Improved Dehydrogenation Properties of Calcium Borohydride Combined with Alkaline-Earth Metal Amides

Abstract

Promotion of dehydrogenation based on the interaction of [BH4]− and [NH2]− sources has been demonstrated to be one of the most effective approaches in developing an advanced borohydride/amide hydrogen storage combined system. The Ca(BH4)2–2Mg(NH2)2 and Ca(BH4)2–2Ca(NH2)2 composites are thereby synthesized in the present work. It is found that the binary combined systems exhibit an onset dehydrogenation temperature of ∼220 °C, which is ∼100 °C lower than that of pristine Ca(BH4)2. The hydrogen release measurements for Ca(BH4)2–2Mg(NH2)2 and Ca(BH4)2–2Ca(NH2)2 samples below 480 °C show desorption amounts of 8.3 and 6.8 wt % hydrogen, respectively. The dehydrogenation of both samples is accompanied by an ammonia emission of <1.4 mol %. The characterizations such as X-ray diffraction and nuclear magnetic resonance on the postdehydrogenated samples indicate that the dehydrogenation reactions are in the pathways of Ca(BH4)2 + 2 Mg(NH2)2 → 1/3 [Ca3Mg6(BN2)6] + 8 H2 and Ca(BH4)2 + 2 Ca(NH2)2 → 1/3 Ca9(BN2)6 + 8 H2, respectively. Compared with pristine Ca(BH4)2 sample, both possess lower activation energy for dehydrogenation. Further investigation reveals that the interaction of B–H and N–H may be one of main driving forces for dehydrogenation of borohydride/amide combined system.

Promoted hydrogen release from 3LiBH4/MnF2 composite by doping LiNH2: Elimination of diborane release and reduction of decomposition temperature

“…2(f)), which corresponds to the asymmetric stretching vibration of NeH bonds. Compared to pure LiNH 2 , characteristic peaks of NeH bonds in LiNH 2 -doped 3LiBH 4 /MnF 2 composites (including the asymmetric and symmetric stretching vibration peaks) shift towards higher wavenumber, which suggests that that the combination of BH 4 À and NH 2 À has taken place during the doping process [21]. weight losses are summarized and inserted in Fig.…”

Calcium-43 chemical shift and electric field gradient tensor interplay: a sensitive probe of structure, polymorphism, and hydration

“…Regardless, the sensitivity boost afforded by MAS experiments comes at the expense of the removal (or at least in the apparent reduction) of a number of anisotropic interactions, such as magnetic shielding anisotropy and the direct dipole-dipole coupling between NMR-active spins. Although not of significance in the systems studied here, one may envision cases where small J-coupling values (e.g., J( 43 Ca, 17 O)) could potentially be measured using samples enriched in both 43 Ca and 17 O, but this is expected to be very challenging. According to recent reviews of the 43 Ca SSNMR literature, [19][20][21] only a handful of attempts have been made to quantify calcium chemical shift anisotropy (CSA), which is the experimentally-observable form of magnetic shielding anisotropy.…”

Complex Metal Borohydrides: From Laboratory Oddities to Prime Candidates in Energy Storage Applications

“…While the dehydrogenation onset of bulk Ca(BH 4 ) 2 is roughly 320° (290 onset -361 peak ), the binary system Ca(BH 4 ) 2 -2Mg(NH 2 ) 2 (8.3 wt.% H 2 ) and Ca(BH 4 ) 2 -2Ca(NH 2 ) 2 (6.8 wt.% H 2 ) starts to release hydrogen at 220 °C, so that a significant ΔT of 100 degrees is produced. Although some NH 3 release was recorded, XRD study of the final dehydrogenated binary systems indicates Equations (68) and (69) as taking place when heating the samples below 480 °C [ 309 ]. …”

“…The binary systems were prepared by BM (ball-milling technique, 200 rpm, 5 h, Ar) while the nature of the evolved gases was assessed by MS-coupled TPD (temperature-programmed desorption) [ 309 ]. This pattern of destabilization has been reported as well for LiBH 4 -LiNH 2 [ 310 ], NaBH 4 -NaNH 2 [ 311 ], Ca(BH 4 ) 2 -LiNH 2 [ 312 , 313 ], and Ca(BH 4 ) 2 -NaNH 2 [ 313 ] systems, and they all led to new complex hydrides.…”