Interaction Of Lithium Hydride And Ammonia Borane In Thf

摘要

The two-step reaction between LiH and NH3BH3 in THF leads to the production of more than 14 wt% of hydrogen at 40℃.rnThe demand for high capacity on-board hydrogen storage systems for hydrogen fuel cell vehicles has stimulated tremendous efforts in materials research and development. Recent research efforts have focused on materials that are composed of hydrogen bound to light elements including borohydrides, MOFs, amide-hydride combination systems, and ammonia borane. With a hydrogen capacity of 19.6 wt%, ammonia borane (NH3BH3, AB for short) shows promise for hydrogen storage; however, decomposition gives a volatile side product, borazine, that will poison PEM fuel cells. In addition, the desorption of hydrogen from this chemical hydride has a sufficient barrier to render the kinetics too slow at temperatures below 80 ℃. Our recent effort to modify the kinetics and thermodynamics of H_2 release from AB by replacing one H with an alkali metal, i.e., alkali amidoboranes (MNH_2BH_3, M = Li and Na) provided some improvement. These amidoboranes release large amount of hydrogen (exp. 10.9 wt%) with no measurable borazine formation, however, the kinetics for H_2 desorption are still insufficient. Previous investigations on hydrogen release from complex hydrides revealed that mass transport or mobility of the reacting species is one of the kinetic controlling factors. The mobility of the species can be enhanced substantially upon dissolution in a solvent. In the present study we investigate the reactivity of AB dissolved in tetrahydrofuran (THF) with a suspension of LiH and observe the formation of LiNH_2BH_3 and enhanced reaction kinetics with an interesting dependence on AB concentration. More than 2.8 equiv. of hydrogen can be released in two steps at a temperature as low as 40 ℃.