Electrochemical Reduction of SiO2 Granules to One-Dimensional Si Rods Using Ag-Si Eutectic Alloy

Abstract

Producing solar grade silicon using an inexpensive method is a key factor in lowering silicon solar cell costs; the direct electrochemical reduction of SiO 2 in molten salt is one of the more promising candidates for manufacturing this silicon. In this study, SiO 2 granules were electrochemically reduced in molten CaCl 2 (850 o C) using Ag-Si eutectic droplets that catalyze electrochemical reduction and purify the Si product. When Ag is used as the working electrode, the Ag-Si eutectic mixture is formed naturally during SiO 2 reduction. However, since the Ag-Si eutectic droplets are liquid at 850 o C, they are easily lost during the reduction process. To minimize the loss of liquid Ag-Si eutectic droplets, a cylindrical graphite container working electrode was introduced and Ag was added separately to the working electrode along with the SiO 2 granules. The graphite container working electrode successfully prevented the loss of the Ag-Si eutectic droplets during reduction. As a result, the Ag-Si eutectic droplets acted as stable catalysts for the electrochemical reduction of SiO 2 , thereby producing one-dimensional Si rods through a mechanism similar to that of vapor-liquid-solid growth.

Transformation of SiO2 Particles to Si Film via Al-Assisted Electrochemical Reduction in Molten CaCl2

“…The growth mechanism was similar to the vapor-liquid-solid (VLS) mechanism although there were no vapor reactants. [23][24][25] Si formed by this process possessed a high purity, but also displayed an irregular morphology that is difficult to control.…”