JPS60133675A - Air electrode - Google Patents

Abstract

PURPOSE:To obtain a thin air electrode that enables heavy load discharge for a long period of time and is also excellent in preservation performance by providing a poly (4-vinylpyridine) thin film coated through a porous film on the gas side surface of the electrode main body. CONSTITUTION:The gas side surface of an electrode main body is coated with a poly (4-vinylpyridine) thin film through a porous film. The material of the porous film is not cared, but if the prous film is assumed to be attached to the electrode main body, it is desirable that the porous film should have full flexibility. The poly (4-vinylpyridine) degree of polymerization is not specifically specified. If the workability when the porous film is applied is assumed, it is desirable that viscosity should not be excessive. As the coating method, the coating method, spray method, dip method, and such can be applied. For example, the porous film coated with poly (4-vinylpyridine) is dried under normal pressure or reduced pressure at normal temperatures or approximately 100 deg.C and then is climped and integrated on the gas side surface of the electrode main body at preset pressure so that the coating surface can face an outer surface.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a hydrogen/oxygen fuel cell, a metal/sudden cell, ! Regarding the air electrode for the elemental sensor, in more detail, even if it is thin, it can discharge nine heavy loads over a long period of time.

Regarding air electrodes with hidden storage performance.

[Technical hell of inventions and their problems]

Conventionally, gas diffusion electrodes have been used as air electrodes in various fuel cells, air-metal batteries including gust/zinc batteries, galvanic oxygen sensors, and the like. Initially, a floating porous 4L electrode with a uniform pore size distribution was used as this gas diffusion electrode, but recently it has been developed to have an electrochemical reduction ability for oxygen gas (ionizes oxygen).
has.

and a porous polarized body that also functions as a current collector.

Electrodes with a 2% structure consisting of a thin film-like water-repellent layer that is integrally formed on the gas-side surface of the electrode body are often used.

In this case, the electrode body is mainly made of nickel-tungstic acid, which has a low oxygen gas reduction overvoltage; tungsten carbide coated with palladium-9-cobalt; nickel; silver; platinum; palladium, etc., supported on a conductive powder such as activated carbon powder. After adding a binder such as polytetrafluoroethylene to the powder, it is made into a porous metal body or a porous carbon body.

Those integrated with carbon fiber non-woven fabric are used.

The water-repellent layer attached to the surface of the electrode body on the scrap side is mainly made of fluororesin such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, or A thin film made of resin such as polypropylene.
For example, a sintered body of these resin powders with a particle size of 0.2 to 40 μIn; a paper-like article made by heating the fibers of these resins and made into a non-woven fabric; a fiber cloth-like article; fluorinated graphite; a film-like product made by rolling these fine powders together with a pore-forming agent, lubricating oil, etc. and then heat-treated; or a film-like product that is not heat-treated after being rolled; It is a porous thin film with a distribution of microscopic pores.

However, in the air electrode of the conventional structure described above,
The water-repellent layer attached to the gas-side surface of the polarization body is impermeable to the electrolyte.

Not impermeable to air or harmful gases in the air.

Therefore, 1. For example, if carbon dioxide gas in the air passes through the water-repellent layer and enters the electrode body and is adsorbed to the active layer, the electrochemical reduction ability for oxygen gas at that part decreases, inhibiting the ability to handle heavy loads. be done. Also.

In the case of iK electrolyte alkaline electrolyte, deterioration of the electrolyte,
This causes phenomena such as a decrease in concentration or, when the cathode is zinc, passivation of the zinc cathode. Furthermore.

In the active layer (the porous part of the electrode body), heavy loading impairs vJA because carbonates are generated to close the pores and reduce the area in which one-gas chemical reduction can take place.

This may lead to a situation where the performance of the battery deteriorates from the design standard when the manufactured battery is left in storage for a long period of time or used for a long period of time.

For this reason, a battery has been proposed in which a layer of a carbon dioxide absorbent such as alkaline earth metal hydroxide is further provided on the waste side (air side) of the water-repellent layer of the air electrode. This can prevent the above-mentioned inconveniences to some extent, but if these absorbents reach a saturated state and lose their absorption capacity after a certain period of time, the effect disappears, so there is no essential effect. There is no solution.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks of the conventional structure, and prevents carbon dioxide gas from entering the electrode body.

Therefore, the object of the present invention is to provide a thin air electrode that is capable of long-term heavy load discharge and has excellent storage performance.

[Summary of the invention]

The air electrode of the present invention has a porous electrode body that has an electrochemical reducing ability for oxygen scum and also has an aggregate function; It is characterized by consisting of a poly(4-vinylpyridine) thin film coated with

The electrode body used in the air electrode of the present invention is a porous body that has an active ability to electrochemically reduce oxygen gas (ionize oxygen gas) and is electrically conductive. Specifically, in addition to the items mentioned above, silver filters, Raney nickel, sintered bodies of silver or nickel, various foam metals, compressed bodies of nickel-plated fine stainless steel wire, and gold.

