Experimental and modeling activities were performed, addressing the performance of solid-oxide cells, operating in steam electrolysis mode for hydrogen production. Experimental results were obtained from a 10-cell planar solid-oxide electrolysis stack. The electrolysis cells are electrolyte-supported, with scandia-stabilized zirconia electrolytes (similar to 140 mu m thick), nickel-cermet steam/hydrogen electrodes, and manganite air-side electrodes. Interconnect plates were fabricated from ferritic stainless steel. Experiments were performed over a range of 800-900 degrees C steam inlet mole fractions (0.1-0.6), gas flow rates (1000-4000sccm), and current densities (0-0.38A/cm(2)). Hydrogen production rates up to 90 Normal liters per hour were demonstrated. Stack performance is shown to be dependent on inlet steam flow rate. A three-dimensional computational fluid dynamics (CFD) model was created. Measurements and CFD predictions of internal stack temperatures show a net cooling effect for operating voltages lower than thermal neutral, and a net heating effect at higher voltages. Model results compare favorably with experimental results obtained from the 10-cell stack. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.