Size-Dependent Hydrogen Storage Properties of Mg Nanocrystals Prepared from Solution

Mg nanocrystals of controllable sizes were prepared in gram quantities by chemical reduction of magnesocene using a reducing solution of potassium with an aromatic hydrocarbon (either biphenyl, phenanthrene, or naphthalene). The hydrogen sorption kinetics were shown to be dramatically faster for nanocrystals with smaller diameters, although the activation energies calculated for hydrogen absorption (115-122 kJ/mol) and desorption (126-160 kJ/mol) were within previously measured values for bulk Mg. This large rate enhancement cannot be explained by the decrease in particle size alone but is likely due to an increase in the defect density present in smaller nanocrystals.