JPH027400B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing an ion exchange resin membrane-electrode assembly. More specifically, the present invention relates to fuel cells, water electrolyzers, salt electrolyzers, hydrochloric acid electrolyzers, electrochemical oxygen separation devices, electrochemical hydrogen separation devices, water electrolysis humidity sensors, and electrolytic redox devices for organic compounds. The present invention relates to a method for producing an ion exchange resin membrane-electrode assembly used in various electrochemical devices such as the present invention.

Conventional technology Electrochemical devices in which an ion exchange resin membrane is used as a solid electrolyte and electrodes are integrally bonded to it have already been used in fuel cells (e.g., U.S. Pat. No. 3,134,697) and water electrolyzers (e.g., JSBone, Proceedings of the 14th
Annual Power Sources Conference, p62-64
(1960)), halide electrolysers (e.g. JP-A-Sho
54-107493), electrochemical oxygen separator (e.g. Japanese Patent Publication No. 43-25001, or Japanese Patent Publication No. 56-33979)
), electrochemical hydrogen separation devices (e.g. Stanley
H. Langer and Robert G. Haldeman, Science;
Vol 142, No. 3587 (1963)) and water electrolysis humidity sensors (e.g. Keiyasu Takenaka, Eiichi Shimayo, Yoji Kawami,
Sensor Technology, Vol. 4 No. 5 (1984)) have been proposed.

Ion-exchange resin membranes used to have styrene-divinylbenzene resin as a core with ion-exchange groups introduced into it, but in recent years, membranes with sulfonic acid groups, carboxylic acid groups, or both have been used. Perfluorocarbon resins having ion-exchange groups have become commonly used because they are superior. As the ion exchange group, a proton type is used in a fuel cell or a water electrolyzer, and a sodium ion type is used in a salt electrolyzer.

A method for integrally bonding an electrode to an ion exchange resin membrane is to heat and press a mixture of an electrode catalyst powder and a fluororesin as a binder to an ion exchange resin membrane (for example, as described in U.S. Pat. No. 3,134,697, No. 58-15544) and a method of electroless plating of an electrode catalyst metal onto an ion-exchange resin membrane (for example, JP-A No. 55-1989)
38934).

Electrodes differ depending on the type of electrochemical device, but can be broadly classified into gas diffusion electrodes and gas generation electrodes. In the case of a gas diffusion electrode, a reactant gas is supplied to the electrode, and in the case of a gas generation electrode, the gas is generated from the electrode by an electrolytic reaction. Gas diffusion electrodes are used in fuel cells, cathodes in electrochemical oxygen separators, anodes in electrochemical hydrogen separators, and cathodes in halide electrolysers when oxygen is used as the cathode depolarizer. Gas generating electrodes are used as anodes in water electrolyzers, electrochemical oxygen separators,
Used as cathodes in electrochemical hydrogen separation equipment, anodes in halide electrolyzers, etc.

Generally, among the methods for integrally bonding an electrode to an ion exchange resin membrane mentioned above, the heat-pressing method can be applied to both gas diffusion electrodes and gas generation electrodes.
Electroless plating can only be applied to gas generating electrodes. In the case of a gas generation electrode, it does not matter if the reaction site of the electrode gets wet with water, but in the case of a gas diffusion electrode, the reaction will occur if the parts that get wet with water and the parts that do not get wet with water coexist. This is because it does not proceed smoothly. In other words, the water repellency of the fluororesin used as a binder in the thermocompression bonding method effectively contributes to the gas diffusion electrode reaction.

