JPH06251779A - Formation of joined body of solid polymer electrolyte layer and electrode for fuel cell - Google Patents

Abstract

PURPOSE:To provide a forming method of a joined body having low electric resistance such as a joined interface or a solid polymer electrolyte layer by which formation becomes simple by forming the first layer by heat treatment after fluorine type polymer solution is applied and dried on the side surface having electrode catalyst. CONSTITUTION:When a joined body is formed, after fluorine type polymer solution being a polymer electrolyte is applied and dried on the surface of an electrode catalyst layer 3 of a gas diffusing electrode 1, the first layer 4 of solid polymer electrolyte is formed by heat treatment. The second layer 5 and the third layer 6 of solid polymer electrolyte are formed by applying fluorine type polymer solution on the first layer 4. An electrode catalyst layer 3 has a pore 9, and gas is supplied to an electrode catalyst particulate 8 by this pore 9. Thereby, the first electrolyte layer 4 requires a thickness in a degree that the pore 9 is not blocked and a gas flow is not hindered, and when the solution is applied on and after the second electrolyte layer 5, a phenomenon that the first layer 4 is dissolved or this pore is reduced or belocked up can be prevented by a method in the present invention.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a joined body of a solid polymer electrolyte for a fuel cell and an electrode constituting a fuel cell.

[0002]

2. Description of the Related Art Among the elements required as a joined body of a solid polymer electrolyte layer for a fuel cell and an electrode, particularly important is a low electric resistance at a joint surface between the electrode and the solid polymer electrolyte, The solid polymer electrolyte itself has low electrical resistance, the polymer electrolyte does not have excessive gas permeability, it has excellent chemical durability and stability for long-term use, and its physical strength. Can be raised.

[0003] Among the above-mentioned factors, the current problem is that the solid polymer electrolyte for a fuel cell itself has a still high electric resistance and accounts for a large portion of the fuel cell output loss. In recent years, fuel cells have been attracting attention as a clean electric energy supply source, and among them, a solid polymer electrolyte fuel cell using an ion exchange membrane as a solid polymer electrolyte layer for a fuel cell has an operating temperature of 100 ° C. Since it has a high energy density even if it is lower than the following, it is expected to be used as a power source for transportation, for example, as a power source for an electric vehicle or a simple auxiliary power source.

A solid polymer electrolyte fuel cell generally has a so-called ion exchange membrane formed by molding a solid polymer electrolyte in a membrane shape, and electrodes are bonded to both sides of the so-called ion exchange membrane. Hydrogen) is supplied, and an oxidant (for example, oxygen or air) is supplied to the other, so that an electrode reaction occurs. In the fuel cell, the supplied fuel is oxidized by the electrode catalyst to generate protons, that is, hydrogen ions, and reaches the other electrode by ion conduction in the ion exchange membrane, and a reaction occurs to generate water by the oxidant. ing.

The ion exchange membrane is in intimate contact with the electrode of the fuel cell, and is used by being formed integrally with the electrode. Therefore, the ion exchange membrane must have both a role as an electrolyte for conducting hydrogen ions in the fuel cell and a role as a diaphragm for preventing the fuel and the oxidant from directly mixing even under pressure.

The ion exchange membrane used in such a fuel cell is a proton exchange type polymer film having a plurality of acid functional groups chemically bonded to the polymer main chain, and may be, for example, sulfonated polystyrene. It may be a substantially fluorinated sulfonic acid polymer. However, in terms of durability, fluorinated sulfonic acid polymers are often used.

However, at present, a practical method for joining the electrode and the ion exchange membrane has not been established yet, and therefore the performance is not constant. Further, the electric resistance of the ion exchange membrane itself cannot be said to be sufficiently low, which is also a major cause of loss of fuel cell output. Fluorine-based ion exchange membranes currently used for fuel cells have polymer structures similar to those used in large quantities in ion exchange membrane chloralkali electrolysis, such as Nafion (registered trademark) manufactured by DuPont. Acid type such as trademark) is often used. However, the ion exchange membrane generally has a thickness of 100 μm or more, and even if an attempt is made to reduce the thickness in order to reduce the electric resistance, there are great difficulties in manufacturing the membrane, and the strength is high when used. Inconveniences such as weakening tended to occur.

