JP2002110190A - Fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell of high performance by improving fuel permeability of a catalyzer, or by controlling fuel transmissivity of a polymer electrolytic membrane in the fuel cell using liquid fuel. SOLUTION: A fuel cell is provided with an electrode having a catalytic layer carrying an electron conductive polymer compound on at least a part of a catalytic metal. The fuel cell is also provided with a polymer electrolytic membrane, wherein a liquid fuel impermeable polymer compound and a hydrogen ion conductive polymer compound are compounded.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a fuel for hydrogen,
Alternatively, the present invention relates to a fuel cell which uses a liquid fuel such as alcohols such as methanol and ethanol, ethers such as dimethyl ether or ketones, and includes a hydrogen ion conductive polymer electrolyte membrane as a component.

[0002]

2. Description of the Related Art A fuel cell using a polymer electrolyte electrochemically reacts a fuel gas containing hydrogen or an alcohol such as methanol with an oxidizing gas containing oxygen such as air. Generates power and heat simultaneously. A general configuration of a conventional polymer electrolyte fuel cell will be described. As shown in FIG. 1, the polymer electrolyte fuel cell was formed by using a fine carbon powder carrying catalyst particles such as platinum as a catalyst, and mixing the catalyst with a hydrogen ion conductive polymer electrolyte. A catalyst layer 2 and a diffusion layer 3 disposed on the outer surface of the catalyst layer 2 and having both fuel permeability and electron conductivity.
And an electrode 4 comprising: A pair of electrodes 4 are arranged on both sides of the polymer electrolyte membrane 1 that selectively transports hydrogen ions. The structure including the pair of electrodes and the polymer electrolyte membrane is referred to as a membrane-electrode assembly (MEA) 5. As the polymer electrolyte membrane 1, perfluorosulfonic acid is generally used, and for the diffusion layer, water-repellent carbon paper or the like is used.

In order to prevent leakage of fuel and oxidant supplied to the electrode and to prevent mixing of fuel and oxidant, a gas seal material or gasket is arranged around the electrode with a polymer electrolyte membrane interposed therebetween. The sealing material and the gasket are preliminarily assembled integrally with the electrode and the polymer electrolyte membrane, and these may be collectively referred to as MEA. FIG. 2 shows a configuration of the unit cell. Outside the MEA 5, a pair of conductive separator plates 6 for mechanically fixing the MEA 5 are arranged. At a portion of the separator plate 6 which comes into contact with the MEA 5, a flow channel 7 for supplying fuel or oxidant to the electrode surface is formed. The gas flow path 7 further includes
It is responsible for carrying away products produced by the reaction and surplus fuel or oxidant that did not contribute to the reaction. Although the gas flow path can be provided separately from the separator plate, a method in which a groove is provided on the surface of the separator plate to form a gas flow path is generally used.

[0004] As described above, the pair of separator plates 6 is used for ME.
By fixing A5, supplying fuel to the flow path of one separator plate, and supplying oxidizing agent to the flow path of the other separator plate, an electromotive force of about 0.8 V can be generated. In order to use a fuel cell as a power source, a voltage of several volts to several hundred volts is usually required. For this reason,
A fuel cell is assembled by connecting the required number of unit cells 8 as shown in FIG. 2 in series. At this time, the gas flow path for supplying the fuel is formed on one surface of the separator plate inserted between the adjacent MEAs, and the gas flow path for supplying the oxidant is formed on the other surface. In this manner, the combination of the separator plate / MEA / separator plate / MEA is repeated to form a series connection configuration. In order to supply the fuel and the oxidant to the gas flow path, the pipe for supplying the fuel and the oxidant is branched into the number of separator plates to be used, and the branch is directly connected to the groove on the separator plate. A jig is required. This is referred to as a manifold, and the type directly connected to the fuel or oxidant supply pipe as described above is referred to as an external manifold. Some manifolds have a more simplified structure called internal manifolds. The internal manifold is one in which a through hole is provided in a separator plate having a flow path formed therein, an inlet and an outlet of the flow path pass through the hole, and fuel or oxidant is directly supplied from the hole.

