Diffusive mass transfer in an electrochemical cell, which produces hydrogen in a copper-chlorine cycle of thermochemical water decomposition, is investigated in this paper. A predictive model of entropy production for the electrochemical reaction of cuprous chloride and hydrochloric acid is developed. The effects of temperature and current density on entropy production are investigated with the new formulation. A comparative study is performed with respect to the relationships between current density and overpotential, using Tafel's equation and a newly proposed method, based on the Nernst equation. The effects of ohmic and activation overpotentials on the thermodynamic irreversibilities in the electrolytic cell are also investigated. The impact of the charge transfer coefficient on the electrochemical reaction is also examined. The results of the new predictive formulation are compared successfully against Tafel's model and past experimental data, in relation to measured electrochemistry data. The operating temperature of the electrochemical cell has a significant effect on the entropy generation. The ohmic resistance appears to have minimal effect on the electrolytic cell performance at high current densities. A significant effect of current density on overpotential was observed at low current densities (0-250 mA/cm(2)). The current density has a significant effect on entropy production between 0 and 400 mA/cm(2). The activation overpotential has the most significant effect on cell performance. Although the ohmic resistance has little effect at high current densities, the effects become significant at lower current densities. Copyright (C) 2010, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.