Electrochemical analysis of CuCl/HCl electrolyser

Abstract

This thesis presents an electrochemical study on a CuCl/HCl electrolyser which is the hydrogen generation step of the CuCl thermochemical hydrogen production cycle. The anode electrolyte is solution of 2 mol.l−1 CuCl(aq) in 10 mol.l−1 HCl(aq) and cathode electrolyte is considered as 11 mol.l−1 HCl(aq). Equilibrium and kinetic analyses are performed for the anode and cathode half-reactions as well as electrolysis full-cell reaction. Gibbs energy minimization method is used to determine equilibrium concentrations of stable anolyte ions. Determination of thermodynamic properties of ions in the solution is carried out via application of the Helgeson-Kirkham-Flowers equation of state and the Debye-Huckel theory. Activation and Ohmic overpotentials of electrolysis are used to determine the required voltage to trigger hydrogen evolution at cathode. At 5% conversion of Cu(I)→Cu(II) species in anolyte, decomposition potential of anode half-reaction is calculated to be -0.51V at room temperature. The cathode half-reaction is found to be spontaneous with an equilibrium potential of 0.11V at 25℃. Full-cell decomposition potentials at 25℃ and 80℃ are -0.40V and -0.44V, respectively, for the full conversion at anode. The cell potential is found to be -0.54V at 25℃ and it rises to -0.59V at 80℃. A higher working temperature results in more potential requirement for the cell while, it increases the overall electrochemical efficiency. Electrochemical efficiency of the cell is found to vary between 10% and 70% from low to high temperatures.