JP2000228204A - Electrode for fuel cell and method for producing the same - Google Patents

Abstract

(57) Abstract: In a fuel cell including a solid polymer electrolyte membrane and a pair of electrodes having a catalyst reaction layer sandwiching the solid polymer electrolyte membrane, the solid polymer electrolyte and the catalyst are sufficiently mixed. Further, the present invention provides a polymer electrolyte fuel cell capable of increasing the reaction area inside the electrode by making uniform contact and exhibiting higher performance. SOLUTION: A fuel cell is constituted by an electrode using a catalyst particle or a carrier of the catalyst particle having a diffusion layer of hydrogen ions on the surface thereof. In particular, a silane compound containing a hydrogen ion dissociable functional group is chemically adsorbed on the catalyst fine particles or the surface of the catalyst carrier of the catalyst layer, and thereby, a hydrogen ion channel is formed also in the catalyst inside the pores of the electrode. And a polymer electrolyte fuel cell exhibiting high discharge performance is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode which is a component of a polymer electrolyte fuel cell and a method for producing the same.

[0002]

2. Description of the Related Art In an electrode which is a component of a polymer electrolyte fuel cell, a pore serving as a supply path of a reaction gas, a hydrogen ion conductive solid polymer electrolyte, and an electrode material which is an electronic conductor are used. The size of the area of the so-called three-phase interface to be formed is one of the important factors affecting the discharge performance of the battery.

Conventionally, in order to increase this three-phase interface,
A layer in which an electrode material and a solid polymer electrolyte are mixed and dispersed,
Attempts have been made to apply it to the interface between the membrane and the porous electrode.
For example, Japanese Patent Publication No. 62-61118, Japanese Patent Publication No. 62-61118
In the technique described in Japanese Patent Application Publication No. 61119, a method in which a mixture of a solution in which a solid polymer electrolyte is dispersed and a catalyst compound is applied onto a solid polymer membrane, and the catalyst compound is reduced after hot pressing with an electrode material, or There has been proposed a method of performing hot pressing after coating after reduction.

In Japanese Patent Publication No. 2-48632,
There has been proposed a method in which after a porous electrode is molded, a solution in which an ion exchange membrane resin is dispersed is sprayed on the electrode, and the electrode and the ion exchange membrane are hot pressed. Further, Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 184266 proposes a method in which a polymer resin surface is coated with a solid polymer electrolyte powder, and Japanese Patent Application Laid-Open No. 3-295172 discloses a method in which a solid polymer electrolyte powder is mixed in an electrode. Also, Japanese Patent Application Laid-Open No. 5-36418 proposes a method in which a solid polymer electrolyte, a catalyst, carbon powder, and a fluororesin are mixed, and a film is formed to form an electrode. In the above techniques, alcohols are used as a solution for forming a solid polymer electrolyte in an electrode.

In the technique described in US Pat. No. 5,221,1984, a solution is prepared by dispersing a solid polymer electrolyte, a catalyst and carbon powder in an ink form using glycerin or tetrabutylammonium salt as a solvent. Is polytetrafluoroethylene (hereinafter referred to as PTFE)
After molding on a film, a method of transferring to the surface of the solid polymer electrolyte membrane, or replacing the exchange group of the solid polymer electrolyte membrane with Na type, and applying the ink dispersion to the surface of the membrane. A method of heating and drying at 125 ° C. or higher and replacing the exchange group with H-form again has been reported.

On the other hand, in order to realize a high output density which is a feature of the polymer electrolyte fuel cell, a supply path (gas channel) of a reaction gas is formed in the electrode catalyst layer to enhance gas permeation / diffusion ability. Is important. Therefore, attempts have been made to form a gas channel by adding a water-repellent material such as a fluororesin to the electrode catalyst layer. For example, in the technique described in JP-A-5-36418, a method is proposed in which a PTFE powder and a carbon powder supporting a catalyst are dispersed and kneaded in a solid polymer electrolyte solution to form a catalyst layer. Also, Japanese Patent Application Laid-Open No. 4-2
In the technology described in Japanese Patent No. 64367, an electrode is proposed using a mixed solution of a carbon powder carrying a catalyst and a colloidal solution of PTFE.

Further, J. J. Electroanal. Ch
em. 197 (1986), p. 195
A gas diffusion electrode for an acidic electrolyte is proposed by mixing a carbon powder that has been subjected to a water-repellent treatment with E and a carbon powder that carries a catalyst. On the other hand, U.S. Pat. No. 5,211,1984 proposes that a catalyst layer of an electrode be formed using only a solid polymer electrolyte, a catalyst, and carbon powder without using a water-repellent material as described above.

[0008]

However, when a carbon powder carrying a catalyst and a water repellent such as a fluororesin or a water repellent treated carbon powder are simultaneously added to a solution in which a solid polymer electrolyte is dispersed, A large amount of the solid polymer electrolyte is adsorbed on the water repellent or the carbon powder subjected to the water repellent treatment. At this time, the degree of contact between the solid polymer electrolyte and the catalyst becomes non-uniform by that much, resulting in a disadvantage that a sufficient reaction area cannot be secured at the interface between the electrode and the ion exchange membrane. Was.

