JP2008066017A - Paste for forming catalyst layer, catalyst electrode using it, membrane electrode assembly using it, and manufacturing methods of them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst electrode excellent in gas permeability, paste for forming a catalyst layer for manufacturing it, a membrane electrode assembly having excellent power generation efficiency using them, and the manufacturing methods of them. <P>SOLUTION: An evaporating substance is contained in the paste for forming the catalyst layer. The evaporating substance is evaporated at temperature in the manufacturing process of the membrane electrode assembly. A perfluorocarbon membrane having a sulfonic group is used as a hydrogen ion conductive polymer electrolyte membrane, and styrene-acrylic copolymer wax is used as the evaporating substance. The drying temperature of a solvent in the manufacturing of a catalyst electrode is set at a temperature less than the boiling point of the evaporating substance. The pressure of the environment for fusion-bonding the catalyst layer of the catalyst electrode and the hydrogen ion conductive polymer electrolyte membrane is set in the pressure lower than the atmospheric pressure (for example, 1×10<SP>3</SP>to 5×10<SP>4</SP>Pa). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a catalyst electrode for a polymer electrolyte fuel cell, a catalyst layer forming paste for the catalyst electrode, a membrane electrode assembly using them, and a method for producing them.

In recent years, fuel cells have attracted attention as devices capable of converting energy with high efficiency.

Fuel cells are available in PAFC (phosphoric acid type), PEFC (solid polymer type), DMFC (direct methanol type), SOFC (solid oxide type), and MCFC (molten carbonate type) depending on the type of electrolyte used. Broadly divided.

Among the fuel cells described above, the solid polymer fuel cell using a solid polymer having hydrogen ion conductivity as an electrolyte does not require a pressurized container, is small, and has a high output density. Therefore, it is attracting attention as a power source for vehicles and portable devices.

As a power generation method for a polymer electrolyte fuel cell, the following electrochemical reaction occurs between hydrogen (contained in the fuel gas) and oxygen (contained in the oxidant gas) through the hydrogen ion conductive polymer electrolyte membrane. Is used.

Anode; H ₂ → 2H ⁺ + 2e ⁻ (1)
Cathode; 4H ⁺ + 4e ⁻ + O ₂ → 2H ₂ O (2)

Conventionally, as a cell design of a polymer electrolyte fuel cell, a plurality of single battery cells in which separators are arranged on both sides of a membrane electrode assembly (MEA) in which catalyst electrodes are provided on both sides of a hydrogen ion conductive polymer electrolyte membrane are used. Individual cell designs are used.

As a catalyst electrode, the thing of the structure by which the catalyst layer was formed on the gas diffusion material is used widely.
The electrochemical reactions of the above formulas (1) and (2) are carried out in the catalyst layer.

As a function required for the catalyst layer,
A gas permeation function for supplying the reaction gas supplied from the gas diffusion material to the catalyst surface;
A function of conducting protons generated by the electrochemical reaction of the above formulas (1) and (2),
A function of conducting electrons generated by the electrochemical reaction of the above formulas (1) and (2),
There is.

As a method for imparting gas permeability to the catalyst layer, a method of forming a catalyst layer having a porous structure and a gas channel by using a fine carbon powder or a pore former having a developed structure is widely used. Yes. (See Patent Document 1)

JP 2006-4916 A

However, in the fuel cell described in Patent Document 1, gas permeability is not sufficient, and there is still room for improvement from the viewpoint of power generation efficiency.

On the other hand, increasing the amount of catalyst supported increases the power generation efficiency, but has a problem that the cost burden increases because the catalyst is expensive.

An object of the present invention is to provide a catalyst electrode excellent in gas permeability, a catalyst layer forming paste for producing the catalyst electrode, a membrane electrode assembly excellent in power generation efficiency using them, and a method for producing them. That is.

The invention according to claim 1 is a paste for forming a catalyst layer used for manufacturing a catalyst electrode of a polymer electrolyte fuel cell,
A catalyst layer forming paste comprising catalyst-supporting carbon particles, a proton conductive polymer electrolyte, an evaporating substance, and a solvent.

