EIS studies on electro-electrodialysis cell for concentration of hydriodic acid

EIS studies were carried out on an electro-electrodialytic cell used for concentration of hydriodic acid using platinum electrodes and nafion117 membrane. Different impedance spectra were obtained where the concentration of iodine was varied while the concentration of HI was kept fixed at 55 wt%. Equivalent circuit model was used to simulate the experimental data and it was found that the impedance of the cell without membrane can be modeled using a single Warburg element along with ohmic resistance in series. This indicates presence of only diffusion transport resistance at the electrode and absence of any non-electroneutral layer. The impedance spectra for cell with membrane can be modeled using a Warburg element and a CPE with capacitive character along with ohmic resistance in series. This indicates formation of a non-electroneutral (heterogeneous transport) layer at the membrane in addition to a diffusion transport layer. It was found that the ohmic resistance increased with increase in the concentration of iodine while the impedances due Warburg and heterogeneous transport layer decreased with increase in iodine concentration.