An element for use in an electrochemical reactor or reactor cell having a first surface capable of reducing oxygen to oxygen ions, a second surface capable of reacting oxygen ions with an oxygen-consuming gas, an electron-conductive path between the first and second surfaces and an oxygen ion-conductive path between the first and second surfaces characterized in that the element comprises (A) a solid multi-component membrane characterized by (1) an intimate, gas-impervious, multi-phase mixture of an electronically-conductive phase and an oxygen ion-conductive phase or (2) a mixed metal oxide material having a perovskite structure and (B) a conductive coating, a catalyst, or a conductive coating comprising a catalyst.