Effects of Al-based additives on the hydrogen storage performance of the Mg(NH2)2–2LiH system

Abstract

The Mg(NH2)2-2LiH composite is a promising hydrogen storage material due to its relatively high reversible hydrogen capacity (~5.6 wt%) and suitable thermodynamic properties that allow hydrogen sorption conducting at temperatures below 90 °C. However, the presence of a severe kinetic barrier inhibits its low-temperature operation. In the present work, Li3AlH6 was introduced to the Mg(NH2)2-2LiH system. Experimental results show that a 3.2% mol Li3AlH6-modified Mg(NH2)2-2LiH sample released hydrogen at a rate ca. 4.5 times as fast as that of the Li3AlH6-free sample at 140 °C. The enhancement of desorption kinetics was simultaneously demonstrated by activation energy (Ea) of ca. 96.3 ± 9 kJ mol(-1) which was significantly decreased by 31 kJ mol(-1) from that of the Li3AlH6-free sample. The interaction of Li3AlH6 and Mg(NH2)2 during ball milling results in the formation of LiAl(NH)2, LiNH2 and Mg3N2. LiAl(NH)2 was actually the active species for the enhancement of dehydrogenation/re-hydrogenation kinetics of the system.

Enhanced hydrogen storage properties of 1.1MgH2–2LiNH2–0.1LiBH4 system with LaNi5-based alloy hydrides addition

“…The N-H weakening acts as an important role in the reduction of desorption barrier and the kinetics enhancement. 8,9,24,39,47 This bond weakening effect may be attributed to the interaction between the lone electron pair of the nitrogen atom and the hybrid orbitals of transition metal elements in the LaNi 5 -based alloy. 24,26,48,49 Besides, the homogenously distributed LaNi 5based alloys in the Li-Mg-B-N-H matrix can rene the particles and enhance the hydrogen atom diffusion, which signicantly accelerate the reaction kinetics.…”

Improved overall hydrogen storage properties of a CsH and KH co-doped Mg(NH2)2/2LiH system by forming mixed amides of Li–K and Cs–Mg

“…Following this study, considerable effort has been devoted to improving the hydrogen sorption properties of the Li-Mg-N-H system, including a reduction of the particle size, an adjustment of the composition and the introduction of additives. [16][17][18][19][20][21][22][23][24][25] Specically, alkali metal compounds, including hydrides, halides and hydroxides, were found to be very effective in reducing the operating temperature and enhancing the reaction kinetics of hydrogen storage in a Mg(NH 2 ) 2 /2LiH system. [23][24][25][26][27][28] A rst attempt to improve hydrogen storage properties of the Mg(NH 2 ) 2 /2LiH system by partially substituting LiH with NaH was conducted by Liu et al in 2007.…”

Mild-condition synthesis of A2ZnH4 (A = K, Rb, Cs) and their effects on the hydrogen storage properties of 2LiH-Mg(NH2)2

“…In practical, this composite still needs to be heated to over 180 °C to release a large amount of hydrogen at reasonable rates even after sufficient ball milling, which means that there exsits high kinetic barriers during the de/re-hydrogenation processes [19] . In the past two decades, researchers devoted to reducing the kinetics barriers and found that adding additives is an effective way to improve the kinetics of 2LiH-Mg(NH 2 ) 2 composite [20][21][22][23][24][25] . Transition metal-based additives play an important role in modifying the hydrogen storage properties [24][25][26][27] .…”