Ceramic oxygen generators (COGs) with a bilayer-electrolyte (erbia stabilized bismuth oxide/samaria-doped ceria) architecture were developed to produce pure oxygen from CO2 at lower temperature (below 700 degrees C) for potential use in NASA's Mars exploration mission. Major factors that influence oxygen generation include the oxygen-ion conductivity of the solid- oxide electrolyte, applied current, operating temperature, and fuel utilization (CO/CO2 ratio). The COG voltage power losses were due to internal resistance and electrode polarization. Higher temperatures resulted in higher oxygen generation rates due to reduced cell resistance. However, lowering the COG operating temperature is very important and the bilayer COGs showed promise for operation below 700 degrees C, thus reducing the required power consumption, expanding ancillary material selection, decreasing fabrication cost, and potentially extending mission time. (c) 2005 The Electrochemical Society. [DOI: 10.1149/ 1.1943592] All rights reserved.