JPH0616416B2 - Air electrode - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to an air electrode useful for an oxygen-hydrogen battery, an air-metal battery, an oxygen sensor, and the like. More specifically, it is capable of performing heavy load discharge and is leak-proof. The present invention relates to an air electrode having excellent liquidity.

[Technical Background of the Invention and Problems Thereof] Conventionally, gas diffusion electrodes have been used as air electrodes of various fuel cells, air cells, galvanic oxygen sensors and the like.

As the gas diffusion electrode, initially, a thick and single porous catalyst layer was used, but now,
Due to the demand for thinner batteries and the demand for improved leakage resistance, a two-layer structure electrode in which a thin layer of a water-repellent material is integrally attached to a thin porous catalyst layer has been used. . Further, when leakage is not allowed, for example, in the galvanic oxygen sensor used for detecting the concentration of dissolved oxygen gas in water, the electrolyte resistance / gas resistance is further increased on the water-repellent layer of the above-mentioned two-layer structure electrode. The air electrode is formed by integrally attaching a transparent non-porous film.

The air electrode basically composed of the porous catalyst layer and the water-repellent layer is a practical air electrode to which a current collector such as nickel net is integrally attached.

Now, in such an air electrode, the porous catalyst layer has three phases in its pores: gas phase (air) -solid phase (catalyst and base material supporting it) -liquid phase (electrolyte) A zone is formed, and an electrochemical reduction reaction of oxygen gas is promoted in the three-phase zone. As a result, an electric current can be taken out through the current collector integrally attached to the porous catalyst layer.

Therefore, the porous catalyst layer is made of a material that is porous and has an oxygen gas reducing ability, and as a typical example thereof,
For example, nickel tungstate with low oxygen reduction overvoltage,
Tungsten carbide coated with palladium and cobalt,
Activated carbon powder supporting nickel, silver, platinum, palladium, etc. is bound with, for example, polytetrafluoroethylene to form a porous body, which is integrated with a metal porous body, a carbon porous body, and a carbon fiber nonwoven fabric. There is one that has been configured into.

The water-repellent layer, which is another element, is repellant typified by a fluororesin such as polytetrafluoroethylene, polytetrafluoroethylene-hexafluoropropylene copolymer, polyethylene-tetrafluoroethylene copolymer, or polypropylene. Widely used are a sintered body of a powder of an aqueous material, a paper-like material obtained by heat-treating fibers, and a woven cloth-like material or a film-like material.

However, the air electrode having the conventional structure as described above is not necessarily thin and has excellent resistance to liquid leakage, and is not sufficiently suitable for applications requiring heavy load discharge (for example, thin air / zinc battery). It was

For example, when a porous film formed by sintering the above-mentioned fluororesin powder is used as the water-repellent layer, it is about 20 mA /
Although it is possible to carry out a considerable heavy load continuous discharge of cm ² , its thickness becomes as thick as about 0.125 to 0.50 mm. Moreover, the pore diameter of the porous membrane is not uniform, and there are pores with a large pore diameter. Therefore, when the internal pressure of the battery rises due to the volume expansion of the counter electrode of the air electrode, it is especially advantageous for the sealed battery. If so, the phenomenon of liquid leakage from the hole may occur. On the other hand, in the air electrode where a thin gas-permeable non-porous film is further attached to the gas side with an adhesive or the like to prevent liquid leakage, the liquid leakage phenomenon can be completely prevented, and its thickness It is possible to reduce the thickness to about 12.5 μm, but in this case, continuous discharge with a large current of 10 mA / cm ² or more becomes very difficult.

On the other hand, as the other type of air electrode, a conductive base material powder such as activated carbon or nickel on which various catalysts are supported is mixed with a powder of a water repellent material such as polytetrafluoroethylene to obtain an air electrode. It is known that the mixed powder obtained is subjected to pressure molding. At this time, the powder of the water repellent material simultaneously functions as a binder for the base powder. In this case, the air electrode does not have a two-layer structure, but the water repellent material is uniformly dispersed in the porous catalyst layer. Since this type of air electrode does not require a water-repellent layer attached to the porous catalyst layer, the porous catalyst layer can be made thicker (the amount of catalyst can be increased) with respect to the entire thickness, so that a heavy load is applied. Discharge becomes possible. On the contrary, the heavy load discharge by the predetermined current can reduce the thickness.

