Enhanced hydriding–dehydriding performance of 2LiBH4–MgH2 composite by the catalytic effects of transition metal chlorides

Abstract

2LiBH₄–MgH₂ is an attractive system for hydrogen storage. However, its dehydriding and rehydriding kinetics have to be further improved for practical applications. To solve these problems, three transition metal chlorides (FeCl₂, CoCl₂ and NiCl₂) were introduced into the 2LiBH₄–MgH₂ system and their catalytic roles in the dehydrogenation–rehydrogenation properties were investigated systematically. The results show that all three chlorides can significantly enhance the dehydriding and rehydriding kinetics of the 2LiBH₄–MgH₂ system with/without hydrogen back pressure, and NiCl₂ is the best modifier among them. The NiCl₂-doped sample exhibits no incubation period for generating MgB₂ during dehydrogenation. X-Ray diffraction and scanning electron microscopy analyses clearly reveal the phase formation of MgNi₃B₂, which may act as the nucleation site for MgB₂ formation, and thus the incubation period shrinks. A highly homogeneous distribution of the in situ formed MgNi₃B₂ nanoclusters can significantly improve the dehydriding–rehydriding kinetics. Single-phase MgNi₃B₂ was successfully synthesized and a similar catalytic effect is obtained by directly doping identical MgNi₃B₂ into the 2LiBH₄–MgH₂ system, which results in a higher hydrogen storage capacity of 9.4 wt%.