Electrodeposition of Crystalline Si Using a Liquid Zn Electrode in Molten KF-KCl-K₂SiF₆

In this study, we propose a novel Si electrodeposition method using a liquid Zn electrode in molten KF–KCl. Electrochemical measurements and electrolysis were conducted in a KF–KCl–K₂SiF₆ melt at 923 K. Cyclic voltammograms at a liquid Zn electrode revealed that the reduction currents at 0.75–1.0 V vs K⁺/K were attributed to the formation of Si–Zn liquid alloy. Additionally, Si was deposited through potentiostatic electrolysis at 0.75 V using liquid Zn in a boron nitride (BN) crucible as an electrode. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that deposited Si was located at the bottom and side of the interface between Zn and the BN crucible instead of at the interface between Zn and the molten salt, indicating the electrodeposition of Si attributed to Si–Zn liquid alloy formation. The obtained Si was confirmed to be the crystalline form by X-ray diffractometry, and the maximum grain size was approximately 2 mm. Galvanostatic electrolysis at –20 mA cm⁻² with varying electrical charges showed that the Si grain size increased with increasing charge, confirming the growth of crystalline Si. Finally, the mechanism of Si electrodeposition on a Zn electrode through Si–Zn alloying was discussed

Electrochemical Behavior of Ti(III) Ions in Molten LiF–LiCl: Comparison with the Behavior in Molten KF–KCl

Ti(III) ions has been prepared by the addition of 0.50 mol% of Li2TiF6 and 0.33 mol% of Ti sponge to LiF–LiCl melt, and their electrochemical behavior has been investigated using cyclic voltammetry and square wave voltammetry at 923 K. The reduction of Ti(III) ions to metallic Ti is observed around 1.2 V vs Li+/Li, whereas the oxidation to Ti(IV) ions is observed at 2.78 V as a reversible electrochemical process. The diffusion coefficient of Ti(III) ions is determined to be 3.2 × 10−5 cm2 s−1. The electrochemical behavior of Ti(III) ions in LiF–LiCl melt is compared to that in KF–KCl melt. The potentials for Ti(IV)/Ti(III) and Ti(III)/Ti(0) couples based on the F2/F− potential in LiF–LiCl melt are more positive than those in KF–KCl melt by 0.41 V and 0.31 V, respectively. Such differences in potential are explained by the difference in interactions between Li+–F− and K+–F−

Optimization of electrolysis conditions for ti film electrodeposition from lif-licl eutectic molten salt

PRiME 2020, Honolulu, USA, October 4-9, 2020.The optimum conditions for electrodepositing compact, smooth, and adherent Ti films in LiF–LiCl–Li₃TiF₆ at 823 K were investigated. The Li₃TiF₆ was formed in-situ in the melt via comproportionation reaction between Li₂TiF₆ and Ti powder. The solubility of Li₃TiF₆ was confirmed to be higher than 7.1 mol% by cyclic voltammetry and ICP-AES measurement. Galvanostatic electrolysis was conducted on Ni plate substrates at various concentrations of Li₃TiF₆ (0.55, 2.6, 7.1 mol%) and cathodic current density (50–1200 mA cm⁻²). Ti films with smoother surface were obtained at higher Li₃TiF₆ concentration and lower current density. In the present study, Ti films having the smoothest surface were obtained at 7.1 mol% of Li₃TiF₆ and 50 mA cm⁻²

Electrochemical Synthesis of Diamond in Molten LiCl-KCl-K₂CO₃-KOH

We propose a novel diamond synthesis method based on molten salt electrolysis. In our method, carbon deposition and hydrogen generation occur simultaneously, and hydrogen reacts selectively with carbon atoms that possess sp² hybrid orbitals to form CH₄ gas. Therefore, only carbon with sp³ hybrid orbitals grows to form a diamond. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy analysis confirmed that diamond was synthesized by potentiostatic electrolysis at 1.1 V vs Li⁺/Li with a 10 C cm⁻² charge density in molten LiCl–KCl–K₂CO₃–KOH at 973 K

Effects of Temperature, Ti(III) Ion Concentration, and Current Density on Electrodeposition of Ti Films in LiF-LiCl Melt

The effects of temperature, Ti(III) ion concentration, and current density on the electrodeposition of Ti films were investigated in the eutectic LiF–LiCl melt at 823–973 K. The Ti(III) ions were prepared by adding Li₂TiF₆ and Ti metal to the melt. The diffusion coefficients of Ti(III) were 1.4, 1.8, 2.3, and 3.2 × 10⁻⁵ m² s⁻¹, at 823, 873, 923, and 973 K, respectively. Galvanostatic electrolysis was conducted at 823–973 K. The surface roughness (Sa) of the Ti films decreases with decreasing temperature. Thus, the electrodeposition of Ti films was conducted at the lowest temperature of 823 K with various Li3TiF6 concentrations (0.55–7.1 mol%) and cathodic current densities (50–1200 mA cm⁻²). The Sa was lower at higher Ti(III) ion concentrations and lower current densities. The smoothest Ti films with a Sa of 1.23 μm and a thickness of 10 μm were obtained at a cathodic current density of 50 mA cm⁻² and Li₃TiF₆ concentration of 7.1 mol%

