A liquid-based eutectic system: LiBH4 · NH3-NH3BH3 with high dehydrogenation capacity at moderate temperature

摘要

A novel eutectic hydrogen storage system, LiBH4 · NH3-nNH3BH3, which exists in a liquid state at room temperature, was synthesized through a simple mixing of LiBH4NH3 and NH3BH3 (AB). In the temperature range of 90-110 °C, the eutectic system showed significantly improved dehydrogenation properties compared to the neat AB and LiBH4 · NH3 alone. For example, in the case of the LiBH4 · NH3/ AB with a mole ratio of 1 : 3, over 8 wt.% hydrogen could be released at 90 °C within 4 h, while only 5 wt. % hydrogen released from the neat AB at the same conditions. Through a series of experiments it has been demonstrated that the hydrogen release of the new system is resulted from an interaction of AB and the NH3 group in the LiBH4 · NH3, in which LiBH4 works as a carrier of ammonia and plays a crucial role in promoting the interaction between the NH3 group and AB. The enhanced dehydrogenation of LiBH4·NH3/AB may result from the polar liquid state reaction environments and the initially promoted formation of the diammoniate of diborane, which will facilitate the B-H···H-N interaction between LiBH4·NH3 and AB. Kinetics analysis revealed that the rate-controlling steps of the dehydrogenation process are three-dimensional diffusion of hydrogen at temperatures ranging from 90 to 110 °C.