To reduce the resistance of the ion exchange membrane, the simplest method is to reduce the thickness of the ion exchange membrane. However, there is a risk that the thickness of the ion-exchange membrane is limited in manufacturing, and that the strength is reduced by reducing the thickness, and there is a problem that the ion-exchange membrane may be damaged during joining with the electrode. At present, when joining an ion exchange membrane and a gas diffusion electrode, a certain amount of a solution of an ion exchange resin component similar to that of the ion exchange membrane is previously applied to the catalyst surface of the electrode, dried, and then integrated by hot pressing. It is joined. The solution of the ion exchange resin component is, for example, about 5% in a mixed solution of water and an organic solvent such as propanol or ethyl alcohol, which is an acid type ion exchange resin such as Nafion (registered trademark) manufactured by DuPont. A dissolved product is often used.

However, when the solution containing the ion exchange resin component is applied to the gas diffusion electrode, the coating amount, the viscosity and concentration of the solution containing the ion exchange resin component, the drying conditions for forming the film, etc. However, the performance of the assembly of the electrode and the ion exchange membrane during the operation of the fuel cell is likely to vary, and it is difficult to obtain reproducible results. From the above points, it was very difficult to manufacture a bonded body of a solid polymer electrolyte for a fuel cell and an electrode, which has excellent adhesion and low electric resistance.

In the fuel cell proposed in Japanese Unexamined Patent Publication No. 4-264367, it is attempted to make the ion exchange membrane in a solid polymer electrolyte fuel cell thin and to reduce the electric resistance. However, the method disclosed in this publication is still inadequate, and in reality, a large amount of solid polymer electrolyte component permeates the electrode catalyst layer, clogging the pores of the electrode and deteriorating the performance, There is also a problem that it is difficult to control the thickness of the molecular electrolyte layer.

[0011]

DISCLOSURE OF THE INVENTION The present invention is simple in the production of a joined body of a gas diffusion electrode for a fuel cell and a solid polymer electrolyte, and the electrical properties of the joint interface and the solid polymer electrolyte layer. An object of the present invention is to provide a method for producing a joined body of a solid polymer electrolyte for a fuel cell and an electrode having low resistance.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted various studies on various methods of manufacturing a bonded body which is easy to manufacture and has excellent adhesion between an electrode and an ion exchange membrane, and has completed the present invention. It is a thing. That is, the present invention is a solution of a fluorinated polymer containing a sulfonic acid group which becomes a polymer electrolyte on the side surface having an electrode catalyst of the electrode when producing a joined body of a solid polymer electrolyte layer for a fuel cell and an electrode. Is applied and dried, and then heat-treated to form a first layer, and a fluoropolymer solution containing a sulfonic acid group is further applied onto the first layer, dried, and then heat-treated at least 1. This is a method for producing a joined body of a solid polymer electrolyte layer for a fuel cell and an electrode, which is characterized in that a layer after the second layer is formed by repeating the process.

A fuel cell is an electrochemical device that directly converts chemical energy into electric energy by oxidizing a fuel supplied to the cell. Although there are several types depending on its structure, the present invention can be used. A fuel cell having a solid polymer electrolyte as an electrolyte, particularly a fluorine-based proton exchange type resin layer. A gas diffusion electrode used in a fuel cell has fine pores through which a gas can permeate. Generally, fine platinum particles are supported on carbon particles such as activated carbon and tetrafluoroethylene powder. What is mixed and hot pressed is used. Electrodes manufactured by E-TEK are often used as this type of gas diffusion electrode.

In the present invention, first, a solution of a fluorinated polymer containing a sulfonic acid group is applied on the catalyst layer of the gas diffusion electrode and dried at 100 ° C. or lower, and the solvent is sufficiently evaporated and dried, and then at 120 ° C. or higher. The first layer is formed by heat treatment, and the second layer is coated again on the first layer with a solution of a fluorinated polymer containing a sulfonic acid group (hereinafter referred to as an ion exchange resin component) and dried. In this way, even if the second layer is applied, the coating solution does not penetrate into the inside of the electrode and a coating film having a required thickness can be obtained.

