JP2001185163A - Method of manufacturing gas diffusion electrode for solid polymeric electrolyte fuel cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a gas diffusion electrode for a solid polymeric electrolyte fuel cell, having good porosity, conductivity, water repellency and durability. SOLUTION: The gas diffusion electrode is manufacturing by removing a solvent from a liquid mixture having a catalyst and a fluorine contained ion exchange resin dispersed or dissolved into the solvent to form particles having an average particle size of 0.1-100 μm and spraying the particles to the surface of an ion exchange membrane to be heated and compression bonded.

Description

DETAILED DESCRIPTION OF THE INVENTION TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method for manufacturing a gas diffusion electrode for a polymer electrolyte fuel cell.

[0002]

2. Description of the Related Art A fuel cell using hydrogen and oxygen has attracted attention as a power generation system whose reaction product is only water in principle and has almost no adverse effect on the environment. In particular, in recent years, solid polymer electrolyte fuel cells using proton-conductive ion exchange membranes as electrolytes have low operating temperatures, high power densities, and can be miniaturized. Have been.

[0003] Such a solid polymer electrolyte fuel cell is characterized by a low operating temperature (50 to 120 ° C) as described above. On the other hand, however, the exhaust heat is effectively used for auxiliaries and the like. There are difficult points. To make up for this, the polymer electrolyte fuel cell is required to have high energy efficiency and high power density even under operating conditions with high utilization rates of hydrogen and oxygen.

In order for a solid polymer electrolyte fuel cell to satisfy the above-mentioned requirements, a gas diffusion electrode and an ion-exchange membrane-electrode assembly having the electrode formed on both surfaces thereof are particularly important among the elements constituting the cell. is there. Conventionally, such a gas diffusion electrode is made of a catalyst powder for accelerating an electrode reaction, a fluorinated ion exchange resin for enhancing conductivity and preventing clogging (flooding) of a porous body by condensation of water vapor, with alcohols such as ethanol. Directly applying the viscous mixture, which is dissolved or dispersed in the above-mentioned solvent, to the surface of the ion exchange membrane, or transferring or bonding a layer obtained by applying the mixture to another sheet-like substrate to the surface of the ion exchange membrane. Is formed.

However, when the gas diffusion electrode is formed in this way, the above-mentioned viscous mixture does not always have good coating properties on an ion-exchange membrane or a sheet-like substrate. Are not always satisfactory in terms of porosity, conductivity, water repellency, and durability.

The characteristics of the solid polymer electrolyte fuel cell using such a gas diffusion electrode are not sufficiently satisfactory, and the output current density and the like are particularly required to be further improved.

[0007]

SUMMARY OF THE INVENTION The present invention solves the conventional problems of a solid polymer electrolyte fuel cell and a gas diffusion electrode, and can be easily formed on the surface of an ion exchange membrane. The obtained gas diffusion electrode also has good porosity, conductivity, water repellency, and durability, and the fuel cell also has excellent characteristics such as output current density for solid polymer electrolyte fuel cells. A method for manufacturing a gas diffusion electrode is provided.

[0008]

According to the study of the present inventors, the above catalyst and fluorine-containing ion exchange resin, which are components of a gas diffusion electrode of a solid polymer electrolyte fuel cell, are dispersed or dissolved in a solvent. It has been found that the following facts exist when a viscous mixture is prepared and applied to the surface of an ion exchange membrane. That is, the dispersion stability of each component in the viscous mixture is not always good, and even when various dispersion stabilizers and the like are added, the composition of the viscous mixture changes during coating and is uniform over the entire ion exchange membrane. It is difficult to form a coating layer having a suitable composition, and it is not always easy to produce a gas diffusion electrode having good performance.

However, instead of the viscous mixture, preferably, the mixture is granulated into particles having a specific average particle size while maintaining a uniform state of the mixture, and the mixture is formed on the surface of the ion exchange membrane in the form of the particles. In the case of applying the method, the coating process is facilitated without concern for the dispersion stability of the viscous mixture, and the workability in forming the electrode is improved. In addition, since it is not necessary to use the third substance such as the above-mentioned dispersion stabilizer and viscosity modifier, it has been found that the characteristics of the obtained gas diffusion electrode and the fuel cell using the same are significantly improved. Was. Thus, the present invention provides a method for producing a gas diffusion electrode for a solid polymer electrolyte fuel cell, which is disposed in contact with an ion exchange membrane, wherein the catalyst and the fluorinated ion exchange resin are dispersed or dissolved in a solvent. From which the average particle size is 0.1 to 100 μm
A method for producing a gas diffusion electrode for a solid polymer electrolyte fuel cell, comprising producing a gas diffusion electrode by granulating the particles into particles, spraying the particles on the surface of an ion exchange membrane, and heat-pressing the particles. It is in.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be further described below. In the gas diffusion electrode manufactured in the present invention, a catalyst and a fluorine-containing ion exchange resin are essential components. As the catalyst, a substance that promotes an electrode reaction at the fuel electrode and the air electrode is used, and preferably, a platinum group metal such as platinum or an alloy thereof is used. The catalyst may be used as it is as fine particles, but activated carbon or carbon black having a specific surface area of preferably 200 m ² / g or more is used as a carrier, and the amount of supported metal is preferably 10% of the total mass of the catalyst. Up to 70% of the supported catalyst can be used.

