Detailed kinetic study of the electrochemical Bunsen reaction in the sulfur–iodine cycle for hydrogen production

Abstract

The electrochemical Bunsen reaction has been proposed as an innovative and promising method compared with the traditional Bunsen reaction for the sulfur–iodine cycle, and its kinetics were studied in this work. Polarization curves were measured using platinum electrode in the different concentrations of SO2–H2SO4–H2O and I2–HI–H2O solutions at a temperature range of 303–353K. Fundamental kinetic parameters, namely exchange current density, Tafel slope, asymmetry factor, were determined for anodic SO2 oxidation reaction and cathodic I2 reduction reaction according to the Tafel plots. The activation energy and pre-exponential factor for the electrode reactions were also analyzed using Arrhenius relation. Results indicated that an increase in the SO2 concentration in the anolyte and the I2 concentration in the catholyte reduced the activation energy, contributing to the easier anode and cathode reaction. Take high electrode reaction rate and easier electrode reactions into account, the initial SO2 concentration of 1.509mol/L and the I2/HI molar ratio of 0.5 could be optimal.