A wall construction for an electrolytic cell to separate oxygen from an oxygen containing gas in which an electrolyte layer of less than 200 microns and a cathode layer of less than 500 microns are supported by an anode that can have a sufficient thickness to also contain the separated oxygen at pressure. The cathode is formed from the same material as the electrolyte and also a noble metal or noble metal alloy and a mixed conductor. The cathode contains a sufficient amount of the noble metal or noble metal allow and the mixed conductor that the total resistance thereof is not greater than about 70 percent of the total resistance of the anode and the cathode. In a preferred embodiment, first and second porous interfacial layers are situated between an anode layer and the electrolyte and the electrolyte and a cathode layer, respectively. The first and second porous interfacial layers increase thermal compatibility between the anode and cathode and the electrolyte, improve the three-phase boundary and allow thinner electrolytes to be employed with fewer manufacturing defects.