Copper(I)-copper reference electrode in molten hydroxides

✍ Scribed by Gilberto Schiavon; Sandro Zecchin; G. Giorgio Bombi

• Publisher: Elsevier Science
• Year: 1972
• Weight: 169 KB
• Volume: 38
• Category: Article
• ISSN: 0022-0728
• DOI: 10.1016/s0022-0728(72)80359-0

✦ Synopsis

In recent years, molten hydroxides have aroused a certain interest as solvents. The most extensive contributions are due to Trdmitlon and coworkers 1, who studied the acid base and redox properties of the NaOH-KOH eutectic mixture and investigated the chemical and electrochemical behaviour of several elements in this solvent. These authors 2 adopted as the origin of the potential scale the standard "sodium" [(Na +, K +) (Na, K)] electrode, and proposed for practical use a reference half-cell based on the copper(II)-copper(I) couple in acidic (hydrated) medium. This half-cell has, however, a limited range of applicability, owing to the use of a porous graphite plug to establish electrolytic contact with the experimental solution, and the above authors found it more convenient to use the half-wave potential of the superoxideperoxide couple to establish the origin of the potential scale in voltammetric measurements. The accuracy of the potential values determined in this way is reported as _+_ 30 mV.

Other types of reference half-cells for use in molten hydroxides have been described by Kern and Bloch 3, who employed a gold electrode, the potential of which is probably determined by the gold(III)-gold couple, and by Bonnemay et al. 4, who proposed the use of a silver silver chloride electrode immersed in a chloride-nitrate solution contained in an alumina tube. However, it should be pointed out that the latter authors apparently did not actually test their half-cell in molten hydroxides.

In the present communication, a reference half-cell based on the copper(I) copper couple will be described. This couple was chosen in view of the independence of its potential of the concentration of water in a relatively wide range 5, and was preferred to the copper(II)-copper(I) couple mainly because the concentration of one species only needs to be fixed in order to determine its potential.