In addition, when a dispersion using an alcoholic solvent is applied on a porous substrate, or when the above-mentioned ink-like dispersion is applied on a porous substrate, the dispersion may enter the substrate. Because of the transmission, it could not be molded directly on the substrate surface, and required complicated processing techniques such as transfer. Further, the above-described method of directly applying an ink-like dispersion to the film surface requires a complicated production technique for replacing the exchange groups of the film many times. Further, the above-described method of adding a fluororesin has a disadvantage that the catalyst fine particles are excessively coated with the fluororesin, the reaction area is reduced, and the polarization characteristics are reduced.

On the other hand, in the above-described J. Electroana
l. Chem. When a carbon powder treated with water repellency with PTFE is used as in the technique described in 197 (1986), p. 195, the phenomenon that the catalyst particles are coated with PTFE can be surely suppressed. But,
In this proposal, the use of a solid polymer electrolyte, whether or not water-repellent carbon powder was added, and the effect of the addition ratio were not examined. Further, when an electrode is made of only a carbon powder carrying a catalyst and a solid polymer electrolyte, a so-called flooding phenomenon occurs due to water generated in the fuel cell, and when the battery is driven at a high current density, the There was a drawback that the voltage became low and became unstable.

[0011] The present invention solves the above-mentioned problems, and the solid polymer electrolyte and the catalyst are brought into sufficient and uniform contact to increase the reaction area inside the electrode and exhibit higher performance. It is an object of the present invention to provide a method of manufacturing a fuel cell.

Further, the hydrogen ion channel and the gas channel are formed without adding an excessive amount of the fluorine resin to cover the catalyst, the gas permeability of the electrode is increased, and even when the battery is driven at a high current density, a high current density is obtained. An object of the present invention is to provide a method for producing a polymer electrolyte fuel cell exhibiting performance.

[0013]

In order to solve the above problems, an electrode for a fuel cell according to the present invention comprises a pair of electrodes having a solid polymer electrolyte membrane and a catalytic reaction layer sandwiching the solid polymer electrolyte membrane. Wherein the electrode has a diffusion layer of hydrogen ions on the surface of the catalyst particles or the carrier of the catalyst particles.

At this time, it is effective to form a diffusion layer of hydrogen ions by chemically bonding a silane compound to the surface of the catalyst particles or the carrier of the catalyst particles.

An organic compound having a basic functional group is modified on the surface of the catalyst particles or the carrier of the catalyst particles,
It is effective that a hydrogen ion diffusion layer is formed by the organic compound and a hydrogen ion conductive solid electrolyte.

At this time, it is effective that the basic functional group has a nitrogen atom having an unshared electron pair.

The organic compound having a basic functional group is
It is effective that it is a silane compound.

At this time, the silane compound preferably has a functional group capable of dissociating hydrogen ions.

It is desirable that the silane compound has at least one of a hydrocarbon chain and a fluorocarbon chain.

The carbon particles or carbon fibers and the silane compound are chemically bonded via at least one functional group selected from phenolic hydroxyl groups, carboxyl groups, lactone groups, carbonyl groups, quinone groups and carboxylic anhydrides. It is effective.

Further, in the method for producing an electrode for a fuel cell according to the present invention, at least one material to be joined selected from catalyst particles, catalyst carriers, carbon particles or carbon fibers is immersed in a solvent containing a silane compound. Then, after chemically adsorbing the silane compound on the surface of the material to be joined, the surface of the material to be joined is chemically bonded to silicon atoms in the molecules of the silane compound, thereby forming a hydrogen ion diffusion layer. It is characterized by forming.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION A hydrolyzable group of a silane compound is
On the surface of the catalyst metal or the surface of the carbon material that is the support for the catalyst,
It is hydrolyzed by water in solution or air and water adsorbed on the catalyst surface. At this time, the hydrolyzable group is converted into an active silanol group (≡SiOH), and reacts with an oxide on the surface of the catalytic metal or a functional group on the surface of the carbon material to form a strong bond. By providing the silane compound with a hydrogen ion dissociating functional group such as a sulfone group or a carboxyl group, the hydrogen ion conductive layer can be monomolecularly coated on the catalyst surface. Then, by coating this with a catalyst metal and a carbon support, a monomolecular hydrogen ion channel can be formed. A single molecule can be controlled to several nm to several tens nm.

Generally, a polymer electrolyte has a depth of about several hundred n.
Up to m, a sufficient gas supply capacity for the electrode reaction of the fuel cell is exhibited. Therefore, the polymer electrolyte layer in the present invention can maintain sufficient gas solubility, and can cover the catalyst surface as in the case of using conventionally used submicron-order PTFE dispersion particles. There is no hindrance to the supply of reaction gas.

