High temperature CO2 electrolysis to produce CO and O-2 was studied with the goal of developing an efficient and practical method for producing fuel from solar energy. Electrolysis of CO2 at temperatures of 660 degrees C-1400 degrees C is performed on an electrolyte-supported cell composed of 8% YSZ electrolyte and Pt/YSZ cermet electrodes. The cell was operated at CO2 concentrations between 42%-99.9% with a balance of CO. This is the first published example of electrolysis measurements conducted at a temperature greater than 1000 degrees C. The average specific differential resistances of the test cell during CO2 electrolysis, including lateral electrode resistance, were 53.8 Ohm . cm(2) at temperatures between 660-670 degrees C, 5.2 Ohm . cm(2) at 950 degrees C, 3.9 Ohm . cm(2) at 1250 degrees C, and 4.8 Ohm . cm(2) at 1400 degrees C. These measurements show an order of magnitude resistance reduction as temperature increases from 660 degrees C to 1250 degrees C, with the lowest cell resistance at 1250 degrees C. The drop in performance as the temperature increases from 1250 degrees C to 1400 degrees C is primarily due to electrode sintering. Furthermore, it was determined that ppm levels of O-2 present in the CO2/CO mixture on the cathode side of the cell increase cell resistance. (C) 2015 The Electrochemical Society.