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 °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 MgNi_2.5B₂, with a hydrogen storage capacity of 3.6 wt% at T = 400 °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 °C to 260–266 °C (ΔT = 42–48 °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.