Mixed-metal (Li, Al) amidoborane: synthesis and enhanced hydrogen storage properties

Abstract

Mixed-metal (Li, Al) amidoborane: synthesis and enhanced hydrogen storage properties AbstractMixed-metal (Li, Al) amidoborane has been synthesized via mechanical ball milling of ammonia borane with lithium hexahydridoaluminate in different molar ratios. The reversible dehydrogenation properties of the thus-synthesized metallic amidoborane and its mixtures with ammonia borane in different ratios were systematically investigated in comparison with neat ammonia borane (AB). On the basis of thermogravimetric analysis and mass spectrometry results, the thus-synthesized mixed-metal amidoborane was shown to release around 10 wt% hydrogen below 200 degrees C, with an effective suppression of volatile side products. Furthermore, a synergistic effect between metallic amidoborane and ammonia borane has been identified, which leads to the release of 9 wt% hydrogen with high purity at 120 degrees C. Additionally, upon treatment with hydrazine in liquid ammonia, the regenerated products from the decomposed Li3AlH6-nAB (n = 4, 5, and 6) composites can release 3.5 wt% hydrogen with high purity, corresponding to an approximate 35%, 30%, and 26% regeneration yield for the post-milled Li3AlH6-nAB (n = 4, 5, and 6) composites, respectively. and ammonia borane has been identified, which leads to the release of 9 wt% hydrogen with high purity at 120 C. Additionally, upon treatment with hydrazine in liquid ammonia, the regenerated products from the decomposed Li 3 AlH 6 -nAB (n ¼ 4, 5, and 6) composites can release 3.5 wt% hydrogen with high purity, corresponding to an approximate 35%, 30%, and 26% regeneration yield for the postmilled Li 3 AlH 6 -nAB (n ¼ 4, 5, and 6) composites, respectively.

Mono- and Bimetalic Amidoboranes

“…11 B NMR spectra of these salts contain a single characteristic signal at ca.´21 ppm (similar to that seen for the parent ammonia borane [18,23,35] On the other hand, the 11 B MAS NMR measurements for the samples in the solid state give one broad peak at about´21 ppm [18,25,29,[38][39][40]43,45]. In Figure 4, we have shown a collection of the 11 B NMR spectra, while, in Table 3, we have listed 11 B NMR chemical shifts and J-coupling constants for various amidoboranes present studied so far.…”

“…On the other hand, several other groups reported for these materials the desorption of hydrogen contaminated with ammonia: α-LiAB [20,25,39,89,90], β-LiAB [20] and NaAB [23,24,87,88,98]. Some amidoborane salts (KAB [25,89], Mg(AB) 2 [29], Al(AB) 3 [35], and LiAl(AB) 4 [35,40]) were reported to desorb pure hydrogen and, currently, there are no contradictory reports. The remaining known amidoborane compounds (RbAB [26], CsAB [26], Sr(AB) 2 [43], Y(AB) 3 [38], LiNa(AB) 2 [39], NaAl(AB) 4 [41], NaMg(AB) 3 [42], Na 2 Mg(AB) 4 [44]) decompose releasing hydrogen contaminated with ammonia, diborane or borazine, all of which are harmful for PEM and alkaline fuel cells.…”

“…Mildly constrained interatomic distances in lithium-sodium amidoborane: N-H: 1.00-1. LiAl(AB) 4 was synthesized by Xia et al via a mechanochemical reaction of Li 3 AlH 6 and ammonia borane [40]. Initially Xia et al used several different molar ratios of the substrates but crystalline product was obtained only when substrates were milled in molar ratio 1:4.…”

“…The milling was performed in a ball mill for 30 min with 30 min breaks. The overall milling time was 3 h [40]. A hypothetical nonbalanced reaction Equation (25) derived from the paper of Xia et al [40] is given below:…”

“…Spectra of Mg(AB) 2 adapted from [16] with permission from Allison L. DeGraffenreid. Spectra of: α-LiAB, NaAB, KAB, RbAB and CsAB adapted from [26]; LiAl(AB) 4 adapted from [40]; and NaMg(AB) 3 adapted from [42], all with permission from The Royal Society of Chemistry. Spectrum of Zn(AB) 2 adapted from [34] with permission from Rafal Owarzany.…”