Stability of a Ni/NiF2 Reference Electrode with a Metallic Membrane for Use in Molten Fluoride Salts

Abstract

In this study, an experimental high-temperature fluoride salt reference electrode (RE) developed by HiFunda LLC was tested in molten FLiNaK at 550 °C. The high-temperature reference electrode (HTRE), based on the Ni/NiF2 redox couple, was tested over a period of 13 d for short-term stability, long-term stability, and electrochemical analysis capabilities. The HTRE was tested using open circuit potentiometry (OCP), cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). The HTRE reference potential was measured against changes in salt composition by increasing FeF2 concentrations in the melt across six additions from 0 to 0.1 mol% FeF2. The long-term stability of the electrode was then tested over ten days at a constant composition of 0.1 mol% FeF2. OCP, SWV, and CV were used to calculate an average potential drift between 7–10 mV per day. Using CV and SWV, the number of electrons transferred for iron reduction and the diffusion coefficient of Fe2+ were measured.