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Europaisches Patentamt 0154 468 J European Patent Office Publication number: B1 Office europeen des brevets

EUROPEAN PATENT SPECIFICATION

M 12/06 Date of publication of patent specification: 04.10.89 intci.4: H 01 M 4/86, H 01

Application number: 85301213.6 Date of filing: 22.02.85

Oxygen permeable membrane.

Priority: 24.02.84 JP 33589/84 Proprietor: KABUSHIKI KAISHA TOSHIBA 24.02.84 JP 33593/84 72, Horikawa-cho Saiwai-ku Kawasaki-shi Kanagawa-ken 210 (JP)

Date of publication of application: 11.09.85 Bulletin 85/37 Inventor: Susuki, Nobukazu c/o Patent Division Kabushiki Kaisha Toshiba 1-1 Shibaura 1-chome Minato-ku Tokyo (JP) Publication of the grant of the patent: Inventor: Tsuruta, Shinji c/o Patent Division 04.10.89 Bulletin 89/40 Kabushiki Kaisha Toshiba 1-1 Shibaura 1-chome Minato-ku Tokyo (JP)

Designated Contracting States: DEFRGB Representative: Eyles, Christopher Thomas et al BATCHELLOR, KIRK & EYLES 2 Pear Tree Court Farringdon Road References cited: London, EC1R0DS(GB) EP-A-0097 770 US-A-3972 732 US-A-4018943 CD

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Note: Within nine months from the publication of the mention of the grant of the European patent, any person may shall give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition been filed until the opposition fee has been 0. be filed in a written reasoned statement. It shall not be deemed to have ) convention). UJ paid. (Art. 99(1 European patent Courier Press, Leamington Spa, England. EP 0 154 468 B1

