Long-life mullite and boron nitride membranes Ag/AgCl and Pb/PbCl₂ reference electrodes for LiCl-KCl eutectic melt

In the pyrochemical reprocessing of spent nuclear fuel (SNFs), a reference electrode with long life and high stability is extremely important for the electrochemical extraction actinides (An). In this work, Ag/AgCl and Pb/ PbCl2 reference electrodes using boron nitride (BN) and mullite tubes as reference electrode membrane materials in LiCl-KCl eutectic melt at different temperature (723 similar to 773 K) were reported. The stability of reference electrodes immersed in melt for a long time and under electrolysis conditions was systematically studied by different electrochemical methods including cyclic voltammetry (CV), open-circuit chronopotentiometry (OCP) and chronoamperometric (CA). The results showed that BN membrane reference electrodes have excellent ions conductivity and can obtain smooth electrochemical curves. But when it was used for a long time (about 30 h), potential drift would occur. Thus, the stability of the membrane was excellent in short time. On the contrary, the ionic conductivity of mullite membrane reference electrodes was more inferior than that of BN. However, this could be improved as the temperature increased. At the same time, the potential was stable during reference electrodes immersed in melt for 48 h and there was only slight drift (145 h, 80 mV for Ag/AgCl and 40 h, 40 mV for Pb/PbCl2 reference electrodes) under long-term electrolysis, which shows that mullite membrane reference electrodes have extremely high stability and practical application prospects.