Examples include porous metal bodies plated with palladium, silver, etc. Furthermore, at this time.

To quickly remove the reduction product ions of oxygen gas generated by the electrode reaction proceeding within the pores of the electrode body from the pores (reaction region) to smoothly continue heavy load discharge of, for example, 5O+nA/- or more. Furthermore, it is preferable that the pore diameters of the pores in the electrode body are divided into a range of about 0.1 to 10 μm.

The air electrode of the present invention has a thin film of poly(4-vinylpyridine) coated on the gas side surface of the electrode main body as described above via a porous film.

The material of the porous membrane in the air electrode of the present invention does not matter, but it is preferably highly flexible in view of attachment to the electrode body.

Note that the pore diameter is not particularly limited, but is preferably 1 μm.
m or less. Further, the porous membrane preferably has the above-mentioned fine pores distributed uniformly, and preferably has a pore volume of the fine pores in a range of 0.1 to 90% of the converted volume.

Examples of such porous membranes include porous fluororesin membranes (trade name, Fluorobor; manufactured by Sumitomo Electric (1)) and porous polycarbonate membranes (trade name, Nucribore; manufactured by Nucribore Goboration).

Examples include a porous cellulose ester membrane (part name, Millibore Membrane Filter, manufactured by Milliboa Corporation), and a porous polypropylene membrane (trade name, Celguard; manufactured by Celanese Plastics).

The air electrode of the present invention is made by press-bonding or adhering a composite membrane prepared by coating one or both sides of the porous membrane described above with poly(4-vinylpyridine) to an electrode body.

Although the degree of polymerization of poly(4-vinylpyridine) is not particularly limited, it is preferable that the viscosity is not too high in consideration of workability when coating a porous membrane. In addition, poly(4-
Vinylpyridine) is preferably used as a solution diluted to a concentration of 2% by weight or less, preferably 10% by weight or less.

The amount of coating liquid should also be adjusted depending on the concentration of the solution used; for example, in the case of a 5% solution, it is 0.1 μl.
It is desirable to fall within the range of about /cl to 50μ/=/, -J. If the amount of liquid is too large, the amount of oxygen gas permeated through the formed film will be reduced, thereby degrading the heavy load dissipation characteristics of the electrode produced. On the other hand, if the amount of liquid is too small, pinholes may occur frequently in the formed film.9. At the same time, the effect of preventing harmful gases such as carbon dioxide from entering is reduced.

The mechanical strength of the coating decreases and becomes easily damaged.

As a coating method, a coating method, a spray method, a dipping method, etc. can be applied. After drying the porous membrane coated with poly(4-vinylpyridine) at room temperature to about 100°C and under normal pressure or reduced pressure, a predetermined pressure is applied to the gas-side surface of the electrode body so that the coated surface faces outward. Crimp and integrate.

The air electrode of the present invention thus manufactured is incorporated into a battery according to a conventional method. in this case.

In order to enable an instantaneous large current supply by electrochemical reduction of the electrode component itself in addition to the a-vapor chemical reduction of oxygen gas when performing intermittent discharge.

A porous layer containing at least a metal, oxide, or hydroxide whose oxidation state changes with a less noble potential within 0.4 V of the redox equilibrium potential of oxygen.

It is preferable to attach it integrally to the electrolyte side of the electrode body. This porous layer is oxidized by oxygen gas by local cell action during discharge under a light load or when the circuit is opened, and returns to the original oxidized state.

The constituent material of such a porous layer is Ag2O+
Examples include fV1n02, Co2O3, PbO2, various perovskite type oxides, and spinel type oxides.

On the other hand, the air electrode is not only incorporated into a battery in the form of a plate, but may also be incorporated into a cylindrical battery.

In that case, a plate-shaped air electrode may be wound into a cylinder. In such cases, in order to provide mechanical stability without damaging the gas electrode during one winding operation, the gas side surface of the metal oxide thin film having oxygen adsorption ability is further coated with:
It is preferable to further integrally fluidize a porous thin film such as a porous fluororesin membrane, a porous polycarbonate membrane, a porous cellulose ester membrane, or a porous polypropylene membrane.

In addition, the poly(4-vinylpyridine) membrane itself does not have very high permeation prevention performance against water vapor.

When the air electrode of the present invention is used in a battery, etc., a membrane with high oxygen/water vapor selective permeation performance is made of poly(4-vinylpyridine) in order to prevent performance deterioration due to changes in electrolyte concentration.
It may also be used in a layered manner with a membrane.

[Embodiments of the invention]

An embodiment of the air electrode of the present invention will be shown below.

