The Effects of Additives on the Dehydrogenation of Amorphous Manganese Borohydride and Its Crystalline Form after Solvent Filtration/Extraction

Abstract

Abstract:A non-stoichiometric, amorphous a-Mn(BH 4 ) (2x) hydride, accompanied by a NaCl-type salt, was mechanochemically synthesized from the additive-free mixture of (2NaBH 4 + MnCl 2 ), as well as from the mixtures containing the additives of ultrafine filamentary carbonyl nickel (Ni), graphene, and LiNH 2 . It is shown that both graphene and LiNH 2 suppressed the release of B 2 H 6 during thermal gas desorption, with the LiNH 2 additive being the most effective suppressor of B 2 H 6 . During solvent filtration and extraction of additive-free, as well as additive-bearing, (Ni and graphene) samples from diethyl ether (Et 2 O), the amorphous a-Mn(BH 4 ) (2x) hydride transformed into a crystalline c-Mn(BH 4 ) 2 hydride, exhibiting a microstructure containing nanosize crystallites (grains). In contrast, the LiNH 2 additive most likely suppressed the formation of a crystalline c-Mn(BH 4 ) 2 hydride during solvent filtration/extraction. In a differential scanning calorimeter (DSC), the thermal decomposition peaks of both amorphous a-Mn(BH 4 ) (2x) and crystalline c-Mn(BH 4 ) 2 were endothermic for the additive-free samples, as well as the samples with added graphene and Ni. The samples with LiNH 2 exhibited an exothermic DSC decomposition peak.

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

“…Alternatively, Desrosiers et al [29] reported that at low gas exposures and heating to 500 K resulted in complete decomposition of B2H6, leaving B bonded to the Ni(100) surface. More recently, we proposed that LiNH2 reacts with B2H6 in an exothermic reaction during desorption, resulting in the formation of either lithium hydride or lithium borohydride accompanied by boron nitride [30].…”