2022-03-30 ローレンス・リバモア国立研究所（LLNL）
・二ホウ化マグネシウム（MgB2）の水素化にかかわる基本的なメカニズムを明らかにするために、分子動力学シミュレーションを行い、マグネシウムイオン（Mg2+）が分子単位の電気分極と電荷の再分配を促進し、元のMgB2材料からホウ素（B）を切り離し、B原子に順次水素結合して水素飽和Mg（BH4）2相を形成させるのに重要であることが判明した。
・具体的には、近傍のMg2+イオンがBHXユニットを分極し、正に帯電した中心のホウ素原子が、Mg2+との相互作用で負に帯電した水素アニオンを引きつけて結合できるようになる。
・この研究は、Applied Materials & Interfaces誌に掲載された。
＜関連情報＞
- https://www.llnl.gov/news/hydrogen-storage-reactions-reveal-complex-dance-toward-faster-uptake
- https://pubs.acs.org/doi/full/10.1021/acsami.1c23524
Ab Initio分子動力学法によるMgB2反応端での水素化化学の解明 Understanding Hydrogenation Chemistry at MgB2 Reactive Edges from Ab Initio Molecular Dynamics
Keith G. Ray*, Leonard E. Klebanoff, Vitalie Stavila, ShinYoung Kang, Liwen F. Wan, Sichi Li, Tae Wook Heo,Mark D. Allendorf, Jonathan R. I. Lee, Alexander A. Baker, and Brandon C. Wood
Applied Materials＆Interfaces Publication Date:March 23, 2022 https://doi.org/10.1021/acsami.1c23524
Abstract
Solid-state hydrogen storage materials often operate via transient, multistep chemical reactions at complex interfaces that are difficult to capture. Here, we use direct ab initio molecular dynamics simulations at accelerated temperatures and hydrogen pressures to probe the hydrogenation chemistry of the candidate material MgB2 without a priori assumption of reaction pathways. Focusing on highly reactive (101̅0) edge planes where initial hydrogen attack is likely to occur, we track mechanistic steps toward the formation of hydrogen-saturated BH4– units and key chemical intermediates, involving H2 dissociation, generation of functionalities and molecular complexes containing BH2 and BH3 motifs, and B–B bond breaking. The genesis of higher-order boron clustering is also observed. Different charge states and chemical environments at the B-rich and Mg-rich edge planes are found to produce different chemical pathways and preferred speciation, with implications for overall hydrogenation kinetics. The reaction processes rely on B–H bond polarization and fluctuations between ionic and covalent character, which are critically enabled by the presence of Mg2+ cations in the nearby interphase region. Our results provide guidance for devising kinetic improvement strategies for MgB2-based hydrogen storage materials, while also providing a template for exploring chemical pathways in other solid-state energy storage reactions.
