Improved Hydrogen Storage Properties of LiBH₄ Destabilized by in Situ Formation of MgH₂ and LaH₃

Abstract

A reactive composite of LiBH4–xLa2Mg17 was successfully prepared by means of mechanochemical reaction under 40 bar of H2. It was found that MgH2 and LaH3 were readily formed in situ during high-pressure ball milling, and a strong dependency of hydrogen storage performance of the LiBH4–xLa2Mg17 composites on the content of La2Mg17 was observed. The as-prepared LiBH4–0.083La2Mg17 composite under 40 bar of H2 exhibits superior hydrogen storage properties as ∼6.8 wt % of hydrogen can be reversibly desorbed and absorbed below 400 °C. It was also purposed that the self-decomposition of MgH2 first occurred to convert into Mg with hydrogen release upon dehydrogenation and subsequently catalyzed the reaction of LiBH4 and LaH3 to liberate additional hydrogen along with the formation of LaB6 and LiH. The in situ formed MgH2 and LaH3 provide a synergetic thermodynamic and kinetic destabilization on the de/hydrogenation of LiBH4, which is responsible for the distinct reduction in the operating temperatures of the as-prepared LiBH4–xLa2Mg17 composites.

Hydrogen storage properties and mechanisms of the Mg(BH4)2–NaAlH4 system

“…Specifically, a 27 C reduction is attained in comparison with the pure Mg(AlH 4 ) 2 (128 C), which implies that NaBH 4 may behave as catalyst to reduce the decomposition temperature of Mg(AlH 4 ) 2 . Similar phenomenon was also observed in the LiBH 4 eMgH 2 system [37,38]. In particular, the operating temperatures for the third step dehydrogenation of the post-milled Mg(BH 4 ) 2 e2NaAlH 4 composite are distinctly lower than that of the pure NaBH 4 as it finishes at 520 C while it is 610 C for the pure NaBH 4 (Fig.…”

Towards easy reversible dehydrogenation of LiBH 4 by catalyzing hierarchic nanostructured CoB

“…According to the SEM and TEM observations, the as-synthesized CoB have the following morphologies: (1) [13,25,26,36]. Meanwhile, those CoB remained in either crystal or amorphous structures each matching the as-synthesized ones respectively.…”

“…Obviously, pure hydrogen, without deleterious B 2 H 6 , was released from all CoB doped LiBH 4 during the dehydrogenation process (Figure 2a-e). Significantly, the TPD-MS results revealed an obvious improvement in the dehydrogenation of LiBH 4 by adding CoB, which is better than LiBH 4 doped with metals/ metal oxides/metal halides/metal hydrides [13,14,[17][18][19][20][21][22][23][24][25][26]. The dehydrogenation initiated at around 175 1C and reached its majority at around 350 1C, but the dehydrogenation evolution was different with different morphologies of CoB.…”

“…For examples, only 2.4 wt% hydrogen was released from LiBH 4 at fifth cycle for LiBH 4 -1/3CeCl 3 [23]. By doping metal hydrides, such as H-La 2 Mg 17 and H-Mg 3 La, into LiBH 4 , the hydrogen storage properties can also be improved, but high temperature was still required for dehydrogenation and the reversibility was poor [25,26]. According to above results, the poor reversibility can be attributed to two reasons: one is the ineffective catalyst; the other is that the added dopants actually serve as reactants instead of catalysts which results in formation of by-product including harmful diborane.…”

Hydrogen storage properties of MgH 2 + 20 wt.% Na 2 WO 4 composite

“…However, the high desorption temperature (>400 o C) and poor dehydriding kinetics of MgH 2 prevent the practical applications [3][4][5][6]. In previous studies, extensive researches have been devoted to reduce the onset dehydrogenation temperature and thus, improve the dehydrogenation kinetics of MgH 2 .…”