JPH06236762A - Polymer electrolytic flue cell - Google Patents

Abstract

PURPOSE:To improve output characteristic by mixing a powdery hole forming component to a catalyst layer forming component to form a catalyst layer, and removing the porous state forming component after the formation to form a hole. CONSTITUTION:The body of a fuel cell is formed of an electrolytic film 1 consisting of a positive ion exchange film, and positive and negative gas diffused electrodes 2, 3 of hydrogen and oxygen gases which are bonded to both surfaces of the film 1. A catalyst is supported on the electrolytic film 1 sides of the gas diffused electrodes 2, 3, and a cell reaction is generated on the critical surface between the catalyst layer of each gas diffused electrode 2, 3 and the electrolytic film 1. Prior to the formation of the catalyst later, a porous state forming component is mixed to the catalyst layer forming composition, and the hole forming component is removed after the formation of the catalyst layer, whereby the hole quantity and average hole diameter can be controlled, and consequently, the output characteristic as a fuel cell can be improved.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polymer electrolyte fuel cell (PEFC).

[0002]

2. Description of the Related Art In recent years, fuel cells have been attracting attention due to their characteristics of low pollution and high efficiency. A fuel cell is a cell in which a fuel such as hydrogen or methanol is electrochemically oxidized using oxygen or air to convert the chemical energy of the fuel into electric energy and to extract it.

Such a fuel cell has a phosphoric acid type, a molten carbonate type, a solid oxide type, and
And the polymer electrolyte type etc. are classified. Among them, a polymer electrolyte fuel cell (PEFC) using a cation exchange membrane as an electrolyte has recently been particularly attracting attention because of its good operability at low temperature and high output density. As shown in FIG. 2, the basic structure of the PEFC main body is composed of an electrolyte membrane 1 composed of a cation exchange membrane and positive and negative gas diffusion electrodes 2 and 3 bonded to both sides thereof. A catalyst is supported on at least the electrolyte membrane 1 side of the gas diffusion electrodes 2 and 3, and a battery reaction occurs at the interface between the catalyst layer and the electrolyte membrane 1 of each gas diffusion electrode 2 and 3.

Then, for example, hydrogen gas is supplied to the gas diffusion electrode 2, oxygen gas is supplied to the gas diffusion electrode 3, and an external load circuit is connected between the gas diffusion electrodes 2 and 3, respectively. At the interface between the catalyst layer and the electrolyte membrane 1,
The reaction of 2H ₂ → 4H ⁺ + 4e ⁻ occurs. H ⁺ (proton) generated by this reaction passes through the electrolyte membrane 1 and e ⁻
The (electrons) move to the opposite gas diffusion electrode 3 through the load circuit, and the reaction of O ₂ + 4H ⁺ + 4e ⁻ → 2H ₂ O occurs at the interface between the electrolyte membrane 1 and the catalyst layer of the gas diffusion electrode 3. As a result, electric energy is obtained at the same time as water is generated.

Therefore, the degree of supply of the reaction gas to the reaction interface greatly affects the output performance of the battery. However, even with the above-mentioned conventional method, the output performance is not sufficient depending on the application, so that the appearance of a PEFC having higher output performance is desired.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art, and is a polymer electrolyte fuel cell (PEF) having higher output performance.
C) is provided.

[0007]

[Means for Solving the Problems] In order to achieve the above object, as a result of intensive studies, as a result, a powdery pore-forming component is mixed before molding a catalyst layer in which a reaction interface is formed, and a post-molding pore-forming component is mixed. The inventors have found that the removal enables control of the amount of pores and the average pore diameter, and as a result, the output characteristics of the fuel cell are greatly improved, leading to the present invention.

That is, the present invention provides a polymer electrolyte fuel cell having an ion exchange membrane serving as an electrolyte and a gas diffusion electrode having a catalyst layer, wherein the catalyst layer is a catalyst layer containing a powdery pore-forming component. The polymer electrolyte fuel cell is characterized in that the powdery pore-forming component is removed after molding with the composition for use to form pores.

