Silicon Electrodeposition in Water-Soluble KF–KCl Molten Salt: Investigations on the Reduction of Si(IV) Ions

Abstract

A new method for electroplating Si using a water-soluble KF-KCl molten salt electrolyte and high-purity gaseous SiCl 4 has been proposed. To gain a fundamental understanding of the process, the electrodeposition of Si from Si(IV) complex ions on a Ag electrode in a molten KF-KCl-K 2 SiF 6 system was investigated by cyclic voltammetry at 923 K. The reduction of Si(IV) ions to metallic Si was observed as a single 4-electron wave, which is explained by an E q E r (quasireversible-reversible electron transfer reactions) mechanism. The diffusion coefficient of the Si(IV) ions in the electrolyte was determined to be 3.2 × 10 −5 cm 2 s −1 at 923 K by chronoamperometry.

Editors' Choice—Silicon Electrodeposition in a Water-Soluble KF–KCl Molten Salt: Utilization of SiCl4as Si Source

“…· f Ar [13] where R is the gas constant, and P 0 is the ambient atmospheric pressure (1.013 × 10 5 Pa). The above relationships are valid only when the gas is ideal, and the evaporation is fast enough to reach equilibrium.…”

“…The working electrodes were Ag wire (Nilaco Corp., diameter: 0.1 mm, 99.98%) and Ag flag electrodes (Nilaco Corp., thickness: 0.1 mm, 99.98%). 13 A glass-like carbon rod (Tokai Carbon Co., Ltd., diam. : 5.0 mm) was used as the counter electrode.…”

“…1), with the aim of developing a new method for the production of polycrystalline Si films for solar cells. [12][13][14] In this process, gaseous SiCl 4 is dissolved into the molten salt to form Si(IV) complex ions. Si films are then electrodeposited onto the cathode of an appropriate substrate, and Cl 2 gas is evolved at a carbon anode.…”

Electrodeposition of Titanium in a Water-Soluble KF–KCl Molten Salt

“…rod (Tokai Carbon Co., Ltd., diameter: 3.0 mm). The structure of the Ni ag electrode was reported in our previous paper 21) . In order to remove the oxide lm before usage, a Ni plate for electrodeposition was electropolished in 50 mass% sulfuric acid at 200 mAcm −2 for 10 s, dipped in aqueous solution containing sodium bi uoride, and followed by washing in hydrochloric acid of pH = 4.0, at room temperature.…”

“…For example, LiF is produced according to the reaction, KF + LiCl → LiF + KCl. In a previous study by our group 21) , compact and smooth Si lms were electrodeposited in KF-KCl-K 2 SiF 6 and the solidi ed salt was easily removed by water washing alone.…”