Next, the electrolyte membrane and the catalyst layer will be described. The electrolyte membrane mainly has the following three functions. The first is
It is a function to take in and transfer hydrogen ions generated in the catalyst layer into the membrane. The second function is to form a conduction path by water molecules in order to quickly transmit the generated hydrogen ions. Third is to maintain a stable structure under the operating conditions of the fuel cell. In general, an electrolyte membrane having a structure in which the main chain has a fluorocarbon skeleton and has a strongly acidic functional group such as sulfonic acid or phosphonic acid at a side chain terminal thereof is used. The fluorocarbon skeleton has a structure excellent in thermal and chemical stability, and the strongly acidic functional group plays a role of hydrogen ion conductivity. Furthermore, the fluorocarbon chains that are water-repellent and the strongly acidic functional groups that are hydrophilic form a cluster structure of water molecules in the film, forming a hydrogen ion conductive path.

[0006] The catalyst layer mainly has the following four functions. The first function is to supply the fuel or oxidant supplied from the diffusion layer to the reaction site of the catalyst. Second,
This is a function to quickly supply hydrogen ions generated from fuel on the catalyst to the electrolyte membrane, and to quickly extract hydrogen ions necessary for the oxidant to react on the catalyst from the electrolyte membrane. The third function is to conduct electrons generated by the reaction on the catalyst and electrons required for the reaction on the catalyst. Fourth, it has a large reaction area and has a function of rapidly performing a catalytic reaction. As described above, the catalyst layer is required to have excellent fuel and oxidant permeability, hydrogen ion permeability, electronic conductivity, and catalytic performance.

As a conventional general technique, regarding gas permeation performance, a fine carbon powder such as acetylene black having a chain structure developed three-dimensionally connected to a catalyst layer is used, or a pore former is added. It has been proposed to deal with this by making the structure porous. Hydrogen ion permeability
By dispersing a hydrogen ion conductive polymer electrolyte near the catalyst in the catalyst layer to form a hydrogen ion network, the electronic conductivity is made up of an electron conductive material such as carbon fine powder or carbon fiber. By doing so, each is realized. Then, catalytic performance, a high metal particle reaction activity represented by Pt as very fine particles of several nanometers, and supported on carbon powder having a specific surface area of several tens to several hundreds of 1000 m ^2, the catalyst It has been improved by having a high dispersion in the layer. Further, in order to cause the reaction gas to react quickly on the catalyst, it is necessary to make the diffusion path of the reaction gas as short as possible.
It is formed in a thin layer of 0 μm, preferably 10 μm or less.

Further, as an electrode catalyst of a fuel cell, a platinum catalyst is used for an air electrode serving as a cathode and a fuel electrode serving as an anode. Hydrogen is used as a fuel, but the infrastructure of hydrogen gas has not been established. Therefore, in general, natural gas is used as the fuel, and alcohols such as methanol are used because of the convenience of being a liquid.
However, liquid fuels such as methanol or fuel obtained by reforming these hydrocarbon-containing fuels into hydrogen-rich gas,
Carbon monoxide, which is a poisoning substance of the electrode catalyst, is generated in the fuel gas or during the catalytic reaction. Efforts have been made to reduce the carbon monoxide content in reformers, but dozens to hundreds of ppm of carbon monoxide are contained in the fuel. When carbon monoxide is contained in the fuel, carbon monoxide is adsorbed on the surface of the platinum catalyst, and a catalyst poisoning phenomenon that hinders the oxidation reaction of hydrogen occurs.

As a solution, Japanese Patent Laid-Open Publication No. 6-24616 discloses
0, JP-A-7-246336, JP-A-7-246
299359, JP-A-8-66632, JP-A-8-509094, JP-A-10-27005
No. 6, JP-A-2000-467, JP-A-2000
Japanese Patent Application Laid-Open No. 10047/1999 and the like discloses that the Pt catalyst is Ru or M
Efforts have been made to oxidize and remove adsorbed carbon monoxide as an alloy with o, Ni, Fe and the like. Further, as disclosed in JP-A-63-97232 and JP-A-3-22361, many of the carbon monoxide resistant poisoning catalysts also function as methanol oxidation catalysts. Efforts have been made to select a suitable metal catalyst for the fuel used in this way.