The fluorinated ion exchange resin contained in the gas diffusion electrode preferably has an ion exchange capacity of 0.5 to 2.0 meq / g dry resin from the viewpoint of conductivity and gas permeability. Particularly suitable are those having 0.8 to 1.5 meq / g dry resin. Further, the fluorinated ion exchange resin is preferably made of a copolymer containing a polymerization unit based on tetrafluoroethylene and a polymerization unit based on perfluorovinyl ether having a sulfonic acid group or a carboxylic acid group. The perfluorovinyl ether having the sulfonic acid group or a carboxylic acid _{group, CF 2 = CF (OCF 2} CFX) m -
O _p - _{(CF 2)} made of n -M is preferred. Here, m is an integer of 0 to 3, n is an integer of 1 to 12, and p is 0
Or 1, X is F or CF ₃ , and M is a sulfonic acid group, a carboxylic acid group, or a precursor group thereof. Preferred examples thereof include the following compounds. In the following formula, q, r, and s are integers of 1 to 8, and t is an integer of 1 to 3. _{CF 2 = CFO (CF 2)} q SO 3 H CF 2 = CFOCF 2 CF (CF 3) O (CF 2) r S
_{O 3 H CF 2 = CF (} OCF 2 CF (CF 3)) t O (C
F ₂ ) _s SO ₃ H

The catalyst and the fluorinated ion exchange resin contained in the gas diffusion electrode may have a mass ratio of catalyst: fluorinated ion exchange resin = 0.4: 0.6 to 0.95: 0.05. Is preferred in terms of conductivity and water repellency. Especially 0.
6: 0.4 to 0.8: 0.2 is appropriate. The mass of the catalyst used here includes the mass of the carrier in the case of a supported catalyst.

In the formation of the gas diffusion electrode in the present invention, other substances are added as required in addition to the above-mentioned components. For example, a water repellent is added to the air electrode to further prevent clogging by generated water. Preferred examples of the water repellent include a copolymer of tetrafluoroethylene and hexafluoropropylene, a copolymer of tetrafluoroethylene and perfluoro (alkyl vinyl ether), and polytetrafluoroethylene.

The catalyst, the fluorinated ion exchange resin, and the like forming the gas diffusion electrode are then dispersed or dissolved in a solvent to form a liquid mixture. As the solvent used here, the above-mentioned electrode components are dispersed well, forming a liquid mixture having a uniform composition in which the components are dissolved, and also having a property that can be quickly dissipated and removed at the stage of powdering. preferable. For example, one or more solvents such as alcohols having 1 to 6 carbon atoms, ethers having 2 to 6 carbon atoms, dialkyl sulfoxide having 2 to 6 carbon atoms, water, and fluorine-containing hydrocarbons are used. When two or more solvents are used in combination, it is preferable to use water as one of them, and to use an aqueous solvent.

The solvent preferably has a boiling point of 40 to 1
Those having a temperature of 60 ° C, particularly 60 to 120 ° C, are suitable. Preferred specific examples corresponding to these include methanol, ethanol, n-propanol, 2-propanol, 1-butanol, 2-butanol, 1,4-dioxane, n-propyl ether, dimethyl sulfoxide,
1,1-dichloro-2,2,3,3,3-pentafluoropropane, 1,3-dichloro-1,2,2,3,3-
Pentafluoropropane, 2,2,3,3,3-pentafluoropropanol and the like can be mentioned.

In the present invention, the liquid mixture is preferably granulated by removing the solvent in a state where the contained electrode components are well dispersed. As a method of granulation, various means can be adopted.For example, after evaporating a solvent by an evaporator or the like, powdering may be performed by an appropriate mill. In addition, the activity of the electrode catalyst is maintained, and it is very good and preferable in combination with the easiness as a granulation means.

