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

Abstract

A system of 2LiH–MgB₂ and its hydrogenated 2LiBH₄–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.