Examples 1 to 3 Porous polypropylene If with a thickness of 25 μl having a uniformly distributed low pore size of 0.2×O, 02 μm
! d (t! 46 product name: Duraguard 2400; manufactured by Polyplastics Takago) on one side of poly(4-vinylpyridino) methanol/tetrahydrofuran m1t-
fflii1ishi.

A composite film was obtained by evaporating a solvent at room temperature to form a film. Next, the outer peripheral portion of this composite membrane on the porous membrane side was compressed onto the electrode body to create an air electrode.

As the electrode body, a scum-permeable water-repellent membrane layer consisting of a polytetrafluoroethylene (PTFE) membrane with a thickness of 100 μm and having uniformly distributed micropores with an average pore diameter of 10 μm; 4% by weight of platinum and a viscosity of 100μIll with an average particle diameter of Charcoal powder 80
A porous catalyst layer with a thickness of 0.5+mm created by mixing 16% by weight of PTFE powder and rolling it by a conventional method; a current collector layer made of nickel-gold-copper with a diameter of 0.1m and 40 meshes. An electrode was used that had a structure in which three layers were integrated under a pressure of 1 ton%.

Examples 4 to 6 Air electrodes were created in the same manner as Examples 1 to 3, except that a composite film was created by forming a poly(4-vinylpyridine) film on both sides of the porous film.

Examples 7 to 9 An n-butanol solution of tin 2-ethylhexanoate was applied to a 1 m piece of the same porous membrane as that used in Examples 1 to 3, and this was partially hydrolyzed in steam. It is then dried to form an oxygen/water vapor selectively permeable film with a thickness of 2000A,
The composite membrane had an oxygen/water vapor permeation ratio of about 3.5. Then,
The outer periphery of this composite membrane on the porous membrane side was pressed onto the poly(4-vinylpyridine) composite membrane of the air electrodes of Examples 1 to 3.

It was used as an air electrode.

Comparative Example 1 Only the electrode body shown in Example was used as an air electrode.

Comparative Example 2 An air electrode was produced in the same manner as in Examples 1 to 3, except that instead of the composite membrane, only the porous membrane used in the practical row was crimped onto the electrode body.

Comparative Example 3 An air electrode was produced in the same manner as in Examples 1 to 3, except that the tin 2-ethylhexanoate composite membrane of Examples 7 to 9 was used instead of the poly(4-vinylpyridine) composite membrane.

Using the above 12 air electrodes, an air-zinc battery was assembled using gelled zinc amalgamated with 3% mercury as the counter electrode, potassium hydroxide as the electrolyte, and polyamide nonwoven fabric as the separator.

After leaving these 12 batteries in air at 25°C for 16 hours, they were discharged with various currents for 5 minutes, and the terminal voltage after 5 minutes was 1.
．． The current density was measured when the current density was 0 V or less.

Furthermore, the battery after storage was subjected to a discharge test similar to the above, and the ratio of the current value to the initial current of 1 cycle (X
) was calculated. This calculated value represents the degree of deterioration of the air electrode of each battery and can be called the discharge characteristic maintenance rate. An electrode with a large value indicates a small degree of deterioration.

In addition, regarding the film attached to each electrode, the oxygen gas permeation rate was measured by the isobaric method using a gas chromatograph as the gas detection means, and the carbon dioxide permeation rate was measured according to JIS Z0208.
(cup method), and the ratio between the two was calculated.

The above results are summarized in the table. J Me Senzumi Haku [Effects of the Invention] Comparing Examples 1 to 6 and Comparative Examples 1 and 2, it can be seen that the air electrode of the present invention is less susceptible to performance deterioration due to the influence of carbon dioxide in the air. Furthermore, as shown in Examples 7 to 9 and Comparative Example 3, by combining the air electrode of the present invention with a membrane that is difficult to permeate water vapor, it was possible to create a ventilated zinc upper pond with extremely little deterioration. .

As is clear from the above results, the air electrode of the present invention is thin as a whole, and carbon dioxide gas in the air does not penetrate into the electrode body. Therefore, it is possible to leave it under heavy load for a long period of time, and it is also easy to store. It has great industrial value because of its excellent performance.

Note that the performance evaluation of the air electrode in the above example was performed using potassium hydroxide as the electrolyte.

It goes without saying that similar effects can be obtained by using other electrolytic solutions 1, such as ammonium chloride, sodium hydroxide, rubidium hydroxide, lithium hydroxide, cesium hydroxide, etc., mixed with these solutions. Furthermore, the air electrode according to the present invention could also be used in an air-iron battery.

Claims (1)

[Claims] A porous electrode body that has an electrochemical reduction ability for oxygen gas and also has a current collector function; The gas side surface of the electrode body is coated with poly(4-vinyl) through a porous film. pyridine) thin film.