By including an evaporating substance in the catalyst layer forming paste, it is possible to evaporate the evaporating substance when forming the membrane electrode assembly to form pores, and to improve the gas permeability of the catalyst layer.

The invention according to claim 2 is characterized in that the proton conductive polymer electrolyte is a perfluorocarbon having a sulfonic acid group,
2. The catalyst layer forming paste according to claim 1, wherein the evaporating substance has a boiling point of 120 to 140 ° C. 3.

A perfluorocarbon having a sulfonic acid group is a proton conductive polymer electrolyte excellent in proton conductivity.
Moreover, when this is used, the load temperature at the time of membrane electrode assembly preparation will be 120-140 degreeC on account of melting | fusing point of the perfluorocarbon which has a sulfonic acid group.
In order to evaporate the evaporated substance only at the time of manufacturing the membrane electrode assembly and not at the time of manufacturing the membrane electrode assembly, it is necessary to set the boiling point of the evaporated substance to 120 to 140 ° C.

The invention according to claim 3 is the catalyst layer forming paste according to claim 1 or 2, wherein the evaporating substance is a styrene-acrylic copolymer wax.

The styrene-acrylic copolymer wax has a boiling point of 120 to 140 ° C., and does not alter the catalyst-supporting carbon particles and the proton conductive polymer electrolyte.

Invention of Claim 4 is a catalyst electrode used for a polymer electrolyte fuel cell,
It is a catalyst electrode formed by laminating | stacking the catalyst layer forming paste of any one of Claim 1 thru | or 3 on a gas diffusion material, and forming a catalyst layer.

Thereby, the catalyst electrode excellent in gas permeability can be obtained.

The invention according to claim 5 is a catalyst layer forming paste generating step for generating a catalyst layer forming paste in which catalyst-carrying carbon particles, a proton conductive polymer electrolyte, and an evaporated substance are dissolved in a solvent;
A catalyst layer forming paste application step for applying the catalyst layer forming paste on the gas diffusion material;
The method for producing a catalyst electrode according to claim 4, further comprising a solvent drying step for drying the solvent in the catalyst layer forming paste applied on the gas diffusion material.
The method for producing a catalyst electrode, wherein a drying temperature of the solvent in the solvent drying step is lower than a boiling point temperature of the evaporated substance.

If the drying temperature of the solvent is equal to or higher than the boiling point temperature of the evaporating substance, the evaporating substance evaporates during the production of the catalyst electrode.

The invention according to claim 6 is a membrane electrode assembly in which the catalyst layer of the catalyst electrode according to claim 4 is bonded to both surfaces of the hydrogen ion conductive polymer electrolyte membrane.

Thereby, the membrane electrode assembly excellent in power generation efficiency can be obtained.

The invention according to claim 7 is an arrangement step for arranging the catalyst layers of the catalyst electrodes on both surfaces of the hydrogen ion conductive polymer electrolyte membrane;
The method for producing a membrane / electrode assembly according to claim 6, further comprising a fusion bonding step for fusion bonding the hydrogen ion conductive polymer electrolyte membrane and the catalyst layer.
The method for producing a membrane / electrode assembly is characterized in that the hydrogen ion conductive polymer electrolyte membrane is made of perfluorocarbon having a sulfonic acid group, and the temperature used in the fusion bonding step is 120 to 140 ° C.

By setting the temperature used in the melt bonding step to 120 to 140 ° C., it is possible to melt a proton conductive polymer electrolyte made of a perfluorocarbon having a sulfonic acid group and excellent in proton conductivity, and to styrene-acrylic copolymer. The polymer wax can be evaporated, and a membrane electrode assembly excellent in power generation efficiency can be obtained.

The invention according to claim 8 is the method of manufacturing a membrane electrode assembly according to claim 7, wherein the fusion bonding step is a step performed under a pressure lower than atmospheric pressure. .

