Formation of Multiple-Phase Catalysts for the Hydrogen Storage of Mg Nanoparticles by Adding Flowerlike NiS

In order to enhance the hydrogen storage properties of Mg, flowerlike NiS particles have been successfully prepared by solvothermal reaction method, and are subsequently ball milled with Mg nanoparticles (NPs) to fabricate Mg-5 wt % NiS nanocomposite. The nanocomposite displays Mg/NiS core/shell structure. The NiS shell decomposes into Ni, MgS and Mg₂Ni multiple-phases, decorating on the surface of the Mg NPs after the first hydrogen absorption and desorption cycle at 673 K. The Mg-MgS-Mg₂Ni-Ni nanocomposite shows enhanced hydrogenation and dehydrogenation rates: it can quickly uptake 3.5 wt % H₂ within 10 min at 423 K and release 3.1 wt % H₂ within 10 min at 573 K. The apparent hydrogen absorption and desorption activation energies are decreased to 45.45 and 64.71 kJ mol^-1. The enhanced sorption kinetics of the nanocomposite is attributed to the synergistic catalytic effects of the in situ formed MgS, Ni and Mg₂Ni multiple-phase catalysts during the hydrogenation/dehydrogenation process, the porthole effects for the volume expansion and microstrain of the phase transformation of Mg₂Ni and Mg₂NiH₄ and the reduced hydrogen diffusion distance caused by nanosized Mg. This novel method of in situ producing multiple-phase catalysts gives a new horizon for designing high performance hydrogen storage material.