LaNi5-Assisted Hydrogenation of MgNi2 in the Hybrid Structures of La1.09Mg1.91Ni9D9.5 and La0.91Mg2.09Ni9D9.4

Energies

Roman V. Denys¹  Volodymyr A. Yartys¹  Evan MacA. Gray²  Colin J. Webb² 

[1] Institute for Energy Technology, P.O. Box 40, Kjeller NO 2027, Norway; E-Mail:;Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan 4111, Brisbane, Australia; E-Mails:

关键词: in situ studies;    neutron powder diffraction;    metal hydrides;    lanthanum;    magnesium;   

DOI  :  10.3390/en8043198

来源: mdpi

【 摘 要 】

This work focused on the high pressure PCT and in situ neutron powder diffraction studies of the LaMg₂Ni₉-H₂ (D₂) system at pressures up to 1,000 bar. LaMg₂Ni₉ alloy was prepared by a powder metallurgy route from the LaNi₉ alloy precursor and Mg powder. Two La_3−xMg_xNi₉ samples with slightly different La/Mg ratios were studied, La_1.1Mg_1.9Ni₉ (sample 1) and La_0.9Mg_2.1Ni₉ (sample 2). In situ neutron powder diffraction studies of the La_1.09Mg_1.91Ni₉D_9.5 (1) and La_0.91Mg_2.09Ni₉D_9.4 (2) deuterides were performed at 25 bar D₂ (1) and 918 bar D₂ (2). The hydrogenation properties of the (1) and (2) are dramatically different from those for LaNi₃. The Mg-containing intermetallics reversibly form hydrides with ΔH_des = 24.0 kJ/mol_H2 and an equilibrium pressure of H₂ desorption of 18 bar at 20 °C (La_1.09Mg_1.91Ni₉). A pronounced hysteresis of H₂ absorption and desorption, ~100 bar, is observed. The studies showed that LaNi₅-assisted hydrogenation of MgNi₂ in the LaMg₂Ni₉ hybrid structure takes place. In the La_1.09Mg_1.91Ni₉D_9.5 (1) and La_0.91Mg_2.09Ni₉D_9.4 (2) (a = 5.263/5.212; c = 25.803/25.71 Å) D atoms are accommodated in both Laves and CaCu₅-type slabs. In the LaNi₅ CaCu₅-type layer, D atoms fill three types of interstices; a deformed octahedron [La₂Ni₄], and [La(Mg)₂Ni₂] and [Ni₄] tetrahedra. The overall chemical compositions can be presented as LaNi₅H_5.6/5.0 + 2*MgNi₂H_1.95/2.2 showing that the hydrogenation of the MgNi₂ slab proceeds at mild H₂/D₂ pressure of just 20 bar. A partial filling by D of the four types of the tetrahedral interstices in the MgNi₂ slab takes place, including [MgNi₃] and [Mg₂Ni₂] tetrahedra.

【 授权许可】

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