueous solution was gently heated to reflux under nitrogen, the solution turned dark gray in about 1 hour. After further refluxing for 3 hours, the mixture was allowed to cool to obtain a dispersion solution of platinum nanoparticles 21 in which the platinum particles 2 were coated with the water-soluble polymer protective layer (PVP) 19. Then, from observation with a transmission electron microscope (TEM) shown in FIG. 5, it was confirmed that the particles were platinum nanoparticles having a particle size of 4 nm.

Next, the solvent was distilled off from the above dispersion solution under reduced pressure, and the residue was redispersed in a 1N aqueous hydrochloric acid solution (200 ml) to promote proton conductivity. to this,
Aniline dissolved in 10 ml of 1N aqueous hydrochloric acid solution (4
44 mg) was added, followed by an ice-salt bath (ice-salt bat).
After cooling to -15 ° C. at h), it was added ammonium persulfate _{((NH 4) 2 S 2} O 8), 1.09g). Then, by raising the temperature to 0 ° C. and stirring for 12 hours,
An oxidative polymerization reaction was performed to obtain a dark green dispersion solution.

Next, this dispersion solution was subjected to an ultracentrifuge to precipitate fine particles, and the supernatant solution was removed.
It was dispersed in 0 ml of a 1N aqueous hydrochloric acid solution. Then, after repeating this operation again and leaving it for 12 hours, the conductive polyaniline is fully doped (that is, polyaniline passes through the water-soluble polymer protective layer 19 and the platinum particles 2
On top).

Further, this dispersion solution was subjected to an ultracentrifuge to precipitate fine particles, and after removing the supernatant solution, freeze-drying (freezing deaeration) was performed to obtain platinum nanoparticles 1 (on platinum particles 2- 0.51 g of black powder 1 was obtained, which consisted of particles coated with an OH group-introduced conductive polymer layer (polyaniline) 18 and further covered with a water-soluble polymer protective layer (PVP) 19.

X-ray diffraction (XRD: X-Ray Di
As shown in FIG. 6, the ffraction) spectrum shows a pattern (d value: lattice spacing (rel.int .: relative intensity)) of the platinum nanoparticles of 1.9494 (5).
8) 2.2425 (100), 1.3803 (4
4) and 1.1787 (48). Then, a pellet was prepared from this black powder, and the electrical resistance when measured by the 4-terminal method was 0.9 S / cm.

In this Example, the particle size of the platinum particles 2 was about 4 nm, and it was found that the particle size did not increase due to the fusion of the platinum particles (however, the organic layer cannot be observed by TEM. : Below, the same).

Example 2 Instead of 1N hydrochloric acid, conductive polyaniline was replaced with -SO.
Example 1 was repeated except that the system was changed to use 0.5 mol of dodecylbenzenesulfonic acid in order to introduce the ₃ H group.

A transmission electron microscope (TEM) photograph of the platinum nanoparticles obtained in this example is shown in FIG. 7. The particle size of the platinum particles is about 4 nm, and the particle size of the platinum particles due to fusion bonding It was found that no increase had occurred.

The X-ray diffraction (XRD) spectrum of the same black powder obtained from the platinum particles showed the same pattern as the above, which is characteristic of platinum nanoparticles. Then, a pellet was prepared by this, and the electrical resistance when measured by the 4-terminal method was 1.1 S / cm.

Example 3 In this example, gas diffusible electrodes (catalyst layers) were formed by mixing the platinum nanoparticles obtained in Examples 1 and 2 with 10 mg / cm ² respectively, and this was formed into an oxygen electrode. On the other hand, a fuel cell having a fuel electrode configured in the same manner as this oxygen electrode was manufactured. Then, the output characteristics of the fuel cell during continuous operation were measured in the following manner.

However, in order to form an oxygen electrode, a carbon sheet was immersed in a 5 wt% ethanol solution of platinum nanoparticles and then dried on a hot plate to obtain a platinum-supporting carbon electrode.

Then, the gas diffusible electrode obtained by the above steps is installed between the ion exchange membrane (proton conducting part) made of Nafion (hereinafter, the same) and the current collecting electrode, and hydrogen is put in the fuel cell. The output of the fuel cell was measured by introducing gas and oxygen gas. That is, this measurement was performed under the condition that hydrogen gas was passed through the fuel electrode and air was passed through the oxygen electrode.

As a result, the output of the gas diffusion electrode of Example 3 was 0.57 V when the platinum nanoparticles of Example 1 were used, and 0.95 V when the platinum nanoparticles of Example 2 were used. All of them showed good output characteristics (the former low electromotive voltage is an effect of chlorine ion).

Although the embodiments and examples of the present invention have been described above, these can be further modified based on the technical idea of the present invention.

For example, the conductive polymer layer (PANI) and the water-soluble polymer protective layer (PVP) are not only completely covered with the catalytic substance, but also partially covered with a predetermined effect. It may be.

