Charge transfer at electrode surfaces with an insulating film in high-temperature molten salts

Molten salt electrochemistry has been widely applied in fields such as electrochemical metallurgy, nuclear material processing, and low carbon techniques. The metal or carbon electrode are generally used as working electrode to reveal the electrochemical reaction mechanism or measure the reaction kinetics. However, these electrodes in high-temperature molten salts may suffer corrosion or oxidation due to the harsh environment, which resulted in errors in electrochemical measurements. In most cases, an insulating film was formed on the electrode surface. Herein we showed the influence of an insulating film on the electrochemical signals based on the experimental tests and numerical simulations. The apparent reaction kinetics gradually became sluggish with the increasing film resistance. The ultra-high film resistance led to the linear potential-current behavior during cyclic voltammetry. Moreover, several typical molten salt electrochemical systems with the existence of an insulating film have also been discussed.