Investigations on the interfacial capacitance and the diffusion boundary layer thickness of ion exchange membrane using electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) is a powerful tool to investigate the electrochemical processes. This work investigated the interfacial properties of ion exchange membranes using EIS. Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potential were also used to characterize the membranes. With the comparison of two equivalent circuits and the consideration of the physical and electrochemical understanding of the ion exchange membrane systems (IEMs), a better equivalent circuit was selected for quantitatively analyzing each component of the systems. The diffusion boundary layer thickness was estimated with the derived equation (δ=3RdCdD). The effects of solution concentration, flow rate and temperature on the IEMs were investigated in a systematic way. The results clearly showed that the effective capacitance and the electrical double layer resistance were consistent with the concentration dependence of the Debye equation; the diffusion boundary layer thickness decreased with the increase of solution concentration, flow rate and temperature. The effective capacitance and the thickness of the membranes interface obtained by EIS were important for understanding the relationship with membrane surface microstructure, ion transport and electrical properties. It is confirmed that the EIS can be used as an alternative method to characterize the ion exchange membrane systems.