Hydrogen storage properties of Nb-compounds-catalyzed LiBH4–MgH2

Abstract

In order to improve the hydrogen storage properties of LiBH4–MgH2 composite, two different kinds of Nb-based catalysts, NbC and NbF5, were added to LiBH4–MgH2 composite by ball milling, and the effect of catalysts on hydrogen storage properties of the modified LiBH4–MgH2 system was investigated. The experimental results show that LiBH4–MgH2 composite is a two-step dehydrogenation process, and Nb-based compounds can remarkably enhance its dehydrogenation kinetics. For the composite without addition of catalysts, the starting decomposition temperature for the first dehydrogenation step is around 320 °C, and there is a long period of incubation time (around 220 min) for the occurrence of the second decomposition step even at high temperature of 450 °C. It needs more than 10 h to complete the decomposition process and release around 9 wt% H2. After addition of 5 mol% NbF5, the starting decomposition temperature for the first dehydrogenation step is around 150 °C, there is no incubation time for the second decomposition step, and it takes around 40 min to complete the second step and reaches a total dehydrogenation capacity of 9.5 wt%. NbF5 has better catalytic effect than NbC. Based on the hydrogenation/dehydrogenation behaviors and structural variation, the mechanism of catalytic effect was discussed.