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

Abstract Boron sources in forms of SiB 4 /FeB/TiB 2 were used to react with LiF/LiH under hydrogen atmosphere to investigate their effectiveness for synthesizing LiBH 4 , 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 LiBH 4 . When using FeB and TiB 2 , few amounts of B H bonds were formed in the hydrogenated samples either reacting with LiH or LiF. When utilizing SiB 4 , the formation of B H bonds was promoted for both systems mixing with LiH and LiF. The results imply that a stepwise process of LiBH 4- x →LiBH 4 possibly took place during the hydrogenation process. Importantly, SiB 4 LiH system exhibited the best hydrogenation performance. At moderate conditions of 250 °C and 10 MPa H 2 , LiBH 4 was successfully synthesized from this system. A facile synthesis pathway, SiB 4 (s) + 4LiH(s) + 6H 2 (g) → 4LiBH 4 (s) + Si(s), having a Δ r H 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 LiBH 4 . A hydrogenation reaction between SiB 4 and CaH 2 or MgH 2 may be also applicable for synthesizing Ca(BH 4 ) 2 or Mg(BH 4 ) 2 , which are regarded as potential hydrogen storage materials.