Development and electrochemistry of a novel Ag/AgCl reference electrode suitable for mixed chloride–fluoride melts

Accurate values of electrode potentials are useful in understanding the electrodeposition of boron from a melt containing fluoride, chloride and fluoroborate, as well as in the determination of the thermodynamic properties of this system. A suitable reference electrode for use with this molten mixture is essential for the determination of these potentials. An Ag/AgCl reference electrode was fabricated for this purpose and its stability, reversibility and polarizability in a melt containing chloride and fluoride were studied in the temperature range 1073–1123 K. Cyclic-voltammograms (CVs) of this melt on a platinum working electrode were recorded at regular intervals over a period of 12 h. These CVs did not show any appreciable variation with time, indicating the stability of this reference electrode. The reversibility of this reference electrode was established by carrying out a micropolarization test. Cathodic and anodic polarization tests were carried out by passing a current of 1 mA and 5 mA through the cell for a duration of 300 s. After these polarization tests, the electrode swung back to its equilibrium potential within about 250 s. Reduction potentials of Fe2+/Fe and Ni2+/Ni couples in the KF–KCl melt were measured for the first time.

Research highlights
► An Ag/AgCl reference electrode for mixed chloride-fluoride melts was developed.
► Non-polarizability, reversibility and stability of the electrode were tested.
► Dependence of emf vs T for Fe/Fe2+ and Ni/Ni2+ couples in KCl–KF melt was reported.