In the above-mentioned spray drying method, the vaporization temperature is preferably from 50 to 100 ° C., and the gas flow rate is from 0.3 to 100 ° C.
1.0 cm ³ / min is preferable, and the supply amount of the liquid is 1 to 20 c
m ³ / min is preferable, and by adjusting these, the particle size of the granulated particles is controlled. In the liquid mixture to be granulated, the catalyst and a part of the fluorinated ion exchange resin are not dissolved in the solvent but exist as a solid in the liquid mixture, so that the viscosity of the liquid mixture increases. Therefore,
It is preferable to control the viscosity by controlling the solid concentration. In this case, the solid content concentration in the liquid mixture is preferably 0.1 to 20% by mass, particularly preferably 0.3 to 10% by mass.

In preparing the liquid mixture, the catalyst and the fluorinated ion exchange resin may be simply dissolved and dispersed in a solvent, or the catalyst and the like may be dispersed in a solution in which the fluorinated ion exchange resin is dissolved or dispersed. May be. In particular, it is preferable because the electrode characteristics obtained when a fluorine-containing ion exchange resin or the like is dissolved in a catalyst dispersed in a solvent are improved. This appears to be due to the good dispersion of the catalyst in the liquid mixture.

Further, other substances can be added to the above-mentioned liquid mixture, if necessary, as long as the object of the present invention is not hindered. For example, a thickener or a diluent, and further, a pore-forming agent and the like can be added. Cellulose and cellosolve-based thickeners can be used, and water, hydrocarbon and the like can be used as diluents. Fluorine-containing hydrocarbons and the like can be used. Silica, alumina, and the like can be used as the pore-forming agent.

The particles obtained by granulating the above liquid mixture have an average particle diameter of 0.1 to 100 μm, preferably 0.1 to 100 μm.
Suitably, it has a thickness of 5 to 40 μm. If it is smaller than the above range, it becomes difficult to disperse particles during electrode formation, and the gas permeability of the obtained electrode layer deteriorates. On the other hand, when the particle size is large, the fluidity at the time of dispersing the particles deteriorates, and all are unsuitable. The bulk density of the particles is preferably 0.1 to 0.9 g / cm ³ ,
It is appropriate to a 0.2~0.7g / cm ^3. When it has such a bulkiness, it is easy to handle from the viewpoint of fluidity when forming an electrode from particles, and the gas permeability of the obtained electrode layer is also good.

When a gas diffusion electrode is formed on the surface of an ion exchange membrane, which is a solid polymer electrolyte, from the obtained powder, particles are directly sprayed on the surface of the ion exchange membrane to form an electrode, or a carbon paper or the like is used. Alternatively, the electrode may be formed by spraying on the surface of another sheet-like substrate, and then transferring or bonding the electrode to an ion exchange membrane. Spraying the particles on the ion exchange membrane or sheet-like substrate, spray coating,
A method such as die coating can be applied. The ion-exchange membrane on which the powder has been sprayed is then preferably heated to a temperature of 130
~ 200 ° C, especially 150 ~ 180 ° C, pressure 0.5
Thermocompression bonding is carried out at a pressure of 10 to 10 MPa, particularly 1.0 to 6.0 MPa.

On the other hand, when the particles are scattered on the another sheet-like base material, they are thermocompression-bonded in the same manner as described above to form an electrode layer, which is then transferred or bonded to the ion exchange membrane surface. In this case, the hot pressing method and the bonding method (Japanese Patent Laid-Open No. 7-2)
20741, JP-A-7-254420) and the like. Thus, the thickness of the formed electrode is preferably 1 to 50 μm, particularly preferably 5 to 30 μm.

In the present invention, the ion exchange membrane having an electrode formed on the surface preferably has an ion exchange capacity of 0.5
２．０2.0 meq / gram, and preferably has a thickness of 10-80 μm. The material constituting the ion exchange membrane can be selected from the materials described as the fluorinated ion exchange resin used for forming the electrode. Among them, preferably a sulfonic acid type fluorinated ion exchange resin, in particular, CF ₂ = CF ₂ and CF ₂ = CF-
_{(OCF 2 CFX) m -O p} - (. Wherein, m is 0 to 3, n is 1 to 12, p is 0 or 1, X is F or _{CF 3) (CF 2) n} -SO 3 H and A sulfonic acid type perfluorocarbon ion exchange resin comprising a copolymer of the above is suitable.

[0024]

EXAMPLES Hereinafter, specific embodiments of the present invention will be described in detail with reference to Examples, but it is needless to say that the interpretation of the present invention is not limited to these.

