In our previous work[1], membranes composed of poly(ionic liquid)s (PlLs) and polyvinylidene fluoride (PVDF) were prepared through simple solution method.The membrane showed excellent chemical stability in 0.5mol/L NaCl solution which was considered impossible for the supported liquid membrane composed of non-polymerizable ionic liquids and porous substrates.The membrane displayed good conductivity and high tensile strength.With the ratio of PILs to PVDF 6∶10, the membrane conductivity reached 5.2× 10-3S/cm, the tensile strength 17.38N/mm2.So far, however, there is no investigation on ion transport characteristics in this kind of membrane, comparing to the well-known Nation membrane.Both membrane composition and preparation condition may have signiticant effects on the ion transport characteristics in membranes composed of PILs and PVDF.It is of great value to investigate the transport behaviors of different ions (e.g.cation and anion) through the membrane.For these purposes, we have designed an ion-transfer device as shown in Figure 1.In this device, NaCl solution of different concentrations (solution side) and deionized water (permeation side) are separated by the membrane.The temperature is controlled by the circulating water flowing through the outer chamber.During the experiment, the concentration of Na+ and Cl-in the permeation side solution is measured by Na+ and Cl-ion-selective electrodes, respectively.Ion-selective electrodes have higher precision compared to other methods, and also convenient for online measuring.The potential of the electrode towards different Na+ and Cl-concentrations are illustrated in Figure 2.During the experiment, the concentration of Na+ and Cl-in the permeation side linear increase with time within 4 hours, as shown in Figure 3.Taking advantage of ion-selective electrodes, we could further investigate the ion-transfer characteristics in membranes composed of PILs and PVDF.