Electrochemistry and thermodynamics of EuCl₃ and EuCl₂ in alkali chloride melts

The electrochemical redox process Eu(III) + e^- ↔ Eu(II) in NaCl-KCl, KCl and CsCl melts in the temperature range 973-1123K on glassy carbon electrodes was studied by linear sweep voltammetry and cyclic voltametry. It was determined that in alkali chloride melts at a polarization rate of ν≤0.1 V s^-1, the electroreduction of Eu(III) to Eu(II) was reversible, but at 0.1<ν≤0.3 V s^-1, a mixed diffusion and electron-transfer control was observed. The diffusion coefficients of Eu(III) and Eu(II) were determined by linear sweep voltammetry. The standard rate constants for the reduction of Eu(III) to Eu(II) were calculated on the basis of cyclic voltammetry data. The formal standard potentials of E^*_Eu(II)/Eu in alkali chloride melts were obtained by open-circuit potentiometry. (author)