An electrochemical reaction occurs at the interface between the electrode and the electrolyte, and the current-voltage characteristics of the electrochemical cell are greatly influenced by the contact area between the electrode and the electrolyte. When the electrolyte is an aqueous solution, the contact area between the electrode and the electrolyte is generally large, whereas when the electrolyte is a solid electrolyte such as an ion exchange resin membrane, the contact area between the electrode and the electrolyte is relatively small. . One of the ways to improve this problem is, for example,
As described in No. 14220, a layer of a mixture of electrode catalyst powder, ion exchange resin powder, and binder is interposed between the ion exchange resin membrane as a solid electrolyte and the electrode, and the ion exchange resin membrane and the electrode are interposed. There is a method of increasing the contact area with the electrode. In such a structure, the mixture layer of electrode catalyst powder, ion exchange resin powder, and binder has both the function of an electrode and the function of an electrolyte, but it cannot be taken as part of the electrode. You can also do it. This is because an electrode layer not containing an ion exchange resin adjacent to this mixture layer is not necessarily required.

Problems to be Solved by the Invention The method of increasing the contact area between the ion exchange resin membrane and the electrode described in the above-mentioned Japanese Patent Publication No. 45-14220 is extremely effective as a basic concept. However, there were problems with the materials used here, and there was a limit to the performance of the electrochemical device using an assembly of an ion exchange resin membrane and an electrode. That is, in the above-mentioned literature, a styrene-divinylbenzene copolymer into which sulfonic acid groups have been introduced is used as an ion exchange resin membrane material, which causes problems in heat resistance and chemical stability. In addition, a sulfonated styrene oxide-divinylbenzene copolymer is used as the ion exchange resin powder material in the mixture layer of the electrode catalyst powder, ion exchange resin powder, and binder, but this material also has heat resistance and chemical properties. There is a problem with stability. In particular, when this material is used for an anode, there is a problem in its resistance to anodic oxidation. Furthermore, the trichlorethylene solution of polystyrene used as a binder has insufficient water repellency and coats the electrocatalyst surface and ion exchange resin powder surface in a film-like manner, so it is virtually impossible to separate the electrocatalyst powder. It is not expected that the contact area with the ion exchange resin powder will increase much.

On the other hand, the inventors of the present application have already filed a patent application
No. 190332, a chemically and thermally more stable ion exchange resin was introduced as a material for the ion exchange resin to be mixed into the ion exchange membrane and electrode, instead of an ion exchange resin based on a styrene-divinylbenzene copolymer. Therefore, we proposed the use of an ion exchange resin based on perfluorocarbon, which has better resistance to anodic oxidation.

However, in this case, when manufacturing the electrode, a mixture of the electrode catalyst powder, a perfluorocarbon ion exchange resin solution in an organic solvent or a mixed solvent solution of an organic solvent and water, and a fluororesin binder is applied to the ion exchange membrane. We adopted a method of heat-pressing and volatilizing the solvent during this process. When the ion exchange membrane-electrode assembly obtained by this method is applied to various electrochemical devices, it shows extremely excellent characteristics in a relatively low current density region, but the concentration in a relatively high current density region is It was found that the problem was that the overvoltage was quite large. This is because the ion exchange resin was used in solution form, so the ion exchange resin excessively covered the surface of the electrode catalyst powder.
This is considered to be because the diffusion or adsorption of the electrode reactant to the electrode catalyst powder (reaction site) is delayed as a result.

Means for Solving the Problems The present invention is a solvent for an organic solvent solution or a mixed solvent solution of an organic solvent and water of an ion exchange resin having a perfluorocarbon as a core and having ion exchange groups such as sulfonic acid groups and carboxylic acid groups. An ion exchange resin powder obtained by volatilizing the
A mixture of an electrode catalyst powder and a binder made of a fluororesin such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or tetrafluoroethylene-ethylene copolymer is mixed with a perfluorocarbon. The above-mentioned problems have been solved by heat-pressing the film onto one or both sides of an ion-exchange resin film having a core of ion-exchange groups such as sulfonic acid groups and carboxylic acid groups.

Function The greatest feature of the present invention is that as a starting material for the ion exchange resin powder to be mixed into the electrode, an organic solvent solution or a mixed solvent solution of an organic solvent and water of an ion exchange resin containing perfluorocarbon as a core is used. The point is to use

A typical ion exchange resin having perfluorocarbon as a core is perfluorocarbon sulfonic acid resin. The affinity of perfluorocarbon sulfonic acid resins with organic solvents varies depending on the number of moles of sulfonic acid groups, and this ion exchange resin has a high exchange capacity in the region of lower aliphatic alcohols, such as n-butanol, and other polar It is known that it is soluble in organic solvents with high concentrations (Japanese Patent Publication No. 13333/1983).

