Dynamic Reference Electrode development for redox potential measurements in fluoride molten salt at high temperature

Abstract

International audienceMeasurement of redox potential in fluoride media is a major problem due to the difficulty to design a reference electrode with high stability, high mechanical resistance and high accuracy. In the frame of molten salt reactor studies, a dynamic reference electrode (DRE) is developed to measure redox potential in fluoride molten salt at high temperature. DRE is based on the in-situ generation of a transient redox system. The choice of the redox couple corresponds to the cathodic limit of the molten salt considered. As a preliminary step, the demonstration of feasibility of generating a DRE was done in LiF-NaF-KF (46.5–11.5–42 mol%) media at 500 °C. In this salt, the reference redox system generated by coulometry at applied current is KF/K, metallic potassium being electrodeposited on a tungsten wire electrode. The validation of the DRE response and the experimental optimization parameters for DRE generation were realized by following the NiF2/Ni redox potential evolution as a function of NiF2 concentration in the fused salt.The current value applied for DRE generation was optimized. It depends on the amount of metallic cations contained in the fused salt and which can be electrochemically reduced simultaneously during the DRE generation. The current corresponding to the DRE generation has to be 4 times greater than the current corresponding to the reduction of the other elements

Electrochemical Behavior of UO2F2and Its Electrodeposition from UO2F2-FLiNaK Melt

“…1. For FLiNaK melt, except for a couple of the intense peaks (G'/G) appeared near the electrochemical limit of the melt, which corresponding to K + /K, 26 27 However, the potential window range in our experiment was only 3.5V and the andic potential on electrode was far away from the formation potential of F 2 , so the H 1 ' and H 2 ' was hardly related to the oxidation of F − . Besides, in our experiment it was discovered that the Pt electrode was indeed dissolved in the melt with this high andic potential for minutes.…”

Solubility of Cr2O3 in Molten Fluorides with Different ZrF4 Contents and Fluoroacidities

“…There appeared two reduction signals C and D. The cathodic signal D is attributed the cathodic window of this system, which can be assumed to the reduction of one melt component. Based on investigations by Baes 43 and Durán-Klie, 44 the signal D and D' corresponded to the electrodeposition of metal potassium and its dissolution. Hence, in the present study, all potentials referenced to a platinum wire were converted to vs alkalis/alkalis + .…”

Electrolytic reduction of CrF3 and Cr2O3 in molten fluoride salt

“…28,29 All potentials in this paper were measured with respect to this reference electrode and then transferred to vs. K/K + reference electrode according to literature. 30,31 An electrochemical analyzer, AUTOLAB (Ecochemie, NL), was used as the source of signal and for storage of data.…”

“…Evidently, one couple of cathodic/anodic signals D and D ′ corresponding to the deposition and dissolution of one of the melt components can be observed. According to heats of formation data for uorides given by Baes 32 and the investigation of Gabriela, 31 it can be presumed that the signal D corresponds to the electrodeposition of potassium, while the oxidation signal D ′ is attributed to the dissolution of potassium (KF / K, 4.97 V vs. F 2 /F − ; NaF / Na 5.03 V vs. F 2 /F − ; LiF / Li, 5.52 V vs. F 2 /F − at 600 °C). The reduction signal D at −1.85 V vs. Pt is shown in inset from Fig.…”