Silicon Electrodeposition in the KCl–K₂SiF₆–SiO₂ Melt

The methods of electrolytic production of silicon and materials based on it with controlled morphology, particle size, and trace element content are important for the development of new microelectronic and renewable energy devices. In this work, the possibility of silicon production by the electrolysis of the KCl–K₂SiF₆ chloride melt with a low content of fluorine ions using quartz (silicon oxide) as a starting material is studied. Cyclic chronovoltammetry is used to determine the silicon electrodeposition parameters (cathode current density) and the recommended SiO₂ content in the melt, which allows stable electrolysis without electrode passivation. A series of experiments on silicon electrodeposition from the melt using a graphite anode and a graphite cathode is performed at various cathode current densities (10–50 mA/cm²). Silicon deposits are formed, and their composition and morphology are studied by scanning electron microscopy, energy dispersive analysis, and X-ray diffraction analysis. Predominant silicon deposition in the form of fibers with an average diameter of 0.3–0.8 μm and larger particles of an arbitrary shape is observed. As the cathode current density increases, the amount of β quartz in the deposit is found to increase, and its appearance is likely to be caused by the codeposition of potassium in the form of silicides and their subsequent hydrolysis during the separation of salts from the deposit in distilled water. The measurement results are used to propose a method for continuous electrolytic silicon production from quartz; it includes periodic removal of the cathode with a deposit from an electrolysis cell and loading quartz into the melt.