Altering the chemical state of boron towards the facile synthesis of LiBH4 via hydrogenating lithium compound-metal boride mixture

Boron sources in forms of SiB4/FeB/TiB2 were used to react with LiF/LiH under hydrogen atmosphere to investigate their effectiveness for synthesizing LiBH4, a promising hydrogen storage material. Fourier transform infrared (FTIR) study revealed the formation of B-H bond vibrations in these hydrogenated systems, and it demonstrated the generation of LiBH4. When using FeB and TiB2, few amounts of B-H bonds were formed in the hydrogenated samples either reacting with LiH or LiF. When utilizing SiB4, the formation of B-H bonds was promoted for both systems mixing with LiH and LiF. The results imply that a stepwise process of LiBH4-x -> LiBH4 possibly took place during the hydrogenation process. Importantly, SiB4 LiH system exhibited the best hydrogenation performance. At moderate conditions of 250 degrees C and 10 MPa H-2, LiBH4 was successfully synthesized from this system. A facile synthesis pathway, SiB4(s) + 4LiH(s) + 6H(2)(g) -> 4LiBH(4)(s) + Si(s), having a Delta H-r(m) of -65 kJ/mol H-2, was proposed. This study supports that the chemical state of boron in the reactant is an important factor affecting the generation of LiBH4. A hydrogenation reaction between SiB4 and CaH2 or MgH2 may be also applicable for synthesizing Ca(BH4)(2) or Mg(BH4)(2), which are regarded as potential hydrogen storage materials. (C) 2018 Elsevier Ltd. All rights reserved.