Enhanced hydriding-dehydriding performance of a 2LiH-MgB2 composite by the catalytic effects of Ni-B nanoparticles

A system of 2LiH-MgB2 and its hydrogenated 2LiBH(4)-MgH2 is an attractive candidate for hydrogen storage. However, its hydriding-dehydriding kinetics have to be further improved for practical application. In the present work, three kinds of Ni-B nanoparticles with different crystalline states and particle sizes were prepared by wet-chemical reduction and mechanochemical methods, and then introduced into a 2LiH-MgB2 composite for catalytic enhancement. The catalytic roles of Ni-B nanoparticles on the hydriding-dehydriding properties were investigated systematically. The results show that all of the Ni-B nanoparticles can significantly enhance the hydriding-dehydriding kinetics of the 2LiH-MgB2 composite, resulting in no incubation period for the formation of MgB2 during dehydrogenation. The more disordered the amorphous structure and the smaller sized the Ni-B particles are, the better the catalytic effect that is obtained. Microstructure analyses clearly reveal the formation of the MgNi3B2 phase in the dehydriding process, which acts as the nucleation agent for MgB2 formation determined by an edge-to-edge model. Directly doping with Ni-B nanoparticles in the 2LiH-MgB2 system shows a higher hydrogen desorption capacity of 9.4 wt% and obtains a better catalytic efficiency than doping with NiCl2.