In-situ formation of ultrafine MgNi3B2 and TiB2 nanoparticles: Heterogeneous nucleating and grain coarsening retardant agents for magnesium borate in Li–Mg–B–H reactive hydride composite

Li–Mg–B–H reactive hydride composite (RHC) has attracted extensive attention over the past decades for its extremely high hydrogen storage capacity (11.5 wt%). But the sluggish desorption kinetics for the second step dehydrogenation reaction need to be further improved. Herein, short rod-like TMTiO3 (TM = Co, Ni) bimetallic oxides, which contain two kinds of transition metal elements, were synthesized and introduced into Li–Mg–B–H RHC for the first time. The NiTiO3 exhibits excellent catalytic effect on the hydrogen desorption kinetic performance of Li–Mg–B–H RHC, and the incubation period for the second step dehydrogenation reaction is eliminated completely by reducing the apparent activation energy for the generation of MgB2 from 296 kJ/mol to 269 kJ/mol. The NiTiO3 doped Li–Mg–B–H RHC can desorb about 9.0 wt% H2 without obvious attenuation of kinetic performance in five cycles. Mechanism analyses reveal that the in-situ generated nano-sized MgNi3B2 and TiB2 species (∼5 nm) both meet the critical value ( < 10%) of the edge-to-edge matching model (5.77% for MgNi3B2 and 2.22% for TiB2), which play a significant role in supporting the nucleation of MgB2. Meanwhile, the extremely fine MgNi3B2 and TiB2 heterogeneous nucleation sites can inhibit the excessive growth for a single crystal nucleus of MgB2. The heterogeneous nucleation and grain refinement mechanisms caused by the novel bimetallic oxide could provide alternative insights into designing an in-situ generated nano-sized catalytic hydrogen storage system with enhanced kinetics and cyclic stability for hydrogen-fueled applications.