Liu Yi-Sheng, Jeong Sohee, White James L, Feng Xuefei, Seon Cho Eun, Stavila Vitalie, Allendorf Mark D, Urban Jeffrey J, Guo Jinghua
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
Chemphyschem. 2019 May 16;20(10):1261-1271. doi: 10.1002/cphc.201801185. Epub 2019 Mar 21.
In this article, the capabilities of soft and hard X-ray techniques, including X-ray absorption (XAS), soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and their application to solid-state hydrogen storage materials are presented. These characterization tools are indispensable for interrogating hydrogen storage materials at the relevant length scales of fundamental interest, which range from the micron scale to nanometer dimensions. Since nanostructuring is now well established as an avenue to improve the thermodynamics and kinetics of hydrogen release and uptake, due to properties such as reduced mean free paths of transport and increased surface-to-volume ratio, it becomes of critical importance to explicitly identify structure-property relationships on the nanometer scale. X-ray diffraction and spectroscopy are effective tools for probing size-, shape-, and structure-dependent material properties at the nanoscale. This article also discusses the recent development of in-situ soft X-ray spectroscopy cells, which enable investigation of critical solid/liquid or solid/gas interfaces under more practical conditions. These unique tools are providing a window into the thermodynamics and kinetics of hydrogenation and dehydrogenation reactions and informing a quantitative understanding of the fundamental energetics of hydrogen storage processes at the microscopic level. In particular, in-situ soft X-ray spectroscopies can be utilized to probe the formation of intermediate species, byproducts, as well as the changes in morphology and effect of additives, which all can greatly affect the hydrogen storage capacity, kinetics, thermodynamics, and reversibility. A few examples using soft X-ray spectroscopies to study these materials are discussed to demonstrate how these powerful characterization tools could be helpful to further understand the hydrogen storage systems.
本文介绍了软X射线和硬X射线技术的能力，包括X射线吸收（XAS）、软X射线发射光谱（XES）、共振非弹性软X射线散射（RIXS）、X射线光电子能谱（XPS）和X射线衍射（XRD），以及它们在固态储氢材料中的应用。这些表征工具对于在从微米尺度到纳米尺寸的基本相关长度尺度上研究储氢材料是必不可少的。由于纳米结构现在已被公认为是改善氢释放和吸收的热力学和动力学的途径，这是由于诸如降低的平均自由程传输和增加的表面积与体积比等特性，因此明确识别纳米尺度上的结构-性能关系变得至关重要。X射线衍射和光谱是探测纳米尺度上尺寸、形状和结构相关材料性能的有效工具。本文还讨论了原位软X射线光谱池的最新进展，它能够在更实际的条件下研究关键的固/液或固/气界面。这些独特的工具为氢化和脱氢反应的热力学和动力学提供了一个窗口，并有助于在微观层面定量理解储氢过程的基本能量学。特别是，原位软X射线光谱可用于探测中间物种、副产物的形成，以及形态变化和添加剂的影响，所有这些都可能极大地影响储氢容量、动力学、热力学和可逆性。文中讨论了一些使用软X射线光谱研究这些材料的例子，以展示这些强大的表征工具如何有助于进一步理解储氢系统。
