United States Patent (19) 11 Patent Number: 4,599,157 Suzuki et al. 45 Date of Patent: Jul. 8, 1986 4,400,242 8/1983 Albery et al. ....................... 204/415 (54) OXYGEN PERMEABLE MEMBRANE 4,419,202 12/1983 Gibson ............... ... 204/192 C (75) Inventors: Nobukazu Suzuki, Tokyo; Shinji 4,421,579 12/1983 Covitch et al. ..................... 204/283 Tsuruta, Yokohama, both of Japan OTHER PUBLICATIONS 73) Assignee: Kabushiki Kaisha Toshiba, Kanagawa, Japan "Thin Film Processes' by J. L. Vossen et al., Academic Press, 1978, p. 48. 21 Appl. No.: 705,015 Primary Examiner-R. L. Andrews 22 Filed: Feb. 25, 1985 Attorney, Agent, or Firm-Banner, Birch, McKie & (30) Foreign Application Priority Data Beckett Feb. 24, 1984 JP Japan .................................. 59-33589 57 ABSTRACT Feb. 24, 1984 JP Japan .................................. 59-33593 There is disclosed a composite membrane and an air 51 Int. Cl. .............................................. C23C 14/00 electrode for use in hydrogen-oxygen fuel cells, metal 52 U.S. Cl. .......................... 204/192 SP; 204/192 C; air cells and oxygen sensors. The composite membrane 204/282; 204/283; 204/295; 204/296; 204/432 includes a porous membrane having micropores with a 58) Field of Search .......... 204/192 C, 192 SP, 192 P, thin layer affixed thereto. The thin layer having metallic 204/295-296, 432, 282, 283 oxide in a carbon matrix, so that oxygen gas is able to (56) References Cited permeate therethrough, but water vapor in air is not U.S. PATENT DOCUMENTS allowed to permeate therethrough. 4,272,353 6/1981 Lawrance et al. .................. 204/283 4,326,927 4/1982 Stetter et al. ....................... 204/432 10 Claims, 1 Drawing Figure 100 80 S.ss 60 40 20 0 20 40 60 80 100 STORED DAYS AT 45°C, 90% U.S. Patent Jul. 8, 1986 4,599,157 t 20 O —20 40 60 80 100 STORED DAYS AT 45°C, 90% 4,599,157 1. 2 the active site to oxygen gas is reduced at the point of OXYGEN PERMEABLE MEMBRANE absorption. Thus, the heavy-load discharge capability of the cell is adversely effected. Moreover, when an BACKGROUND OF THE INVENTION alkaline electrolyte is used, there will be a change in the This invention relates to an oxygen permeable mem 5 properties of the electrolyte, a reduction in the concen brane which permits oxygen gas to pass through while tration of the electrolyte and, if the cathode is zinc, substantially blocking water vapor. The present inven passivation of the zinc cathode. Furthermore, heavy tion has application in hydrogen-oxygen electric fuel load discharge may be hindered because the area of electrochemical reduction is reduced by the production cells, metal-air battery cells and oxygen sensoring de O WCCS. of carbonate in the active site which blocks the pores. In the prior art, gas diffusion electrodes have been These factors lead to a decline in the performance of the used for air electrodes in various fuel cells, air-metal cell from its design rating after the cell is stored or used cells, such as air-zinc cells, and Galvanic oxygen sen for a long period of time. sors. Thick porous electrodes having distributed pores In order to overcome the aforementioned disadvan with a uniform diameter were used as the gas diffusion 15 tages, there has been proposed a cell in which a water electrode. In recent years, however, electrodes having a repellent layer for the air electrode is provided on the two-layer structure have been used. The electrode com gas side (air side) thereof with a layer comprising a prised a porous electrode body with an electrochemical water-absorbing agent, such as calcium chloride, or a reduction function for oxygen gas (a function for ioniz carbon dioxide gas-absorbing agent, such as a hydroxide ing oxygen) and a current collector function. The elec 20 of an alkaline earth metal. Such a cell is disclosed in trode also had a thin water repellent layer deposited Japanese Patent Publication No. 8411/1973. This type integrally on the gas-side surface of the electrode body. of cell can prevent the above-mentioned problems to In such electrodes, the electrode body may be formed some extent. However, when the absorbing agent has by a conductive powder, a porous metallic body, a been saturated with water or carbon dioxide gas, it porous carbon body or a non-woven carbon fabric ma 25 becomes wholly ineffective. terial. This may be accomplished by use of a binder such There have also been attempts to laminate an oxygen as polytetrafluoroethylene. Such conductive powders permeable membrane on the abovementioned water may be selected from among active carbon powders repellent layer. Such a membrane is disclosed in Japa carrying a nickel tungstate with a low reduction over nese Patent Publication No. 26896/1973. However, a voltage to oxygen gas, a tungsten carbide coated