溶融塩中の反応種を解読する(Decoding reactive species in molten salts)

ad

2024-06-14 オークリッジ国立研究所(ORNL)

オークリッジ国立研究所のチームは、アルミニウム塩化物とカリウム塩化物の高度に反応性のある溶融塩混合物で、振動特性とイオン交換を観察することで化学種の形成を明らかにしました。塩化物塩の混合物は、電池性能を理解するための電気化学研究において重要です。塩化物の塩基性を決定することは、耐食性材料の開発に不可欠です。研究チームはスーパーコンピュータを使用してナノ秒単位の電子レベルのシミュレーションを実行し、反応性種が形成、進化、分解する過程を示しました。振動スペクトルのモデリングにより、塩中の主要なイオン種の分布を他の方法よりも正確に決定し、イオン交換の速度理論を用いて新しい種の形成過程を理解しました。

<関連情報>

反応性溶融塩の平衡に向かう機構論的経路と反応速度を追跡する Tracing mechanistic pathways and reaction kinetics toward equilibrium in reactive molten salts

Luke D. Gibson, Santanu Roy, Rabi Khanal, Rajni Chahal, Ada Sedova  and  Vyacheslav S. Bryantsev
Chemical Science  Published:22 Jan 2024
DOI:https://doi.org/10.1039/D3SC06587A

Abstract

In the dynamic environment of multi-component reactive molten salts, speciation unfolds as a complex process, involving multiple competing reaction pathways that are likely to face free energy barriers before reaching the reaction equilibria. Herein, we unravel intricate speciation in the AlCl3–KCl melt compositions with rate theory and ab initio molecular dynamics simulations. We find that the compositions with 100 and 50 mol% AlCl3 exclusively comprise neutral Al2Cl6 dimers and charged AlCl4 monomers, respectively. In intermediate AlCl3–KCl compositions, the chemical speciation proves to be a very complex process, requiring over 0.5 nanosecond to reach an equilibrium distribution of multiple species. It is a consequence of the competitive formation and dissociation of additional species, including charged Al dimers, trimers, and tetramers. Here, the species formation occurs through ion exchange events, which we explain by computing free energy landscapes and employing a Marcus-like rate theory. We show that both interspecies and intraspecies ion exchanges are probable and are dictated by the local structural reorganization reflected in the change of local coulombic fields. The species distributions are validated by comparing computed Raman spectra and neutron structure factors with the available experimental data. We find an excellent simulation-experiment agreement in both cases. Nevertheless, Raman spectroscopy turns out to be particularly advantageous for distinguishing between unique species distributions because of the distinct vibrational signatures of different species. The mechanistic insight into reaction dynamics gained in this study will be essential for the advancement of molten salts as reactive media in high-temperature energy applications.

溶融塩中の反応種を解読する(Decoding reactive species in molten salts)

0500化学一般
ad
ad
Follow
ad
タイトルとURLをコピーしました