In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH 4 . The Li/Mg based dual-cation borohydride (LiMg 2 (BH 4 ) 5 , LMBH) was successfully synthesized by wet chemical ball milling of LiBH 4 and MgCl 2 . The optimal (LMBH (4.5:1) sample, LiBH 4 and MgCl 2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF 3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH 4 . The LMBH (4.5:1) doped with TiF 3 system releases 7.98 wt% H 2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H 2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF 3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB 2 and TiH 2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB 2 /TiH 2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.