JPS622635B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to various electrochemical devices using an ion exchange resin membrane as an electrolyte. The purpose is to improve the polarization characteristics of the electrochemical device and at the same time make it easier to manage the water vapor pressure, thereby making the operation of the electrochemical device easier.

Electrochemical devices that use ion exchange resin membranes as electrolytes include water electrolyzers, alkali chloride electrolyzers, hydrochloric acid electrolyzers, devices that electrolytically separate only chlorine from hydrochloric acid, devices that separate oxygen from air, and double or triple hydrogen electrolytes. Examples include devices that separate hydrogen, devices that separate hydrogen from a mixed gas containing hydrogen, carbon monoxide sensors, humidity sensors, and fuel cells.

In these various electrochemical devices, there are cases in which a bonded body in which an ion exchange resin membrane and an electrode are joined together, and cases in which they are not used, and the present invention relates to the former case.

Conventionally, methods for integrating an ion-exchange resin membrane and an electrode can be roughly divided into the chemical plating method described in Japanese Patent Publication No. 56-36873, and the method using electrode materials as described in Japanese Patent Publication No. 58-15544. There is a method of heat-pressing a mixture of powder and a binder onto an ion exchange resin membrane. However, in either method, the reaction zone of the electrode is the contact interface between the ion exchange resin membrane and the electrode, and the electrode reaction occurs only two-dimensionally.

Therefore, if the contact point between the ion exchange resin membrane and the electrode is made three-dimensional, the effective area of action of the electrode will increase, and the electrode reaction should proceed more quickly.
Based on this viewpoint, Japanese Patent Publication No. 14220/1983 proposes a fuel cell in which an ion exchange resin membrane and an electrode are bonded together with a mixture of an ion exchange adhesive and an electrode catalyst.

However, the cited reference states that the ion-exchange resin membrane is based on a styrene-divinylbenzene copolymer with sulfonic acid groups introduced, and that it cannot be mixed with the ion-exchange resin powder of the ion-exchange adhesive. The use of polystyrene as the binder to be used and the binder to be mixed with the electrocatalyst posed at least two problems.

One of the problems is that the polarization characteristics of the fuel cell are poor and the operating current density is only a few mA/cm ² in the case of the above-mentioned combination of materials.The other problem is that the mechanical strength is low and the durability is low. It is a lack of gender.

The present invention has the same concept and basic structure as the above-mentioned Japanese Patent Publication No. 45-14220 in terms of making the electrode reaction zone three-dimensional. This will solve these problems and dramatically improve the performance of electrochemical devices.

That is, in the present invention, the ion exchange resin membrane is based on a fluorine-containing polymer such as perfluorocarbon, and one or two cation exchange groups such as sulfonic acid groups or carboxylic acid groups are added thereto.
A mixture of an electrode catalyst powder and a fluorine-containing polymer binder is used as an electrode.
The layer interposed between the ion exchange resin membrane and the electrode is characterized by using a mixture of short fibers of sulfonated styrene oxide-divinylbenzene copolymer, electrode catalyst powder, and fluorine-containing polymer binder. .

When such a combination of materials is employed, the polarization characteristics of the electrode will be dramatically improved due to the ion exchange resin membrane which is based on a fluorine-containing polymer and into which cation exchange groups have been introduced.

Next, in the mixed layer of the electrode catalyst powder, ion exchange resin short fibers, and fluorine-containing polymer binder, due to the presence of the fluorine-containing polymer binder, there are parts that get wet with water and parts that are wet with water. Ideal distribution of non-wetted areas also greatly contributes to improving the polarization characteristics of the electrode.

On the other hand, in the triple-layer assembly of the ion-exchange resin membrane, ion-exchange resin-catalyst mixed layer, and electrode described above, the presence of fluorine-containing polymers in each layer means that these layers have good affinity; Cohesion is improved, resulting in increased durability. Furthermore, the fact that the ion exchange resin used in the mixed layer of the ion exchange resin and the catalyst is in the form of short fibers also forms a strong layer due to the entanglement of the fibers.

