Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound

Abstract

In order to find out the optimal composition of novel Nd-Mg-Ni alloys for hydrogen storage, the isothermal section of Nd-Mg-Ni system at 400 °C is established by examining the equilibrated alloys. A new ternary compound Nd4Mg80Ni8 is discovered in the Mg-rich corner. It has the crystal structure of space group I41/amd with lattice parameters of a = b = 11.2743(1) Å and c = 15.9170(2) Å, characterized by the synchrotron powder X-ray diffraction (SR-PXRD). High-resolution transmission electron microscopy (HR-TEM) is used to investigate the microstructure of Nd4Mg80Ni8 and its hydrogen-induced microstructure evolution. The hydrogenation leads to Nd4Mg80Ni8 decomposing into NdH2.61-MgH2-Mg2NiH0.3 nanocomposites, where the high density phase boundaries provide a great deal of hydrogen atoms diffusion channels and nucleation sites of hydrides, which greatly enhances the hydriding/dehydriding (H/D) properties. The Nd4Mg80Ni8 exhibits a good cycle ability. The kinetic mechanisms of H/D reactions are studied by Real Physical Picture (RPP) model. The rate controlling steps are diffusion for hydriding reaction in the temperature range of 100 ~ 350 °C and surface penetration for dehydriding reaction at 291 ~ 347 °C. In-situ SR-PXRD results reveal the phase transformations of Mg to MgH2 and Mg2Ni to Mg2NiH4 as functions of hydrogen pressure and hydriding time.

Electrochemical Compression Technologies for High-Pressure Hydrogen: Current Status, Challenges and Perspective

“…Based on this, primary energy sources must be transformed into energy carriers for consumers. Here, hydrogen is a versatile primary energy source that can be converted into other forms of energy through five different approaches, including flame combustion, direct steam production, catalyst combustion [4], chemical reaction (hydrating) [5] and electrochemical conversion (fuel cells) [6]. In addition, based on the conversion efficiency of hydrogen into thermal, mechanical and electrical forms, it is more efficient to convert hydrogen into desired energy forms than other fuels [7].…”

The Mg-Rich Phase NdNiMg15: Structural and Magnetic Properties

“…The Mg-rich corner of many RE-TM-Mg ternary systems (RE = Rare-Earth, TM = Transition Metal) have been also studied for solid hydrogen storage, in order to combine the low weight of magnesium and the catalytic effect of rare-earth and transition metal 13,14,15 . Among these systems one can cite the La-Ni-Mg 15,16 and Nd-Ni-Mg [17][18][19][20][21] systems. The different studies show a decomposition of the intermetallic compounds into MgH2, binary rareearth hydrides (e.g.…”

“…The LPSO phases are long period stacking variants of the structure of hexagonal close-packed (hcp)-Mg and the most frequently observed polytypes crystallizing with a 18R, 14H, or 10H structure. , The RE and Zn atoms are located in some of the layers, and they form Zn 6 RE 8 clusters. The Mg-rich corner of many RE–TM–Mg ternary systems (TM = transition metal) have been also studied for solid hydrogen storage, to combine the low weight of magnesium and the catalytic effect of rare-earth and transition metal. − Among these systems one can cite the La–Ni–Mg , and Nd–Ni–Mg − systems. The different studies show a decomposition of the intermetallic compounds into MgH 2 , binary rare-earth hydrides (e.g., LaH 3 ), and ternary magnesium transition-metal hydrides (e.g., Mg 2 NiH 4 ).…”

Curious Catalytic Characteristics of Al–Cu–Fe Quasicrystal for De/Rehydrogenation of MgH2

“…For hydrogen to become a viable energy carrier, there is a clear need for safe, lightweight, and affordable hydrogen storage media. , This has led to an extensive search for potential hydrogen storage materials. − There is a large number of published results and review articles which reveal that solid state hydrogen storage in the form of hydrides offers high storage capacity and practical operating pressures. ,, Therefore, most of the research on storage is being focused on this type of storage mode. − Magnesium and magnesium based alloys are attractive options, and they have become the center of extensive investigations in recent years. − MgH 2 is considered to be one of the most suitable candidates for hydrogen storage due to its abundance (eighth most abundant element on the earth crust), low cost, nontoxicity, reversibility, and high gravimetric and volumetric hydrogen capacity of 7.6 wt % and 110 g L –1 , respectively. , However, the practical use of magnesium hydride as a hydrogen storage medium has been hindered due to its high thermal stability and sluggish de/rehydrogenation kinetics which makes hydrogen release at moderate temperature very difficult . Also, high temperature (>400 °C) is required for hydrogen de/rehydrogenation processes .…”