JPS5955315A - Manufacture of composite film having selective oxygen permeability - Google Patents

Abstract

PURPOSE:To obtain a favorable composite film having oxygen permselectivity for manufacturing an air electrode without intruding water vapor or carbon dioxide in the air into the electrode itself, by forming a thin film consisting a metallic oxide having a rutile-type crystal structure on a porous film surface. CONSTITUTION:As a porous film, a porous fluororesin film and a porous polycarbonate film are given as an example. Metallic oxide having a rutile-type crystal structure may be interpreted as a substance having a structure which consists of aggregates sharing the edges of oriented regular octahedrons and being arranged in one dimension. In case of a composite film having a two layered structure, the metallic oxide thin film having the rutile-type crystal structure is coated directly on one side of the porous film.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention provides an oxygen gas selectively permeable composite membrane that is effective for use in manufacturing air electrodes for hydrogen/oxygen fuel cells, metal/air batteries, and oxygen sensors. For more details on the manufacturing method,
Even if it is thin, it lasts for a long time! The present invention relates to a method for manufacturing an oxygen gas selectively permeable composite membrane for air electrodes that is capable of 7-load discharge and has excellent storage performance.

[Technical background of the invention and its problems] Gas diffusion electrodes have traditionally been used as air electrodes in various fuel cells, air metal batteries including air/zinc batteries, and galvanic oxygen sensors. ing. Initially, a prototypical porous electrode with a uniform pore size distribution was used as this gas diffusion electrode, but recently, electrochemical reduction ability for oxygen gas (ionizing oxygen) has been used.
Electrodes with a two-layer structure consisting of a porous electrode body that also has a current collector function and a thin film-like water-repellent layer that is integrally attached to the gas side surface of the electrode body are often used. ing.

In this case, the electrode body is mainly composed of nickel tungstic acid, which has a low oxygen gas reduction overpotential; tungsten carbide coated with radium and cobalt; nickel; silver; platinum;
) After adding a binder such as polytetrafluoroethylene to a powder made by supporting radium or the like in a conductive powder such as live carbon powder, this is mixed into a porous metal body or a porous carbon body. However, the water-repellent layer attached to the gas side surface of the electrode body is mainly made of polytetrafluoroethylene or polytetrafluoroethylene-hexane. A thin film composed of a fluororesin such as a fluoropropylene copolymer, a polyethylene-tetrafluoroethylene copolymer, or a resin such as polypropylene, for example, by sintering powder of these resins with a particle size of 0.2 to 10 μm. Materials; paper-like materials made by heating the fibers of these resins and making them into non-woven fabrics; similar fiber cloth-like materials; materials in which part of the powder of these resins is replaced with graphite fluoride; these fine powders are used as pore-forming agents. - A porous thin film with fine pores distributed, such as a film that is heat-treated after being rolled with lubricating oil or the like, or a film that is not heat-treated after being rolled.

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
It is impermeable to the alpha electrolyte, but not to air or water vapor in the air.

Therefore, for example, water vapor in the air may pass through the water-repellent layer and enter the electrode body, resulting in dilution of the electrolyte, or conversely, water in the electrolyte may evaporate from the water-repellent layer as water vapor. This may cause the electrolyte to become concentrated. As a result,
This causes a situation in which the concentration of the electrolyte fluctuates, making it impossible to maintain stable discharge 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. However, when the electrolyte is an alkaline electrolyte, phenomena such as deterioration of the electrolyte, reduction 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 causes a situation in which the performance of the battery deteriorates from the design standard when the manufactured battery is stored or used for a long period of time.

This battery has a structure in which a layer of a moisture absorbent such as calcium chloride or a carbon dioxide 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.

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. It can't be a solution.

Furthermore, attempts have been made to further integrally laminate a thin film selectively permeable to oxygen gas, such as a polysiloxane film, on the water-repellent layer described above. However, to date, no sufficiently effective oxygen gas selectively permeable membrane has been developed.

