A cyclic voltammetry study of the electrochemical behavior of platinum in oxide-ion rich LiCl melts

Electrochemical behavior of platinum in LiCl and LiCl-(1-3) wt% Li2O melts at 650 °C was studied by cyclic voltammetry in the context of its use as anode in the direct electrochemical reduction of solid uranium oxide to uranium metal. By CV measurements with graphite and platinum (anodic polarization) and tungsten (cathodic polarization) working electrodes, the decomposition potential of LiCl and electrochemical potential of the reaction Pt + 2LiCl → PtCl2 + 2Li were determined as 3.46 V and 3.14 V respectively. Three anodic reactions viz. (i) formation of Li2PtO3, (ii) oxygen evolution and (iii) platinum dissolution were found to occur on the platinum electrode in Li2O containing LiCl melts. The Li2PtO3 formation was found to be a fast reaction with diffusion coefficient of O2− ions in the melt as 4.53 × 10−7cm2/s. Oxygen evolution showed very high current densities when compared to that of the surface area limiting Li2PtO3 formation. The platinum electrode surface was corroded by formation of Li2PtO3 when the electrode was polarized for a longer period of time in the melt. The results of the study indicated that LiCl-2 wt.% Li2O melt could be the optimum electrolyte composition in the electro-reduction of uranium oxide with platinum anode.