High‐Pressure Synthesis of Hydrogen Storage Materials

AbstractDevelopment of safe, efficient, and low‐cost hydrogen storage is a key technological issue that must be realized to generate a hydrogen‐based nonpolluting energy cycle and ultimately a feasible hydrogen economy. Lightweight hydrogen storage is also desired for automotive applications. As hydrogen becomes extremely reactive under high pressure, high‐pressure synthesis is a powerful method for fabricating novel hydrides. In situ synchrotron radiation X‐ray diffraction measurements enable optimal synthetic conditions to be determined quickly. Theoretical calculations can be used to predict the thermodynamic stability of the target material before initiating a high‐pressure synthesis, and they also provide crystallographic and electronic structural information about the target material. This article covers high‐pressure synthetic studies of novel metal hydrides using a cubic‐type multi‐anvil apparatus. The experimental details of high‐pressure generation, hydrogenation of metals under high pressure and high temperature, and in situ synchrotron radiation X‐ray diffraction measurements are presented. Synthetic studies on aluminum‐based interstitial hydrides and lithium‐containing complex hydrides are offered as successful examples of high‐pressure synthesis. Aluminum‐based interstitial hydrides, which were thought to be difficult to obtain, are shown to be accessible using high‐pressure techniques. Theoretically predicted Li4FeH6has been synthesized under high pressure and high temperature. In situ synchrotron radiation X‐ray diffraction measurements reveal the reaction conditions required for its formation and its thermodynamic stability.