[0010]

When a liquid fuel such as methanol is directly supplied to a fuel cell using a polymer electrolyte membrane as described above, the methanol permeation effect (methanol crossing) in which methanol permeates from the fuel electrode to the air electrode. Over) occurs. When a gas containing hydrogen is used as the fuel, hydrogen ions generated by the reaction shown in the formula (1) at the fuel electrode flow through the perfluorosulfonic acid membrane, which is a polymer electrolyte, through water molecules to form air. Equation (2) transmitted to the pole
Is performed. On the other hand, when methanol is used as fuel,
In addition to the hydrogen ions generated by the reaction of the formula (3) at the fuel electrode, unreacted methanol permeates through the perfluorosulfonic acid membrane, which is a polymer electrolyte membrane, and at the air electrode, the reaction of the formula (2) In addition, a direct oxidation reaction of methanol occurs. For this reason, the number of catalyst sites for the electrochemical reaction is reduced, oxygen is consumed, the overvoltage at the air electrode increases, and a sufficient battery voltage cannot be obtained.

H ₂ → 2H ⁺ + 2e ⁻ (1) 1 / 2O ₂ + 2H ⁺ + 2e ⁻ → H ₂ O (2) CH ₃ OH → CO + 4H ⁺ + 4e ⁻ (3) CO + H ₂ O → CO ₂ + 2H ⁺ + 2e ⁻ ( 4)

In order to reduce the crossover phenomenon of methanol, the fuel, methanol, must be reduced by several moles.
It must be diluted to a low concentration of 1 / L. Therefore, in order to extend the life of the battery, it is necessary to hold a container for storing a large amount of diluted fuel, and it has been difficult to make the battery itself compact. As is clear from the above, in order to obtain a high-performance battery, it is an issue to provide the electrolyte membrane with the ability to suppress methanol permeation.

Further, when methanol is used as a fuel, the reaction of the formula (3) occurs at the fuel electrode. Therefore, a large overvoltage is required at the fuel electrode as compared with the case where hydrogen gas is used as the fuel. Battery voltage cannot be obtained. In order to obtain a high-performance battery, it is also an issue to perform a methanol oxidation reaction at the fuel electrode smoothly and promptly.

[0014]

In order to solve the above problems, a fuel cell according to the present invention comprises a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, Means for supplying fuel to one of the electrodes and supplying an oxidizing agent to the other, wherein the electrode has a catalyst layer bonded to the proton conductive polymer electrolyte membrane, The catalyst layer is characterized by including catalyst particles having an electron conductive polymer compound supported on at least a part of the surface. The polymer compound is preferably a polymer compound having a heterocyclic ring.

The present invention also provides a hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and a fuel supply to one of the electrodes and an oxidant to the other. A fuel cell comprising:
The fuel cell is characterized in that the hydrogen ion conductive polymer electrolyte membrane is composed of a composite of a liquid fuel impermeable polymer compound and a hydrogen ion conductive polymer compound. It is preferable that the liquid fuel impermeable polymer compound is a linear aliphatic polymer compound or a linear aromatic polymer compound. The hydrogen ion conductive polymer compound is preferably a heterocyclic polymer compound having an unshared electron pair. The fuel includes alcohols, ethers,
And ketones.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention comprises a hydrogen ion conductive polymer electrolyte membrane and a pair of electrodes having a catalyst layer sandwiching the hydrogen ion conductive polymer electrolyte membrane. The present invention relates to a fuel cell in which at least a part of a metal surface carries or adheres a polymer compound having electron conductivity. That is, the greatest feature of the present invention is that at least a part of the catalytic metal in the electrode is in contact with the electron conductive polymer compound. With this electron conductive polymer compound, the oxidizing ability of the liquid fuel of the catalyst metal, for example, methanol can be promoted.

The electrode used in the present invention is preferably manufactured as follows. First, a catalyst body made of fine carbon powder carrying a platinum group metal catalyst and a dispersion of a hydrogen ion conductive polymer are mixed to prepare a catalyst layer forming ink, and a catalyst layer is formed from this ink. Next, the catalyst layer is immersed in a monomer solution of the electron conductive polymer compound, and an oxidative polymerization reaction of the monomer is performed, so that the polymerized polymer film is applied to at least a part of the catalyst metal.

The oxidative polymerization reaction is carried out by a chemical oxidative polymerization method using a Lewis acid catalyst such as FeCl ₃ or 1.5 V v
s. An electrochemical oxidation polymerization method by constant potential electrolytic polymerization to which a constant potential of about Ag / AgCl is applied can be used. When the electrochemical oxidation polymerization method using electrolytic polymerization is used, various characteristics such as the thickness of the polymer film can be electrically controlled. That is, the electrode performance can be easily controlled by controlling the polymer film.