[Object of the invention] The present invention has excellent selective permeability for oxygen gas, and therefore,
When applied to air electrodes, water vapor or carbon dioxide in the air will not be allowed to enter the electrode body, making it possible to produce thin air electrodes that can perform heavy load discharge over long periods of time and have excellent storage performance. The object of the present invention is to provide a method for manufacturing a suitable oxygen gas permselective composite membrane.

[Summary of the Invention] The method for manufacturing a composite membrane of the present invention has a first aspect in which the pore size is 01 μm.
A thin layer of a metal oxide with a rutile type crystal structure is formed on the surface of a porous film having micropores of 1.0 m or less, and the metal oxide is used as a sputtering or vapor deposition source, and the reaction tank gas contains 10% or less of oxygen. A method for producing a two-layer composite film, characterized in that the film is formed using a sputtering or vapor deposition method using an inert gas that does not contain a porous film and a thin film of the metal oxide. This is a method for manufacturing a composite membrane having a three-layer structure in which a water-repellent layer is interposed between the layers and the entire membrane is integrated.

In the method for producing a composite membrane of the present invention, the material of the porous membrane does not matter as long as it has micropores with a pore diameter of 0.1 μm or less, but it is possible if it is attached to the electrode main body. It is preferable that the material is highly flexible. Also,
The porous membrane is preferably one in which the above-mentioned micropores are uniformly distributed, and the pore volume of the micropores is 0 relative to the total volume of the membrane.
．． A range of 1 to 90% is preferred.

Such porous membranes include, for example, porous fluororesin membranes (trade name, Fluoropore; manufactured by Sumitomo Electric Industries, Ltd.), porous polycarbonate membranes (trade name, Nuclepore; manufactured by Niclepore Corporation), and porous cellulose esters. Examples include a membrane (trade name, Millibore Membrane Filter; manufactured by Millibore Co., Ltd.) and a porous polypropylene membrane (trade name, Celguard; manufactured by Cerans Plastics Co., Ltd.). In these porous membranes, if the pore diameter exceeds 0.1 μm, pinholes may be formed in the thin metal oxide layer or water-repellent layer, which will be described later, when formed on the porous membrane. This occurs frequently, and the effect of preventing water vapor or carbon dioxide from entering is lost, and its mechanical strength decreases, making it more likely to break.

Next, the metal oxide with the rutile crystal structure according to the present invention is represented by the chemical formula AO2, and the coordination polyhedron is a regular octahedron, and it is composed of aggregates arranged one-dimensionally sharing the edges of this octahedron. It refers to something that has a combined structure, specifically,
Tin dioxide (SnO2), titanium dioxide (TiO2)
, vanadium dioxide (■02), molybdenum dioxide (M
OO2), tungsten dioxide (WO2).

Rubidium dioxide (RuO2), niobium dioxide (
NbO2).

Chromium dioxide (CrO2), rhenium dioxide (α-Be
o2).

Osmium dioxide (O502), rhodium dioxide (R
hO2).

Vanadium dioxide (1r02), platinum dioxide (P0□
) may be used alone or in combination of two or more of them.

The composite membrane of the present invention can be manufactured as follows. First, in the case of a two-layer composite membrane, a thin layer of a metal oxide having a rutile crystal structure is directly attached to one side of the porous membrane as described above.

As a method of impregnation, vapor deposition and sputtering methods, which are often used for forming thin films, are used, and the reaction tank gas is saturated with oxygen.
It is preferable to use an inert gas containing 0% or less or no inert gas. At this time, the thickness of the thin layer is 0.01 to 1.0
If the thickness is less than 0.01 μm, pinholes will occur frequently in the formed thin layer, and at the same time the effect of preventing water vapor or carbon dioxide from entering will be reduced. Mechanical strength decreases, making it more likely to break.

On the other hand, if it exceeds 11 Im, the amount of oxygen gas permeated decreases, which deteriorates the heavy load discharge characteristics of the prepared electrode.

Next, in the case of a three-layer composite membrane, a water-repellent layer is first formed on one side of the porous membrane, and then vapor deposition or sputtering is applied in the same way as in the case of a two-layer composite membrane. A thin layer of metal oxide of rutile type crystal structure is formed on the water-repellent layer.