When the solution of the ion exchange resin component is applied on the catalyst layer of the gas diffusion electrode, the solution penetrates into the electrode. At that time, the catalyst in the pores in the electrode is covered with the solution, and as a result, after drying, the catalyst surface is covered with the thin film of the ion exchange resin component which is also the electrolyte. However, if the amount of the solution to be applied is too large, the pores in the electrode will be blocked with the ion exchange resin component, and gas permeation will be hindered.
On the other hand, if the amount is too small, there is no electrolyte on the surface of the catalyst particles and the electrode reaction does not proceed. Therefore, an appropriate amount of ion exchange resin component is required for the electrode catalyst layer.

For this reason, conventionally, it has been unavoidable to empirically determine the optimum amount to be applied on the electrode catalyst layer, apply the amount in advance, and bond it to the ion exchange membrane. However, in the case of the present invention, the first layer is 120 ° C.
Since the heat treatment is performed at the above temperature, even if a solution containing an ion exchange resin component is newly applied onto the first layer, it does not soak into the inside of the electrode, and the second layer can be applied with an arbitrary thickness. is there. The second and subsequent layers are portions corresponding to the ion exchange membrane in the conventional concept, and if the thickness of this portion can be controlled arbitrarily, it means that the ion exchange membrane can have virtually any thickness. Therefore, it is possible to reduce the resistance of the ion exchange membrane and to control the diffusion amount of water in the ion exchange membrane, which is another important factor for the fuel cell, to some extent.

In the present invention, the drying temperature of the first layer is preferably a temperature at which the solvent of the ion exchange resin component does not evaporate too rapidly. For that, 100 ℃ or less 20
The temperature is preferably not lower than 0 ° C, more preferably not higher than 80 ° C, particularly preferably not higher than 60 ° C.
In addition, the temperature for heat treatment after coating the first layer of the ion exchange resin layer and drying is preferably 120 ° C. or higher,
More preferably 130 ° C or higher, particularly preferably 140 ° C
The above is appropriate. The reason why it is necessary to treat at such a temperature is not clear, but the coated and dried ion exchange resin layer still has an array of polymer molecules, and if there is a solvent capable of dissolving the polymer, it is very difficult. Although it has a structure in which it is easily dissolved, it is presumed that when it is treated at a high temperature of 120 ° C. or higher, the polymers are complicatedly entangled with each other due to the influence of heat and the polymer is easily dissolved in a solvent.

The upper limit of the temperature during the heat treatment may be virtually any temperature as long as the polymer does not deteriorate.
Actually, 250 ° C. or lower, preferably 200 ° C. or lower is desirable because it has little influence on the polymer. The thickness of the first layer varies depending on the type of gas diffusion electrode and is often empirically determined. Further, since the solution permeates into the electrode, there is a surface where the thickness cannot be uniquely determined.
However, it is necessary that the thickness is such that the gas can be sufficiently diffused into the electrode catalyst, and it is usually 5 μm or less, preferably 1 μm or less on the surface of the electrode catalyst.

When the second and subsequent layers are applied, the solution containing the ion exchange resin component may simply be applied on the first layer. However, when it is desired to apply an arbitrary thickness, it is necessary to repeat the application. In that case, a certain amount of the solution is applied on the first layer and dried at 100 ° C. or below, then 120
A method is preferable in which after heat treatment at a temperature of not less than 0 ° C., coating is further applied thereon in the same manner and repeated until the second and subsequent layers have an arbitrary thickness. Further, an ion exchange resin component having an exchange capacity different from that of the first layer can be applied to the second and subsequent layers.

The thickness of layers other than the first layer is preferably as thin as possible in order to reduce the electric resistance of the ion exchange resin layer, but the strength of the fuel cell and the risk of short circuit between electrodes during energization. It is necessary to make a decision in consideration of the fact that there is no In consideration of this, the total thickness of the second and subsequent layers needs to be 5 μm or more, and more preferably 10 μm or more.

The solution containing the ion exchange resin component used in the present invention may be any solution containing the fluorine ion exchange resin component, but for example, a polymer having the following chemical formula is preferable.

