Evaluation of ion transport properties characterizing concentration polarization in membrane-solution system under different factors

Abstract

Abstract The ion transport properties across the membrane under conditions of different membrane types, solution concentrations, flow rates and temperatures were investigated in a four-compartment reactor. By combining linear sweep voltammetry and chronopotentiometry, the limiting current density (I lim), the ion transition time (τ) and the difference between ion transport numbers in the membrane and the solution (t m–t s) were determined. And the diffusion boundary layer thickness (δ) of the membrane-solution system at steady-state conditions was measured by electrochemical impedance spectroscopy. The results show that the use of Selemion membrane and the increase of solution concentration, flow rate and temperature, I lim and τ increase, t m–t s and δ decrease. This means the concentration polarization of the system is weaker and complete concentration polarization is more difficult to occur. At the same time, I lim, τ and t m–t s are strongly related to solution concentration and temperature, while the diffusion boundary layer thickness is mainly affected by solution concentration and flow rate. Additionally, I lim of anion exchange membranes is larger than that of cation exchange membranes due to the difference in migration rates of anion and cation.