By setting the pressure of the environment in which the melt bonding process is performed to a pressure lower than the atmospheric pressure (for example, 1 × 10 ^{3 to} 5 × 10 ⁴ Pa), it is possible to easily remove the evaporated substance by evaporation.

By using the present invention, a catalyst electrode excellent in gas permeability, a catalyst layer forming paste for producing the catalyst electrode, and a membrane electrode assembly excellent in power generation efficiency using them can be obtained.

A catalyst electrode of the present invention and a method for producing a membrane electrode assembly using the catalyst electrode will be described with reference to FIG.

First, the catalyst layer 2 is laminated on the gas diffusion material 1 to form the catalyst electrode 3. (See Fig. 1 (a))

As the gas diffusion material 1, carbon paper and carbon cloth can be used.

As the material of the catalyst layer 2, catalyst-supporting carbon particles, proton conductive polymer electrolytes, and evaporating substances can be used.

As the catalyst, gold, platinum, palladium, rhodium, ruthenium, osmium and iridium can be used.

As the carbon particles, fullerene, acetylene black, ketjen black, carbon nanotube, carbon nanohorn, or the like can be used.
The particle diameter of the carbon particles is preferably 0.001 to 0.1 μm, and more preferably 0.02 to 0.06 μm.

As the proton conductive polymer electrolyte, perfluorocarbon having a sulfonic acid group can be used.

A styrene-acrylic copolymer wax can be used as the evaporating substance.

As a method for forming the catalyst layer 2, the catalyst-supporting carbon particles, the proton conductive polymer electrolyte, and the evaporating substance are dissolved in an alcohol solvent such as isopropyl alcohol, normal propyl alcohol, and propanol to prepare a catalyst layer forming paste. After the formation, the catalyst layer forming paste is bar-coated, spray-coated, or screen-printed on the gas diffusion material 1, and then the solvent is dried at a temperature lower than the boiling point of the evaporated substance. Can do.

Finally, the membrane electrode assembly 5 is obtained by sandwiching the hydrogen ion conductive polymer electrolyte membrane 4 with the catalyst layers 2 of the two catalyst electrodes 3 facing each other and thermocompression bonding. (See FIGS. 1B and 1C)

As a material of the hydrogen ion conductive polymer electrolyte membrane 4, perfluorocarbon having a sulfonic acid group can be used.

As the thermocompression bonding temperature, a temperature exceeding the softening temperature or glass transition temperature of the resin (perfluorocarbon having a sulfonic acid group) of the catalyst layer 2 and the hydrogen ion conductive polymer electrolyte membrane 4 can be used.

As thermocompression bonding conditions, thermocompression bonding conditions of a temperature of 100 ° C. to 300 ° C., a pressure of 1 MPa to 15 MPa, and a time of 500 seconds to 700 seconds can be used.

It is preferable to set the pressure of the environment in which thermocompression bonding is performed to a pressure lower than the atmospheric pressure (for example, 1 × 10 ^{3 to} 5 × 10 ⁴ Pa), and by doing so, it is possible to facilitate evaporative removal of the evaporated substance. .

First, 25 g of acetylene black (specific surface area 257 m ² / g) (manufactured by Cabot, Vulcan XC-72R) was put into 10 liter of 0.5 mol / liter potassium permanganate aqueous solution and reacted at 75 ° C. for 5 hours. .

Next, the reaction product is filtered off, washed with distilled water at 75 ° C., dried at 105 ° C., and then hexaammineplatinum (IV) chloride having a platinum content of 10 g / liter ([Pt (IV ) (NH ₃ ) ₆ ] Cl ₄ ) in aqueous solution at room temperature.

Next, the reaction product is filtered off from the reaction solution, and then the reaction product is washed with distilled water at 75 ° C., then dried at 105 ° C., and then in a hydrogen stream at a temperature of 180 ° C. By reduction, acetylene black (catalyst-supported carbon particles) carrying platinum was obtained.

