For separating water into hydrogen and oxygen through intermediate Cu-Cl compounds, the new system configurations for 5-step, 4-step and 3-step thermochemical cycles using electrolysis of CuCl/HCl or CuCl and Brayton cycle are addressed in Aspen Plus' environment. To address the feasible predictions by thermodynamic systems, we found that (i) the pressure and temperature affect the product yields of CuO * CuCl2 and CuCl in the hydrolysis and oxygen production processes; (ii) the internal heat recovery ratio (IHRR) and the feed ratio of H2O/CuCl2 dominate the energy efficiencies and Cl-2 production, respectively. Based on the prescribed operating conditions, the comparative evaluations show that the 5-step Cu-Cl cycle using CuCI electrolyzer can ensure the highest energy efficiency while IHRR = 72%, the 3-step Cu Cl cycle using CuCl electrolyzer can ensure the less equipment and the highest energy efficiency while IHRR = 100%. The 4-step Cu Cl cycle using CuCl/HCl electrolyzer, where the electrolyzer prevents copper crossovers and safely produces the pure hydrogen gas at low temperature, has a high possibility of commercialization due to the lower grade heat requirement, the less number of equipment and the higher energy efficiency. (C) 2017 Hydrogen Energy publications LLC. Published by Elsevier Ltd. All rights reserved.