Here, the catalyst layer means a portion of the gas diffusion electrode on which the catalyst is carried. Further, the composition for forming a catalyst layer has at least a powdery hole forming component and a catalyst-supporting conductive material, and if necessary, a proton conducting agent, a water repellent,
It contains a binder and the like. This catalyst layer may support a catalyst after being molded, and in this case, a conductive material that does not support a catalyst is used.

In the polymer electrolyte fuel cell of the present invention, the ion exchange membrane serving as an electrolyte has a fluorinated polymer as a skeleton, and ion exchange groups include a sulfonic acid group, a carboxyl group, a phosphoric acid group, and a phosphonic acid. Those having any one or a plurality of groups are included. As such an ion exchange membrane, for example, one or more kinds of monomers represented by the following formula (1) are essential components, and one or more kinds of monomers selected from the group of monomers described below are copolymerized therewith. There is a copolymer. _{Y- (CF 2) a - (} CFR 1) b - (CFR 1 ') c -O- - _{[CF (CF 2 X) -CF 2} -O ] _{n -CF = CF 2 ............ (1} ) (wherein, -Y _{is, -SO 3 H, -SO 2 F} , -SO 2 N
_{H 2, -SO 3 NH 4,} -CN, -COOH, -CO
F, -COOR (R is an alkyl group having 1 to 10 carbon atoms),
-PO is a ₃ H ₂ or PO ₃ H. a is an integer of 0 to 6, b is an integer of 0 to 6, c is 0 or 1, and a
+ B + c ≠ 0, and n is an integer of 0 to 6. X is
When n ≧ 1, it is any one kind of Cl, Br, or F, or a combination of plural kinds, and R ₁ and R ₁ ′ are
Are independently selected from F, Cl, perfluoroalkyl groups having 1 to 10 carbon atoms, and fluorochloroalkyl groups having 1 to 10 carbon atoms. ) And, as the monomer group to be copolymerized with this, tetrafluoroethylene, trifluoromonochloroethylene, trifluoroethylene, vinylidene fluoride,
1,1-difluoro-2,2-dichloroethylene, 1,
1-difluoro-2-chloroethylene, hexafluoropropylene, 1,1,1,3,3-pentafluoropropylene, octafluoroisobutylene, ethylene, vinyl chloride, and alkyl vinyl esters.

The catalyst layer included in the gas diffusion electrode in the present invention is composed of a conductive material carrying fine particles of a catalytic metal, and if necessary, a proton conductive material, a water repellent, and a binder. May be included. Further, a layer containing a conductive material that does not support a catalyst and optionally a water repellent or a binder may be formed outside the catalyst layer.

The catalyst metal used in this catalyst layer may be any metal that promotes the oxidation reaction of hydrogen and the reduction reaction of oxygen, such as lead, iron, manganese, cobalt, chromium and gallium. , Panadium, tungsten, ruthenium, iridium, palladium, platinum or rhodium, or alloys thereof.

The particle size of the metal serving as the catalyst is, for example, 10 to 30.
Set to 0Å. The smaller the particle size, the higher the catalytic performance,
If it is less than 10 Å, it is difficult to make it, and
If it is larger than Å, the required catalyst performance cannot be obtained. The preferable particle size of the catalytic metal is 15 to 100Å. The supported amount of the catalyst is, for example, 0.01 to 10 m when the electrode is molded.
g / cm ² is preferred. If it is less than 0.01 mg / cm ² , the performance of the catalyst is not exhibited, and if it exceeds 10 mg / cm ² , the cost increases. This value is 0.1-0.5 mg / c
It is preferably m ² .

Any material can be used as the conductive material as long as it is an electrically conductive material, and examples thereof include various metals and carbon materials. Examples of the carbon material include carbon black such as furnace black, channel black, and acetylene black, activated carbon, graphite, and the like, and these are used alone or in combination. As the water repellent, for example, fluorinated carbon or the like is used.

