ZrO2 Solid Electrolyte Aided Investigation on Electrodeposition in Na3AlF6-SiO2 Melt
Received date: 2021-03-21
Revised date: 2021-04-30
Online published: 2021-09-17
Supported by
National Natural Science Foundation of China(51174148)
Electrodeposition of silicon from a cryolite-based melt is a possible solution for the mass production of silicon with high purity. Currently, deposition of Si from dissolved SiO2 in cryolite-based melts occurs primarily in a graphite crucible using graphite and quasi-reference electrodes, resulting in series of problems, such as CO x emissions due to carbon participation, non-significant peak positions on cyclic voltammetry (CV) curves due to melt electronic conduction, various reference standards of metal deposition potential, and insufficient investigations on electrode reaction mechanism due to melt composition complexity. In this work, a novel three-electrode electrochemical cell with Pt, O2(air)|YSZ reference (RE), and counter electrodes (CE) was constructed using a Y2O3 stabilized ZrO2 solid electrolyte (YSZ) tube, CV and potentiostat electrolysis tests were performed on Ir wire working electrode in Na3AlF6-5%SiO2 (mass fraction) melt under the conditions of a complete carbon-free and 1323 K. The precipitation potentials of related metals on the cathode in the melt were investigated, and the electrodeposition law in the melt at different potentials was analyzed, using a combination of thermodynamic theoretical calculations, SEM observation, and EDS analysis. The results show that Si can be deposited on the Ir wire in a single step, and its peak potential is about -1.65 V on the CV curve, while the deposition potentials of Al, Na (Zr) are all negative than -1.8 V and increase negatively in turn. During potentiostatic electrolysis, intermetallic compound particles of Zr5Si4 are observed to generate at -1.8 V or -2.0 V, with a generation potential of -1.7 V to -1.8 V. The deposited Si, Al, and Na metals are mainly derived from oxygen-containing compounds produced by the Na3AlF6-SiO2 melt itself but Zr metal from the ZrO2 of the corrosion of YSZ tubes by the melt. The precipitation potentials of related metals (or intermetallic compounds) relative to Pt, O2(air)∣YSZ RE agree well with thermodynamic calculations.
Key words： silicon; silica; cryolite; zirconia solid electrolyte; electrodeposition
Yunming GAO , Lin HE , Qingwei QIN , Guangqiang LI . ZrO2 Solid Electrolyte Aided Investigation on Electrodeposition in Na3AlF6-SiO2 Melt[J]. Acta Metall Sin, 2022 , 58(10) : 1292 -1304 . DOI: 10.11900/0412.1961.2021.00132
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