Comparative Study of Structural Changes in NH₃BH₃, LiNH₂BH₃, and KNH₂BH₃ During Dehydrogenation Process

Abstract

The thermal decomposition pathways of ammonia borane (AB, NH 3 BH 3 ), lithium amidoborane (LiAB, LiNH 2 BH 3 ), and potassium amidoborane (KAB, KNH 2 BH 3 ) have been investigated in detail by using solid state 11 B MAS NMR spectroscopy. During the first decomposition process of AB, the complex structural entities were observed, which have been attributed to polyaminoborane (PAB, (NH 2 BH 2 ) n ). On the other hand, polyiminoborane (PIB, (NHBH) n ) formed in the second process showed a single 3-fold coordination III B signal above 125 °C, suggesting a [BN] n network structure. LiAB and KAB did not show the PAB-like structure, and the PIB-like structure was directly formed by the hydrogen desorption. Quantitative analyses of the 11 B NMR spectra suggested that the general route of the thermal decomposition of alkali metal amidoboranes (LiAB, NaAB, and KAB) is similar. Also, 39 K MAS NMR spectra of KAB and its decomposition products indicated the formation of KH and an amorphous K−N−B−H phase during the hydrogen release.

Accelerating the Understanding and Development of Hydrogen Storage Materials: A Review of the Five-Year Efforts of the Three DOE Hydrogen Storage Materials Centers of Excellence

“…Burrell and his colleagues made a unique contribution to this area by demonstrating that classical solution organometallic chemistry synthetic techniques utilizing reactions between metal-alkyls, hydrides, amides, or other bases strong enough to deprotonate ammonia borane could be used to prepare and isolate a variety of pure metal amidoboranes that could then be studied in detail. [97][98][99] All of the monometallic MAB's studied to date released hydrogen too exothermically to allow for subsequent direct rehydrogenation of the spent fuel with hydrogen gas. No safe path forward was identified for direct chemical regeneration of the spent fuel MNBH x so work in monometallic MAB's was discontinued.…”

Ammonia borane–metal alanate composites: hydrogen desorption properties and decomposition processes

“…6,7 To overcome these disadvantages, several approaches have been developed, such as infusion of AB in nanoscaffolds, 8 doping with transition metals as catalysts, 9 size and catalytic effects from graphitic carbon nitride, 10 and chemical modification of AB by replacing one of H atoms with an alkali or alkaline earth metal to form metal amidoboranes. 11 In previous reports, many kinds of AB-MH (Metal Hydride) composites, such as AB-LiH, [11][12][13][14][15][16] AB-NaH, were synthesized and their dehydrogenation properties were investigated. Recently, we experimentally verified that AB-MAlH 4 (M = Na, Li) composites, which were prepared based on the indicator we proposed, can suppress the emission of NH 3 , B 2 H 6 and B 3 H 6 N 3 .…”

Li2(NH2BH3)(BH4)/LiNH2BH3: The first metal amidoborane borohydride complex with inseparable amidoborane precursor for hydrogen storage

“…Also worthy of mentioning is the problematic NH 3 evolution. As shown in the MS profiles, the H 2 release from Li 2 (NH 2 BH 3 )(BH 4 )/LiAB composite was accompanied with NH 3 evolution in a similar level to that from LiAB [43]. In this regard, further study is still required for properly addressing this problem.…”