Revisiting the von Neumann–Wigner noncrossing rule and validity of a dynamic correlation diagram method

The noncrossing rule for potential energy surfaces can be applied only, as originally postulated by von Neumann and Wigner, to slowly occurring changes; it has, however, over many years, been widely used to rationalize fast chemical reactions. Taking the conversion of Dewar benzene to benzene as an example, we demonstrate a reaction that has a timescale for which crossings are allowed. Since it is now established that elementary chemical reactions proceed over ca. 10–100fs, as revealed experimentally by Zewail, the noncrossing rule cannot any longer be said to be valid for most chemical reactions. We further demonstrate that the mechanism of the chemiluminescent conversion of Dewar benzene to benzene is explained by an electronic state diagram derived using a dynamic correlation diagram method which allows crossings, whereas the reaction is not explained by a conventional approach, applying the noncrossing rule using a static correlation diagram method

Amide‐Based Ionic Liquid Electrolytes for Alkali‐Metal‐Ion Rechargeable Batteries

Ionic liquids (ILs) have a wide variety of applications in energy storage and material production. ILs are composed of only cations and anions, without any molecular solvents, and are generally known as “designer liquids (solvents)” because their physicochemical properties can be tuned by the combination of ionic species. In recent several decades, research and development activities of rechargeable batteries have garnered considerable attention because certain groups of ILs exhibit high electrochemical stability and moderate ionic conductivity, rendering them suitable for application in high-voltage batteries. ILs with amide anions are representative electrolytes and are extensively researched by many research groups, including our group. This paper focuses on amide-based ILs as electrolytes for alkali-metal-ion rechargeable batteries, introducing their history, characteristics, and existing challenges to be addressed

Electrochemical Production of Silicon

Silicon solar cells are crucial devices for generating renewable energy to promote the energy and environmental fields. Presently, high-purity silicon, which is employed in solar cells, is manufactured commercially via the Siemens process. This process is based on hydrogen reduction and/or the thermal decomposition of trichlorosilane gas. The electrochemical process of producing silicon has attracted enormous attention as an alternative to the existing Siemens process. Thus, this article reviews different scientific investigations of the electrochemical production of silicon by classifying them based on the employed principles (electrorefining, electrowinning, and solid-state reduction) and electrolytes (molten oxides, fluorides, chlorides, fluorides–chlorides, ionic liquids [ILs], and organic solvents). The features of the electrolytic production of silicon in each electrolyte, as well as the prospects, are discussed

Electrodeposition of Molybdenum in LiTFSI-CsTFSI Melt at 150ºC

Electrodepostion of molybdenum was studied in the eutectic LiTFSI-CsTFSI (0.07: 0.93 in mole fraction, m.p., 112ºC) melt at 150ºC. MoCl5 was selected as molybdenum ion sources. Metallic molybdenum was electrodeposited on nickel substrate. Quality of the deposits was improved by using galvanostatic electrolysis and pulsed current electrolysis

<Advanced Energy Utilization Division> Chemical Reaction Complex Processes Research Section

3-1. Research Activities in 202

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−