Measurements and Utilization of Consistent Gibbs Energies of Transfer of Single Ions: Towards a Unified Redox Potential Scale for All Solvents

Abstract

Utilizing the "ideal" ionic liquid salt bridge to measure Gibbs energies of transfer of silver ions between the solvents water, acetonitrile, propylene carbonate and dimethylformamide results in a consistent data set with a precision of 0.6 kJ mol^-1 over 87 measurements in 10 half-cells. This forms the basis for a coherent experimental thermodynamic framework of ion solvation chemistry. In addition, we define the solvent independent ${\mathrm{pe}}_{\mathrm{abs}}^{H_{2}O}$ - and the $E_{\mathrm{abs}}^{H_{2}O}$ values that account for the electronating potential of any redox system similar to the ${\mathrm{pH}}_{\mathrm{abs}}^{H_{2}O}$ value of a medium that accounts for its protonating potential. This $E_{\mathrm{abs}}^{H_{2}O}$ scale is thermodynamically well-defined enabling a straightforward comparison of the redox potentials (reducities) of all media with respect to the aqueous redox potential scale, hence unifying all conventional solvents' redox potential scales. Thus, using the Gibbs energy of transfer of the silver ion published herein, one can convert and unify all hitherto published redox potentials measured, for example, against ferrocene, to the $E_{\mathrm{abs}}^{H_{2}O}$ scale.

Keywords: electrochemistry; ionic liquids; salt bridges; single ion Gibbs transfer energy; thermodynamics.