Electrode reaction of plutonium at liquid cadmium in LiCl–KCl eutectic melts

The electrode reaction of the Pu3+/Pu couple at the surface of a liquid Cd electrode was investigated by cyclic voltammetry at 723, 773 and 823 K in LiClKCl eutectic melt. It was found that the diffusion of Pu3+ in the salt phase was a rate-determining step in the cathodic reaction, but the dissolution of Pu from the liquid Cd phase was so slow that the anodic wave broadened slightly. The redox potentials of the Pu3+/Pu couple at the liquid Cd electrode at 723, 773 and 823 K were observed at more positive potentials, 0.299, 0.269 and 0.239 V, respectively, than those at a solid Mo electrode. This potential shift was thermodynamically analyzed by a lowering of activity of Pu in the Cd phase due to the formation of the alloy PuCd6 at the interface. As well as the Gibbs energy of formation of PuCd6, the Gibbs energies of formation of the other intermetallic compounds PuCd2 and PuCd4 could also be estimated by the analysis of the anodic peaks in cyclic voltammograms of the Pu3+/Pu redox couple at a Cd-coated Mo electrode.