JPH0213426B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an air electrode for hydrogen/oxygen fuel cells, metal/air batteries, and oxygen sensors, and a method for manufacturing the same. , relates to an air electrode with excellent storage performance and a method for manufacturing the same. [Technical background of the invention and its problems] Gas diffusion electrodes have traditionally been used as air electrodes in various fuel cells, air metal oxidation batteries including air/zinc batteries, and galvanic oxygen sensors. It's coming. As this gas diffusion battery,
Initially, thick porous electrodes with a uniform pore size distribution were used, but recently, electrodes have been used that have electrochemical reduction ability for oxygen gas (ionizes oxygen) and also function as a current collector. Electrodes with a two-layer structure consisting of a porous electrode body and a thin film-like water-repellent layer integrally attached to 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 overpotential; tungsten carbide coated with palladium and cobalt; nickel; silver; platinum; palladium, etc., supported on a conductive powder such as activated carbon powder. A powder is used in which a binder such as polytetrafluoroethylene is added and then this is integrated with a porous metal body, a porous carbon body, a nonwoven fabric of carbon fiber, or the like. In addition, the water-repellent layer attached to the gas side surface of the electrode body is mainly polytetrafluoroethylene,
A thin film composed of a fluororesin such as a polytetrafluoroethylene-hexafluoropropylene copolymer, a polyethylene-tetrafluoroethylene copolymer, or a resin such as polypropylene, with a particle size of, for example, 0.2 to 40 μm. Powder sintered bodies; Paper-like products made by heating the fibers of these resins and making them into non-woven fabrics; Similarly, fiber cloth-like products; Parts of these resin powders replaced with graphite fluoride; It is a porous thin film in which fine pores are distributed, such as a film that is heat-treated after roll pressure with a pore-forming agent, lubricating oil, etc., or a film that is not heat-treated after roll pressure. However, in the air electrode of the conventional structure described above, the water-repellent layer attached to the gas side surface of the electrode body is impermeable to the electrolyte, but is impermeable to air or water vapor in the air. Not impermeable. Therefore, for example, water vapor in the air may pass through the water-repellent layer and enter the electrode body, diluting the electrolyte, or conversely, water in the electrolyte may evaporate from the water-repellent layer as water vapor, causing the electrolyte to dissolve. may be concentrated. As a result, the concentration of the electrolyte fluctuates, resulting in a situation where stable discharge cannot be maintained for a long period of time. When carbon dioxide gas in the air passes through the water-repellent layer, enters the electrode body, and is adsorbed on the active layer, the electrochemical reduction ability for oxygen gas at that location decreases, and heavy load discharge is inhibited. In addition, when the electrolyte is an alkaline electrolyte, phenomena such as deterioration of the electrolyte, decrease in concentration, or passivation of the zinc cathode when the cathode is zinc are caused. Furthermore, in the active layer (the porous part of the electrode body), carbonate is generated to block the pores and reduce the area where electrochemical reduction takes place, thereby inhibiting heavy load discharge. This may lead to a situation where the performance of the battery deteriorates from the design standard when the manufactured battery is stored or used for a long period of time. For this reason, a battery has a structure in which a layer of a moisture absorbent such as calcium chloride or a carbon dioxide gas absorbent such as alkaline earth metal hydroxide is further provided on the gas side (air side) of the water-repellent layer of the air electrode. is proposed. Although this can prevent the above-mentioned inconvenience to some extent, after a certain period of time,
If these absorbents reach a saturated state and lose their absorption capacity, their effectiveness will disappear, so this cannot be an essential solution. [Object of the Invention] The present invention eliminates the above-mentioned drawbacks of the conventional structure, prevents water vapor or carbon dioxide gas from entering the electrode body, and therefore enables long-term heavy load discharge and storage. The purpose is to provide a thin air electrode with excellent performance and a method for manufacturing the same. [Summary of the Invention] The air electrode of the present invention has a porous electrode body that has an electrochemical reduction ability for oxygen gas and also has a current collector function; The structure is characterized by consisting of a thin film of a water-containing or hydratable metal oxide that is integrally attached via a chemical film, and the method for producing it is characterized in that it has an electrochemical reduction ability for oxygen gas. A thin film of a hydrous or hydrated metal oxide is formed by depositing a hydrous or hydrated metal oxide on the gas side surface of the porous electrode body, which also functions as a current collector, by a vapor deposition method or a sputtering method. In another embodiment, on one side of a porous membrane having micropores with a pore diameter of 0.1 μm or less, by a vapor deposition method or a sputtering method,
A hydrous or hydratable metal oxide is deposited to form a thin layer of the metal oxide, and then the other side of the porous membrane is coated with a membrane having an electrochemical reduction capacity for oxygen gas and a thin layer of the metal oxide. , which is characterized by being press-bonded and integrated with the gas-side surface of a porous electrode body that also functions as a current collector. The electrode body used in the air electrode of the present invention is an electrically conductive porous body that has an active ability to electrochemically reduce oxygen gas (ionize oxygen gas). Specifically, in addition to the things mentioned above,
Examples include silver filters, Raney nickel, sintered bodies of silver or nickel, various foamed metals, compressed bodies of fine stainless steel wire plated with nickel, and porous metal bodies made by plating these with gold, palladium, silver, etc. can. At this time, the reduction product ions of oxygen gas generated by the electrode reaction proceeding within the pores of the electrode body are quickly removed from the pores (reaction region), for example.