Description

This invention relates to an permeable membrane which permits oxygen gas to pass through while substantially blocking other gases. The present invention has application in -oxygen 5 electric fuel cells, metal-air battery cells and oxygen sensing devices. In the prior art, gas diffusion electrodes have been used for air electrodes in various fuel cells, air-metal cells, such as air- cells, and Galvanic oxygen sensors. Thick porous electrodes having distributed pores with a uniform diameter were used as the gas diffusion electrode. In recent years, however, electrodes having a two-layer structure have been used. The electrode comprised a porous electrode body with an 10 electrochemical reduction function for oxygen gas (a function for ionising oxygen) and a current collector function. The electrode also had a thin water repellent layer deposited integrally on the gas-side surface of the electrode body. In such electrodes, the electrode body may be formed by a conductive powder, a porous metallic body, a porous body or a non-woven carbon fabric material. This may be accomplished by the use of a 15 binder such as polytetrafluoroethylene. Such conductive powders may be selected from among active carbon powders carrying a tungstate with a low reduction overvoltage to oxygen gas, a carbide coated with , , nickel, , platinum or palladium. US — A — 3972732 describes a catalytic electrode which comprises a metallic and a carbonaceous material. 20 The aforementioned water repellent layer, which is deposited integrally on the gas-side surface of the electrode body, is a porous thin membrane which comprises a fluorine-containing resin such as polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer or ethylene-tetrafluoro- ethylene copolymer. The membrane may also be comprised of a resin, such as polypropylene, in the form of a porous material including, for example, a sintered powder material having a particle size of from 0.2 to 25 40 urn; a paper-like non-woven fabric material prepared by heat treatment of fibres comprising polypropylene resin or a similar woven fabric material; a powder material wherein the polypropylene resin is partially replaced by a fluorinated graphite; a film material prepared by rolling fine powder together with a pore-increasing agent or a lubricant oil followed by heat treatment or a film material prepared by rolling without being followed by heat treatment. Such materials are disclosed in Japanese Patent Publication No. 30 44978/1973. In an air electrode having the structure as described above, however, the water repellent layer deposited on the gas-side surface of the electrode body is impervious to electrolyte but is not impervious to air and water vapour in the air. For this reaosn, water vapour in the air may penetrate the electrode body through the water repellent layer and dilute the electrolyte or the water in the electrode may otherwise 35 dissipate through the water repellent layer, therby increasing electrolyte concentration. As a result, the concentration of the electrolyte will fluctuate and it will thus be impossible to maintain stable discharge characteristics over a long period of time. When gas in the air penetrates the electrode body through the water repellent layer and is absorbed by an active site (a porous portion of the electrode body), the electrochemical reducing 40 function of the active site to oxygen gas is reduced at the point of absorption. Thus, the heavy-load discharge capability of the cell is adversely affected. Moreover, when an alkaline electrolyte is used, there will be a change in the properties of the electrolyte, a reduction in the concentration of the electrolyte and, if the cathode is zinc, passivation of the zinc cathode. Furthermore, heavy-load discharge may be hindered because the area of electrochemical reduction is reduced by the production of carbonate in the active site 45 which blocks the pores. These factors to a decline in the performance of the cell from its design rating after the cell is stored or used for a long period of time. In order to overcome the aforementioned disadvantages, there has been proposed a cell in which a water repellent layer for the air electrode is provided on the gas side (air side) thereof with a layer comprising a water-absorbing agent, such as chloride, or a carbon dioxide gas-absorbing gent, so such as a hydroxide of an alkaline earth metal. Such a cell is disclosed in Japanese Patent Publication No. 841 1/1 973. This type of cell can prevent the above-mentioned problems to some extent. However, when the absorbing agent has been saturated with water or carbon dioxide gas, it becomes wholly ineffective. There have also been attempts to laminate an oxygen permeable membrane on the above-mentioned water repellent layer. Such a membrane is disclosed in Japanese Patent Publication No. 26896/1973. 55 However, a sufficiently effective oxygen gas permeable membrane has not been developed thus far. The present invention accordingly seeks to provide a selectively permeable composite membrane, and an air electrode being made therefrom, which is permeable to oxygen gas while at the same time being impervious to water vapour in air. It also seeks to provide an air electrode comprising an oxygen gas permeable membrane which eo enables a heavy-load discharge to be maintained over a long period of time. According to a first aspect of this invention, there is provided a composite membrane for passing oxygen gas, said membrane comprising a metallic oxide and and a carbonaceous material characterised in that the membrane comprises: a porous membrane having micropores the diameter of which is equal to or less than 1 um; and 65 a thin layer affixed to at least one surface of said porous membrane and having a thickness in the range EP 0154 468 B1 said metallic oxide being of 0.01 to 1 |im, said thin layer containing a metallic oxide in a carbon matrix, oxide, selected from among the group consisting of dioxide, , oxide, dioxide, dioxide, cuprous oxide, monoxide, nickel oxide, tricobalt tetroxide, dioxide, dioxide, tungsten dioxide, dioxide, dioxide, dioxide and platinum 5 dioxide, dioxide, dioxide, dioxide, dioxide.. The invention thus provides a selectively permeable composite membrane having a two-layer construction. The membrane comprises a porous membrane layer having micropores and a thin layer the containing, in a carbon matrix, a water-containable or wettable metallic oxide, a metal oxide having The thin is 10 capability of absorbing oxygen or a metal oxide having a -type crystal structure. layer laminated integrally on to one or both surfaces