A single reversible solid oxide fuel cell (RSOFC) can accomplish two functions: (1) as a solid oxide steam electrolyzer (SOSE) for hydrogen production and (2) as a solid oxide fuel cell (SOFC) for power generation. An electrochemical model was developed to study the performance of an RSOFC based on a proton-conducting electrolyte (RSOFC-H). In both SOSE and SOFC modes, the hydrogen electrode-supported configuration was identified as the most favorable design to achieve high energy conversion efficiency of RSOFC-H. For comparison, in a previous study on conventional RSOFC based on an oxygen ion-conducting electrolyte (RSOFC-O), the hydrogen electrode-supported configuration was found to be favorable in the SOFC mode but such configuration would cause high concentration overpotential in the SOSE mode. Thus, the oxygen electrode-supported configuration was desirable for RSOFC-O operating in the SOSE mode. The results obtained in this study show that RSOFC-H has a natural advantage over RSOFC-O in terms of structural design. The modeling study signifies the difference between RSOFC-H and RSOFC-O and can serve as a useful tool for further design optimization. (C) 2007 Elsevier B.V. All rights reserved.