Xuelian Zhang,Xin Zhang,Lingchao Zhang,Zhenguo Huang,Fang Fang,Yaxiong Yang,Mingxia Gao,Hongge Pan,Yongfeng Liu
Nanoscaled catalysts have attracted much more attention due to their more abundant active sites and better dispersion than their bulky counterparts. In this work, VH x nanoparticles smaller than 10 nm in average size are successfully synthesized by a simple solid-state ball milling coupled with THF washing process, which are proved to be highly effective in enhancing the hydrogen absorption/desorption kinetics of MgH 2 at moderate temperatures. The nano-VH x -modified MgH 2 releases hydrogen from 182 °C, which is 88 °C lower than additive-free MgH 2 . The release of hydrogen amounts to 6.3 wt% H within 10 min at 230 °C and 5.6 wt% H after 30 min at 215 °C with initial vacuum. More importantly, the dehydrogenated MgH 2 +10 wt.% nano-VH x rapidly absorbs 5.2 wt% H within 3 min at 50 °C under 50 bar H 2 . It even takes up 4.3 wt% H within 30 min at room temperature (25 °C) under 10 bar H 2 , exhibiting superior hydrogenation kinetics to most of the previous reports. Mechanistic analyzes disclose the reversible transformation between V and V-H species during the hydrogen desorption-absorption process. The homogeneously distributed V-based species is believed to act as hydrogen pump and nucleation sites for MgH 2 and Mg, respectively, thus triggering fast hydrogenation/dehydrogenation kinetics.
Shun Wang,Mingxia Gao,Zhihao Yao,Kaicheng Xian,Meihong Wu,Yongfeng Liu,Wenping Sun,Hongge Pan
Magnesium hydride (MgH 2 ) is one of the most promising hydrogen storage materials for practical application due to its favorable reversibility, low cost and environmental benign; however, it suffers from high dehydrogenation temperature and slow sorption kinetics. Exploring proper catalysts with high and sustainable activity is extremely desired for substantially improving the hydrogen storage properties of MgH 2 . In this work, a composite catalyst with high-loading of ultrafine Ni nanoparticles (NPs) uniformly dispersed on porous hollow carbon nanospheres is developed, which shows superior catalytic activity towards the de-/hydrogenation of MgH 2 . With an addition of 5 wt% of the composite, which contains 90 wt% Ni NPs, the onset and peak dehydrogenation temperatures of MgH 2 are lowered to 190 and 242 °C, respectively. 6.2 wt% H 2 is rapidly released within 30 min at 250 °C. The amount of H 2 that the dehydrogenation product can absorb at a low temperature of 150 °C in only 250 s is very close to the initial dehydrogenation value. A dehydrogenation capacity of 6.4 wt% remains after 50 cycles at a moderate cyclic regime, corresponding to a capacity retention of 94.1%. The Ni NPs are highly active, reacting with MgH 2 and forming nanosized Mg 2 Ni/Mg 2 NiH 4 . They act as catalysts during hydrogen sorption cycling, and maintain a high dispersibility with the help of the dispersive role of the carbon substrate, leading to sustainably catalytic activity. The present work provides new insight into designing stable and highly active catalysts for promoting the (de)hydrogenation kinetics of MgH 2 .
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