High catalytic efficiency of amorphous TiB2 and NbB2 nanoparticles for hydrogen storage using the 2LiBH4–MgH2 system

Abstract

LiBH4–MgH2 system in a 2 : 1 molar ratio constitutes a representative reactive hydride composite (RHC) for hydrogen storage. However, sluggish kinetics and poor reversibility hinder the practical applications. To ease these problems, amorphous TiB2 and NbB2 nanoparticles were synthesized and employed as catalysts for the 2LiBH4–MgH2 system. Isothermal de-/rehydrogenation and temperature programmed mass spectrometry (MS) measurements show that amorphous TiB2 and NbB2 nanoparticles can significantly improve the hydrogen storage performance of the 2LiBH4–MgH2 system. 9 wt% hydrogen can be released within only 6 min for nanoTiB2-doped 2LiBH4–MgH2, while for the undoped composite limited hydrogen of 3.9 wt% is released in 300 min at 400 °C. The dehydrogenation activation energies for the first and second steps are dramatically reduced by 40.4 kJ mol−1 and 35.2 kJ mol−1 after doping with nanoTiB2. It is believed that TiB2 and NbB2 nanoparticles can first catalyze the dehydrogenation of MgH2, and then induce the decomposition of LiBH4 and meanwhile act as nucleation agents for MgB2, thereby greatly enhancing the kinetics of dehydrogenation. The present study gives clear evidence for the significant performance of transition metal boride species in doped RHCs, which is critically important for understanding the mechanism and further improving the hydrogen storage properties of RHCs.