Oxide Monitoring in Molten NaCl–KCl with Stationary and Rotating Electrodes: A Comparative Study of Au, Pt, W, and Ni

Accurate measurement of oxide concentration in molten chloride salts is essential for mitigating impurity-driven corrosion and experimental drift in molten salt experiments and applications. Most reported electrochemical methods have been developed for quiescent baths with stationary working electrodes (WEs) and Ag/AgCl reference electrodes (REs). Here, we evaluate an in-situ oxide sensor with both stationary and rotating WEs to assess the sensitivity and responsiveness of electrochemical sensors to changes in oxide concentrations and flow conditions. Experiments were performed in the eutectic NaCl–KCl system using a Ni/NiO RE and four WEs: nickel, gold, platinum, and tungsten. We compare sensor performance with stationary and rotating WEs and quantify the signal responsiveness and sensitivity of different WEs to oxides. Tungsten and gold exhibited the lowest detection limits, reaching approximately 51 ppm and 143 ppm O 2 − (w/w), respectively, while platinum and nickel required higher oxide concentrations to produce stable responses. The WE material substantially impacts sensitivity, with W providing the strongest response. Overall, this work furthers the development and improvement of monitoring of oxide concentration in quiescent and flowing molten salt systems relevant to molten-salt reactors and related high-temperature electrochemical processes.