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Lightweight Intermetallics with Laves Structures as Potential Hydrogen Storage Materials.

机译：具有Laves结构的轻金属间金属化合物作为潜在的储氢材料。

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摘要

Hydrogen storage was identified by the US Department of Energy as a "grand challenge" for the implementation of hydrogen-powered fuel cell vehicles for reduced CO2 emissions from transportation vehicles. None of the hydrogen storage options currently developed can satisfy the high gravimetric, volumetric and system design requirements. Intermetallic compounds with Laves structures in the formula of AB2 have long been known to store hydrogen in their interstitial sites to serve as reversible hydrogen storage materials (A and B are metallic elements). They have the potential to be hydrided to a maximum of ~ AB2H6 due to the impeding H-H interactions at neighboring interstitial sites. To achieve the highest weight percent of hydrogen storage in AB2H6, the lowest combined atomic weight of AB2 is required. The CaLi2 compound is the lightest known Laves phase, but it could not maintain its Laves structure when it was hydrided. Existing work of Akiba's group showed that a ternary Laves phase CaLi1.8Mg0.2 could be hydrided to form a hydrogenated Laves phase, but the absorbed hydrogen could not be released for reversible storage. Substitutions (Ca,X)Li1.8Mg0.2 are explored in the present study to see whether heavier elements [X = Sr, Ba and Ce] in small quantities can make the lightweight Laves compounds reversibly store hydrogen.;Induction melting was successful in obtaining the desired Laves phases. The base system, CaLi1.8Mg0.2, formed a single phase, consistent with the literature result. Both Ca0.9Ba0.1Li 1.8Mg0.2 and Ca0.9Ce0.1Li1.8Mg 0.2 also formed a single-phase C14 Laves, whereas both Ca0.9Sr 0.1Li1.8Mg0.2 and Ca0.8Sr0.2Li 1.8Mg0.2 formed two seperature Laves phases with the same crystal structure, indicating a phase separation. The Ca0.8Ba 0.2Li1.8Mg0.2 composition completely lost the Laves-phase structure, forming CaLi2, CaMg2, BaLi 4 and Ca.;All compounds tested at temperatures from 25 °C to 150 °C show the characteristic "plateau" behavior in the pressure-composition isotherms and the "plateau" pressure decreases with increasing temperature of the adsorption scans, which is opposite to all reversible hydrides indicating non-reversibility and different hydriding mechanisms. When Sr or Ba was added, the plateau pressure decreased with Ba being more potent in the reduction. Cerium (Ce) substitution, on the other hand, increases the plateau pressure. None of the synthesized and tested samples reversibly stored hydrogen.;Post hydriding structure analysis showed that CaH2 was the primary phase observed in the XRD patterns of all compounds, instead of forming the desired hydrogenated Laves phases. When CaLi1.8Mg0.2 was charged with hydrogen, it did not maintain its C14 Laves structure, but forming CaH2 (and very likely also amorphous LiH). This result is contradictory to what was reported in the literature. For Ca0.9Ba 0.1Li1.8Mg0.2, only a small amount of the Laves structure remained with a slighted expaned lattice parameters together with the formation of CaH2 and BaH2. The XRD pattern of hydrogenated Ca0.9Ba0.1Li1.8Mg0.2 sample also showed the presence of LiH. Therefore, none of the materials has formed the desired Laves hydride in significant quantities. Future work, if any, is suggested to perform some B site substitutions with a metal (such as Al) with less affinity with hydrogen.
机译：氢存储被美国能源部确定为实施氢动力燃料电池汽车以减少运输车辆的CO2排放的“巨大挑战”。当前开发的储氢方案均不能满足高重量，体积和系统设计要求。长期以来，人们一直知道具有AB2式Laves结构的金属间化合物会在其间隙位置存储氢，以用作可逆的氢存储材料（A和B是金属元素）。由于相邻间隙位置处的H-H相互作用受阻，它们有可能被氢化至最大〜AB2H6。为了获得AB2H6中最高的储氢重量百分比，需要AB2的最低组合原子量。 CaLi2化合物是已知的最轻的Laves相，但氢化后无法保持其Laves结构。 Akiba小组的现有工作表明，三元Laves相CaLi1.8Mg0.2可以被氢化形成氢化Laves相，但是吸收的氢不能释放出来用于可逆储存。本研究探索了取代基（Ca，X）Li1.8Mg0.2，以查看少量的较重元素[X = Sr，Ba和Ce]是否可以使轻质Laves化合物可逆地存储氢。获得所需的Laves相。基本系统CaLi1.8Mg0.2形成单相，与文献结果一致。 Ca0.9Ba0.1Li 1.8Mg0.2和Ca0.9Ce0.1Li1.8Mg 0.2也形成单相C14 Laves，而Ca0.9Sr 0.1Li1.8Mg0.2和Ca0.8Sr0.2Li 1.8Mg0.2均形成具有相同晶体结构的两个分离的Laves相表示相分离。 Ca0.8Ba 0.2Li1.8Mg0.2组成完全失去Laves相结构，形成CaLi2，CaMg2，BaLi 4和Ca。所有在25°C至150°C的温度下测试的化合物均表现出特征性的“高原”行为在压力-组成等温线中，“平台”压力随吸附扫描温度的升高而降低，这与所有可逆氢化物相反，表明不可逆性和不同的氢化机理。当添加Sr或Ba时，平台压降低，而Ba在还原中更有效。另一方面，铈（Ce）替代会增加平台压力。合成和测试的样品中没有一个可逆地存储氢。氢化后结构分析表明，CaH2是所有化合物的XRD图谱中观察到的主要相，而不是形成所需的氢化Laves相。当CaLi1.8Mg0.2充有氢时，它不会维持其C14 Laves结构，而是会形成CaH2（很可能还会形成无定形LiH）。这个结果与文献报道相矛盾。对于Ca0.9Ba 0.1Li1.8Mg0.2，仅保留少量的Laves结构，并具有轻微的扩展晶格参数以及CaH2和BaH2的形成。氢化Ca0.9Ba0.1Li1.8Mg0.2样品的XRD图谱也显示出LiH的存在。因此，没有一种材料能大量形成所需的拉夫氢化物。如果有的话，建议未来的工作是用对氢的亲和力较小的金属（如Al）进行一些B位取代。

著录项

  • 作者

    Billet, Beau Austin.;

  • 作者单位

    The Ohio State University.;

  • 授予单位 The Ohio State University.;
  • 学科 Materials science.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 102 p.
  • 总页数 102
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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