Next, 10 g of acetylene black (catalyst-supported carbon particles) supporting platinum (platinum weight: acetylene black weight = 1: 1), perfluorocarbon having a sulfonic acid group (5 wt% Nafion solution) (DE520, manufactured by DuPont) (Registered trademark) (solvent propanol)) 100 g, styrene-acrylic copolymer wax (Suzuki Yushi Kogyo Co., Ltd., S-9671, boiling point 124 ° C.) 10 g are mixed and dispersed using a homogenizer for 60 minutes to form a catalyst layer. A forming paste was produced.

When the viscosity of the catalyst layer forming paste was measured using a rotational viscometer (manufactured by Rion, Viscotester VT-04 (registered trademark)), the viscosity of the catalyst layer forming paste was 3.0 at 25 ° C. × 10 ² mPa · s.

Next, carbon paper (TGP-H-030, manufactured by Toray Industries, Inc.) having a porosity of 80% and a thickness of 110 μm was cut into a size of 110 mm × 110 mm.

Next, after removing dust attached to the cut carbon paper using an air gun,
Set on a screen printer.

Next, the prepared paste for forming a catalyst layer was placed on a screen of # 250SUS mesh × emulsion thickness 20 μm × wire diameter 0.05 mm.

Next, the catalyst layer forming paste was extruded onto the carbon paper (screen printing) under the conditions of a squeegee pressure of 5 kgf / cm ² , a squeegee speed of 100 mm / second, and a clearance between the screen and the carbon paper of 2.5 mm, and then Heat treatment was performed at 100 ° C. for 1 hour in a nitrogen atmosphere, and then allowed to cool for 30 minutes to produce two catalyst electrodes.

Next, in an environment of 1 × 10 ⁴ Pa, the catalyst layers of the two catalyst electrodes face each other, and a perfluorocarbon membrane (hydrogen ion conductive polymer electrolyte membrane) having a sulfonic acid group having a thickness of 50 μm therebetween ( A membrane electrode assembly was manufactured by sandwiching a DuPont Nafion 117 (registered trademark)) and thermocompression bonding under conditions of a temperature of 130 ° C., a pressure of 10 MPa, and a time of 10 minutes.

The thickness of the catalyst layer of the membrane / electrode assembly was 6 μm to 7 μm.
Moreover, the platinum usage-amount per unit area in the catalyst layer of a membrane electrode assembly was 0.5 mg / cm < ² >.

Next, when the porosity of the catalyst layer was confirmed by an image processing method from an SEM photograph, the porosity of the catalyst layer was 7.5%.

Next, as for the output of the membrane electrode assembly, a fuel using an electrochemical interface (SI-1287 manufactured by Solartron), a frequency response analyzer (SI-1260 manufactured by Solartron), and an electronic loader (890CL manufactured by Scribner) is used. It measured as follows using battery measurement system GFT-SG1 (made by Toyo Technica Co., Ltd.).

First, the membrane electrode assembly was attached to a power generation cell made of graphite and stored for 10 hours under the conditions of 40 ° C. and relative humidity of 100%.
During this time, a direct current of 1 A / cm ² was continuously supplied in the power generation mode to the membrane electrode assembly for the purpose of sufficiently wetting the perfluorocarbon membrane having a sulfonic acid group having a thickness of 50 μm.

Next, the cell temperature is 80 ° C., the anode humidifier temperature is 80 ° C., the cathode humidifier temperature is 80 ° C., the piping temperature is 120 ° C., and the reformed gas (fuel gas) of the anode (H ₂ : CO ₂ : H ₂ O = 82: 8: 10) When the output of the membrane electrode assembly was measured under the conditions of a flow rate of 0.3 liter / min and a cathode oxygen gas flow rate of 1.0 liter / min, the current density was 100 mA / cm ^2. It was confirmed that an electromotive voltage of 0.89V was obtained and a good output was obtained.
Also, this characteristic did not change after 1 month.

A membrane / electrode assembly was prepared in the same manner as in Example 1 except that the membrane / electrode assembly was prepared under atmospheric pressure. As in Example 1, the porosity of the catalyst layer and the electromotive voltage of the membrane / electrode assembly were adjusted. confirmed.

