Direct electrolytic reduction of solid silicon dioxide in molten LiCl-KCl-CaCl2 at 773 K

We investigated electrolytic reduction of solid SiO2 by a contacting electrode method in molten LiCl-KCl-CaCl2 at 773 K. The results of cyclic voltammetry indicated that reduction of SiO2 occurs at potential more negative than 0.85 V (vs Ca2+, Li+/Ca-Li). Samples were prepared by potentiostatic electrolysis for 2 h at 0.25, 0.50, 0.70, and 1.00 V. Energy dispersive X-ray analysis and Raman spectra clarified that the reduction products at 0.50 and 0.70 V are composed of amorphous Si and microcrystalline Si. Scanning electron microscope (SEM) observations revealed that the morphology of the produced Si is spongelike with a particle size smaller than 50 nm. The mechanism of Si formation was discussed by comparing the SEM observations and the Raman spectra of the Si samples prepared at 773 and 1123 K. The reduction mechanism of the direct electrolytic reduction of SiO2 at lower temperature was also discussed. (c) 2005 The Electrochemical Society.