Electrochemical preparation and spectroelectrochemical study of neptunium chloride complexes in LiCl–KCl eutectic melts

We prepared neptunium chloride complexes electrochemically and performed spectroelectrochemical measurements of neptunium ions in LiCl–KCl eutectic melts at 450 °C, where the neptunium concentrations studied were in the range of 0.1–1 mM. We observed a highly absorbing f – d transition band of Np 3+ at 383 nm, which was used to determine an formal potential of the Np 4+ |Np 3+ redox couple ( E ° ′ = 0.45 V vs. Ag|Ag + ) with a solution of concentration as low as ~0.1 mM. This result agreed well with the value ( E ° ′ = 0.42 V vs. Ag|Ag + ) determined by cyclic voltammetry with a ~15 mM solution.