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

Abstract Hydrazine borane N 2 H 4 BH 3 (HB) and its alkali metal derivatives, i.e . sodium hydrazinidoborane NaN 2 H 3 BH 3 (NaHB) and lithium hydrazinidoborane β -LiN 2 H 3 BH 3 ( β -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 °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 °C). ( ii ) NaHB forms from −38 °C, melts at ca . 60 °C, and decomposes upon melting at higher temperatures. ( iii ) β -LiHB dehydrogenates to a small extent starting from 40 °C, but mostly transforms to the high-temperature phase α -LiHB at 91 °C; up to around 150 °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.