FIG. 3 shows a model of the catalyst body in the catalyst layer according to the present invention. Reference numeral 9 denotes carbon fine particles in the catalyst layer, and the electron conductive polymer compound 11 is in contact with at least a part of the metal catalyst 10 supported on the carbon fine particles 9. Thereby, the supply of the fuel to the catalyst metal 10 is promoted. Further, the electron conductive polymer compound 11 improves the methanol oxidation ability of the catalyst metal. As the electron conductive polymer compound, a heterocyclic polymer compound which is suitable for oxidative polymerization and has conductivity can be used. Polypyrrole, polyaniline, polythiophene and the like are suitable as the electron conductive polymer compound.

According to another aspect of the present invention, there is provided a hydrogen ion conductive polymer electrolyte membrane, and a pair of electrodes having a catalyst layer sandwiching the hydrogen ion conductive polymer electrolyte membrane. The present invention relates to a fuel cell in which an ion-conductive polymer electrolyte membrane is a composite membrane composed of a liquid fuel-impermeable polymer compound and a hydrogen ion-conductive polymer compound. As the liquid fuel impermeable polymer compound, a material having an appropriate liquid fuel impermeability can be selected. Liquid fuel impermeability is measured by TOC (Total Organic) using methanol as fuel.
Carbon) measurement can be digitized. The liquid fuel impermeable polymer compound does not have the hydrogen ion conductivity required for the polymer electrolyte membrane as it is. Thus, in the present invention, by functioning as a composite with a hydrogen ion conductive polymer compound, the compound functions as a polymer electrolyte.

In order to form the composite membrane, for example, first, a liquid fuel-impermeable polymer compound membrane is immersed in a monomer of the ion-conductive polymer compound to impregnate the monomer into the membrane. Next, this film is immersed in a solution containing a Lewis acid catalyst such as FeCl ₃ to cause an oxidative polymerization reaction of the monomer. ) Hydrogen ion conductive polymer compounds are suitable for oxidative polymerization,
Further, a heterocyclic polymer compound having ionic conductivity can be used. Polypyrrole, polyaniline, polythiophene are suitable. Further, by using the polymer electrolyte composite membrane having liquid fuel impermeability, it is possible to use a high-concentration fuel, and it is possible to achieve higher performance, longer life, and compactness of the battery.

[0022]

The present invention will now be described in detail with reference to Examples.
The present invention is not limited only to them.

Example 1 A platinum catalyst and a ruthenium catalyst were supported on Ketjen Black EC (furnace black manufactured by Ketjen Black International) as conductive carbon powder. The weight ratio of the carbon powder, platinum and ruthenium was 45:30:25. 10 g of this catalyst powder, 35 g of water and 70 g of a polymer electrolyte alcohol dispersion (manufactured by Asahi Glass Co., Ltd., trade name: 9% FFS) were weighed and dispersed using an ultrasonic stirrer to prepare a catalyst layer forming ink X. . Also, in the same carbon powder as above,
A platinum catalyst was supported. The weight ratio between the carbon powder and platinum was 50:50. 10 g of this catalyst powder, 35 g of water and 70 g of an alcohol dispersion of the same polymer electrolyte as above
Was measured and dispersed using an ultrasonic stirrer to prepare an ink Y for forming a catalyst layer.

After washing with an aqueous solution of nitric acid, an ink X for forming a catalyst layer was applied onto the gold electrode which was electrolytically washed with an aqueous solution of sulfuric acid, and dried to produce an electrode X having the catalyst layer X. 0.25 mol / L pyrrole, 0.2 m sodium carbonate
ol / L of the aqueous solution was degassed with nitrogen for 15 minutes, and then the electrode X was immersed in this aqueous solution, and 1.5 V vs. Ag / Ag
Electrolysis was performed for 30 minutes at a constant potential of Cl ₃ to generate polypyrrole on the surface of the catalyst layer. Thus, an electrode A having a catalyst layer A having polypyrrole disposed on the surface was produced. Electrode A for working electrode, gold wire for counter electrode, Ag / A for reference electrode
Using gCl ₃ , methanol and sulfuric acid were each 1.0 m
In an aqueous solution containing ol / L, cyclic voltammetry was performed under the conditions of a scanning speed of 50 mA / sec and a scanning range of −0.12 to +1.2 V vs. Ag / AgCl ₃ . The same test was performed using the electrode X as a comparative example.

