Electrochemical Behavior of Silicon Species in Cryolite Melt

Abstract

Electrodeposition of Si from cryolite based melts is a possible solution for mass production of solar grade silicon. The deposition potential of Si on the candidate cathode, such as graphite, is fundamental information that needs to be measured and applied to restrict the co-deposition of impurities. In this study this potential was measured using cyclic voltammetry. As the activity of SiO 2 in the electrolyte affects the deposition potential, the measurements were carried out in a range of SiO 2 concentrations, allowing the prediction of potential change during the actual deposition process, where the SiO 2 content undergoes fluctuations. The kinetics of the oxidation and reduction reactions were also studied using the recorded voltammograms, showing that reduction of Si is a two steps process controlled by diffusion.

Lunar Soil Simulant Electrolysis Using Inert Anode for Al-Si Alloy and Oxygen Production

“…16 and 17, it has been reported that the reduction of Si (IV) in fluoride molten salt proceeds by a two-step process. 19,[25][26][27][28] Although Si (II) compounds are usually unstable, the existence of some Si (II) compounds such as SiO and SiF 2 were reported in the cryolite-based melts. 28 In this study (NaF-AlF 3 -SiO 2 melt), Si (II) compound (SiF 2 ) is assumed to be formed by reaction 18 and 19.…”

Determination of Cell Potential for Silicon Electrodeposition

“…The detailed experimental procedure is provided in previous publications. [10,26] A typical voltammograms recorded with two different scan rates, in cryolite-5 wt pct SiO 2 at 1313 K (1040°C), is shown in Figure 2. Major cathodic and corresponding anodic peaks form due to Si deposition and re-oxidation.…”

“…The standard decomposition potential of SiO 2 has been calculated from the Nernst's equation as À1.75 V at 1313 K (1040°C). [3,10,11] In most of the researches, graphite has been used as the anode due to its resistance to the corrosive environment of molten salts. Graphite reacts with the evolved O 2 and results in the release of CO and CO 2 on the anode surface.…”

Formation of Si thin films by electrodeposition in ionic liquids for solar cell applications

“…Thin-film solar cells can potentially be fabricated by electrodeposition, which allows the formation of nanostructures over a large area without the use of high-voltage and high-vacuum equipment. Considering these characteristics and the very negative reduction potential of Si together with the high sensitivity of Si precursors to water, Si electrodeposition has recently been attempted in nonaqueous systems such as molten salts, [20][21][22][23][24][25] organic solvents, [26][27][28][29][30] and ionic liquids. [31][32][33] In particular, Yang et al 24) and Zou et al 25) reported the electrochemical formation of photoresponsive Si films and p-n junctions in a CaCl 2 -based molten salt mixture.…”