Impedance spectroscopic determination of effect of temperature on the transport resistances of an electro-electrodialysis cell used for concentration of hydriodic acid

摘要

Effect of temperature on different transport resistances of an electro-electrodialysis (EED) cell used for concentration of hydriodic acid (HI) was found by equivalent circuit modeling of the measured impedance response of the cell. The EED cell consisted of two compartments separated by Nafion 117 membrane and each compartment had a platinum electrode. Both the compartments were filled with aqueous solution of 55 wt% HI containing 0.5 M iodine. Impedance measurements were carried out at four different temperatures in the range of 308-353 K. Equivalent circuit for the cell consisted of a resistor for ohmic resistance of the cell, a Warburg element for the resistance due to diffusion boundary layer and a constant phase element for the resistance to transport of ions due to non-electro neutral heterogeneous transport layer at the membrane. Effect of temperature on impedance due to heterogeneous transport was lower than the Warburg impedance and the solution and membrane resistance. Effective capacitance of the heterogeneous transport layer was found to reduce with temperature. The dynamics of the heterogeneous transport layer along with the diffusional boundary layer were found to reduce with increase in the cell operating temperature.