Example 2 A hydrogen ion conductive polymer electrolyte was prepared by using the catalyst layer A peeled off from the electrode A prepared as described above as an anode and the catalyst layer Y prepared from the catalyst layer forming ink Y as a cathode. Membrane (Dupont, USA: N
afion112) to assemble MEA-A. Next, carbon powder (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name:
Aqueous dispersion of polytetrafluoroethylene (Denkin, trade name: Lubron LDW)
-40) was mixed with 50 g to prepare a water-repellent layer ink, and this was coated with carbon paper (trade name: TGPH060, manufactured by Toray Industries, Inc.).
H) coated on one side and 380 ° C using hot air dryer
To form a diffusion layer. The pair of diffusion layers thus produced was joined to both sides of the above MEA-A to form a cell A
Was assembled. As a comparative example, the catalyst layer X was used as an anode, and the catalyst layer Y was used as a cathode.
X was produced. Then, the same diffusion layer as described above was joined to each of the catalyst layers, thereby producing a cell X.

Example 3 A polyimide (PI) film (thickness: 30 μm) (a product name: Kapton, manufactured by Du Pont-Toray Co., Ltd.), which is a liquid fuel-impermeable polymer compound, was used. This was cut into a 6 cm square, immersed in a 100% pyrrole solution (manufactured by Kanto Kagaku) for 24 hours, and then washed with pure water. Subsequently, the film was immersed in a 1.0 mol / L aqueous solution of FeCl ₃ for 24 hours to perform chemical oxidative polymerization of pyrrole impregnated in the polyimide film, and then washed with pure water. Thus polyimide-
A polypyrrole (PI-Py) composite membrane was produced. The polyimide-polypyrrole composite membrane was used as a hydrogen ion conductive polymer electrolyte, the catalyst layer X was adhered to the anode side thereof, and the catalyst layer Y was adhered to the cathode side thereof to produce MEA-B. The layers were joined to form cell B.

Example 4 A polypropylene (PP) film (thickness: 30 μm) which is a liquid fuel impermeable polymer compound
(Toray Co., Ltd .: Trefan 50-2500) in the same manner as in Example 3, using polypropylene-polypyrrole (P
A P-Py) composite film was produced. The catalyst layer X
And Y were pasted to produce MEA-C, and a diffusion layer was joined to produce Cell C.

Example 5 A polyvinylidene fluoride (PVdF) film (thickness: 3) which is a liquid fuel impermeable polymer compound
0 μm), a polyvinylidene fluoride-polypyrrole (PVdF-Py) composite membrane was prepared in the same manner as in Example 3, and the catalyst layers X and Y and the diffusion layer were joined to form MEA-D.
And cell D. As a comparative example, a cell Y was prepared by using a Nafion membrane as the proton conductive polymer electrolyte and bonding the catalyst layers X and Y and the diffusion layer in the same manner.

Production of unit cell: Next, a rubber gasket plate having a manifold hole was joined to the outer periphery of each cell produced as described above. A unit cell was formed by laminating a separator plate made of a resin-impregnated graphite plate having an outer dimension of 12 × 12 cm ² , a thickness of 1.5 mm, and a gas channel depth of 0.8 mm on both sides of the cell sheet. A current-collecting plate made of gold-plated stainless steel, an insulating plate made of an electric insulating material, and an end plate were sequentially stacked on both ends of the unit cell, and these were fixed with fastening rods. The fastening pressure was 20 kgf / cm ² per unit area of the separator plate. Battery A, Battery B, Battery C, Battery D, Battery X, and Battery Y were assembled from Cell-A, Cell-B, Cell-C, Cell-D, Cell-X, and Cell-Y, respectively, by the above method. .