FIG. 1 shows a cross section of an electrode for a fuel cell according to an embodiment of the present invention. In FIG. 1, since the polymer electrolyte layer is uniformly adsorbed on the catalyst powder as described above, inside the catalyst layer 2 of the electrode 1, the catalyst fine particles 3, the carbon fine powder 4, and the polymer electrolyte 5 are exchanged. It can be brought into a state of evenly contacting the surface.

With such a structure of the catalyst layer 2, a gas channel 7 in which pores are formed between the carbon powder 4 and the supply path of a fuel gas such as hydrogen or an oxidizing gas such as oxygen.
And a hydrogen ion channel 8 formed by the polymer electrolyte layer 5
And an electron channel 6 formed by connecting the carbon fine powders to each other
Can be efficiently formed very close inside the same catalyst layer. In the figure, 9 is a gas diffusion layer, and 10 is a solid polymer electrolyte membrane.

At this time, at the hydrogen electrode and the oxygen electrode,

[0027]

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[0028]

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The reaction shown in the above occurs. At this time, when the electrode shown in FIG. 1 is used, the supply of hydrogen and oxygen gas and the transfer of hydrogen ions and electrons are performed simultaneously and smoothly over a wide range, the reaction speed and the reaction area are increased, and higher discharge is achieved. A polymer electrolyte fuel cell exhibiting high performance can be realized.

Further, since the size of the single molecule is sufficiently small, the conventionally used polyelectrolyte molecules of the order of several hundred nm can coat the catalyst inside the pores that could not be adsorbed. For this reason, a hydrogen ion channel can also be formed in the catalyst inside the pores and contribute to the reaction.

At this time, the water repellency of the polymer layer can be increased by giving the silane compound a hydrocarbon chain, and the water repellency of the polymer layer can be further increased by giving the silane compound a fluorocarbon chain. Can be.

The terminal of the silane compound is -SO3H
When the electrode is replaced with -COOH group or the like to increase the hydrophilicity, the water retention of the electrode is improved. For example, the fuel cell is operated at a low current density, and when the generated water is small or the air is operated with low humidification air In addition, the electrode maintains a constant water holding power, and high performance is obtained. When the water repellency is increased, for example, the fuel cell is operated at a high current density, and the gas diffusion capacity of the electrode is improved even in the case of generating a large amount of water or operating in a highly humidified air. can get.

As shown in FIG. 2, a hydrogen ion channel is formed on the surface of the catalyst by using a water-repellent silane compound having a hydrogen ion dissociating functional group and a hydrocarbon chain, and further having a fluorocarbon chain. A gas channel can also be formed on the catalyst surface using a strongly water-repellent silane compound. By using this, it becomes possible to realize a polymer electrolyte fuel cell exhibiting higher polarization characteristics in a high current density region. By coating a water-repellent silane compound having a fluorocarbon chain on carbon powder not carrying a catalyst, a water-repellent monolayer 11 can be formed, and the gas channel can be formed without reducing the catalyst surface area. 7 can be formed.

Further, by mixing the polymer electrolyte layer used in the above configuration and a polymer electrolyte such as "Nafion solution" conventionally used by Aldrich Chemical Co., USA, the catalyst inside the pores is mixed. , A continuous hydrogen ion channel can be formed from the surface to the surface of the electrolyte membrane, and a high-performance electrode having a large reaction area and small internal resistance can be realized.

In addition, the hydrolyzable groups of the silane compound are hydrolyzed on the surface of the catalyst metal or the surface of the carbon material as a support of the catalyst by the water in the solution or in the air, or the water adsorbed on the surface of the catalyst. At this time, the hydrolyzable group is converted into an active silanol group (≡SiOH), and reacts with an oxide on the surface of the catalytic metal or a functional group on the surface of the carbon material to form a strong bond. When the silane compound has a basic functional group having a nitrogen atom having an unshared electron pair, such as an amide group or an amine group, at the terminal, interaction with a polymer electrolyte having an acid group such as sulfonic acid occurs. be able to. At this time, the polymer electrolyte can be strongly attracted to the monomolecular surface, that is, in the vicinity of the surface of the catalyst carrier, to form a polymer electrolyte layer. This makes it possible to form a hydrogen ion channel, which is a dense hydrogen ion conductive layer, on the surfaces of the catalyst and the catalyst carrier.

This effect is due to the interaction between the basicity of the monolayer coated with the catalyst support and the acidic nature of the polymer electrolyte, which allows the presence of the polymer electrolyte closer to the catalytic metal.

Further, a polymer electrolyte exists near the catalyst,
The increase in the rate of coating with the catalytic metal enables the formation of a hydrogen ion channel for effectively transporting the hydrogen ions generated by the catalytic reaction, and the improvement of the catalytic efficiency.

