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 particles coated nitrogen-doped carbon spheres (Ni@NCS) were synthesized by chemical reduction method, and then introduced into Mg to form an MgH2–Ni@NCS composite via a hydriding combustion and subsequent high-energy ball milling process. Results showed that the MgH2–Ni@NCS composite owned a 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 has negligible degradation after 10 cycles, indicating that the MgH2–Ni@NCS composite had a good cycling stability. Even at relatively low temperature (373 K), MgH2–Ni@NCS composite still absorbed 4.2 wt.% H2 within 60 min compared to 0.9 wt.% H2 for the milled MgH2. The improvement in hydrogen storage properties is ascribed to that an in-situ formed Mg2NiH4 induced dehydrogenation of MgH2, and that the carbon materials effectively prevented the agglomeration of magnesium during the hydriding/dehydriding reaction.