[0022]

[Chemical 1]

The equivalent weight of the ion exchange resin component is preferably as small as possible from the viewpoint of electric resistance, but if it is too small, there is a problem that the strength is weakened, and so practically 1100 g /
eq-600 g / eq is preferable. The solvent of the solution containing the ion exchange resin component is not particularly limited, but for example, a mixed solvent obtained by adding water to isopropanol, propanol, ethanol, methanol or the like can be used.

FIG. 1 schematically shows the joined body of the present invention. In FIG. 1, the gas diffusion electrode 1 is composed of a hydrophobic layer 2 and an electrode catalyst layer 3, and a solid polymer electrolyte layer first layer 4 is formed from the inside of the electrode catalyst layer 3 to the surface thereof. A solid polymer electrolyte layer second layer 5 is formed on the solid polymer electrolyte layer first layer 4, and a solid polymer layer third layer 6 is further formed thereon. The electrode catalyst layer 3 has electrode catalyst fine particles 8 supported on carbon 7, and a solid polymer electrolyte layer first layer 4 is coated thereon.

The first layer of the solid polymer layer also covers the carbon 7 on which the electrode catalyst fine particles 8 are partially impregnated in the electrode catalyst layer 3. The electrode catalyst layer 3 has holes 9, and gas is supplied to the electrode catalyst 8 through the holes 9. The solid polymer electrolyte layer first layer 4 has pores 9 in the electrode catalyst layer 3.
The thickness must be such that it does not block the gas flow and obstruct the flow of gas. Therefore, when applying the second and subsequent layers of the solid polymer electrolyte layer, the first layer of the solid polymer electrolyte layer is dissolved again or the solid polymer electrolyte component permeates through the first layer, and the pores are reduced. It is important not to block or block it. When the first layer is formed by the method of the present invention, such a phenomenon does not occur, so that a high performance fuel cell can be constructed.

When a fuel cell is constructed by using a joined body of a solid polymer electrolyte layer and an electrode as shown in FIG. 1, an electrode having two or more solid polymer electrolyte layers and the other one is the first layer. A method in which an electrode having only a solid polymer electrolyte layer and a side having a solid polymer electrolyte layer are brought into close contact with each other and hot press bonding is performed, or a method in which electrodes having two or more solid polymer electrolyte layers are similarly bonded is preferable. Bonding of an electrode having two or more solid polymer electrolyte layers to one electrode and an electrode not having such a layer is not preferable because the adhesion with the electrode becomes poor and the electric resistance tends to increase. .

The temperature at which the electrodes having the solid polymer electrolyte layer are joined is preferably a temperature at which the solid polymer electrolyte becomes soft to some extent, usually 120 ° C. or higher, and 140 ° C. or higher to obtain good adhesion. preferable. The pressure at the time of joining is not particularly limited as long as it is determined to a pressure at which good adhesion can be easily obtained with respect to the joining temperature. In this way
A fuel cell is constructed by using the joined body of the solid polymer electrolyte layer and the electrode obtained by the production method of the present invention, and when electricity is taken out from oxygen gas and hydrogen gas as raw materials, conventional electrode and ion exchange membrane bonding The fuel cell output is higher than when the body is used, and the stability is the same as that of the conventional one.

Thus, according to the present invention, when a joined body of a solid polymer electrolyte for a fuel cell and an electrode is prepared, a layer of the polymer electrolyte on the electrode is treated with a solution of a fluorinated polymer containing a sulfonic acid group as an electrode catalyst. Formed by forming a first layer by coating on the side having and heat treatment, and by further coating a fluoropolymer solution containing a sulfonic acid group on the first layer to form the second and subsequent layers. Therefore, the solid polymer electrolyte layer can be made thin, and the junction interface and the solid polymer electrolyte layer have low electric resistance and mass transfer resistance with excellent adhesion, and a fuel cell with high output can be constructed.

Next, the present invention will be described with reference to examples, but the present invention is not limited thereto.

[0030]

【Example】

[0031]

Example 1 Equivalent weight 1000 g /
A solution A containing 5% by weight of an ion exchange resin component which is a solid polymer electrolyte of eq was prepared.