In order to smoothly continue heavy load discharge of 50 mA/cm ² or more, the pore diameters of the electrode body are preferably distributed in a range of about 0.1 to 10 μm. The air electrode of the present invention has a structure in which a thin film of a hydrous or hydrated metal oxide is integrally attached to the gas side surface of the electrode body as described above, either directly or via a porous film. The hydrous or hydratable metal oxide used in the present invention has an excellent ability to adsorb water, and has the property that the adsorbed water can exist as surface hydroxyl groups, chemically adsorbed water, and physically adsorbed water. point to something,
Specifically, tin dioxide (SnO ₂ ), zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO) , titanium dioxide (TiO ₂ ), and silicon dioxide (SiO ₂ ), each singly or optionally a composite of two or more in combination. In order to integrally attach a thin film of these water-containing or hydrated metal oxides to the gas side surface of the electrode body, the following method is applied. The first method is to directly deposit a water-containing or hydrated metal oxide on the gas-side surface of the electrode body using a commonly used thin film forming method such as vapor deposition or sputtering to form a thin film of a predetermined thickness. This is a method of forming. The second method is to first deposit a hydrous or hydratable metal oxide on one side of a flexible porous membrane having micropores with a pore diameter of 0.1 μm or less by vapor deposition or sputtering. A thin layer of the metal oxide is formed to form a composite thin film with a two-layer structure, and then the other side of this composite thin film, that is, the other side of the porous membrane, is placed on the gas side surface of the electrode body in a predetermined position. This is a method of crimping and integrating with pressure. In both the first method and the second method, when forming a thin film of a hydrous or hydrated metal oxide,
These hydrous or hydrated metal oxides themselves can be used as the vapor deposition source or sputter source, but various metal elements that react with oxygen to produce these metal oxides can also be used as the vapor deposition source or sputter source. and when the atmosphere is oxygen atmosphere,
This is preferable because the rate of forming a thin film of the metal oxide is increased and the operation for forming the thin film is also facilitated. Furthermore, the thickness of the formed thin film of hydrous or hydrated metal oxide is preferably adjusted to a range of 0.01 to 1.0 μm, and if it is less than 0.01 μm, pinholes will increase in the thin film. As a result, the effect of preventing the intrusion of water vapor and carbon dioxide gas in the air is reduced, and the mechanical strength of the thin film is also reduced, making it more likely to be damaged. On the other hand, if it exceeds 1.0 μm, the amount of permeation of oxygen gas supplied to the electrode body decreases, making it difficult for the electrode to discharge under heavy load. Furthermore, the material of the porous membrane used in the second method does not matter as long as it has micropores with a pore diameter of 0.1 μm or less. For example, porous fluorocarbon membrane (trade name, Fluoropore; manufactured by Sumitomo Electric Industries, Ltd.), porous polycarbonate membrane (trade name, Nuclepore; manufactured by Nuclepore Corporation), porous cellulose ester membrane (trade name, Millipore) Examples include flexible porous membranes such as membrane filters (manufactured by Millipore Corporation) and porous polypropylene membranes (trade name: Celguard; manufactured by Celanese Plastics). When the pore diameter of a porous membrane exceeds 0.1 μm, pinholes are likely to occur in the thin film when a hydrous or hydrated metal oxide thin film is formed on the porous membrane, and the function of the thin film is impaired. Along with this loss, its mechanical strength also decreases, making it more susceptible to breakage. The air electrode of the present invention thus manufactured is incorporated into a battery according to a conventional method. In this case, when performing intermittent discharge, in addition to the electrochemical reduction of oxygen gas, it is possible to instantaneously supply a large current by electrochemical reduction of the electrode components themselves, so that the redox equilibrium potential of oxygen It is also possible to integrally attach a porous layer containing at least a metal, oxide or hydroxide whose oxidation state changes with a base potential within a range of 0.4V on the electrolyte side of the electrode body. preferable. This porous layer is oxidized by oxygen gas in the local cell action during discharge under a light load or when the circuit is opened, and returns to the original oxidized state.
