Nano-Ni doped Li-Mn-B-H system as a new hydrogen storage candidate

摘要

In this work, we report the synthesis and characterization of LiMn(BH_4)_3, member of a new class of complex borohydrides for hydrogen storage. This new complex hydride was prepared with a 3:1 ratio of precursor materials LiBH_4 and MnCl_2 via the solid-state mechano-chemical process. The B-H stretch occurrence at 2374 cm~(-1) in addition to two other B-H bonding bands of LiBH_4 (2228 and 2297 cm~(-1)) from the FTIR investigation confirm the formation of LiMn(BH_4)_3 at room temperature. Thermogravimetric analysis (TGA) of LiMn(BH_4)_3 indicated that a large amount of hydrogen (～ 8.0 wt%) can be released between 135 and 155 ℃ in a single dehydrogenation reaction step. Reduction in the decomposition temperature was achieved by doping this Li-Mn-B-H system with small fractions of nano-Ni. An amount of 1.5 mol% nano-Ni was estimated and found to be the optimum concentration for effective decomposition. Nano-Ni loading in the host hydride lowers the melting and thermal decomposition temperatures (at least by 20 ℃) as evidenced from the simultaneous TGA, DSC and TPD measurements. The doped LiMn(BH_4)_3 exhibits lower activation energy (112 kJ/mole) by 20 kJ/mole as compared to the undoped sample (131 kJ/ mole). Moreover, the gas chromatography studies of the undoped and doped LiMn(BH_4)_3 demonstrate that the evolved gas is mainly hydrogen and does not contain members of the borane family.