The hybrid copper-chlorine (Cu-Cl) thermo/electrochemical cycle for decomposing water into its constituents is a novel method for hydrogen production. The process involves a series of closed-loop chemical reactions. The cycle is assumed driven in an environmentally benign manner using nuclear energy. The cycle involves five steps of which three are thermally driven chemical reactions and one has an electrochemical reaction. In the present study, the electrochemical reaction, copper (Cu) production step, is described with its operational and environmental conditions, and analyzed thermodynamically. Various parametric studies are carried out on energetic and exergetic aspects of the step, considering variable reaction and reference-environment temperatures. At a reaction temperature of 45 degrees C, the reaction heat of the Cu production step is 140,450 kJ/kmol H-2. At a constant reaction temperature of 45 degrees C, the exergy destruction of the step varies between 50 kJ/kmol H-2 and 7000 kJ/kmol H-2 when the reference-environment temperature increases from 0 degrees C to 30 degrees C. At a reaction temperature of 45 degrees C and a reference-environment temperature of 25 degrees C, the exergy efficiency of this step is 99% and decreases with increasing reference-environment and/or reaction temperatures. (C) 2008 Elsevier B.V. All rights reserved.