Solvation Effect Facilitates Ion Transfer across Water/1,2- Dichloroethane Interface Jacques Nsabimana, Uwitonze Nestor, Girum Girma, Ndagijimana Pamphile, Dongping Zhan,* and Zhong-Qun Tian [a] Dedicated to Professor Christian Amatore on the occasion of his 65th birthday 1. Introduction In electrochemistry, the liquid/liquid interface refers to the in- terface between two immiscible electrolyte solutions (ITIES) such as the water/nitrobenzene interface, [1] water/1,2-dichloro- ethane (W/1,2-DCE) interface, [2] water/ionic liquid interface, [3] and so forth. Charge transfer across ITIES is considered impor- tant for ion detection in analysis and membrane processes, [4] phase-transfer catalysis, [5] and energy conversation and stor- age. [6] Strikingly, ion transfer across ITIES can generated farada- ic current without involving any redox reaction at the interface. Ion-selective electrodes (ISEs) based on the faradaic current re- sponse are much more sensitive than the conventional poten- tiometric ISEs. [7] Thus, ion transfer across ITIES arouses much attention of researchers in both analytic and biological domains. [8] Traditionally, if the coupling reactions are not taken into ac- count, charge transfer across ITIES is classified into three cata- logues: simple ion transfer, facilitated ion transfer (FIT), and electron transfer. [4] As most inorganic ions are very hydrophilic, the Gibbs energy of ion transfer across ITIES is too high to be observed in the potential window of the investigated ITIES system. To solve the problem, one solution is to widen the po- tential window by using more hydrophilic salts in the aqueous phase and more hydrophobic slats in the organic phase as the supporting electrolytes. [9] In our experience, for the commer- cially available organic supporting electrolyte (tetrabutylammo- nium tetrakis(4-chlorophenyl)borate, BTPPA-TPBCl), the poten- tial window of the W/1,2-DCE interface can reach more than 0.8 V when Li 2 SO 4 is used as the supporting electrolyte in aqueous solution. Another way is to lower the transfer poten- tial by using ionic ligands, as the supramolecular interaction between them can lower the Gibbs energy of ion transfer across ITIES. [10] To improve the selectivity and sensitivity, FIT has been well investigated by using either natural or artificial ionic ligands. For example, valinomycin was demonstrated as a good ligand for potassium cations. [11] Owing to the development of supra- molecular chemistry, various crown ethers, calixarenes, and polyethers were adopted as the ligands for different cat- ions. [7–11] However, there are only a few reports on the facilitat- ed anion transfer (FAT) across ITIES, owing to the difficult avail- ability of anion ligands. [12] Furthermore, the potentials of FAT are usually too close to the edge of the potential window to be amperometric ISEs. Recently, we demonstrated that the solvation effect can act as the driving force for the lithium-ion (Li + ) transfer across the W/1,2-DCE interface. [13] The solvation between Li + and propyl- ene carbonate (PC) can decrease the Gibbs transfer energy of Li + . Herein, we adopted the micropipette to support the W/ 1,2-DCE interface and found, owing to the ionic solvation effect of PC, that not only the cation but also the anion trans- fer is facilitated without using any artificial ligands. The amphi- pathic solvent PC provides a more “comfortable” environment for the ions in 1,2-DCE and lowered the Gibbs energy of ion transfer. 2. Results and Discussion The typical cyclic voltammograms of Na + transfer across the micropipette-supported W/1,2-DCE interface are shown in Fig- Ion transfer across the interface between two immiscible elec- trolytes can produce a Faraday current involving non-redox re- actions, which is useful for both ion detection and phase-trans- fer catalysis. To decrease the transfer energy and improve the selectivity, artificial ligands are needed, which are usually un- available because of the difficulty in the synthesis. Herein, we demonstrate that the solvation effect can act as the driving force for ion transfer across the micropipette-supported water/ 1,2-dichloroethane interface, including the anions SO 4 2 , NO 3  , NO 2  , CO 3 2 , and so forth. The thermodynamic properties are discussed, including the diffusion coefficients, Gibbs energy of ion transfer, stoichiometric ratios, and apparent association constants. Meanwhile, the research also provides a method to investigate the solvation effect. [a] J. Nsabimana, U. Nestor, G. Girma, N. Pamphile, Prof. D. Zhan, Prof. Z.-Q. Tian State Key Laboratory for Physical Chemistry of Solid Surfaces Department of Chemistry, College of Chemistry and Chemical Engineering Xiamen University, 422 Siming South Road, Xiamen 361005 (China) E-mail : dpzhan@xmu.edu.cn This is an invited contribution for the Christian Amatore Festschrift ChemElectroChem 2016, 3,1–6  2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 & These are not the final page numbers! ÞÞ These are not the final page numbers! ÞÞ Articles DOI: 10.1002/celc.201600389