Kinetic and electrochemical analyses of a CuCI/HCl electrolyzer

Abstract

An electrochemical analysis is carried out from a kinetic electrochemistry perspective of a CuCl/HCl electrolysis cell, within the CuCl thermochemical water splitting process for hydrogen production. The anolyte is a solution of 2 mol L−1 CuCl(aq) and 10 mol L−1 HCl(aq) while the catholyte solution is 11 mol L−1 HCl(aq). The cell current density of 0.5 A cm−2 and voltage of 0.7 V are the desired working conditions for a CuCl/HCl electrolyzer. The current density of 0.5 A cm−2 is assumed to occur at a 5% anolyte conversion degree. At 25°C, the activation overpotential of the anode half-reaction is found to be 53 mV for a current density of 0.5 A cm−2 while the activation overpotential of the cathode half-reaction for the same condition is 87 mV. An increase in working temperature decreases the overpotential of the anode half-reaction and increases the cathode half-reaction activation overpotential. The ohmic overpotential of the cell membrane is almost 1000 times smaller than that of the activation overpotentials of the electrode half-reactions for the same temperature and current density. A higher working temperature results in a lower membrane ohmic overpotential. The required voltage to trigger electrolysis for a current density of 0.5 A cm−2 is found to be 0.53 V at 25°C and 0.59 V at 80°C and a higher temperature results in a higher electrochemical efficiency. The cell electrochemical efficiency increases linearly with working temperature while the voltage efficiency peaks at 75% at 60°C.