Belof Jonathan L, Stern Abraham C, Eddaoudi Mohamed, Space Brian
Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, CHE205, Tampa, Florida 33620-5250, USA.
J Am Chem Soc. 2007 Dec 12;129(49):15202-10. doi: 10.1021/ja0737164. Epub 2007 Nov 14.
Monte Carlo simulations were performed modeling hydrogen sorption in a recently synthesized metal-organic framework material (MOF) that exhibits large molecular hydrogen uptake capacity. The MOF is remarkable because at 78 K and 1.0 atm it sorbs hydrogen at a density near that of liquid hydrogen (at 20 K and 1.0 atm) when considering H2 density in the pores. Unlike most other MOFs that have been investigated for hydrogen storage, it has a highly ionic framework and many relatively small channels. The simulations demonstrate that it is both of these physical characteristics that lead to relatively strong hydrogen interactions in the MOF and ultimately large hydrogen uptake. Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction. Previous simulations of hydrogen storage in MOFs and other materials have not focused on the role of polarization effects, but they are demonstrated here to be the dominant contribution to hydrogen physisorption. Indeed, polarization interactions in the MOF lead to two distinct populations of dipolar hydrogen that are identified from the simulations that should be experimentally discernible using, for example, Raman spectroscopy. Since polarization interactions are significantly enhanced by the presence of a charged framework with narrow pores, MOFs are excellent hydrogen storage candidates.
进行了蒙特卡罗模拟，以模拟氢气在一种最近合成的金属有机骨架材料（MOF）中的吸附情况，该材料展现出较大的分子氢吸收容量。这种MOF很引人注目，因为在78 K和1.0个大气压下，考虑到孔内氢气密度时，其吸附氢气的密度接近液氢（在20 K和1.0个大气压下）的密度。与大多数其他已研究用于储氢的MOF不同，它具有高度离子化的骨架和许多相对较小的通道。模拟表明，正是这两种物理特性导致了MOF中相对较强的氢相互作用，并最终实现了大量的氢吸收。从微观角度来看，氢通过三种主要的吸引势能贡献与MOF相互作用：范德华力、电荷-四极矩和感应。先前对MOF及其他材料中储氢的模拟并未关注极化效应的作用，但在此处证明极化效应是氢物理吸附的主要贡献。实际上，MOF中的极化相互作用导致了两种不同的偶极氢群体，这是从模拟中识别出来的，应该可以通过例如拉曼光谱等实验方法辨别出来。由于带电骨架和窄孔的存在显著增强了极化相互作用，MOF是优秀的储氢候选材料。
