Zhewen Ma,Qiuyu Zhang,Subrata Panda,Wen Zhu,Fengzhan Sun,Darvaish Khan,Jinjian Dong,Wenjiang Ding,Jianxin Zou
Nano-confinement (NC) of Mg/MgH2 in suitable host materials is a promising strategy for simultaneously tuning the thermodynamics and kinetics of Mg-based hydride materials. In the present study, the fabrication of multifunctional host materials for NC of MgH2 was firstly attempted with the aim of improving the hydrogen sorption properties of MgH2. The NC of MgH2 in the mesoporous structure of a Ni-based metal–organic-framework (denoted as MgH2@Ni-MOF) was successfully conducted via a combination of solvothermal method and wet impregnation method followed by hydrogenation at relatively lower temperatures. Structural inspections through X-ray diffraction and high resolution transmission electron microscopy demonstrate the in situ formation of Mg2NiH4 around the MgH2 nanocrystals (∼3 nm), due to the reaction between Ni ions from the Ni-MOF and Mg ions from the dibutyl-magnesium (MgBu2) precursor in a hydrogen atmosphere. Hydrogen sorption tests reveal that the thermodynamics (−65.7 ± 2.1 and 69.7 ± 2.7 kJ mol−1 H2 for ab-/desorption, respectively) and kinetics (41.5 ± 3.7 and 144.7 ± 7.8 kJ mol−1 H2 for ab-/desorption, respectively) of Mg/MgH2 in the MgH2@Ni-MOF composite have been significantly improved. Meanwhile, the Ni-MOF scaffold acts as an “aggregation blocker” to impede the growth and agglomeration of Mg/MgH2 nanocrystals during hydriding/dehydriding cycles, leading to outstanding hydrogen cycling stability. The improvement in thermodynamics and kinetics of MgH2@Ni-MOF has been attributed to the synergistic “nanosize effect” of nanoconfined Mg/MgH2 and catalytic effects from in situ formed Mg2Ni/Mg2NiH4.
Linglong Yao,Xuanyu Lyu,Jiguang Zhang,Yana Liu,Yunfeng Zhu,Huaijun Lin,Yao Zhang,Liquan Li
Nanostructuring and catalyzing are effective methods for improving the hydrogen storage properties of MgH 2 . In this work, transition-metal-carbides (TiC, ZrC and WC) are introduced into Mg–Ni alloy to enhance its hydrogen storage performance. 5 wt% transition-metal-carbide containing Mg 95 Ni 5 (atomic ratio) nanocomposites are prepared by mechanical milling pretreatment followed by hydriding combustion synthesis and mechanical milling process, and the synergetic enhancement effects of Mg 2 NiH 4 and transition-metal-carbides are investigated systematically. Due to the inductive effect of Mg 2 NiH 4 and charge transfer effect between Mg/MgH 2 and transition-metal-carbides, Mg 95 Ni 5 -5 wt.% transition-metal-carbide samples all exhibit excellent hydrogen storage kinetic at moderate temperature and start to release hydrogen around 216 °C. Among them, 2.5 wt% H 2 (220 °C) and 4.7 wt% H 2 (250 °C) can be released from the Mg 95 Ni 5 -5 wt.% TiC sample within 1800 s. The unique mosaic structure endows the Mg 95 Ni 5 -5 wt.% TiC with excellent structural stability, thus can reach 95% of saturated hydrogen capacity within 120 s even after 10 cycles of de-/hydrogenation at 275 °C. And the probable synergistic enhancement mechanism for hydrogenation and dehydrogenation is proposed.
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