Effect of Temperature on Crystal Structure of W Films Electrodeposited from Molten CsF-CsCl-WO₃

The electrodeposition of W was studied in detail using CsF–CsCl–WO₃. Prior to electrodeposition, the WO₃ solubility was confirmed to be 1.0 mol% at 773 K and increase with temperature. To investigate the effect of temperature on the crystal structure, electrodeposition was conducted at 6–25 mA cm⁻² between 773 and 923 K with a unified charge density of 90 C cm⁻². X-ray diffraction analysis confirmed that the crystal structures of the electrodeposited W films were β-W at 773 and 823 K, a mixed phase (α-W and β-W) at 873 K, and α-W at 923 K. The shape of the crystal grains varied with temperature: grains of β-W obtained at 773 and 823 K were spherical, while those of α-W obtained at 923 K were angular. Scanning electron microscopy observations showed that W films with smoother surfaces were obtained at lower current densities at all temperatures. In particular, a dense and smooth W film (surface roughness: 0.66 μm, thickness: 10 μm) was obtained at 6 mA cm⁻² and 773 K. When the charge density was increased to 210 C cm⁻² at 6 mA cm⁻² and 773 K, a W film with a smooth surface and thickness of 30 μm was obtained

Electrodeposition of Tungsten from Molten KF–KCl–WO₃ and CsF–CsCl–WO₃

PRiME 2020, Honolulu, USA, October 4-9, 2020.The electrodeposition of W films was investigated in KF–KCl eutectic melts after adding 0.5–2.0 mol% of WO₃ at 923 K. Cyclic voltammetry at a Ag electrode suggested that the electrodeposition of W from W(VI) ions proceeds from 1.65 V vs. K/K. Electrodeposition of α-W was confirmed by XRD analysis. The effect of current density and added amount of WO₃ on the morphology of W films was investigated by surface and cross-sectional SEM, which indicated that the best W film having thickness of ca. 15 μm was obtained at 12.5 mA cm⁻² and 2.0 mol% of WO₃. Although the film thickness was increased to ca. 30 μm by increasing the charge density, the surface roughness was significantly increased. To suppress the growth of crystal grains, electrodeposition of W was also investigated in CsF–CsCl eutectic melts at lower temperature of 873 K. The XRD confirmed the existences of both α-W and β-W in the W films. The SEM observations revealed that dense and smooth W films having thickness of ca. 30 μm was successfully obtained

Electrodeposition of Tungsten from Molten KF–KCl–WO3 and CsF–CsCl–WO3

Electrodeposition of W coatings in KF–KCl eutectic melts was investigated after adding 0.5–2.0 mol% of WO3 at 923 K. Cyclic voltammetry at a Ag electrode suggested that the electrodeposition of W from W(VI) ions proceeds from 1.65 V vs K+/K. Electrodeposition of the α-W phase was confirmed by X-ray diffractometry (XRD). The effects of current density and amount of WO3 on the morphology of W coatings were investigated by surface and cross-sectional scanning electron microscopy (SEM). The smoothest W coating with a thickness of ~15 μm was formed at 12.5 mA cm−2 and 2.0 mol% WO3 in KF–KCl eutectic melts. By increasing the charge density, a coating thickness of ~30 μm was attained; however, it significantly increased the surface roughness of the coating. The electrodeposition of W was also performed in CsF–CsCl eutectic melts at a lower temperature of 873 K to suppress the growth of crystal grains. XRD confirmed the existence of both α-W and β-W phases in the W coatings deposited in the CsF–CsCl eutectic melts. SEM analyses revealed the successful formation of dense and smooth W coatings with ~30 μm thickness in the CsF–CsCl eutectic melts

Anodization of electrodeposited titanium films towards TiO2 nanotube layers

Ti films electrodeposited on Ni foils from molten salts were anodized towards TiO2 nanotube formation for the first time. The resulting TiO2 nanotube (TNT) layers were compared with TNT layers prepared under identical conditions on Ti foils by means of scanning electron microscopy (SEM), X-ray diffraction (XRD) measurements, X-ray photoelectron spectroscopy (XPS), and photocurrent measurements. No significant differences were found between the TNT layers prepared on the two different substrates. Electrodeposited Ti films prepared in this way could thus be a viable option for anodization purposes

単一カチオンで構成されるフッ化物–塩化物混合溶融塩からの金属チタン電析

京都大学0048新制・課程博士博士(エネルギー科学)甲第22551号エネ博第402号新制||エネ||77(附属図書館)京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻(主査)教授 野平 俊之, 教授 萩原 理加, 教授 佐川 尚学位規則第4条第1項該当Doctor of Energy ScienceKyoto UniversityDGA