Improved hydrogen storage properties of MgH₂ by nickel@nitrogen-doped carbon spheres

Magnesium hydride is considered to be one of the most desirable hydrogen storage materials due to its high weight capacity (7.6 wt% H₂) and low price. However, its relatively high operating temperatures and slow dynamics have always hampered its commercial applications. In this paper, nano-nickel particle coated nitrogen-doped carbon spheres (Ni@NCS) were synthesized by a chemical reduction method and then introduced into Mg to form an MgH₂-Ni@NCS composite via hydriding combustion and subsequent high-energy ball milling processes. The results showed that the MgH₂-Ni@NCS composite possessed high hydrogen storage capacity and fast absorbing/desorbing kinetics, absorbing 5.7 wt% H₂ and desorbing 4.3 wt% H₂ within 8 min at 623 K. Moreover, the capacity shows negligible degradation after 10 cycles, indicating that the MgH₂-Ni@NCS composite has good cycling stability. Even at relatively low temperature (373 K), the MgH₂-Ni@NCS composite still absorbed 4.2 wt% H₂ within 60 min compared to 0.9 wt% H₂ for milled MgH₂. The improvement in hydrogen storage properties is ascribed to the in situ formed Mg₂NiH₄ induced dehydrogenation of MgH₂ and effective prevention of the agglomeration of magnesium during the hydriding/dehydriding reaction by the carbon material.