In this sense, it should be noted that the feature of the present invention lies in the new combination of materials of this triple-layer assembly. Furthermore, although Japanese Patent Publication No. 45-14220 is limited to fuel cells, the present invention is also significant in that it has been found that it can be applied to various electrochemical devices other than fuel cells as described above.

Suitable examples of the fluorine-containing polymer binder include polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polytetrafluoroethylene chloride, etc. Although it is also effective to use a mixture of these, polytetrafluoroethylene is most suitable.

The reason why polytetrafluoroethylene is optimal is that its transition point is relatively high at 327°C, and as will be described later, the hot press temperature when producing the triple layer bonded body is in the range of 50 to 300°C. It is related to that. In other words, in this range, polytetrafluoroethylene shows almost no melt fluidity, and especially in the mixed layer of ion exchange resin short fibers and catalyst powder, polytetrafluoroethylene forms a film. Since these materials are in point-like contact without being coated, areas that are easily wetted by water and areas that are not easily wetted by water are appropriately distributed.

Regarding this point, the above-mentioned Special Public Service
As seen in No. 14220, when polystyrene is used as a binder for a mixed layer of ion exchange resin powder and catalyst powder, the surfaces of the ion exchange resin powder and catalyst powder are covered with a film of polystyrene. Otherwise, the distribution of water will not be in a desirable state, and the number of points of contact between the ion exchange resin powder and the catalyst powder will decrease.

Although the electrode catalyst material varies depending on the electrochemical device, a conductive material may be mixed in addition to the catalyst powder in the mixed layer of ion exchange resin short fibers and electrode catalyst powder or in the electrode.

The reason why a mixed layer of an electrode catalyst and an ion exchange resin is interposed between the ion exchange resin membrane and the electrode is as follows.
Generally, it is preferable to perform this on both the cathode side and the anode side, but depending on the type of electrochemical device, either one may be used.

The electrodes of the electrochemical device described above can be classified into electrodes that generate gas and electrodes that are supplied with gas from the outside.Generally, applying the present invention to the latter electrodes has a relatively large effect. .

The type of electrode that supplies gas from the outside is the cathode (air electrode) of a device that separates only chlorine from hydrochloric acid, the cathode (air electrode) of a device that separates oxygen from air, and the cathode (air electrode) of a device that separates hydrogen from a mixed gas containing hydrogen. These include device anodes (mixed gas electrodes containing hydrogen) and fuel cell cathodes (air electrodes, oxygen electrodes) and anodes (hydrogen electrodes, methanol electrodes, hydrazine electrodes).

In various electrochemical devices, when a mixed layer of electrode catalyst and ion exchange resin is not interposed,
The electrode may be bonded directly to the ion exchange resin membrane by a conventionally known chemical plating method or hot pressing method.

Another advantage obtained by interposing a layer of a mixture of an electrode catalyst, ion exchange resin short fibers, and a fluorine-containing polymer binder between the ion exchange resin membrane and the electrode is water management. In other words, the method of operating the electrochemical device is simplified.

For example, in a device for separating oxygen from air, which has an air electrode as a cathode and an oxygen generating electrode as an anode, water is supplied to the anode side, air is supplied to the cathode, and the cathode and anode are separated. When a DC voltage is applied between them, a reaction occurs at the cathode: O ₂ (in air) + 4H ⁺ + 4e ^- → 2H ₂ O at the anode: 2H ₂ O → O ₂ (pure oxygen) + 4H ⁺ + 4e ^- , and the air on the cathode side At the same time, water is generated at the cathode as only the oxygen in the cathode is transferred from the cathode side to the anode side. Further, during this reaction, protons (H ⁺ ) move from the anode side to the cathode side in the ion exchange resin membrane together with several moles of water molecules. Therefore, a large amount of water will collect on the cathode side. In this device, if the cathode is directly bonded to the ion exchange resin membrane, the pores of the cathode will be filled with water, inhibiting oxygen diffusion, and making it difficult for the above-mentioned cathode reaction to proceed. Therefore, it becomes necessary to take in and remove water that collects on the cathode side into the air flow, but if too much dry air is supplied, the relationship between the cathode and the ion exchange resin membrane will be adversely affected. Since water is lost at the interface and the substantial electrode reaction area is reduced, the oxygen reduction reaction is also inhibited.

