Investigation of W, Ag, and Pt Quasi-Reference Electrode Stability in Molten NaCl-CaCl₂ with Ce(0)/Ce(III) as an Internal Reference Redox Reaction

Abstract

This work reports on the stability of quasi-reference electrode (QRE) material candidates for use in a NaCl-CaCl2 molten salt eutectic at 823 K in comparison to that of the conventional Ag(I)/Ag reference electrode in a mullite sheath with cyclic voltammetry (CV) and an internal reference of the cerium redox couple (Ce(0)/Ce() via CeCl3 addition). In addition, effects of QRE size, working electrode surface area, and scan rate were investigated for potential QRE candidates. A tungsten rod (1.5 mm) has been determined to be most stable with repeatable results and a long usable life of the QRE materials studied. The stability of the measured current using the tungsten quasi-reference electrode is affected by both scan rate (mV/s) and surface area of the working electrode during the CV technique. In contrast to tungsten, the stability of the platinum wires in this system were considered poor. Silver wire becomes more stable with increasing size.

Communication—The Development of a Stable and Practical Saturated Reference Electrode for Molten Chloride Salt Systems

“…First is the quasi-RE-a bare electrode, often platinum or tungsten, in contact with the system salt-which has limited application in measuring thermodynamic properties due to its instability. 8,9 It is unreliable because the bulk salt composition, including dilute contaminants, influences its potential. The dependency on dilute contaminants makes it difficult to replicate a quasi-RE's potential.…”

Long-Term Stability of Mullite and Magnesia-encased Ag|Ag+ Reference Electrodes in Molten MgCl2-KCl-NaCl

“…Many instances of use of quasi-reference electrodes (QRE) have been reported using bare Pt, W, Ag, and graphite that are simple to fabricate and work adequately well for some electrochemical tests. [7][8][9] However, thermodynamic reference electrodes (TRE) are needed to make accurate potential measurements that can be related to a selected standard state based on a selected specific oxidation/reduction reaction. Consider the Nernst equation as shown in Eq.…”