A single reversible solid oxide fuel cell (RSOFC) can perform dual functions: (1) as a solid oxide steam electrolyzer (SOSE) for hydrogen production and (2) as a solid oxide fuel cell (SOFC) for power generation. Thus, RSOFC can potentially offer a low-cost approach to support hydrogen economy. A modeling study has been conducted to analyze the important concentration overpotentials in both SOSE and SOFC modes of operation. The quantitative analyses show that in the SOSE mode, the hydrogen electrode is vulnerable to high concentration overpotential and limiting current density. Oppositely, in the SOFC mode, the oxygen electrode is vulnerable to above problems. If the SOSE and SOFC modes are considered separately, a RSOFC should be oxygen-electrode-supported and hydrogen-electrode-supported, respectively. For this reason, comprehensive analysis is very important to optimize the structure of the electrode-support to maximize the overall efficiency of a RSOFC performing dual functions. The modeling study signifies the difference between the SOSE and SOFC modes and provides insights in the operating mechanisms of RSOFC. The present model can be further extended to conduct more simulations for design optimization. (c) 2006 Elsevier B.V. All rights reserved.