the invention concerns an oxide ion conductive ceramic membrane , characterized in that it comprises a non - null finite volume with non - null total thickness e , comprising , a dense layer of a solid electrolyte , a so - called bonding layer , of mixed conductive porous cathode and porous anode , a cathode current collector and an anode current collector , a coating porous layer , and a coating porous layer , and characterized in that the volume e of said membrane , is equal to the sum of the thickness of said elements . the membrane is used for separating oxygen from air or from a gas mixture containing same and in particular for producing ultra - pure oxygen under high pressure in a closed chamber .