The effects of filamentary Ni, graphene and lithium amide (LiNH2) additives on the dehydrogenation behavior of mechano-chemically synthesized crystalline manganese borohydride (Mn(BH4)2) and its solvent filtration/extraction

(a) Apparent activation energy (kJ/mol) for dehydrogenation for the samples with and without additives after 1h ball milling and (b) comparison of isothermal dehydrogenation curves at 100 °C for the samples with and without additives. [Display omitted] •Effect of graphene, filamentary Ni and LiNH2 on the synthesis of Mn(BH4)2 investigated.•Mechanical dehydrogenation observed for filamentary Ni and LiNH2 but not for graphene.•All additives suppressed the release of B2H6 during thermal decomposition of Mn(BH4)2 with filamentary Ni being the strongest suppressor.•The LiNH2 additive reduced the apparent activation energy for dehydrogenation to 44.9 ± 4.3 kJ/mol.•After solvent filtration and extraction of the (Mn(BH4)2/LiCl) sample, a dimetallic hydride [{Li(Et2O)2}Mn2(BH4)5] was found. Dehydrogenation properties of mechano-chemically synthesized crystalline Mn(BH4)2 hydride without and with ultrafine filamentary carbonyl nickel (Ni), graphene and LiNH2 were investigated. It is reported for the first time that all additives suppressed the release of B2H6 with the filamentary Ni additive being the most effective suppressor of B2H6. In DSC, the decomposition peak of Mn(BH4)2 was endothermic. The estimated apparent activation energy for isothermal dehydrogenation was dramatically reduced to 44.9 ± 4.3 kJ/mol for the 5 wt.% LiNH2 additive from about 76–81 kJ/mol range for the additive-free sample and 5 wt.% filamentary Ni and graphene additives. The most striking finding, that has never been reported in the literature, is that the process of solvent filtration and extraction of the mechano-chemically synthesized (Mn(BH4)2/LiCl) sample, resulted in the crystallization of a dimetallic borohydride solvate [{Li(Et2O)2}Mn2(BH4)5] instead of crystalline Mn(BH4)2. Its dehydrogenation behavior was investigated isothermally and by TGA/DSC.