[0032]

[Chemical 2]

The composition of solution A was propyl alcohol 85.
Part, water 10 parts, and ion exchange resin component 5 parts. As a gas diffusion electrode for fuel cells, size 3 cm x
3cm E-TEK company made platinum catalyst 0.35mg / c
Two sheets of m ² were prepared. 117 mg of the solution A was applied on the catalyst surfaces of the two electrodes and dried at a temperature of 40 ° C. for about 1 hour. Then, it was further heat-treated in a hot air dryer at a temperature of 140 ° C. for 10 minutes to form a first layer. After forming the first layer, 117 mg on the first layer of the two electrodes
Solution A is applied and dried at 40 ° C. for 1 hour.
It heat-processed for 10 minutes in a 0 degreeC hot air dryer, and formed the 2nd layer. After forming the second layer, the third layer, the fourth layer, and the fifth layer were formed in the same manner as the second layer.

Next, the coated layers of the two electrodes were brought into close contact with each other, and were heat-pressed at 145 ° C. and 60 kg / cm ^2.
The bonded body B was obtained by hot pressing for 90 seconds under the above condition. In the joined body B thus produced, the thickness of the solid polymer electrolyte layer was about 20 μm, the joined state was strong, and peeling did not occur easily. The fuel cell main body is mounted by attaching this joined body B to both sides of a power feeding body for taking out electricity and mounting it between the flanges having an inner size of 2 cm × 2 cm and an outer size of 3 cm × 3 cm, which have a gas inlet and outlet. Configured. The fuel cell was connected to an external load, and the output current and the output voltage were measured under the conditions of 55 ° C. and 1 atm while supplying hydrogen gas to one side and oxygen gas to the other side. The result is shown in FIG.

[0035]

Comparative Example 1 Solution A and a gas diffusion electrode exactly the same as in Example 1 were prepared. Nafion 117 manufactured by DuPont, which is a fluorinated sulfonic acid type ion exchange membrane, was also prepared as an ion exchange membrane. The same two electrodes as in Example 1 were prepared, and the first layer was formed under the same conditions as in Example 1 except that heat treatment was not performed at 140 ° C.

The ion exchange membrane was previously treated with 8% sulfuric acid for 2 hours at 100 ° C., washed with pure water, and then immersed in boiling pure water for about 1 hour. After wiping off the water droplets on the surface of the ion exchange membrane, the coated surfaces of the two electrodes are brought into close contact with each other so that the ion exchange membrane side is brought into contact, and a heat press device is used to remove the 145
The bonded body C was obtained by hot pressing for 90 seconds at 60 ° C. and 60 kg / cm ² .

A fuel cell was constructed from this joined body C in exactly the same manner as in Example 1, and the performance was measured. The results are shown in Figure 2.
It is apparent that the joined body of the solid polymer electrolyte layer for a fuel cell and the electrode prepared by the method of the present invention has good fuel cell performance.

[0038]

According to the manufacturing method of the present invention, when a solid polymer electrolyte for a fuel cell and an electrode are manufactured, the solid polymer electrolyte layer can be formed thin, so that the electric resistance of the solid polymer electrolyte layer can be improved. It is possible to construct a fuel cell that has a small mass transfer resistance, excellent adhesion, and a large output.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a joined body of a solid polymer electrolyte of the present invention and an electrode, and a partially enlarged view thereof.

FIG. 2 is a graph showing the output current and output voltage characteristics of the solid polymer electrolyte fuel cells of Example 1 and Comparative Example 1 of the present invention.

[Explanation of symbols]

 1 Gas Diffusion Electrode 2 Hydrophobic Layer 3 Electrocatalyst Layer 4 Solid Polymer Electrolyte Layer First Layer 5 Solid Polymer Electrolyte Layer Second Layer 6 Solid Polymer Electrolyte Layer Third Layer 7 Carbon 8 Electrocatalyst Fine Particles 9 Voids

Claims (1)

[Claims] 1. When preparing a joined body of a solid polymer electrolyte layer for a fuel cell and an electrode, a solution of a fluorinated polymer containing a sulfonic acid group which becomes a polymer electrolyte is formed on the surface of the electrode having an electrode catalyst. After coating and drying, a first layer is formed by heat treatment, and a fluoropolymer solution containing a sulfonic acid group is further coated on the first layer, dried, and then heat treated at least once. By doing
A method for producing a joined body of a solid polymer electrolyte layer for a fuel cell and an electrode, which comprises forming the second and subsequent layers.