INTERNAL REFERENCE SYSTEMS FOR ELECTROCHEMICAL STUDIES IN MOLTEN SODIUM-FLUORIDE AT 1025-DEGREES-C

The design of reliable reference electrodes for molten fluorides is a major problem, and therefore internal reference systems obtained by in-situ generation of a redox couple were investigated. The Na+/Na, Ni2+/Ni, Mo3+/Mo and Fe2+/Fe couples were examined using convolution voltammetry, and the last of these was selected. Galvanostatic pulses were used to generate ferrous ions at the interface between a solid iron electrode and the electrolyte, and then the current was switched off and the system allowed to relax. The redox system was reversible, the theoretical equations were obeyed and the electrode potential determinations were very reproducible. The potential measured at a given time could be used to check the potential of a classical reference or pseudo-reference electrode in molten NaF at 1025 degrees C within +/-2 mV.