Here, the material constituting the water repellent layer may be any material as long as it has water repellency and electrolyte resistance, and in practical use, for example, polytetrafluoroethylene (PTFIii), fluoroethylene propylene (FBP), etc. -' Riphenylene oxide (Pro), polyphenylene sulfide (
PPS), polyethylene (PE), polypropylene (P
P), copolymers thereof, or mixtures thereof.

At this time, polyfluoroethylene propylene (FEP) and HoIJ ethylene (PR) are used as the material for the water pumping layer.
If a heat-sealable material such as ethylene-tetrafluoroethylene copolymer is used, the water-lifting layer according to the present invention may further contain various organic compounds such as pencitrifluoride, m-chlorobencitrifluoride, Fluorinated organic compounds such as hexafluorobenzene, pentafluorobenzene, pentafluorostyrene, and mixtures thereof; for example, C1-012 saturated hydrocarbon compounds, 01-C12 unsaturated hydrocarbon compounds, Cr-C14 alkylbenzene compounds, Examples include a thin layer formed on a porous membrane by plasma polymerizing hydrocarbon compounds such as styrene, α-methylstyrene, and mixtures thereof. All of these thin layers are free of pinholes and have excellent permselectivity for oxygen gas. In particular, the above-mentioned fluorinated organic compounds are useful because the thin layer formed by plasma polymerizing their single molecules has an excellent effect of preventing water vapor or carbon dioxide from entering. The thickness of the thin film to be formed is practically 0.
The thickness is preferably in the range of 0.01 to 1.0 μm, and when the thickness is less than 0.01 μm, the formed thin layer becomes island-like and can uniformly cover the surface of the porous membrane. First, the effect of preventing the intrusion of carbon dioxide gas or water vapor is reduced. Moreover, the mechanical strength of the entire thin layer is also reduced. On the other hand, if the thickness exceeds 1.0 μm, the amount of oxygen gas supplied to the electrode body will be insufficient when the electrode is assembled, and the discharge characteristics of the electrode will deteriorate (heavy load discharge becomes difficult).

Further, the above-mentioned thin layer may be formed as a single layer, but it is also possible to further form a polymer thin film made of another type of organic compound on this layer.

A thin layer of a metal oxide having a rutile-type packed crystal structure is further laminated on the water-pumping layer thus formed. Its thickness is 90.01 for the same reason as for the pumping layer.
It is preferable that it is -1.0 micrometer.

[Examples of the invention] Examples 1 to 13 A porous polycarbonate membrane (trade name,
Nucleipore; Nucleipore Corporation, thickness 5
A sputtering process was performed on one side of the rutile-type crystal structure metal oxides using various rutile-type crystal structure metal oxides as a sputtering source in oxygen-free argon gas at a pressure of 2 x 10-3 TOrr and a high-frequency power of 100 W. A thin layer of metal oxide with a type crystal structure was formed. Thickness: 0.2 μm0 Examples 14 to 26 One side of a porous polycarbonate membrane having the same specifications as those used in Examples 1 to 13 was heated with argon gas (without oxygen) at a pressure of I
Fluoroethylene propylene (FFfP) was sputtered under the conditions of XIF2 Torr and high frequency output of 200 W to form a water pumping layer with a thickness of 0.2 μm. Then, on top of this,
A thin layer (thickness: 0.2 μm) of various metal oxides having a rutile crystal structure was formed in the same manner as in Examples 1 to 13.

Examples 27-39 A porous polycarbonate membrane having the same specifications as used in Examples 1-13 was loaded into a plasma reactor, and 13.
Applying high frequency power of 56 MHz, oxygen-free argon in the tank is 600 ml/in, pentafluorostyrene monomer gas is 600 m4/rr in 5
r: was introduced and a plasma polymerization reaction was carried out under the conditions of RF output of 0.4 W/cr/l to form a thin layer of pentafluorostyrene polymer having a thickness of 0.2 μm on one side of the polycarbonate film.

Then, as in Examples 1 to 13, a thin layer (0.2 μm) of various metal oxides having a rutile crystal structure was formed thereon.