of the porous membrane layer. According to the second aspect of this invention, there is provided an air electrode for a cell comprising a metallic oxide and a carbonaceous material characterised in that it comprises: with a main electrode body having the capability of electro-chemical reduction of oxygen gas a is laminated 15 collector function; and the composite membrane according to the invention. The thin layer membrane integrally on the gas side surface of the main body of the electrode with a porous layer between. The metallic oxide which is contained in the carbon matrix is a water-containable or wettable metallic oxide or has the ability of absorbing oxygen or has a rutile-type crystal structure. The water- containable or wettable metallic oxide used in this invention is a material having the ability to absorb water absorbed 20 and having properties for permitting water absorbed to exist as chemically and physically water. The water-containable (wettable) properties means that a metallic oxide exists in combination with water molecules or in a state having an interaction with water molecules. Examples of the above mentioned metallic include tin dioxide (SnO2), zinc oxide (ZnO), oxide (AI2O3), oxide silicon (MgO), (CaO), (SrO), (BaO), (TiO2) and of 25 dioxide (SiO2). These oxides may be used alone or in the form of a composite comprising a combination two or more types thereof. The above described metal oxides having the capability of absorbing oxygen refers to those oxides which have the property of absorbing oxygen in the form of molecules (O2) or ions (O2 , 0 , 0 ). Such metal oxides include tin dioxide (SnO2), zinc oxide (ZnO), cuprous oxide (Cu20), manganese monoxide 30 (MnO), nickel oxide (NiO), and tricobalt tetroxide (Co3O4). These oxides may be used alone or in the form of ZnO a composite comprising a combination of two or more types thereof. Among these oxides, SnO2, are particularly useful. Figure 1 of the drawing is a graph showing the gas permeation ratio versus time of a composite membrane according to the present invention where the test sample is maintained at 45°C and 90% relative 35 humidity. The composite membrane of the present invention is manufactured as follows. A thin layer contained of in a carbon matrix, a water-containable or wettable metal oxide, or a metal oxide having the capability to or absorbing oxygen, or metal oxide of a rutile-type crystal structure is affixed or deposited directly one the both surfaces of a porous membrane. An appropriate method of affixing the thin layer to porous thin 40 membrane is by reactive sputtering. Reactive sputtering is a well known method of forming membranes. In the reactive sputtering method, the above mentioned metallic oxides are used as sputter of the formula sources. The gas used in the sputtering process is argon gas containing alkanes general CnH2n+2, such as CH4, C2H6 or C3Ha, alkenes of the general formula CnH2n, such as C2H4, C3H6 or C4H8, or alkynes of the general formula CnH2n_2, such as C2H2. Argon gas containing various fluonnated 45 hydrocarbons in which a part or all of the hydrogen of the hydrocarbon compound has been substituted by substances also fluorine may also be used. Argon gas containing two or more of the above-mentioned can be used. It is preferred that the proportion of such hydrocarbon compound is less than 20 vol % so as not to make a thin layer consisting of only hydrocarbon. Provided the porous membrane mentioned above has micropores of a diameter of 1.0 urn or less, any so material would serve the purpose. However, from the viewpoint of affixing the membrane to the main body of the electrode, a material that is highly flexible is preferred. If the diameter of the pores is in excess of 1 .0 oxide in carbon matrix urn, pinholes will appear in large numbers in the thin layer containing the metal a when the layer is formed on the porous membrane. This results not only in the penetration of water vapour and carbonic acid, but also a reduction in mechanical strength, with the consequent risk of breakage. it 55 Further, the porous membrane should have the micropores described above distributed over uniformly. It is appropriate for the volume of the cavities of the micropores to be from 0.1 to 90% of the total volume of the film. Examples of this type of porous membrane include porous fluoro-resin membrane (trade name, Fluoropore; manufactured by Sumitomo Electric Industries, Ltd.); porous polycarbonate membrane (trade membrane 60 name, Nuclepore; manufactured by the Nuclepore Corporation); porous cellulose ester (trade name, Millipore Membrane Filter; manufactured by the Millipore Corporation); and porous polypropylene membrane (trade name, Celguard; manufactured by Celanese Plastics Co. Ltd.). The thickness of the thin layer mentioned above is 0.01—1 .0 urn. The reason for this is that if it is less reduces its than 0.01 urn, numerous pinholes appear in the thin layer when it has been formed which the 65 effectiveness in preventing the penetration of water vapour or carbon dioxide. At the same time, EP 0 154 468 B1 mechanical strength of the thin layer is reduced so that it becomes susceptible to breakage. If on the other hand, the thickness of the thin layer exceeds 1.0 urn, the heavy-load discharge properties of the electrode are impaired because the amount of oxygen gas which penetrates the membrane is reduced. The present invention will be described in detail in accordance with the following Examples. 5 Examples 1 to 9 Each composite membrane was made by forming a thin layer of 0.4 urn in thickness containing various water-containing or wettable metal oxides in a carbon matrix on one surface of a porous polycarbonate membrane with micropores of a mean pore diameter of 0.08 |im distributed uniformly over its surfaces and w with a pore volume of 3% (trade name, Nuclepore; Nuclepore Corporation, thickness 5 urn). The thin layer was formed by a reactive sputtering treatment with SnO3, ZnO, AI2O3, MgO, CaO, SrO, BaO, TiO2 and SiO2 as the sputter sources and using a mixture of argon and methane gas (Ar; 90 vol% CH4; 10 vol%) at a pressure of 2.67 x 10~6 bar (2 x 10~3 Torr) with a high frequency (13.56 MHz) electric power source of 100W. 15 Examples 10 to 15 A composite membrane was made by forming a thin layer of 0.4 |im thickness containing, in a carbon matrix, various metal oxides having the capability of absorbing oxygen on one surface of a porous membrane of the same composition as that used in Examples 1 — 9 with SnO2, ZnO, Cu2O, MnO, NiO and 20 CO3O4 as the sputter sources and under the same conditions as set forth for Examples 1 — 9.

