Using Serial Open Circuit Potentiometry to Study Ce and Gd Deposition in Molten LiCl-KCl Eutectic

The ability to electrochemically separate individual species in a pyrochemical reprocessing salt relies on first being able to detect a separation in their reaction potentials. This requires the ability to measure reaction potentials with extreme precision. In this work, we introduce a novel technique called serial open circuit potentiometry (SOCP) and demonstrate its effectiveness at precisely measuring metal deposition reaction potentials. SOCP has several advantages over traditional open circuit potentiometry, including its abilities to quantify the error of measured equilibrium potentials by averaging many individual OCP measurements, determine overpotential deposition nucleation potentials to instrument precision, and simultaneously determine the nucleation and growth mechanism. We tested SOCP by studying molten salt mixtures containing CeCl3, GdCl3, and both CeCl3 and GdCl3 in LiCl-KCl eutectic. We calculated the standard reduction potentials of Ce and Gd deposition and the activity of their nucleation onto W in the LiCl-KCl eutectic. We found Ce and Gd to be electrochemically inseparable under the conditions under which we studied them.