with 30 sufficiently effective oxygen gas permeable membrane palladium, cobalt, nickel, silver, platinum or palladium. The aforementioned water repellent layer, which is has not been developed thus far. deposited integrally on the gas-side surface of the elec SUMMARY OF THE INVENTION trode body, is a porous thin membrane which comprises a fluorine containing a resin such as polytetrafluoroeth 35 It is therefore an object of the present invention to ylene, tetrafluoroethylene-hexafluoropropylene co provide a selectively permeable composite membrane, polymer or ethylene-tetrafluoroethylene copolymer. and an air electrode being made therefrom, which is The membrane may also be comprised of a resin, such permeable to oxygen gas while at the same time being as polypropylene, in the form of a porous material in impervious to water vapor in air. cluding, for example, a sintered powder material having 40 It is another object of the invention to provide an air a particle size of from 0.2 to 40 um; a paper-like non electrode comprising an oxygen gas permeable mem woven fabric material prepared by heat treatment of brane which enables a heavy-load discharge to be main fibers comprising polypropylene resin or by a similar tained over a long period of time. woven fabric material; a powder material wherein the According to a first aspect of this invention, a selec polypropylene resin is partially replaced by a fluori 45 tively permeable composite membrane having a two nated graphite; a film material prepared by rolling fine layer construction is provided. The membrane com powder together with a pore-increasing agent or a lu prises a porous membrane layer having micropores and bricant oil followed by heat treatment or a film material a thin layer containing, in a carbon matrix, a water-con prepared by rolling without being followed by heat tainable or wettable metallic oxide, a metal oxide having treatment. Such materials are disclosed in Japanese 50 the capability of absorbing oxygen, or a metal oxide Patent Publication No. 44978/1973. having a rutile-type crystal structure. The thin layer is In an air electrode having the structure as described laminated integrally on to one or both surfaces of the above, however, the water repellent layer deposited on porous membrane layer. the gas-side surface of the electrode body is impervious According to a second aspect of this invention, an air to electrolyte but is not impervious to air and water 55 electrode is provided which comprises a main body vapor in the air. For this reason, water vapor in the air having the capability of electrochemical reduction of may penetrate the electrode body through the water oxygen gas with a collector function and a thin layer repellent layer and dilute the electrolyte or the water in containing metallic oxide in a carbon matrix. The thin the electrode may otherwise dissipate through the layer is laminated integrally on to the gas side surface of water repellent layer, thereby increasing electrolyte 60 the main body of the electrode either directly or with a concentration. As a result, the concentration of the porous membrane layer between. In this embodiment of electrolyte will fluctuate and it will thus be impossible the invention the metallic oxide may be a water-contain to maintain a stable discharge characteristics over a able or wettable metallic oxide or have the capability of long period of time. absorbing oxygen or have a rutile-type crystal struc When carbon dioxide gas in the air penetrates the 65 ture. The water-containable or wettable metallic oxide electrode body through the water repellent layer and is used in this invention is a material having the ability to absorbed by an active site (a porous portion of the elec absorb water and having properties for permitting the trode body), the electrochemical reducing function of water absorbed to exist as chemically and physically 4,599,157 3 4. absorbed water. The water-containable (wettable) can also be used. It is preferred that the proportion of properties means that a metallic oxide exists in combina such hydrocarbon compound is less than 20 vol% so as tion with water molecules or in a state having an inter not to make a thin layer consisting of only hydrocarbon. action with water molecules. Examples of the above Provided the porous membrane mentioned above has mentioned metallic oxides include tin dioxide (SnO2), 5 micropores of a diameter of 1.0 um or less, any material Zinc oxide (ZnO), aluminum oxide (Al2O3), magnesium would serve the purpose. However, from the viewpoint oxide (MgO), calcium oxide (CaO), strontium oxide of affixing the membrane to the main body of the elec (SrO), barium oxide (BaO), titanium dioxide (TiO2) and trode, a material that is highly flexible is preferred. If silicon dioxide (SiO2).