Electrode reaction of the Np3+/Np couple at liquid Cd and Bi electrodes in LiCl–KCl eutectic melts

Abstract

The electrode reactions of the Np 3+ /Np couple at liquid Cd and Bi electrodes were investigated by cyclic voltammetry at 723, 773 and 823 K in the LiCl-KCl eutectic melt. It was found that the diffusion of Np 3+ in the salt phase was the rate-determining step in the cathodic reaction when the concentration of NpCl 3 was less than about 1 wt % and the liquid Cd or Bi phase was not saturated with Np. The redox potentials of the Np 3+ /Np couple at the liquid Cd electrode at 723, 773 and 823 K were observed to be more positive than those at the Mo electrode by 0.158, 0.140 and 0.126 V, respectively. The potential shift results from a lowering of the activity of Np in the Cd phase according to the formation of the NpCd 11 alloy at 723 K and NpCd 6 at 773 and 823 K. The redox potentials of the Np 3+ /Np couple at the liquid Bi electrode at 723, 773 and 823 K were more positive than those at the Mo electrode by 0.427, 0.419 and 0.410 V, respectively, which is attributable to a lowering of the activity of Np in the Bi phase due to the formation of NpBi 2 .