In situ thermodiffraction to monitor synthesis and thermolysis of hydrazine borane-based materials

Hydrazine borane N2H4BH3 (HB) and its alkali metal derivatives, i.e. sodium hydrazinidoborane NaN2H3BH3 (NaHB) and lithium hydrazinidoborane beta-LiN2H3BH3 (beta-LiHB), are novel materials under investigation for solid-state chemical hydrogen storage. Herein, we report in situ thermodiffraction experiments developed to monitor synthesis of NaHB at low temperatures (from -173 degrees C) and a thermolysis of each of the boranes, manifesting the following main observations. (i) Dehydrogenation of HB starts with the liquid phase and dehydrocoupling involves the formation of a crystalline intermediate (at 90-197 degrees C). (ii) NaHB forms from -38 degrees C, melts at ca. 60 degrees C, and decomposes upon melting at higher temperatures. (iii) beta-LiHB dehydrogenates to a small extent starting from 40 degrees C, but mostly transforms to the high-temperature phase alpha-LiHB at 91 degrees C; up to around 150 degrees C, the two crystalline phases dehydrogenate according to a complex stepwise mechanism. Our results help in gaining insight in synthesis and thermolysis of the aforementioned novel hydrazine borane-based materials. (C) 2015 Elsevier B.V. All rights reserved.