In Situ Introduction of Li3BO3 and NbH Leads to Superior Cyclic Stability and Kinetics of a LiBH4-Based Hydrogen Storage System

Abstract

LiBH4 is a high-capacity hydrogen storage material; however, it suffers from high dehydrogenation temperature and poor reversibility. To tackle those issues, we introduce a new LiBH4-based system with in situ formed superfine and well-dispersed Li3BO3 and NbH as co-reactants. Those are synthesized by the addition of niobium ethoxide [Nb(OEt)5] to LiBH4, heat treatment of the mixture, and then hydrogenation, where Li3BO3 and NbH are generated from the reaction of Nb(OEt)5 and LiBH4. After optimization, the system with a normalized composition of LiBH4-0.04(Li3BO3 + NbH) in molar fraction shows superior hydrogen storage reversibility and kinetics. The initial and main dehydrogenation temperatures of the system are 200 and 90 °C lower than those of the pristine LiBH4, respectively, and 8.2 wt % H2 is released upon heating to 400 °C. A capacity of 7.2 wt % H2, corresponding to a capacity retention of 91%, is sustained after 30 cycles in an isothermal cyclic regime of dwelling at 400 °C for 60 min for dehydrogenation and dwelling at 500 °C and 50 bar H2 pressure for 20 min for hydrogenation. Such a high cyclic stability for a LiBH4-based system has never been reported to date. The in situ introduced Li3BO3 and NbH have a synergistic catalysis effect on the improvement of the hydrogen storage performance of LiBH4, showing highly effective bidirectional action on both dehydrogenation and hydrogenation.