Equilibrium potential for the electrochemical Bunsen reaction in the sulfur–iodine cycle

The electrochemical Bunsen reaction was carried out in an electrochemical cell, where the anodic and cathodic compartments were separated by a Nafion 117 membrane. The equilibrium potential of the cell was experimentally measured and theoretically modeled. The effect of electrolyte concentration and temperature was explored. An increase in SO2 or I2 concentration reduced the equilibrium potential, whereas increasing H2SO4 or HI concentration had a contrary effect. The cell equilibrium potential decreased with increasing temperature. The derived theoretical equilibrium potential model was verified by the experimental data. The regression parameters M and Z in the model were independent of electrolyte concentration, but M decreased and Z kept constant with increasing temperature. An empirical equilibrium potential formula was proposed based on the theoretical and experimental results. The good reproducibility of this formula for measured data indicated its feasibility to estimate the equilibrium potential and also its guidance for optimizing the electrochemical Bunsen reaction.