However, in this type of air electrode, since the hydrophilic substrate or the surface of the catalyst is exposed to a considerable extent, the electrolytic solution gradually permeates into the porous catalyst layer with the lapse of time to form a three-phase zone. The effective area can be gradually reduced. As a result, an inconvenient situation occurs in which the stability of heavy load discharge is impaired.

[Object of the Invention] The present invention provides an air electrode which solves the above-mentioned problems in the air electrode having the conventional structure, is thin, can perform heavy load discharge for a long period of time, and is excellent in liquid leakage resistance. With the goal.

[Summary of the Invention] An air electrode of the present invention is an air electrode having an integral structure composed of a current collector, a water-repellent layer, and a catalyst layer, and the water-repellent layer contains fusible graphite and a water-repellent binder. Is a porous layer bound by, the catalyst layer is a porous layer obtained by binding activated carbon or activated carbon supporting a catalyst having an oxygen reducing ability with a water repellent binder, and both layers Is characterized in that a liquid fluorine compound having oxygen dissolving ability is carried.

First, in the air electrode of the present invention, any current collector may be used as long as it is a conductive material and is porous, and examples thereof include a molded body of nickel net, activated carbon or graphite powder. In these current collectors, the pore size is 0.05 to 5
Those having 30 to 90% distribution of mm holes are preferred. The reason is that, when the electrode is activated, the rate of removal of oxygen reduction product ions is increased, a current with a high current density can be easily taken out, and the water-repellent layer to be described later can be attached more uniformly. This is because the mechanical strength can be improved.

Next, the catalyst layer according to the present invention is a conductive porous catalyst layer, and is coated with nickel tungstate, cobalt phthalocyanine, cobalporphyrin, palladium-cobalt, which has an electrochemical reducing ability with respect to oxygen gas. After a predetermined amount of a liquid fluorine compound having an oxygen-dissolving ability described below is adsorbed and supported on activated carbon powder or a single powder of activated carbon supporting a catalyst such as tungsten carbide, nickel, silver, platinum or palladium, it is made water repellent. It can be obtained by mixing or kneading with a powder or liquid of a binder and subjecting it to a predetermined method, for example, roll forming into a sheet having a predetermined thickness. The adsorption / supporting treatment of the liquid fluorine compound medium having an oxygen-dissolving ability, in addition to the above-described method, is performed in advance by using a conductive powder having an electrochemical reducing ability with respect to oxygen gas and a water-repellent binder. From a porous sheet,
A liquid fluorine compound having an oxygen-dissolving ability may be impregnated and supported thereon under reduced pressure, for example. As the water-repellent binder used for producing the catalyst layer, any binder having good water repellency and electrolytic solution resistance together with the binding property may be used,
In particular, polytetrafluoroethylene, polyethylene, polystyrene, polyamide resin, acrylic resin, epoxy resin, and synthetic rubber such as neoprene and chloroprene are preferred.

In addition, the water-repellent layer according to the present invention comprises a powder of fusible graphite, which maintains a water-repellent effect for a long time with respect to an acid or alkaline aqueous solution, in the same manner as in the production of the catalyst layer. It can be produced using a liquid fluorine compound having a function.

A water-repellent layer formed by simply forming a sheet of fluorinated graphite powder using a water-repellent binder is compared to a conventional porous film formed by firing fluorine resin powder, compared to a catalyst layer or a current collector. Although the adhesion to the layer is improved, a decrease in water repellency, which is considered to be due to the effect of residual hydrophilic groups in the fluorinated graphite, is recognized. Therefore, by containing the liquid fluorine compound having the oxygen-dissolving ability of the present invention in the water-repellent layer, the effect of the residual hydrophilic group of the fluorinated graphite is suppressed and the water-repellency and oxygen The uptake ability can be greatly improved.