Constituent materials for such a porous layer include:
Examples include Ag ₂ O, MnO ₂ , Co ₂ O ₃ , PbO ₂ , 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 which case the air electrode in the form of a plate may be wound to form a cylinder. In such cases, in order to provide mechanical stability without damaging the air electrode during the winding process, a porous fluororesin is further added to the gas side surface of the water-containing or hydratable metal oxide thin film. It is preferable to integrally attach a porous thin film such as a membrane, a porous polycarbonate membrane, a porous cellulose ester membrane, or a porous polypropylene membrane. [Embodiments of the Invention] Examples 1 to 9 A Raney-nickel plate (thickness: 200 μm) with an average pore diameter of 5 μm and a porosity of 80% was used as the electrode body. This was set in a vapor deposition apparatus, the temperature was maintained at 150°C, and the oxygen partial pressure inside the equipment was set at 5×10 ^-3 Torr. The vapor deposition source is
Nine types of metals were used: Sn, Zn, Al, Mg, Ca, Sr, Ba, Ti, and Si. Each of the above metals was deposited directly onto one side of the Raney nickel plate by a conventional vapor deposition method.
In both cases, metal oxide with a thickness of 0.2 μm was formed on the surface of the Raney nickel plate. Then, these were immersed in a 2% palladium chloride solution and cathodically polarized to precipitate palladium to a thickness of about 0.5 μm, including inside the Raney nickel pores, thereby forming the air electrode of the present invention. Examples 10 to 18 Air electrodes of the present invention were manufactured in the same manner as in Examples 1 to 9, except that the sputtering method was applied instead of the vapor deposition method. The spatuta conditions are
Mixed gas of argon and oxygen (Ar90vol%,
O ₂ 10vol%), pressure 2×10 ^-3 Torr, high frequency power
It was hot at 100W. The thickness of each metal oxide thin film was 0.2 μm. Examples 19-27 Porous polycarbonate membrane with a thickness of 5 μm (trade name;
Nucleipore (manufactured by Nucleipore Corporation) was set in a vapor deposition apparatus and maintained at 100°C.
A thin film of metal oxide was formed on one side of the film by setting the oxygen partial pressure in the apparatus to 5 x 10 ^-3 Torr and using the vapor deposition source used in Examples 1 to 9. A thin film of 0.2 μm was formed. Then, the other side of this porous membrane was pressed onto one side of a Raney nickel plate (thickness: 200 μm) with an average pore diameter of 5 μm and a porosity of 80%. This was immersed in a 2% palladium chloride solution and cathodically polarized to approximately 0.5μ, including the inside of the pores of the Raney nickel plate.
m of palladium was deposited to form an air electrode of the present invention. Examples 28-36 Air electrodes were manufactured in the same manner as Examples 19-27, except that the sputtering method under the sputtering conditions applied in Examples 10-18 was used instead of the vapor deposition method. Comparative Example 1 Activated carbon powder was suspended in an aqueous solution of palladium chloride, and then reduced with formalin to obtain palladium-attached activated carbon powder. Next, this powder was waterproofed with 10 to 15% polytetrafluoroethylene dispersion, mixed with PTFE powder as a binder, and rolled into a sheet. This sheet was crimped onto a nickel net to form an electrode body with a thickness of 0.6 mm. Next, PTFE dispersion is mixed with artificial graphite powder and then heat treated to make waterproof graphite powder.
This was mixed with PTFE powder as a binder and rolled. The obtained sheet was crimped to the above-mentioned electrode body to form an air electrode with a thickness of 1.6 mm. Comparative Example 2 A polysiloxane membrane (thickness: 50 μm), which is an oxygen gas selective permeation membrane, was pressure-bonded to one side of a Raney nickel plate (thickness: 200 μm) with an average pore diameter of 5 μm and a porosity of 80%, and then the whole was immersed in a 2% palladium chloride solution. Polarization was performed to deposit 0.5 μm of palladium, including inside the pores of the Raney nickel plate, to form an air electrode. Comparative Example 3 A water vapor absorbing layer of calcium chloride was attached to the air side of the air electrode manufactured in Comparative Example 1. Comparative Example 4 One side of a 5 μm thick porous polycarbonate membrane (trade name: Nuclepore, manufactured by Nuclepore Corporation) in which pores with an average pore diameter of 0.15 μm are distributed was coated with a film having a thickness of 0.2 μm in the same manner as in Examples 1 to 9. μm
Form a thin film of SnO ₂ , and cover the other side with an average pore size of 5 μm.
