Fabrication of Multiple-Phase Magnesium-Based Hydrides with Enhanced Hydrogen Storage Properties by Activating NiS@C and Mg Powder

Magnesium hydride is considered as a promising candidate for hydrogen storage; however, the sluggish kinetics and thermodynamic stability seriously obstruct its industrial applications. Hence, in order to improve the hydrogen storage performances of magnesium hydride, NiS@C additive was ball-milled with Mg powder to build NiS@C/Mg. The MgH₂/Mg₂NiH₄ polyphase hydrides were in situ formed after hydrogenated activation and turned into Mg/Mg₂Ni phases during the dehydrogenation process, establishing a cycle of hydrogen absorption and desorption. The NiS@C/Mg composite showed enhanced de/hydrogenation rates: it could quickly absorb 6.02 wt % H₂ within 5 min at 250 °C and desorb 5.34 wt % H₂ at 300 °C. Moreover, even at the temperature of 50 °C, it could reach 3.23 wt % hydrogen absorption capacity, and the apparent hydrogen desorption activation energy for MgH₂ decreased to 60.45 kJ mol^–1. It also delivered a high cyclic stability performance of 98.9% for hydrogen absorption and 98.5% for hydrogen desorption after 50 cycles. The enhanced de/absorption kinetics of NiS@C/Mg were ascribed to the synergistic effects of multiple-phase MgH₂/Mg₂NiH₄ hydrides and the in situ formed MgS catalyst, and the existence of C also effectively prevented the passivation and agglomeration of multiple-phase particles. The method of in situ generating of multiple-phase hydrides and catalysts provides a new view for the preparation of high-performance hydrogen storage materials.