The performance of solid oxide electrolysis (SOE) cells while operating in the natural gas assisted steam electrolysis (NGASE) mode was evaluated. The SOE cells used yttria-stabilized-zirconia (YSZ) as the oxygen ion conducting electrolyte, Co-CeO2-YSZ as the H-2-H2O electrode, and Pd-doped CeO2. YSZ as the CH4-oxidation electrode. The cell electrochemical performance was evaluated as a function of the H2O/H-2 ratio and the extent of conversion of CH4. The results of this study provide insight into the factors that control electrode performance and further demonstrate the viability of an NGASE cell for the production of H-2. (C) 2007 Elsevier Ltd. All rights reserved.