Examples 16—28 A composite membrane was made by forming a thin layer of 0.4 um thickness containing, in a carbon 25 matrix, various metal oxides having a rutile-type crystal structure on a porous membrane of the same composition as that used in Examples 1—9 with SnO2, TiO2, VO2, MoO2, WO2, RuO2, NbO2, CrO2, a-ReO2, OsO2, RhO2, lrO2and PtO2 as the sputter sources under the same conditions as set forth for Examples 1 — 9.

30 Comparative Examples 1 — 9 A composite membrane was made by forming a thin layer of 0.4 um thickness consisting of various water-containable or wettable metal oxides on one surface of a porous polycarbonate membrane with micropores of a mean pore diameter of 0.03 urn distributed uniformly over its surfaces and with a pore volume of 0.42% (trade name, Nuclepore; Nuclepore Corporation, thickness 5 |im) by a reactive sputtering 35 treatment with SnO2, ZnO, AI2O3, MgO, CaO, SrO, BaO, TiO2 and SiO2 as the sputter sources and using argon gas at a pressure of 2.67 x 10~6 (2 x 10~3 Torr) and with a high frequency electric power source of 100W.

Comparative Examples 10 — 15 40 A composite membrane was made by forming a thin layer of 0.4 um thickness consisting of various metal oxides having the capability of absorbing oxygen on one surface of a porous membrane of the same composition as that used in Comparative Examples 1 — 9 with SnO2, ZnO, Cu2O, MnO, NiO and Co3O4 as the sputter sources and under the same conditions as set forth for Comparative Examples 1 — 9.

45 Comparative Examples 16 — 34 A composite membrane was made by forming a thin layer of 0.4 um thickness consisting of various metal oxides having a rutile-type crystal structure on one surface of a porous membrane of the same composition as that used in Comparative Examples 1 — 9 with SnO2, TiO2, VO2, MoO2, WO2, RuO2, 50 NbO2,CrO2, a-ReO2, OsO2, RhO2, lrO2 and PtO2 as the sputter sources under the same conditions as set forth for Comparative Examples 1 — 9. The rate of permeation of oxygen gas(JO2: m3/s.m2-bar) was measured in each of the above Examples 1 — 28 and Comparative Examples 1 — 28 by the equilibrium pressure method in which a gas chromatograph is used for detection of the gas. The rate of permeation of water vapour (JH2O: m3/s.m2bar) 55 was measured in accordance with the JIS SZ0208 measuring standard (cup method), and the ratio of the two (J02/JH20) was calculated as the gas permeation ratio. The results are given in Tables 1 — 3. Table 3 lists the results of measurements of JO2 and JH2O, and of the subsequent calculation of the JO2/JH2O ratio with respect to a polysiloxane membrane of thickness 50 um (Comparative Example 29), a medium- polyethylene membrane of thickness 20 urn (Comparative Example 30), a biaxially-oriented polypropylene so membrane of thickness 20 um (Comparative Example 31), a polytetrafluoroethylene membrane of thickness 20 um (Comparative Example 32), a commercial FEP membrane of thickness 20 um (Comparative Example 33), and a FEP thin layer of 0.4 um thickness made by forming a membrane on a porous polycarbonate membrane of the same specifications as that used in the Comparative Examples by the sputtering method (Comparative Example 34). ("FEP" is an abbreviation for "Fluoro-Ethylene-Propylene" 65 and indicates a copolymer of fluoroethylene and fluoropropylene).

