Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH2 prepared by mechanical milling

We examined the catalytic effect of nanoparticle 3d-transition metals on hydrogen desorption (HD) properties of MgH2 prepared by mechanical ball milling method. All the MgH2 composites prepared by adding a small amount of nanoparticle Fe-nano, Co-nano, Ni-nano, and Cu-nano metals and by ball milling for 2 h showed much better HD properties than the pure ball-milled MgH2 itself. In particular, the 2 mol % Ni-nano-doped MgH2 composite prepared by soft milling for a short milling time of 15 min under a slow milling revolution speed of 200 rpm shows the most superior hydrogen storage properties: A large amount of hydrogen (similar to 6.5 wt %) is desorbed in the temperature range from 150 to 250 degrees C at a heating rate of 5 degrees C/min under He gas flow with no partial pressure of hydrogen. The EDX micrographs corresponding to Mg and Ni elemental profiles indicated that nanoparticle Ni metals as catalyst homogeneously dispersed on the surface of MgH2. In addition, it was confirmed that the product revealed good reversible hydriding/dehydri ding cycles even at 150 degrees C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH2 could be understood by a modified first-order reaction model, in which the surface condition was taken into account.