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A computational study on novel carbon-based lithium materials for hydrogen storage and the role of carbon in destabilizing complex metal hydrides.

机译：新型碳基锂材料用于储氢的计算研究以及碳在使复杂金属氢化物稳定中的作用。

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摘要

One of the major impediments in the way of the realization of hydrogen economy is the storage of hydrogen gas. This involves both the storage for stationary applications as well as that of storage onboard vehicles for transportation applications. For obvious reasons, the system targets for the automotive applications are more stringent. There are many approaches which are still being researched for the storage of hydrogen for vehicular applications. Among them are the high pressure storage of hydrogen gas and the storing of liquid hydrogen in super insulated cryogenic cylinders. While both of them have been demonstrated practically, the high stakes of their respective shortcomings is hindering the wide spread application of these methods. Thus different solid state storage materials are being looked upon as promising solutions. Metal hydrides are a class of solid state hydrogen storage materials which are formed by the reaction of metals or their alloys with hydrogen. These materials have very good gravimetric storage densities, but are very stable thermodynamically to desorp hydrogen at room temperatures. Research is going on to improve the thermodynamics and the reaction kinetics of different metal hydrides.;This dissertation tries to address the problem of high thermodynamic stability of the existing metal hydrides in two ways. First, a novel carbon based lithium material is proposed as a viable storage option based on its promising thermodynamic heat of formation. Pure beryllium (Be) clusters and the carbon-beryllium (C-Be) clusters are studied in detail using the Density Functional Theory (DFT) computational methods. Their interactions with hydrogen molecule are further studied. The results of these calculations indicate that hydrogen is more strongly physisorbed to the beryllium atom in the C-Be cluster, rather than to a carbon atom. After these initial studies, we calculated the geometries and the energies of more than 100 different carbon based lithium materials with varying amounts of hydrogen. A detailed analysis of the heats of reactions of these materials using different reaction schemes is performed and based on the promising thermodynamic and gravimetric storage density, LiC4Be2H5 is divulged as a promising novel carbon based lithium material.;In the later part, this dissertation performs a detailed study on the effect of carbon when it is used as a dopant in four different well known complex hydrides, lithium beryllium hydride (Li2BeH4), lithium borohydride (LiBH4), lithium aluminum hydride (LiAlH 4) and sodium borohydride (NaBH4). Initially, the unit cells of the crystal structure are fully resolved using the plane-wave pseudopotential implementation of DFT. The supercells of each of these are then constructed and optimized. Varying amounts of carbon is introduced as impurity in these crystals in different sites such as the top, subsurface and the bulk of the crystal lattice. Using the electronic structure calculations, it is established that (i) C-Be-H, C-B-H or C-Al-H compounds are formed respectively in the cases of Li2BeH4, LiBH4 and LiAlH4 when carbon is doped in them; (ii) and carbon dopant causes a decrease in the bond strengths of Be-H, B-H and Al-H in respective cases. This reduction in the bond strengths combined with the fact that there is a decrease in the ionic interaction between the cation and the anionic hydride units of these complex hydrides causes a destabilization effect.
机译：实现氢气经济的主要障碍之一是氢气的储存。这涉及固定应用的存储以及运输应用的车载车辆的存储。出于显而易见的原因，汽车应用的系统目标更加严格。有许多方法正在研究用于车辆应用的氢存储。其中包括氢气的高压存储和超绝缘低温钢瓶中的液态氢存储。虽然这两种方法都已得到实际证明，但它们各自缺点的高风险阻碍了这些方法的广泛应用。因此，不同的固态存储材料被视为有希望的解决方案。金属氢化物是一类固态储氢材料，其通过金属或其合金与氢反应形成。这些材料具有非常好的重量存储密度，但是在热力学上非常稳定，可以在室温下脱氢。目前正在进行改善不同金属氢化物的热力学和反应动力学的研究。本文试图以两种方式解决现有金属氢化物的高热力学稳定性问题。首先，基于其有希望的热力学形成热，提出了一种新型的基于碳的锂材料作为可行的存储选择。使用密度泛函理论（DFT）计算方法详细研究了纯铍（Be）簇和碳-铍（C-Be）簇。他们与氢分子的相互作用进一步研究。这些计算结果表明，氢在C-Be团簇中的铍原子更强烈地物理吸附，而不是碳原子。经过这些初步研究，我们计算了100多种不同氢含量的碳基锂材料的几何形状和能量。对这些材料在不同反应方案下的反应热进行了详细的分析，并基于有希望的热力学和重量存储密度，将LiC4Be2H5泄露为有前途的新型碳基锂材料。当碳用作四种不同的复合氢化物，氢化铍锂（Li2BeH4），硼氢化锂（LiBH4），氢化铝锂（LiAlH 4）和硼氢化钠（NaBH4）的掺杂剂时，碳的效果的详细研究。最初，使用DFT的平面波伪电位实现完全解析晶体结构的晶胞。然后，构建并优化其中每个的超级单元。在这些晶体的不同位置（例如，晶格的顶部，子表面和大部分）中，不同数量的碳作为杂质引入。使用电子结构计算，可以确定：（i）当在其中掺杂碳的Li2BeH4，LiBH4和LiAlH4的情况下，分别形成C-Be-H，C-B-H或C-Al-H化合物； （ii）和碳掺杂剂分别导致Be-H，B-H和Al-H的结合强度降低。结合强度的这种降低，加上这些复合氢化物的阳离子与阴离子氢化物单元之间的离子相互作用降低的事实，会导致去稳定作用。

著录项

  • 作者

    Ghouri, Mohammed Minhaj.;

  • 作者单位

    Louisiana Tech University.;

  • 授予单位 Louisiana Tech University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 222 p.
  • 总页数 222
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

  • 入库时间 2022-08-17 11:38:25

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