The optimum powder to ball ratio was examined, which is one of the important conditions in reactive mechanical grinding processing. Yttria (Y₂O₃)-stabilized zirconia (ZrO₂) (YSZ), Ni, and graphene were chosen as additives to enhance the hydriding and dehydriding rates of Mg. Samples with a composition of 92.5 wt% Mg + 2.5 wt% YSZ + 2.5 wt% Ni + 2.5 wt% graphene (designated as Mg-2.5YSZ-2.5Ni-2.5graphene) were prepared by grinding in hydrogen atmosphere. Mg-2.5YSZ-2.5Ni-2.5graphene had a high effective hydrogen-storage capacity of almost 7 wt% (6.85 wt%) at 623 K in 12 bar H₂ at the second cycle (n = 2). Mg-2.5YSZ-2.5Ni-2.5graphene contained Mg₂Ni phase after hydriding-dehydriding cycling. Mg-2.5YSZ-2.5Ni-2.5graphene had a larger quantity of hydrogen absorbed for 60 min, H_a (60 min), than Mg-2.5Ni-2.5graphene and Mg-2.5graphene. The addition of YSZ also increased the initial dehydriding rate and the quantity of hydrogen released for 60 min, H_d (60 min), compared with those of Mg-2.5Ni-2.5graphene. Y₂O₃-stabilized ZrO₂, Ni, and graphene-added Mg had a higher initial hydriding rate and a larger H_a (60 min) than Fe₂O₃, MnO, or Ni and Fe₂O₃-added Mg at n = 1.

Keywords: Hydrogen storage, Grinding in H₂, Scanning electron microscopy (SEM), X-ray diffraction, YSZ, Ni, graphene addition