When the main chain skeleton of the silane compound forming the monomolecular layer is a hydrocarbon chain, the water repellency of the hydrocarbon chain is relatively weak, so that the entire catalyst layer is in a painted state. This indicates that the water retention capacity of the electrode has been improved. In other words, it shows that the electrode maintains a constant water retention capacity and high performance can be obtained even when the fuel cell is operated at a low current density and the amount of generated water is small or when the fuel cell is operated with low humidified air.

On the other hand, the hydrogen fluoride chain has high water repellency,
As shown in the above, when the monomolecular layer 71 is formed using a silane compound having a hydrogen fluoride chain, and a polymer electrolyte having a hydrogen fluoride chain (for example, Flemion manufactured by Asahi Glass) is used for both, The water-repellent layer 73 can be formed between the monomolecular layer 71 and the polymer electrolyte layer 72 by the water-repellent effect. At this time, the water present in the water-repellent layer 73 makes it easier to take out the reaction product water out of the system due to the water-repellent effect of both layers described above, and the effect of humidifying the inside of the electrode in an appropriate state (flooding suppression effect). Can be maintained.

As described above, even when the polymer fuel cell is operated at a high current density and a large amount of water is generated, or when highly humidified air is used, a sufficient gas diffusion capacity is provided in the electrode due to the water repellent effect. It can be exerted and a sufficiently high battery performance can be obtained.

When a silane compound having a hydrocarbon chain is used, a hydrogen ion channel can be formed on the surface of the catalyst, and when a silane compound having a hydrogen fluoride chain is used, a hydrogen ion channel can be formed on the surface of the catalyst. Gas channels can be formed. As described above, by changing the main chain skeleton of the silane compound, the characteristics of the catalyst layer in the electrode can be designed according to an appropriate operating environment, and a polymer fuel cell exhibiting high discharge characteristics can be realized. And

Hereinafter, the fuel cell of the present invention will be described with reference to the drawings.

[0043]

EXAMPLES (Example 1) As shown in FIG.
catalyst particles 3 made of platinum in a particle size of about 10 nm to 10 nm
Was directly reacted with a silane compound by chemical adsorption in a nitrogen gas atmosphere on the surface of the carbon particles 4 carrying 20% by weight of the compound to form a monomolecular protective film made of the silane compound. As the silane compound, CH3- (CH2) n-SiCl3 having a linear hydrocarbon chain (n is 1
(0 to 25), n-hexane dissolved at a concentration of 1% by weight was prepared, and the above-mentioned carbon powder carrying platinum particles was immersed therein.

At this time, a natural oxide film is formed on the surface of the catalyst particles 3, and contains a -OH group and an oxide. The carbon powder 4 used had a surface functional group such as a phenolic hydroxyl group, a carboxyl group, a lactone group, a carbonyl group, a quinone group, and carboxylic anhydride present on the surface. Therefore, by performing a dehydrochlorination reaction with -SiCl3 group, -OH group, and other functional groups and oxides, the monomolecular adsorption film 12 made of a silane compound is formed on the surface of the catalyst metal 3 and the surface of the carbon carrier 4. About 2 nm to 10 n
m. Further, by changing the molecular weight of a single molecule, it was possible to mold the film to a thickness of about 1 nm to 100 nm.

Examples of the material for chemical adsorption include a —OH group and a group having a binding property to an oxide, for example, ≡SiCl
It is not limited to the silane compound used above as long as it contains a group or the like.

As shown in FIG. 4, SiCl 3-(CH 2) is a silane compound containing, for example, a sulfone group or a carboxyl group as a hydrogen ion dissociating functional group.
2) n-SO2Cl (n: integer) or SiCl3- (C
H2) n-COOCH3 (n: integer), SiCl3-
(CH2) n- (C6H4) -SO2Cl (n: integer), SiCl3- (CH2) n- (C6H4) -CO
OCH3 (n: integer) or the like was used, and this was hydrolyzed and used. By this method, a hydrogen ion conductive monolayer 13 was formed on the surfaces of the catalyst metal 3 and the carbon support 4.

Example 2 In this example, a silane compound containing fluorine in a part of a linear hydrocarbon chain,
Using iCl3- (CH2) 2-CF3 dissolved in recirculated silicon oil (KF994 manufactured by Shin-Etsu Chemical Co., Ltd.), the water-repellent monomolecular layer 11 was converted to a carbon carrier by the same method as described in Example 1 above. Formed on the surface. By using such a silane compound, the water repellency in the electrode could be improved, and a gas channel for supplying a reaction gas could be formed.

As a silane compound containing fluorine as a part of a linear hydrocarbon chain, SiCl3- (C
H2) 2- (CF2) m-CF3 (m is an integer of 0 or more and 9 or less) could also be used.

Example 3 In this example, SiCl3- (CH2) is a silane compound containing a sulfone group as a hydrogen ion dissociating functional group and containing fluorine in a part of a linear hydrocarbon chain. n- (CF2) m-SO3
By using H (n and m are integers from 2 to 10),
A hydrogen ion conductive monolayer 13 was formed on the surfaces of the catalyst metal 3 and the carbon carrier 4.

