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

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.