Now, the catalyst layer according to the present invention, the liquid fluorine compound having an oxygen-dissolving ability that is adsorbed and supported on the water-repellent layer enhances the oxygen concentration in the water-repellent layer attached to the air-side surface of the air electrode to improve the heavy load discharge characteristics. At the same time, it contributes to the liquid leakage resistance by significantly improving the water repellency of each layer.

The catalyst layer according to the present invention, the liquid fluorine compound having an oxygen-dissolving ability to be adsorbed and supported on the water-repellent layer, a fluorine-containing aliphatic hydrocarbon, for example, a low polymer of 1-chloro-1,2,2-trifluoroethylene A fluorine-containing aromatic hydrocarbon, for example 1,2,
4,6-tetrafluorobenzene, a fluorine-containing amide, such as N-bis (pentafluoropropyl) acetamide, which is a fluorine compound in which a part of hydrogen bonded to carbon in an organic compound having a hydrocarbon group is replaced by fluorine And a liquid having oxygen-dissolving ability (hereinafter referred to as "partially substituted fluorine compound"). As the partially substituted fluorine compound, a compound that is liquid at room temperature, has a relatively high boiling point and oxygen dissolving ability, and has a relatively small surface tension may be used. Since the partially substituted fluorine compound can permeate into the fine pores of either the catalyst layer or the water repellent layer, the water repellency of each layer is remarkably improved and the liquid leakage resistance is contributed.

Actually, the boiling point is 100 ° C to 200 ° C, and the oxygen dissolving ability is 40.
It is preferable to use one having a vol% or more and a surface tension of 30 dyne / cm or less. For example, a low polymer of 1-chloro-1,2,2-trifluoroethylene (n = 4-8, molecular weight 500-90).
0). The low polymer of 1-chloro-1,2,2-trifluoroethylene has a large oxygen solubility of 10 times or more,
Further, it is excellent in alkali resistance, acid resistance and heat resistance and can be said to be particularly suitable for the present invention.

Further, as the liquid fluorine compound having an oxygen-dissolving ability which is adsorbed and supported on the catalyst layer and the water-repellent layer according to the present invention, perfluorotri-n-butylamine (FC-43), perfluorotripropylamine (FTPA), perfluoro Decalin (F
DC), perfluoromethyldecalin (FMD), perfluorinated ethers (Freon E ₄ ), etc., a fluorine compound in which all of the hydrogen bonded to carbon in the organic compound having a hydrocarbon group is substituted with fluorine. Also, a liquid having oxygen-dissolving ability (hereinafter referred to as "perfluoro compound") can be used. These perfluoro compounds are excellent in water repellency, have a large oxygen dissolution capacity of about 40 vol% or more, and have a large oxygen transfer rate of 14 to 26 msec. The transfer of oxygen is almost instantaneous, and this reaction is also reversible. It is a target.

The perfluoro compound enhances the oxygen concentration in the water-repellent layer and significantly improves the heavy load discharge characteristics of the entire electrode,
In addition, it contributes to quick electrode responsiveness by improving leakage resistance with improved water repellency and having a high rate of oxygen transfer.

These liquid fluorine compounds having an oxygen-dissolving ability are added to the catalyst powder of the catalyst layer or the fluorinated graphite powder of the water repellent layer in an amount of 0.00
1% by weight is adsorbed and carried, and begins to exert its effect,
If too much is loaded, the internal resistance of the electrode is increased. From the viewpoint of suppressing the internal resistance and preventing the voltage drop due to heavy load discharge, it is usually preferable to use 0.001% by weight or more and less than 20% by weight in practice.

In particular, when the partially substituted fluorine compound and the perfluoro compound coexist, the water repellency is further improved and the liquid leakage resistance can be improved. Further, the heavy load discharge characteristic can be further improved.

That is, when a partially substituted fluorine compound and a perfluoro compound are allowed to coexist, the partially substituted fluorine compound is adsorbed on the surfaces of the activated carbon and fluorinated graphite that form the water repellent layer and the catalyst layer, and a thin liquid film is formed. It Further, the perfluoro compound is present in this liquid film. The perfluoro compound in the liquid film exhibits high water repellency and improves liquid leakage resistance. In addition, the liquid perfluoro compound in the liquid film has a high oxygen-dissolving ability, transports oxygen in the air electrode to the surface of activated carbon and the like, and has a high oxygen transfer rate, so that high heavy load discharge characteristics can be realized.

