Comprehensive Electrochemical Impedance Spectroscopy Study of Flow-Electrode Capacitive Deionization Cells

Thisresearch points at the opportunity of utilizing electrochemicalimpedance spectroscopy to understand the distributions of resistanceand capacitance across flow-electrode capacitive deionization cells. Flow-electrode capacitive deionization (FCDI) offersinfinite ionadsorption for continuous desalination of high-concentration salinewater by supplying a flow-electrode to the cell. Although extensiveefforts have been made to maximize the desalination rate and efficiencyof FCDI cells, the electrochemical properties of these cells are notfully understood. This study investigated the factors affecting theelectrochemical properties of FCDI cells containing activated carbon(AC; 1-20 wt %) and various flow rates (6-24 mL/min)for the flow-electrode using electrochemical impedance spectroscopybefore and after desalination. Examination of the impedance spectrausing the distribution of relaxation time and equivalent circuit fittinganalysis revealed three distinctive resistances such as internal,charge transfer, and ion adsorption resistances. The overall impedancedecreased significantly after the desalination experiment due to increasedion concentrations in the flow-electrode. The three resistances decreasedwith increasing concentrations of AC in the flow-electrode due tothe extension of electrically connected AC particles that participatedin the electrochemical desalination reaction. The ion adsorption resistancedecreased significantly due to the flow rate dependence of the impedancespectra. In contrast, the internal and charge transfer resistanceswere invariant.