Investigations on electrochemical properties of membrane systems in ion-exchange membrane transport processes by electrochemical impedance spectroscopy and direct current measurements

Electrochemical impedance spectroscopy (EIS) and direct current method (DC) are two powerful techniques to investigate the electrochemical properties in ion exchange membrane transport processes. This work investigated the resistance of membrane systems obtained by EIS and DC with different solution velocity and temperature. Analysis of experimental data from EIS revealed that EIS can be used to analyze each sublayer of ion exchange membrane systems separately and quantitatively and that the resistance of interfacial layers was related to Donnan exclusion. The Bode plots of EIS data were corrected for ohmic resistance to determine the evident constant phase element (CPE) behavior in the data, and the effects of flow velocity and temperature on ohmic-resistance-corrected Bode plots were also analyzed. With the comparison of data obtained from EIS and DC, the sum of pure membrane resistance, diffusion boundary layer resistance and electrical double layer resistance determined by EIS equaled to the overall resistance of membrane systems determined by DC. The results confirmed the linear relationship between the overall conductivity of membrane systems from DC and the pure membrane conductivity from EIS. These results are of major importance for applications of ion exchange membranes in various electro-membrane processes and applications of EIS on characterization of membrane transport properties.