Electrochemical study of the thermodynamics and kinetics of hydrophilic ion transfers across water n-octanol interface

International audienceThermodynamics and kinetics of hydrophilic ion transfers across water | n-octanol (W | OCT) interface have been electrochemically studied by means of novel three-phase and thin-film electrodes. Three-phase electrodes used for thermodynamics measurements comprise edge plane pyrolytic graphite (EPPGE), the surface of which was partly modified with an ultra thin film of OCT, containing hydrophobic bis(tetra-tert-butylphthalocyaninato) (Lu[tBu4Pc]2) as a redox probe. The transfers of anions and cations from W to OCT was electrochemically driven by reversible redox transformations of Lu[tBu4Pc]2 to chemically stable lipophilic monovalent cation (Lu[tBu4Pc]2+) and anion (Lu[tBu4Pc]2-), respectively. Upon reduction of Lu[tBu4Pc]2, the transfers of alkali metal cations from W to OCT have been studied for the first time, enabling estimation of their Gibbs transfer energies. For kinetic measurements, a thin-film electrode configuration has been used, consisting of the same electrode covered completely with a thin layer of OCT that contained the redox probe and a suitable electrolyte. Combining the fast and sensitive square-wave voltammetry with thin-film electrodes, the kinetics of ClO4-, NO3- and Cl- transfers have been estimated