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Theoretical design of catalysts for the heterolytic splitting of H-2

机译：H-2杂化裂解催化剂的理论设计

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Here, we briefly review recent advances in H-2 storage technologies relying on mixed proton-hydride and destabilized hydride materials. We establish a general relationship across different materials: the higher the effective H content, the higher the temperatures needed to completely desorb H-2. Nevertheless, several systems show promising thermodynamics for H-2 desorption; however, the desorption kinetics still needs to be improved by the use of appropriate catalysts. Prompted by the importance of heterolytically splitting stable dihydrogen molecules for proton-hydride technologies, we attempt to theoretically design novel H-2 transfer catalysts. We focus mainly on M4NM4H8 catalysts (M = V, Ti, Zr, Hf, and Nm = Si, C, B, N), which should be able to preserve their functionality in the strongly reducing environment of a H-2 storage system. We are able to determine the energy of H-2 detachment from these molecules, as well as the associated energy barriers. In order to optimize the properties of the catalysts, we use isoelectronic atom-by-atom substitutions, vary the valence electron count, and borrow the concept of near-surface alloys from extended solids and apply it to molecular systems. We are able to obtain control over the enthalpy and electronic barriers for H-2 detachment. Molecules with the coordinatively unsaturated > Ti=Si < unit exhibit particularly favorable thermodynamics and show unusually small electronic barriers for H-2 detachment (> 0.27 eV) and attachment (> 0.07 eV). These and homologous ZrSi frameworks may serve as novel H-2 transfer catalysts for use with emerging lightweight hydrogen storage materials holding 5.0-10.4 wt % hydrogen, such as Li2NH,Li2Mg(NH)(2), Mg2Si, and LiH/MgB2 (discharged forms). Catalytic properties are also anticipated for appropriate defects on the surfaces and crystal edges of solid Ti and Zr silicides, and for Ti=Si ad-units chemisorbed on other support materials.
机译：在这里，我们简要回顾了依赖于混合质子氢化物和不稳定的氢化物材料的H-2储存技术的最新进展。我们在不同材料之间建立了一般关系：有效H含量越高，完全解吸H-2所需的温度越高。然而，有几种系统显示出H-2解吸的热力学。然而，仍然需要通过使用合适的催化剂来改善解吸动力学。由于质子氢化技术中杂化分裂稳定的二氢分子的重要性提示，我们尝试从理论上设计新颖的H-2转移催化剂。我们主要关注M4NM4H8催化剂（M = V，Ti，Zr，Hf和Nm = Si，C，B，N），该催化剂应能够在H-2存储系统的强烈还原环境中保留其功能。我们能够确定H-2从这些分子脱离的能量以及相关的能垒。为了优化催化剂的性能，我们使用等电子原子-原子取代，改变价电子数，并从扩展固体中借用近表面合金的概念并将其应用于分子系统。我们能够控制H-2分离的焓和电子屏障。配位不饱和> Ti = Si <单元的分子表现出特别良好的热力学，并且显示出H-2脱离（> 0.27 eV）和附着（> 0.07 eV）异常小的电子势垒。这些和同源的ZrSi骨架可用作新型H-2转移催化剂，可与含有5.0-10.4 wt％氢的新兴轻质储氢材料一起使用，例如Li2NH，Li2Mg（NH）（2），Mg2Si和LiH / MgB2（已释放）形式）。对于固态Ti和Zr硅化物的表面和晶体边缘上的适当缺陷，以及化学吸附在其他载体材料上的Ti = Si ad-units，也预期有催化性能。

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