A silane compound containing, for example, a sulfone group or a carboxyl group as a hydrogen ion dissociating functional group and containing fluorine in a part of a linear hydrocarbon chain is used. (CF2) m-S
O2Cl (n and m are integers), SiCl3- (CH2) 2
-(CF2) m-COOCH3 (n and m are integers), Si
Cl3- (CH2) 2- (CF2) m- (C6H4)-
SO2Cl (n and m are integers), SiCl3- (CH2)
Even if 2- (CF2) m- (C6H4) -COOCH3 (m is an integer) was hydrolyzed, an effect could be obtained.

(Comparative Example 1) For comparison, a "5% by weight-Nafion solution" manufactured by Aldrich Chemical Company, USA was used, and this was mixed with 20% by weight of ultrafine platinum catalyst particles 3 having a particle size of about 1 nm to 10 nm. A supported carbon fine powder 4 was prepared. After mixing this carbon fine powder 4 and butanol and dispersing them in a ball mill, carbon paper (manufactured by Toray, TGP-
The electrode 1 was formed by coating and forming a catalyst layer 2 on H-120 (thickness: 360 μm).

(Evaluation 1) As described above, the electrode catalyst powders described in Example 1, Example 2, Example 3, and Comparative Example were used, and this was used as a carbon paper as a gas diffusion layer 9 (manufactured by Toray, TGP- H-120, thickness 360 μm) was applied to form a catalyst layer 2, which was used as an electrode 1. The electrode fabricated in this manner was connected to a Nafion film (manufactured by Dupont, N
afion112) 10 and hot-pressed to produce an electrode-electrolyte assembly. These cells were tested by preparing a fuel cell measurement cell shown in FIG.

In FIG. 5, reference numeral 10 denotes a solid polymer electrolyte membrane. In FIG. 5, 14 and 15 are a negative electrode and a positive electrode, respectively. The amount of the solid polymer electrolyte added was 1.0 mg / cm 2 per apparent electrode area for both electrodes, but 0.1 mg / cm 2.
In the range of ｍｇ3.0 mg / cm 2, equivalent characteristics were obtained. The amount of platinum added was 0.5 mg / cm 2 in weight per electrode area.

The hydrogen gas was supplied to the negative electrode 14 of these cells, and the air was supplied to the positive electrode 15. The battery temperature was 75 ° C., the fuel utilization was 80%, the air utilization was 30%, and the gas humidification was 7 hydrogen.
The battery was subjected to a discharge test by adjusting the temperature to 5 ° C. and the air to a dew point of 65 ° C.

The cells prepared using the methods of Examples 1, 3 and Comparative Example were designated A, B and X, respectively, and the catalyst powder treated in Example 1 and the carbon support treated in Example 2 were mixed. Thus, the unit cell on which the catalyst layer was formed was designated as C.

FIG. 6 shows the current-voltage characteristics of the batteries A, B, C and X of the example of the present invention and the comparative example 1. The current density characteristics when the battery voltage was 850 mV, which is a reaction rate-determining region, and the current density of the battery was 1000 mA /
Table 1 shows the battery voltage in cm 2.

[0057]

[Table 1]

In Table 1, looking at the current density when the battery voltage was 850 mV, the battery C of Comparative Example 1 was 9 mA.
/ Cm 2, the batteries A, B, and C using the electrodes of this example were 48, 50, and 50 mA / cm 2, respectively.
, And the characteristics were about 5 times or more superior to those of the comparative example. It is considered that the reason for this is that the electrode of the present invention has a reaction area five times or more that of the electrode of the comparative example.

In the electrode of the present invention, 1 nm to 100 nm
A polymer single molecule having a thickness of about nm could be formed. Since the size of the single molecule is sufficiently small, it is possible to coat the catalyst inside the pore where the polyelectrolyte molecules of the order of several hundred nm, such as the conventional “Nafion solution”, could not be adsorbed. It is considered that a hydrogen ion channel was also formed in the catalyst, which could contribute to the reaction, and that a high current density was obtained.

When the current density was 1000 mA / cm 2, the battery voltage of each of the batteries A, B, and C was 0.59 V, compared to that of the battery C of the comparative example of 0.29 V.
A high value of 5, 0.64, 0.66 V was maintained. This is considered to be because the electrode of the present invention has a large reaction area as described above, so that even when driven at a high current density, higher characteristics were obtained as compared with the comparative example. further,
In the battery B, since the hydrogen ion conductive monolayer itself contains fluorine in a part of the hydrocarbon chain, the gas solubility can be improved, the gas supply capability to the catalyst is improved, and the high current It is considered that the characteristics in the density region have been improved. Further, in the battery C, the catalyst powder in which the treated hydrogen ion conductive monolayer of Example 1 was adsorbed and the monolayer containing fluorine in a part of the linear hydrocarbon chain of Example 2 were used. It is considered that, since the catalyst layer was formed by mixing with the adsorbed carbon carrier, the gas supply capability in the catalyst layer was further increased, and the characteristics in the high current density region were improved.

