Direct electrochemical determination of thermodynamic factors in aprotic binary electrolytes

We propose a novel method to determine the thermodynamic factor of binary salts dissolved in aprotic solvents as a function of salt concentration. The method is based on cyclic voltammetry experiments conducted in a three-electrode cell with the fer-rocene/ferrocenium redox couple being used as an internal standard. The main advantage of this experimental setup is the direct electrochemical determination of the thermodynamic factor from a single type of experiment without the necessity of additional assumptions on other transport parameters. The theoretical derivation of the used relationship between peak/half-wave potentials and the thermodynamic factor as well as non-ideal effects which distort the experimental results, such as uncompensated resistances or concentration overpotentials are discussed in detail. Different strategies are suggested to avoid these non-ideal effects using the peak separation of the cyclic voltammograms as an inherent quality measure for the experimental data. Applicability of the experimental procedure is demonstrated for LiClO₄ in EC:DEC (1:1, w:w) in the range from 5 mM to 2 M and repeated for typical LiPF₆ containing electrolytes. At the end, the obtained results are compared to thermodynamic factors of similar electrolyte solutions published in literature.