Achieving High Dehydrogenation Kinetics and Reversibility of LiBH4 by Adding Nanoporous h-BN to Destabilize LiH

Lithium borohydride (LiBH4) is a potential high-capacity hydrogen storage material but is limited by its high thermal stability and poor reversibility. Nanostructured hexagonal boron nitrides (h-BNs) with thin-layer (TL-BN) and nanoporous (NP-BN) structures have been prepared by treating h-BN in a hydrolysis process of LiBH4 and then mixing with LiBH4 by ball-milling to investigate their catalyzing effect on dehydrogenation and rehydrogenation. Nanostructured h-BN, in particular NP-BN, with an average pore size of 40 nm, significantly promotes the dehydrogenation kinetics, dehydrogenation capacity, and reversibility of LiBH4. For a LiBH4 + NP-BN (mole ratio 1:0.3) composite, the dehydrogenation capacity reaches 13.9 wt % for LiBH4 at 400 degrees C, which is very close to its theoretical one. The cycling capacity could remain stable at, similar to 7.6 wt % with rapid kinetics after de/rehydrogenation cycles under 10 MPa of hydrogen at 400 degrees C. The improved de/hydrogenation performance of LiBH4 depends on the nanoconfinement structure of LiBH4 in NP-BN. After dehydrogenation, a lithium-intercalated h-BN(LixBN) nanocrystal was formed by the reaction of h-BN and LiH. This LixBN nanocrystal confined the dehydrogenation products of the amorphous structure during dehydrogenation. Thus, this nanocrystal-confine-amorphous structure destabilizing LiH and benefiting the rehydrogenation and reversible capacity of the composite.