Example 4 As shown in FIG. 8, a nitrogen gas atmosphere was applied to the surface of carbon particles 82 carrying 20% by weight of catalyst particles 81 made of particulate platinum having a particle size of about 1 nm to 10 nm. The silane compound was directly adsorbed and reacted by chemical adsorption in the inside to form a monomolecular protective film made of the silane compound. As the silane compound, CH ₃ — (CH ₂ ) n—Si (OCH ₃ ) ₃ having a linear hydrocarbon chain
(N is a positive number of 2 or more and 10 or less), an ethanol solution dissolved at a concentration of 1% by weight was prepared, and the above-mentioned carbon powder carrying platinum particles was immersed in the solution and heated at 60 ° C for 1 hour. did.

At this time, a natural oxide film is formed on the surface of the catalyst particles 81, and contains a —OH group and an oxide. The carbon powder 82 used had surface functional groups such as a phenolic hydroxyl group, a carboxyl group, a lactone group, a carbonyl group, a quinone group, and carboxylic anhydride present on the surface. So, -Si (OCH _{3) 3} group,
By performing a dealcoholation reaction with —OH groups and other functional groups and oxides, the monomolecular adsorption film 83 made of a silane compound is formed.
On the surface of the catalyst metal 81 and the surface of the carbon support 82,
It was formed with a thickness of about 2 nm to 10 nm. Further, by changing the molecular weight of a single molecule, it was possible to mold the film to a thickness of about 1 nm to 100 nm.

As a material for the chemical adsorption, an —OH group or a group having a binding property to an oxide, for example, ≡Si (O
It is not limited to the silane compounds used above as long as they contain CH ₃ ) and ≡Si (OC ₂ H ₅ ) groups.

As shown in FIG. 7, as a basic functional group having a nitrogen atom having an unshared electron pair, a silane compound containing an amine group, Si (OCH ₃ ) _3- (C
_{H 2) n-NH 2 (} n used the integer of 10 or less) at 2 or more. By this method, a monomolecular layer 83 was formed on the surface of the carbon powder 82. Further, by the action of the terminal basic group, a polymer electrolyte layer 84 is formed densely near the surface of the catalyst metal and the carbon support so as to cover the monomolecular layer 83, and hydrogen ion transport is effectively performed. Was formed.

In this embodiment, as a basic functional group having a nitrogen atom having an unshared electron pair, for example, a silane compound containing an amide group or an amine group, Si (OCH ₃ ) _3- (C
H ₂ ) n-NH ₂ (n is an integer of 2 or more and 10 or less), S
_{i (OCH 3) 3 - (} CH 2) m-NH- (CH 2) n-NH
₂ (m and n are integers of 2 or more and 10 or less), Si (OCH
_{3) 3 - (CH 2)} n- (C 6 H 4) -NH 2 (n is integer of 10 or less in 2 _{above), Si (OCH 3) 3} - (CH 2) m-N
(CH ₃ ) ₂ (m is an integer of 2 or more and 10 or less), Si
_{(OCH 3) 3 - (CH} 2) n- (C 6 H 4) -N (CH 3)
₂ (n is an integer of 2 or more and 10 or less), Si (OC ₂ H ₅ ) <sub>3
- (CH 2) n-N</sub> (CH 2 CH 2 OH) 2 (CH 2) n (n
Is an integer of 2 or more and 10 or less).

Example 5 In this example, Si (OCH ₃ ) ₃ was used as a basic functional group in which a part of a linear hydrocarbon chain of a silane compound containing an amine group contained fluorine.
_{- (CH 2) n- (CF} 2) m-NH 2 (n, m is an integer of 2 to 10) By using a straight-chain monolayer 12 catalyst metal 3 and similar to that of hydrocarbon It was formed on the surface of the carbon support 4.

The silane compound to be used is
A part of a linear hydrocarbon chain to contain
Si (OCH_Three)_Three− (CH_Two) N
− (CF_Two) M-NH_Two(N and m are integers from 2 to 10),
Si (OCH_Three)_Three− (CH_Two) M-NH- (CH_Two) N-
(CF_Two) L-NH_Two(N, m, l are integers from 2 to 7),
Si (OCH_Three)_Three− (CH_Two) N- (CF_Two) M-N (C
H_Three)_Two(N and m are integers from 2 to 8), Si (OCH_Three)_Three−
(CH_Two) N- (CF_Two) M- (C₆H_Four) -NH_Two(N,
m is an integer of 2 to 7), Si (OCH_Three)_Three− (CH_Two) N
− (CF_Two) M- (C₆H_Four) -N (CH_Three)_Two(N and m are 2
To an integer of 7), Si (OC_TwoH_Five)_Three− (CH _Two) N (CF
_Two) M-N (CH_TwoCH_TwoOH)_Two(N and m are integers from 2 to 7)
Number) could also be used.

