Nanoscale Mg-based materials for hydrogen storage

摘要

Hydrogen storage materials research has entered a new and exciting period with the advance of the nanocrystalline alloys, which show substantially enhanced absorption/desorption kinetics, even at room temperatures. In this work, we study experimentally the structure and electrochemical properties of nanocrystalline Mg_2Cu, (Mg_(1-x)M_x)_2Ni alloys, as well as Mg_2Cu/M' and (Mg_(1-x)M_x)_2Ni/M' (x =0, 0.5; M = Al, Mn; M' =C, Pd) nanocomposites. These materials were prepared by mechanical alloying (MA). In the nanocrystalline Mg_2Cu powder, discharge capacity up to 26 mA hg~(-1) was measured. It was found that nickel substituting copper in Mg_2Cu_(1-x)Ni_x alloy greatly improved the discharge capacity of studied material. In nanocrystalline Mg_2Ni powder, discharge capacities up to 100 mA h g~(-1) were measured. Additionally, it was found that Al or Mn substituting magnesium in Mg_(2-x)M_rNi alloy greatly improved the discharge capacity of studied material. For example, in nanocrystalline Mg_(1.5)Mn_(0.5)Ni powder, discharge capacities up to 241 m Ah g~(-1) were measured. On the other hand, mechanically coated Mg-based alloys with graphite or palladium have effectively reduced the degradation rate of the studied electrode materials. Finally, the properties of nanocrystalline alloys and their nanocomposites are compared to that of microcrystalline samples. The substitution of Mg by transition metals leads to significant modifications of the shape and width of the XPS valence band of the nanocrystalline as well as microcrystalline samples. Especially, the valence bands of the MA nanocrystalline alloys are considerably broader compared to those measured for the microcrystalline samples. Results also showed that the strong modifications of the electronic structure of the nanocrystalline alloys could significantly influence their hydrogenation properties.