When platinum nanoparticles are prepared without doping the conductive polymer layer with a proton-dissociative group or substance, and the platinum nanoparticles are used to prepare a gas-diffusing electrode body, In addition, a substance that imparts proton conductivity (for example, Nafion) or the like may be mixed to impart proton conductivity to the gas diffusible electrode.

Further, since the water-soluble polymer protective layer (PVP) has a binder function, it should not be mixed with Teflon (registered trademark) (PTFE) particles or the like having a similar binder function in the gas diffusion electrode. However, it may be mixed in some cases. Water-soluble polymer protective layer (PV
In some cases, it is not necessary to provide P).

Further, although the above electrochemical device is applied to the generation of protons by decomposition of H ₂ etc., it can be adapted to the production of H ₂ or H ₂ O ₂ by reversing the reaction. .

[0118]

According to the present invention, since the granular catalyst substance is the catalyst particles coated with the conductive polymer substance,
The effective surface area of contact between the catalyst substance and the reaction gas is increased to improve the catalytic reaction, and in the diffusible electrode, the electron conductivity of the catalyst particles themselves is improved to improve the electrode reaction.

Since the conductive polymer substance is formed on the surface of the granular catalyst substance, the polymer substance improves the shape retention of the catalyst particles, and the catalyst particles are aggregated to form a chain structure. Is easily formed, and the retention of the catalyst layer, the catalytic reaction, and the electron conductivity are sufficient in the electrode.

[Brief description of drawings]

FIG. 1 is an enlarged cross-sectional view of platinum nanoparticles according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of the gas diffusing electrode.

FIG. 3 is a diagram showing a process of producing platinum nanoparticles in the same.

FIG. 4 is a diagram showing the molecular structures of polyaniline and polyvinylpyrrolidone.

FIG. 5 is a transmission electron micrograph of platinum nanoparticles obtained in an example of the present invention.

FIG. 6 is a diagram showing a lattice plane spacing and relative intensity of platinum by X-ray diffraction.

FIG. 7 is a transmission electron micrograph of platinum nanoparticles obtained in another example of the present invention.

FIG. 8 is a schematic configuration diagram of the fuel cell.

FIG. 9 is a structural diagram of polyhydroxylated fullerene, which is an example of a usable fullerene derivative.

FIG. 10 is a schematic diagram showing an example of the same fullerene derivative.

FIG. 11 is a partially enlarged view of a gas diffusion electrode in a conventional example.

FIG. 12 is a partially enlarged view of the gas diffusion electrode.

FIG. 13 is a partially enlarged view of the gas diffusing electrode of the same.

FIG. 14 is a partially enlarged view of the gas diffusing electrode.

FIG. 15 is a partially enlarged view of the gas diffusing electrode.

[Explanation of symbols]

1 ... Platinum nanoparticles, 2 ... Platinum particles (catalyst), 4
... load, 5 ... ionic conduction part (proton conductor membrane), 7 ... fuel side,
8 ... Air side 9 ... Graphite, 10 ... Gas diffusion electrode (catalyst layer), 11 ... Gas permeable current collector (carbon sheet), 12 ... H
₂ channel, 13 ... O ₂ channel 14, 15 ... Terminal, 16 ... Negative electrode, 17 ... Positive electrode, 18 ... Conductive polymer layer 19 ... Water-soluble polymer protective layer, 20 ... Pore, 21 ... Platinum nanoparticles

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G069 AA02 AA08 BA22B BC75B                       CC32 EB18Y EE01 FB03                 5H018 AA06 AS01 BB08 BB16 CC06                       DD01 DD08 EE03 EE17 EE18                       HH01                 5H026 AA06 BB04 BB08 BB10 CC01                       CC03 CX01 CX05 CX07 EE02                       EE18 EE19 HH01

Claims (43)

