Studying the half-cells’ behavior during cyclic voltammetry in NaNO3-KNO3 melts at 240 °C

Abstract

Thermal Energy Storage (TES) systems, particularly those based on nitrate salts are recognized for their significant potential in supporting intermittent renewable sources. Cyclic voltammetry is a powerful and popular electrochemical technique that could be used to regularly monitor the melt and its corrosive impurities. This research takes a step towards a deeper understanding of the electrochemical reactions of the KNO3-NaNO3 system by introducing a novel experimental setup that enables optical visualization of both electrodes and distinguishes between the gases produced at each electrode. The formation of the sparingly soluble sodium oxide at the cathodic peak on the working electrode, as suggested in the literature, could be verified through various cyclic voltammetry ranges and also visually confirmed. The dependency of the anodic oxidation reaction on the preceding cathodic reaction and its relation to the electrode surface regeneration has been also verified. Furthermore, this work demonstrates, using the half-cell setup with gas analysis, that NO is produced at the counter electrode during the cathodic peak, whereas the literature so far assumes mainly NO₂ formation. Based on that, a hypothesis suggests that NO and O2 are produced at the counter electrode during the cathodic peak (C), which would behave differently based on the melt composition. On the other hand, no gases are recorded to be produced at the anodic peak(s).