Comparative Example 2 For comparison, a "5% by weight-Nafion solution" manufactured by Aldrich Chemical Company, USA was used, and this was mixed with 20% by weight of platinum catalyst ultrafine particles 3 having a particle size of about 1 nm to 10 nm. A supported carbon fine powder 4 was prepared. After mixing this carbon fine powder 4 and butanol and dispersing them in a ball mill, carbon paper (manufactured by Toray, TGP-
The electrode 1 was formed by coating and forming a catalyst layer 2 on H-120 (thickness: 360 μm).

(Evaluation 2) As described above, the electrode catalyst powders described in Examples 4, 5 and Comparative Example 2 were used, and this was used as a carbon paper (TGP-H-12, manufactured by Toray Co., Ltd.) as a gas diffusion layer.
0, a film thickness of 360 μm) to form a catalyst layer by coating, and this was used as an electrode. The electrode thus produced was used as a Nafion film (manufactured by Dupont, Nafion 11).
2) Disposed on both sides of 10 and hot-pressed to produce an electrode-electrolyte assembly. These cells were tested by preparing a fuel cell measurement cell shown in FIG.

A hydrogen gas was supplied to the negative electrode 14 of these cells, and air was supplied to the positive electrode 15. The cell temperature was 75 ° C., the fuel utilization was 80%, the air utilization was 30%, and the gas humidification was 7 hydrogen.
The battery was subjected to a discharge test by adjusting the temperature to 5 ° C. and the air to a dew point of 65 ° C.

Batteries prepared using the electrodes prepared in Examples 4 and 5 and Comparative Example 2 were designated D (hydrocarbon chain type),
E (hydrogen fluoride chain type) and Y (non-surface treatment type).

FIG. 9 shows the current-voltage characteristics of the batteries D, E and Y of the examples and comparative examples of the present invention. Further, the driving current density of the battery was set to 300 mA / cm, which is a low current density.
Table 2 shows the battery voltage at a high current density of 700 mA / cm2, which is a high current density of 700 mA / cm2.

[0073]

[Table 2]

In Table 2, it was confirmed that the batteries D and E using the electrode of the present invention had higher battery characteristics than the comparative example Y.

When the electrode of the present invention is compared with the conventionally proposed electrode as a comparative example, the batteries D and D have the same amount of polymer electrolyte and the same amount of platinum catalyst contained in the electrode. E has improved characteristics over battery Y because the silane compound having a basic group coats the surface of the catalyst carrier to form a monolayer, and this monolayer further forms a dense polymer electrolyte near the catalyst carrier. It is believed that the formation of the layer enabled more efficient hydrogen ion exchange.

Further, in Table 2, it was confirmed that the difference in the main chain skeleton of the silane compound affected the battery characteristics. That is, a battery using an electrode using a silane compound having a relatively weakly hydrophobic hydrocarbon chain has a particularly large effect when the driving current of the battery is low, and a silane having a strongly hydrophobic hydrogen fluoride chain. The battery using the electrode using the compound was particularly effective when the driving current of the battery was high.

In the above embodiments, the surface treatment was performed on the carbon powder as the catalyst carrier. However, if the catalyst metal has an —OH group or an oxide on the surface, the structure of the present invention can be applied to the catalyst metal itself. Available.

[0078]

As described above, the electrode of the present invention is characterized in that it has a surface diffusion function of hydrogen ions on the surface of the catalyst particles or the catalyst carrier, and adsorbs a functional polymer. This increases the reaction area by uniformly adsorbing the monomolecular polymer electrolyte layer on the surface of the catalyst metal or the surface of the carbon carrying the catalyst, and forming a hydrogen ion channel also in the catalyst inside the pores. As a result, a polymer electrolyte fuel cell exhibiting higher discharge performance can be realized.

The hydrophilicity of the polymer layer can be enhanced by giving the silane compound a hydrocarbon chain. For example, when the fuel cell is operated at a low current density and the amount of generated water is small, or when the humidified air is used. The electrode maintains a constant water retention capacity even when operated, and high performance is obtained.

Further, by having a fluorocarbon chain, it is possible to increase the water repellency of this polymer layer. In addition, the gas diffusion capacity of the electrode is improved, and high performance is obtained.

Further, since the reaction area is increased, the amount of the noble metal catalyst used for the electrode catalyst layer can be reduced as compared with the conventional case, and there is an advantage that a cost reduction effect can be expected.

Further, the electrode of the present invention is characterized in that a functional polymer having a surface diffusion function of hydrogen ions is adsorbed on the surface of the catalyst particles or the catalyst carrier. This functional polymer functions as a polymer electrolyte layer. For this formation, a monomolecular layer as a functional polymer was formed using a silane compound having a basic functional group. In this way, by modifying the surface of the catalyst carrier with a functional polymer that has a hydrogen ion surface diffusion function, a dense polymer electrolyte layer is formed near the catalyst, and efficient hydrogen ion channels and gas channels are created. Form. As a result, a polymer fuel cell exhibiting high discharge performance was realized.