A 2 mol / l aqueous methanol solution as a representative example of a liquid fuel was applied to the anode of each of the above cells at a temperature of 60 ° C.
The cathode was supplied with air through a bubbler at 70 ° C., and a discharge test as a direct methanol fuel cell was performed under the conditions of a cell temperature of 75 ° C. and an air utilization of 40%. Further, under the same measurement conditions, the thickness of each liquid fuel-impermeable polymer compound was changed, and a discharge test of the battery was performed. The battery voltage at a current density of 200 mA / cm ² was compared.
Further, the concentration of methanol as a liquid fuel is adjusted to 1 to 10 mo.
The discharge test of the battery was performed by changing the range of 1 / L, and the battery voltage at a current density of 200 mA / cm ² was compared.

Evaluation test: As a result of cyclic voltammetry measurement using each of the electrode A having the catalyst layer A of the above example and the electrode X having the catalyst layer X of the comparative example, both the electrodes A and X were +0. 0.5V and + 0.7V
A peak was observed. This indicates that the oxidation reaction of methanol represented by the formula (3) occurs on the catalyst at the electrodes A and X. Table 1 shows + 0.5V,
And the oxidation current value of the electrode A and the electrode X at a potential of 0.7 V.

[0032]

[Table 1]

When electrode A is used, that is, when polypyrrole contacts at least a part of the catalyst metal,
Compared with the electrode X, the methanol oxidation current value at +0.5 V was from 1.2 mA / cm ² to 1.7 mA / cm ² (+
0.5 V). This is presumably because polypyrrole supported on the catalyst metal promoted the supply of methanol and improved the methanol oxidation ability of the catalyst.

FIG. 4 shows a battery A of the present invention using a catalyst layer A,
7 shows a comparison of current-voltage characteristics of a battery X of a comparative example using the catalyst layer X. In each of the batteries, a perfluorosulfonic acid membrane was used as the electrolyte membrane, and thus high output was not obtained due to crossover of methanol. However, comparing the battery voltage at a current density of 200 mA / cm ² ,
Battery A was shown to be higher than Battery X. This indicates that the effect of polypyrrole in the catalyst layer can be obtained in an actual battery.

FIG. 5 shows the current-voltage of the batteries B, C, D, E and the battery Y of the comparative example using the composite membrane comprising the liquid fuel impermeable polymer compound and the hydrogen ion conductive polymer compound. Show characteristics. In the battery Y of the comparative example, the battery voltage sharply decreases in the high current density region, whereas the batteries B, C, and D using the composite membrane according to the present invention have stable outputs even in the high current density region. Was obtained.
Above all, the battery C, that is, the one using the polypropylene-polypyrrole composite membrane as the electrolyte membrane showed a high battery voltage. This indicates that the composite membrane of the present invention can be used in a fuel cell using methanol as a fuel. Among them, it can be seen that the composite membrane in which polypropylene was selected as the liquid fuel impermeable polymer compound gives a high battery voltage.

FIG. 6 shows a current density of 200 m when the thickness of the liquid fuel-impermeable polymer compound serving as the base of the composite membrane was changed in the batteries B, C, D and the battery Y of the comparative example.
A comparison of the battery voltage at A / cm ² is shown. Battery Y of the comparative example showed the highest voltage when the film thickness was around 120 μm. On the other hand, Battery B, Battery C, and Battery D exhibited the highest voltage when the film thickness was 30 μm or less. Above all, the battery B, that is, the battery using the polyimide-polypyrrole composite film, showed the highest value when the film thickness was about 10 μm. This is because in the battery Y of the comparative example, since the perfluorosulfonic acid membrane of the electrolyte membrane easily permeated methanol,
If there is no film thickness of about 0 μm, methanol crossover cannot be sufficiently controlled. On the other hand, the composite membrane of the present invention has low methanol permeability, sufficiently suppresses the crossover of methanol even when the film thickness is small, and also improves the hydrogen ion conductivity by reducing the film thickness, High battery performance was obtained.

FIG. 7 shows a current density of 200 mA / cm ² when the methanol concentration of the aqueous methanol solution supplied to each fuel electrode of the batteries B, C, D and the battery Y of the comparative example was changed.
The comparison of the battery voltage in the above was shown. Battery Y of the comparative example is
The battery voltage rose to a methanol concentration of 2 mol / L, but then dropped sharply. On the other hand, battery B, battery C,
And the battery D, the methanol concentration 5 mol / L and the battery Y
The highest battery voltage was shown at a concentration of twice or more of the above. From these results, it can be seen that the composite membrane of the present invention has an effect of improving battery characteristics in a high methanol concentration region. This indicates that the battery of the present invention has a longer life than the battery of the comparative example when the fuel of the same capacity is used.

