Journal Article Electrolytic Production of Silicon Using Liquid Zinc Alloy in Molten CaCl2

Yasuda, Kouji  ,  Shimao, Takeyuki  ,  Hagiwara, Rika  ,  Homma, Takayuki  ,  Nohira, Toshiyuki

164 ( 8 )  , pp.H5049 - H5056 , 2017-05-04 , Electrochemical Society
A new electrolytic production process for solar-grade Si has been proposed utilizing liquid Si–Zn alloy cathode in molten CaCl2. To establish this process, the behavior of liquid Zn metal in molten CaCl2 at 1123 K was investigated. Evaporation of Zn metal was largely suppressed by immersion in the molten salt, which enabled the use of a Zn electrode despite its high vapor pressure. Cyclic voltammetry results suggested that the reduction of SiO2 on a Zn cathode proceeded at a more negative than 1.45 V vs. Ca2+/Ca. After potentiostatic electrolysis at 0.9 V, Si particles with sizes of 2–30 μm were precipitated in the solidified Zn matrix by a slow cooling process. The rate-determining step for electrochemical reduction of SiO2 on the Zn cathode was discussed on the basis of a measurement of the alloying rate between solid Si and liquid Zn.

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