Voltammetry measurements in lithium chloride-lithium oxide (LiCl–Li₂O) salt: An evaluation of working electrode materials

Instrumentation to provide process monitoring (PM) and safeguards for the oxide reduction (OR) step in the electrochemical processing of used oxide nuclear fuel is necessary to ensure equipment is operated as declared. Cyclic voltammetry (CV) has been proposed for real-time monitoring of the operation of an OR process for safeguards purposes. In this study, 316L stainless steel (SS), tantalum (Ta), molybdenum (Mo), tungsten (W), platinum (Pt), and iridium (Ir) were evaluated as potential working electrode (WE) materials based on their chemical inertness, corrosion resistance, and sensitivity in detecting lithium oxide (Li₂O) and other chloride salts in the OR electrolyte. Of the electrodes evaluated, 316L SS, Ir, and Pt all performed reasonably well in the lithium chloride-lithium oxide (LiCl-Li₂O) electrolyte. SS was operated in the cathodic potential, had reasonable corrosion resistance, and is relatively inexpensive. Ir could be operated in both the cathodic and anodic potentials and was the most corrosion-resistant of the materials evaluated. Pt is limited to the anodic potential range, had reasonable corrosion resistance, and was the most sensitive to Li₂O concentrations in the salt. In the development of a stand-alone safeguards instrumentation, our recommendation is a CV probe fitted with both Ir and Pt WEs. The results of this study may also be helpful for anode material selection in other electrometallurgy industries, such as molten salt electrolysis.