Example 1 1.05 g of a catalyst in which 40% by mass of platinum was supported on carbon black powder was used. Ion exchange capacity was 1.1 meq / g. CF ₂ = CF ₂ and CF ₂ = CF which are dry resins _{-OCF 2 CF (CF 3) -OCF} 2 CF 2 S
7.2 g of a 6.25 mass% ethanol solution of a fluorine-containing ion exchange resin comprising a copolymer with O ₃ H and 6.75 g of water
And a solid content concentration of 10% of the total mass.
% Liquid mixture was obtained. By spray drying such a liquid mixture, vaporization temperature 80 ° C., the gas flow rate 0.5 cm ³
Per minute and a liquid supply amount of 10 cm ³ / min, to obtain particles having an average particle diameter of 30 μm and a bulk density of 0.5 g / cm ³ .

On the other hand, Flemion S is used as an ion exchange membrane.
Membrane (Sulfonic acid type perfluorocarbon ion exchange membrane, trade name of Asahi Glass Co., Ltd., ion exchange capacity 1.0 meq / g
Dry resin, film thickness 50 μm) was used. The ion exchange membrane was moved in the horizontal direction at a speed of 5 meters per minute, and the particles obtained above were sprayed on both surfaces thereof so that the platinum content was 0.5 mg / cm ² . Then, it is thermocompression-bonded with a pressure roller at 160 ° C. and 5.0 M Pa to form an ion-exchange membrane-electrode assembly having a 15 μm-thick porous air electrode side and hydrogen electrode side gas diffusion electrodes on its surface ( The electrode area was 10 cm ² ).

A fuel cell is assembled using the ion exchange membrane / electrode assembly, and the fuel cell is
MPa, hydrogen / air system, 0.6 at cell temperature 70 ° C
Continuous operation with 0V constant voltage drive, output current density (A / c
When the change over time of m ² ) was measured, the results shown in Table 1 were obtained.

Example 2 The solvent of the liquid mixture having a solid concentration of 10% by mass prepared in the same manner as in Example 1 was blown off by an evaporator, and the remaining solid was zirconia beads (diameter: 1 m).
In the ball mill using m), the particles were atomized over 3 hours. Thereby, the average particle size is 70 mm, and the bulk density is 0.8 g.
/ Cm ³ particles were obtained.

Using these particles, an ion-exchange membrane / electrode assembly was prepared in the same manner as in Example 1. Using this, a fuel cell was assembled and the performance was measured in the same manner as in Example 1. The results shown in Table 1 were obtained.

Comparative Example 1 A liquid mixture having a solid content of 10% by mass prepared in the same manner as in Example 1 was applied to both surfaces of an ion exchange membrane by a bar coater without powdering, and the platinum content was determined. In addition, the ion exchange membrane / electrode assembly was produced by carrying out the process so that the thickness was exactly the same as in Example 1. Using this, a fuel cell was assembled in the same manner as in Example 1, and the performance was measured.
The results shown in Table 1 were obtained.

[0031]

[Table 1]

[0032]

According to the production method of the present invention, a gas diffusion electrode can be conveniently and easily formed on the surface of an ion exchange membrane, and the obtained gas diffusion electrode has good porosity, conductivity, and water repellency. Further, the solid polymer electrolyte fuel cell using such a gas diffusion electrode has excellent characteristics such as high output current density, and has little deterioration over time.

Claims (5)

[Claims] 1. A method for producing a gas diffusion electrode for a solid polymer electrolyte fuel cell, which is disposed in contact with an ion exchange membrane, wherein a catalyst and a fluorine-containing ion exchange resin are dispersed or dissolved in a solvent from a liquid mixture. Removing the solvent, granulating the particles into particles having an average particle diameter of 0.1 to 100 μm, spraying the particles on the surface of the ion exchange membrane, and heat-pressing to produce a gas diffusion electrode; A method for producing a gas diffusion electrode for a molecular electrolyte fuel cell. 2. The liquid mixture according to claim 1, wherein said liquid mixture has a solid content of 0.1 to 2%.
The method for producing a gas diffusion electrode according to claim 1, wherein the amount is 0 mass%, and the granulation is performed by a spray drying method. 3. The thermocompression bonding is performed at a temperature of 100 to 250 ° C.
The method for producing a gas diffusion electrode according to claim 1, wherein the method is performed using a calender roll at a pressure of 0.5 to 10 MPa. 4. The solvent according to claim 1, wherein the solvent is at least one selected from alcohols having 1 to 6 carbon atoms, ethers having 2 to 6 carbon atoms, dialkyl sulfoxide having 2 to 6 carbon atoms and water. 3. The method for producing a gas diffusion electrode according to item 3. 5. A method for producing a solid polymer electrolyte fuel cell, wherein the gas diffusion electrode obtained by the production method according to claim 1 is arranged in contact with an ion exchange membrane.