EP 0154 468 B1

For the composite membranes of the above Example 1 and Comparative Example 1, the variation with respect to time was determined for the gas permeation ratio JO2/JH2O at a temperature of 45°C at 90% relative humidity. Figure 1 shows this characteristic plotted as a graph. Relative values are shown, taking the initial value of the gas permeation ratio as 100%. In Figure 1, A is the characteristic curve of Example 1, 5 and B is the characteristic curve of Comparative Example 1. As explained above, even though the composite membrane of this invention is extremely thin, it does not allow permeation of water vapour in the air but has a high selective permeability for oxygen gas. It also has excellent durability so that when it is combined with the main electrode body, it enables the realisation of an air electrode that is capable of heavy-load discharge over a long period of time and shows a marked 10 improvement in retention of these properties and is resistant to leakage. The air electrode of this invention is made by affixing the thin layer containing the metal oxides described above in a carbon matrix to the surface on the gas side of the main body of the electrode with a porous membrane in between. The method applied is to make a composite membrane by forming the thin layer containing the metal oxides in a carbon matrix on one side of a flexible porous membrane having 15 micropores of a diameter of 1.0 urn or less by the reactive sputtering method and then to bond the other side of this composite membrane (i.e. the other side of the porous membrane) at a prescribed pressure on to the surface of the gas side of the main body of the electrode. The air electrode prepared as described above may be incorporated into a cell in a conventional manner. In this case, in order to permit the supply of a momentarily large current the electrochemical 20 reduction of an electrode-constituting element itself in addition to the electrochemical reduction of oxygen gas, it is preferable to deposit integrally, on the electrolyte side of the electrode body, a porous layer containing at least one material selected from metal, an oxide or a hydroxide, in which the can vary by a more ignoble potential in the range of 0.4V than the oxidation-reduction balanced potential of oxygen. This porous layer can be oxidized with oxygen gas by a local cell action during discharge under a 25 light load, or at a time of open circuit, to return to the original oxidation state. Examples of materials that can be used for this porous layer include Ag2O, MnO2, Co2O3, PbO2, a variety of perovskite type oxides and spinel type oxides. Comparative Examples 40 — 48 Raney nickel plate (thickness 200 urn) of 80% porosity and with a mean pore diameter of 5 um was 30 used for the main body of the electrode. On one surface of the plate, a thin layer (thickness 0.4 um) containing water-containable or wettable metal oxide in a carbon matrix was formed by reactive sputtering with SnO2, ZnO, AI2O3/ MgO, CaO, SrO, BaO, TiO2 and SiO2 as the sputter sources. and with a gas mixture of argon and methane (Ar, 90 vol%, CH4, 10 vol%) at a pressure of 2.67 x 10~6 bar (2 x 10"3 Torr) and with a high frequency electric power source. 35 The Raney nickel plate with the above thin layer was then dipped in a 0.2% solution of palladium chloride and palladium was deposited to a thickness of 0.5 um over the entire surface of the air electrode by cathode polarization, including those parts of the surface containing the pores in the Raney nickel plate. Examples 29 — 37 40 A composite membrane was prepared by forming, on one surface of a porous polycarbonate membrane with uniformly distributed micropores of mean diameter of 0.08 um and a pore volume of 3.0% (manufactured by the Nuclepore Corporation; trade name, Nuclepore; thickness 5 urn), a thin layer of 0.4 um thickness containing water-containable or wettable metal oxides in a carbon matrix by reactive sputtering with SnO2, ZnO, AI203, MgO, CaO, SrO, BaO, TiO2 and SiO2 as the sputter sources and with a gas 45 mixture of argon and methane (Ar, 90 vol%; CH4, 10 vol%) at a pressure of 2.67 x 10~6 bar (2 x 10~3 Torr) with a high frequency electric power source of 100W. After bonding the composite membrane to one surface of a Raney nickel plate (thickness 200 um) of 80% porosity and with a mean pore diameter of 5 um, the device was dipped in a 0.2% solution of palladium chloride and palladium was deposited to a thickness of 0.5 um, the device was dipped in a 0.2% solution of palladium chloride and palladium was deposited to a so thickness of 0.5 um over the entire surface of the air electrode by cathode polarization, including those parts of the surface containing the pores in the Raney nickel plate. Comparative Examples 49 — 54 A thin layer of 0.4 um thickness containing, in a carbon matrix, metal oxides capable of absorbing 55 oxygen was formed on one surface of the main body of an electrode similar to that employed in Comparative Examples 40 — 48 with SnO2, ZnO, Cu2O, MnO, NiO and Co3O4 as the sputter sources and under the same conditions as set forth above in Examples 1 — 9. The air electrodes were then manufactured by the same method as used for Comparative Examples 40 — 48.

60 Examples 38 — 43 A thin layer of 0.4 um thickness containing, in a carbon matrix metal oxides capable of absorbing oxygen was formed on one surface of a porous membrane of the same composition as that employed in Examples 29 — 37 with SnO2, ZnO, Cu2O, MnO, NiO and Co304 as the sputter sources, and under the same conditions as set forth above in Examples 29 — 37. The air electrodes were then manufactured by the same 65 method as used for Examples 29 — 37.

