Significantly improved dehydrogenation of LiBH4·NH3 assisted by Al2O3 nanoscaffolds

Enhanced dehydrogenation properties for ammine lithium borohydride (LiBH4·NH3) melt-infiltrated into Al2O3 nanoscaffolds are reported. X-ray diffraction measurements verified the formation of intermediate phase of amorphous state during heating the composites at 65 °C. Subsequently, it was revealed by combination of gravimetric and volumetric measurements that a hydrogen desorption capacity of 12.8 wt.%, accounting for 91 mol% of the total amount of the released gas at 230 °C, was achieved for the LiBH4·NH3/Al2O3 composite with a mass ratio of 1:4, while in the pristine LiBH4·NH3 merely trace amount of H2 was detected at this temperature. Moreover, Fourier transform infrared spectra and 11B nuclear magnetic resonance spectra were combined to clarify the facilitated recombination of NH3 groups and BH4−1 anions in the composites. As a consequence, the mechanisms for the promoted dehydrogenation in the composites were reasonably deduced as twofold, firstly, the nanosize effects of the loaded LiBH4·NH3 on the dehydrogenation properties in the presence of the oxide nanoscaffolds, which serve as the highly dispersing support for the loaded materials, and assist the formation of the amorphous phase during heating; secondly, the impact of Al2O3 nanoscaffolds on the dehydrogenation of the loaded materials, via promotion of the recombination between BH and NH groups.

► Nanostructured LiBH4·NH3/Al2O3 composites were prepared via a melting technique.
► Onset dehydrogenation occurs below 100 °C with the formation of B–N bond.
► A prominent dehydrogenation appears at 230 °C with a hydrogen capacity of 12.8 wt.%.