In Situ Monitoring of Molten Chloride Salt Chemistry and Corrosion Using a Microelectrode

This study investigated, for the first time, the applicability of a borosilicate glass-coated tungsten microelectrode for in situ monitoring of localized surface electrochemical processes, such as corrosion. The diffusion of Eu³⁺ ions was analyzed via cyclic voltammetry from 400 to 550 °C. The microelectrode consistently overestimated diffusion coefficients compared to the macroelectrode results due to additional intrinsic glass electrode current (IGEC) originating from the borosilicate glass coating, as confirmed by EIS. Further analysis revealed that the effective capacitance of the borosilicate glass increases with temperature, and corrected diffusion values were obtained after subtracting the IGEC. To assess the microelectrode's performance for novel high-temperature scanning electron-chemical microscopy applications, approach curve tests were conducted near insulating alumina and corroding Ni-20Cr surfaces. The current response depended strongly on approach speed and temperature. Approaching the insulating alumina at lower temperatures and faster speeds induced artifacts likely from convection-driven interference and limited ionic mobility. Near the corroding Ni-20Cr surface, slower approach speeds enhanced deposition effects at more negative potentials. Additionally, time-dependent OCP profiling near Ni-20Cr captured the evolution of local redox potential gradients. These results emphasize the need to carefully optimize operational parameters and highlight the potential of microelectrodes for localized electrochemical measurements in molten salt environments.