[Claims] 1. Catalyst particles comprising a granular catalyst substance and a conductive polymer substance formed on the surface of the granular catalyst substance. 2. The catalyst particles according to claim 1, wherein the conductive polymer substance is provided with proton conductivity. 3. The catalyst particles according to claim 1, wherein the conductive polymer substance coating the granular catalyst substance is further coated with a polymer protective layer. 4. The size is 0.1 to 1000 nm,
The catalyst particles according to claim 1. 5. The catalyst particles according to claim 1, wherein the granular catalytic material comprises platinum powder or granules. 6. The catalyst particles according to claim 1, wherein the conductive polymer substance is polyaniline. 7. The catalyst particles according to claim 2, wherein the conductive polymer substance is provided with proton conductivity by introducing a proton dissociative group or substance. 8. The proton dissociative group or substance is —O.
_{H, -OSO 3 H, -SO 3} H, -COOH, -OPO
The catalyst particles according to claim 7, which are selected from the group consisting of (OH) ₂ , HCl and Brensted acid such as H ₂ SO ₄ . 9. The catalyst particles according to claim 3, wherein the polymer protective layer comprises ponivinylpyrrolidone. 10. The catalyst particles according to claim 1, which aggregate to form a chain structure. 11. A method of preparing a first dispersion liquid of a compound which becomes a granular catalyst substance, a step of performing a reaction for decomposing the compound, a granular catalyst substance generated thereby, and a constitution of a conductive polymer substance. Catalyst particles comprising a step of preparing a second dispersion liquid containing a monomer, and a step of producing the conductive polymer substance coating the granular catalyst substance by a polymerization reaction in the dispersion liquid. Manufacturing method. 12. The method for producing catalyst particles according to claim 11, wherein an aqueous dispersion is used as the first and second dispersions. 13. The method for producing catalyst particles according to claim 11, wherein a substance imparting proton conductivity is added to the second dispersion liquid containing the constituent monomer of the conductive polymer substance. 14. The method for producing catalyst particles according to claim 11, wherein a proton dissociative group is introduced into the constituent monomer of the conductive polymer substance in order to impart proton conductivity. 15. A polymer substance which becomes a protective layer of the conductive polymer substance is added to the first dispersion liquid.
1. The method for producing catalyst particles according to 1. 16. The method of producing the granular catalytic material covered with the protective layer of polymeric material and then performing the polymerization reaction in the second dispersion liquid containing the granular catalytic material, wherein the granular catalytic material is The method for producing catalyst particles according to claim 15, wherein the catalyst particles are formed by being covered with the conductive polymer substance and the conductive polymer substance being covered with a protective layer of the polymer substance. 17. The method for producing catalyst particles according to claim 11, wherein the granular catalyst particles having a size of 0.1 to 1000 nm are obtained. 18. The method for producing catalyst particles according to claim 11, wherein platinum powder or particles are used as the granular catalyst material. 19. The method for producing catalyst particles according to claim 11, wherein the conductive polymer substance is polyaniline. 20. The proton conductivity is --OH, --OS.
_{O 3 H, -SO 3 H,} -COOH, -OPO (OH) 2,
The method for producing catalyst particles according to claim 13 or 14, wherein the addition is carried out by a proton-dissociative group or substance selected from the group consisting of Bronsted's acid such as HCl and H ₂ SO ₄ . 21. The method for producing catalyst particles according to claim 15, wherein ponivinylpyrrolidone is used as the polymer substance. 22. A gas diffusive electrode body comprising a catalyst particle comprising a granular catalyst material and a conductive polymer material formed on the surface of the granular catalyst material. 23. The gas-diffusing electrode body according to claim 22, wherein the conductive polymer substance is provided with proton conductivity. 24. The gas-diffusing electrode body according to claim 22, wherein the conductive polymer substance coating the granular catalyst substance is further coated with a polymer protective layer. 25. The catalyst particles have a size of 0.1-10.
The gas-diffusing electrode body according to claim 22, which is 00 nm. 26. The gas-diffusing electrode body according to claim 22, wherein the granular catalyst substance is platinum powder or granules. 27. The gas-diffusing electrode body according to claim 22, wherein the conductive polymer substance is polyaniline. 28. The gas-diffusing electrode body according to claim 23, wherein the conductive polymer substance is provided with proton conductivity by introducing a proton-dissociative group or substance. 29. The proton dissociative group or substance is
_{OH, -OSO 3 H, -SO 3} H, -COOH, -OPO
29. The gas-diffusing electrode body according to claim 28, which is selected from the group consisting of (OH) ₂ , HCl and Brensted acid such as H ₂ SO ₄ . 30. The gas-diffusing electrode body according to claim 24, wherein the polymer protective layer is made of polyvinylpyrrolidone. 31. The gas-diffusing electrode body according to claim 22, wherein the catalyst particles aggregate to form a chain structure. 32. A granular catalyst material comprising a first electrode, a second electrode, and an ionic conductor sandwiched between these electrodes, and a conductive polymer formed on the surface of the granular catalyst material. An electrochemical device in which catalyst particles composed of a substance constitute at least the first pole of the first pole and the second pole. 33. The electrochemical device according to claim 32, wherein the conductive polymer substance is provided with proton conductivity. 34. The electrochemical device according to claim 32, wherein the conductive polymeric material coating the particulate catalytic material is further coated with a polymeric protective layer. 35. The catalyst particles have a size of 0.1 to 10.
33. The electrochemical device according to claim 32, which is 00 nm. 36. The electrochemical device of claim 32, wherein the particulate catalytic material comprises platinum powder or granules. 37. The electrochemical device according to claim 32, wherein the conductive polymer substance is polyaniline. 38. The electrochemical device according to claim 33, wherein proton conductivity is imparted to the conductive polymer substance by introducing a proton dissociative group or substance. 39. The proton dissociative group or substance is-
_{OH, -OSO 3 H, -SO 3} H, -COOH, -OPO
(OH) _2, is selected from the group consisting of Burensutezu acids such as HCl and H ₂ SO _4, the electrochemical device according to claim 38. 40. The electrochemical device according to claim 34, wherein the polymer protective layer comprises polyvinylipyrrolidone. 41. The electrochemical device according to claim 32, wherein the catalyst particles aggregate to form a chain structure. 42. The electrochemical device according to claim 32, wherein at least one of the first electrode and the second electrode is a gas electrode. 43. The electrochemical device according to claim 32, configured as a fuel cell.