The porosity of the catalyst layer was 6.9%, and the electromotive voltage of the membrane electrode assembly was 0.84V.

<Comparative Example 1>
A membrane / electrode assembly was prepared in the same manner as in Example 1 except that the styrene-acrylic copolymer wax was not used. As in Example 1, the porosity of the catalyst layer and the electromotive voltage of the membrane / electrode assembly were adjusted. confirmed.

The porosity of the catalyst layer was 2.4%, and the electromotive voltage of the membrane electrode assembly was 0.46V.

<Comparative example 2>
A membrane / electrode assembly was prepared in the same manner as in Example 2 except that the styrene-acrylic copolymer wax was not used. As in Example 2, the porosity of the catalyst layer and the electromotive voltage of the membrane / electrode assembly were adjusted. confirmed.

The porosity of the catalyst layer was 2.4%, and the electromotive voltage of the membrane electrode assembly was 0.46V.

It was confirmed that the use of styrene-acrylic copolymer wax increases the porosity of the catalyst layer of the membrane electrode assembly and increases the electromotive voltage of the membrane electrode assembly.

A paste for forming a catalyst layer, a catalyst electrode using the same, a membrane electrode assembly using the same, and a method for producing the same are disclosed in an electric vehicle, a mobile phone, a vending machine, an underwater robot, a submarine, and a spacecraft. It can be used for a polymer electrolyte fuel cell used for an underwater vehicle, a power source for an underwater base, and the like.

It is sectional drawing for demonstrating the manufacturing method of the catalyst electrode of this invention, and a membrane electrode assembly using the same.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas diffusion material 2 ... Catalyst layer 3 ... Catalyst electrode 4 ... Hydrogen ion conductive polymer electrolyte membrane 5 ... Membrane electrode assembly

Claims (8)

A catalyst layer forming paste used in the manufacture of a catalyst electrode of a polymer electrolyte fuel cell,
A catalyst layer forming paste comprising catalyst-supporting carbon particles, a proton conductive polymer electrolyte, an evaporating substance, and a solvent. The proton conductive polymer electrolyte is a perfluorocarbon having a sulfonic acid group,
2. The catalyst layer forming paste according to claim 1, wherein the evaporation substance has a boiling point of 120 to 140 ° C. 3. The catalyst layer forming paste according to claim 1 or 2, wherein the evaporating substance is a styrene-acrylic copolymer wax. A catalyst electrode used in a polymer electrolyte fuel cell,
The catalyst electrode formed by laminating | stacking the catalyst layer forming paste of any one of Claim 1 thru | or 3 on a gas diffusion material. A catalyst layer forming paste generation step for generating a catalyst layer forming paste in which catalyst-supporting carbon particles, proton conductive polymer electrolyte, and evaporated substance are dissolved in a solvent;
A catalyst layer forming paste application step for applying the catalyst layer forming paste on the gas diffusion material;
The method for producing a catalyst electrode according to claim 4, further comprising a solvent drying step for drying the solvent in the catalyst layer forming paste applied on the gas diffusion material.
The method for producing a catalyst electrode, wherein a drying temperature of the solvent in the solvent drying step is lower than a boiling point temperature of the evaporating substance. The membrane electrode assembly formed by joining the catalyst layer of the catalyst electrode of Claim 4 to both surfaces of a hydrogen ion conductive polymer electrolyte membrane. An arrangement step for arranging the catalyst layers of the catalyst electrodes on both sides of the hydrogen ion conductive polymer electrolyte membrane;
The method for producing a membrane / electrode assembly according to claim 6, further comprising a fusion bonding step for fusion bonding the hydrogen ion conductive polymer electrolyte membrane and the catalyst layer.
The method for producing a membrane electrode assembly, wherein the hydrogen ion conductive polymer electrolyte membrane is made of perfluorocarbon having a sulfonic acid group, and a temperature used in the melt bonding step is 120 to 140 ° C. The method for producing a membrane / electrode assembly according to claim 7, wherein the fusion bonding step is a step performed under a pressure lower than atmospheric pressure.

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