ZrO₂ Solid Electrolyte Aided Investigation on Electrodeposition in Na₃AlF₆-SiO₂ Melt

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 COx 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, O-2(air)IYSZ reference (RE), and counter electrodes (CE) was constructed using a Y2O3, stabilized ZrO2 solid electrolyte (YSZ) tube, CV and potentios at electrolysis tests were performed on Ir wire working electrode in Na(3)AIF(6)-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 Na(3)AIF(6)-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, O-2(air)IYSZ RE agree well with thermodynamic calculations.