Such an ion exchange resin solution is manufactured by, for example, Aldrich Chemical Co., Ltd. in the United States.
Nafion Solution (NAFION Company)
It is sold under the name Solution. Nafion solution is a 5% perfluorocarbon sulfonic acid resin trademarked as NAFION, which is sold by Du Pont in the United States.
It is a lower aliphatic alcohol (containing 10% water) solution.

A fine powder of an ion exchange resin based on a perfluorocarbon resin can be obtained by volatilizing the solvent from an ion exchange resin solution such as a naphion solution by a spray drying method, a freeze vacuum drying method, or the like.

Ion exchange resins that have perfluorocarbon as a core have far superior heat resistance, chemical stability, and anodic oxidation resistance compared to ion exchange resins that have a styrene-divinylbenzene copolymer core as described above. Excellent.

Next, a method for incorporating an ion exchange resin based on perfluorocarbon resin into an electrode will be described. In other words, as mentioned above, when manufacturing an electrode, if a mixed dispersion of an ion exchange resin solution and an electrode catalyst powder is used, the ion exchange resin may form too fine a shape (less than 1 μm) on the surface of the electrode catalyst. ), whereas in the present invention, an ion-exchange resin powder of around 10μ obtained by volatilizing the solvent from an ion-exchange resin solution by spray drying or freeze-vacuum drying is applied to the electrode. When an electrode is made by mixing catalyst powder and a binder, the surface of the electrode catalyst is not covered excessively with ion exchange resin, and sufficient adsorption sites for electrode reactants are secured, resulting in a relatively high current density. The polarization characteristics in this region become even better.

As the ion exchange group of the ion exchange resin mixed into the electrode, a sulfonic acid group, a carboxylic acid group, or a mixture of both can be used. Also,
The mobile ions of ion exchange groups are proton type,
A sodium ion type, a potassium ion type, etc. may be selected depending on the target electrochemical device. Further, the replacement of protons with other ions may be performed after the electrode is bonded to the ion exchange resin membrane.

All conventionally known electrode catalyst powders can be used.

As the binder made of fluororesin, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polytetrafluorochloride ethylene may be used alone or in mixtures. is used. These fluororesins are used in the form of powder, water suspension, or organic solvent suspension. It is also effective to use a suspension of fluororesin mixed and dispersed with powdered fluororesin.

As the ion exchange resin membrane material, it is preferable to use a perfluorocarbon resin having an ion exchange group consisting of a sulfonic acid group, a carboxylic acid group, or a mixture thereof. In addition, as mobile ions,
Proton type, sodium ion type, potassium ion type, etc. may be selected depending on the electrochemical device to be used.

Various methods can be used to bond the electrode to the ion exchange resin membrane. The first method is to make a thin film sheet from a mixed dispersion of electrode catalyst powder, ion exchange resin powder, and a binder made of fluororesin, and heat and press the sheet after the dispersion medium has been volatilized onto the ion exchange resin membrane. The first method is to spray the above-mentioned mixed dispersion onto an ion exchange resin membrane, volatilize the dispersion medium, and then heat press. This method involves screen printing a mixed dispersion liquid onto an ion exchange resin membrane, followed by hot pressing. However, the present invention is not limited to these methods.

In any case, since the ion exchange resin and binder used in the present invention are all fluorine-containing polymers, they not only have excellent heat resistance, chemical stability, and anodic oxidation resistance, but also have excellent heat resistance, chemical stability, and anodic oxidation resistance. The bonding strength between each material and between the electrode and the ion exchange resin membrane is extremely high.

The method for producing an ion exchange resin membrane-electrode assembly of the present invention may be applied to both the cathode side and the anode side, or only to one side. That is, a conventional electrode not containing an ion exchange resin may be bonded to either the cathode or the anode.

