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

2LiBH(4)-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 2LiBH(4)-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 2LiBH(4)-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 2LiBH(4)-MgH2 system, which results in a higher hydrogen storage capacity of 9.4 wt%.