Various resins are used as the binder, but a fluororesin having water repellency is also preferable. And
Among the fluororesins, those having a melting point of 400 ° C. or lower are more preferable, and examples thereof include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and tetrafluoroethylene-hexafluoropropylene copolymer.

The proton conducting material may be any compound as long as it has a functional group capable of conducting a proton, but a fluorinated polymer is used as a skeleton and a functional group capable of conducting a proton is a sulfonic acid group or a carboxyl group. Those having any one or more of a phosphoric acid group and a phosphoric acid group are preferable. Examples of such a material serving as a proton conductive material include [A] one or more types of monomers represented by the above formula (1) as an essential component, and one or more types selected from the above-mentioned monomer group. A copolymer obtained by copolymerizing at least one type of monomer, [B] a polymer obtained by polymerizing at least one type of monomer represented by the above formula (1), and [C] represented by the above formula (1). monomers [D] trifluoromethanesulfonic acid, fluoro sulfonic acid, trifluoroacetic ethanesulfonic acid, tetrafluoro-propanesulfonic acid, perfluoroalkyl (C ₄ ~
C ₁₂₎ sulfonic acid, 3- [fluoroalkyl (C ₆ -C
₁₁ ) oxy] -1-alkyl (C ₃ -C ₄ ) sulfonic acid, and 3- [ω-fluoroalkanoyl (C ₆ -C
₈ ) Monofunctional fluorine-containing hydrocarbon sulfonic acids such as -N-ethylamino] -1-propanesulfonic acid, difunctional fluorine-containing hydrocarbon sulfonic acids such as [E] tetrafluoroethanedisulfonic acid,
[F] Fluorine-containing aromatic sulfonic acid derivative such as trifluoromethanebenzenesulfonic acid, [G] trifluoroacetic acid, fluoroalkyl (C ₂ -C ₂₀ ) carboxylic acid, perfluoroalkyl (C ₇ -C ₁₃ ) carboxylic acid, etc. Monofunctional fluorine-containing hydrocarbon carboxylic acids, [H]
Bifunctional fluorine-containing hydrocarbon carboxylic acids such as difluoromethane dicarboxylic acid and tetrafluoroethane dicarboxylic acid, [I] fluorine-containing hydrocarbon phosphonic acids such as difluoromethane diphosphonic acid, [J]
Fluorine-containing hydrocarbon thiosulfonic acids, fluorosulfonimides such as [K] trifluoromethanesulfonimide, [L] monoperfluoroalkyl (C _6-
C ₁₆ ) Fluorine-containing hydrocarbon phosphoric acids such as phosphoric acid, and the like, which may be used alone or in admixture of two or more.

In the case of a polymer, two or more monomers are linked, but a molecular weight of 5,000 or more is preferable. The larger the molecular weight, the better the degree of entanglement with the conductive material in the catalyst layer, and the better the durability. Although the low molecular weight compound can be used alone,
In that case, it is limited to solid compounds. This is because if the proton conductive material is liquid, it is highly likely that it will be dissolved in water generated by the cell reaction and removed outside the system when it is operated as a fuel cell.

As a method for allowing the proton conductive material to exist in the catalyst layer, the proton conductive material may be mixed in a solution state or a powder state with the raw material powder forming the catalyst layer, and the mixture may be molded to form the catalyst layer. Alternatively, the catalyst layer of the gas diffusion electrode formed in advance may be impregnated with the solution of the proton conductive material. Examples of the solvent for the proton conductive material include alcohols such as methanol, ethanol, propanol, and butanol, N, N′-dimethylacetamide,
Examples of the solvent include polar solvents such as N, N′-dimethylformamide, dimethyl sulfoxide and sulfolane, and hydrophilic solvents such as cyclic ethers such as tetrahydrofuran. Two or more kinds of mixed solvents selected from these solvents, or a mixed solvent thereof. It is also possible to use a mixed solvent of a solvent and water.

