Increase in the dehydrogenation rates and hydrogen-storage capacity of Mg-graphene composites by adding nickel via reactive ball milling

Abstract Ni was added to increase the dehydrogenation rates of graphene-added Mg with a composition of 95 wt% Mg + 5 wt% graphene (named Mg-5graphene). For this, samples with a composition of 95 wt% Mg + 2.5 wt% Ni + 2.5 wt% graphene (named Mg-2.5Ni-2.5graphene) were prepared by ball milling in hydrogen. Mg-2.5Ni-2.5graphene had significantly higher initial hydrogenation and dehydrogenation rates, with significantly larger quantities of hydrogen absorbed and released over 60 min, than Mg-5graphene. Mg-2.5Ni-2.5graphene exhibited a very high effective hydrogen-storage capacity of approximately 7 wt% at the second cycle (n = 2). We believe that the increase in the Mg crystallite size, leading to a decrease in the grain boundaries, with cycling contributed partly to decreases in the hydrogenation and dehydrogenation rates as n increases. We attributed the partial transformation of graphene into C60 fullerene to the processing of reactive ball milling and the introduction of heat during cycling.