Comprehensive hydrogen storage properties and catalytic mechanism studies of 2LiBH_4-MgH_2 system with NbF_5 in various addition amounts

摘要

In the present work, the role of NbF_5 addition amount in affecting the comprehensive hydrogen storage properties (dehydrogenation, rehydrogenation, cycling performance, hydrogen capacity) of 2LiBH_4-MgH_2 system as well as the catalytic mechanism of NbF_5 have been systematically studied. It is found that increasing the addition amount of NbF_5 to the 2LiBH_4-MgH_2 system not only results in dehydrogenation temperature reduction and hydriding-dehydriding kinetics enhancement but also leads to the de/rehydrogena-tion capacity loss. Compared with other samples, 2LiBH_4-MgH_2 doping with NbF_5 in weight ratios of 40:4 exhibits superior comprehensive hydrogen storage properties, which can stably release ～8.31 wt.% hydrogen within 2.5 h under 4 bar H_2 and absorb ～8.79 wt.% hydrogen within 10 min under 65 bar H_2 at 400 ℃ even up to 20 cycling. As far as we know, this is the first time that excellent reversibility as high as 20 cycles without obvious degradation tendency in both of hydrogen capacity and reaction rate has been achieved in the 2LiBH_4-MgH_2 system. The further experimental study reveals that the highly catalytic effects of NbF_5 on the 2LiBH_4-MgH_2 system are derived from the reaction between NbF_5 and LiBH_4, which provides a fundamental insight into the catalytic mechanism of NbF_5.