In other words, this involves the complexity of having to precisely control the relationship among air temperature, humidity, supply amount, and current supply.

However, as in the present invention, when a mixed layer of an electrode catalyst, ion exchange resin short fibers, and fluorine-containing polymer is interposed between the ion exchange resin membrane and the electrode,
Since the electrode reaction zone is widely distributed from the interface between the ion exchange resin membrane and this intervening mixture layer to the interface between the intervening mixture layer and the electrode, sufficient oxygen reduction reaction can occur even if water vapor management is a little rough. I found out.

On the other hand, in the material structure proposed in the above-mentioned Japanese Patent Publication No. 14220/1983, the electrode catalyst/ion exchange resin mixed layer is too easily wetted by water, so water vapor management as described above is not necessary. The problem was that it did not go well.

In order to form a triple layer consisting of an ion exchange resin membrane, an electrocatalyst, an ion exchange resin short fiber, a fluorinated polymer binder mixed layer, and an electrode catalyst and a fluorinated polymer binder mixed layer, An effective method is to knead each layer in advance into a thin film, then laminate the layers and hot press, but the method is not necessarily limited to this method. When forming the mixed layer of electrode catalyst - ion exchange resin short fibers - fluorine-containing polymer binder, an aqueous suspension is used as the fluorine-containing polymer binder, and a so-called paper-making method is used. Forming a thin film sheet is also an effective method.

Note that the electrode may be a single layer of a mixture of an electrode catalyst and a fluorine-containing polymer binder, or as a backing layer for this layer, a conductive material that does not have a catalytic effect, such as carbon powder, and a fluorine-containing polymer binder may be used. mixed layer with binder,
Alternatively, it may be effective to provide a porous polytetrafluoroethylene membrane.

An embodiment of the present invention will be described in detail below.

Embodiment FIG. 1 shows a schematic cross-sectional structure of an apparatus for separating oxygen from air according to an embodiment of the present invention.

In FIG. 1, 1 is an ion exchange resin membrane made by introducing sulfonic acid groups into perfluorocarbon;
2 is an ion exchange resin short fiber made by introducing a sulfonic acid group into a styrene-divinylbenzene copolymer with a short fiber diameter of several microns and a length of 1 to 2 mm, platinum black powder as an electrode catalyst, and a binder as a binder. 3 is an ion exchange resin-electrode catalyst mixed layer with polytetrafluoroethylene, and 3 is an air electrode made of a mixture of platinum black powder and polytetrafluoroethylene as a binder.

On the other hand, an oxygen generating electrode 4 made of rhodium is bonded to the other surface of the ion exchange resin membrane 1.

The air electrode 3 acts as a cathode and the oxygen generating electrode acts as an anode.

The oxygen generating electrode 4 is first bonded to the ion exchange resin membrane 1 by a chemical plating method, and then once dried, the ion exchange resin-electrode catalyst mixed layer 2 and the air electrode 3 are bonded by a hot pressing method. 5 and 5' are current collectors made of expanded titanium plated with platinum, 6 is a cathode end plate made of a titanium plate, and 7 is an anode end plate made of a titanium plate. 8 and 8' are cell frames, 9 is an air inlet, 10 is an air outlet, 11 is a water supply port, and 12 is an oxygen outlet.

In an apparatus for separating oxygen from air having such a structure, when a direct current is applied between the cathode end plate 6 and the anode end plate 7, a reduction reaction of oxygen in the air occurs at the air electrode 3, and the air outlet 10 At the same time, gas whose oxygen concentration has become lower than that of air is discharged, and at the same time, an oxygen generation reaction occurs at the oxygen generation electrode 4, and pure oxygen comes out from the oxygen outlet 12.

Therefore, such a device for separating oxygen from air functions as a deoxidizing device when the gas coming out from the air outlet 10 is the target object.
When the target object is pure oxygen coming out of the oxygen outlet 12, it functions as an oxygen generator or an oxygen concentrator.

Next, we tested the performance of this device that separates oxygen from air when it was operated as an oxygen generator by comparing it with a conventional example.