In the present invention, when forming a catalyst layer, a powdery pore-forming component is included and removed by post-treatment to form controlled pores. That is, for example, a catalyst-supporting powdery conductive material (in the case of supporting the catalyst after molding, a conductive material that does not support the catalyst), a pore-forming component, and, if necessary,
The proton conducting material, the binder, and the water repellent are uniformly mixed in, for example, water and dried to obtain a catalyst layer forming composition which is a raw material powder for the catalyst layer. Liquids such as solvent naphtha, toluene and benzene are added to this raw material powder to form a paste, which is molded into a required catalyst layer shape. After drying, the pore-forming agent is removed by post treatment such as washing with water, washing with alkaline water, and heat treatment depending on the pore-forming agent used.

Examples of the pore-forming agent include water-soluble inorganic salts such as [M] sodium chloride, potassium chloride, ammonium chloride, sodium carbonate, calcium carbonate, sodium sulfate and sodium phosphate, [N] silica gel and silica sol. Inorganic salts soluble in alkaline aqueous solution such as alumina, thermally decomposable organic polymer compounds such as [O] polyacetal and Avicel, and water-soluble organic compounds such as [P] polyvinyl alcohol and polyethylene glycol. The particle size of the pore-forming agent powder and its distribution have a great effect on the average particle size and distribution of the pores formed in the catalyst layer together with the particle size of the conductive material used. Therefore, the particle size of the conductive material and the particle size of the pore-forming agent are selected according to the required average pore size and distribution. It is also effective to use two or more of the above pore-forming agents in combination in order to obtain the required average pore diameter and distribution.
Various types of silica sol having a substantially uniform particle size are commercially available, which is very effective for controlling the pore size.

Further, sodium chloride and the like can be removed completely easily by washing with water, which is very effective. Furthermore, polyacetal can be treated at a relatively low temperature of about 200 ° C. and completely removed, so that a special feature is that a step for removing pore-forming components is not particularly required. The addition amount of the pore-forming component depends on the required amount of pores, but is preferably 30 to 160% by volume with respect to the volume of the catalyst layer-forming composition. If it is too small, the amount of voids will be insufficient, and the reaction gas supply will be small, resulting in performance degradation. On the other hand, if the amount is too large, the amount of voids becomes too large, which causes a decrease in output density.

In the method of impregnating the catalyst layer with the solution of the proton conductive material, for example, the concentration of the solution is set to 1 to 10% by weight, and this is impregnated into the pores of the catalyst layer which is a porous body and then dried. The ion exchange membrane as the electrolyte and the gas diffusion electrode are joined using a device capable of heating and pressurizing. Generally, for example, a hot press machine, a roll press machine or the like is used. The pressing temperature at that time may be equal to or higher than the glass transition temperature of the ion exchange membrane used as the electrolyte, and is preferably 120 to 250 ° C. The pressing pressure depends on the hardness of the gas diffusion electrode used, but is, for example, 5 to 200 kg / cm ² . If it is less than 5 kg / cm ² , bonding between the ion exchange membrane and the electrode will be insufficient and 2
When it exceeds 00 kg / cm ² , the gas diffusion electrode has too few pores. The preferred value of pressing pressure is 20-100
It is kg / cm ² .

It is preferable to insert a spacer thinner than the thickness of the electrode during hot pressing because it is possible to prevent the number of holes in the gas diffusion electrode from decreasing. Further, it is preferable to perform hot pressing in a state where the ion exchange membrane is wet in the coexistence of water, a solvent or the like, because the output performance is improved. The reason for this is not clear, but it is considered that the water content in the ion-exchange membrane increases.

In the polymer electrolyte fuel cell of the present invention, by using the catalyst layer having pores formed by adding the pore forming agent, the reaction gas can be sufficiently supplied to the reaction point. As a result, it is possible to improve the output characteristics, especially the performance in high current density measurement.

[0025]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples.

