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

Abstract

The thermal decomposition pathways of ammonia borane (AB, NH3BH3), lithium amidoborane (LiAB, LiNH2BH3), and potassium amidoborane (KAB, KNH2BH3) have been investigated in detail by using solid state 11B MAS NMR spectroscopy. During the first decomposition process of AB, the complex structural entities were observed, which have been attributed to polyaminoborane (PAB, (NH2BH2)n). On the other hand, polyiminoborane (PIB, (NHBH)n) formed in the second process showed a single 3-fold coordination IIIB 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 11B NMR spectra suggested that the general route of the thermal decomposition of alkali metal amidoboranes (LiAB, NaAB, and KAB) is similar. Also, 39K 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.