Electrochemical Behavior of Carbonate Ion in the LiF–NaF–Li₂CO₃ System

Abstract

The electrochemical behavior of carbonate ion at a Ni electrode in LiF–NaF–Li₂CO₃ molten salt was investigated using cyclic voltammetry, square wave voltammetry, and chronopotentiometry. The results show that the electrochemical reduction of carbonate ion to carbon is a simple four-electron transfer that occurs in a one-step process. The reduction of carbonate ion at a Ni-wire working electrode is an irreversible process with diffusion-controlled mass transfer. The diffusion coefficient of carbonate ion at 973, 993, 1023, 1043, and 1063 K is 4.46 × 10⁻⁵, 4.82 × 10⁻⁵, 5.31 × 10⁻⁵, 5.90 × 10⁻⁵, and 6.54 × 10⁻⁵ cm² s⁻¹, respectively, and the results obey the Arrhenius law, with an activation energy of 35.8 kJ mol⁻¹. The X-ray diffraction results show that hexagonally structured graphitized carbon can be obtained by potentiostatic electrolysis. Scanning electron microscopy images show that the deposits exhibit a spherical morphology.