As mentioned above, in addition to forming the electrode with only a mixture of electrode catalyst powder, ion exchange resin powder, and fluororesin, the electrode catalyst powder and fluororesin, which do not contain ion exchange resin powder, are formed on top of this mixture layer. A second electrode formed of a mixture of may be bonded.

Example 1 A 5% naphion solution (manufactured by Aldrich Chemical Co., USA, mixed solvent solution of perfluorocarbon sulfonic acid resin with lower aliphatic alcohol and water) was spray-dried to volatilize the solvent, and perfluorocarbon sulfonic acid A fine resin powder was obtained.

0.5 g of this fine powder, 10 g of platinum black powder as an electrode catalyst powder, 4 ml of a 60% polytetrafluoroethylene aqueous suspension, and 10 ml of water were thoroughly mixed, rolled, vacuum dried, and the thickness was reduced. A 0.2mm electrode sheet was manufactured.

This electrode sheet was hot pressed on both sides of Nafion 117, a perfluorocarbon sulfonic acid resin membrane manufactured by DuPont, USA, at a temperature of 100° C. and a pressure of 200 kg/cm ² .

The ion exchange resin membrane-electrode assembly thus obtained becomes an electrochemical oxygen separation device. That is,
When one side of this bonded body is used as a cathode and the other side is used as an anode, air is supplied to the cathode side, water is supplied to the anode side, and DC current is applied to both electrodes, pure oxygen is generated from the anode side. On the cathode side, a gas from which oxygen has been removed from the air is obtained.

Next, the ion exchange resin membrane-electrode assembly obtained in the example is referred to as A, and in the example, when manufacturing the electrode, an organic perfluorocarbon sulfonic acid resin is used instead of the powder form as the ion exchange resin. The conjugate used in the form of a mixture of solvent and water is designated as C, and the results of determining the polarization characteristics of both as an electrochemical oxygen separation device are shown in FIG. From FIG. 2, it can be seen that conventional method C is superior in the current density region of 200 mA/cm ² or less, but method A is superior in the current density region of 200 mA/cm ² or more.

Effects of the Invention The ion exchange resin membrane-electrode assembly obtained in the example is referred to as A, and in the example, the conventional sulfonated styrene oxide resin was used instead of the perfluorocarbon sulfonic acid resin as the ion exchange resin powder mixed into the electrode. - When divinylbenzene resin was used, the bonded body was assembled into an electrochemical oxygen separation device, and a life test was conducted at a current density of 200 mA/cm ^2. As a result, the operating time and A relationship with voltage was obtained. That is, in the case of the product A of the present invention, no abnormality was observed, whereas in the case of the conventional product B, the voltage increased abnormally as the operating time elapsed. This is simply because the perfluorocarbon sulfonic acid resin mixed in the anode in case A has better anodic oxidation resistance than the sulfonated styrene-divinylbenzene resin in case B.

[Brief explanation of drawings]

Figure 1 is a diagram comparing the change in voltage over time when an ion exchange resin membrane-electrode assembly according to an embodiment of the present invention is applied to an electrochemical oxygen separation device with that of a conventional product. FIG. 2 is a comparison diagram of the polarization characteristics of ion exchange resin membrane-electrode assemblies obtained by the invention method and the conventional method as an electrochemical oxygen separation device.

Claims (1)

[Claims] 1 Ions obtained by volatilizing the solvent of an organic solvent solution or a mixed solvent solution of an organic solvent and water of an ion exchange resin having a perfluorocarbon as a core and an ion exchange group such as a sulfonic acid group or a carboxylic acid group. Exchangeable resin powder, electrode catalyst powder, and a binder made of a fluororesin such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, etc. An ion exchange resin membrane-electrode assembly characterized in that the mixture is heat-pressed to form a membrane on one or both sides of an ion exchange resin membrane having perfluorocarbon as a core and ion exchange groups such as sulfonic acid groups and carboxylic acid groups. manufacturing method.