Electrochemical Kinetics of Reduction of Zinc Oxide to Zinc Using 2:1 Urea/ChCl Ionic Liquid

Abstract

Electrochemical reduction of zinc oxide to zinc was investigated in 2:1 urea/choline chloride electrolyte at applied cell potentials of 3.2 - 3.5V. Concentration polarization was observed at the beginning of electrochemical reduction process. The diffusion coefficient of zinc species in the electrolyte was calculated to be 7.85×10−13m2/s at 363K. An increase in the current density was observed after a sharp initial decrease due to activation polarization, in which case, a linear relationship was established between log (current density) and over-potential. The electrochemical kinetic parameters was investigated in the steady-state current region. The transfer coefficient was calculated to be 0.2 indicating an irreversible charge transfer process. The XRD analysis confirmed that the electrodeposits consists of high purity zinc. The SEM analysis showed the formation of dendrites at higher over-potential (≥0.65V), which is comparable to the calculated critical over-potential for Zn dendrite formation. The estimated energy consumption varied from 3.04 to 3.66 kWh/kg and current efficiency from 78.5 to 88.9%.