A discussion on ion conductivity at cation exchange membrane/solution interface

By Gouy–Chapman–Stern–Grahame (CGSG) model, the electric double layer at ion exchange membrane/solution interface consists of two parts: the Stern layer and the diffusion layer. The ions in Stern layer are compacted and considered to be immobile. The relation of diffusion layer mean conductivity K with outer Stern layer potential φ0, the boundary potential φδ and the electrolyte concentration C0 is educed for symmetric electrolyte system. The results show that K is higher than that of the bulk solution and is greatly influenced by φ0, φδ and C0.The examination of PE01 cation exchange membrane/solution interface resistance Re measured by ac impedance technique, shows that Re value decreases quickly as the KCl electrolyte concentration rises. The effect of electrolyte concentration on the resistance of EDL can be explained by the electrical interactions between ions and charged groups of the membrane. Since the membrane/solution interface resistance is much higher than that of bulk solution, therefore, a further analysis based on the theory developed in this study proves that the ion transfer resistance Re of membrane–solution interface predominantly occurs at Stern layer as a result of static electrical interaction.