An elementary reaction-based solid oxide electrolysis cell (SOEC) model that is coupled with cathodic elementary heterogeneous reactions and electrochemical elementary charge transfer reactions for a CO/CO2 mixture gas is developed. This model is calibrated and validated using experimental data obtained in a button cell for various CO/CO2 gas mixtures at 650, 700 and 750 degrees C. To obtain further information for electrode design and optimization, cell performance improvement and product composition tuning, the effects of operating conditions on the cell performance and the detailed species concentration distribution are predicted. Finally, carbon deposition in the SOEC cathode with a CO/CO2 mixture gas is experimentally measured and simulated using the elementary reaction model. The results indicate that the carbon deposition phenomenon at the cathode/electrolyte interface is more serious when compared to deposition at the electrode surface. The carbon deposition risk in SOEC operation can be decreased by keeping the CO content at a lower level. (c) 2012 Elsevier Ltd. All rights reserved.