[0026]

Example 1 18 g of Tokai Black # 5500 (trademark manufactured by Tokai Carbon Co., Ltd.) and 1.25 g of Triton X-100 (trademark manufactured by Wako Pure Chemical Industries, Ltd.) were added to 450 g of water, and the mixture was stirred and mixed at room temperature for 30 minutes. . Next, 12.9 g of Polyflon D-2 [trademark of Dickin Co., Ltd.] and silica sol [Snowtex 50 trademark of Nissan Kagaku Co., Ltd.] were added to this mixture.
41.5 g was added and mixed with stirring for 30 minutes. The mixture was dried in a hot air drier at 100 ° C. for 2 days. The obtained powder was finely divided by a mill and 5 g was weighed from the fine powder. To this, 16 ml of solvent naphtha (manufactured by Kishida Chemical Co., Ltd.) was added, and after mixing, a film was formed on a suspension 304 plate. This film was baked in a hot air drier at 250 ° C. for 1 hour and further at 350 ° C. for 2 minutes. The membrane was washed with a 0.8 mol / l sodium hydroxide solution (water: ethanol = 50: 50% by volume). Then, it was washed with water, and after confirming that it was neutral, it was dried. The obtained film was impregnated with a 12% by weight solution prepared from chloroplatinic acid [special grade manufactured by Wako Pure Chemical Industries, Ltd.] and ethanol [special grade manufactured by Wako Pure Chemical Industries, Ltd.], followed by drying, and further under a hydrogen atmosphere, The reduction reaction was performed at 150 ° C. The amount of platinum carried was 3.0 mg / cm ² . The porosity of this catalyst layer is measured by a pore size distribution measuring device Poisizer 9320.
It was 0.76 when measured by [manufactured by Shimadzu Corporation].

10 cm ² was cut out from this catalyst layer, and the weight was measured and found to be 0.191 g. This catalyst layer was impregnated with 0.24 ml of a 5% by weight Nafion solution [manufactured by Andrich Corporation] concentrated to 10% by weight and dried to form an electrode. The weight of this electrode was measured and found to be 0.215 g. Two electrodes and a thickness of 100 μm
Was joined by hot pressing at 140 ° C. for 90 seconds to prepare the fuel cell of the present invention.

The output performance was evaluated by the single cell evaluation device shown in FIG. H ₂ gas flow rate 100 ml / min, oxygen gas flow rate 50 ml / min, cell temperature 55 ° C., humidification temperature 7
It was carried out under the conditions of 0 ° C. and normal pressure. The results are shown in Fig. 1.

[0029]

Example 2 Tokai Black # 5500 [trademark manufactured by Tokai Carbon Co., Ltd.] 18 g and Triton X-100 [trademark manufactured by Wako Pure Chemical Industries, Ltd.] 1.25 g were added to 450 g of water, and the mixture was stirred and mixed at room temperature for 30 minutes. . Next, 12.9 g of Polyflon D-2 (trademark manufactured by Dickin Co., Ltd.) and 13 g of homopolymer raw material powder (average particle size 250 μm) for Tenac [trademark of Asahi Kasei Corporation] type 5010 were added to this mixture. Stir and mix for minutes.

This mixture was dried in a hot air dryer at 100 ° C. for 2 days. The obtained powder was finely divided by a mill and 5 g was weighed from the fine powder. To this, 16 ml of solvent naphtha (manufactured by Kishida Chemical Co., Ltd.) was added, and after mixing, a film was formed on a suspension 304 plate. This film was placed in a hot air dryer at 250 ° C. for 1 hour,
Further, it was baked at 350 ° C. for 2 minutes. The obtained membrane was impregnated with a 12% by weight solution prepared from chloroplatinic acid [special grade manufactured by Wako Pure Chemical Industries, Ltd.] and ethanol [special grade manufactured by Wako Pure Chemical Industries, Ltd.], followed by drying, and further under a hydrogen atmosphere, The reduction reaction was performed at 150 ° C. The amount of platinum carried was 3.5 mg / cm ² . The porosity of this catalyst layer was 0.80 when measured with a pore size distribution measuring device Poisizer 9320 (manufactured by Shimadzu Corporation).