10 EP 0 154 468 B1

Comparative Examples 55—67 A thin layer of 0.4 |im thickness containing, in a carbon matrix, metal oxides of a rutile-tye crystal that structure was formed on one surface of the main body of an electrode of the same composition as a-ReO2, employed in Comparative Examples 40—48 with SnO2, TiO2, VO2, MoO2, WO2, RuO2, NbO2, CrO2, forth above 5 OsO2, RhO2, lrO2 and PtO2 as the sputter sources under the same conditions as set in Comparative Examples 40—48. The air electrodes were manufactured by the method used for Comparative Examples 40 — 48. Examples 44—56 io A thin layer of 0.4 urn thickness containing, in a carbon matrix, metal oxides of rutile-type crystal in structure was formed on one surface of a porous membrane of the same composition as that employed and Examples 29-37 with SnO2, TiO2, VO2, Mo02, W02, RuO2, NbO2, CrO2, a-ReO2, OsO2, RhO2, lrO2 PtO2 The electrodes as the sputter sources under the same conditions as set forth above in Examples 29—37. air were manufactured by the same method as used for Examples 29 — 37. 15 Comparative Example 35 After suspending activated carbon powder in an aqueous solution of palladium chloride and reducing This it with formalin, what is known as "palladium-coated activated carbon powder" was produced. after powder was then waterproofed with a 10—15% polytetrafluoroethylene dispersion; subsequently, 2Q pjpe powder was mixed with it as a binding agent, it was rolled into a sheet. This sheet was pressed on to a nickel net to make the main body of an electrode having a thickness of 0.6 mm. Next, a PTFE dispersion was rolled. mixed with synthetic graphite powder and then mixed with a PTFE powder as a binding agent and An air electrode having a thickness 1.6 mm was manufactured by pressure-bonding the sheet thus obtained on to the above-mentioned main body. 25 Comparative Example 36 After pressure-bonding a membrane of polysiloxane (which is selectively permeable to oxygen gas) of and 50 thickness to a Raney nickel plate of 80% porosity and with a mean pore diameter of 5 urn, urn and thickness of 200 urn, the entire device was dipped in a 0.2% solution of palladium chloride palladium 30 was deposited to a thickness of 0.5 urn, over the entire surface of the air electrode by cathode polarization, including those parts of the surface having pores in the Raney nickel plate. .Comparative Example 37 An air electrode was manufactured similar to that of Comparative Example 35 except that a water of the electrode. 35 vapour absorbent layer of calcium chloride was affixed to the air side Comparative Example 38 A composite membrane was prepared by forming, on one surface of a porous polycarbonate membrane with uniformly distributed micropores of a mean diameter of 0.08 urn and a pore volume of 40 3.0% (manufactured by the Nuclepore Corporation; trade name, Nuclepore; thickness 5 urn), a thin layer of 0.005 urn thickness containing SiO2 in a carbon matrix as in Examples 29 — 37. After pressure bonding the porous polycarbonate side of the composite membrane to one surface of a Raney nickel plate (thickness 200 urn) of 80% porosity and with a mean pore diameter of 5 urn, the device was dipped in a 0.2% solution of palladium chloride and palladium was deposited to a thickness of 0.5 urn over the entire surface of the air 45 electrode by cathode polarization, including those parts of the surface having pores in the Raney nickel plate. Comparative Example 39 An air electrode similar to that of Comparative Example 38 was manufactured except that the thickness of the thin layer containing SiO2 in a carbon matrix was 2.0 urn. so Using the above-mentioned 61 air electrodes, air-zinc cells were assembled with the anode made of amalgamated zinc gel (3% by weight of in the amalgam), electrolyte of hydroxide and a separator of non-woven fabric of polyamide. After the 61 cells were left for 16 hours in air at a temperature of 25CC, they were discharged at various values of current for 5 minutes. The current density, at a terminal voltage of 1.0V or less, was measured after the 5 minutes. The cells were also stored at a temperature of 55 45°C at 90% relative humidity and observed for leakage of the electrolyte. Discharge tests similar to the above were performed after the cells were removed from storage, and the ratio (%) of the current value at that time to the initial current value was calculated. This calculated value constitutes the "maintenance proportion of discharge properties", which indicates the degree of deterioration of the air electrode of each cell. The higher the value for an electrode, the less it had so deteriorated. With respect to the thin membrane affixed to each electrode, the oxygen gas permeation rate was measured by the equilibrium pressure method in which a gas chromatograph is used for detection of the gas. The water vapour permeation rate was measured in accordance with the JISZ0208 measuring standard (cup method) and a comparison made between the two. The results are listed in Tables 4 and 5 65 below.

11 EP 0 154 468 B1 Potassium hydroxide was used as the electrolyte when the air electrodes of the Examples described above were evaluated. Similar results can be obtained, however, if other electrolytes are used, for example, ammonium chloride or hydroxide or a mixed electrolyte of hydroxide, hydroxide, caesium hydroxide, etc. The air electrode of this invention has been found to be equally suitable for air- 5 cells. As described above, the air electrode of this invention is a significant improvement over the prior art in that while it is thin in size, it prevents the penetration of water vapour into the main body of the electrode as well as being capable of heavy-load discharge over a long period of time and shows a marked improvement in storage properties and resistance to electrolytic leakage. to In Tables 4 and 5 "Raney n.p." is used as an abbreviation for "Raney nickel plate".

