Tailoring dehydrogenation in lithium borohydride - magnesium nickel hydride hydrogen storage systems with metal halide additives

Solid state hydrogen storage may have a strong impact on future storage of renewable energy. Here we explore possible synergy effect in multi-component systems based on the lithium borohydride magnesium nickel hydride reactive hydride composite (LiBH4-Mg2NiH4). The composites of LiBH4-Mg2NiH4 are prepared by ball milling of LiBH4 with Mg2NiH4-MgNi2 or Mg2NiH4-MgH2-Ni. Thermal analysis reveals that LiBH4-Mg2NiH4-MgNi2 provides 20 degrees C lower onset dehydrogenation temperature compared to Mg2NiH4-MgH2-Ni. The Powder X-ray diffraction analysis of dehydrogenated samples indicates the similar dehydrogenation mechanisms producing the reversible phase MgNi2.5B2, with a hydrogen storage capacity of 3.6 wt% at T = 400 degrees C under 5 bar of hydrogen back pressure. The addition of transition metal halide additives (MnF2, NbF5, TiF3, ZnF2, and TiCl3) further reduces dehydrogenation temperatures from 308 degrees C to 260-266 degrees C (Delta T = 42-48 degrees C and initiates the dehydrogenation process by destabilizing LiBH4. Among all additives, ZnF2 shows the best performance offering an improved hydrogen capacity (3.76 wt%), lower dehydrogenation temperature, and suppression of diborane gas formation.