Preparation And Measurement Of Reference Electrode For Fluoride Molten Salt

High-temperature molten salt is widely used,such as molten salt electrolytic preparation of metals and alloys,extraction and separation of spent fuel by electrolytic refining.However,the high temperature and strong corrosion of molten salt make it difficult to select and establish a stable and reliable reference electrode in molten salt,which results in that there is no uniform reference electrode in fluoride molten salt and fluoride-chlorine mixed molten salt.This work is to prepare a reference electrode suitable for fluoride molten salt system and test its performances.（1）Preparation and characterization of Ni/NiF₂ reference electrode.NiF₂ was directly prepared from the reference salt in an alumina tube by the anodic dissolution Niwire and then a Ni/NiF₂ reference electrode was assembled.The stability of the reference electrode was determined by cyclic voltammetry（CV）in LiF-KF molten salt and the potential deviation was10 mV for 50 h.The reproducibility was measured by square wave voltammetry（SWV）and the potential deviation was 5 mV during multiple cooling and melting processes.Open-circuit chronopotentiometry（OCP）was used to determine its reusability and the potential deviation was 5 mV by multiple experiments.The polarization reversibility was measured by chronopotentiometry method（CP）and the polarization potential was less than 152 mV,and the time to return the potential to equilibrium less than 105 s at±1 mA polarization currents.The temperature reversibility was measured by CP.Under the conditions of 600-700℃,the increasing temperature,the error between the experimental value and the calculated value was1.9%,1.4%and 2.1%,respectively;the decreasing temperature,the error between the experimental value and the calculated value was 1.1%,0.4%,and 2.1%,respectively.（2）Preparation and characterization of Ag/AgF₂ reference electrode.AgF₂ was directly prepared from the reference salt in an alumina tube by the anodic dissolution Agand a Ag/AgF₂ reference electrode was assembled.In LiF-KF molten salt,the stability of the reference electrode was measured by SWV and the potential deviation was 7 mV for 50 h.The reproducibility was measured by CV and the potential deviation was 8 mV during multiple cooling and melting processes.OCP was used to determine its reusability and the potential deviation of the reference electrode was 10 mV by multiple experiments.The polarization reversibility was measured by CP and the polarization potential was less than 872mV,and the time to return the potential to equilibrium was less than 180 s at±2 mA polarization current.The temperature reversibility was measured by CP.Under the conditions of 550-650℃,the temperature rising,the error between the experimental value and the calculated value is 0.4%,0.6%,0.8%,0.4%and 1.5%,respectively;the decreasing temperature,the error between the experimental value and the calculated value was 1.2%,1.0%,0.6%,0.19%and 2.1%,respectively.（3）Preparation and characterization of M/M⁺（M=Liand K）reference electrode.The metal M（M=Liand K）was directly prepared on the tungsten electrode in the alumina tube by molten salt electrolysis,and the reference electrode M/M⁺（M=Liand K）was assembled.The stability of M/M⁺（M=Liand K）reference electrode was determined in LiF-KF,LiF-LiCl and LiCl-KCl molten salts by CV.The potential shifted less than 2 mV for 15 h.The reproducibility of M/M⁺（M=Liand K）reference electrode was determined by CV and the potential deviation by multiple experiments was less than 1 mV.The temperature recovery characteristics of M/M⁺（M=Liand K）reference electrode were also determined by CV.The reference potential changed with the increasing and decreasing temperature of the molten salt;when the temperature of molten salt was restored to its original value,and the potential was quickly restored to its original potential.It was found that the stability and reproducibility of M/M⁺（M=Liand K）reference electrode were not affected by temperature and the amount of alkali metal deposition.