In the above embodiment, polyimide, polypropylene, and polyvinylidene fluoride are used as the liquid fuel impermeable polymer compound, but the present invention is not limited to these. Polyethylene terephthalate, polyphenylene sulfide, ethylene-tetrafluoroethylene copolymer, polyimide, polyethylene, polybenzimidazole and the like can also be used. Further, in the examples, polypyrrole was used as the proton conductive polymer compound, but the present invention is not limited to this, and polyaniline, polythiophene, and the like may be used. Further, although methanol was used as the liquid fuel, the invention is not limited to this, and alcohols such as ethanol, ethers such as dimethyl ether, or ketones can also be used. The liquid fuel may be heated in advance and supplied in gaseous form.

[0039]

As described above, according to the catalyst layer of the present invention,
It is possible to provide a fuel cell in which the catalyst metal has an improved fuel oxidizing ability and exhibits higher performance. In addition, an electrolyte membrane in which a liquid fuel-impermeable polymer compound and a hydrogen ion-conductive polymer compound are combined can control the amount of fuel permeated through the electrolyte membrane, thereby providing a fuel cell exhibiting higher performance. it can.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view showing an MEA which is a component of a fuel cell.

FIG. 2 is a schematic longitudinal sectional view showing a configuration of a unit cell of a fuel cell.

FIG. 3 is a diagram showing a model of a catalyst layer of the present invention.

FIG. 4 is a diagram showing current-voltage characteristics of a battery A of an example of the present invention and a battery X of a comparative example.

FIG. 5 is a diagram showing current-voltage characteristics of batteries B, C, and D of an example of the present invention and battery Y of a comparative example.

FIG. 6 is a diagram showing a comparison between the thickness of the composite film and the voltage and voltage at a current density of 200 mA / cm ² of the batteries B, C, and D of the example of the present invention and the battery Y of the comparative example.

FIG. 7 is a diagram showing a comparison between the concentration of methanol supplied to the fuel electrode and the voltage and voltage at a current density of 200 mA / cm ² in the batteries B, C, and D of the example of the present invention and the battery Y of the comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 polymer electrolyte membrane 2 catalyst layer 3 diffusion layer 4 electrode 5 MEA 6 separator plate 7 gas channel 8 unit cell 9 carbon particle 10 catalyst particle 11 electron conductive polymer compound

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 8/10 H01M 8/10 // B01D 71/34 B01D 71/34 F-term (Reference) 4D006 GA12 HA41 KE18Q MA03 MA09 MA10 MB06 MC23 MC23X MC28 MC28X MC29 MC29X MC58 MC58X MC71 MC71X NA12 NA51 NA54 PA01 PB32 PC80 5H018 AA06 AA07 AS02 AS03 EE03 EE05 EE17 5H026 AA06 AA08 CX05 EE18

Claims (6)

[Claims] 1. A hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and means for supplying fuel to one of the electrodes and supplying an oxidant to the other. In a fuel cell, the electrode has a catalyst layer bonded to the proton conductive polymer electrolyte membrane, and the catalyst layer carries an electron conductive polymer compound on at least a part of its surface. A fuel cell comprising the catalyst particles prepared as described above. 2. The fuel cell according to claim 1, wherein the polymer compound is a polymer compound having a heterocyclic ring. 3. A hydrogen ion conductive polymer electrolyte membrane, a pair of electrodes sandwiching the hydrogen ion conductive polymer electrolyte membrane, and means for supplying fuel to one of the electrodes and supplying an oxidizing agent to the other. The fuel cell according to claim 1, wherein the hydrogen ion conductive polymer electrolyte membrane is a composite of a liquid fuel impermeable polymer compound and a hydrogen ion conductive polymer compound. 4. The fuel cell according to claim 3, wherein the liquid fuel-impermeable polymer compound is a straight-chain aliphatic polymer compound or a straight-chain aromatic polymer compound. 5. The hydrogen ion conductive polymer compound,
4. A heterocyclic polymer having an unshared electron pair.
Or the fuel cell according to 4. 6. The fuel according to claim 1, wherein the fuel is selected from the group consisting of alcohols, ethers, and ketones.
6. The fuel cell according to any one of 5.