10 cm ² was cut out from this catalyst layer, and the weight was measured and found to be 0.181 g. This catalyst layer was impregnated with 0.24 ml of a 5% by weight Nafion solution [manufactured by Andrich Corporation] concentrated to 10% by weight and dried to form an electrode. The weight of this electrode was measured and found to be 0.205 g. Two electrodes and a thickness of 100 μm
And the Aciplex membrane (trademark, manufactured by Asahi Kasei Kogyo Co., Ltd., equivalent weight 1000 g / equivalent) were joined by hot pressing at 140 ° C. for 90 seconds to prepare the fuel cell of the present invention.

Single cell evaluation was performed under the same conditions as in Example 1. The results are shown in Fig. 1.

[0033]

Comparative Example 1 Tokai Black # 5500 (trademark manufactured by Tokai Carbon Co., Ltd.) 18 g and Triton X-100 [trademark manufactured by Wako Pure Chemical Industries, Ltd.] 1.25 g were added to 450 g of water, and the mixture was stirred and mixed at room temperature for 30 minutes. . Next, 12.9 g of Polyflon D-2 [trademark of Dickin Co., Ltd.] was added to this mixture, and 3
Mix for 0 minutes with stirring. 100 parts of this mixture in a hot air dryer
C, dried for 2 days. Finely pulverize the obtained powder with a mill,
5 g of it was weighed. To this, add 16 ml of solvent naphtha (manufactured by Kishida Chemical Co., Ltd.), mix, and then add suspension 304
The film was formed on the plate. This membrane is heated in a hot air dryer at 250 ° C,
It was further baked for 1 hour at 350 ° C. for 2 minutes. The obtained membrane was impregnated with a 12% by weight solution prepared from chloroplatinic acid [special grade manufactured by Wako Pure Chemical Industries, Ltd.] and ethanol [special grade manufactured by Wako Pure Chemical Industries, Ltd.], followed by drying, and further under a hydrogen atmosphere, 150 ° C
The reduction reaction was carried out at. Platinum loading is 2.9mg / cm
^{Was 2} . The porosity of this catalyst layer was 0.66 when measured with a pore size distribution measuring device Poisizer 9320 (manufactured by Shimadzu Corporation).

10 cm ² was cut out from this catalyst layer, and the weight was measured and found to be 0.206 g. This catalyst layer was impregnated with 0.24 ml of a 5% by weight Nafion solution [manufactured by Andrich Corporation] concentrated to 10% by weight and dried to form an electrode. The weight of this electrode was measured and found to be 0.230 g. Two electrodes and a thickness of 100 μm
Of the Aciplex film (trademark of Asahi Kasei Kogyo Co., Ltd., equivalent weight 1000 g / equivalent) was joined at 140 ° C. for 90 seconds by hot pressing.

The results of the single cell evaluation conducted in the same manner as in the example are shown in FIG. From the graph of FIG. 3, it can be seen that the results of Examples 1 and 2, which are electrodes prepared using the pore-forming component of the present invention, are superior to the results of Comparative Example 1 in output performance. .

[0036]

According to the polymer electrolyte fuel cell of the present invention, high output performance can be achieved.

[Brief description of drawings]

FIG. 1 is a graph showing the results of output performance evaluation in Examples and Comparative Examples.

FIG. 2 is a schematic diagram showing the basic structure of a polymer electrolyte fuel cell.

FIG. 3 is a schematic diagram showing an evaluation device used in Examples and Comparative Examples.

[Explanation of symbols]

 1 Electrolyte Membrane 2 Gas Diffusion Electrode 3 Gas Diffusion Electrode 4 Fuel Cell 5 Humidifying Base 6 Pure Water

Claims (1)

[Claims] 1. A polymer electrolyte fuel cell having an ion exchange membrane serving as an electrolyte and a gas diffusion electrode having a catalyst layer, wherein the catalyst layer contains a powdery pore-forming component. A polymer electrolyte fuel cell, characterized in that the powdery pore-forming component is removed after molding using, to form pores.