Further, by utilizing the high-efficiency hydrogen ion exchange capacity, the discharge characteristics did not deteriorate, the amount of the noble metal catalyst used in the electrode catalyst layer could be reduced, and the cost could be reduced. .

Further, by selecting the skeleton structure of the silane compound to be surface-modified, the wettability of the electrode could be controlled. As a result, an electrode catalyst optimal for driving conditions of the fuel cell could be produced.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross section of an electrode according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a cross section of an electrode according to a second embodiment of the present invention.

FIG. 3 is a conceptual diagram showing a cross section of a catalyst fine particle or a catalyst carrier adsorbing a monomolecular film in the first and second embodiments of the present invention.

FIG. 4 is a view showing the concept of an adsorbed monolayer in the first and second embodiments of the present invention.

FIG. 5 is a diagram showing a schematic cross section of a fuel cell constituted by using the electrodes of the first, second and third embodiments of the present invention.

FIG. 6 is a diagram showing characteristics of a fuel cell constituted by using the electrodes of the first, second and third embodiments of the present invention.

FIG. 7 is a conceptual diagram in which the surface of the catalyst carrier is enlarged in the first and second embodiments of the present invention.

FIG. 8 is a conceptual diagram showing a cross section of catalyst fine particles or a catalyst carrier adsorbing a monomolecular film in the first and second embodiments of the present invention.

FIG. 9 is a diagram showing characteristics of a fuel cell configured using the electrodes of the first and second embodiments of the present invention.

[Explanation of symbols]

 Reference Signs List 1 electrode 2 catalyst layer 3 catalyst particles 4 carbon powder 5 polymer electrolyte 6 electron channel 7 gas channel 8 hydrogen ion channel 9 gas diffusion layer 10 solid polymer electrolyte membrane 11 water-repellent monolayer 12 monomolecular adsorption film 13 hydrogen ion Conductive monolayer 14 Negative electrode 15 Positive electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hisao Gyoten 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Yasushi Sugawara 1006 Kadoma, Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Kazuhito Hajito 1006 Odaka, Kazuma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. Hideo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture, Japan Matsushita Electric Industrial Co., Ltd. (72) Kazufumi Nishida 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside the Matsushita Electric Industrial Co., Ltd. 1006 Matsushita Electric Industrial Co., Ltd. (72) Inventor Teruhisa Kamihara 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Nora Ono 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Yasuo Takebe 1006 Odakadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. 4G069 AA03 AA08 BA08A BB08A BB08B BC75B BE05A BE32A BE34A CC32 EB18Y FA03 FB13 5H018 AA06 AS02 BB05 BB12 BB16 DD05 DD08 EE01 EE05 EE11 EE16 EE17 EE18

Claims (9)

[Claims] 1. A fuel cell comprising a solid polymer electrolyte membrane and a pair of electrodes having a catalyst reaction layer sandwiching the solid polymer electrolyte membrane, wherein the electrode is formed of catalyst particles or a carrier of the catalyst particles. An electrode for a fuel cell, comprising a hydrogen ion diffusion layer on the surface. 2. The fuel cell electrode according to claim 1, wherein a diffusion layer of hydrogen ions is formed by chemically bonding a silane compound to the surface of the catalyst particles or the carrier of the catalyst particles. . 3. An organic compound having a basic functional group is modified on the surface of the catalyst particle or the carrier of the catalyst particle, and a hydrogen ion diffusion layer is formed by the organic compound and a hydrogen ion conductive solid electrolyte. The fuel cell electrode according to claim 1, wherein: 4. The fuel cell electrode according to claim 3, wherein the basic functional group has a nitrogen atom having a lone pair. 5. The fuel cell electrode according to claim 2, wherein the organic compound having a basic functional group is a silane compound. 6. The silane compound has a functional group capable of dissociating a hydrogen ion.
Or the fuel cell electrode according to 5. 7. The fuel cell electrode according to claim 2, wherein the silane compound has at least one of a hydrocarbon chain and a fluorocarbon chain. 8. A phenolic hydroxyl group, a carboxyl group,
The carbon particles or carbon fibers and the silane compound are chemically bonded via at least one functional group selected from a lactone group, a carbonyl group, a quinone group and a carboxylic anhydride. Or the fuel cell electrode according to 7. 9. A silane compound is immersed in a solvent containing a silane compound by immersing at least one type of material to be bonded selected from catalyst particles, a catalyst carrier, carbon particles, and carbon fibers. 3. A hydrogen ion diffusion layer is formed by chemically bonding the surface of the material to be joined and silicon atoms in the molecules of the silane compound after the chemical adsorption. 6. The method for producing an electrode for a fuel cell according to 3, 4, or 5.