Nanosize-Controlled Reversibility for a Destabilizing Reaction in the LiBH₄–NdH_2+x System

A reversible reaction, 4LiBH 4 + NdH 2 ↔ NdB 4 + 4LiH + 7H 2, which destabilizes the dehydrogenation thermodynamics of LiBH 4, has been found in the present work. Significantly, we prove that the reversibility only exists when NdH 2+ x is in size of less than about 10 nm. With this reaction, the estimated dehydrogenation enthalpy change is reduced from 74 kJ mol –1 H 2 for pristine LiBH 4 to 64 kJ mol –1 H 2; the theoretical hydrogen capacity is 6.0 wt %, and there is no emission of deleterious BH 3 and B 2 H 6 . Moreover, the dehydrogenation kinetics of this reaction are fast—6.0 wt % hydrogen was released within 1.5 h at 370 °C. When the NdH 2+ x becomes stable owing to its significant growth, the thermodynamic destabilization effect does not occur after several hydrogenation/dehydrogenation cycles. However, the presence of NdH 2+ x also has a positive effect upon the dehydrogenation kinetics of LiBH 4 . This novel finding is beneficial for modifying the reversibility of the reactive hydride composite systems through nanosize controlling.