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EP 0154 468 B1

This invention has been described in detail in connection with preferred embodiments, but these embodiments are merely for example only and this invention is not restricted thereto. It will be easily understood by those skilled in the art that other variations and modifications can be easily made within the scope of this invention, as defined by the appended claims. 5 Claims oxide and 1. A composite membrane for passing oxygen gas, said membrane comprising a metallic a w carbonaceous material characterised in that the membrane comprises: less than 1 and a membrane having micropores, the diameter of which is equal to or urn; porous thickness the a thin layer affixed to at least one surface of said porous membrane and having a in range oxide of 0 01 to 1 said thin layer containing a metallic oxide in a carbon matrix, said metallic being urn, oxide, selected from among the group consisting of tin dioxide, zinc oxide, aluminium dioxide, magnesium calcium oxide, strontium oxide, barium oxide, titanium dioxide, , cuprous oxide, manganese 15 dioxide, monoxide, nickel oxide, tricobalt tetroxide, vanadium dioxide, molybdenum dioxide, tungsten ruthenium dioxide, niobium dioxide, chromium dioxide, thenium dioxide, osmium dioxide, rhodium dioxide, iridium dioxide and platinum dioxide... 2. An air electrode for a cell comprising a metallic oxide and a carbonaceous material characterised in 20 that it comprises: . of with a a main electrode body having the capability of electro-chemical reduction oxygen gas collector function; and the composite membrane according to claim 1. 3. A method for manufacturing an oxygen gas permeable composite membrane comprising a metallic of: 25 oxide and a carbonaceous material characterised in that it comprises the step membrane forming a thin layer having a thickness in the range of 0.01 to 1 urn on a porous having mixed micropores with a diameter less than 1.0 urn, by a reactive sputtering treatment in a gas containing metallic oxide and a hydrocarbon or substituted hydrocarbon compound, the sputter source being a argon oxide, is selected from the group consisting of tin dioxide, zinc oxide, , magnesium 30 calcium oxide, strontium oxide, barium oxide, titanium dioxide, silicon dioxide, cuprous oxide, manganese monoxide, nickel oxide, tricobalt tetroxide, vanadium dioxide, molybdenum dioxide, tungsten dioxide, ruthenium dioxide, niobium dioxide, chromium dioxide, rhenium dioxide, osmium dioxide, rhodium dioxide, iridium dioxide and platinum dioxide. 4. A method according to claim 3, in which said thin layer is deposited on the surface of said porous 35 membrane using a reactive sputtering treatment with a mixed gas containing argon and a hydrocarbon or substituted hydrocarbon compound. 5. A method according to claim 4, wherein said hydrocarbon compound is selected from the group consisting of alkanes of the general formula CnH2n+2, alkenes of the general formula CnH2n, alkynes of the the general formula CnH2n_2 and fluorinated hydrocarbons in which part or all of the hydrogen of 40 hydrocarbon compound has been substituted by fluorine. 6. A method according to claim 5 wherein the proportion of said hydrocarbon compound is less than 20 voi %.

Patentanspriiche 45 Material, 1. Durchlassige Membran fur Sauerstoff mit einem Metailoxid und einem kohlenstoffhaitigen gekennzeichnet durch klemer. 1 und eine porose Membran mit Mikroporen, deren Durchmesser gleich oder urn ist, eine dunne Schicht, die an wenigstens einer Flache der prosen Membran befestigt ist und eine Stake Kohlenstoffmatrix so im Bereich von 0,01 bis 1 urn aufweist, wobei die dunne Schicht ein Metailoxid in einer aufweist und das Metailoxid aus der Gruppe ausgewahlt ist, die Zinndioxid, Zinkoxid, Aummiumoxid, Magnesiumoxid, Kalziumoxid, Strontiumoxid, Bariumoxid, Titandioxid, Siliziumdioxid, Kupferoxid, Wolframdioxid, Manganmonoxid, Nickeloxid, Trikobalttetroxid, Vanadiumdixoid, Molybdandioxid, Rutheniumdioxid, Niobdioxid, Chromdioxid, Rheniumdioxid, Osmiumdioxid, Rhodiumdioxid, 55 Iridiumdioxid und Platindioxid aufweist. 2 Luftelektrode fiir eine Zelle mit einem Metailoxid und einem Kohlenstoffmaterial, gekennzeichnet durch eine Hauptelektrode mit der Fahigkeit zur elektro-chemischen Reduktion von Sauerstoff mit Kollektorfunktion und die Membran gemaB Anspruch 1.. Metailoxid und ein eo 3. Verfahren zur Herstellung einer fiir Sauerstoff durchlassigen Membran, die em Kohlenstoffmaterial aufweist, gekennzeichnet durch folgende Verfahrensschritte: auf Ausbildung einer diinnen Schicht, die eine Starke im Bereich von 0,01 bis 1,0 urn aufweist, einer als 1,0 durch eine porosen Membran, die Mikroporen aufweist mit einem Durchmesser geringer Mm, reaktive Zerstaubungsbehandlung in einem Mischgas, das Argon und ein Kohlenwasserstoff oder eine Metailoxid 55 substituierte KohlenwasserstofFverbindung enthalt, wobei der Zerstaubungsausgangsstoff ein