Comparative Examples 1 to 4 Thin layers of metal oxides with various rutile crystal structures ( 0
, 2 μm) was formed.

Comparative Examples 5-8 Various thin layers of metal oxides with rutile crystal structure ( 0.2 μm) was formed.

Comparative Examples 9-12 Thin layers of metal oxides with various rutile crystal structures ( 0.2 μm) was formed.

Comparative Examples 13 to 18 Similarly, for comparison, a polysiloxane film (comparative example 13) with a thickness of μm and a medium-density polyethylene film with a thickness of μm (
Comparative Example 14), biaxially oriented polypropylene film with a thickness of (to) μm (Comparative Example 15), polytetrafluoroethylene film with a thickness of μm (Comparative Example 16), FEP film with a thickness of mμm (Comparative Example 17), implementation A 0.2 μm thick 0FFiP film (Comparative Example 18) formed by the sputtering method of Examples 14 to 26 was used, respectively.

For the above 57 types of composite membranes and comparative membranes, their oxygen permeation rates (J O2: c9/5ec-d -crrLHg
) to Gask 0? It is measured by a method such as using a spike rough as a detection means, and the water vapor permeation rate (JH2o: cc/5ec
-c, n ・cm) Ig) to J I 8 Z0208 (
cup method), and the ratio of the two (JO
2/JH20) as the gas permeation ratio and the results of 0 or more are collectively shown in the table.

Margins below [Effects of the Invention] As is clear from the above description, the composite membrane of the present invention does not allow the permeation of water vapor in the air and has a high oxygen gas selective permeability, despite its extremely thin thickness. Therefore, an air electrode made by combining this with the electrode body can be made thinner overall.
Moreover, it is possible to discharge heavy loads for a long time, and
Its storage performance is also improved. It also improves leakage resistance.

Therefore, the industrial value of the composite membrane of the present invention is extremely limited.

Claims (1)

Scope of Claims: (1) On the surface K of a porous film having micropores with a pore diameter of 0.1 μm or less, a thin layer of a metal oxide with a rutile type crystal structure is formed using the metal oxide as a sputtering or vapor deposition source. A method for producing an oxygen gas selectively permeable composite membrane, characterized in that the membrane is formed by sputtering or vapor deposition in a reactive gas containing 1% of oxygen. (2) The metal oxide is tin dioxide, titanium dioxide, vanadium dioxide, molybdenum dioxide, tungsten dioxide, rubidium dioxide, niobium decide, chromium dioxide, rhenium dioxide, osmium dioxide, rhodium dioxide, iridium dioxide, platinum dioxide. The method for producing an oxygen gas selectively permeable composite membrane according to claim 1, wherein at least one metal oxide having a rutile crystal structure is selected from the group consisting of: (3) The method for producing an oxygen gas selectively permeable composite membrane according to claim 1, wherein the thin layer has a thickness of o, o i to 1.0 μm. (A water repellent layer and a thin layer of a metal oxide with a rutile crystal structure are formed on the surface of a porous film having micropores with a pore diameter of 0.1 μm or less by sputtering in a reactive gas containing O to IQ vol% oxygen. A method for producing an oxygen gas permselective composite membrane, characterized in that the metal oxide is formed by vapor deposition and integrally laminated in this order. (5) The metal oxide is tin dioxide, titanium dioxide, or Vanadium, molybdenum dioxide, tungsten dioxide, rubidium dioxide, dioff dioxide, chromium dioxide,
rhenium dioxide, osmium dioxide, rhodium dioxide,
The method for producing an oxygen gas selectively permeable composite membrane according to claim 4, which is at least one metal oxide having a rutile crystal structure selected from the group of iridium dioxide and platinum dioxide. (6) The method for producing an oxygen gas selectively permeable composite membrane according to claim 4, wherein the water-repellent layer is a thin layer of a monomolecular plasma polymer of a fluorinated organic compound. (7) The method for producing an oxygen gas permselective composite membrane according to claim 4, wherein the water repellent layer and the metal oxide thin layer each have a thickness of 0.01 to 1.0 μm.