An electrical impedance spectroscopic (EIS) study on transport characteristics of ion-exchange membrane systems.

This study aimed at investigating ion-exchange membrane systems using impedance spectroscopy. Nyquist plots showed that the impedance obtained in this study described the ion-exchange membrane system well, as consisting of (i) an ion-exchange membrane immersed in solution, (ii) electrical double layers at the membrane surface, and (iii) diffusion boundary layers arising from the interface between the ion-exchange membrane and the electrolyte solutions. Taking into account the physical and electrochemical understanding of the ion-exchange membrane system, an equivalent circuit was suggested to quantitatively analyze each component of the ion-exchange membrane system. To confirm the reliability of the proposed equivalent circuit, the resistance and capacitance were estimated from the impedance data and the values were compared with other experimental results (e.g., I-V curves). The comparison showed good agreement and validated the equivalent circuit. Moreover, the impedance measurements made it possible to confirm the electroconvective effects in the over LCD region.