Research on the Electrochemical Behavior of Si(IV) on the Tungsten Electrode in CaCl2–CaF2–CaO Molten Melt

Abstract

At 1023 K, the electrochemical behavior of Si(IV) on the tungsten electrode in CaCl₂–CaF₂–CaO–SiO₂ molten salt was studied by cyclic voltammetry, square-wave voltammetry and open-circuit chronopotentiometry. The reduction potential of Si(IV) started at –0.68 V, and the intermediate product CaC₂ was observed at –1.78 V. The reduction of Si(IV) on the tungsten electrode was a one-step four-electron transition, which was a diffusion-controlled mass transfer process. The diffusion coefficient for the reduction process of Si(IV) ions was estimated to be 3.22 × 10^–5 cm² s^–1 at 1023 K. With the temperature interval from 993 to 1183 K, the diffusion activation energy was calculated to be 4.425 kJ mol^–1. Moreover, the deposition of Si(IV) occurs when the applied potential is less than –0.6 V (vs. Pt wire). The present electrochemical study on Si(IV) in the molten salt will be a theoretical reference for future silicon electrorefining.