A detailed one-dimension mechanistic model for solid oxide direct carbon-assisted steam electrolysis cell (SO-DCEC) is well developed by considering heterogeneous elementary reactions in both the carbon bed and the cell, coupling with mass and charge transfer processes. The model is calibrated and validated by experimental data from a button cell test with different anode carrier gases at 800 degrees C. The experimental and modeling results show that using CO2 instead of argon gas as the carrier gas benefits the cell performance. A mismatching between CO production in the carbon bed, its diffusion from the carbon bed to the cell and its consumption in the cell results in different transition zones in the cell polarization curve. A concept of producing H-2 and CO simultaneously in the SO-DCEC system is proposed, and analyses Indicate that working voltages of the cell and the carbon bed height greatly influence the system performance and production rates of gaseous fuels. (C) 2016 Elsevier B.V. All rights reserved.