A New Ammine Dual‐Cation (Li, Mg) Borohydride: Synthesis, Structure, and Dehydrogenation Enhancement

Abstract

A new ammine dual-cation borohydride, LiMg(BH(4))(3)(NH(3))(2), has been successfully synthesized simply by ball-milling of Mg(BH(4))(2) and LiBH(4)·NH(3). Structure analysis of the synthesized LiMg(BH(4))(3)(NH(3))(2) revealed that it crystallized in the space group P6(3) (no. 173) with lattice parameters of a=b=8.0002(1) Å, c=8.4276(1) Å, α=β=90°, and γ=120° at 50 °C. A three-dimensional architecture is built up through corner-connecting BH(4) units. Strong N-H···H-B dihydrogen bonds exist between the NH(3) and BH(4) units, enabling LiMg(BH(4))(3)(NH(3))(2) to undergo dehydrogenation at a much lower temperature. Dehydrogenation studies have revealed that the LiMg(BH(4))(3)(NH(3))(2)/LiBH(4) composite is able to release over 8 wt% hydrogen below 200 °C, which is comparable to that released by Mg(BH(4))(3)(NH(3))(2). More importantly, it was found that release of the byproduct NH(3) in this system can be completely suppressed by adjusting the ratio of Mg(BH(4))(2) and LiBH(4)·NH(3). This chemical control route highlights a potential method for modifying the dehydrogenation properties of other ammine borohydride systems.

Decomposition Mechanism of Zinc Ammine Borohydride: A First-Principles Calculation

“…23, 33 Among these AMBs, As reported in a previous literature study, [Zn(NH 3 ) 2 ][BH 4 ] 2 is able to release 8.9 wt% hydrogen below 115 o C within 15 min without concomitant release of undesirable gases such as ammonia and boranes. 22The dehydrogenation of some of the AMBs may be achieved through combining hydrides from [BH 4 ]and protons from NH 3 , ultimately yielding amorphous metal boronitrides 19,[23][24][25][26][34][35][36]. The experimental observation of the formation of well-crystallized Zn during…”

Metal‐Borohydride‐Modified Zr(BH4)4⋅8 NH3: Low‐Temperature Dehydrogenation Yielding Highly Pure Hydrogen

“…a) MS and b) TG profiles of Zr(BH 4 ) 4 ·8NH 3 -n LiBH 4 (n = 0, 2, 4) at aheating rate of 5 8Cmin À1 underana tmosphereofargon.c)Isothermal dehydrogenation data for Zr(BH 4 ) 4 ·8NH 3 -4 LiBH 4 at various temperatures. [8,11] In addition, it has been reported that DADB was formed on the decomposition of Cr(BH 4 ) 3 ·6NH 3 . [12] Hence, it was assumed that ad ual-cation (Li, Zr) borohydridea mmoniate was first formed by the combination of Zr(BH 4 ) 4 ·8NH 3 andL iBH 4 ,w hicht hen could decompose with formationofD ADB as an intermediate.…”

Immobilization of Aluminum Borohydride Hexammoniate in a Nanoporous Polymer Stabilizer for Enhanced Chemical Hydrogen Storage

“…The conversion of BH 4 into a sp 2 boron species in PSDB-confined Al(BH 4 ) 3 ·6 NH 3 occurred at lower temperatures than for other MBAs; for those, a temperature greater than 300 8C is required to completely consume the BH groups. [14] Motivated by recent examples of the use of hydrazine for the regeneration of dehydrogenated residues of BÀN based hydrides (such as ammonia-borane [15] and lithium amidoborane [16] ), we implemented the same approach for Al(BH 4 ) 3 ·6 NH 3 . After treatment with hydrazine in liquid ammonia, the 11 B NMR signals of decomposed residues of Al(BH 4 ) 3 ·6 NH 3 /PSDB diminished; this was accompanied by the appearance of a broad resonance at 0-30 ppm that corresponds to the superimposition of the BH, BH 2 , and BH 3 signals (Figure 5 a).…”