Electrochemical Behavior of Neptunium in NaCl–2CsCl Melt

Abstract

The electrochemical behavior of neptunium in NaCl–2CsCl melt at 823–923 K was investigated by cyclic voltammetry, differential pulse voltammetry, and open-circuit chronopotentiometry after polarization. The results show that Np4+ ions are reduced to Np metal by a two-step mechanism via Np3+ ions in the NaCl–2CsCl melt. The diffusion coefficients of Np3+ and Np4+ ions were determined from cyclic voltammograms. The apparent standard potentials of Np3+/Np0 and Np4+/Np3+ redox couples have been determined to be E*(Np3+/Np0) = −3.353 + 7.67 × 10−4 T and E*(Np4+/Np3+) = −1.175 + 4.99 × 10−4 T vs. Cl2/Cl− (V), respectively. The activity coefficients of Np3+ and Np4+ ions were also determined using the reported data on the Gibbs free energy of formation for NpCl3 and NpCl4 in a supercooled liquid state.

Keywords

• np
• molten salt
• electrochemistry
• reduction