NOVELTY - The electrochemical device comprises a cathode, an immobilized liquid membrane (202) coupled to the cathode, and a thin film of material having a thickness of less than or equal to 10 microns formed on the metallic host matrix. The immobilized liquid membrane comprises a porous metallic host matrix with a pore size of less than 10 microns and immobilized silicon oil, forms a selective cathode barrier in the device, is capable of increasing the durability of the device by 50%, and permeates first type of molecule such as oxygen and second type of molecule such as water.    USE - Used as an electrochemical device such as lithium/air pouch-type battery and fuel cells.    ADVANTAGE - The electrochemical device can be manufactured with improved durability, performance, lifespan and energy density and without water penetration and electrolyte loss, and ensures efficient permeation of oxygen.    DETAILED DESCRIPTION - The electrochemical device comprises a cathode, an immobilized liquid membrane (202) coupled to the cathode, and a thin film of material having a thickness of less than or equal to 10 microns formed on the metallic host matrix. The immobilized liquid membrane comprises a porous metallic host matrix with a pore size of less than 10 microns and immobilized silicon oil, forms a selective cathode barrier in the device, is capable of increasing the durability of the device by 50%, and permeates first type of molecule such as oxygen and second type of molecule such as water. The porous metallic host matrix has a porosity of greater than 90%, a thickness of less than or equal to 50 microns and a pore size of less than 2 microns. The thin film is capable of enhancing adhesion of the immobilized silicon oil to the porous metallic host matrix. INDEPENDENT CLAIMS are included for:    (1) a selective membrane; and    (2) a method for oxygen permeation in a battery device using a selective membrane.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a lithium/air pouch type battery assembly.    Lithium/air pouch-type cell (200)    Immobilized liquid membrane (202)    First surface (212)    Second surface (214)    Adhesive. (226)