Cathodic behavior of graphite in KF-AlF₃-based melts with various cryolite ratios

摘要

The cathodic behavior of graphite in KF-AlF₃-based melt with various cryolite ratios (CR; molar ratio of KF to AlF₃) were investigated by means of cyclic voltammetry, sampled-current voltammetry, and chronopotentiometry. The limiting current of aluminum deposition and critical current density of potassium intercalation on graphite cathode in KF-AlF₃-based melt decreased with the increase of CR of the melt. Lowering the CR of KF-AlF₃-based melt suppressed the potassium intercalation but enhanced the formation of aluminum carbide. In the KF-AlF₃-based melt with CR of 1.0, formation of Al₄C₃ seriously occurred, which resulted not only from the chemical reaction of aluminum and carbon but also from the electrochemical reduction of carbon under higher overpotential. However, both the X-ray diffraction and scanning electron microscopy failed to detect the existence of potassium–graphite intercalation compound and Al₄C₃ in the resultants after galvanostatic electrolysis.