In the air electrode of the present invention, for example, both sides of the current collector are sandwiched between the catalyst layer and the water repellent layer described above, or both sides of the catalyst layer are sandwiched between the current collector and the water repellent layer described above, and an appropriate pressure ( Usually 50
~ 100 kg / cm ² ) is applied and pressure-bonded to form a monolithic laminated body. It goes without saying that the water repellent layer side is arranged on the air side when the obtained electrode is assembled into a battery.

[Examples of the invention] Examples 1 to 5 and Comparative Examples 1 to 3 Activated carbon powder carrying 1% by weight of platinum (average particle size 80 µ
m), and fluorinated graphite powder (average particle size 40 μm). 1-chloro-1,2,2-trifluoroethylene (n = 4-6, molecular weight 5 as a liquid fluorine compound having oxygen-dissolving ability)
00 to 700) was selected as perfluorodecalin as a liquid perfluoro compound having an oxygen-dissolving ability.

Each of the above powders was immersed in a liquid fluorine compound containing 0.1 vol% of a liquid fluorine compound or a liquid perfluoro compound, or a liquid perfluoro compound for adsorption treatment. The adsorption amount of the liquid fluorine compound, the liquid fluorine compound containing the liquid perfluoro compound, and the liquid perfluoro compound was 5% by weight, respectively.

The two powders obtained were kneaded using a dispersion of polytetrafluoroethylene (average particle size 15 μm), and the kneaded product was roll-formed by a conventional method to obtain a thickness of 200 μm each.
The catalyst layer and the water-repellent layer were used as the sheet.

Next, on both sides of 0.15φ-40 mesh nickel net,
Contact the catalyst layer sheet and water repellent layer sheet respectively,
The whole was pressure-bonded with a pressure of 75 kg / cm ² to form an electrode having an integral structure. Thickness 500 μm.

For comparison, an air electrode was manufactured in the same manner as in Example except that a sheet of a PTFE powder sintered body and a polypropylene film were used as the water-repellent layer sheet. Further, an air electrode was manufactured in the same manner as in the example except that the water-repellent layer sheet did not contain the liquid fluorine compound and the liquid perfluoro compound.

Then, these electrodes and gel powder of zinc powder that passed through a mesh of 60 to 150 mesh and amalgamated with 3% mercury by volume ratio were prepared by dispersing a gelling agent in a sodium hydroxide solution. An air / zinc battery was assembled from a zinc electrode dispersed in the above and a separator made of a polyamide nonwoven fabric.

After leaving these batteries in air at 25 ° C. for 16 hours, they were discharged with various currents for 5 minutes, and the current value when the terminal voltage dropped to 1.0 V or less after 5 minutes was measured. Also, 500 for each battery
A constant resistance of Ω was connected and continuously discharged at 25 ° C. Then, the time until the electrolyte leaked from the air side layer was measured.

The results are collectively shown in Table 1 below.

[Effects of the Invention] As is clear from the above description, the air electrode of the present invention is
It has excellent heavy load discharge characteristics, excellent leakage resistance, and is extremely thin, and its industrial value is great.

In the above examples, an air-zinc battery using sodium hydroxide as an electrolytic solution was assembled and its performance was evaluated, but other electrolytic solutions such as ammonium chloride, potassium hydroxide, lithium hydroxide, and cesium hydroxide were used. Needless to say, the same effect can be obtained by using a solution obtained by mixing rubidium hydroxide or the like with these solutions. It can also be used in air-iron batteries and the like.

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Claims (1)

[Claims] 1. An air electrode having an integral structure comprising three layers of a current collector, a water repellent layer and a catalyst layer, wherein the water repellent layer is a porous structure obtained by binding fluorinated graphite with a water repellent binder. Is a porous layer, and the catalyst layer is a porous layer obtained by binding activated carbon or activated carbon supporting a catalyst having oxygen reducing ability with a water repellent binder, and both layers have oxygen dissolving ability. An air electrode, wherein a liquid fluorine compound is carried.