Electrochemical behaviour of americium ions in LiClKCl eutectic melt

International audienceThis work presents a study on the electrochemical properties of AmCl3 in a molten LiClKCl eutectic, at a temperature range of 733833 K. Transient electrochemical techniques, such as cyclic voltammetry and chronopotentiometry, on inert metallic tungsten working electrode have been used to investigate the reduction mechanism of Am3+ ions. The results show that Am3+ is reduced to Am metal by a two-step mechanism corresponding to the Am3+/Am2+ and Am2+/Am0 transitions. Formal standard potentials of Am3+/Am2+ (E0′ Am3+/Am2+ = -2.695 V versus Cl2/Cl at 733 K) and Am2+/Am0 (E0′ Am2+/Am0 = -2.911 V versus Cl2/Cl at 733 K) redox couples as well as diffusion coefficients of Am3+ and Am2+ (2.4 × 105 and 1.15 × 105 cm2 s1 at 733 K, respectively) have been calculated at three different temperatures. In the studied range of temperature, the DAm3+/DAm2+ ratio was found to be around 2. In addition, thermodynamic properties have been calculated for Am3+ (ΔG∞AmCl3= -933.7 + 0.152 T) and Am2+ (ΔG∞AmCl2= -623.9 + 0.085 T) and compared to thermodynamic reference data in order to estimate activity coefficients (Am3+ = 4.7 × 103 and Am2+ = 2.7 × 102 at 733 K) in the molten LiClKCl eutectic