Long-Term Stability of Mullite and Magnesia-encased Ag|Ag+ Reference Electrodes in Molten MgCl2-KCl-NaCl

In this study, the stability of Ag|Ag+ molten chloride reference electrodes was studied using mullite and magnesia tubes as reference electrode membrane materials in molten MgCl2-KCl-NaCl for continuous immersion up to 31 d. Two electrochemical methods were used to characterize the long-term performance of the reference electrodes at 500 °C in an inert atmosphere using a Mg rod as the working electrode: open circuit potential (OCP) and onset of Mg(II) reduction as measured by cyclic voltammetry (CV). There was only a 3% difference between the average OCP measured versus the mullite and MgO reference electrodes. Potential drift was higher for mullite (−1.34 mV d−1) than MgO (0.22 mV d−1). But both drift rates were very low compared to the OCP data standard deviation, indicating that no significant drift was measured for us to 31 d.