It was crimped onto one side of a Raney nickel plate with a porosity of 80%. The entire body was immersed in a 2% palladium chloride solution and cathodically polarized, and approximately
Palladium of 0.5 μm was deposited to form an air electrode. Comparative Example 5 An air electrode was manufactured in the same manner as in Comparative Example 4, except that a porous polycarbonate membrane with an average pore diameter of 0.03 μm was used and the thickness of the SnO ₂ thin film was 0.005 μm. Comparative Example 6 An air electrode was manufactured in the same manner as Comparative Example 5, except that the thickness of the SnO ₂ thin film was 2.0 μm. Using the above 42 air electrodes, the counter electrode is 3 by weight.
% mercury amalgamated gelled zinc, potassium hydroxide as the electrolyte, and a polyamide nonwoven fabric as the separator, an air-zinc battery was assembled. These 42 batteries were left in air at 25° C. for 16 hours, then discharged for 5 minutes with various currents, and the current density was measured when the terminal voltage after 5 minutes was 1.0 V or less. In addition, these batteries were kept in an atmosphere of 45° C. and 90% relative humidity, and leakage of the electrolyte was observed. Furthermore, the same discharge test as above was performed on the battery after storage, and the ratio (%) of the current value at that time to the initial current value 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. The larger the value of the electrode, the smaller the deterioration. In addition, regarding the thin film attached to each electrode, the oxygen gas permeation rate was measured using an isobaric method using a gas chromatograph as a gas detection means, and the water vapor permeation rate was measured.
It was measured by a method according to JISZ0208 (Kuppu method), and the ratio between the two was calculated. The following results are collectively shown in the table.

【table】

【table】

〔Effect of the invention〕

As is clear from the above results, the air electrode of the present invention is thin as a whole and does not allow water vapor or carbon dioxide gas in the air to enter the electrode body.
It has great industrial value because it enables long-term heavy load discharge and has excellent storage 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 such as ammonium chloride, sodium hydroxide, rubidium hydroxide, lithium hydroxide, cesium hydroxide, etc., mixed therein. Furthermore, the air electrode according to the method of the present invention could also be used in air-iron batteries.

Claims (1)

[Claims] 1. Having electrochemical reducing ability for oxygen gas,
and a porous electrode body that also has a current collector function; a thin film of a hydrous or hydratable metal oxide that is integrally attached to the gas side surface of the electrode body, either directly or via a porous film. An air electrode characterized by comprising: 2. The hydrous or hydratable metal oxide is at least one metal oxide selected from the group of tin dioxide, zinc oxide, aluminum oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, titanium dioxide, and silicon dioxide. The air electrode according to claim 1, which is a product. 3. The air electrode according to claim 1, wherein the electrode body has pores having a pore diameter of 0.1 to 10 μm. 4. The air electrode according to claim 1 or 2, wherein the thin film of the hydrous or hydratable metal oxide has a thickness of 0.01 to 1.0 μm. 5 Has electrochemical reduction ability for oxygen gas,
In addition, a hydrous or hydrated metal oxide is deposited on the gas side surface of the porous electrode body, which also functions as a current collector, by a vapor deposition method or a sputtering method to form a thin film of the metal oxide. A method for manufacturing an air electrode, characterized by: 6 The hydrous or hydrated metal oxide is at least one metal oxide selected from the group of tin dioxide, zinc oxide, aluminum oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, titanium dioxide, and silicon dioxide. A method for manufacturing an air electrode according to claim 5, which is a product. 7. The method for manufacturing an air electrode according to claim 5, wherein the electrode body has pores having a pore diameter of 0.1 to 10 μm. 8. The method for producing an air electrode according to claim 5 or 6, wherein the thin film of the hydrous or hydratable metal oxide has a thickness of 0.01 to 1.0 μm. 9 A thin layer of a hydrous or hydrated metal oxide is formed by depositing a hydrous or hydrated metal oxide on one side of a porous membrane having micropores with a pore diameter of 0.1 μm or less by a vapor deposition method or a sputtering method. Then, the other surface of the porous membrane is pressed and integrated with the gas-side surface of a porous electrode body that has an electrochemical reducing ability for oxygen gas and also has a current collector function. A method for manufacturing an air electrode, characterized by: 10 The hydrous or hydrated metal oxide is tin dioxide, zinc oxide, aluminum oxide, magnesium oxide, calcium oxide, strontium oxide,
10. The method for producing an air electrode according to claim 9, wherein the metal oxide is at least one metal oxide selected from the group of barium oxide, titanium dioxide, and silicon dioxide. 11. The method for manufacturing an air electrode according to claim 9, wherein the electrode body has pores having a pore diameter of 0.1 to 10 μm. 12. The method for manufacturing an air electrode according to claim 9, wherein the thin layer has a thickness of 0.01 to 1.0 μm.