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ist, das aus der Gruppe ausgewahlt ist, die Zinndioxid, Zinkoxid, Aluminiumoxid, Magnesiumoxide, Kalziumoxid, Strontiumoxid, Bariumoxid, Titandioxid, Siliziumdioxid, Kupferoxid, Manganmonoxid, Nickeloxid, Trikobalttetroxid, Vanadiumdioxid, Molybdandioxid, Wolframdioxid, Rutheniumdioxid, Niobdioxid, Chromdioxid, Rheniumdioxid, Osmium-dioxid, Rhodiumdioxid, Iridiumdioxid und Platindioxid 5 enthalt. 4. Verfahren nach Anspruch 3, bei dem die diinne Schicht auf die Flache der porosen Membran aufgberacht wird, indem ein reaktives Zerstaubungsverfahren mit einem Mischgas verwendet wird, das Argon und einen Kohlenwasserstoff Oder eine substituierte Kohlenwasserstoffverbindung enthalt. 5. Verfahren nach Anspruch 4, bei dem die Kohienwasserstoffverbindung ausgewahlt ist aus der 10 Gruppe, die Alkane der allgemeinen Formel CnH2n+2, Alkene der allgemeinen Formel CnH2n, Alkine der allgemeinen Formel CnH2n_2 und fluorierte Kohlenwasserstoffe enthalt, bei denen ein Teil oder samtlicher Wasserstoff der Kohlenwasserstoffverbindung durch Fluor substituiert ist. 6. Verfahren nach Anspruch 5, bei dem der Anteil an Kohlenwasserstoffverbindungen geringer als 20 Vol.-% ist. 15 Revendications

1. Membrane composite permeable a I'oxygene, qui comporte un oxyde metallique et une matiere carbonee caracterisee en ce qu'elle presente des micropores dont le diametre est egal ou inferieur a 1 um; 20 et une mince couche fixee sur I'une, au moins, des faces de ladite membrane poreuse et don I'epaisseur est de I'ordre de 0,01 a 1 um, ladite couche contenant un oxyde metallique loge dans une matrice carbonee, ledit oxyde metallique faisant partie du groupe comprenant le bioxyde d'etain, I'oxyde de zinc, I'oxyde de strontium, i'oxyde de baryum, le bioxyde de titane, le bioxyde de silicium, I'oxyde cuivreux, le monoxyde 25 de manganese, I'oxyde de nickel, le tetraoxyde de tricobalt, le bioxyde de vanadium, le bioxyde de molybdene, le bioxyde de tungstene, le bioxyde de ruthenium, le bioxyde de niobium, le bioxyde de chrome, le bioxyde de rhenium, le bioxyde d'osmium, le bioxyde de rhodium, le bioxyde d'iridium et le bioxyde de platine. 2. Electrode d'air pour un element de pile qui comprend un oxyde metallique et une matiere carbonee, 30 caracterise en ce qu'elle comprend une electrode principale capable de reduire I'oxygene par voie electro- chimique avec une fonction collectrice et une membrane composite telle que specifiee dans la revendication 1. 3. Procede pour fabriquer une membrane composite permeable a I'oxygene comprenant un oxyde metallique et une matiere carbonee, caracterise en ce que: 35 on forme une mince couche, ayant une epaisseur comprise entre 0,01 et 1 um sur une membrane poreuse ayant des micropores dont le diametre est inferieur a 1 urn par un traitement de pulverisation reactive dans un melange de gaz contenant de I'argon et un hydrocarbure ou un compose d'hydrocarbure substitue, la source de substance de pulverisation etant un oxyde metallique choisi dans le groupe comprenant le bioxyde d'etain, I'oxyde de zinc, I'oxyde de d'aluminium, I'oxyde de magnesium, I'oxyde de 40 calcium, I'oxyde de strontium, I'oxyde de baryum, le bioxyde de titane, le bioxyde de silicium, I'oxyde cuivreux, le monoxyde de manganese, I'oxyde de nickel, le tetraoxyde de tricobalt, le bioxyde de vanadium, le bioxyde de niobium, le dioxyde de chrome, le bioxyde de rhenium, le bioxyde d'osmium, le bioxyde de rhodium, le bioxyde d'iridium et le bioxyde de platine. 4. Procede selon la revendication 3, caracterise en ce qu'on depose ladite mince couche a la surface de 45 ladite membrane poreuse en utilisant un traitement de pulverisation reactif avec un melange gazeux contenant de I'argon et un hydrocarbure ou un compose d'hydrocarbure substitue. 5. Procede selon la revendication 4, caracterise en ce que Ton choisit ledit compose d'hydrocarbure dans le groupe comprenant les alcanes de la formuie generale CnH2n+2, les alcenes de la formule generale CnH2n-2 et le hydrocarbure fluores dans lesquels tous les hydrogenes ou une partie d'entre eux ont ete so remplace par du fluor. 6. Procede selon la revendication 5, caracterise en ce que la proportion dudit compose d'hydrocarbure est inferieure a 20% en volume.

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