Electrochemical study of UO22+-UO2+-UO2 system in molten LiCl+KCl eutectic

Abstract The redox system UO 2 2+ -UO 2 + -UO 2 in LiCl+KCl eutectic has been studied with potentiometry, normal pulse polarography and cyclic voltammetry on glassy carbon and tin oxide electrodes. In the electroreduction of UO 2 2+ taking place in two steps via the intermediate UO 2 + , the standard potential of UO 2 + /UO 2 , E 0 (UO 2 + /UO 2 ), was found to be more positive than E 0 (UO 2 2+ /UO 2 + ; E 0 (UO 2 2+ /UO 2 + )=−0,487 V, E 0 (UO 2 + /UO 2 )=−0.049 V and E 0 (UO 2 2+ /UO 2 )=−0.268 V vs. 1 M Pt(II)/Pt at 450°C (on the molarity scale). The equilibrium constant of the disproportionation reaction (UO 2 2+ +UO 2 =2 UO 2 + ) was calculated at K =10 −3.0 mol dm −3 at 450°C. On the basis of the data presented, a potential-pO 2- diagram of uranium was constructed. Instability of UO 2 + was confirmed by the kinetic study, as well as by thermodynamic considerations. The diffusion coefficients of UO 2 2+ and UO 2 + , and the deposition of UO 2 with and without nucleation overvoltages were also described.