First, let A be the device of the present invention described above, and let B be a conventional device in which the air electrode 3 is directly bonded to the ion exchange resin membrane 1 without intervening the ion exchange resin-electrode catalyst mixed layer 2 in the above embodiment. In the above embodiment, an ion exchange resin membrane formed by introducing sulfonic acid groups into a styrene-divinylbenzene copolymer was used as the ion exchange resin membrane 1,
The device in which a trichlorethylene solution of polystyrene is used as the binder for the ion exchange resin powder-electrode catalyst mixed layer is designated as C, and in the example, polystyrene is used as the binder for the ion exchange resin short fiber-electrode catalyst mixed layer. The devices using the trichlorethylene solution were designated as D, and the current density-voltage characteristics of these devices were determined, and the results shown in FIG. 2 were obtained.

In other words, it is clear that device A according to the present invention exhibits overwhelmingly excellent characteristics.

This is because when comparing device A and device B, the reaction zone of the air electrode of the latter is two-dimensional, whereas that of the former is three-dimensional.
This is simply because the effective area of action has become larger. Further, when comparing device A and device C, the ion exchange resin membrane used in the former is superior. Furthermore, when comparing Device A and Device D, the binder of the ion exchange resin-electrode catalyst mixed layer of the former is polytetrafluoroethylene, while that of the latter is a trichloroethylene solution of polystyrene. It comes from something. That is, in the former case, the electrode catalyst and the ion exchange resin are in better contact with each other.

Next, we compared the changes in voltage over time when device A and device D were operated continuously at a current density of 100 mA/ ^cm2 , and the results shown in Figure 3 were obtained. . That is, it can be seen that device A of the present invention exhibits a longer lifespan. This is clearly due to the fact that polytetrafluoroethylene is superior to polystyrene as a binder for the ion exchange resin-electrode catalyst mixed layer.

On the other hand, when comparing the cases where air with a dew point of 5℃ and air with a dew point of 30℃ were supplied to each device using device A and device B, it was found that 100mA/cm ²
At a current density of
The voltage was unstable, showing 1.2V at 1.4V and 30°C. This fact differs from the case of device A according to the present invention, which shows that due to the presence of the ion exchange resin-electrocatalyst mixture layer, the electrode reaction zone moves appropriately and exhibits a constant voltage regardless of the dew point of the air. On the other hand, in the absence of the above-mentioned mixture as in the conventional case, the area near the interface between the electrode and the ion exchange resin membrane becomes too dry or too wet. In this sense, the effect of the present invention is enormous in terms of simplifying the operation of the device.

As described in detail above, the present invention provides an electrochemical device using an extremely excellent ion exchange resin membrane as an electrolyte, and has extremely high industrial value.

[Brief explanation of the drawing]

Fig. 1 is a schematic cross-sectional structure diagram of an apparatus for separating oxygen from air according to an embodiment of the present invention, and Fig. 2 is an apparatus A for separating oxygen from air according to an embodiment of the present invention, and conventional apparatuses B and C. , D. FIG. 3 is a diagram showing a comparison of the life test results of device A for separating oxygen from air according to an embodiment of the present invention and conventional device D. be. DESCRIPTION OF SYMBOLS 1... Ion exchange resin membrane, 2... Ion exchange resin-electrode catalyst mixed layer, 3... Air electrode, 4... Oxygen generating electrode, 5... Current collector, 6... Cathode end plate,
7... Anode end plate, 8, 8'... Cell frame, 9... Air inlet, 10... Air outlet, 1
1...Water supply port, 12...Oxygen outlet.

Claims (1)

[Claims] 1 Electrode catalyst powder, short fibers of sulfonate oxide of styrene-divinylbenzene copolymer, and fluorine-containing polymer are coated on one or both sides of an ion-exchange resin membrane that is based on a fluorine-containing polymer and has a cation exchange group introduced therein. A mixed layer with a molecular binder is arranged, and an electrode made of a mixture of an electrode catalyst powder and a fluorine-containing polymer binder is arranged as a layer adjacent to the mixed layer,
An electrochemical device using an ion-exchange resin membrane as an electrolyte, characterized by comprising a bonded body made by integrating these.