Characterization of ice electrodes

Abstract

In order to investigate the mechanism of ion transfer across an interface between frozen aqueous and organic phases, a novel ice electrode which consists of the frozen aqueous electrolyte solution has been developed and characterized in 1,2-dichloroethane (DCE) containing various electrolytes. The transfer of tetraethylammonium (TEA+), potassium (K+) and protonated piperidine (Hpip+) cations was studied by cyclic voltammetry at −15.0°C. All the half-wave potentials of these ion transfers shift in the negative direction in the frozen electrolyte system compared with the transfers from the liquid aqueous solution with the same composition at 25.0°C, and some transfers from the frozen phase exhibit slight irreversibility. The degree of the negative shift increases in the order TEA+ < Hpip+ < K+. An interfacial redox reaction between the Fe(III)(CN)3−6Fe(II)(CN)4−6 couple in the frozen aqueous phase and the ferrocene/ferricenium cation couple in the DCE phase was studied at −15.0°C, and the half-wave potential of this reaction (the electron transfer across the interface from the aqueous to the organic DCE phase) was also more negative than that of the liquid aqueous system at 25.0°C. The size of this shift is between those of TEA+ and Hpip+. The shifts in the half-wave potential are discussed in detail, considering a microscopic structure of water molecules near an ion and a network structure of bulk water associated through hydrogen bonds.